Cell surface properties of the demulsifying strain Alcaligenes sp. S-XJ-1 governing its behavior in oil–water biphasic systems

Bacterial behavior in oil–water biphasic systems plays an essential role in hydrophobic contaminant degradation, oil recovery, and emulsion breaking. Less is known about the cell surface properties that govern their behaviors in oil–water biphasic systems. In this study, biphasic partitioning and aggregation of a demulsifying strain of Alcaligenes sp. S-XJ-1 were experimentally measured and evaluated based on the cell surface properties of surface charge, surface free energy, and cell surface hydrophobicity (CSH). The S-XJ-1 was cultivated with five different carbon sources, and the results showed a highly varied partitioning, aggregation behavior, and cell surface properties. The calculated interaction energies, based on the cell surface properties, were consistent with the results of their behavior. Among the cell surface properties, the electron-donor character (γ^?, range 8.8–57.0 mJ/m²), which correlated well with CSH (ΔG_bwb), was an essential indicator of cell behavior. A low γ^? value enhanced the cell–interface and cell–cell interaction energies, which promoted cell partitioning and aggregation eventually leading to demulsification. The results and analysis provide important information for researchers concerned with cell–cell and cell–interface interactions.     

Inverse gas chromatography for determining the dispersive surface free energy and acid–base interactions of sheet molding compound—Part II 14 Ligno‐cellulosic fiber types for possible composite reinforcement

Composites reinforced with natural plant fibers are currently actively researched. Inverse gas chromatography (IGC) is a technique that is used to characterize the surface energy and polar characteristics of materials. The theoretical approaches used with IGC are reviewed and applied to the study of 14 ligno‐cellulosic fiber types including grass fibers, bast fibers, leaf fibers, seed fibers, and fruit fibers. This was done to provide insight into the impact of fiber composition on the surface characteristics of the different fiber types and explore possible correlations among the data. The dispersive surface energy, and K_a, K_b constants are reported for the 14 fiber types and compared with values reported in the literature. The dispersive energies ranged from 35.5 mJ/m² to 44.2 mJ/m² at 20°C with K_a from 0.01 to 0.38 and K_b from 0 to 1.05. A correlation was found at 40°C for surface energy related to fiber composition and fiber type where the surface energy decreases with increasing lignin and hemicellulose composition but increased with increasing cellulose concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Unveiling surface stability and oxygen diffusion of rare-earth zirconate pyrochlores by density functional theory

The surface structures, bond variations, and segregation of oxygen vacancies play crucial roles in the structural stability and functionality of nanocrystalline rare-earth zirconate pyrochlores. In this work, the stabilities of (1 0 0), (1 1 0), and (1 1 1) surfaces of pyrochlore A₂Zr₂O₇ (A = La, Ce, Pr, Nd, Pm, Sm, Eu, or Gd) are investigated by first-principles calculations. Surface reconstruction occurs on (1 1 0) surface with a transition of ZrO₆ octahedron to ZrO₄ tetrahedron, leading to their large relaxation energies. In combination with the small amount of broken bonds during the surface formation process, the (1 1 0) surfaces are identified having the lowest surface formation energies than the (1 0 0) and (1 1 1) surfaces. Moreover, the reconstructed (1 1 0) surface has characteristics of the segregation of oxygen vacancies. The surface oxygen vacancies have the low migration barriers (<1.2 eV), which are comparable with those in bulk and ensure the long-distance diffusion of oxygen vacancies in A₂Zr₂O₇. These discoveries provide fundamental insight to the surface structure and related oxygen vacancy behavior, which are expected to guide the optimization of the surface related properties for nanocrystalline rare-earth zirconates.     

