Microphase separation and liquid-crystalline ordering of rod-coil copolymers

Microphase separation and liquid-crystalline ordering in diblock and triblock rod-coil copolymers (with rod-to-coil fraction f = 0.5) were investigated using the dissipative particle dynamics method. When the isotropic disordered phases of these systems were cooled down below their order-disorder transition temperatures TODT, lamellar structures were observed. For rod-coil diblock copolymers, the lamellar layers were obtained below T = 2.0. This temperature was found to be higher than the TODT for normal coil-coil diblock copolymers. Significant ordering of the rods was observed only below T = 0.9 which is the isotropic-nematic transition temperature for rodlike fluids. For the triblock rod-coil copolymers, both microphase separation and rod ordering occurred at T = 0.9. Normal coil-coil triblock copolymers were found to undergo microphase separation at T = 0.8, which is about half the TODT of the normal diblock copolymers. Investigations of the mean square displacement and the parallel and the perpendicular components of the spatial distribution function revealed that at low temperatures, the rod-coil diblock copolymers exhibit smectic-A and crystalline phases, while the triblock copolymers show smectic-C and crystalline phases. No nematic phases were observed at the density and interaction parameters used in this stud

Geometric approach to the pressure tensor and the elastic constants

Expressions are obtained for the pressure tensor in the canonical and the microcanonical ensemble for both isolated and periodic systems, using the same geometric approach to thermodynamic derivatives as has been used previously to define the configurational temperature. The inherent freedom of the method leads to a straightforward proof of the equivalence of atomic and molecular pressures, for short molecules and for molecules exceeding the dimensions of a periodic simulation box. The effect of holonomic constraints on the pressure is discussed. Expressions for the elastic constants are derived in the same manner

Liquid–crystalline ordering in rod—coil diblock copolymers studied by mesoscale simulations

Using mesoscale dissipative particle dynamics (DPD) simulations, which ignore all atomistic details, we show the formation of lamella mesophases by cooling a fully disordered system composed of symmetric (A7B7) rod–coil diblock copolymers. Equilibration is achieved very rapidly using DPD, and isotropic, smectic A and crystalline phases of the rod–like blocks can be observed either by heating or cooling. An interesting pseudo–smectic phase can be characterized when the order–disorder transition temperature is above the clearing temperature. This phase gradually fades into a normal microphase–separated structure as the system is heated through the clearing temperature. Simulations of pure rods, however, show the formation of isotropic, nematic, smectic A and crystalline phase

Liquid-crystalline ordering in ord-coil diblock copolymers studied by mesoscale simulations

Using mesoscale dissipative particle dynamics (DPD) simulations, which ignore all atomistic details, we show the formation of lamella mesophases by cooling a fully disordered system composed of symmetric (A7B7) rod–coil diblock copolymers. Equilibration is achieved very rapidly using DPD, and isotropic, smectic A and crystalline phases of the rod–like blocks can be observed either by heating or cooling. An interesting pseudo–smectic phase can be characterized when the order–disorder transition temperature is above the clearing temperature. This phase gradually fades into a normal microphase–separated structure as the system is heated through the clearing temperature. Simulations of pure rods, however, show the formation of isotropic, nematic, smectic A and crystalline phase