Study of Spontaneous Imbibition of Water by Oil-Wet Sandstone Cores Using Different Surfactants

The mechanism of spontaneous imbibition of water by sandstone cores and the relationship between reservoir wettability and imbibition recovery were studied by investigating factors influencing the spontaneous imbibition of different surfactants by oil-wet sandstone cores. Ultimate oil recovery of cores using the cationic surfactant CTAB was higher than that of the cores using the nonionic surfactant TX-100 and the anionic surfactant POE (1) at the same concentration. For CTAB and TX-100, the ultimate oil recovery by spontaneous imbibition increased with increase in surfactant concentration. In regard to imbibition recovery, TX-100 and POE(1) at high temperatures were superior to those at low temperatures. Ultimate oil recovery of the high-permeability core was higher than that of the low-permeability core at room temperature. According to changes in the driving force during the imbibition process, the imbibition curve could be divided into three regions: (1) mainly capillary force, (2) both capillary and gravity forces, and (3) mainly gravity force. The stronger the hydrophilicity of the rock surface, the higher the spontaneous imbibition recovery.     

Polarographic behavior of nicotinamide in surfactant media and its determination in cetyltrimethylammonium bromide surfactant system

The behavior of nicotinamide has been studied by differential pulse polarography and cyclic voltammetry in the presence of certain ionic and nonionic surfactants, viz. cetyltrimethylammonium bromide (CTAB), sodium dodecylsulfate (SDS) and Triton X-100 (TX-100). The cathodic peak potential (E(p(c))) and peak current (I(p(c))) of nicotinamide were found to be remarkably dependent on the charge and concentration of the surfactant. The presence of SDS and that of TX-100 cause a shift in peak potential and a change in peak current of nicotinamide. In the presence of the cationic surfactant, CTAB, an enhancement in the sensitivity of nicotinamide was observed. A sharp peak with more than two-fold increase in current was used to determine the limit of detection and linear working range using the differential pulse polarographic technique. The present method was successfully used for the simultaneous determination of nicotinamide and pyridoxine hydrochloride, and for the determination of nicotinamide in multivitamin pharmaceutical preparations.     

表面活性剂形成的微环境对SOD和水杨酸铜配合物 SOD样活性的影响

合成水杨酸铜配合物,用X射线衍射测定了它的结构,并用改进的NBT法研究了它和SOD在pH=7.8磷酸缓冲液、表面活性剂CTAB、TX-100形成效团、层状液晶中的SOD样活性。结果表明,在不同微环境中SOD和水杨酸铜配合物的SOD样活性顺序是：在pH=7.8磷酸缓冲液中＞在CTAB胶团中＞在CTAB层状液晶中;在TX-100有序组合体中＞在CTAB有序组合体中。加入少量三氯化镨(PrCl3)也能抑制NBT的还原。而且,PrCr3对NBT的抑制作用与Cu(Ⅱ)配合物的抑制作用是叠加的。     

Effect of Surfactant Microenvironment on SOD-like Activity of Cu(II)-Salicylate Complex

Cu(II)-salicylate was synthesized and characterized by X-ray diffraction. The reaction mechanism of the Cu(II) complex with superoxide anion was studied by ESR spectroscopy, and its (superoxide dismutase) SOD-like activity was determined by a modified illumination method in phosphate buffer (pH = 7.8), micelle solutions and lamellar liquid crystals formed from surfactants CTAB and TX-100. X-ray diffraction indicated that the Cu(II) complex had a formula Cu₂(Hsal)₄EtOHH₂O and a similar structure to the SOD active site. EPR spectra proved that the reaction mechanism of the Cu(II) complex catalyzing O ₂ ^.- dismutation was the same as that of the proposed dismutation reaction catalyzed by SOD. Results obtained by the NBT method indicated that the Cu(II)-complex showed SOD-like activity, and the effect of microenvironment created by surfactants on its activity was same as on SOD activity. The order of the inhibition of NBT reduction by the Cu(II)-complex in different microenvironments was: in phosphate buffer (pH = 7.8) > in TX-100 micelle > in TX-100 liquid crystal, and in nonionic TX-100 organized assemblies > in cationic CTAB organized assemblies. These results were explained by the catalytic effect of micelles, and by the space restriction and high viscosity of organized assemblies of surfactants.     

