A study on the components of surface free energy of quartz from contact angle measurements

Measurements of the contact angle for water, glycerol, formamide, diiodomethane and 1,1,2,2-tetrabromoethane on a quartz surface were made. Using the results obtained, the geometric mean approach and long-range and acid-base interaction approach, the dispersion, non-dispersion, Lifshitz-van der Waals and acid-base components of the surface free energy of quartz were determined and compared with those determined in different ways. On the basis of the measurements and calculations it was found that the surface free energy of quartz depends largely on the amounts of silanol groups and physically adsorbed water molecules on its surface. It was also found that the two tested approaches to surface free energy of solids and liquids gave similar results, and it is suggested that the surface free energy of quartz results mainly from dispersion and hydrogen-bond intermolecular interactions.     

Influence of surface modification of porous glasses on their surface free energy

Investigations of zeta-potential changes of initial and thermally treated controlled-porosity glasses (CPGs), whose surfaces were covered with different amounts of n-octane and/or nitromethane, are presented. The dispersive ( _s ^d ) and non-dispersive ( _s ⁿ ) components of the surface free energy were then calculated using the relationships obtained. _s ^d was found to be practically independent of the treatment time (a small increase in the range of 4 mJ m^–2 can be seen), but a considerable decrease in _s ⁿ was observed (from 76.95 to 27.2 4 mJ m^–2). In the case of CPG modified with -aminopropyltriethoxysilane an increased hydrophobic character of the surface was found. This was reflected in increased _s ^d and decreased _s ⁿ values.     

Effects of shot-peening on surface contact angles of biomaterials

It was shown previously that (i) if the surface of a biomaterial is covered with TiO₂ (tetragonal structure oxide), it shows a high initial contact angle and a high change rate in contact angle (i.e. a higher spreading process); while (ii) cubic structure oxides show relatively lower spreading rates in 1% NaCl solution at 25°C. Shot-peening has been applied to biomaterials (especially titanium and its alloys) to improve their fatigue strength. It is well known that shot-peening causes surface roughening. The effects of surface roughness on wettability are not well documented. Therefore, in the present study, the effects of shot peening on the initial contact angle and changes in it as a function of time, were investigated. In addition, the spontaneous half-cell potential of all tested biomaterials were measured to correlate the wettability phenomenon to initial surface chemistry. Pure titanium and its alloys, including Ti-6AI-4V and NiTi alloys, AISI Type 316L stainless, Co-Cr alloy, and pure nickel, were mechanically polished, shot-peened and pre-oxidized at 300°C for 30 min in pure oxygen. It was found that (i) shot-peening homogenized the surface conditions in terms of initial contact angles, (ii) TiO₂ oxide shows a higher spreading coefficient, while cubic structure oxides show a lower value, and (iii) the spreading coefficient was correlated to the magnitude of the spontaneous half-cell potential.     

Determination of water film pressure and surface free energy on qraphite

From the adsorption Isotherm the water film pressure π on a graphite surface was determined. An interpretation of Π dependence on the film thickness and the value of work of wetting processes has been proposed. It has been concluded that the measured characteristic film pressure values correspond to the work of immersional, adhesional and immersional-cohesional wetting. On the basis of the values π_I, π_A, and π_max the values of the dispersion component γ_G^d of the graphite surface free energy were determined.     

The equivalency of surface tension,surface energy and surface free energy

In much of the available literature, there is confusion regarding the correct use of the terms surface tension, surface energy and surface free energy. As a result, these three terms have been used interchangeably to describe the same quantity. This problem is particularly serious in the area of solid surface science. Linford has examined and discussed such inconsistencies but failed to differentiate the three quantities clearly. In the present paper, the definitions and the relationships between surface tension, surface energy and surface free energy are examined and their proper usage clarified.     

Adsorption of anionic polyacrylamide onto coal and kaolinite: Changes of surface free energy components

The wettability of floc has a large effect on the selective flocculation flotation process of fine coal separation. The changes of thermodynamic characterization of coal and kaolinite have been investigated by Washburn dynamic method and Fourier transform infrared spectroscopy (FTIR) before and after the adsorption of anionic polyacrylamide. Lipophilic hydrophilic ratio (LHR), surface free energy, and its components were calculated by Washburn equation combined with Van Oss–Chaudhury–Good theory according to the wetting curves of coal and kaolinite samples wetted by n-hexane, α-bromonaphthalene, formamide, and water. After PAM A401 adsorption, the peaks of hydrophilic functional groups of coal (the amide group, free-NH2, secondary amide N–H, C–N) were increased, while the peaks of the hydrophobic functional group, including methyl (-CH3) and methylene (–CH2–), was decreased. The LHR value of coal decreased from 9.23 to 7.28. The polar components of coal were increased, the non-polar components were decreased, and the surface free energy was increased from 39.92 to 40.43 mN m^?1. The coal surface became more hydrophilic. For kaolinite, both hydrophilic and hydrophobic functional groups were increased, while its LHR values increased from 1.44 to 1.65. The polar component was decreased from 58.27 to 55.05 mN m^?2. Results of FTIR were corresponding to the surface property.     

Components of surface free energy of galena

Measurements of the contact angle for water, diiodomethane, bromoform and 1,1,2,2-tetrabromoethane on non-oxidized and oxidized surfaces of galena were made. Using the results obtained, the geometric mean approach, and the long-range and short-range interactions approaches, the dispersion and non-dispersion, and Lifshitz-van der Waals and acid-base components of the surface free energy of galena were determined and compared with those calculated from adsorption isotherms ofn-octane andn-propanol. On the basis of the measurements and calculations it was found that the surface free energy of galena depends on its degree of oxidation and arise mainly from London's and acid-base intermolecular interactions. It was also found that values of the dispersion and non-dispersion components of galena surface free energy determined from the contact angle assuming that a film is present around the water and diiodomethane drops, are close to those obtained from adsorption isotherms ofn-octane andn-propanol.     

