Surfactant Dispersion Research Articles

Carbon nanotube-based flexible biocathode for enzymatic biofuel cells by spray coating

Enzymatic biofuel cells are emerging technologies which gain a lot of interest as a power source for implantable devices. Effective enzyme wiring and simplification of the cell architecture are the main limitations of the fuel cell development nowadays. In the present study, spray coating was used as a reliable process to produce flexible biocathodes. That was achieved through spray coating of a conductive ink formulated by surfactant assisted carbon nanotubes dispersion. A thin continuous layer of carbon nanotubes (CNTs) was successfully coated on top of a gas diffusion layer paper. The film thickness was modulated by varying the CNT load in the ink and the number of deposited layers. It varied between 1 and 7.8 μm for a number of deposited layers between 5 and 100. Laccase enzyme was then wired to printed CNT electrodes thanks to the host-guest interaction between the hydrophobic pocket of laccase and pyrene-adamantane. Electrochemical investigations showed that laccase was effectively wired to the CNTs and presented a favorable orientation toward oxygen reduction. The biocathode current density was dependent of the number of deposited CNT layers and reached an optimum at 170 μA cm−2 for 50 deposited layers.

Emulsification using a “Sonolator” liquid whistle: A new correlation for droplet size from pilot-scale experiments

Emulsification experiments have been carried out on a pilot-scale Model ACIP2 Sonolator liquid whistle device by examining the change in droplet size distributions of silicone oil in water emulsions, using SLES as a surfactant, before and after processing. The process variables considered were mass flow rate, pressure drop across Sonolator, oil viscosity (from 10 to 10,000 cSt), oil concentration (0.5–10 wt%), surfactant concentration (0.00003–0.5 wt%) and orifice size. All experiments were carried out in the turbulent flow regime. The oil phase was added as either a pure phase or as a pre-emulsion stabilised using SLES. The oil was injected just before the blade or mixed at a T-junction prior to the Sonolator; the pre-emulsion was exclusively introduced via the latter method. The resultant droplet size distributions were obtained from offline sampling using laser diffraction. The most significant parameters found to influence the drop size were found to be pressure drop, dispersed phase viscosity and surfactant (SLES) concentration, which formed the basis for an empirical power law correlation. Indices in this correlation were compared to findings in the literature for other emulsification devices, and to those predicted from the theories of droplet breakage in turbulent inertial flow. Despite an expected regime change from turbulent inertial to turbulent viscous break-up being common in the literature as the dispersed phase viscosity is increased, this phenomenon was not observed in the experimental data obtained, suggesting breakage in an intermediate regime.

Effect of Graphene Flakes Modified by Dispersion in Surfactant Solutions on the Fluorescence Behaviour of Pyridoxine.

The influence of graphene (G) dispersions in different types of surfactants (anionic, non-ionic, and cationic) on the fluorescence of vitamin B6 (pyridoxine) was studied. Scanning electron microscopy (SEM) was used to evaluate the quality of the G dispersions via measuring their flake thickness. The effect of surfactant type and concentration on the fluorescence intensity was analyzed, and fluorescence quenching effects were found for all of the systems. These turn out to be more intense with increasing both surfactant and G concentrations, albeit they do not depend on the G/surfactant weight ratio. For the same G concentration, the magnitude of the quenching follows the order: cationic > non-ionic ≥ anionic. The cationic surfactants, which strongly adsorb onto G via electrostatic attraction, are the most effective dispersing agents and they enable a stronger interaction with the zwitterionic form of the vitamin; the dispersing power improves with increasing the surfactant chain length. The fit of the experimental data to the Stern-Volmer equation suggests either a static or dynamic quenching mechanism for the dispersions in non-ionic surfactants, while those in ionic surfactants show a combined mechanism. The results that were obtained herein have been compared to those that were reported earlier for the quenching of another vitamin, riboflavin, to elucidate how the change in the vitamin structure influences the interactions with G in the surfactant dispersions.

