Method for producing elongated structures such as fibers from polymer solutions by straining flow spinning
A method of molecular self-assembly is disclosed using two interacting streams that are allowed to interact and are subsequently forced through an orifice. A first stream of a dope solution of polymer molecules is extruded out of a capillary. The dope stream is surrounded by a focusing fluid which is miscible with the dope solution. The interaction between the jet of dope solution and surrounding focusing fluid creates hydrodynamic stretching and allows for extracting solvent from the dope solution. Concentrated polymers within the solution at stretched regions of the jet interact, and finally self-assembly takes place after the fluids are forced through the outlet of a converging nozzle. The formation of the structure can be optionally completed in a coagulating space. The structures thus obtained such as fibers or threads can be wound onto a mandrel.
1. A method of molecular self-assembly, comprising: extruding a stream of a dope solution of polymer molecules out of a capillary into a surrounding environment of a coaxially flowing focusing fluid miscible with the dope solution in a space limited by a convergent nozzle with an outlet that the dope and focusing fluid are forced to traverse;
hydrodynamically stretching the extruded stream of polymer dope solution inside the convergent nozzle due to its interaction with the focusing fluid while simultaneously and selectively extracting solvent into the focusing fluid from the dope solution by molecular diffusion;
wherein polymer concentration in the dope solution at a stretched region of the stream reaches a level such that contact among polymer molecules results in molecular self-assembly of the polymer molecules and subsequently, a stretching is imposed when the dope solution and the focusing fluid are forced through the convergent nozzle outlet; and
continuously extracting an elongated structure of self-assembled polymer molecules such as a fiber or a thread;
wherein the capillary-nozzle system presents the following parameters: distance between the end of the capillary and the outlet of the convergent nozzle (d 6 ) between 400 and 15000 pm, diameter of convergent nozzle outlet (d 6 ) between 250 and 800 pm, dope capillary tapering angle (α) of 100 to 900, and the rate of flow of the dope solution and focusing fluid flow is at least 10− 20 m 3 /s.
2. The method according to claim 1 , wherein the length of the convergent region of the convergent nozzle (d 7 ) is between 2000 to 4000 μm.
3. The method according to claim 1 , wherein the convergent nozzle outlet is circular.
4. The method according to claim 1 , wherein the convergent nozzle outlet is a slit in a plate.
5. The method according to claim 1 , wherein the dope solution and the focusing fluid go through the outlet of the convergent nozzle and enter a coagulating space.
6. The method according to claim 5 , wherein the coagulating space is a coagulating tube.
7. The method according to claim 5 , wherein the coagulating space is a coagulating bath.
8. The method according to claim 7 , wherein the focusing fluid and/or the coagulating bath comprise an alcohol, acetone, an aqueous salt solution or mixtures thereof.
9. The method according to claim 7 , wherein the pH of the focusing fluid and/or the pH of the coagulating bath differs from the pH of the dope solution by more than 0.1.
10. The method according to claim 1 , wherein the dope solution and the focusing fluid go through the outlet of the convergent nozzle and enter a coagulating space, wherein the convergent nozzle outlet is a slit in a plate and wherein the coagulating space is a space created by two parallel plates.
11. The method according to claim 1 , wherein the polymer comprises amino acids.
12. The method according to claim 11 , wherein the polymer is a peptide of at least 5 amino acids.
13. The method according to claim 11 , wherein the polymer includes at least one amino acid motif selected from the group consisting of: -GA-, -A n -, -GPG- and -GGX-, wherein n is the number of amino acids A and ranges from 2 to 20 and where X is an amino acid other than Glycine.
14. The method according to claim 1 , wherein the ratio of dope flow rate Q d to the focusing fluid flow rate Q f is less than 0.7%.
15. The method according to claim 14 , wherein Q f is less than 0.2%.
16. The method according to claim 1 , wherein the spun fiber or thread is retrieved on a take up device such as a rotating mandrel or a suction instrument.
17. The method according to claim 16 , wherein the ratio of the speed of the fiber or thread at the take up device to the speed of the focusing fluid ranges between 20% and 500%.
18. The method according to claim 16 , wherein the ratio of the speed of the fiber or thread at the take up device to the speed of the focusing fluid ranges between 50% and 200%.