Open AccessEffects of structural imperfections on the dynamic mechanical response of main‐chain smectic elastomers
Author(s) -
Patil Harshad P.,
Hedden Ronald C.
Publication year - 2007
Publication title -
journal of polymer science part b: polymer physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.65
H-Index - 145
eISSN - 1099-0488
pISSN - 0887-6266
DOI - 10.1002/polb.21329
Subject(s) - elastomer , isotropy , materials science , relaxation (psychology) , swelling , chain (unit) , side chain , loss factor , polymer chemistry , composite material , chemical physics , chemistry , polymer , optics , physics , dielectric , psychology , social psychology , optoelectronics , astronomy
We examine the influence of structural imperfections on mechanical damping in polydomain smectic main‐chain liquid crystalline elastomers (MCLCE) subjected to small strain oscillatory shear. The mechanical loss factor tan δ = G ″(ω)/ G ′(ω) exhibits a strong maximum (tan δ ≈ 1.0) near the smectic‐isotropic (clearing) transition. “Optimal” elastomers that exhibit minimal equilibrium swelling in a good solvent are compared with highly swelling “imperfect elastomers” that contain higher concentrations of structural imperfections such as pendant chains. For the imperfect elastomers, tan δ is markedly enhanced in the isotropic state because of relaxation of pendant chains and other imperfections. However, within the smectic state, the magnitude of tan δ and its temperature dependence are similar for optimal and imperfect elastomers at ω = 1 Hz. The prominent loss peak near the clearing transition arises from segment‐level relaxations that are insensitive to the details of chain connectivity. Smectic MCLCE can be tailored for applications as vibration‐damping materials by manipulating the clearing transition temperature through the backbone structure or by deliberate introduction of structural imperfections such as pendant chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3267–3276, 2007