Sol-Gel Transition in Semidilute Conditions

The properties of semidilute mixtures of the protein bovine serum albumin and azopolymers mateh well with the simple idea of a photodestruction of the cross-links. As shown by stress relaxation experiments, the shear modulus (at time zero in Fig. 7.9a) is markedly diminished by exposure to UV, whereas the chain dynamics and relaxation time(s) appear not significantly affected. A decrease by more than a factor of 10 of the modulus indicates clearly the dissociation of most interchain associates (Fig. 7.9b). Nevertheless, the dissociation of the protein-polymer complexes may not occur when the cross-links disappear. As pointed by Leibler and colleagues in the case of interpolymer complexes (Pezron et al., 1988), and by Borrega in the case of protein polymer physical gels (Borrega et al., 1999), 

CHAPTER ASSOCIATION BETWEEN AZOBENZENE MODIFIED POLYMERS 

Consequently, the following four components were selected to prepare the photoresponsive emulsion system equal volumes of n-dodecane and 0.3 M NaNOs aqueous solution, the C12E4 surfactant, and an azobenzene-modified poly(acrylate). C12E4 is known to stabilize direct and inverse emulsions below and above the so-called phase inversion temperature (PIT here 24°C), respectively. Emulsions are unstable in the vicinity of the PIT, a temperature domain corresponding to the CTR of the light-responsive system. Emulsions made of equal oil and water volumes are directly below the PIT (and display a high electric conductivity because of the water continuum), but inverse (and of low conductivity) above the PIT (Khoukh et al., 2005). 

In Fig. 7.11, the open triangles show that temperature can be used to generate the conductivity drop at the PIT. The emulsion sequences observed on a 

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