Fluorinated acrylic polymers: Surface properties and XPS investigations

A series of polymers based on methylmethacrylate, butylacrylate, and ω‐perfluorooctylalkylacrylate were prepared by radical polymerization. By changing both the length of the hydrocarbon spacer, between the fluorinated chain and the ester function of the fluorinated monomer, and its concentration, the surface properties of the resulting terpolymers were greatly influenced. Polymers containing small amounts of fluorinated comonomer units had considerably reduced surface energies compared to the copolymer poly (methylmethacrylate‐co‐butylacrylate) taken as reference. The outermost surface composition has been investigated by the XPS technique, confirming the strong fluorine enrichment. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 821–827, 2006     

Unveiling surface stability and oxygen vacancy segregation of Yb2SiO5 and Lu2SiO5 by first-principles calculations

RE₂SiO₅ (RE = Yb and Lu) are significant environmental barrier coating (EBC) materials, in which surface and oxygen vacancy play crucial roles in their structural stability and functionality. In this work, the structural configuration and thermodynamics of (1 0 0), (0 1 0), and (0 0 1) surfaces of RE₂SiO₅ are investigated by first-principles calculations. The (0 0 1) surface is preferred energetically, which is attributed to the weak bond broken environment and large rare-earth polyhedron distortion on this surface. Moreover, the formation energies of various oxygen vacancies on the stable (0 0 1) surface are estimated and the optimal location for oxygen vacancies is held by the [SiO₄] tetrahedron. The oxygen vacancies are more likely to segregate on the surface because of the lower formation energies on the surfaces compared with those in the bulk. These findings are expected to enable the development of RE₂SiO₅-based EBCs by tuning grain size and/or thin film growth orientation.     

Studying the drying mechanism of microalgae Chlorella vulgaris and the optimum drying temperature to preserve quality characteristics

Drying harvested microalgae from an average moisture content of 80% wet basis to a safe moisture content of 10% is challenging. Removing this high amount of water from microalgal biomass is time-consuming and is not as easy as agricultural crop dehydration. The long drying time results in large drying costs. Although drying is a suitable technique for algal-based fuel production, it has not been commercialized due to its associated challenges. This study was performed to fulfill the knowledge gap in the microalgae drying mechanism and to understand the reason for long drying times. For this purpose, the thin-layer drying of microalgae Chlorella vulgaris at the temperature range of 40 to 140°C was studied in a convective oven. The effect of drying air temperature on Chlorella elemental and chemical composition, surface color, and surface structure in the aforementioned temperature range was also analyzed. The results revealed that the dominant mechanism in Chlorella drying is diffusion, which is attributed to the collapse of microalgal cells structure with increased drying temperature. In fact, moisture is entrapped in the Chlorella cells and it takes a long time for them to reach the biomass surface and evaporate. The result was that both low and high drying temperatures have adverse effects on Chlorella surface color, structure, and carbohydrate and lipid composition. This suggests that microalgae should be dried at an optimum medium (60–80°C) temperature.     

Effects of surface treatments on the shear bond strength of luting cements to zirconia

Objective: The aim of this in vitro study was to evaluate the effect of surface treatments on the shear bond strength of resin cements to zirconia. Material and methods: Sintered zirconia specimens (n = 192) were divided into four different surface treatment groups: control (no treatment); airborne-particle abrasion; glaze layer and hydrofluoric acid (HF) application, and hot etching solution application. Then, each group was divided into four subgroups (n = 12), and three different resin cements were applied to the zirconia surfaces. The shear bond strength value of each specimen was measured after 5000 thermo cycles. The failure types were examined with a stereomicroscope and the effects of the surface treatments were evaluated with a scanning electron microscope. Results were analyzed using analysis of variance and Tukey’s post hoc tests (α = 0.05). Results: The surface treatment and resin cement type significantly affected the bond strength results (p < 0.05). For all resin cements, the airborne-particle abrasion treatment increased the shear bond strength values (p < 0.05). The glaze layer & HF application increased shear bond strength values for all groups, except the Single Bond Universal-RelyX Unicem Aplicap group (p < 0.05). The surface roughness values of airborne-particle abraded specimens were similar to comparable values for specimens from the control group and the hot etching solution group (p > 0.05). The glaze layer & HF application group produced the highest surface roughness values (p < 0.05). Conclusion: The results of this study recommend using the appropriate combination of surface treatment and adhesive/silane coupling agent to achieve durable zirconia-resin bonding.     

