Modular Click Synthesis of Aligned Liquid Crystal Elastomers
Abstract
Liquid crystal elastomers (LCEs) are shape-responsive materials that combine the elastic properties of a polymer network with the molecular ordering and responsiveness of liquid crystals. The combination of network elasticity, low crosslink density, and liquid crystal ordering results in versatile shape-responsive materials which can exhibit large and fully reversible shape changes (in excess of 100 %). However, despite over two decades of work with LCEs, the preparation of LCEs remains a significant challenge. An LCE with shape-responsive properties must have the following characteristics: 1) light network crosslinking to maximize elasticity and shape change; 2) global (macroscopic) alignment of the liquid crystal director; 3) a low glass-transition temperature, ideally below room temperature; and 4) a network with liquid crystalline ordering at or near room temperature. The goal of this proposal is to establish simple, versatile, and modular approaches to LCE synthesis using click chemistry. Our specific approach involves the coupling of reactive liquid crystal mesogens and flexible linking groups under mild, solvent-free conditions. This enables reaction in the liquid crystal phase and alignment using mechanical deformation and patterned surfaces. Our approach is modular - the synthesis is compatible with different reactive linkers and mesogens. This enables systematic tailoring and rational design of the LCE molecular structure to achieve a desired phase behavior, network anisotropy, elasticity, and shape response. Our work will involve the following specific research objectives: 1)Objective 1: Develop solvent-free, liquid crystal-phase click chemistry approaches for the synthesis of LCEs. Our first objective is to demonstrate and evaluate LCE synthesis using click coupling of reactive liquid crystal mesogens and linking groups. Three different click coupling reactions will be tested in solvent-free coupling reactions in the liquid crystal phase. This will enable a modular, systematic approach to LCE synthesis and design. 2)Objective 2: Systematically investigate the connection between molecular structure and macroscopic LCE properties and produce adaptable LCE networks. We will take advantage of modular click LCE synthesis to increase the shape-response of aligned LCEs, incorporate reversible network crosslinking, and understand the connection between molecular structure and macroscopic LCE properties. The use of adaptable polymer networks in LCEs can enable network re-alignment and stress relaxation, and we will explore the use of photo-initiated addition-fragmentation reactions to restructure the LCE network in the liquid crystal phase. Our work will also explore light-responsive functionalities in LCEs. 3)Objective 3: Understand the mechanical properties of modular click LCEs and the coupling between network elasticity and liquid crystal director rotation. This objective focuses on investigating soft elasticity in LCEs produced by click chemistry, the polydomain-to-monodomain transition, and the effect of adaptable network structures on network stress relaxation and network deformation. This work will lead to the development of new chemistries for LCE synthesis, a strong fundamental understanding of the relationship between network molecular structure and macroscopic properties, and new shape-responsive materials for a broad range of applications directly relevant to the Army such as soft robotics, micro-actuators, remote sensors, and responsive surface coatings.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 14, 2019
- Source ID
- W911NF1810289
Entities
People
- Rafael Verduzco
Organizations
- Army Contracting Command
- Rice University
- United States Army