AC electric field electrode system and method for fiber production

Abstract

An electrode system for use in an AC electrospinning process includes a charged component electrode and at least one of an AC field attenuation component and a precursor liquid attenuation component. The charged component electrode is electrically coupled to an AC source, which applies a predetermined AC voltage to the charged component electrode. When the electrode system includes the AC field attenuation component, the AC field attenuation component attenuates the AC field generated by the charged component electrode to better shape and control the direction of fiber flow. When the electrode system includes the precursor liquid attenuation component, the precursor liquid attenuation component serves to increase fiber production even when the top surface of the liquid precursor is not ideally shaped or is lower than the rim or lip of the reservoir containing the liquid on the charged component electrode.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to fiber production, and more particularly to an AC electric field electrode system and method for use in producing fibers by electrospinning. [Background technology]

[0002] Electrospinning is a process used to create microfibers and nanofibers. In electrospinning, fibers are typically produced by extruding a polymer-based melt or solution through a capillary needle while applying an electric field (DC or AC) to form a propagating polymer jet, or from the surface of a layer of liquid precursor on an electrode surface. A high voltage causes the solution to form a cone, from the tip of which a fluid jet emerges and accelerates toward a collector. The contracting jet thins as the solvent evaporates, becoming a continuous, solid fiber. The fiber is then collected on a collector.

[0003] The use of non-capillary (needleless, free-surface, slit, wire, or cylinder) fiber-producing electrodes improves process productivity by simultaneously generating multiple jets, but at the expense of higher process voltages. Applying a periodic alternating current (AC) electric field (instead of a typical electrostatic field (DC electrospinning)) improves fiber production conditions by increasing the effect of "corona" or "ionic" wind phenomena, which efficiently carry away the generated fibers. Compared to DC electrospinning, AC electrospinning offers higher fiber production rates per electrode area, higher process productivity, and easier fiber handling. However, the periodic nature of AC electrospinning can severely limit the spinning characteristics of many precursor solutions due to the stronger magnetic field being confined to the fiber-producing electrode, altering precursor properties. Summary of the Invention

[0004] The present disclosure relates to an AC electrospinning system and an electrode system for use in an AC electrospinning process. The electrode system includes a charged component electrode and at least one of an AC field attenuation component and a precursor liquid attenuation component. The charged component electrode is electrically coupled to an AC source, which delivers an AC signal to the charged component electrode and applies a predetermined AC voltage to the charged component electrode.

[0005] According to one embodiment, the electrode system includes an AC field attenuation component but not a precursor liquid attenuation component, and a predetermined AC voltage is also applied to the AC field attenuation component, which attenuates the AC field created by applying the predetermined AC voltage to the charged component electrode.

[0006] According to one embodiment, the charged component electrode is donut-shaped. According to another embodiment, the charged component electrode is disk-shaped.

[0007] According to one embodiment, the charged component electrode has a top surface and a rim or lip that together define a reservoir for holding the precursor liquid, with the top surface of the charged component electrode acting as the bottom of the reservoir.

[0008] According to one embodiment, the AC electric field attenuation component is a ring. According to one embodiment, the ring is circular. According to one embodiment, the ring is rectangular.

[0009] According to one embodiment, at least one of the position, orientation, and tilt of the AC field-attenuating component relative to the charged component electrode is adjustable.

[0010] According to one embodiment, the electrode system includes a precursor liquid damping component but no AC field damping component, and the charged component electrode has a top surface and a rim or lip that together define a reservoir for holding precursor liquid, with the top surface of the charged component electrode acting as the bottom of the reservoir. The precursor liquid damping component promotes fiber production even when the level of precursor liquid on the charged component electrode is lower than the lip or rim of the charged component electrode.

[0011] According to one embodiment, the precursor liquid damping component is cylindrical in shape. According to one embodiment, the precursor liquid damping component is disc in shape. According to another embodiment, the precursor liquid damping component is spherical in shape.

[0012] According to one embodiment, the precursor liquid damping component is made of a non-conductive material having a relatively low dielectric constant.

[0013] According to one embodiment, the precursor liquid damping component contacts the precursor liquid and the upper surface of the charged component electrode. According to another embodiment, the precursor liquid damping component contacts the precursor liquid and either contacts or is spaced from the upper surface of the charged component electrode. The precursor liquid damping component is rotated when contacting the precursor liquid.

