Chain Length Of Cationic Surfactants Research Articles

Fabrication of the Pesticide-Attapulgite composites regulated by mixed-surfactants

The SB (DTAB, TTAB, CTAB, OTAB)-AP complex was obtained by modifying attapulgite (AP) with surfactant of SB (DTAB, TTAB, CTAB, OTAB). The structures were characterized by XRD, FT-IR, TGA/DTA and SEM. A new lamellar structure is formed by introducing surfactant. The basal spacing increases with the increase of alkyl chain length of cationic surfactants. Then, the beta-cypermethrin (BCT) composites of BCT/SB-AP, BCT/DTAB (TTAB, CTAB, OTAB)-SB-AP were prepared and investigated. The basal spacings of BCT composites were larger than those of SB-AP and the corresponding DTAB (TTAB, CTAB, OTAB)-AP. The existence of BCT and surfactants molecules into BCT composites was further confirmed. The BCT/DTAB (TTAB, CTAB, OTAB)-SB-AP have the smaller specific surface areas than DTAB (TTAB, CTAB, OTAB)-AP due to the increase of AP exfoliation in the presence of SB. Fabrication mechanism of BCT composites was put forward. Release behaviors of BCT were investigated and analyzed in different buffer solutions. The existence of mixed-surfactants influenced distinctly the release rates. BCT composites had the slow release property. The release behaviors were well fitted by pseudo second-order and parabolic diffusion models. This study provided a new approach to improve the utilization efficiency of pesticide and could be applied as a pesticide delivery system.

Wettability reversal on oil-wet calcite surfaces: Experimental and computational investigations of the effect of the hydrophobic chain length of cationic surfactants

HypothesisOil recovery from carbonate reservoirs is often low, in a large part due to the oil-wet state of the constituent rocks. Cationic surfactants are among the most effective compounds capable of reversing the carbonate wettability to more water-wet, which significantly enhances oil recovery. Screening for the most effective cationic surfactants can be facilitated by studying the effects of specific molecular properties, such as the hydrophobic chain length, on the wettability reversal efficiency using molecular dynamics (MD) simulations. Experiments and simulationsWettability reversal by quaternary ammonium cationic surfactants with varying hydrophobic chain length was studied by the combination of MD simulation and experimental contact angle measurements on oil-wet calcite chips. Both experiments and simulations also featured model oils consisting of different size hydrocarbons in order to explore the potential size-specific interactions between the surfactants and oil molecules. FindingsWe found strong correlation between the wettability reversal and the surfactant length, with the longer surfactants universally rendering calcite surfaces more water-wet. By contrast, the wettability reversal is independent of the model oil used, implying that the effect is not due to specific hydrocarbon size. Instead, the superior wettability reversal performance of the more hydrophobic surfactants is due to their greater affinity to the oil/brine interfaces.

Transition from antagonistic to synergistic interaction in mixed micellar system by increase in alkyl chain length of alkyl trimethylammonium bromide

Herein, the electrical conductivity technique used to measure the critical micelle concentration (cmc) for pure cationic surfactants (Dodecyl/cetyltrimethylammonium bromides) and phenothiazine drug (Promethazine hydrochloride), as well as their different mole fractions in 10−3 ​mol/kg 1-methyl-3-octylimidazolium chloride (C8mim.Cl) at different temperatures. By using the cmc values the regular solution theory used to evaluate the micellar mole fraction for DTAB/CTAB-PMT mixed systems. The clint's model used to calculate the ideal critical micelle concentration (cmc∗) that helps to evaluate the ideal micellar mole fraction for studied mixed systems, both explain the deviation from ideality. In addition, interaction parameter βm helps to confirm the nature of interaction (either antagonistic or synergistic) for the studied systems. The calculated parameters confirm a transition in the binding nature from antagonistic to synergistic with the increase in alkyl chain length of cationic surfactant i.e., component of the binary mixed system. The ease of micellization for the studied systems discussed by the standard Gibb's energy of micellization (ΔGm0), as well as the standard enthalpy and standard entropy of micellization were (ΔHm0) and (ΔSm0), respectively to discuss the stability of the studied systems.

