Micellization and Adsorption Properties of New Cationic Gemini

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Micellization and Adsorption Properties of New Cationic Gemini Surfactants Having Hydroxyisopropyl Group Ziyafaddin H. Asadov,† Gulnara A. Ahmadova,† Ravan A. Rahimov,*,†,‡ Seyid-Zeynab F. Hashimzade,† Etibar H. Ismailov,† Nahida Z. Asadova,§ Samira A. Suleymanova,† Fedor I. Zubkov,∥ Ayaz M. Mammadov,† and Durna B. Agamaliyeva† †

Institute of Petrochemical Processes of Azerbaijan National Academy of Sciences, Hojaly ave. 30, AZ 1025, Baku, Azerbaijan Department of Chemical Engineering, Baku Engineering University, Hasan Aliyev str. 120, Baku, Absheron AZ0101, Azerbaijan § Faculty of Biology, Baku State University, Z. Xalilov str. 23, Az 1148 Baku, Azerbaijan ∥ Organic Chemistry Department, Faculty of Science, Peoples’ Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya St., Moscow, 117198, Russian Federation

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‡

S Supporting Information *

ABSTRACT: A series of cationic gemini surfactants, N,N′-bis(alkyl)-N,N′-bis(2hydroxypropyl)ethylenediammonium dibromide, [CnH2n+1(CH3CH(OH)CH2)NH(CH2)2NH(CH2CH(OH)CH3)CnH2n+1]Br2 (where n is the tail chain length, n = 9, 12, and 14), referred to as CnC2Cn[iso-Pr(OH)] was synthesized. Via conductometric and tensiometric methods, at different temperatures (283 to 313 K), specific electrical conductivities and surface tensions of the aqueous solutions of these cationic gemini surfactants were determined. According to the obtained values, micellization and adsorption parameters such as critical micellization concentration (CMC), maximum surface excess (Γmax), minimal cross sectional surface area of surfactant polar group (Amin), adsorption efficiency (pC20), surface pressure (π), and binding degree of counterion (β) were calculated. The values of standard Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were also computed. Via the dynamic light scattering method, diameters of aggregates of the synthesized cationic gemini surfactants were determined in water. It was established that the diameters of these aggregates decrease with a temperature rise. Antibacterial properties of the synthesized cationic surfactants against sulfate-reducing bacteria (SRB) were studied.

1. INTRODUCTION In recent years, the attention of researchers has been focused on gemini surfactants, which are also termed surfactants with dialkyl groups. In gemini surfactants, there are two hydrophobic and two hydrophilic groups. These hydrophilic groups are bridged between each other. The groups linking them are called spacers.1,2 Gemini surfactants are different from one another by hydrophobic chain length, hydrophilic group nature, and spacer group length and nature. Gemini surfactants have some advantages over surfactants with monoalkyl groups of similar structure. Thus, these surfactants possess a low CMC, a small surface tension value, a good wetting capacity, a low Krafft temperature, and effective rheological properties.3−5 From this point of view, obtaining and studying new kinds of gemini surfactants is of scientific and practical interest.6 The gemini surfactants studied most of all are of the following structure: [CnH2n+1(Alk)2N(CH2)sN(Alk)2CnH2n+1]Br2, where s = 2− 10, n = 10−18, Alk = Me, Et, Pr, Bu. The surfactants of this type are abbreviated as m-s-m(Alk). As is seen from the formula, in such surfactants, when varying the length of the alkyl chain, the length of the spacer chain, and © XXXX American Chemical Society

the nature and length of the alkyl group in the hydrophilic part, it is possible to change properties of the surfactants.2,7 The gemini surfactants containing a hydroxyl group may be divided into two parts:8−11 (1) the gemini surfactants having an OH fragment in the headgroup and (2) the gemini surfactants having fragments with OH groups in the spacer. Using various methods, Huang et al.12 have studied properties of the 12-s12(OH) type gemini surfactants where two −CH2CH2OH groups are linked to a nitrogen atom in the headgroup, to form aggregates. It was established that, in these surfactants, distinct from the surfactants where the methyl group is connected to the nitrogen atom, hydrogen bonding between head-groups is observed and propensity to self-assembly is much stronger. The formation of hydrogen bonds increases elasticity between adsorption layers and, as a result, enables the obtainment of stable emulsions and foams. Borse et al.13,14 have studied surface tension and specific electric conductivity properties of the 12-s-12(OH) type cationic surfactants having methyl and Received: September 13, 2018 Accepted: February 6, 2019

A

DOI: 10.1021/acs.jced.8b00815 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Specification of Chemical Samples final mole fraction purity

analysis method

none recrystallization

>95%

synthesis

recrystallization

>96%

NMR,a IRb NMR, IR

synthesis

recrystallization

>97%

NMR, IR

synthesis

recrystallization

>95%

NMR, IR

chemical name 1-bromononane 1-bromododecane 1-bromotetradecane Propylene oxide ethylenediamine N,N′-Bis(2-hydroxypropyl)ethylenediamine N,N′-bis(nonyl)-N,N′-bis(2-hydroxypropyl) ethylenediammonium bromide N,N′-bis(dodecyl)-N,N′-bis(2-hydroxypropyl) ethylenediammonium bromide N,N′-bis(tetradecyl)-N,N′-bis(2-hydroxypropyl) ethylenediammonium bromide

source

initial mass fraction purity

CAS no.

>99%

693-58-3

none

>98% >97% >99%

143-15-7 112-71-0 75-56-9

none none none

≥99%

107-15-3

Alfa Aesar GmbH & Co KG Alfa Aesar Sigma-Aldrich “Organic Synthesis” factory Alfa Aesar synthesis

purification method

a

Nuclear magnetic resonance. bInfrared spectroscopy.

