Hexadecyltrimethylammonium Bromide Concentration Research Articles

Electro‐Optic Topological Defect Devices Utilizing Nematic Liquid Crystal Binary Mixtures

Topological defects (TDs) manifest in many condensed matter systems. In liquid crystals (LCs), they occur as point or line singularities in the otherwise smooth director profile. Engineered and controllable TDs are of great interest for functional optoelectronic devices; however, the formation mechanism in patterned devices is not fully understood. In this work, electrically addressable TDs in doped mixtures of prototypical n‐alkyl‐cyanobiphenyl LCs 4‐cyano‐4′‐pentylbiphenyl (5CB) and 4‐cyano‐4′‐octylbiphenyl (8CB) are focused on. Doping concentrations of hexadecyltrimethylammonium bromide (CTAB) are varied and the effect of varying the host LC properties (through binary 5CB:8CB mixtures) on defect formation is studied. In the results, a strong correlation between LC “fluidity” and the ease of defect array formation is presented, with 0.5 wt% CTAB‐doped 5CB giving the best controllability/uniformity of TDs at low‐threshold voltages. Furthermore, it is demonstrated that the devices can be utilized as electrically switchable optical diffractive elements. In these findings, directions are mapped out that future studies can take in designing deterministic, electrically or magnetically tunable TD‐based photonic devices using LC systems.

An Evaluation of Surface-Active Agent Hexadecyltrimethylammonium Bromide with Vertical Self-Alignment Properties to Align Liquid Crystals for Various Cell Gap Conditions

We evaluated hexadecyltrimethylammonium bromide (HTAB) for liquid crystals (LCs) in layered ITO cells with various cell gap conditions. HTAB is a surfactant that can self-align vertically on the surface of indium tin oxide (ITO) substrates and induce homeotropic alignment of the LC molecules. For implementing RF devices with HTAB and LCs, we should consider limitations caused by the design conditions which are different from conventional liquid crystal displays such as cell gap. We quantified the concentration of HTAB ([HTAB]) that is necessary to form and maintain a sufficiently dense vertical alignment of 5CB (4-Cyano-4′-pentylbiphenyl). The required [HTAB] for full-homeotropic alignment was increased to the cell gap until it was too large to support the transfer of the surface alignment to the LC molecules, due to the weak anchoring nature of HTAB. We also showed the phase-change characteristic of the LC mixture related to [HTAB] for the design of RF devices driven by light or heat. This study may help to guide the development of new approaches to designing efficient RF devices that use LCs.

Evaporative Deposition of Surfactant-Laden Nanofluid Droplets over a Silicon Surface.

Morphologies of evaporative deposition, which has been widely applied in potential fields, were induced by the competition between internal flows inside evaporating droplets. Controlling the pattern of deposition and suppressing the coffee-ring effect are essential issues of intense interest in the aspects of industrial technologies and scientific applications. Here, evaporative deposition of surfactant-laden nanofluid droplets over silicon was experimentally investigated. A ring-like deposition was formed after complete evaporation of sodium dodecyl sulfate (SDS)-laden nanofluid droplets with an initial SDS concentration ranging from 0 to 1.5 CMC. In the case of initial SDS concentrations above 1.3 CMC, no cracks were observed in the ring-like deposition, indicating that the deposition patterns of nanofluid droplets could be completely changed and cracks could be eliminated by sufficient addition of SDS. With the increase of the initial concentration of hexadecyl trimethylammonium bromide (CTAB), the width of the deposition ring gradually decreased until no ring-like structure was formed. On the contrary, with the increase of the initial Triton X-100 (TX-100) concentration, the width of the deposition ring gradually increased until a uniform deposition was generated. Moreover, when the initial TX-100 concentration was high, a "tree-ring-like" pattern was discovered. Besides, morphologies of evaporative pattern due to the addition of surfacants were qualitatively analyzed.