[0014] According to one embodiment, the position of the precursor liquid attenuation component relative to the charged component electrode is adjustable.

[0015] According to one embodiment, the electrode system includes a precursor liquid attenuation component and an AC field attenuation component, and a predetermined AC voltage is also applied to the AC field attenuation component. The charged component electrode has a top surface and a rim or lip that together define a reservoir for holding precursor liquid, with the top surface of the charged component electrode acting as the bottom of the reservoir. The precursor liquid attenuation component promotes fiber production even when the level of precursor liquid on the charged component electrode is lower than the lip or rim of the charged component electrode.

[0016] The method comprises:

[0017] placing a precursor liquid in a reservoir of an electrode system comprising a charged component electrode and at least one of an AC field attenuation component and a precursor liquid attenuation component;

[0018] delivering an AC signal to the charged component electrode from an AC source electrically coupled to the charged component electrode to apply a predetermined AC voltage to the charged component electrode.

[0019] These and other features and advantages will become apparent from the following description, drawings and claims. [Brief explanation of the drawings]

[0020] [Figure 1A-1B] High-speed camera snapshots of fibers produced by a known AC electrospinning process using the underlying "general" electrode design are shown within 1 and 10 minutes of the process initiation, respectively.

[0021] [Figure 2A] 1A and 1B show high-speed camera snapshots of fiber production during an AC electrospinning process according to a representative embodiment using precursor X, which has poor spinning properties when used in known AC electrospinning processes of the type shown in FIGS. 1A and 1B.

[0022] [Figure 2B] 1A and 1B show high-speed camera snapshots of fiber production during an AC electrospinning process according to a representative embodiment using precursor Y, which has poor spinning properties when used in known AC electrospinning processes of the type shown in FIGS. 1A and 1B.

[0023] [Figure 3-6] 1 shows examples of several possible electrode system configurations using various arrangements of components A, B, and C.

[0024] [Figures 7A-7B] High-speed camera snapshots of fiber production during the AC electrospinning process using one of the electrode system configurations shown in Figures 3-6.

[0025] [Figure 8A-8B] 1A-1C are side perspective views of two different electrode system configurations with components A and B, according to a representative embodiment.

[0026] [Figure 9A-9B] 1A-1C show plan views of two different electrode system configurations that can be constructed using component A and component B, according to a representative embodiment.

[0027] [Figure 10] FIG. 1 is a side perspective view of an electrode system configuration comprising component A and component B, where component B is tilted relative to the axis of the electrode system configuration, according to a representative embodiment.

[0028] [Figure 11A] FIG. 1 is a side perspective view of an electrode system configuration comprising component A and component B, according to a representative embodiment.

[0029] [Figures 11B-11C]11B is a photograph of the electrode system shown in FIG. 11A showing the effect of the AC field attenuation component on fiber production when the AC field attenuation component is moved in line with or slightly below the liquid precursor fluid layer.

[0030] [Figure 12A] FIG. 1 is a side perspective view of an electrode system configuration comprising a component A electrode and a precursor liquid attenuation component C, according to a representative embodiment.

[0031] [Figures 12B-12C] FIG. 12B is a photograph of an electrode system having the configuration shown in FIG. 12A but with three rotating coaxial component C-disks during the fiber production process.

[0032] [Figure 13-15] 10A-10C illustrate schematic diagrams of fiber production during AC electrospinning for different configurations of the electrode system and different conditions of precursor fluid for the component A electrode, according to a representative embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0033] Disclosed herein are exemplary embodiments of an electrode system for use in AC electrospinning that reduce or eliminate the above-mentioned limitations and restrictions, thereby significantly improving the productivity and expanding the applicability of the AC electrospinning process. The electrode system includes a charged component electrode and at least one of an AC field attenuation component and a precursor liquid attenuation component. The charged component electrode is electrically coupled to an AC source, which delivers an AC signal to the charged component electrode and applies a predetermined AC voltage to the charged component electrode. When the electrode system includes the AC field attenuation component, the AC field attenuation component attenuates the AC field generated by the charged component electrode to better shape and control the direction of fiber flow. When the electrode system includes the precursor liquid attenuation component, the precursor liquid attenuation component serves to increase fiber production even when the top surface of the liquid precursor is not ideally shaped or is lower than the rim or lip of the reservoir containing the liquid on the charged component electrode.

