Three ball clays (SP from England, TSMA from France and UK from the Ukraine) were characterized for their dry and wet colloidal properties. On the basis of X-ray diffraction and chemical analyses the clays were classified as kaolinite-rich clay, smectitic kaolinite-rich clay and illitic kaolinite-rich clay. The ζ (zeta) potential at the clay-water interface as a function of pH, in three different electrolytes, was investigated using an electroacoustic technique. Starting from measurements of dynamic mobility, the calculated ζ potential was found to be almost constant as a function of pH for the TSMA and UK clays, while it increased from −20 to −60 for the SP clay, when potassium nitrate was used as an electrolyte. The behavior of the three clays in calcium and magnesium nitrate was slightly different: SP showed a smaller increase in ζ potential, while a small deviation from the constant behavior of the UK clay was found. The results are explained in terms of the surrounding-ion atmosphere in light of the chemical-physical properties measured. Our results may well be of use to those involved in ceramic processing.

Quasicrystals of synthetic fluoromagnesian smectite (FMS) in dodecyltrimethylammonium chloride (DTAC) solutions were investigated as a function of the DTAC concentration by wet type X-ray diffraction (XRD) ζ potential measurements, and dispersion and coagulation (DC) tests. The FMS had an electronegative potential and it was dispersed randomly in an aqueous suspension without DTAC. When the DTAC concentration was 0.002 mol/dm3, FMS tactoids started to develop a structure in which the layer thickness was 1.85 nm. At the isoelectric point, the DTAC concentration was 0.012 mol/dm3 and the FMS tactoid formed a regular stacked structure with a 2.25 nm layer thickness. As the ζ potential of FMS changed from negative to positive, the DC test and XRD measurement showed that the FMS association gradually changed from coagulation to dispersion, which indicates that the formation of the bilayer of surfactants on the surface of FMS produces a repulsion between DTA+ adsorbed on the silicate layer of the FMS surfaces. When the equilibrium concentration of DTAC in solution exceeded the critical micelle concentration (CMC), the ζ potential of FMS became greater than the previous values. The XRD analysis of this suspension showed that there were two kinds of rational FMS stackings; one has a layer thickness of 3.20 nm, and the other has a layer thickness of 5.45 nm due to an interstratified structure composed of 3.20 and 2.25 nm layers. The interstratified structure was confirmed by the calculated XRD profiles.

The adsorption behavior of quaternary ammonium cationic surfactants with different hydrocarbon chain lengths, i.e. HDTMA (hexadecyltrimethylammonium), TDTMA (tetradecyltrimethylammonium) and DDTMA (dodecyltrimethylammonium), onto clinoptilolite has been investigated. The adsorption isotherms of these surfactants are correlated with the ζ potential curves of clinoptilolite. Accordingly, the applicability of the hemimicelle hypothesis to the adsorption of cationic surfactants at the clinoptilolite/water interface considering in the electrical double layer (EDL) of clinoptilolite is discussed. Even though the adsorption occurs in the EDL of clinoptilolite, the adsorption of HDTMA, TDTMA and DDTMA onto clinoptilolite is not conveniently described by the hemimicelle hypothesis. The absence of all expected marked increase in the ζ potential curves at the hemimicelle concentration is ascribed to the large external cation exchange capacity of clinoptilolite. The hydrocarbon chain length of surfactant molecules is found to have a significant effect on the ion exchange as well as hydrophobic interaction mechanisms. The effectiveness of both ion exchange and hydrophobic interactions increases with increasing chain length, and so the greatest surfactant adsorption onto clinoptilolite was obtained by HDTMA.

This study reports physical and chemical changes that occur at early dentin remineralization stages. Extracted human third molars were sectioned to obtain dentin discs. After polishing the dentin surfaces, three groups were established: (1) untreated dentin (UD), (2) 37% phosphoric acid application for 15 s (partially demineralized dentin—PDD), and (3) 10% phosphoric acid for 12 h at 25° C (totally demineralized dentin—TDD). Five different remineralizing solutions were used: chlorhexidine (CHX), artificial saliva (AS), phosphate solution (PS), ZnCl2, and ZnO. Wettability (contact angle), ζ potential and Raman spectroscopy analysis were determined on dentin surfaces. Demineralization of dentin resulted in a higher contact angle. Wettability decreased after immersion in all solutions. ζ potential analysis showed dissimilar performance ranging from −6.21 mV (TDD + AS) up to 3.02 mV (PDD + PS). Raman analysis showed an increase in mineral components after immersing the dentin specimens, in terms of crystallinity, mineral content, and concentration. This confirmed the optimal incorporation and deposition of mineral on dentin collagen. Organic content reflected scarce changes, except in TDD that appeared partially denatured. Pyridinium, as an expression of cross-linking, appeared in all spectra except in specimens immersed in PS.