Rheology of emulsions advances in chemistry acs publications. Exhibited in the german apothekenmuseum drugstore museum, heidelberg. The obtainable rheology profile with polyurethane thickeners in emulsion systems depends on the kind of emulsion and other factors which will be discussed in this chapter. Understanding the principles that govern the flow characteristics of the dispersions is essential for formulating a dispersion and its longterm stability1,2. There are many studies about microemulsions and their rheological properties but the amount of research about nanoemulsion rheology is very. Definition of rheology rheology is the sciencephysics that concerns with the flow of liquids and the deformation of solids. According to its definition, rheology is the science of the deformation and flow of mater. Introduction the flow properties of an emulsion are obviously among some of its more important physical attributes in either technical or aesthetic terms.
The rheology of the emulsion was characterized using flow curves and mechanical spectra, and the microstructural level characterized by studying the droplet size distribution. Applied rheology 352001 volume 21 issue 3 abstract. Examples are found in many industrial applications, including emulsions, suspensions, foams, and geld. Hence the ability to measure, adjust and, if possible, predict such properties is very important. Rheological characterization and stability study of an. Secondly, we will discuss the relevance of these results to the formation and stability of pr emulsions and bijels. Rheology of attractive emulsions harvard university. It presents results on the rheological behavior of complex materials, including macromolecular, colloidal and particulate solids, and fluids. Emulsion formation, stability, and rheology tharwat f. Extensional rheology of concentrated emulsions as probed. As a result rheology describes forces and deformations over time. Once the threshold of critical stress has been reached, the material yields to flow, hence the term, yield. The effect of aqueous phase content and temperature north sea crude oil emulsion viscoelastic behavior has been studied. Bottle from the 19th century bearing the inscription tinctur rhei vinum darel.
For the preparation of the wo emulsion, the surfactant span 83 was added to the crude oil and agitated for 5 minutes under a. Using rheology to characterize flow and viscoelastic properties of hydrogels, adhesives. Oscillatory rheology measuring the viscoelastic behaviour of soft materials measuring this time dependent stress response at a single frequency immediately reveals key differences between materials, as shown schematically in figure 1b. Barnes unilever research, port sunlight laboratory, bebington, uk received 11 november 1993. For shear flow to take place a shear force must act on the fluid. Emulsion formation, stability, and rheology emulsion. Emulsions stabilized by polymeric surfactants principles of rheological techniques rheology of oil. Rheology and structure of emulsions and suspensions. This site is like a library, use search box in the widget to get ebook that you want. Elasticities of attractive and repulsive emulsions differ below random close packing but are similar above it.
Lecithin in cosmetic emulsions produces a unique skin feel, which can be related to its rheological properties. Water ow emulsions stabilized with polyvinyl alcohol. Rheology of emulsions performance of the emulsion depends on flow properties removal of an emulsion from a bottle or tube flow of an emulsion through a hypodermic needle. A basic introduction to rheology technology networks. Gels and emulsions of medium to high viscosity and smooth texture. Rheology of pharmaceutical emulsions download ebook pdf. Weitz 1department of physics, harvard university, cambridge, ma 028, usa 2department of mechanical engineering, brigham young university, provo, ut 84602, usa 3departments of chemistry and physics, and california. A basic introduction to rheology rheology and viscosity introduction. Understanding the rheological flow properties of a polymer helps obtain optimized material properties during the molding process. If the material is an ideal elastic solid, then the sample stress is pro.
In an ow emulsion the freezing point of water is depressed due to the dispersed oil phase. Steady shear rheology of a viscous emulsion in the presence of finite inertia at moderate volume fractions. The control of their flow characteristics rheology is essential in their preparation, longterm physical stability and application. Interaction energies forces between emulsion droplets and their combinations. Emulsions consist of droplets of one liquid dis persed in another immiscible liquid. The liquid droplets the disperse phase are dispersed in a liquid medium the continuous phase. The rheology and structure analysis is very important from the point of view of flow, friction factors and reynolds number for nonnewtonian fluids and food production processes. Adsorption of surfactants at the liquidliquid interface. The emulsions were stabilized by a nonionic surfactant. The rheology and microstructure of complex fluids are intimately related, and this relationship is explored to gain a deeper understanding of the physics of colloidal dispersions, emulsions and polymer solutions. Rheology is not a measure of viscosity but an area of physics focused on the study of a substances change in flow characteristics under applied stress or force.
It will start with the interfacial rheology of adsorbed emulsifier films. In this study, waterinoil wo and oilinwater ow emulsions were made from a cosmeticgrade capryliccapric triglyceride with deoiled lecithin and hydroxylated lecithin. It illustrates one of the most important nonlinear effects in rheology, namely, the existence of normal stresses. By contrast to microemulsion phases, emulsions are not thermo dynamic. The uppermost layer has maximum velocity while the bottom layer is stationary. At very low interfacial tensions and low volume fractions, the viscosity decreases with increasing shear rate and becomes constant at high shear rates. We study the emulsions using oscillatory rheology on a straincontrolled rheometer using a roughened coneandplate geometry with a vapor trap. Using rheology to characterize flow and viscoelastic. Suspension stability increasing the zeroshear viscosity of the continuous phase of an emulsion or suspension is a popular method of increasing physical stability.
Introduction waterincrude oil wo emulsions are formed during the stages of crude oil processing and transportation from the mixtures of crude oil and water contained in the reservoir the content of water may be increased towards the end of reservoir life 1. Rheometry is the method used to analyze the rheological behavior of a material. To characterize emulsions and suspensions, first the particle size distributions were made. The book considers the forces of electrical origin that participate in the physical events at liquidliquid interfaces, taking into account electron transfer.