Molecular and dissociative adsorption of a single water molecule on a β‐dicalcium silicate (100) surface explored by a DFT approach

The adsorption of water on a C₂S surface initiates belite to hydrate. In the present work, the adsorption behavior of single water molecule on a β‐C₂S (100) surface is explored using density functional theory (DFT) due to the lack of alternative approaches for direct observation. Four possible calcium atom sites on the β‐C₂S (100) surface slab are considered in our calculations. The results show that water can adsorb on the 2 five‐coordinated calcium sites only via molecular adsorption with adsorption energies of 0.59 and 0.85 eV, respectively, but can dissociate on the other 2 six‐coordinated calcium sites with higher adsorption energies of 0.96 and 0.99 eV, respectively. The energy barriers to the dissociative adsorption of water at the Ca(III) site(0.10 eV) is much lower than that at the Ca(IV) site, indicating that water prefers to adsorb and dissociate on Ca(III) sites. The dissociative adsorption of water causes more obvious surface calcium shifts and Si–O bond length increases than molecular adsorption. The dissociative adsorption of a water molecule changes the electron distribution, and the overlap between Ca 2p and O 2s orbitals leads to new Ca–O bond formations.     

Characterisation of Surface Activity of Carbon Black and its Relation to Polymer‐Filler Interaction

The surface activity of commercial and experimental carbon blacks varying in particle size and primary aggregate structure was investigated with regard to surface roughness and energetic surface structure of primary particles. The energetic surface structure was described by the site energy distribution function f(Q), which was determined mainly from the gas adsorption isotherms of ethene. It was found that the surface of carbon black was energetically very heterogeneous. It consisted of at least four different adsorption sites (I: Q ≈ 16 kJ · mol^?1; II: Q ≈ 20 kJ · mol^?1; III: Q ≈ 25 kJ · mol^?1; IV: Q ≈ 30 kJ · mol^?1). The fraction of the sites I–IV depended on the production process of the carbon black grades and the particle size. For the furnace blacks, the fraction of high‐energy sites decreased significantly with particle size and disappeared almost completely during graphitisation. This indicates that the reinforcing potential of carbon black is closely related to the amount of highly energetic sites that can be well quantified by the applied gas adsorption technique. The surface roughness was characterised by the surface fractal dimension, D_s, which was determined by two different techniques: the yardstick‐method and the extended Frenkel‐Halsey‐Hill‐theory (fractal FHH‐theory). It is found that the furnace blacks have an almost equal roughness with a surface fractal dimension of D_s ≈ 2.6 beyond a length scale z ≈ 6 nm. This result is shown to be in fair agreement with analytical models and computer simulations of surface growth of carbon black in a furnace reactor.

     

Calendar of events

This review reports the successful synthesis of novel oligomeric silanes having end-capped fluoroalkyl groups. Glass surface was effectively modified by these oligomeric silanes. In particular, oligomeric silanes were more reactive and effective in the surface fluoroalkylation than monomeric silanes. From contact angle measurements, surface free energies were reduced to 15–20 and 1–3 mJ/m² for the dispersive and the polar components, respectively, and the surfaces were shown to be both highly water- and oil-repellent. Modified glass surface was analyzed using XPS. A linear correlation was observed between the dispersive component of surface free energy γ_S ^d and the area ratio of the F1s peak to the Si2p peak. The structure of the siloxane layer on the modified glass surface is discussed in terms of a network interphase model.     

Effect of Membrane Surface Properties During the Fast Evaluation of Cell Attachment

Abstract

The biofouling potential is one of the important factors to design and to select membranes for water and wastewater treatment. In this investigation, the effect of membrane surface properties during the attachment of S. cerevisiae cells was examined using a laboratory‐scale membrane filtration cell enabling direct microscopic observation of microbial cell deposition. The experimental results from 6 commercially available membranes showed that the initial adhesion rate, k _d , was affected by the zeta potentials, hydrophobicity, and roughness of membrane surfaces. The k _d value was significantly lower at the membrane which had more negative, hydrophilic, and smooth surfaces. The results will be helpful to minimize the time for selecting membranes in different situations, and for testing the performance of newly designed membranes.     