Single-Use Electrochemical Platform for Monitoring of Antimicrobial Activity in Comparison to Minimum Inhibitory Concentration Assay

Determination of antimicrobial properties of (bio)molecules has been conventionally performed using minimum inhibitory concentration (MIC) assay based on visual monitoring of turbidity which may cause incorrect interpretations. Surfactants are widely used as disinfectants because of their antimicrobial properties, especially in todays’ world struggling with infections. In this study, surfactants are chosen as the model molecules for the fabrication of a voltammetric biosensor for monitoring antimicrobial activity for the first time in the literature. The antimicrobial effect of anionic and cationic surfactants on E. coli and S. aureus and the effect of alkyl chain length of cationic surfactants were investigated. Anodic peak current (Ia) value was measured by cyclic voltammetry (CV) in a redox probe containing K3[Fe(CN)6] and K4[Fe(CN)6] ions to understand the biointeraction mechanisms. The effect of the surfactants on the microorganisms was characterized by optical microscopy, SEM, and FTIR. The electrochemical biosensor could detect the antimicrobial properties of the surfactants by obtaining consistent results with MIC assay and spectroscopy. While cationic surfactants were more effective on the microorganisms, hexadecyltrimethylammonium bromide (CTAB) is the most effective surfactant by reaching a low MIC level. This article has novelty using disposable PGEs in combination with the CV technique for antimicrobial activity evaluation.

Mixed micellization of cationic/anionic amino acid surfactants: Synergistic effect of sodium lauroyl glutamate and alkyl tri-methyl ammonium chloride

In the cleaning field of the cosmetics industry, amino acid surfactants with low irritation and degradability have attracted more and more attention. However, in the actual application system, the amino acid type surfactant has the application difficulty that is not easy to thicken. In this study, the surface activities and application of the surfactant mixtures containing the cationic surfactant dodecyl tri-methyl ammonium chloride (DTAC) and anionic amino acid surfactant sodium lauroyl glutamate (SLG) (cationic/anionic amino acid surfactant system) were systematically studied, which will provide theoretical guidance for practical applications. First, the surface tension of the cationic/anionic amino acid surfactant system was measured, and the CMC value, interaction parameters, Gibbs free energy and other data were obtained. From this, the behavior characteristics of the adsorption and aggregation of SLG and DTAC in the solution can be judged. Then through dynamic light scattering instrument, rheometer, polarizing microscope, etc., we analyze the phase behavior of the cationic/anionic amino acid surfactant system under different compound ratios and different concentrations, and draw a pseudo-ternary phase diagram. Finally, the influence of the length of the hydrophobic chain of cationic surfactants on the phase behavior of amino acid surfactants was investigated. Experiments have found that the addition of cationic surfactant DTAC can significantly reduce the CMC value of the SLG system, and the CMC changes with the increase of the SLG ratio as follows: first decrease and then increase. The interaction parameters show that DTAC and SLG have a strong interaction. Contrary to the phenomenon of precipitation after the compounding of conventional cationic/anionic surfactants, the compounding of DTAC and SLG increases the solubility, reduces the Krafft point of SLG, and increases the application performance. At the same time, the problem of difficult control of the viscosity of the amino acid surfactant system has also been better solved. DTAC and SLG form a worm-like mixed micelle, which has a higher and controllable viscosity. Finally, it was found that changing the hydrophobic chain length of cationic surfactants has a direct effect on the viscosity of the system.

Effects of alkyl chain length on synergetic interaction and micelle formation between a homologous series of n-alkyltrimethylammonium bromides and amphiphilic drug propranolol hydrochloride

The aggregation behavior of a homologous series of n-alkyltrimethylammonium bromides (CnH2n+1TAB; n = 12, 14, and 16) in the presence of amphiphilic drug propranolol hydrochloride (PPL) in aqueous solutions were studied using conductometric technique. The critical micelle concentrations (CMCs) were determined for pure PPL and surfactant as well as mixed micelles [surfactant(1)/PPL(2)] using the Carpena method. Various physicochemical parameters such as ideal CMC (CMCid), degree of counter-ion binding (α), micellar mole fractions of surfactant (X1m and X1id), interaction parameter (βm), the activity coefficients of components (f1m and f2m), standard Gibbs free energy of micellization (ΔGmic0) and the excess free energy of micellization (GmicE) values have been calculated and compared in detail using Clint's and Rubingh's theories. The activity coefficients of surfactant and PPL are less than 1 (f1m < 1 and f2m < 1) and the values of βm are negative in all mixtures, which indicates the synergistic interaction between surfactant and PPL. Also, the results show that the synergistic effects of mixed micelles strongly depend on the chain length of cationic surfactant, and the values of interaction parameter increase with increasing the alkyl chain length of surfactant. Of the several interactive interactions, it seems hydrophobic interaction is the most dominant interaction between the molecules of the mixed systems among all observed interactive interactions in this study.

