R.J.J. Jongschaap

A new transient network model for associative polymer networks

A new model for the linear viscoelastic behavior of polymer networks is developed. In this model the polymer system is described as a network of spring segments connected via sticky points (as in the Lodge model). [Lodge, A. S., “A network theory of flow birefringence and stress in concentrated polymer solutions,” Trans. Faraday Soc. 52, 120–130 (1956).] An important extension (with respect to previous models) is that chain connectivity is taken into account. All segments that are located in between connected stickers are supposed to carry stress. The attachment and detachment of stickers is described with kinetic equations in which activation energies play a role. Simultaneous transitions involving groups of stickers are allowed. The model shows a strong dependence upon the number of segments per chain. Broad relaxation spectra can be obtained. The storage modulus can have more than one plateau corresponding with the fact that stress relaxation may need the breakup of several bonds.

Generalized Rouse model for a dilute solution of clustered polymers

A theory analogue to tha of Rouse is given, to describe the rheological behavior of dilute solutions consisting of clusters of crosslinked polymers. The frequency-dependent behavior of the dynamic moduli of these fluids differs substantially from that of the well-known Rouse-like fluid (G′∼G′∼ω1/2). In our case the storage modulus becomes proportional to ω3/2, while the loss modulus is proportional to ω. The loss modulus dominates the dynamic behavior for frequencies smaller than the largest normal frequency of the clusters.

A new transient network model applied to guar gum

Guar gum is a linear polymer with associative sites which can connect and disconnect reversibly. Experimental visco-elastic moduli showed two storage modulus plateaus, a broad relaxation spectrum and partial time temperature superposition.