Membrane surface hydrophobicity through electro-hydrodynamic film patterning

Abstract

A method of creating a hydrophobic polymer membrane surface includes depositing a polymer material onto a heated carrier, using the heated carrier, transporting the polymer material past an electrode field generator, generating an electric field adjacent the carrier, using the electric field to form a pattern in the polymer material to form a patterned polymer membrane, rinsing the patterned polymer membrane in a first bath, and setting the pattern into the patterned polymer membrane in a second bath.

Claims

1. A method of creating a hydrophobic polymer membrane surface, comprising: depositing a polymer material onto a heated carrier; using the heated carrier, transporting the polymer material past an electrode field generator; generating an electric field adjacent the carrier; using the electric field to form a pattern in the polymer material to form a patterned polymer membrane; rinsing the patterned polymer membrane in a first bath; and setting the pattern into the patterned polymer membrane in a second bath.

2. The method of claim 1, wherein depositing the polymer material onto a heated carrier comprises depositing the polymer material onto a heated carrier belt.

3. The method of claim 1, wherein transporting the polymer material past an electric field generator comprises transporting the polymer material past an electrode belt.

4. The method of claim 3, wherein generating an electric field adjacent the carrier comprises generating an electric field adjacent the electrode belt.

5. The method of claim 1, wherein using the electric field to form the pattern comprises using the electric field to transfer a pattern from the carrier belt to the polymer material.

6. The method of claim 1, wherein rinsing the patterned polymer membrane comprises immersing the patterned polymer membrane in a non-solvent that removes a solvent from the patterned polymer membrane.

7. The method of claim 1, wherein setting the pattern comprises setting the pattern in a bath selected to gelatinize the patterned polymer membrane to set the pattern.

8. The method of claim 1, wherein depositing the polymer material comprises depositing one of either a slurry or a liquid.

9. The method of claim 1, wherein using the electric field to form the pattern comprises using the electric field to form the pattern at of one of micro-scale or nano-scale.

10. The method of claim 1, wherein using the electric field to form the pattern comprises using the electric field to form a periodic pattern of one of pillars or posts.

11. The method of claim 10, wherein the pillars or posts have one of a rectangular, circular, or square cross-section.

12. A method of creating a hydrophobic polymer membrane surface, comprising: depositing a polymer material onto a heated carrier belt; using the heated carrier belt, transporting the polymer past an electrode having a patterned electric field; using the patterned electric field to form a pattern in the polymer membrane surface to form a patterned polymer membrane; rinsing the patterned polymer membrane in a first bath; and setting the pattern into the patterned polymer membrane in a second bath.

13. The method of claim 12, wherein rinsing the patterned polymer membrane comprises immersing the patterned polymer membrane in a non-solvent that removes a solvent from the patterned polymer membrane.

14. The method of claim 12, wherein setting the pattern comprises setting the pattern in a bath selected to gelatinize the patterned polymer membrane.

15. The method of claim 12, wherein depositing the polymer material comprises depositing one of either a slurry or a liquid.

16. The method of claim 12, wherein using the electric field to form the pattern comprises using the electric field to form a periodic pattern of one of pillars or posts.

17. The method of claim 16, wherein the pillars or posts have one of a rectangular, circular, or square cross-section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1-4 show examples of patterned polymer film.

(2) FIG. 5 shows an electric field generator for electrohydrodynamic film patterning.

(3) FIG. 6 shows an embodiment of an electrohydrodynamic film patterning system.

(4) FIG. 7 shows a flowchart of an embodiment of a method to electrohydrodynamically pattern a polymer film.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) Specifically, the embodiments here propose a technology to form hydrophobic membranes from hydrophilic polymers with charged surfaces in an efficient roll-to-roll process. The polymers that are of interest are termed polyelectrolytes and they include: carboxymethyl cellulose, polystyrene sulfonates, polyacrylic acid, polyaniline, polyallylamine hydrochloride, poly(2-acrylamido-2-methyl-1-propanesulfonic acid), polyaspartic acid, alginates, pectin, carrageen. Hydrophobic membranes can be formed from these polymers directly or from typical membrane polymers containing amounts of these polyelectrolytes as additives.

