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    • 专利摘要:
    Production of viscoelastic capillary jets through gas focus. A method for the formation of elongated filaments or viscoelastic capillary jets is described. The method includes forcing an elastic liquid of constant viscosity, such as a boger liquid composed of a polymeric solution, through the channel of a power supply into the ambient interior of a pressurized chamber; forcing a gas into the pressurized chamber so that it leaves the chamber through the outlet orifice of the chamber located directly downstream of the path of the liquid leaving the power source; the gas focuses on the liquid, decreasing its diameter substantially and the polymers present in the liquid allow the liquid to form an elongated and stabilized jet by means of an axial tension, with a weber number close to zero. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2625035A1
    申请号:ES201531844
    申请日:2015-12-18
    公开日:2017-07-18
    发明作者:Alberto TORRES PONCE；Emilio José VEGA RODRÍGUEZ；José María MONTANERO FERNÁNDEZ；Alfonso M. GAÑÁN CALVO
    申请人:Universidad de Sevilla；Universidad de Extremadura；
    IPC主号:
    专利说明:

    FIELD OF THE INVENTION The invention refers in a general way to the field of fluid dynamics, and, in particular, to a method for forming a capillary stream of a viscoelastic liquid, said stream flowing concentrically with an accelerated gas stream and much faster so that a stabilized filament is formed by a tension stretching mechanism.
    BACKGROUND OF THE INVENTION The production and control of jets on the micrometer scale is of great interest in technological fields as varied as the pharmaceutical industry (1], biotechnology [2, 3], industrial engineering (4], food industry and agriculture (5 In the Newtonian regime, the jets produced break into drops with diameters of the order of the jet due to Rayleigh's capillary instability [6]. Thus, collections of relatively monodispersed drops (same size and morphology) can be obtained from of different experiments in "jetting" mode with applications in, for example, medicine and pharmacy (1). On the other hand, a great variety of physical-chemical processes are used to solidify the micro-puppies produced before their rupture. viscous liquids are continuously stretched in a jetting regime (stable jet emission) and subsequently solidified to form glass submillimeter fibers or silk (7), with obvious applications in the telecommunications and textile industry, respectively.
    Many of the applications mentioned above involve the treatment of polymeric viscoelastic liquids, where the interactions between the processing conditions and the rheology (non-Newtonian character) of the fluid play a fundamental role. These interactions fundamentally alter the dynamic response of the system and considerably complicate the analysis of the problem. However, the rheology becomes more manageable when working with Boger fluids (8) .This type of fluids are polymer solutions diluted in solvents with a sufficiently high viscosity so that elastic stresses are measurable.In addition, Boger fluids exhibit a constant viscosity (the effect of "shear thinning", a pseudoplastic behavior characterized by the decrease in viscosity under a shear stress, can be neglected), of
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    so that the elastic effects can be separated from the viscous ones. The constitutive equation Oldroyd-B (9) provides reasonably accurate predictions for these viscoelastic liquids under certain conditions.
    Various methods have been proposed to form micro and nanometric fibers from viscoelastic jets. Among them, electrospinning (or electro-spinning) [10] is one of the most popular because it can be applied to mass production of fibers "one by one" using different polymers. However, this method makes use of intense electric fields, which imposes certain restrictions on the electrical properties of the liquid used. Micrometric viscoelastic jets are also produced that solidify into fibers by purely mechanical or hydrodynamic means. In the classical "melt spinning" technique (so called because it originally referred to fusion spinning and stretching under centrifugal forces) (11), the liquid is extruded through a small hole and collected at a speed greater than the average extrusion speed The resulting filament undergoes self-sustained oscillations when the ratio between the collection speed and the extrusion speed exceeds a critical value close to 20. This is called draw resonance instability (11). , 12], which considerably limits both the production rate and the minimum diameter of the fiber that can be obtained. The "selective withdrawar" method (13) allows fibers to be produced from polymer solutions by suctioning a liquid stream through a hole located in front of the viscoelastic bath. The drag and suction forces (viscosity and pressure) produced by the current and they collaborate to deform the bath interphase, form a meniscus and stretch it until it emits a small stream from its tip. There are other examples where hydrodynamic forces have been applied to obtain fibers with sizes ranging from the millimeter scale to the nanometric scale. Among them is the coaxial atomization of viscoelastic ligaments, used in turn to measure the rheological properties (14). Benavides et al. [15] obtained nanofibers by exposing a polymeric drop drop to a high velocity gas stream (aerodynamic method). In the "melt blowing" method, a stream of molten polymer is carried by two convergent jets of air symmetrically directed to both sides of a two-slot die [16, 17).
    Flow focusing, [18, 19], has become a very popular method for producing submillimeter Newlonian jets using only hydrodynamic forces. In this technique, a meniscus hangs from a feeding capillary through which liquid is injected at a constant flow rate. An external fluid current focuses and stretches the meniscus in front of a hole. He
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    Meniscus emits a fine stream that co-flows with the external current through the hole. In the original axis focusing configuration of flow focusing [18], the external medium was a high velocity gas stream driven by an applied pressure drop. This configuration was subsequently adapted to the flat or two-dimensional topology (20) (19] to form jets that co-flow with an external liquid stream, which boosted its application in microfluidics (1). In both cases, the capillary distance hole and its diameters are of the same order and all the jet emitted is influenced by the focusing effect (19,20).
    Flat flow focusing has been used in liquid-liquid configuration to produce micrometric jets of Boger fluids [21, 22, 23, 24, 25, 26]. For weak elastic effects, the "pinch-off" (clamping or narrowing of the jet interface causing the rupture thereof) is initiated by capillary inertia mechanisms followed by an elasto-capillary regime [22]. As time The relaxation of the polymer increases, the dynamics of the filament becomes mainly controlled by the elasto-capillary mechanism, and both the length of the jet and the clamping time increase [22]. The flow rates [25, 26], the Resulting droplet size (21, 23], the effects of surfactants [24], or the appearance of flow asymmetries [27] have been analyzed both numerically and experimentally.
