Entanglement network Subject

Lack of steady flow of a liquid-bearing colloidal solution requires the existence of a space-filling, three-dimensional structure. As we might select a perfect crystal as a csuionical solid, or liquid argon as a prototypical liquid, we csui choose the covalently crosslinked network, without any entanglements, to represent the ideal gel state. Then an appropriate time scale for reversible gels would be the lifetime of a typical crosslink bond if subjected to conditions that would cause flow in a pure... 

Analysis of networks in terms of molecular structure relies heavily on the kinetic theory of rubber elasticity. Although the theory is very well established in broad outline, there remain some troublesome questions that plague its use in quantitative applications of the kind required here. The following section reviews these problems as they relate to the subject of entanglement. 

The poled and cured film of the polyimide/ASD has NLO coefficient, d33, of 28 pmAf-This d33 value is comparable to that of lithium niobate. The temporal stability at 25 and 120 °C of the second-order nonlinearity after poling and curing of the polyimide/ASD is demonstrated in Figure 3. The sample shows excellent temporal stability at room temperature. In contrast to the stability of a poled/cured ASD sample which showed a rapid decay of the d33 value at 100 °C,20 the poled/cured polyimide/ASD sample shows a stable d33, after an initial reduction of 27%, as it is subjected to a thermal treatment at 120 °C for over 168 h. The existence of polyimide in the ASD network shows a tremendous improvement in the temporal stability. This synergistic property is a result of high Tg of polyimide and the chain entanglement between the two polymers in the composite. 

Meanwhile, developments in polymer science established that most long-chain linear polymers above their glass-transition temperatures can also exhibit rubberlike behavior whereby a network of molecular entanglements can serve the function of chemical cross links for deformation histories with oscillation periods shorter than the relaxation times of entanglement drift. It is this form of behavior of glassy polymers resembling that of rubbers which is a subject of principal concern and is discussed in Section 6.7. 

A discussion of this subject is presented below. The additional oMitribution GX is said to arise from permanently trapped (inter-chain) entanglements in the network. Linear polymers of high molecular wd t exhibit a storage modulus G (constant over a wide range of frequencies This plateau modulus... 

Equilibrium stress-strain data on bulk samples were difficult to obtain because of the aforementioned problems. Therefore, the behavior of PBD networks in which the fluctuations of the junctions are highly constrained was explored with Network D-1, which is highly cross-linked. Although the junctions in highly cross-linked networks are subject to smaller relative constraint from entanglements, these junctions will remain highly constrained. Measurements on samples swollen with hexa-decane eliminate the problem of equilibrium and provide a measure of this limit the experimental data exhibit large departures from phantom behavior. But these departures are within the framework of the theory Network D-1 exhibits affine-like behavior. 

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