Ionic polymers polyelectrolytes

Positively or negatively charged indicators can be made lipophilic by ionpairing with surfactants. However, they can also be directly immobilised on the polymer by ion-pairing with ionic polymers (polyelectrolytes) (Table 9). Solutions or suspensions of the polymer are then mixed with aqueous or alcoholic solutions of the dye. 

The most common emulsions used in dermatological therapy are creams. These are two-phase preparations in which one phase (the dispersed or internal phase) is finely dispersed in the other (the continuous or external phase). The dispersed phase can be either hydrophobic based (oil-in-water creams, O/W) or aqueous based (water-in-oil creams, W/O). Whether a cream is O/W or W/O is dependent on the properties of the system used to stabilize the interface between the phases. Given the fact that there are two incompatible phases in close conjunction, the physical stability of creams is always tenuous, but may be maximised by the judicious selection of an appropriate emulsion stabilizing system. In most pharmaceutical emulsions, stabilizing systems are comprised of either surfactants (ionic and/or non-ionic), polymers (non-ionic polymers, polyelectrolytes or biopolymers) or mixtures of these. The most commonly used surfactant systems are sodium alkyl sulphates (anionic), alkylammonium halides... 

It Is nearly odorless powder, and its functional uses are as the thickening agent and stabilizer. Natural gums can be classified according to their origin and as uncharged or ionic polymers (polyelectrolytes). 

Ionic polymers (polyelectrolytes and polyampholytes) constitute an important class of water-soluble maaomole-cules. ° Their monomer units are capable of ionization in polar solvents, for example, in water. The ionization occurs via either dissociation of hydrogen ions H from the acidic groups or dissociation of water molecules and protonation of the basic groups on the polymer chain. The solubility of polyelectrolytes in polar solvents is determined first of all by a huge gain in translational entropy of the counterions. The majority of bio-maaomolecules (proteins, nucleic acids, and polysaccharides) operating in aqueous environment carry ionizable groups (carboxyl, sulfate, amine, etc.) and are included in this class of polymers. 

The conformations adopted by polyelectrolytes under different conditions in aqueous solution have been the subject of much study. It is known, for example, that at low charge densities or at high ionic strengths polyelectrolytes have more or less randomly coiled conformations. As neutralization proceeds, with concomitant increase in charge density, so the polyelectrolyte chain uncoils due to electrostatic repulsion. Eventually at full neutralization such molecules have conformations that are essentially rod-like (Kitano et al., 1980). This rod-like conformation for poly(acrylic acid) neutralized with sodium hydroxide in aqueous solution is not due to an increase in stiffness of the polymer, but to an increase in the so-called excluded volume, i.e. that region around an individual polymer molecule that cannot be entered by another molecule. The excluded volume itself increases due to an increase in electrostatic charge density (Kitano et al., 1980). 

Of the preponderance of small ions, the colligative properties of polyelectrolytes in ionising solvents measure counterion activities rather than Molecular weight. In the presence of added salt, however, correct Molecular weights of polyelectrolytes can be measured by membrane osmometry, since the small ions can move across the membrane. The second virial coefficient differs from that previously defined, since it is determined by both ionic and non-ionic polymer-solvent interactions. 

Hesselink23) attempted to calculate adsorption isotherms for flexible polyelectrolytes. He assumed that, when adsorbed on a surface, a flexible polyelectrolyte takes a conformation consisting of one train and one tail. The theoretical treatment of Hoeve et al.4I) (cf. B.3.1) for non-ionic polymers was extended by taking into account the change in electrical free energy that occurs when the polyelectrolyte is brought from the solution onto the interface. The partition function Q for a system of N polyelectrolytes each consisting of n units, in which Na polyions are adsorbed on the surface of area S and Nf(Nf = N - N ) polyions remain in the bulk solution of volume V, is then represented by... 

Adsorption of polyelectrolytes onto solid surfaces are not yet explored as extensively as that of non-ionic polymers, and most studies are limited to adsorbance measurements. 

Non-ionic polymer gel, swollen with dielectric solvent, can be extremely deformed as is the case for non-ionic polymer plasticised with non-ionic plasticiser. Instead of the charge-injected solvent drag as a mechanism of the gel actuation, the principle is based on local asymmetrical charge distribution at the surface of the gel18. The mechanism can also be applied to non-ionic elastomers in which the motion of the polymer chain is relatively free. In spite of their many difficulties for practical actuators, polyelectrolyte gels and related materials are the most interesting electroactive polymer materials. 

