Nanostructures confined in micro- and nano-cavities: Direct measurement of consequent surface forces

From moving cartilages in a mammalian joint, to dispersed pigment particles in household paint, the situations where surfaces come to close proximity are ubiquitous. The interactions between these surfaces (called surface forces) are critical in achieving desirable material properties and facilitating designed technological processes, and underpin many natural and biological phenomena. With the rapid development of nanotechnology, the surface-to-volume ratio ever grows and so does the importance of surface interactions. Given such importance, much effort has been dedicated to improving our understanding of surface forces, both theoretically and experimentally. As a result, we have plenty of tricks up our sleeves to arrange and modify surface forces to facilitate different applications or material properties. These tricks most notably include adjusting solution conditions, such as electrolyte concentrations, in order to control the electric double layer force, and adding soft condensed matter (polymers and surfactants) to the surface and the intervening medium. Thanks to a steady drive towards smaller and smaller structures in modern technologies, we increasingly find nanostructures (or nanoparticles) of different materials, sizes and shapes added as an ingredient to our product formulations, particularly in personal care products and biomedical applications, in order to achieve desirable material properties or to preform a particular function. There are clear indications that the effective roles of nanostructures in these applications have much to do with how they interact with various surfaces and how they mediate surface forces between macroscopic surfaces. Many promising biomedical and bioanalytical applications of nanoparticles also exploit their interactions with complex biological tissue surfaces embedded with biopolymers and lipids. However, there is a public perception, correctly so, that we don't fully understand the impact of nanostructures on our health and environment. We can improve that understanding on different levels. In this project, we propose to perform a series of measurements of surface forces mediated by nanostructures, to comprehensively probe the effects of a range of parameters such as the size, shape and surface chemistry of the nanostructures on surface forces they mediate. This will improve our understanding on a fundamental level of how nanostructures facilitate surface interactions, and such knowledge will help us to harness nanostructures' full potential in modern technologies and medical applications.

Given the fundamental nature of this proposed research, there are a number of direct and potential beneficiaries. First of all, it will allow the PI as a recently appointed lecturer to establish a surface force laboratory to perform the proposed experiments, which will be a solid foundation for an independent research group. Secondly, the School of Chemistry at Bristol will guarantee funding for a PhD student in the event that this proposal is funded. This project will thus provide a tremendous training opportunity for the student in an area relevant to nanotechnology. The student will not only obtain knowledge specific to this project, but will also develop a range of transferrable skills such as problem solving, project management and interpersonal communication, which will be invaluable to his or her future career. Thirdly, the results from this project may also benefit companies in the areas of paints, personal care products and lubricants, such as Proctor & Gamble (P&G), Lubrizol and Unilever. There is a current drive from these companies to fully utilise nanoparticles or nanostructures in their product formulations to enhance the effectiveness or desired properties of the products. However, industrial formulations for these products tend to be complex and it is difficult to examine the roles of nanoparticles. The results from the model experimental systems in this project will offer physical insight for nanoparticle mediated interactions, and thus help these companies when they consider their product formulations. To this end, P&G and Lubrizol have already been approached, with future meetings planned to discuss possible joint projects in related areas. Fourthly, the interactions between nanoparticles and soft matter structures (e.g., polymer brushes and lipid bilayers) are relevant to the toxicity of nanoparticles - how they interact with biological tissues and in turn affect bio-functionalities. Again, this proposed research is fundamental in nature, and the experimental systems to be explored do not have direct analogues in biological systems. However, the fundamental interactions of nanoparticles with, e.g., polymer brushes and lipid bilayers, are relevant to our understanding of nanoparticle interactions with cell and tissue surfaces and thus to nanoparticle toxicity. To fully explore this, the PI has already contacted Dr. P. Case, a Bristol pathologist who has been working on toxicity of metal nanoparticles generated from artificial implants, and Dr. Case has recognised the relevance and importance of such a fundamental study to his nanotoxicity research. As a result, the PI and Dr. Case plan to meet regularly to explore overlapping interest and possible future joint proposals. Lastly, the results from this research may be relevant to the wider public. There is a public conception that we do not fully understand the impact of nanoparticles on our health and environment. For relevant government agencies to assess such an impact and establish guidelines to regulate the production and commercial usage of nanoparticles, dedicated efforts should be made to improve our understanding of the impact of nanoparticles on different levels. The proposed research would fall in the category of trying to improve such an understanding on a fundamental level.