Adsorption behaviour of surfactant-nanoparticles at the gas-liquid interface: Influence of the alkane chain length

Silica nanoparticles (NPs) have shown tremendous application potential as stabilising agents in foams. The adsorption of cationic surfactants on the surface of NPs through electrostatic interactions forms integrated surfactant-NP compounds and endows the NPs with surfactancy. The aim of this study was to investigate the influence of the alkane chain length of cationic surfactants on NP surfactancy and foam stability. The results demonstrate that the surface tension decreases and dilational elasticity modulus increases with surfactant chain length. Simultaneously, coalescence of bubbles is markedly suppressed and the stability of surfactant-NP foams is enhanced in static and dynamic tests. With a coarse-grained molecular dynamics simulation (CGMD), it was found that the surfactant-NP complexes evolve into an asymmetric Janus structure at the gas-liquid interface from their symmetric configuration in the aqueous phase. In addition, the resistance force during the pulling of a NP away from the interface increases with surfactant chain length. The simulation results imply that surfactant-NPs have a high surfactancy and the adsorption stability is improved with increasing surfactant chain length, which is in good agreement with the experimental results.

Nano‐Vehicles for Drug Delivery Using Low‐Cost Cationic Surfactants: A Drug Induced Structural Transitions

AbstractTailor‐made application of catanionic aggregates as drug delivery vehicle and as templates for organized nano‐assemblies makes them the best alternatives to liposomes and niosomes. Catanionic aggregates formed by using hydrotropic drug as one of the components pave way for the increased bioavailability thorough sustained contact time and release of the charged drug. In the present investigation, the molecular interaction between the anti‐inflammatory hydrotropic drug, diclofenac sodium (DS) with traditional low cost cationic surfactants with varying chain length is studied. A strong structural transition was observed using turbidity, viscosity, dynamic light scattering, zeta potential, 1H‐NMR, AFM, TEM and SANS techniques. The results suggested that spherically/elliptical shaped micellar aggregates are converted into vesicles through intermediate cylindrical/wormlike aggregates. We have characterized (size and shape) the drug‐surfactant system based on the concentration of the drug, and alkyl chain length of cationic surfactants. The drug loaded vesicles were tested at physiological temperature and were found to stable even at high loading. Due to low cost and high stability, present system could be used as low cost drug delivery vehicle.

Mixed surfactant (altering chain length and head group) aggregates as an effective carrier for tuberculosis drug

Surface properties and aggregation behavior of cationic-cationic and cationic-non-ionic mixed surfactant systems viz. Dodecylethyldimethylammonium bromide (DDAB) with a series of double chain cationic surfactants (DiDDAB, DMDTAB, and DODAB) and non-ionic surfactants (Brij 96, Tyloxapol and Tween 80) were analysed using surface tension and transmission electron microscopy (TEM). The effect of chain length of cationic surfactant and hydrophilic-lypophilic balance (HLB) prominently observed in critical aggregation (cac) value. The aqueous solubility of anti-tuberculosis drug: rifampicin (RIF) was comparatively studied by UV–vis spectroscopy in presence of formulated micelles and vesicles. RIF was significantly solubilised in aqueous medium using all the formulated aggregates. RIF is very unstable in basic medium (above pH-7) and in oxidizing media. Therefore, stability at pH-13 as well as in strong oxidising environment was monitored using UV–vis spectroscopy. To trace the locus of the drug encapsulation in the micelles/vesicles, fluorescence spectroscopy and TEM studies were carried out. Both the techniques stemmed in complimentary results and confirmed that, RIF is majorly populated at polar medium in cationic-cationic vesicles and favour to reside at hydrophobic medium of the nonionic-cationic micelles.