The stability of electrostatically charged sols has been studied extensively and is now reasonably well understood. More recently the stabilising action of adsorbed or chemically anchored non-ionic polymers has received much attention. There has been however little systematic work on polyelectrolyte stabilisers apart from a number of investigations of the flocculation of particles bearing adsorbed biopolymers, usually proteins, by simple salts ( 2). These have shown that polyelectrolyte covered particles can be more stable with respect to the addition of salt than simple charged systems, and the extra stability has been ascribed to the polymeric nature of the surface layer. The precise mechanism by which polyelectrolytes stabilise dispersions in the presence of high concentrations of salt has however remained unclear. 

The theories of polymer solutions upon which steric-stability theories are based are usually formulated in terms of a portmanteau interaction parameter (for example Flory s X Parameter and the excluded volume integral) which does not preclude electrostatic interactions, particularly under conditions where these are short range. It is thus appropriate to consider whether polyelect-roly te-stabilisation can be understood in the same broad terms as stabilisation by non-ionic polymers. It was this together with the fact that polyelectrolyte solutions containing simple salts show phase-separation behaviour reminiscent of that of non-ionic... 

Kulicke W-M and Clasen C, "Viscosimetry of Polymers and Polyelectrolytes , Springer Verlag, Berlin, 2004. Longworth R, "Developments in Ionic Polymers", Appl Sci PublLondon, 1983. 

Lysaght, M. I. Technology of polyelectrolyte complexes. In Ionic polymers, Holliday, L., (ed.). New York Halsted Press 1975... 

And this may not just be due to the fact that you ve got a ham-fisted lab partner. In systems with strong intermolecular interactions, such as solutions of ionic polymers or polyelectrolytes, severe deviations from linear behavior can be observed, even at low concentrations (Figure 12-28). This should... 

Gibbs monolayers are widespread. The simplest system is that of the surface of a fully miscible binary liquid. More complex ones are monolayers of uncharged molecules adsorbed from dilute solutions (example aliphatic alcohols from aqueous solution) electrolytes surfactants (non-ionic or ionic) polymers and polyelectrolytes and yet more. On the other hand, the methods for characterizing... 

Due to the pronounced tolerance of the Suzuki reaction towards additional functional groups in the monomers, precursor strategies as well as so called direct routes can be applied for polyelectrolyte synthesis. However, the latter possibility, where the ionic functionalities are already present in the monomers, was rejected. The reason is too difficult determination of molecular information by means of ionic polymers. Therefore the decision was to apply precursor strategies (Scheme 1). Here, the Pd-catalyzed polycondensation process of monomers A leads to a non-ionic PPP precursor B which can be readily characterized. Then, using sufficiently efficient and selective macro-molecular substitution reactions, precursor B can be transformed into well-defined PPP polyelectrolytes D, if appropriate via an activated intermediate C. 

Synthetic polymers are widely applied to modify the surface properties of materials, and their adsorption mechanism is very different from small ions or molecules discussed in previous sections. Moreover, special methods are applied to study polymer adsorption, thus, polymer adsorption became a separate branch of colloid chemistry. Polymers that carry ionizable groups are referred to as polyelectrolytes. Their adsorption behavior is more sensitive to surface charging than adsorption of neutral polymers. Polyelectrolytes are strong or weak electrolytes, and the dissociation degree of weak polyelectrolytes is a function of the pH. The small counterions form a diffuse layer similar to that formed around a micelle of ionic surfactant. 

These results confirm the observation that polyelectrolyte aqueous solutions show two separate decay modes in the autocorrelation function and support our contention that ionic polymer systems generally behave similarly in polar solvents [23], To support this, it may be added that similar dynamic scattering behavior was recently reported for another type of ionomer, polyurethane ionomer, dissolved in a polar solvent, dimethylacetamide (e = 38) [92], Finally, it should be stressed that the explanation given above for light scattering (both static and dynamic) behavior of salt-free polyelectrolytes is based on the major role of intermolecular electrostatic interactions in causing characteristic behavior. No intramolecular interactions are explicitly included to explain the behavior. This is in accord with our contention that much of the polyelectrolyte behavior, especially structure-related aspects, is determined by intermolecular interactions [23]. 

Random ionomers having very small ion contents (e.g., 0.3 mol% for a 400,000 molecular weight PS) and telechelic ionomers show some deviations from the behavior noted herein. Although these deviations are of interest in studies of the essential features of polyelectrolyte behavior of ionic polymer solutions, we have limited our discussion to typical random ionomers (having an ion content of over 1.0 mol%). 

DSA (see Pig. 2), they were able to extract indirectly information of the structure and dynamics of the complex formed [86] in dependence of the surfactant concentration and the pH. Such complexes of hydrophobic ally modified polyelectrolytes or ionic polymers with surfactant have unusual properties (in particular rheological) and are therefore widely used in, e.g., cosmetics or food applications. 

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