在结晶性聚合物-纳米填料复合体系中存在两种效应--表面(界面)效应和空间受限效应，这两种效应决定了聚合物的结晶特性和复合材料的最终性能。如何清楚地认识纳米粒子表面聚合物的凝聚态结构及其与纳米粒子之间的相互作用本质，从而精确预测和控制聚合物纳米复合材料的结构和性能，成为制备纳米复合材料的主要挑战之一。本项目拟选用分子量分布窄的聚乙烯作为研究对象，分子量从1000到二十多万，重点研究高含量纳米二氧化硅粒子对聚乙烯结晶的诱导效应，探讨二氧化硅微球的尺寸（曲率半径）、表面特性（亲水或疏水）、聚乙烯链长等因素对复合体系结晶的影响，阐明界面效应以及空间受限效应对聚乙烯链段运动和晶体成核生长的影响规律，从而建立加入无机粒子填料后聚合物结晶时的成核生长和晶型转变模型，深入理解纳米无机粒子-聚合物复合体系的结构和性能关系。

Polymer nanocomposites (PNC) are an emerging class of hybrid materials composed of hard nanoparticles or "fillers" dispersed in soft polymer matrices. Owing to the improvement of properties including conductivity, toughness and premeability, PNC are slated for application ranging from membranes to fuel cells. Nevertheless, the complex crystallization behaviors of polymers with high molecular weight and broad molecular weight distribution hinder the in-depth understanding of crystallization mechanism of PNC from molecular level, especially in the existance of external inorganic fillers. Therefore, the main challenge for establishing the correlations between structure and properties of crystalline polymer based PNC relys on elucidating two kinds of effects: surface or interface effect and confinement effect. Investigating the crystalline structure formation and phase transition of polymer matrices on the surface of nanoparticles is essential to predict and control the properties of PNC. The present project chooses polyethylene (PE) samples with a series of molecular weight and narrow molecular weight distribution and a series of monodisperse silica particles as PNC main components, aiming to study the confined crystallizaiton features of PE on the surface of nanosized silica. The size (curvature), surface characteristic (hydrophilic or hydrophobic) of silica as well as the chain length of PE will be considered as the key factors to study the surface inducing effect, crystallite nucleation and growth, phase transition behavior of polymers in silica nanocomposites. The phase transition behavior will be discussed in terms of a possible crossover from fullly extended molecule nuclei with shorter chain length to folded "bundle" nuclei with longer chain length of PE. The investigation on the crystallization behavior of PE in confined geometry will provide not only well-defined model systems for investigating crystallization mechanism of polymers, but also the theoretical aid for the design of inorganic particle-polymer nanocomposites with high performances.