Acid-base Interaction Energy Research Articles

Quantitative Analysis of Membrane Fouling Mechanisms Involved in Microfiltration of Humic Acid–Protein Mixtures at Different Solution Conditions

A systematical quantitative understanding of different mechanisms, though of fundamental importance for better fouling control, is still unavailable for the microfiltration (MF) of humic acid (HA) and protein mixtures. Based on extended Derjaguin–Landau–Verwey–Overbeek (xDLVO) theory, the major fouling mechanisms, i.e., Lifshitz–van der Waals (LW), electrostatic (EL), and acid–base (AB) interactions, were for the first time quantitatively analyzed for model HA–bovine serum albumin (BSA) mixtures at different solution conditions. Results indicated that the pH, ionic strength, and calcium ion concentration of the solution significantly affected the physicochemical properties and the interaction energy between the polyethersulfone (PES) membrane and HA–BSA mixtures. The free energy of cohesion of the HA–BSA mixtures was minimum at pH = 3.0, ionic strength = 100 mM, and c(Ca2+) = 1.0 mM. The AB interaction energy was a key contributor to the total interaction energy when the separation distance between the membrane surface and HA–BSA mixtures was less than 3 nm, while the influence of EL interaction energy was of less importance to the total interaction energy. The attractive interaction energies of membrane–foulant and foulant–foulant increased at low pH, high ionic strength, and calcium ion concentration, thus aggravating membrane fouling, which was supported by the fouling experimental results. The obtained findings would provide valuable insights for the quantitative understanding of membrane fouling mechanisms of mixed organics during MF.

A criterion for the characterization of modified surfaces during crystallization fouling based on electron donor component of surface energy

Surface treatment is gaining increased attention as an environmentally-friendly approach to combat crystallization fouling by minimizing adhesion energies between precursors and the substrate. What specific components of the surface energy cause this to happen though is still a matter of much debate. The present study aims at developing a criterion by identifying what interaction energies and surface energy components would cause a surface to foul. The proposed criterion shows that the Lewis acid-base interaction energy has a strong implication on the adhesion process. Most notably, increased Lewis base polarity component provides a higher repulsive energy, which in turn reduces the adhesion force between precursors and the substrate. The criterion was validated with the experimental data of this study and some previous studies of crystallization- and bio-fouling which showed that the tendency of surfaces to foul decreases when the electron donor component increases.

Harvesting of microalgal biomass using MF membrane: Kinetic model, CDE model and extended DLVO theory

In this paper, the Carman–Kozeny (C–K) model is proposed as a means of predicting flux decline for every stage of membrane cleaning, which can be strongly affected by pore blockage and by the growth of a cake layer. A combination of a kinetic model and the C–K model was utilized to determine specific parameters that can be used to estimate the decline in flux. The model was shown to be in excellent agreement with the experimental data obtained during the crossflow microfiltration of microalgal biomass over several cleaning cycles. The mean flux, given suitable transmembrane pressure (TMP), was also predicted by the model. The cleaning kinetics of the process suggested that a higher energy barrier Ec and a higher rate constant k0 were present for the final cycle of cleaning process, resulting from the extra energy required to break the bonds between the deposited cells and the membrane. This paper also focused on the electrostatic interaction between the microalgal cells and the membrane surface. The concentration polarization (CP) thickness of microalgae on a cellulose acetate (CA) membrane was calculated by the CDE model based on the balance of three transport mechanisms, namely, convection, diffusion and electrophoretic migration, with consideration being given to the negative charge of the microalgae and the membrane surface. The CP thickness was found to be strongly dependent on the membrane surface charge and the number of membrane cleaning cycles. The full interaction between the microalgae and the membrane was characterized according to a DLVO and an extended DLVO approach based on the strength of three separate interactions, namely, the van-der-Waals interaction (vdW), electrostatic (ES) repulsion and acid–base (AB) interactions. Both DLVO and XDLVO analysis provide useful methods for predicting the potential role of these interactions in the adhesion of microalgae to membranes. The XDLVO analysis determined a higher repulsion than did the DLVO analysis as a result of the high AB interaction energy in aqueous systems.

