Coupled Dewetting and Phase Separation in Thin Film Binary Mixtures

这个简短的项目将启动与宾夕法尼亚大学的Russell Composto的合作。我们对聚合物材料微观结构的演变有着共同的兴趣。除了促进英国和美国在聚合物科学方面的联系外，我们还将利用这次访问来规划未来在多组分聚合物混合物的相分离和除湿方面的合作研究计划。这项合作将使在薄膜混合物的相分离和除湿这一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，以增强我们优化工艺条件以实现所需材料性能的能力。从粘合剂到塑料电子产品，聚合物薄膜正越来越多地被用于先进材料应用。对于许多技术来说，感兴趣的薄膜通常是多组分的聚合物混合物。除了部件的那些特性之外，新的特性通常是由于微结构的存在而产生的，该微结构可能具有从纳米到微米的相关长度尺度，甚至多个长度尺度。形成微观结构的一种方法是温度的阶跃变化，使最初可混溶的混合物变得不相容。由此产生的相分离过程的动力学控制着所形成的结构。例如，共混物可以自发地相分离成具有首选长度-尺度主导的共连续结构，这一过程被称为调幅分解。初始的“旋节”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。在一种温度下，薄膜可能更倾向于铺展在表面上，而在不同的温度下，它可能更倾向于形成液滴。温度变化后，铺展的薄膜变成孤立的液滴的过程称为去湿。在除湿过程中形成的显著的高度起伏也会影响薄膜的微结构。纳米颗粒的使用也引起了人们的兴趣，特别是在改善韧性、气体不渗透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的器件越来越受到人们的关注，但由于对纳米粒子分散的作用缺乏了解，目前还不可能控制其微观结构和性能。Composto小组一直处于实验的前沿，旨在了解薄膜二元混合物中相分离和去湿的组合过程，PI从理论角度开发了第一个模型来解决这一问题。最近，Composto研究小组已经证明，它们的加入会导致共混物中微观结构的演变，因为它们会堵塞界面而冻结。在这个项目中，我们将利用我们的集体专业知识，考虑现有模型能够在多大程度上解释最近的观察结果，该模型可以改进的方式，它如何扩展以描述添加纳米颗粒的后果，以及哪些新的实验将最好地测试新的理论。

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.