Highly magnetizable superparamagnetic colloidal aggregates with narrowed size distribution from ferrofluid emulsion

An empirical model for the concentrations of monomeric and micellized surfactants in solution is presented as a consistent approach for the quantitative analysis of data obtained with different experimental techniques from surfactant solutions. The concentration model provides an objective definition of the critical micelle concentration (cmc) and yields precise and well defined values of derived physical parameters. The use of a general concentration model eliminates subjective graphical procedures, reduces methodological differences, and thus allows one to compare directly the results of different techniques or to perform global fits. The application and validity of the model are demonstrated with electrical conductivity, surface tension, NMR chemical shift, and self-diffusion coefficient data for the surfactants SDS, CTAB, DTAB, and LAS. In all cases, the derived models yield excellent fits of the data. It is also shown that there is no need to assume the existence of different premicellar species in order to explain the chemical shifts and self-diffusion coefficients of SDS as claimed recently by some authors.     

Interactions between zwitterionic and conventional anionic and cationic surfactants

Critical micelle concentration (cmc) values have been determined for the mixed zwitterionic/anionic surfactant systems of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12)/sodium dodecyl sulfate (SDS), N-dodecyl-N,N-(dimethylammonio)butyrate (DDMAB)/SDS, N-octyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-08)/sodium octyl sulfate (SOS), and the zwitterionic/cationic systems of ZW3-12/dodecyltrimethylammonium bromide (DTAB), DDMAB/DTAB. Conductivity studies and nuclear magnetic resonance (NMR) spectroscopy were the methods employed for cmc determinations. The degree of nonideality of the interaction in the micelle (beta(m)), for each system, was determined according to Rubingh's nonideal solution theory. Evidence was found for the existence of strong interactions between zwitterionic and anionic surfactants in each of the zwitterionic/anionic systems. The ZW3-08/SOS and DDMAB/SDS systems behaved synergistically at all mole fractions studied while the ZW3-12/SDS system exhibited synergistic behavior above mole fractions of 0.30. Greater negative deviations from ideal behavior were demonstrated in the DDMAB/SDS system than in the other two zwitterionic/anionic systems. The zwitterionic/cationic systems of ZW3-12/DTAB and ZW3-08/OTAB displayed only slight deviations from ideal behavior, therefore indicating near ideal mixing.     

Effect of type and concentration of surfactants on swelling behavior of poly[<Emphasis Type="Italic">N</Emphasis>-[3-(dimethylamino)propyl]methacrylamide-co- <Emphasis Type="Italic">N,N</Emphasis>-methylenebis(acrylamide)] hydrogels

A series of thermosensitive hydrogels were prepared from N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) monomer by using 11.6–17.8% (m/m) N,N-methylenebis(acrylamide) (MBAAm) as the crosslinker and comonomer in water. A kinetic study of the absorption determined the transport mechanism. The diffusion coefficients of these hydrogels were calculated for the Fickian mechanism. It was shown that the swelling behavior of the P(DMAPMA-co-MBAAm) hydrogels can be controlled by changing the amount of MBAAm. The swelling equilibrium of the P(DMAPMA-co-MBAAm) hydrogels was also investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). In pure water, irrespective of the amount of MBAAm, the P(DMAPMA-co-MBAAm) hydrogels showed a discontinuous phase transition between 30 and 40 °C. However, the transition changed from discontinuous to continuous with the addition of surfactants, this is ascribed to the conversion of non-ionic P(DMAPMA-co-MBAAm) hydrogel into polyelectrolyte hydrogels due to binding of surfactants through the hydrophobic interaction. Additionally, the amount of free SDS and DTAB ions was measured at different temperatures by a conductometric method, it was found that the electric conductivity of the P(DMAPMA-co-MBAAm) – surfactant systems depended strongly on both the type and concentration of surfactant solutions.     

