Dr. Omkar Deshmukh, postdoctoral researcher at University of Queensland, Brisbane, Australia

In his nobel lecture and subsequent publications, de Gennes referred to colloidal systems as ultra divided matter [1,2] and highlighted their ubiquitous nature. Irrespective of their application, the fundamental laws that govern the behaviour of these colloidal systems are the same. Through this seminar, I would like to highlight some of the key findings from my research career so far. To begin with, we look at the use of soft microgel particles based on a thermosensitive polymer, poly-N-isopropylacrylamide (PNIPAM) to stabilize a fluid interface. We also study the effect of temperature on the adsorption kinetics and the interfacial behaviour[3,4] of these particles on air-water and oil-water interfaces. The stimuli responsive nature of these particles provides us with a handle to control the particle interactions, their interfacial microstructure and interfacial rheology and consequently on the stability of foams and emulsions prepared using such particles as stabilisers. Next we explore how fundamental physics can be used to solve industrially relevant problems. From the first bite to the point of swallow, food undergoes tremendous transformation, which often also takes place in a very short period of time. The process is extremely dynamic and complex as it involves multiple processes such as comminution, mixing, dissolution, dilution, hydration and enzymatic breakdown that occur in tandem. This gives rise to different sensory perceptions as the process of mastication progresses[5]. The intensity of these sensory percepts depends on the the

structure, composition and the mechanical properties of the bolus during that particular phase of oral processing. We use novel invitro methods to determine properties of solid snack foods relevant to the dynamic sensory response. The specific focus here is on capturing the physical mechanisms behind different sensory attributes experienced during various stages of oral processing of Potato Chips (PCs). We study four different types of commercially available PCs: Regular Crinkle Cut Fried PCs, Kettle Fried PCs, Reconstituted Fried PCs and Reconstituted Baked PCs. The results of the sensory analysis in combination with the mechanical and microscopic characterisation will elucidate the physical mechanisms governing the sensory response. Majority of food suspensions encountered in everyday life are water based and have been widely studied. Suspensions based in fats, oils or other non-aqueous mediums present unique challenges as the nature of the solvent would govern the Brownian forces, hydrodynamic forces as well as the inter particle and particle-solvent interactions[6]. We investigate the rheology of one such fat-based system i.e. biscuit cream, as a function of phase volume and particle size distribution with the aid of an

underlying theoretical model[7, 8]