Nanomechanical properties of biocompatible particles: from bulk to interface

Pickering乳液和泡沫是液体或空气在由固体颗粒稳定的不相容液体中的亚稳分散体。与表面活性剂稳定体系相比，由于颗粒在流体-流体界面的分离能高出数量级，由颗粒稳定的体系在防止聚结和Ostwald熟化方面具有非凡的稳定性。然而，对于许多应用来说，能够根据需要破坏它们的稳定也是至关重要的，例如，在口腔中释放油滴和气味，或者在皮肤或叶子表面释放油分散的活性化合物。为了实现这种失稳，通过温度、酶、剪切或pH等刺激，颗粒本身必须具有刺激响应性，因此“生物聚合物微凝胶”(即亚微米大小的软水凝胶颗粒)是理想的候选者。由于微凝胶的变形能力，微凝胶可以在界面上以不同的吸附形式被捕获-从高度分散，到压缩和紧密堆积，甚至坍塌。在这篇博士论文中，我们将回答一系列问题：这种变形性与微凝胶的潜在互穿或两相对微凝胶的渗透以及它们的稳定性能之间有什么关系？单个微凝胶颗粒的结构如何随着各种刺激的变化而变化？要回答这些基本问题，了解单个生物相容颗粒在块体和界面上的纳米力学性质以及它们对刺激的反应变得至关重要。目前，这方面的知识很少，因为测量单个纳米级软材料物理性质的实验技术有限。在这个涉及食品胶体、纳米物理和百事可乐合作者的跨学科博士项目中，我们的目标是使用一系列先进的界面和原子力显微镜技术，对单个微凝胶的性质与它们在界面和块体中的集体性质之间的关系有一个新的理解。

Pickering emulsions and foams are metastable dispersions of liquids or air in an immiscible liquid stabilized by solid particles. Compared to stabilization by surfactants, systems stabilized by particles offer extraordinary stability against coalescence and Ostwald ripening due to the orders of magnitude higher detachment energies of particles at the fluid-fluid interface. However, for many applications it is also crucial to be able to destabilize them on demand, e.g. release of oil droplets and flavours in the mouth, or oil dispersible active compounds on skin or leaf surfaces. To achieve such destabilization, via stimuli such as temperature, enzymes, shear or pH, the particles themselves have to be stimuli-responsive and consequently "biopolymeric microgels" (i.e., sub-micron-sized soft hydrogel particles) are the ideal candidate. Due to their deformability, microgels can be trapped in various configurations on adsorption at the interface - from highly spread, to compressed and close packed, and even collapsed. In this PhD, we will answer a series of questions: What is the relationship between such deformability and potential interpenetration of microgels, or penetration of the two phases into the microgel, and their stabilizing properties? How does the structure of single microgel particles change in response to the various stimuli? To answer these fundamental questions, knowledge of the nanomechanical properties of individual biocompatible particles in the bulk and at the interface, and their response to stimuli, becomes vitally important. Currently this knowledge is sparse because experimental techniques for measuring the physical properties of individual nanoscale soft materials are limited. In this interdisciplinary PhD project involving academics from Food Colloids, Nanoscale Physics and Collaborators from Pepsico, we aim to create a new understanding of the relationship between the properties of individual microgels and their collective properties at the interface and in the bulk, using a range of advanced interfacial and atomic force microscopy techniques.