Addition Of Cationic Surfactant Research Articles

Cationic surfactant as methane–water mass transfer enhancer for the fermentation of Methylosinus trichosporium OB3b

Abstract In this paper, we conducted an investigation into the use of bubbles modified with cationic surfactants in bubble coalescence inhibition and enhancement of methane-water volumetric mass transfer rate. Various cationic surfactants including hexyltrimethylammonium bromide (HTAB), octyltrimethylammonium bromide (OTAB), dodecyltrimethylammonium bromide (DTAB), and hexadecyltrimethylammonium bromide (HDTAB) were added to aqueous solution and the methane-water volumetric mass transfer coefficient (k L a) values were determined for each of the solutions. Enhancement of methane-water k L a was observed from 14 h −1 to 69 h −1 , depending on the cationic surfactant type and concentration. Enhanced methane-water k L a in aqueous solution by addition of cationic surfactants was employed for the fermentation of methanotroph ( Methylosinus trichosporium OB3b), and cell growth rate and maximum optical density was increased by 391% and 498%, respectively.

Development of Tetrahydrofuran/Water Optical Waveguide and Its Application to the Observation of Extraction Behavior of 1-Anilino-8-naphtalene Sulfonate at the Tetrahydrofuran/Water Interface.

A stable two-phase sheath flow using tetrahydrofuran (THF) for an inner flow and water for an outer flow was formed in a glass capillary, and worked as a stable liquid-core/liquid-cladding optical waveguide (THF/water LLW). Although THF and water were miscible with any ratio, the length of the stable THF/water LLW at 0.9 - 2.1 cm s-1 reached at least 150 mm. The THF/water LLW was applied to the observation of extraction behavior of solvatochromic fluorescence dye, 1-anilino-8-naphtalene sulfonate (ANS), through the THF/water interface. ANS was added to the water phase (clad solution) and its fluorescence, which was excited with the guided light (355 nm) through the LLW, was observed by changing the position of the detector. While the ANS stayed in the region of 70% THF to the end of the LLW without the addition of cationic surfactant, hexadecyltrimethylammonium ion (CTA+) at pH 3 and 11, the ion-pair of ANS and CTA+ was extracted into the higher concentration region of THF with the addition of CTA+ at pH 11.

Effect of Surfactant Additives on Phase Inversion in Oil-Water Pipe Flow System

This research investigates the effect of surfactant additives on phase inversion point in the oil-water flow in horizontal pipe. Two types of surfactants were used in the experiments; anionic type (sodium lignosulfonate (SLS)) at 200 ppm and cationic type (hexadecyltrimethyl ammonium bromide (CTAB)) at 100 ppm. The experiments were carried at mixture velocities (0.8, 1, 1.9 and 2.3) m/s. The results showed that the phase inversion points are unaffected by surfactant addition or velocity at low mixture velocities while they shifted downward at high mixture velocities. The experiments show also that anionic surfactant addition caused a forward shifting in phase inversion point and downward shifting in the addition of cationic surfactant at high mixture velocities.

The Effect of HTAC Addition on the Efficiency of PEO in Turbulent Flow

Objectives: Polyethylene Oxide (PEO) is one of the most effective drag reduction additives. However, it limits and degrades under high share stress. The improvement of its Drag Reduction (DR) efficiency and degradation resistant with the addition of cationic surfactant was investigated. Methods/Statistical Analysis: PEO at concentrations of 10 and 20 ppm were mixed with a different concentration of Hexadecyltrimethylammonium Chloride (HTAC). Capillary viscometer and Rotating Disk Apparatus (RDA) were used to measure the viscosity and the %DR, respectively. Findings: The results showed an improvement in both the DR ability and degradation resistance when the complex polymer-surfactant was used, compared to the pure polymer. The maximum DR was recorded as 36% at 10ppm and 42% at 20ppm PEO and 125ppm HTAC. This improvement was due to the interaction between the micelles and the polymer. Application/Improvements: This improvement will promote the use of PEO/HTAC mixture in higher share stress flow application.