Studies of the surface free energy of sulphur

From adsorption isotherms the water film pressure values on a sulphur surface were determined. An interpretation of the changes with film thickness and the value of the work of wetting processes is proposed. It is concluded that the characteristic film pressure values determined correspond to the work of immersional, adhesional and immersional-cohesional wetting. On the basis of water film pressure values, values of the dispersion component of sulphur surface free energy were determined.     

Low-voltage field emission from silver-modified porous glass

Planar silver layers have been produced on the surface of porous glass (PG) membranes by multiple impregnations with an aqueous AgNO₃ solution, followed by hydrogen reduction of the salt to silver metal. In all cases, electron emission from the surface of the metallized porous glasses is observed above threshold electric fields lower than 2 V/μm. The emittance of the Ag/PG membranes decreases as the amount of silver increases above a nominal monolayer.     

Checking contact angles of radial-thrust bearings

Summary On the basis of the above method of measurement, using expression (4), highly productive semiautomatic devices were made for sorting out bearings by their contact angles into three groups: small, good and large.The adoption by our industry of these measuring devices for checking the contact angles will raise considerably the quality and life of radial-thrust bearings.     

Wetting contact angles of certain systems

The wetting contact angles of a number of systems are determined experimentally. The measurements are carried out in air at temperatures of 20–70°C by a variety of methods.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 6, pp. 1000–1003, June, 1977.     

Determination of free energy of the crystal-melt interface

The results of calculation of the free energy ?? of the crystal-melt interface using the molecular dynamics method are presented. The interfacial energy is determined from analysis of the capillary fluctuations spectrum in the two-phase system. The free energy values of the crystal-melt interface are found for aluminum on the melting line in the temperature range of 935 to 1110 K. The anisotropy value of the interfacial free energy is estimated for different interface orientations. It is shown that the free energy values for the basic planes are arranged in the order ??₁₀₀ > ??₁₁₀ > ??₁₁₁. It is revealed that the free energy of the crystalmelt interface increases with the rise in temperature along the melting line.     

Static solvent contact angle measurements, surface free energy and wettability determination of various self-assembled monolayers on silicon dioxide

In many fields and applications, a good knowledge of the wetting behaviour of solvents on a surface is crucial. Self-assembled monolayers (SAMs) have enabled improved control over surface properties, while more recent fields such as organic electronics gave rise to new applications and requirements regarding solvent-substrate interactions. However, most reported wettability studies are limited to practically less relevant solvents such as water, diiodomethane or hexadecane. Herein we report static contact angle measurements of various, typical SAM-modified surfaces, characterizing these surfaces' wettabilities over a wide range of practically relevant solvents. Surface energies, both the polar and the disperse component, of these SAM-modified surfaces are extracted with various methods from the contact angle data. Reliable methods for surface energy extraction, such as the Owens-Wendt-Rabel-Kaelble method and the method after Wu, yield values which could be expected from the chemical structure and nature of the self-assembled molecules and which correspond well to the few reported literature values. We also determined wetting envelopes for the various surfaces which allow easy prediction of the surfaces' wettability for a certain solvent and which ensure relevance for current and future solvents.     

Measurement of the specific free surface energy of solids

A set of equations is proposed that makes it possible to obtain calculation equations for experimental determination of the specific free surface energy of solids. __________ Translated from Izmeritel’naya Tekhnika, No. 10, pp. 68–69, October, 2007.     

Instrument for measuring peripheral angles of contact

Measurement Techniques -     

On the determination of the surface free energy of quartz

Studies of water vapor adsorption on quartz by the method analogous to the dynamic gas chromatography step profile method are described. The adsorption was determined by changes in the capacitance of the capacitor (detector) between the coverings of which the quartz powder was placed. Prom the adsorption isotherm the film pressure π of the water film on quartz were determined, obtaining $\text{π}{}_{\max }\text{= 380}\text{erg}\text{cm}{}^2$.An interpretation of the π changes in relation to the film thickness and the kind of wetting process has been proposed. It is concluded that the characteristic film pressure values result from the work of spreading, immersional and adhesional wetting and correspond to thicknesses of about 2, 3 and 4 statistical water monolayers, respectively. The maximum π value, however, probably corresponds to the work of quartz- water adhesion + water cohesion work. On the basis of the thus determined values of π_s, π₁, and π_max, the value of the polar component γ_q^p of the quartz surface free energy was determined, using the value $\text{γ}{}_{\mathrm{q}}{}^{\mathrm{p}}\text{= 76}\text{erg}\text{cm}{}^2$. The calculated average of the γ_q^p value equals 115 $\text{erg}\text{cm}{}^2\text{2}$.     

Determination of particle density of lightweight aggregates with porous surface

Particle density is one of the most important values to characterize lightweight aggregates. Various test methods yield various densities, because the grain volume is defined by the test fluid used to determine the volume of the aggregate particles. Several standardized test methods are analysed and compared with each other. The test results are reported. An improved test method is presented, which embeds the aggregate particles in cement paste to simulate the real conditions in fresh concrete.     

Determination of effective surface energy of dynamic failure

A method is presented for determining the effective surface energy under dynamic loading. It is based on combining the effect of a valuewise different static tensile load and similar tensile pulses on identical specimens. It is shown that the method is insensitive to the sharpness of the originally made notch. This facilitates the form of the moving crack front to be controlled and eliminates the need to set up a fatigue crack. Graphs of variation in time of the SIF and length and velocity of the crack are given.Translated from Problemy Prochnosti, No. 7, pp. 10–14, July, 1992.