Lifshitz-van Der Waals Research Articles

Nanoscale Cell Wall Deformation Impacts Long-Range Bacterial Adhesion Forces on Surfaces

Adhesion of bacteria occurs on virtually all natural and synthetic surfaces and is crucial for their survival. Once they are adhering, bacteria start growing and form a biofilm, in which they are protected against environmental attacks. Bacterial adhesion to surfaces is mediated by a combination of different short- and long-range forces. Here we present a new atomic force microscopy (AFM)-based method to derive long-range bacterial adhesion forces from the dependence of bacterial adhesion forces on the loading force, as applied during the use of AFM. The long-range adhesion forces of wild-type Staphylococcus aureus parent strains (0.5 and 0.8 nN) amounted to only one-third of these forces measured for their more deformable isogenic Δpbp4 mutants that were deficient in peptidoglycan cross-linking. The measured long-range Lifshitz-Van der Waals adhesion forces matched those calculated from published Hamaker constants, provided that a 40% ellipsoidal deformation of the bacterial cell wall was assumed for the Δpbp4 mutants. Direct imaging of adhering staphylococci using the AFM peak force-quantitative nanomechanical property mapping imaging mode confirmed a height reduction due to deformation in the Δpbp4 mutants of 100 to 200 nm. Across naturally occurring bacterial strains, long-range forces do not vary to the extent observed here for the Δpbp4 mutants. Importantly, however, extrapolating from the results of this study, it can be concluded that long-range bacterial adhesion forces are determined not only by the composition and structure of the bacterial cell surface but also by a hitherto neglected, small deformation of the bacterial cell wall, facilitating an increase in contact area and, therewith, in adhesion force.

Electrodynamic Pressure Modulation of Protein Stability in Cosolvents

Cosolvents affect structural stability of proteins in aqueous solutions. A clear understanding of the mechanism by which cosolvents impact protein stability is critical to understanding protein folding in a biological milieu. In this study, we investigated the Lifshitz-van der Waals dispersion interaction of seven different solutes with nine globular proteins and report that in an aqueous medium the structure-stabilizing solutes exert a positive electrodynamic pressure, whereas the structure-destabilizing solutes exert a negative electrodynamic pressure on the proteins. The net increase in the thermal denaturation temperature (ΔTd) of a protein in 1 M solution of various solutes was linearly related to the electrodynamic pressure (PvdW) between the solutes and the protein. The slope of the PvdW versus ΔTd plots was protein-dependent. However, we find a positive linear relationship (r(2) = 0.79) between the slope (i.e., d(ΔTd)/dPvdW) and the adiabatic compressibility (βs) of the proteins. Together, these results clearly indicate that the Lifshitz's dispersion forces are inextricably involved in solute-induced stabilization/destabilization of globular proteins. The positive and/or negative electrodynamic pressure generated by the solute-protein interaction across the water medium seems to be the fundamental mechanism by which solutes affect protein stability. This is at variance with the existing preferential hydration concept. The implication of these results is significant in the sense that, in addition to the hydrophobic effect that drives protein folding, the electrodynamic forces between the proteins and solutes in the biological milieu also might play a role in the folding process as well as in the stability of the folded state.

Computations of Lifshitz–van der Waals interaction energies between irregular particles and surfaces at all separations for resuspension modelling

The phenomenon of particle resuspension plays a vital role in numerous fields. Among many aspects of particle resuspension dynamics, a dominant concern is the accurate description and formulation of the van der Waals (vdW) interactions between the particle and substrate. Current models treat adhesion by incorporating a material-dependent Hamaker's constant which relies on the heuristic Hamaker's two-body interactions. However, this assumption of pairwise summation of interaction energies can lead to significant errors in condensed matter as it does not take into account the many-body interaction and retardation effects. To address these issues, an approach based on Lifshitz continuum theory of vdW interactions has been developed to calculate the principal many-body interactions between arbitrary geometries at all separation distances to a high degree of accuracy through Lifshitz's theory. We have applied this numerical implementation to calculate the many-body vdW interactions between spherical particles and surfaces with sinusoidally varying roughness profile and also to non-spherical particles (cubes, cylinders, tetrahedron etc) orientated differently with respect to the surface. Our calculations revealed that increasing the surface roughness amplitude decreases the adhesion force and non-spherical particles adhere to the surfaces more strongly when their flatter sides are oriented towards the surface. Such practical shapes and structures of particle–surface systems have not been previously considered in resuspension models and this rigorous treatment of vdW interactions provides more realistic adhesion forces between the particle and the surface which can then be coupled with computational fluid dynamics models to improve the predictive capabilities of particle resuspension dynamics.

