Polymers microemulsion additives

Of notable significance to the discussion of UV-vis studies of PAT solvation is the work of Fraleoni-Morgera et al. [184]. They have found that the addition of a surfactant. Tween 80, can solubilize PHT in water. This process was studied using UV-vis by treating the polymer as its own optical probe. The spectrum of the aqueous polymer microemulsion shows a redshift with respect to the same polymer in THF, and vibronic structure similar to that of a drop cast film of the same. The results reveal that while the polymer is in solution, it is conformationally ordered due in part to the formation of aggregates and the interaction of the side chains with the solvent. 

At diblock concentrations above bicontinuous microemulsion ( tE) and of lamella ordered phases were identified [46]. While the lamella phase was predicted by mean field theory, the observation of a microemulsion phase was unexpected. Polymer microemulsion phases are presently the subject of active research both from theory [85] and experiment [52] and, in addition, seem to generate interest for industrial application because of its homogeneous structiue on the pm length scale. 

Effects due to the addition of water-soluble polymers (polyoxyethylene glycol, polyacrylamide, and polyvinyl alcohol) on water/AOT/decane w/o microemulsions have been reported [190],... 

Hilder, E.F. et al.. Separation of hydrophobic polymer additives by microemulsion electrokinetic chromatography, J. Chromatogr A, 922, 293, 2001. 

W. T. Osterloh and M. J. Jante, Jr. Surfactant-polymer flooding with anionic PO/EO surfactant microemulsions containing polyethylene glycol additives. In Proceedings Volume, volume 1, pages 485 94. 8th SPE/DOE Enhanced Oil Recovery Symp (Tulsa, OK, 4/22-4/24), 1992. 

Micellar aggregates are considered in chapter 3 and a critical concentration is defined on the basis of a change in the shape of the size distribution of aggregates. This is followed by the examination, via a second order perturbation theory, of the phase behavior of a sterically stabilized non-aqueous colloidal dispersion containing free polymer molecules. This chapter is also concerned with the thermodynamic stability of microemulsions, which is treated via a new thermodynamic formalism. In addition, a molecular thermodynamics approach is suggested, which can predict the structural and compositional characteristics of microemulsions. Thermodynamic approaches similar to that used for microemulsions are applied to the phase transition in monolayers of insoluble surfactants and to lamellar liquid crystals. 

Corpart and Candau [68, 69] described the formulation of polyampholytes containing both positive and negative charges in inverse microemulsions. The copolymers can show very different behaviors in the aqueous solution, ranging from insoluble, water-swollen hydrogels to water-soluble compounds, depending on the monomer composition. For polyampholytes with balanced stoichiometry, the polymer behavior is controlled by attractive electrostatic forces. The compound is usually insoluble in water, but becomes soluble upon the addition of salt. 

In the methodology developed by us [24], the incompatibility of the two polymers was exploited in a positive way. The composites were obtained using a two-step method. In the first step, hydrophilic (hydrophobic) polymer latex particles were prepared using the concentrated emulsion method. The monomer-precursor of the continuous phase of the composite or water, when that monomer was hydrophilic, was selected as the continuous phase of the emulsion. In the second step, the emulsion whose dispersed phase was polymerized was dispersed in the continuous-phase monomer of the composite or its solution in water when the monomer was hydrophilic, after a suitable initiator was introduced in the continuous phase. The submicrometer size hydrophilic (hydrophobic) latexes were thus dispersed in the hydrophobic (hydrophilic) continuous phase without the addition of a dispersant. The experimental observations indicated that the above colloidal dispersions remained stable. The stability is due to both the dispersant introduced in the first step and the presence of the films of the continuous phase of the concentrated emulsion around the latex particles. These films consist of either the monomer-precursor of the continuous phase of the composite or water when the monomer-precursor is hydrophilic. This ensured the compatibility of the particles with the continuous phase. The preparation of poly(styrenesulfonic acid) salt latexes dispersed in cross-linked polystyrene matrices as well as of polystyrene latexes dispersed in crosslinked polyacrylamide matrices is described below. The two-step method is compared to the single-step ones based on concentrated emulsions or microemulsions. 

A major drawback of conventional microemulsion polymerization is the high surfactant-to-monomer ratio usually needed to form the initial microemulsion. Surfactant can be used more efficiently in semi-continuous or fed polymerization processes. Several polymerization cycles can be run in a short period of time by stepwise addition of new monomer. After each cycle of monomer addition, most of the surfactant is still available to stabilize the growing hydro-phobic polymer particles, or to forms microemulsion again when a polar monomer is used. For instance, in the polymerization of vinyl acetate (VA) by a semi-continuous microemulsion process [21], latexes with a high polymer content of about 30 wt% were obtained at relatively low AOT concentrations of about 1 wt%. Moreover, their particle sizes and molecular weights were much smaller than those obtained by conventional emulsion polymerization. 

