Effect of pH on surface energy of glass and Teflon and theoretical prediction of Staphylococcus aureus adhesion

The surface energy of glass and Teflon at various pH values was examined. Contact angle was used to determine physico-chemical substratum properties. The surface energy of both substratums including, hydrophobicity, and electron donor/electron acceptor (Lewis acid–base properties) were found to depend on pH of contact solution. The maximum of hydrophobicity (higher negative value of ΔG_iwi) was obtained at pH 11 and pH 6.5 for glass and Teflon respectively. The electron donor property was higher at pH 5 and pH 3 for glass and Teflon respectively. Moreover, prediction of Staphylococcus aureus adhesion on both substratums was estimated by calculating the total interaction free energy (ΔG^Tot). Based on the value of ΔG^Tot, S. aureus should adhere to glass at pH 2, pH 3 and pH 11 with the maximal adhesion obtained at pH 3 and pH 11. For Teflon, regardless of pH values, S. aureus should be able to attach on this substratum with the high adhesion level at pH 5. The relation between surface energy of substratum and the total interaction free energy was also examined. Based on this relation and the value of the components of total interaction free energy, we show that adhesion to glass could be governed by both short range forces (Lewis acid–bases forces) and by long range forces (van der Waals forces) and the adhesion to Teflon could be mediated only by the short range forces.     

Effect of acclimatization of microorganisms to heavy metals on the performance of activated sludge process

Although selected heavy metals (HMs) stimulate biological reactions at low concentrations, all HMs are toxic to microorganisms (MOs) at moderate concentrations and can cause inhibitory effects on the biological processes. Therefore, MOs must be acclimated to HMs or other toxic substances present in wastewaters (WWs) before they are used in an activated sludge process (ASP). In this study, combined effect of Cu(2+) and Zn(2+) ions in a synthetic WW on the efficiency of a laboratory-scale ASP without recycle was investigated using acclimated MOs at different extents.A synthetic feed solution of 1222 mg L(-1) proteose-peptone (corresponding to 1300 mg COD L(-1)) served as a source of carbon. Cu(2+) and Zn(2+) ions at different concentrations (1.5, 4.5 and 9, 27 mg L(-1), respectively) were introduced in the feed to a continuously stirred activated sludge reactor at different hydraulic residence times (2-40 h) keeping pH, temperature and stock feed composition constant. The combined effects of copper and zinc ions were determined by mixing these metallic ions at the specified combinations of concentrations such as "1.5 mg L(-1) of Cu(2+)+9 mg L(-1) of Zn(2+)" and "4.5 mg L(-1) of Cu(2+)+27 mg L(-1) of Zn(2+)". It was observed that using seed MOs acclimatized to two times of the combined threshold concentration of these HMs for an unduly long period of time (1-4 months) caused adverse effects on the ASP performance. Besides, it was found that usual inhibition effects of these HMs were enhanced with increasing period of acclimation. Substantially lower substrate removal efficiencies were obtained with acclimatized MOs than those obtained with non-acclimatized MOs. At the higher initial substrate concentration of 2500 mg COD L(-1), substrate-inhibition occurred causing a decrease in the specific growth rate constant (k); however, HM inhibition was suppressed, resulting to about 20% increase in treatment efficiency of the ASP. It can be concluded that the time period necessary for acclimatization of seed MOs must be adjusted carefully with concentrations of HMs lower than their threshold concentrations to achieve an optimal operation of an aerobic biological process.     

Determination of porous glass surface free energy components from contact angles

The contact angles of water drops and diiodomethane drops on pellets made of controlled porosity glasses have been measured. The surface of the glasses was modified by thermal treatment at 873 K which led to an increase in the surface concentration of boron atoms. Glass modified with Carbowax 20M (polyethylene glycol) and fully hydroxylated glass have also been studied. Using the measured contact angles and modified Young equation, the dispersion and nondispersion components of the glass surface free energy have been calculated. The values show that with increasing heating time (increasing surface density of boron atoms) an increase in the surface polarity takes place. However, the polarity of the same samples decreases after treatment with Carbowax, increasingly so with higher boron atom concentrations.     

基于表面自由能理论研究改性沥青-集料复合材料黏附性能

基于表面自由能理论,首先测定不同沥青、集料与已知试剂的接触角,然后通过相关公式计算得到沥青-集料复合材料的黏附功、剥落功及水稳定性指标ER,并分析老化前后沥青-集料复合材料的黏附性变化。研究结果表明:沥青-集料复合材料的黏附过程和剥落过程均对外放热且自发进行;同种沥青不同集料的复合材料黏附性和抵抗水损害能力排序为沥青-石灰岩沥青-玄武岩沥青-花岗岩,不同沥青同种集料复合材料黏附性强弱和抵抗水损害能力排序为复合改性沥青(CM)-集料胶粉改性沥青(CRM)-集料苯乙烯-丁二烯-苯乙烯改性沥青(SBSM)-集料复合材料;老化后沥青-集料复合材料的黏附性能和抵抗水损害能力均呈现下降趋势,且压力老化(PAV)比旋转薄膜烘箱老化(RTFOT)更为明显,但老化过程并未改变沥青与集料间的配伍性;对三种改性沥青的SEM图像进行分析,发现老化后沥青与集料界面黏结特性发生变化,导致沥青-集料复合材料黏附能力下降。     

Effect of interfacial free energy anisotropy on silicon whisker growth

Data are presented which demonstrate that the {111} and {100} surfaces of a silicon whisker in contact with a liquid metal solvent droplet are more anisotropic than those in contact with the vapor phase. Melting of metal solvent particles on a silicon substrate is accompanied by wettability anisotropy: the (111) close-packed faces of silicon are more poorly wetted by liquid solvent droplets than are the other faces.     

