Surface free energies have been calculated for solid fluorocarbon materials by employing a method that utilizes dielectric data and theoretical predictions of van der Waals (dispersion) interactions. Excellent agreement between the results of direct force measurements and those of the theory for retarded van der Waals interactions supports the methodology. Two relatively new fluorocarbon polymers have been identified as having the lowest known surface free energies of all bulk homogeneous polymeric solids. This study provides confirmation that estimates of solid surface free energies based on contact angle measurements with dispersive organic liquids depend on the dielectric properties of both the liquids and the solid.
The thermal decolouration of the photoinduced merocyanine form of l'-hexadecyl-3',3'-dimethyl-6-nitrospiro[2Hl-benzopyran-2,2'-indoline] (SP-16) has been examined in a number of different aqueous unilamellar surfactant vesicle solutions and solvent-cast surfactant film matrices. The thermal decolouration of SP-16 in solvent cast dihexadecylphosphate (DHP) films and unilamellar dimyristoyl phosphatidylcholine (DMPC) vesicles exhibits single first-order kinetics. In DHP vesicles and solvent-cast DMPC films the thermal decolouration deviates from single first-order behaviour. The thermal decolouration in both these systems is well described by the superposition of two first-order rate processes. Dual first-order kinetics in the vesicular DHP media has been attributed to the merocyanine moieties of SP-16 partitioning between two residential sites within the vesicles, probably the surfactant/water interfacial region and the hydrocarbon chain domain. Dual first-order kinetics in the DMPC films has been ascribed to part of the merocyanine population being complexed with phosphatidylcholine headgroups and the other part of the population being located in hydrocarbon chain domains. In solvent-cast poly(dially1 dimethylammonium) dihexadecylphosphate (DHPP) films the thermal decolouration of SP-16 deviates from single first-order behaviour. The thermal decolouration in DHPP films is inadequately described as a dual first-order process but is well described as a dispersive process.
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