Matrix elasticity, polymer

Asloun, El. M., Nardin, M. and Schultz, J. (1989). Stress transfer in single-fiber composites Effect of adhesion, elastic modulus of fiber and matrix and polymer chain mobility. J. Mater. Sei. 24, 1835-1844. 

Two atomistic approaches have been presented briefly above molecular dynamics and the transition-state approach. They are still not ideal tools for the prediction of diffusion constants because (i) in order to obtain a reliable chain packing with a MD simulation one still needs the experimental density of the polymer and (ii) though TSA does not require classical dynamics it involves a number of simplifying assumptions, i.e. duration of jump mechanism, elastic polymer matrix, size of smearing factor, that impair to a certain degree the ab initio character of the method. However MD and TSA are valuable achievements, they are complementary in several... 

So far the micro-mechanical origin of the Mullins effect is not totally understood [26, 36, 61]. Beside the action of the entropy elastic polymer network that is quite well understood on a molecular-statistical basis [24, 62], the impact of filler particles on stress-strain properties is of high importance. On the one hand the addition of hard filler particles leads to a stiffening of the rubber matrix that can be described by a hydrodynamic strain amplification factor [22, 63-65]. On the other, the constraints introduced into the system by filler-polymer bonds result in a decreased network entropy. Accordingly, the free energy that equals the negative entropy times the temperature increases linear with the effective number of network junctions [64-67]. A further effect is obtained from the formation of filler clusters or a... 

Figure 12. Hypothetical increase in the internal osmotic swelling pressure, II, and counteractive polymer matrix elasticity (reflected in an increasing cohesive energy density, E), with increasing water content, n. n0 is the number of moles of water, per ionic sidechain, for which Tl-E = 0 (24).

The neutron bubble detector (trade name BD-IOOR) is a reusable, passive integrating dosimeter that allows instant, visible detection of neutron dose. The bubble detector consists of a glass tube filled with thousands of superheated liquid drops in a stabilizing matrix. When exposed to neutrons, these droplets vaporize, forming visible permanent bubbles in an elastic polymer. The total number of bubbles formed is proportional to the neutron dose equivalent H. The bubbles can be counted manually or by a machine. Figure 16.15 shows the response of the bubble detector as a function of neutron energy. 

As it is known [2, 12], within the frameworks of cluster model the elasticity modulus E value is defined by stiffness of amorphous polymers structure both components local order domains (clusters) and loosely packed matrix. In Fig. 13.3, the dependences E(v J are adduced, obtained for tensile tests three types with constant strain rate, with strain discontinuous change and on stress relaxation. As one can see, the dependences E(yJ are approximated by three parallel straight lines, cutting on the axis E loosely packed matrix elasticity modulus E different values. The greatest value E is obtained in tensile tests with constant strain rate, the least one - at strain discontinuous change and in tests on stress relaxation E = 0 [1]. 

The treatment of amorphous glassy polymers as natural nanocomposites allows to use for their elasticity modulus (and, hence, the reinforcement degree where is loosely packed matrix elasticity modulus) de-... 

The ratio in the left-hand part of Equation 926 should be considered as a reinforcement degree of crosslinked epoxy polymers treated as a natural nanocomposite. Let us note again that a loosely packed matrix is a structure reinforcing element for a crosslinked polymer, unlike for linear amorphous polymers. Nevertheless, for both indicated classes of polymers the reinforcement degree is defined equally, namely as polymer and loosely packed matrix elasticity moduli ratio and in both cases the nanoclusters are assumed as a nanofiller. Confirmation of this postulate can be obtained within the frameworks of the model [50] where three basic cases of the dependence of the reinforcement degree of the composites EJE (where E and E are elasticity moduli of the composite and the matrix polymer, respectively) on filler content (p were considered. It has been shown that the following basic types of the dependence EJ exist ... 

The mechanics of FRC composites is very much dependent on the strength of the matrix, its modulus of elasticity and the fibre-matrix bond. Modification of these characteristics can be particularly useful for optimizing the efficiency of the fibres. A drastic change in the matrix properties can be achieved by combining the matrix with polymers, in various forms. Some attempts have been made to explore this approach, and there are some promising results, but the full potential of this combination is far from being realized. 

In a semicrystalline polymer, the crystals are embedded in a matrix of amorphous polymer whose properties depend on the ambient temperature relative to its glass transition temperature. Thus, the overall elastic properties of the semicrystalline polymer can be predicted by treating the polymer as a composite material... 

The mechanical properties of plastics materials may often be considerably enhanced by embedding fibrous materials in the polymer matrix. Whilst such techniques have been applied to thermoplastics the greatest developents have taken place with the thermosetting plastics. The most common reinforcing materials are glass and cotton fibres but many other materials ranging from paper to carbon fibre are used. The fibres normally have moduli of elasticity substantially greater than shown by the resin so that under tensile stress much of the load is borne by the fibre. The modulus of the composite is intermediate to that of the fibre and that of the resin. 

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