Thermodynamics of Micelle Formation of Gemini Surfactants Hexylene

Article pubs.acs.org/jced

Thermodynamics of Micelle Formation of Gemini Surfactants Hexylene-1,6-bis(dimethyloctylammonium bromide) and Dodecylene-1,12-bis(dimethyloctylammonium bromide) by Electric Conductance Mesurements K. Łudzik,* K. Kustrzepa,* and H. Piekarski Department of Physical Chemistry, University of Łódź, Pomorska 165, 90-236 Łódź, Poland S Supporting Information *

ABSTRACT: The subject of this study concerns the aggregation process of cationic gemini surfactants with formulas 8−6−8 and 8−12−8. Conductivity measurements carried out within the temperature range of (288.15−323.15) K made it possible to determine the values of critical micelle concentration and dissociation degree of micelles for the system investigated within this temperature range. Using various models, the basic thermodynamic functions (enthalpy, entropy, and free Gibbs energy of micellization) were determined. The data obtained allowed us to assess their usability and the effect of temperature on the micellization process. It has been shown that an increase in temperature causes a linear decrease in the values of ΔHmic and ΔSmic, which results from the increase in the repellent interaction force between ammonium groups and increase in the disorder of water structure influencing the hydrophobic effect. Slight changes in the free enthalpy indicate the occurrence of enthalpy−entropy compensation. It has been shown that regardless of the model used, the trend of these changes is retained, nevertheless the differences in the values obtained are considerable.

1. INTRODUCTION Surfactants are surface-active compounds that because of their properties resulting from amphiphilic character, have found their use in many fields of industry as washing agents, disinfectants, etc. The structure of gemini surfactants resembles two monomeric surfactants joined to each other. On account of the molecule structure, from these surfactants one can distinguish molecules composed of two amphiphilic fragments joined together by a link at a level of polar groups or nonpolar chains. An increasing interest in surfactants of this group results from the unique properties of these compounds.1−3 More and more literature reports concern the potential application of gemini surfactants to medicine as gene carriers.4−6 The main applications of surfactants are connected with their use in the form of aqueous or aqueous−organic solutions. This explains the great interest in studies carried out to understand, elucidate, and describe the micellization process occurring in both aqueous and aqueous−organic solvents as well as to find a relationship between the surfactant molecule structure and its trend to micellization.7,8 Conductometry is an effective method of investigating the interactions between ions in solution, the basis of which is the measurement of electric conductivity. In the case of aqueous solutions of ionic surfactants, 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 © 2014 American Chemical Society

of association processes in surfactant solutions and also characterizes to some extent the capability of the micelles formed of them to dissociate into ions.8,9 In this study, using the conductometric method, we examined the micellization of gemini surfactants, alkylene-α,ω-bis(dimethylalkylammonium bromides) belonging to the group of cationic gemini surfactants with a symmetric structure.

Figure 1. General formula of alkylene-α,ω-bis(dimethylalkylammonium bromide).

The regular structure of the dimeric surfactant mentioned above allows one to present a general formula of these compounds by means of the following notion: m−s−m, where m indicates the number of carbon atoms in the hydrophobic chain, while s is the number of carbon atoms in the connecting bridge. These compounds stand out from the group of cationic gemini surfactants showing among other things special Received: August 29, 2014 Accepted: November 6, 2014 Published: November 17, 2014 4165

dx.doi.org/10.1021/je500804j | J. Chem. Eng. Data 2014, 59, 4165−4172

Journal of Chemical & Engineering Data

Article

(designed in our Chair) and an automatic bridge for conductivity measurement, type 6440 B from Wayne Kerr (Great Britain). The operating frequency of the bridge was 1 kHz (± 0.005 %), while the variable current voltage was 500 mV (± 1 mV). The use of the bridge described allowed us to measure conductivity values with an accuracy of ± 0.05 %. The temperature stability was provided by a main thermostat (Thermo Haake K40, stability 5·10−2 K). All the solutions were prepared by weight using 3-fold distilled and deionized water, for which the conductivity value (∼1·10−6 S at 298.15 K) was negligible compared to the conductivity values of the solutions. To a three-electrode measurement vessel filled with 30 cm3 of 3-fold distilled and deionized water were added specified volumes of concentrated surfactant solution constituting a titrant. The surfactant solution concentration was selected in this way so that the final concentration exceeded the c.m.c. value. A measured titrant quantity (1 μL) was dosed by a Crison automatic titrating buret and introduced into the measurement vessel through the main neck. A magnetic stirrer was used to agitate the solution in the measurement vessel. Every single addition of the solution entailed a change in conductivity that constituted a measured quantity. The titration procedure described was used for the surfactants investigated within the temperature range of (288.15 to 323.15) K in 5 K intervals. All experimental data are collected in the Supporting Information.

capabilities to solubilize insoluble compounds in water, such as benzene or n-heptane.10 In the conductivity measurements within the temperature range of (288 to 323) K we used compounds 8−6−8 and 8−12−8. So far these compounds have been examined by the densimetric and calorimetric methods.11 Unfortunately, these methods are unsuitable for the determination of the micelle dissociation degree and thereby for the description of the association process with the models designed for ionic surfactants. The aim of this study was to assess the effect of temperature on the thermodynamic parameters of the surfactant micellization with the use of models taking into account the degree of micelle dissociation.

