Liquids that Freeze when Mixed: Homogeneous Cocrystallization Kinetics of Polyoxacyclobutane–Water Hydrate
Liquids that Freeze when Mixed: Homogeneous Cocrystallization Kinetics of Polyoxacyclobutane–Water Hydrate
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DOI：
10.1021/acsapm.1c01626
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发表时间：
2021-12
影响因子：
5
通讯作者：
Emily F. Barker;S. Banerjee;T. Meyer;S. Velankar
中科院分区：
文献类型：
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作者：
Emily F. Barker;S. Banerjee;T. Meyer;S. Velankar
本文报道了聚氧环丁烷(POCB)与水形成共晶水合物的结晶动力学，这是首次研究含小分子聚合物的结晶动力学。POCB在与水混合时具有不同寻常的共晶行为，可用于各种应用，包括提高碳纳米管器件的非易失性存储能力、净水和生物医学应用，如药物输送。用体积法和局部球晶生长法测量了一系列含水高达24wt%的混合物的水合物结晶速率。在这些组成下，所有混合物在水合物结晶之前都是单相均相液体，并且与共晶化学计量比相比，所有混合物都是富含POCB的。结晶动力学与时间的关系可用Avrami方程很好地描述。降低温度，即增加过冷度，增加Avrami指数，增加球晶生长速度，符合Hoffmann-Lauritzen模型。减少水分含量会降低球晶的生长速度。在球晶生长过程中，速度也随着时间的延长而降低，这让人联想到结晶过程中的杂质效应。滑石粉具有加速成核的作用。广泛地说，从组分的均匀混合物开始的共结晶过程类似于均聚物结晶，但复杂的是，当混合物的组成偏离共晶化学计量比时，多余的物种不能完全结晶。
We report on the kinetics of crystallization of polyoxacyclobutane (POCB) and water to form a cocrystal hydrate, the first paper to explore the kinetics of crystallization of a polymer with a small molecule. POCB has unusual cocrystallization behavior when mixed with water, which could be exploited for a variety of applications including improving the nonvolatile memory storage capabilities of carbon nanotube devices, water purification, and biomedical applications such as drug delivery. The rates of hydrate crystallization of a series of mixtures containing up to 24 wt % water were measured using both a bulk, volumetric and a localized, spherulite growth approach. At these compositions, all mixtures were single-phase homogeneous liquids prior to hydrate crystallization, and all mixtures were POCB-rich as compared to the cocrystal stoichiometry. The time dependence of crystallization kinetics is well described by the Avrami equation. Reducing temperature, i.e., increasing undercooling, increases the Avrami exponents and increases spherulite growth velocities consistent with the Hoffmann–Lauritzen model. Reducing water content reduces spherulite growth velocities. The velocities also reduce with time during spherulite growth reminiscent of impurity effects in crystallization. Talc was found to accelerate nucleation. Broadly, the cocrystallization process starting from the homogeneous mixtures of the components resembles homopolymer crystallization, but with the complexity that when the mixture composition deviates from the cocrystal stoichiometry, the excess species cannot crystallize fully.