Work of adhesion and activity of aqueous solutions of ternary mixtures of hydrocarbon and fluorocarbon nonionic surfactants at the water–air and polymer–water interfaces

The values of the surface tension and contact angle on the polytetrafluoroethylene surface (PTFE) of aqueous solutions of the ternary mixtures of hydrocarbon surfactants, TX100 and TX165, and fluorocarbon FSN100 at different mole fractions of surfactants in the bulk phase were applied for the studies of the correlation between the adsorption of surfactants at the solution–air and polymer–solution interfaces, the work of adhesion determined from the Young–Dupree equation, the parameter of the intermolecular interactions and the spreading coefficient of aqueous solutions of the studied mixtures on the PTFE surface. For this purpose the values of the total mole fraction and activity of surfactants at the polymer–solution interface obtained from the Sprow and Prausnitz equation were compared to those at the solution–air one. Also on the basis of the mole fraction of the particular surfactants at the PTFE–solution and water–air interface and on the assumption of the additivity of the adhesion work, the work of adhesion of the fluorocarbon tail to the PTFE surface as well as the Lifshitz–van der Waals component of the PTFE surface tension were calculated.

Influence of oxygen‐inhibited layer on dentin bond strength of chemical‐cured resin composite

This study evaluated the influence of an oxygen-inhibited layer on the surface free energies of three single-step self-etch adhesives and on the bond strength of chemical-cured resin. Adhesives were applied to bovine dentin and light irradiated, and the oxygen-inhibited layer was either retained or removed. Surface free energies were determined by measuring the contact angles of test liquids placed on the cured adhesives. Dentin bond strengths of chemical-cured resin with and without the oxygen-inhibited layer were measured. Ultrastructural observation of the restorative-dentin interface was made by scanning electron microscopy. For all surfaces, values of the estimated surface tension component, Lifshitz-Van der Waals force (γS(LW)), were relatively constant. Values for the Lewis acid (γS(+)) component increased slightly when the oxygen-inhibited layer was removed, whereas those of the Lewis base (γS(-)) component decreased significantly. The bond strength of the chemical-cured resin composite was significantly higher in specimens without an oxygen-inhibited layer (7.6-8.0 MPa) than in those with an oxygen-inhibited layer (4.8-5.2 MPa). Small gaps between adhesive and resin composite were found for the group with an oxygen-inhibited layer. These results indicate that the absence of an oxygen-inhibited layer in single-step self-etch adhesives promotes higher dentin bond strength of the chemical-cured resin.

Physico-chemical surface properties of microalgae

This study reports a comprehensive set of experimentally measured physico-chemical surface properties of 12 different microalgae including fresh and seawater species of green algae, diatoms and cyanobacteria. The surface free energy and its components including the acid-base (AB), van der Waals (LW), electron donor/acceptor parameters were quantified based on contact angle measurements along with the Lifshitz–van der Waals acid–base approach using the probe liquid surface tension parameters proposed by van Oss et al. as well as by Della Volpe and Siboni. Moreover, the zeta and surface potentials of all species were determined using electrophoretic mobility measurements along with using Smoluchowski's model. Finally, the free energy of cohesion of the microalgae was also determined based on the calculated surface energy properties. The results showed that the electron donor parameter correlated well with the free energy of cohesion in all groups of microalgae. Moreover, species known to form colonies and exhibit benthic cultures had distinctly hydrophobic surfaces compared to microalgae prefering planktonic growth. These results indicate the importance of surface hydrophobicity for causing biofouiling or flocculation of cultures. Finally, the zeta potentials did not show a distinctive trend with the types of microalgae but the surface potentials were markedly larger for the salt water species. The reported methods and data are expected to provide critical information for researchers and technology developers concerned with cell to cell and cell to substrata interactions of microalgae in algal biomass cultivation and harvesting, biofouling of membranes and surfaces, as well as cell-surface interactions in photosynthetic microbial fuel cell technologies.