2. EXPERIMENTAL SECTION 2.1. Materials and Procedures. The surfactants investigated included hexylene-1,6-bis(dimethyloctylammonium bromide) and dodecylene-1,12-bis(dimethyloctylammonium bromide) prepared by the synthesis according to the procedure of Zana.12 The general scheme of the equation of gemini surfactants synthesis is shown in Figure 2.

■

RESULTS AND DISCUSSION The dependences of conductivity on molality determined by conductometric titration at 288.15 K to 323.15 K for the aqueous gemini surfactants investigated are presented in Figures 3 and 4. Figure 2. Scheme of the synthesis equation of alkylene−α,ωbis(dimethylalkylammonium bromides).

Compound 8−6−8 was crystallized from the mixture of ethyl acetate and propan-2-ol (10:1), while compound 8−12−8 was synthesized from ethyl acetate. The description of the NMR spectra is given below. 1 H NMR for Hexylene-1,6-bis(dimethylooctyloammonium bromide). 1H NMR (600 MHz, CDCl3) δ = 0.72 (t, 6H, J = 6.9 Hz, 2CH2CH3), 1.05−1.15 (m, 12 H, 6CH2), 1.16−1.26 (m, 8H, 8CH2), 1.38−1.42 (m, 4H, 2CH2), 1.52−1.60 (m, 4H, 2CH2), 1.80−1.88 (m, 4H, 2CH2), 3.22 (s, 12H, 2N(CH3)2), 3.32−3.40 (m, 4H, 2N−CH2), 3.53−3.60 (m, 4H, 2N−CH2) 13 C NMR for Hexylene-1,6-bis(dimethylooctyloammonium bromide). 13 C NMR (150 MHz, CDCl3) δ = 14.0 (CH3), 21.8; 22.6; 22.9; 24.7; 26.4; 29.1; 29.2; 31.6 (16CH2), 51.1 (NCH3), 64.2 (NCH2), 64.8 (NCH2). The description of the NMR spectra is given in a following section. 1 H NMR for Dodecylene-1,12-bis(dimethylooctyloammonium bromide). 1H NMR (600 MHz, D2O): 3.35−3.24 (8H, m, N-okt-1-CH2 i N- dod-1,12- CH2), 3. 09 (12H, s, N−CH3), 1.76−1.65 (8H, br s, N-okt-2-CH2 i N-okt-2,11-CH2), 1.50− 1.24 (36H, m, N-dod-3,4,5,6,7,8,9,10 i N-okt-3,4,5,6,7-CH2), 0.93 (6H, t J = 7,2 Hz, N-okt-8-CH3) ppm. 13C NMR (150 MHz, D2O): 62.67; 67.60; 51.86; 31.60; 29.12; 28.88; 28.69; 28.62; 28.57; 25.74; 25.70; 22.51; 22.04; 13.93 ppm. 2.2. Conductivity Measurements. The conductivity measurement system used in this study consisted of a glass measurement vessel containing three platinum electrodes

Figure 3. Specific conductivity, κ, of 8−12−8 surfactant as a function of concentration at the temperature range 288.15 K to 323.15 K.

As in the case of electrolyte solutions, an increase in temperature results in the increase in the conductivity of surfactant solutions. The trend observed is due to the increase in the mobility of ions as a result of the reduction in the medium resistance caused by changes in the solution viscosity. At the given temperature the conductivity of surfactant is an ascending function of concentration with a characteristic slope change at some concentration (Figure 5). 4166



Article

Figure 4. Specific conductivity, κ, of 8−6−8 surfactants as a function of concentration at temperature range 288.15 K to 323.15 K.

