Anomalous rheology in a nanostructured diblock copolymer/hydrocarbon system and its kinetic origin

Abstract

Nanostructured squalane solutions (5-20 wt %) of a diblock copolymer, poly(styrene-b-hydrogenated isoprene), were prepared by a cosolvent-casting method. The as-cast solutions behaved as viscous liquids with terminal flow behavior at room temperature. Upon heating, the solutions gelled, and they did not return to their starting liquidlike state upon cooling. Small-angle X-ray scattering (SAXS) revealed a random array of spherical micelles in the as-cast solutions, which were hypothesized to be in a nonequilibrium state. This abnormal solidification with increasing temperature was correlated with the formation of body-centered-cubic (BCC) structures. Isothermal SAXS and rheology measurements also indicated that the rate of formation of BCC structures in the as-cast solutions increased with temperature. A diffusion-controlled nucleation-and-growth mechanism was proposed for the ordering process in the as-cast polystyrene-b-hydrogenated polyisoprene/squalane solutions.

Ordering Kinetics of the BCC Morphology in Diblock Copolymer Solutions over a Wide Temperature Range

“…Many previous studies [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] of the ordering kinetics of block copolymers have confirmed the nucleation and growth mechanism. For example, experimental observations by Rosedale and Bates 5 and Floudas et al 8,12,13 revealed the relationship ln t 0.5 ∝ (T ODT -T) -n , with n varying between 1 and 2 for several block copolymer melts subjected to a shallow quench.…”

Dynamic birefringence and non-linear rheology of diblock copolymer micellar solutions

“…[15][16][17][18][19] Liu et al reported an irreversible viscosity increase with temperature in a diblock copolymer/squalane system. 20,21 Dynamic birefringence measurements, being birefringence measurements under oscillatory deformation, are a useful technique to investigate the molecular origin of stress and molecular dynamics of polymers. This is because the strain-induced birefringence, Dn, of polymeric materials has a strong relationship with the stress s. For example, for rubbery materials, the stressoptical rule (SOR) holds well.…”

“…Liu et al reported an irreversible viscosity increase with temperature in a diblock copolymer/squalane system. 20,21 In this paper, we investigate the dynamic birefringence and viscoelasticity of diblock copolymer micellar solutions in a less selective solvent and clarify the relaxation modes of such a micellar system in detail. The shear modulus of this system varies slowly with time after temperature quench and shows the transition of viscous to plastic response.…”