    The flow focusing axisimetric has been applied to the formation of viscoelastic jets, focused by an oil phase (28). A transition from "dripping" to stable emission of the jet ("jetting") was observed for values sufficiently high injected flow This transition has been explained in terms of equilibrium between the destabilizing capillary force and the stabilizing tension associated with polymer elongation [29). An effective value of this tension was estimated taking into account the polymeric elongation produced by both the Poiseuilie type flow in the feeding capillary (30) and the subsequent stretching of the filament in the focused region.In all experiments, the meniscus stretched it remained anchored to the end of the feeding capillary.
    SUMMARY OF THE INVENTION The present invention describes both a method for creating elongated capillary jets (filaments) and the jet itself obtainable according to the method. The method comprises forcing a viscoelastic liquid, such as a liquid or Boger fluid, through the channel of a capillary tube, preferably cylindrical, as a power source. The viscoelastic liquid imposes a speed of passage through the channel that causes the liquid to exit the outlet opening of the channel maintaining its filament or jet shape. The end or exit opening of the channel is inside a pressurized chamber.
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    The passage of a gas, such as air, is forced through the pressurized chamber
    that the gas leaves said pressurized chamber through the exit orifice of the chamber that is just in front of the water and down the path of the viscoelastic liquid. Also, the gas focuses the flow of the viscoelastic liquid, so that liquid and gas flow concentrically, and transforms the jet of the liquid into an elongated jet that has a diameter substantially smaller than the diameter of the initial jet leaving the opening of the channel. Finally, the narrow elongated stream of viscoelastic liquid and the surrounding gas leave the pressurized chamber through the exit orifice. Said elongated capillary jet or filament can be collected as it exits through the outlet port of the pressurized chamber. According to particular embodiments, the method is performed so that the resulting Weber number is less than one, less than 1x10- less than 1x10-2, less than 1x10 ·
    J, less than 1x10-4, or less than 1x10-6
    According to other particular embodiments of the invention, the viscoelastic liquid, such as a Boger liquid, is introduced through the channel at a rate in the range of 0.001 to 100 microliters per second, or between 0.01 and 10 microliters per second. , or between 50 microliters and 2,000 microliters per second, or 100 to 500 microliters per second.
    According to other particular embodiments of the invention, the gas is forced through the orifice of the pressurized chamber at a speed within the range of 50 ¡Jl / sec to 20,000 ¡Jl / sec, or between 100 to 500 ¡Jl / sec . As indicated above, the gas velocity must be greater than the velocity of the viscoelastic liquid that exits the opening of the channel.
    The channel of the power supply is a feeding tube or capillary, which may be in the form of a cylindrical or substantially cylindrical tube. According to certain variants of the invention, the feed capillary has an outlet diameter of less than 0.5 mm, less than 0.4 mm, less than 0.2 mm, or less than 0.1 mm.
    The outlet of the capillary channel or tube is preferably located at a distance less than 0.5 mm from the outlet opening of the pressurized chamber. In a particular embodiment, the outlet opening of the power supply is located at a point at a distance in the range of 0.2 to 0.5 mm from the outlet opening of the pressurized chamber. In order to obtain an especially appropriate result, once an initial jet is formed, it is convenient to gradually increase the capillary-hole distance, until reaching a
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    final or maximum capillary-hole distance of for example about 12 mm or less,
    such as about 11 mm, 10 mm, 9 mm or less.
    The outlet opening of the pressurized chamber, which is located directly in front of the outlet opening of the power supply, is generally circular. Preferred diameters for said exit port of the pressurized chamber are below 0.25 mm, for example in the range of 0.1 mm to 0.25 mm.
    According to certain variants of the invention, the feeding tube or capillary has an outlet diameter of less than 0.5 mm, less than 0.4 mm, less than 0.2 mm, or less than 0.1 mm, and the outlet of the capillary channel or tube is located at a distance less than 0.5 mm from the outlet opening of the pressurized chamber.
    According to certain variants of the invention, the outlet opening of the power supply channel has a diameter less than 0.5 mm, the outlet opening of the pressurized chamber has a diameter less than 0.25 mm, and the opening of The output channel of the power supply is located at a point less than 0.5 mm from the outlet hole of the pressurized chamber.
    According to certain variants of the invention, the outlet opening of the power supply channel has a diameter in the range of 0.1 mm to 0.5 mm, the outlet opening of the pressurized chamber has a diameter in the range of 0.1 mm to 0.25 mm, and the outlet opening of the power supply channel is located at a point at a distance in the range of 0.2 to 0.5 mm from the outlet hole of the pressurized chamber .
    As indicated above, the initial or minimum distance between the outlet opening of the power supply channel and the outlet opening of the pressurized chamber, which is generally less than 0.5 mm, preferably increases progressively during the method until reaching a final or maximum capillary-hole distance of for example about 12 mm or less, such as about 11 mm, 10 mm, 9 mm or less.
    In general, gas (for example, air) can be forced into the pressurized chamber at a pressure in the range of 50 to 2,000 mbar above atmospheric pressure and viscoelastic liquid (for example, a Boger liquid) can have a velocity in the range of 1x10
    4 kg / m / sec at 1kg / m / sec. 6
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    An important aspect of the invention is a method of focusing viscoelastic jets of a liquid, such as a Boger liquid, using an air stream. The axisimetric air flow focuses the Boger liquid so that said Boger liquid produces micrometric jets.
    According to the present invention, the viscoelastic liquid is a low concentration polymer solution, for example less than 1500 ppm, such as 1000 ppm, 500 ppm or 250 ppm. In principle, the nature of the polymer is not important, since the person skilled in the art knows a wide variety of polymers leading to viscoelastic solutions. Polymers contemplated in the present invention include, but are not limited to, polymers based on carbon chemistry, polymers based on silicon chemistry, fluoropolymers, proteins, DNAs, RNAs, etc. In a particular embodiment, the viscoelastic liquid is a solution of poly (acrylic) acid (PM).
