Elastic energy-driven phase separation of phospholipid monolayers at the nematic liquid-crystal-aqueous interface.

Experimental measurements and a thermodynamic model reveal that nematic elasticity can induce lateral phase separation of amphiphilic molecules assembled at interfaces between thermotropic liquid crystals (LCs) and immiscible aqueous phases. The morphologies of the phase-separated domains of amphiphiles induced by nematic elasticity are shown to be strongly dependent on the nature of the deformation of the LC. This study provides important insight into the physics that controls the ordering of molecules at interfaces of soft anisotropic materials, and identifies a new mechanism of phase separation at these interfaces.

The nature of 'overexchanged' copper and platinum on zeolites.

The uptake of platinum and copper tetra-ammine (PTA and CTA, [(NH(3))(4)Pt](2+) and [(NH(3))(4)Cu](2+)) into zeolites was compared over silica and three zeolites (Y, MOR and MFI) with different points of zero charge and aluminium content. Adsorption was determined as a function of pH at several metal concentrations, and pH shifts relative to metal free control experiments were carefully monitored. The uptake of both metal ammine complexes onto silica is well described by electrostatic adsorption. We suggest that the metal cations interact with zeolites by two mechanisms, ion exchange at the Al exchange sites and electrostatic adsorption at silanol groups. The former is the dominant mechanism at low to mid pH, and the latter at high pH. This effect is most clearly manifested in zeolites with low aluminium content such as ZSM5; electrostatic adsorption at high pH in ZSM5 yields metal loadings much in excess of the ion exchange capacity and so gives rise to 'overexchange'. Differences between PTA and CTA can be explained by the weaker stability of the CTA complex and its response to the decrease in local pH near the adsorption plane of low PZC zeolites. This change in local pH near oxide surfaces is characteristic of electrostatic adsorption. As the local pH decreases, the CTA ion is probably converted to a dimerized copper complex, perhaps Cu(2)(OH)(2)(2+). A portion of the released ammonia is protonated, increasing the solution pH. In high PZC, high aluminium zeolites with high ion exchange capacity, there is relatively little contribution from electrostatic adsorption.