Infrared light- and thermal-responsive graphene oxide hydrogel polymer composites

1. A composite hydrogel comprising graphene oxide flakes distributed in and covalently bonded to a thermo-responsive hydrogel polymer, wherein the swelling ratio for the composite hydrogel is at least 50% greater than the swelling ratio for the thermo-responsive hydrogel polymer in the absence of the graphene oxide flakes at a temperature below the lowest critical solution temperature of the composite hydrogel.

2. The composite hydrogel of claim 1 , wherein the temperature below the lowest critical solution temperature of the composite hydrogel is 10° C.

3. The composite hydrogel of claim 1 , wherein the thermo-responsive hydrogel polymer comprises polyisopropylacrylamide.

4. A composite hydrogel comprising graphene oxide flakes distributed in and covalently bonded to a thermo-responsive hydrogel polymer, wherein the swelling ratio for the composite hydrogel is at least 50% greater than the swelling ratio for the thermo-responsive hydrogel polymer in the absence of the graphene oxide flakes at a temperature below the lowest critical solution temperature of the composite hydrogel, wherein the thermo-responsive hydrogel polymer comprises polyisopropylacrylamide, the polyisopropylacrylamide polymer comprising acrylamide functionalities, and wherein the covalent bonds between the graphene oxide and the polyisopropylacrylamide polymer are formed by reactions between the acrylamide functionalities and methacrylate functionalities on the graphene oxide.

5. The composite hydrogel of claim 3 , comprising from about 0.1 and about 10 weight percent graphene oxide flakes.

6. The composite hydrogel of claim 5 , wherein the average number of graphene oxide sheets in the graphene oxide flakes is no greater than about 2.

7. The composite hydrogel of claim 3 , wherein the swelling ratio for the composite hydrogel is at least 100% greater than the swelling ratio for the thermo-responsive hydrogel polymer in the absence of the graphene oxide flakes at a temperature of 10° C.

8. The composite hydrogel of claim 1 , wherein the composite hydrogel is photopatternable with ultraviolet light.

9. The composite hydrogel of claim 3 , wherein the polyisopropylacrylamide is not polymerized from stimuli-responsive monomers other than N-isopropylacrylamide.

10. A composite hydrogel comprising graphene oxide flakes distributed in and covalently bonded to a thermo-responsive hydrogel polymer, wherein the swelling ratio for the composite hydrogel is at least 50% greater than the swelling ratio for the thermo-responsive hydrogel polymer in the absence of the graphene oxide flakes at a temperature below the lowest critical solution temperature of the composite hydrogel, wherein the thermo-responsive hydrogel polymer comprises polyisopropylacrylamide and wherein the polyisopropylacrylamide is an N-isopropylacrylamide homopolymer.

11. A microfluidic device comprising:

a flow channel having an internal surface that defines an internal diameter of the flow channel; and

a valve comprising the composite hydrogel of claim 1 affixed to the internal surface of the flow channel, wherein, in a swollen state, the composite hydrogel has a volume sufficient to block fluid flow through the flow channel.

12. A method of using the microfluidic device of claim 11 , the method comprising heating the composite hydrogel in the swollen state to a temperature sufficient to shrink the volume of the swollen composite hydrogel and permit fluid flow though the flow channel.

13. The method of claim 12 , wherein heating the swollen composite hydrogel comprises irradiating the swollen composite hydrogel with infrared radiation.

14. The method of claim 12 , further comprising allowing the composite hydrogel to cool and re-swell to a volume sufficient to block fluid flow through the flow channel.

15. A lens structure comprising:

a fluid cavity;

a fluid housed within the fluid cavity, the fluid forming a meniscus configured to act as a lens; and

a ring actuator comprising the composite hydrogel of claim 1 disposed around the fluid, wherein, when the composite hydrogel is in a swollen state the lens has a first focal length and when the composite hydrogel is in an unswollen state the lens has a second focal length that differs from the first focal length.

16. A method of using the lens structure of claim 15 , the method comprising heating the composite hydrogel in the swollen state to a temperature sufficient to shrink the volume of the swollen composite hydrogel, thereby changing the focal length of the lens.

17. The method of claim 16 , wherein heating the swollen composite hydrogel comprises irradiating the swollen composite hydrogel with infrared radiation.

18. The method of claim 16 , further comprising allowing the composite hydrogel to cool and re-swell.

19. The composite hydrogel of claim 4 , wherein the acrylamide functionalities are formed by reactions between bisacrylamide crosslinkers and N-isopropylacrylamide monomers.