Binary Mixed Systems Research Articles

Effect of anionic surfactant and temperature on micellization behavior of promethazine hydrochloride drug in absence and presence of urea

The interaction between promethazine hydrochloride (PMH) drug and sodium dodecyl sulfate (NaDS) have been carried out conductometrically at various temperatures and concentration to examine the monomeric as well as micellar phases of aqueous solutions of mixed systems in absence and attendance of urea (NH2CONH2). PMH is belonged to the group of drugs called phenothiazines and is employed to care for allergy symptoms. Urea increases the cmc value because of enhancement in the surface charge of the micelles/mixed micelles. Relevant parameters were evaluated using the various theoretical models for binary mixed systems. The values of micellar mole fraction (X1m) and the ideal micellar mole fraction (X1id) were found to higher than the corresponding mole fraction (α1) of surfactant. The micellar interaction parameters (β), were determined from the critical micelle concentration (cmc) values using the approach of Rubingh's regular solution theory. Clint's model was also used to explain the nonideal behavior of the systems. In presence of urea the interaction between the studied components decreases. The evaluated excess free energy (ΔGexRub) explains the more stability of mixed micelles in comparison to micelles of the pure component; the stability decreases in attendance of urea. Also, activity coefficients (f1 and f2) are always less than unity suggesting non-ideality in the mixed solution. The ΔG0m for all studied systems were found out to be negative i.e., micellization processes are energetically favourable.

Thermodynamic properties of metamizol monohydrate in pure and binary solvents at temperatures from (283.15 to 313.15) K

Abstract The thermodynamic properties of metamizol monohydrate in pure solvents (methanol, ethanol, n-propanol and isopropanol) and two binary mixed solvent systems including (methanol + ethanol) and (methanol + isopropanol) were measured from 283.15 K to 313.15 K by gravimetric method under atmospheric pressure thought as 0.1 MPa. The modified Apelblat equation, the CNIBS/R-K equation, the Hybrid model and the NRTL model were used to correlate the solubility of metamizol monohydrate, respectively. The results show that the solubility of metamizol monohydrate in all the tested solvents increases with the rising temperature which means that it has temperature dependence. What's more, the effects of solvent components of the binary solvent mi x tures on solubility were discussed, it illustrates that the increasing of the molar fraction of methanol gives the system a greater dissolving power. Furthermore, according to the NRTL model, the enthalpy, the Gibbs energy and the entropy of the mixing process were also obtained and discussed.

Characterization of the paclitaxel loaded chitosan graft Pluronic F127 copolymer micelles conjugate with a DNA aptamer targeting HER-2 overexpressing breast cancer cells

In this work we report the isolation of DNA aptamer that is specifically bound to a HER-2 overexpressing SK-BR-3 human breast cancer cell line, using SELEX strategy. Paclitaxel (PTX) loaded chitosan graft Pluronic F127 copolymer micelles conjugate with a DNA aptamer was synthesized and its structure was confirmed by TEM image. This binary mixed system consisting of DNA aptamer modified Pluronic F127 and chitosan could enhance PTX loading capacity and increase micelle stability. Morphology images confirmed the existence of PTX micelles, with an average size of approximately 86.22 ± 1.45 nm diameters. Drug release profile showed that the PTX conjugate maintained a sustained PTX release. From in vitro cell experiment it was shown that 89%–93%, 50%–58%, 55%–62%, 24%–28% and 2%–7% of the SK-BR-3, NS-VN-67, LH-VN-48, HT-VN-26 and NV-VN-31, respectively, were dead after 6–48 h. These results demonstrated a novel DNA aptamer-micelle assembly for efficient detection and a system for the delivery of PTX targeting specific HER-2 overexpressing. We have also successfully cultivated cancer tissues of explants from Vietnamese patients on a type I collagen substrate. The NS-VN-67, LH-VN-48, HT-VN-26 and NV-VN-31cell lines were used as cellular model sources for the study of chemotherapy drug in cancer.