Figure 6. Temperature dependence of micelle ionization degree from specific conductance measurements for of 8−6−8 (■) and 8−12−8 (○) solutions.

momomer region and micelle region Smn and Smic allows one to calculate the dissociation degree of micelles α20−23 and the degree of bonding counter-ions by micelle β: α=

Smic Smn

β=1−α

(1) (2)

The shape of the curve κ = f(m) for 8−6−8 on the solution concentration shows beside the point corresponding to the value of c.m.c. (point 2), the characteristic breakdown point at lower concentrations than that of c.m.c. (point 1) (Figure 5). The occurrence of breakdown in the vicinity of concentration 0.02 mol·dm−3 for surfactant 8−6−8 was observed by Zana.24 Initially, on account of the narrow range of the gemini surfactant solution concentrations, there was observed only the first breakdown that was misinterpreted as a point indicating the process of micellization.24 Further studies within a wider concentration range showed that two characteristic points occurred in the conductivity diagram.25 The position of the second one overlapped with the results of an investigation carried out by other methods. Therefore, the concentration, at which the second characteristic point was observed, was defined as the critical micellization concentration. The first characteristic breakdown was interpreted as a point of aggregation preceding the process of the real micellization. Frindii and coworkers suggested that this region could witness the formation of ionic pairs composed of Br − and the cation of dimethylammonium group or a premicellar aggregation.25 The formation of such pairs has been previously speculated on the basis of the conductivity measurements of aqueous solutions of bolaform surfactant and the surface-tension measurements of other gemini surfactants.26,27 The results obtained indicate that in the case of surfactant 8−6−8, the structural changes mentioned occur regardless of temperature. The presence of two characteristic points for the 8−6−8 system at the similar concentration range was also observed in the course of the dependence Cp,φ = f(m), examined earlier by us.11 For that reason the results of electric conductance measurements might allow a calculation of the thermodynamic

Figure 5. Specific conductivity, κ, of 8−12−8 surfactant (○) and 8− 6−8 (◇) as a function of molality at 298.15 K. In the case of 8−6−8 surfactant two breakdown spots are indicated.

The change observed in the conductivity of aqueous surfactant solutions as a function of concentration results from different degrees of surfactant dissociation. Within the range of lower concentration than the c.m.c., the monomers of surfactants behave as strong electrolytes. On this account each addition of solution results in an increase in the solution conductivity. After exceeding the critical concentration of micellization, the ions of surfactants are formed only as a result of partial dissociation of micelles. Incomplete micelle dissociation into ions and the combination of some counterions with the charged micelle in the Stern layer result in the slowing down of conductivity caused by the increased surfactant quantity in relation to the initial changes produced by the addition of titrant (Figure 5). From the above, it follows that the concentration, at which there was a sudden change in the value of the straight line slope, corresponds to that of c.m.c. Therefore, the two-sided extrapolation of the linear sections of function describing the system before and after exceeding the c.m.c allows one to determine the concentration above which self-association begins13−19 (Figure 6 and Table 1). The knowledge of the straight line slope values describing the 4167



Article

Table 1. Values of Critical Micelle Concentration c.m.c. Obtained from Conductivity and Literature Data Determined by Means of Other Methods11

T /K

conduct.

288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

0.085 0.072 0.065 0.064 0.066 0.062 0.064 0.065

8−6−8

8−12−8

c.m.c./mol kg−1

c.m.c./mol kg−1

densim.11

calorim.11

conduct.

densim.11

calorim.11

0.070 0.063 0.060 0.057 0.055

0.075 0.071 0.065 0.062 0.055 0.052 0.051

0.026 0.025 0.024 0.023 0.022 0.024 0.025 0.027

0.035 0.027 0.025 0.024 0.024 0.029 0.031 0.037

0.026 0.025 0.024 0.023 0.024 0.025 0.026

Standard uncertainty is u(T) = 0.01 K, the combined expanded uncertainties Uc (c.m.c.conduct.) = 0.05 c.m.c. (level of confidence = 0.95).

The literature values of c.m.c. for surfactants 8−6−8 and 8− 12−8 are well consistent with the c.m.c. values obtained experimentally by us as well as by other investigators11,25 (Table 1). The dependence of the critical concentration on temperature obtained, with a clear minimum, is in conformity with the data reported for these and other self-organizing systems.14,28−34 The characteristic course of the function results from the fact that the value of the c.m.c. is the outcome of two competing effects: the first one dominating at lower temperature, is connected with the hydration of polar parts of amphiphile, while the second dominating at higher temperatures, results from the hydrophobic hydration of the surfactant hydrocarbon chains. The formation of salvation sheaths around the hydrophobic heads impedes the self-association process. On this account within the range of lower temperature, one can observe higher values of c.m.c. indicating that the micellization process is impeded. An increase in temperature decreases the trend toward hydrogen-bond formation, which entails a weaker hydration of polar heads and consequently facilitates the formation of micelles. This is manifested with lower values of c.m.c. A further increase in temperature results in the relaxation of the water structure also around the hydration sheaths, which might weaken hydrophobic interactions, and thereby inhibits the micellization process, shifting it toward higher concentrations.9 The area of slight changes in the values of c.m.c. observed within the temperature range of (298.15−323.15) K can show a mutual compensation of the effects mentioned above. The micellization process occurs easier in the case of 8−12− 8 surfactants which is confirmed by a lower c.m.c. as well as more negative free Gibbs energy. It can be explained as a result of stronger repulsion between ammonium groups for a surfactant with shorter spacer chain length (8−6−8) because positively charged groups are closer than in molecule of 8−12− 8 surfactant. It is also worth emphasizing that the c.m.c. value for the 8−12−8 system is less than half of that indicated for the 8−6−8 system. It means that the hydrophobic effect of the spacer chain decreases nonlinearly with the increasing number of carbon atoms. An increase in temperature increases the mobility of molecules, which may also influence the stability of micelles. Despite the fact that changes in the dissociation degree of micelles as a function of temperature are small, they may indicate that at temperatures above 333.15 K the trend toward the decomposition of micelles or the formation of less condensed structures is higher. This observation confirms that the increase in kinetic energy in the system entails the rise of