A New Method for Quantifying SWCNT Dispersion Quality from Absorption Spectra

Individualization of single-walled carbon nanotubes (SWCNTs) in aqueous surfactant dispersions can vary greatly. We will present a new method for quantitatively assessing dispersion quality based on simple absorption spectra. In this method, the visible and short-wave infrared portions of a sample’s absorption spectrum are modeled as a superposition of two components. One component (labeled “S”) has sharp resonant features and is associated with the subpopulation of SWCNTs that are suspended as individuals or very small aggregates; the other (labeled “B”) has broad absorption features and is associated with stably dispersed materials such as carbonaceous impurities, imperfect nanotubes, and larger aggregates. Using absorption spectra from samples in various stages of purification by centrifugation or magnetic processing, we apply the method of multivariate curve resolution to extract the S and B component spectra and determine their relative contributions in samples of interest. The ratio of S to B content then provides a simple index of dispersion quality. We illustrate this new characterization method with measurements on both shear-dispersed and tip-sonicated SWCNT samples purified by three different processes: centrifugation, ultracentrifugation, and magnetic purification. We determine the dispersion efficiency of each sample preparation and find results that correlate well with those of established analytical techniques. In addition, we have further characterized the effects of these purification processes on the SWCNT length distribution (using the diffusion-based LAND method) and on SWCNT emissive properties (through variance spectroscopy). We believe that our new absorption-based method provides a practical tool for quickly assessing the dispersion quality of SWCNT samples.

(Invited) Variance Spectroscopy Studies of Single-Walled Carbon Nanotube Aggregation

Understanding aggregation in samples of dispersed, well-individualized single-walled carbon nanotubes (SWCNTs) is important for many basic studies and applications. We will describe a study that uses the recently developed technique of variance spectroscopy to monitor aggregation kinetics of SWCNTs in aqueous surfactant dispersions. Unlike other techniques used to investigate colloidal dispersions, variance spectroscopy resolves individual subpopulations in mixed samples based on their distinct fluorescence signatures. Following the addition of NaCl coagulant to unsorted SWCNT dispersions, we monitored changes in the independent particle concentrations of six semiconducting (n,m) species. These data were supplemented by time-resolved measurements of fluorescence intensity, which showed pseudo-first order kinetics that was independent of SWCNT structure and was attributed to quenching by energy transfer to metallic SWCNTs. The decreases in particle concentration directly revealed aggregation. They were found to fit reasonably well to a second-order rate law with some dependence on structure at higher salt concentrations. Finally, covariance analysis was applied to the variance data to monitor correlated spectral fluctuations arising from specific heteroaggregates. Those results showed equivalent associations between different semiconducting SWCNT species during salt-induced aggregation.

Enhanced Oil Recovery Study of a New Mobility Control System on the Dynamic Imbibition in a Tight Oil Fracture Network Model

Aiming at increasing the recovery in tight oil reservoir with fractures, a new kind of mobility control system with function of imbibition (MCSI) was prepared with dispersed particle gel (DPG) and surfactant. The dynamic imbibition can effectively control the mobility ratio in a tight oil fracture network and increase oil recovery. Based on the characteristics of tight oil reservoir fractures, the preparation method of a multiple fracture network model was established. The prepared fracture network model has the characteristics of controllable fracture length, width, and height. The MCSI system can reduce the oil–water interfacial tension to 10–2 mN/m. It features low viscosity, strengthening water wet, thus promoting the imbibition effect. Dynamic imbibition tests of the multiple fracture network model show that the MCSI system has higher oil recovery than each single component. At the same time, the subsequent water flooding after soaking also has the function of enhancing oil recovery. The effects of f...

Development and Evaluation of High Oxaliplatin Loaded CS-g-PNIPAAm Co-Polymeric Nanoparticles for Thermo and pH Responsive Delivery