Wormlike micelles of CTAB with phenols and with the corresponding phenolate derivatives - When hydrophobicity and charge drive the coacervation

HypothesisHydrophobicity and the presence or absence of charge in phenol derivatives are relevant on the rheology and phase behavior when they are assembled with a cationic surfactant, forming wormlike micelles. The incorporation of phenols with a greater number of rings into the micellar palisade is entropically favored, but a solubilization limit or coacervation are two paths followed by the solutions, depending on the electrical nature of the aromatic co-solutes. ExperimentsThe investigations were carried out with systems formed by a fixed concentration of hexadecyltrimethylammonium bromide (CTAB) and increasing concentrations of neutral phenols (1-naphthol, 2-naphthol, 2,3-dihydroxynaphthalene and R and S-binol) and with their corresponding phenolate derivatives. The monophasic limits of the systems were established, as well as their linear and non-linear rheology. The structural investigation of the coacervates formed with the phenolates were done using SAXS and Cryo-TEM. FindingsThe zero-shear viscosity of the solutions reaches maxima values close to the solubility limit of the aromatics, which depends on the numbers of rings and hydroxyl groups (position and number). However, when the correspondent ionized phenols were investigated, beyond the maxima values for the zero-shear viscosity, liquid–liquid biphasic systems are formed, in which the upper phase contains a coacervate, associated with branched wormlike micelles. However, when the ratio between phenolate and CTAB is around 3:1 the coacervate evolves to a lamellar structure.

Control Of Particle Adhesion On InGaAs Surface In Basic Solution By The Addition Of Cationic Surfactant

InGaAs has a higher electron mobility and saturation velocity than Si, making it a potential candidate for a channel material of next generation metal-oxide-semiconductor devices. To introduce InGaAs into semiconductor devices as a channel material, a series of chemical mechanical polishing (CMP) processes are required after InGaAs deposition processes [1]. However, silica particles may remain on the InGaAs surface after CMP processes, and the particles reduce the yield of semiconductor manufacturing. In order to remove silica particles from the InGaAs surface, post-CMP cleaning process is required. However, the behavior of silica particles on the InGaAs surface has not been extensively investigated yet. In this study, the behavior of silica particles on the InGaAs surface in ammonium hydroxide (NH4OH)–hydrogen peroxide (H2O2)–H2O mixture (APM) solution containing cationic surfactant was investigated. Also, the interaction forces between the silica particle and the InGaAs surface in the APM solution with different concentrations of hexadecyltrimethylammonium bromide (CTAB) were examined. To investigate the behavior of silica particles on the InGaAs surface in the APM solution, silica particles were intentionally contaminated on the InGaAs surface by dipping the InGaAs in the solution where silica particles were dispersed. CTAB was added to the APM solution at the concentrations of 10-4–10-2 M to modify the interaction forces between the silica particle and the InGaAs. To estimate the interaction forces (van der Waals force, acid–base force and electrostatic force) between the silica particle and the InGaAs surface in the solution, the surface properties of InGaAs and silica particle, such as zeta potential, surface energy components, acid–base energy constant and Hamaker constant, were examined from the contact angles and surface charges. As shown in Fig. 1, the number of particles per InGaAs surface area was observed to be 4.5×105 particles/mm2 after dipping the InGaAs in particle-dispersed APM solution. When 10-4 M CTAB was added to the APM solution, the number of particles per InGaAs surface area slightly increased, but it decreased the concentration of CTAB in the APM solution increased to 10-2 M. It is believed that the addition of CTAB to the APM solution changes the interaction force between silica particles and the InGaAs surface, thereby determining the adhesion behavior of silica particle to the InGaAs surface. The interaction force between the silica particle and the InGaAs surface in the APM solution is obtained by sum of the attraction (van der Waals) and the repulsions (acid–base and electrostatic). Since van der Waals force, acid–base force and electrostatic force were proportional to Hamaker constant, acid–base energy constant and zeta potential, respectively, the change of each force was estimated from the change of surface property. Compared to their surface properties in the APM solution without CTAB, Hamaker constant, acid–base energy constant and zeta potential were reduced by the addition of 10-4 M CTAB. The results suggest that van der Waals force, acid–base force and electrostatic force decrease in the APM solution with the addition of 10-4 M CTAB. However, since the decrement in acid–base force and electrostatic force was larger than that in van der Waals force, the attraction was dominant over the repulsion in the 10-4 M CTAB-added APM solution. Therefore, the adhesion of silica particles in the APM solution with the CTAB addition of 10-4 M may be facilitated by attraction force. When 10-2 M CTAB was added to the APM solution, Hamaker constant, acid–base energy constant and zeta potential increased, indicating that van der Waals, acid–base and electrostatic forces are enhanced. However, since the increments in acid–base force and electrostatic force were larger than that in van der Waals force, the repulsion was dominant over the attraction in the 10-2 M CTAB-added APM solution. It is suggested that the adhesion of silica particles to the InGaAs surface is suppressed by repulsion force. From the estimation for the change in the interaction forces, it is proposed that the APM solution with the addition of 10-2 M CTAB capable of suppressing the adhesion of silica particles may be a potential candidate for the InGaAs surface cleaning. Reference [1] E. E. Remsen, S. Anjur, D. Boldridge, M. Kamiti, S. Li, T. Johns, C. Dowell, J. Kasthurirangan, P. Feeney, J. Electrochem. Soc., 153, G453–G461 (2006). Figure 1