parameters of the premicellar aggregation process for the 8−6− 8 system. In the case of the 8−12−8 system, the first breakdown in the dependence of conductivity with the surfactants concentration was not observed. Analogically, the course of Cp,φ = f(m) showed only one characteristic point.11 This may result from the fact that the value of c.m.c. for the 8−12−8 system is too low (about 0.025 mol·dm−3) to impede the determination of the first breakdown region that should be expected within a similar range of concentration. The values of α and c.m.c. determined for the systems examined by the conductometric method are presented as a function of temperature in Figures 6 and 7. In the case of the

Figure 7. Temperature dependence of the c.m.c. of 8−6−8 (■) and 8−12−8 (○) in water.

8−6−8 system, the values of the c.m.c. were calculated on the basis of the data before the first breakpoint up to the main c.m.c., S2, and the region where micelle appeared S3. In this case the α value, the micelle region S3, and monomer region S1 were taken into account. From the data presented it follows that the temperature increase favors a slight increase in the dissociation degree of micelles (Figure 6). A little lower dissociation degree of the molecule with chain s = 12 at a range of (283.15 to 308.15) K can suggest that the stability of structures formed by this compound can be greater. 4168



Article

repulsion between positively charged polar groups with a simultaneous decrease in attraction between polar heads and bromide ions. The formation of micelles by the surfactant molecules is inevitably connected with changes in thermodynamic functions. These parameters can be calculated on the basis of the values of c.m.c. determined experimentally with the use of an appropriate model. In our manuscript, in the calculation of ΔGom and ΔHom we used equations taking into account the micelle charge neutralization by the counterions35−37 (model 1) as well as the procedure proposed by R. Zana designed for gemini surfactant with a monovalent counter-ion37 (model 2): The values of the thermodynamic functions obtained on the basis of the above models for ionic surfactants were presented in Figures 8 to 11 as a function of temperatures and were

Figure 10. Thermodynamic parameters for micellization of 8−12−8 as a function of temperature for model 1: ○, ΔHmic; ●, ΔGmic; ◑, TΔSmic.

Figure 8. Thermodynamic parameters of micellization of 8−6−8 as a function of temperature for model 1: □, ΔHmic; ■, ΔGmic; ◨, TΔSmic.

Figure 11. Thermodynamic parameters for micellization of 8−12−8 as a function of temperature for model 2: ○, ΔHmic; ●, ΔGmic; ◑, TΔSmic.

Despite differences in the values of thermodynamic parameters, the use of the assumptions constituting the basis of each of the models described allows one to perform comparative characteristics as well as to draw conclusions concerning the effect of temperature on the self-association of surfactants. A characteristic feature of the micellar system within the temperature range of (288.15−323.15) K, regardless of the model used for calculations, is the linearly decreasing dependences ΔHom = f(T) as well as TΔSom = f(T). The micellization enthalpy trend toward changes with temperature increase confirms the previously reported in literature behavior of both monomeric and gemini surfactant.8,23−30,38,39 A gradual decrease in the value of micellization enthalpy is, first of all, due to electrostatic and hydrophobic interactions that are its components. The energetic effect connected with electrostatic interactions is generally accepted as negative. The energetic effect of hydrophobic interactions results mainly from the transfer of alkyl chains from water to the core of micelles and depends on two contributions: a positive one connected with the destruction of sheath formed by a water molecule around

Figure 9. Thermodynamic parameters for micellization of 8−6−8 as a function of temperature for model 2: □, ΔHmic; ■, ΔGmic; ◨, TΔSmic.

collected in Tables 2 and 3. Other results of calculations of the thermodynamic functions of formation micelles from preaggregates (on the basis of S3/S2 ratio) were presented in the supplementary data). 4169