Abstract: Background: Chitosan-g-poly(N-isopropylacrylamide) (CS-g-PNIPAAm) co-polymer was reported as a much efficient drug carrier but it shows very low percentage of drug loading in to the nanoparticles. Objective: The objective of the present study was to develop highly loaded pH and thermo responsive CS-g-PNIPAAm co-polymeric nanoparticles for tumor specific oxaliplatin delivery. Methods: CS-g-PNIPAAm co-polymer was synthesized by surfactant free dispersion copolymerization method and characterized for its structure (FTIR1H NMR), morphology and lower critical solution temperature (LCST). Different drug loading approaches like direct drug loading during polymerization and self-assembly methods were used. In direct drug loading method the chitosan concentration was varied and in self assembly method the polymer ratio and sonication time were varied for study. Drug loaded nanoparticles were evaluated for particle size, zeta potential, percent drug loading efficiency, percent drug content and in-vitro drug release study. Results: It was observed that, self-assembly method give a high amount of oxaliplatin loaded nanoparticles. Further, in direct loading method, as the concentration of chitosan in co-polymer increases, the percent drug loading and drug release at above LCST of copolymer also increases. Nanoparticles prepared by self assembly method (F-5) showed the maximum drug release at above LCST (pH 7.2) and trace amount of drug release below LCST (pH 7.5), indicating thermo and pH responsive delivery of oxaliplatin. Conclusion: In conclusion, higher oxaliplatin loading can be achieved by using self-assembly method with sonication time 5 min and drug:polymer ratio of about 3:10 and oxaliplatin release can be controlled by varying chitosan concentration in co-polymer. Key words: Oxaliplatin, Chitosan-g-poly(N-isopropylacrylamide), Self assembly method, Thermo and pH responsive delivery.

Purifying carbon nanotube wires by vacuum annealing

We propose vacuum annealing to purify carbon nanotube wires (CNTWs) manufactured from surfactant dispersions by removing residual carbonaceous impurities (surfactant and solvent) included during wire-spinning. We analysed the CNTW purity post-annealing vs. treatment temperature and time by scanning electron microscopy, Raman spectroscopy, and thermogravimetry. Our results suggest that maximal purification is achieved after annealing at 800 °C (for ≥3 h) or at 1000 °C (for ≥1 h). The optimally purified wires show higher CNT content and G/D (∼93 wt% and >30, respectively) than the untreated wires (∼71 wt% and 25, respectively).

Characterization and Application of Surfactant Foams Produced from Ethanol‐Sodium Lauryl Sulfate‐Silica Nanoparticle Mixture for Soil Remediation

Soils contaminated with diesel oil spilling from industrial areas, pipelines constitute a major environmental problem. This subsequently leads to the contamination of groundwater as well. Hence recently there is an increasing trend of usage of better techniques and agents that can perform diesel oil contaminated soil remediation with greater efficiency. The aim of this study is to report the potential, efficiency of using silica nanoparticle stabilized anionic surfactant foams for diesel contaminated soil remediation and also the different characteristics of the foam produced. Also comparison in terms of soil remediation efficiency using surfactant dispersions only were performed. The foams were produced from dispersions comprising of ethanol, anionic surfactant sodium lauryl sulfate (SLS) and silica nanoparticles, both hydrophobic and hydrophilic. The foamability and stability of the different foams were determined using the Dynamic Foam Analyzer DFA 100 (Kruss GmbH, Germany). The surfactant foams generated were then applied to the contaminated soil using a fabricated column. The results showed the gradual stabilization of the SLS foams by the use of the silica nanoparticles. The maximum diesel oil removal efficiency obtained by applying foam stabilized with 0.3 wt% hydrophobic silica nanoparticle, 10 vol% ethanol, 0.1 vol% SLS was 94.5%. The 0.3 wt% hydrophobic silica nanoparticle, 10 vol% ethanol, 0.1 vol% SLS surfactant solution showed only 61.5% maximum oil removal efficiency.

Adsorption of alkylamine cations on montmorillonite (001) surface: A density functional theory study

Hydrophobic aggregation in cationic surfactant dispersion is an effective method for the dewatering of clay-rich tailing. The effect of head groups type and alkyl chain length on the adsorption of alkylamine cations on montmorillonite (001) surface was investigated by density functional theory (DFT), sedimentation and measurement of contact angle and adsorption quantity. The results showed that the strongest active sites were located above the six-membered oxygen ring (SOR) of montmorillonite layer, around the H atoms on N atom in the head group for alkyl primary amine (CnPA+), secondary amine (CnSA+), tertiary amine (CnTA+) cations and around H atoms in the –CH3 groups for quaternary amine (CnQA+) cation. The alkylamine cations interacted with surfaces by electrostatic attraction and hydrogen bonding where PA+, SA+, and TA+ cations formed three, two and one NHn⋯Os hydrogen bonds with the montmorillonite (001) surface, respectively, while QA+ cations formed non-traditional CHc⋯Os hydrogen bonds. The adsorption energies of Cn alkylamine cations decreased with the increasing substitution degree of –CH3 groups to Hn atoms in the head group. Moreover, the adsorption energies increased with the n increasing from 12 to 16, but changed slightly when beyond 16. The experimental results were consistent with the theoretically calculated results.