Scheme 1. Reaction Scheme of the Synthesis of N,N′-Bis(2-hydroxypropyl)ethylenediamine

Scheme 2. Synthesis of Cationic Gemini Surfactants by Interaction of N,N′-Bis(2-hydroxypropyl)ethylenediamine with 1Bromoalkanes

(Alfa Aesar GmbH & Co. KG, Germany), 1-bromododecane (Alfa Aesar, England), and 1-bromotetradecane (SigmaAldrich, Japan) of analytical grade were used. Information on the chemicals, their purities, and suppliers is given in Table 1. 2.2. Method of N,N′-Bis(2-hydroxypropyl)ethylenediamine Synthesis. N,N′-bis(2-hydroxypropyl)ethylenediamine was synthesized through interaction of ethylenediamine with PO at a 1:2 molar ratio according to the following scheme (Scheme 1). To synthesize N,N′-bis(2-hydroxypropyl)ethylenediamine, 0.1 mol of ethylenediamine was entered into a flat-bottom flask, and 0.2 mol of PO was added to it. The reaction was conducted at room temperature, in a nitrogen atmosphere over 24 h stirring with a magnetic mixer. As the reaction is exothermal, the flask was placed into a water bath, and in this way, a high temperature was prevented. Thus, generation of byproducts did not take place. The yield of the reaction product was 95%. It is a white paste-like substance. It dissolves well in water, ethanol, acetone, ethyl acetate, and CCl4 and partially in hexane. The structure of the synthesized N,N′bis(2-hydroxypropyl)ethylenediamine was confirmed by methods of NMR and IR spectroscopy. The spectra are given in Figures S1 and S2 (Supporting Information). 2.3. Synthesis of Cationic Gemini Surfactants Based on N,N′-Bis(2-hydroxypropyl)ethylenediamine. A total of 0.025 mol of N,N′-bis(2-hydroxypropyl)ethylenediamine and 25 mL of hexane were poured into a flat-bottom two-neck flask. After formation of a homogeneous mixture, 0.055 mol of 1-bromononane (1-bromododecane or 1-bromotertadecane) was added to it. The reaction was carried out in a flask equipped with a magnetic stirrer, a reflux condenser, and a heater over 18−20 h at the temperature of the boiling mixture.

hydroxyethyl groups at the nitrogen atom of the headgroup. They have established that the values of CMC and micelle dissociation degree decrease with a rise of polarity of the headgroup, but with an elongation of the spacer chain, the mentioned values increase. As is seen, with a rise in polarity of the headgroup in the surfactant molecules, their properties are improved still more. There is an option to change properties of the surfactant under the action of not only ethylol but also the isopropylol group.15 However, in the literature, the gemini surfactants containing a headgroup having an isopropylol fragment at the nitrogen atom are actually not described. At the same time, synthesis of the surfactants containing an isopropylol group is easier and simpler.16 Moreover, in the case of the surfactants having an isopropylol fragment in the headgroup, effective petroleum-collecting, antibacterial, and other properties are observed.15,17−19 From this standpoint, the submitted article is dedicated to obtaining new-class gemini surfactants containing an isopropylol fragment, studying of their colloidal-chemical properties, as well as calculation of thermodynamic parameters of micellization and adsorption processes. Bactericide properties of the obtained gemini surfactants against SRB are also investigated.

2. EXPERIMENTAL PROCEDURES 2.1. Reagents and Instrumentation. Spectra of 1H NMR and 13C NMR were recorded using a Bruker TOP SPIN spectrometer (300.13 and 75.46 MHz) with chemical shifts (δ in ppm) downfield from TMS using such a solvent as DMSOd6. IR spectra were registered by ALPHA FT-IR spectrometer (Bruker) using KBr disks. Propylene oxide (PO) was a product of the “Organic Synthesis” factory (Sumgayit, Azerbaijan). Ethylenediamine (Alfa Aesar, Great Britain), 1-bromononane B



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doses of 15, 75, and 150 mg/kg. Incubation of the system was made at a contact time of 3.0 h; all of the systems were cultured in specific media for SRB over 21 days at a temperature of 303 K.

