Influence of thermal history on mesoscale ordering in polydomain smectic networks

Abstract

Dramatic changes in mesoscale ordering and macroscopic mechanical behavior are observed in smectic polydomain networks after annealing at a temperature well above the glass transition temperature but below the clearing temperature. Tensile testing reveals gradual stiffening and loss of extensibility, and X-ray linewidth measurements confirm that stiffening is initially due to thickening of domains. At long annealing times, a more highly ordered smectic mesophase forms, further stiffening the networks and reducing their exten-sibility. Increasing the concentration of (flexible) crosslinkers hinders domain growth and suppresses formation of the higher order mesophase, a useful guideline for design of smectic networks that exhibit reduced sensitivity to thermal history.

Factors Influencing the Shear and Tensile Moduli of Smectic Polydomain Networks

“…However, the MCLCN having higher crosslinker concentration (e.g. ρ = 0.09) did not form a higher order mesophase even after 18 h of annealing at 75 °C, while exhibiting minimal changes in domain thickness during annealing . Thus, besides domain size effects, part of the observed increase in modulus (Fig.…”

“…The higher order mesophase is characterized by improvements in the packing of mesogens, and is evidenced by a secondary layering reflection at 2θ = 3.38° (d ≈ 28 Å). The MCLCN having ρ ≤ 0.06 were able to form the higher order mesophase, as evidenced by the appearance of the secondary layering reflection in their XRD patterns . However, the MCLCN having higher crosslinker concentration (e.g.…”

“…. Details of their synthesis from the allyloxy‐functional mesogens (B 2 ), the silane‐functional flexible spacer 1,1,3,3,5,5 hexamethyltrisiloxane (A 2 ) and the silane‐functional crosslinker “tetrakis(dimethylsiloxy)silane” (A 4 ) are provided in a previous communication; the samples studied here were obtained from the same batch of materials.…”