Passivation of High-Surface-Energy Sites of Milled Ibuprofen Crystals via Dry Coating for Reduced Cohesion and Improved Flowability

Ibuprofen micronization with dry coating is investigated to examine its influence on passivation/stabilization of high-surface-energy sites and reduced cohesion. A fluid energy mill was used to micronize ibuprofen particles down to 5-28 μm with or without simultaneous nanosilica coating. Powder flow property and dispersibility were characterized using FT4 powder tester and Rodos/Helos laser diffraction particle sizer. Surface energy was characterized using a next generation inverse gas chromatography instrument. Uncoated micronized ibuprofen showed an increased Lifshitz-van der Waals (LW) dispersion component of surface energy with increasing milling intensity. In contrast, dry-coated milled powders showed a significant reduction in the LW component, whereas physical mixture of uncoated micronized ibuprofen and silica exhibited no reduction in surface energy, indicating that dry coating is necessary for the passivation of high-energy sites of ibuprofen created during micronization. Surface energy of pure micronized ibuprofen was highly heterogeneous, whereas dry-coated ibuprofen had greatly reduced heterogeneity. Micronization with dry coating also improved flowability and bulk density as compared with pure active pharmaceutical ingredient micronization without coating, or just blending with silica. Overall, dry coating leads to decreased cohesion and improved flowability because of reduced LW dispersive component of surface energy and creating nanoscale surface roughness.

Effect of chemical modification on surface free energy components of Aerosil silica powders determined with capillary rise technique

Abstract The knowledge about interfacial energy interactions and surface free energy is necessary for understanding and modeling many surface and interface processes. The aim of this paper is to study the effect of the chemical modification on the surface free energy components of Aerosil OX50. This fumed silica is chemically modified using the hydrophobic organosilane hexadecyltrichlorosilane (HTS). The modification process is studied by Fourier transform infrared spectroscopy (FTIR) and total carbon mass measurements performed on solid silica samples. The combination of these two techniques allows the determination of the adsorption isotherm of HTS onto silica showing the formation of a plateau for an initial concentration of 3 mM. The quantity adsorbed of HTS at maximum coverage is 2.14 μmol/m 2 . However, the chemical modification does not elaborate a compact layer. The HTS density is approximately 1.2 molecules/nm 2 which is close to the density of hydroxyl groups on the surface. A recent method, developed by Chibowski and Perea-Carpio, based on imbibition of probe liquids into a thin porous layer (capillary rise), is used for the determination of the surface free energy components. The surface free energy γ s decreases continuously from 54.2 mJ/m 2 for bare silica to 46.7 mJ/m 2 for silica treated at an initial concentration of 4 mM following a linear diminution of γ s with the HTS adsorbed amount. The apolar Lifshitz-van der Waals component γ s LW is reduced from 41.1 mJ/m 2 to 35.8 mJ/m 2 . The electron-donor parameter γ s − drops from 53.9 mJ/m 2 to 27.5 mJ/m 2 while the electron-acceptor parameter γ s + remains roughly constant (1 mJ/m 2 ). Trends in the surface free energy components are notably linked to observations in infrared spectra and give additional information about the structure of the HTS layer.

Surface free energy analysis of adsorbents used for radioiodine adsorption

In this work, the surface free energy of biomass-based activated carbons, both fresh and impregnated with triethylenediamine, has been evaluated. The contribution of Lifshitz van der Waals components was determined by the model proposed by van Oss et al. The results obtained allowed predicting the most probable configurations of the impregnant onto the carbon surface and its influence on the subsequent adsorption of radioactive methyl iodide.

Surface energy characterization of carbonate rocks

Carbonate rocks (calcite and dolomite) account for more than half of the world's hydrocarbon reserves. Despite the complexity posed by these rocks, it is important to understand the fundamental forces of adhesion responsible for the spreading and distribution of reservoir fluids, such as crude oil/brine on the reservoir rock surface. These physico-chemical interactions determine the surface energetics of a reservoir and affect their wetting characteristics. Inverse gas chromatography is introduced to characterize the surface energy of carbonates (calcite and dolomite). The behavior of the polar and non-polar interaction forces was investigated at varying water coverage and at different temperatures. The results indicated that in general as the water coverage increased, the Lifshitz–van der Waals component of surface energy decreased to nearly that of the bulk water, while the acid–base component also showed a decreasing trend. The Lifshitz–van der Waals component of surface energy always decreased with increase in temperature, while the acid–base properties showed contrasting trends for the two minerals.

