Experiments on the Internal Structure of Latexes Using SmallAngle Neutron Scattering

这项研究的目的是获得有关形成动力学的基本信息，以及这些动力学如何影响胶乳颗粒的最终结构。这些材料被用作涂料和涂料，也用作抗冲击改性剂。这项工作对现代工业的价值在于，随着对乳胶粒子结构和行为的更好理解，可以生产出更好的材料。有关成膜动力学、材料强度以及包括医学和生物技术在内的特殊用途的问题取决于对胶乳结构和行为的详细了解。结构胶乳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。当链的尺寸大约是胶乳直径的一半时，会出现某种类型的偏析，第一种聚合物质出现在粒子中心附近。在技术上，最重要的结构化乳胶是具有橡胶芯和玻璃外壳的核壳型。这种类型通常代表高抗冲聚合物，更具体地说是ABS(丙烯腈-丁二烯-苯乙烯)塑料和丙烯酸类抗冲改性剂。PI计划使用小角中子散射(SAS)来跟踪聚合过程，同时观察均聚和共聚乳液。为了阐明均聚物的结构，我们将使用聚苯乙烯。他们计划测试一个假设，即分子尺寸约为乳胶颗粒大小的一半的聚苯乙烯分离成看起来像是核和壳的东西，第一个聚合的链倾向于靠近颗粒的中心。在单体的第二部分聚合之前存在多少分离的问题，以及聚合过程中分离程度如何变化的问题，将是有计划的实验的主题。该模型假定体系的内部粘度很高，和/或正在发生玻璃化，最终体系的玻璃化温度低于其玻璃化转变温度，聚合物可溶于单体。为了观察共聚体系，将在第二组分开始聚合之前进行小角中子散射测量，并在聚合过程中进行多次测量。结果应该阐明是否发生分离，或者，如果不是，随着体系内粘度的增加和/或单体增塑颗粒的玻璃化转变的接近，脱离速率降低。

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.