Thermosensitive poly(N-isopropylacrylamide-co-acrylamide) hydrogels: Synthesis, swelling and interaction with ionic surfactants

Thermosensitive hydrogels were prepared by free-radical polymerization in aqueous solution from N-isopropylacrylamide (NIPA) and acrylamide (AAm) monomers. N,N-Methylenebis(acrylamide) (MBAAm) was used as a crosslinker. A kinetic study of the absorption determined the transport mechanism. The diffusion coefficients of these hydrogels were calculated for the Fickian mechanism. It was shown that the swelling behavior of the P(NIPA-co-AAm) hydrogels can be controlled by changing the amount of MBAAm. The swelling equilibrium of the P(NIPA-co-AAm) hydrogels was also investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). In SDS and DTAB solutions, the equilibrium swelling ratio of the hydrogels increased, this is ascribed to the conversion of non-ionic P(NIPA-co-AAm) hydrogel into polyelectrolyte hydrogels due to binding of surfactant molecules through the hydrophobic interaction. Additionally, the amount of free SDS and DTAB ions was measured at different temperatures by a conductometric method, it was found that the electric conductivity of the P(NIPA-co-AAm)—surfactant systems depended strongly on both the type and concentration of surfactant solutions.     

Fluorescence studies of interactions of ionic surfactants with poly(amidoamine) dendrimers

The pyrene fluorescence measurements have been carried out for the micelle formation of sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and dimethylene bis(dodecyldimethylammonium bromide) (12-2-12) in the presence of fixed different amounts of various generations of poly(amidoamine) (PAMAM). The critical micelle concentration (cmc) of SDS decreases with an increase in the fixed amount of PAMAM, suggesting the facilitation of micellization due to the participation of SDS-PAMAM complex in the micelle formation. This behavior has not been observed for DTAB/12-2-12 in the presence of various generations of PAMAM. The results indicate that SDS always has stronger interactions with all the generations of PAMAM in comparison to those of DTAB and 12-2-12.     

Hexafluoroisopropanol-induced coacervation in aqueous mixed systems of cationic and anionic surfactants for the extraction of sulfonamides in water samples

Hexafluoroisopropanol (HFIP)-induced coacervation in aqueous mixed systems of catanionic surfactants of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS) was described in detail, and its application in the extraction of strongly polar sulfonamides (SAs) was investigated. With 10 % (v/v) HFIP inclusion, coacervation formation and two-phase separation occur in a wide range of SDS/DTAB mole ratios (88:12～0:100 mol/mol) and total surfactant concentrations (10～200 mmol/L). The interactions between HFIP and DTAB play an important role in coacervation formation. The HFIP-induced SDS–DTAB coacervation extraction proves to be an efficient method for the extraction and preconcentration of SAs. Both hydrophobic interaction and polar interactions (hydrogen–bond, electrostatic, and π-cation) contribute to the distribution of SAs into coacervate phase. The proposed HFIP-induced SDS–DTAB coacervation extraction combined with HPLC–UV was employed for the extraction and quantitative determination of SAs in environmental water samples. Limits of detection were 1.4～2.5 ng mL^?1. Excellent linearity with correlation coefficients from 0.9990 to 0.9995 was obtained in the concentration of 0.01～10 μg mL^?1. Relative recoveries were in the range of 93.4～105.9 % for analysis of the lake, underground, and tap water samples spiked with SAs at 0.01, 1.0, and 10 μg/mL, respectively. Relative standard deviations were 0.7～3.2 % for intraday precision and 1.3～4.6 % for interday precision (n?=?3). Concentration factors were 17～49 for three water samples spiked with 0.01 μg/mL SAs. The results demonstrate that the proposed extraction method is feasible for the preconcentration and determination of trace SAs in real water samples. Graphical abstract

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Laser flash photolysis and time-resolved fluorescence measurements of the aggregation number of SDS-biopolymer complexes