A scheme of the obtainment of the surfactants may be presented as in Scheme 2. To isolate the synthesized gemini surfactant from the reaction mixture, vacuum distillation was performed. In this way, the gemini surfactant was separated from the solvent and unreacted 1-bromalkane. To purify the synthesized gemini surfactants, they were recrystallized from acetone three times. The yield of the obtained gemini surfactants equaled 93−95%. They dissolve well in ethanol, acetone, and ethyl acetate and partially in water. The purity degree of the cationic gemini surfactants was determined by methods of NMR and IR spectroscopy. The NMR and IR spectra of the surfactants and their identification are given in Figures S4−S12 (Supporting Information). 2.4. Surface-Tension Measurements. The values of surface tension at the border of aqueous solutions of the synthesized cationic gemini surfactants with air were determined using a KSV Sigma 702 tensiometer (Finland), functioning according to the ring detachment method with an accuracy of ±0.1 mN/m. For preparing these solutions, deionized water was used. The surface tension of this water at the border with air at 298 K equals 72.1 mN/m. The measurements were conducted at 283, 293, 303, and 313 K with a temperature deviation ±0.01 K. For maintaining the needed temperature, water was circulated via the jacket of the container.17 2.5. Electrical Conductometric Measurements. Specific electrical conductivity (κ) of the aqueous solutions of the purified cationic gemini surfactants was measured using an “ANION 4120” (Russian Federation) conductometer.17 The range of these measurements was 10−4 S/m to 10 S/m with a relative error of no more than ±2%. Temperature variation was in the range from 273 up to 373 K. To carry out measurements of specific electrical conductivity, aqueous solutions of the gemini surfactants were prepared at various concentrations in the interval 0.001−2%. The solutions of these surfactants were thermostated at a necessary temperature in a water bath (deviations were no more than ±0.1 K). After each dilution, measurements were made 3 min later. An average value of three to five measurements was taken. In these measurements, bidistillate water was used. Specific electrical conductivity of this water had a value in the range 1.2−1.5 μS/cm at 298 K. 2.6. Dynamic Light Scattering (DLS) Measurements. Dynamic light scattering (DLS) measurements were performed via particle size analyzer (HORIBA LB-550, Japan). The interval of size measurements was from 1 nm up to 6 μm. The light source was a 650 nm laser diode of power 5 mW. The measurements were conducted three times in the temperature range 293−323 K. To estimate hydrodynamic diameter (dh), the Stokes−Einstein equation (dh = kBT/ (3πηD) was applied, D being the diffusion coefficient; kB, the Boltzmann constant; and η, solvent viscosity at absolute temperature T.20 To carry out DLS measurements, three concentrations were taken: 0.1, 0.2, and 0.3%. 2.7. Bactericidal Effectiveness Activity against Sulfate-Reducing Bacteria. The bactericide effectiveness of the synthesized gemini surfactants against SRB growth was studied in accordance with the serial dilution method. The used water was put to a microbial inhibition test. This test was performed according to ASTM D4412-84.21 A growth of about 1 000 000 bacteria cells in 1 g of water was reached. The synthesized gemini surfactants were tested as a bactericide against SRB at

3. RESULTS AND DISCUSSION 3.1. Surface Properties of Synthesized Gemini Surfactants. 3.1.1. Critical Micelle Concentration (CMC). Surface tension values of the aqueous solutions of the synthesized cationic gemini surfactants at the border with air were determined at different temperatures (283, 293, 303, and 313 K), and γ−f(C) plots were built (Figures 1−3 or

Figure 1. Surface tension vs concentration plot of C9C2C9[isoPr(OH)] at different temperatures. Temperature, K: (1) 283, (2) 293, (3) 303, (4) 313.


Supporting Information Tables S1−S4). As is seen from these plots, the surface tension values for these surfactants become stabilized after a certain concentration. This indicates full micellization at these concentrations. This concentration corresponds to CMC. The CMC values for all three gemini surfactants were determined at four different temperatures, and these values are listed in Table 2. As is evident from the table, with a temperature increase, the CMC value of the synthesized cationic gemini surfactants decreases. This decrease of CMC with a temperature increase is related to dehydration at the C



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ethylol and propylol groups, the CMC values are lowered when temperature rises. The CMC value of the similar monomer-type surfactants containing an isopropylol group is smaller than the value for surfactants having an ethylol group. When the number of ethylol groups bonded to a nitrogen atom rises, the CMC value decreases still more.13,14 As is seen from Table 2, when the length of the alkyl chain in the synthesized gemini surfactants is increased, the values of the CMC are lowered, owing to more intensive hydrophobic interactions between the surfactant molecules and micellar core. This situation is observed in the case of similar surfactants with the respective monoalkyl chain.22,23 3.1.2. Efficiency (pC20). The negative logarithmic value of the surfactants concentration (C20) required lowering of the surface tension at the water−air border by 20 mN/m, which is called adsorption efficiency. It is expressed as pC20. The adsorption efficiencies of the synthesized cationic gemini surfactants are shown in Table 2. As is apparent from the table, the values of pC20 for the obtained gemini surfactants vary in the range 4.19−4.97. The pC20 value decreases as temperature rises. If the pC20 value of the C12C2C12[iso-Pr(OH)] gemini surfactant is compared with that of dodecylisopropylol ammonium bromide,22 it will be clear that the pC20 value of the gemini surfactant is higher. In comparison with dodecylethylolisopropylol ammonium bromide, the values of pC20 at the same temperature are very close to each other.22 When the alkyl chain of the obtained cationic gemini surfactants becomes elongated, the pC20 value augments. Therefore, elongation of the alkyl chain brings about a greater tendency of the surfactant to be adsorbed at the water−air interface. A similar regularity is observed in the case of other gemini surfactants.24,25 3.1.3. Effectiveness or Surface Pressure (πCMC). The surface pressure values were computed using the following formula: πCMC = γ0 − γCMC, where γ0 is the surface tension at the border of water with air in the absence of surfactants and γCMC is the surface tension value at the CMC. In Table 2, the values of the surface pressure of the synthesized cationic gemini surfactants are given at different temperatures. As is evident from the table,


hydrophilic groups of the surfactants molecules. If, with a temperature increase, the CMC value were increased, it would be related to the destruction of water aggregates near the hydrophobic fragments. Thus, of these two possible and opposite processes, a prevalent one will determine the character of the CMC variation in the given temperature interval. Therefore, in the case of the synthesized surfactants, the first phenomenondehydration near the hydrophilic groupsis dominant, and this process continues in the studied temperature interval.7 In the headgroup of butanediyl-1,4-bis(dodecyldialkyl)ammonium bromide-type surfactants, an increase of alkyl group volume in the series methyl-, ethyl-, propyl-, and butyl- causes a decrease in CMC.7 In the case of the surfactants having methyl- and ethyl fragments in the headgroup, with a temperature increase from 287.15 to 318.15 K, the CMC decreases at the beginning of this temperature range, then rises.7 But, in the case of the surfactants with propyl and butyl fragments, the CMC decreases in most of that temperature range and only then increases.7 In the case of the surfactants containing both

