Surfactant Coatings Research Articles

Surfactant effects on the shapes of cobalt nanoparticles

The effect of surfactant coatings on the shapes and sizes of cobalt nanoparticles has been investigated. Cobalt nanoparticles were synthesized by thermal decomposition of a cobalt containing precursor in the presence of various surfactants. At room temperature the cobalt nanoparticles have a β-manganese structure also known as the ε-cobalt structure. The shapes of the cobalt nanoparticles include: spherical, triangular, rod-like, and hexagonal. The shapes of cobalt nanoparticles depend on the type of the surfactant used in the synthesis and the temperature at which the cobalt precursor was added to the reaction mixture.

Viscosity and yield stress reduction in non-colloidal concentrated suspensions by surface modification with polymers and surfactants and/or nanoparticle addition

A custom-designed apparatus termed the yield stress adaptor (YSA) has been used to evaluate the effect of polymer–surfactant coatings, and the addition of nanoparticles of different size, shape and surface chemistry, on the rheological properties of large hydrophilic particulates, sand, with the aim of reducing interparticle friction forces. Experimental results show that the flow properties of sand slurries at high volume fractions of sand (>50%) can be significantly enhanced by adding nanoparticles, and by surface modification with polymer/surfactant mixtures. A lesser effect is observed for polymer-only and surfactant-only coated samples. X-ray photoelectron spectroscopy was used to determine the concentration of organic species at the surface. The effect of polymer/surfactant concentration, adsorption time, polymer molecular weight, as well as surfactant charge and chemical structure were also addressed.

Molecular Adsorption at Particle Surfaces: A PM Toxicity Mediation Mechanism

Fine atmospheric particles depositing in the lung present a large adsorbent surface for the adsorption of bronchoalveolar lining fluid (BALF) components, including lung surfactant and its associated proteins. Such adsorption at invading particle surfaces is known to be important in biological particle clearance, and the immunological and toxicological fate of these particles. In the experiments conducted here, it was hypothesized that this is also true for particles of nonbiological origin, and that fine particles with large surface areas would selectively adsorb the opsonizing components of BALF. This work quantifies the adsorption rates (adsorption of compound per unit surface area) of isolated BALF components. Elemental carbon (EC) is a ubiquitous component of fine urban particulate matter (PM2.5), and particular forms of EC are extremely surface active (e.g., activated carbon). EC originates largely from fossil fuel combustion, and vehicles in particular contribute a significant proportion of PM2.5 EC mass in urban areas. Since the size distribution of EC is submicrometer, industrially produced carbon blacks in the 25–100 nm size range can be used as a surrogate for urban EC, in terms of surface area and chemistry. Three types of carbon black (CB) particles were used. Two were identical in size (25 nm) but different in surface treatment; R330, a CB with a nonoxidized surface, and R400, a CB produced with an oxidized surface. The third particle type, M120, was 75 nm, different in size from R330 and R400, but similar to R330 in surface chemistry, that is, nonoxidized. Particles were first washed and resuspended in phosphate-buffered-saline (PBS, pH 7.0) three times to remove surfactant coatings added during their manufacture. Colloidal suspensions of M120, R330, and R400 particles with decreasing surface areas were then generated and separated into reaction vials. BALF proteins were added spanning physiological concentrations while the dominant phospholipid in surfactant was added at a fixed concentration lower than physiological lung lavage concentrations to ensure the lipid remained in suspension during experimentation ex situ. For dipalmitoylphosphatidylcholine (DPPC) combinations with particles, visible particle agglomeration occurred within 1 h. Marked changes in the size distribution of the immersed particles were observed, compared to a phosphate buffer control. Differences in particle agglomeration and particle settling were observed between M120, R330, and R400. Reduction of DPPC occurred in a surface- and size-dependent manner. This indicates that surface adsorption was responsible for the observed agglomeration and the gross reductions in phospholipid concentrations. Combination of particles with fibrinogen and albumin revealed little agglomeration/precipitation at the protein concentrations chosen. However, surfactant protein (SP-D) was completely eliminated from suspension upon combination with all three-particle types. This reaction between SP-D particles was therefore concluded to be independent of surface chemistry. Further investigation as to whether this is size- or surface-area-dependent is recommended. The biological implication is that molecular adsorption at nonbiological particulate matter (PM) surfaces in BALF may mediate the toxicity of PM via one or both of these mechanisms, as in the case of biological particles.

