The time dependence of chitosan/nonionic surfactant solution viscosity

The measurement of the viscosity of semiconcentrated chitosan (0.08–0.14%) solutions in the system with octaethyleneglycolmonon-dodecylether (C₁₂E₈) was carried out using Cannon-Fenske capillary viscometer. The interaction was—as expected—very weak, vut when the time dependent hydrodynamic behaviour of the system was considered, the interaction has been established at particular surfactant concentrations. The most significant time dependence is shown in a form of sudden viscosity drop in a region close to and above CMC value of the surfactant, which implied existence of the interaction between chitosan and surfactant. At low surfactant concentrations viscosity values vere constant with increasing surfactant concentration, but solution also showed time dependent decrease in the viscosity which has been connected with well known time dependent viscosity of pure chitosan solution.The viscometry enabled monitoring of the extent of chitosan/surfactant association by establishing the viscosity decrease rate constant. The rate constant was derived from the first order constant of the quadratic polynomial curves used for the approximation of experimental values when these are presented in the form of viscosity-time profiles. This method showed the existence of critical surfactant concentration values (C ₁,C ₂ andC ₃). These values are closely connected with the proposed interaction model which is based on the assumption that spherical surfactant micelles are bound by chitosan molecule.On leave from Textile Engineering Dept., Faculty of Technology and Metallurgy, University of Belgrade, Yugoslavia     

Extraction and separation of cationic surfactants from river sediments: application to a spectrophotometric determination of cationic surfactant in an aquatic environment using membrane filters.

The quantitative extraction of cationic surfactant (CS+) in river sediments was studied. Further, the developed method was applied to the spectrophotometric determination of CS+ in urban river sediment samples by solid-phase extraction with membranes. A mixture of methanol and hydrochloric acid was proposed as an eluent. Dried sediment was digested in the eluent under ultrasonic irradiation. After elution, the eluent was evaporated to almost dryness. The residue was dissolved in a small volume of methanol and diluted to a certain volume with water. The pH of the solution was adjusted to 4-5 to separate iron and some other metals as precipitates of hydroxides. The solution was passed through two-piled membranes: first glass-fiber and then polytetrafluoroethylene (PTFE) membranes. A small volume of methanol was passed through the membranes to elute any CS+ retaining on the membranes. After passing the methanol solution through a cationic exchange resin column, the retained CS+ was eluted with methanol containing a high concentration of sodium chloride. Water, Bromophenol Blue (BPB) and hydrochloric acid were added to the solution. The solution was passed through a mixed cellulose ester membrane filter to retain an ion associate of CS+.BPB-. The retained ion associate was dissolved in a small volume of N,N-dimethylformamide together with the membrane filter, followed by the addition of triethanolamine to make the solution alkaline. The absorbance due to BPB2- was measured at 603 nm against a reagent blank. This method was applied to the determination of CS+ in river water and sediment. A cationic surfactant in sediments at 10(-5) mol kg-1 levels was detected with satisfactory precision. It was found that CS+ was about 500-fold enriched in the sediment from water at the place where domestic wastewater was discharged.     

Influence of hydrocarbon surfactant on the aggregation behavior of silicone surfactant: observation of intermediate structures in the vesicle-micelle transition

Intermediate structures of the aggregates in the aqueous solution of an ABA-type silicone surfactant and in the process of an SDS-induced vesicle-micelle transition are reported. In single ABA silicone surfactant aqueous solutions, large multilamellar vesicles (MLV), small single lamellar vesicles (SLV), threadlike micelles (TLM), and spheroidal micelles were observed. Interestingly, a large amount of TLMs were found entrapped into the large MLVs, but not in SLVs. Disintegration of the small vesicles inside the MLVs indicates that the entrapped TLM are from the disintegrated membrane of the entrapped small vesicles. Addition of SDS induced a transition from vesicles or threadlike micelles to spheroidal micelles. The intermediate structures, such as the appearance of small holes in the vesicle membrane, the budding of threadlike micelles from the membrane fracture, and the clusters of spheroidal micelles, were observed with increase of the SDS concentration. The electrical conductivity measurements indicated that complex micelles of SDS and silicone surfactant were formed in the solution due to the interaction between the SDS and PEO part of the silicone surfactant.     

