New Principles for Targeting and Triggering based on Molecular Self-Assembly in Topological Defects of Liquid Crystals
Abstract
Molecular self-assembly in aqueous systems arises from a delicate interplay of entropic and enthalpic effects associated with the structuring of water. This interplay also underlies many of the remarkable macroscopic material responses to molecular cues that are encountered in biological systems. Recently, new insight into self-assembly of amphiphilic molecules in an alternative class of structured solvents, specifically nematic solvents, has been reported. The presence of long-range orientational order in nematic solvents was shown to open new avenues to control of molecular assemblies that are not possible in aqueous systems. One key opportunity revolves around the formation of topological defects in nematic solvents, which can serve as virtual templates for triggering and hosting molecular assemblies. Motivated by these observations, this proposal seeks to develop a fundamental understanding of equilibrium and dynamic aspects of molecular self-assembly of amphiphiles in defects of nematic solvents, and to leverage that understanding to demonstrate principles that permit formation of single nanoscopic assemblies to be amplified into macroscopic outputs. The approach described in this proposal builds from recent observations by PI Abbott that the nanoscopic cores of topological defects formed in nematic solvents, which are molecularly disordered relative to bulk nematic solvents, selectively trigger cooperative self-assembly of amphiphiles. These observations generate a range of questions regarding the equilibrium and dynamic properties of these assemblies, the answers to which will enable development of new principles for amplification of signals across multiple time and length scales. The research is organized into three parts. First, experiments will be performed to provide insight into the thermodynamics of molecular self-assembly in topological defects, including the relationship between amphiphile molecular structure and assembly morphology, and the role of entropy and enthalpy in driving self-assembly. The experiments will be enabled by synthesis of families of polymeric amphiphiles by reversible addition fragmentation chain transfer (RAFT) and ring-opening metathesis polymerization (ROMP) in the research group of co-PI Gianneschi. Second, the coupling between dynamics of molecular self-assembly and dynamics of defect motion will be elucidated, building on the preliminary observation that macroscopic dynamics of defects can report formation of a single nanoscopic amphiphilic assembly. A key aspect will be synthesis of amphiphiles with tailored dynamics using ROMP and RAFT. Third, we will design amphiphilic polymers that can be triggered (e.g., by light) to undergo self-assembly in defects, and in doing so, generate macroscopic changes in the dynamic and equilibrium organization of nematic liquid crystalline systems that can be observed visually. This goal will integrate a new approach for preparing ROMP-based amphiphilic polymers that uses a light-activated ruthenium catalyst. In summary, this project will advance our understanding of molecular self-assembly in nematic solvents and offers the potential to provide new principles that lead to macroscopic responses from molecular cues. The focus is fundamental, but the long-term impact of the research has the potential to guide new designs of triggerable and responsive soft materials of broad utility to DoD, including for (i) amplification of molecular events into the optical scale, (ii) design of sentient materials, and (iii) interfacial designs of chemical and biological sensors.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 08, 2019
- Source ID
- W911NF1910071
Entities
People
- Nicholas Abbott
Organizations
- Army Contracting Command
- Cornell University
- United States Army