Water vapour permeability, diffusion and solubility in latex films

Water vapour diffusion D, solubility S and permeability P coefficients have been determined for films obtained from carboxylated styrene‐butadiene (SB) copolymer latexes. The experimental method is water vapour sorption performed in the range 30–60d̀C. Using the small angle neutron scattering (SANS) method and a selective labelling with D2O vapour, it has been shown that water molecules mainly diffuse in the films through the particle‐particle interfaces, which consist of a polar carboxyl‐rich copolymer. It has been shown that the degree of cross‐linking of the particles does not significantly affect the values of D and S. Moreover, the effect of neutralization conditions, regarding both the pH value of the initial latex and the nature of the neutralizing agent, has also been investigated. It has been found that D does not depend on these parameters, whereas S appears to be very sensitive to them. The results have been interpreted on the basis of the structural modifications of the films induced by neutralization. Finally, the hydrophilicity (or hydrophobicity) of the neutralizing agent has been identified as one of the key features for controlling the affinity of the latex film for water vapour and hence its permeability properties.