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We present experimental results for the glass transition behavior of polystyrene (PS) films on grafted PS layers of the same chemical identity as a function of film thickness. Our results suggest that the T g of PS films on brush substrates decreases with decreasing film thickness. The thickness dependence of T g was observed to be more pronounced for the films on the shorter brushes with the high grafting density. We propose a qualitative rationalization of the observations by invoking both interfacial energy considerations as well as by adapting the percolation model for the glass transition of polymer films.

The effect of hydrostatic pressure (P) on closed-loop phase behavior of deuterated polystyrene-block-poly(n-pentyl methacrylate) copolymers [dPS-PnPMA] was investigated by using small-angle neutron scattering and birefringence. For P<20.7 bar, dPS-PnPMA exhibited a lower disorder-to-order transition temperature (T(LDOT)) at 175 degrees C, and then an upper order-to-disorder transition temperature (T(UODT)) at 255 degrees C. With increasing pressure both T(LDOT) and T(UODT) were markedly changed, where dT(LDOT)/dP was 725 degrees C/kbar and dT(UODT)/dP was -725 degrees C/kbar. These are consistent with predictions by the Clausius-Clapeyron equation using measured values of the volume and enthalpy changes of both transitions. The large pressure coefficients imply that the closed-loop phase behavior observed for PS-PnPMA is an entropic-driven phase transition.

In the temperature range of 303–333 K, the self‐assembled structures of a mixture of Pluronic F127 triblock copolymer [PEO106PPO70PEO106; PEO is poly(ethylene oxide) and PPO is poly(propylene oxide)] and an organic derivative, 5‐methyl salicylic acid (5mS), in aqueous solution have been investigated using small‐angle neutron scattering (SANS). Above a 5mS concentration of 1.93 g l−1, the F127–5mS mixture solution became cloudy with a blue colour arising from the Tyndall effect, indicating that large polymer aggregates had formed in the mixture solution. SANS measurements showed that the self‐assembled structure of the F127–5mS mixture transformed from a spherical to a cylindrical micelle with increasing the concentration of 5mS in the temperature range of 303–323 K. When the 5mS concentration was increased to 3.3 g l−1, the self‐assembled structure of the F127–5mS mixture at 333 K underwent an additional phase transition from a cylindrical to a spherical micelle of large size at a 5mS concentration of 2.75 g l−1, although its self‐assembled structure changed from a spherical to a cylindrical micelle at a 5mS concentration of 1.93 g l−1 as well. The phase transitions are explained by the variation of the mass fraction of the hydrophilic part of F127 and the coupled effect of the limited solubility and the strong tendency to bind with amphiphilic molecules of 5mS. Using a simple material balance equation and the structural information obtained from SANS model analyses, the numbers of D2O and of 5mS molecules in the core and corona regions are calculated. This result can provide a simple and easy way to prepare various nanostructures using a Pluronic triblock copolymer in aqueous solution and may be very useful for practical applications of a Pluronic polymer such as various nanobuilding blocks or nanotemplates.

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