Growth kinetics of sulfur nanoparticles in aqueous surfactant solutions

Sulfur is an important element has many practical applications when present as nanoparticles. Despite the practicable applications, limited studies are available in the literature related to synthesis of sulfur nanoparticles. Growth kinetics of colloidal sulfur particles synthesized from aqueous solutions using different surfactants have been studied here. The effects of different parameters such as reactant concentration, temperature, sonication, types of acids, types of surfactants, and even surfactant concentration are studied on the growth kinetics. Since the reaction rate is fast, particle growth depends on the parameters which affect diffusion of sulfur molecules. There is a linear relationship found among the reactant concentration and the particle coarsening rate constant. The growth kinetics was studied in the presence of different surfactants such as nonionic (poly(oxyethylene) p-tert-octylphenyl ether, TX-100), anionic (sodium dodecylbenzene sulfonate, SDBS), cationic (cetyltrimethyammonium bromide, CTAB) and results show the coarsening constant changes according to the following order: water>TX-100>SDBS>CTAB. The particle growth rate also depends on the surfactant concentration, coarsening rate constant decreases with the increase in surfactant concentration and become constant close to the critical micellar concentration (CMC). The coarsening rate constant also highly depends on the types of acid used as catalyst.     

Interaction of poly(vinylpyrrolidone) with cationic and nonionic surfactants in aqueous solution studied by <Superscript>1</Superscript>H NMR

Aqueous solutions of surfactant at various concentrations with 0.2% poly(vinylpyrrolidone) (PVP) were studied by ¹H NMR methods, including relaxation time and self-diffusion coefficient measurements and two-dimensional nuclear Overhauser enhancement spectroscopy. Two surfactants were concerned: cationic cetyltrimethylammonium bromide (CTAB) and nonionic Triton X-100 (TX-100). In the presence of 0.2% PVP, the variation of the T ₂ values of CTAB protons is similar to that in the absence of PVP. Relaxation times of PVP protons are not significantly affected by the increasing concentration of CTAB. This indicates that no interaction between PVP and CTAB could be detected. However, in the presence of 0.2% PVP, TX-100 micelles are formed at a concentration lower than its normal critical micellization concentration. According to the results of relaxation time measurement of water protons, the presence of 0.2% PVP also induces the contraction of the hydrophilic layer of the TX-100 micelle. This indicates some interaction between PVP and TX-100, but the mechanism of this interaction needs further investigation.     

Interaction of Nonionic Surfactant Triton-X-100 with Ionic Surfactants

The interaction in two mixtures of a nonionic surfactant Triton-X-100 (TX-100) and different ionic surfactants was investigated. The two mixtures were TX-100/sodium dodecyl sulfate (SDS) and TX-100/cetyltrimethylammonium bromide (CTAB) at molar fraction of TX-100, α_TX-100 = 0.6. The surface properties of the surfactants, critical micelle concentration (CMC), effectiveness of surface tension reduction (γ_CMC), maximum surface excess concentration (Γ_max), and minimum area per molecule at the air/solution interface (A _min) were determined for both individual surfactants and their mixtures. The significant deviations from ideal behavior (attractive interactions) of the nonionic/ionic surfactant mixtures were also determined. Mixtures of both TX-100/SDS and TX-100/CTAB exhibited synergism in surface tension reduction efficiency and mixed micelle formation, but neither exhibited synergism in surface tension reduction effectiveness.     

Kinetics of colloidal MnO<Subscript>2</Subscript> reduction by L-arginine in absence and presence of surfactants

The kinetics of the oxidation of L-arginine by water-soluble form of colloidal manganese dioxide has been studied using visible spectrophotometry in aqueous as well as micellar media. To obtain the rate constants as functions of [L-arginine], [MnO₂] and [HClO₄], pseudo-first-order conditions are maintained in each kinetic run. The first-order-rate is observed with respect to [MnO₂], whereas fractional-order-rates are determined in both [L-arginine] and [HClO₄]. Addition of sodium pyrophosphate and sodium fluoride enhanced the rate of the reaction. The effect of externally added manganese(II) sulphate is complex. It is not possible to predict the exact dependence of the rate constant on manganese(II) concentration, which has a series of reactions with other reactants. The anionic surfactant SDS neither catalyzed nor inhibited the oxidation reaction, while in presence of cationic surfactant CTAB the reaction is not possible due to flocculation of reaction mixture. The reaction is catalyzed by the nonionic surfactant TX-100 which is explained in terms of the mathematical model proposed by Tuncay et al. Activation parameters have been evaluated using Arrhenius and Eyring equations. On the basis of observed kinetic results, a probable mechanism for the reaction has been proposed which corresponds to fast adsorption of the reductant and hydrogen ion on the surface of colloidal MnO₂.     