A set of 31 cosmetic emulsions, as the most frequent cosmetic dispersions, comprising lotions and creams ow, wo, was analyzed by rheological procedures rheostress 300, thermo fischer scientific and by sensory profiling. Predictive correlations for emulsion viscosity are discussed in detail. Solids are said to have an elastic response, and can resist. Rheological properties of emulsion systems springerlink. Feb 26, 2018 rheology is the study and control of the flow properties1,2. Rheology on the way from dilute to concentrated emulsions. An illustration of the types of shear induced orientation which can occur for various shear thinning materials is shown in figure 4. Deformation and breakup of droplets in emulsions during. Further details and the rheology data for the sdsstabilized repulsive emulsions are presented in 1, 2. Wo emulsions the emulsions were prepared in 2080 and 4060 vol. Interfacial rheology deals with the response of the adsorbed interfacial layer on the deformation. Rheometrytexture analysis of emulsions rheology is the science that describes the response of a material deformation to a superimposed stress force per unit area.
An emulsion is a mixture of two immiscible liquid phases where one phase is dispersed into another. Waterincrude oil wo emulsions are found in many industries such as cosmetic, pharmaceutical, and petroleum. However, zeroshear viscosity measurements are outside of the capability of most typical laboratory viscometers as they lack the sensitivity and precision motor control necessary to. He also showed that for many real fluids a critical level of stress must be attained in order to initiate flow. Rheology on the way from dilute to concentrated emulsions s. Rheology and stability of sterically stabilized emulsions. The term rheology, as with most scientific fields, has its roots in ancient greek with the stem rheo meaning flow in. The response depends on the layer composition, and thus interfacial rheology is relevant in many applications in which adsorbed layer play a crucial role, for example in development surfactants, foams and emulsions. The effect of added solids to an emulsion is fully treated, and its relation to a bimodel system is discussed. Study of flow properties of liquids is important for pharmacist working in the manufacture of several dosage forms, viz.
Effect of droplet size on the rheology of emulsions pal. Thermodynamics of emulsion formation and breakdown. The term rheology modifier is being used erroneously to refer to chemicals that modify the. For example, emulsions occur as oil in water ow emulsions or water in oil wo emulsions. Synthetic surfactants commonly used in commercial cosmetic products were used as controls. To determine the rheological properties of the emulsion, a thermohaake brand usa haake mars. It is reasonable to think that their rheology is similar to the rheology of emulsions when zero viscosity of dispersed droplets is assumed. Rheology and stability of phospholipidstabilized emulsions. Mason corporate research science laboratory, exxon research and engineering co. Wyss weitzlab group meeng tutorial 10x1035 0 5 10 strain 0 2 4 6 8 10 12 time s. Emulsions have been widely used in different industrial processes. Rheological tests to measure the viscosity of a polymer ranging from single point tests to variable shearrate tests.
Butter milk is an abundant industrial byproduct with remarkable emulsifying properties conferred by proteins that help to control the texture and also improve the. Electrohydrodynamics principles studies phenomena at liquidliquid interfaces, including finely dispersed particles or structures, in particular emulsions, double emulsions and biological cells. The development and production of good quality emulsions depend on the knowledge of emulsion preparation, stability mechanisms and rheological studies. Rheologists describe the deformation and flow behavior of all kinds of material. The latter class may be exemplified by an emulsion consisting of a polar oil e. The effect of interfacial tension on the steadyflow and dynamic viscoelastic behavior of emulsions are studied experimentally. Finally, typical features of emulsion rheology will be discussed with special emphasis on the distinct differences between dispersion and emulsion rheology. Introduction emulsions are a biphasic liquidliquid system in which the two. The effect of added solids to an emulsion is fully treated, and its relation to a bimodel system is.
Results indicate that the droplet size has a dramatic influence on emulsion rheology. Pdf rheology of emulsions svetlana derkach academia. Inertial effects on the rheology of a dilute emulsion. These emulsions do not have a sharp freezing point. In qualitative terms the rheology of emulsions is well understood, i. Pdf emulsion types, stability mechanisms and rheology. Understanding rheology of structured fluids keywords. The figures 4 and 5 show the viscosity build with increasing dosage of tafigel pur 40 to acrylic emulsions figure 4 and to styreneacrylic and pu emulsions figure 5. The effect of droplet size on the rheological behavior of water. The nonequilibrium microstructure and rheological properties of dispersions in steady, simple shear flow are calculated by solving the smoluchowski equation as a function of.
This process refers to aggregation of the droplets without any change in primary droplet size. The book considers the forces of electrical origin that participate in the physical events at liquidliquid. Moreover direct measurements of velocity profiles carried out by the method of dynamic light scattering 68 showed that wall slip is undoubtedly present in channel flow of dilute emulsions. Stress induced flow changes during manufacture milling. Rheological and textural properties of cosmetic emulsions. The journal of rheology is a vital resource for fields as diverse as polymer physics and fluid mechanics. The rheological behaviors of crude oilxanthan gum emulsions were studied in terms of viscosityshear rate and shear stressshear rate to understand the flow behavior of these emulsions. New fundamental concepts in emulsion rheology emory physics. Emulsions are a class of disperse systems consisting of two immiscible liquids. Tatar, sumnu, and sahin 2017 describe the effect of several factors, including volume fraction, droplet size, and colloidal interactions on emulsions rheology. Click download or read online button to get rheology of pharmaceutical emulsions book now. Cooling below the freezing point has a major effect on temperature stability in an wo emulsion, the dispersed water droplets freeze, but not the matrix. Both interfacial elasticity and viscosity play an important role in stabilisation of emulsions and. The highshearrate newtonian viscosity is not affected by interfacial tension, but the transition from.