Aqueous solutions of 0.5% sodium carboxymethyl cellulose, NaCMC, and 2-hydroxyethyl cellulose, HEC, and variable concentration of sodium dodecyl sulfate, SDS, were studied by the intensities ratio of pyrene fluorescence bands (I/III and monomer/excimer) and conductance measurements to determine the critical aggregation concentration, cac, and the degree of micellar dissociation, alpha, respectively. The cac of these systems is close to 2-4 x 10(-3)M and values of alpha are consistent with the formation of SDS micelles adsorbed cooperatively to the polymer backbone. Laser flash photolysis (LFP) and time-resolved fluorescence (TRF) techniques were employed to determine the micellar aggregation number, N, using the probes flavone and pyrene, respectively. The obtained N for HEC/SDS and NaCMC/SDS were 48 and 68, respectively. The presence of the counterions at the NaCMC backbone is the main factor responsible for this number. Besides, the transient spectra of flavone and present in 0.5% HEC or NaCMC with and in absence of SDS are discussed. Flavone triplet state exit rate constant from the biopolymer/SDS complexes showed that these systems are completely different from a pure SDS micelle.     

Effects of arginine and other solution additives on the self-association of different surfactants: an investigation at single-molecule resolution

Fluorescence correlation spectroscopy is used to monitor the self-association of SDS and DTAB monomers at single-molecule resolution. Tetramethylrhodamine-5-maleimide (TMR) has been chosen as a probe because rhodamine dyes have been shown to bind surfactant micelles. Correlation functions obtained by FCS experiments have been fit using conventional discrete diffusional component analysis as well as the more recent maximum entropy method (MEM). Hydrodynamic radii calculated from the diffusion time values increase with surfactant concentration as the monomers self-associate. Effects of several solution additives on the self-association property of the surfactants have been studied. Urea and glycerol inhibit self-association, and arginine shows a dual nature. With SDS, arginine favors self-association, and with DTAB, it inhibits micelle formation. We propose surfactant self-association to be a "supersimplified" model of protein aggregation.     

Effects of interactions on the formation of mixed micelles of 1,2-diheptanoyl-sn-glycero-3-phosphocholine with sodium dodecyl sulfate and dodecyltrimethylammonium bromide

Mixed micelles of the phospholipid 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) with sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) in aqueous solutions and the effects of interactions between the components were studied by fluorescence and NMR measurements. The regular solution theory (RST) was applied to analyze the experimental critical micelle concentration values determined from the fluorescence spectra of pyrene in the mixed micelles. Negative values for the interaction parameter (beta12) were obtained for both DHPC + SDS and DHPC + DTAB mixtures, with the value being more negative in the former case. The negative beta12 values for the two systems imply that the interaction between the phospholipid and the two ionic surfactants is attractive in nature, being more intense in the case of DHPC + SDS. The interaction parameter, beta12, varies with composition of the mixtures indicating changes in packing. The proton NMR shifts are quite different for the two systems and also vary with composition. An interpretation of these experimentally determined chemical shifts in terms of the degree of compactness attributed to electrostatic and steric interactions in the mixed micelle supports the conclusions derived from the fluorescence cmc experiments.     

卵清蛋白与离子型表面活性剂的相互作用

本文通过荧光光谱法、紫外-可见吸收光谱法和透射电镜并结合电导率测定分别研究了水中卵清蛋白与阴离子表面活性剂十二烷基硫酸钠（SDS）和阳离子表面活性剂十二烷基三甲基溴化铵（DTAB）和十六烷基三甲基溴化铵（CTAB）之间的相互作用。研究结果表明卵清蛋白可以增加SDS和CTAB的临界胶束浓度,但对DTAB的临界胶束浓度没有影响。阴离子表面活性剂可以使卵清蛋白构象完全伸展,而阳离子表面活性剂却不具备此种作用。表面活性剂单体与卵清蛋白的相互作用强于表面活性剂胶束与卵清蛋白的相互作用。     

Spontaneous vesicle formation of single chain and double chain cationic surfactant mixtures

The concentration vs composition diagram of aggregate formation of the dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB) mixture in aqueous solution at rather dilute region was constructed by analyzing the surface tension, turbidity, and electrical conductivity data and inspected by cryo-TEM images and dynamic light scattering data. Although the aqueous solution of DTAB forms only micelles, the transition from monomer to small aggregates and then to vesicle was found at 0.1 < X2 相似文献   

