Hydrophilic group part

An important step in tire progress of colloid science was tire development of monodisperse polymer latex suspensions in tire 1950s. These are prepared by emulsion polymerization, which is nowadays also carried out industrially on a large scale for many different polymers. Perhaps tire best-studied colloidal model system is tliat of polystyrene (PS) latex [9]. This is prepared with a hydrophilic group (such as sulphate) at tire end of each molecule. In water tliis produces well defined spheres witli a number of end groups at tire surface, which (partly) ionize to... 

Phospholipids are amphiphilic substances i.e. their molecules contain both hydrophilic and hydrophobic groups. Above a certain concentration level, amphiphilic substances with one ionized or polar and one strongly hydrophobic group (e.g. the dodecylsulphate or cetyltrimethylammonium ions) form micelles in solution these are, as a rule, spherical structures with hydrophilic groups on the surface and the inside filled with the hydrophobic parts of the molecules (usually long alkyl chains directed radially into the centre of the sphere). Amphiphilic substances with two hydrophobic groups have a tendency to form bilayer films under suitable conditions, with hydrophobic chains facing one another. Various methods of preparation of these bilayer lipid membranes (BLMs) are demonstrated in Fig. 6.10. 

Performance of surfactants is closely related to surface activity and to micelle formation. Both these are due to amphiphilic nature of the surfactant molecule. The molecule contains a nonpolar hydrophobic part, usually, a hydrocarbon chain, and a polar hydrophilic group, which may be nonionic, zwitterionic, or ionic. When the hydrophobic group is a long straight chain of hydrocarbon, the micelle has a small liquid like hydrocarbon core (1,2). The primary driving... 

This generalized structure was mimicked by a very simplified artificial molecule 1. The hydrophilic core part 2 was substituted simply by an oligoether carboxylate anion. The carboxylate may act as the polar ionic head group outside the membrane and the ether part of the molecule may be located in the interior part of the membrane to make an ion-conducting pathway. The molecular lengths were adjusted to fit the lipid monolayer in an extended or a helical conformation, with n being 2 or 3 in 1. The hydrophobic exterior was substituted by dioctadecyldimethyl-ammonium cation, which was ion-paired with the carboxylate. 

Structures for Cy and the molecular complexes have been described many times before [5] and require no repetition here. Suffice it to say that the hydrophobic center of the truncated conical shape of the host is the favored site for interaction with any non-polar group that is part of the guest on molecular association. Hydrophilic groups of the guest are left outside to interact with the... 

The hydrophobic part of a silicone surfactant is a permethylated siloxane or polydimethyl-siloxane group. Many different polar or hydrophilic groups have been used, some of which are listed in the table below. 

Rather less information is available concerning hydrophilic solutes than for apolar solutes (Section 7), although considerable effort has been made in recent years to overcome this deficiency. The chemistry of aqueous solutions of these solutes is equally fascinating, the importance of the different factors which affect hydration being readily apparent (p. 239). In molecules having two or more hydrophilic groups, the stereochemistry of the solute plays an important part in their hydration. 

When adsorbing from aqueous solution on a hydrophobic surface one expects the molecule to adsorb with its hydrophobic moiety towards the solid. For hydrophilic surfaces adsorption may be the other way around if the affinity of the hydrophilic groups for the surface exceeds that for the water, and if in the adsorbate layer association occurs, reducing extensive exposure of the hydro-phobic parts to water. If these auxiliary phenomena do not occur, the outcome is less predictable. 

When a dry polymer film is immersed into liquid water, an opposite process to what described above takes place. Hydrophilic groups migrate to the interface, and hydrophobic moieties move to the inner part of the surface state of a polymer. The main driving force for these movements is the interfacial tension. The greater the interfacial tension, the greater is the surface configuration change. 

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