Experiments on the Internal Structure of Latexes Using SmallAngle Neutron Scattering

本研究的目的是获得关于形成动力学的基本信息以及这些动力学如何影响乳胶颗粒的最终结构。这些材料可用作涂料和油漆，也可用作抗冲击改性剂。这项工作对现代工业的价值在于，随着对乳胶颗粒结构和行为的了解的提高，可以生产出更好的材料。与薄膜形成动力学、材料强度以及包括医学和生物技术在内的特殊用途应用有关的问题取决于对乳胶结构和行为的详细了解。结构乳胶是亚微米大小的颗粒，具有一些独特的内部形态，悬浮在流体介质中，通常是水。当链的尺寸约为乳胶直径的一半时，就会出现某种类型的分离，第一个聚合材料出现在颗粒的中心附近。从技术上讲，最重要的结构乳胶是核壳型，具有橡胶芯和玻璃壳。这种类型通常代表高冲击聚合物，更具体地说，是ABS（丙烯腈-丁二烯-苯乙烯）塑料和丙烯酸冲击改性剂。pi计划使用小角中子散射（SAS）跟踪聚合过程来观察均聚物和共聚物乳胶。为了阐明均聚物的结构，将使用聚苯乙烯。他们计划测试一种假设，即分子尺寸约为乳胶颗粒大小一半的聚苯乙烯分离成一个核和一个壳，第一个聚合链倾向于靠近颗粒中心。在单体的第二部分聚合之前存在多少偏析的问题，以及在聚合过程中偏析的程度如何变化，将是计划实验的主题。该模型假设体系的内部粘度很高，并且/或者正在发生玻璃化，最终体系低于其玻璃化转变温度，并且聚合物可溶于单体。为了观察共聚物体系，在第二组分开始聚合之前进行小角度中子散射测量，在聚合过程中进行多次测量。结果应阐明是否会发生偏析，如果没有，则会随着体系内部粘度的增加而降低偏析的速率和/或单体塑化颗粒的玻璃化转变是否接近。

The purpose of this research is to obtain basic information about the kinetics of formation and how these kinetics affect the final structure of latex particles. These materials are used as coatings and paints, also as impact modifiers. The value of this work to modern industry is that with an improved understanding of the structure and behavior of latex particles, better materials can be produced. Questions relating to film formation kinetics, strength of materials, and special purpose applications including medicine and biotechnology depend on a detailed knowledge of the structure and behavior of the latexes. Structured latexes are submicron sized particles, with some unique internal morphology, suspended in a fluid medium, most often water. When the dimensions of the chains are about half those of the latex diameter, some type of segregation is present, with the first polymerized material appearing near the center of the particle. Technologically, the most significant structured latex is the core-shell type with a rubbery core and a glassy shell. This type generically represents high-impact polymers, and more specifically ABS (acrylonitrile-butadiene-styrene) plastics and acrylic impact modifiers. The PIs plan to look at both homopolymer and copolymer latexes using small-angle neutron scattering (SAS) to follow the course of the polymerization. To elucidate homopolymer structure, polystyrene will be used. They plan to test the hypothesis that polystyrene of molecular dimension about half of the latex particle size segregates into what appears to be a core and a shell, with the first polymerized chains tending to be near the center of the particle. The question of how much segregation exists before the second portion of the monomer is polymerized, and how the extent of segregation changes during polymerization, will be the subject of planned experiments. The model assumes that the internal viscosity of the system is high, and/or vitrification is occurring, the final system being below its glass transition temperature, and the polymer soluble in the monomer. To look at copolymer systems, small-angle neutron scattering measurements will be made before polymerization of the second component is initiated, and several times during the polymerization. The results should elucidate if segregation occurs or, if not the rate of desegregation decrease as the internal viscosity of the system increases and/or if the glass transition of monomer-plasticized particles is approached.