Interactions of fully formulated epoxy with model cement hydrates

The surface energy of cement paste components (calcium silicate hydrate [C-S-H], ettringite and portlandite) before and after treatment with an organic coating has been characterised by X-ray photoelectron spectroscopy (XPS) and inverse gas chromatography at 35 °C using n-alkanes, 1-alkene, chloroform, tetrahydrofuran, diethyl ether and CCl4 molecular probes. Complementary investigations on the interfacial chemistry were also conducted by Fourier transform infrared spectroscopy and Differential scanning calorimetry analyses. Changes in the dispersion contribution to the surface energy () and acid–base interaction energies were found to be significantly reduced by the organic coating. The XPS allowed the surface chemistry changes induced by the organic coating to be monitored. In particular, the C1s spectra were peak fitted in order to deduce the contribution of the organic coating materials to the total carbon content on the surface. This study showed not only the existence of hydrate-hardener donor–acceptor adduct formation but also presence of interactions between the hydroxide groups OH of the epoxy and portlandite.

Surface energetics of cementitious materials and their wettability by an epoxy adhesive

The surface thermodynamic properties of cementitious materials and the wettability of these substrates by an epoxy adhesive were investigated using various surface analysis techniques. In a first step, surface energies of hardened cement pastes were assessed either by contact angle measurements using the Owens and Wendt approach, or by inverse gas chromatography (IGC). A good correspondence was found between the two techniques for the dispersion contribution γ s d , and a strong amphoteric behavior of these materials was also demonstrated. Additionally, a surface carbonaceous contamination detected by X-ray photoelectron spectroscopy (XPS) was found to lower the surface energy of as-received samples, whereas an acetone cleaning treatment resulted in increased γ s d values. In a second part, surface characterizations were performed on three synthetic compounds, representative of the main hydration products of hardened cement pastes, i.e. calcium hydroxide, ettringite and calcium silicate hydrate (C -S -H). IGC experiments provided γ s d values ranging from 45.6 up to 96.3 mJ m −2 at 35 °C, and the acid–base behavior was correlated to the water content. Last, XPS and IGC analyses were performed on cement paste powders coated either with an epoxy resin (R) or with an amine hardener (H), separately, at mass loadings up to 10 wt.%. Changes in the dispersion contribution to the surface energy ( γ s d ) and Lewis acid–base interaction energy were found to be significantly dependent on the adsorption of both H and R, showing a substantial wetting of the mineral substrate by the adhesive components. In addition, XPS evidenced interfacial hydrogen bonding between the hardener and the cementitious substrates.

Interfacial interactions of structural adhesive components with cement pastes: Studies by inverse gas chromatography (IGC)

The surface energy of hardened cement pastes, before and after treatment by organic coating, and two individual cement paste components (CSH and ettringite) have been characterized by inverse gas chromatography (IGC) at 35°C, using n-alkanes, 1-alkenes, benzene, chloroform and CCl4 molecular probes. The cement pastes were prepared by mixing an ordinary Portland cement (OPC) with water at a water/cement ratio (W/C) equal to 0.3 and 0.5. They were further coated with an epoxy resin (R) and triethylenetetramine hardener (H), separately, at a mass loading of 1 and 10wt.%, respectively. Changes in the dispersive contribution to the surface energy (γsd) and Lewis acid–base interaction energies were found to be significantly dependent on the W/C parameter on the one hand, and the adsorption of H and R, on the other hand.