Preparation of surfactant anion-selective electrodes with different selectivity coefficients and a trial to determine each component in binary surfactant mixtures

Functional membrane electrodes with different charge densities were prepared from partly cationic poly(vinyl chloride) (PVC) and a plasticizer. The modified PVC polymers were synthesized by the co-polymerization of vinyl chloride (VC) and 3-acrylamido-N,N-dimethylpropylamine (ADPA) in different ratios followed by alkylation of the amine segments with methyl iodide. These membrane electrodes showed a nearly Nernstian response to sodium dodecyl sulfate (SDS) below the critical micelle concentration (CMC). In mixtures of SDS and other surfactants, the electrode response was examined and the selectivity coefficient K for the added surfactant was determined. The charge density of the functional membrane altered K; the greater the charge density of the membrane, the greater the value of K. Two membrane electrodes with different K were used to determine the concentration of each component in a binary surfactant mixture. They determined the concentration of the primary surfactant with reasonable accuracy, but the error in determining the concentration of the secondary surfactant was great. The error analysis indicated that a large difference in K for two electrodes is necessary to determine the concentrations of both components in binary surfactant mixtures with reasonable accuracy.     

Comblike poly(ethylene oxide)/hydrophobic C6 branched chitosan surfactant polymers as anti-infection surface modifying agents

A series of structurally well-defined poly(ethylene oxide)/hydrophobic C₆ branched chitosan surfactant polymers that undergo surface induced self assembly on hydrophobic biomaterial surfaces were synthesized and characterized. The surfactant polymers consist of low molecular weight (M_w) chitosan backbone with hydrophilic poly(ethylene oxide) (PEO) and hydrophobic hexyl pendant groups. Chitosan was depolymerized by nitrous acid deaminative cleavage. Hexanal and aldehyde-terminated PEO chains were simultaneously attached to low M_w chitosan hydrochloride via reductive amination. The surfactant polymers were prepared with various ratios of the two side chains. The molecular composition of the surfactant polymers was determined by FT-IR and ¹H NMR. Surface active properties at the air–water interface were determined by Langmuir film balance measurements. The surfactant polymers with PEO/hexyl ratios of 1:3.0 and 1:14.4 were used as surface modifying agents to investigate their anti-infection properties. E. coli adhesion on Silastic^® surface was decreased significantly by the surfactant polymer with PEO/hexyl 1:3.0. Surface growth of adherent E. coli was effectively suppressed by both tested surfactant polymers.     

Chitosan based surfactant polymers designed to improve blood compatibility on biomaterials

We developed chitosan based surfactant polymers that could be used to modify the surface of existing biomaterials in order to improve their blood compatibility. These polymers consist of a chitosan backbone, PEG side chains to repel non-specific protein adsorption, and hexanal side chains to facilitate adsorption and proper orientation onto a hydrophobic substrate via hydrophobic interactions. Since chitosan is a polycationic polymer, and it is thrombogenic, the surface charge was altered to determine the role of this charge in the hemocompatibility of chitosan. Charge had a notable effect on platelet adhesion. The platelet adhesion was greatest on the positively charged surface, and decreased by almost 50% with the neutralization of this charge. A chitosan surface containing the negatively charged SO(3)(-) exhibited the fewest number of adherent platelets of all surfaces tested. Coagulation activation was not altered by the neutralization of the positive charge, but a marked increase of approximately 5-6 min in the plasma recalcification time (PRT) was displayed with the addition of the negatively charged species. Polyethylene (PE) surfaces were modified with the chitosan surfactant resulting in a significant improvement in blood compatibility, which correlated to the increasing PEG content within the polymer. Adsorption of the chitosan surfactants onto PE resulted in approximately an 85-96% decrease in the number of adherent platelets. The surfactant polymers also reduced surface induced coagulation activation, which was indicated by the PEG density dependent increase in PRTs. These results indicate that surface modification with our chitosan based surfactant polymers successfully improves blood compatibility. Moreover, the inclusion of either negatively charged SO(3)(-) groups or a high density of large water-soluble PEG side chains produces a surface that may be suitable for cardiovascular applications.     

Application of membrane filters for spectrophotometric determination of cationic surfactants in river water and sediment.