[0034] In the following detailed description, several exemplary or representative embodiments are described to explain the principles and concepts of the present invention. For purposes of explanation, not limitation, a representative embodiment disclosing specific details is described to enable a thorough understanding of one embodiment according to the present teachings. However, it will be apparent to one skilled in the art having the benefit of this disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Furthermore, descriptions of well-known devices and methods may be omitted so as not to obscure the description of the representative embodiments. Such methods and devices are clearly within the scope of the present teachings.

[0035] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in this specification and the appended claims, the terms "a," "an," and "the" include both singular and plural referents unless the context clearly dictates otherwise. Thus, for example, "a device" includes one device and multiple devices. Relative terms may be used to describe the relationship of various elements to one another, as illustrated in the accompanying drawings. These relative terms are intended to encompass different orientations of the devices and / or elements in addition to the orientation shown in the drawings. When an element is referred to as being "connected," or "coupled," or "electrically coupled" to another element, it will be understood that the elements may be directly connected or coupled, or that intervening elements may be present.

[0036] Exemplary or representative embodiments will be described with reference to the drawings, wherein like reference numerals represent like components, elements, or features. It should be noted that the features, elements, or components in the figures are not intended to be drawn to scale, emphasis instead being placed upon illustrating the principles and concepts of the present invention.

[0037] Figures 1A and 1B show high-speed camera snapshots of fibers produced by a known AC electrospinning process using an electrode with a basic "generic" electrode design. The snapshot shown in Figure 1A was taken within 1 minute of the start of the AC electrospinning process. The snapshot shown in Figure 1B was taken 10 minutes after the start of the known AC electrospinning process. Although AC electrospinning is a relatively new process for high-yield production of microfibers and nanofibers, two significant problems have been identified with known AC electrospinning processes: (1) many precursors in the AC electrospinning process that typically have good spinning properties in the DC electrospinning process have poor spinning properties, and (2) the high fiber production rate and electric field distribution that confines the fiber to the electrode result in the accumulation of spun material at the outer edges of the electrode typically used in AC electrospinning.

[0038] Challenge (1) limits the precursors that can be used in AC electrospinning, while challenge (2) rapidly reduces fiber production yield and ultimately results in halting fiber production. The result of challenge (2) can be seen in Figure 1B, which shows a white "crown" of spun material forming around the outer edge of the electrode. The resulting reduction in upward fiber flow caused by the accumulation of spun material at the outer edge of the electrode is evident from a comparison of Figures 1A and 1B.

[0039] The AC electrospinning system and method of the present disclosure overcomes these limitations and constraints. The present disclosure provides an electrode system for use in AC electrospinning systems and processes that not only reduces or eliminates material buildup on the outer edges of the electrodes, but also enables fibers to be produced from precursors that have no or poor spinning properties with typical electrode designs currently used in AC electrospinning processes. By achieving these goals, productivity of AC electrospinning methods is significantly improved while achieving much better control of fiber generation and propagation.

[0040] Figure 2A shows high-speed camera snapshots of fiber production during an AC electrospinning process, according to a representative embodiment. The fiber shown in Figure 2A was produced using precursor X, which has poor spinning properties when used in a known AC electrospinning process of the type shown in Figures 1A and 1B. Figure 2B shows high-speed camera snapshots of fiber production during an AC electrospinning process, according to a representative embodiment. The fiber shown in Figure 2B was produced using precursor Y, a precursor that has poor spinning properties when used in a known AC electrospinning process of the type shown in Figures 1A and 1B.

[0041] In the exemplary embodiment shown in Figures 2A and 2B, novel electrodes including components labeled A and B were used in the AC electrospinning system. The novel electrode system can have a variety of configurations, as described in more detail below with reference to Figures 3-6. By using the novel electrode system, the AC electrospinning process achieves high spinning properties using precursors X and Y, which previously had poor spinning properties. In Figure 2A, the high spinning properties of precursor X fiber are achieved with uniform columnar fiber flow. In Figure 2B, a conical flow of precursor Y fiber is achieved. To provide some idea of ​​the scale of fiber production, the width of the photographs shown in Figures 2A and 2B is approximately 250 millimeters (mm). It should be noted that the principles and concepts of the present invention are not limited with respect to the precursors used in the AC electrospinning process or with respect to the thickness of the produced fibers.

