Colloidal Jamming at Interfaces: a Route to Fluid-bicontinuous Gels

Colloidal particles or nanoparticles, with equal affinity for two fluids, are known to adsorb irreversibly to the fluid-fluid interface. We present large-scale computer simulations of the demixing of a binary solvent containing such particles. The newly formed interface sequesters the colloidal particles; as the interface coarsens, the particles are forced into close contact by interfacial tension. Coarsening is dramatically curtailed, and the jammed colloidal layer seemingly enters a glassy state, creating a multiply connected, solid-like film in three dimensions. The resulting gel contains percolating domains of both fluids, with possible uses as, for example, a microreaction medium

Nonequilibrium steady states in sheared binary fluids

We simulate by lattice Boltzmann the steady shearing of a binary fluid mixture undergoing phase separation with full hydrodynamics in two dimensions. Contrary to some theoretical scenarios, a dynamical steady state is attained with finite domain lengths $L_{x,y}$ in the directions ($x,y)$ of velocity and velocity gradient. Apparent scaling exponents are estimated as $L_{x}\sim\dot{\gamma}^{-2/3}$ and $L_{y}\sim\dot{\gamma}^{-3/4}$. We discuss the relative roles of diffusivity and hydrodynamics in attaining steady state.Comment: 4 pages, 3 figure

Survey, characterisation and condition assessment of Palustriella dominated springs 'H7220 petrifying springs with tufa formation (Cratoneurion)in Wales

This report contains baseline information for Article 17 reporting in Wales for the Annex 1 habitat H7220 Petrifying springs with tufa formation (Cratoneurion). Natural Resources Wales selected a total of 14 sites, across Wales for inclusion within the study. Only one site, Nant Peris, is part of a designated SAC (Eryri SAC) where petrifying springs are a notifiable feature and as such they had benefited from prior study (see Creer, 2012). The remaining sites included within this survey were associated with a mixture of designated and undesignated sites for which there was little to no baseline information on the petrifying spring habitats. A methodology was devised and applied where possible at each site, involving an ecologist (Jonathan Graham) and a hydrogeologist (Gareth Farr) working together. It was important that both the hydrological and ecological surveys were undertaken simultaneously in order to make important linkages between hydrological supporting condition, the occurrence of species and condition of the site. Each survey started with a ‘site walkover’ to allow familiarisation with the site and to help form initial conceptual ideas. Following this a vegetation survey and collection of species for detailed identification for both bryophytes, lichens and flowering plants was undertaken, using the DAFOR scale. A total of 130 species were recorded including 77 flowering plants, 46 bryophytes, one club moss, two ferns, 3 horsetails, 2 blue green algae and one charophyte. Detailed maps were drawn for key sites within this study. Elevation data shows that Palustriella falcata occurs over a smaller range within an upland setting and Palustriella commutata occurs over a wider range in a primarily (but not exclusively) lowland setting. In situ water quality readings and lab analysed samples were collected proving the sites were dominantly Calcium Bicarbonate type waters, however some sites such as Nant Peris were much less calcareous, with the majority of sites having very low levels of nutrients. Vegetation transects accompanied by field readings of water quality were undertaken whenever possible showing that there can be dramatic changes in pH over very small distances (<1m). An assessment was made of the immediate catchment, with the aim of identifying any hydrological threats or pressures to the habitats. Two broad group are proposed for this habitat in Wales Group 1: mainly upland or open hills and dominated by Palustriella falcata, it is species rich and has a greater number of associated flowering plant species. Group 2: mainly lowland and dominated by Palustriella commutata, it is species poor and associated more with partially shaded (i.e not open) sites. Each group is further divided into two subgroups ‘ Group A and Group B’ . Palustriella dominated springs occurred across a range of geologies (not all Carboniferous Limestone) and also associated with a mixture of bedrock, superficial and made ground. Importantly active or historic tufa deposition was not observed at all sites. Visual estimates of flow varied but were frequently low and diffuse. Condition assessments suggest that all of the sites included within this study should be considered as being in both favourable ecological and hydrogeological condition

Binary fluids under steady shear in three dimensions

We simulate by lattice Boltzmann the steady shearing of a binary fluid mixture with full hydrodynamics in three dimensions. Contrary to some theoretical scenarios, a dynamical steady state is attained with finite correlation lengths in all three spatial directions. Using large simulations we obtain at moderately high Reynolds numbers apparent scaling expon ents comparable to those found by us previously in 2D. However, in 3D there may be a crossover to different behavior at low Reynolds number: accessing this regime requires even larger computational resource than used here.Comment: 4 pages, 3 figure