ORIENTATIONAL ORDERING OF A POLY( OXYETHYLENE)-POLY(OXYBUTYLENE) DIBLOCK COPOLYMER GEL UNDER STEADY SHEAR-FLOW

Orientational ordering was investigated in the hexagonally packed rod phase formed by a poly(oxyethylene)-poly(oxybutylene) diblock copolyme r in concentrated aqueous solution. The resulting soft gel was subject ed to steady shear in a Couette cell, with simultaneous small-angle X- ray scattering (SAXS) experiments. Orientation function coefficients w ere extracted from SAXS patterns to quantify the degree of orientation . It is found that the averaged Legendre polynomial orientational orde r parameters increase logarithmically with a linear increase in shear rate. A limiting degree of orientation of (P) over bar(2) similar to 0 .6 is reached for a shear rate of y = 100 s(-1), above which an increa se in shear rate does not significantly improve the orientation. Time- resolved measurements reveal that the steady-state degree of orientati on was developed within the gel over a time scale t similar to 30 s an d upon cessation of shear relaxed to an intermediate orientation level over a time scale of t similar to 1 h.