Concentration dependent phase behavior and collapse dynamics of PNIPAM microgel by dielectric relaxation
Concentration dependent phase behavior and collapse dynamics of PNIPAM microgel by dielectric relaxation
复制标题
通过介电弛豫研究 PNIPAM 微凝胶的浓度依赖性相行为和塌陷动力学
DOI：
10.1039/c7cp01378g
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发表时间：
2017
影响因子：
3.3
通讯作者：
Zhao Kongshuang
中科院分区：
文献类型：
--
作者：
Yang Man;Liu Chunyan;Zhao Kongshuang
研究了三种不同浓度的热敏性聚N-异丙基丙烯酰胺(PNIPAM)微凝胶在40~110 MHz频率范围内的介电行为随温度的变化，观察到两个显著的温度相关的弛豫过程。慢弛豫源于整个温度范围内的分段运动。快弛豫是由于反离子在低临界溶液温度(LCST)以下的起伏和在LCST以上的界面极化引起的。结果表明，微凝胶浓度不会影响微凝胶悬浮液的相行为，但不会影响微凝胶悬浮液的相行为：致密体系经历了胶体晶液相变和体积相变，而稀释体系仅经历了体积相变。根据界面极化理论，利用Hanai方程计算了微凝胶各组成相的电学参数(介电常数、电导率、微凝胶的体积分数(εp，κp，ϕ)和水的电导率κa)以及微凝胶中的水分含量(Fw)。此外，根据Eyring方程计算了两种弛豫过程的热力学参数。电学和热力学参数表明，微凝胶浓度影响微凝胶的体积、电荷密度、双电层厚度和微凝胶链段的自由度，从而导致微凝胶崩塌动力学的不同。
The dielectric behavior of thermo-sensitive poly-(N-isopropylacrylamide) (PNIPAM) microgel with three different concentrations was investigated for the frequencies ranging from 40 Hz to 110 MHz as a function of temperature from 10 to 60 °C. Two remarkable and temperature-dependent relaxation processes were observed. The slow relaxation originates from the segmental motion over the whole temperature range. The fast relaxation is due to the fluctuation of counterions below the lower critical solution temperature (LCST) and the interfacial polarization above the LCST. It was concluded from the temperature-dependent dielectric parameters that the microgel concentration will not influence the LCST but affects the phase behavior of the microgel suspension: the dense system experienced a colloidal crystal-to-liquid transition and volume phase transition, while the dilute system only underwent a volume phase transition. Based on the interfacial polarization theory, the electrical parameters for the constituent phases (permittivity, conductivity, and volume fraction of the microgel (εp, κp, ϕ) and the conductivity of water κa) and the water content in the microgel (fw) were calculated using Hanai's equation. In addition, the thermodynamics parameters of the two relaxations were calculated from the Eyring equation. The electrical and thermodynamic parameters indicate that the microgel concentration influences the volume, charge density, thickness of the electric double layer, and degrees of freedom of the segments of the microgel, thereby resulting in the differences in collapse dynamics.