Magnetically induced structural anisotropy in binary colloidal gels and its effect on diffusion and pressure driven permeabilityElectronic supplementary information (ESI) available: A complete derivation of eqn (3) and details regarding the calculation of the adsorbed water layer thickness is available. See DOI: 10.1039/c4sm00315b

We report on the synthesis, microstructure and mass transport properties of a colloidal hydrogel self-assembled from a mixture of colloidal silica and nontronite clay plates at different particle concentrations. The gel-structure had uniaxial long-range anisotropy caused by alignment of the clay particles in a strong external magnetic field. After gelation the colloidal silica covered the clay particle network, fixing the orientation of the clay plates. Comparing gels with a clay concentration between 0 and 0.7 vol%, the magnetically oriented gels had a maximum water permeability and self-diffusion coefficient at 0.3 and 0.7 vol% clay, respectively. Hence the specific clay concentration resulting in the highest liquid flux was pressure dependent. This study gives new insight into the effect of anisotropy, particle concentration and bound water on mass transport properties in nano/microporous materials. Such findings merit consideration when designing porous composite materials for use in for example fuel cell, chromatography and membrane technology. Here we study diffusion and flow through a new hydrogel formed from colloidal silica and nontronite clay that was made anisotropic by magnetic alignment of the microstructure.