Table 2. Surface Activity Parameters (Temperature, T; Critical Micelle Concentration, CMC; Equilibrium Surface Tension at the CMC, γCMC; Effectiveness, πCMC; Efficiency, pC20; Maximum Surface Excess, Γmax; Minimum Surface Area, Amin; Degree of Counterion Binding to Micelles, β; Free Energy of Micellization, ΔGmic ° ; Free Energy of Adsorption, ΔGad ° ) of the Synthesized Gemini Surfactants at 283, 293, 303, and 313 Ka surfactants C9C2C9[iso-Pr(OH)]

C12C2C12[iso-Pr(OH)]

C14C2C14[iso-Pr(OH)]

T, K

β

283 293 303 313 283 293 303 313 283 293 303 313

0.55 0.53 0.51 0.48 0.52 0.50 0.46 0.43 0.49 0.44 0.40 0.36

CMC × 103, mol/kg 1.68b 1.45 1.27 1.07 0.93 0.73 0.62 0.56 0.84 0.66 0.53 0.47

1.69c 1.44 1.26 1.05 0.91 0.74 0.62 0.55 0.82 0.65 0.53 0.45

Γmax × 1010, mol/cm2 Amin, Å2 0.94 0.82 0.73 0.66 1.16 1.08 1.02 0.93 1.01 0.92 0.85 0.79

177.4 201.7 226.7 250.5 142.9 153.5 162.5 177.8 165.2 180.6 194.8 210.6

π, mN/m

pC20

γCMC, mN/m

ΔG°mic, kJ/ mol

ΔG°ad, kJ/ mol

43.4 42.7 41.2 40.1 46.3 45.8 45.0 43.7 43.3 42.1 41.5 40.7

4.19 4.40 4.62 4.88 4.35 4.47 4.64 4.82 4.34 4.54 4.74 4.97

30.9 30.1 30.0 29.4 28.0 27.0 26.2 25.8 31.0 30.7 29.7 28.8

−51.38 −52.98 −54.40 −55.27 −52.88 −54.68 −55.14 −55.76 −51.81 −51.99 −52.41 −52.46

−56.01 −58.17 −60.03 −61.32 −56.86 −58.92 −59.55 −60.44 −56.12 −56.57 −57.27 −57.62

a The standard uncertaintiesu are u(T) = 0.01 K and u(p) = 10 kPa. The combined expanded uncertainties Uc are Uc(β) = 0.005, Uc(CMC) = 2 × 10−5 mol/kg, Uc(Γmax × 1010) = 0.01 mol/cm2, Uc(Amin) = 0.5 Å2, Uc(π) = 0.1 mN/m, Uc(pC20) = 0.02, Uc(γ) = 0.1 mN/m, and Uc(ΔG°) = 0.03 kJ/mol (0.95 level of confidence). bThe CMC value is determined by surface tension measurements. cThe CMC value is determined by specific electroconductivity measurements.

D



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the values of the surfactants surface pressures are reduced as temperature is raised. When the alkyl chain length in the obtained gemini surfactants is elongated from C9 to C14, at first, the value of surface pressure rises then decreases. For the gemini surfactants with a C12 alkyl chain, the πCMC value is higher. 3.1.4. Maximum Surface Excess (Γmax). Maximum surface excess (Γmax) characterizes the surface area occupied by surfactant molecules at the unit area of the interface. This quantity varies depending on the length of the hydrophobic chain, nature and structure of the hydrophilic group as well as temperature. The Γmax values were computed according to the surface tension isotherm using the Gibbs equation:26 Γmax = −

dγ 1 lim nRT C → CCMC d ln C

(1)

Figure 4. Dependence of specific electrical conductivity on concentration of C9C2C9[iso-Pr(OH)] at different temperatures. Temperature, K: (1) 283, (2) 293, (3) 303, (4) 313.

where dγ/(d ln C) denotes surface activity at a certain absolute temperature T and R is the universal gas constant. From Table 2, it may be seen that the Γmax value decreases with a temperature increase. In the case of gemini surfactants with an alkyl chain length of C12, the Γmax value is higher as compared with the other surfactants. As temperature increases, thermal motion of the surfactant molecules is intensified, and packing capacity becomes deteriorated. As a result, the number of the surfactant molecules adsorbed on a unit area, i.e., the Γmax value, becomes lowered. 3.1.5. Minimum Surface Area (Amin). When an area of minimal surface of a polar group is spoken about, a minimum surface area occupied by one molecule during adsorption at the interface is meant. This parameter is calculated by the formula shown below: A min = 1016 /NA Γmax

(2) Figure 5. Dependence of specific electrical conductivity on concentration of C12C2C12[iso-Pr(OH)] at different temperatures. Temperature, K: (1) 283, (2) 293, (3) 303, (4) 313.

