Aging viscoelastic properties

The effect of aging and of process variables on the rheological properties of solid proplnts has been the subject of mechanical shear relaxation spectroscopy (Ref 4). The technique is of interest to such filled polymer systems generally in that anisotropy in the viscoelastic properties can be readily observed... 

Several studies have been published where different aspects of the solid state behavior of nonlinear block copolymers (like the adhesive properties, viscoelastic properties after aging and solvent treatment, thermal properties, etc.) vary with varying architectures [367-373]. Much work has still to be done in order to understand the structure-property relationship of these complex macromolecules. 

However, for chemical sensing applications these generally sealed devices have to be opened and their surface functionalized with a chemically sensitive coating. Just open the case reduces the quality factor, Q, by 1/3, and the aging is 100-1000 times larger [6]. Viscoelastic properties of macromolecular coating materials can have a strong impact on the vibration behavior of the crystal and diminish the Q factor. 

Learoyd, B.M., and Taylor, M.G. 1966. Alterations with age in the viscoelastic properties of human arterial walls. Circ. Res. 18 278. 

A schematic representation of a creep experiment is given in Fig. 13.11. Similar to enthalpic relaxation measurements, in a creep test the sample is quenched from above Tg to the annealing temperature T. A series of short (typically less than 10 % of the aging time ta) load-unload tests are performed. As shown in Fig. 13.11, the applied stress, a, is constant and the time-dependent response, the strain, is measured following both load and unload steps. Because times fe during which creep response is measured are kept deliberately short, the creep response gives a snapshot of the viscoelastic properties of the material at a particular aging time. 

DMA Measurement of viscoelastic properties of solid materials as a function of temperature and time Glass transition, brittleness, anisotropy, crystallinity, residual stress, residual cure, and aging. 

Mahomed, A., Hukins, D. W. L., Kukureka, S. N. Shepherd, D. E. T. (2010a) Effect of accelerated aging on the viscoelastic properties of ElastEon a polyurethane with soft poly(dimethylsiloxane) and poly(hexamethylene oxide) segments. Materials Science and Engineering C, 30, 1298-1303. 

Saber-Sheikh, K., Clarke, R. L. Braden, M. (1999) Viscoelastic properties of some soft lining materials. II Ageing characteristics. Biomaterials, 20, 2055-2062. 

Wagner, W. C., Kawano, R, Dootz, E. R. Koran, A. (1995) Dynamic viscoelastic properties of processed soft denture liners. Part 2. Effect of aging. Journal of Prosthetic Dentistry, 74, 299-304. 

In this article on physical aging, the phenomena associated with structural recovery and physical aging are described, starting with discussion of volume recovery, enthalpy recovery, viscoelastic properties, and failure. There are more in-depth reviews of the phenomena and models associated with the glass transition... 

On the other hand, when the effects of aging on calcium sulfate-filled PLA composites were studied for 1 year under a normal environment, molecular, thermal, and viscoelastic properties showed that the performance of the PLA-calcium sulfate composites was maintained after aging [25]. The storage modulus of the samples actually increased after aging. The structural reorganization of the PLA material in terms of increase of local order in the amorphous phase of PLA was thought to be responsible for such behavior. 

In 90% of patients, skin elasticity was improved by 10-12% on average compared to initial value and remained at this level for 3 months after procedure completion. The ageing skin is known to feature reduced viscoelastic properties as a result of qualitative and... 

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