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NanoemulsionsPreparation, Stability, and Application in Food
Published in C. Anandharamakrishnan, S. Parthasarathi, Food Nanotechnology, 2019
P. Karthik, Sayantani Dutta, C. Anandharamakrishnan
Coalescence is a process in which two droplets collide with each other and merge together in the emulsion system. It is the destabilization process over the time evolution of the droplet size which expresses different behaviors from homogeneous growth to strongly heterogeneous growth. Nano-sized emulsions are more stable to coalescence compared to micro-sized emulsions (Capek, 2004); further decrease in particle size is directly related to the increase in coalescence due to higher Brownian motion (Kong and Park, 2011). Tadros et al. (2004) stated that the rate of coalescence is determined by the adsorption ability of the surfactant, which is governed by surfactant surface activity and concentration. In the case of protein-stabilized emulsions, coalescence was slower than creaming and flocculation; however, it was highly increased in the presence of shear stress. Different factors such as salt concentration, pH, composition, formulation, and storage conditions are more relatively influenced by the rate of coalescence in nanoemulsion (Britten and Giroux, 1991).
Acrylic Adhesives
Published in István Benedek, Mikhail M. Feldstein, Technology of Pressure-Sensitive Adhesives and Products, 2008
Coalescence, initially between micelles and particles and later between particles, is particularly important in determining the particle size distribution and stability of an emulsion under an applied shear stress. Coalescence is affected by the size and surface charge density of the particles, as well as the degree of agitation. Nomura [105] demonstrated that higher agitation increases the particle size distribution. The polymerization kinetics are also affected by shear-induced reduction of monomer droplet size, which reduces the aqueous emulsifier concentration and the number of micelles and increases monomer diffusion out of the droplet. One practical consequence is that emulsion PSA polymerization, in comparison with homogeneous solution polymers, is much more sensitive to the details of reactor and agitator geometry and mixing.
Fluid–Fluid Dispersions: Liquid–Liquid and Gas–Liquid Systems
Published in Wioletta Podgórska, Multiphase Particulate Systems in Turbulent Flows, 2019
The coalescence rate depends on the dispersed phase volume fraction, drop size, viscosity, and density of the dispersed and continuous phases, interfacial tension, mass transfer between phases, as well as the presence of fine particles, nonionic and ionic surfactants of low molecular weight, polymeric surfactants, macromolecules, electrolytes, and, of course, the amount of energy supplied to the system. The increase in energy and drop diameters favors drop collisions, whereas the effect of these factors on coalescence efficiency is more complex, and associated with the droplet deformation and the mobility of interfaces, which in turn is determined by the dispersed phase viscosity and the presence of surface-active compounds. Emulsions are usually stabilized by surfactants. Small molecule nonionic surfactants stabilize droplets through the Gibbs–Marangoni effect. Small molecule ionic surfactants stabilize oil-in-water (O/W) emulsions through electrostatic repulsion as well as the Gibbs–Marangoni effect (Tobin and Ramkrishna, 1999; Urbina-Villaba and Garcia-Sucre, 2001; He et al., 2002; Podgórska and Marchisio, 2016). The performance of an ionic surfactant is strongly dependent on the pH and ionic strength of the solution. The presence of salt may destabilize the dispersion. At low electrolyte concentration, the double layer is extended. The repulsion at intermediate distances is larger than van der Waals attraction. The increase in salt concentration causes charge screening, which enhances the attraction between drops (Binks et al., 2000). On the other hand, it facilitates surfactant adsorption, which increases the surface potential and decreases interfacial tension (Kumar et al., 2006; Saien and Akbari, 2006; Saien et al., 2013; Podgórska and Marchisio, 2016).
Stabilization mechanism of reverse emulsions containing chromium (III): effect of interphase modification and dispersed phase viscosity
Published in Journal of Dispersion Science and Technology, 2023
Victoria Lovis, Vera D. Radnaeva, Gerald Brezesinski, Boris B. Tanganov
The coalescence rate is determined by the frequency of droplet collisions and the coalescence time. Under stirring conditions coalescence occurs only if the coalescence time is smaller than the duration of the droplets contact. Two essential steps contribute to the coalescence time: (1) the rupture of the interlayer between two droplets in contact which results in a fused droplet, and (2) reorganization of this fused droplet into its final shape, including the decrease of the interface area and the local mass transport. As well-known, the interphase rupture can be inhibited by repulsion of droplets due to an electrical double layer and/or by mechanical stabilization of the interphase. These effects contribute to the coalescence rate and depend on the chemical composition, structure and the corresponding physical-chemical properties of the phases.
Impact of mixed surfactant composition on emulsion stability in saline environment: anionic and nonionic surfactants
Published in Journal of Dispersion Science and Technology, 2023
Yue Zheng, Eduard A. Caicedo-Casso, Cole R. Davis, John A. Howarter, Kendra A. Erk, Carlos J. Martinez
Before looking into different surfactant ratios, the effect of single surfactant concentration on emulsion stability against coalescence was investigated. We looked at the emulsions prepared with either SLES or Triton X-100 at concentrations ranging from 100 to 1000 ppm. As shown in Figure 2, SLES emulsions were not stable and significant coalescence (circled region in Figure 2) could be observed at concentrations below 200 ppm. Similar behavior was observed for Triton X-100 at concentrations below 300 ppm. These unstable emulsions were difficult to measure using the Mastersizer due to rapid coalescence. At concentrations above 200 ppm for SLES and 300 ppm Triton X-100, the emulsions were stable against coalescence, and the distributions were almost identical for surfactant concentrations up to 1000 ppm, as shown in Figure 3. We expect that 200–300 ppm is the minimum surfactant concentration to ensure the emulsion stability at different surfactant ratios. Increasing surfactant concentration would further improve the emulsion stability against coalescence.
Oil separation from oil in water emulsion by coalescence filtration using kapok fibre
Published in Environmental Technology, 2023
Chandra Jeet Singh, Samrat Mukhopadhyay, R. S. Rengasamy
A coalescence filter is a type of filter that separates liquid aerosols and droplets from a gas or effluent stream. They are designed to filter out submicron oil, water, and other liquid droplets from air/emulsion flows. The process through which two or more liquid droplets combine to produce one bigger droplet is known as coalescence. Coalescence filtering has been successfully utilised to extract relatively small amounts of oil from large amounts of water with a hydrophobic filter medium [22,23]. As oil–water emulsions are transported to the fibrous filter, they attach to the fibre surface prior to coalescence. This depends on the spreading coefficient of oil on the fibre surface, determined by the surface wettability of fibre. The surface energy of the fibre affects its wettability by oil.