Polymer mobility, confinement effect

A more direct verification of tube/reptation features was possible with systems where the soHd matrix and the mobile polymer chains confined to nanopores are of similar organic chemical composition. In the experiments referred to in the following, Hnear polymers were confined in a solid, that is strongly cross-linked, polymer environment. Under such conditions, the geometry effect can be expected to dominate whereas the wall adsorption phenomenon is of neghgible influence. 

Polymers can be confined one-dimensionally by an impenetrable surface besides the more familiar confinements of higher dimensions. Introduction of a planar surface to a bulk polymer breaks the translational symmetry and produces a pol-ymer/wall interface. Interfacial chain behavior of polymer solutions has been extensively studied both experimentally and theoretically [1-6]. In contrast, polymer melt/solid interfaces are one of the least understood subjects in polymer science. Many recent interfacial studies have begun to investigate effects of surface confinement on chain mobility and glass transition [7], Melt adsorption on and desorption off a solid surface pertain to dispersion and preparation of filled polymers containing a great deal of particle/matrix interfaces [8], The state of chain adsorption also determine the hydrodynamic boundary condition (HBC) at the interface between an extruded melt and wall of an extrusion die, where the HBC can directly influence the flow behavior in polymer processing. 

Hoffmann et al. [2000] demonstrated that the low-frequency modulus of exfoU-ated PS-based nanocomposites was higher than for intercalated nanocomposites. This conclusion was confirmed by Mohanty and Nayak [2007], who studied the effect of the MMT exfoliation in PA-6-based CPNCs. The large increase in contact surface between the two phases resulted in improved mechanical properties. The high aspect ratio, p = 200 to 1000, the high tensile modulus of the inorganic filler E 170 GPa), and the large specific surface area (Asp 150 m /g) all play a role in the confinement of the polymer chain—hence in mobility under stress [Yasmin et al., 2006 Utracki, 2009],... 

The confinement of water in nanometer-size pores between the walls of the polymer material affects the structure of water. The observed freezing-point suppression [49,50] and reduced dielectric constant of water [115-117], are macroscopic manifestations of this effect. The interfacial area between polymer and water provides a complex environment for proton transport. The complications for the theoretical description are caused by the flexibiHty of the sidechains, their random distributions and their partial penetration into the bulk of water-filled pores. The charged polymer sidechains contribute elastic ( entropic ) and electrostatic terms to the free energy [54,55]. Distribution and mobilities of protons depend strongly on the resulting sidechain-water interactions [54,56,118]. 

Compared to Nafion , a stronger confinement of water in the narrow channels of the sulfonated aromatic polymers leads to a significantly lower dielectric constant of the waters of hydration (20 compared to 64 in fully hydrated Nafion [185,186]). Of particular relevance to macroscopic models are the diffusion coefficients of water. As the amount of water sorbed by the membrane increases and molecular-scale effects are reduced, the properties approach those of bulk water on the molecular scale. Figme 26 shows the trend in proton mobility. Da, and water self-diffusion, Dh20. for Nafion and the sulfonated polyetherketone membrane [134]. 

In addition to particle breakup, the coalescence process may be affected as well. It has been speculated that exfoliated clay platelets or well-dispersed nanoparticles may hinder particle coalescence by acting as physical barriers [19,22]. Furthermore, it has been suggested that an immobilized layer, consisting of the inorganic nanoparticles and bound polymer, forms around the droplets of the dispersed phase [50]. The reduced mobility of the confined polymer chains that are bound to the fillers likely causes a decrease in the drainage rate of the thin film separating two droplets [44]. If this is the case, this phenomenon should be dependent on filler concentration this is shown in Figure 2.8, which shows the effect of nanoclay fillers on the dispersed particle size of a 70/30 maleated EPR/PP blend [19]. 

Elmahdy, M. M., Chrissopoulou, K., Afratis, A., Floudas, G., and Anastasiadis, S. H. 2006. Effect of confinement on polymer segmental motion and ion mobility in PEO/layered silicate nanocomposites. Macromolecules 39 5170-5173. 

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... 

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