    In another aspect, the present invention is directed to the elongated liquid capillary jet (filament) obtainable according to the method of the invention. In addition, from said elongated capillary jet a solid filament or solid fiber can be obtained by a process of solidification or phase change between those considered, but not restricted to: solvent evaporation, cooling, chemical curing, chemical interaction with the forcing gas, chemical interaction with the environment gas in which the capillary jet is discharged, or heat hardening.
    The filament or fiber obtained from the elongated capillary jet is useful in different industries, for example, such as: textile material, material for biomedical, surgical or prosthetic use, material for structural use in mechanical applications, material for the elaboration of wires or cables of very high resistance to breakage, such as mechanical reinforcement fiber in materials with low tensile strength, substrate for biotechnological use,
    or material associated with telecommunication.
    Viscoelastic capillary jets can be produced by flow focusing. In this technique, the liquid is injected at preferably constant flow through a feed capillary located in front of a discharge orifice. A gaseous stream co-flows with the jet through the orifice driven by a constant pressure drop. The gas stream sucks and drags the liquid, reducing the diameter of the jet to values far below the diameter of the hole. Due to the rheological nature of the liquid, this phenomenon
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    The focus differs from that observed in the Newtonian regime in several aspects. The conditions under which especially satisfactory results are obtained are those that lead to the "jetting" mode. Outside this interval, the jet could suffer from instability called "pull-out" or rupture before reaching the hole. Thanks to the stabilizing effect of the polymeric contribution to axial stress, micrometer jets of up to 1 cm in length can be produced, and Weber numbers of the order of 104 can be achieved.
    These and other objectives, advantages and characteristics of the present invention can be made apparent to those skilled in the art after reading the details of the method described more fully below.
    BRIEF DESCRIPTION OF THE FIGURES The invention is better understood on the basis of the detailed description that follows when read in combination with the accompanying figures. It should be emphasized that, according to usual practice, the different details of the figures are not to scale. On the contrary, the dimensions of some details are augmented or arbitrarily reduced for clarity. Included in the drawings are the following figures:
    Figure 1 is a schematic view of the basic components used in connection with an example according to the present invention. Q: flow rate at which viscoelastic liquid is injected through the feed capillary, LJp: pressure drop that drives the gaseous current through the discharge orifice, H: distance between the feed capillary (feed channel outlet opening ) and the discharge hole of the pressurized chamber.
    Figure 2 consists of two graphs that we refer to as the graph on the left and the graph on the right. The graph on the left is a schematic view of an experimental assembly of the components that are used in relation to the method of the invention and that allow the observation and measurement of various system parameters. (A) capillary, (B) discharge hole, (C) orientation system, (D) translation platform, (E) ultra-high speed camera, (F) triaxial translation platform, (G) fiber optic, and (H) anti-vibration isolation system. The graph on the right shows an example of a jet, in relation to the present invention, of a solution of poly (acrylic) acid (PAA) with c = 1000 ppm, .8.p = 250 mbar produced at a flow rate Q = 4 , 5 mi / h. H = 6.7 mm.
    Figure 3 consists of two graphs that we refer to as the graph on the left and the graph on the right. The graph on the left shows the dependence of the shear viscosity of the J.l solution on the shear rate and. and the graph on the right shows the first viscometric function 4J 1 versus the shear rate and, for
    5 PAA solutions In this experiment, c = 250 ppm (hollow symbols) and 1000 ppm(solid symbols). The starting points of the curves are determined by theRheometer sensitivity
    Figure 4 consists of six connected images shown to illustrate the
    10 meniscal de-anchoring phenomenon ("pull-ounce. The meniscus of the fluid leaving the end of the capillary oscillates around an equilibrium position inside the feeding capillary. The jet emitted from the capillary occurred with c = 1000 ppm, Q = 40 mUh, and H = 2 mm.
    15 Figure 5 shows a graph of the temporal dependence of the radius of the free surface at 114 IJm (solid symbols) and 539 IJm (hollow symbols) of the capillary end. The jet was produced with e = 1000ppm, Q = 40ml / h, and H = 0.93mm.
    Figure 6 shows six different connected images that are a sequence of
    20 images illustrating the rupture of the capillary jet due to the bulging effect. The jet was produced using e = 1 OOOppm, Q = 5ml / h, and H = 6.25mm.
    Figure 7 is a graph showing the minimum and maximum values, Hmin and Hmax, of the distance from the capillary to the hole in which the triple contact line anchors the end of the
    25 capillary The hollow and solid symbols correspond to the PAA solutions with c = 250 and 1000ppm respectively.
    Figure 8 is a graph showing the experimental results of the number ofReynolds and the aspect ratio values of the experiments with c = 250ppm
    30 (hollow symbols) and 1000 ppm (solid symbols).
    Figure 9 is a graph showing the results of both the velocity distribution v (dotted line) and the gauge pressure Pg (solid line) along the axis of the hole as a function of the distance Z to the center of the hole. The speed is divided by its value 35 in the internal section of the hole V1. The simulation was performed with air at a pressure of
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    6p = 250 mbar and a hole with a pitch diameter D = 200IJm. The inserted box
    shows the pressure field near the hole.
    Figure 10 consists of two separate graphs that we refer to as graph
    left and right graphic. The left graph shows the experimental values of the Weber and Reynolds numbers. The right graph shows the experimental values for the Deborah number and the dimensionless polymeric stress. The hollow and solid symbols correspond to PAA solutions with c = 250 and 1000 ppm respectively.
    Figure 11 consists of two separate graphs which we refer to as the left graph and the right graph. The left graph shows the radius of the jet R1 just in front of the hole according to the aspect ratio A. The right graph shows the number of Deborah (De) versus the aspect ratio A. The hollow and solid symbols correspond to the PM solutions of c = 250 and 1000ppm, respectively.
    Figure 12 shows a graph of the shear velocity versus the tension of
    shear. The graph is provided to show the properties of a Newtonian fluid relative to the increase in shear rate versus shear stress in Newtonian and Non-Newtonian fluids.