In Table 2, the Amin values of the synthesized gemini surfactants are given at various temperatures. As is seen from the table, with a temperature increase, the Γmax value is lowered. So, the Amin value increases. It is known that, in the case of gemini surfactants, with an elongation of the alkyl chain, the Amin value augments. However, for the synthesized gemini surfactants, as the alkyl chain length increases from C9 to C12, the Amin value decreases, but at the transition from C12 to C14, the value of Amin starts to increase. A similar regularity is observed in the case of surfactants of other classes, too.27,28 Small values of Amin indicate that the molecules of that surfactant are placed at the interface more tightly and compactly. Among main factors impacting the Amin value, nature and structure of the polar group of surfactant should be named. In gemini surfactants, with an elongation of the spacer chain and with an increase of the number of hydroxy groups, the Amin value rises.13 In the case of cationic-type gemini surfactants, when methyl groups linked to the nitrogen atom in the polar group are replaced by ethylol groups, an increase of the Amin value is observed.14 Similarly, in conventional cationic surfactants, when the ethylol group in the polar fragment is substituted by a isopropylol group, an increase in the Amin value takes place.23 3.2. Specific Electrical Conductivity. The values of specific electrical conductivity values of aqueous solutions of the synthesized gemini surfactants have been determined at different (273, 283, 303, and 313 K) temperatures. According to these values, plots of specific electrical conductivity from surfactant concentration were built (Figures 4−6). As is

Figure 6. Dependence of specific electrical conductivity on concentration of C14C2C14[iso-Pr(OH)] at different temperatures. Temperature, K: (1) 283, (2) 293, (3) 303, (4) 313.

evident from the figures, there is a linear dependence of the κ values on the concentration. This dependence is expressed in the form of two straight lines. Their intersection point corresponds to CMC. To find more correct results, the derivative plots were also used (Figure S13, Supporting Information). The values of CMC determined by conductoE



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of dodecylisopropylolammonium bromide, which is a conventional cationic surfactant with a similar headgroup, is 0.28 at 298 K.22 In the case of C9C2C9[iso-Pr(OH)], at 293−313 K, β varies in the interval 0.43−0.52. 3.3. Dependence of Aggregates Dimensions on Surfactant Concentration and Temperature. The diameters of the aggregates formed by the synthesized gemini surfactants in aqueous solutions have been determined via dynamic light scattering (DLS) method. With this purpose, solutions at three different concentrations higher than CMC have been prepared, and the diameters of the surfactant aggregates formed in them have been determined (Figures 8−10). As is seen in Figure 8, when the concentration of

metric method are presented in Table 2. It is noticed from the table that CMC values determined via the tensiometric method are close to those found via the conductometric method. The ratio of the slopes at the concentrations higher (S2) and lower (S1) than CMC equals a dissociation degree (α) of a counterion: α = S2/S1. A binding degree of the counterion (β) is found via the following formula: β=1−α

(3)

In Table 2, the values of β for the obtained gemini surfactants are given at various temperatures. As is seen from the table, the β values diminish as temperature rises. One of the reasons for such correlation is intensification of thermal motion of the surfactant aggregates with temperature increasing and the resulting transition of the counterions from the inner parts of the aggregates to the aqueous phase. The other reason is discussed in the next section. The plot β vs temperature is depicted in Figure 7. As is clear from the figure, this

Figure 8. DLS measurements of the size distributions for C9C2C9[isoPr(OH)] at different concentrations. Concentration, wt %: (1) 0.1, (2) 0.2, (3) 0.3.

Figure 7. Variation of degree of counterion association (β) with temperature (T) for the gemini surfactants: C9C2C9[iso-Pr(OH)] (1), C12C2C12[iso-Pr(OH)] (2), and C14C2C14[iso-Pr(OH)]. The solid lines are fitted curves (eq 4).

dependence is linear, and it may be expressed by the following equation: β = a + bT

(4)

where a and b are fitting parameters, their values being given in Table 3. As is seen from Table 3, with an elongation of the Table 3. Fitting Constants Obtained by Fitting the Plots of β versus T (a, b) with eq 4 Gemini surfactants

a

b

C9C2C9[iso-Pr(OH)] C12C2C12[iso-Pr(OH)] C14C2C14[iso-Pr(OH)]

1.2029 1.4013 1.7039

0.0023 0.0031 0.0043

Figure 9. DLS measurements of the size distributions for C12C2C12[iso-Pr(OH)] at different concentrations. Concentration, wt %: (1) 0.1, (2) 0.2, (3) 0.3.

alkyl chain of the gemini surfactants, the value of a augments, whereas the b value decreases. Moreover, when the alkyl chain in the gemini surfactants is elongated, the β values diminish. This effect is explained by a decrease in surface charge density inside micelles. A longer hydrocarbon group promotes micellization of surfactants with a lower surface/volume ratio. This indicates a more compact packing of headgroups and their binding a larger amount of counterions. The β value

C9C2C9[iso-Pr(OH)] rises from 0.1 to 0.2%, the diameter of the aggregates increases from 11.4 to 450 nm. When the concentration reaches 0.3%, the diameter of the aggregates decreases down to 250 nm. Furthermore, with an increase of the aggregates diameter, their polydispersity rises as well. In the case of C12C2C12[iso-Pr(OH)] and C14C2C14[iso-Pr(OH)] gemini surfactants, an increase in the concentration from 0.1 to 0.3% actually does not impact the dimensions of their F



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Figure 10. DLS measurements of the size distributions for C14C2C14[iso-Pr(OH)] at different concentrations. Concentration, wt %: (1) 0.1, (2) 0.2, (3) 0.3.

