4 research outputs found
Adsorption of aminefluorides onto glass and the determination of surface free energy, zeta potential and adsorbed layer thickness
Get PDFAminefluorides are known to affect bacterial adhesion to enamel. In order to obtain information on the structure of adsorbed aminefluoride coatings, dihydroaminefluoride (AmF 297) and oleylaminefluoride (AmF 335) were adsorbed onto glass from solutions with concentrations up to 10 mM. Surface tensions of the solutions were measured at 25°C. After coating the glass surfaces, surface free energies, zeta potentials and adsorbed layer thicknesses were determined from contact angles, electrophoresis and ellipsometry, respectively. Surface free energies decreased after coating with both types of aminefluoride from 109 to _ 45 mJ m-*. Coating with only high concentrations (> 5 mA4) of AmF 297 again resulted in surface free energies above 100 mJ m-‘. Zeta potentials, originally - 45 mV, became positive after coating with both types of aminefluoride (approximately + 5 mV). Coating with only AmF 297 at concentrations above 5 mM gave zeta potentials of + 20 mV. Adsorbed layer thicknesses were in the monolayer range, though AmF 297 on its own clearly formed thicker layers at higher concentrations. Both surfactants showed a tendency to form micelles in solution at concentrations higher than 1 n&f. The results indicate that both aminefluorides adsorb with the positively charged, polar group towards the glass, but only AmF 297 can form double layers at higher concentrations. The second layer, however, adsorbs with the positively charged polar groups towards the solution and is bound to the first layer by relatively weak forces between the hydrocarbon chains. Gentle rinsing with distilled water is sufficient to remove the double layers. This paper shows how a combination of surface techniques can yield a detailed picture of the structure and orientation of adsorbed layers on solid substrata
Adsorption of aminefluorides on human enamel
Get PDFChanges in surface characteristics of ground and polished human enamel after adsorption of two types of aminefluorides (AmF 297 and AmF 335) have been studied. After adsorption of aminefluorides from solutions with concentrations up to 10 mM for 2 min followed by rinsing of the surface with distilled water, contact angle measurements were carried out to yield surface free energies and ellipsometry was performed to yield the adsorbed layer thickness. In a separate experiment on powdered enamel, set up in an analogous way, zeta potential changes after adsorption of aminefluorides were determined in a 10 mM potassium phosphate buffer at pH 7·0. Surface free energies decreased from 88 erg·cm−2 to 52 erg·cm−2 and 35 erg·cm−1 after adsorption of AmF 297 and AmF 335 respectively at c = 1 mM. Increasing the aminefluoride concentration in solution did not affect the values obtained. Zeta potentials, originally −36 mV, became positive after adsorption, while ellipsometry indicated the buildup of adsorbed layers with a thickness between 3 run and 12 nm. All three types of experiments indicated that both AmF 297 and AmF 335 form an adsorbed monolayer on ground and polished enamel at a concentration of 1 mM. Negligible additional adsorption takes place at higher concentrations under the present experimental circumstances. In vivo, adsorbed aminefluoride layers will be rapidly covered by adsorbed protein layers, shielding both the adsorbed aminefluoride layer as well as its physicochemical characteristics. This effect has been studied in vivo by measuring surface free energy changes of ground and polished enamel, with AmF 297 and AmF 335 adsorbed at c = 2·5 mM as a function of the time, these samples were carried by test persons in partial dentures. On both types of AmF-coated enamel the surface free energies increased within 30 min to values approaching the one obtained previously for pellicle-coated ground and polished enamel (110 ± 9 erg·cm−2)
