István Pászli

Surface free energy of natural and surface-modified tropical and European wood species

To describe the wetting properties of various wood types from a practical point of view, the surface free energy of six tropical (guava, almond, teak, cloves, mango and neem) and six European wood species (English oak, Norway maple, hazel, ash, alder and Scots pine) were calculated using contact angles by the sessile-drop method. In order to provide water-repellent characteristics to the samples, they were silanized by a less used silylating reagent (using chloroform solution of trimethylsilyl N, N-dimethylcarbamate) and the results were compared with the effect of two commonly used reagents (chloroform solutions of chlorotrimethylsilane and octadecyltrichlorosilane). Since the Lifshitz–van der Waals/acid–base model is widely used in studies of biological surfaces, the energetics of the resultant wood surfaces were quantitatively described in terms of this model. For the mainly hydrophobic wood samples, anomalous surface behaviour (i.e. extremely high water contact angles (130–145°) and in certain cases unreasonably low surface free energy values) was found. Since the Lifshitz–van der Waals/acid–base model did not yield numerical results in some cases and the calculated surface free energies depended on the test liquid triplet used, the limitations in the applicability of this model are also discussed. For comparison, we analyzed our data also in terms of the Chang model.

Colloidal stability of electrostatically stabilized sol particles. Part I: The role of hydration in coagulation and repeptization of ferric hydroxide sol

FeO(OH)·0.5 H2O powders were prepared by drying portions of a FeO(OH)·0.5 H2O sol at different relative vapor pressures, and the adsorption of water on the powders was determined. The magnitude of electrostatic potential barrier for the sol is of about 9 mJ·m−2. The reduction in the immersion enthalpy and in the surface free-energy in a range of the relative vapor pressures of 0.0–0.9 is as high as 140 mJ·m−2 and 130 mJ·m−2, respectively.It follows from the foregoing that two potential barriers may form. The electrostatic barrier presumably regulates the rate of flocculation and the “hydration barrier” (at closer separations) regulates the rate of particle coalescence or sintering.Peptizability of the FeO(OH)·0.5 H2O powders dried at relative vapor pressures between 0.4 and 0.9 was found to be fairly high, presumably because the adsorbed water prevented the formation of close contacts between the primer particles. Lowering the vapor pressure, however, resulted in a notable decrease in the peptizable amount, and also a considerable increase in the particle size of the peptized sol.

Colloidal stability of electrostatically stabilized sol particles.

The colloid stability of ferric hydroxide sol has been investigated at three different HCl concentrations. The total HCl concentration in the sols was A>B>C, the amount of HCl adsorbed was A=B>C. The parameters which characterize the stability (flocculation value, gelation concentration, repeptizability) are related to the amount of adsorbed HCl, because this property governs the hydrophility of the sols. In contrast, the peptizability of powders after drying the sols depends on the total concentration of HCl in the system. The hydrochloric acid impedes the condensation of surface groups to 〉Fe−O−Fe〈 bonds.From water vapor adsorption and heat of immersion data the hydration potential barrier is constructed which is comparable to the barrier according to the DLVO theory The differences and anomalies in the stability of sols are interpreted as differences in the hydrophility of samples.

Stagnation phenomenon of solid/fluid interfaces

In this article we focus on the adsorption of binary nonelectrolytes, where we try to find that specific feature of the layer structure which supports the interpretation of experimental data. Our hypothesis, consistent with thermostatical considerations, is related to the criteria of the incidence of the phases and provides a uniform description for both the adsorption from liquid mixtures and electrokinetic interactions.

Autophobic Wetting and Captation

Not all cases of spreading equilibrium can be described by the Young equation. However, assuming that the wetting is achieved in two steps – the equilibrium state is developed not directly on the solid surface but on the liquid film formed on the solid surface – the Young equation perfectly describes this latter state.

On the Magnitude of Line Tension

It was shown in our analysis of the internal energy determining the state of the capillary system that the magnitude of the intensive and non-canonical line tension depends on the size of the penetrating zone. Therefore, its effect is negligible for macroscopic systems.

The extended capillary theory

The quantities and relationships of capillary theory are summarized in a consistent formalism. Its constituents are the canonical thermostatics of the excess quantities, the interpretation of the surface tension according to deformation theory, and the formalism of parametric theory. A generalized concept of surface excess quantities is established by introducing the factors νφ and defining the individual quantities. The deformation quantities can also be incorporated into the theory, but the changes in the phase volumes have to be restricted. The theoretical difficulties of the traditional hypotheses do not arise in this unified approach and quantities that are not open to measurement can be calculated.

State equation of the boundary layer

A surface state equation that is independent of the physical state of the phases is introduced. This relationship exists between individual variables and holds for any phase. Using this equation, quantities that are either inaccessible to measurement or not easily available can be calculated. It can therefore also be applied to the interface of amorphous solid phases or crystal lattices of different Miller indices.