Colloids micellar

One of the models best able to describe the properties of micellar colloid solutions is the closed-association model. In it, we start by assuming the colloid comprises n molecules of monomer. We approximate by saying the colloid forms during a single step ... 

In milk, the caseins and minerals are in dynamic equilibrium between the micellar (colloidal) and the serum phase. When the native environment of caseins and minerals is altered by the addition of mineral salts, the partitioning of minerals and caseins between the serum and colloidal phases is altered. 

The foregoing method was used to study fluctuations in solutions of strong electrolytes (45) and in ionogenic and nonionogenic micellar colloids (22). Strong electrolytes were chosen to represent 1 1 electrolytes with nearly equal (NaCl) and significantly different (HCl) mobilities of anions and cations and a 2 1 electrolyte (CaCl2). 

Indeed, much higher levels of conductance fluctuations were reported for electrolytes that contain polystyrene latex suspensions (21) or micellar colloids (22). Fluctuations were shown to depend on concentration, characteristic size, and the charge of colloid particles. For uncharged nonconductive spherical particles that occupy volume fraction F of the total sample volume... 

Further subdivision of the colloids concerned many researchers. For example, studies of coagulation processes lead Miiller to connect suspensions with physical disintegration processes and large molecules with chemical precipitation methods. He designated as high molecular such substances as albumin and colloidal silica. The later classification by Staudinger into colloidal dispersions, micellar colloids (assocation colloids), and colloidal molecules (macromolecules) proved to be very suitable and forms the foundation of modern textbooks on colloid science. ... 

Colloid, micellar n. Colloid composed of micelles. A micellar colloid is an aggregation of molecules, usually arranged in a definite order, whose dimensions are less than 0.05 pm. Example a colloidal solution of soap in water. 

The first possibility is spontaneous reversible association (aggregation) of some low molecular weight unstable organic and inorganic substances in true solutions, as a consequence of attractive forces associative colloids or micellar colloids appear. An example of micellar coUoids is casein micelles in milk. 

Micellar colloids represent dynamic association-dissociation equilibria. However, the theoretical treatment of micelles depends on whether the micelle is regarded as a chemical species or as a separate phase. The mass action model which has been used ever since the discovery of micelles, takes the former point of view," " whereas the phase separation model regards micelles as a separate phase. To apply the mass action model strictly, one must know every association constant over the whole stepwise association from monomer to micelle, a requirement almost impossible to meet experimentally. Therefore, this model has the disadvantage that either monodispersity of the micelle aggregation number must be employed or numerical values of each association constant have to be assumed. " The phase separation model, on the other hand, is based on the assumption that the activity " of a surfactant molecule and/or the surface tension of a surfactant solution remain constant above the CMC. In... 

Micellar colloids are in a dynamic association-dissociation equilibrium, and the kinetics of micelle formation have been investigated for a long time. " In 1974, a reasonable explanation of the experimental results was proposed by Aniansson and Wall, " and this conception has been accepted and used ever since. The rate of micelle dissociation can be studied by several techniques, such as stopped flow, pressure jump, temperature jump, ultrasonic absorption, NMR, and ESR. The first three methods depend on tracing the process from a nonequilibrium state brought about by a sudden perturbation to a new equilibrium state— the relaxation process. The last two methods, on the other hand, make use of the spectral change caused by changes in the exchange rate of surfactant molecules between micelle and intermicellar bulk phase. 

This chapter focuses on the study of solubilizates in micellar colloids and develops a mode consistent with thermodynamics. Furthermore, the... 

Kekicheff P, Christenson FI K and Ninham B W 1989 Adsorption of cetyltrimethylammonium bromide to mica surface below the critical micellar concentration Colloid Surf. 40 31-41... 

K. L. Mittal, ed.. Colloidal Dispersions and Micellar Behavior, ACS Symposium Series 9, American Chemical Society, Washington, D.C., 1975. 

Colloidal suspensions are systems of small mesoscopic solid particles suspended in an atomic liquid [1,2]. We will use the term colloid a little loosely, in the sense of colloidal particle. The particles may be irregularly or regularly shaped (Fig. 1). Among the regular shapes are tiny spherical balls, but also cylindrical rods or flat platelets. As the particles are solid, fluctuations of their form do not occur as they do in micellar systems. Not all particles in a suspension will, in general, have the same form. This is an intrinsic effect of the mesoscopic physics. Of course in an atomic system, say silicon, all atoms are precisely similar. One is often interested in the con-... 

Kitahara, A., Kon-No, R. Micelle formation in non aqueous media, in Colloidal dispersions and micellar behaviour. ACS-Symposia Series 9, 225 (1975)... 

A number of diblock copolymers of NIPAM and hydrophobic comonomers have been prepared by various groups and assessed in terms of micellar structure, thermosensitivity, and applications. For example, PS-fo-PNIPAM was shown to form either micelles consisting of a PS core and a PNIPAM corona, or vesicles. The assemblies were colloidally stable at elevated temperature [262-266]. 

In the micellar region the trend to decreasing colloid stability is arrested and a partial improvement, in line with the enhanced level of polymer adsorption, is noted until the conditions for gross phase separation are reached. Only the intermediate block copolymer BC 42 shows indications of discontinuities in behavior at the solvent composition for micelle formation. The results presented here do not show the sharp transition from stability to instability found experimentally (4,8,17) by Napper and generally expected on theoretical grounds. However, there are important differences in experimental methodology that must be emphasised. 

This concept is well illustrated in Figure 10.11, which shows the way n dictates the proportion of monomer units incorporated into the micelle colloid. As the value of n increases, the steeper the graph in Figure 10.11 becomes. For example, a micelle formed from 30 monomer units has a very steep concentration dependence, i.e. almost a step , but below a certain concentration - which is characteristic of the temperature and the monomer - about 10 per cent of the colloid is micellar. Above this limit, however, more than 90 per cent is bound up within the micelle. 

---