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The conformational transition of ι-carrageenan in different salt solutions under nongelling conditions has been studied by light scattering (WALLS). The focus is on the thermodynamic interactions and the concentration dependence of the reduced scattering intensity at zero angle. An upward curvature of (KC p /R 0) in conditions of conformational ordering has been interpreted as due to a concentration-dependent reversible chain association. The open association model of Elias has been applied to analyze the data. In conditions of conformational ordering a decrease of polymer concentration, C p , is accompanied by a decrease of (M̄ w)assoc. These results have been confirmed by using low-angle light scattering (LALLS). In the lowest range of C p , the decreasing values of (M̄ w)assoc are already very close to that of the single-stranded disordered conformation. In the same range, the values of the specific optical activity remain constant. This is a confirmatory evidence that the fundamental ordered conformation of ι-carrageenan is a single helix.

Light scattering (LS) investigations have additionally confirmed the intramolecular nature of the fundamental ordered conformation (single helix) of κ-carrageenan in aqueous 0.1 M NaI. The partial replacement of sodium with cesium ions induces a (thermoreversible) intermolecular association of the polysaccharide in the ordered conformation. The association-inducing effect can be observed already at the lowest investigated concentration of the cation. We found no significant change of the thermodynamic properties related to an alleged composition threshold value in the range of the cesium equivalent fraction, X Cs, from 0.12 to 0.40. The extent and the rate of the association process strongly increase with the concentration of cesium. Equilibrium values for the association constant could be obtained except for the case of X Cs = 0.40, where the process is too massive to allow long-time LS investigation. In the latter condition, some additional stiffening of the chain was noticed.

We present a review of experimental data on the nonlinear optical properties of thermotropic and lyotropic liquid crystals probed by the Z-scan technique. Depending on the time scale, different processes originate a nonlinear optical response. Particularly, at nanosecond range, the physical processes associated with the nonlinear response in thermotropics are not completely understood. In lyotropics, the nonlinear response at ms time scale is from thermal origin and depends on the particular mesophase, relative concentration of the components, and temperature.