Kinetics of Coil-to-Globule Transition of DansyI-Labeled Poly（N-isopropyl- acrylamide） Chains in Aqueous Solution

The coil-to-globule transition of thermally sensitive linear poly（N-isopropylacrylamide） （PNIPAM） labeled with dansyl group is induced by 1.54 μm laser pulses （widths10 ns）. The dansyl group is used to follow the transition kinetics because its fluorescence intensity is very sensitive to its micro-environment. As the molar ratio of NIPAM monomer to dansyl group increases from 110 to 300, the effect of covalently attached dansyl fluorophores on the transition decreases. In agreement with our previous study in which we used 8-anilino- l-naphthalensulfonic acid ammonium salt free in water as a fluorescent probe, the current study reveals that the transition has two distinct stages with two characteristic times, namely, Tfast≈0.1 ms, which can be attributed to the nucleation and formation of some ＂pearls＂ （locally contracting segments） on the chain, and tslow≈0.5 ms, which is related to the merging and coarsening of the ＂pearls＂.Tfast is independent of the PNIPAM chain length over a wide range （Mw=2.8× 10^6-4.2 × 10^7 g/mol）. On the other hand, Tslow only slightly increases with the chain length.

Preparation and Characterization of Temperature-Sensitive Hydrogels Composites by Coating Method

In this study,the hydrogels composites with coatings based on a temperature-sensitive linear copolymer of N-tert-butylacrylamide(NTBA)and acrylamide(AAm)on cotton fabrics have been developed.The cotton fabrics were coated using aqueous solution of the linear copolymer,1,2,3,4-butanetertracarboxylic acid(BTCA)as a cross-linker and sodium hypophosphite(SHP)as a catalyst,followed by drying and curing.The effects of cross-linking reaction conditions in coating process on water-impermeable ability of coated cotton fabrics were investigated in detail.The results indicate that the coated fabrics have temperature sensitivity.The coatings of poly(NTBA-co-AAm)hydrogels were bonded on the surface of the cotton fabrics,as verified by SEM and optical microscopy,which gave the water-impermeable ability to the hydrogels composites.Moreover,the hydrogels formed in the coating process also identified that - COOH of BTCA reacted with -NH2 in the linear polymer and formed three-dimensional network hydrogels.FTIR and XPS were used to characterize the cross-linking reaction of - COOH of BTCA and - OH of cellulose.

Smart drug delivery system based on nanocelluloses

Nanocelluloses,also referred as nano-structured cellulose,including cellulose nanocrystals(CNC),cellulose nanofibrils(CNF)and bacterial cellulose(BC),are a family of abundant biomass and renewable materials in nature.Because of their excellent physical,mechanical,and biological properties,in particular biocompatibility,biodegradability,and low cytotoxicity,nanocelluloses have become indispensable for the design of new biomaterials.