Influence of surfactants on the adsorption and elektrokinetic properties of the system: guar gum/manganese dioxide

The adsorption of non-ionic polysaccharide—guar gum (GG) in the presence or absence of the surfactants: anionic SDS, cationic CTAB, nonionic TX-100 and their equimolar mixtures SDS/TX-100, CTAB/TX-100 from the electrolyte solutions (NaCl, CaCl₂) on the manganese dioxide surface (MnO₂) was studied. The increase of GG adsorption amount in the presence of surfactants was observed in every measured system. This increase results from formation of complexes between the GG and the surfactant molecules. This observation was confirmed by the determination of the influence of GG on surfactants adsorption on the MnO₂ surface. The increase of GG adsorption on MnO₂ was the largest in the presence of the surfactant mixtures (CTAB/TX-100; SDS/TX-100) which is the evidence of the synergetic effect. The smallest amounts of adsorption were obtained in the presence of TX-100, which results from non-ionic character of this surface active agent. In the case of single surfactant solution CTAB has the best efficiency in increasing the amount of GG adsorption on MnO₂ which results from strong interactions with GG and also with the negatively charged surface of the adsorbent. In order to determine the electrokinetic properties of the system, the surface charge density of MnO₂ and the zeta potential measurements were performed in the presence of the GG macromolecules and the above mentioned surfactants and their mixtures. The obtained data showed that the adsorption of GG or GG/surfactants complexes on the manganese dioxide surface strongly influences the diffused part of the electrical double layer (EDL)—MnO₂/electrolyte solution, but has no influence on the compact part of the electric double layer. This is the evidence that the polymers chains are directly bonded with the surface of the solid and the surfactants molecules are present in the upper part of the EDL.     

Applicability of Positive Cooperativity Model of Enzyme Catalysis on Surfactant-Mediated Reaction of Pararosaniline Hydrochloride Carbocation with Hydroxide Ion

The reaction of hydroxide ion with stabilized pararosaniline hydrochloride carbocation was investigated in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulfate (SDS). Pseudo-first-order kinetics were followed by the reaction system and rate constant depends on surfactant concentration. The reaction was strongly inhibited in the presence of SDS micelles whereas catalyzed in the presence of CTAB micelles. Micellar data were analyzed by applying positive cooperativity model of enzyme catalysis. The value of index of cooperativity (n) was greater than 1 for all reaction systems. Inhibitory and catalytic effect in the presence of micelles had been explained on the basis of hydrophobic and electrostatic interactions of various species present in the reaction systems. Presence of counterions in the reaction system inhibited the reaction rate.     

UV-Visible Spectrometric Study and Micellar Enhanced Ultrafiltration of Alizarin Red S Dye

Ultraviolet spectrometric study of alizarin red S (ARS) showed the substantial change in dye spectra by cationic CTAB as compared to anionic SDS and nonionic TX-100 surfactant. High spectral change by CTAB confirms the anionic nature of ARS dye and thus ARS-CTAB complex formation takes place due to electrostatic force of attraction. A little spectral change by SDS is the result of similarly charged repulsive forces that overcome weak hydrophobic-hydrophobic interaction between dye and surfactant micelles. TX-100 exhibited moderate spectral effect responsive to weak hydrophobic-hydrophobic interaction alone. MEUF study of ARS dye justified the spectral changes and dye rejection percentage (R) decreases in the following order: cationic > nonionic > anionic surfactant. Permeate flux (J) slightly decreases in presence of CTAB and it remains virtually constant for both SDS and TX-100. Addition of copper salt (i.e., CuCl₂) in dye-CTAB complex solution, favors rejection (%) removing dye and copper simultaneously via micellar enhanced ultrafiltration.     