High pressure densities for mixed ionic liquids having different functionalities: 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

In this work, high pressure density measurements were made of mixed ionic liquid systems (1-butyl-3-methylimidazolium chloride ([bmim]Cl) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N])) for the purpose of developing efficient reaction and separation systems for processing biomass. The mixed ionic liquids were prepared at mole ratios, [bmim]Cl:[bmim][Tf2N] of 0.75: 0.25, 0.50: 0.50 and 0.25: 0.75. Density data were measured (10–200MPa, 312–392K) and correlated (up to 100MPa) with the ε∗-modified Sanchez-Lacombe equation of state (ε∗-mod SL EoS). The density of the binary mixed ionic liquid system was modeled in two ways: (i) as a single pseudo-component or (ii) as two discrete components. By treating the mixed ionic liquids as a single pseudo-component, the ε∗-mod SL EoS could correlate the high pressure density data to within a maximum average relative deviation (ARD) of 0.06%. On the other hand, by treating the mixed ionic liquids as discrete components, higher ARD values (0.15%) were obtained from the ε∗-mod SL EoS that can be attributed to the EoS mixing rules. Both approaches for modeling the ionic liquid mixtures had sufficiently low deviations and will be applied to multicomponent CO2-containing systems in future works.

Improved oral absorption and anti-lung cancer activity of paclitaxel-loaded mixed micelles

The aim of this study was to establish a paclitaxel (PTX)-loaded mixed micelle delivery system (PTX-TP-M) with vitamin E-TPGS (TPGS) and Plasdone®S-630 Copovidone (PVPS630) as carriers to improve the solubility, oral absorption, and anti-tumor activity of PTX against lung cancer. In this study, PTX-TP-M was prepared using the ethanol thin-film dispersion method followed by characterization of the binary mixed micelles system. The average size of the PTX-TP-M was 83.5 ± 1.8 nm with a polydispersity index of 0.265 ± 0.007 and the drug loading (DL%) and entrapment efficiency (EE%) were 3.09 ± 0.09% and 95.67 ± 2.84%, respectively, which contributed to a high solubility of PTX about 24947-fold increase in water (4.78 ± 0.14 mg/mL). In addition, TEM analysis showed that the PTX-TP-M appeared spherical in structure and was well dispersed without aggregation and adhesion. In vitro release studies showed that the PTX-TP-M displayed a sustained release compared to free PTX in the dialysis bag. The efflux ratio of PTX reduced from 44.83 to 3.52 when formulated as PTX-TP-M; a 92.15% reduction, studied using the Caco-2 monolayer model. The oral bioavailability of PTX also improved by 4.35-fold, suggesting that PTX-TP-M can markedly promote the absorption in the gastrointestinal tract. Using in vitro MTT assays, it was observed that cytotoxicity was markedly increased, and IC50 values of PTX-TP-M (3.14 ± 0.85 and 8.28 ± 1.02 μg/mL) were lower than those of PTX solution (5.21 ± 0.93 and 14.53 ± 1.96 μg/mL) in A549 and Lewis cell, respectively. In vivo anti-tumor studies showed that PTX-TP-M achieved higher anti-tumor efficacy compared with PTX in Lewis bared C57BL/6 mice. Furthermore, a gastrointestinal safety assay also proved the safety of PTX-TP-M. All results demonstrated that the PTX-TP-M exhibited great potential for delivering PTX with increased solubility, oral bioavailability, and anti-cancer activity and this binary mixed micelles drug delivery system has potential to be used clinically.

Fast and accurate inference on gravitational waves from precessing compact binaries

Inferring astrophysical information from gravitational waves emitted by compact binaries is one of the key science goals of gravitational-wave astronomy. In order to reach the full scientific potential of gravitational-wave experiments we require techniques to mitigate the cost of Bayesian inference, especially as gravitational-wave signal models and analyses become increasingly sophisticated and detailed. Reduced order models (ROMs) of gravitational waveforms can significantly reduce the computational cost of inference by removing redundant computations. In this paper we construct the first reduced order models of gravitational-wave signals that include the effects of spin-precession, inspiral, merger, and ringdown in compact object binaries, and which are valid for component masses describing binary neutron star, binary black hole and mixed binary systems. This work utilizes the waveform model known as "IMRPhenomPv2". Our ROM enables the use of a fast reduced order quadrature (ROQ) integration rule which allows us to approximate Bayesian probability density functions at a greatly reduced computational cost. We find that the ROQ rule can be used to speed up inference by factors as high as 300 without introducing systematic bias. This corresponds to a reduction in computational time from around half a year to a half a day, for the longest duration/lowest mass signals. The ROM and ROQ rule are available with the main inference library of the LIGO Scientific Collaboration, LALInference.

Solubilization of Polycyclic Aromatic Hydrocarbons by Single and Binary Mixed Rhamnolipid-Sophorolipid Biosurfactants.