Adsorption and retention behaviors of heterogeneous combination flooding system composed of dispersed particle gel and surfactant

Heterogeneous combination flooding system composed of dispersed particle gel (DPG) and tetradecyl hydroxyl sulfo betaine (THSB) has been developed as a cost-effective EOR method due to highly beneficial synergistic behavior of improving both sweep efficiency and displacement efficiency. However, the combination flooding system suffered from surfactant loss and chromatographic separation which would raffect synergistic effect of chemical components for extra oil recovery. In this paper, static adsorption and dynamic adsorption of combination flooding system were systematically investigated. Additionally, effects of core permeability, DPG concentration and flow distance on chromatographic separation were also investigated by means of core flooding experiments. Static adsorption experiments indicated that after DPG particles and THSB surfactant were combined, adsorption of THSB surfactant on the quartz sand was lowered while the adsorption of DPG particles was improved, which was attributed to the interactions between DPG particles and THSB surfactant. Dynamic adsorption experiments showed that DPG particle could reduce the surfactant mobility and lead to increase of surfactant retention. Core flooding experiments confirmed that chromatographic separation phenomenon existed when combination flooding system flowed through porous media and the degree of separation phenomenon was lower than that of surfactant and polymer combination flooding system. Smaller surfactant losses, higher particle adsorption and lower chromatographic separation were all responsible for better synergistic behavior of heterogeneous combination flooding system.

Experimental and numerical study for drop size distribution in oil-water dispersions with nonionic surfactant Tween 80

The effect of nonionic surfactant (Tween 80) concentration on the evolution of drop size distributions (DSDs) of oil/water dispersion in a stirred tank was investigated experimentally and numerically. It was found that as the surfactant concentration increases, the mean droplet size decreases, the number density of small droplets increases and the dispersion stability is enhanced. It could be attributed to the augmentation of the breakage frequency caused by a dramatic reduction of interfacial tension and the suppression of the coalescence efficiency by an immobilized interface. When applying population balance equation (PBE) to surfactant dispersions, the effect of surfactant concentration was characterized by its influence on both breakage and coalescence process. The combined effect of surfactant molecules, drop size, and the number density of droplets on the turbulence intensity was considered in the breakage model. Models of coalescence time that consider partially mobile and immobile interfaces were employed to describe the film drainage at surfactant concentrations below and above CMC (critical micelle concentration) respectively. The effect of surfactant concentration on the critical film thickness was probed by adjusting the Hamaker constant and measuring the interfacial tension, while its influence on the coalescence efficiency was investigated by further balancing the contact and coalescence time. Both the predicted Sauter mean diameter and cumulative DSD agree with the experimentally measured values at different surfactant concentrations, while the discrepancies that exist could be due to the underestimation of coalescence rate between small droplets.

Molecular dynamics study of the aggregation rate for zwitterionic dodecyldimethylamine oxide and cationic dodecyltrimethylammonium chloride micelles

We studied dynamic scaling law for the early stage domain growth in the micelle aggregation process of dispersed surfactant molecules in water for zwitterionic dodecyldimethylamine oxide (DDAO) and cationic dodecyltrimethylammonium chloride (DTAC) based on all-atomistic molecular dynamics calculations. For both surfactants, the aggregation number N increases in proportion to tα′, where t and α′ are the simulation time and exponent of the dynamic scaling, respectively. When the aggregation is controlled by diffusion, it follows the well-known Lifshitz–Slyozov (LS) law giving the exponent α′ = 1. The values of α′ obtained for DDAO and DTAC are 0.6 and 0.3, respectively, indicating that the aggregation rate is suppressed compared with purely diffusion controlled LS process. The aggregation of DDAO and DTAC may be partly controlled by electrostatic interaction between the aggregates.