Corrosion behavior of Ni-P-nano-Al2O3 composite coating in the presence of anionic and cationic surfactants

Ni-P-nano-Al2O3 composite coatings on the mild steel were obtained by adding Al2O3 nanoparticles into the traditional electroless Ni-P bath. Cationic and anionic surfactants were used to prevent the agglomeration of the incorporated nano-Al2O3. Surface morphology, compositions and microstructures of the coating were studied using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) as well. Corrosion resistances of the modified mild steel samples were evaluated in 3.5wt.% NaCl solution by electrochemical impedance spectroscopy (EIS). The results showed that compared to the pure Ni-P coating on the mild steel, the coating formed in the bath with 6g/L nano-Al2O3 performed the highest resistance. Under the optimal conditions, the adding of anionic surfactant (SDBS) improved the anti-corrosion performance of the samples further, while the addition of cationic surfactant led to a worse corrosion resistance. The potential mechanism was that anionic surfactant molecules would contact with active sites of Ni-P composite coating and nano-Al2O3 in the bath, which would improve the dispersion of nano-Al2O3, thus leading to a homogeneous coating with better corrosion resistance.

Surfactant effect on the physicochemical characteristics of cationic solid lipid nanoparticles

Solid lipid nanoparticles (SLNs) may be considered as a new approach for therapeutics for many diseases. In addition to drug delivery, their use as non-viral vectors for gene delivery can be obtained by including cationic lipids, which provide a positive surface potential that favors binding to the nucleic acids as DNA, siRNA, miRNA, etc. In fact, the addition of cationic surfactants is indispensable for obtaining nanoparticles with surface positive charge. In this study, three different cationic lipids (dioctadecyl dimethyl ammonium bromide, cetyltrimethyl ammonium bromide, cetylpyridinium chloride) and Brij 76 as nonionic surfactant were employed to formulate Precirol ATO 5 based cSLN using pEGFP-LUC as model plasmid. The physicochemical properties of cSLN were influenced by both type and amount of surfactants. Thermal analyses of bulk cSLN showed endothermic peaks significantly different from the ones of the single pure components, hinting a complete entanglement of the lipid matrix with the surfactants and justifying the different behavior of the cSLN in the ability to interact with the plasmid DNA. Finally, the biocompatibility of cSLN was demonstrated by hemolytic assays. These results may give an insight into the choice of surfactants in order to obtain non-toxic and highly effective delivery systems for gene therapy.

A simple method for preserving environmental DNA in water samples at ambient temperature by addition of cationic surfactant

Environmental DNA (eDNA) analysis is a powerful tool within ecology for the study of the distribution or abundance of aquatic species, although the simplification of water sampling is required for enabling light and fast field sampling to expand further application of eDNA analysis. Here, certain candidate chemicals belonging to the group of cationic surfactants were examined for their effectiveness as preservatives for eDNA water samples by simply adding the chemicals to water samples to suppress the degradation of eDNA. The quaternary ammonium compound benzalkonium chloride (BAC) at a final concentration of 0.01% was effective to retain 92% of eDNA derived from the bluegill sunfish Lepomis macrochirus in an 8-h incubation test at ambient temperature, which assumed a transportation of water samples in 1-day field sampling during the daytime. Meanwhile, eDNA in water samples without BAC retained only 14% of the initial eDNA. Moreover, an additional long-term incubation test (up to 10 days) revealed BAC-treated samples retained ~70 and 50% of bluegill DNA compared to the initial amount after 1- and 10-day incubation at ambient temperature, respectively. Meanwhile, eDNA in naïve samples reduced to 20% after 1-day incubation and reached undetectable levels after 10 days. Up to now, many eDNA studies have adopted on-site filtration followed by filter fixation, which requires many pieces of equipment. Addition of BAC can protect eDNA in water samples with less effort and equipment resulting in an increase of measurement accuracy of the eDNA quantity and detection probability of rare species by preventing the disappearance of rare sequences in water samples.

Amido‐Amine‐Based Cationic Gemini Surfactants: Thermal and Interfacial Properties and Interactions with Cationic Polyacrylamide

