Guest-host van der Waals interactions decisively affect the molecular transport in mesoporous media

We present clear evidence that the global (macroscopic) transport from/to mesoporous materials is significantly affected by the interactions between the mesoporous host and the guest molecules. The problem is considered in a most general way so the solutions apply for a variety of cases such as the release of a guest from porous matrices, catalysis occurring in porous materials or processes taking place in separation techniques. The concept is proved on the experimentally determined release profiles of a model drug (indomethacin) from accurately designed SBA-15 and MCM-41 mesoporous silicates. In order to allow for a full quantitative analysis, a very high frequency of sampling was carried out at short release times. The agreement between the experimentally determined and the theoretically predicted curves is excellent not only in shape but also in all major trends. In the broadest sense, one might say that the host-guest interactions change the effective cross-section of pores through which the transport of guest occurs. In addition, the interactions lower the efficiency of utilization of the guest. In drug release this is observed as a decrease of released matter at long times, in catalysis this would correspond to a decrease of global turnover efficiency etc. However, it is not only the final outcome that is affected but also the transport pattern (e. g. the shape of release curves) during a wide range of timescales. Our finding might have a profound influence on the design of various devices based on meso- or macroporous materials.