Method of Spinning Conductive Poly(3,4-Ethylenedioxythiophene): Polystyrene Sulfonate Fibers

Abstract

A method of producing poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) fibers includes the step of extruding a PEDOT:PSS dope through a spinneret into a coagulation bath of a non-solvent to PEDOT:PSS polymer to produce an individual filament that floats to an upper surface of the coagulation bath. The non-solvent to PEDOT:PSS polymer has a boiling point less than 125 C. and a density higher than the PEDOT:PSS nascent filament. The individual filament is dried and then contacted with other dried filaments to make a multifilament tow.

Claims

1. A method of spinning conductive poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) fibers, comprising: extruding a PEDOT:PSS dope through a spinneret into a coagulation bath of formic acid to produce an individual filament that floats to an upper surface of the coagulation bath.

2. The method of claim 1, further including extruding the PEDOT:PSS dope upward into the coagulation bath of formic acid.

3. The method of claim 2, further including removing the individual filament from the upper surface of the coagulation bath of formic acid by pulling upward onto a guide surface.

4. The method of claim 3, further including pulling the individual filament from the guide surface into the air.

5. The method of claim 4, further including drying the individual filament after the pulling from the guide surface.

6. The method of claim 5, further including contacting the individual filament with other PEDOT:PSS filaments only after the individual filament and the other PEDOT:PSS filaments have been dried.

7. The method of claim 6, further including forming and collimating a tow of PEDOT:PSS fibers from the dried individual filament and the other dried PEDOT:PSS filaments to provide a multifilament tow of PEDOT:PSS fibers.

8. The method of claim 7, further including taking up the tow of PEDOT:PSS fibers on the surface of a rotating cylindrical core.

9. The method of claim 8, wherein the drying of the individual filament is by subjecting the individual filament to a column of heated air that quickly evaporates the formic acid.

10. The method of claim 1, wherein the PEDOT:PSS dope has about 1:2.5 PEDOT:PSS weight ratio.

11. The method of claim 10, wherein the PEDOT:PSS dope has a solids concentration of about 2.5 wt. %.

12. The method of claim 1, wherein the coagulation bath of formic acid has a concentration greater than 85%.

13. The method of claim 1, wherein the spinneret includes at least one capillary having a diameter of about 100 m and a length to diameter of L/D=5.

14. A method of producing poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) fibers, comprising: extruding a PEDOT:PSS dope through a spinneret into a coagulation bath of a non-solvent to PEDOT:PSS polymer to produce an individual filament that floats to an upper surface of the coagulation bath wherein the non-solvent to PEDOT:PSS polymer has a boiling point of less than 125 C. and a density higher than the PEDOT:PSS nascent filament.

15. The method of claim 14, further including extruding the PEDOT:PSS dope upward into the coagulation bath.

16. The method of claim 15, further including removing the individual filament from the upper surface of the coagulation bath onto a guide surface.

17. The method of claim 16, further including removing the individual filament from the guide surface into the air.

18. The method of claim 17, further including drying the individual filament after the removing from the guide surface.

19. The method of claim 18, further including forming and collimating a tow of PEDOT:PSS fibers from the dried individual filament and the other dried PEDOT:PSS filaments to provide a multifilament tow of PEDOT:PSS fibers.

20. A method of producing poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) fibers, comprising forming a multifilament PEDOT:PSS fiber tow by upward solution spinning of a PEDOT:PSS dope in a formic acid-based coagulation bath.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0013] The accompanying FIGURE incorporated herein and forming a part of the specification, illustrates certain aspects of the new and improved method and together with the description serves to explain certain principles thereof. A person of ordinary skill in the art will readily recognize from the following discussion that alternative embodiments of the method may be employed without departing from the principles described below.

[0014] FIG. 1 is a schematic illustration of one possible embodiment of an apparatus for conducting the method for spinning electrically conductive PEDOT:PSS fibers.

[0015] Reference will now be made in detail to the present preferred embodiments of the method for spinning electrically conductive PEDOT:PSS fibers.

DETAILED DESCRIPTION

[0016] The new and improved method for spinning electrically conductive PEDOT:PSS fibers may be broadly described as including the step of extruding a PEDOT:PSS dope through a spinneret into a coagulation bath of a non-solvent to PEDOT:PSS polymer to produce an individual filament that floats to an upper surface of the coagulation bath. The non-solvent to PEDOT:PSS polymer preferably has a boiling point of less than 125 C. and a density higher than the PEDOT:PSS dope or nascent PEDOT:PSS filament being formed in the coagulation bath. In some embodiments, the boiling point is less than 120 C. In some embodiments, the boiling point is less than 115 C., more preferably less than 110 C. and still more preferably less than 105 C. In some embodiments, the density of the non-solvent to the PEDOT:PSS polymer is greater than 1.0 g/cm.sup.3, more preferably greater than 1.1 g/cm.sup.3 and still more preferably greater than 1.2 g/cm.sup.3.

