Study On Heat Capacity Of Nano-Confined Water And Glass Transition Of Atactic Polystyrene

The heat capacity of the water confined in SWNTs, the glass transition of PS, and the melting of 1, 4-diphenylbutane were studied by DSC and FTIR. The heat capacity curves of confined water showed no melting peak for the samples not reach the saturated water content of SWNTs, while the heat capacity curves of the saturated sample showed a wide melting peak. The heat capacity of the confined water was significantly lower than the bulk water, which was resulted from the weakening of the hydrogen bonding of confined water. The theoretical model predicted a 18% maximum water content for SWNTs, about 2% higher than the experimental value.The FTIR investigation on the glass transition of PS showed that the intensity of four conformation insensitive bands of PS showed step-like increases during glass transition. Three bands assigned to C-H vibrational mode showed much higher intensity increase rates than the bands assigned to C-C vibrational mode, indicating that the formers were more sensitive than the latter. The PS samples aged for different time also showed the step-like increases in intensity-temperature curves of the four bands during glass transition. The onset point of the glass transition shifted to higher temperature with aging time, however, the end point stayed constant, indicating that this method to determine Tg is more accurate for aged PS. The decrease rates of increase rates for the intensity of PS side group were less than the main chain, indicating that the side group was more sensitive to physical aging. The onset point of the main chain of PS samples plasticized by OTP were lower than those of the side group and DSC result, indicating that the plasticization was dominated by gel mechanism. The Tg derived from DSC result was the same as that of the side group, indicating that the glass transition of PS was dominated by the phenyl side group. The 2935 cm-1 band of 1, 4-diphenylbutane split into two bands in crystalline state, which resulted from the coupling of the adjacent molecules. The two bands merged together during melting indicating that the coupling disappeared in the unordered structure.