Studies on the molecular interaction of Erythrosine ‘B’ with surfactants

The spectroscopic investigation on anionic dye, Erythrosine ‘B’(EB) with three different types of surfactants such as CTAB (cationic), sodium lauryl sulphate (SLS; anionic) and Triton X-100 (TX-100),Tween-20, 40, 60 and 80 (nonionic) in aqueous media shows that EB forms a 1:1 molecular complex with TX-100, Tweens and CTAB. No interaction is observed between EB and SLS. The thermodynamic and spectrophotometric properties of these complexes suggest that EB forms a strong charge transfer (CT) complex with TX-100 and Tweens whereas the interaction of EB with CTAB is coulombic in nature. Photogalvanic and photoconductometric studies also support the above interactions. In addition to this, the electron-donating ability among the nonionic surfactants, i.e. TX-100 and Tweens towards dye, role of surface in CT interaction, the site of CT interaction and the intensity and stability of CT interaction between EB and nonionic surfactants have been pointed out.     

Studies on the molecular interaction of safranin-T with surfactants

The spectrophotometric studies of safranin-T (Saf-T) dye in an aqueous solution containing three different types of surfactants such as CTAB (cationic), SLS (anionic) and Triton X-100 (TX-100), Tween-20, 40, 60 and 80 (nonionic) show that Saf-T forms a 1:1 molecular complex with TX-100, Tweens and SLS. Such a type of interaction is absent in Saf-T and CTAB. The thermodynamic and spectrophotometric properties of these complexes suggest that Saf-T forms a strong charge transfer (CT) complex with TX-100 and Tweens, whereas the interaction of Saf-T with SLS is coulombic in nature. Photogalvanic and photoconductometric studies also support the above interactions. In addition to this, the electron-donating ability among the nonionic surfactants i.e. TX-100 and Tweens towards dye, role of surface in CT interaction, the site of CT interaction and the intensity and stability of CT interaction between Saf-T and nonionic surfactants have been pointed out.     

Effect of cationic micellar aggregates on the kinetics of oxidation of aminoalcohols by N-bromosuccinimide in alkaline medium

The kinetics of oxidation of some aminoalcohols (AA), viz. ethanolamine, diethanolamine, and triethanolamine, by N-bromosuccinimide (NBS) in alkaline medium has been investigated in the absence as well as in the presence of cetyltrimethylammonium bromide (CTAB), a cationic surfactant. The reaction always followed a first-order dependence of rate on NBS, while the order in each AA and alkali was found to decrease from unity to zero at higher [AA] and [OH-], respectively. The reaction is strongly catalyzed by CTAB even before the critical micelle concentration (CMC) of CTAB. However, the observed rate constants attained constancy at higher [CTAB] (>CMC of CTAB). The premicellar kinetics has been rationalized in the light of the Piszkiewicz positive cooperativity model [J. Am. Chem. Soc. 99 (1977) 1550]. The binding constants between the reactants and the surfactant have also been evaluated using the Raghvan and Srinivasan model [Proc. Ind. Acad. Sci. 98 (1987) 199], which is applicable to bimolecular micellar catalyzed reaction and predicts constancy in the observed rate constant at higher [surfactant]. The binding constants obtained by both the models are in good agreement.     

Fluorescence probing of albumin-surfactant interaction

Protein-surfactant interactions were studied using bovine serum albumin (BSA) and the three surfactants sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and poly(oxyethylene)isooctyl phenyl ether (TX-100). The surfactants used belong to three broad classes, i.e., anionic, cationic, and nonionic. These categories of surfactants were used to elucidate the mechanism of surfactant binding to BSA, at pH 7. The interactions were followed fluorimetrically using both intrinsic tryptophan (Trp) fluorescence and the fluorescence of an external label. The aggregation behavior of the surfactants were studied in the presence of BSA. Steady-state fluorescence studies indicate that all three surfactants bind to BSA in a cooperative manner. This cooperative binding affects the binding of the external label to BSA. All these effects are also manifested in time-resolved fluorescence studies. The effects of surfactants on acrylamide quenching and energy transfer from Trp in BSA to bound dye provided valuable insights into the structural modification of BSA in presence of surfactants. The surfactant-induced conformational change of BSA was also confirmed by circular dichroism studies. However, among the three categories of surfactants, the nonionic surfactant shows the least interaction with BSA.     

