Emulsions and dispersions
Interfacial chemistry measuring methods for mixability and stability
With emulsions and dispersions, product characteristics such as the size and stability of the particles or droplets and also the separating behavior such as flocculation or creaming are determined by wettability and interfacial tension. Surfactants are often used to form and stabilize the mixture. Our instruments contribute to the characterization of surfactants and the optimization of products with regard to interfacial chemistry.
Typical product areas for emulsions and dispersions
- Paints, varnishes, inks
- Fat-water mixtures in foodstuffs
- Coolants and lubricants
Surfactants as emulsifiers reduce the interfacial tension between grease/oil and water. In this way, they enable smaller droplets to be formed and reduce the mechanical effort when mixing. In addition, and often in conjunction with dispersed particles, they prevent or slow down destabilizing processes such as the merging of droplets (coalescence). Our force sensor tensiometers provide methods for characterizing surfactants:
- Direct measurement of the interfacial tension between the phases to be mixed
- Measurement of the surface tension of surfactant solutions
- Measurement of the critical micelle concentration (CMC)
Micro-emulsions are transparent, thermodynamically stable oil-water mixtures which are formed with the help of at least two surfactants. The interfacial tension falls by several decimal powers in the narrow temperature or concentration range for the production of micro-emulsions. The Spinning Drop Tensiometer – SITE100 works in this lowest measuring range.
Some technical applications of micro-emulsions are:
- Tertiary crude oil production
- Transportation of fat-soluble medicines in the body (bioavailability)
- Solvent-free degreasing, for example of animal skins
In the case of solid-liquid dispersions, the distribution and the tendency to flocculation depend on the surface characteristics of the solid and liquid phase. Our measuring instruments characterize surfactants which are used to improve the wetting and stability.
The surface free energy of the powder is also measured based on the contact angle using the Washburn method. At the same time, additional calculations of the wetting enthalpy help in matching the surface characteristics of the powder and liquid.
The direct quality control of a finished dispersion by measuring the sedimentation speed is included in the range of methods in our Force Tensiometer – K100.
At high process speeds, surfactants as emulsifiers and dispersing agents must reach the interface quickly and act there. Information relating to the mobility of a surfactant and the time required for it to take effect is therefore required. Our mobile and stationary Bubble Pressure Tensiometers – BP50 and BP100 and our Drop Volume Tensiometer – DVT50 measure the dynamic surface tension or interfacial tension over a large speed range for this purpose.
AR276: Interfacial rheological measurements on crude oil emulsions
During oil production, oil/water-emulsions occur. These are broken using demulsifiers in order to reduce corrosion as well as the viscosity when pumping. Interfacial rheological analyses on asphaltenes show how the quality of demulsifiers can be predicted based on the storage modulus E’. The results for different demulsifiers correlated with their efficiency in dewatering and pumping energy tests.
AR224: Dispersibility predictions - Some practical examples
The free surface energy of differently coated carbon black particles and different plastics is measured. The degree of mixability in the melt is predicted in each case based on calculated adsorption enthalpies and confirmed by stirring tests.
AR209: Evaluating the Efficacy of Lignosulphonates as Dispersing agents
Loam suspensions are stabilized with solutions of different lignosulphonates. The quality of the samples as dispersing agents is investigated based on sedimentation measurements.