Cationic surfactant (CS+) in urban river water and sediment was extracted and determined spectrophotometrically with 2 membrane filters. The CS+ in the water samples, mostly in the form of an ion associate with the coexisting anionic surfactant (AS), was collected on a polytetrafluoroethylene (PTFE) membrane filter and eluted with methanol. Bromphenol blue (BPB), hydrochloric acid, and water were added to the methanol solution successively, and the mixed solution was filtered through a mixed cellulose ester membrane filter. The CS+-BPB- ion associate, formed by a counter ion exchange, was collected on the filter and dissolved into N,N-dimethylformamide (DMF) together with the mixed cellulose ester membrane filter. After addition of 2 drops of triethanolamine, the absorbance of the DMF solution was measured. The CS+ in sediment samples was extracted with methanol by ultrasonic irradiation; the methanol solution was then passed through a PTFE membrane filter and evaporated to dryness. The CS+ was redissolved in a small amount of methanol. For water samples, recoveries and relative standard deviations for 0.30 microM benzyldimethyl-tetradecylammonium ion, a standard material, were > or =93 and < or =5%, with a detection limit of 0.02 microM. Concentrations of CS+ in sediments were much higher than those in water samples, indicating that CS+ is adsorbed on the surface of the sediment.     

Ceramic membrane ultrafiltration of anionic and nonionic surfactant solutions

The ultrafiltration of two types of surfactants, sodium dodecyl sulfate (SDS, anionic) and Tergitol NP-9 (nonylphenol polyethylene glycol ether, nonionic), using a 20 nm ZrO₂ tubular membrane was investigated. The influence of crossflow velocity, temperature, pressure, and surfactant concentration on the permeate flux, close to and above the critical micelle concentration (CMC), is reported. Permeate flux and surfactant retention were measured in order to evaluate concentration polarization and fouling phenomena, and also the variation of these parameters due to surfactant/membrane interactions. High surfactant retentions (60–70%) were achieved depending on the feed concentration.     

Factors influencing the mechanism of surfactant catalyzed reaction of vitamin C-ferric chloride hexahydrate system

The kinetics of vitamin C by ferric chloride hexahydrate has been investigated in the aqueous ethanol solution of basic surfactant viz. octadecylamine (ODA) under pseudo-first order conditions. The critical micelle concentration (CMC) of surfactant was determined by surface tension measurement. The effect of pH (2.5–4.5) and temperature (15–35°C) in the presence and absence of surfactant were investigated. Activation parameters, ΔE _a, ΔH ^#, ΔS ^#, ΔG ^≠, for the reaction were calculated by using Arrhenius and Eyring plot. Surface excess concentration (Γ_max), minimum area per surfactant molecule (A _min), average area occupied by each molecule of surfactant (a), surface pressure at the CMC (Π_max), Gibb’s energy of micellization (ΔG _M°), Gibb’s energy of adsorption (ΔG _ad°), were calculated. It was found that the reaction in the presence of surfactant showed faster oxidation rate than the aqueous ethanol solution. Reaction mechanism has been deduced in the presence and absence of surfactant.     

Mechanism of oil-in-water emulsification using a water-soluble amphiphilic polymer and lipophilic surfactant

A new O/W (oil-in-water) emulsification system was developed using the amphiphilic polymer HHM-HEC (hydrophobically-hydrophilically modified hydroxyethylcellulose) and a lipophilic surfactant. HHM-HEC was used as a thickener and polymeric surfactant, and the addition of small quantities of various types of nonionic lipophilic surfactant (hydrophilic-lipophilic balance <5) decreased the droplet size of several types of oil due to a lowering of the tension at the water/oil interface. The oil droplets were held by the strong network structure of the aqueous HHM-HEC solution, preserving the O/W phase without inversion. These stable O/W emulsions were prepared without the addition of hydrophilic surfactants and thus show improved water repellency.     

Pervaporation separation of methanol/methyl t-butyl ether through chitosan composite membrane modified with surfactants

We investigated the efficiency of pervaporation separation of methanol/methyl-t-butyl ether (MTBE) mixture through chitosan composite membrane modified with sulfuric acid and four surfactants. Effects of feed concentration, temperature, crosslinking degree and type of surfactants were studied. The chitosan composite membrane modified with sulfuric acid showed the pervaporation performance of over 70 wt% methanol in the permeate and flux of 100 g/m² h measured at 25°C. At 50°C, the separation factor decreased while the flux increased exceeding 300 g/m² h. For the membrane complexed with surfactants, the permeate showed 98.3 wt% methanol concentration and 470 g/m² h of permeate flux at 25°C. With increasing operating temperature, the permeate flux remarkably increased to 1170 g/m² h and the permeate showed 97.8 wt% methanol concentrations.     