Control of adhesion and desorption behavior of silica particles on InGaAs surfaces by addition of hexadecyltrimethylammonium bromide in ammonium hydroxide–hydrogen peroxide mixture solution

The surface properties of InGaAs, such as zeta potential, surface energy components, acid–base energy constant, and Hamaker constant and its interaction force with silica particles, have not yet been elucidated. In this study, the adhesion of silica particles on an InGaAs surface in a 1/1/100 ammonium hydroxide (NH4OH)–hydrogen peroxide (H2O2)–H2O mixture (APM) solution was investigated. In particular, the effect of the addition of cationic surfactants and the concentration of hexadecyltrimethylammonium bromide (CTAB) on the particle adhesion/desorption was examined. To understand the adhesion behavior of silica particles on the InGaAs surface, the Lifshitz–van der Waals energy, acid–base interaction energy, and electrostatic energy between the silica particles and the InGaAs surface were estimated. It was found that the behavior of the energy barrier was strongly related to the number of silica particles that were adhered to the InGaAs. The energy barrier was reduced in the APM solution with 10−4 M CTAB, facilitating the adhesion of silica particles. However, when the CTAB concentration increased to 10−2 M, the energy barrier was elevated, and the adhesion of silica particles was reduced. The adhesion and desorption behaviors of silica particles on the InGaAs surface can be explained by the change in the energy barrier between the particles and InGaAs.

Modification of Activated Carbon from Rice Husk using Hexadecyltrimethylammonium Bromide (HDTMA-Br) Surfactant and ZnCl2 activator and Microwaves for Nitrate Ion Adsorption

Surfactant Modified Activated Carbon (SMAC) is a surfactant-modified activated carbon product. The surfactant used in this study was the cationic surfactant Hexadecyltrimethylammonium Bromide (HDTMA-Br). These surfactants can change the activated carbon's surface to be positively charged due to the presence of the surfactant hydrophilic groups. This SMAC is more selective in absorbing anions, which in this study is for the adsorption of nitrate anions. This research aims to prepare a new material that is superior to activated carbon in absorbing nitrate anions. This research was conducted in several stages. In the first stage, rice husk was carbonized through pyrolysis at 300°C for 10 minutes. In the second stage, carbon was activated using 30% ZnCl2 and microwaves for 5 minutes and 400 W. The third stage was modifying activated carbon by contacting or adsorbing HDTMA-Br on activated carbon. The concentration of HDTMA-Br varied at 200-400 ppm and the adsorption time was 3-7 hours. The success of the modification was measured by the efficiency of HDTMA-Br in modifying activated carbon. This is supported by the results of the characterization of FTIR, GSA, SEM, and thermodynamic parameters. The resulting SMAC was applied for the adsorption of nitrate anions, and the results were compared to carbon and activated carbon. The results indicate that the best SMAC is formed at an optimum concentration of 300 ppm, within 4 hours, with an adsorption efficiency of 97.345%. The characterization results also show that SMAC has been formed, as evidenced by the presence of a peak at a wavenumber of about 1500 cm-1, a C-N group derived from N(CH3)3 in the HDTMA-Br surfactant structure. The SMAC spectra also appeared weak peaks at the wave number 2918 cm-1, which indicated the CH2-R group stretching from the HDTMA-Br surfactant. SEM image shows that HDTMA-Br has covered the pores of activated carbon. Meanwhile, the SMAC surface area is lower than that of activated carbon. Thermodynamic parameters indicate that HDTMA-Br interacts physically with activated carbon. The adsorption capacity of nitrate anion by SMAC is 3,638 mg/g, higher than carbon and activated carbon.