Quantification of counterion binding to and its effects on aqueous dispersions of dialkyl cationic surfactants

Dialkyl cationic surfactants, such as dioctadecyl dimethyl ammonium bromide (DODAB) form vesicles upon dispersion in water. In order to study the influence of the surfactant's counterion, the same dialkyl surfactant was prepared with a fluoride counterion (DODAF). Visually, quite transparent dispersions were prepared when fluoride was selected as counterion, whereas more turbid dispersions were obtained using the bromide surfactant. LR-NMR revealed that the permeability of the DODAF dispersions for water was much larger, which indicated that these rather contained uni- or oligolamellar vesicles, whereas the DODAB dispersions were multilamellar. These observations seemed to indicate an increasing degree of surface charge neutralization by the heavier anions, in line with the Hofmeister series, which was indeed confirmed by electrophoretic light scattering measurements. In order to further quantify the surfactant-counterion interaction, HR-NMR diffusometry measurements were performed on dispersions of a dialkyl cationic surfactant with methyl sulphate counterion in deuterated water. The diffusion data showed that the mobility of this organic anion increased when adding different sodium halides, with a stronger effect from fluoride over chloride and bromide to iodide, which clearly indicated the gradual displacement of the methyl sulphate counterion from the vesicular surface by the stronger binding anions.

Self-assembly and gelation of TX-100 in water

Self-organization of Triton X-100 (TX-100) surfactants in aqueous dispersion leading to their signature self-assembly is reported based on experimentally determined static structure factor data obtained from small-angle neutron scattering (SANS) experiments. Surfactant gels were formed for dispersions having 40% ≤ [TX-100] ≤ 55% (v/v). An unexplored correlation peak was noticed at a specific wave vector q* whose value increased with surfactant concentration. The form factor data could be described by modeling the micelles as core-shell structures (hydrophobic core with a polar shell). The intermicellar interactions were modeled with hard sphere, sticky hard sphere, and hard sphere in square well potential designations. We used a lattice model based on random walk formalism to theoretically describe this self-assembly, and observed that the cluster size decreased with TX-100 concentration consistent with experimental data. The self-organization of TX-100 in aqueous medium is presented.

High-concentration shear-exfoliated colloidal dispersion of surfactant–polymer-stabilized few-layer graphene sheets

To exploit the remarkable properties of graphene fully, an efficient large-scale production method is required. Sonication-assisted liquid-phase exfoliation of graphite, for example, has been extensively used for the production of few-layer graphene sheets, but suffers from low efficiency and high energy consumption and thus is not viable for large-scale production. Here we demonstrate a method that is more efficient and has higher scalability potential than sonication. We show that a few-layer graphene at high concentration of up to 1.1 mg ml−1 can be achieved in aqueous-based medium by highly efficient shear exfoliation of graphite in a processing time of just 2 h. The exfoliation process was carried out in a commercially available high shear colloidal mixer fixed with a three-stage rotor–stator shear generator for optimum exfoliation with a continuous circulation system. The high efficiency and a significant improvement over sonication adopting our method were demonstrated by the fact that the conversion to few-layer graphene sheets produced after just 30 min by shear exfoliation required, in contrast, 100s of hours by sonication. High-concentration defect-free few-layer graphene in aqueous medium, produced at short shearing time, demonstrates that this method has high potential for large-scale production. The produced graphene films exhibit additionally a high electrical conductivity of about 29000 S m−1.

Exploration of the Effect of Chitosan and Crosslinking Agent Concentration on the Properties of Dual Responsive Chitosan-g-Poly (N-Isopropylacrylamide) Co-polymeric Particles

