Viscoelastic spectrum entanglement

Chompff and Duiser (232) analyzed the viscoelastic properties of an entanglement network somewhat similar to that envisioned by Parry et al. Theirs is the only molecular theory which predicts a spectrum for the plateau as well as the transition and terminal regions. Earlier Duiser and Staverman (233) had examined a system of four identical Rouse chains, each fixed in space at one end and joined together at the other. They showed that the relaxation times of this system are the same as if two of the chains were fixed in space at both ends and the remaining two were joined to form a single chain with fixed ends of twice the original size. 

Entanglements among component-two s chains will eventually occur as W2 increases above a certain point. As they occur, the constraint effect due to entanglement will render the spectrum in the low-frequency region where the main viscoelastic response of component two occurs no longer described by the Rouse theory. Assuming that entanglements never did occur to... 

The system can be further characterised by measurement of the mechanical spectrum at a strain within the linear viscoelastic region defined by the strain sweep. Here the storage (G ) and loss (G") modulus, and complex viscosity (r) ) are measured as a function of frequency (u)) and plotted on double logarithmic plots. Typical mechanical spectrum of entanglement solutions are shown in Figure 2.9. 

Relaxation of Single and of Entangled Macromolecules. In the absence of hydrodynamic interactions (HI) the normal modes of a polymer are Rouse modes, which act as overdamped harmonic oscillators. With HI the Rouse modes are still nearly normal modes, but the relaxation spectrum is modified. The HI are screened in semidilute solutions. At higher concentrations and in bulk disentanglement by reptation and tube renewal dominate slow viscoelastic processes. 

In aqueous cold alkali, chitin also dissolves and behaves as a macromolecular solution, as verified by its mechanical spectrum when tested by small-deformation oscillatory measurements. At 4°C and 1.5% (w/w) the system could be described as a transparent sol phase with a viscoelastic response characteristic of an entangled concentrated network, which is comparable to the spectrum exhibited by chitosan (in 0.1 mol acetic acid), but no yield stress is... 

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