[0042] As noted above, the electrode system of the present disclosure not only reduces or eliminates material buildup at the outer edges of the electrodes, but also allows fibers to be produced from precursors that have no or poor spinning properties with typical electrode designs used in AC electrospinning processes. Additionally, the electrode system of the present disclosure further improves AC electrospinning productivity and allows for much better control over fiber generation and propagation.

[0043] According to a representative embodiment, the electrode system configuration comprises at least component A, typically component A and at least one of components B and C. Component A is a charged component electrode. Component B is an AC field attenuation component. Component C is a precursor liquid attenuation component, which is a rotating non-conductive component. According to a preferred embodiment, when the electrode system configuration comprises component A and at least one of components B and C, at least two of the components are arranged such that they have at least one common axis of symmetry.

[0044] Electrode systems for AC electrospinning according to the principles and concepts of the present invention can have a variety of configurations, some of which are shown in Figures 3-6 and have the following attributes: 1) The electrode system configuration has a charged component electrode (interchangeably referred to herein as "component A") and at least one of an AC field attenuation component (interchangeably referred to herein as "component B") and a precursor liquid attenuation component (interchangeably referred to herein as "component C") having at least one common axis of symmetry. 2) The components comprising the electrode system configuration are optimally positioned relative to each other, whether it is an AB component configuration, an AC component configuration, or an ABC component configuration. 3) At least one of the components of the electrode system configuration having the attribute described in 1) above is non-conductive. 4) All components of an electrode system configuration having the attributes described in 1) above are capable of moving relative to each other in at least one degree of freedom (either translational or rotational). 5) At least one of the components of the electrode system configuration having the attributes described in 1) above includes a magnetic element, which may be present in any or all of components A, B, and C for mechanical coupling of the parts, allowing them to be quickly replaced, thereby making the system more adaptable to different processes. 6) When an electrode system configuration having the attributes described in 1) above includes a component C, the component C is positioned in the primary direction of fiber generation (upward) and flow propagation relative to the component A. 7) If an electrode system configuration having the attributes described in 1) above includes a component C, then component C does not have direct electrical contact with either component A or component B. 8) Any of the electrode system configurations having the attributes (AB, AC, or ABC) described in 1) above can be grouped into multi-electrode configurations.

[0045] Some examples of possible electrode system configurations having at least some of the attributes described above in 1) through 8) are shown in Figures 3 through 6. The electrode configuration shown in Figure 3 has components A, B, and C. Component B is located along the central axis 1 of the electrode system and has a sidewall surrounded by component A in the X direction, also referred to herein as the lateral direction. Component B may be, for example, annular. Component B may be a solid element having a circular, cylindrical, or rectangular cross section. Component C is stacked on top of component A. Component C may have any shape that allows it to rotate, such as a cylinder, ring, sphere, disk, or other shape. Component B may be recessed relative to component C, i.e., the Y coordinate of B is smaller than the Y coordinate of C. Components A and C may rotate about a central axis 1 parallel to the Y axis of the X, Y, Z Cartesian coordinate system shown below in Figures 3 through 6. Component B may be movable along the central axis 1.

[0046] The electrode system configuration shown in FIG. 3 can be modified in several ways. For example, component C shown in FIG. 3 can be removed, leaving an electrode system with an AB configuration. As another example, component B shown in FIG. 3 can be removed, leaving an electrode system with an AC configuration. In either case, in the configuration shown in FIG. 3, central axis 1 is a common axis for all components, regardless of whether the electrode system configuration has an AB, AC, or ABC configuration. Therefore, the system configuration shown in FIG. 3 has attribute 1). Regardless of which components are used to form the electrode system configuration shown in FIG. 3, the components can be optimally positioned relative to each other, which satisfies attribute 2). At least one of the components can be non-conductive, which satisfies attribute 3). All of the components making up the configuration of FIG. 3 can move relative to each other in at least one degree of freedom, which satisfies attribute 4). For example, components A and C can rotate relative to central axis 1, while component B can move along central axis 1. At least one of components A, B, or C can be a magnetic element, which satisfies attribute 5). In Figure 3, component C is positioned in the primary direction of fiber generation and flow propagation to satisfy attribute 6). Component C is spaced apart from components A and B, and there is no direct electrical connection between component C and components A and B, which satisfies attribute 7). This attribute can also be achieved by placing a dielectric material or spacer between the components, if necessary. Multiple electrodes having the configuration shown in Figure 3 can be grouped together to achieve a multi-electrode arrangement that satisfies attribute 8).

