Adsorption of aminefluorides onto glass and the determination of surface free energy, zeta potential and adsorbed layer thickness

Aminefluorides 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

Spreading pressures of water and n-propanol on polymer surfaces

Spreading pressures of water and n-propanol on polytetrafluoroethylene (PTFE), polystyrene (PS), polymethylmethacrylate (PMMA), polycarbonate (PC), and glass are determined from ellipsometrically measured adsorption isotherms by graphical integration, yielding for water 9, 37, 26, 33, and 141 erg · cm−2 on PTFE, PS, PMMA, PC, and glass, respectively, while for n-propanol 5, 38, 26, 23, and 37 erg · cm−2, respectively. The spreading pressures for water as well as n-propanol are comparable to values previously obtained from contact angle data with water, water/n-propanol mixtures and α-bromonaphthalene using the geometric mean equation. This method yielded spreading pressures of 9, 14, 30, 27, and 70 erg · cm−2 for PTFE, PS, PMMA, PC, and glass, respectively. The numerical correspondence between the spreading pressures for water and n-propanol determined ellipsometrically with the values derived from contact angles indicates the necessity as well as the validity of taking the spreading pressures of water/n-propanol mixtures into account as a constant, if surface free energies of high energy substrata are approximated by contact angle measurements

Kinetic roughening of vicinal Si(001)

The kinetic roughening behavior of vicinal Si(001) surfaces is studied with scanning tunneling microscopy. By analyzing the height-height correlation function of the Si layers that have been grown we found, in the case of islands growth, an algebraic roughening behavior with a roughness exponent of 0.68 ± 0.05. In the step flow mode, however, we found non-algebraic roughening behavior

Adsorption of aminefluorides on human enamel

Changes 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)

Exposing nanobubble-like objects to a degassed environment

The primary attribute of interest of surface nanobubbles is their unusual stability and a number of theories trying to explain this have been put forward. Interestingly, the dissolution of nanobubbles is a topic that did not receive a lot of attention yet. In this work we applied two different experimental procedures which should cause gaseous nanobubbles to completely dissolve. In our experiments we nucleated nanobubble-like objects by putting a drop of water on HOPG using a plastic syringe and a disposable needle. In method A, the nanobubble-like objects were exposed to a flow of degassed water (1.17 mg l−1) for 96 hours. In method B, the ambient pressure was lowered in order to degas the liquid and the nanobubble-like objects. Interestingly, the nanobubble-like objects remained stable after exposure to both methods. After thorough investigation of the procedures and materials used during our experiments, we found that the nanobubble-like objects were induced by the use of disposable needles in which PDMS contaminated the water. It is very important for the nanobubble community to be aware of the fact that, although features look and behave like nanobubbles, in some cases they might in fact be induced by contamination. The presence of contamination could also resolve some inconsistencies found in the nanobubble literature