Side-Chain Liquid Crystalline Polymer Networks: Exploiting Nanoscale Smectic Polymorphism To Design Shape-Memory Polymers

Suk-kyun Ahn†, Prashant Deshmukh‡, Manesh Gopinadhan§, Chinedum O. Osuji§, and Rajeswari M. Kasi†‡*
† Polymer Program, The Institute of Materials Science
‡ Department of Chemistry
University of Connecticut, Storrs, Connecticut 06269, United States
§ Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06520, United States
ACS Nano, 2011, 5 (4), pp 3085–3095
DOI: 10.1021/nn200211c
Publication Date (Web): March 14, 2011
Copyright © 2011 American Chemical Society
*Address correspondence to kasi@ims.uconn.edu.
Physical Properties of Synthetic High Polymers

Abstract

Abstract Image

Herein, we investigate the influence of nanoscale smectic polymorphism within end-on fixed side-chain liquid crystalline polymer networks (SCLCNs) on macroscopic shape-memory and actuation properties. We have synthesized a series of SCLC-type linear (TP-n) and cross-linked random terpolymers (XL-TP-n) with varying length of flexible methylene spacers (n = 5, 10, and 15) between polynorbornene main-chain and cholesteryl ester side-chains. Thermal and mechanical analyses by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) confirm a glass transition (Tg), a clearing temperature (Tcl), and a network structure in the XL-TP-n. Detailed structural investigation conducted using wide-angle and small-angle X-ray scattering (WAXS and SAXS) at room temperature proves self-assembled smectic A (SmA) polymorphism of the XL-TP-n which evolves from non-interdigitated bilayer (SmA2) for n = 5 to mixed layers of monolayer-like highly interdigitated layer (SmA1) and SmA2 for n = 10 and to SmA1 for n = 15. In addition, TP10 at temperatures above 60 °C interestingly shows transformation of SmA structure from mixed layer (SmA1 + SmA2) to interdigitated structure (SmAd). The SmA polymorphism developed in TP-n during shape-memory cycles (SMCs) significantly impacts the ultimate strain responses. A mechanism for the unique interdigitation-based thermostrictive behavior is proposed. More importantly, this new actuation mechanism observed in these XL-TP-n can be exploited to develop intelligent thermal actuators.

Keywords:

shape-memory materials; liquid crystals; self-assembly; nanostructured smart materials; structure−property relationships; actuators
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History

  • Published In Issue April 26, 2011
  • Article ASAPMarch 23, 2011
  • Just Accepted ManuscriptMarch 14, 2011
  • Received: January 19, 2011
    Accepted: March 14, 2011

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