[0047] The electrode configuration shown in FIG. 4 has components A, B, and C. Component A is located along the central axis 11 of the electrode system and has a sidewall that is laterally surrounded by component B. Component B may be, for example, annular. Component A may be a solid element with a circular, cylindrical, or rectangular cross-section. Component C may also be a solid element with a circular, cylindrical, or rectangular cross-section and may be stacked on top of component A. Component B may rotate about central axis 11, which is parallel to the Y axis of the X, Y, Z Cartesian coordinate system shown below in FIGS. 3-6. Components A and B may be movable along central axis 11.

[0048] The electrode system configuration shown in FIG. 4 can be modified in several ways. For example, component C shown in FIG. 4 can be removed, leaving an electrode system with an AB configuration, as shown in FIGS. 2A and 2B, except that in FIGS. 2A and 2B, component A protrudes along central axis 11 relative to component B. As another example, component B shown in FIG. 4 can be removed, leaving an electrode system with an AC configuration. In all cases, in the configuration shown in FIG. 4, central axis 11 is the axis common to all components, regardless of whether the electrode system configuration has an AB, AC, or ABC configuration. Thus, the system configuration shown in FIG. 4 has attribute 1). Regardless of which components are used to form the electrode system configuration shown in FIG. 4, the components can be optimally positioned relative to each other, which satisfies attribute 2). Component C can be non-conductive, which satisfies attribute 3). Typically, components A and B are conductive, and component C is non-conductive. All of the components comprising the configuration shown in FIG. 4 can be moved relative to each other in at least one degree of freedom, which satisfies attribute 4). For example, component B can rotate relative to central axis 11, while components A and C can move along central axis 11. At least one of components A, B, or C can contain a magnetic element, which satisfies attribute 5). In FIG. 4, component C is positioned in the primary direction of fiber generation and flow propagation, which satisfies attribute 6). Component C is spaced apart from components A and B, and there is no direct electrical connection between component C and components A and B, which satisfies attribute 7). This attribute can also be achieved by placing a dielectric material or spacer between the components, if necessary. Multiple electrodes having the configuration shown in FIG. 4 can be grouped together to achieve a multi-pole arrangement, which satisfies attribute 8).

[0049] The electrode configuration shown in FIG. 5 has components A, B, and C, which are located along the central axis 21 of the electrode system and have one side adjacent to component B. If component C is ring-shaped, it must rotate around its central axis, which is perpendicular to the plane of the ring. Component A may be a solid element with a circular, cylindrical, or ring-shaped cross section. Component C may be stacked on top of component A. Component B may move, for example, in the XZ plane. Components A and C may be movable along the central axis 21. Component B may be movable in the Y direction, which is parallel to the central axis 21. Components A and / or C may be movable in the XZ plane, which is perpendicular to the central axis 21.

[0050] The electrode system configuration shown in FIG. 5 can be modified in several ways. For example, component C shown in FIG. 5 can be removed, leaving the electrode system in an AB configuration. As another example, component B shown in FIG. 5 can be removed, leaving the electrode system in an AC configuration. In either case, in the configuration shown in FIG. 5, central axis 21 is an axis common to at least components A and C. Therefore, the system configuration shown in FIG. 5 has attribute 1). Regardless of which components are used to form the electrode system configuration shown in FIG. 5, the components can be optimally positioned relative to each other, which satisfies attribute 2). At least one of the components shown in FIG. 5 can be non-conductive, which satisfies attribute 3). As noted above, all components making up the configuration shown in FIG. 5 can be moved relative to each other in at least one degree of freedom, which satisfies attribute 4). At least one of components A, B, or C shown in FIG. 5 can be a magnetic element, which satisfies attribute 5). In FIG. 5, component C is positioned in the primary direction of fiber generation and flow propagation, which satisfies attribute 6). Component C is spaced apart from components A and B, and there is no direct electrical connection between component C and components A and B, which satisfies attribute 7). This attribute can also be achieved by placing a dielectric material or spacer between the components, if necessary. Multiple electrodes having the configuration shown in Figure 5 can be grouped together to achieve a multi-pole arrangement, which satisfies attribute 8).