Synthesis and characterization of a new silicone-based polyurethane surfactant

ω-N,N-Dihydroxyethyl aminopropylpolymethylhydrosiloxane (DAPS) a monotelechelic polydimethylsiloxane with a diol-end group, which is used to prepare polyurethane surfactant, was successfully synthesized. The preparation included four steps, which are hydroxyl protection, alkylation, hydrosilylation, and deprotection. Then, a novel silicone-based polyurethane surfactant was prepared by the addition polymerization of isophorone diisocyanate to DAPS, polypropylene glycol, and methanol and was used in the preparation of polystyrene by emulsion polymerization. The DAPS was characterized by FTIR, ¹H NMR, ¹³C NMR and elemental analysis. The results showed that each step was successfully carried out and the targeted products were synthesized in all cases.     

Photoluminescence of ZnO nanoparticles prepared by laser ablation in different surfactant solutions

ZnO nanoparticles were prepared by laser ablation of a zinc metal plate in a liquid environment using different surfactant (cationic, anionic, amphoteric, and nonionic) solutions. The nanoparticles were obtained in deionized water and in all surfactant solutions except the anionic surfactant solution. The average particle size and the standard deviation of particle size decreased with increasing amphoteric and nonionic surfactant concentrations. With the increase of the amphoteric surfactant concentration, the intensity of the defect emission caused by oxygen vacancies of ZnO rapidly decreased, while the exciton emission intensity increased. This indicates that anionic oxygen in the amphoteric surfactant molecules effectively occupied the oxygen vacancy sites at the ZnO nanoparticle surface due to charge matching with the positively charged ZnO nanoparticles.     

Preparation and characterization of stable chitosan nanofibrous membrane for lipase immobilization

Nanofibrous membrane with a fiber diameter of 80-150 nm was fabricated from mixed chitosan/poly(vinyl alcohol) (PVA) solution by an electrospinning process. Field emission scanning electron microscope and transmission electron microscope were used to characterize the morphology of the nanofibrous membrane. It was found that chitosan nanofibrous membrane with stabilized morphology could be prepared through removing most of PVA from the nascent one with 0.5 M NaOH aqueous solution. This treatment also resulted in an obvious decrease in fiber diameter. The stabilized chitosan nanofibrous membrane was explored as support for enzyme immobilization due to the characteristics of excellent biocompatibility, high surface/volume ratio, and large porosity. Lipase from Candida rugosa was immobilized on the nanofibrous membrane using glutaraldehyde (GA) as coupling reagent. The properties of the immobilized lipase were assayed and compared with the free one. Results showed that, the observed lipase loading on this nanofibrous membrane was up to 63.6 mg/g and the activity retention of the immobilized lipase was 49.8% under the optimum condition. The pH and thermal stabilities of lipase were improved after it was immobilized on the chitosan nanofibrous membrane. In addition, the experimental results of reusability and storage stability indicated that the residual activities of the immobilized lipase were 46% after 10 cycles and 56.2% after 30 days, which were obviously higher than that of the free one.     

Complexation behaviour of cellulose derivative/surfactant mixtures investigated by nonlinear enhanced Rayleigh scattering

Complexation behaviour of cellulose derivative/surfactant mixtures in aqueous solution was investigated by nonlinear enhanced Rayleigh scattering (NERS). The NERS spectra of polymer solutions, including second-order scattering, third-order scattering, frequency doubling scattering and triplet frequency scattering were created using by spectrofluorometer. The results indicated that NERS intensity of cellulose derivative/surfactant systems changes differently with continuing addition of surfactant due to the complexation between cellulose derivative and surfactant. The critical micelle concentration of cellulose derivatives/surfactants system is easy to obtain. The change of NERS intensity reveals the complexation behaviour of cellulose derivative/surfactant and the aggregation state of polymer chains in evidence. Therefore, NERS had been successfully developed to study complexation behaviour of cellulose derivative/surfactant mixtures in solution.     