AbstractExperimental studies were conducted to investigate thermal and interfacial properties of two in‐house synthesized amido‐amine‐based cationic gemini surfactants namely: dodecanoic acid [3‐({4‐[(3‐dodecanoylamino‐propyl)‐dimethyl‐amino]‐butyl}‐dimethyl‐amino)‐propyl]‐amide dibromide (12‐4‐12) and dodecanoic acid [3‐({6‐[(3‐dodecanoylamino‐propyl)‐dimethyl‐amino]‐hexyl}‐dimethyl‐amino)‐propyl]‐amide dibromide (12‐6‐12). Thermogravimetric analysis showed the excellent thermal stability of surfactants and no structural degradation was observed at temperatures up to 250 °C. The long‐term thermal stability of the surfactants was investigated with the aid of spectroscopic techniques such as nuclear magnetic resonance (NMR (1H and 13C) and Fourier transform infrared (FTIR) spectroscopy. Both surfactants were found to be thermally stable, and no changes in structure were observed after aging for 10 days at 90 °C. The interfacial tension of the surfactants was measured at three different temperatures (30, 60, and 80 °C), and the results showed a decrease in interfacial tension with increasing temperature and increasing spacer length of the surfactants. Rheological measurements were used to assess the interactions between the cationic gemini surfactant and cationic polyacrylamide. The addition of cationic surfactant reduced the viscosity and storage modulus of the polymer at low shear rate and frequency due to surfactant–polymer interactions and charge screening. The investigated surfactant–polymer system has great potential in high‐temperature carbonate reservoirs, where conventional anionic surfactants are not recommended due to high adsorption.

Counterion effect of cationic surfactants on the oxidative degradation of Alizarin Red-S photocatalysed by TiO2 in aqueous dispersion

Abstract The TiO 2 photocatalyzed degradation of a hazardous texile dye, 3,4-dihydroxy-9,10-dioxo-2-anthracenesulfonic acid sodium salt (Alizarin Red-S, ARS), has been assisted by various cationic surfactants and examined in air-equilibrated aqueous medium under UV light irradiation. Absorption spectral analysis showed that ARS degrades slowly via a pH-dependent process in TiO 2 dispersions containing no surfactant. The photodegradation efficiency of the dye was significantly enhanced, especially in alkaline media, by the addition of surfactants such as cetyltrialkylammonium salts (CTRAX). Since both ARS and the TiO 2 surface are negatively charged in basic conditions, the addition of cationic surfactants has effectively allowed the mutual interaction among the dye, CTRAX and TiO 2 . The cooperation between the inorganic and organic components, which is very likely realized through the formation of cationic surfactant bilayers on the TiO 2 particles, permitted an improvement in the coadsorption of ARS onto the TiO 2 particles and thus rendering ARS more available to the action of the photo-yielded oxidative species formed on the semiconductor surface. The crucial influence of the surfactant adsorption was clearly pointed out by the investigation of the counterion effect on the degree of ARS photodecomposition as a function of the cetyltrimethylammonium salt (CTAX) concentration. Two particularly significant aspects have emerged from this investigation: the almost complete degradation of ARS was achieved, for all surfactants used, at a concentration close to 1 mM (value well above the cmc in the experimental conditions); also, by increasing the surfactant concentration, the photocatalytic reaction became less and less efficient and significantly dependent on the counterion nature. These results have allowed to gain insight and a better understanding of the surfactant-assisted photocatalytic degradation mechanism of the dye.

Surfactant-Triggered Fluorescence Turn "on/off" Behavior of a Polythiophene-graft-Polyampholyte.

Polythiophene-graft-polyampholyte (PTP) is synthesized using N,N-dimethylaminoethyl methacrylate and tert-butyl methacrylate monomers by grafting from polythiophene backbone, followed by hydrolysis. The resulting polymer exhibits aqueous solubility via formation of small-sized miceller aggregates with hydrophobic polythiophene at the center and radiating polyionic side chains (cationic or anionic depending on the pH of the medium) at the outer periphery. The critical micelle concentration of PTP in acidic solution (0.025 mg/mL, pH = 2.7) is determined from fluorescence spectroscopy. PTP exhibits reversible fluorescence on and off response in both acidic and basic medium with the sequential addition of differently charged ionic surfactants, repeatedly. The fluorescence intensity of PTP at pH 2.7 increases with the addition of an anionic surfactant, sodium dodecyl benzenesulfonate (SDBS), due to the self-aggregation forming compound micelles. The fluorescence intensity of these solutions again decreases on addition of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), because of assembling of SDBS with CTAB, thus deassembling the PTP-SDBS aggregates. At pH 9.2, these turn on and turn off responses are also shown by PTP with the sequential addition of cationic surfactant (CTAB) and anionic surfactant (SDBS), respectively. This result shows that PTP has potential for surfactant-induced reversible fluorescence turn on and off using ionic surfactant (SDBS and CTAB) through self-assembling and deassembling of the ionic aggregates. The reversible aggregation and disaggregation process of PTP with the surfactants at both acidic and basic pH is supported from dynamic light scattering and Fourier transform infrared spectroscopy. The morphology of the above systems studied by transmission and scanning electron microscopy also supports the above aggregation and disaggregation process.

