The role of detergent formulation on the cleaning of a complex carbohydrate-fat food soil from stainless steel surfaces was studied using a modified version of the millimanipulation device described by Ali et al. (2015b) which allowed the force required to scrape the soil from the surface to be measured as the soil is immersed, in situ and in real time. This allowed the influence of temperature, solution chemistry and time on the mechanical forces (rheology) and removal behaviour of the soil to be studied-in effect quantifying the relationships in Sinner's cleaning circle. The soil simulated a burnt-on baked-on deposit and featured regular cracking in the 300 m thick layer. The removal force decreased noticeably on hydration: the cleaning mechanism was then determined by the agents present. At 20C, below the temperature at which the fat phase was mobile, removal was characterised by cohesive failure except in the presence of the cationic surfactant CTAB, which promoted adhesive failure and fast decay in removal force. At 50C, when the fat was mobile, a transition between cohesive and adhesive failure was observed at pH 7 which was inhibited at higher pH. Adhesive failure and fast decay in removal force was observed at higher pH and 50C in the presence of the anionic and non-ionic surfactants, SDBS and TX-100, respectively.
An innovative fluid-dynamic gauging (FDG) device to study the initial as well as longterm swelling or removal of soft solid layers immersed in a liquid environment in real time and in situ is presented. This sideways FDG (SiDG) device was developed for soft solid layers whose properties change significantly on contact with liquid. Calibration tests indicated a resolution of ±10 μm. The open source computational fluid dynamics (CFD) code OpenFOAM was used to model the flow in the SiDG nozzle. Good agreement was obtained between experimental and CFD results at different nozzle clearances, so that the shear stress exerted by the gauging flow can be computed accurately. A series of demonstration studies are presented, on layers of petroleum jelly, polyvinyl acetate, gelatin and a complex model soil. Initial swelling dynamics are captured and the influence of pH on initial swelling behavior, previously inaccessible, is reported.
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