Article

From the point of view of thermodynamics, the formation of micelles described in this study is spontaneous. The ΔGom values of the systems investigated are negative within the whole temperature range, and their small changes result from the enthalpic−entropic compensation effect. The temperature dependences of the thermodynamic functions obtained on the basis of the models used for the description of conductometric data suggest that the aggregation process is enthalpy driven at higher temperature range. Thus, it follows that changes in the water structures within higher temperature ranges also determine the value of the entropy contribution of the micellization process TΔSom. The decrease in the contact zone of hydrophobic chains with the molecules of solvent occurring during self-association, is inevitably connected with the increase in the system disorder as a result of releasing water molecules surrounding hydrophobic chains. These changes are less visible in the case of systems with weaker hydrophobic bonds between solvent molecules.41 Therefore, in the case of higher temperature, one should expect a decrease in the entropic contribution, which is confirmed by the values of TΔSom obtained experimentally. The different shape of the curve κ = f(m) for 8−6−8 (with the characteristic breakdown point at lower concentrations than that of c.m.c.) allows us to determine the thermodynamic functions of premicellar aggregation. For that reason we calculated the degree of ionization of premicellar aggregates αp as a ratio of straight line slope values after and before the first break point Figure 5.

Table 2. Thermodynamic Functions of the Micellization Processa model 1

model 2

ΔGom

ΔHom

TΔSom

ΔGom

ΔHom

TΔSom

T/K

kJ mol−1

kJ mol−1

kJ mol−1

kJ mol−1

kJ mol−1

kJ mol−1

288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

−27.0 −28.0 −28.4 −28.5 −29.1 −29.7 −29.4 −29.6

35.7 28.9 21.4 13.7 6.2 −1.9 −10.2 −19.0

62.8 56.9 49.8 42.2 35.3 27.2 19.2 10.5

−20.1 −20.8 −20.9 −20.8 −21.3 −21.2 −21.4 −21.5

26.1 21.2 15.7 10.2 4.9 −0.7 −6.5 −12.7

46.2 42.0 36.6 31.0 26.2 20.4 14.8 8.8

ΔGro, free Gibbs energy of micellization, ΔHro, enthalpy of micellization, ΔSor , entropy of micellization for aqueous solutions of surfactant 8−6−8 determined on the basis of ratios S1 (straight line slope values describing monomer region) and S3 (straight line slope values describing micellar region) and the following models: Model 1 for ionic surfactants and model 2 for gemini surfactants with monovalent counter-ion. Standard uncertainty is u(T) = 0.01 K, the combined expanded uncertainties Uc (ΔGor , ΔHor , TΔSor ) = 0.07 (ΔGor , ΔHor , TΔSor ) (level of confidence = 0.95). a

Table 3. Thermodynamic Functions of the Micellization Process Processa model 1

model 2

ΔGom

ΔHom

TΔSom

ΔGom

ΔHom

TΔSom

T/K

kJ mol−1

kJ mol−1

kJ mol−1

kJ mol−1

kJ mol−1

kJ mol−1

288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

−30.4 −30.7 −31.2 −31.5 −31.7 −31.5 −31.6 −31.2

−2.0 −7.7 −13.7 −20.1 −26.6 −33.2 −40.1 −46.9

28.4 23.0 17.4 11.4 5.0 −1.7 −8.5 −15.7

−22.0 −22.2 −22.4 −22.5 −22.6 −22.3 −22.3 −22.0

−7.3 −11.5 −16.0 −20.6 −25.4 −30.0 −34.8 −39.5

15.1 13.3 11.5 9.6 7.4 5.3 3.2 0.6

αp =

S2 S1

(3)

The concentration, above which self-association begins, was determined as an intersection of linear function-described points before and after the first break point. The thermodynamic functions of premicellar aggregation were calculated by the earlier mentioned models for ionic surfactants. Obtained data were collected in Table 4.

ΔGro, free Gibbs energy of micellization, ΔHro, enthalpy of micellization, ΔSor , entropy of micellization within the temperature range of 288.15 K to 323.15 K for aqueous solutions of surfactant 8− 12−8 determined on the basis of conductometric data and the following models: Model 1 for ionic surfactants and model 2 for gemini surfactants with monovalent counter-ion. Standard uncertainty is u(T) = 0.01 K, the combined expanded uncertainties Uc (ΔGor , ΔHor , TΔSor ) = 0.07 (ΔGor , ΔHor , TΔSor ) (level of confidence = 0.95). a