Mixed Micellization of Dimeric (Gemini) Surfactants and Conventional Surfactants

The aqueous solutions of mixtures of various conventional surfactants and dimeric anionic and cationic surfactants have been investigated by electrical conductivity, spectrofluorometry, and time-resolved fluorescence quenching to determine the critical micelle concentrations and the micelle aggregation numbers in these mixtures. The following systems have been investigated: 12-2-12/DTAB, 12-2-12/C(12)E(6), 12-2-12/C(12)E(8), 12-3-12/C(12)E(8), Dim3/C(12)E(8), and Dim4/C(12)E(8) (12-2-12 and 12-3-12=dimethylene-1,2- and trimethylene-1,3-bis(dodecyldimethylammonium bromide), respectively; C(12)E(6) and C(12)E(8)=hexa- and octaethyleneglycol monododecylethers, respectively; Dim3 and Dim4=anionic dimeric surfactants of the disodium sulfonate type, Scheme 1; DTAB=dodecyltrimethylammonium bromide). For the sake of comparison the conventional surfactant mixtures DTAB/C(12)E(8) and SDS/C(12)E(8) (SDS=sodium dodecylsulfate) have also been investigated (reference systems). Synergism in micelle formation (presence of a minimum in the cmc vs composition plot) has been observed for the Dim4/C(12)E(8) mixture but not for other dimeric surfactant/nonionic surfactant mixtures investigated. The aggregation numbers of the mixed reference systems DTAB/C(12)E(8) and SDS/C(12)E(8) vary monotonously with composition from the value of the aggregation number of the pure C(12)E(8) to that of the pure ionic component. In contrast, the aggregation number of the dimeric surfactant/C(12)E(8) mixtures goes through a minimum at a low value of the dimeric surfactant mole fraction. This minimum does not appear to be correlated to the existence of synergism in micelle formation. The initial decrease of the aggregation number of the nonionic surfactant upon addition of ionic surfactant, up to a mole fraction of ionic surfactant of about 0.2 (in equivalent per total equivalent), depends little on the nature the surfactant, whether conventional or dimeric. The results also show that the microviscosity of the systems containing dimeric surfactants is larger than that of the reference systems. Copyright 2001 Academic Press.     

MICELLE FORMATION BY ANIONIC AND CATIONIC SURFACTANTS IN AQUEOUS 18-CROWN-6 ETHER,P-CYCLODEXTRIN,AND 1,10-PHENANTHROLINE SOLUTIONS AT DIFFERENT TEMPERATURES

The conductances of sodium perfluorooctanoate (SPFO), sodium dodecylsulphate (SDS), dodecyltrimethylammonium bromide (DTAB), and tetradecyltrimethylammonium bromide (TTAB) in 18-crown-6 ether + water (CR+W), p-cyclodextrin + water (CY+W), and 1,10-phenanthroIine + water (Phen+W) mixtures with fixed 4 mM of each additive were determined over the temperature range of 5-55 °C. The conductivity plots for all the surfactants showed single break from which the critical micellization concentration (cmc) and degree of micelle ionization (x) were computed. From the pre and the post micellar slopes of the conductivity curves, the equivalent conductivities of the monomeric (Aass) and the micellar states (Amjc), respectively, were calculated and discussed with respect to the surfactant-additive complexation. It was observed that the micelle formation of all the ionic surfactants irrespective of the nature of their head groups were delayed in CYC+W in comparison to that in CR+W and Phen+W systems over the temperature range studied. The micelle formation of SPFO and SDS in CR+W and Phen+W systems showed stabilization of the respective micelles due to the adsorption of Na⁺-CR and Na+-Phen complexes at the micelle solution interface in comparison to that of DTAB and TTAB.     

