Lucyna Holysz

On the use of Washburn's equation for contact angle determination

A systematic study on the possibility of Youngs contact angle determination from Washburns equation was performed using the so-called thin-layer wicking technique in which the rate of penetration of a liquid into the porous layer of a solid is measured. Commercial (Merck) SiO2 deposited on the glass plate for thin-layer chromatography was used as a model solid and n-alkanes (from pentane to hexadecane), diiodomethane, and α-bromonaphthalene were employed as the probe liquids. It was shown that the contact angle calculated from Washburns equation was not equal to Youngs contact angle of a drop of the same liquid, placed on a flat surface of the solid. Consequently, the solid surface free energy components calculated using contact angles from Washburns equation are not the true values. However, the approach previously suggested by us has been verified again, as it gives consistent values of the surface free energy components determined from all the liquids used.

Time-dependent changes of zeta potential and other parameters of in situ calcium carbonate due to magnetic field treatment

Abstract Effects of permanent magnetic fields, north–south (N–S, 0.45 T), south–south (S–S, 0.1 T), and two south–south (2(S–S), 2×0.1 T) on sodium carbonate solution were investigated in a kinetic condition for various exposure time of the solution to the magnetic fields. From the solution and equimolar CaCl2 solution CaCO3 was precipitated. It was found that depending on the exposure time, the magnetic fields decreased surface tension of the sodium carbonate by 1–4 mN m−1. From the magnetized solution the rate of calcium carbonate precipitation was different than from untreated solution, as well as the sedimentation rates. Also electrokinetic potentials of in situ precipitated calcium carbonate were significantly affected in comparison to the reference system. The effects must be due to the magnetic field molecules of CaCO3, possible carbon atoms, where valency electron spins can be unpaired.

Changes in zeta potential and surface free energy of calcium carbonate due to exposure to radiofrequency electric field

Abstract A calcium carbonate (Fluka; more than 99.0% pure) suspension or a thin layer of its powder deposited on a glass slide was exposed to an r.f. electric field (44 MHz; 60 V peak-to-peak no-load amplitude) for 5–30 min. The zeta potential of the suspension in water (natural pH, 9.9 ± 0.1) or in 10−2 M NaCl (natural pH, 9.6 ± 0.1) was then measured electrophoretically. The surface free energy components, i.e. non-polar Lifshitz—van der Waals (γLWS) and polar (acid—base) electron donor (γ−S) and electron acceptor (γ+S) were determined by the “thin-layer wicking technique”. It was found that a negative zeta potential of CaCO3 in water measured immediately (within 2–3 min) after the exposure to the r.f field changed in an oscillatory fashion depending on the exposure time. For the sample treated for 15 min with the r.f field the zeta potential decreased by 5–7 m V in relation to an untreated sample. Residual changes occurred also in an oscillatory fashion during the 40 min after field removal. A similar behavior was found for the suspension in 10−2 M NaCl. The observed zeta potential changes were accompanied by changes in the electron donor component of the surface free energy and the appearance of a small electron acceptor component, which resulted from the presence of hydrogen bonding on the calcium carbonate surface. The r.f. field treatment led to a decrease in γ−S from 83 mJ m−2 (untreated sample) to 40 mJ m−2 (15-min-treated sample) and 64 mJ m−2 (25-min-treated sample) and caused the appearance of γ+S components of 1.34 and 1.77 mJ m−2. The observed changes in the zeta potential and the surface free energy components are believed to result from the changes in the surface charge of calcium carbonate and the structure of the water film at the surface.

Synthesis of hydroxyapatite for biomedical applications

The current need for long lasting implants and bone substitutes characterized by biocompatibility, bioactivity and mechanical properties, without the immune rejection is a great challenge for scientists. These bone substitute structures should be prepared for individual patients with all details controlled on the micrometer level. Similarly, nontoxic, biocompatible targeted drug delivery systems which allow controlling the rate and time period of the drug delivery and simultaneously eliminating toxic and side effects on the healthy tissues, are of great interest. Extensive attempts have been made to develop a simple, efficient, and green method to form biofunctional scaffolds and implant coatings possessing the above mentioned significant biocompatibility, bioactivity and mechanical strength. Moreover, that could also serve as drug delivery systems. Hydroxyapatite (HA) which is a major mineral component of vertebrate bones and teeth is an excellent material for these purposes. In this literature review the biologically inspired scaffolds, bone substitutes, implants characterized by mechanical strength and biocompatibility, as well the drug delivery systems, based on hydroxyapatite are discussed.

