Polymer confinement

A. Yethiraj, C. K. Hall. Monte Carlo simulation of polymers confined between flat plates. Macromolecules 25 1865-1872, 1990. 

The fraction of polymer confined in the interphase layers was estimated using the empirical formula [60, 61] ... 

A similar effect may exist for hydrophobic interaction between solute and stationary phase, as one solute may adsorb more strongly to the stationary phase than another. It has also been remarked that a flexible polymer confined to a pore should be at a lower entropy than one in bulk solution, leading to exclusion in excess of that expected for a simple geometric solid.23 Even in the absence of interactions, a high concentration of a small component can lead to an excluded volume effect, since the effective volume inside the pore is reduced. 

Scheme 5.2 Wolfand lamb stoichiometric benzoylation ofy-butryrolactone using two polymer-confined reagents [17].

The behavior of polymers confined between surfaces is of importance in a number of problems of practical interest. These include polymer processing,... 

This chapter is concerned with the application of liquid state methods to the behavior of polymers at surfaces. The focus is on computer simulation and liquid state theories for the structure of continuous-space or off-lattice models of polymers near surfaces. The first computer simulations of off-lattice models of polymers at surfaces appeared in the late 1980s, and the first theory was reported in 1991. Since then there have been many theoretical and simulation studies on a number of polymer models using a variety of techniques. This chapter does not address or discuss the considerable body of literature on the adsorption of a single chain to a surface, the scaling behavior of polymers confined to narrow spaces, or self-consistent field theories and simulations of lattice models of polymers. The interested reader is instead guided to review articles [9-11] and books [12-15] that cover these topics. 

The diffusion of the electroactive ions is both physical and due to electron transfer reactions.45 The occurrence of either or both mechanisms is a function of the electroactive species present. It has been observed that the detailed electrochemical behaviour of the electroactive species often deviates from the ideal thin film behaviour. For example, for an ideal nemstian reaction under Langmuir isotherm conditions there should be no splitting between the anodic and cathodic peaks in the cyclic voltammogram further, for a one-electron charge at 25 °C the width at half peak height should be 90.6 mV.4 In practice a difference between anodic and cathodic potentials may be finite even at slow scan rates. This arises from kinetic effects of phase formation and of interconversion between different forms of the polymer-confined electroactive molecules with different standard potentials.46... 

The model was developed with the following hypothesis (Scheme in Fig. 6-11) At the metal polymer-interface (y = 0), we assume a Butler-Volmer kinetics for the polymer confined redox couple P/Q. 

Temperature distribution in a polymer confined in a narrow-gap Couette device. 

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]. 

In addition to familiar phenomena such as these, new phenomena arise because of the synergism between the properties of the polymer and those of the particle filler. One such synergistic effect is enhanced shear thinning, which occurs because the shear rate experienced by the polymer confined between two particles can be much larger than the overall imposed shear rate (Khan and Prud homme 1987). Another general observation is that the filled melt is often effectively less elastic than the polymer alone, evidently because the filler enhances the viscosity more than it does the first normal stress difference Ni (Han 1981 Han et al. 1981). Thus, Fig, 6-38 shows that at fixed shear stress the first normal stress difference Nj for polypropylene decreases upon addition of CaC03 particles. ... 

In Chapter 3, we will learn that a linear polymer confined to an air-water interface is a fractal object with fractal dimension T> — 4/3. What is the ratio... 

In Ref. [40], the onset of polymer confinement is discussed, which leads to a higher sensitivity of the polymer effect. Although this effect is real, we do not want to discuss details in the context of bicontinuous microemulsions. For our purpose it should be mentioned that if the polymer and the domains resemble in size the polymer effects are enforced. 

Nakaya, K., Imai, M., Komura, S., Kawakatsu, T. andUrakami, N. (2005) Polymer-confinement-induced nematic transition of microemulsion droplets. Europhys. Lett., 71, 494-500. 

Figure 2.30. Backbone of side chain liquid crystalline polymer confined between smectic layers. (From Finkehnann, 1991. Reproduced by permission of John Wiley Sons, Inc.)...

C. B. Roth and J. R. Dutcher, Hole growth as a microrheological probe to measure the viscosity of polymers confined to thin films. J. Polym. Sci. B 44, 3011 (2006). 

In a dynamic experiment, a small-amplitude oscillatory shear is imposed to a molten polymer confined in the rheometer. The shear stress response of the polymeric system can be expressed as in Equation 22.14. In this equation, G and G" are dynamic moduli related to the elastic storage energy and dissipated energy of the system, respectively. For a viscoelastic fluid, two independent normal stress differences, namely, first and second normal stress differences can be defined. These quantities are calculated in terms of the differences of the components of the stress tensor, as indicated in Equation 22.15a and 22.15b, and can be obtained, for instance, from the radial pressure distribution in a cone-and-plate rheometer [5]. Some other experiments used in the determination of the normal stress differences can be found elsewhere [9, 22] ... 

In highly interactive polymer-particle systems, solidlike yield behavior can be observed even at temperatures above the glass transition temperature of the polymer [54]. Polymer molecules can adopt stretched configurations that allow them to adsorb to the surfaces of many particles. Relative motion between polymer chains is retarded by immobilization due to polymer confinement between nanoparticle surfaces. The equilibrium thickness of the immobilized polymer layer is of the order of the radius of gyration of the molecule. Eiller particles can be regarded as hard cores surrounded by immobilized polymer shells of comparable size. 

Zimmerman et al. were the first to have synthesised a dendrimer imprinted with a porphyrin derivative using the sacrificial spacer methodology a single cavity within a single polymer confinement structure [30]. 

Napolitano S, Wiibbenhorst M (2011) The lifetime of the deviations from bulk behaviour in polymers confined at the nanoscale. Nat Commun 2 260... 

P. Chen, J. Zhang, and J. He. Morphology evolution of a liquid crystalline polymer confined by highly packed glass beads in polycarbonate. Polymer, 46(18) 7652-7657, August 2005. 

Volume versus temperature Dilatometry (polymer confined by mercury)... 

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