Biosurfactants are promising additives for surfactant enhanced remediation (SER) technologies due to their low toxicity and high biodegradability. To develop green and efficient additives for SER, the aqueous solubility enhancements of polycyclic aromatic hydrocarbons (PAHs; naphthalene, phenanthrene, and pyrene) by rhamnolipid (RL) and sophorolipid (SL) biosurfactants were investigated in single and binary mixed systems. The solubilization capacities were quantified in terms of the solubility enhancement factor, molar solubilization ratio (MSR), and micelle-water partition coefficient (). Rughbin's model was applied to evaluate the interaction parameters (β) in the mixed RL-SL micelles. The solubility of the PAHs increased linearly with the glycolipid concentration above the critical micelle concentration (CMC) in both single and mixed systems. Binary RL-SL mixtures exhibited greater solubilization than individual glycolipids. At a SL molar fraction of 0.7 to 0.8, the solubilization capacity was the greatest, and the MSR and reached their maximum values, and β values became positive. These results suggest that the two biosurfactants act synergistically to increase the solubility of the PAHs. The solubilization capacity of the RL-SL mixtures increased with increasing temperature and decreased with increasing salinity. The aqueous solubility of phenanthrene reached a maximum value at pH of 5.5. Moreover, the mixed RL-SL systems exhibited a strong ability to solubilize PAHs, even in the presence of heavy metal ions. These mixed biosurfactant systems have the potential to improve the performance of SER technologies using biosurfactants to solubilize hydrophobic organic contaminants by decreasing the applied biosurfactant concentration, which reduces the costs of remediation.

Determination and correlation of solubility and thermodynamic properties of eszopiclone in pure and mixed solvents

The solid-liquid equilibrium data of eszopiclone in six pure organic solvents and two binary mixed systems was determined by employing a gravimetric method under atmospheric pressure at temperatures ranging from 288.15K to 328.15K. For each selected solvent, the solubility data of eszopiclone increases with increasing temperature. It was found that composition of mixed solvents has a significant influence on the solubility of eszopiclone, that there exhibits a synergistic effect at some certain composition points for both mixed systems. Experimental solubilities were fitted by different models including the modified Apelblat equation, λh model, CNIBS/R-K model and the Hybrid model, the calculated results were found to agree well with the experimental data. At last, the van't Hoff equation was employed to calculate the thermodynamic parameters of all selected solutions, corresponding results confirm that these dissolving processes are endothermic and entropy-driving.

Development of chitosan graft pluronic®F127 copolymer nanoparticles containing DNA aptamer for paclitaxel delivery to treat breast cancer cells

HER-2/ErbB2/Neu(HER-2), a member of the epidermal growth factor receptor family, is specifically overexpressed on the surface of breast cancer cells and serves a therapeutic target for breast cancer. In this study, we aimed to isolate DNA aptamer (Ap) that specifically bind to a HER-2 overexpressing SK-BR-3 human breast cancer cell line, using SELEX strategy. We developed a novel multifunctional composite micelle with surface modification of Ap for targeted delivery of paclitaxel. This binary mixed system consisting of Ap modified pluronic®F127 and chitosan could enhance PTX loading capacity and increase micelle stability. Polymeric micelles had a spherical shape and were self-assemblies of block copolymers of approximately 86.22 ± 1.45 nm diameter. PTX could be loaded with high encapsulation efficiency (83.28 ± 0.13%) and loading capacity (9.12 ± 0.34%). The release profile were 29%–35% in the first 12 h and 85%–93% after 12 d at pH 7.5 of receiving media. The IC50 doses by MTT assay showed the greater activity of nanoparticles loaded paclitaxel over free paclitaxel and killed cells up to 95% after 6 h. These results demonstrated unique assembly with the capacity to function as an efficient detection and delivery vehicle in the biological living system.

Complex Behaviour of Bile Salts at Various Temperatures Under the Influence of Antidepressant Drug (Imipramine) in Aqueous Solution

The present method was based on the effect of bile salt (Sodium cholate and Sodium deoxy cholate) on the dissolution of Antidepressant drug like Imipramine. Sodium cholate and Sodium deoxycholate is a type of anionic surfactants form mixed micelle with Imipramine and influence its rate of dissolution. The micellization behavior of binary anionic bile salt surfactant mixtures was investigated by conductivity method and various thermodynamical parameters are calculated. The results of the study have been analyzed by using Clint’s, Rubingh’s, and Motomura’s theories for mixed binary systems.

