Distinct Dynamics Pattern during the Ripening of Nanocomposite GelsPolymer Preprints (2009)
AbstractThere is a large class of physical gels that develop their structure slowly. Most of the structural development occurs in the solid state after having passed through an early liquid-to-solid transition. Such physical gels are often called “soft glasses” because of their slow out-of-equilibrium dynamics. Here we examine the ripening of an out-of-equilibrium model colloidal solid that consists of clay particles that swell and exfoliate into randomly oriented clay sheets through the action of end-functionalized (“sticky”) polymer molecules. The nano-composite gel serves as model material in search of regular patterns in the non-equilibrium dynamics in the approach of equilibrium. Surprisingly, there exists a stunningly simple pattern in the time-resolved viscoelasticity: the product of equilibrium modulus and longest relaxation time, Ge(tr)lmax(tr), remains constant throughout the ripening process. Parameter is the duration of the isothermal ripening process (“ripening time”, tr). The product Gelmax has the dimension of a viscosity but belongs to the solid state of the gel. As a consequence of Gelmax =constant, a single scaling relation with two power law regions, a fast ripening process (~ tr-2) followed by slow ripening (~ tr-1/2), defines the state of ripening, e.g. the time necessary to reach equilibrium. Experiments on a wider group of physical gels is in progress with the objective of confirming or rejecting universality of the novel findings. The experimental protocol includes time-resolved rheometry (Rheol Acta 33:385-397, 1994) and rescaling of data (Rheol Acta 45:331-338, 2006). Acknowledgment: NSF support through CBET-0651888.
Citation InformationH Henning Winter, X. L Wang, G. J Xue and P. Sun. "Distinct Dynamics Pattern during the Ripening of Nanocomposite Gels" Polymer Preprints Vol. 50 Iss. 2 (2009)
Available at: http://works.bepress.com/hhenning_winter/8/