Chains, conformations neutral

The behavior of poly-methacrylyl-glutamic acid, which is similar to that of poly-acrylyl-glutamic acid, was interpreted on the basis of the changes in the main chain conformation, which depend on the percentage of neutralized carboxyl groups. 

Figure 2. Schematic representation of chain conformation in the micelles for neutralized diacid and tetracid polyesters.

Neutralizing these polyesters with different hydroxyamines made it possible to obtain stable micellar systems. The size of these micelles was shown to essentially be a function of the structure and the polyester molecular weight. The smallest micelles are obtained with diacid polyester of lower molecular weight. A model for the chain conformation of polyester in a micelle was proposed, taking into account the area occupied by one end group located at the micelle surface. Furthermore, such micelles were demonstrated to be able to solubilize non-neutralized polyester chains, as well as monomers like styrene or butylmethacrylate (BMA). 

All the above-mentioned facts, although many are only qualitatively imderstood, str the importance of chain structure, the nature of side Fig. 7. Dependence of the apparent groups, and of the environment pK on the degree of neutralization of upon chain conformation and, conse-the add poup) for o maleic physicO-chemical... 

The conformation of a polyelectrolyte in solution is known to be highly dependent on the pH and ionic strength of the solution. Previous studies have shown that these also affect ionization of the polar groups and chain conformation of the adsorbed polymer so that thickness, surface roughness and charge density of the polyelectrolyte multilayers become a function of pH and ionic strength of the solutions used for layer-by-layer assembly [85-89]. In fact, SEM pictures of PAH/PSS membranes prepared either from acid or neutral solution, or acid solution in presence of sodium chloride, indicate... 

For c > c, electrostatic interactions no longer perturb the chain conformation, and the solution properties are expected to be similar to that of a semidilute solution of neutral polymers in a good solvent [Colby et al., 1994] In the semidilute entangled neutral polymer regime [Colby et al., 1994],... 

A pronounced bimodal distribution of chain conformations in a micelle that contains about 10 chains is something that one would hardly expect in an equilibrium system, even though bimodal distributions have been tentatively proposed for some other equilibrium polymer systems [145]. To elucidate the studied problem, we performed a series of simulations for modified micellar shells using the MC technique for neutral systems and the combined MC-mean field simulation. The simulations are described later (see Sect. 4.2). 

Since the chain conformation appears as unperturbed in the concentrated solutions, the coil sizes will not depend on the concentration any more. With further increase of concentrations, C 1, and eventually the electrostatic repulsion between charged monomers will be completely screened. In the end, the polyelectrolyte chain will behave like a charge-neutral polymer chain in highly concentrated solutions. Correspondingly, the coil sizes will increase in a sudden, leading to an increase of characteristic relaxation time as well as the intrinsic viscosity, and appearing as a gelation process, as demonstrated in Fig. 4.13 (Dobrynin and Rubinstein 2005). 

Fig. 3.13. Flocculation and stabilisation of suspensions by neutral polymers, (a) Lone particles. The range of electrostatic repulsion has been represented dotted line), (b) When a small quantity of polymer is added, the adsorbed layer remains thin since the chain conformation is highly flattened, (c) When the quantity of polymer is such that the size of loops becomes greater than twice the range of electrostatic repulsion, links can be established between particles. Aggregates form in the solution and precipitate out. (d) The particles are saturated with polymer and repel each other via steric effects, (e) The saturation of particle surfaces by polymers with low molecular weight can favour stability, without increasing the risk of flocculation...

For polyelectrolyte brashes, the chain conformation is governed by the electrostatic interactions between the charged monomer units [56]. At high pH, the amine groups of the polymer chains are deprotonated, and the polymer is considered to be neutral. As a result, the polymer chains tend to attain a collapsed conformation due to the hydrophobic interactions, and the diffusion of the positively charged Ru(NH3)6 is not sterically hindered by the polymer brash, nor is it repelled electrostatically. In contrast, at low pH, the polymer brash becomes protonated and stretches away from the surface as a result of electrostatic repulsions between the charged monomer units and between the polymer chains. The diffusion of Ru(NH3)6 + in this case is blocked as a result of both electrostatic repulsion from the positively charged polymer chains and as a result of the steric hindrance. 

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