[0051] The electrode configuration shown in FIG. 6 includes components A, B, and C. Component A is positioned along the central axis 31 of the electrode system and has a sidewall laterally surrounded by component B. Component A may be, for example, annular. Component B, located on the central axis 31, may be a solid element with a circular, cylindrical, or rectangular cross-section. The outermost component, component B, may be, for example, a ring. Component C may be stacked on top of component A and rotate around its axis and / or move along the surface of component A. In such a case, component C may be cylindrical or spherical. Ring-shaped components A and B may rotate about a central axis 31 parallel to the Y axis of an X, Y, Z Cartesian coordinate system. Components A, B, and C that are not ring-shaped may be movable along axes parallel to the X, Y, and / or Z directions.

[0052] The electrode system configuration shown in FIG. 6 can be modified in several ways. For example, component C shown in FIG. 6 can be removed, leaving the electrode system in an AB configuration. As another example, component B shown in FIG. 6 can be removed, leaving the electrode system in an AC configuration. In either case, in the configuration shown in FIG. 6, the central axis 31 is a common axis for all components, regardless of whether the electrode system configuration has an AB, AC, or ABC configuration. Therefore, the system configuration shown in FIG. 6 has attribute 1. Regardless of which components are used to form the electrode system configuration shown in FIG. 6, the components can be optimally positioned relative to each other, which satisfies attribute 2). At least one of the components shown in FIG. 6 can be non-conductive, which satisfies attribute 3). As noted above, all components making up the configuration shown in FIG. 6 can be moved relative to each other in at least one degree of freedom, which satisfies attribute 4). At least one of components A, B, or C can be a magnetic element, which satisfies attribute 5). In FIG. 6, component C is positioned in the primary direction of fiber generation and flow propagation, which satisfies attribute 6). Component C is spaced apart from components A and B, and there is no direct electrical connection between component C and components A and B, which satisfies attribute 7). This attribute can also be achieved by placing a dielectric material or spacer between the components, if necessary. Multiple electrodes having the configuration shown in FIG. 6 can be grouped together to achieve a multi-electrode arrangement, which satisfies attribute 8). It should also be noted that electrode systems having the configurations shown in FIGS. 3-6, or modifications thereof, can be grouped together to form a multi-electrode arrangement.

[0053] Suitable materials for component A include, but are not limited to, metals and alloys that have good resistance to common solvents, acids, and bases. Stainless steel is an example of a suitable material for component A. Suitable materials for component B, which typically does not come into contact with the fluid, include, but are not limited to, metals and alloys of copper, aluminum, and stainless steel that have good resistance to common solvents, acids, and bases. Suitable materials for component C, which does come into contact with the fluid, include, but are not limited to, Teflon, polypropylene, and other chemically stable polymers with low dielectric constants.

[0054] 7A and 7B show high-speed camera snapshots of fiber production during an AC electrospinning process using one of the novel electrode system configurations described above with reference to FIGS. 3-6. FIGS. 8A and 8B show side perspective views of examples of different electrode system configurations including components A and B. FIGS. 9A and 9B show top plan views of examples of different electrode system configurations that may be configured with components A and B. In the configuration shown in FIG. 9A, component A is a donut-shaped electrode, and component B comprises an inner electrode and an outer electrode. In the configuration shown in FIG. 9B, component A is a disk-shaped electrode, and component B comprises an outer electrode. Note that the exemplary configurations shown in FIGS. 8A-9B are provided to illustrate some examples of the principles and concepts of the present invention and are not intended to be limiting, as will be understood by one of ordinary skill in the art in light of the description provided herein.

