Polymers, conformation ionic

The ionic strength of the solution also significantly influences polyelectrolyte adsorption. In general, the higher the ionic strength of the medium, the less extended and the more coiled the polymer conformation becomes (due to preferential interaction with counter ions in solution rather than with other segments of the polymer chain). The coiled polymer becomes more accessible to the internal porous structure and adsorption is increased. However, for the same reason, it is less influential on the surface charge. 

Counterion effects similar to those in ionic chain copolymerizations of alkenes (Secs. 6-4a-2, 6-4b-2) are present. Thus, copolymerizations of cyclopentene and norbomene with rhenium- and ruthenium-based initiators yield copolymers very rich in norbomene, while a more reactive (less discriminating) tungsten-based initiator yields a copolymer with comparable amounts of the two comonomers [Ivin, 1987]. Monomer reactivity ratios are also sensitive to solvent and temperature. Polymer conformational effects on reactivity have been observed in NCA copolymerizations where the particular polymer chain conformation, which is usually solvent-dependent, results in different interactions with each monomer [Imanishi, 1984]. 

The molecular conformation of a macromolecule is one of the fundamental physical properties of polymers, since it controls macroscopic properties, such as viscosity or solubility. There have been many attempts to stimulate reversible changes in polymer conformation under controlled and reproducible conditions in order to create responsive polymers. One approach is to induce a structural change in photosensitive groups incorporated into the polymer chains, such as a trans-cis isomerization. Another method is to generate ionic charges along the polymer chains. The repulsive interactions thus created force the chain to adopt a different conformation. 

Hydrophobic associations can dominate polymer conformation in solution and solution rheological properties. Intrinsic viscosity and Huggins interaction coefficients provided information on the conformation and intramolecular aggregation behavior of these polymers in dilute solution. The presence of hydrophobic associations caused a decrease in the intrinsic viscosity and an increase in the Huggins constant. These effects could be counterbalanced by increasing the ionic charge on the polymer through hydrolysis or by copolymerization with sodium acrylate. 

The conformations of charged (regular) star-burst polymers (flexible ionic dendrimers), were analyzed theoretically in [33]. Referring to Fig. 4a, relevant architectural parameters for a star-burst polymer are the number of generations. 

The change in polymer conformation from order to disorder or helix to coil occurs at a specific transition or melting temperature (T ). Many researchers have attempted to establish the relationship between T and the ionic strength. Ash et al. formulated the following equation [25] ... 

Bridging flocculation of charged particles is enhanced by iuCTeasing the ionic strength (i.e., reducing k ). In the aggregates thus formed, the particles are not in direct contact with each other. Their separation compares with the polymer layer thickness because closer separation would be detrimental to the polymer conformational entropy and, hence, causes Gbr(/t) to become less negative. 

Oxidation processes have not yet been considered, since they are complicated by polymer conformational relaxation processes and the low electronic conductivity of the starting fully reduced state. Other workers have considered ionic diffusion through the thickness of a PPy.C104 film during oxidation [50], but these results cannot be directly compared with Smela et al. because in one case the anion is dominant and in the other case the cation is dominant. 

The polymerization of optically active acetals and vinyl acrylamides has been described but only in a few cases. Poly-[(-)-7V-propyl-7V-phenylethyl-acrylamide] and poly-[(+)-A -methyl-A -phenyl-ethyl-acrylamide] (VIII) of different tacticity were prepared by Schultz and Kaiser [18] from the corresponding monomers using radical or ionic initiators. No assumptions on polymer conformation in solution have been made. 

Major questions concerning the differences between small and big molecules and between natural and synthetic polymers oriented a part of the effort to verify the existence or nonexistence of ordered polymer conformations and of molecular or ionic interactions. 

Ionic strength of medium, surface structure and non-spherical particles can affect diffusion speed of particles. The thickness of the electric double layer (Debye length) changes with the ions in the medium and the total ionic concentration. An extended double layer of ions around the particle results from a low conductivity medium. So, the diffusion speed reduces and hydrodynamic diameter increases. The diffusion speed can be affected with a change in surface area. The diffusion speed will reduce with an adsorbed polymer layer. Polymer conformation can alter the apparent size. 

Figure 26. An electric (ionic) pulse arrives from the brain through a nerve to the muscle, where it triggers conformational changes in proteins and chemical reactions. All the processes are three-dimensional. The generator (brain) is at the same time an ionic conductor. (Reprinted from T. F. Otero in Polymer Sensors and Actuators, Y. Osada and D. De Rossi, eds., Fig. 1, p., 19. Copyright 19XX. Reprinted with permission of Springer-Verlag.)...

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