Dynamic crossover effects observed in solutions of a hydrophobically associating water-soluble polymer

Influence of associations on self-diffusion of styrene-methylmethacrylate random copolymers in semidilute acetone solution

“…7,17-20. In two recent articles on gelling systems by Nyström et al, 18,19 the authors detected an increasing nonexponentiality of S inc (q,t) vs. q 2 t with progressing gelation. 18 The asserted anomalous diffusion is, however, not visible in their published data.…”

“…Nyström et al could also well approximate the measured S inc (q,t) with a stretched exponential for other associating polymers in solution. 18,19 Of particular importance is the ability of a stretched exponential to describe the fast initial decay of the echo attenuation. On the other hand, the D in eq.…”

“…The failing of the q 2 -scaling (splitting of the curves with respect to g alone) in Figure 6 of ref. 19 has no theoretical explanation (S inc only depends on the product g ⅐ ␦), and must be regarded as an experimental artefact. Obviously, the t c of the gelling systems, cf.…”

“…Above the gel point, the cluster size of the still free-moving clusters in the gel decreases. Nyström et al have investigated aqueous solutions of a Pluronics polymer (polyethyleneoxide-b-polypropyleneoxide-b-polyethyleneoxide) 18 and a hydrophobically modified polyoxyethylene 19 during gelation by PFG NMR. In our group, the formation of physical gels on cooling of a polypropyleneglycole melt was confirmed by detection of anomalous restricted diffusion of the network chains.…”

Guides to solving the glass transition problem

“…This crossover property is found also in other many-body relaxation systems besides glass-formers [7,[56][57][58][59][60][61][62], and hence it is a general property. The magnitude of t c depends on the intermolecular potential V (r ).…”