Sorption Properties of Organo Modified Montmorillonite Clay for the Reclamation of Chromium (VI) from Waste Water

The natural Montmorillonite (Mt) clay was modified with three newly synthesized cationic surfactants such as 2-(dodecanoyloxy)-N,Nbis(2-hydroxyethyl)-N(oxiran-2-ylmethyl)ethane-1-ammonium chloride, 2-hydroxy- N- (2-hydroxyethyl) - N (oxiran-2-ylmethyl)-N-(2-(tetradecanoyloxy) ethyl) ethane-1-ammonium chloride and 2-hydroxy- N- (2-hydroxyethyl)-N-(oxiran-2-ylmethyl)-N- palmitoyloxy)ethyl) ethane-1-ammonium chloride to get organo OMt-I, OMt-II and OMt- III respectively. The three modified clays were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Thermo gravimetric Analysis (TGA), X - Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) techniques. The three modified OMts were utilized to reclaim Cr (VI) from wastewater and batch adsorption studies were conducted with various operational parameters such as initial Cr (VI) concentration, pH, amount of adsorbent dosage and agitation rate. The effect of pH on the adsorption of Cr (VI) indicates that the adsorption was favorable in the pH range of 6. As the amount of adsorbent dosage increases, the efficiency in the removal of Cr (VI) ions increases. Langmuir and Freundlich adsorption isotherm best fitted with the experimental isotherm data. The results show that the modified Mt has a good affinity toward the reclamation of Cr (VI) ion and the degree of the efficacy was in the order of the surfactant modified OMt III > OMt II > OMt I. This can be attributed to the increasing hydrophobic chain length of cationic surfactants.

Controlling mesoporous silica-coating of layered double hydroxide nanoparticles for drug control release

Layered double hydroxide (LDH) nanoparticles (NPs) have found various potential applications in control delivery of therapeutics, including many negatively charged drugs, oligonucleotides, genes, and peptides/proteins. The current study specifically investigated the surface coating with mesoporous silica (mSiO2) to make an LDH@mSiO2 core/shell structure and precisely control the release of the payload. Mg2Al-LDH NPs were coated with mSiO2 by varying the reagent concentration and the chain length of cationic surfactants in order to tailor the thickness and the pore size of the mSiO2 shell. TEM images and FTIR spectra evidenced the successful mSiO2 coating onto the surface of LDH NPs. Within the tested conditions, the thickness of the mSiO2 shell can be tailored from 5 to 20 nm and the pore size from 1.9 to 3.3 nm. We further demonstrated that the exchanging property of Mg2Al-Cl-LDH NPs, combined with the diffusion control of the mSiO2 shell, resulted in an effective controlled release of the payload. Thus we have established a foundation for the development of a multifunctional smart delivery platform.

Loading capacity and interaction of DNA binding on catanionic vesicles with different cationic surfactants.

Cationic and anionic (catanionic) vesicles were constructed from the mixtures of sodium laurate (SL) and alkyltrimethylammonium bromide (CnTAB, n = 12, 14, and 16) and were used to control the loading capacity of DNA. The binding saturation point (BSP) of DNA to catanionic vesicles increases with the chain length of cationic surfactants, which is at 1.0, 1.3 and 1.5 for CnTAB with n = 12, 14, and 16, respectively. Our measurements showed that the loading capacity and affinity of DNA can be controlled by catanionic vesicles. It increases with the chain length of cationic surfactants. Because of a large reduction in surface charge density, catanionic vesicles are prone to undergo re-aggregation or fusion with the addition of DNA. DNA molecules can still maintain original coil state during the interaction with catanionic CnTAL vesicles. (1)H NMR data reveals that the obvious dissociation of anionic ions, L(-), from catanionic C14TAL vesicles is due to the interaction with DNA; however, this phenomenon cannot be observed in C12TAB-SL vesicles. Agarose gel electrophoresis (AGE) results demonstrate that the electrostatic interaction between the two oppositely charged cationic and anionic surfactants is stronger than that between DNA and cationic surfactant, CnTAB (n = 12, 14, and 16). Not only is the dissociation of L(-) simply determined by the charge competition, but it also depends largely on the variations in the surface charge density as well as the cationic and anionic surfactant competing ability in geometry configuration of catanionic vesicles. The complicated interaction between DNA and catanionic vesicles induces the deformation of cationic vesicles. Our results should provide clear guidance for choosing more proper vectors for DNA delivery and gene therapy in cell experiments.

