Anomalous time effect on particle-bubble interactions studied by atomic force microscopy.

The atomic force microscope was employed to investigate the time effect on normal interactions between a hydrophilic silica particle and an air bubble deposited onto a hydrophobic Teflon surface in pure water and 10 mM methyl isobutyl carbinol solutions. The force versus separation distance curves taken at different times after bubble generation were qualitatively compared. It has been found that the penetration distance, jump-in force, contact angle, rupture distance, force required for the film to rupture, interfacial spring constant, and bubble shape were time-dependent.

Tuneable control of interfacial rheology and emulsion coalescence.

Breaking point: Switchable peptide surfactants are used to demonstrate that the extent of cross-linking in an interfacial surfactant layer can control the rate of emulsion coalescence. Pictured is the rupture of an aqueous thin film where the peptide layer lacks sufficient strength to prevent hole formation, but nonetheless dramatically slows the rate of hole expansion.

Systematically altering the hydrophobic nanobubble bridging capillary force from attractive to repulsive.

Atomic force microscopy (AFM) was used to examine how ethanol/water concentration affects the nanobubble bridging capillary force between a hydrophobic silica colloidal probe and a hydrophobic silica wafer. Nanobubbles were produced on the solid surfaces by a previously utilised method which uses solvent-exchange and surface scanning. In pure water a strong, long range attractive force ( approximately 230 nm) with a single jump in step was measured, typical of an interaction between two nanobubbles attached to the hydrophobic surfaces.

Results of a phase I pilot clinical trial examining the effect of plant-derived resveratrol and grape powder on Wnt pathway target gene expression in colonic mucosa and colon cancer.

Context: Resveratrol exhibits colon cancer prevention activity in animal models; it is purported to have this activity in humans and inhibit a key signaling pathway involved in colon cancer initiation, the Wnt pathway, in vitro.

Design: A phase I pilot study in patients with colon cancer was performed to evaluate the effects of a low dose of plant-derived resveratrol formulation and resveratrol-containing freeze-dried grape powder (GP) on Wnt signaling in the colon. Eight patients were enrolled and normal colonic mucosa and colon cancer tissue were evaluated by Wnt pathway-specific microarray and quantitative real-time polymerase chain reaction (qRT-PCR) pre- and post-exposure to resveratrol/GP.

The importance of aspect ratio in profile analysis tensiometry.

The latest developments in profile analysis tensiometry (PAT) for determining surface tension and interfacial viscoelastic parameters involve the determination of a digital interface profile and its best fit with the Young-Laplace equation. In this short communication, we show that the results for surface tension and other interfacial parameters determined by PAT are extremely sensitive to the (aspect) ratio of length to width of a pixel. Fine calibration (to five decimal digits) for the aspect ratio required to obtain physically consistent results is not always achieved with conventional numerical procedures due to nanometer resolution limit of optical imaging devices but can be manually adjusted using the known surface tension of pure water and/or surfactant solutions at reference temperature.

Effect of nanobubbles on friction forces between hydrophobic surfaces in water.

The interaction between hydrophobic surfaces in aqueous solutions is particularly important because it is encountered in many industrial processes. Even though advances in surface science have been tremendous, the nature of the hydrophobic interaction remains one of the greatest challenges to the field. In this work an atomic force microscope (AFM) was used to measure the normal and lateral interactions between a silica bead and a smooth silica substrate hydrophobized by esterification with 1-octanol.

Anomalous ion effects on rupture and lifetime of aqueous foam films formed from monovalent salt solutions up to saturation concentration.

We report the effects of ions on rupture and lifetime of aqueous foam films formed from sodium chloride (NaCl), lithium chloride (LiCl), sodium acetate (NaAc), and sodium chlorate (NaClO 3) using microinterferometry. In the case of NaCl and LiCl, the foam films prepared from the salt solutions below 0.1 M were unstable they thinned until rupturing.

Identification of plant defence genes in canola using Arabidopsis cDNA microarrays.

