Date of Award

12-2012

Degree Name

MS in Polymers and Coatings

Department

Chemistry & Biochemistry

Advisor

Raymond H. Fernando

Abstract

Nanotechnology is the manipulation of matter and devices on the nanometer scale. Below the critical dimension length of 100nm, materials begin to display vastly different properties than their macro- or micro- scale counterparts. The exotic properties of nanomaterials may trigger the start of a new technological revolution, similar to the electronics revolution of the late 20th century. Current applications of nanotechnology primarily make use of nanoparticles in bulk, often being made into composites or mixtures. While these materials have fantastic properties, organization of nano and microstructures of nanoparticles may allow the development of novel devices with many unique properties. By analogy, bulk copper may be used to form the alloys brass or bronze, which are useful materials, and have been used for thousands of years. Yet, organized arrays of copper allowed the development of printed circuit boards, a technology far more advanced than the mere use of copper as a bulk material. In the same way, organized assemblies of nanoparticles may offer technological possibilities far beyond our current understanding.

In the first project, 1D assemblies of nanoparticles were explored. 1D anisotropic assemblies of nanoparticles are the simplest organized nanostructures which may be fabricated. One of the greatest difficulties in developing commercial products is in the transfer of a process from the laboratory to manufacturing scale. While many techniques may be used to develop 1D assemblies in lab, simple techniques are needed to allow the fabrication of these assemblies on a large, cost effective scale. Use of shear, shown previously to induce colloidal ordering in solutions, is a technique that may be readily adapted from the coatings industry as a process for forming 1D assemblies, if the optimal conditions can be found. Atomic force microscopy was used to study the role of shearing forces produced by drawdown and spraying application in the formation of 1D assemblies of nanoparticles. Formation of 1D strings was observed to increase with greater application of simple shear, but greater spraying forces were found to decrease formation of strings. This is explained in terms of greater simple shear providing a greater driving force for string formation, while greater spraying shear acted to irreversibly disperse the particles.

The second project focused on the development of a learning module for education of students at various academic levels on the significance of the surface area of nanomaterials. This project was commissioned by the Global Waste Research Institute, a multidisciplinary organization based at Cal Poly, concerned with performing research and education in areas related to waste management, particularly of emerging waste streams. As nanotechnology and nanoparticles become more prevalent in consumer products and industrial processes, the volume of nanowaste is increasing rapidly. To address challenges associated with processing this unique form of waste, understanding of the fundamental processes controlling the unique properties of nanoparticles is necessary. A learning module was developed using a laboratory demonstration and video presentation to illustrate concepts related to differences in the properties between microparticles and nanoparticles. The laboratory demonstration was designed to be simple to understand, and quick, simple, and inexpensive to perform. The video presentation was designed to be a 15 minute presentation relating the concepts of nanotechnology, nanoparticles, surface area, and fundamental differences as compared to conventional materials. Dispersions of particles within aqueous media were used as a framework for the discussion, in a manner comprehensible by students ranging from 12th grade high school students to graduate students in relevant programs.

The third and final project focused on self-assembly of particles in nematic liquid crystalline colloids. Dispersions of colloidal particles in liquid crystals (LCs) are a relatively new set of composite materials, host to a variety of interactions not seen in colloids in isotropic media. Presence of colloidal particles disrupts the local nematic director, resulting in a loss of long-range elastic energy. Interactions between particles and LC molecules results in dipolar or quadrupolar defects, depending on the nature of the interactions between particle and LC. The loss of long-range elastic energy can be minimized through aggregation of particles. The defects formed by interactions between particles and LC stabilize these aggregations as linear chains, either along the nematic director in the case of dipolar defects, or at an offset angle in the case of quadrupolar defects. Dispersions of silica microspheres in the nematic phase of a thermotropic liquid crystal were studied using polarizing light microscopy. Strong homeotropic anchoring was observed, indicated by the abundant formation of hedgehog defects. These defects were found to play a role in self-assembly of particles along the nematic director, resulting aggregates containing up to a dozen aligned particles. In addition, particles were observed to aggregate in chains along grain boundaries in the liquid crystal, acting to stabilize the high energy interface between different grain directions, an effect not previously reported in the scientific literature for nematic colloids.

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