Use of marker ion and cationic surfactant plastic membrane electrode for potentiometric titration of cationic polyelectrolytes

A plasticized poly (vinyl chloride) (PVC) membrane electrode sensitive to stearyltrimethylammonium (STA) ion is applied to the determination of cationic polyelectrolytes such as poly (diallyldimethylammonium chloride) (Cat-floc) by potentiometric titration, using a potassium poly (vinyl sulfate) (PVSK) solution as a titrant. The end-point of the titration is detected as the potential change of the plasticized PVC membrane electrode caused by decrease in the concentration of STA ion added to the sample solution as a marker ion due to the ion association reaction between the STA ion and PVSK. The effects of the concentration of STA ion, coexisting electrolytes in the sample solution and pH of the sample on the degree of the potential change at the end-point were examined. A linear relationship between the concentration of cationic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 2×10⁻⁵ to 4×10⁻⁴ N for Cat-floc, glycol chitosan, and methylglycol chitosan.     

Interactions of mixed surfactant solution with liposome membrane

Interactions of the mixed surfactant solution of dodecylamido propyl dimethyl aminoacetate and sodium dodecyl sulfate with the liposomal membrane were studied. Lytic activities of the surfactants were measured as a function of the concentrations of surfactant and phospholipid and the composition of mixed surfactants. The solubilization limits of phospholipid by surfactants were determined from the change of their aggregation behavior in suspensions at equilibrium by means of quasi-elastic light scattering. The mixed surfactant solutions showed lower lytic activity than single component surfactant solution in spite of the strong adsorption onto the liposome surface. This was attributed to low solubilization power of binary mixture for phospholipid.     

Microfiltration of amphoteric surfactant using ceramic membranes

The microfiltration of commercially available amphoteric surfactant using ceramic membranes has been investigated. Various combinations operating conditions such as pH, electrolyte and surfactant concentrations were employed. Zeta potential and adsorption isotherms were obtained for the components of membrane surfactant system as functions of pH using surfactant or indifferent electrolyte (KCl). The shift in the membrane isoelectric point induced by the surfactant is linked to the carboxylic groups present on the surfactant which are believed to play a dominant role in the net surface charge of the membrane. A minimum in the permeate flux was found at the pH corresponding to the isoelectric point of the zwitterionic surfactant. This behaviour is ascribed to the interactions occurring between the surfactant–surfactant molecules and the surfactant–membrane. The higher fluxes obtained at low pH as compared to high pH arise from different fouling mechanisms and ionic strengths. Lower fluxes were found when inorganic electrolytes were used in conjunction with surfactant. However, as the valency of the salt increases, flux behaviour of the zwitterionic surfactant (close to isoelectric point) does not vary whilst the cationic and anionic state of the surfactants are much more affected. Interactions between surfactant molecules as a result of the charge screening effects by the larger valence ions are encouraged. The permeate flux declines with an increasing surfactant concentration even though some concentrations fall under the critical micelle concentration (c.m.c.). This is attributed to concentration polarisation in which the accumulated surfactant concentration at the membrane surface could form a stable viscous phase which is resistant to permeate flow in the secondary layer next to the membrane surface. This paper demonstrates the role interactions such as surfactant–surfactant and surfactant–membrane play in influencing the filterability of surfactant solutions using ceramic membranes.     

Mixed micellization of gemini surfactant with nonionic surfactant in aqueous media: a fluorometric study

Herein we report on the study of the interactions between alkanediyl-α,ω-type cationic dimeric (gemini) surfactant and the nonionic Triton X-100 in aqueous medium. The critical micelle concentrations of binary mixtures were determined by fluorometric study. Using the regular solution theory for the analysis of the experimental data, the attractive nature of interactions and synergistic behavior of gemini surfactant and Triton X-100 mixture were demonstrated. The micelle aggregation number was measured using steady state fluorescence quenching method. The micropolarity, binding constant and dielectric constant of mixed systems were determined from the ratio of peak’s intensity (I ₁/I ₃) in the pyrene fluorescence emission spectrum.     

Stoichiometric complexes of polyelectrolyte and azo-functionalized surfactant

The Stoichiometric (1:1) complexes, comprising of a quaternary ammonium surfactant derived from azobenzene and the anionic polyelectrolyte poly(styrene sulfonate), were studied in solution. The studies were based on UV/Visible spectroscopy. Furthermore, aqueous solutions were prepared by the addition of excess surfactant. The kinetic data (t _1/2 and % cis) for the complexes in water with added dodecyltrimethylammonium bromide (DTAB) were collected, which suggests that the 1:1 complexes are resolubilized in water by the additional DTAB.