The effect of cationic surfactant additives on flow properties of crude oil

ABSTRACTPretreatment of the crude oil with flow improver or pour point depressants has received the greatest acceptance due to its simplicity and economy. Three cationic surfactants Bola form based on urea were prepared by quaternization reaction with alkyl dihalides of different chain length (hexayl, decyl-, and dodecyl-dibromide). The prepared compounds (U6, U10, and U12) were evaluated as surface active agents as well as pour point depressant for crude oil compared to monosurfactant (U12a) corresponding to (U12). The surface parameters of each synthesized surfactant were calculated from their surface tension profile including the critical micelle concentration, maximum surface excess (Γmax), and the minimum surface area (Amin). The free energies of micellization (ΔG°mic) and adsorption (ΔG°ads) were also calculated. Its pour point and viscosity decreased significantly after adding surfactants. FTIR studies of crude-surfactant mixture showed remarkable decrease in concentration of viscosity enhancing groups such as alkanes, alcoholic, and acidic groups, indicating the effectiveness of both the surfactants.

Hydroformylation of 2,5‐norbornadiene in organic/aqueous two‐phase system and acceleration by cationic surfactants

The organic/aqueous biphasic hydroformylation of 2,5‐norbornadiene (NBD) was investigated for the first time using HRh(CO)(TPPTS)3 (TPPTS: trisodium salt of tri(m‐sulphonylphenyl)phosphine) as the catalyst precursor. A comparison was made of homogeneous and biphasic systems. The optimum reaction parameters are discussed and the reaction mechanism is presented. In order to ensure the process attained high activity under moderate conditions, the effect of various cationic surfactants was tested in the biphasic hydroformylation of NBD. The results indicated that the hydroformylation of NBD in the biphasic system exhibited high activity and high selectivity to dialdehyde products under mild conditions. The addition of cationic surfactants markedly accelerated the reaction. A single long‐chain surfactant seemed to exert a greater impact on the hydroformylation of NBD than a double long‐chain surfactant. Moreover, the recycling of aqueous solution containing catalyst with or without surfactant was investigated. In the absence of the surfactant, the aqueous catalyst could be recycled six times without a significant decrease in activity and selectivity. Copyright © 2016 John Wiley & Sons, Ltd.

Influence of Ionic Surfactants on the Properties of Nanoemulsions Emulsified by Nonionic Surfactants Span 80/Tween 80

The instability of nanoemulsions were mainly due to Ostwald ripening. The droplet charge was influenced by the stability of nanoemulsions significantly. In this work, the properties of the shea butter oil-loaded nanoemulsions were investigated in detail with the addition of cationic surfactants (cetyl trimethyl ammonium chloride, 1631; octadecyl trimethyl ammonium chloride, 1831), anionic surfactants (alcohol ethoxysulfate, AES; dodecyl phosphate ester sodium salt, MAP), and zwitterionic surfactants (cocoamidopropyl betaine, CAB; dodecyl hydroxysulfobetaine, 20HD). By increasing the concentration of cationic surfactants, the positively charged nanoemulsions were prepared and the smallest droplets were being formed with 0.05% 1831. Upon the addition of anionic surfactants, a more negative value was obtained and the smallest droplets were being formed with 0.1% AES. The ionic surfactants by increasing the electrostatic interactions between droplets and incorporation into the oil phase improved the stability of the nanoemulsions via lowering the Ostwald ripening rate, and especially improved the high temperature stability. By increasing the concentration of zwitterionic surfactants, a less negative zeta potential was observed and the stability of the nanoemulsions did not improve. The results proved that the electrosteric repulsion had an appreciable impact on the stability of the nanoemulsions.

