Multiscale modelling of soft matter is an emerging field that has made rapid progress in the past decade.Several methods for systematic coarse-graining of molecular liquids and soft matter systems have been proposed in recent years. Herein, we review these methods and discuss a selected number of applications as well as limitations of the models and remaining challenges in developing representative and transferable pair potentials.

Dissolved electrolytes interact with peptides and proteins in aqueous solution. Herein, we study small amide compounds in aqueous electrolyte solutions and link their salting-in and salting-out propensities to molecular-level structural details obtained with molecular simulations. Aqueous solutions of NaF, NaCl, NaBr, NaI, NaNO(3), and NaClO(4) with N-isopropylacrylamide (NiPAM) and N-methylacetamide (NMA) have been investigated. Our results show that NiPAM is salted-in by NaI, mediated through iodide interactions with nonpolar groups, while being salted-out by the other salts. Hydrogen-bonding interactions of anions with the amide group of NiPAM could not be identified, while in the systems with NMA all Hofmeister anions formed stable hydrogen bonds with the amide group. These results indicate that the immediate chemical environment of the backbone amide groups should be considered in studies of protein destabilization by dissolved electrolytes. We furthermore report that all salts but NaI provoke a hydrophobic collapse transition of poly(N-isopropylacrylamide) in water at 300 K, in qualitative agreement with experimentally measured salt effects on the lower critical solution temperature of this system.

The thermal conductivity of single-walled and multi-walled carbon nanotubes has been investigated as a function of the tube length L, temperature and chiral index using non-equilibrium molecular dynamics simulations. In the ballistic-diffusive regime the thermal conductivity follows a L(alpha) law. The exponent alpha is insensitive to the diameter of the carbon nanotube; alpha approximately 0.77 has been derived for short carbon nanotubes at room temperature. The temperature dependence of the thermal conductivity shows a peak before falling at higher temperatures (>500 K). The phenomenon of thermal rectification in nanotubes has been investigated by gradually changing the atomic mass in the tube-axial direction as well as by loading extra masses on the terminal sites of the tube. A higher thermal conductivity occurs when heat flows from the low-mass to the high-mass region.

The thermal rectification in nanotubes with a mass gradient is studied by reverse non-equilibrium molecular dynamics simulations. We predict a preferred heat flow from light to heavy atoms which differs from the preferential direction in one-dimensional monoatomic systems. This behavior of nanotubes is explained by anharmonicities caused by transverse motions which are stronger at the low-mass end. The present simulations show an enhanced rectification with increasing tube length, diameter and mass gradient. Implications of the present findings for applied topics are mentioned concisely.

The thermal conductivity (lambda) of stretched amorphous atactic polystyrene (PS) swollen in supercritical carbon dioxide (sc CO(2)) has been investigated over a wide temperature, pressure, and concentration range. Nonequilibrium molecular dynamics simulations with a full atomistic force-field have been employed to calculate the thermal conductivity of neat stretched PS and of different mixtures of supercritical CO(2) with stretched PS. As the energy transport in PS parallel and perpendicular to the stretching direction differs, an anisotropy in the thermal conductivity occurs. The magnitude of lambda is enhanced with an increasing number of carbon-carbon backbone bonds oriented parallel to the direction of the heat transport. The degrees of freedom in the side chain of the polymer are rather unimportant for the thermal conductivity. To understand the conditions leading either to an equivalence or nonequivalence of the system degrees of freedom for the heat transport, we have analyzed lambda of PS, CO(2), binary PS-CO(2) mixtures and other model systems as a function of the bond constraints in the computational model. Furthermore, we have commented on differences in the thermal conductivity provided either by a vibrational energy transfer or by collisions.

The thermal conductivity of amorphous atactic polystyrene (PS) swollen in supercritical carbon dioxide (sc CO(2)) has been investigated over wide temperature, pressure, and concentration ranges. Nonequilibrium molecular dynamics simulations with a full atomistic force field have been used to calculate the thermal conductivity of neat PS and sc CO(2) as well as of the binary system at different compositions. An analytical interpolation formula for the thermal conductivity of the binary mixture on the basis of PS and CO(2) data has been obtained. Particular attention has been paid to the implications of the quasi-degeneracy and finite-size effects in the simulated polymer system. It has been found that, in addition to the degrees of freedom per volume, the orientation of the carbon-carbon bonds in the backbone relative to the direction of the temperature gradient is important for the heat transport in PS.

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