Studies into the swelling of gelatine films using a scanning fluid dynamic gauge

Abstract

Fluid dynamic gauging (FDG) has been developed to measure both the thickness and strength (cohesive or adhesive) of a range of fouling deposits, in situ and in real time. We report the development of a scanning FDG device (sFDG) with fully automated movement and deposit thickness measurement. Thickness-time profiles can be collected for several points on the surface over the course of a single experiment. sFDG is employed here to study the cleaning kinetics of model gelatine fouling layers when contacted with aqueous solutions at different pHs and temperatures, and with a commercial dishwasher formulation containing enzymes. Solution pH is an important parameter: above ∼pH 10.6 the gelatine layers swell markedly, due to protonation of the amino acids proline and hydroxyproline, and subsequent charge repulsion within the gel. An unusual behaviour (discontinuity) is reported during swelling in the commercial formulation. It is proposed that hydration of the deposit and an extent of swelling (ratio of the final to the initial deposit thickness) of ∼12 is necessary before the enzymes can promote deposit removal.