LAPONITE CLAY--A SYNTHETIC INORGANIC GELLING AGENT 255 DISCUSSION 51R. 5I. G. •_: NAVARRE: IS there more than one type of Laponite? DR. NEU•AN•: Yes. Laponite CP is the straight-forward hydrophilic gel-forming clay. We also have a version named SP which forms a sol in water with a low viscosity at a very high concentration, and this has the advantage that it is more readily mixed with other systems than the Laponite CP powder. Laponite SP sols will set up a structure only when other solids are also present, or after long standing. I n addition, organophilic modifications of Laponite are being developed at present. MR. M. G. DE NAVARR•: What is the microbiology of Laponite - are the counts of micro-organisms high? DR. Nr U•AN•: We have no counts, but we think that they are low because the last stage of processing of Laponite is drying at high temperature. DR. J. J. MAUSN•R: You mentioned the very important effect of electrolytes on the properties of Laponite gels. Could you draw up some relationship between pH values and the basic properties of these gels? DR. NEUMANN: The pH of Laponite gel is about 8.3. Between pH 6 and 12 it is stable, but slowly flocculates outside this range. Since it is a good buffer, a large quantity of either acid or alkali is required to bring the pH outside the stable range flocculation is then caused by the high concentration of electrolyte. DR. ]. ]. MAUSNER: Could these systems be modified to work in non-polar organic systems? DR. N•u•: The dispersion of the clay in non-polar organic systems can only be achieved if the clay is first modified by giving it an organophilic surface. This can be done by the well-known methods that have been used for a long time for bentonires and other swelling clays, by replacing the exchangeable ions of the clay with long- chain organic ammonium ions. If the organic molecule is sufficiently large, then the whole surface becomes organophilic, and the clay will then disperse in non-polar organic solvents. D•. R. M•c}•so•o: It is not quite clear how synthetic your material is. Do you start from a natural hectorire and build it up, or from simple inorganic materials? DR. S•so•: It is entirely synthetic. For many years clays have been referred to as synthetic when people have simply just exchanged the cation. Our synthetic clay is made up from pure simple chemicals, we do not start with another clay. MR. C. A. W•so•: When we were talking about the Laponite - glycerine - water difficulty {8), it seems that our trouble was that it took a very long time to form the gel. I wonder whether we are using the correct procedure for making the gels. DR. SANsoft: Our water-glycerol-Laponite gels have reached, as far as we are aware or can determine, complete equilibrium after 24 h. One of the problems is that the gel forms almost immediately, making it difficult to homogenise the system. Pre-wetting the clay with the organic solvent helps the dispersion. In the work (3)•ratson, C. A. Hyd, ocolloidsand dentifrices. J. Soc. Cosmetic Chemists • (1070) in the press .

256 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS reported here, however, we mixed the glycerol and water in the proportions required, then stirred in the Laponite with a high speed stirrer. MR. J. M. BLAKEWAY: Do you have any intention of producing these materials as organic modified bentones? DR. NEUMANN: We are hoping to start production soon. MR. A. Mogs: According to Carless and Nixon (4) soluble fluoride was less than 1.5% in Laponite. Is your product non-toxic and suitable for internal use? De. NEUMANN: As always happens in the development of any new product, early tests are done on material which is later improved. When we gave samples to Prof. Carless and Dr. Nixon we had a material which contained fluoride. Since then we developed a material which contains no fluoride at all, soluble or insoluble. Had Prof. Carless started his work two years, rather than three years ago, he would have had this new material from us. (We have had Dunlop Committee approval for internal use since the meeting.) DR. J. J. MAusN•.R: What is the effect of uv light on these gels? DR. SANSOM: We have not studied the effect of uv radiation on Laponite gels, but with the system we have, it is difficult to foresee that there would be any problem. MR. J. B. W•LK•NSON: Clearly these types of clays are surface active because you can make various exchange reactions take place at their surfaces. Do they give any problem in long-term storage with reactive groups, for instance in the presence of various types of alcohols? Will the nature of the gel change with time because you are actually getting surface reactivity? DR. NEUMANN: NO change is expected to take place with alcohols. Ion exchange reactions can be expected if the system contains amine groups or other cationic com- pounds. If the cation is large, the ion exchange tends to be irreversible, so I would watch the stability of these systems. Me. A. FOSTER: Have you any data on the long-term effect of high shear rates or other mechanical action on these gels as regards eventual recovery of yield values? De. SANSOM: The gels are thixotropic. They will break down with the application of high enough shear, and reform on standing. This property is not lost when the gels are left standing for many months. DR. NEUMANN: Just to add to this--we have found that the application of really high shear rates (18 000 s-•) does not destroy the thixotropic properties, or lower the final gel strength. Me. S. J. STRiA•-s•.: Do you have any experience in making rigid gel structures with Laponite? (4) Carless, J. E. and Nixon J. R. Some applications of rigidity and yield values in a study of gelatin and Laponit• gels. J. Soc. Cosmetic Chemists gl (1970) in the press.