Figure 12. DLS measurements of the size distributions for C12C2C12[iso-Pr(OH)] at different temperatures.

aggregates in water. The diameters of aggregates of these two gemini surfactants are very close to each other, equaling ∼150 nm. When temperature rises from 293 to 323 K, the character of variation of the aggregates diameters has been determined (Figures 11−13). The impact of temperature on the diameters


the aggregates increases. At 313 and 323 K, dispersity degrees are approximately the same. Influence of temperature on the dimensions of aggregates formed in a 0.2% aqueous solution of C14C2C14[iso-Pr(OH)] gemini surfactant is the same as in the case of C12C2C12[iso-Pr(OH)] (Figure 13). But, when temperature rises from 293 to 323 K, the diameter of the aggregates of C14C2C14[iso-Pr(OH)] diminishes; up to 313 K the monodispersity degree increases and after 313 K decreases. Many authors29,30 came to the conclusion that the binding degree (β) of the surfactant counterion depends on dimensions of the aggregates. When these dimensions increase, more convenient conditions are created for the interaction of a counterion with an aggregate. As dimensions of aggregates decrease with a temperature increase, the value of β diminishes as well. Though many researchers mentioned a decrease of aggregate dimensions when the temperature is elevated, a reason for this phenomenon was not explained.29−31 3.4. Gibbs Energy of Micellization and Adsorption. The change of Gibbs free energy in the micellization process for gemini surfactants having two alkyl chains and two monovalent counterions was computed according to the following formula:32


of the aggregates formed in 0.2% aqueous solution of the C9C2C9[iso-Pr(OH)] gemini surfactant is depicted in Figure 11. As is seen from the figure, at 293 K the dimensions of the aggregates vary in the range 100−1000 nm. When temperature rises up to 303 K, the average diameter of the aggregates decreases down to 8.7 nm, and monodispersity of the aggregates increases 2.5 times. As temperature increases from 303 up to 323 K, the dimensions of the aggregates actually do not alter. But monodispersity of the aggregates decreases, and the tendency toward the formation of aggregates of small diameters is enhanced. The influence of temperature on the dimensions of the aggregates formed in an aqueous solution of C12C2C12[iso-Pr(OH)] of 0.2% concentration is demonstrated in Figure 12. As is noticeable from the figure, when the temperature rises, the average diameter of the surfactant aggregates decreases. So, at 293 K, the average diameter is around 150 nm, whereas at 323 K, this diameter equals 87 nm. In addition, with a temperature increase, the monodispersity of

° = RT (1 + 2β) ln X CMC ΔGmic G

(5) DOI: 10.1021/acs.jced.8b00815 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


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where R is the universal gas constant, T is the absolute temperature, β is the binding degree of the counterion, and XCMC is the CMC in molar fraction. XCMC = CMC/55.4, where CMC is expressed in mol/L; 55.4 shows the number of moles in 1 L of water (298 K). Using eq 5, ΔG°mic values for the synthesized gemini surfactants were calculated at different temperatures and are presented in Table 2. As is clear from the table, the values of ΔG°mic are negative, and they decrease as temperature rises. Therefore, in the studied temperature interval, the micellization process in an aqueous solution of the obtained gemini surfactants occurs spontaneously. As the length of the alkyl chain of the gemini surfactants increases from C9 to C12, the ΔG°mic value is lowered. But when the alkyl chain is elongated from C12 to C14, the value of ΔGmic ° rises. As is seen from eq 5, under isothermal conditions, the ΔGmic ° value depends on CMC and β. As the alkyl chain length rises from C9 to C14, the values of CMC and β decrease. According to eq 5, when XCMC decreases, ΔGmic ° values are lowered, and when β decreases, the ΔGmic ° values are increased. When the alkyl chain elongates from C12 to C14, an impact of the β value diminution is predominant, and it influences the value of ΔG°mic more. As a result, the value of ΔGmic ° increases. A little larger decrease of the β value is stipulated by hindrances created by isopropylol fragments in the headgroup as well as the alkyl chain for interaction of positively and negatively charged ions of the surfactant. A similar regularity was observed in other classes of surfactants as well.33 The change of Gibbs free energy for the adsorption process of the surfactants at the water−air interface was calculated via the formula given below:26 ° = ΔGmic ° − 0.6023πCMCA CMC ΔGad

Figure 14. Variation of ΔGmic ° (1), ΔHmic ° (2), and − TΔSmic ° (3) with temperature for C9C2C9[iso-Pr(OH)] in aqueous solutions.

(6)

In Table 2, the values of ΔG°ad for the obtained gemini surfactants at the water−air border are given. As becomes evident from the table, with a temperature rise, the value of ΔGad ° diminishes abruptly. In the case of C14C2C14[isoPr(OH)], with a temperature increase, the ΔG°ad value is lowered insignificantly. From a comparison of the values of ΔGmic ° and ΔGad ° , it is evident that the adsorption process takes place more readily than the micellization process. 3.5. Enthalpy−Entropy Compensation for Micellization. The enthalpy change for the micellization process of the synthesized gemini surfactants in aqueous solution was calculated according to the Gibbs−Helmholtz equation:32 ° = −T 2 ΔHmic

° /T ) ∂(ΔGmic ∂T


(7)

Using ΔGmic ° and ΔHmic ° , the value of the entropy change for the micellization process was computed via the following formula:32 ° = ΔSmic

° − ΔGmic ° ΔHmic T

(8)

The dependences of ΔG°mic, ΔH°mic, and ΔS°mic on temperature are given in Figures 14−16. As is seen from the figures, distinct from ΔGmic ° , the temperature dependences of ΔHmic ° and ΔSmic ° are more abrupt. When temperature rises, hydrogen bonding in water becomes weaker. As a result, for hydrophobic hydration, the entropic term becomes less important, whereas dispersion interactions acquire prevalence.34 In this case, the value of the −TΔS term increases, but the value of ΔH decreases. As is seen from the figures, the ΔH value is negative


for C9C2C9[iso-Pr(OH)] in the 283−313 K interval and for C12C2C12[iso-Pr(OH)] and C14C2C14[iso-Pr(OH)] in the 293−313 K range; i.e., at these temperature intervals, micellization is an exothermal process. As is known, the H