Effect of zwitterionic surfactants on wetting of quartz surfaces

Advancing contact angle (θ), for aqueous solutions of the zwitterionic surfactants, hexadecanol glycidyl ether glycine Betaine (C16PB), guerbet alcohol hexadecyl glycidyl ether glycine Betaine (C16GPB), hexadecanol polyoxyethylene(3) glycidyl ether glycine Betaine (C16(EO)3PB) and guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether glycine Betaine (C16G(EO)3PB), were measured on the quartz surface by the sessile drop analysis. The atomic force microscope (AFM) has been used to detect the nature of adsorption film at quartz surface. The obtained results indicate there are only slightly changes of contact angle as a function of bulk concentration for four surfactants during the experimental concentration range caused by the random arrangement of surfactant molecules at quartz surface through Lifshitz–van der Waals interactions. For C16PB and C16GPB, a similar adsorption density at water–air and quartz–water interface is observed. In the case of C16(EO)3PB and C16G(EO)3PB solutions, a smaller surfactants adsorption at quartz–water interface than at water–air interface probably results from steric effect due to parallel orientation of surfactants in the monolayer at quartz–water interface resulted from the interaction between EO group and quartz. The adsorption characteristics of zwitterionic surfactants remain less variation with the insertion of EO group and the presences of branched-chain in the hydrophobic group are quite opposite. For C16PB and C16(EO)3PB, a three-stage adsorption mechanism has been provided, while a four-stage mechanism must be taken into account for C16 G PB and C16G(EO)3PB. The characteristics of force curves measured by AFM between alkyl-modification tips and surfactant-modification quartz plates can strongly confirm the nature of modified film on quartz surface and ensure the adsorption mechanism provided above.

Surface energy characterization of sandstone rocks

The fundamental forces of adhesion are responsible for the spreading of fluids such as crude oil/brine on the reservoir rock surface. These physico–chemical interactions determine the surface energetics of a reservoir and thus their wetting phenomena. Inverse Gas Chromatography (IGC) is introduced to characterize the surface energy of sandstones (Ottawa sand and Berea sandstone). The surface chemistry of the sandstone rocks is further elucidated using X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) techniques. The behavior of the polar and non-polar interaction forces was investigated at varying water coverage and at different temperatures. The results indicated that in general as the water coverage increased, the Lifshitz–van der Waals component of surface energy decreased to nearly that of the bulk water, while the acid–base component also showed a decreasing trend. The Lifshitz–van der Waals component of surface energy always decreased with increase in temperature, while the acid–base properties showed contrasting trends in line with changes in surface chemistry of the sandstones, due to the change in temperature. Finally, the wetting properties arising in reservoir sandstones were related to the surface chemistry of the reservoir fluids and their interactions with the reservoir rock surface.

Wetting behavior and mechanism of wetting agents on low-energy surface

Wetting behavior and wetting mechanism of wetting agents on low-energy surface (LES) are well investigated in this paper. Four wetting agents, namely Lignin sulfonate, Tannic acid, Methylcellulose and Triton X-100, were involved in our study. Wetting behavior was well examined through discussion of surface energy of LES, interfacial interaction and zeta potential of polymer resins. Experimental results demonstrate that adsorption of wetting agents changes the surface energy parameters of LES; interfacial free energy between wetting agent molecule and LES exhibits hydrophobic attraction between them fails to be the dominant driving force of adsorption; the effect of wetting agent on zeta potential of polymer illustrates electrostatic force is not the major factor of interfacial interaction between wetting agent molecule and LES. Based on wetting action of wetting agents, we discussed wetting mechanism of wetting agents on LES in detail, and an adsorption model was proposed. Adsorption of wetting agent on LES is achieved through hydration shell taken as mesophase, namely, hydrophobic attraction between LES and water molecule results in the formation of hydration shell, and wetting agents molecules approach to hydration shell under the effect of Lifshitz–van der Waals attraction and they adsorb on hydration shell through hydrogen bond. In terms of post-consumer plastics composed of polymer and additives, apart from hydrophobic attraction and hydrogen bond, wetting action depends also on chelating ability between wetting agent molecule and additive ions due to the chemical adsorption between wetting agent and additives. In addition, wetting ability, adsorption and selective desorption of wetting agents are well examined.

