Forces between surfaces in the presence of a cationic polyelectrolyte and an anionic surfactant

An atomic force microscope has been used to investigate the interaction forces between a mica surface and a colloidal glass sphere in the presence of a high molecular weight cationic polyelectrolyte, and the anionic surfactant sodium dodecylbenzenesulfonate (SDbS). The effect of addition of SDbS on the interaction forces between the polyelectrolyte coated surfaces was investigated. At low concentrations of SDbS the electrostatic repulsion initially present was progressively neutralized as a function of increasing surfactant concentration. Neutralization resulted in a strong attraction between the surfaces. As the SDbS concentration was increased further, additional surfactant association took place and the surfaces were recharged. At these surfactant concentrations the surfaces became less attractive at small separations. At high SDbS concentrations the interaction profile became purely repulsive as the surfaces were recharged. Diffuse double layer potentials derived from the direct force measurement data correlated well with zeta-potential measurements of silica particles treated with the polyelectrolyte and surfactant. Particulate stability behaviour was also seen to compare well with the force measurement and electrostatic potential data

Optimization of the hydroxylation reaction of epoxidised rice-bran oil using a response surface methodology

Polymeric materials, such as polyurethanes (PUs) are traditionally derived from petrochemical polyols but as oil reserves are depleting and prices continue to rise, the development of alternatives is becoming necessary. Vegetable oil-based polymers are gaining popularity due to some attractive properties (e.g. viscosities) related to the specific structure of oils, as well as addressing previous concerns about the environment and sustainability. Epoxidized rice bran oil (ERBO) can be used as potential feedstock for polyol production. It is derived by expoxidation of native RBO. During the hydroxylation reaction, epoxy groups in the epoxidized oil are converted to hydroxyl groups. This work determined the optimal conditions for the hydroxylation reaction using a response surface methodology. The goal was to maximize the hydroxyl value of the resulting polyol. Response surface methodology (RSM) provides an efficient experimental strategy to study the influence of imposed variables discover a final optimum. Furthermore, RSM has additional benefits as it allows determination of interaction effects between variables and saves times as a reduced number of experiments are required. The optimal conditions for hydroxylation reaction of the ERBO were a reaction time of 125.5 min at temperature of 49°C.Edy Purwanto, Yung Ngothai, Brian O'Neill, Kristen Bremmellhttp://www.chemeca2011.com

Adsorption of ionic surfactants in particulate systems: flotation, stability, and interaction forces

The flotation efficiency of silica particles using the ionic surfactants, sodium dodecylbenzenesulfonate (SDbS) and cetyltrimethylammonium bromide (CPB), have been investigated. Results from adsorption, electrophoretic mobility, dispersion stability and direct interaction force measurements are used to develop an understanding of the role of ionic surfactants in particulate flotation. Adsorption and mobility data indicate that SDbS adsorbs at the silica/solution interface, though without improving the flotation efficiency. CPB was found to adsorb on the silica particles as a result of electrostatic interaction; initially to neutralize the surface charge and destabilize the suspension, and at higher surfactant concentrations, to reverse the particle charge and re-stabilize the suspension. Direct force measurements in the presence of CPB confirm that the electrostatic interactions between approaching surfaces are neutralized at low CPB concentrations. Additionally, evidence for a strong adhesive interaction after contact is seen. At higher concentrations, the surfaces begin to recharge, and the adhesive interaction decreases in magnitude. The flotation efficiency was found to correlate well with the measured particle interactions, and to be a function of the particulate electrophoretic mobility

Molecular-level removal of proteinaceous contamination from model surfaces and biomedical device materials by air plasma treatment

Established methods for cleaning and sterilising biomedical devices may achieve removal of bioburden only at the macroscopic level while leaving behind molecular levels of contamination (mainly proteinaceous). This is of particular concern if the residue might contain prions. We investigated at the molecular level the removal of model and real-life proteinaceous contamination from model and practical surfaces by air plasma (ionised air) treatment. The surface-sensitive technique of X-ray photoelectron spectroscopy (XPS) was used to assess the removal of proteinaceous contamination, with the nitrogen (N1s) photoelectron signal as its marker. Model proteinaceous contamination (bovine serum albumin) adsorbed on to a model surface (silicon wafer) and the residual proteinaceous contamination resulting from incubating surgical stainless steel (a practical biomaterial) in whole human blood exhibited strong N1s signals [16.8 and 18.5 atomic percent (at.%), respectively] after thorough washing. After 5 min air plasma treatment, XPS detected no nitrogen on the sample surfaces, indicating complete removal of proteinaceous contamination, down to the estimated XPS detection limit 10 ng/cm2. Applying the same plasma treatment, the 7.7 at.% nitrogen observed on a clinically cleaned dental bur was reduced to a level reflective of new, as-received burs. Contact angle measurements and atomic force microscopy also indicated complete molecular-level removal of the proteinaceous contamination upon air plasma treatment. This study demonstrates the effectiveness of air plasma treatment for removing proteinaceous contamination from both model and practical surfaces and offers a method for ensuring that no molecular residual contamination such as prions is transferred upon re-use of surgical and dental instruments.

Nanomechanical Properties of Dead or Alive Single-Patterned Bacteria

International audienceThe main goal of this paper is to probe mechanical properties of living and dead bacteria via atomic force microscopy (AFM) indentation experimentations. Nevertheless, the prerequisite for bioAFM study is the adhesion of the biological sample on a surface. Although AFM has now been used in microbiology for 20 years, the immobilization of micro-organisms is still challenging. Immobilizing a single cell, without the need for chemical fixation has therefore constituted our second purpose. Highly ordered arrays of single living bacteria were generated over the millimeter scale by selective adsorption of bacteria onto micrometric chemical patterns. The chemically engineered template surfaces were prepared with a microcontact printing process, and different functionalizations of the patterns by incubation were investigated. Thanks to this original immobilization strategy, the Young moduli of the same cell were measured using force spectroscopy before and after heating (45 °C, 20 min). The cells with a damaged membrane (after heating) present a Young modulus twice as high as that of healthy bacteria