Complex Behavior of Bile Salts (SC and SDC) at Various Temperatures under the Influence of Tricyclic Antidepressant Drug (Imipramine) in Aqueous Solution

Objective: The present method was based on the effect of bile salt (Sodium Cholate (SC) and Sodium Deoxycholate (SDC)) on the dissolution of Antidepressant drug like Imipramine. SC and SDC is a type of anionic surfactants form mixed micelle with Imipramine and influence its rate of dissolution. The micellization behaviour of binary anionic bile salt surfactant mixtures was investigated by conductivity method and various thermodynamical parameters are calculated. The results of the study have been analyzed by using Clint’s, Rubingh’s, and Motomura’s theories for mixed binary systems. Method: The Critical Micelle Concentration (CMC) of the binary mixtures (Bile salt and Drugs) were studied using conductivity measurements, at different mole fractions and different temperatures. Results: The micellization behaviour of binary anionic surfactant and drug mixtures was investigated by conductivity CMC, extent of counter ion binding (α), thermodynamic parameters (ΔG°m, ΔH°m, ΔS°m) and various parameters like cmcid, xid, X1 and the β parameter for micellization process have been reported and discussed. Conclusion: The thermodynamic parameters of the process of micellization have been calculated for each system. ΔG°m is negative and becomes less negative with increase in concentration. This suggests the micellization formation is becomes less spontaneous with increasing temperatures. The entropy of micellization is positive indicated that the micellization process is somewhat entropy dominated.

Investigations on zwitterionic alkylsulfobetaines and nonionic triton X-100 in mixed aqueous solutions: Effect on size, phase separation and mixed micellar characteristics

Zwitterionic sulfobetaine surfactants are widely applied in industries dealing with personal care products, mainly due to an advantage of minimal irritating effects to skin as compared to ionic surfactants. We investigate on the aqueous solution behaviour of zwitterionic surfactant, namely alkyl N,N-dimethyl-3-ammonio-1-propanesulfonate (CnPS, n=10, 12, 14, 16) in pure and mixed state with Triton X-100 (non-ionic surfactant) by using surface tensiometry, dynamic light scattering (DLS) and cloud point measurements. The critical micelle concentration (CMC) for aqueous CnPS solutions decreases with corresponding increase in alkyl chain length and is also accompanied by an increase in aggregation number. The calculated interfacial parameters for binary mixed aqueous systems involving zwitterionic surfactant and TX-100 depict almost independent behaviour of πCMC and Γmax, indicating a non-associative ideal mixing. The calculated interaction parameter (βm) for TX-100+CnPS mixed system reveals insignificant deviation from ideal behaviour as confirmed by calculated values in proximity to zero. As concluded from size measurements using DLS, the apparent hydrodynamic size of the mixed micelles decreases with gradual addition of alkylsulfobetaines due to demicellization of formerly present ellipsoidal aggregates of TX-100. The clouding temperature of formed mixed micelles increases on gradual addition of CnPS due to corresponding increase of ionic charge and accordingly improved solubility. It is assumed that electrically neutral nature of sulfobetaines confines its electrostatic interactions with non-ionic TX-100 and accordingly deters feasible interactions leading to synergism.

Characterization and in vitro biocompatibility of catanionic assemblies formed with oppositely charged dicetyl amphiphiles

In this study, cationic dicetyldimethylammonium bromide (DCB) and anionic dicetyl phosphate (DCP) were mixed to form catanionic assemblies in water, and their colloidal morphology, size, charge characteristics, phase behavior, membrane fluidity, and in vitro biocompatibility are comprehensively investigated for the first time. Our results show that the catanionic DCB and DCP mixtures in water are capable of forming circular vesicles and this binary mixed system expresses the miscibility with deviation from the ideal mixing. Compared to the nanoscale DCB-rich vesicles, the DCP-rich vesicles have smaller size, higher negative zeta potential, higher main transition temperature, and better storage stability. The temperature and molecular cooperativity of the main transition phase for the DCP vesicles can be reduced by an addition of DCB. This work demonstrates that the head groups and the relative composition of the two considered dicetyl amphiphiles remarkably affect the phase behavior, membrane rigidity, encapsulation ability and in vitro biocompatibility of DCB/DCP vesicles. The iso-stoichiometric mixed DCB/DCP vesicle, showing low cytotoxicity, long storage time, and high drug loading, is a potential candidate for the drug delivery system.

