Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 35: Focus: Rheology I (joint focus with DRG)

CPP 35.9: Talk

Thursday, March 29, 2012, 17:30–17:45, C 243

Rheological Distinction between Gels and Soft Glasses during Critical Slowdown of their Relaxation Dynamics — •Horst Henning Winter — National Science Foundation, Arlington VA, USA, and University of Massachusetts Amherst MA, USA

Gels and soft glasses are difficult to distinguish rheologically because both show a critical slow down in the approach of the liquid-to-solid transition. The dynamics is dominated by the diverging, longest relaxation time, tau,max, which assumes a noticeably large values and is hard to measure because of that. The difference between gels and soft glasses, however, becomes apparent in the distinct pattern of the relaxation spectrum of the critical slowdown. While the long-time component of the relaxation time spectrum follows a powerlaw in relaxation time for both, log H~n log tau, their powerlaw exponent n is of different sign: negative n for the critical gel(material at the gel point) (Chambon et al. Polym Bull 13:499,1885; Winter et al. J Rheology 30:367, 1986; Chambon et al. J Rheol 31:683,1987) and positive n for the soft glass (Siebenbürger et al. J Rheology 53:707,2009; Winter et al. Rheol Acta 48:747, 2009).The powerlaw spectrum is cut off by the diverging, longest relaxation time (called alpha relaxation time for the soft glass, tau,max=tau,alpha) in the approach of the liquid-to-solid transition. In summary, patterns in the relaxation data provide a clear distinction between these two classes of materials.