(6) FIG. 1 shows an example of a patterned polymer film 10. Hydrophobic films have a high contact angle, meaning that drops of solution do not wet the surface. Increasing the surface roughness of the film by patterning, increases the contact angle and therefore the hydrophobicity. The equation used to calculate the theoretical marginal values of the dimension H, b and a, where H is the height of the pillars and/or posts in the pattern, referred to here collectively as posts, b is the gap between the posts, and a is the width of the posts. In the expanded view 12, b is the gap between the posts 14 and 16, and a is the width of post 16. The equation is:

(7) $\frac{b}{a}=\sqrt{-\frac{4\cos {}_i}{\left(\cos {}_i\right)\left(\frac{}{H}\right)}}-1.$

(8) The pattern infused into the polymer film may have nanopatterned roughness, meaning that the roughness patterned into the film is on a nanometer scale, superimposed over a micropatterned roughness. However, even if the patterned roughness is only on the micropatterned scale, the hydrophobicity increases. FIG. 2 shows an embodiment of a post 16. FIG. 3 shows an embodiment of an array of posts such as 17, and FIG. 4 shows a pattern of stripes such as 18.

(9) Current patterning methods include focused ion beam milling for silicon wafers, laser etching metals, XeF.sub.2 gas phase etching and wafer dicing for silicon wafers. Another method of generating patterns is to use electrohydrodynamic (EHD) film patterning (EHD-FP). In one use of EHD-FP, in U.S. Pat. No. 9,348,231, an electric field is used to align liquid forms inside the polymer films such as nanotubes and nanowires and then cure the film.

(10) The alignment results from the application of an electric field from an electric field generator 20, such as that shown in FIG. 5. In FIG. 5, a current source such as 26 generates a field that is applied to a set of electrodes, a positive electrode 22 and a negative electrode 24. When the current is applied, an electric field is generated in the region 28 between the two electrodes.

(11) As used here, rather than to cause liquid forms in the polymer material as in the patent mentioned above, the field is used to form the pattern in the film itself, creating pattern roughness. Control of the field controls the resulting pattern, in one embodiment. In another embodiment, the carrier belt, discussed in more detail in FIG. 3, has a pattern that is infused into the polymer upon the application of the field.

(12) The embodiments here use roll-to-roll processing, which makes them faster, cheaper, and scalable compared to sheet at a time processing or microfabrication. FIG. 6 shows an embodiment of a system 30 to perform EHD-FP, and FIG. 7 shows an embodiment of a method to use the system. A repository 40 deposits a polymer material 42 onto a carrier belt 47 at 60. The polymer material 42 may consist of a polymer mixed with a solvent to allow the material to be easily dispensed. The polymer material may consist of a slurry or a liquid. For processing that is not roll-to-roll, the carrier may consist of something besides a belt, such as a chip carrier or other transport means. The term carrier as used here includes any carrier that can receive the polymer material and transport it.

(13) The carrier 47 is heated by a heater 46. The carrier transports the polymer material at 62 through an electric field generated by the electric field generator 32 at 64 that is arranged adjacent the electrode belt 37. For non-roll-to-roll processing, the electrode field generator may not require the electrode belt. The field generator 32 generates an electric field through which the polymer material travels and forms a pattern 44 at 66.

(14) As mentioned previously, the pattern may be formed on a microscale or a nanoscale with a repeating pattern. The repeating pattern may have pillars and/or posts may have a circular, rectangular or square cross-section. It has been shown that repeated patterns of roughness increase the hydrophobicity.

(15) Once formed in the polymer, the pattern can be set in many different ways. In one embodiment, the now-patterned polymer film may be heated to a higher temperature than originally heated. This may be accomplished by the heater 46, or by the second roller 49. The second temperature is high enough to evaporate any of the solvent in the polymer material. The pattern may be set with the use of a chilling roller 48 or other cooling mechanisms.

(16) Alternative to evaporating the solvent in the polymer material, the patterned polymer film may be rinsed by submersion in a solvent bath 50, along transport rollers 52 and 54. The patterned film may undergo a second solvent bath 56 along rollers 55 and 57 to gelatinize or otherwise set the pattern at 68. In this manner, a roll-to-roll process can implement EHD to pattern films to create a periodic roughness pattern that increases the hydrophobicity of the film.

(17) It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.