Internal phase separation

At concentrations above ( ), a phase separation would lead to the formation of particles dispersed in a liquid matrix. The composition of such particles should be given by the binodal line. Thus such particles will still contain enough solvent to undergo a phase separation. Indeed such an internal phase separation can be used to prepare porous polymeric particles with potential for application as chromatography beads [48]. 

Abstract. An overview of the synthesis and applications of microgels and coreshell particles is provided, with emphasis on work originating from the author s laboratory. Microgels, which are cross-linked polymer latex particles, can be used for selective uptake of ions or polymers, or the controlled release of various compounds. Various methods for the synthesis of core-shell particles are described such as interfacial polymerization, layer-by-layer deposition, colloidosomes , internal phase separation, and silica shells. The release kinetics for controlled (sustained or triggered) release purposes is discussed. 

R. Atkin, P. Davies, J. Hardy, and B. Vincent, Preparation of aqueous core/polymer shell microcapsules by internal phase separation, Macromolecules 37, 7979-7985 (2004). 

Preconcentration of As(III) diethyldithiocarbamate on silica chemically modified with hexadecyl groups was examined [1]. Emulsion liquid membrane (made up of L113A surfactant, liquid paraffin as stabilizer and kerosene as solvent with HCl and KOH as external and internal phases) separation of As(III) and As(V) was applied prior to detection with silver diethyldithiocarbamate ( =510 nm) [2]. The method was applied to Cu ore and slagged ash. 

When block copolymers with immiscible blocks are synthesized directly via (mini)emulsion polymerization, the particles might exhibit internal phase separation during the polymerization, without the need for a cosolvent to induce... 

Figure 9 Nanostructured multicompartment cylinders, (a and b) Bright-field TEM images. Dark regions represent polypentafluorostyrene-chain-rich areas, (c and d) High-angle annular dark-field images of cylindrical micelles with internal phase-separated cores, (e) Cryogenic TEM image of uniform cylindrical micelles at 40% water/THF solution, (f) Cryogenic TEM image of cylindrical micelles with internal phase-separated cores at 67% water/THE solution. Chemical structures and schematic illustration of the formation of multicompartment cylinders (bottom). Reproduced with permission from...

Emulsion Formulation. The emulsion consists of two separate phases the membrane (oil) phase and the internal stripping phase. The membrane phase encapsulates the aqueous internal phase, separating it from the low concentration stream of wastewater being treated (the external phase). The membrane phase is composed of a complexing agent, a surfactant, a solvent, and a co-solvent. The solvent is kerosene. The co-solvent is n-decanol. Both the complexing agent and the surfactant are proprietary materials. The extractant complexes with the anionic... 

The difunctional derivative DIAMA has also been used in emulsion polymerization (Figure 17) 30,231 enabling a significant reduction in particle size and narrower distribution compared to latexes prepared using monoflinctional BlocBuilder MA . Polystyrene-I -poly(n-butyl acrylate)-Zi-polystyrene triblock copolymers were made using the difunctional alkoxyamine, and allowed nanostmctured particles to be formed upon internal phase separation. A refined semibatch process shortened overall process time compared to earlier efforts. ... 

Coalescence and Phase Separation. Coalescence between adjacent drops and between drops and contactor internals is important for two reasons. It usually plays a part, in combination with breakup, in determining the equiHbrium drop si2e in a dispersion, and it can therefore affect holdup and flooding in a countercurrent extraction column. Secondly, it is an essential step in the disengagement of the phases and the control of entrainment after extraction has been completed. 

If there is particle—particle interaction, as is the case for flocculated systems, the viscosity is higher than in the absence of flocculation. Furthermore, a flocculated dispersion is shear thinning and possibly thixotropic because the floccules break down to the individual particles when shear stress is appHed. Considered in terms of the Mooney equation, at low shear rates in a flocculated system some continuous phase is trapped between the particles in the floccules. This effectively increases the internal phase volume and hence the viscosity of the system. Under sufficiently high stress, the floccules break up, reducing the effective internal phase volume and the viscosity. If, as is commonly the case, the extent of floccule separation increases with shearing time, the system is thixotropic as well as shear thinning. 