Thermodynamics of surface and oxygen vacancy in rare earth stannates by first-principles calculations

The research of nanocrystalline pyrochlores highlights the importance of the surface structure, composition and segregated point defect in their thermal, electrical, optical, magnetic, and catalytic performances. In order to provide a basic view on the surface-related phenomena, thermodynamic stabilities of three low-index (100), (110), and (111) surfaces for A₂Sn₂O₇ (A = La, Ce, Pr, Nd, Pm, Sm, Eu, or Gd), together with their configurations, electronic structures and related oxygen vacancies are investigated using first-principles calculations. The (111) surfaces with A₃SnO₈ and ASn₃O₆ terminations are predicted to be stable due to their low surface energies. Meanwhile, the (110) surfaces with A₂Sn₂O₈ and A₂Sn₂O₆ terminations are found to may also form. For these surface structures, the amount of broken bonds play the main role in their structural stability, and the local coordination environment variation also has minor contribution to it. Moreover, oxygen vacancies are observed to segregate on the surface layer, owing to lower energy of breaking bonds accompanying with oxygen vacancy formation and the larger relaxation space comparing to the counterpart in bulk. These results are expected to provide guidance on optimizing the performances of these compounds through surface engineering.     

Bacterial Retention in Lipopolysaccharide Coated Silica Sand

Abstract

Wastewater reclamation has been widely practiced in agriculture. When reclaimed wastewater is used for irrigation, among other requirements, it is important that the pathogenic bacteria are removed. Consequently, technologies such as immobilization or sorption barriers have been developed. To enhance the removal efficiency, biopolymers have been introduced to amend these immobilization or sorption barriers. In this study, removal of pathogenic bacteria by lipopolysaccharide (LPS)‐amended barriers was investigated by means of laboratory column experiments. Two typical gram‐negative pathogenic bacterial strains of Escherichia coli and Pseudomonas fluoresences and one gram‐positive bacterial strain of Streptococcus mitis were selected as the model bacteria in this research. Bacterial adhesion to uncoated and LPS‐coated silica sand was correlated to their interaction free energies. Both E.coli, P. fluorescens, and S. mitis had negative interaction free energies with silica sand, demonstrating their adhesion potentials to silica sand. After LPS coating, bacterium‐sediment interaction free energies decreased (negatively increased), and consequently, bacterial retention increased. Bacterial deposition coefficient in silica sand corresponded to their interaction free energies with silica sand. This study demonstrated that bacterial retention in porous media was determined by their interactions with the sediments, which could be predicted based on independently determined bacterial and medium physicochemical surface properties.     

Organic filler surface analysis by column wicking

Organic fillers derived from biomass waste streams are commonly formulated with phenol-formaldehyde resoles in the production of veneer-based wood composites. The surface characteristics of three fillers, flours of walnut shell (Juglans regia), red alder (Alnus rubra) bark, and corn cob (Zea mays) furfural production residue, were investigated with the column wicking method using the Washburn equation. A series of n-alkanes (spreading liquids) provided reliable estimates of interstitial pore radii, which then enabled contact angle estimates for a variety of non-spreading liquids. Among the three fillers, only alder bark data were complicated by swelling effects, which were eliminated with strict data quality criteria. Corn cob residue exhibited the highest total surface free energy, but all fillers had low energies that were dominated by dispersive effects. The minor polar contributions were basic. Specific surface areas determined from wicking substantially disagreed with Brunauer–Emmett–Teller measurements using N₂ adsorption, where the former were more consistent with measured particle size.     