Influence of surfactant alkyl length in functionalizing sol–gel derived microporous cobalt oxide silica

The size or alkyl chain length of cationic surfactants can be used to tailor both the pore morphology and the functionality or oxidation state of cobalt in silica materials.

Micellar properties of β-casein–cationic surfactant solutions

The micellar properties of b-casein in solution with a homologous series of cationic surfactants have been investigated using turbidity, fluorescence spectroscopy, and quenching fluorescence measurements. Turbidity mea- surements indicated that monomeric cationic surfactants initially bind cooperatively with a site on the b-casein micelle in negatively charged amino acids. This leads to the formation of low-soluble b-casein micelle-monomeric surfactants complexes. Further addition of surfactant leads to the formation of more highly soluble complexes of b- casein micelle-cationic surfactant. The fluorescence experiments were also used to study the formation of b- casein-cationic surfactant complexes and to determine critical micelle concentration of surfactants and b-casein. The mean aggregation number of b-casein and cationic surfactant micelles at various experimental conditions and the dependence of aggregation phenomenon on the chain length of cationic surfactants were investigated. The mean aggregation number for b-casein micelle has been deter- mined to be 45.70 using quenching fluorescence.

Effects of Electrolytes on Micellar and Surface Properties of Some Monomeric Surfactants

Micellar and surface properties of cationic surfactants, that is, cetyldiethylethanolammonium bromide (CDEEABr), cetyldimethylethanolammonium bromide (CDMEABr), cetyltrimethylammonium bromide (CTAB), and tetradecyldiethylethanolammonium bromide (TDEEABr) in the presence of sodium halide (NaCl, NaBr, and NaI) have been investigated by conductivity and surface tension measurements at 300 K. The critical micelle concentration (cmc) and interfacial parameters, such as the maximum surface excess (Гmax), minimum area per molecule (Amin) and surface pressure at the cmc (πcmc) were computed from the surface tension data. The effects of chain length of cationic surfactants in absence and presence of salts have also been studied. The cmc and degree of micellar ionization (α) values were found to decrease with an increase concentration of salts and values decrease in the order NaCl <NaBr <NaI. Thermodynamic parameters, standard Gibbs free energy of micellization (ΔG°m) and adsorption at air/water interfaces (ΔG°ads) were also evaluated.

Thermal-induced dynamic self-assembly of adenine-grafted polyoxometalate complexes

A new kind of organic-inorganic hybrid complexes based on polyoxometalate were synthesized through symmetrically grafting two adeninyl groups onto Anderson-type MnMo(6) clusters and encapsulating the clusters by organic surfactants. The resultant complexes exhibited thermal-induced dynamic self-assembly behaviors which greatly depended on the ambient temperature and the chain length of cationic surfactants. With the encapsulation of a short surfactant tetrabutyl ammonium, the complex assembled into fibrous, rod-like, and tubular architectures respectively upon heating; while for the case of using a long surfactant dimethyldioctadecyl ammonium as counter ions, the assemblies of the complex transformed from fibers to spheres with the increased temperature. Moreover, the two types of transformations were both reversible during a cooling process. The related mechanism was investigated by combining multiple characterization methods including X-ray crystallography, XPS, FT-IR and temperature-dependent (1)H NMR, which indicated that such a thermal-induced morphological transformation resulted from a synergy effect of the variation of the multiple hydrogen bonds among the complexes and the rearrangement of the surfactants surrounding the MnMo(6) clusters. These results demonstrated a new concept that hydrogen bonds can be rationally employed as the driving force for the fabrication of polyoxometalate-based materials with smart responsive properties.

