Designing Viruses for Studies of Liquid-Crystals and Self-Assembly

Brandeis University, Waltham MA

Investigators

Abstract

The long term goals of this project are to understand the phase behavior of macromolecular suspensions that are either partially or totally composed of liquid crystalline forming molecules. The property of matter that two particles cannot be in the same place at the same time leads to the concept of excluded volume, a region of space that one molecule prevents the other from entering and is a function of the particles' shape, mutual orientation, and separation. Reducing excluded volume gives molecules more freedom of motion and thus increases entropy. Consequently molecules are driven to undergo phase transitions that have molecular configurations which minimize excluded volume. In order to reveal the role of entropy in phase transitions "entropic surfactants" will be synthesized consisting of molecules composed of two parts that separately have a tendency to phase separate, but which are bound together forming a block co-polymer. The blocks will be filamentous virus, a long, thin, semi-flexible polymer that forms liquid crystals and DNA, a flexible polymer too long to form liquid crystals. The phase behavior of this system will be studied, as well as the phase behavior of mixtures of the shape amphiphiles with the individual components. Entropy is the dominant feature controlling the phase behavior of these charge stabilized colloids and this system can be theoretically modeled with high precision. The entropic surfactants in this study share features with three important classes of materials, surfactants, block co-polymers and liquid crystals, which self-assemble into complex structures. Understanding the self-organization of these materials is a basic goal of nanotechnology and soft matter research. This work will serve as a foundation for theory, simulation, and experimental study of microphase separation in general. The students involved with this project will receive training in both theory and experiment, which will prepare them for productive careers in biophysics and nanotechnology. %%% The second law of thermodynamics (entropy increases) is so well established that the US patent office does not accept applications that violate its principles. Entropy is often associated with disorder, and consequently it is counter-intuitive that structured phases occur as a result of maximizing entropy. The objectives of this project, involving a collaboration with Wellesley College, are to create molecules, denoted "entropic surfactants", that self-assemble into complex structures driven by entropy. Understanding the self-organization of these materials is a basic goal of nanotechnology and complex fluids research. Graduate and undergraduate students will receive training in the synthesis of bionanoparticles and will build molecules composed of two parts that separately have a tendency to phase separate, but which are bound together forming a block co-polymer. The blocks will be filamentous virus, a long, thin, semi-flexible polymer that forms liquid crystals and DNA, a flexible polymer too long to form liquid crystals. The phase behavior of this system will be studied, as well as the phase behavior of mixtures of the entropic surfactants with the individual components. Entropy is the dominant feature controlling the phase behavior of these charged molecules and because of the size, shape, and simplicity of the interparticle interactions this system can be theoretically modeled with high precision. This training in both theory and experiment will prepare students for productive careers in biophysics and nanotechnology. This work will serve as a foundation for theory, simulation, and experimental study of phase separation that is applicable to a wide number of fields including nanotechnology, surfactants, and polymers.