Characterisation and evaluation of novel surfactant bacterial anti-adherent coatings for endotracheal tubes designed for the prevention of ventilator-associated pneumonia.

It is accepted that ventilator-associated pneumonia is a frequent cause of morbidity and mortality in intensive care patients. This study describes the physicochemical properties of novel surfactant coatings of the endotracheal tube and the resistance to microbial adherence of surfactant coated endotracheal tube polyvinylchloride (PVC). Organic solutions of surfactants containing a range of ratios of cholesterol and lecithin (0:100, 25:75, 50:50, 75:25, dissolved in dichloromethane) were prepared and coated onto endotracheal tube PVC using a multiple dip-coating process. Using modulated temperature differential scanning calorimetry it was confirmed that the binary surfactant systems existed as physical mixtures. The surface properties of both surfactant-coated and uncoated PVC, following treatment with either pooled human saliva or phosphate-buffered saline (PBS), were characterised using dynamic contact angle analysis. Following treatment with saliva, the contact angles of PVC decreased; however, those of the coated biomaterials were unaffected, indicating different rates and extents of macromolecular adsorption from saliva onto the coated and uncoated PVC. The advancing and receding contact angles of the surfactant-coated PVC were unaffected by sonication, thereby providing evidence of the durability of the coatings. The cell surface hydrophobicity and zeta potentials of isolates of Staphylococcus aureus and Pseudomonas aeruginosa, following treatment with either saliva or PBS, and their adherence to uncoated and surfactant-coated PVC (that had been pre-treated with saliva) were examined. Adherence of S. aureus and Ps. aeruginosa to surfactant-coated PVC at each successive time period (0.5, 1, 2, 4, 8 h) was significantly lower than to uncoated PVC, the extent of the reduction frequently exceeding 90%. Interestingly, the microbial anti-adherent properties of the coatings were dependent on the lecithin content. Based on the impressive microbial anti-adherence properties and durability of the surfactant coating on PVC following dip coatings, it is proposed that these systems may usefully reduce the incidence of ventilator-associated pneumonia when employed as luminal coatings of the endotracheal tube.

Characterizing electroosmotic flow in microfluidic devices

The current-monitoring method was used to measure the electroosmotic flow (EOF) in borosilicate glass capillaries and zeonor plastic microfluidic devices. The surface of the zeonor devices must be oxidized to support EOF and this treatment shows signs of aging within 6 days. Oxidized zeonor devices showed the same response to changes in applied field, pH, and ionic concentration as the capillaries. The effects of several common dynamic surfactant coatings on the walls were also studied (0.1%, v/v solutions of POP-6, POP-4, Pluronics L81, and NP-40). These generally significantly suppressed the EOF but required several days to stabilize.

Semi-permanent surfactant coatings for inorganic anion analysis in capillary electrophoresis

Capillary electrophoretic separations of inorganic anions are performed using a capillary coated with a mixture of the cationic surfactant didodecyldimethylammonium bromide (DDAB) and the zwitterionic surfactant 1,2-dilauroyl- sn-phosphatidylcholine (DLPC). These double-chained surfactants form semi-permanent coatings on the capillary wall, which allows the excess surfactant to be removed from the buffer prior to separation. Interactions between surfactant aggregates in the buffer and analyte anions are thus eliminated. The electroosmotic flow (EOF) can be altered from fully reversed (100% DDAB) to near zero (100% DLPC) using different ratios of DDAB and DLPC. Controlling the EOF allows for improved resolution of the anions while maintaining a rapid, co-EOF separation, free from analyte–surfactant additive interactions.

Characterization of surfactant coatings in capillary electrophoresis by atomic force microscopy.

This paper describes the adsorption mechanisms and aggregation properties of cetyltrimethylammonium bromide (CTAB) and didodecyldimethylammonium bromide (DDAB) surfactants that are used for dynamic coatings in capillary electrophoresis (CE). Atomic force microscopy is used to directly visualize surfactant adsorption on fused silica. It was found that the single-chained surfactant CTAB forms spherical aggregates on silica while the double-chained surfactant DDAB forms a bilayer. Aggregation at the surface occurs at approximately the same surfactant concentration in which EOF reversal is observed in CE. The nearest-neighbor distance between CTAB aggregates varies inversely with buffer pH and becomes constant at the point when the silanol groups are fully ionized. DDAB forms a flat, uniform coating independent of pH. Increasing the buffer ionic strength changes the morphology of the CTAB aggregates from spherical to cylindrical. The change in morphology can alter the surface coverage, which is related to the "normalized" EOF measured in identical buffers. The morphology of a surfactant coating is also shown to affect its ability to inhibit protein adsorption to the capillary wall. Specifically, the full surface coverage provided by DDAB proved superior in a head-to-head comparison with CTAB.

