Phase Behavior of Colloidal Suspensions of Rods and Spheres

Brandeis University, Waltham MA

Investigators

Abstract

This research focuses on determining the phase behavior of rodlike colloids, and mixtures of rodlike and spherical colloids. Biological examples of rodlike colloids include proteins such as actin and microtubules, DNA, and filamentous viruses. The rodlike colloids on interest in this work consist of genetically engineered filamentous phage fd virus. The spherical particles are , either polystyrene latex or water soluble polymers such as poly(ethylene) oxide. Knowledge gained from these well characterized materials has implications for the fundamental understanding of liquid crystals, colloid-polymer mixtures, and the biophysics of the intracellular environment, as well as the design of composite materials where molecular ordering and self-assembly is important. A primary goal will be determining fundamental properties of the liquid crystalline phase of pure rod suspensions, then mixtures of rod and spheres, mixtures of rods of different lengths, and mixtures of rods of different diameters. Specifically, the angular distribution function of the rodlike colloids, co-existence concentrations, and virial coefficients will be obtained. These experiments are designed to determine the roles of attraction and repulsion in governing phase behavior, as well as to explore further rich and unexpected microphase behavior discovered in mixtures of rods and spheres during the previous NSF grant. The kinetics of phase transformation in mixtures of rods and spheres will be examined, including the identification of metastable phases. Finally, the dynamics of individual rods and spheres seen as tracers will be studied. Students participating in the research receive interdisciplinary training that will prepare them for a variety of careers in academe, industry, and government. %%% This research focuses on determining the states of matter exhibited by rodlike colloids and by mixtures of rodlike and spherical colloids. Rodlike colloids, though less studied than spherical colloids, are of considerable importance. Biological examples of rodlike colloids being proteins such as actin and microtubules, DNA, and filamentous viruses. The rodlike colloids studied in this project consist of genetically engineered filamentous phage fd virus. For spheres, the well known polystyrene latex or water soluble polymer poly(ethylene) oxide are employed. All these colloids are well characterized, uniform particles for which an established theoretical framework exists for understanding their phase behavior. What is learned about these particular systems has implications for the fundamental understanding of liquid crystals, colloid-polymer mixtures, the biophysics of the intracellular environment, as well as the design of composite materials where molecular ordering and self-assembly is important. This research lies at the intersection of chemistry, biology, and physics. Biological molecules and processes are increasingly being understood at a mechanistic level, and physics is making significant gains in understanding non-equilibrium and disordered systems. Thus these two fields, which traditionally have been widely separated, are swiftly growing towards each other. Students participating in the research receive interdisciplinary training that will prepare them for a variety of careers in academe, industry, and government.