Molecular dynamics of poly(N-isopropylacrylamide) in protic and aprotic solvents studied by dielectric relaxation spectroscopy.
Molecular dynamics of poly(N-isopropylacrylamide) in protic and aprotic solvents studied by dielectric relaxation spectroscopy.
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DOI：
10.1021/jp210376u
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发表时间：
2012-01
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影响因子：
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通讯作者：
S. Nakano;Yasuhiro Sato;R. Kita;N. Shinyashiki;S. Yagihara;S. Sudo;M. Yoneyama
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文献类型：
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作者：
S. Nakano;Yasuhiro Sato;R. Kita;N. Shinyashiki;S. Yagihara;S. Sudo;M. Yoneyama
本文报道了聚N-异丙基丙烯酰胺[PNiPAM]在不同溶剂中的介电弛豫谱的实验结果，频率范围为40 kHz ~ 20 GHz，溶液温度为25.0 °C。本研究中使用的溶剂为质子溶剂（水、甲醇、乙醇和1-丙醇）和非质子溶剂（丙酮、甲乙酮和二甲亚砜）。两个弛豫过程中观察到的频率约为1 MHz和10 GHz的所有解决方案。两个弛豫过程的起源被认为是在中频（m-过程）和在较高的频率（h-过程）的溶剂分子的偶极的PNiPAM链的重定向。对于除1-丙醇外的质子溶剂组成的PNiPAM溶液，h过程的弛豫时间随着PNiPAM浓度的增加而增加，而1-丙醇的h过程随着PNiPAM浓度的增加而减小。相反，非质子溶剂的H-过程的弛豫时间是独立的氢键位点的密度。对于归因于PNiPAM的局部链运动的m-过程，对于所有质子溶剂，外推到零聚合物浓度的弛豫时间τ（m0）由溶剂粘度缩放，而对于非质子溶剂，τ（m0）显示与溶剂粘度无关。聚合物链和溶剂分子在其溶液状态下的动力学澄清的合作运动，这是与通过氢键在分子水平上的相互作用。
We report the experimental results of dielectric relaxation spectroscopy for the systems of poly(N-isopropylacrylamide) [PNiPAM] in various solvents in the frequency range of 40 kHz to 20 GHz at the solution temperature of 25.0 °C. The solvents used in this study were protic solvents (water, methanol, ethanol, and 1-propanol) and aprotic solvents (acetone, methyl ethyl ketone, and dimethyl sulfoxide). Two relaxation processes were observed at frequencies of approximately 1 MHz and 10 GHz in all the solutions. The origins of the two relaxation processes are considered to be the reorientation of dipoles of the PNiPAM chains at middle frequencies (m-process) and that of solvent molecules at higher frequencies (h-process). For the PNiPAM solutions composed of protic solvents except for 1-propanol, the relaxation time of the h-process increased with increasing PNiPAM concentration, whereas that of the h-process for the 1-propanol decreased with increasing PNiPAM concentration. In contrast, the relaxation times of the h-process for the aprotic solvents were independent of the density of hydrogen-bonding sites. For the m-process, which is attributed to the local chain motion of PNiPAM, the extrapolated relaxation time to zero polymer concentration τ(m0) was scaled by the solvent viscosity for all the protic solvents, whereas for the aprotic solvents τ(m0) showed no correlation with the solvent viscosity. The dynamics of polymer chains and solvent molecules in their solution state are clarified in terms of cooperative motion, which is associated with the interactions through hydrogen bonding at the molecular level.