Patent GB-483221-A (GB)
Title: Process of shaping colloidal particles
IPC: B01J2/00
Filed: 1936-07-07
Abstract: Aqueous dispersions of solid organic compounds which are insoluble or difficultly soluble in water are obtained with particles in (a) anisotropic or elongated form or (b) isotropic or spherical form by introducing into water a solution in an organic solvent of the compound whereby a dispersion is obtained and adding to the dispersion medium before or at an early stage in the formation of the particles (a) an additional colloid which temporarily delays the change into the dispersed form of the organic compound, the temperature being maintained below a certain critical temperature, or (b) an additional colloid which at once decreases the solubility of the organic compound in the dispersion medium, the temperature being maintained above said critical temperature.  The critical temperature for any given substance depends upon the size of the particles and upon the nature and amounts of the solvent, additional colloid and water present.  It is determined empirically for any particular set of conditions, and is usually considerably lower than the melting point of the pure solid substance.  The substance to be dispersed is dissolved in an organic solvent and anisotropic particles are produced by adding the solution to water in the presence of a suitable colloid at a temperature sufficiently low to ensure the production of some anisotropic particles.  The dispersion is examined microscopically in a dark field while being gradually heated.  The critical temperature is that at which the lustre due to reflection from the anisotropic particles disappears.  For the formation of anisotropic particles, if desired the organic solvent may be removed, the added colloid tending to maintain the substance to be dispersed in solution in the medium.  In the case of organic solids having elongated molecules or polar molecules, baciliform particles may be obtained by using the added colloid at a lower concentration than the substance to be dispersed, and plate-shaped or prismatic particles are obtained by using the added colloid at a higher concentration. The size of the particles thus produced may be maintained by adding a further colloid which decreases their solubility in the dispersion medium and prevents further growth.  When the dispersed solid is a lipoid, the sol may be stabilized by the addition of colloidal albumen or carbohydrates; dispersed albumens by means of carbohydrates and dispersed carbohydrates by means of lipoids.  To obtain very small particles, e.g. below 10-4 or 10-5 cm., a solution of low concentration in an organic solvent is rapidly mixed with a large volume of water, excess dispersion medium being evaporated if desired, and the working temperature maintained close to the critical temperature.  According to examples, dispersions of cholesterin, Sudan blue and Aniline blue in both anisotropic and isotropic form are obtained using albumen, gelatine, glycogen, lecithin, phosphatides, sodium oleate, alkyl naphthalene sulphonic acids and similar compounds, starch or gum-arabic as additional colloids. Temperatures from 18-60 DEG  C. are used.  The molecular structure of Aniline blue is oblong and polar, and tends to form anisoptropic particles, but by replacing the polar ion for example by the acid residue of a higher fatty acid, the formation of isotropic particles is facilitated.  Reference has been directed by the Comptroller to Specifications 242,711 and 269,960, [both in Class 1 (i)].