Structure and Dynamics of Asymmetric Block Copolymers

NON-TECHNICAL SUMMARY

Block polymers are a class of macromolecules that combine the physical properties of two or more different compounds into a single material. Recent advances in understanding the molecular-scale structure associated with block polymers has led to innovative new applications in numerous areas of technology including batteries, cardiovascular stents, tough versatile plastics for use in packaging and health care products, and manufacturing of computer chips. Surprising new states of nanoscale molecular organization have recently been discovered in the simplest type of such compounds known as 'diblock copolymers', which contain just two polymer molecules linked end-to-end. When designed with an asymmetric composition these diblock copolymers form a variety of ordered structures that mimic the behavior of metals and alloys. This research program aims to uncover the fundamental molecular phenomena associated with this remarkable phase behavior, with the goal of establishing the basic principles responsible for the development of low-symmetry phases including quasicrystals in self-assembled soft materials. Students and post docs will synthesize useful quantities of model diblock copolymers and investigate the structure and dynamics of these materials using a host of experimental tools including X-ray scattering, electron microscopy, mechanical spectroscopy, and optical methods. This research will simultaneously train future leaders in the field of polymers while advancing the fundamental base of knowledge enabling expanded application of block polymers to myriad technologically advanced products that serve society. A collaboration with the Science Museum of Minnesota will engage the public in the exciting field of materials science and engineering.

TECHNICAL SUMMARY

Block copolymers command a leading position in the field of synthetic polymers, offering innumerable opportunities to advance our fundamental understanding of soft materials while addressing myriad technological applications across various disciplines associated with materials science and engineering. Recent advances with diblock copolymers, the simplest molecular architecture in this category of self-assembling materials, have exposed extraordinary new concepts regarding order and disorder in the limit of asymmetric molecular architectures leading to the formation of discrete, nominally spherical particles. This project outlines an ambitious experimental program designed to uncover the basic principles responsible for the formation of tetrahedrally close-packed Frank-Kasper phases and quasicrystals in diblock copolymer melts. Model materials will be synthesized in nearly monodisperse form and characterized structurally using small-angle X-ray scattering and electron microscopy. The molecular transport phenomena that govern phase transition dynamics will be assessed using time-resolved techniques including small-angle neutron scattering, optical methods and dynamic mechanical spectroscopy. This program will establish the principles that govern the formation of low symmetry phases as a function of molecular architecture, dispersity, compositional and conformational asymmetry, and molecular weight in pure block copolymers and blends.

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.