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. 2010 Oct 14;141(12):1297–1308. doi: 10.1007/s00706-010-0402-5

Volumetric and viscometric studies on dodecyltrimethylammonium bromide in aqueous and in aqueous amino acid solutions in premicellar region

M Farhad Hossain 1, Tapan Kumar Biswas 1, M N Islam 1, M Entazul Huque 1,✉
PMCID: PMC4494842  PMID: 26166851

Abstract

Abstract

The densities and viscosities of dodecyltrimethylammonium bromide (DTAB), glycine, and rac-alanine in water and DTAB in glycine/alanine aqueous solutions have been determined at 288.15, 296.15, 304.15, 312.15, and 320.15 K. The apparent molar volumes (φ v) were obtained from these density data. The limiting apparent molar volumes (φ 0v) and experimental slopes (S v) were derived from the Masson equation and interpreted in terms of solute–solute and solute–solvent interactions. The sign of [δ2(φ 0v)/δT 2]p, which corresponds to structure-making or structure-breaking properties of solutes, was determined. The viscosity coefficients A, B, and D were obtained from viscosity data on the basis of the Jones–Dole equation. Glycine/alanine in aqueous solutions exhibit structure-breaking behavior. In premicellar region, DTAB in aqueous solutions exhibits structure-breaking behavior, and DTAB in aqueous glycine/alanine solutions exhibits structure-making behavior. The free energy, enthalpy, and entropy of activation were calculated using the Nightingale and Benck, and Eyring equations. The values of (∆μ #1 − ∆μ #0) for solutions were calculated. The effects of solutes on the structure of water were interpreted in terms of viscosities and the thermodynamic parameters.

Graphical Abstract

graphic file with name 706_2010_402_Figa_HTML.jpg

Keywords: Apparent molar volume, Partial molar volume, Viscosity coefficient, Activation parameter

Introduction

Volumetric, viscometric, and other thermodynamic data provide valuable information regarding solute–solvent, solute–solute, and solvent–solvent interactions [1, 2]. Although volumetric, viscometric, and related thermodynamic parameter values in binary systems are abundantly available, data on ternary systems are limited. Physicochemical studies on aqueous ternary systems are gaining importance, because sometimes it is difficult to arrive at a definite conclusion regarding structure and properties of solutions from studies on binary systems alone. DTAB–water and amino acid–water mixtures are of great importance in protein stability and denaturation phenomena [3–10].

The effect of DTAB and amino acids on protein structure is now recognized to be more complex than simply disruption of hydrogen bonds and, in particular, causes the breaking of hydrophobic bonds [11–13]. The effects of added DTAB and amino acids upon the properties of water are continuously investigated in order to understand the mechanism of protein stability and denaturation by DTAB and amino acids. These effects are reported to be intimately connected with the local liquid structure [14, 15]. In this study we made an attempt to: (a) interpret the apparent and partial molar volume and the viscosity coefficients A, B, and D in terms of ion–ion, solute–solvent, and solute–solute interactions; (b) study the effect of DTAB on these interactions; (c) investigate the structure-making/breaking properties of the amino acids; and (d) discuss the species involved in viscous flow by their characteristic activation parameters ∆G #, ∆S #, ∆H #, and (∆μ #1 − ∆μ #0) in the premicellar region of DTAB.

Results and discussion

Volumetric properties of glycine, alanine, and DTAB in aqueous solutions and DTAB in aqueous amino acid solutions were determined at 288.15, 296.15, 304.15, 312.15, and 320.15 K. The apparent molar volume (φ v) and partial molar volume of binary and ternary solutions are shown in Tables 1, 2, and 3 (alanine solution data are not shown because they are very similar to glycine data). The apparent molar volumes depend on solute concentration as well as on temperature [16]. In aqueous glycine solutions, the apparent molar volumes show linear variation with concentration [17] (Fig. 1). Similar behavior was also seen in case of temperature rise. Comparatively higher apparent molar volumes (φ v) for DTAB in aqueous amino acid solutions are more progressively structure than in the aqueous system alone.