SIMULTANEOUS ADSORPTION AND ANTIBACTERIAL ACTIVITIES OF SURFACTANT-MODIFIED KAOLINITE

Water contamination problems caused by various contaminants (i.e. anionic and cationic compounds, and pathogenic bacteria) necessitate the advanced material development for simultaneous adsorption and antibacterial actions. In this study, kaolinite (Kao) was modified with surfactant hexadecyltrimethyl ammonium bromide (HDTMA-Br) (0.1, 1.0 and 4.0 mM) and they were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and dispersion behaviour. No structural changes occurred after the adsorption of HDTMA-Br molecules on the Kao. In the simultaneous action study, the samples were tested for their adsorption capacity for cationic (methylene blue, MB) and anionic dyes (acid orange 7, AO7), and for antibacterial activities against Gram-negative (Escherichia coli ATCC11229) and Gram-positive bacteria (Staphylococcus aureus ATCC6538). HDTMA-modified Kao enhanced the adsorption of AO7 and the trend was correlated with the HDTMA adsorbed on Kao. The modified Kao with the highest HDTMA-Br concentration (KaoH4.0) showed 100% removal capacity for both dyes (AO7 and MB) and reduced the highest amount of both bacterial colonies. Therefore, the kaolinite modified with surfactant simultaneously enhanced the adsorption capacity of both positive and negative compounds, and increased the antibacterial activities against a wide spectrum of bacteria.

The influences of hexadecyl trimethyl ammonium bromide on lanthanum titanate photocatalyst for ofloxacin degradation

The use of template to introduce porous structure in titanate is a novel research topic, especially if photocatalytic activity of the material can be improved. The porous lanthanum titanate photocatalyst was synthesized using hexadecyl trimethyl ammonium bromide (HTAB) as the template in a sol–gel route. The addition of HTAB in the precursor could obviously influence the porous structure and surface morphology of the lanthanum titanate samples. All the samples were composed of perovskite La2Ti2O7, and crystallization of La2Ti2O7 was reduced with rising HTAB concentration. There was a slight enlargement in the band gap energy after using HTAB, and the chemical environments of the elements in the porous lanthanum titanate samples did not change. The enhancement in photocatalytic degradation efficiency was achieved on the lanthanum titanate samples obtained using HTAB. The first order reaction rate constants were increased from 0.0131 min−1 of the nonporous sample to 0.0253 min−1 of the porous sample. All the ofloxacin molecules were degraded on the porous lanthanum titanate sample after 120 min of reaction. Decomposition of ofloxacin in photocatalytic process was identified by the reduced absorption intensities of the organic groups in the UV–Vis spectra.

Optimal Optical Properties–Hardness Ratio of Antireflection Coating Produced from a Silica Sol with Hexadecyltrimethylammonium Bromide on Silicate Glass

The effect of the hexadecyltrimethylammonium bromide concentration in the silica sol, which is used to obtain antireflection coatings over silicate glass, on the light transmission of coated glass and the hardness of the coatings was studied. An increase in the concentration of hexadecyltrimethylammonium bromide in the sol from 1.37 × 10–2 to 5.20 × 10–2 M increases the maximum light transmission of glass with an antireflective coating from 94.7 to 99.0%, and minimum, from 84.7 to 93.6%, reduces the refractive index of the coating from 1.43 up to 1.27. The 3H–4H coating hardness acceptable for practice can be achieved provided that the maximum light transmission of glass with a single-layer double-sided coating is ≤96.0–97.0%, the refractive index of the antireflection coating is ≥1.35–1.36, and the maximum volume content of nanopores in the coating is not more than 20.0–23.0 vol % .

