Conformation of comb-like liquid crystal polymers in isotropic solution probed by small-angle neutron scattering

The conformational characteristics of a comb-like side-chain liquid crystal polysiloxane (SCLCP), dissolved in deuterated chloroform, were evaluated by small-angle neutron scattering (SANS) measurements over a wide q range. SANS studies were carried out on specimens with constant backbone length (DP = 198) and variable spacer length (n = 3, 5, and 11), and with constant spacer length (n = 5) and variable DP (45, 72, 127, and 198). The form factor P(q) at high q was analyzed using the wormlike chain model with finite cross-sectional thickness (R,) and taking into account the molecular weight polydispersity. The analysis generated values of persistence length in the range l(p) 28-32 angstrom, considerably larger than that of the unsubstituted polysiloxane chain (l(p) = 5.8 angstrom), with contour lengths per monomer comparable to the fully-extended polysiloxane backbone (l(m) = 2.9 angstrom). This indicates a relatively rigid SCLCP chain due to the influence of the densely attached mesogenic groups. The SCLCP with n = 11 is more flexible (l(p) = 28 angstrom) than those with n = 3 and n = 5 (l(p) = 32 angstrom). The cross-sectional thickness increases with spacer length, R-c similar to n(0.21 +/- 0.02) (3 <= n <= 11), and the contour length per monomer decreases with increasing spacer length, l(m) similar to n(-0.35 +/- 0.01). (c) 2006 Wiley Periodicals, Inc.