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An investigation of the effect of leachable sucrose on the permeability of polymer latex films showed that the additive can be used to vary the solute permeability in a systematic manner, as a result of increased free volume resulting from additive leaching. However, the extent of the permeability enhancement is dependent on both the glass transition temperature of the polymer and its ability to sustain porosity and prevent pore reduction by wet sintering and/or film drying, and also the compatibility of the sucrose additive with the polymer. The loading of additive dictates how readily it is leached and, hence, the presence, or not, of continuous porosity through the full thickness of film. Although continuous porosity can be conferred on the film by the sucrose leaching, the resulting porosity still greatly inhibits the permeation of electrolyte, and the film fails well before the level of porosity approaches that required for unimpeded transport.

The influence of two distinct types of water leachable polymeric additives upon the transport properties across polymer latex films is considered. Hydroxypropyl methylcellulose, added as an aqueous solution, and a methyl methacrylate–methacrylic acid copolymer, added as latex particles, are both shown to be more effective than lower molecular weight rapidly water soluble additives, typified by sucrose, in enhancing solute transport and creating pathways for convective diffusion.

A range of permeation techniques were employed to investigate the transport mechanisms across polymer films cast from lattices containing either no or only low levels of water soluble leachates such as residual surfactant from polymerisation or added plasticiser essential to film formation. Hydrophilic pathways can provide a mechanism of transport, in addition to partition into and solution‐diffusion in the polymer phase. Loss of porosity by low Tg polymers on drying highlights the value of solute probes in studying film morphology.