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.     

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.     

Cell/surface interactions and adhesion on bioactive glass 45S5

This paper examines the effects of surface texture (smooth versus rough) on cell/surface interactions on the bioactive glass, 45S5. The cell surface interactions associated with cell spreading are studied using cell culture experiments. Subsequent energy dispersive x-ray spectroscopy is also used to reveal the distributions of calcium, phosphorous, sodium and oxygen on the surfaces of the bioactive glasses. The implications of the results are then discussed for the applications of textured bioactive glasses in medicine.     

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.     

Quantification of the adhesion free energy between bacteria and hydrophobic and hydrophilic substrata

In this paper, the bacterial adhesion to hydrophilic glass and hydrophobic indium tin oxide (ITO) coated glass surfaces was investigated. The aim of this work was to examine the effect of the hydrophobicity of two bacterial strains (Pseudomonas stutzeri PS, and Staphylococcus epidermidis SE) and substrata surfaces on the adhesion mechanism. The hydrophobicity of the surfaces of the bacterial strains as well as of the surfaces of the tested materials was characterized using the contact angle measurement via sessile drop technique. The water contact angle measurements of the intrinsic cell hydrophobicity showed that the PS strain is more hydrophobic (θ = 40°) than SE strain (θ = 21°). For both tested materials, this angle was 12° for glass surface and 84° for ITO-coated glass surface. Based on the thermodynamic approach, the Lifshitz van der Waals interaction free energy, the hydrophobic interaction free energy and the total interaction free energy between the bacteria and the substratum through the suspending medium were quantified. In order to verify the thermodynamic approach predictions of the bacterial adhesion on each substratum, adhesion tests were carried out for each bacteria/substratum combination. The results revealed that for both materials surfaces, the adhesion energy of the hydrophobic PS strain (26.1 mJ/m² for glass and − 3.8 mJ/m² for ITO-coated glass) is higher than that of SE strain (31.8 mJ/m² for glass and 14.3 mJ/m² for ITO-coated glass). For both bacterial strains, the effect of the hydrophobicity property of the substratum seems more important in the initial adhesion step. However, the second step of adhesion involves the biological approach, since a discrepancy was found between physicochemical theoretical approach and adhesion tests for SE strain.     

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.     

Effect of ultrasound on the adhesion of metal coating to nonferrous metals

The effect of ultrasound on the adhesion of metal coating to nonferrous metals has been studied. It is established that the ultrasonic treatment of metal coatings increases their adhesion strength. This effect is explained by the fact that the momentum imparted by ultrasound to atoms of the coating is sufficient to cause their migration over a certain distance from the surface into depth of the nonferrous metal substrate.     

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 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.     

Self-organised growth on strained substrates: the influence of anisotropic strain, surface energy and surface diffusivity

The morphological stability of coherent thin films subjected to unequal in-plane biaxial strains is investigated to determine how non-uniform strain states can be used to influence the growth of self-organised island nanostructures. The evolution via surface diffusion is modelled analytically using a small perturbation approach and allows for anisotropies in the surface energy and the surface diffusivity. It is shown that conventional uniform biaxial epitaxy does not provide a driving force towards a particular wavelength as is popularly assumed. This reduces the potential for highly self-organised growth. It is predicted that improvements in island size, shape and spatial distributions can be obtained under certain conditions of anisotropic strain, surface energy and surface diffusivity. This increase in uniformity would be beneficial to the construction of practical devices. Enhancing surface diffusivity anisotropy via the application of an applied strain could offer the most realistic opportunity for controlling the growth of self-assembled structures this way.     

Effect of water on the mechanical adhesion of the glass/epoxy interface

In recent years, the quality of the fibre/matrix bonding in polymer composites has been quantified by means of a single mechanical parameter, the interfacial shear strength, based on measurements made using micromechanical techniques. It has gradually appeared, however, that this parameter is both ambiguous in terms of its physical meaning and, at the same time, difficult to measure reliably in many cases. Moreover, different micromechanical techniques yield differing values of the interfacial shear strength. Finally, it has been suggested in a few studies that it may not be the critical factor governing fibre/matrix debonding. In this paper an energy balance approach is proposed, by which the degree of fibre/matrix bonding is now quantified by means of the interfacial energy, as a function of the fibre geometrical and mechanical characteristics, the stress transfer length and the debonding length. The validity of the approach is discussed in the case of the single-fibre composite test, in which progressive fragmentation of a single brittle fibre in a more ductile polymeric matrix takes place, using data for E-glass fibres embedded in epoxy, both in the dry state and in the presence of hot distilled water.