Streaming potential of some polycarbonate microporous membranes when bathed by LiCl, NaCl, MgCl2 and CaCl2 aqueous solutions

Characterization of molecule clustering and liquid transport at nearly ideal solid surfaces

Vapor adsorption, mobility, two-dimensional (monolayer formation) and three-dimensional (multilayer formation) clustering is evaluated. Two-dimensional vapor diffusion is compared to results obtained from molecular kinetic (MK) model fits. Three-dimensional clustering results in condensation of multimolecular vapor layers to thin films. Thin films are characte-rized by line tension and liquid spreading by hydrodynamic (HD) models. Although it is experimentally shown that steady-state wetting ranges are intersected by a chaotic slip-stick range, MK and HD models are combined to molecular hydrodynamic (MH) models with the aim to cover this slip-stick range. The results of MK, HD and MH model fits are, however rather poor (unphysical results). Thin film (α-phase) models are compared to thick film (β-phase) models. In order to improve model designs, established phenomenological relation-ships known from irreversible thermodynamics are presented. Forced wetting, expressed as generalized fluxes can be made dependent on multiple generalized conjugate forces which enables identification of dominant interactions to be introduced in future improved transport models.

On the mechanism of calcium carbonate polymorph selection via confinement

Organisms deposit various biominerals in the course of their biomineralisation. The most abundant of these is calcium carbonate, which manifests itself in several polymorphs. While organisms possess the ability to...

Confinement generates single-crystal aragonite rods at room temperature

The topic of calcite and aragonite polymorphism attracts enormous interest from fields including biomineralization and paleogeochemistry. While aragonite is only slightly less thermodynamically stable than calcite under ambient conditions, it typically only forms as a minor product in additive-free solutions at room temperature. However, aragonite is an abundant biomineral, and certain organisms can selectively generate calcite and aragonite. This fascinating behavior has been the focus of decades of research, where this has been driven by a search for specific organic macromolecules that can generate these polymorphs. However, despite these efforts, we still have a poor understanding of how organisms achieve such selectivity. In this work, we consider an alternative possibility and explore whether the confined volumes in which all biomineralization occurs could also influence polymorph. Calcium carbonate was precipitated within the cylindrical pores of track-etched membranes, where these enabled us to systematically investigate the relationship between the membrane pore diameter and polymorph formation. Aragonite was obtained in increasing quantities as the pore size was reduced, such that oriented single crystals of aragonite were the sole product from additive-free solutions in 25-nm pores and significant quantities of aragonite formed in pores as large as 200 nm in the presence of low concentrations of magnesium and sulfate ions. This effect can be attributed to the effect of the pore size on the ion distribution, which becomes of increasing importance in small pores. These intriguing results suggest that organisms may exploit confinement effects to gain control over crystal polymorph.