Emulsification is essential for the development of all types of skin- and hair-care preparations and a variety of makeup products. Emulsions (qv) are fine dispersions of one Hquid or semisoHd ia a second Hquid (the contiauous phase) with which the first substance is not miscible. Generally, one of the phases is water and the other phase is an oily substance oil-ia-water emulsions are identified as o/w water-ia-oil emulsions as w/o. When oil and water are mixed by shaking or stirring ia the absence of a surface-active agent, the two phases separate rapidly to minimize the iaterfacial energy. Maintenance of the dispersion of small droplets of the internal phase, a requirement for emulsification, is practical only by including at least one surface-active emulsifier ia the oil-and-water blend. 

Models of a second type (Sec. IV) restrict themselves to a few very basic ingredients, e.g., the repulsion between oil and water and the orientation of the amphiphiles. They are less versatile than chain models and have to be specified in view of the particular problem one has in mind. On the other hand, they allow an efficient study of structures on intermediate length and time scales, while still establishing a connection with microscopic properties of the materials. Hence, they bridge between the microscopic approaches and the more phenomenological treatments which will be described below. Various microscopic models of this type have been constructed and used to study phase transitions in the bulk of amphiphihc systems, internal phase transitions in monolayers and bilayers, interfacial properties, and dynamical aspects such as the kinetics of phase separation between water and oil in the presence of amphiphiles. 

A review of the properties of silica as applied to reversed phase separations summarizes a number of issues that have been debated for many years.71 The review categorizes unmodified silanols as free, geminal, vicinal, and internal. The pK, values of silanols average about 7.1, but some silanols may have pK, values as low as 3. As reported in Chapter 4, heavy metal... 

S.A. Cohen, T. Dourdeville, D. Della Rovere and J. Holyoke, Abstracts 22nd International Symposium on High Performance Liquid Phase Separations and Related Techniques, St. Louis, MO (1998), Paper P-0418-T. 

Changes in the natures of individual phases of or phase separation within a formulation are reasons to discontinue use of a product. Phase separation may result from emulsion breakage, clearly an acute instability. More often it appears more subtly as bleeding—the formation of visible droplets of an emulsion s internal phase in the continuum of the semisolid. This problem is the result of slow rearrangement and contraction of internal structure. Eventually, here and there, globules of what is often clear liquid internal phase are squeezed out of the matrix. Warm storage temperatures can induce or accelerate structural crenulation such as this thus,... 

Chemically, the preparation of a "stable" foam or emulsion requires the use of a surfactant to aid in dispersion of the internal phase and prevent the collapse of the foam (or emulsion) into separate bulk phases. The selection of a surfactant is made on the basis of severity of conditions to be encountered, the gas to be entrained (N2, C02, LPG, CH, or air), the continuous phase liquid (water, alcohol, or oil), and half-life of foam stability desired. 

Lubricants can be classified as internal or external lubricants. Internal lubricants should be partially miscible with the polymer at processing temperatures (i.e., behave similar to a plasticiser), but phase separate at ordinary temperatures. Whereas plasticisers are completely miscible with the bulk polymer, lubricants have a limited solubility. 

The above model assumes that both components are dynamically symmetric, that they have same viscosities and densities, and that the deformations of the phase matrix is much slower than the internal rheological time [164], However, for a large class of systems, such as polymer solutions, colloidal suspension, and so on, these assumptions are not valid. To describe the phase separation in dynamically asymmetric mixtures, the model should treat the motion of each component separately ( two-fluid models [98]). Let Vi (r, t) and v2(r, t) be the velocities of components 1 and 2, respectively. Then, the basic equations for a viscoelastic model are [164—166]... 

All liposphere formulations prepared remained stable during the 3-month period of the study, and no phase separation or appearance of aggregates were observed. The difference between polymeric lipospheres and the standard liposphere formulations is the composition of the internal core of the particles. Standard lipospheres, such as those previously described, consist of a solid hydrophobic fat core composed of neutral fats like tristearin, whereas, in the polymeric lipospheres, biodegradable polymers such as polylactide or polycaprolactone were substituted for the triglycerides. Both types of lipospheres are thought to be stabilized by one layer of phospholipid molecules embedded in their surface. 

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