3. CONCLUSIONS The use of various models designed for an ionic surfactant has shown that regardless of the model used, the values of functions TΔSom = f(T) and ΔHom = f(T) show a decreasing trend. The occurrence of the enthalpic−entropic compensation showing small changes in the course of ΔGom = f(T) is also typical. The temperature dependence of the dissociation degree of micelles is linear and shows that an increase in temperature increases the dissociation degree of micelles, which is more visible in the case of a surfactant with a longer spacer. At room temperature the stability of micelles formed by 8−12−8 seems to be higher than that of 8−6−8. The temperature rise causes an increase in the exothermic characteristic of the micellization process as a result of increasing force of electrostatic repulsion and the disappearance of hydrophobic hydration. An increase in the disorder of water structure also appears in the decrease in the micellization entropy. As a result, at higher temperatures the process of micellization can be enthalpy controlled. It was observed that the hydrophobic effect of the linker chain decreases nonlinearly with the increasing number of carbon atoms.

hydrophobic chains, and the other one, negative results from the condensation of alkyl chains in the micelle core. An increase in temperature contributes to a decrease in the values of the first component, practically without any influence on the condensation effect of chains formed in the structures formed. This results from the fact that the process of hydrophobic hydration decays with increasing temperature. On this account the energetic effect of hydrophobic interactions of repelling character becomes more negative at higher temperatures.14,28,38,40 Additionally, the temperature increase is accompanied by an increase in electrostatic interactions of repelling character, which results in the emission of a higher quantity of energy. The sum of the contributions discussed decides that at higher temperatures the value of micellization enthalpy becomes more negative. 4170



Article

Table 4. Values of Premicellization Parametersa model 1

model 2

αp

c.p-m.c.

ΔGom

ΔHom

TΔSom

ΔGom

ΔHom

TΔSom

T/K

αp

mol kg−1

kJ mol−1

kJ mol−1

kJ mol−1

kJ mol−1

kJ mol−1

kJ mol−1

288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

0.71 0.70 0.73 0.74 0.75 0.78 0.78 0.79

0.026 0.020 0.021 0.018 0.017 0.019 0.019 0.021

−23.6 −24.6 −24.5 −25.5 −26.0 −25.3 −25.7 −25.6

39.8 33.6 26.6 19.1 11.5 3.5 −4.6 −13.0

63.5 58.2 51.1 44.7 37.4 28.9 21.1 12.6

−15.3 −15.9 −15.7 −16.2 −16.4 −15.8 −16.1 −15.9

20.3 16.3 11.6 6.7 1.8 −3.2 −8.1 −13.2

35.6 32.2 27.3 22.9 18.3 12.6 7.9 2.7

c.p-m.c., critical premicellar concentration; αp, degree of dissociation of premicellar aggregates) and thermodynamic functions of the premicellization process (ΔGor , free Gibbs energy of premicellization; ΔHor , enthalpy of premicellization; ΔSor , entropy of pre micellization) within the temperature range of 288.15 K to 323.15 K for aqueous solutions of surfactant 8−6−8 determined on the basis of conductometric data and the following models: Model 1 for ionic surfactants and model 2 for gemini surfactants with monovalent counter-ion. Standard uncertainty is u(T) = 0.01 K, the combined expanded uncertainties are Uc (c.p-m.c.) = 0.05·c.p-m.c., Uc(α) = 0.05·α, Uc(ΔGor , ΔHor , TΔSor ) = 0.07 (ΔGor , ΔHor , TΔSor ) (level of confidence = 0.95). a

■

(7) Sohrabi, B.; Moallemi, M.; Amani, R.; Kiasadegh, M. Electrolytecosolvent effects on the properties of micellar and monolayer phases in the cationic-rich region of catanionic mixture: The phase transition between microstructures and nanostructures. Fluid Phase Eq. 2014, 375, 168−175. (8) Chauhan, S.; Jyoti, J.; Sharma, K.; Kumar, K. A conductance study to analyze the effect of organic solvents on micellization behavior of carbohydrate−surfactant system at variable temperatures. Fluid Phase Equil. 2014, 375, 286−292. (9) Kumar, B.; Tikariha, D.; Ghosh, K. K.; Barbero, N.; Quagliotto, P. Effect of polymers and temperature on critical micelle concentration of some gemini and monomeric surfactants. J. Chem. Thermodyn. 2013, 62, 178−185. (10) Rosen, M. J.; Tracy, D. J. Gemini surfactants. J. Surf. Det. 1998, 4, 547−554. (11) Łudzik, K.; Piekarski, H.; Kubalczyk, K.; Wasiak, M. Micellization properties of cationic gemini surfactants in aqueous solution. Thermochim. Acta 2013, 558, 29−35. (12) Zana, R. Alkanediyl-α,ω-bis(dimethylalkylammonium bromide) surfactants: 10. Behavior in aqueous solution at concentrations below the critical micellization concentration: An electrical conductivity study. J. Colloid Interface Sci. 2002, 246, 182−190. (13) Zhang, Q.; Gao, Z.; Xu, F.; Tai, S. Effect of hydrocarbon structure of the headgroup on the thermodynamic properties of micellization of cationic gemini surfactants: An electrical conductivity study. J. Colloid Interface Sci. 2012, 371, 73−81. (14) Alimohammadi, M. H.; Javadian, S.; Gharibi, S. J. H.; TehraniBagha, A. R.; Alavijeh, M. R.; Kakaei, K. Aggregation behavior and intermicellar interactions of cationic Gemini surfactants: Effects of alkyl chain, spacer lengths and temperature. J. Chem. Therm. 2012, 44, 107−115. (15) Rao, K. S.; Singh, T.; Trivedi, T. J.; Kumar, A. Aggregation behavior of amino acid ionic liquid surfactants in aqueous media. J. Phys. Chem. B 2011, 115, 13847−13853. (16) Rehman, N.; Khan, A.; Bibi, I.; Siddiq, M. Micellar parameters of diblock copolymers and their interactions with ionic surfactants. Chin. J. Polym. Sci. 2012, 30, 217−226. (17) Wang, X.; Wang, J.; Wang, Y.; Ye, J.; Yan, H.; Thomas, R. K. Micellization of a series of dissymmetric gemini surfactants in aqueous solution. J. Phys. Chem. B 2003, 107, 11428−11432. (18) Din, K.; Rub, M. A.; Naqvi, A. Z. Mixed micelles of amphiphilic drug promethazine hydrochloride and surfactants (conventional and gemini) at 293.15 to 308.15 K: Composition, interaction and stability of the aggregates. J. Colloid Interface Sci. 2011, 354, 700−708. (19) Tiwari, A. K.; Sowmiya, S. M.; Saha, S. K. Study on premicellar and micellar aggregates of gemini surfactants with hydroxyl substituted

ASSOCIATED CONTENT

S Supporting Information *

Tables with conductivity data and one table with thermodynamic functions. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Funding

This work was partially supported by the University of Lodz− Young Investigators Project. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Shirai, A.; Sumitomo, T.; Yoshida, M.; Kaimura, T.; Nagamune, H.; Maeda, T.; Kourai, H. Synthesis and biological properties of gemini quaternary ammonium compounds, 5,5′-[2,2′-(α,ω-polymethylnedicarbonyldioxy) diethyl]bis-(3-alkyl-4-methylthiazolium iodide) and 5,5′-[2,2′-(p- phenylenedicarbonyldioxy)diethyl]bis(3alkyl-4-methylthiazolium bromide). Chem. Pharm. Bull. 2006, 54, 639−645. (2) Tan, H.; Xiao, H. Synthesis and antimicrobial characterization of novel L-lysine gemini surfactants pended with reactive groups. Tetrahedron Lett. 2008, 49, 1759−1761. (3) Laatiris, A.; El Achouri, M.; Infante, M. R.; Bensouda, Y. Antibacterial activity, structure and CMC relationships of alkanediyl α,ω-bis(dimethylammonium bromide) surfactants. Microbiol. Res. 2008, 163, 645−650. (4) He, Y.; Shang, Y.; Shao, S.; Liu, H.; Hu, Y. Micellization of cationic gemini surfactant and its interaction with DNA in dilute brine. J. Col. Int. Sci. 2011, 358, 513−520. (5) Kirby, A. J.; Camilleri, P.; Engberts, J. B. F. N.; Feiters, M. C.; Nolte, R. J. M.; Söderman, O.; Bergsma, M.; Bell, P. C.; Fielden, M. L.; GarcíaRodríguez, C. L.; Guédat, P.; Kremer, A.; McGregor, C.; Perrin, C.; Ronsin, G.; van Eijk, M. C. P. Gemini surfactants: New synthetic vectors for gene transfection. Angew. Chem. Int. Ed. 2003, 42, 1448− 1457. (6) Wang, C.; Li, X.; Wettig, S. D.; Badea, I.; Foldvari, M.; Verrall, R. E. Investigation of complexes formed by interaction of cationic gemini surfactants with deoxyribonucleic acid. Phys. Chem. Chem. Phys. 2007, 9, 1616−1628. 4171



Article

and its dynamic adsorption on sandstone. J. Phys. Chem. B 2008, 112, 15320−15326. (40) Bai, G.; Yan, H.; Thomas, R. T. Microcalorimetric studies on the thermodynamic properties of cationic gemini surfactants. Langmuir 2001, 17, 4501−4504. (41) Lumry, R.; Rajender, S. Enthalpy−entropy compensation phenomena in water solutions of proteins and small molecules: A ubiquitous property of water. Biopolymers 1970, 9, 1125−1227.

