Aging effect dynamics

The three polymers studied display remarkable physical aging effects [24], with a strong increase of modulus and changes in the location and intensity of the glass transition. This phenomenon is exemplified in Fig. 17 where the changes of dynamic moduli in a PDEB sample aged for 14 months are very apparent. 

Yamaguchi, M., K. Ozaka, and Y. Suketa. 1989a. Alteration in bone metabolism with increasing age effects of zinc and vitamin D3 in aged rats. Jour. Pharmacobio-Dynamics 12 67-73. 

The formation of an adsorbed surface layer is not an instantaneous process but is governed by the rate of diffusion of the surfactant through the solution to the interface. It might take several seconds for a surfactant solution to attain its equilibrium surface tension, especially if the solution is dilute and the solute molecules are large and unsymmetrical. Much slower ageing effects have been reported, but these are now known to be due to traces of impurities. The time factor in adsorption can be demonstrated by measuring the surface tensions of freshly formed surfaces by a dynamic method for example, the surface tensions of sodium oleate solutions measured by... 

The aim of this chapter is to show how the concepts of FDT violation and effective temperature can be illustrated in the framework of the above quoted system, as done experimentally in Ref. 12 and theoretically in Refs. 15-19. We do not discuss here the vast general domain of aging effects in glassy systems, which are reviewed in Refs. 2-4. Since the present contribution should be understood by beginners in the field, some relevant fundamental topics of equilibrium statistical physics—namely, on the one hand, the statistical description of a system coupled to an environment and, on the other hand, the fluctuation-dissipation theorem (in a time domain formulation)—are first recalled. Then, questions specifically related to out-of-equilibrium dynamics, such as the description of aging effects by means of an effective temperature, are taken up in the framework of the above-quoted model system. 

When out-of-equilibrium dynamic variables are concerned, as will be the case in the following sections of this chapter, the equilibrium fluctuation-dissipation theorem is not applicable. In order to discuss properties such as the aging effects which manifest themselves by the loss of time translational invariance in... 

A. Mauger and N. Pother, Aging effects in the quantum dynamics of a dissipative free particle Non-Ohmic case. Phys. Rev. E 65, 056107 (2002). 

A modulus value increase upon storage under ambient conditions is also reported for other semi-crystalline polymers like, for instance, polypropylene. Struik [11] measured for PP a continuously increasing dynamic stiffness at 20°C in combination with a decrease of the intensity of the glass-rubber (S) transition of PP (the temperature location of the S-transition did not change). Struik called this phenomenon an amorphous phase ageing effect a densification process of the amorphous PP phase due to a free volume relaxation effect. 

It is generally the case that when a system is driven out of thermodynamic equihbrium, its dynamical properties exhibit ageing effects. This means that quantities that at equilibrium were time independent now become functions of time. Time correlation functions, which at equilibrium only depend on a time... 

Dynamic Mechanical Analysis (qv) (DMA) or dynamic thermal mechanical analysis (DTMA) indicate damage in polymers or PMC (34), and aging effects in polymers by a shift in the transition temperature (35). Limitations are the volume of the test chamber or the required specimen shape. 

Coating mechanical properties can be affected by the degree of cure, aging effects, and ambient conditions (e.g. temperature and humidity), making it difficult to establish a useful database. Moreover, organic coatings are viscoelastic, so that their properties depend on strain rate and temperature. A complete treatment of viscoelastic theory is beyond the scope of this chapter, and the interested reader is referred to Chapter 12 of this volume for a more complete discussion. The reader may also wish to consult refs. [1,2], which are review articles of transient and dynamic methods of coating characterization. 

Dynamic relaxation phenomena of the double layer upon contact (aging effects) due to ion migration along the surface or Ifom one surface to another these processes are, again, expected to appear for polymeric colloids having the random-coil structure. 

Fatigue is a collective concept for processes that take place (especially in metallic materials) under repeated, cyclic mechanical and/or thermal loading which typically impair the functionality of the component part as loading proceeds. In plastics, the concept of fatigue involves the aging effects of dynamic loads, such as crack formation and propagation as well as the associated fatigue structures. 

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