In addition to the practical interest, the process presents challenges encouraging further fundamental exploration. A thorough study not reported here, has been performed on the mechanism and kinetics of the polymerization of acrylamide in AOT/water/toluene microemulsions (Carver, M.T.r Dreyer, U. Knoesel, R. Candau, F. Fitch, R.M. J. Polym. Sci. Polym. Chem. Ed., in press. Carver, M.T. Candau, F. Fitch, R.M. J. Polym. Sci. Polym. Chem. Ed., in press). The termination reaction of the polymerization was found to be first order in radical concentration, i.e. a monoradical reaction instead of the classical biradical reaction. Another major conclusion was that the nucleation of particles is continuous all throughout the polymerization in contrast to conventional emulsion polymerization where particle nucleation only occurs in the very early stages of polymerization. These studies deserve further investigations and should be extended to other systems in order to confirm the unique character of the process. 

The polymeric material based on nonionic surfactant (Neodol 91-5) has diferent pore morphology (Figure5(f)) as compared to the anionic system. Even the polymeric material based on the anionic system with a different cosolvent, butyl cellosolve, shows a different morphology (Rgure5(g)). Figure5(h) illustrates the structure of polymers obtained from a microemulsion using a different nonionic surfactant (Emsorb 6916). Thus, the pore morphology depends on the initial microstructure of the microemulsion as determined by the type of surfactant and cosolvent in addition to composition and polymerization conditions. 

Examples of such developments are sulfation of transesterified rapeseed oil phosphatides (17) and the use of bicontinuous microemulsions obtained by the addition of aliphatic alcohols (18, 19). The stability of these systems promises to be more reliable than those in present use. Oils from wood (tall oil) can be sulfo-nated for self-emulsifying fatliquors (20). Polymerizable oils have been used in fatliquors (21). We expect more progress on the use of high polymers, such as the already commercial alkyl acrylate esters developed by Hodder et al. (22-24), and material based on elastomers (6). We anticipate the development of novel systems to be encouraged by the demand for leather in washable garments and automobile upholstery. 

In addition to the surfactant, a white oil was a component of the microemulsion. This oil was added in the minimum amount required to solubilize enough xanthan polymer to produce the target viscosity. In the absence of the white oil, the polymer could not be solubilized. The xanthan polymer itself was required for mobility control. To prevent biodegradation of the polymer, formaldehyde was added. Citric acid was also a component of the microemulsion, added to prevent the oxidation of ferrous ion present in the brine to ferric ion. The presence of ferric ion would lead to precipitation of iron compounds as well as cross-linking of the biopolymer. 

The signiflcant recent advances in both colloidal and polymer chemistries have enabled the successful fabrication of complex, defect-free tianoslruclures following a bottom-up approach [353]. Two recent related examples are mentioned to stress the point. Recently, triblock copolymer with divalent counter-ions in mixed solvents led to the formation of particles with tunable internal structure mimicking lipid anphiphiles for potential use in drug delivery. The mechanism of formation involves either nanophase separation within the triblock copolymer nanoparticle upon addition of water or microemulsion formation similar to that in lipid systems... 

A significant amount of work has demonstrated the feasibility and the interest of reversed micelles for the separation of proteins and for the enhancement or inhibition of specific reactions. The number of micellar systems presently available and studied in the presence of proteins is still limited. An effort should be made to increase the number of surfactants used as well as the set of proteins assayed and to characterize the molecular mechanism of solubilization and the microstructure of the laden organic phases in various systems, since they determine the efficiency and selectivity of the separation and are essential to understand the phenomena of bio-activity loss or preservation. As the features of extraction depend on many parameters, particular attention should be paid to controlling all of them in each phase. Simplified thermodynamic models begin to be developed for the representation of partition of simple ions and proteins between aqueous and micellar phases. Relevant experiments and more complete data sets on distribution of salts, cosurfactants, should promote further developments in modelling in relation with current investigations on electrolytes, polymers and proteins. This work could be connected with distribution studies achieved in related areas as microemulsions for oil recovery or supercritical extraction (74). In addition, the contribution of physico-chemical experiments should be taken into account to evaluate the size and structure of the micelles. 

Addition of oil yields an oil-in-water microemulsion with nearly spherical drops. Within limits, the higher the molecular weight of the oil added to produce an oil-in-water microemulsion, the less oil is needed to formulate single phases with polymer for mobility control (Hirasaki et al., 2008). During screening tests, a clear surfactant-polymer solution with oil added does not mean the corresponding aqueous solution without oil will be clear. Therefore, aqueous stability tests with polymer added in the surfactant solution are necessary and important. 

The properties of a variety of surfactants (36-41), novel cationic phases (42-44), mixed micelles (45-49), microemulsions (50), vesicles (51-55), liposomes (56, 57), and synthetic polymers (58-65) have all be screened by LSER. Micelle structural modifications by differing head groups (66) and spacers (67,68), chain lengths (69), and counterions (70), as well as the use of deuterated water buffers (71) and the addition of cyclodextrins (72) and organic solvents (73) to the micellar medium, have also been characterized by LSER studies. 

The research on microemulsions currently concentrates on even more complex mixtures. By adding amphiphilic macromolecules the properties of microemulsions can be influenced quite significantly (see Chapter 4). If only small amounts of amphiphilic block copolymers are added to a bicontinuous microemulsion a dramatic enhancement of the solubilisation efficiency is found [27,28]. On the other hand, the addition of hydrophobically modified (HM) polymers to droplet microemulsions leads to a bridging of swollen micelles and an increase of the low shear viscosity by several orders of magnitude [29]. 

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