[0017] In one possible embodiment, the non-solvent to PEDOT:PSS polymer has a boiling point of less than 101 C. and a density of at least 1.15 g/cm.sup.3. In one particularly useful embodiment, the non-solvent coagulation bath comprises formic acid having a concentration greater than 85%. The PEDOT:PSS dope used in the method may have approximately a 1:2.5 PEDOT:PSS weight ratio and a solids concentration of about 2.5 wt. %. The spinneret used in the method may include at least one capillary having a diameter of about 100 m and a length to diameter of L/D=5.

[0018] Preferably the method further includes extruding the PEDOT:PSS dope upward into the coagulation bath of the non-solvent/formic acid as described in greater detail below and illustrated in FIG. 1. The method further includes removing the individual filament from the upper surface of the coagulation bath of formic acid when it rises to the surface. The method also includes drying the individual filament after removing from the coagulation bath of non-solvent/formic acid.

[0019] The method further includes contacting the individual filament with other PEDOT:PSS filaments only after the individual filament and the other PEDOT:PSS filaments have been dried. This is of importance as the emerging nascent filaments must dry prior to being collimated together as a tow or else the neighboring filaments will tend to fuse together. Fused filaments destroy the utility of the tow, rendering it similar to a brittle rod. Thus, the method further includes forming and collimating a tow of PEDOT:PSS fibers from the dried individual filament and other dried PEDOT:PSS filaments to provide a multifilament tow of PEDOT:PSS fibers wherein the filaments are not fused together. Next, the method includes taking up the tow of PEDOT:PSS fibers on the surface of a rotating cylindrical core.

[0020] The drying of the filaments may be completed by any appropriate means known in the art, including, but not limited to drying in a column of heated air that quickly evaporates the formic acid. Here, it should also be noted that those other filaments may be spun in parallel in the same coagulation bath with the individual filament.

[0021] As illustrated in FIG. 1, a concentrated, degassed aqueous dispersion dope of poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is transferred to multiple syringes 12. The syringes 12 are connected to a multi-syringe pump 14 that allows precise control of the flow rate. In operation, each syringe 12 equivalently meters the dope through a filter 16 before exiting through tubing 18 connected to a 100 m diameter capillary spinneret 20 (length to diameter of the capillary, L/D=5) into the coagulation bath 22. The spinnerets 20 may be positioned/fixed in the bottom 24 of the coagulation bath 22 as shown. In an alternative embodiment (not shown), a metering pump provides dope flow to a spin pack with filtration and distribution to a multifilament spinneret.

[0022] As should be appreciated, the dope D from the spinnerets 20 is extruded upward into the bath 22 of concentrated formic acid (>85% assay), which destabilizes the nascent PEDOT:PSS dope extrudates forming gel-like filaments F. The filaments F then begin to float upward in the dense formic acid towards the surface 26 of the formic acid bath 22. As they do, the filaments F further solidify such that, by the time they reach the surface 26, they can be picked up with tweezers by hand and pulled upward into the air above, continuously, without breaking. To pin filaments F in place when exiting the formic acid bath 22, the filaments may first be pulled up and onto a guide surface 25 prior to being pulled into the air. This prevents the filaments F from wandering around the bath 22, where they are prone to collide forcefully with one another or with the coagulation bath container, which can lead to filament fusion or breakage. It also keeps the filaments F separated prior to and as they are being dried.

[0023] As the individual filaments F are pulled upward above the guide surface 25, they pass through a column of heated air 27 that dries the filaments. The dried filaments F are then fixed to the surface of a rotating take-up core 28. Critically, the filaments do not contact neighboring filaments in this process until after the drying process. The drying of each filament in the air column 27, is facilitated by the low boiling point of the formic acid.

EXPERIMENTAL

Dope Preparation:

[0024] Poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) aqueous dispersion (Heraeus Clevios PH 1000) dope is first concentrated by evaporation of water to 2.5 wt. % polymer solid content. The starting Clevios PH 1000 is 1.3 wt. % solids content in water with 1:2.5 PEDOT:PSS weight ratio [28.57 wt. % PEDOT in the polymer phase]. The PEDOT:PSS dispersion is placed on a hot plate at 100 C. while magnetically stirring and the mass of evaporated water is monitored until the solids concentration reaches 2.5 wt. %.