Surface modification of indium tin oxide for direct writing of silver nanoparticulate ink micropatterns

Surface treatment techniques were deployed to alter the surface of indium tin oxide (ITO) samples to attain a favorable interface between printed nano-inks and ITO surface. Surface free energy components of treated ITO substrates were calculated for each treatment using the van Oss–Chaudhury–Good method. The surface treatments of ITO changed the Lifshitz–van der Waals and Lewis acid–base components, and contact angle hysteresis significantly. Among all the surface treatments, air plasma treated samples showed high polar in nature, whereas dodecyltrichlorosilane self-assembled monolayer treated sample showed the lowest. In addition to the polarity and homogeneity, the surface roughness of the ITO was studied with respect to the surface treatment. Silver nanoparticulate ink was printed on treated ITO surfaces using aerosol jet printing system. Printed silver nano-ink line width and morphology strongly depended on the surface treatment of the ITO, ink properties and printing parameters.

Effects of surfactants on cell surface tension parameters and hydrophobicity of Pseudomonas putida 852 and Rhodococcus erythropolis 3586

The interaction between bacteria and surfaces is central to many environmental, industrial and medical applications. Surfactants are commonly used in these applications and can potentially influence the bacterium/surface interaction. The effect of surfactants upon bacterial cell surface thermodynamic properties was examined using a combination of contact angle measurements and LW-AB surface free energy calculation. Two bacterial strains, hydrophilic Pseudomonas putida 852 and hydrophobic Rhodococcus erythropolis 3586, and two surfactant types, the anionic biosurfactant rhamnolipid and the non-ionic chemical surfactant tergitol, were examined. The study demonstrated that surfactant treatment could modify cell surface tension parameters including Lifshitz-van der Waals (γLW), electron-donor (γ−) and electron-acceptor (γ+) and thereby the bacterial cell hydrophobicity, depending on the surfactant type and concentration and the bacterial surface characteristics. Rhamnolipid and tergitol were found to increase P. putida 852 hydrophobicity, but decrease the hydrophobicity of R. erythropolis 3586. The extent of change was dependent on surfactant concentration. Among the three surface tension parameters, γ− was found to be the most important in predicting bacterial cell hydrophobicity.

Adsorption Behavior of Cationic and Zwitterionic Surfactants on Poly(methyl methacrylate)

The wetting behavior of poly(methyl methacrylate) (PMMA) surfaces by aqueous solutions of cationic surfactants, hexadecanol glycidyl ether ammonium chloride (C16PC), hexadecanol polyoxyethylene (3) glycidyl ether ammonium chloride (C16(EO)3PC), and zwitterionic surfactants, hexadecanol glycidyl ether glycine betaine (C16PB) and hexadecanol polyoxyethylene(3) glycidyl ether glycine betaine (C16(EO)3PB), were investigated by sessile drop analysis. The influence of surfactant type and concentration on contact angle was determined. The PMMA surface is modified hydrophobically only slightly at low bulk concentration because the surfactant molecules are parallel to the substrate surface and the hydrophilic groups are close to the surface. However, at high concentration, the surfactant molecules can adsorb onto the PMMA surface through Lifshitz-van der Waals interactions and hydrophilic groups directed towards the bulk phase of solution, which increases the hydrophilic character of the PMMA surface. The contact angles of cationic surfactants show little variation following the insertion of polyoxyethylene units. However, the presence of polyoxyethylene units in the zwitterionic surfactants leads to an obvious decrease of contact angle because of the formation of hemimicelles on the PMMA surface.