Targeted delivery of anticancer drugs by aptamer AS1411 mediated Pluronic F127/cyclodextrin-linked polymer composite micelles

Aptamers are single-stranded RNA or DNA ligands that can specifically bind to various molecular targets with high affinity. Owing to this unique character, they have become increasingly attractive in the field of drug delivery. In this study, we developed a multifunctional composite micelle (CM) with surface modification of aptamer AS1411 (Ap) for targeted delivery of doxorubicin (DOX) to human breast tumors. This binary mixed system consisting of AS1411 modified Pluronic F127 and beta-cyclodextrin-linked poly(ethylene glycol)-b-polylactide could enhance DOX-loading capacity and increase micelle stability. Cellular uptake of CM-Ap was found to be higher than that of untargeted CM due to the nucleolin-mediated endocytosis effect. In vivo study in MCF-7 tumor-bearing mice demonstrated that the AS1411-functionalized composite micelles showed prolonged circulation time in blood, enhanced accumulation in tumor, improved antitumor activity, and decreased cardiotoxicity. In conclusion, aptamer-conjugated multifunctional composite micelles could be a potential delivery vehicle for cancer therapy. From the Clinical EditorIn this study, a multifunctional composite micelle with surface modification of aptamer AS1411 was used for targeted delivery of doxorubicin to human breast tumors, demonstrating significantly higher tumor volume reduction than doxorubicin alone.

Behavior of Sodium Lauroyl Sarcosinate in Solution and Binary Mixtures by Means NMR

Measurements of the 1H and 13C chemical shifts as well as 1H spin–lattice relaxation times of sodium lauroyl sarcosinate (SLAS) in aqueous solutions and mixed binary systems with co-surfactants were carried out at various concentrations. It will be shown that changes in the chemical shifts for the N–CH2 groups in SLAS with increasing surfactant concentration can be used to estimate the ratio pcis/ptrans of cis- and trans-isomers. The relative fraction ptrans of molecules in trans-configurations increases the most in a narrow concentration range 0.007–0.034 mol/l, i.e., at the transition from the monomeric state to the micelle. The ratio pcis/ptrans asymptotically decreases with increasing concentration, reaching a constant value at concentrations significantly above the critical micelle concentration. Thus, the ratio can be related to the process of micellization. If micellization takes place, the cis-isomer starts to transform into trans-isomer because the trans-isomer is more favorable in micelles. Because of the smaller cross section of the polar group region, the trans-conformation can be more easily incorporated into the micelle. In summary, the occurrence of micellar aggregates at low SLAS concentration in mixed systems can be clearly inferred from the nuclear magnetic resonance spectra.

Mixed micellization of gemini and cationic surfactants: Physicochemical properties and solubilization of polycyclic aromatic hydrocarbons

The micellar and surface properties of single as well as equimolar binary mixed systems of some cationic gemini and monomeric ionic surfactants have been studied by conductivity, surface tension and fluorescence measurements at 300K. The critical micelle concentration (CMC), Γmax (maximum surface excess), Amin (minimum surface area per molecule), πcmc (surface pressure at the CMC) and thermodynamic parameters viz. standard Gibbs free energies of adsorption (ΔGads°), standard Gibbs free energies of micellization (ΔGm°) and minimum free energy of the surface (ΔGmin(s)) of gemini with cationic monomeric surfactants were also evaluated. The negative values of ΔGads° and ΔGm° indicate the spontaneity and stability of the mixed micelle. The experimental CMC values are less than the ideal CMC values, indicating negative deviation from ideal behavior for all the equimolar binary surfactant systems. Aggregation number (Nagg) and Stern–Volmer quenching constant (Ksv) have been evaluated by Fluorescence measurement. The solubilization capacities of selected single and equimolar binary surfactant systems toward polycyclic aromatic hydrocarbons (PAHs), i.e., naphthalene, anthracene and pyrene have been evaluated and discussed in terms of the molar solubilization ratio (MSR), the micelle-water partition coefficient (K(m)), the deviation ratio (R), and the free energy of solubilization (ΔGs°) of PAHs. The negative value of ΔGs° shows spontaneity of solubilization process.

Experimental and theoretical approach to mixed surfactant system of cationic gemini surfactant with nonionic surfactant in aqueous medium

The surface and mixed micellization properties of the aqueous binary mixed system of alkanediyl-α, ω-type cationic gemini surfactant, 14–4–14 and conventional nonionic surfactant, Brij-58 in an aqueous medium have been investigated over the entire mole fractions at 298.15K. The critical micelle concentration (cmc) for each mixture have been measured by tensiometric and fluorescence measurements. The solution and adsorption characteristics like composition, activity coefficients and mutual interaction parameters have been computed using different proposed theoretical models like Clint, Rosen, Rubingh, Motomura and Maeda. The strength of interaction of the surfactant is attributed to the sterical and electrical factors on mixed monolayer and micelle formation and of surfactant–surfactant interactions. The micellar aggregation number (Nagg) has also been measured using steady state fluorescence quenching method at a total concentration of ~1mM of pure components as well as their mixtures of different ratios. The micropolarity and binding constant were determined from the ratio of intensity (I1/I3) of peaks of pyrene fluorescence emission spectrum.