The utility of Bacillus subtilis as a bioflocculant for fine coal

The application of Bacillus subtilis as a flocculant for fine coal has been reported here. Zeta-potential measurements showed that both the coal and bacteria had similar surface charge as a function of pH. Surface free energy calculations showed that the coal was hydrophobic while the bacterium was hydrophilic. The adhesion of the bacteria to coal and subsequent settling was studied in detail. Adhesion of bacteria to coal surface and subsequent settling of coal was found to be quick. Both adhesion and settling were found to be independent of pH, which makes the process very attractive for field applications. The presence of an electrolyte along with the bacterium was found to not only enhance adhesion of bacteria, but also produce a clear supernatant. Further, the settled fraction was more compact than with bacteria alone. Interaction energy calculations using the extended DLVO theory showed that the electrical forces along with the acid–base interaction energy play a dominant role in the lower pH range. Above pH 7, the acid–base interaction energy is the predominant attractive force and is sufficient enough to overcome the repulsive forces due to electrical charges to bring about adhesion and thus settling of fine coal. With increase in electrolyte concentration, the change in total interaction energy with pH is minimal which probably leads to better adhesion and hence settling.

Estimation of surface free energy of pyrites by contact angle measurements

The surface properties of coal-pyrite play a major role in determining its separation from coal in processes such as flotation. The solution pH is an important parameter in determining the surface properties of both coal and coal-pyrite such as surface free energy and zeta-potential. In the present investigation, the effect of pH on the surface free energy of pyrites from different sources was studied. The surface free energy of solids is made up of two components, i.e. the dispersive surface free energy and the acid-base interaction energy. Various methods have been used by previous researchers to evaluate these two components for different solids. In the present study, a new approach was developed and used to study the surface free energy of pyrite surfaces. Results indicate that the dispersion surface free energy of various pyrites is independent of pH while the acid-base interaction energy is strongly dependent on the pH. The acid-base interaction energy is different for each pyrite sample and also the change with pH varies with the type of pyrite. Coal-pyrite was found to be more hydrophobic than ore-pyrite which may be attributed to the presence of carbon in coal-pyrites. The acid-base interaction energy varied little with pH for coal pyrites than ore-pyrite. Comparison of acid-base interaction energy with zeta-potential measurements shows a good correlation between the minimum in acid-base interaction energy and the pH pzc.

Influence of casting substrate on the acid–base interaction energies of various polyesters

The acid–base surface characteristics of four polyesters: poly(l-lactic acid) (PLLA), poly(dl-lactic acid) (PDLLA), polyhydroxybutyrate (PHB) and copoly(hydroxy butyrate–20% hydroxyvalerate)P(HB–20% HV) have been determined from contact angle and surface tension experimental data. Smooth surfaced polyester films were prepared by solution casting against a number of substrates ranging from high surface energy (aluminium, mercury, glass and freshly-cleaved mica) to low surface energy (poly(ethyleneterephthalate)(PET), poly(tetrafluoroethylene)(PTFE) and dry nitrogen gas).Results show that the acid–base interaction energy of the polyester surface is dependent on the casting substrate and ageing time. For a particular casting substrate, the equilibrium acid–base interaction energy between a polyester surface and an acidic liquid decreases in the order: PDLLA; PLLA; PHB; P(HB–20%HV).The time dependence of the acid–base interaction energy is interpreted in terms of orientation of surface acidic or basic sites. Furthermore, detailed results suggest that the initial acidic or basic character of the cast polyester surface is influenced by the acid/base surface properties of the casting substrates.