    DEFINITIONS In this document, the term non-Newtonian fluid refers to any fluid with properties that differ in some way from those that have Newtonian fluids. In a non-Newtonian fluid, the relationship between shear stress and shear rate is different and may even vary over time. The difference is shown in Figure 12, the difference with respect to a direct linear relationship can be 5% or greater, 10% or greater, 20% or greater, 40% or greater, etc. Therefore, with a non-Newtonian fluid not
    a constant viscosity coefficient can be defined. Mostly, the viscosity (the measure of the ability of a fluid to withstand the gradual deformation produced by the tensile or shear force) of non-Newtonian fluids depends on the shear rate at the time or time. Some non-Newtonian fluids even having a viscosity independent of the shear force, have other behaviors other than normal versus the force or other non-Newtonian behaviors. Many salt solutions or molten polymers are non-Newtonian fluids, as are many common substances such as ketchup, custard, toothpaste, yeast suspensions, paint, blood and shampoo. In a Newtonian fluid, the relationship between the shear force and the
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    Shear speed is linear, passing through the origin, the viscosity coefficient being the constant of proportionality as shown in Figure 12.
    The Weber number (We) is a dimensionless number in fluid mechanics and is useful in the analysis of fluid flows in which there is an interface between two fluids, especially in multiphase fluids with very curved surfaces. Its name comes from Moritz Weber (1871-1951). It can be considered as a measure of the relative importance of fluid inertia compared to surface tension. The value is useful for the analysis of thin layer flows and the formation of drops and bubbles.
    Weber's number can be defined as:
    We = pv '
    (J
    wherePes the density of the fluid (kg / m3);you see its speed (mIs);I is its characteristic length, usually the drop diameter (m); Yu is the surface tension (N / m).
    As mentioned, liquids called "Boger" type are elastic fluids with constant viscosity. This creates an effect on the fluid that makes it flow like a liquid, although it behaves like an elastic solid when stretched. Most elastic fluids show a pseudoplastic behavior (viscosity decreases when shear stress is applied), because the solutions contain polymers. But Boger fluids are exceptions since they are highly diluted solutions, so that the pseudoplastic behavior caused by polymers can be ignored. Boger fluids are made by adding a small amount of polymer to a Newtonian fluid of high viscosity, the most original solution is polyacrylamide mixed with corn syrup. It is a very simple compound to synthesize but important for the study of rheology because the elastic effects and shear effects can be distinguished in experiments performed with Boger fluids. In Boger fluids it is difficult to determine whether non-Newtonian effects are caused by elasticity, pseudoplasticity or both; Non-Newtonian flow caused by elasticity is rarely identified. As Boger fluids can have constant viscosity, experiments can be performed where the result of the flow rates of a Boger liquid and a Newtonian liquid with the same viscosity can be compared, and the difference in flow rates could
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    show the change caused by the elasticity of the Boger liquid. A Boger fluid is an elastic liquid with a constant viscosity. Because the viscosity is independent of the shear rate or almost, the elastic effects can be separated from the viscoelastic flow viscous effects because the latter can be determined with Newtonian fluids.
    DETAILED DESCRIPTION OF THE INVENTION Before describing the method and product resulting from this invention, it should be understood that this invention is not limited to the particular steps and components described, since these, of course, may vary. It should also be understood that the terminology used herein is only intended to describe particular embodiments of the invention, and is not intended to be limiting since the scope of the present invention is limited only by the claims that are included.
    When a range of values is provided, it is understood that each value, up to one tenth of the lower limit unit as long as the text does not clearly indicate otherwise, between the lower limit and the indicated upper limit is specifically included. Each range below that existing between a indicated value or a value included within a indicated range and any other value indicated or included in said range, is covered by the invention. The upper or lower limits of these smaller ranges may be included or excluded from the range independently, and each of the ranges in which neither or both limits are included in the small ranges are included in the invention, subject to the specific exclusion of the limits of the ranges indicated. In cases where the ranges indicated include one or both limits, the ranges that exclude one or both of those limits included are also included in the invention.
    Unless defined differently, all the technical and scientific terms used here have the same meaning as the one commonly understood by a person skilled in the art as to which the invention belongs. Although methods and materials similar or equivalent to those described herein can be used for the practice or testing of the present invention, some preferred methods and potential materials are described below. All the mentioned publications are incorporated as a reference to show and describe the methods and / or material related to the cited publications. It is understood that the present invention supersedes any other description of any incorporated publication when there is a contradiction.
    It should be noted that as used herein and in the claims included, the
    singular forms "an" and "the" include the reference to plurals unless the
    context clearly indicate otherwise. For example, the reference to "a current"
    indicates a plurality of said stream and the reference to "the jet" includes the reference to
    5 one or more jets and thus different equivalents known to those skilled in the
    matter.
    The publications shown here are provided with the intention of displaying them.
    prior to the date of application of the present invention. Nothing should be interpreted
    1 o as an acknowledgment that the present invention has no right to precede these
    publications under a priority invention. Moreover, the publication dates
    displayed may be different from the current publication dates that must be
    individually confirmed.
    fifteen Figure 1 provides a schematic view of an example of fluid configuration of the
    method of the invention A cylindrical feeding capillary, which has a length of
    several times its diameter, it is located in front of the discharge hole, whose diameter is of
    order of capillary diameter. The viscoelastic fluid is injected through the capillary of
    constant flow feed Q, while a gas stream flows through the hole
    twenty discharge driven by a constant pressure drop J: jp. Results are obtained
    especially satisfactory if the distance H between the feed capillary and the orifice of
    discharge is within a certain range, then a liquid stream of a
    Boger fluid that begins at the edge of the capillary end and extends downstream in
    a flow direction far from the end of the capillary.