[0055] With either of these electrode system configurations, precursor fluid 3 is loaded onto the top surface of the component A electrode. The precursor fluid 3 is typically pumped to the top surface of the component A electrode by a pump (not shown) through tubing 5 of the electrode system configuration. Identical AC voltages are applied to the component A and B electrodes. When an AC field is applied to components A and B, a liquid jet is generated. As shown in Figures 8A and 8B, fibers 4 form as the solvent in precursor fluid 3 evaporates and the fiber flow is pulled toward the component A electrode by the "ionic wind" phenomenon.

[0056] In many cases, the absence of Component B, the AC field-attenuating component, can result in the fiber jet spreading too much or being difficult to initiate. Furthermore, the absence of Component B can result in the formation of the aforementioned fibrous residue around the rim of the Component A electrode. Component B is a field-attenuating electrode that operates at the same AC voltage as the Component A electrode from the same power source. The field-attenuating effect of Component B improves fiber generation, improves the shape of the fiber flow (Figure 8B), and allows for control of the flow direction (Figures 7B and 8B). Component B is typically positioned around the periphery of the Component A electrode (Figure 9A), but Component B can also have an inner portion (Figure 9A) in the case of a hollow or donut-shaped Component A electrode (Figure 9A). In Figures 7A-9B, Component B is shown as being ring-shaped and circular. However, Component B can have other shapes. For example, Component B can have a rectangular (e.g., square) shape.

[0057] 10, component B can be tilted relative to the central axis of component A electrode, which is coaxial with tube 5, to control flow direction. In some embodiments, a translation mechanism (not shown) mechanically coupled to component B allows the user to control the position, orientation, and / or degree of tilt of component B, allowing the field attenuation effect of component B to be adjusted to better control fiber generation, fiber flow shape, and / or fiber flow direction.

[0058] FIG. 11A is a side perspective view of an electrode system configuration including a component A electrode and a component B electrode, according to a representative embodiment. If the precursor fluid 3 does not have an optimal surface profile (convex) on the top surface of the component A electrode, jetting may be difficult or even impossible to initiate. If there is too much precursor fluid 3 on the top surface of the component A electrode, the fluid 3 may overflow the component A electrode, causing the AC electrospinning process to stop. On the other hand, as described in more detail below with reference to FIG. 14, jet generation typically stops when the fluid level is below the outer edge of the lip or rim of the component A electrode. Also, as shown in FIG. 11A, jet generation typically stops when component B rises above the top surface of the precursor fluid 3 (in the +z direction).

[0059] 11B and 11C are photographs of the electrode system shown in FIG. 11A, showing the effect of AC field attenuation component B on fiber generation when it is moved in-line with or slightly below liquid precursor fluid layer 3. As seen in FIGS. 11B and 11C, a jet is generated, and by adjusting the height (Z direction) of component B relative to component A electrodes while maintaining component B at or slightly below the Z position of precursor fluid layer 3, the fiber flow can be tuned minutely in width, shape, and mass of the generated fibers. The width, shape, and velocity of the fiber flow are determined by the electric field voltage and frequency, as well as the composition, viscosity, electrical conductivity, and surface tension of the liquid precursor.

[0060] FIG. 12A is a side perspective view of an electrode system configuration including a component A electrode and a precursor liquid damping component, component C, according to a representative embodiment. FIGS. 12B and 12C are photographs of an electrode system having the configuration shown in FIG. 12A but with three rotating coaxial component C disks during the fiber production process. The addition of the precursor liquid damping component C, ideally made of a low-dielectric-constant, non-conductive material (e.g., Teflon or polypropylene, or other plastic), makes it possible to solve the problems described above with reference to FIG. 11A. According to a representative embodiment, component C rotates, and charged precursor fluid 3 forms a layer on the surface of component C. The precursor fluid 3 layer has a preferred convex shape that increases the number of jets generated per unit area, thus increasing the fiber production rate. In this way, it is no longer necessary to maintain an optimal water level of precursor fluid 3 on the component A electrode, thus preventing overflow and residue buildup around the component A electrode.