Table 1.

Concentration dependence of apparent molar volumes and partial molar volumes for glycine in aqueous solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

Conc. m (mol kg−1) Apparent molar volume φ v (cm3 mol−1) Partial molar volume Inline graphic (cm3 mol−1)
288.15 K 296.15 K 304.15 K 312.15 K 320.15 K 288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
0.0499 41.51 42.29 43.14 43.39 44.00 41.56 42.36 43.48 43.48 44.06
0.1003 41.49 42.62 43.23 43.51 44.04 41.58 42.78 43.68 43.68 44.15
0.1501 41.90 42.88 43.35 43.57 44.21 42.04 43.10 43.83 43.83 44.37
0.1997 42.20 43.05 43.54 43.77 44.32 42.38 43.35 44.11 44.11 44.54
0.2504 42.17 43.24 43.68 43.98 44.47 42.40 43.62 44.40 44.40 44.74
0.2998 42.19 43.29 43.81 44.02 44.42 42.47 43.74 44.53 44.53 44.75
0.3486 42.07 43.23 43.80 44.00 44.43 42.40 43.76 44.59 44.59 44.80
0.3985 42.18 43.34 43.89 44.11 44.52 42.55 43.94 44.79 44.79 44.95
0.4498 42.00 43.46 43.99 44.22 44.60 42.42 44.14 44.99 44.99 45.09
0.4998 42.03 43.42 43.95 44.19 44.56 42.50 44.17 45.04 45.04 45.10
0.5488 42.07 43.61 44.13 44.38 44.74 42.58 44.44 45.31 45.31 45.33
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Table 2.

Concentration dependence of apparent molar volumes and partial molar volumes for DTAB in aqueous solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

Conc. m (mol kg−1) Apparent molar volume φ v (cm3 mol−1) Partial molar volume Inline graphic (cm3 mol−1)
288.15 K 296.15 K 304.15 K 312.15 K 320.15 K 288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
0.0005 274.56 274.93 281.52 280.19 278.96 275.62 276.32 282.89 282.19 281.78
0.0010 283.57 285.98 288.58 290.34 290.20 284.99 287.70 290.17 292.50 293.15
0.0015 278.55 280.28 284.21 285.60 286.45 280.29 282.39 286.14 288.25 290.02
0.0020 276.55 281.45 284.03 286.78 288.15 278.54 283.83 286.20 289.70 292.04
0.0025 284.16 286.58 289.99 291.96 293.67 286.35 289.16 292.24 294.99 297.67
0.0030 283.89 286.64 289.58 291.34 293.26 286.29 289.45 292.02 294.63 297.58
0.0034 281.49 286.03 289.58 292.12 294.22 284.04 289.01 292.15 295.56 298.73
0.0040 284.55 286.47 289.83 292.10 294.53 287.30 289.67 292.59 295.78 299.35
0.0080 284.65 287.45 290.44 292.97 295.40 288.50 291.88 294.17 297.92 301.89
0.0100 284.71 287.44 290.25 292.83 295.27 289.01 292.36 294.38 298.31 302.45
0.0130 284.95 287.77 290.69 293.40 295.88 289.84 293.35 295.35 299.56 303.95
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Table 3.

Concentration dependence of apparent molar volumes and partial molar volumes for DTAB in 0.25 m aqueous glycine solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

