Rheology and Structure of Emulsions and Suspensions

Abstract

This article contains the results of experimental investigation of the rheological characteristics and structures of emulsions and suspensions. The emulsions had the oil volume fraction in the range from 0.1 to 0.4. The suspensions with nanoparticles are represented by suspensions of silica with concentrations from 1 to 4%. Paprika and coffee suspensions with concentrations of 5, 10, and 20% were studied. The material was subjected to rheological measurements using a concentric cylinder viscometer in the shear rate range of 16.2 to 1326s−1. A lot of food products are either in the form of emulsions or suspensions whose rheological and interfacial properties are important to achieve stability of the products. The rheology and structure analysis is very important from the point of view of flow, friction factors and Reynolds number for non-Newtonian fluids and food production processes. To characterize emulsions and suspensions, first the particle size distributions were made. The experiments presented have shown that the rheological characteristics of composite systems (emulsions and suspensions) depend on concentration and properties of dispersed phase. Concentration of dispersed phase has an effect on the character of the fluid. The fluid can have Newtonian character at low concentrations of dispersed phase. Above certain concentrations the nature of non-Newtonian fluid will appear. Emulsions have a polydisperse character. Emulsions with ϕ up to 0.4 show approximately linear increase of emulsion viscosity on the oil concentration. Silica represents suspension with aggregates, agglomerates or network formed. The increase in shear rate causes gradual destruction of the structure. The rheological behaviors confirm these processes. The paprika and coffee suspensions have non-Newtonian rheological properties. The suspensions have more and more non-Newtonian characteristics increasing particles concentration. The solid particles do not form structures. The correlation equation for rheological properties of systems studied has been shown. The results may be used for example to verify numerical models or comparisons with respect to similar fluids.