6.2.2. Definition of Effective Properties 3064 6.3. Response Properties to Magnetic Fields 3066 6.3.1. Nuclear Shielding 3066 6.3.2. Indirect Spin−Spin Coupling 3067 6.3.3. EPR Parameters 3068 6.4. Properties of Chiral Systems 3069 6.4.1. Electronic Circular Dichroism (ECD) 3069 6.4.2. Optical Rotation (OR) 3069 6.4.3. VCD and VROA 3070 7. Continuum and Discrete Models 3071 7.1. Continuum Methods within MD and MC Simulations 3072

/pdf/quantum-mechanical-continuum-solvation-models-3edv963g14.pdf

Quantum mechanical continuum solvation models.

We critically review dissipative particle dynamics (DPD) as a mesoscopic simulation method. We have established useful parameter ranges for simulations, and have made a link between these parameters and χ-parameters in Flory-Huggins-type models. This is possible because the equation of state of the DPD fluid is essentially quadratic in density. This link opens the way to do large scale simulations, effectively describing millions of atoms, by firstly performing simulations of molecular fragments retaining all atomistic details to derive χ-parameters, then secondly using these results as input to a DPD simulation to study the formation of micelles, networks, mesophases and so forth. As an example application, we have calculated the interfacial tension σ between homopolymer melts as a function of χ and N and have found a universal scaling collapse when σ/ρkBTχ0.4 is plotted against χN for N>1. We also discuss the use of DPD to simulate the dynamics of mesoscopic systems, and indicate a possible problem with...

https://www.physics.iitm.ac.in/~iol/lecture_notes/groot-warren.pdf

Dissipative particle dynamics : bridging the gap between atomistic and mesoscopic simulation

We present an extensive molecular‐dynamics simulation for a bead spring model of a melt of linear polymers. The number of monomers N covers the range from N=5 to N=400. Since the entanglement length Ne is found to be approximately 35, our chains cover the crossover from the nonentangled to the entangled regime. The Rouse model provides an excellent description for short chains N<Ne, while the dynamics of the long chains can be described by the reptation model. By mapping the model chains onto chemical species we give estimates of the times and distances of onset of the slowing down in motion due to reptation. Comparison to neutron spin‐echo data confirm our mapping procedure, resolving a discrepancy between various experiments. By considering the primitive chain we are able to directly visualize the confinement to a tube. Analyzing the Rouse mode relaxation allows us to exclude the generalized Rouse models, while the original reptation prediction gives a good description of the data.

Dynamics of entangled linear polymer melts: A molecular‐dynamics simulation

https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Schuh-ActaMater07-Mechanical%20behaviour%20of%20amorphous%20alloys.pdf

Mechanical behavior of amorphous alloys

Block copolymers are all around us, found in such products as upholstery foam, adhesive tape and asphalt additives. This class of macromolecules is produced by joining two or more chemically distinct polymer blocks, each a linear series of identical monomers, that may be thermodynamically incompatible (like oil and vinegar). Segregation of these blocks on the molecular scale (5–100 nm) can produce astonishingly complex nanostructures, such as the “knitting pattern” shown on the cover of this issue of PHYSICS TODAY. This striking pattern, discovered by Reimund Stadler and his coworkers, reflects a delicate free‐energy minimization that is common to all block copolymer materials.

Block Copolymers—Designer Soft Materials

Conformational transitions in chain molecules have been shown to proceed via a reaction coordinate which is a localized mode involving rotations about bonds, and also bond angle bending and bond stretching. By investigating the kinetics as a function of the force constants (flexibility) for bond angle bending and bond stretching, the role of the localized mode is probed. The study reported here consists of computer simulations of the Brownian dynamics of chain motions, and of kinetic calculations of rates and reaction modes. The theory accurately predicts the relative effects of force constant variations on transition rates determined by simulation.

The kinetics of conformational transitions: Effect of variation of bond angle bending and bond stretching force constants

A theory is developed to describe an interface that on one side has a pure polymer A and on the other side has a mixture of polymers B and C. Quantitative results are obtained for the concentration profiles, the interfacial tension, a characteristic overlap between the Aand the BC phase and the amount of B adsorbed to the interface. The discussion is carried out in terms of parameters reduced by values appropriate to the A/B interface

Theory of the homopolymer/binary-polymer-mixture interface

Diffusion in strongly segregated block copolymers

Elastically Ineffective Polymer Chains in Rubbers

A procedure is developed for inverting the linear laws of irreversible thermodynamics in spite of the singular nature of the admittance matrix when barycentric diffusion currents are employed. The procedure is symmetric in that it is unnecessary to identify one species as a reference solvent. Explicit relations are given for the new coefficients (resistance matrix, heats of transport, Soret thermal conductivity) in terms of the old. Constraints on the new coefficients are also obtained.

Eugene Helfand

Papers

The kinetics of conformational transitions: Effect of variation of bond angle bending and bond stretching force constants

Theory of the homopolymer/binary-polymer-mixture interface

Diffusion in strongly segregated block copolymers

Elastically Ineffective Polymer Chains in Rubbers

On Inversion of the Linear Laws of Irreversible Thermodynamics