Electrokinetic potential and flocculation of bentonite suspensions in solutions of surfactants, polyelectrolytes and their mixtures

The effects of cationic and anionic surfactants and polyelectrolytes, as well as their binary mixtures, on the electrokinetic potential and the degree of aggregation/sizes of particle flocs in bentonite suspensions have been studied. The amounts of the above reagents, compositions and ratios of positive and negative charges in the mixtures, charge densities of the polyelectrolytes, and the order of the introduction of the components into systems have been varied. It has been shown that the addition of cationic surfactants or polyelectrolytes and mixtures thereof causes a substantial reduction of the negative ζ-potentials of the particles and reversal of the sign of their charge. The addition of anionic surfactants or polyelectrolytes leads to a twofold increase in the ζ-potential as a result of adsorption of negatively charged surfactant ions/polymer segments on negatively charged clay particles via non-Coulomb forces. In the presence of mixtures of anionic and cationic polyelectrolytes, irrespective of their composition and the order of the introduction of the components into a suspension, the particles acquire a negative ζ-potential, which is characteristic of particles that adsorb an anionic polyelectrolyte alone. Synergistic flocculating action is observed for mixtures of weakly and moderately charged anionic and cationic polyelectrolytes. This effect takes place even for mixtures with a manifold excess of negatively charged segments relative to positively charged ones. The observed regularities have been explained by the structural peculiarities of mixed adsorption layers of polyelectrolytes, i.e., the coexistence of a thin layer of adsorbed cationic polymer chains characterized by a large number of contacts with the surface and an extended layer of an anionic polyelectrolyte (long loops and tails of macromolecules), in which the cationic polymer layer is “drowned.” The electrokinetic potential and the ability of the particles to aggregation (via the formation of polymer bridges) in mixed solutions of anionic and cationic polyelectrolytes are primarily determined by the adsorption value of the anionic polymer.

Effect of cationic surfactants on characteristics and colorimetric behavior of polydiacetylene/silica nanocomposite as time–temperature indicator

Abstract Polydiacetylene (PDA)/silica nanocomposites were synthesized by self-assembly method using polymerizable amphiphilic diacetylene monomers, 10,12-pentacosadiynoic acid (PCDA). Addition of cationic surfactants (PDADMAC and CTAB) to PDA/SiO2 nanocomposites induced higher intermolecular force which affected their size, shape and color transition. Pure PDA, PDA/SiO2, PDA/SiO2/PDADMAC and PDA/SiO2/CTAB were investigated by particle size analysis, TEM, SEM, UV–vis spectroscopy and FT-IR. It was found that the PDA/SiO2 nanocomposites exhibited slightly larger particle sizes than those of other samples. The PDA/SiO2 nanocomposites with a core–shell structure were almost regarded as spherical-shaped particles. Cationic surfactants, especially CTAB, presumably affected the particle size and shape of PDA/SiO2 nanocomposites due to the disruption of hydrogen bonding between PDA head group and ammonium group. The colorimetric response of both PDA/SiO2/surfactant and surfactant-free PDA/SiO2 aqueous solutions directly changed in relation to time and temperature; thus they were expected to be applied as a new polymer-based time–temperature indicator (TTI).

Interaction mechanism of miscible DDA–Kerosene and fine quartz and its effect on the reverse flotation of magnetic separation concentrate

In this study, a modification of oil assisted flotation processes of quartz particles has been proposed, which is based on introduction of miscible Dodecylamine (DDA)-Kerosene as collector with DDA cationic surfactant coated on kerosene to the hydrophilic quartz particles in the pulp. The property of miscible DDA–Kerosene emulsion was investigated. Due to the adsorption of DDA at kerosene/water interface, a smaller and uniform kerosene emulsion formed. Addition of cationic surfactant to the kerosene emulsion changed the zeta potential value from negative to positive, which resulted in enhancing the adhesion of the oil droplets to negatively charged quartz. The results showed that agglomeration and flotation process can be realized simultaneously with DDA–Kerosene. The agglomeration of fine quartz minerals in the presence of miscible DDA–Kerosene led to the formation of very large compact agglomerates resulting in increasing hydrophobicity of the particles and inducing a higher probability of collision and adhesion to air bubble. Experimental data indicated that miscible DDA–Kerosene had better selectivity and stronger collectability to quartz than DDA–HCl, which can be used as an efficient collector in the reverse flotation of magnetic separation concentrate of TISCO. At the same DDA dosage (60g/t), separation efficiency got to 18.53% when using DDA–HCl as collector; while a better result was obtained with DDA–Kerosene, the efficiency of separation reached 59.07% which was identical with 120g/t DDA–HCl.