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results, with an elongation of the alkyl chain of the synthesized gemini surfactants, their antibacterial properties against SRB are weakened. The highest antibacterial effect among the obtained gemini surfactants is demonstrated by C9C2C9[isoPr(OH)]. The biocidal impact of cationic surfactants is based on electrostatic interaction. This interaction occurs between a negatively charged cellular membrane and a positively charged fragment of the surfactant. The main impact is related to the positive charge, but a length of the alkyl chain is also important. Thus, in conventional surfactants, with an elongation of the alkyl chain, their adsorption ability rises. One of the main reasons for a high antibacterial effect is a good adsorption capacity.42 Some authors mentioned that the cationic surfactants with the C12 chain possess a more effective bactericidal property.43 But, in some cases, information is reported that the cationic surfactants are more effective bactericides when they contain a C10 chain.27 It may be supposed that the surfactant C9C2C9[iso-Pr(OH)] has a higher adsorption capacity due to a smaller value of ΔGad ° , and therefore, it manifests a stronger antibacterial property.

enthalpy change of micelle formation in aqueous solution is mainly a result of hydrophobic and electrostatic interactions.34,35 When micellization takes place in water, the hydrocarbon chains of gemini surfactant molecules have a tendency to transition from the aqueous phase to the bulk of micelles, and the hydrating H2O molecules are simultaneously separated from the hydrocarbon fragment. This process is exothermal.36 An overview of electrostatic interactions may be taken from two standpoints. The first is repelling between headgroups and counterions, this interaction being exothermal. The second of them is attraction forces between headgroups and counterions. This process is endothermal.37,38 In the given case, repelling between gemini cations is stronger in comparison with attraction. Hence, the overall character of the electrostatic interactions is exothermal as well. The values computed for ΔS°mic are positive. This indicates that the micelles are of a lesser order in comparison with the free surfactant. Entropy is the main driving force for micelle formation, where a very regular structure of the water near the hydrophobic chains of surfactants is formed.39 With a rise in temperature, the contribution of entropy to micellization decreases, as at higher temperatures H2O molecules near the hydrophobic chains of the surfactant molecule get certain randomness; i.e., destruction of the iceberg structure takes place.40 So, micelle formation is characterized by a prevalent contribution of entropy at low temperatures, whereas contributions of both the entropy and enthalpy are dominant at high temperatures.38 At low temperatures, the micelle formation process is driven by entropy (−TΔS < ΔH), but at high temperatures, enthalpy becomes more decisive (−TΔS > ΔH). Obviously, ΔGmic values are dependent on the relative quantities of enthalpy and entropy in the two processes taking place within the system.41 3.6. SRB Bactericidal Properties of the Gemini Surfactants. SRBs are one of the main sources of H2S, which raises the acidity and corrosiveness of brine, causing cracking and blistering in metals, especially in the field of petroleum production. To fight SRBs, special reagents called bactericides are used to inhibit the development of these very dangerous bacteria. The obtained gemini cationics were tested in accordance with the serial dilution method against SRB in water. From Table 4, it is seen that the gemini surfactant

4. CONCLUSION A new class of gemini surfactants was synthesized on the basis of N,N′-bis(2-hydroxypropyl)ethylenediamine and alkyl bromides. The colloidal-chemical parameters of the synthesized surfactants have been determined by tensiometric and conductometric methods at various temperatures (283, 293, 303, and 313 K). It was established that, with a temperature increase, CMC, πCMC, Γmax, and β decrease, but Amin and pC20 increase. At the same time, ΔGmic ° , ΔHmic ° , and ΔSmic ° are lowered with a temperature increase. Via the method of dynamic light scattering, it was shown that the diameters of aggregates of the cationic gemini surfactants C12C2C12[isoPr(OH)] and C14C2C14[iso-Pr(OH)] in water do not actually depend on the surfactant concentration, but with a temperature increase, the diameters of the aggregates decrease. The antibacterial properties of the synthesized cationic surfactants against SRB depend on the length of the alkyl chain. With an elongation of this chain, the antibacterial properties are weakened.

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Table 4. Antibacterial Effect of the Synthesized Gemini Surfactants against SRBa

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00815.

concentration of gemini surfactants, mg/kg Gemini surfactants

15

75

150

C9C2C9[iso-Pr(OH)] C12C2C12[iso-Pr(OH)] C14C2C14[iso-Pr(OH)]

Nil 103 104

Nil Nil 103

Nil Nil Nil

ASSOCIATED CONTENT

S Supporting Information *

The figure in the table show the number of bacteria cells in 1 g of water.

a

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C9C2C9[iso-Pr(OH)] can completely stop the SRB growth at a very low concentration (15 mg/kg). The gemini surfactant C12C2C12[iso-Pr(OH)] does not fully inhibit development of SRB at a concentration 15 mg/kg, but at a 75 mg/kg concentration, it has an effective action. The gemini surfactant C14C2C14[iso-Pr(OH)] exhibits a relatively weak effect at low concentrations. At a concentration of 150 mg/kg, it is able to fully stop the growth of SRB. As is evident from the obtained

IR, 1H NMR, and 13C NMR spectra of N,N′-bis(2hydroxypropyl)ethylenediamine and gemini surfactants (Figures S1−S12); dependence of surface tension on natural logarithm of molality for gemini surfactants at different temperatures (Tables S1−S3); dependence of specific electrical conductivity on concentration of gemini surfactants at different temperatures (Tables S4−S6) (PDF)