Surface Tension of Polytetrafluoroethylene and Polymethyl Methacrylate under the Influence of the Fluorocarbon Surfactant Film

Measurements of the contact angle for water, formamide, and diiodomethane on polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA) covered by Zonyl FSN-100 (FSN100) and Zonyl FSO-100 (FSO100) films were made. On the basis of the obtained values, the Lifshitz–van der Waals component and electron-acceptor and electron-donor parameters of the acid–base component of PTFE and PMMA covered by the surfactant film surface tension were determined by the use of van Oss et al. approach to the interfacial tension and Young’s equation. The components and parameters of surface tension were discussed in the light of the sorption of fluorocarbon surfactants at the polymer/solution interface and proper orientation of the surfactant molecules to this interface. Taking into account the changes of determined values of the components and parameters of PTFE and PMMA surface tension under influence of the surfactant films, the relationship between the adhesion tension and the surface tension, as well as between the cosine of contact angle and the surface tension of aqueous solution of fluorocarbon surfactants, was explained.

Studies and comparison of the liquid adsorption behavior and surface properties of single- and multiwall carbon nanotubes by capillary rise method

The liquid adsorption behaviors and surface properties of single- (SWCNT) and multiwall (MWCNT) carbon nanotubes were studied and compared by the capillary rise method. It was found that these CNTs both adsorbed the diiodomethane greatly as compared with other liquids, e.g. water, formamide and hexane, and the reason is due to the total surface free energy of these CNTs both dominated by the Lifshitz–van der Waals interactions component, especially the SWCNTs at about 95%. Comparison further indicated that the SWCNT adsorbed the polar liquid greatly due to stronger in the Lewis base component and the MWCNT adsorbed the non-polar liquid greatly due to stronger in the Lewis acid component. The total surface free energy of SWCNT is about 50mN/m slight greater than that of the MWCNT.

Combined Poisson and Soft-Particle DLVO Analysis of the Specific and Nonspecific Adhesion Forces Measured between L. monocytogenes Grown at Various Temperatures and Silicon Nitride

Adhesion forces between pathogenic L. monocytogenes EGDe and silicon nitride (Si(3)N(4)) were measured using atomic force microscopy (AFM) under water and at room temperature for cells grown at five different temperatures (10, 20, 30, 37, and 40 °C). Adhesion forces were then decoupled into specific (hydrogen bonding) and nonspecific (electrostatic and Lifshitz-van der Waals) force components using Poisson statistical analysis. The strongest specific and nonspecific attraction forces were observed for cells grown at 30 °C, compared to those observed for cells grown at higher or lower temperatures, respectively. By combining the results of Poisson analysis with the results obtained through soft-particle Derjaguin-Landau-Verwey-Overbeek (DLVO) analysis, the contributions of the Lifshitz-van der Waals and electrostatic forces to the overall nonspecific interaction forces were determined. Our results showed that the Lifshitz-van der Waals attraction forces dominated the total nonspecific adhesion forces for all investigated thermal conditions. However, irrespective of the temperature of growth investigated, hydrogen bonding forces were always stronger than the nonspecific forces. Finally, by combining Poisson analysis with soft-particle analysis of DLVO forces, the closest separation distances where the irreversible bacterial adhesion takes place can be determined relatively easily. For all investigated thermal conditions, the closest separation distances were <1 nm.

Deposition and remobilization of graphene oxide within saturated sand packs

In this research, we examined the deposition kinetics of graphene oxide (GO) particles within saturated sand packs as a function of ionic strength as well as the remobilization of previously retained GO particles due to chemical perturbation. The retention of GO particles within saturated quartz sand was found to be strongly dependent on ionic strength. At low ionic strength (e.g., 1mM of NaCl), little retention of GO particles occurred. When the ionic strength was increased to 100mM of NaCl, the retention of GO particles increased significantly but would be limited by its retention capacity. The reduction of ionic strength from 100mM (NaCl) to 1mM (NaCl) released ∼100% of previously retained GO particles. The transport behavior of GO particles within saturated sand packs could be described by the Langmuir-type of transport model. The extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory, which considers Lifshitz–van der Waals (LW) interaction, the electrostatic double layer (EDL) interaction as well as the Lewis acid–base (AB) (i.e., hydrophobic) interaction between GO plates and the surface of quartz sand, could explain the observed trend of GO retention under various ionic strength conditions.