Polymer dynamics, confined

If concentrated polymer solutions confined in thin film geometry are considered, it turns out that the static properties readily match the theoretic expectations (Fig. 17) whereas the problem with dynamics is more complex [16,17] writing Zgff = -f-1, one expects a corresponding decrease in the... 

A. Milchev, K. Binder. Dynamics of polymer chains confined in slit-like pores. J Physique 7/5 21-31, 1996. 

T. Aoyagi, J. Takimoto, and M. Doi, Molecular dynamics study of polymer melt confined between walls, J. Chem. Phys. 115, 552-559 (2001). 

The static and dynamic properties of polymer-layered silicate nanocomposites are discussed, in the context of polymers in confined spaces and polymer brushes. A wide range of experimental techniques as applied to these systems are reviewed, and the salient results from these are compared with a mean field thermodynamic model and non-equilibrium molecular dynamics simulations. 

In addition to their potential applications, PLS nanocomposites are unique model systems to study the statics and dynamics of polymers in confined environments. Using both delaminated and intercalated hybrids, the statics and dy-... 

Intercalated compounds offer a unique avenue for studying the static and dynamic properties of small molecules and macromolecules in a confined environment. More specifically, layered nanocomposites are ideal model systems to study small molecule and polymer dynamics in restrictive environments with conventional analytical techniques, such as thermal analysis, NMR, dielectric spectroscopy and inelastic neutron scattering. Understanding the changes in the dynamics due to this extreme confinement (layer spacing < Rg and comparable to the statistical segment length of the polymer) would provide complementary information to those obtained from traditional Surface-Force Apparatus (SFA) measurements on confined polymers (confinement distances comparable to Rp [36]. 

As described in the section Nanoscopically Confined Polymer Dynamics, an enthalpic force enables the polymer to penetrate into the clay layer (as shown in Fig. 7A), while the clay acts as a blockade to this penetration. 

The dynamics of molten polymer chains confined between air and a solid and low-molecular probes dissolve in stretched polymers was also studied by H-NMR. Polymer complexes like blends and copolymers have been investigated by H-,... 

In the previous chapter, we discussed the dynamics of a polymer in a fixed network. We shall now discuss the polymer dynamics in concentrated solutions and melts. In these systems, though aU polymers are moving simultaneously it can be argu that the reptation picture will also hold. Consider the motion of a certain test polymer arbitrarily chosen in melts. If the test polymer moves perpendicularly to its own contour, it drags many other chains surrounother hand the movement of the test polymer along its contour will be much easier. It will be thus plausible to assume that the polymer is confined in a tube-like region, and the major mode of the dynamics is reptation. 

McCormick et al. (2003) studied the structure and dynamics of adsorbed water and polymer components in PEM films and the bulk PEC using H MAS NMR spectroscopy. The films (1-5 bilayers) with poly(diallyl dimethylammonium chloride) (PDADMAC) and poly(sodium-4-styrenesulfonate) (PSS) were adsorbed onto colloidal silica particles. Relaxation and line width measurements showed that the adsorbed water is less mobile in the films than in the analogous PEC. This result can be explained by compacting of the adsorption layer at a surface and enhancement of confined space effects for bound water. Relaxation measurements and H double-quantum (DQ) NMR experiments revealed that polymer dynamics in the PEMs was strongly influenced by the layer number and water content (Eigures 5.18 and 5.19). 2D spin... 

Recently, polymer nanocomposites based on clay minerals have attracted great interest from researchers, both in industry and in academia, because they often exhibit concurrent improvement in several properties of neat polymer. These improvements can include high moduli, increased strength and heat resistance, decreased gas permeability and flammability, and increased degradability of biodegradable polymers [7-12]. These materials have also been proven to be unique model systems to study the structure and dynamics of polymers in confined environments [20]. 

Field-cycling NMR relaxometry is a versatile and powerful method for investigating molecular dynamics over a large range of timescales. It has been applied to manifold materials which show broad distributions of molecular motions, for example proteins, liquid crystals, synthetic polymers, and liquids confined in porous materials. Figure 7A represents an example for the investigation of polymer dynamics. The T -dispersion curve in the double-logarithmic scale shows the typical slopes observed in polyethylene oxide melts above the critical molecular... 

Such novel experimental findings have prompted very active theoretical studies of polymer interfaces that encompass both analytical models and simulation methods in order to obtain a fundamental understanding of both the equilibrium and dynamic properties of polymer melts confined by various interfaces. Because of the inherent difficulties encoimtered in analytical approaches, simulations have been the more popular theoretical approach. 

The previous section has emphasized how glass forming polymers under confinement generally exhibit pronounced bulk-like equilibrium dynamics. This is tme in the vast majority of cases, except for those polymers where strong interactions with... 

Discussions on the glass transition of confined polymer systems are often couched in the context of polymer dynamics. Maaoscopically, the glass transition is associated with the... 

---