Study on the lifetime and attenuation properties of microbubbles coated with carboxylic acid salts

Four kinds of surfactants, sodium laurate, sodium myristate, sodium palmitate and sodium oleate were used to study the effects of surfactant coatings on the lifetime and attenuation of microbubbles. The changes in the size distribution of microbubbles prepared with these surfactants in saline were measured with a Coulter Multisizer (Coulter Electronics Ltd., Luton, UK). Frequency characteristics of ultrasonic attenuation of the microbubble suspensions were measured between 400 kHz and 6 MHz. From the changes in attenuation in the microbubble suspensions over time, it was found that the lifetime of microbubbles in a suspension also depends on the frequency of the irradiating ultrasound. The effect of surfactants on the frequency characteristics of attenuation was also studied, and characteristics of the surfactant coating, including shell elasticity and shell friction parameters were calculated from the measurement results. Microbubbles produced with sodium palmitate had the longest lifetime and the smallest average size. The shell had very little effect on the ultrasonic properties of microbubbles produced with sodium palmitate, suggesting that the sodium palmitate microbubbles behaved ultrasonically as free microbubbles.

Airway surfactant, a primary defense barrier: mechanical and immunological aspects.

Epidemiologic studies have shown strong associations between mortality and morbidity from respiratory and cardiac causes and exposure to fine (PM10), but not coarse, particulates. A plausible mechanistic explanation for these associations is lacking. It has been shown that particles may be retained for an extended period of time in the airways, and that their clearance is inversely proportional to particle size. Such particles are localized in close association with the airway epithelium, and if they consist of low surface energy material, will be coated with an osmiophilic layer, consistent with surfactant. Particles are displaced into this position by surface and line tension forces exerted by the surfactant film at the air-aqueous interface. Particle displacement due to line tension is much greater for smaller particles in the micrometer range. The surface forces acting on the particles leave deep indentations on the epithelial cells. During the displacement process they may come into contact with airway macrophages in the mucous layer and/or dendritic cells situated in the airway epithelium. The smallest particles may even penetrate the mucosa to enter the interstitial compartment. In addition to altering the physical properties of particles, surfactant coatings reduce particle toxicity and enhance phagocytosis by opsonization. We speculate that surfactant acts as a primary defense barrier and plays a role in antigen presentation and elimination at the air-mucus interface of the airways.

Surfactant coatings for the stabilization of barium peroxide and lead dioxide in pyrotechnic compositions

AbstractBaO2 and PbO2 are widely used oxidizers which have been observed to suffer degradation after storage in unsealed systems. It is evident that reaction occurs with atmospheric water and carbon dioxide forming carbonates. The inhibition of these reactions by the application of protective coatings is considered, Such techniques appear to be gaining importance in pyrotechnic applications, and criteria for suitable coatants are discussed. Various surfactants were applied to BaO2 and evaluated in an accelerated aging test. Selected anionic and non‐ionic surfactants conferred improved aging resistance, with stearic acid giving the greatest advantage. A very high degree of protection was also afforded to PbO2. Low energy fuses based on a BaO2/Si composition were evaluated and a high resistance to aging was realized using the coated BaO2. There were no adverse effects on other properties, thus satisfying the criteria established for coatants.

Nonionic surfactant polarity index determination by inverse gas chromatography

AbstractPolyglycol nonionic surfactants are widely used in industrial and consumer products. Two classes of these surfactants, made from selected combinations of 1,2‐butylene oxide, propylene oxide and ethylene oxide, were compared to alcohol ethoxylate (AE) and nonyl phenol ethoxylate nonionic surfactants in this study. Polyglycol copolymers consisted of either a polypropylene glycol (PPG) or polybutylene glycol (PBG) central hydrophobe. Ethoxylation of the hydrophobes produced polyethylene glycol hydrophilic blocks. Differences in hydrophobe polarity were determined by inverse gas chromatography (IGC). IGC is a useful analytical method by which the physical and chemical characteristics of a material are studied. The stationary surfactant material under study was coated onto an inert support and used as the packing for the column. A probe mixture, containing simple organic molecules of varying polarity, was injected, and the retention characteristics were measured. The retention characteristics of the standard probe mixture were used to reveal relative polarity information about the stationary surfactant coatings. Polarities of the four hydrophobes were (in decreasing order): PPG, PBG, nonyl phenyl and fatty alkyl. Comparisons were then made between the calculated hydrophile‐lipophile balance values and polarity indices of the hydrophobes and their ethoxylates. The effects of hydroxyl groups on polarity were also studied and quantified.