Conc. m (mol kg−1) Apparent molar volume φ v (cm3 mol−1) Partial molar volume Inline graphic (cm3 mol−1)
288.15 K 296.15 K 304.15 K 312.15 K 320.15 K 288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
0.0005 527.06 526.37 516.16 518.21 524.64 512.68 512.24 502.77 504.89 510.90
0.0010 342.66 341.33 342.19 345.26 352.56 322.32 321.34 323.26 326.42 333.13
0.0015 296.96 301.41 304.08 305.60 309.28 272.06 276.94 280.90 282.52 285.49
0.0020 296.30 299.27 300.93 302.77 307.27 267.54 271.01 274.16 276.12 279.79
0.0025 288.41 292.04 294.67 296.27 300.42 256.26 260.44 264.74 266.47 269.70
0.0030 273.93 276.66 278.55 281.59 285.45 238.71 242.05 245.76 248.95 251.80
0.0035 267.82 272.46 274.43 276.25 280.22 229.78 235.07 239.01 241.00 243.87
0.0040 272.12 275.25 278.05 280.25 283.85 231.45 235.28 240.19 242.56 244.99
0.0080 294.92 297.52 299.93 302.51 305.25 237.41 241.00 246.38 249.21 250.29
0.0099 289.79 292.66 295.32 297.84 301.03 225.81 229.79 235.75 238.55 239.89
0.0130 287.21 289.73 292.36 294.92 297.94 213.89 217.69 224.10 226.97 227.88
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Fig. 1.

Fig. 1

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Plots of apparent molar volume versus molality of glycine in aqueous solutions at different temperatures

The variation of apparent molar volume of DTAB in aqueous and in aqueous amino acid solutions in the low-concentration region (Inline graphic plots) shows a sudden change in the φ v value at a particular molality (Figs. 2, 3). The apparent molar volume of DTAB in aqueous and in aqueous amino acid solutions may have two components, viz. the true size of the molecule and the free space between the molecules. In premicellar region, the molecules exist as monomers, and the monomer-monomer interaction may account for φ v with concentration having the free space between the molecules [18].

Fig. 2.

Fig. 2

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Apparent molar volume versus (molality)1/2 of DTAB in aqueous solutions at different temperatures

Fig. 3.

Fig. 3

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Apparent molar volume versus (molality)1/2 of DTAB in 0.25 m aqueous glycine solutions at different temperatures

For DTAB, glycine, and alanine in aqueous solutions, the value of Inline graphic increases with increasing molality and the value of Inline graphic slightly decreases. This suggests that ion–solvent interactions increase with increasing molality of the solute. On the other hand, DTAB in aqueous amino acid solutions shows the opposite effect.

The apparent molar volume at infinite dilution (φ 0v) was calculated using a least-squares fit to the linear plots of experimental values of φ v versus the square root of molar concentration (Inline graphic) using the Masson equation [19]:

graphic file with name 706_2010_402_Article_Equ1.gif 1

where S v is the experimental slope, which is sometimes considered to be the volumetric pairwise interaction coefficient [20, 21]. The limiting apparent molar volume (φ 0v) and S v values along with standard errors are given in Table 4. It is evident from the table that the values of S v are positive for DTAB in water at different temperatures. Since S v is a measure of solute–solute/ion–ion interactions, the result indicates the presence of very strong ion–ion interactions. For DTAB in aqueous amino acid solutions, the values of S v are negative, which indicates the very weak ion–ion interactions in this region.

Table 4.

Limiting apparent molar volumes (φ 0v) and experimental slopes (S v) for binary and ternary solutions at different temperatures

System Temperature (K) φ 0v (cm3 mol−1) S v (cm3 dm3/2 mol−1) [δ2 φ 0v/δT 2]p
DTAB + water 288.15 276.93 (±5.36E−04) 84.52 (±2.06E−02) −1.2428 (±8.57E−07)
296.15 279.14 (±4.79E−04 94.55 (±1.86E−02)
304.15 283.87 (±4.32E−04) 75.66 (±1.67E−02)
312.15 284.54 (±3.73E−04) 99.39 (±1.49E−02)
320.15 284.41 (±3.16E−04) 130.02 (1.34E−02)
Glycine + water 288.15 41.72 (±6.99E−03) 3.31 (±8.19E−01) −0.0928 (±4.21E−04)
296.15 42.47 (±9.10E−03) 2.20 (±7.84E−01)
304.15 43.10 (±8.97E−03) 1.93 (±7.75E−01)
312.15 43.36 (±8.92E−03) 1.88 (±7.75E−01)
320.15 43.99 (±8.04E−03) 1.34 (±7.73E−01)
rac-Ala + water 288.15 58.64 (±8.06E−03) 3.25 (±6.00E−01) −0.2828 (±1.83E−04)
296.15 59.76 (±6.92E−03) 2.06 (±5.92E−01)
304.15 60.54 (±6.21E−03) 1.32 (±5.88E−01)
312.15 60.66 (±6.62E−03) 1.46 (±5.89E−01)
320.15 61.12 (±6.20E−03) 1.37 (±5.87E−01)
DTAB + 0.25 m Gly + water 288.15 390.52 (±7.38E−04) −1,286.07 (±1.99E−02) 2.2186 (±5.21E−06)
296.15 391.67 (±6.87E−04) −1,263.80 (±1.79E−02)
304.15 388.72 (±6.16E−04) −1,197.30 (±1.60E−02)
312.15 390.64 (±5.66E−04) −1,191.80 (±1.45E−02)
320.15 397.12 (±5.41E−04) −1,228.90 (±1.29E−02)
DTAB + 0.25 m rac-Ala + water 288.15 373.92 (±7.07E−04) −1,156.60 (±2.22E−02) 0.7872 (±2.50E−06)
296.15 373.94 (±6.57E−04) −1,120.80 (±2.04E−02)
304.15 375.81 (±6.03E−04) −1,111.10 (±1.85E−02)
312.15 374.65 (±5.44E−04) −1,066.70 (±1.68E−02)
320.15 378.94 (±5.14E−04) −1,085.80 (±1.55E−02)
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The limiting apparent molar volume (φ 0v), which is taken to be the partial molar volume at infinite dilution of DTAB in aqueous and in aqueous amino acid solutions, reflects the true volume of the solute and the volume change arising from solute–solvent interactions. The variation of φ 0v with the molality of DTAB can be rationalized in terms of the cosphere overlap model [22].

According to the model, the overlap of the cospheres of two ions or polar groups or an ion with that of a hydrophilic group always produces a positive volume change. On the other hand, the overlap of the cosphere of an ion with that of hydrophobic groups results in a negative volume change. On the overlap of the cospheres of DTAB–DTAB and DTAB–hydrophilic groups, zwitterionic interactions may take place. The overlap of the cospheres of DTAB gives a positive change in volume due to relaxation of the electrostricted water molecules due to strongly localized ion–zwitterion interactions from the cospheres of amino acid and DTAB, which may cause an increase in volume [23].

The positive volume change due to the overlap of the cospheres of amino acids with those of the hydrophilic groups of DTAB outweighs the negative volume change due to the overlap of cospheres of amino acids and hydrophobic groups of DTAB (negligible), giving a greater φ 0v value in amino acid compared with that in water in this region (Table 4). The water–water and water–amino acid interactions are assumed to be the same and do not produce a considerable change in volume. An increase in the molality of DTAB increases the ion–zwitterion and also the DTAB–DTAB interactions, giving rise to increased φ 0v values.

The increase of φ 0v with temperature may be due to the result of the following effects [24]:

  1. At higher temperature the thermal energy of the water molecules is increased, causing fast movement of the bulk electrostricted water molecules from the interaction region of (CH3)3N+– and –COOH groups, resulting in a positive volume change.

  2. An increase in temperature decreases the DTAB–DTAB interaction, giving rise to a small negative volume change.

  3. A decrease in DTAB–water interactions causes a positive volume change.

  4. The water–water interactions decrease with increasing temperature, giving rise to a small negative change in volume.

In DTAB in aqueous and in aqueous amino acid solutions, the DTAB–DTAB and DTAB–zwitterion interactions increase, giving rise to an increased φ 0v value.

The φ 0v value of DTAB in ternary solution can alternatively be thought of as arising from four constituents [25]:

graphic file with name 706_2010_402_Article_Equ2.gif 2

where V w and V f are van der Waals volumes [26] and volume of empty spaces present therein. V n and V s represent contributions due to hydrophobic and hydrophilic hydration.

