Hydrophobic polyelectrolytes, physical

We have used molecular simulation to examine configurational properties of isolated polyelectrolytes In solution. Studies on hydrophilic polyelectrolytes indicate that existing polyelectrolyte-expansion theories are inconsistent with the physical model on which they are based. Studies on hydrophobic polyelectrolytes are useful for examining the factors which Influence and induce structural transitions in these systems. 

A similar physical picture of counterion binding can be adopted for systems containing surfactant counterions, although in this case some additional effect may be expected. The main factors that influence the binding of ionic surfactants to polyelectrolytes with opposite charge are (1) the charge density of the polyion, A, (2) the hydrophobic character of the surfactant (the length of its hydrocarbon chain), (3) the additional attractive forces between the... 

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... 

After all our efforts, membrane research is still challenging and in need of fresh and innovative ideas. It is a highly interdisciphnary field, based on molecular chemistry, polymer physics, interfacial science and the science of random heterogeneous media. Could it be possible that the future lies in ordered nanostructured materials such as, for example, ordered polyelectrolyte brushes In such materials, studying the role of the sidechains (length, separation, controlled flexibility, hydrophobicity) and mechanisms of self-assembly, which will determine proton distribution at the mesoscopic scale, will be central for design and optimization. 

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