Capillary electrophoretic separations of proteins using nonionic surfactant coatings

Capillary zone electrophoretic separations of proteins have been achieved by using nonionic surfactant coated capillaries. Capillaries were prepared by derivatization of the silica surface with octadecylsilane followed by the deposition of a layer of nonionic surfactant from an aqueous solution above the critical micelle concentration. This coating is of sufficient thickness and hydrophilicity to reduce both protein adsorption and electroosmotic pumping. This hydrophilic coating reduces electroosmotic pumping 5-8-fold while resolving proteins quickly and efficiently with good recovery. The coating provides a stable and reproducible means of deactivation, while the rate of electroosmotic pumping stays relatively constant throughout the pH range 4-11. This allows the pH to be varied to enhance selectivity without adversely affecting the flow rate.

Synthesis and response of new microsensor coatings—II Acridinium betaines and anionic surfactants

Four acridinium betaines and two ionic surfactants were synthesized, and evaluated as chemical microsensor coatings by exposure to vapors of chloroethyl ethyl sulfide (CEES) and dimethyl methylphosphonate (DMMP). Two of the acridinium betaines showed selective and reversible responses (of 9.8 and 6.8 kHz) as SAW (surface acoustic wave) coatings in the detection of CEES vapor: there appears to be a connection between the long alkyl chain (C-12 and C-14) in the acridinium molecules and the response. Response times were generally less than 30 sec but desorption was significantly slower. The ionic surfactant coatings show small SAW changes (> 0.5 kHz) in response to DMMP vapor, and somewhat greater responses (20- and 68-fold), as chemiresistors, to CEES vapor. In each case the response occurred within 3 min, with return nearly to baseline levels within 6 min of cessation of exposure to the vapor. The responses were reproducible within ± 5%.

Interparticle correlations in Fe3O4 ferrofluids, studied by the small-angle neutron scattering technique

Aggregation in sterically stabilized Fe3O4 ferrofluids has been studied with the small-angle neutron scattering technique. The influence on the aggregation of the particle volume fraction, varying between 0.02 and 7 vol % Fe3O4, and the influence of an applied magnetic field is examined. Contrast variation enabled the scattering of particles and surfactants to be measured independently. The particle size distribution derived from the scattering is in good agreement with the field dependence of the magnetization and the optical anisotropy. From the anisotropy in the neutron scattering patterns of fluids subjected to a magnetic field of 0.10 T perpendicular to the neutron beam, it is derived that at all volume fractions below 1 vol % Fe3O4 most of the particles are located in small chainlike aggregates oriented parallel to the field direction. Larger, three-dimensional aggregates arise at higher volume fractions, both in the applied field and in zero field. The interparticle distance within an aggregate corresponds to surface-to-surface contact of the surfactant coatings.

Observations on diagenesis in North Sea reservoir sandstones

Pressure solution If there were a grain-boundary solution phenomenon due solely to pressure it would be a function of depth of burial and have important consequences for the prediction of porosity reduction trends in hydrocarbon reservoirs. However, many of the interpenetrant grain contacts that have been illustrated by speakers at this meeting and termed 'pressure solution' require additional explanation. From our own work on both outcrop and core materials we have been unable to find any convincing correlation between burial depth and 'pressure solution'—for a variety of facies. Furthermore, Hancock (1978) does not claim to have seen pressure-solution phenomena although his sediments were recovered from a greater depth than any others described at this meeting. We suspect that the nature of the pore fluids flushing through the sediment is very important, particularly where grain-boundary reactions have been catalysed by surfactant coatings such as clays and micas. Reservoir sandstones did not become 'closed systems' until hydrocarbon emplacement was completed. Before this occurred pore-fluid evolution was probably continuous. Fibrous illite In our own studies on offshore core material from probable Old Red Sandstone in the Buchan Field, we have found fibrous outgrowths on clays and micas (Pl 1, fig. 1) in fractures. In this case, therefore, the fibres post-dated fracture development. We are not convinced that the fibres are simple illites (as has been proposed by several speakers) for the following reasons: 1. Using non-dispersive X-ray analysis it may be possible to show that the fibres are composed mainly of K 2 O,