Phase inversion phenomenon

The described phase inversion phenomenon can be used in practice to prepare very fine and stable emulsions, so called PIT-emulsions. An example for the procedure is given in Figure 3.25. 

Flow Induced Phase Inversion Phenomenon and PI in Particle Technology... 

Akay, G. Dogru, M. Calkan, B. Calkan, O.F. Flow induced phase inversion phenomenon in process intensification and micro-reactor technology. Process intensification in water-in-crude oil emulsion separation by simultaneous application of electric field and polymeric demulsifiers. In Microreact Technology and Process Intensification Wang, Y., Halladay, J., Eds. Oxford University Press Oxford, 2005 Chapter, 18. 

In this study, after a brief introduction to PI we provide the bases of a technique for the preparation of polymeric micro-porous materials, known as polyHIPE polymers (PHPs) which are now used extensively in PIM, and micro-reactor technology. These polymers are prepared through the high internal phase emulsion (HIPE) polymerization route. In order to control the pore size, the flow-induced phase inversion phenomenon is applied to the emulsification technique. The metalization of these polymers and formation of nano-structured micro-porous metals for intensified catalysis are also discussed. Finally, we illustrate the applications of these materials in chemical- and bioprocess intensifications and tissue engineering while examining the existence of several size-dependent phenomena. 

By analyzing data of Figure 2.6, it was found that PHB forms a continuous matrix in the molten polymer at any ratio. The experimental values of the viscosity are close to the bottom theoretical curve, which corresponds to the calculation for the case of the formation of the matrix of PHB. Thus, during the melting of PHB observed phase inversion phenomenon in accordance with the laws of Ref. [4, 6] more fluid melt PHB forms a continuous phase in the entire range of concentrations. 

Figure 7.1 Phase inversion phenomenon from left PANI, as prepared intermediate...

A combination of the EMMS/matrix model for clusters and the EMMS/ bubbling model for bubbles was presented in this work. To close this set of equations, they adopted a simple criterion to quantify the phase inversion phenomenon, which is if/>l-/, then the system has dispersed bubbles in continuous dense phase, else it has continuous gas phase with dispersed clusters. Furthermore, clusters wiU exist only when input solids flux is greater than zero. The traditional stability condition of EMMS was, however, adopted to determine these structures, irrespective of bubble or cluster. 

At this point, the phenomenon of phase inversion occurs and the rubber in monomer phase becomes dispersed as discrete particles in a matrix of the polymer in monomer phase. Usually in a mass polymerization process, the rubber will contain occlusions of polymer/monomer, which serve to swell the volume of the rubber particle. In the course of polymerization, monomer is converted to polymer, the viscosity of the mixture increases and greater power is needed to maintain the temperature and the compositional uniformity throughout the polymerized material (8). 

While the above system is an example where two-dimensional phase separation in the sense of Fig. la,b (or Fig. 5) occurs, there exist also good examples where no lateral phase separation exists in equilibrium, and the system forms a single interface parallel to the surfaces (Fig. Id). However, if one chooses the initial state such that the phase preferred by air is close to the substrate and the phase preferred by the substrate is next to the air surface [77], the system is unstable and surface phase inversion takes place. A laterally inhomogeneous state then occurs only as a transient phenomenon necessary to trigger the inversion kinetics, but not as an equilibrium state [77]. 

At a certain volume ratio between the phases, the dispersed phase is converted into the continuous phase and vice versa. In the water/kerosene/polyethoxylated sorbitan monostearate system, when this phenomenon, which is known as phase inversion , occurs identical volumes of both phases are used to obtain o/w emulsions with an US horn at 20 kHz [51]. 

Phase inversion is a commonly observed phenomenon in which the continuous phase abruptly becomes the dispersed phase and vice versa (see Pacek et al. and Pacek, Nienow, and Moore Systematic studies on the effect of surfactant concentration and mixing on phase inversion and emulsion drop size have been carried out by Brooks and Richmond. Fig. 5 shows schematically the steps occurring during phase inversion. Although conflicting information exists on the subject, the following conclusions can be made ... 

Flow-Induced Phase Inversion (FIPI) Phenomenon... 

Flow-induced phase inversion (FIPI) phenomenon was observed by Akay[ and used extensively in phenomenon-based PI, especially in particlet and emulsion technologies po.21,27-32] pjpj readily observed in multi-phase systems and most... 

Alternatively, the dispersion can be subjected to a well-prescribed deformation, characterized by its rate and type (deformation state variables, DSVs) in order to invert the dispersion under constant thermodynamic conditions this phenomenon is known as FIPI. It is found that FIPI is not catastrophic and the dispersion goes through an unstable co-continuous state denoted by [AB], followed by a relatively stable multidispersion state denoted as [A-in-B]-in-A, before complete phase inversion to [B-in-A]. Therefore, the interchange ability of TSVs with DSVs forms the basis of FIPI processes. 

The glass transition temperature change deserves attention because is a sharp jump in the of PHB content of 50-60 per cent by weight. This phenomenon may also be due to the probable phase inversion (previously established by microscopy methods) at said ratio of the components. Con-... 

Nevertheless, it is now understood that HLB essentially depends on the surfactant, while the phase behavior and emulsion properties are also related to the water and oil phase nature, as well as to the temperature (100). The temperature was the preferred variable in the case of nonionic surfactants which are very sensitive to it, and an experimentally based concept was first introduced by Shinoda to quantify the formulation, i.e., the phase inversion temperature (PIT) (105, 106). It is known that the hydrophilicity of a nonionic surfactant decreses when temperature decreases. In water solution there exists a temperature at which the surfactant is no longer soluble and thus produces a separate phase. This so-called cloud point occurrence is related to the Shinoda PIT, which is essentially the same phenomenon, but in the presence of an oil phase whose nature could facilitate this separation and make it happen at a lower temperature. Although the PIT is limited to the liquid water temperature range of nonionic surfactants, its introduction was an important milestone because it was related not only to the surfactant, but also to the whole physicochemical environment (107), a feature that was shown to be essential by Winsor. 

The phenomenon of the phase inversion itself has been investigated by Molau (1965), who studied the graft-type polyblending of styrene with... 

The phase-inversion temperature (PIT) is the temperature at which the continuous and dispersed phases of an emulsion system are inverted (e.g. an o/w emulsion becomes a w/o emulsion, and vice versa). This phenomenon, introduced by Shinoda (16), occurs for emulsion systems containing non ionic surfactants, and can be a valuable tool for predicting the emulsion behaviour of such systems. The phase inversion occurs when the temperature is raised to a point where the interaction between water and the nonionic surfactant molecules decreases and the surfactant partitioning in water decreases. Hence, surfactant molecules... 

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