Study on the effect of chain-length compatibility of mixed anionic–cationic surfactants on the cloud-point extraction of selected organophosphorus pesticides

The chain-length compatibility of mixed anionic-cationic surfactants was investigated for the extraction of organophosphorus pesticides (OPPs). Cationic surfactants with different chain lengths (n = 12 and 16) were mixed with sodium dodecyl sulfate (SDS; n = 12) for the mixed anionic-cationic surfactants-based extraction. Six OPPs were studied including azinphos-methyl, parathion-methyl, fenitrothion, diazinon, chlorpyrifos, and prothiophos. Reversed-phase high-performance liquid chromatography was used for the determination of the studied OPPs. The extraction was performed using mixtures of SDS and cationic surfactants including dodecyltrimethyl ammonium bromide or dodecyltrimethylammonium bromide (DTAB; n = 12) and cetyltrimethyl ammonium bromide or cetyltrimethyl ammonium bromide (CTAB; n = 16). The parameters affecting the extraction efficiencies of two extraction systems were studied and discussed. The optimum condition for SDS-DTAB was 15 mmol L(-1) SDS and 1 mmol L(-1) DTAB in the presence of 15% (w/v) sodium chloride (NaCl). Meanwhile, the condition for SDS-CTAB was 10 mmol L(-1) SDS and 1.0 mmol L(-1) CTAB with 10% (w/v) NaCl. Under the optimum conditions, the extraction efficiency of SDS-DTAB (66-85%) was slightly higher than that of SDS-CTAB (61-82%). In addition, the SDS-DTAB system also gave greater enrichment factor than SDS-CTAB for all the studied OPPs. This result may be due to the compatibility of chain length between SDS and DTAB. The extraction using SDS-DTAB was successfully applied to determine OPPs in fruit samples (i.e., pomelo, apple, and pineapple). No contamination by the studied OPPs in samples was observed. Good accuracy with recoveries ranging from 77 to 105% was obtained. Low limits of detection were in the range of 0.003-0.01 mg kg(-1) which are below the MRLs established by EU-MRLs for the OPPs residues in fruit samples.     

Study of Fuchsin Acid Fading in Micellar Media

The rate constant of alkaline fading of fuchsin acid (FA^2?) was measured in the presence of nonionic (TX‐100), cationic (dodecltrimethylammonium bromide, DTAB), and anionic (sodium dodecyl sulfate, SDS) surfactants. FA^2? has three negatively charged substituents and one positive charge, and this makes the behavior of FA^2– different from dyes such as bromophenol blue. It was observed that the reaction rate constant decreased in the presence of TX‐100, DTAB, and SDS. Binding constants of FA^2? to TX‐100, DTAB, and SDS and the related thermodynamic parameters were calculated by the stoichiometric (classical) model. The results show that the binding of FA^2? to SDS is endothermic in both regions, and the binding of FA^2? to DTAB and TX‐100 is exothermic in one region and endothermic in another region of the used concentration range of these surfactants. Also, the binding constants of FA^2? to surfactant molecules of SDS/TX‐100 and DTAB/TX‐100 mixed micelles were obtained.     

Estimation of degree of counterion binding and thermodynamic parameters of ionic surfactants from cloud point measurements by using triblock polymer as probe

Cloud point (C(P)) was measured for ternary mixtures of different ionic surfactants such as sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and dimethylene bis(dodecyldimethylammonium bromide) (12-2-12) plus triblock polymer (TBP) ((PEO)(2)(PPO)(15.5)(PEO)(2)) plus water, keeping the concentration of TBP constant and varying the surfactant concentration from pre- to postmicellar regions. These experiments were also performed in the presence of different fixed amounts of NaBr to evaluate the salt effect on the clouding behavior of these ternary mixtures. The C(P) value of TBP exhibits a drastic change at the cmc of each surfactant. The cmc values thus obtained both in the absence and in the presence of NaBr were used to evaluate counterion binding (beta) with the Corrin-Harkins method. beta values were also used to evaluate the thermodynamic parameters of these ionic surfactants. The results suggest that the beta values evaluated using this method, especially at low [TBP], are in good agreement with those reported in the literature.     

