ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Thermoelastic measurements conducted at constant pressure on systems of fixed composition must be corrected to constant volume in order to achieve the desired resolution of the stress into its energy and entropy components. In the case of simple elongation deduction of the energy component f9 =(∂E/∂L)T,V = [∂(f/T)/∂(1/T)]L,Vof the tension f from measurements at constant pressure requires the equation of state p(T, V, L), or equivalent information. If the system is a polymer network swollen with a diluent or a diluent mixture, and equilibrium is maintained with a surrounding diluent phase, additional complications may arise from changes in composition with deformation and/or temperature. If, however, the diluent mixture is so chosen as to render the equilibrium volume of swelling independent of temperature, then, as we have pointed out previously, fe may be equated to the coefficient = [∂(f/T)/∂(1/T)]L,p,eq, which may be determined directly from measurements on the system maintained in equilibrium with excess diluent. The basis for this simplification is set forth in detail. The conversion of measurements conducted at constant pressure to constant volume is obviated by this procedure, and a simple means is provided for evaluating the internal energy changes accompanying distortion of a polymer network and the concurrent orientation of the chains of which it is composed. Allegations that the indicated procedure is invalidated by disregard of changes of composition of the network phase with temperature and deformation are unfounded. Inconsistencies in recent publications on the analysis of thermoelastic data for networks in swelling equilibrium are pointed out.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1962.1206017009
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