1,721,128 research outputs found
Coupling of particle simulations with a continuum description: Speeding-up collective processes
No full textGeometry-Controlled Interface Localization-Delocalization Transition in Block Copolymers
No full textLamellar copolymers confined into a film of thickness D by two stripe-patterned surfaces, which are rotated against each other by a twist angle alpha, form lamellar domains that register and align with the respective chemical surface patterns. The two domains of thickness x and D - x are separated by an interface that resembles a twist grain boundary. At small twist angles alpha or strong selectivity of the surface patterns, this interface fluctuates around the middle of the film, x approximate to D/2, while the interface is localized at one of the surfaces, x approximate to 0 or x approximate to D, in the opposite limit. These two morphologies are separated by an interface localization-delocalization transition (ILDT) that can be controlled by the twist angle alpha. For thin films, we find a second-order ILDT while the ILDT is first-order for large D values. A phenomenological interface Hamiltonian is used to relate the findings to the ILDT of symmetric mixtures, and the predictions are confirmed by molecular simulation
Coupling of particle simulations with a continuum description: Speeding-up collective processes
No full textStudying Amphiphilic Self-assembly with Soft Coarse-Grained Models
Full text linkHighly coarse-grained models for investigating the self-assembly of lipids and copolymer materials are discussed. Soft interactions between segments that represent many atoms naturally arise in the course of systematic coarse-graining, and they are necessary for modeling fluctuation effects whose strengths is dictated by a large invariant degree of polymerization. The soft non-bonded interactions of the coarse-grained models are related to the excess free-energy functional of an equivalent field-theoretic description. The connection between the particle-based model and the field-theoretic description helps to identify the physical significance of the model interactions. Non-bonded interactions, which describe the complex phase behavior of compressible mixtures or include local fluid-like packing effects of the coarse-grained segments, can be systematically constructed based on liquid-state theory or classical density functional theory. Details of the computational implementation and limitations of soft coarse-grained models are discussed. Two computational techniques-field-theoretic force-matching and umbrella sampling-are devised for computing a free-energy functional from a particle-based description. They can be employed to (i) derive the non-bonded free-energy functional of a soft coarse-grained model from a more detailed computational model or to (ii) derive a field-theoretic description from a particle-based model. Moreover, different strategies for accurately calculating free energies of self-assembled systems are described and selected applications presented.Volkswagen foundation; Deutsche Forschungsgemeinschaft (DFG) [Mu1674/11
Modulating the domain morphology of A-B diblock copolymer brushes in selective solvents by grafting homopolymers C
No full textMemory Effects of Diblock Copolymer Brushes and Mixed Brushes
No full textMemory effects of microphase segregation in diblock copolymer brushes and binary mixed homopolymer brushes exposed to solvents of different quality and selectivity are studied using Single-Cliain-in-Mean-Field (SCMF) simulations. We gauge these memory effects by a fluctuation memory measure, reflecting the correlation between the quenched fluctuations of grafting points and the microphase-separated morphology, and a domain memory measure, quantifying the correlation between Surface morphologies during cyclic exposure to different solvents. The fluctuation and domain memory measures are closely correlated, and both of them have their root in the broken translational symmetry of the distribution of grafting points. They become stronger upon increasing the fluctuations of the grafting points. The effects of solvent quality and selectivity, grafting density, and composition of brushes on the memory measures are discussed
Correlation between surface topography and slippage: a Molecular Dynamics study
No full textUsing Molecular Dynamics simulations of a polymer liquid flowing past flat and patterned surfaces, we investigate the influence of corrugation, wettability and pressure on slippage and friction at the solid-liquid interface. For one-dimensional, shallow, rectangular grooves, we observe a gradual crossover between the Wenzel state, where the liquid fills the grooves, and the Cassie state, where the corrugation supports the liquid and the grooves are filled with vapor. Using two independent flow set-ups, we characterize the near-surface flow by the slip length, delta, and the position, z(h), at which viscous and frictional stresses are balanced according to Navier's partial slip boundary condition. This hydrodynamic boundary position depends on the pressure inside the channel and may be located above the corrugated surface. In the Cassie state, we observe that the edges of the corrugation contribute to the friction.European Union [PITN-GA-2008-214919 (MULTIFLOW)
Modulating the domain morphology of A-B diblock copolymer brushes in selective solvents by grafting homopolymers C
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