The objective of the present study was to synthesize and evaluate the effect of change in concentration of chitosan (CS) and N,N-methylenebisacrylamide (MBA)- a cross linking agent, on various properties such as lower critical solution temperature (LCST), zeta potential, particle size and poly dispersity index (PDI) of the synthesized co-polymer. Nine different formulations of chitosan-g-poly (N-isopropylacrylamide) (CS-g-PNIPAAm) co-polymer with varying CS and MBA concentrations were synthesized by a surfactant free dispersion copolymerization method. The synthesized co-polymer was further characterized and confirmed for its structure, morphology, particle size, zeta-potential, thermo and pH responsive properties, in-vitro cyto-compatability and stability studies using various analytical tools. The data confirms the successful synthesis of co-polymer. The increase in the concentrations of CS and MBA during the polymerization of co-polymer, resulted in proportional increase of LCST and zeta potential with decrease in particle size of co-polymeric nanoparticles. pH responsive studies showed that as the pH of the medium increases particle size and zeta potential decreases with increase in LCST of co-polymeric nanoparticles. From the results, it can be inferred that the synthesized co-polymeric nanoparticles exerted thermo and pH responsive properties with biocompatibility. By varying the CS and MBA concentrations in the co-polymer, desired LCST, particle size and zeta potential for co-polymeric nanoparticles can be obtained and thus the synthesized co-polymer may have great potential to be used as a drug carrier (nanoform) with both thermo and pH responsiveness.

Segregated network formation of multiwalled carbon nanotubes in natural rubber through surfactant assisted latex compounding: A novel technique for multifunctional properties

In the present study Vulcastab VL (polyethylene oxide condensate) has been used as a non-ionic surfactant to get stable aqueous dispersions of multiwalled carbon nanotubes (MWCNTs). Sonication time and surfactant concentration were optimised by UV-vis spectroscopy and dynamic light scattering technique. Homogeneously dispersed surfactant coated individual MWCNTs in water were clearly evident from Transmission electron microscopy (TEM). Natural rubber –Multiwalled carbon nanotube (NR-MWCNT) nanocomposites were prepared by latex stage mixing. Instead of being randomly dispersed, MWCNTs were found to retain at the boundary of rubber particles resulting in a segregated network as evidenced from TEM. Addition of very small amount of MWCNT showed remarkable improvement in mechanical, thermal, electrical and barrier properties of NR. Segregated network of CNTs resulted in very low electrical percolation threshold (0.043 vol%) for the composite with enhanced dielectric properties.

Interfacial rheology of asphaltene emulsions in the presence of nanoemulsions based on a polyoxide surfactant and asphaltene dispersant

The development of oil-in-water nanoemulsions for application as demulsifiers has attracted a great deal of interest from chemical supply companies in the oil sector, due to the cost savings and advantages of replacing organic solvents with water. In this study, the efficiency of the nanoemulsions developed in a previous work in breaking down water/oil emulsions was correlated with assessments obtained by interfacial rheology studies of the systems used in the preparation of model emulsions. The results show that the performance of nanoemulsions developed for breaking oil emulsions depends on the oil phase used in the system’s composition and droplet size distribution. The results obtained from the interfacial rheology confirmed the activity of dodecylbenzene sulfonic acid (LBS) in dispersing asphaltenes in the demulsification step, resulting in more fragile and less elastic interfacial films.

Spray drying of folic acid within nano-emulsions: Optimization by Taguchi approach

ABSTRACTResearch over recent decades has shown that inadequate folate concentrations may contribute to some disorders. Cereal flours have been a primary candidate for fortification by folic acid as they are consumed by most of the people but the main obstacle is destruction of this vitamin by the process and environmental deteriorating factors. So, it can be nano-encapsulated for protection and efficient delivery. Our main goal was to find the optimum conditions in spray drying of pectin–whey protein concentrate (WPC) double emulsions containing folic acid. Five independent variables including pectin and WPC content, dispersed phase content, pH, and surfactant type of span and polyglycerol polyricinoleate (PGPR) were considered along with water activity (aw) and bulk density as the main responses. The experiment design was performed by Taguchi approach and 16 treatments were determined. The grand average of aw and bulk density for folic acid powders was approximately 0.371 and 343 kg/m3, respectively. The main effect analysis with Taguchi technique revealed that pectin content was the most important factor affecting aw (39.5%), and WPC had the minimum influence (6%). In terms of bulk density, it was found that the most important parameter was WPC (29.6%) and the minimum influence was related to surfactant system (8.1%). Finally, optimum conditions were determined as 0.5% pectin, 4.0% WPC, 10% dispersed phase, and pH 8, with a PGPR micro-emulsion, which resulted in aw = 0.229, and 1.5% pectin, 8.0% WPC, 10% dispersed phase, and pH 9, with a PGPR nano-emulsion, which resulted in density = 245.45 kg/m3 for folic acid powders.