BMAT: Shape Driven Self-Assembly

Brandeis University, Waltham MA

Investigators

Abstract

ID: MPS/DMR/BMAT(7623) 0907428 PI: Fraden, Seth ORG: Brandeis Title: Shape Driven Self Assembly INTELLECTUAL MERIT: The objectives of this proposal are to elucidate general principles for how molecular architecture (size, shape), molecular properties (flexibility, charge), molecular interactions (attraction, repulsion), and suspension composition influence phase behavior. Molecular shape is a fundamental property governing phase behavior. The concept of excluded volume describes a region of space that one molecule prevents another from entering. Reducing excluded volume gives molecules more freedom of motion and thus increases entropy. Consequently molecules are influenced to undergo phase transitions that have molecular configurations which minimize excluded volume. In order to reveal the role of entropy in phase transitions the PI will create shape amphiphiles or entropic surfactants, molecules composed of two parts that separately have a tendency to phase separate, but which are bound together forming a block co-polymer. Two experimental systems will be created. The first colloid will be formed of blocks of the filamentous virus fd, a long, thin, semi-flexible polymer that forms liquid crystals and DNA, a polymer too flexible to form liquid crystals. The second system will be PRINT particles ? nanosized colloids produced by a high throughput molding technology developed by collaborator, Joseph. DeSimone. The phase behavior of these systems 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. Because of the size, shape, and simplicity of the interparticle interactions this system can be theoretically modeled and simulated with high precision. To study the phase behavior of shape amphiphiles the PI will employ a microfluidic device, the PhaseChip, which can precisely meter, mix, and store sub-nanoliter amounts of sample, solvent, and other reagents. Tens of thousands of individual mixtures can be stored on a chip in individual wells. Each well is in contact with a reservoir through a membrane through which only water can pass, but not salt, polymer, or amphiphile. This enables the concentration of all solutes in a sample to be reversibly, rapidly, and precisely varied. BROADER IMPACTS: This project has important scientific implications in terms of what will be learned about the factors that drive self assembly and determine the ultimate architecture of the assemblies. The proposal describes an already highly developed program for interdisciplinary training of Brandeis life science and biophysics graduate students, including an IGERT in Quantitative Biology. Undergraduate participation in research is actively encouraged, and both graduate and undergraduate students learn to incorporate microfluidics technology into life sciences research. The PI is involved in K-12 outreach through the Brandeis POSSE program designed to bring inner city students to Brandeis and to encourage and support their success in the sciences.