Surface rearrangement of vinyl acetate and acrylate terpolymer adhesives investigated by dynamic contact angles

Terpolymer solution-based adhesives of vinyl acetate and acrylates with different long alkyl side chains were prepared by radical polymerization. Dynamic contact angles of the adhesives-coated films measured by the Wilhelmy plate technique indicated that the reorientation of the adhesive surface varied with the length of the alkyl side chain. It was found that the changes of advancing contact angles (θ_a) and receding contact angles (θ_r) were relatively great within the range of lower immersion speeds at various temperatures, but approaching a certain velocity the contact angles became stable. The lower activation energies of the change in contact angles revealed that the rearrangement of surface groups can be achieved by small-scale secondary transitions. In addition, the activation energies required for rearrangement from apolar to polar medium and the reverse process were different. ©1997 SCI     

The effect of surface treatments on the bonding strength of ceramic inlays to dentin

Aim: To compare and evaluate the effects of different surface treatments on surface roughness and the microtensile bonding strengths of four different ceramics to dentin. Methods: 160 human molar teeth were used. The teeth were divided into four groups (n = 40). FC (Finesse), LC (IPS Empress Esthetics), LDC (IPS Empress e-Max) and MZC (Zirkonzahn Prettau) ceramic restorations were prepared. The specimens were divided into eight groups: (1) control, (2) air abrasion (AA), (3) HF acid etching (HF), (4) experimental hot etching (EHE), (5) Nd:YAG laser irradiation, (6) Nd:YAG laser + air abrasion, (7) Nd:YAG laser + HF acid, and (8) Nd:YAG laser + experimental hot etching. The surface roughness of the ceramics was determined with atomic force microscopy. After the cementation process, the specimens were thermal cycled and subjected to a microtensile bond strength (MBS) test. Two-way ANOVA and a Tukey’s test were used to analyse the surface roughness and MBS values of variance (p = 0.05). Results: HF acid etching showed the highest surface roughness in FC (p < 0.05). HF increased MBS in LC specimens where AA and HF increased MBS in LCD specimens. For the MZC specimens, AA and Nd:YAG + AA was effective in increasing the MBS (p < 0.05). Conclusion: Different surface treatments must be applied to different ceramics to improve the mechanical retention and MBS.     

The Use of AFM and Surface Energy Measurements to Investigate Drug-Canister Material Interactions in a Model Pressurized Metered Dose Inhaler Formulation

The aim of the project was to investigate the interactions between micronized salbutamol sulphate, budesonide, and formoterol fumarate dihydrate and different canister surfaces materials (Aluminium, anodized aluminium, perfluoroalkoxy, fluorinated ethylene propylene—polyether sulphone, and polytetrafluoroethylene) used in pressurized metered dose inhalers (pMDIs).

The surface component approach for polar and apolar interfacial interactions was used to predict the adhesion behavior of micronized drugs with the inner surfaces of pMDI canisters. This was achieved using a combination of in situ colloid probe atomic force microscopy (AFM) measurements and theoretical treatment of the surface free energy measurements, via a contact angle–based technique of the interacting surfaces.

All three drugs exhibited similar dispersive surface energy free values. A greater variation was, however, found in the polar component of the surface free energy measurements. These results were also reflected in the dispersive and polar components of the canister materials. Moreover, the linear relationship between the work of adhesion and AFM measured adhesion was shown to be correlated on the polar contributions of the surface free energies of the interacting materials. AFM measurements indicated that salbutamol sulphate was found to have the strongest adhesive forces with respect to the canister surface materials while budesonide and formoterol fumarate dihydrate appeared to have similar adhesive characteristics. The present study suggests that investigations into the design and characterization of pMDI formulations would benefit from considerations of the polar contribution of the surface free energy and relative work of adhesion of the drug and various components of a pMDI system.     

