L. Grigorov

Zirconium pyrophosphate activated with europium and terbium

Abstract Luminescence properties of ZrP2O7-doped with Eu3+ and Tb3+ were studied. It was established that Eu2+ centers were formed when the activation temperature increased. Sensitization of Tb3+ emission by Sn2+ or Cu+ was realized.

Luminescence efficiency of SnO2:Eu and rate of SnO oxidation

Abstracts are not published in this journal

Luminescence of Tb3+-activated zirconium pyrophosphate: influence of compensating and sensitizing impurities

Abstracts are not published in this journal

On the photosensitivity of poly (acryloylacetone) in solution

Abstract The influence of UV irradiation on the keto-enol ratio of poly (acryloylacetone) (PAA) in solution was examined. The tautomeric equilibrium is strongly displaced to the keto form. Important differences in the photosensitivity of the monomeric β-diketone (acetylacetone) (AA) and PAA were established depending on the structural features. The polymeric structure of PAA is an important parameter in the process. A possible route for the formation of the keto form is discussed.

Photoinduced ketonization of poly(ethylacrolylacetate) in solution

Abstract The influence of UV irradiation on the keto to enol ratio of poly(ethylacrolylacetate) (PEAA) in solution was examined. The major process is photoketonization, which is rapid and reversible. The role of the polymer chain is discussed in terms of its effect on the phototransformation. It is suggested that the high rate of photoketonization may be associated with the formation of sandwich complexes between the different units.

The three-phase contact parameters of thin water films on mineral surfaces

Abstract A new method for the characterization of the wettability of opaque solid surfaces by measuring 9a) the lifetime of thin liquid films, (b) the kinetics of expansion of the three-phase contact (TPC), (c) the equilibrium contact angle is developed. The method is tested with galexa-xanthate and copper mineral-pyrite-Aerodri 104 systems. The experimental results from TPC parameter measurements of galena and flotation tests indicate the important role of the TPC expansion rate in flotation. The effect of Aerodri 104 on three-phase froth stability is investigated. It is found that the breakdown of the three-phase froth can be correlated directly with the equilibrium contact angle.

Polyoxyalkylated diethylenetriamine polymeric surfactants: molecular structure effect on thin wetting films

Thin wetting films from aqueous solution of four polyoxyalkylated diethylenetriamine (DETA) polymeric surfactants (named A, B, C, and D) are studied. Surfactants A, B, and C have a star-like structure differing only by the number of polymeric branches: four, six, and nine in the mentioned order while the forth one, D, is of a dendritic type with four to six primary and two to three secondary branches. The receding contact angles θr of the solution on hydrophilic SiO2 glass surface and the contact angle θaq of a drop of doubly distilled water on SiO2 glass surface pretreated with DETA polymeric surfactant solution are measured. The θr values on hydrophobicity of SiO2 glass surface, respectively, increase in the following order: surfactant A, surfactant C, surfactant B, and surfactant D. The equilibrium thickness heq of wetting films from DETA aqueous solution on hydrophilic SiO2 glass surface is measured using the micro-interferometric method. Results show an unexpected course of the heq vs. Cs curves with a maximum. Results from the studies indicate that differences in polymeric surfactant molecular structure affect the properties exhibited at air/liquid and solid/liquid interfaces, such as the value of surface tension, degree of hydrophobicity of solid surface, equilibrium film thickness, etc.

Calculation of van der Waals interactions involving lipid vesicles

Abstract Van der Waals energies of interaction involving vesicles and lipid layers are calculated for different geometries. Results from exact and approximate calculations are compared with some existing experimental data. It is shown that sufficient accuracy can be obtained using relatively simple ‘additivity’ approximations for the contribution of dispersion interactions. A set of calculated results is presented for a small unilamellar vesicle interacting with coated and uncoated metal and polymer surfaces. A lipid coating lowers magnitude of the interaction energy approximately two-fold. The procedure gives a simple possibility to estimate Hamaker constants (and ‘Hamaker functions’) from handbook data taking into account the existing uncertainity in the materials constants of the interacting substances.

Wetting properties of phospholipid dispersion on tunable hydrophobic SiO2–glass plates

We study the wetting properties of very small droplets of salty aqueous suspensions of unilamellar liposomes of DMPC (dimyristoylphosphatidylcholine), situated on SiO2-glass surfaces with different levels of hydrophobicity. We evaluated two different measures of hydrophobicity of solid surfaces - receding contact angles and the thickness of wetting films trapped between an air bubble and the solid surface at different levels of hydrophobicity. We established a good correlation between methods which differ significantly in measurement difficulty and experimental setup. We also reveal details of the mechanism of wetting of different surfaces by the DMPC liposome suspension. Hydrophilic surfaces with water contact angles in the range of 0° to 35° are readily hydrophobized by the liposomes and only showed corresponding contact angles in the range 27°-43°. For same range of surface hydrophobicities, there was a clear reduction of the thickness of the wetting films between the surface and a bubble, reaching a minimum in the 35°-40° range. At higher levels of hydrophobicity both pure water and the liposome suspension show similar contact angles, and the thickness of wetting films between a bubble and those surfaces increases in parallel. Our analysis showed that the only force able to stabilize the film under these experimental conditions is steric repulsion. The latter suggests that nanobubbles adsorbed on hydrophobic parts of the surface, and coated with a DMPC layer, may be the cause of the 40-70 nm thickness of wetting films we observe.

On the mechanical equilibrium in anisotropic heterogeneous systems

The conditions for equilibrium of liquid surfaces dividing two anisotropic bulk phases have been deduced by means of variational analysis.It has been shown that the presence of an anisotropic tensor in the bulk requires a gradient of surface tension in a state of equilibrium.