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In this study, the effect of the level of crosslinking on the properties of poly(N-isopropylacrylamide) (PNIPAAm) hydrogels was investigated in terms of their lower critical solution temperature (LCST), interior morphology, equilibrium swelling, and deswelling and swelling kinetics. The thermal analysis showed that PNIPAAm hydrogels, having a wide range of crosslinking levels, exhibited almost the same LCSTs, and this was different from what the conventional theory would have predicted. Scanning electron micrographs revealed that the interior network structure of the PNIPAAm matrix became more porous with an increase in the level of crosslinking. This more porous matrix provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to the external temperature changes during the deswelling process and the swelling process.

Copper-tin sulphides I T is well known that copper and tin form complex sulphides. In two preliminary studies, Moh (1960, 1963) identified four phases in the system Cu-Sn-S. Both Cu2SnS 3 and Cu2Sn2S 5 are on the join Cu2S-SnS 2. Cu2SnS 3 is characterized by a tetragonal-cubic transition at 780~ whereas CuESnES 5 exhibits an extensive range of solid solution between Cu2SnS 3 and SnS 2. The other two phases, CusSnS4 and CusSnS6, are stable below 600 ~ Subsequent studies suggested that Cu2SnES 5 and CusSnS4 be discarded (Wang, 1974), and seven new copper-tin sulphides were proposed: