Article pubs.acs.org/jced
Application of Conductance Study to Analyze Micellization Behavior of Cationic Gemini Surfactants in Water and Water−Ethanol Solvent Mixed Media Katarzyna Łudzik,* Kinga Kustrzepa,* Henryk Piekarski, and Małgorzata Józw ́ iak University of Łódź, Faculty of Chemistry, Department of Physical Chemistry, Pomorska 165, 90-236 Łódź, Poland S Supporting Information *
ABSTRACT: The paper presents the analysis of micellization behavior of cationic gemini surfactants with similar structures with varying atom n umber in spacer: heptylene-1,7-bis(dimethyloctylammonium) bromide (8−7−8) and octylene-1,8bis(dimethyloctylammonium) bromide (8−8−8) in water and water−ethanol solvent mixed media. Experiments were carried out by using conductometric method within the temperature range of 288.15−323.15 K. The values of micellization parameters and thermodynamic functions of aggregation [critical micelle concentration (cmc), the degree of dissociation of micelles (α), enthalpy of micellization (ΔHom), entropy of micellization (ΔSom), Gibbs free energy of micellization (ΔGom] within the temperature range investigated were determined. Based on the investigations performed it has been shown that the systems containing the additives ethanol have a positive value ΔGotrans, a more positive value ΔGom, and a higher value of α and cmc as compared to pure water what confirms that the micellization process is delayed. The less spontaneous micellization behavior was observed for the surfactant with odd number of carbon atoms in spacer: 8−7−8. In this case the value of cmc was higher than the nearest homologues with even number of carbon atoms in spacer (8−8−8 and 8− 6−8 surfactants). At higher temperatures, the differences in aggregation behavior became less visible.
1. INTRODUCTION The persisting interest in dimeric surfactants, as confirmed by about 10 000 international patent specifications, is connected with a high application potential of this group of compounds.1,2 Due to their capabilities to effectively decrease interfacial tension, solubility and emulsifying properties, chelating properties,3 and antibacterial effects,4−6 gemini surfactants are used for soil remediation, as additives to fuels7 and preserving, disinfecting, and washing agents.8 In addition to the conventional uses of gemini surfactants mentioned above, there have appeared new opportunities of their therapeutic applications. The most recent trends include studies carried out on the use of dimeric surfactants as carriers of drugs and genes.9−14 Owing to the wide diversity of these compounds and the possibility of their modification, the number of reports on potential uses of the properties of these surfactants permanently increases.15 One of the more important properties of surfactants and also the feature that characterizes the given system is their capability to form micellar aggregates, whose shape and tendency is determined by the structure of molecule and the composition of solvent. A key role in the formation of associates play the number of atoms in hydrophobic chain, the length and type of the spacer,16−18 the pH values, the ionic strength of solution, organic cosolvent, or temperature.3,19 By changing the conditions one can influence the micellization process to inhibit or accelerate it. There is no doubt that organic cosolvents affect the tendency to form micelles of ionic surfactants via the modification of water−surfactant interactions © XXXX American Chemical Society
by changing the properties of the mixed solvent. Generally, in ethanol-containing mixtures the addiction of the alcohol causes that the structure of water breaks. As a result, the main driving force of aggregation processthe hydrophobic effect decreases and the ability to form hydrogen bond is significantly lower than in case of pure water that influences on micellization process.19−21 However, the micellization tendency of surfactants in mixed media depends also on the structure of surfactants what makes the results unpredictable and attracts attention of researcher. There are some data of the micellization process of surfactants from 8−s−8 group22,23 but there are no reports on the degree of formation of the micelles of 8−s−8 surfactants in aqueous solutions and in the presence of organic cosolvents. One of the more helpful properties allowing one to assess the process of self-association is the degree of dissociation of micelles and the thermodynamics of micellization. Quite simple, reliable and convenient method for investigation of micellization processes of ionic surfactant is conductometric titration. The values of electric conductivity are closely connected with the quantity of ions present in solution and also with their mobility. Therefore, their analysis constitutes a valuable source of information about the progress of association processes in surfactant solutions and also characterizes to some Received: June 12, 2015 Accepted: February 19, 2016
A
DOI: 10.1021/acs.jced.5b00485 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Table 1. Information on Chemicals in This Work chemical name octylene-1,8bis(dimethyloctylammonium) bromide heptylene-1,7bis(dimethyloctylammonium) bromide ethanol a
source
purity
purification method
water mass fractionb
final purity
analysis method
synthesis
Recrystallization, and heating under vacuum at 333 K for minimum 48 h
0.98
NMRc
synthesis
recrystallization and heating under vacuum at 333 K for minimum 48 h
0.96
NMRc
SigmaAldrich
0.998a
none
