摘要
考察了２０％十二烷基磺酸钠（ＳＤＳ）－水体系在不同状态下的红外光谱，通过特征谱带频率的变化，观察到体系能以烷基链堆积方式不同的两种凝聚胶状态存在，确定了体系由凝聚胶相到液晶相的转变温度为４７℃，相应的逆相变温度为３５℃，并讨论了不同相态中的分子构象变化以及水分子对十二烷基磺酸钠分子构象的影响。
Abstract Fourier transform infrared spectroscopy has been used to study the thermotropic phase transitions of 20% sodium n-dodecyl sulfonate-water system.Two kinds of coagel phase(opaque and microscopically inhomogenious system with hydrated crystals and water ) with different thermal hystereses were prepared for the SDS-water system.The C-H stretching, CH 2 scissoring and SO - 3 stretching bands of SDS and the O-H stretching band of water are discussed in each phase. The temperature dependence of the bands show that both unannealed and annealed samples exhibit the phase transition from coagel to liquid crystal at 47℃ and the reverse transition around 35℃. Although the main disinction between the two kinds of coagel phase is difference of the packing form of alkyl chain,the alkyl chains are in all-trans conformation and the internal rotation of the terminal CH 3 group is highly restricted in both coagel phase.In the liquid crystal phase,the alkyl chains are in disordered liquid-like state with the collapse of transzig-zag planes and free rotation of the methyl groups.The spectra of sample in both coagel phases below 0℃ exhibit the ice band originated from free water above 0℃,The shoulder band originated from the bound water can be also distinguished from the band of free water.The states of the hydrophilic sulfonic group are closely related to the states of water molecule in different phases.The spectra also indicated that the packing of alkyl chain is strongly affected by the evaporation of water.