Correlation between physical bonding and mechanical properties of wood plastic composites: Part 1: interaction of chemical and mechanical treatments on physical properties

Abstract

This study investigated the mode of action between wood and thermoplastic interphases. For this purpose, the effect of sanding and chemical treatments on the wood surface wettability has been simultaneously evaluated. Contact angle measurements were tested on wood veneers (spruce) using Van Oss-Chaudhury-Good (VOCG) method to determine the surface free energies (SFE). To better understand the mechanism of treatments on the physical interactions, veneers were either/both sanded or/and treated by maleic anhydride grafted with polyethylene (MAPE) so that the analysis of surface pre-coating and its influence on the polarity and the dispersive properties of the wood-polymer interface can be further studied. The results showed a significant increment of both surface roughness and interfacial area after sanding which improved pre-coating of plastic on the wood surface consequently. Analysis of wetting parameter showed compatibility between two types of surface modification, as the treatment of veneers by sanding and MAPE together resulted in higher contact angles and lower surface free energy (SFE) on the wood surfaces. MAPE could entirely cover the wood veneers and form a non-polar surface, which suggests the effectiveness of this chemical and its compatibility with the sanding operation on the wood surface.     

Fixed-bed column performance of methylene blue biosorption by Luffa cylindrica: statistical and mathematical modeling

Abstract

This study aimed to investigate the adsorption capacity of Iranian Luffa cylindrica as a natural lignocellulosic adsorbent for biosorption of methylene blue (MB) using a fixed-bed column. The response surface methodology based on central composite design was used to evaluate the interactive effects of three major operating parameters (inlet MB concentration, Luffa dosage, and feed flow rate) on the dye removal percentage (response variable). The significance of the proposed quadratic model was validated by a high coefficient of determination (R²?=?0.995) and a low p value (<0.001). The optimum biosorption conditions were determined as inlet MB concentration 38.66?mg?L^?1, Luffa dosage 2.78?g, and feed flow rate 5?mL?min^?1, and the maximum MB removal efficiency was founded to be 51% (q_max?=?21.4?mg?g^?1) at optimum conditions. The breakthrough curves were predicted by the Adams–Bohart and Thomas models using nonlinear regression analysis, whereas the experimental data fitted well with the Thomas model (R²?≈?0.96–0.98). Further surface modification studies enabled us to achieve the maximum MB removal efficiency of 77% (q_max?=?46.58?mg?g^?1) with NaOH-modified Luffa, which is attributed to the intensification of the negatively charged surface of the base-modified adsorbent with hydroxyl groups. The nature of biosorbent–dye interactions was also evaluated by FTIR analysis. The highest desorption performance of MB from Luffa fibers was obtained with HCl solution reaching a desorbed amount of q_des?=?130.5?mg in the column studies. The ion exchange is introduced as the dominant biosorption mechanism of MB onto Luffa fibers in this study.     

Effects of different surface treatments of zirconia on the bond strength of self-adhesive resinous cement

Purpose: The aim of this study was to evaluate the effects of different zirconia surface treatments on the bond strength of two self-adhesive resinous cements (SARC).

Methods: Two hundred and eight cylindrical specimens were obtained from Y-TZP zirconia (half with diameter 3.2 mm and half with 4.8 mm). After sintering and polishing, specimens were divided into four groups (n = 26), according to surface treatment: Control (no treatment); Sandblasting (Al₂O₃ particles); Rocatec (Al₂O₃ particles, tribochemical silica coating and silane application); Laser (Nd: YAG laser: 20 Hz, 100 mJ, 0.2 J/cm²). The surface roughness (Ra) was evaluated after the surface treatments, and the groups were divided into two subgroups (n = 13), according to the SARC tested: RelyX U200 and Bifix SE. The 2.2-mm cylinders were bonded to 4.8-mm cylinders and stressed until failure under shear using a universal testing machine. Bond strength and Ra were analyzed using ANOVA, and Tukey’s test (α = 0.05).

Results: Surface treatment was significant (p < 0.0001), but cement type (p = 0.73) was not. Related to roughness, significant differences were found for the treatment type (p < 0.0001), with laser being the treatment with higher Ra values.

Conclusions: Nd:YAG laser produced a rougher surface and a higher bond strength compared with sandblasting, silicatization, and control groups.