冷却速率对温敏聚N-异丙基丙烯酰胺胶体结晶过程的影响  

Effect of cooling rate on crystallization process of thermo-sensitive poly-N-isopropylacrylamide colloid

作　　者：王理林[1] 王志军[2] 林鑫[2] 王锦程[2] 黄卫东[2] 

机构地区：[1]西安理工大学材料科学与工程学院,西安710048 [2]西北工业大学凝固技术国家重点实验室,西安710072

出　　处：《物理学报》2016年第10期256-262,共7页Acta Physica Sinica

基　　金：中央高校基本科研业务费(批准号:3102015ZY020);国家重点基础研究发展计划(批准号:2011CB610402);国家自然科学基金(批准号:50971102)资助的课题~~

摘　　要：冷却速率对结晶过程具有重要的影响.本文采用温敏poly-N-isopropylacrylamide（PNIPAM）胶体晶体体系实时观察了冷却速率对结晶晶粒尺寸的影响.通过高倍透射明场观察和Bragg衍射观察研究连续冷却下的晶粒形核和生长实时演化过程,发现随着冷却速率的增加,PNIPAM胶体晶体晶粒尺寸不断减少.晶粒尺寸与冷却速率符合幂指数关系,与金属体系具有相似的演化规律.Grain size has a significant influence on the performances of materials.Cooling rate is a key process parameter for controlling the size of crystal grain.Real-time observations of crystallization process on an atomic scale under different cooling rates are helpful for an in-depth understanding of this scientific issue.However,it is very difficult to observe directly the crystallization process on an atomic scale because it is small in size and fast in motion.Over last decades,colloidal suspension has attracted many researches＇ attention as a model system of condensed matter to investigate phase transition kinetics at a particle scale level because colloidal particles are micrometer-sized and their thermal motions can be directly visualized and measured with an optical microscope.Thermo-sensitive poly-Nisopropylacrylamide（PNIPAM）colloidal suspension is one of the model systems and its phase transition can be easily controlled by temperature.In this paper,the PNIPAM colloidal system is used to make the real-time observation of the influence of the cooling rate on crystal grain size.Firstly,the crystal nucleation and growth process of PNIPAM colloidal suspension at a cooling rate of 30.0℃/h is observed with a high-resolution transmission microscope.It is found that liquid-solid phase transition of the PNIPAM colloidal suspension begins from a sudden transient nucleation,followed by a rapid grain growth as temperature decreases.The variation of crystal phase fraction with temperature undergoes three stages：slow,rapid and slow.In the initial stage,nuclei are limited and the growth driving force is low,therefore the crystal phase fraction changes slowly.In the middle stage,as temperature decreases,the growth driving force further increases and the crystal phase fraction increases rapidly.In the final stage,the crystal grains begin to adjoin with each other and the left liquid volume becomes less and less,so the crystal phase fraction increases in a slow mode again.Secondly,the PNIPAM colloidal crystal under d

关 键 词：结晶 形核 胶体 凝固组织 

分 类 号：O633.22[理学—高分子化学]