Seedless synthesis of gold nanorods by using hydrogen peroxide as a weak reducing agent

A new seedless wet chemistry synthesis of gold nanorods by using hydrogen peroxide as the weak reducing agent is reported. A reduced concentration of hexadecyltrimethylammonium bromide is used in our experiment, and the synthesized gold nanorods exhibit tunable longitudinal surface plasmon resonance peaks ranging from 725 to 945 nm. The influence on gold nanorods growth by adjusting the amounts of sodium hydroxide, silver nitrate, sodium borohydride, and hexadecyltrimethylammonium bromide were investigated by the visible-near infrared spectroscopy. Under the proper experimental parameters, the longitudinal surface plasmon resonance peaks can be tuned by varying the hydrogen peroxide amounts. Furthermore, it can be seen that the redshift of the longitudinal absorption peak of the prepared gold nanorods with increasing hydrogen peroxide amount is consistent with the increase tendency of the length-to-width aspect ratio obtained from the transmission electron microscopy images. The method provides a facile pathway to prepare gold nanorods with tunable longitudinal surface plasmon resonance peaks, which have potential applications in biomedicine and nanophotonics.

Structural and textural influences of surfactant-modified zeolitic materials over the methamidophos adsorption behavior

ABSTRACTIn this work, a natural zeolite previously conditioned with NaCl solution was modified with different hexadecyltrimethylammonium-bromide concentrations for methamidophos removal. All materials were characterized by diverse analytical techniques. Methamidophos adsorption behavior was studied by using batch experiments. Main structural and textural differences of surfactant-modified zeolitic materials were correlated with methamidophos adsorption capacity. Methamidophos adsorption was enhanced when zeolitic materials were modified with HDTMA and, more significantly, when a 25 mmol/L surfactant concentration was used, achieving a maximum adsorption capacity of 1.13 mg/g due to its pore surface modification. In this way, methamidophos adsorption present in aqueous solution was improved.

Synthesis of microporous interconnected polymeric foam of poly (glycidyl methacrylate-co-divinyl benzene-co-butyl acrylate) by using aqueous foam as a template

Hexadecyltrimethylammonium bromide (HTAB) modified nano silica were used as pore stabilizer for the preparation of interconnected macroporous copolymer foam of Glycidyl methacrylate (GMA), Divinylbenzene (DVB) and tert-Butyl acrylate (BA). The polymerization of air infused aqueous foam is carried out through free radical thermal initiator. The porosity of the polymerized foam depends on the concentration of HTAB used to control the hydrophobic and hydrophilic behavior of silica nanoparticle. Modified silica particle results to form closed cell foam with 74% of porosity for 60% of air infusion during aqueous foaming. The preliminary structure of microfoam was observed through optical microscopy, whereas for a better understanding of morphology SEM was used. The proposed route is an eco-friendly route for synthesizing polymeric microporous polymer as compared to other chemical and additive-based routes available.

Simultaneous action of surfactant modified clinoptilolite: Adsorbent of dyes and antibacterial agent

In this study, the simultaneous action of surfactant modified clinoptilolite (SMC) as adsorbent for dyes and its antibacterial activity was investigated. Methylene blue (MB) and acid orange 7 (AO7) represent cationic and anionic dyes, respectively were used as adsorbate in this study and the antibacterial activity was studied against Gram-negative (Escherichia coli ATCC 11229) and Gram-positive bacteria (Staphylococcus aureus ATCC 6538 and Enterococcus faecalis ATCC 2921). Initially, natural zeolite clinoptilolite was modified with 3 different concentrations (0.1, 1.0 and 4.0 mM) of cationic surfactant hexadecyltrimethyl ammonium bromide (HDTMA-Br). The SMC samples were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), amount of HDTMA adsorbed and dispersion behaviour. Result from XRD shows that the HDTMA-Br molecules caused no effect on primary structure of the clinoptilolite since the clinoptilolite structure remained the same after modification with HDTMA-Br. Compared to the unmodified clinoptilolite, FTIR spectra of the SMC shows peak corresponds to C-H stretches which proved the attachment of HDTMA onto the clinoptilolite surfaces. In the dispersion behaviour study, SMC samples were located at the adjacent phase between the water and oil mixture. The amount of HDTMA-Br adsorbed onto the clinoptilolite increased with the increasing concentrations of the surfactant. The use of SMC as adsorbent and antibacterial agent were further studied against the ionic dyes and bacteria simultaneously. The results show that the adsorption capacity of SMC towards both ionic dyes increase with the increasing HDTMA-Br concentration. While for the antibacterial activity, the number of colony forming unit of bacteria seem to be highly reduced at the highest concentration of the HDTMA (4.0 mM) attached on the clinoptilolite. Hence, this study had shown that SMC has high adsorption capacity towards the ionic dyes at the same time reducing the growth of both Gram positive and negative bacteria in aquoes solution.