V w and V f are assumed to be the same in aqueous amino acids as in water. The variation of φ 0v is therefore due to the change in (V n + V s) resulting from DTAB–amino acid, amino acid–amino acid, and amino acid–water interactions; the contribution from water–water is assumed to be negligible.

The temperature dependence of the limiting apparent molar volume φ 0v for binary and ternary solution can be expressed by the expression

graphic file with name 706_2010_402_Article_Equ3.gif 3

The sign of Inline graphic, i.e., the second derivative of the limiting apparent molar volume of the solution with respect to temperature at constant pressure, which correspond to structure-making or structure-breaking properties of solution, was determined [27]. For binary and ternary solutions, the values of Inline graphic are shown in Table 4. Glycine, alanine, and DTAB in aqueous solutions show negative values of Inline graphic indicating that glycine, alanine, and DTAB act as structure breakers for water solvent systems [28]. Similar information was reported by Devine and Lowe [29]. Again, the value of Inline graphic was found to be positive for DTAB in aqueous amino acid solutions, corresponding to structure-making property of water [27].

Viscosity properties of glycine and DTAB in aqueous and DTAB in aqueous amino acid solutions were measured at 288.15, 296.15, 304.15, 312.15, and 320.15 K. The relevant data are shown in Tables 5 and 6.

Table 5.

Concentration dependence of viscosity for glycine in aqueous solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

Conc. m (mol kg−1) Viscosity η (cP)
288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
0.0499 1.137880 0.942678 0.793556 0.673591 0.580944
0.1003 1.147339 0.948971 0.797374 0.676478 0.582315
0.1501 1.150220 0.954667 0.802681 0.683000 0.587100
0.1997 1.165109 0.960280 0.808677 0.687347 0.591364
0.2504 1.167401 0.966909 0.813114 0.691004 0.595743
0.2998 1.172076 0.973330 0.819991 0.701196 0.599757
0.3486 1.186965 0.979896 0.825447 0.707964 0.608078
0.3985 1.192241 0.986627 0.829158 0.703235 0.607041
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Table 6.

Concentration dependence of viscosity for DTAB in aqueous and DTAB in 0.25 m glycine aqueous solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

DTAB DTAB + 0.25 m glycine
Conc. m (mol kg−1) Viscosity η (cP) Viscosity η (cP)
288.15 K 296.15 K 304.15 K 312.15 K 320.15 K 288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
0.0005 1.140515 0.942544 0.780821 0.666754 0.578572 1.163237 0.966766 0.818132 0.685966 0.603104
0.0010 1.137853 0.940308 0.784959 0.664363 0.576847 1.174014 0.972239 0.817642 0.689824 0.598130
0.0015 1.137689 0.942212 0.787145 0.660770 0.576553 1.169530 0.977138 0.814032 0.688972 0.593354
0.0020 1.136180 0.957896 0.790749 0.660949 0.574375 1.169226 0.981347 0.820553 0.691945 0.593703
0.0025 1.135044 0.955332 0.789985 0.658062 0.573453 1.172392 0.976990 0.812960 0.693833 0.594558
0.0030 1.138992 0.954772 0.797780 0.661215 0.574824 1.180319 0.971528 0.817157 0.688168 0.593483
0.0034 1.134168 0.945214 0.782197 0.669451 0.582811 1.168365 0.972365 0.814383 0.686140 0.597807
0.0040 1.137100 0.946604 0.794392 0.663339 0.579485 1.174915 0.970780 0.814982 0.687410 0.583213
0.0080 1.136934 0.947222 0.780352 0.663789 0.578529 1.174910 0.970893 0.815146 0.682075 0.590829
0.0100 1.140350 0.951443 0.787082 0.667042 0.579036 1.176227 0.970982 0.821448 0.682591 0.592583
0.0130 1.144537 0.959352 0.783562 0.662832 0.576318 1.183795 0.972362 0.827889 0.683742 0.594707
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The representative curves (viscosity versus molality) for binary and ternary systems are linear and are shown in Figs. 4, 5, and 6. The values of η increase with increase in molality and decrease with temperature. According to the “flickering cluster” [30] models of water, there are large void spaces within the hydrogen-bonded framework of the water structure. The linear increase of η with concentration may be interpreted by the fact that the molecules may have penetrated into the void spaces and may have a positive interaction with water.