    25
    The gas stream sucks and drags the Boger liquid, which reduces the diameter of the
    jet up to much lower values than the discharge hole. For example the diameter of the
    jet downstream of the end of the capillary is focused by the surrounding gas so that
    it can be 50% or less, 25% or less, 10% or less, or 1% or less than the diameter of the
    30 jet when it leaves the end of the capillary. Both the liquid jet and the
    gas stream that flows together flows through the outlet hole. Due to the character
    rheological of the liquid, this focusing phenomenon differs substantially from that produced
    in Newlonian regime. In particular, the appropriate values of the capillary-hole distance
    H are normally much larger than their counterparts in the classic flow configuration
    35 focusing. The aerodynamic focusing effect can be confined within a region
    very small compared to the total length of the jet. Therefore, the liquid flows
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    freely, without significant interaction with the surrounding environment. The instability mechanisms that prevent steady jetting from being achieved are also different from those of the Newtonian mode. Polymeric forces stabilize the liquid filament, allowing jets to be formed with Weber numbers close to zero.
    The present invention is directed to the long (of the order of millimeters) jets formed between the end of the feed capillary and the discharge orifice. The invention specifies appropriate conditions for obtaining the "jetting" regime as well as the instability mechanisms that limit this regime. Some of the candidates for such mechanisms are reviewed, including capillary instability [28] and the fact that the supertitial tension makes waves grow on the jet's surface until they finally pinch the interphase. Absolute instability [31] as well as convective instability could prevent the system from reaching the "jetting" mode. If the downstream convection disturbances pinch the interphase before reaching the hole, the suction effect is interrupted. This causes the ejection of the filament to cease, and prevents the jetting regime from recovering. This phenomenon does not occur when the process is carried out using a Newtonian fluid, where capillary waves grow beyond the hole [20].
    Capillary instability is not desirable and can be modulated by elastic axial stress. The tension associated with polymeric stretching results in a strong increase in extensional viscosity. This partially inhibits capillary instability [32, 33]. The flow of Poiseuille in the feeding capillary causes a first stretching of the polymers. If a jet evolves at a constant speed (diameter), then the polymers relax at their winding state at distances from the capillary end that are equivalent to the diameter of the jet [34, 35, 36]. However, the acceleration of the jet caused by the co-flowing gas stream maintains the polymer tension and can increase the polymer tension near the hole.
    Lateral oscillations ("whipping") may appear in jets that co-flow with a current that has a much higher velocity [37, 38]. In this case, the surface tension has a stabilizing effect, and the destabilization mechanism is aerodynamic: a disturbance in the interphase causes the co-flowing fluid to accelerate as it passes through a ridge, reducing the pressure at that point and causing the growth in size of said crest. A question that arises naturally is whether "whipping" can play an important role in fluidic settings. Experiments have shown that this is the case when Newlonian liquids are focused within a
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    convergent nozzle [39], where the gas stream has an important axial impulse in
    the focus region. However, the "whipping" is confined upstream of the discharge hole in the classic flow focusing configuration (20, 40). This is because the flow of radial gas in front of the hole constitutes a hydrodynamic barrier to lateral disturbances.
    The instability of the jet may also be due to the so-called "pull-out" of the filament which occurs due to fiber spinning [41, 42, 43] under axial stresses above the stability limit. If the filament is stretched by a sufficiently high spinning force, its retraction can occur with respect to the end of the feeding capillary. The balance between the spinning force and the normal tension in the capillary determines the new position of the meniscus inside the capillary. The meniscus can remain motionless in the capillary or oscillate around the equilibrium position (43). There are other instability mechanisms such as stretch resonance ~ mentioned
    previously (11] or known as "melt fracture" (44). The stretching resonance is linked to the prescribing of the jet velocity at some point downstream [45]. This condition does not apply to flow focusing, and therefore this phenomenon does not occur in relation to the present invention.
    Information on both the stability and the forces that characterize the "jetting" regime in flow focusing of viscoelastic jets is provided here. The experimental procedure and the rheological properties of working liquids are described in the later section of Materials and Methods. Experimental data is presented and analyzed in the subsequent Results section.
    EXAMPLES The following examples are presented to provide those skilled in the art with a complete explanation and a description of how to make and use the present invention. and it is not intended to limit the scope of what the inventors recognize as their invention nor is it intended to indicate that the experiments described below are the only experiments performed. An effort has been made to ensure the accuracy of the numbers used (eg quantities, temperature, etc.) but it must be taken into account that there may be errors or experimental deviations. Unless otherwise indicated, the parts are parts by weight, the molecular weight is the average molecular weight, the temperature is in degrees Centigrade and the pressure is or is very close to atmospheric.
    MATERIALS AND METHODS
    Figure 2 shows a non-Newtonian fluid injected at a constant flow rate Q by a stepper motor (not shown) through a steel capillary (A), for example, 3.5 cm in length and 200 I -Im in diameter, with a sharp capillary end. Said end of the capillary is placed in front of a hole (B) perforated in the upper face of a stainless steel cell. The hole (B) is, for example, 200 I-Im in diameter and 500 I-Im thick. A negative gauge pressure 1J.p is applied inside the cell by using a suction pump (not shown). A high precision orientation system (C) and a translation system (D) are used to ensure the correct alignment of the elements of the f10w focusing, and to establish the capillary-hole distance H. The viscoelastic jet is formed outdoors due to the action of the air stream sucked through the orifice of the cell. Digital images can be acquired using two or more cameras (E) with optical axes perpendicular to each other, and equipped with very different magnification lenses. The camera with the highest magnification moves both horizontally and vertically using a triaxial translation platform (F) to focus part of the liquid jet, while the other camera acquires images of the entire ligament. In this way, the radius of the jet R (of the order of tens of microns) and the capillary distance H (of the order of millimeters) can be measured simultaneously. The fluid configuration is backlit on the two axes (in front of the two cameras) by cold white light provided by two optical fibers (G) connected to light sources. All these elements are mounted on an optical table with a pneumatic anti-vibration isolation system (H) to dampen vibrations from the surrounding environment.
    Experiments are carried out at 24 ± 2 oC. The feed capillary is placed at a distance from the cell hole that is substantially the same as the hole diameter. The pressure drop is set at fJ.p = 250 mbar in the air stream. A liquid, like non-Newtonian, injects a flow rate Q through the capillary.
