Stimuli-responsive gels as reaction vessels and reusable catalysts.

As part of a continuing scientific challenge, a substantial effort during the past few decades has been devoted towards altering the selectivity of chemical transformations by arranging the potential reactants in a number of organized and confining media. Such systems, having features significantly different from those of isotropic solutions, include, for example, micelles, microemulsions, molecular aggregates, liquid crystals, and zeolites. Among these materials, stimuli-response gels constitute another important class of nanostructured and dynamic systems with high active surface areas and remarkable diffusion properties. Within this group, polymer gels have been traditionally used to obtain catalytic and reactive soft materials. Moreover, gels made of low-molecular-weight compounds represent a major novelty in this area as potential soft-vessels to carry out chemical reactions with control on product selectivity. In addition, the possibility of integrating switchable catalytic functions in both organo- and hydrogels shall accelerate the development of robust platforms for the 'bottom-up' tailor-fabrication of more sophisticated functional materials. The present critical review reports on the most important results published during the last decade regarding the use of 'smart' gels that has displayed promising properties as selective soft-nanoreactors and/or heterogeneous recyclable catalysts (152 references).

Free-surface thin-film flows over uniformly heated topography.

The long-wave (lubrication) approximation governing the evolution of a thin film over a uniformly heated topographical substrate is solved numerically. We study the initial-value problem for a variety of governing dimensionless parameters and topographical substrates. We demonstrate that the dynamics is characterized by a slow relaxation process with continuous coarsening of drops up to a large time where coarsening is terminated and the interface organizes into a series of drops each of which is located in a trough in topography.