AUTHOR INFORMATION

Corresponding Author

*Tel.: +99450 545 20 48. Fax: +99412 490 24 76. E-mail: [email protected]. ORCID

Ravan A. Rahimov: 0000-0001-5619-4041 Fedor I. Zubkov: 0000-0002-0289-0831 I



Article

Funding

hydroxyethyl and hydroxypropyl head group. J. Chem. Eng. Data 2017, 62, 3297−3305. (18) Sun, Y.; Wang, Ch.; Wang, W.; Yang, X.; Di Serio, M.; Zhi, L. Micellar Properties for Propoxylated Surfactants in Water/Alcohol Solvent Mixtures and Their Antibacterial and Polyester Fabric Antistatic Performances. J. Surfactants Deterg. 2016, 19, 543−552. (19) Liu, W.; Liu, W.; Wei, D.; Li, M.; Zhao, Q.; Xu, Sh. nthesis of N,N-Bis(2-hydroxypropyl)laurylamine and its flotation on quartz. Chem. Eng. J. 2017, 309, 63−69. (20) Taleb, K.; Mohamed-Benkada, M.; Benhamed, N.; SaidiBesbes, S.; Grohens, Y.; Derdour, A. Benzene ring containing cationic gemini surfactants: Synthesis, surface properties and antibacterial activity. J. Mol. Liq. 2017, 241, 81−90. (21) ASTM D4412-84, Standard Test Methods for Sulfate-Reducing Bacteria in Water and Water-Formed Deposits; ASTM International, 2009. (22) Asadov, Z. H.; Rahimov, R. A.; Ahmadova, G. A.; Mammadova, Kh.A.; Gurbanov, A. V. Synthesis and Characteristics of Dodecyl Isopropylolamine and Derived Surfactants. J. Surfactants Deterg. 2016, 19, 145−153. (23) Burczyk, B.; Wilk, K. A. Solution properties of selected functionalized surfactants. Prog. Colloid Polym. Sci. 1990, 82, 249− 252. (24) Xu, D.; Ni, X.; Zhang, C.; Mao, J.; Song, Ch. Synthesis and properties of biodegradable cationic gemini surfactants with diester and flexible spacers. J. Mol. Liq. 2017, 240, 542−548. (25) Ao, M.; Xu, G.; Zhu, Y.; Bai, Y. Synthesis and properties of ionic liquid-type Gemini imidazolium surfactants. J. Colloid Interface Sci. 2008, 326, 490−495. (26) Rosen, M. J. Surfactants and Interfacial Phenomena, third ed.; John Wiley: New Jersey, 2004. (27) Li, H.; Yu, Ch.; Chen, R.; Li, J.; Li, J. Novel ionic liquid-type Gemini surfactants: Synthesis, surface property and antimicrobial activity. Colloids Surf., A 2012, 395, 116−124. (28) Li, X.; Hu, Zh.; Zhu, H.; Zhao, S.; Cao, D. Synthesis and Properties of Novel Alkyl Sulfonate Gemini Surfactants. J. Surfactants Deterg. 2010, 13, 353−359. (29) Frizzo, C. P.; Bender, C. R.; Salbego, P. R. S.; Black, G.; Villetti, M. A.; Martins, M. A. P. Thermodynamic properties of the aggregation behavior of a dicationicionic liquid determined by different methods. Colloids Surf., A 2016, 494, 1−8. (30) Ao, M.; Huang, P.; Xu, G.; Yang, X.; Wang, Y. Aggregation and thermodynamic properties of ionic liquid-type gemini imidazolium surfactants with different spacer length. Colloid Polym. Sci. 2009, 287, 395−402. (31) Wu, X.; Dai, C.; Fang, S.; Li, H.; Wu, Y.; Sun, X.; Zhao, M. The effect of hydroxyl on the solution behavior of quaternary ammonium gemini surfactant. Phys. Chem. Chem. Phys. 2017, 19, 16047−16056. (32) Kabir-ud-Din; Koya, P. A. Micellar Properties and Related Thermodynamic Parameters of the 14−6-14, 2Br- Gemini Surfactant in Water + Organic Solvent Mixed Media. J. Chem. Eng. Data 2010, 55, 1921−1929. (33) Xing, H.; Yan, P.; Zhao, K-Sh.; Xiao, J.-X. Effect of headgroup size on the thermodynamic properties of micellization of dodecyltrialkylammonium bromides. J. Chem. Eng. Data 2011, 56, 865−873. (34) Myers, D. Surfaces, Interfaces, and Colloids: Principles and Applications, 2nd ed.; Wiley-VCH: New York, 1999. (35) Muller, N. Temperature dependence of critical micelle concentrations and heat capacities of micellization for ionic surfactants. Langmuir 1993, 9, 96−100. (36) Li, Y. J.; Reeve, J.; Wang, Y. L.; Thomas, R. K.; Wang, J. B.; Yan, H. K. Microcalorimetric study on micellization of nonionic surfactants with a benzene ring or adamantane in their hydrophobic chains. J. Phys. Chem. B 2005, 109, 16070−16074. (37) Shimizu, S.; Pires, P. A. R.; El Seoud, O. A. Thermodynamics of micellization of benzyl (2-acylaminoethyl) dimethylammonium chloride surfactants in aqueous solutions: A conductivity and titration calorimetry study. Langmuir 2004, 20, 9551−9559.

The publication was prepared with the support of the “RUDN University Program 5-100.” The authors thank the Institute of Petrochemical Processes of National Academy of Sciences of Azerbaijan for supporting this research. Notes

The authors declare no competing financial interest.

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Micellization and Adsorption Properties of New Cationic Gemini

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