Stress conformational changes

In other cases the conformational changes are small, but in the sense of lengthening of the unit height in the chain conformation. This has been for instance, recently observed for s-PB. The transition from form I (s(2/l)2 helices) toward form II (s(5/3)2 helices (see Sect. 2.2) occurs under tensile stress and involves only... 

Exchange of counter-ions (and solvent) between the polymer and the solution in order to keep the electroneutrality in the film. In a compacted or stressed film, these kinetics are under conformational relaxation control while the structure relaxes. After the initial relaxation, the polymer swells, and conformational changes continue under counter-ion diffusion control in the gel film from the solution. 

OLED on an Al-PET substrate. The device performance does not deteriorate after repeated bending, suggesting that there is no significant stress-induced change in the characteristics of the OLEDs fabricated on PET foil [71,82]. The results demonstrate the feasibility of fabricating flexible displays using a variety of plastic substrates including metal-laminated plastic foils, or a metal film sandwiched between two plastic foils. The flexible device structures enable a display to conform, bend, or roll into any shape and thus make possible other product concepts. 

The stress-optical coefficient of PE networks is calculated, and results are compared with experimental data. Observed temperature coefficients of AT and the optical anisotropy for unswollen samples are much larger than those calculated using acceptable values of E(g), the energy of the gauche conformation, relative to that of Vans. It is concluded that observed temperature coefficients should Include some contributions other than those implied in the theory, i.e., those arising from the conformational change with temperature. 

The first conformational changes occur at the end of the purely elastic behaviour, corresponding to a stress value a. By applying higher and higher... 

In the temperature range where side group motions occur, leading to a secondary transition like the ft transition of PMMA, these motions soften the surrounding of the moving units and, consequently, allow local conformational changes of the main chain under a lower stress than in the low temperature case. In the case of the ft transition of PMMA, on the low temperature side, the ester group n-flips are localised and the mechanism above described operates. 

Regarding the effect of physical ageing, the associated densification hinders the intramolecular ft-a cooperativity (as discussed in [1], Sect. 8.1.3). This makes the conformational changes more difficult and, so, require a larger stress. The resulting increase of ay corresponds to the situation encountered at a temperature shifted downward by 20 °C. The physical ageing densification does not influence the plastic flow stress. The reason is that the plastic flow happens in a material that has been strained, and it is known that strain induces a disappearance of the physical ageing effects, this is called rejuvenation . 

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