We report the identification of novel defence genes in canola by using a cDNA microarray from Arabidopsis. We examined changes that occur in the abundance of transcripts corresponding to 2375 Arabidopsis expressed sequence tags (selected for defence gene identification) following inoculation of canola plants with the fungal necrotrophic leaf pathogen, Alternaria brassicicola. Microarray data obtained from this cross-hybridisation experiment were compared to expression profiles previously obtained from the equivalent Arabidopsis experiment.

Transcriptome for photobiological hydrogen production induced by sulfur deprivation in the green alga Chlamydomonas reinhardtii.

Photobiological hydrogen production using microalgae is being developed into a promising clean fuel stream for the future. In this study, microarray analyses were used to obtain global expression profiles of mRNA abundance in the green alga Chlamydomonas reinhardtii at different time points before the onset and during the course of sulfur-depleted hydrogen production. These studies were followed by real-time quantitative reverse transcription-PCR and protein analyses.

Effect of alcohol-water exchange and surface scanning on nanobubbles and the attraction between hydrophobic surfaces.

Atomic force microscopy (AFM) was used to examine how different alcohols affect the hydrophobic attraction between a hydrophobic silica colloidal probe and a hydrophobic silica wafer. The experiments were performed in water and in water after rinsing alcohol (methanol, ethanol, or 1-propanol) throughout the AFM system. In all three cases the range of the attractive force increased after alcohol-water exchange, with 1-propanol showing the largest increase in range followed by ethanol and methanol.

Effect of ionic surfactants on drainage and equilibrium thickness of emulsion films.

This paper presents new theoretical and experimental results that quantify the role of surfactant adsorption and the related interfacial tension changes and interfacial forces in the emulsion film drainage and equilibrium. The experimental results were obtained with plane-parallel microscopic films from aqueous sodium dodecyl sulphate solutions formed between two toluene droplets using an improved micro-interferometric technique. The comparison between the theory and the experimental data show that the emulsion film drainage and equilibrium are controlled by the DLVO interfacial forces.

Molecular features of the air/carbonate solution interface.

The nature of the air/carbonate solution interface is considered with respect to water structure by sum-frequency vibrational spectroscopy (SFVS) and molecular dynamics simulations (MDS). Results from this study provide further understating regarding previous observations that the surface tensions of structure making sodium carbonate solutions have been shown to be significantly greater than the surface tensions of structure breaking bicarbonate solutions at equivalent concentrations. This difference in surface tension and its variation with salt concentration is related to the organization of water and ions at the air/solution interface.

Wnt pathway-related gene expression in inflammatory bowel disease.

The purpose of this study was to examine the expression of Wnt pathway-related genes in patients with ulcerative colitis (UC). RNA from colonoscopic biopsies from noninflammatory bowel disease (non-IBD) subjects and UC patients were obtained and examined with a Wnt-specific microarray for the expression of Wnt pathway-related genes. Paired samples from uninflamed and inflamed areas of the colon were obtained for the UC patients.

Decentralized sanitation implementation in Vietnam: a peri-urban case study.

This research presents one of the first comprehensive case studies of a small-scale wastewater management project in Vietnam. The research demonstrates how the community integrated a small-scale wastewater management system based on household participation and community management. It is argued that local resources of peri-urban and small towns could be used more efficiently to contribute to wastewater management in Vietnam if appropriate technologies are used and if their management and technical capacities are reinforced.

Effect of aluminium sulphate on interactions between silica surfaces studied by atomic force microscopy.

Surface interaction forces between different types of silica surfaces (pure silica beads, borosilicate glass beads, polished silicon wafers and fused silica slides) were measured by atomic force microscopy (AFM) in solutions of aluminium sulphate (alum) in order to understand the role of hydrated aluminium species on the coagulation of negatively charged oxide colloids in drinking water treatment. The alum coagulant concentration used in this study was 150 microM aluminium. The alum solutions were prepared from analytical grade Al2(SO4)3.

Regulation of norrin receptor frizzled-4 by Wnt2 in colon-derived cells.