The effect of silica nanoparticles on the stability of aqueous foams

An experimental study was performed on aqueous foams stabilized by a mixture of hexadecyltrimethylammonium bromide (HTAB) and negatively-charged silica nanoparticles. The effects of the nanoparticles on the stability of foams at different HTAB concentrations were investigated. The foams were characterized by measuring their foamability and stability. Rheological behavior of the foams was also studied. Furthermore, rheology of the air–water interfaces was studied in the linear and nonlinear deformation ranges. The thickness of the monolayer at the interface was measured. The actual size of the silica nanoparticles at the air–water interface was measured by transmission electron microscopy. Based on these measurements, the interaction between the monolayers across the foam film containing HTAB and nanoparticles was investigated. Smaller silica nanoparticles (i.e. diameter less than 10 nm) adsorbed at the air–water interface whereas the larger particles remained in the sub-phase or in the bulk liquid phase. It was found that these nanoparticles strongly influenced the foaming behavior at the low HTAB concentrations (i.e. below the CMC). A Langmuir-type monolayer was formed. The presence of the nanoparticles at the air–water interface provided mechanical strength to the foam films and prevented their rupture. This hindered coalescence of the bubbles, which resulted in a stable foam.

Micro‐Segmented Flow Technology Applied for Synthesis and Shape Control of Lead Styphnate Micro‐Particles

AbstractIn this study, the technology of micro‐segmented flow was applied for continuous synthesis safely and shape control accurately to lead trinitroresorcinate (LTNR) particles. Besides, a micro chemical reaction and crystallization system were built. Crystal shape control technology of LTNR and micro‐segmented flow technology were first combined using the system. Additionally, the effects of the flowing rate and chemical additives on LTNR micro‐particles preparation were researched for shape control. The LTNR micro‐particles were analyzed by XRD, DSC, laser scanning confocal microscope and laser particle size analyzer. The results shows that the LTNR particles size can be controlled from 20 to 400 μm by the flow rate and the concentration of hexadecyl trimethyl ammonium bromide (CTAB), while the shape of LTNR can be controlled by the concentration of glycerol and CTAB. Besides, there is a good linear relationship between the size and the activation energy. This illustrates that the LTNR particles with smaller size are more stable and have higher heat release. This study demonstrated the power of micro‐segmented flow for generation of LTNR micro‐particles with high quality and for tuning of particle properties.

ELECTROCHEMICAL INVESTIGATION OF DA AND UA ON CARBOXYLATED GRAPHENE OXIDE/LANTHANUM ELECTRODES WITH SUNDRY CONTENT OF CTAB

Glassy carbon electrodes (GCE) were modified by carboxylated graphene oxide/lanthanum with various concentrations of hexadecyl trimethyl ammonium bromide (CTAB), and the treated electrodes, called CTAB/GO-COOLa/GCE, were prepared for the detection of uric acid (UA) and dopamine (DA) by using the differential pulse voltammetry (DPV) and the cyclic voltammetry (CV). The results show that the modified electrode’s electrocatalytic activity could be affected by several factors in the examination, they are the pH value of the system, the main content of CTAB, various concentrations and rates of scan. With a combination of carboxylated graphene oxide/lanthanum and CTAB, the resulted CTAB/GO-COOLa/GCE sensors showed preeminent selectivity and obvious catalytic property toward the electro-oxidation of UA and DA. In optimized conditions, the response of the CTAB/GO-COOLa/GCE electrode for DA was linear in the region of 0.03–500.0[Formula: see text][Formula: see text]M with detection limits of 0.036[Formula: see text][Formula: see text]M [Formula: see text]. Two linear response ranges for the determination UA were obtained from ranges of 1 to 200[Formula: see text][Formula: see text]M and 200 to 1300[Formula: see text][Formula: see text]M with a detection limit of 0.42[Formula: see text][Formula: see text]M [Formula: see text]. Moreover, the refined electrode was used in the inspection of DA and UA in real samples of serum and urine successfully, displaying its potential application of real samples involved in electroanalysis.

