Hydrophilic colloids Colloidal particles that

Hydrophilic colloids Colloidal particles that attract water molecules. 

Hydrophilic colloids are colloidal particles that attract water molecules, whereas hydrophobic colloids are colloidal particles that repel water molecules. 

Coacervation consists in separating from the solution the colloidal particles that agglomerate into a separate liquid phase called coacervate. Coacervation can be simple or complex. Simple coacervation involves only one type of polymer with an addition of strongly hydrophilic agents to the colloidal solution. For complex coacervation, two or more types of polymers are used. Active molecules are entrapped in the matrix during coacervate formation by adjusting precisely the ratio between the matrix polymer and the entrapped molecule (Figure 38.2). 

A Figure 13.26 Hydrophilic colloidal particle. Examples of the hydrophilic groups that help to keep a giant molecule (macromolecule) suspended in water. 

It is postulated that the main thermodynamic driving force for particle adsorption at the liquid-liquid interface is the osmotic repulsion between the colloidal particles and hydrophilic starch polymer molecules. This leads to an effective depletion flocculation of particles at the boundaries of the starch-rich regions. At the same time, the gelatin has a strong tendency to adsorb at the hydrophobic surface of the polystyrene particles, thereby conferring upon them some degree of thermodynamic... 

Bentonite is a colloidal clay that is both hydrophilic and organophilic. It is waterswelling with some types of clay absorbing as much as 5 times their own weight in water. It is used in emulsions, adhesives, and sealants. It is a gritty, abrasive white particle filler. A macroscopic particle of bentonite is composed of many thousands of stacked and/or overlapped submicroscopic flakes. 

The hydrophobic colloids do not have affinity for water thus, they do not contain any bound water. In general, inorganic colloids are hydrophobic, while organic colloids are hydrophilic. An example of an inorganic colloid is the clay particles that cause turbidity in natural water, and an example of an organic colloid is the colloidal particles in domestic sewage. 

The adsorption of a strongly hydrated hydrophilic colloid thus increasing the affinity of the particle to water so that it exceeds any mutual attraction between particles... 

Colloidal properties that influence RES uptake are particle size, surface charge, surface hydrophobicity, and the adsorption of macromolecules onto the particle surface. The surface of colloidal particles can be altered to avoid RES uptake by adsorption or grafting of a hydrophilic polymer onto the surface of a particle and thereby creating an energy barrier to particle interaction (e.g., the non-ionic surfactant Tween 20 can be adsorbed).Both biological and synthetic polymers have been used for RES masking of colloidal particles, for example, albumin,immunoglobulin car-... 

The DLVO theory, which was developed independently by Derjaguin and Landau and by Verwey and Overbeek to analyze quantitatively the influence of electrostatic forces on the stability of lyophobic colloidal particles, has been adapted to describe the influence of similar forces on the flocculation and stability of simple model emulsions stabilized by ionic emulsifiers. The charge on the surface of emulsion droplets arises from ionization of the hydrophilic part of the adsorbed surfactant and gives rise to electrical double layers. Theoretical equations, which were originally developed to deal with monodispersed inorganic solids of diameters less than 1 pm, have to be extensively modified when applied to even the simplest of emulsions, because the adsorbed emulsifier is of finite thickness and droplets, unlike solids, can deform and coalesce. Washington has pointed out that in lipid emulsions, an additional repulsive force not considered by the theory due to the solvent at close distances is also important. 

Micelles are colloidal particles formed by the concentration-dependent aggregation of surfactant molecules (1). In an aqueous environment micelles form when the hydrophobic portions of the surfactant molecules begin to associate at a surfactant concentration that is referred to as the "critical micelle concentration", or CMC, as a result of hydrophobic effects In water, a micelle has a hydrophobic core and a charged surface that is the result of the orientation of ionizable or hydrophilic functional groups out into the bulk solution At concentrations prior to the CMC the surfactant molecules migrate to the solution-air interface which disturbs the structure of the water molecules and results in a decrease in the solution s surface tension (2), At concentrations greater than the CMC, increasing... 

The main objective of this chapter is to report on the preparation and characterization of thermally sensitive particles, and the pertinent aspects that should be considered before their utilization as a polymer support in the biomedical field. This is followed by an examination of the preparation of such hydrophilic thermally sensitive latex particles bearing reactive groups. Subsequently, the colloidal characterizations that are to be taken into consideration are presented. Finally, the chapter concludes by presenting and illustrating recent applications of thermally sensitive polymer colloids as solid supports in the biomedical field. 

---