Relaxation of polymers

Plasticization and Other Time Effects Most data from the literature, including those presented above are taken from experiments where one gas at a time is tested, with Ot calculated as a ratio of the two permeabihties. If either gas permeates because of a high-sorption coefficient rather than a high diffusivity, there may be an increase in the permeabihty of all gases in contact with the membrane. Thus, the Ot actually found in a real separation may be much lower than that calculated by the simple ratio of permeabilities. The data in the hterature do not rehably include the plasticization effect. If present, it results in the sometimes slow relaxation of polymer structure giving a rise in permeabihty and a dramatic dechne in selectivity. 

She et al. [128] used rolling contact to estimate the adhesion hysteresis at polymer/oxide interfaces. By plasma oxidation of the cylinders of crosslinked PDMS, silica-like surfaces were generated which could hydrogen bond to PDMS r olecules. In contrast to unmodified surfaces, the adhesion hysteresis was shown to be larger and proportional to the molecular weight of grafted polymer on the substrate. The observed hysteresis was interpreted in terms of the orientation and relaxation of polymer chains known as Lake-Thomas effect. 

This averaging process somewhat obscurses the relationship between Pf and S(Q,t). For many relaxation processes, however, where the quasi-elastic width varies with power laws in Q, the smearing of (12) is of no practical importance. For example, for internal relaxation of polymers in dilute solution, we have S(Q, t) = S(Q2t2/3) [34]. Since Q varies with /X and t with 3, the wavelength dependence drops out completely. For illustration, Fig. 3 shows a technical... 

When this model is applied to the interpretation of spin relaxation of polymers in solution the extent of cooperation motion can he measured hy a parameter R = (W /Wb) / which is found to take on values from 1 to 50. If a bond is the smallest moving unit, then R, called the "range", corresponds approximately to the number of bonds Involved in cooperative or coupled motion ( ). Both Wg and are strongly temperature dependent and vary non-monoton-Ically with temperature which appears to complicate this simple identification of R. 

Maxwell element or model Model in which an ideal spring and dashpot are connected in series used to study the stress relaxation of polymers, modulus Stress per unit strain measure of the stiffness of a polymer, newtonian fluid Fluid whose viscosity is proportional to the applied viscosity gradient. 

Einaga.Y., Osaki.K., Kurata,M., Kimura,S.,Tamura,M. Stress relaxation of polymers of polymers under large strain. Polymer J. (Japan) 2,550-552 (1971). See also Polymer J. (Japan) 5,91-96 (1973). 

This is the motion of short sections of main chains which seems to be virtually independent of the free volume (density) of polymers. Such a local residual mobility is the only possible cause of secondary relaxations of polymers without side chains12. It manifests... 

Since 13C relaxation of polymers has already been reviewed (Schaefer, 1974) we can restrict ourselves here to a few general remarks and to more recent papers in this field. Although i3C relaxation in polymers is generally dominated by dipolar relaxation, the NOE factors do not reach the maximum of tj = 2 commonly observed for small molecules. This is due to the fact that polymers usually do not satisfy the extreme narrowing limit only for which this NOE maximum is valid. In this case it is helpful to compare H relaxation data (Cutnell and Glasel, 1977). 

L. Monnerie, Segmental orientation and chain relaxation of polymer by spectroscopic techniques A molecular approach to polymer viscoelasticity, in Developments in Oriented Polymers - 2,1. M. Ward, ed., page 199, Elsevier Applied Science, London and New York (1987). 

Although the microscopic theory remains to be the real foundation of the theory of relaxation phenomena in polymer systems, the mesoscopic approach has and will not lose its value. It will help to understand the laws of diffusion and relaxation of polymers of various architecture. The information about the microstructure and microdynamics of the material can be incorporated in the form of constitutive relation, thus, allowing to relate different linear and non-linear effects of viscoelasticity to the composition and chemical structure of polymer liquid. 

Baumgaertel M, Schausberger A, Winter HH (1990) The relaxation of polymers with linear flexible chains of uniform length. Rheol Acta 29(5) 400—408... 

Broadband Dielectric Spectroscopy provides a direct experimental access to the molecular relaxations of polymers over a broad frequency and temperature range. It is also especially suitable for the investigation of thin polymer films, because it does not suffer sensitivity loses with decreasing sample amount. This technique does require a special sample preparation for thin films, because of the need to have metal electrodes and good electrical contacts at both interfaces. Spin-coating, one of the most commonly employed methods for the preparation of... 

VII. Molecular Motion and Magnetic Relaxation of Polymers in Solution... 

Rheology of various polymer layered-silicate nanocomposites - intercalated, exfoliated and end-tethered exfoliated (prepared by in-situ polymerization from reactive groups tethered to the silicate surface), have been performed in a conventional melt-state rheometer in both oscillatory and steady shear modes. These experimental studies have provided insight into the relaxation of polymer chains when confined by the layers of inorganic silicates, as well as the role of shear in orienting the layered nanocomposites. 

The effect of entanglements on the relaxation of polymer chains is illustrated in Fig. 3-22, which shows the storage modulus G for a series of polystyrene melts of differing... 

In this paper we will concentrate on the diffraction techniques (SANS and reflectometry), and hence static measurements. However, it should be pointed out that through inelastic scattering, aspects of polymer dynamics are accessible. In particular, it has been possible to access single chain dynamics in bulk systems, deformation and relaxation of polymer melts under shear, shed new light on viscoelasticity in polymer melts, and obtain direct information on polymer reputation and particle fluctuations. 

Ct break point at 54°C. This temperature may correspond to the transition temperature (Tg) attributable to the local mode relaxation of polymer main chains. A long alkyl substituent at the nitrogen atom of the indoline moiety enhances the effect of local mobility of polymer chains on the thermal reversion. 

The stress relaxation of polymer networks on long time scales is believed to be due to arm retraction of dangling ends (Fig. 7.7). The polydispersity of dangling ends is determined during crosslinking. Assume the number fraction distribution of linear dangling ends [Eq. (1.52)]... 

Ray, S.S. Okamoto, M. Polymer/layered silicate nanocomposites a review from preparation to processing. Prog. Polym. Sci. 2003,28, 1539-1641. Manias, E. Kuppa, V. Yang, D.K. Zax, D.B. Relaxation of polymers in 2nm slit-pores confinement induced segmental dynamics and suppression of the glass transition. Colloids Surf. A 2001, 187-188, 509-521. 

The work discussed here has related not only to structure relationships but also to means of protection of the macromolec-ular material and the protective functions of these materials. There are many modes of failure, by chemical reaction, failure by fracture, environmental stress cracking and creep. Further there are complicating interactions arising from chemical reaction during relaxation of polymer networks, and in multiphase polymer systems and cos osites, failure at interfaces by adhesive failxire or stress-stress dilation. 

Deformation such as drawing, compression, annealing, strain, creep and stress relaxation of polymers including fibers may produce quite different orientational behavior, the results of which can be examined with solid-state NMR from both the static and dynamic viewpoints. The accurate model produced on the basis of atomic resolution of the local structure and the local dynamics can be built up in order to interpret the mechanical properties of polymers and the deformation mechanisms. 

M. Tasaka, O. Sekiguchi, M. Urahama, T. Matsubara, R. Kiyono and S. Suzuli, Relaxation of polymer chains dissolved in the liquid phase of membranes under a pressure gradient, J. Membr. Sci., 1990, 48, 91-102. 

Priestley RD, Ellison CJ, Broadbelt LJ, Torkelson JM (2005) Structural relaxation of polymer glasses at surfaces, interfaces, and in between. Science 309 456-459... 

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