Adsolubilization-induced structural change in adsorbed surfactant aggregates: Equilibrium and kinetics monitored by AFM and QCM-D

Organic solutes with low water-solubility are solubilized into surfactant aggregates formed at solid/aqueous solution interfaces by the process of adsolubilization. In this study, we have characterized the adsolubilization of 1-hexanol (C6OH) into hexadecyltrimethylammonium bromide (HTAB) aggregates adsorbed on a silica surface, by means of atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D) techniques. The adsolubilization reduces electrostatic head-to-head repulsion between HTAB molecules forming the surface aggregates, along with additional adsorption of HTAB molecules at the solid/aqueous solution interface. At an HTAB concentration above the critical micelle concentration (cmc), the adsolubilization led to (i) a greater magnitude of repulsive interactions in the AFM force-distance data, (ii) a morphological change of the surface aggregates from a spherical or partially wormlike assembly into a flat bilayer, and (iii) an increased energy dissipation, reflecting an increased elasticity of the adsorbed aggregates. The kinetics of the adsolubilization-induced structural change was also studied at an HTAB concentration below the cmc; the increased C6OH concentration resulted in increased initial responses in frequency and dissipation. It seems likely that the kinetics is primarily driven by the diffusion of HTAB and C6OH molecules toward the silica surface, and the molecular reorganization within the adsorbed aggregates may also contribute to the kinetics especially at a low C6OH concentration.

ADSORPTIVE REMOVAL OF METHYLENE BLUE AND ACID ORANGE 7 BY HEXADECYLTRIMETHYLAMMONIUM BROMIDE MODIFIED RICE HUSK

The feasibility of rice husk (RRH) and surfactant modified rice husk (SMRH) to adsorb cationic dye, methylene blue (MB) and acid orange 7 (AO7) from aqueous solution was studied. SMRH was prepared by reacting RRH with different initial concentrations (1.0, 2.5 and 4.0 mM) of cationic surfactant quaternary ammonium compound, hexadecyltrimethylammonium bromide (HDTMABr). RRH and SMRH were characterized using Fourier transform infrared (FTIR) spectroscopy to determine surface functional group and effect of surfactant modification on the structure of RRH. Adsorption studies were performed in a series of batch experiment and effect of initial dye and HDTMABr concentrations on the adsorption capacity of RRH and SMRH were evaluated. The results showed that the removal of MB was higher for RRH compared to SMRH meanwhile AO7 removal was higher for SMRH compared to RRH. Modification of rice husk by cationic surfactant was proven to decrease the adsorption site for MB. On the other hand, the presence of surfactant on SMRH increased the adsorption site and allows more adsorption to occur for AO7. The equilibrium data were better described by Langmuir isotherm with maximum adsorption capacity for MB was 100.0 mg/g and 200.0 mg/g for AO7. In conclusion, the modification of rice husk by HDTMABr decreased the adsorption towards cationic dye but increased the adsorption towards anionic dye

Interaction of Myoglobin with Cationic and Nonionic Surfactant in Phosphate Buffer Media

Interaction of myoglobin with cationic surfactants hexadecyltrimethylammonium bromide (HTAB), gemini surfactant 16-2-16 (dimethylene-1,2-bis(hexadecyldimethylammonium bromide)) and nonionic surfactant Mega 10 (N-decanoyl-N-methylglucamine) have been studied in phosphate buffer at pH 7.4 using surface tension, UV–visible, fluorescence, and circular dichroism spectroscopies and differential scanning calorimetry. With increasing concentration of HTAB, metal ion of the heme group changes its spin states; but in case of 16-2-16 and Mega 10, spin change does not occur. Fluorescence spectra clearly denote the unfolding process in HTAB media. With increasing HTAB concentration, α-helicity of myoglobin decreases with the appearance of β-sheet and random coil more rapidly than other two surfactants. Melting temperature of myoglobin is reduced drastically upon interaction with HTAB than their corresponding gemini and nonionic surfactants.