Entanglement structures

The relationship between degree of cross-linking and trapping of the entangled structure (the trapping is nearly complete in the present work). 

Thus, the simplified Two-Network experiment shows by a direct comparison of forces at constant length that the trapped entangled structure of a well cross-linked elastomer contributes to the equilibrium modulus by an amount that is approximately equal to the rubber plateau modulus. The modulus contribution from the trapped entangled structure will be less for lower molecular weights and especially at low degrees of cross-linking (14). 

The small values of the quantity 100(f-f )/f prove that chain scission is absent or small for this system. his is important since the interpretation of the experimental results would be difficult or even impossible in the case of substantial chain scission. It should also be stressed that the functionality of the cross-links need not be known, and that a distribution of cross-link functionalities as well as Inhomogeneous cross-linking is unimportant. The reason being that the cross-links merely serve the purpose of trapping the entangled structure. 

The viscoelastic response of polymer melts, that is, Eq. 3.1-19 or 3.1-20, become nonlinear beyond a level of strain y0, specific to their macromolecular structure and the temperature used. Beyond this strain limit of linear viscoelastic response, if, if, and rj become functions of the applied strain. In other words, although the applied deformations are cyclic, large amplitudes take the macromolecular, coiled, and entangled structure far away from equilibrium. In the linear viscoelastic range, on the other hand, the frequency (and temperature) dependence of if, rf, and rj is indicative of the specific macromolecular structure, responding to only small perturbations away from equilibrium. Thus, these dynamic rheological properties, as well as the commonly used dynamic moduli... 

The principle rheological properties which reflect the polymer process dynamics are the loss modulus (C), storage modulus (G"), dynamic complex viscosity (n ), and tan delta parameters. In simplified form the loss modulus describes the viscous or fluid component of viscosity. That is, how easily the molecules can move past each other. The storage modulus describes the elastic or network entanglement structure of the polymers. It is, therefore, sensitive to cross linking, reaction formation and the elastomeric modifiers. The complex dynamic viscosity is the combined effect of both moduli discussed. It, therefore. 

In most cases the elastic response of filled polymers is severely reduced with respect to that of the polymer, though occasionally fillers may form an entangled structure with the melt exhibiting an anomalous elastic response. The study of the flow behavior of polymers filled with interacting particles presents serious complications. A major one is the agglomeration of... 

The unique dependence of Qc on the width of the interface has also been found for interfaces between high molecular weight random copolymers and homopolymers [69,70]. It is apparent from Fig. 40b, however, that while regimes I and II are also observed, the critical width, where the transition from regime I to regime II occurs, varies for different PS-based systems even though the bulk entanglement structure is the same. 

The nonlinear elastic properties can be described by both the Mooney-Rivlin model and the molecularly based slip-tube model. Both of these models stress the fact that the low-strain modulus of the adhesives is controlled by the entanglement structure of the isoprene -i- resin phase, while the high-strain modulus is controlled by the physical crossHnk structure. The incorporation of diblocks in the adhesive dramatically reduces the density of crossHrrks and causes a more pronounced softening in the high-strain part of the stress-strain curve. 

When a flexible, nonaromatic polyamide such as nylon-6,6 is dissolved in a solvent, the chains behave like random coils. As the polyma- concentration increases, these become entangled. Subsequent spinning and drawing produces a fiber in which the chains retain this entangled structure and are only partially extended, thereby reducing their potential modulus and tenacity. In solutions of the rigid, rodlike aramids, random eoil struetures do not form and, instead, the rigid ehains pack in... 

We have talked about different types of polymer molecules. Now it seems the right time to ask how all these various types are actually made, ranging from the simplest linear polymer chain to a polymer network of a complex, densely entangled structure. 

Kim et al. electrochemically deposited PPy on a CNT/silica film substrate using a potential cycling method at room temperature. After removal of silica with hydrofluoric acid (HF), CNT/PPy composites with controlled pore size in a three-dimensional (3D) entangled structure of a CNT film were prepared as electrode materials for a pseudo-capacitor [36]. The pore size of the final CNT/PPy composite film could be controlled by changing the amount of silica in the mixed suspension of CNTs and nanosize silica. The SC of the CNT/PPy composite with 83.4 wt.% PPy was 250 F/g at a potential scan rate 10 mV/s in 1.0 mol/L KCl and it decreased by only 15% to 211 F/g at 500 mV/s. 

---