Flotation and adsorption of quaternary ammonium cationic collectors on diaspore and kaolinite

The flotation and adsorption behaviors of dodecyltrimethylammonium chloride(DTAC) and cetyltrimethylammonium chloride(CTAC) on diaspore and kaolinite were studied. Solution depletion methods were used to determine adsorption isotherms. Fluorescence probe test along with Zeta potential measurement was also conducted for further investigation into the adsorption of quaternary amines at the mineral-water interface. The results show that the flotation recovery of kaolinite decreases with an increase in pH when DTAC and CTAC are used as collectors, while diaspore is on the contrary. As the carbon chain length of the collectors increases, the flotation recoveries of minerals increase. However, the increment rate of kaolinite is significantly lower than that of diaspore. In the low surfactant concentration range, the cationic surfactants adsorb readily on diaspore surfaces just due to electrostatic interactions. As for kaolinite surfaces, ion exchange process also exists. With a further increase in surfactant concentration, the adsorption was ascribed to the hydrophobic association of chain-chain interactions. Micro-polarity of mineral surfaces study shows that CTAC has a better hydrophobic characteristic than DTAC. Larger aggregates are formed with CTAC on diaspore than on kaolinite in the same solution concentration. The results also indicate that the chain length of cationic surfactants has a greater influence on the adsorption of diaspore than on kaolinite, which is consistent with the flotation result.

Functional role of cationic surfactant to control the nano size of silica powder

Preparation of dispersed, amorphous, spherical silica nanoparticles using cationic surfactant as organic template, tetraethoxysilane (TEOS) as silica precursor and ammonia as catalyst has been carried out using sol gel process. The aim of the present study was to evaluate the simultaneous effects of cationic surfactant on the textural and structural properties of silica nanoparticles. We used a series of the cationic surfactants, dodecytrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB) to evaluate the effects of the chain length of cationic surfactant on the grain size of silica nanoparticles. The size of silica nanoparticles can be finely tuned in the range ~50–100 nm by changing the chain length of cationic surfactant. Decreasing the particle size of silica nano particles resulted in increase in chain length of cationic surfactant. Further, these silica nanoparticles are incorporated with cement paste to evaluate the beneficial effect on mechanical properties of cement. Synthesized silica nanoparticles were analyzed using scanning electron microscopy (SEM), 29Si MAS NMR, powder X-ray diffraction techniques (XRD) and IR studies.

Molecular interaction of Congo Red with conventional and cationic gemini surfactants

Interaction of tetradecyltrimethylammonium bromide (TTAB), octylophenylpolyoxyethylene ether (TX-100), sodium dodecylsulfate (SDS), N,N′-ditetradecyl-N,N,N′,N′-tetramethyl-N,N′-butanediyl-diammonium dibromide (14,4,14) and N,N′-didodecyl-N,N,N′,N′-tetramethyl-N,N′-butanediyl-diammonium dibromide (12,4,12) with an anionic diazo dye, Congo Red, was investigated using conductometry, spectroscopy, tensiometry, and pulsed field gradient NMR (PFG-NMR). The formation of dye–surfactant ion pairs, their small mixed aggregates (below the critical micelle concentration (CMC) of these surfactants) and surfactant micelles were detected successfully. Above the CMC, the dye reverted to its monomeric state and solubilized in the micelles. Job's method was used to determine the stoichiometric ratio of dye and surfactant in ion pairs and revealed the formation of more hydrophile ion pairs for geminis compared to their conventional analogs. Quantitative results obtained from tensiometry indicated the existence of considerable synergism for cationic surfactants and antagonism for anionic SDS. In addition, the synergism observed for TX-100 revealed the effect of π–π stacking and hydrophobic forces on ion pair and mixed micelle formation. The increase of dye–surfactant interactions by increasing the electrical charge and chain length of cationic surfactants confirmed the importance of both electrostatic and hydrophobic forces in binary dye/surfactant systems. The hydrodynamic radii of the micelles were determined by self-diffusion coefficient measurements. The average size of the cationic and nonionic micelles increased in the presence of CR molecules.

Interaction of 8-hydroxypyrene-1,3,6-trisulphonate in alkyltrimethylammonium bromide (C nTAB) micellar medium

Interaction of 1-hydroxy-pyrene-3,6,8-trisulphonate (HPTS) has been investigated in well-characterized, monodispersed, micellar media of cationic surfactants of a homologous series having the general formula C n TAB and with trisodium citrate, employing absorption and fluorescence spectroscopy. The interaction of HPTS with cationic micelles depends on the hydrophobic chain length of the cationic surfactants. The binding constant of HPTS with C n TAB micelles decreases with decreasing n. Micelles have strong effect on the interaction of HPTS with trisodium citrate. Fluorescence of HPTS is quenched by citrate ion at the surface of the micelle and the rate of fluorescence quenching decreases with decreasing alkyl chain length of cationic surfactants.