Blooming Surfactants: Small Molecule Segregation from PVA Films

Abstract

The segregation of small molecules in polymers is hugely relevant for a wide
range of industrial systems. This thesis focuses on the segregation of surfactants
in poly(vinyl alcohol) films, which are models for the films used to encapsulate
detergent in unit-dose applications. The aim is to isolate and understand factors
responsible for segregation observed in a range of model systems, that can
ultimately be used to predict and control this behaviour. A diverse range of surfactant segregation behaviours has been identified. The
anionic surfactant, SDS, segregates extensively from PVA, with plasticisation by
glycerol enhancing the surface excess, and enabling the formation of thermodynamically stable, stacked structures on the film surface. However, the behaviour of zwitterionic amine oxide surfactants in PVA has been shown to reflect their behaviour in water, forming a single monolayer on the surface.
By considering the interactions of these lm components in solution using
surface tensiometry and by determining their phase behaviour, the roles of surface
energy and compatibility in segregation have been assessed. A significant
synergistic effect was observed in model lm systems comprising two surfactants,
and these observations could also largely be explained by surface energy and
compatibility arguments.Assessing the effect of temperature on the distribution of film components has revealed some further migration, or surfactant restructuring after spin-coating. The properties of the polymer matrix is particularly important for this, particularly as the incorporation of plasticisers has been shown to have a significant impact on the distribution of surfactant in films. This has been addressed by exploring the effect of plasticisation and resin degree of hydrolysis on the free volume properties, which are likely to be linked to additive mobility.