Polymers surfactant system models

Linse P., Piculell L., Hansson P., Models of polymer—surfactant complexation. In Kwak J. C., ed. Polymer—Surfactant Systems. Surfactant Science Series 77. New York Marcel Dekker, 1998 193-238. 

Obviously many variables were not investigated, such as the effect of the type of nonionic surfactant, broader ranges of surfactant concentration, and broader ranges of monomer concentration. However, the results of this work are sufiBcient to demonstrate that the block copolymer architecture can be modified in MHAP by modifying the anionic surfactant concentration and type. These results have supported but not proved the block copolymer theory for this type of polymer-surfactant system. This model system is also a simple means of studying some aspects of mixed surfactant systems, an area of much current interest (e.g., ref 37). 

To model the polymer-surfactant system, we consider a mixture of polymers and low-molecular weight surfactant molecules in a solvent. Each polymer is assumed to carry the number / (> 2) of associative groups of the volume ro along its chain, which is composed of r/ statistical units. Each surfactant molecule is modeled as a molecule of a volume r carrying a single hydrophobe connected to the hydrophilic head (see Figure 10.1) [1]. 

Although surface force theories have been incorporated into the PBE, the current models require experimentally determined parameters such as solid-liquid interface potential, adsorbed polymer layer thickness and particle surface coverage. Future efforts should focus on integrating polymer adsorption dynamics models with P B M s. These models should be extended subsequently for systems involving a mixture of polymers or polymer-surfactant systems. 

Recommended model particle systems are enzymes immobilised on carriers ([27,44,45,47,49]), oil/water/surfactant or solvent/water/surfactant emulsions ([27, 44, 45] or [71, 72]) and a certain clay/polymer floccular system ([27, 42-52]), which have proved suitable in numerous tests. The enzyme resin described in [27,44,47] (acylase immobilised on an ion-exchanger) is used on an industrial scale for the cleavage of Penicillin G and is therefore also a biological material system. In Table 3 are given some data to model particle systems. 

Finally, it should be mentioned that a combination of COSMO-RS with tools such as MESODYN [127] or DPD [128] (dissipative particle dynamics) may lead to further progress in the area of the mesoscale modeling of inhomogeneous systems. Such tools are used in academia and industry in order to explore the complexity of the phase behavior of surfactant systems and amphiphilic block-co-polymers. In their coarse-grained 3D description of the long-chain molecules the tools require a thermodynamic kernel... 

In this area, recent unrelated efforts of the groups of Bhattacharya and Fife toward the development of new aggregate and polymer-based DAAP catalysts deserve mention. Bhattacharya and Snehalatha [22] report the micellar catalysis in mixtures of cetyl trimethyl ammonium bromide (CTAB) with synthetic anionic, cationic, nonionic, and zwitterionic 4,4 -(dialkylamino)pyridine functional surfactant systems, lb-c and 2a-b. Mixed micelles of these functional surfactants in CTAB effectively catalyze cleavage of various alkanoate and phosphotriester substrates. Interestingly these catalysts also conform to the Michaelis-Menten model often used to characterize the efficiency of natural enzymes. These systems also demonstrate superior catalytic activity as compared to the ones previously developed by Katritzky and co-workers (3 and 4). 

The goals of this work have been to determine the effect of polymers on the phase behavior of aqueous surfactant solutions, prior to and after equilibration with oil, to understand the mechanism of the so-called "surfactant-polymer interactions (SPI) in EOR, to develop a simple model which will predict the salient features of the phase behavior in polymer-microeraulsion systems, and to test the concept of using sulfonate-carboxylate mixed microemulsions for increased salt tolerance. 

Because of the interaction of the two complicated and not well-understood fields, turbulent flow and non-Newtonian fluids, understanding of DR mechanism(s) is still quite limited. Cates and coworkers (for example, Refs. " ) and a number of other investigators have done theoretical studies of the dynamics of self-assemblies of worm-like micelles. Because these so-called living polymers are subject to reversible scission and recombination, their relaxation behavior differs from reptating polymer chains. An additional form of stress relaxation is provided by continuous breaking and repair of the micellar chains. Thus, stress relaxation in micellar networks occurs through a combination of reptation and breaking. For rapid scission kinetics, linear viscoelastic (Maxwell) behavior is predicted and is observed for some surfactant systems at low frequencies. In many cationic surfactant systems, however, the observed behavior in Cole-Cole plots does not fit the Maxwell model. 

N. R. Washburn, T. P. Lodge, F. S. Bates, Ternary Polymer Blends as Model Surfactant Systems. J. Phys. Chem. B 2000,104,6987-6997. 