Effects of Surfactants on the Performance ofCeO2Humidity Sensor

NanosizedCeO2powders were synthesized via hydrothermal method with different types of surfactants (polyethylene glycol (PEG), cetyltrimethylammonium bromide (CTAB), and sodium dodecylbenzenesulfonate (SDBS)). X-ray diffraction, Raman spectroscopy, and transmission electron microscopy were utilized to characterize the phase structures and morphologies of the products. The sample with CTAB as surfactant (CeO2-C) has the largest specific surface area and the smallest particle size among these three samples. The humidity sensor fabricated byCeO2-C shows higher performance than those usedCeO2-P andCeO2-S. The impedance of theCeO2-C sensor decreases by about five orders of magnitude with relative humidity (RH) changing from 15.7 to 95%. The response and recovery time are 7 and 7 s, respectively. These results indicate that the performance ofCeO2humidity sensors can be improved effectively by the addition of cationic surfactant.

Fabrication of positively charged catanionic vesicles from ion pair amphiphile with double-chained cationic surfactant

In this study, a pseudodouble-chained ion pair amphiphile, hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), was prepared from a mixture of cationic surfactant, hexadecyltrimethylammonium bromide, and anionic surfactant, sodium dodecylsulfate. Positively charged catanionic vesicles were then successfully fabricated from HTMA-DS with the addition of cationic surfactants, dialkyldimethylammonium bromide (DXDAB), including ditetradecyldimethylammonium bromide (DTDAB), dihexadecyldimethylammonium bromide, and dioctadecyldimethylammonium bromide (DODAB), with a mechanical disruption approach. The control of charge characteristic and physical stability of the catanionic vesicles through the variations of DXDAB molar fraction and alkyl chain length was then explored by size, zeta potential, and Fourier transform infrared analyses. It was found that the molecular packing and/or molecular interaction of HTMA-DS with DXDAB rather than the electrostatic repulsion between the charged vesicles dominated the physical stability of the mixed HTMA-DS/DXDAB vesicles. The presence of DTDAB, which possesses short alkyl chains, could adjust the packing of the unmatched chains of HTMA+ and DS− and promote the vesicle formation. However, the weak molecular interaction due to the short chains of DTDA+ could not maintain the vesicle structures in long-term storage. With increasing the alkyl chain length of DXDAB, it was possible to improve the vesicle physical stability through the enhanced molecular interaction in the vesicular bilayer. However, the long alkyl chains of DODAB unmatched with those of HTMA-DS, resulting in the vesicle disintegration in long-term storage. For the formation of stable charged catanionic vesicles of HTMA-DS/DXDAB, a good match in hydrophobic chains and strong molecular interaction were preferred for the vesicle-forming molecules.

Sensitive voltammetric determination of testosterone in pharmaceuticals and human urine using a glassy carbon electrode in the presence of cationic surfactant

In this work, the electrochemical investigation of testosterone, a steroid hormone from the androgen group, was carried out in aqueous and aqueous/surfactant solutions using a glassy carbon (GC) electrode. In cyclic voltammetry, the compound showed one irreversible and adsorption-controlled reduction peak. Addition of cationic surfactant (cetyltrimethylammonium bromide, CTAB) was found to enhance the reduction current signal of testosterone, whereas, anionic (sodium dodecylsulfate, SDS) and non-ionic (Tween 80) surfactants exhibited opposite effect. Using square-wave adsorptive stripping voltammetry, the current showed a linear dependence with concentration in the range between 10 and 70nM in Britton–Robinson buffer, pH 5.0 containing 3mM CTAB. A detection limit of 1.18nM (0.34ngmL−1), and relative standard deviation of 4.12% for a concentration level of 35nM (n=11) were calculated. This method was successfully applied for the analysis of testosterone in oil-based pharmaceutical preparations and urine samples without any separation.

Rapid visual detection of quaternary ammonium surfactants using citrate-capped silver nanoparticles (Ag NPs) based on hydrophobic effect

In this work, a rapid, sensitive and low-cost colorimetric method for detection of quaternary ammonium surfactants using citrate-capped silver nanoparticles (Ag NPs) was developed. The quaternary ammonium surfactants induce the aggregation of Ag NPs through the hydrophobic effect, which is a novel aggregation mechanism of Ag NPs. The addition of cationic surfactant results in color change of Ag NPs solution from yellow to red and finally to colorless, which is due to the broadening of the surface plasmon band. The color change was monitored using a UV-vis spectrophotometer. The LOD of different cationic surfactants was in the range of 0.5-5 µM. More importantly, this detection method was successfully utilized to the disinfectant residual sample.