Coupled Dewetting and Phase Separation in Thin Film Binary Mixtures

这个简短的项目将与宾夕法尼亚大学的Russell Composto展开合作。我们对高分子材料微观结构的演变有着共同的兴趣。除了促进英美在聚合物科学方面的联系外，我们还将利用这次访问计划未来在多组分聚合物混合物的相分离和脱湿方面的合作研究项目。该合作将允许在薄膜混合物的相分离和脱湿的特定主题上取得快速和重大的进展。我们的目标是开发改进的模型和设计新的实验，这将增强我们优化加工条件的能力，以实现所需的材料性能。聚合物薄膜越来越多地应用于先进材料，从粘合剂到塑料电子产品。对于许多技术，感兴趣的薄膜通常是多组分聚合物共混物。由于微观结构的存在，通常会产生超出组件的新特性，微观结构可能具有相关的长度尺度，甚至多个长度尺度，范围从纳米到微米。形成微观结构的一种方法是温度的阶跃变化，使最初可混溶的共混物变为不可混溶的。相分离过程的动力学控制了所形成的结构。例如，混合物可以自发地相分离成具有优先长度尺度的共连续结构，这一过程被称为旋量分解。初始的“旋量”长度尺度可以由温度变化的程度来控制；变化越大，长度尺度越细。在薄膜中，另一个重要因素是薄膜是否在表面上扩散或形成孤立的液滴。这取决于表面和薄膜之间的相互作用是否有利。这些相互作用的强度也可以通过温度变化来控制。在某种温度下，薄膜可能倾向于在表面上扩散，而在不同的温度下，它可能倾向于形成液滴。铺开的薄膜在温度变化后变成孤立的液滴的过程称为脱湿。在脱湿过程中产生的高度波动的显著模式也影响了薄膜的微观结构。纳米颗粒的使用也引起了人们的兴趣，特别是在提高韧性、不透气性和阻燃性等性能方面。尽管基于功能纳米粒子与多相聚合物共混物的设备越来越受到关注，但由于缺乏对纳米粒子分散作用的理解，对其微观结构和性能的控制尚不可能。Composto小组一直处于实验的最前沿，旨在了解薄膜二元混合物中相分离和脱湿的组合过程，PI已经开发了第一个从理论角度解决问题的模型。最近，复合材料组的研究表明，它们的加入会导致混合物中微观结构的演变，因为界面被“干扰”而冻结。在这个项目中，利用我们的集体专业知识，我们将考虑现有模型在多大程度上能够解释最近的观察结果，模型可以改进的方式，如何扩展它来描述添加纳米粒子的后果，以及哪些新的实验将最好地测试新理论。

This short project will initiate collaboration with Russell Composto at the University of Pennsylvania. We share a common interest in the evolution of microstructure in polymer materials. In addition to fostering UK/US links in polymer science, we will use the visit to plan a future collaborative research program in phase separation and dewetting in multi-component polymer mixtures. The collaboration will permit rapid and significant advances in the specific topic of phase separation and dewetting in thin-film mixtures. Our aim is to develop improved models and design new experiments that will enhance our ability to optimise processing conditions to achieve desired material properties. Polymeric thin films are being increasingly utilised in advanced materials applications, ranging from adhesives to plastic electronics. For many technologies, the thin films of interest are typically multi-component polymer blends. New properties, beyond those of the components, often arise due to the existence of a microstructure, which may have an associated length-scale, or even multiple length-scales, ranging from nanometres to microns. One method of forming microstructures is a step change in temperature that causes an initially miscible blend to become immiscible. The dynamics of the resultant phase separation process control the structures that develop. For example, the blend may phase separate spontaneously into a co-continuous structure with a preferred length-scale dominating, a process known as spinodal decomposition. The initial 'spinodal' length-scale can be controlled by the extent to which the temperature is changed; the greater the change the finer the length-scale.In thin films, another significant factor is whether a film spreads or forms isolated droplets on a surface. This depends on whether the interactions between the surface and the film are favourable. The strength of these interactions can also be controlled by temperature changes. At one temperature a film may favour being spread over a surface, whilst at a different temperature it may prefer to form droplets. The process by which a spread film becomes isolated droplets after a change in temperature is known as dewetting. The remarkable patterns of undulations in height that develop during dewetting also impact upon the microstructure of the film. The use of nanoparticles is also attracting interest, particularly to improve properties such as toughness, impermeabilty to gases and flame retardancy. Although devices based on blending functional nanoparticles with multiphase polymer blends are of increasing interest, control over their microstructure and properties is not yet possible because of a lack of understanding over the role of nanoparticle dispersion. The Composto group has been at the forefront of experiments aimed at developing an understanding of the combined processes of phase separation and dewetting in thin-film binary mixtures, and the PI has developed the first model to address the problem from a theoretical viewpoint. Recently, the Composto group has shown that their addition can result in microstructure evolution in blends being frozen due to 'jamming' the interface. In this project, using our collective expertise, we will consider the extent to which the existing model is able to explain recent observations, the ways in which the model can be improved, how it can be extended to describe the consequences of adding nanoparticles, and what new experiments will best test the new theories.