A complexation study of 15-crown-5 with Co2+ cation in some pure and mixed organic solvents

The stability constant (log Kf) and the thermodynamic parameters (free energies, enthalpies, and entropies) of the complexation of Co2+ cation with 15-crown-5 (15C5) in acetonitrile-methanol (AN/MeOH), acetonitrile-nitrobenzene (AN/NB), acetonitrile-dichloromethane (AN/DCM) and acetonitrile-1,2-dichloroethane (AN/DCE) binary solvent solutions were calculated from the experimental conductance data at different temperatures. The complexation behavior of the crown ether used in these media was discussed in view of the estimated parameters. In all solvent systems, 15-crown-5 formed a 1: 1 complex with Co2+ cation. The stability order of (Co-15C5)2+ complex in the binary mixed solvents at 25°C was found to be: AN/NB > AN/DCM ≈ AN/DCE > AN/MeOH. In most cases, a non-linear relationship was observed for changes of log Kf of (Co-15C5)2+ complex versus the composition of the binary mixed solvent systems. The experimental results show that the standard thermodynamic parameters of the complexation process change with the nature and composition of the binary solvent solutions.

Temperature Dependant Mixed Micellization Behavior of a Drug-AOT Mixture in an Aqueous Medium

The mixed micellization behavior of an amphiphilic antidepressant drug amitriptyline hydrochloride (AMT) in the presence of the conventional anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) was studied at five different temperatures and compositions by the conductometric technique. The critical micelle concentration (cmc) and critical micelle concentration at the ideal state (cmc id ) values show mixed micelle formation between the components (i.e., drug and AOT). The micellar mole fractions of the AOT (X1) values calculated using the Rubingh, Motomura, and Rodenas models show a higher contribution of AOT in the mixed micelles. The interaction parameter (β) is negative at all temperatures and the compositions show attractive interactions between the components. The activity coefficients (f1 and f2) calculated using the different proposed models are always less than unity indicating non-ideality in the systems. The ΔGm Ө values were found to be negative for all the binary mixed systems. However, ΔHm Ө values for the pure drug as well as the drug-AOT mixed systems are negative at lower temperatures (293.15- 303.15 K) and positive at higher temperatures (308.15 K and above). The ΔSm Ө values are positive at all temperatures but their magnitude was higher at T=308.15 K and above. The excess free energy of mixing (ΔGex) determined using the different proposed models also explains the stability of the mixed micelles compared to the pure drug (AMT) and surfactant micelles.

Application of solubility parameters in a D-sorbitol-based organogel in binary organic mixtures.

The gelation behaviour of a low molecular weight gelator 2,4-(3,4-dichlorobenzylidene)-D-sorbitol (DCBS) in a binary solvent system has been studied. DCBS was soluble in pure ethanol and insoluble in pure methylcyclohexane. However, DCBS formed opaque gels in ethanol-methylcyclohexane mixtures when the methylcyclohexane content varied from 50% to 80%. Within this range, an increase in the amount of methylcyclohexane reduced the gelation time and also caused the minimum gelation concentration to decrease. Scanning electron microscopy showed that the three-dimensional network structures of the xerogels became denser (from tape-like structures to uniform fibres) when the methylcyclohexane content increased from 40% to 80%. The precipitates that formed in 90% and 100% methylcyclohexane had rod-like structures. X-ray diffraction of the xerogels showed that in the gel state, the DCBS gelator had lamellar packing, which was different from the structure of the precipitate. Fourier transform infrared spectroscopy of the xerogels showed that H-bonding was a driving force for the self-aggregation of the DCBS and it was enhanced as the methylcyclohexane content increased. To estimate the gelator-solvent interactions, the Flory-Huggins parameter was calculated for the DCBS gelator in the binary mixed solvent systems. Based on the values of the Flory-Huggins parameter, the gelation behaviours could be grouped into four domains (solution, partial gel, gel and precipitation). This is a simple method to predict the gelation behaviour of DCBS in some mixed solvents.