Experimental and theoretical investigation of the micellar-assisted solubilization of ibuprofen in aqueous media

Surfactants can be used to increase the solubility of poorly soluble drugs in water and to increase drug bioavailability. In this article, the aqueous solubilization of the nonsteroidal, antiinflammatory drug ibuprofen is studied experimentally and theoretically in micellar solutions of anionic (sodium dodecyl sulfate, SDS), cationic (dodecyltrimethylammonium bromide, DTAB), and nonionic (dodecyl octa(ethylene oxide), C12E8) surfactants possessing the same hydrocarbon "tail" length but differing in their hydrophilic headgroups. We find that, for these three surfactants, the aqueous solubility of ibuprofen increases linearly with increasing surfactant concentration. In particular, we observed a 16-fold increase in the solubility of ibuprofen relative to that in the aqueous buffer upon the addition of 80 mM DTAB and 80 mM C12E8 but only a 5.5-fold solubility increase upon the addition of 80 mM SDS. The highest value of the molar solubilization capacity (chi) was obtained for DTAB (chi = 0.97), followed by C12E8 (chi = 0.72) and finally by SDS (chi = 0.23). A recently developed computer simulation/molecular-thermodynamic modeling approach was extended to predict theoretically the solubilization behavior of the three ibuprofen/surfactant mixtures considered. In this modeling approach, molecular-dynamics (MD) simulations were used to identify which portions of ibuprofen are exposed to water (hydrated) in a micellar environment by simulating a single ibuprofen molecule at an oil/water interface (modeling the micelle core/water interface). On the basis of this input, molecular-thermodynamic modeling was then implemented to predict (i) the micellar composition as a function of surfactant concentration, (ii) the aqueous solubility of ibuprofen as a function of surfactant concentration, and (iii) the molar solubilization capacity (chi). Our theoretical results on the solubility of ibuprofen in aqueous SDS and C12E8 surfactant solutions are in good agreement with the experimental data. The ibuprofen solubility in aqueous DTAB solutions was somewhat overpredicted because of challenges associated with accurately modeling the strong electrostatic interactions between the anionic ibuprofen and the cationic DTAB. Our results indicate that computer simulations of ibuprofen at a flat oil/water interface can be used to obtain accurate information about the hydrated and the unhydrated portions of ibuprofen in a micellar environment. This information can then be used as input to a molecular-thermodynamic model of self-assembly to successfully predict the aqueous solubilization behavior of ibuprofen in the three surfactant systems studied.     

A Comparative Study of the Direct Calorimetric Determination of the Denaturation Enthalpy for Lysozyme in Sodium Dodecyl Sulfate and Dodecyltrimethylammonium Bromide Solutions

The complexes of lysozyme with the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB) have been investigated by isothermal titration calorimetry at pH=7.0 and 27 °C in a phosphate buffer. A new direct calorimetric method was applied to follow the protein denaturation and study the effect of surfactants on the stability of proteins. The extended solvation model was used to represent the enthalpies of lysozyme + SDS interaction over the whole range of SDS concentrations. The solvation parameters recovered from the new equation are attributed to the structural change of lysozyme and its biological activity. At low SDS concentrations, the binding is mainly electrostatic with some simultaneous interaction of the hydrophobic tail with nearby hydrophobic regions of lysozyme. These initial interactions presumably cause some protein unfolding and expose additional hydrophobic sites. The induced enthalpy of denaturation of lysozyme by SDS is 160.81±0.02 kJ⋅mol⁻¹. The lysozyme-DTAB complexes behave very differently from those of the lysozyme-SDS complexes. SDS induces a stronger unfolding of lysozyme than DTAB. The induced enthalpy of lysozyme denaturation by DTAB is 86.46±0.02 kJ⋅mol⁻¹.     

用弱电解质理论研究水溶液中SDS胶团的电离行为

在临界胶团浓度以上,十二烷基硫酸钠(SDS)在溶液中形成聚集态的胶团,从而表现出不同于一般强电解质的电导行为.针对这一特点提出了一种胶团电离模型,即将胶团作为一种弱电解质,用弱电解质电导理论来描述其溶液电导的变化规律,导出SDS胶团电离度的计算式,并得到该溶液电导实测数据的验证.