Thermally induced sign change of Soret coefficient for dilute and semidilute solutions of poly(N-isopropylacrylamide) in ethanol.
Thermally induced sign change of Soret coefficient for dilute and semidilute solutions of poly(N-isopropylacrylamide) in ethanol.
复制标题
聚（N-异丙基丙烯酰胺）乙醇稀溶液和半稀溶液的索雷系数的热诱导符号变化。
DOI：
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发表时间：
2004
影响因子：
4.4
通讯作者：
S. Wiegand
中科院分区：
文献类型：
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作者：
R. Kita;G. Kircher;S. Wiegand
我们通过热扩散强迫瑞利散射研究了聚（N-异丙基丙烯酰胺）（PNiPAM）在T = 14.0°C至T = 40.0°C温度范围内的乙醇中的热扩散行为。获得的 PNiPAM 索雷系数 S(T) 在较低温度（T < 34 ℃）下为正值，而在较高温度（T > 34 ℃）下 S(T) 为负值。这意味着当温度 T < 34 摄氏度时，PNiPAM 分子会移至冷侧，而当温度 > 34 摄氏度时，它们会移至暖侧。这是第一个观察到符号随温度变化的非水聚合物体系。我们在相同的温度范围内进行了静态和动态光散射实验。通过静态光散射 (SLS) 从稀溶液中确定的第二维里系数在可比较的温度范围内为正值。半稀溶液的 SLS 结果显示，PNiPAM 链之间存在很强的排斥力，这种排斥力随着温度的升高而增强。这些结果意味着观察到的 S(T) 热诱导符号变化并不依赖于 PNiPAM 链之间的分子间相互作用。
We studied the thermal diffusion behavior of poly(N-isopropylacrylamide) (PNiPAM) in ethanol in a temperature range from T = 14.0 degrees C to T = 40.0 degrees C by means of thermal diffusion forced Rayleigh scattering. The obtained Soret coefficient S(T) of PNiPAM was positive for lower temperatures (T < 34 degrees C), while S(T) showed a negative value for higher temperatures (T > 34 degrees C). This means PNiPAM molecules move to the cold side for temperatures T < 34 degrees C, whereas they move to the warm side for T > 34 degrees C. This is the first nonaqueous polymeric system for which a sign change with temperature has been observed. We performed static and dynamic light scattering experiments in the same temperature range. The second virial coefficient determined from dilute solutions by static light scattering (SLS) was positive in the comparable temperature range. The results of SLS for the semidilute solution showed a strong repulsion among PNiPAM chains which was enhanced by increasing temperature. These results imply that the observed thermally induced sign change of S(T) does not depend on the intermolecular interactions among PNiPAM chains.