相变微胶囊限域成核机理及其竞争行为

Microencapsulated phase change material (MEPCM) slurries can be used as the same mediums either to transport or store energy, so their tremendous potential applications are very attractive. The solidification in MEPCMs occurring in a very small space, called as a confined crystallization, is different from that in a large space. However, the solidification behavior cannot be illustrated by the existing nucleation theories. The research plan will focus on the MEPCM size effect on the nucleation modes and phase change properties, solidification temperature, nucleation rate and so on, combined with the synergistic effect of surface wetting characteristic and nucleating agent concentration. The main contents include: 1) thermodynamic characteristics and formation conditions of every nucleation modes in confined space; 2) the effect of particle diameter, as well as surface contact angle and nucleating site numbers on the phase change properties for all modes; 3) the influencing factors and their effects on the nucleation competition behaviors. In this plan, the method microfluidic double emulsion-photo curing we discovered is applied to prepare MEPCMs with monodispersity of particle diameters, from 1μm to 1000μm. These MEPCMs can be made into the same structures to keep the consistency of research objects. The one-to-one correspondence of microscopic nucleation phenomenon to the data measured by DSC analyzer will be made in subtle ways. The confined crystallization theory is meant to be found based on the crystallization kinetics. Also, the phase change properties of a single MEPCM particle due to the nucleation competition behavior will be investigated, and then these properties will develop to the correlations including average diameter and polydisperse coefficient for the bulk of MEPCM particles with different sizes.

相变微胶囊悬浮液可同时实现储能和传热，在传热、蓄热领域有着巨大的应用潜力。微胶囊中的限域凝固不同于大空间凝固的相变特性，现有的成核理论不能很好诠释这些现象。本项目重点研究微胶囊颗粒成核方式和相变特性的微尺度效应，考察粒径与表面润湿特性、成核剂浓度对相变温度和成核率的协同作用。主要内容包括：（1）限域成核方式的热力学特性与发生条件；（2）各种成核方式的相变性能随粒径、接触角及成核点数量的变化规律；（3）成核方式竞争行为的调控规律。本项目采用自有的“微流控双重包裹-光固化”方法精准制备结构可控、且具有单分散性的相变微胶囊，粒径覆盖全微米范围，确保研究对象的一致性。巧妙建立单颗粒胶囊凝固过程微观随机成核现象与DSC热分析数据的精准对应关系，提出基于晶体动力学的限域成核理论；从单颗胶囊成核竞争行为的相变特性推演到多粒径胶囊间的成核竞争行为的作用，总结调控微胶囊凝固相变性能参数的方法。

相变微胶囊悬浮液可同时实现储能和传热，在传热、蓄热领域有着巨大的应用潜力。微胶囊中的限域凝固不同于大空间凝固的相变特性，现有的成核理论不能很好诠释这些现象。本项目以烷烃类相变微胶囊为对象，重点研究了微胶囊颗粒成核方式和凝固相变特性的微尺度效应，揭示了胶囊粒径大小及其均匀性、成核剂种类和浓度、囊壁表面特性对相变微胶囊过冷度和成核率的协同作用。主要内容包括：（1）限域成核方式的热力学特性与发生条件；（2）各种成核方式的相变性能随胶囊粒径、成核剂种类和浓度以及囊壁表面特性的变化规律；（3）成核方式竞争行为的调控规律。本项目采用自有的“微流控双重包裹-光固化”方法精准制备了结构可控、且具有单分散性的相变微胶囊，粒径覆盖全微米范围，确保了研究对象的一致性。建立了胶囊颗粒凝固过程微观成核现象与DSC热分析数据的精准对应关系，提出了胶囊囊壁微孔成核模型，补充完善了限域成核理论；从单颗胶囊成核竞争行为的相变特性推演到多粒径胶囊间的成核竞争行为的作用，总结了调控微胶囊凝固相变性能参数的方法。