Hydration and Dehydration Kinetics: Comparison between Poly( N-isopropyl methacrylamide) and Poly(methoxy diethylene glycol acrylate) Films.

Thermoresponsive films of poly( N-isopropyl methacrylamide) (PNIPMAM) and poly(methoxy diethylene glycol acrylate) (PMDEGA) are compared with respect to their hydration and dehydration kinetics using in situ neutron reflectivity. Both as-prepared films present a homogeneous single-layer structure and have similar transition temperatures of the lower critical solution temperature type (TT, PNIPMAM 38 °C and PMDEGA 41 °C). After hydration in unsaturated D2O vapor at 23 °C, a D2O enrichment layer is observed in PNIPMAM films adjacent to the Si substrate. In contrast, two enrichment layers are present in PMDEGA films (close to the vapor interface and the Si substrate). PNIPMAM films exhibit a higher hydration capability, ascribed to having both donor (N-H) and acceptor (C═O) units for hydrogen bonds. While the swelling of the PMDEGA films is mainly caused by the increase of the enrichment layers, the thickness of the entire PNIPMAM films increases with time. The observed longer relaxation time for swelling of PNIPMAM films is attributed to the much higher glass transition temperature of PNIPMAM. When dehydrating both films by increasing the temperature above the TT, they react with a complex response consisting of three stages (shrinkage, rearrangement, and reswelling). PNIPMAM films respond faster than PMDEGA films. After dehydration, both films still contain a large amount of D2O, and no completely dry film state is reached for a temperature above their TTs.

Enhanced Stain Removal and Comfort Control Achieved by Cross-Linking Light and Thermo Dual-Responsive Copolymer onto Cotton Fabrics.

Enhanced capabilities of stain removal and comfort control are simultaneously achieved by the light and thermo dual-responsive copolymer poly(triethylene glycol methyl ether methacrylate- co-ethylene glycol methacrylate- co-acrylamide azobenzene) (P(MEO3MA- co-EGMA- co-AAAB)) cross-linked on cotton fabrics. P(MEO3MA- co-EGMA- co-AAAB) is synthesized by sequential atom transfer radical polymerization with a molar ratio of 8 (MEO3MA):1 (EGMA):1 (AAAB). The MEO3MA units induce a thermoresponsive behavior to the copolymer. The hydrophilicity of the copolymer films can be further improved by the light-induced trans- cis isomerization of the AAAB units with UV radiation. The copolymer is facilely immobilized onto cotton fabrics with 1,2,3,4-butane tetracarboxylic acid as cross-linker. Due to the immobilization of P(MEO3MA- co-EGMA- co-AAAB), the hydrophilicity of the fabric surface is increased under UV radiation. Therefore, by simply installing a UV light source in the washing machine, better capability of stain removal is realized for the cross-linked cotton fabrics. It can prominently reduce the consumption of energy, water, and surfactants in laundry. In addition, the trans-AAAB units of the copolymer cause the cross-linked P(MEO3MA- co-EGMA- co-AAAB) layer to be more hydrophobic under ambient conditions. Hence, the copolymer can more easily collapse and form a porous structure on the fabrics. Thus, the air permeability of cotton fabrics cross-linked with P(MEO3MA- co-EGMA- co-AAAB) is enhanced by 13% at human body temperature as compared to P(MEO3MA- co-EGMA), giving improved comfort control during daily wear.