Associative phase separation

CHAPTER 7 ASSOCIATION BETWEEN AZOBENZENE MODIFIED POLYMERS 

CHAPTER ASSOCIATION BETWEEN AZOBENZENE MODI FI E D POLYM ERS 

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B B Crocker/ SM , P.E./ Consulting Chemical Engineer Fellow, Amencan Institute of Chemical Engineers Member, Air Pollution Control Association. (Phase Separation)... 

Guillemet F., Piculell L. Interactions in aqueous mixtures of hydrophobically modified polyelectrolyte and oppositely charged surfactant. Mixed micelle formation and associative phase separation. J. Phys. Chem. 1995 99 9201-9209. 

FIGURE 6.19 Idealized cases of phase separation in aqueous mixtures of two polymers, concentrations c2 and c 5. (a) Segregative phase separation or incompatibility. (b) Associative phase separation or complex coacervation. The heavy lines denote the binodal (solubility limit), the thin ones are tie lines. The dots indicate critical points. 

Phase separation in mixtures of polymers especially occurs at high concentrations and for large molar mass. The separation can be of two kinds. If the two polymers show mutual affinity, associative phase separation or complex coacervation occurs, i.e., a separation into a solution high in both polymers (a complex coacervate) and a very dilute solution. In most other cases, segregative phase separation or incompatibility is observed, i.e., separation in a phase rich in polymer A but poor in polymer B, and vice versa. 

FROM CLOUD POINT TO ASSOCIATIVE PHASE SEPARATION... 

Effing JJ, McLennan IJ, Kwak JCT. 1994. Associative phase separation observed in a hydrophobically modified poly(acrylamide)/sodium dodecyl sulfate system. J Phys Chem 98(10) 2499 2502. 

Figure 7.4. Associative phase separation of complexes between surfactants and azobenzene-modified polymers. See page 251-253 for text discussion of this figure.

Preparation of y-irradiation cross-linked matrices In preparation for y-irradiation cross-linking, the polymer is dissolved in water at low temperature. On raising the temperature above that of the inverse temperature transition for hydrophobic association, phase separation occurs. The phase-separated state is then exposed to 20Mrad of y-irradiation from a cobalt-60 source. 

The associative phase separation at low salt contents is also understood from the entropy of the counterion... 

Figure 20.21. A mixture of an ionic surfactant and an oppositely charged polyelectrolyte typically gives an associative phase separation, as exemplified here by tetradecyltrimethyl-ammonium bromide (TTAB) and sodium hyaluronate (NaHy). (Redrawn from B. Lindman and K. Thalberg, in Interactions of Surfactants with Polymers and Proteins, E. D. Goddard and K. P. Ananthapadmanabhan (Eds), CRC Press, Boca Raton, FL, 1993, p. 252)...

Piculell and Lindman [29] recently discussed the phase separation of aqueous mixtures of polymer/polymer and polymer/surfactant solutions in terms of association and segregation. When one of the phases is concentrated with both of the components, the phase separation is termed associative, and when the separating phases contain components of comparable total concentrations it is called a segregative phase separation. Mixtures of nonionic polymer and ionic surfactant mainly show an associative phase separation. However, this may be due to the fact that most studies performed in the chemical literature have been specifically concerned with systems where P—S association has been important. Systematic experiments on P—S systems where both are negatively charged are reported to show a segregative phase separation. 

Figure 15.1. (A) Schematic of surface plasmon resonance based on Kretchmann configuration used in most of the commercial SPR instruments. (B) Typical sensorgram showing the binding of analyte with its immobilized ligand on the chip surface (association phase), separation of the two binding partners (dissociation phase), and, finally, regeneration of the surface.

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