Influence of impurity ions and magnetic field on the properties of freshly precipitated calcium carbonate

Static magnetic field (MF) effects on the properties of freshly precipitated calcium carbonate have been investigated in the presence of impurity ion Mg(2+), Fe(2+), or SO4(2-). One or both solutions, CaCl2 and Na2CO3, were exposure to MF (0.5T) for 20min at 20 degrees C. Then calcium carbonate was precipitated and zeta potential, pH and light absorbance (lambda=543.3 nm) were measured. The same parameters were also determined for the reference systems in which the solutions were not MF-treated. It was found that in all the systems tested MF effects as determined by the above mentioned parameters had appeared. They depended on the kind of the impurity ion present, as well as on which solution, CaCl2, Na2CO3 or both, MF interacted. For example, if Mg(2+) ion was present in CaCl2 solution, the largest shift in the zeta potential toward higher positive values was observed if Na2CO3 was MF-treated (e.g. from 2 to 12mV) and the same was true as for the maximum in the light absorbance and the pH increase. Interestingly, if (CaCl2 + Mg(2+)) was MF-treated pH of the slurry had decreased. Moreover, a correlation between above mentioned MF effects and the entropy of hydration of the ions has also been found. This points to the changes in the hydrating water structure caused by magnetic field.

Correlation of surface free energy changes and flotability of quartz

Abstract Samples of natural Brazilian quartz were variously covered with dodecylamine chloride (DDACl) from methanolic solutions. Then they were subjected to flotation tests and ζ potential measurements in doubly distilled water. In the second series of experiments the samples covered with DDACl were then covered with known amounts of n -hexane or n -hexanol and ζ potentials were determined. From this relationship dispersion and polar components of surface free energy of the quartz samples were calculated. The results obtained allow us to conclude that already at 0.25 statistical monolayer of DDACl the sample of quartz floats in 90%, which is connected with drastic reduction of the polar component of quartz surface free energy from 115 mJ/m 2 (bare surface) to 7.2 mJ/m 2 . The maximum flotation activity appears at one statistical monolayer of the amine, and corresponds to complete reduction of the polar interactions at the quartz-water interface.

A study of n-alkane films on solids by zeta-potential measurements

Abstract Energetic properties of n -heptane film adsorbed on quartz and polypropylene surfaces have been investigated as a function of its thickness. Calculations based on the results of streaming potential measurements in solid/n-alkane—water systems lead to the conclusion that the film pressure values determined correspond first to a spreading wetting process and then, with increasing thickness of the film, to an immersional wetting process. The surface dispersion free energy of the solids, calculated from the film pressure, is in good agreement with data in the literature. A verification of the relevance of the systems has been done for the polypropylene/ n -heptane—water system by the use of two-liquid-phase contact angle method. If the thickness of the n -heptane film on the polypropylene surface further increases, additional changes in zeta potential are observed. It is suggested that such changes could be indicative of n -heptane—water interactions. Calculations for the process of n -heptane wetting the water surface and for alkane film pressures are presented which support the mechanism suggested.

Reversible charging of the ice–water interface: II. Estimation of equilibrium parameters

An ice electrode was constructed in order to measure dependency of the surface potential on pH. The electrode had a Plexiglas body with a platinum plate on the bottom, which was cooled by passing the cooling liquid through a tube mounted inside the electrode. The temperature inside the electrode was -7 degrees C, while the electrolyte solution was kept at 0.02 degrees C, so that an ice layer was formed on the platinum plate. In the acidic region fast equilibration of electrode was observed. The slope dphi(0)/dpH was found to be between -40 and -46 mV. The maximum of the slope was observed at pH 4.4, which coincides with the isoelectric point of ice-water interface. In the basic region the equilibration was slow and more pronounced deviation from the Nernstian behavior was observed. The results were explained on the basis of the surface complexation model, assuming an amphotheric nature of surface OH groups. In the basic region the surface bears high negative charge so that binding of sodium ions at the interface influenced the results. Copyright 2000 Academic Press.

SURFACE FREE-ENERGY COMPONENTS OF GLASS FROM ELLIPSOMETRY AND ZETA-POTENTIAL MEASUREMENTS

Two different experimental approaches based on ellipsometry and zeta potential measurements have been employed to determine the dispersion and polar surface free energy components of glass. From ellipsometry the adsorption isotherms of n-octane and water have been determined, yielding values for the film pressures of n-octane and water and the dispersion and polar surface free energy components of glass. Similarly, zeta potentials in water of glass covered with various amounts of n-octane and n-hexanol have been determined. Next, the film pressures of these liquids and surface free energy components of glass were also calculated. Thus determined values are 32 and 80 mJ/m2 (from ellipsometry) and 25 and 80 mJ/m2 (from zeta potentials) for the dispersion and polar components, respectively. The correspondence between the surface free energies obtained by two completely independent methods gives confidence to the approaches employed.

Some theoretical and experimental limitations in the determination of surface free energy of siliceous solids

Abstract The components of surface free energy of silica gel were calculated according to various theoretical approaches, and based on the data from different experimental methods (i.e., gas chromatography and thin column wicking). The results are compared, and widely discussed in terms of theoretical imperfections, accuracy of the liquid surface tension components data, as well as specific conditions (affecting the surface properties) implied by the used experimental method. Special attention was paid to adsorbed water layers. The differences in the results (especially those, dealing with donor–acceptor interactions) are discussed in terms of the mechanism of water vapour adsorption. The adsorbed water may provide an increase of electron-donor interactions of the surface.