Soap solutions, association

Moreover, Shi and his group reported electrochemical deposition of PPy microcontainers onto soap bubbles associated with O2 gas released from the electrolysis of H2O in an aqueous solution of /3-naphthalenesulfonic acid (/3-NSA), camphorsulfonic acid (CSA), or poly(styrene sulfonic acid) (PSSA), which act both the surfactant and dopant [79-81]. Morphologies such as bowls, cups, and bottles could be controlled by electrochemical conditions (Figure 11.6). However, the microcontainers were randomly located on the electrode surface, which limited further applications, Shi and coworkers reported a linear arrangement of PPy microcontainers by self-assembly with gas bubbles acting as templates on a silicon electrode surface patterned by photolithography [82]. They found that capillary interactions between the gas bubbles and the polymer photoresist walls led the microcontainers to be arranged linearly. 

During the controversy over the question whether polymeric substances, which show colloidal properties in solution, are to be considered as molecules or as particles built up from many small molecules, the question was raised whether soap solutions might not serve as the model for polymeric colloids. It was in fact known that soap solutions owe their colloidal properties to a reversible association of the fatty acid anions or molecules. It became however ever more clear that the polymeric colloids must be considered as macromolecules — that is to say many monomers are bound together by ordinary valencies to form a polymer. It can be deduced from many properties of the polymers that these are indeed macromolecules. 

We prefer the concept association colloids above other terms — for example colloidal electrolyte — because we want to leave open the possibility that non-electrolytes or undissociated electrolytes form particles with colloidal properties by association. Tlie association of small molecules or ions into micelles seems to us the more characteristic, not the electrolyte character which naturally plays a great part in soap solutions. Indeed particles which owe their character as colloids to their large molecules (for example proteins) also come under the concept of colloidal electrolyte. 

The difference between the viscosity of soap solutions in water and alcohol (Fig. 4) demonstrates clearly that it is only in water that association to larger aggregates takes place... 

Now the changes of the osmotic properties (lowering of the freezing point etc.) do not run parallel to the electrochemical properties and from these differences Me Bain calculates the number of colloidal particles at various concentrations. Colloidal soap can exist in two forms the anions can associate, but it is also possible that undissociated soap molecules form an aggregate. In a soap solution (for example Na-palmitate, NaP) the following particles can therefore occur ... 

There must be some kind of connection between the structure of the soap micelles and the mechanical properties of soap solutions. We have already seen that many soaps can form elastic or gelatinous systems and there is therefore every reason for establishing the connection between the properties and the X-ray observations. We have to thank Philippoff in particular for attempts in this direction. To what extent — he asks himself — will the viscosity depend on the aggregation Since the specific volume of the dissolved material will undergo little or no change through association of the particles, the shape factor must be influenced. In this connection various possibilities can be envisaged ... 

When we start from the Hartley micelles there are thus two possibilities of association a loose association of the micelles and an increase in the si2 e of the micelles, whereby plate-shaped aggregates are formed. It must be possible to understand all the phenomena of soap solutions with the aid of these two types of association. 

One would not expect this a priori. Indeed the dissociation of the polar groups decreases, thus the supposed decrease of the association of the micelles cannot be attributed to this. A consideration of a very schematic picture of the course of the events furnishes the solution of the poblem. We know (Fig. 39a) that an association of the soap micelles occurs in a soap solution of a fairly high concentration. On the other hand it is probable that large plate-shaped micelles are produced (Fig. 39c)... 

The presence of small leaks is generally indicated by odor alone, and such leaks may be found with indicating detectors or soap solution (bubble checking). Occasionally, leaks may become manifest as frosted areas of drips of liquid and may have a hissing sound associated with them. Even small leaks can be dangerous in areas of poor ventilation, particularly indoors. Leaks should always be repaired rapidly. 

Dislocations may be demonstrated by means of a soap bubble analogy. This consists of a raft of small bubbles, all the same size, generated on the surface of a soap solution. The bubbles represent atoms and are subjected to two forces just as the atoms in a metal are. Surface tension causes the bubbles to attract each other and form a dense array, while pressure within the bubbles prevents them from approaching each other closer than a characteristic distance. When a raft of bubbles is formed on a fluid surface, grain boundaries are evident as well as dislocations (Fig. 8.10). When such a raft of bubbles is sheared, deformation is seen to occur as dislocations move across the crystal. While the forces at work are not identical to those associated with atoms, the soap bubble model is a useful analogy. A film has been produced by Sir Lawrence Bragg who devised the soap bubble analogy, and this film lends considerable credibility to the relatively sophisticated dislocation concept. 

What is most amazing of all in this picture is the degree of microscopic order present in a solution that appears quite unexceptional to the imaided eye. Usually, we associate T>eauty and aesthetic appeal with symmetry and regular shapes, just as in the examples of the ordered lamellar phase and lamellar focal conics. However, sometimes also asymmetric shapes have that special quaUty about them that conveys what we call beauty. Figure 4 shows a water-rich foam composed of dish soap with coconut oil. It consists of tightly-packed bubbles of very different sizes that create an asymmetric pattern of astounding beauty [3]. 

Wakbukton s method of effecting the purification of rape oil is by treatment with caustic alkali, ia which, the albuminous and other impurities are soluble, and are. separated, associated with soapy matters. In a suitable vessel, containing fifty-two parts of. caustic soda solution, of specific gravity 1-010, are to be put one hundred pounds of the refined oil those are to be stirred with a wooden ladle till well mixed. The mixture is then allowed to stand twenty-four hours undisturbed, in a cold place, after which it is then slowly warmed, and again well stirred. After twenty-four hours subsidence all the oil will have separated if such should not bo entirely the case, the complete separation may be effected by the addition of a small quantity of spirit of wine. The oil drawn off from the liquor is afterwards well washed with hot water, till the pure oil is obtained without taste or color, and if desired, may be passed through a filter. The soap which deposits may be used as an ordinary detergent... 

It is convenient to classify sols into three types (I) tvophilii (solvent loving) colloids, for example, are solutions or gelatin or starch in water (2 association colloids, of which a solution of Soap in water at moderate concentration is an example and (3) Iwphohic (solvent repelling) colloids, for example, sulfur in water. Both lyophilic and association colloids can be prepared in thermodynamic equilibrium, so that when solvent is removed and then returned to the system, the original properties of the system are regained. 

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