Interactions between nonpolar surfaces in mixed solutions of cationic and nonionic surfactants

The interaction energy between hydrophobic SiO₂ particles in aqueous solutions of a cationic surfactant (dodecylpyridinium bromide, DDPB), a nonionic surfactant (Triton X-100, TX-100), and their mixed solutions was measured as a function of concentration. Synergism has been observed in mixed surfactant solutions: the surfactant concentration required for achieving the set interaction energy in the mixed solutions was lower than in the solutions of the individual surfactants. The molecular interaction parameters in surfactant mixtures were calculated using the Rosen model. Chain-chain interactions between nonionic and cationic surfactants were suggested as the main reason for the synergism.     

Hydrophobic terminal group of surfactant initiating micellization as revealed by 1H NMR spectroscopy

The critical aggregation concentration (CAC) of four with three kinds of conventional surfactants, namely, two cationic surfactants [hexadecyltrimethyl ammonium bromide (CTAB) and tetradecyltrimethyl ammonium bromide (TTAB)], one anionic surfactant [sodium dodecyl sulfate (SDS)], and a nonionic surfactant [Triton X-100 (TX-100)], were determined by variation of ¹H chemical shifts with surfactant concentrations. Results show that the CAC values of protons at different positions of the same molecule are different, and those of the terminal methyl protons are the lowest, respectively, which suggests that the terminal groups of the alkyl chains aggregates first during micellization. Measurement of the transverse relaxation time (T₂) of different protons in SDS also show that the terminal methyl protons start to decrease with the increase in concentration first, which supports the above mentioned tendency.     

Kinetics of metribuzin degradation by colloidal manganese dioxide in absence and presence of surfactants

The kinetics of the degradation of metribuzin by water-soluble colloidal MnO₂ in acidic medium (HClO₄) were studied spectrophotometrically in the absence and presence of surfactants. The experiments were performed under pseudo-first-order reaction conditions in respect of MnO₂. The degradation was observed to be of the first order in respect of MnO₂ while of fractional order for both metribuzin and HClO₄. The rate constant for the degradation of metribuzin was observed to decrease as the concentration of MnO₂ increased. The anionic surfactant, sodium dodecyl sulphate (SDS), was observed to be ineffective whereas the non-ionic surfactant, Triton X-100 (TX-100), accelerated the reaction rate. However, the cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), caused flocculation with oppositely-charged colloidal MnO₂; hence further study was not possible. The catalytic effect of TX-100 was discussed in the light of the available mathematical model. The kinetic data were exploited to generate the various activation parameters for the oxidative degradation of metribuzin by colloidal MnO₂ in the absence as well as the presence of the non-ionic surfactant, TX-100.     

Submicellar catalytic effect of cetyltrimethylammonium bromide in the oxidation of ethylenediaminetetraacetic acid by MnO4-

The effects of cetyltrimethylammonium bromide (CTAB), sodiumdodecyl sulphate (SDS) and Triton X-100 (TX-100) on the oxidative degradation of ethylenediaminetetraacetic acid (EDTA) by MnO₄⁻ have been studied spectrophotometrically at 525 and 420 nm, respectively. It was found that cationic surfactant catalyse the reaction rate while anionic and non-ionic have no effect. The premicellar environment of CTAB strongly catalyses the reaction rate which may be due to the favorable electrostatic binding of both reactants (MnO₄⁻ and EDTA) with the positive head groups of the CTAB aggregates. The influence of different parameters such as [MnO₄⁻], [EDTA], [H⁺] and [surfactants] were also considered. The reaction follows the first- and fractional-order kinetics with respect to [MnO₄⁻] and [EDTA]. The proposed mechanism and the derived rate law are consistent with the observed kinetics.     

两相催化体系中烯烃氢甲酰化的高区域选择性

采用水溶性铑膦配合物催化剂在两相(水/有机物)体系中进行长链烯烃氢甲酰化反应合成高碳醛,具有反应条件缓和、催化剂与产物容易分离的优点,而且用水作溶剂既便宜、又安全,有利于环境保护,因此引起国内外化学家重视,进行了大量研究[1,2].