Bacterial cellulose gels, process for producing and methods for use
Disclosed are cellulose-based flexible gels containing cellulose nanorods, ribbons, fibers, and the like, and cellulose-enabled inorganic or polymeric composites, wherein the gels have tunable optical, heat transfer, and stiffness properties. The disclosed gels are in the form of hydrogels, organogels, liquid-crystal (LC) gels, and aerogels. Further disclosed are highly transparent and flexible cellulose nanofiber-polysiloxane composite aerogels featuring enhanced mechanical robustness, tunable optical anisotropy, and low thermal conductivity. Further disclosed are gels comprising cellulosic material derived from bacteria and processes for preparing bacterial cellulose gels and methods of use.
1 . A method of forming a gel, the method comprising the steps of
contacting an aqueous dispersion of cellulose with a oxidizing system that oxidizes the cellulose to form an aqueous solution of oxidized cellulose nanofibers;
reacting the oxidized cellulose nanofibers with a surface modifying agent to form an aqueous solution of surface modified cellulose nanofibers;
contacting the surface modified cellulose nanofibers with an agent to form an aqueous polysiloxane precursor; and
hydrolyzing the polysiloxane precursor in the presence of an acid catalyst to form a hydrogel.
2 . The method of claim 1 , further comprising a step of exchanging the water contained in the hydrogel with a volatile solvent to form an organogel.
3 . The method of claim 2 , further comprising a step of removing the volatile solvent to form an aerogel.
4 . The method of claim 3 , wherein the aerogel is a transparent aerogel.
5 . The method of claim 4 , wherein the transparent aerogel has a transmission of electromagnetic radiation in a range of from about 95% to 100.
6 . The method of claim 1 , wherein an aspect ratio of the nanofibers is between about 1:10 and about 1:100.
7 . The method of claim 1 , wherein a diameter of the nanofibers is greater than 3 nm and less than 10 nm.
8 . The method of claim 1 , wherein the oxidizing system comprises (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO).
9 . The method of claim 8 , wherein the oxidizing system comprises an admixture of TEMPO and NaClO.
10 . The method of claim 1 , comprising a step of adding silicon to the hydrogel.
11 . The method of claim 3 , further comprising a step of adding a surface modifier to the hydrogel to modify a surface of the aerogel.
12 . The method of claim 11 , wherein the surface is hydrophobic.
13 . The method of claim 1 , wherein a length of the nanofibers is at least ten times a diameter of the nanofibers.
14 . The method of claim 1 , wherein the gel comprises cellulosic nanocomposites that are aligned in ordered liquid crystal phases.
15 . The method of claim 1 , wherein the gel comprises nematic cellulosic gel, and wherein the method further comprises applying a layer of aligned cholesteric cellulose film to the gel.