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合作。我们对聚合物材料的微观结构的演变有着共同的兴趣。除了促进英国/美国在聚合物科学方面的联系外，我们还将利用此次访问计划未来在多组分聚合物混合物中的相分离和去湿方面的合作研究计划。该合作将允许在薄膜混合物中的相分离和去湿的特定主题方面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，以提高我们优化加工条件的能力，从而实现所需的材料性能。聚合物薄膜越来越多地用于先进材料应用，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。新的性能，超出了那些组件，往往是由于存在的微观结构，它可能有一个相关的长度尺度，甚至多个长度尺度，从纳米到微米。形成微结构的一种方法是温度的阶跃变化，其导致最初可混溶的共混物变得不可混溶。所得到的相分离过程的动力学控制所形成的结构。例如，共混物可以自发地相分离成具有优选的长度尺度主导的共连续结构，该过程被称为亚稳分解。初始的“旋节线”长度尺度可以通过温度变化的程度来控制;温度变化越大，长度尺度越精细。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。在一个温度下，膜可能有利于在表面上铺展，而在不同的温度下，它可能优选形成液滴。在温度变化后，展开的薄膜变成孤立的液滴的过程称为去湿。在去湿过程中形成的高度起伏的显著图案也影响膜的微观结构。纳米颗粒的使用也引起了人们的兴趣，特别是为了改善诸如韧性、气体不渗透性和阻燃性的性能。尽管基于将功能性纳米颗粒与多相聚合物共混物共混的装置越来越受关注，但由于对纳米颗粒分散体的作用缺乏了解，因此对其微观结构和性质的控制尚不可能。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去湿的组合过程，PI开发了第一个从理论角度解决问题的模型。最近，Composto小组已经表明，它们的加入可能会导致混合物中的微观结构演变，由于“堵塞”界面而被冻结。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，如何扩展到描述添加纳米粒子的后果，以及什么样的新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.