Dope Metering

[0025] First, as shown in FIG. 1 and described above, the degassed dope is transferred carefully to multiple syringes 12 connected to a multi-syringe pump 14 that allows precise control of the flow rate. Each syringe 12 then equivalently meters the dope through a filter 16 and a 100 m diameter capillary spinnerets 20 (length to diameter of the capillary, L/D=5) into the coagulation bath 22. The spinnerets 20 are positioned/fixed in the bottom 24 of the coagulation bath 22 such that the nascent filaments F are extruded upward and into the coagulation bath liquid. Each spinneret 20 is spaced approximately 2 centimeters from its nearest neighbor spinneret.

Filaments Formation/Coagulation

[0026] The nascent filaments F are extruded upward into the bath of concentrated formic acid (>85% assay), and then begin to float upward in the dense formic acid towards the surface 26 of the formic acid bath 22. The solidified filaments F are then picked up with tweezers by hand and pulled upward into the air above, continuously, without breaking. To pin filaments in place when exiting the formic acid bath, filaments are first pulled up and onto a guide surface 25 prior to being pulled into the air.

Filaments Drying

[0027] Filaments F reaching the surface 26 of the formic acid bath are routed upward, by-hand, with tweezers or other means through a column of (heated) air 27 and eventually fixed to the surface of a rotating take-up core 28. Critically, the filaments do not contact neighboring filaments in this process until after the drying process. Each filament dries in this air column, which is facilitated by the low boiling point of the formic acid.

Take-Up

[0028] After drying of the individual filaments, a tow of PEDOT:PSS fibers is formed and collimated, then taken up on the surface of the rotating cylindrical core 28, forming a multifilament tow of non-fused PEDOT:PSS filaments that may be subsequently unwound from the core.

[0029] A balance of characteristic processing times and dimensions is targeted to successfully generate a separable, multifilament PEDOT:PSS fiber tow. These include: [0030] a. Pump volumetric flow rate and spinneret dimension (average exit velocity, V.sub.0 m/min) [0031] b. Coagulation residence time: The coagulation time (t.sub.c sec) is governed by the take-up speed (V.sub.f m/min) and bath depth (d cm) [0032] c. Drying residence time: The drying time (t.sub.d sec) is governed by the take-up speed (V.sub.f m/min) and the air path length (a cm) prior to collimation of the filaments [0033] d. Take-up speed (V.sub.f m/min)

[0034] In one possible embodiment for low rate spinning, where V.sub.0 is quite small (1.1 m/min), the variables may be as follows:

[00001]$V_0=1.1-4.2m/\min ;$$V_f=2.m/\min ;$$d=2.5-24\mathrm{cm};$$t_c=0.8-6.6s;$$a=43-91\mathrm{cm};\mathrm{and}$$t_d=13-25s.$

[0035] From the above, it should be appreciated that the method of spinning conductive poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) fibers disclosed in this document provides a number of benefits and advantages. These include: [0036] (1) The PEDOT:PSS fiber is formed upon extrusion into a bath of formic acid. Formic acid functions as a good non-solvent for the nascent PEDOT:PSS fibers, causing the fibers to form into coherent filaments while remaining miscible with water diffusing out of the PEDOT:PSS fibers. [0037] (2) The relatively high density of formic acid causes the forming fiber to float upwards. Therefore the coagulated/solidified nascent PEDOT:PSS fiber floats to the top of the formic acid bath. This allows for facile manipulation of the filament towards downstream take-up. This is of practical importance for start-up of the spinning processing. [0038] (3) Unlike sulfuric acid (as used in the prior art), formic acid has a very low boiling point and tends to evaporate. This is critical, as the emerging nascent filaments MUST dry prior to being collimated together as a tow. Otherwise, neighboring filaments will fuse. Fused filaments destroy the utility of the tow, rendering it similar to a brittle rod.

[0039] The unique combination of (1), (2), and (3), that results from the present method, allows, for the first time, the formation of a multifilament PEDOT:PSS fiber tow by upwards solution spinning. This upward spinning method is similar to classic dry spinning notably used to fabricate cellulose acetate fibers from solution in acetone. In some ways the process can be thought of as upside down hybrid dry/wet spinning. The process described herein is novel and unique, using an upward or flotation of the forming fiber through formic acid (wet), followed by a drying process (evaporation of formic acid) as the filaments are routed further upwards through heated or unheated air.

[0040] Although the method of this disclosure has been illustratively described and presented by way of specific exemplary embodiments, and examples thereof, it is evident that many alternatives, modifications, or/and variations, thereof, will be apparent to those skilled in the art. Accordingly, it is intended that all such alternatives, modifications, or/and variations, fall within the spirit of, and are encompassed by, the broad scope of the appended claims.