Fundamental Principles of Multivalency in Nanoscale and Macromolecular Systems

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professor Robert Macfarlane at the Massachusetts Institute of Technology (MIT) will investigate an important gap in knowledge for extending principles of multivalency to more complex materials systems involving polymers and nanoparticle assemblies. In contrast to weak monovalent binding, multivalent interactions offer the advantage of a multiple and thus dramatically enhanced binding on a molecular scale. Multivalent structures function in a number of systems to generate a strong but reversible interaction between two objects and is a key design tool that can be used to precisely program material properties in a manner that is unobtainable through traditional organic synthesis. The fundamentals of multivalency have largely been examined with molecular models, however these models have limitations and do not permit full explanation of how multivalency occurs in polymer- or nanoparticle-based materials. This proposal will permit this challenge to be addressed via a “stepwise” approach to increasing complexity in multivalent systems. By first measuring the supramolecular behaviors of individual molecules, then measuring additional systems with gradually increasing modifications, each of the complicated factors that may influence supramolecular multivalency can be individually examined. As a result, the proposed work seeks to permit rational examination of massively multivalent systems consisting of 100s or 1000s of individual supramolecular groups. The design principles gained from this research are then to be translated to fundamental studies explaining how nanoscale systems of massively multivalent binders can be used to control the behaviors of macroscopic systems in the context of both recyclable and easily processed polymers, and the self-assembly of nanoparticle superlattices. This proposal will also be used as the basis of an outreach program for students from underrepresented groups in local community colleges, providing them with the technical expertise and research experience to pursue either higher STEM (science, technology, engineering and mathematics) education goals or careers in STEM fields. To achieve the goal of better understanding how to use a systems-level approach to control multivalency, established experimental techniques will first be used to measure the thermodynamic parameters of model monovalent supramolecular binders (SMBs). Subsequent experiments will introduce “step-wise” increases in complexity (e.g. molecular modification to the SMB, grafting the SMB to a polymer chain, binding multiple polymer-tethered SMBs to nanoparticle scaffolds), and these same thermodynamic parameters will be re-measured to determine how each step-wise increase in system complexity affects SMB interactions. Using the information on monovalent binding thermodynamics obtained from these experiments, trends in multivalency as a function of nanoscale scaffold design will be examined. Multivalency numbers will be measured for both macromolecules and brush-grafted nanoparticles modified with SMBs deposited onto substrates expressing complementary SMBs (to measure the thermodynamics of a single multivalent binding event), and for binary assemblies of particle- and polymer-scaffolds that express complementary SMBs. The ability to tune the breadth and onset temperature of multivalent dissociation will then be investigated to allow the use of supramolecular chemistry to alter polymer processability. Tailorable multivalent binding between short-chain polymers will be examined as an approach to produce polymers that are easily processed, recycled, or reconfigured but still mechanically strong. Separately, the effects of altering supramolecular multivalency on nanoparticle self-assembly will be used as a means to understand how collective supramolecular interactions dictate the hierarchical organization of nanoparticles within superlattice architectures. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.