Polymers, gels hydrophobically modified

Another interesting system containing a surface active betaine ester is the dilute aqueous mixture of dodecyl betainate and hydrophobically modified hydroxyethylcellulose (HM-HEC) that has been studied by Karlberg et al. [33]. It is well known that the viscosity of mixtures of HM polymers and surfactants is strongly dependent on the concentration of the amphiphile. By preparing a mixture of a surface active betaine ester and HM-HEC in a solution buffered at a pH where the surfactant is hydrolyzed, it is possible to make a gel with a time-dependent viscosity. 

Ortega-Ojeda, F. E., Larsson, H., Eliasson, A. C. (2005). Gel formation in mixtures of hydrophobically modified potato and high amylopectin potato starch. Carbohydr. Polym., 59, 313-327. 

The viscosity emphasized in this chapter, called elongational or extensional viscosity, was originally designated (34) tensile viscosity. When this bulk-phase parameter is near the interface, its two-dimensional equivalent is called the surface dilational viscosity. The importance of this parameter in the foaming of coatings, which arises from differences in surfactant structures, has been discussed (35). In cosmetic applications, foam and gel structures are important and probably reflect the reason the hydrophobically modified acrylic acid polymers were emphasized in the last section of Ghapter 7. 

Similarly, Wasserman and coworkers have studied a wide selection of polymeric materials in aqueous solution that are associative of some kind, i.e., that form some sort of self-assembly through non-covalent interactions [96]. Their study mainly deals with hydrogels of hydrophobically modified polymers, aqueous solutions of polymeric micelles created by block copolymers, and hydrogels based on poly (acrylic acid) and macrodiisocyanates. The spin probes of choice were hydrophobic, such as 5- and 16-DSA (see Eig. 2) or even spin labeled polymers. It was, e.g., possible to screen for the effect of chemical stmcture on the gel formation by recording and understanding the local mobility of the hydrophobic, long chain spin probes as a function of temperature. 

It is not unreasonable to expect that aqueous polymer dispersions will be effective in gels and mousses. Furthermore, the technology of hydrophobically modified acrylate thickeners discussed in Section II.A.3.a, useful for suspending latex particles, fits naturally into fixative gels. 

Hydrophobically modified polymer chains, referred to as associative thickeners, can produce gels at low concentrations, e.g. hydrophobically modified hydroxyethyl cellulose (Natrosol Plus, Hercules) or hydrophobically modified poly(ethylene oxide) (Rhom and Haas). 

For hydrophobically modified polymers [such as hydrophobically modified hy-droxyethyl cellulose or poly(ethylene oxide)] the interaction between the surfactant micelles and the hydrophobic chains on the polymer can result in the formation of cross-links, i.e. gel formation (Figure 15.4). However, at high surfactant concentrations, there will be more micelles that can interact with the individual polymer chains and the cross-links are broken. 

This chapter describes the most important fluorescence studies of the behavior of polymer chains in solutions, gels, and melts and in the bulk amorphous state. Because the book contains several chapters devoted to specific systems and methods, we try to avoid duphcities concerning, e.g., self-assembled core-shell nanoparticles, the behavior of hydrophobically modified chains, and PCS studies of polymers in solutions, and turn our attention to other aspects. Nevertheless, it was sometimes necessary to mention some topics treated in the other chapters. 

Abstract This paper reviews possible phase diagrams of associating polymer solutions in which phase separation and molecular association interfere. Paying special attention on the structure and reorganisation of the network junctions, we study competition between phase separation and gelation. The molecular structure of associating micelles, or multiple cross-link junctions, in the networks is analyzed from the sol/gel transition lines. The effect of added surfactants on the formation of reversible gels in hydrophobically modified polymer solutions is also studied under the assumption of the existenee of a minimum multiplicity required for stable cross links. To describe... 

The formation of responsive clusters of macromolecular chains, or gels of interconnected chains is achieved using hydrophobically modified polymers in presence of various additives, such as micelles of surfactants, CDs or proteins which bind to the hydrophobic side groups of the polymers. Hydrophobically modified polymers show the strong vlscoslflcatlon and high sensitivity to external stimuli. The use of mixtures of azobenzene-modified polymers with CD polymers allows to achieve photoviscosity swings by ca a decade at submillimolar concentrations of azo dyes [71]. 

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