MESOSCOPIC MODELLING OF STRUCTURED LIQUIDS: RHEOLOGY TO MORPHOLOGY RELATIONSHIP

Abstract

It is common to believe that a product's foaming properties are related to its cleansing properties. People incorrectly believe that less foam in their detergent or shampoo implies a non-effective cleaning product. The research detailed in this thesis focuses on the factors contributing to cleansing product effectiveness. First and foremost, the main factor influencing the ease of applicability and its effectiveness is viscosity, which has a leading role in industrial applications during product manufacturing. Various approaches have been taken in the past to calculate viscosity that involve macroscopic or microscopic procedures; however, it still is challenging to link the underlying morphology of the product to its macroscopic rheological properties. These challenges are amplified when the system under study involves surfactant molecules with inherent complexity. Mesoscopic simulation techniques have been proven to be a powerful tool in predicting such systems' structural and transport properties. Thus, the Dissipative Particle Dynamics (DPD) mesoscopic technique has been employed to study these systems throughout the current thesis. In the case of surfactant systems, different morphologies are present, and the resulting viscosity of the product is expected to be affected. This is particularly important when the microstructure changes dramatically by adding salt into the system. The viscosity is expected to change by varying the salt concentration and increasing the micelles' length. The first step in this direction was to validate the salt effects on the mixture's microstructure. Having accomplished this step through DPD simulations, the research was directed towards calculating the dynamical properties and, in particular, the zero-shear viscosity. Considering the similarities of long wormlike micelles to polymers and the dependence of viscosity on micelle's length, two equilibrium methodologies were assessed on polymer solutions aiming to establish a length to viscosity relation. The obtained results were reasonable, with higher viscosity for longer polymers, as expected. The successful application of equilibrium methods in polymer solutions suggested that any difficulty in obtaining viscosity from complex surfactant systems comes from the limited access we have to the micelles' slowest relaxation times. This conclusion emphasized the need for a supramolecular model that will give access to the micelle's relaxation and lead to the first attempts to model the wormlike micelles as living polymers by a standard DPD model based on earlier DPD simulations of surfactants in brine.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Robert Prosser (Supervisor) & Paola Carbone (Supervisor)