    After a brief transitory regime, the capillary emits a liquid filament that crosses the orifice driven by the air current. The capillary-hole distance H is progressively increased, keeping fJ.p and Q constant. In order to achieve the "jetting" regime, it is convenient to strictly follow the above sequence. For example, if the process is started using a H value much greater than the diameter of the hole, then the air flow cannot
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    Easily establish a necessary degree of elastic tension in the liquid filament, thus hindering the formation of the jet.
    The procedure described above can be repeated for different flow rates Q and two polymer solutions. You can acquire images during the course of the process. The position of the free surface can be determined by processing the images with a super-resolution technique at the sub-pixel level (46).
    The behavior of two solutions of poly (acrylic acid) (PAA) (Mw = 18) (106 g / mol) in pure distilled water with concentrations of c = 250 and 1000 ppm can be examined. Non-Newtonian fluid solutions can be prepared by dissolving polymer in a solvent by stirring at very low speeds, in order to avoid breakage of the polymer chains. The shear viscosity dependence 1J of the solution and first viscometric function ~ 1 versus the shear rate can be measured and can be measured with a Physica MCR 301 rheometer. The results are shown in Figure 3.
    The polymeric relaxation time A can be measured with the HAAKE CABER 1 extensional rheometer by applying the slow retraction method (47). The values were A = 20 and 140 ms for 250 and 1000 ppm, respectively. The surface tension V can be measured with the TIFA method (48). It can be verified that V -72 mN / m and ~ 997 kg / mJ in all cases, that is, these two properties do not depend significantly on the polymer concentration. Figure 2 shows a jet with c = 1000 ppm produced at a flow rate Q = 4.5 mi / h.
    The gaseous flow focusing of the two viscoelastic liquids described above behaves as follows. When the feeding capillary is located near the discharge orifice, the liquid meniscus separates from the edge of the capillary end and climbs up the inner wall of the capillary. The meniscus either reaches an equilibrium position inside the capillary or oscillates around it. This is the phenomenon called "pull-out" that has been observed in fiber spinning [41, 42, 43]. The final position of the triple contact line is essentially determined by the balance between the tensile force caused by the flow of Poiseuille in the capillary, and that exerted by the emitted jet. A small lateral disturbance causes the jet to touch the inner surface of the capillary. Due to the strong tendency of the liquid to wet the steel, the jet remains in contact with the wall while sliding on it. The result is the steady emission of a jet ("steady jetting") that passes through the discharge orifice driven by the air flow.
    A sequence of images is shown in Figure 4 to illustrate the phenomenon of "pullout". The steel capillary is replaced by one made of silica (transparent).
    5 Carefully pushing the feed capillary and the discharge hole, the flowing filminside the capillary goes outside and becomes part of the outdoor jet. Thisprocess continues until the end of the capillary reaches the meniscus position. Isthen when the triple contact line anchors to the edge of the capillary.
    10 Contrary to what happens with Newtonian liquids, both the triple contact line and the free surface of the jet oscillate. This oscillatory behavior is caused by a transient bulge ("swell-die effect"), which appears continuously just outside the capillary, probably stimulated by the local relaxation of the elastic tension at that point. The bulge of the filament is conveyed downstream, making
    15 let the entire jet oscillate.
    Figure 5 shows the temporal dependence of the radius of the free surface for two sections of the jet. The magnitude of the oscillation increases with H. There is a maximum capillary-orifice distance in which the emission is interrupted (Figure 6). This occurs because the strain rate in that case is not high enough to convene the bulging of the interphase. Then, the jet continues to bulge at the outlet of the feed capillary, so that a drop is formed anchored to its edge. The drop sucks the liquid from the quasi-cylindrical thread that hangs from it. The radius of the thread is reduced by an elastocapillary regimen similar to that shown in a rheometer
    25 capillary rupture [47, 49], which ultimately leads to the "beads-on-a-string" structure and the free surface clamping.
    The symbols Hm1n and Hméx are used to represent the capillary-orifice distances at which the triple contact line first anchor to the capillary edge and the emission of
    30 jet, respectively. "Steady jetting" with "pull-out" is obtained for H <Hm1n, while an oscillating jet is observed for Hm1n <H <Hmi! Jx.
    Figure 7 shows the values of Hm1n and Hmax corresponding to PAA solutions with c = 250 and 1000 ppm. The lines delimit the parametric regions where the jets
    35 anchor to the feeding capillary. No jets could be produced for Q <1 mi / h. In
    P201 531844
    Next, we will focus on the jet configurations that have their contact lines anchored to the end of the feed capillary.
    Figure 8 shows the experimental values of the Reynolds number Re = pvoRoIl1o defined in terms of the radius Ro and the velocity Vo of the jet at the outlet of the feed capillary, the density of the liquid p and the shear viscosity at shear rates for gradients of small velocity ("zero-shear viscosity») 110. This last value was obtained by extrapolating the curves of Figure 3 for y '= O. As can be seen, Re: S10 · 2 and, consequently, the tensions of shear are dominant over the inertia of the liquid.Therefore, it can be assumed that the viscous radial diffusion of the moment flattens the velocity profile just at the exit of the capillary, forcing the Poiseuille type velocity field to evolve towards a flat distribution Very close to the capillary.
    Figure 8 also shows the aspect ratio values A. = Ro / H. Slender liquid filaments (A. -10-2) are formed between the feeding capillary and the discharge hole. Under these conditions, equation 10 (or slenderness) of amount of axial movement provides an accurate description of the dynamics of the liquid.
    In the present flow focusing configuration, the air flow is accelerated in the region located in the vicinity of the discharge orifice, said region having a size much smaller than that of the liquid filament. In order to illustrate this, numerical simulations with FLUENT 6.3 of the laminar and incompressible flow of air crossing the circular orifice used in the experiments were carried out.
    Figure 9 shows both the velocity distribution and the manometric pressure distribution along the axis of the hole as a function of the distance Z to the center of the hole. As can be seen, the focusing effect is confined within a region of size Z10 -1, where O is the diameter of the hole. In this region, the force per unit volume exerted by the stream of air in the jet scales as LJp / O [50). The size of the focusing region is much smaller than the length of the jet and, therefore, most of the liquid filament flows freely, without significant interaction with the surrounding air.
