NER: Ordered liquid crystal nano-colloids

Kent State University, Kent OH

Investigators

Abstract

Complex three dimensional structures of nanoparticles can be produced in liquid crystals. Our preliminary research demonstrates that a moving liquid crystal to isotropic phase boundary collects and pushes and periodically deposits nanoparticles. By adjusting a variety of conditions, such as the rate of the phase transition, the alignment of type of liquid crystal, the size and shape of particles, we can produce a wide variety of three dimensional structures. We have also found that application of external fields and in particular patterned external fields can be combined with the phase transition to produce very complex structures. This proposal outlines an aggressive research project to explore the basic mechanisms of these newly discovered phenomena potential to produce complex three dimensional structures. This project is most closely related to the Nanoscale Structures, Novel Phenomena and Manufacturing Processes at the Nanoscale, while having relevance for the Nanoscale Devices and System Architecture theme. We propose to deploy the unique research strengths at the Liquid Crystal Institute (Kent State University, Ohio) to rapidly result in new electro-optical materials and establish a theoretical base to understand this complex process We will focus on precisely controlling the position of nano-particles dispersed in liquid crystalline matrices. Particles dispersed in the liquid crystal phase produce distortions in the liquid crystal director and introduce defects in the liquid crystal phase. The added energy found in these distortions and defects provide the forces that move the nanoparticles. In order to minimize the free energy of the system, particles will share defects and tend to form organized structures. These structures will tend to reside at defect lines and planes separating liquid crystal domain providing the simplest mechanism to produce complex three dimensional structures. Anchoring at the particle surface can induce a gradient in the magnitude of the nematic order parameter in their neighborhood, leading to an attractive short-range interaction between particles. More complex interactions arise from restrictions of thermal fluctuations in the director field near the particle surfaces. By modulating these complex systems of energies we have the potential to precisely control the placement of nano-particles. As an example of the power of this new approach we will build complex three dimensional photonic crystals that arrange particles of different sizes and physical properties in ordered arrays. For example we can segregate particles of different types: ferro-electric, ferro-magnetic, and carbon nanotubes. The elastic, electro-, magneto-, and nonlinear optical properties of these suspensions will be investigated experimentally and theoretically as a function of the physical properties, concentration, size, and shape of the particles. These complex arrays can be used to produce new optical devices, artificial muscles, responsive membranes and biological sensors. Intellectual merit The result of our research will be a new set of tools researchers can use to build nano-particle structures and create entirely new affects. We will also expand our general understanding of the liquid crystal phase. For example, we have already found that the movement of nanoparticles at the isotropic interface provides new insight into the properties of this complex boundary. Broader impact We will utilize our existing Industrial Partnership Program to assure that our results are quickly transmitted to the marketplace. Through the LCI summer internship program and the KSU REU program we will reach out to undergraduate students and through our established education outreach program we will interact with K-12 students in the area.