[0061] The precursor liquid damping component C can have various shapes or configurations. For example, it can be a cylinder, a disk, a sphere, or a combination thereof, and can have various surface profiles, such as a corrugated surface, that modulate fluid motion and further increase jet generation. The precursor liquid damping component C can be one or more cylinders, disks, or rings of different diameters and thicknesses (lengths). The precursor liquid damping component C can be partially immersed in the liquid precursor 3 and rotated at various speeds (ω) in combination with linear x-y motion on the surface of the component A electrode. The working side of the component C can be smooth or structured (e.g., with notches, holes, protrusions, etc.) to achieve retention of the liquid precursor 3. In the embodiment shown in Figures 12B and 12C, the rotating coaxial component C disk shape is a 30 mm diameter plastic (e.g., Teflon) disk with a channel along its rim placed on a rectangular Teflon component A electrode partially filled with liquid precursor 3. As the disk assembly rotates, fibers are generated from each side of the rim along each disk. In the exemplary configuration shown in Figures 12B and 12C, the length of the assembly comprising components A and C is 100 mm, however, the principles and concepts of the present invention are not limited with respect to the dimensions of the assembly or its components.

[0062] An AC field attenuator component B can be used in conjunction with component C. The x, y, and z positions of the component B electrode are typically below the x, y, and z positions of the top surface of component C to better shape and direct fiber flow. Depending on the shape and area of ​​the component A electrode and component C, component C can be moved in the x and y directions while rotating. The bottom side of component C can slide on the top surface of the component A electrode as it rotates, or it can be positioned slightly above the top surface of the component A electrode, so that component C contacts precursor fluid 3 as it rotates but does not directly contact the top surface of the component A electrode.

[0063] Figures 13-15 schematically illustrate fiber generation during the AC electrospinning process for different configurations of the electrode system relative to the component A electrode and different precursor fluid 3 conditions, according to a representative embodiment. A field-attenuating component B electrode is not included, but it could be included. Typically, the component A electrode has a dish or cup shape, as shown in Figures 13-15. The precursor fluid 3 water surface required to influence fiber generation, and its appropriate convex profile (Figure 13), are predicted. However, no numerical model currently exists that accounts for the possible occurrence of Faraday instability in a viscous fluid layer under an AC electric field and the associated appearance of surface wave patterns that can promote jet formation. In either case, if the fluid 3 water surface falls below the rim 7 of the component A electrode, no jet is generated (Figure 14). A rotating plastic disk or cylinder containing component C draws fluid from the component A electrode (Figure 15). This charged fluid 3 can easily form multiple jets due to the curved surface of component C, thus generating a fiber flow. Furthermore, as shown above, the use of component C typically increases fiber production over electrode system configurations that do not include component C (FIG. 13). Adding component B electrodes to the configurations shown in FIGS. 13 and 15 would allow for better control of the shape and direction of fiber flow.

[0064] It should be noted that exemplary embodiments are described herein for the purpose of illustrating the principles and concepts of the present invention. As will be understood by those skilled in the art in light of the description provided herein, many modifications may be made to the embodiments described herein without departing from the scope of the present invention. For example, while the principles and concepts of the present invention have been described primarily with reference to a particular electrode system configuration, the principles and concepts of the present invention are equally applicable to other electrode system configurations. Also, many modifications may be made to the embodiments described herein without departing from the principles and concepts of the present invention, and all such modifications will be understood by those skilled in the art to be within the scope of the present invention.

Claims

1. 1. An electrode system for use in an alternating current (AC) electrospinning system, comprising: a charged component electrode, the charged component electrode being electrically coupled to an AC source, the AC source delivering an AC signal to the charged component electrode and applying a predetermined AC voltage to the charged component electrode; an AC field attenuation component; applying the predetermined AC voltage to the AC field attenuation component, the AC field attenuation component attenuating an AC field created by the application of the predetermined AC voltage to the charged component electrode; An electrode system wherein the charged component electrode is donut-shaped.

2. 10. The electrode system of claim 1, wherein the charged component electrode has a top surface and a rim or lip that together define a reservoir for holding precursor liquid, the top surface of the charged component electrode acting as the bottom of the reservoir.

3. The electrode system of claim 1 , wherein the AC field attenuation component is a ring.

4. The electrode system of claim 3 , wherein the ring is circular.

5. The electrode system of claim 3 , wherein the ring is rectangular.

6. The electrode system of claim 3 , wherein at least one of the position, orientation, and tilt of the AC field-attenuating component relative to the charged component electrode is adjustable.

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