    The equation of quantity of movement 1 D can be expressed as a function of the following dimensional quantities: the density p of the liquid and its supertitial tension and, the viscosity of the solvent (water) I1s (¡Js = 10- :) kg / ms) , the radius of the jet R (z) and the axial velocity time) along the axis of the jet z, as well as the spatial distributions of the contributions
    Polymers axial oz (z) and radial orfz) to the total effort. If the aerodynamic force is neglected, then the equation 1 D becomes (37] v dv = _ ydC + ~~ r (cr _cr + 3 ~., DV) R2]
    dz pdz R 'dz 2, P dz
    where e is the local curvature of the free surface. In order to establish the ranking of the terms that appear in the equation, the radial and axial lengths are scaled with Ro Y 5 H, respectively; the speed of the jet with Vo and the polymeric stresses with the axial polymeric stress at the outlet of the ozO feed capillary. This last magnitude can be estimated as azO = '+' 1 1, where '+' 1 (Y) is the first viscometric function (Figure 3) and y. is the "effective" shear rate ("shear rate ~) that characterizes the flow of Poiseuille in the capillary, that is, and. = 4Q / (TT R ~) (Re is the radius of the capillary) [28]. equation
    The resulting dimensionless is:
    fi.'vv '= -We-1fi.'C' + We-1Te [fi. '(& - & l]' + 3ARe-1 (fi.'v ')'
    ~ -----. J 2 '1 ' I Y ~ Y Y
    1 II III IV
    Where R. = R / Roy 11 = v / va are the radius and speed of the jet scaled, respectively; We = p v5 Roly is the Weber number, C = CRo is the dimensionless local cUlv of the
    15 free surface, Te = azcl {and I Ro) is the axial polymeric stress at the outlet of the feed capillary as a function of capillary pressure, Res = pvoRo / ~ s is the Reynolds number based on the viscosity of solvent J. 1s Y ar.z = a,.: I OzO is the field of scaled polymeric stresses. In addition, the premium denotes the derivative d / di with respect to the scaled axial coordinate i = z / H.
    The variations along the jet of its radius and velocity are of the order of Ro and va, respectively. Due to the slenderness of the jet, C = 1 / R. Therefore, R.-11-fj'-C'-l, and
    (R. 2fj ')' $ 1. Consider now the Deborah number defined as De = 2J ... dvldz. According to, for example, the Oldroyd-B model [9], if (De)> the polymeric contribution to the effort
    Axial Oz grows exponentially, while the radial component or is negligible [37]. In the experiments the average Deborah number (De) == 2A (VI -Vo) IH was measured, where VI is the velocity of the jet just in front of the discharge orifice. If (De)> 1, then it can be assumed that [R.2 (Oz-Or)] 'grows exponentially throughout the entire stream.

    Figure 10 shows the experimental values of the numbers of Weber, Reynolds, and Deborah, as well as the dimensionless polymeric tension Te. As you can see, We, /l.Re¡; l «1 in all cases and, consequently, 11» 1 »IV in the dimensionless equation
    of paragraph [0070]. In addition, (De)> 1 in all experiments and hence the term 111 of the aforementioned equation is expected to grow exponentially downstream. It is concluded that the movement of the jet away from the hole is driven by the gradient of the
    effort axialpolymeric,Whilethatthetensionsuperficialgenerateaforcefrom
    resistance significant.Inotherwords,heBalancefromforcesbereduce
    approximately to:
    í 2c '= Te (ÍFoz)'
    Importantly, very small Weber number values were obtained in the experiments. In fact, capillary jets with We-6 x 10.4 were produced for the highest polymer concentration and the lowest flow rate.
    If one compares their kinetic and interfacial energies, it can be said that these jets hang virtually at rest from the feeding capillary. For these small Weber numbers, the jet must be expected to be absolutely unstable [31]. This implies that the waves grow and travel both upstream and downstream on the free surface, avoiding "steady jetting", steady jet emission, perfect. As mentioned above, self-sustained oscillations of small amplitude over the entire liquid domain were observed in the experiments. Absolute instability may contribute in part to the occurrence of such oscillations.
    It should be noted that, contrary to what could happen to Newtonian liquids, these oscillations fail to clamp the free surface due to the stabilizing role played by the polymeric axial stress not only in the linear deformation, but also in the non-linear strangulation process.
    Finally, attention is paid to the radius R1 of the viscoelastic jet just in front of the hole. The radius of the jet decreases with A (Figure 11-left). This result can be interpreted in terms of the effective Deborah number (De) measured in the experiments. This parameter also decreases with A (Figure 11-right), which implies that both the average strain rate and the extensional (apparent) viscosity associated with the stretching of the
     18-1 2-2015
    polymer also decrease with 1 . Therefore, the dissipation of energy in the entire liquid filament should decrease with 1 . Because op remained constant in all experiments, the injection of energy into the jet was essentially the same in all cases. Then, it can be concluded that the kinetic energy of the jet (radius) in front of the hole should increase (decrease) when the aspect ratio decreases.
    CONCLUSIONS The invention described herein shows the production of viscoelastic capillary jets of non-Newtonian fluids using the gaseous flow focusing configuration. The rheological nature of the liquid alters the phenomenon of focusing on several important aspects. This technique allows to form jets with lengths of more than a hundred times its radii, and with Weber numbers of the order of 10.4. Although the focusing region is confined in a small region near the discharge orifice, the polymer chains transmit the suction effect upstream along the entire liquid wire. In this way, the resistance offered by surface tension is overcome despite the fact that the kinetic energy is much smaller than the interfacial. The Ujetting ~ (stable jet emission) regime can be achieved within a range of the capillary-terror distance that depends largely on both the polymer concentration and the flow rate (see Figure 7). For distances below that interval, a pull-out of the liquid meniscus was found, while if the distance exceeds the maximum value of the interval, the jet breaks. The attainment of a perfect steady jetting was a relatively rare event. In most jet configurations, significant oscillations of the free surface were observed.
