Nanomechanical properties of biocompatible particles: from bulk to interface

Pickering乳液和泡沫是液体或空气在不混溶液体中的亚稳分散体，由固体颗粒稳定。与通过表面活性剂的稳定化相比，通过颗粒稳定化的系统由于在流体-流体界面处的颗粒的数量级更高的分离能而提供了针对聚结和奥斯特瓦尔德熟化的非凡稳定性。然而，对于许多应用而言，能够根据需要使它们不稳定也是至关重要的，例如在口中释放油滴和香味，或者在皮肤或叶子表面释放油分散性活性化合物。为了通过诸如温度、酶、剪切或pH的刺激实现这种去稳定化，颗粒本身必须是刺激响应性的，因此是"生物聚合物微凝胶"（即，亚微米尺寸的软水凝胶颗粒）是理想的候选物。由于它们的可变形性，微凝胶可以在界面处吸附时以各种构型被捕获-从高度分散到压缩和紧密堆积，甚至塌陷。在这个博士学位，我们将回答一系列的问题：这种变形性和微凝胶的潜在相互渗透，或两个阶段的渗透到微凝胶，和他们的稳定性能之间的关系是什么？单个微凝胶颗粒的结构如何响应于各种刺激而变化？为了回答这些基本问题，个体生物相容性颗粒在本体和界面处的纳米力学性质的知识，以及它们对刺激的响应，变得至关重要。目前，这方面的知识是稀疏的，因为测量单个纳米级软材料的物理特性的实验技术是有限的。在这个涉及来自食品胶体，纳米物理学和百事可乐合作者的学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其在界面和体积上的集体性质之间的关系进行新的理解。

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.