Background: Norrin is a potent Wnt pathway ligand. Aberrant activation of this signaling pathway can result in colon tumors but the role of norrin-based signaling in the genesis of colon cancer, and its relationship to activation of the pathway by traditional Wnt ligands, is not defined.

Results: Fresh normal human colon tissue and all the cell lines studied expressed mRNA for Fz4, LRP5 and norrin, except Colo205 which lacked Fz4 expression.

A novel technique for improving interferometric determination of emulsion film thickness by digital filtration.

Determination of the thickness of emulsion films by using the film interferometric images is usually less accurate than that of foam films, due to the close values of the refractive indices of the liquid film and adjacent liquid phases (hence, low contrast and high level of noise at high magnification). A new technique was developed to improve the thickness determination by obtaining the interferometric images without directly filtering the illuminating light, as is usually done in the classical Scheludko interferometric technique. The new method then uses digital filtration during the off-line image post-processing to obtain monochromatic interferometric images required for the thickness determination.

Hydrophobic attraction as revealed by AFM force measurements and molecular dynamics simulation.

Spherical calcium dioleate particles ( approximately 10 mum in diameter) were used as AFM (atomic force microscope) probes to measure interaction forces of the collector colloid with calcite and fluorite surfaces. The attractive AFM force between the calcium dioleate sphere and the fluorite surface is strong and has a longer range than the DLVO (Derjaguin-Landau-Verwey-Overbeek) prediction. The AFM force between the calcium dioleate sphere and the mineral surfaces does not agree with the DLVO prediction.

Influence of electrical double-layer interaction on coal flotation.

In the early 1930s it was first reported that inorganic electrolytes enhance the floatability of coal and naturally hydrophobic minerals. To date, explanations of coal flotation in electrolytes have not been entirely clear. This research investigated the floatability of coal in NaCl and MgCl2 solutions using a modified Hallimond tube to examine the role of the electrical double-layer interaction between bubbles and particles.

Liquid drainage in single plateau borders of foam.

This paper reports on an investigation of the influence of the interfacial shear viscosity on the liquid drainage in single Plateau borders of foam. The simplified Navier-Stokes equation governing the liquid flow is solved for the liquid velocity by the numerical computational method. The numerical results show significant influence of the interfacial shear viscosity on the liquid velocity in the Plateau border.

Empirical equations for meniscus depression by particle attachment.

In this paper the problem of calculating the depression of the gas-liquid meniscus by the particle attachment was solved. The analytical approximate equations obtained for small and large radii, r(tpc), of the three-phase contact were analyzed and compared to the available numerical results. The Derjaguin equation for small r(tpc) and the analytical results for large r(tpc) are accurate for r(tpc)/L< or =0.

The liquid flow force on a particle in the bubble-particle interaction in flotation.

In this paper the problem of calculating the liquid flow force on a particle in interaction with an air bubble with a mobile surface in flotation as a function of the separation distance was solved. The force equation was obtained by first deriving the disturbed flow confined between the surfaces. The model for the force includes the separation distance between the bubble and the particle, the particle size, the bubble's Reynolds number, the bubble rise velocity, and the polar position of the particle on the bubble surface.

The dynamic nature of contact angles as measured by atomic force microscopy.

Atomic force microscopy appears to be a useful tool for determining the contact angle for small particles. It is shown in this paper that the contact angle of a spherical polyethylene particle changes with the speed of the AFM piezoelectric translator. Such dynamic behavior of the contact angle and other uncertainties such as the position of the three-phase contact on the particle surface during bubble-particle interaction make it difficult to decide whether or not the AFM single-particle contact angle can be used to describe the hydrophobic state of the particle surface.

Combining hydrodynamics and molecular kinetics to predict dewetting between a small bubble and a solid surface.

This paper examined the dewetting between a small air bubble and a solid surface in deionised water. Hydrodynamics was used in conjunction with surface molecular kinetics to model and predict the velocity of the moving contact line as a function of the dynamic macroscopic contact angle. The dewetting hydrodynamics was modelled following the approach developed specifically for drops and bubbles using the (absolute) coordinate system with the origin located at the centre of the contact area, which does not move with the moving contact line.