    The rupture of the jet that takes place behind the discharge orifice was not examined, since it does not differ substantially from the process widely analyzed in the literature (see, for example, (21, 37, 49, 51, 52)). Solution suppress the formation of satellite drops, and produce extensive extensional efforts, which lead to the formation of blisters ("blistering") and structures "beads-on-string ~ (pearl chain).
    The competition between surface tension and polymeric stresses is the result of a complex interaction between liquid rheology, flow rate, and applied pressure drop, as well as geometric constraints.
    The above simply illustrates the principles of the invention. It is aware that those skilled in the art will be able to imagine realizations that, although they are not
     18-1 2-2015
    explicitly described or shown here, are based on the foundation and principles
    of the invention and therefore be included in its spirit and scope. Additionally, all the examples and conditional language used here have the main intention of helping the reader understand the principles of the invention and the concepts that the inventors contribute to promote the subject, and their intention is not to limit the invention to the examples and conditions shown. Moreover, all statements describing principles, aspects and embodiments of the invention, as well as the specific examples shown, are intended to cover both structural equivalents and functional equivalents. Additionally, the intention is that those equivalents include both those currently known and those that will be developed in the future, eg any element developed to perform the same function regardless of its structure. The scope of the present intention, therefore, is not intended to be limited to the embodiments included in the examples and described herein. Moreover, the scope and spirit of the present invention is what is framed by the following claims.
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    权利要求:
    Claims (13)
    [1]
    1. A method for creating an elongated capillary jet or filament of a viscoelastic liquid, characterized by:
    5 forcing a viscoelastic liquid through a channel of a power supply at a speed that causes the liquid to exit the outlet opening of the channel, said opening being inside a pressurized chamber;
    force a gas into the pressurized chamber to exit through a positioned hole
    10 in front of the path of the viscoelastic liquid leaving the outlet opening of the channel, so that the gas flows concentrically with the viscoelastic liquid leaving the outlet opening of the channel, the gas velocity being greater than the velocity of the liquid ;
    15 where the dynamic forces that the gas exerts on the surface of the viscoelastic liquid that exits the outlet opening of the channel cause an elongated capillary jet or filament of the liquid to form, as a consequence of which said dynamic forces generate as a global result on the viscoelastic liquid an axial tension maintained along the axis of the jet, which stabilizes it;
    20 and allow the elongated capillary jet or filament to exit, surrounded by the gas, from the chamber pressurized by the hole in the chamber.
    [2]
    2. Method according to Claim 1, characterized in that the viscoelastic liquid is a Boger liquid.
    [3]
    3. Method according to any one of the preceding claims, characterized in that the Weber number of the jet is less than 1.
    Method according to any one of the preceding claims, characterized in that the Weber number of the jet is less than 1x10 · 1 •
    [5]
    5. Method according to any one of the preceding claims, characterized in that the Weber number of the jet is less than 1x10 · 2.
    [6]
    6. Method according to any one of the preceding claims, characterized in that the
    Viscoelastic liquid is forced through the channel at a speed within the range of 0.001 ~ l / sec to 100 ~ l / sec.
    [7]
    7. Method according to any one of the preceding claims, characterized in that the
    5 gas is forced through the orifice of the pressurized chamber at a speed within the range of 50 ~ l / sec to 20,000 ~ l / sec.
    [8]
    8. Method according to any one of the preceding claims, characterized in that the
    gas is forced through the orifice of the pressurized chamber at a speed within the range of 100 ~ l / sec to 500 ~ l / sec.
    [9]
    Method according to any one of the preceding claims, characterized in that the channel of the power supply is a capillary or cylindrical tube.
    Method according to any one of the preceding claims, characterized in that the channel of the power supply has an outlet diameter of less than 0.5 mm.
    [11 ]
    eleven . Method according to any one of the preceding claims, characterized in that the
    The outlet opening of the power supply channel and the outlet opening of the pressurized chamber 20 are located at a distance of less than 0.5 mm.
    [12]
    12. Method according to any one of the preceding claims, characterized in that the outlet opening of the power supply channel has a diameter of less than 0.5 mm, the outlet opening of the pressurized chamber has a diameter of less than 0.25 mm , Y
    25 The outlet opening of the power supply channel is located at a point less than 0.5 mm from the outlet opening of the pressurized chamber.
    [13]
    13. Method according to any one of the preceding claims, characterized in that the outlet opening of the power supply channel has a diameter in the range of
    30 0.1 mm to 0.5 mm, the outlet opening of the pressurized chamber has a diameter in the range of 0.1 mm to 0.25 mm, and the outlet opening of the power supply channel is located at a point at a distance in the range of 0.2 to 0.5 mm from the outlet hole of the pressurized chamber.
    Method according to any one of the preceding claims, characterized in that the distance between the outlet opening of the power supply channel and the outlet opening of the pressurized chamber increases progressively until reaching a maximum final distance of 12 mm or less. .
    [15]
    15. Elongated capillary jet or viscoelastic liquid filament obtainable according to method 5 defined in any one of the preceding claims.
    [16]
    16. Solid filament or solid fiber obtainable according to the method defined in any one of claims 1 to 14 followed by a solidification or phase change process.
    17. Solid filament or solid fiber according to claim 16, characterized in that the solidification or phase change process is carried out by solvent evaporation, cooling, chemical curing, chemical interaction with the forcing gas, chemical interaction with the gas of the environment in which the hair jet is discharged, or heat hardening.
    15. Use of the filament or fiber according to claim 17 as textile material, material for biomedical, surgical or prosthetic use, material for structural use in mechanical applications, material for the elaboration of wires or cables of very high resistance to breakage, such as fiber of mechanical reinforcement in materials with low tensile strength, substrate for biotechnological use, or material associated with telecommunication.
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    WO2017103314A1|2017-06-22|
    ES2625035B1|2018-06-21|
    引用文献:
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