This chapter presents a summary of manuscripts published in the perissod of June 2011-June 2012 focusing on the use of NMR techniques to elucidate the microstructure and dynamics of self-assembling systems. In section 2 reviews and articles on general methods and models have been included. In section 3 the papers on thermotropic and lyotropic liquid crystals, phospholipids, vesicles and bicelles have been covered. Section 4 has been devoted to micellar solutions including ionic and non ionic surfactant systems, polymer amphiphiles and mixed amphiphiles systems. 

Hydrophobic association is also enhanced in polymer systems. Although polymer surfactants are considered to form micelles via intrapolymer hydrophobic interaction, our recent study (2r,s) revealed that a polyionene bearing anthryl groups as the hydrophobic domain showed a clear cmc UHtical micelle concentration) at the segment concentration around 3 x 10 5m. Reference experiments with a polyionene without anthryl groups and the monomer and dimer model compounds have indicated that the cmc is particularly low for the polymer. Taking the excimer intensity of anthracene fluorescence as an index of interchromophore interaction, we confirmed the existence of interpolymer association by the concentration dependent excimer intensity. Under the same condition to the polymer, any model systems either monomeric or dimeric do not associate intermolecularly. 

The second (and third) models for polyelectrolyte/surfactant interaction are based on the solubility and phase characteristics of the mixed systems. The general form of the solubility diagram of a polyelectrolyte/oppositely charged surfactant system, as illustrated by the Polymer JR/TEALS combination, has been referred to (57). It showed an intermediate zone of precipitation, but clarity for high (and low) concentrations of the surfactant. The line representing systems of maximum insolubility in the log polymer/log surfactant concentration plot had a 45° slope indicating constant composition of the insoluble complexes. 

Blankschtein and co-workers [65] have done pioneer work through theoretical modeling, aided by the computer, to predict the properties of mixed surfactant systems. Also, based on the necklace model proposed by Shirahama et al. [67,68], they have proposed a molecular thermodynamic theory of the com-plexation of nonionic polymers and surfactants in diluted aqueous solutions [66], Application of this method can help predict the interaction parameters for several nonionic polymer-surfactant mixtures. 

Abstract A molecular interaction model of nonionic polymer-surfactant complex formation was developed by modifying the free-energy expression of micelles for interaction with polymer segments. Using the small systems thermodynamics the composition of the surfactant aggregates with respect to the aggregation number, the number of polymer segments involved in the... 

Keywords Polymer-surfactant interaction Small systems thermodynamic model Aggregation number... 

The model calculations utilise a recently developed small systems thermodynamic model for polymer surfactant complex formation [9]. In the framework of this model the polymer-surfactant macroscopic system is considered as a three-component (water, polymer and surfactant) macroscopic ensemble in which the surfactant can be present in monomer, polymer surfactant complex and free micelle forms. The polymer surfactant complex molecules and the micelles are considered as small systems that contain a fluctuating number of building blocks (surfactant molecules in the case of micelles and surfactant aggregate subsystems in the case of the complex molecules). The description of the microstructure of the polymer-surfactant small system is based on Shirahama s necklace model. The subsystem of the polymer-surfactant complex molecules is an individual surfactant aggregate wrapped around by the polymer segments in which both the number of surfactant molecules and the number of polymer segments can fluctuate. 

The problem of solubilization in complex mixed fluids still remains open. Model mixed systems include surfactant solutions in the presence of inorganic two-dimensional objects such as clay, surfactants in the presence of linear polymers, and surfactants in the presence of globular nanoparticles, either inorganic or globular proteins. All of these model systems may be used to mimic solubilization in the environment. A general approach to this open problem is dealt with by Klumpp and Schwuger (59), who demonstrated that surfactants and multivalent ions are competitors for exchange at the surface of clays (as they should also be on humic acids). Once the mixed system is formed, the solubilization power (MAC) of the mixed surfactant system may be widely enhanced by reference to the separated surfactant and colloid. A spectacular example has been described... 

In this chapter we introduce a simple methodology based on molecular mechanics that can be used to estimate the free energy of mixing nanotubes with polymers and apply it to predicting the thermodynamic stability of polystyrene-CNT composites as a function of nanotube radius. We anticipate that this approach can be adapted to other systems of interest by tailoring the constituent molecular models to represent the polymers, surfactants, and functional groups under consideration as part of a rational strategy to determine the best approach to the preparation of well-dispersed and stable polymer-CNT composites. 

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