Surface characterization of industrial fibers with inverse gas chromatography

Inverse gas chromatography (IGC) was applied for the determination of the surface characteristics of Tenax carbon fibers and Akzo Nobel Twaron fibers. Furthermore, IGC procedures for the determination of dispersive and acid–base interactions were validated. The data show that too high values for the dispersive component of the surface energy are obtained when the adsorption area occupied by a single adsorbed n-alkane molecule is estimated from parameters of the corresponding liquid. Comparable values are obtained when the Doris–Gray methodology (area per methylene unit) or measured probe areas are employed. For the fibers studied in this work meaningful Gibbs energy values of the acid–base interaction were only obtained with the polarizability approach. When the dispersive interaction of the polar probes with the fiber surface was scaled to the n-alkane interaction via surface tension, the boiling point, or the vapor pressure of the probes often negative acid–base interaction energies were found. From the temperature dependence of the Gibbs energy, the enthalpy of the acid–base interactions of various probes with the carbon and Twaron aramid fibers was determined. However, from these enthalpy values no meaningful acid–base surface parameters could be obtained. Generally, the limited accuracy with which these parameters can be obtained make the usefulness of this procedure questionable. Also the Gibbs energy data of acid–base interaction can provide a qualitative basis to classify the acidity–basicity of the fiber surface. This latter approach requires only a limited data set and is sufficiently rapid to enable the use of IGC as a screening tool for fibers at a production site. For several polar probes significant concentration effects on carbon fibers were observed. At very low probe loadings the interaction with the fiber surface suddenly increases. This effect is caused by the heterogeneity of the interaction energy of the active sites at the surface. A simple procedure to measure the adsorption isotherm at infinite dilution was developed. The determination of the concentration dependence of the interaction of an n-alkane, an acidic and a basic probe was incorporated in the IGC screening procedure of carbon fibers to monitor this heterogeneity.

Basis-set effects on computed acid-base interaction energies using the Dunning correlation-consistent polarized split-valence basis sets

Ab initio calculations have been performed at correlated levels of theory to investigate the convergence of the binding energies of hydrogen-bonded neutral, positive ion and negative ion complexes with systematic expansion of the basis set. For this study, the Dunning correlation-consistent polarized split-valence basis sets augmented with diffuse functions only on nonhydrogen atoms (aug'-cc-pVXZ, where X = D for double-split, T for triplesplit, and Q for quadruple-split) have been used. Computed hydrogen bond energies of all complexes converge with increasing basis set size, with satisfactory convergence occurring at aug'-cc-pVTZ. Binding energies are not sensitive to the presence of diffuse f functions in the aug'-cc-pVTZ basis set, and these f functions may be omitted. The presence or absence of diffuse d functions has little effect on the computed binding energies of neutral and positive ion complexes. However, these functions are important for describing the binding energies of the negative ion complexes. In contrast, quantitatively accurate proton affinities for corresponding neutral and anionic monomeric bases require the presence of both diffuse f and diffuse d functions in the aug'-cc-pVTZ basis set. For neutral and positive ion hydrogen-bonded complexes, MP4/aug'-cc-pVTZ binding energies are within 0.1 kcal mol −1 of CCSD+T(CCSD) binding energies, but may be as much as 1 kcal mol −1 smaller for the negative ion complexes.

A modified sessile drop technique for the determination of the interactions at carbon-liquid interfaces

The interactions at the carbon fiber surfaces are of fundamental importance for the reinforcement of polymers with carbon fibres. A modified sessile drop technique is proposed for the determination of the surface free energy of carbons and the interactions at carbon surfaces (work of adhesion). The method is based on the advancing contact angle (film-free surface) of aqueous solutions with pH values ranging from 1 to 14. The works of adhesion calculated from the advancing contact angle show a distinct dependence on the pH value. This dependence allows the determination of the dispersion component of the surface free energy and the acid-base interaction energies. The method was tested with high-temperature polymers and successfully applied to carbons.

Role of electron correlation in the quantum‐mechanical calculations of the coulomb interaction energy in the DNA base pairs

AbstractThe intermolecular electronic correlation contributions to the Coulomb component of the nucleic acid base interaction energy are estimated. The Coulomb energy is evaluated with the use of atomic monopoles, which are determined from the π‐electronic densities calculated by the SCF method and by employing partially or completely optimized APSG wave functions. When the correlation is thus taken into account, a systematic decrease in atomic charges occurs; this effect is considerable only if an optimized orbital set is used. As a result, the Coulomb interaction energy due to the π‐electronic atoms decreases from −1.13 to −0.85 kcal/mol for the AT pair and from −7.15 to −4.61 kcal/mol for the GC pair.