Study of relaxation process in the incommensurate phase by means of specific-heat spectroscopy.

最近我们发现，当温度在不相称相内突然变化时，铁电亚硝酸钠的热容表现出时间依赖性。这种热容的动态行为以前只在有限的情况下被报道过，包括在玻璃化转变附近，这是第一次在不相称相中发现“随时间变化的热容”。在开始测量之前，量热计的精度得到了提高。在新装置中，热浴温度的测量采用交流驱动的惠斯通电桥，它比直流驱动的电桥灵敏得多。一个锁相放大器，一个数字万用表等，由拨款购买。利用该仪器，用松弛法对亚硝酸钠进行了测量。结果表明，非相称相的弛豫持续了几百秒以上，且弛豫与简单的指数行为有明显的偏差。我们还同时测量了热容量和介电常数，发现它们的弛豫过程非常吻合。我们还发现，在磷脂酰胆碱基水悬浮液（如DPPC、DMPC和DSPC）的主转变过程中也可以看到类似的弛豫过程。从多频交流模式测量中，估计了弛豫时间和表征弛豫时间分布的参数β。值得注意的是，弛豫时间在很大程度上取决于侧链长度。

Recently we found that the heat capacity of ferroelectric sodium nitrite shows time-dependence when the temperature is changed suddenly within the incommensurate phase. Such a dynamic behavior of the heat capacity has been reported before for only limited cases including in the vicinity of the glass transition, and this is the first case that the "time-dependent heat capacity" is found in the incommensurate phase.Before starting the measurement, the precision of the calorimeter was improved. In the new apparatus, the temperature of the thermal bath is measured using an ac-driven wheatstone bridge, which is much more sensitive than the dc-driven bridge. An lock-in amplifier, a digital multimeter, etc, were purchased by the grant.Using the new apparatus, measurements were done on sodium nitrite by the relaxation method. It was found that the relaxation in the incommensurate phase proceeds over more than a few hundreds seconds, and that the relaxation shows a distinct deviation from the simple exponential behavior. We also done a simultaneous measurement of heat capacity and dielectric constant, and found that their relaxation processes agree quite well with each other.We also found that similar relaxation processes are seen during the main transition in aqueous suspensions of phosphatidylcholinesky such as DPPC, DMPC, and DSPC. From multi-Frequency ac-mode measurements, the relaxation time and the parameter beta which characterizes the distribution of relaxation time have been estimated. It is to be noted that the rexlaxation time strongly depends on the side-chain length.