spacers in aqueous solution using a probe showing TICT fluorescence properties. J. Photochem. Photobiol. A: Chem. 2011, 223, 6−13. (20) Evans, H. C. Alkyl sulphates. Part I. Critical micelle concentrations of the sodium salts. J.Chem. Soc. 1956, 579−586. (21) Zana, R. Ionization of cationic micelles: Effect of the detergent structure. J. Colloid Interface Sci. 1980, 78, 330−337. (22) Bhattacharya, S.; Haldar, J. Thermodynamics of micellization of multiheaded single-chain cationic surfactants. Langmuir 2004, 20, 7940−7947. (23) Del Castillo, J. L.; Suarez − Filloy, M. J.; Castedo, A.; Svitova, T.; Rodriguez, J. R. Some physicochemical properties of TTAB− butanol micellar aqueous solutions. J. Phys. Chem. B 1997, 101, 2782− 2785. (24) Zana, R.; Benrraou, M.; Rueff, R. Alkanediyl-α,ω-bis(dimethylalky1ammonium bromide) surfactants. 1. Effect of the spacer chain length on the critical micelle concentration and micelle ionization degree. Langmuir 1991, 7, 1072−1075. (25) Frindi, M.; Michels, B.; Lévy, H.; Zana, R. Alkanediyl α,ωbis(dimethylalkylammonium bromide) surfactants. 4. Ultrasonic absorption studies of amphiphile exchange between micelles and bulk phase in aqueous micellar solution. Langmuir 1994, 10, 1140− 1145. (26) Devínsky, F.; Lacko, I.; Imam, T. Relationship between structure and solubilization properties of some bisquaternary ammonium amphiphiles. J. Colloid Interface Sci. 1991, 143, 336−342. (27) Devínsky, F.; Masárová, L.; Lacko, I. Surface activity and micelle formation of some new bisquaternary ammonium salts. J. Colloid Interface Sci. 1985, 105, 235−239. (28) Grosmaire, L.; Chorro, M.; Chorro, C.; Partyka, S.; Zana, R. Alkanediyl-α,ω-bis(dimethylalkylammonium bromide) surfactants: 9. Effect of the spacer carbon number and temperature on the enthalpy of micellization. J. Colloid Interface Sci. 2002, 246, 175−181. (29) Paula, S.; Süs, W.; Tuchtenhagen, J.; Blume, A. Thermodynamics of micelle formation as a function of temperature: A high sensitivity titration calorimetry study. J. Phys. Chem. 1995, 99, 11742− 11751. (30) Király, Z.; Dekány, I. A thermometric titration study on the micelle formation of sodium decyl sulfate in water. J. Colloid Interface Sci. 2001, 242, 214−219. (31) Kim, H. U.; Lim, K. H. Description of temperature dependence of critical micelle concentration. Bull. Korean Chem. Soc. 2003, 24, 1449−1454. (32) Galán, J.; Rodriguez, J. R. Thermodynamic study of the process of micellization of long chain alkyl pyridinium salts in aqueous solution. J. Therm. Anal. Calorim. 2010, 101, 359−364. (33) Wettig, S. D.; Verrall, R. E. Thermodynamic studies of aqueous m−s−m gemini surfactant systems. J. Colloid Interface Sci. 2001, 235, 310−316. (34) Fisicaro, E.; Compari, C.; Duce, E.; Contestabili, C.; Viscardi, G.; Quagliotto, P. First evaluation of the thermodynamic properties for spheres to elongated micelles transition of some propanediyl-α,ωbis(dimethylalkylammonium bromide) surfactants in aqueous solution. J. Phys. Chem. B 2005, 109, 1744−1749. (35) Bai, G.; Lopes, A. N.; Bastos, M. Thermodynamics of micellization of alkylimidazolium surfactants in aqueous solution. J. Chem. Therm. 2008, 40, 1509−1516. (36) Perron, G.; Côté, J. F.; Lambert, D.; Pageau, J.; Desnoyers, J. E. Volume and heat capacity of model non-aqueous self-assembly systems. J. Sol. Chem. 1994, 23, 121−133. (37) Zana, R. Critical micellization concentration of surfactants in aqueous solution and free energy of micellization. Langmuir 1996, 12, 1208−1211. (38) Grosmaire, L.; Chorro, M.; Chorro, C.; Partyka, S.; Lagerge, R. S. Micellar structure of gemini cationic surfactants: Influence of the spacer length. Thermochim. Acta 2001, 379, 255−260. (39) Páhi, A. B.; Király, Z.; Dudás, Á .J.; Purkás, S.; Vágó, Á . Thermodynamics of micelle formation of the counter-ion coupled gemini surfactant bis(4-(2-dodecyl)benzenesulfonate)−Jeffamine salt 4172


Thermodynamics of Micelle Formation of Gemini Surfactants Hexylene

Recommend Documents