Fig. 4.

Fig. 4

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Viscosity versus molality of glycine in aqueous solutions at different temperatures

Fig. 5.

Fig. 5

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Viscosity versus molality of DTAB in aqueous solutions at different temperatures

Fig. 6.

Fig. 6

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Viscosity versus molality of DTAB in 0.25 m aqueous glycine solutions at different temperatures

To calculate the viscosity coefficient B, the viscosity data were analyzed in terms of the semi-empirical Jones–Dole equation [31]. The viscosity coefficient B represents information regarding solute–solvent interaction and shape and size effect on the solvent structure [32, 33]. The calculated values of the B coefficient are presented in Table 7. The B coefficient values of the studied electrolyte in aqueous solutions are based on the fact that there exists around an ion a region of modified solvent differing from the bulk in structure and in properties. Gurney’s [34] cosphere, Frank and Wens [30] A, B, and C zones, and Nightingale’s hydrated radius are recent reflections of this idea. From the above approaches, Kaminsky indicated that the observed viscosity changes result from competition between various effects occurring in the neighborhood of the ion. The viscosity of a dilute electrolyte solution can be equated to that of the solvent plus the contributions from four other sources in the following manner [35]:

graphic file with name 706_2010_402_Article_Equ4.gif 4

where ∆η * is the positive increment in the viscosity caused by coulombic interactions, and ∆η E is the viscosity increment arising from the size and shape of an ion, which is closely related to the Einstein effect; it is always positive and normally increases with increasing ion size [36, 37]. ∆η A is the increment due to the alignment or orientation of polar molecules by the ionic field. Since the freedom of movement of these molecules is restricted, this generally results in a “stiffening” of the solution, and the increment will again be positive. ∆η D is the viscosity change associated with distortion of the solvent structure leading to greater fluidity. This distortion can be thought of as due to competing forces from the solvent structure in the bulk and from the ionic field and/or the oriented molecules associated with the ion. In mixed solvents, ∆η D is of considerable magnitude due to significant distortion in the solvent molecules present in the vicinity of the ionic field [38].

Table 7.

The viscosity coefficient values A/D, B, and Inline graphicfor binary and ternary solutions as functions of temperature

Temperature (K) A (coefficient) B (coefficient) [dB/dT]
System
 DTAB + water 288.15 −0.0894 (±1.50E–03) 0.7710 (±2.84E–04) 0.3707 (±3.44E–04)
296.15 0.3552 (±9.87E–04) −1.5858 (±2.47E–03)
304.15 0.0898 (±4.98E–04) −0.1300 (±1.12E–03)
312.15 −0.2788 (±2.56E–03) 2.1265 (±9.76E–04)
320.15 −0.0804 (±1.45E–03) 0.7684 (±2.86E–04)
 DTAB + 0.25 m (aq) Gly 288.15 −0.2114 (±2.07E–04) 2.5888 (±9.06E–06) −0.0093 (±3.55E–06)
296.15 −0.2390 (±1.04E–04) 2.7845 (±6.58E–05)
304.15 −0.1010 (±6.21E–04) 1.7190 (±3.42E–04)
312.15 −0.5489 (±1.06E–03) 4.0708 (±5.58E–04
320.15 −0.2329 (±1.27E–04) 1.8993 (±2.73E–04)
 DTAB + 0.25 m (aq) Ala 288.15 −0.2523 (±2.08E–03) 4.6372 (±2.57E–04) −0.0196 (±3.98E–05)
296.15 −0.2758 (±2.18E–03) 5.4044 (±3.73E–04)
304.15 0.3495 (±4.92E–04) −2.9214 (±1.74E–03)
312.15 0.1195 (±4.90E–04) 0.3120 (±9.21E–04)
320.15 0.1739 (±2.57E–04) 6.4004 (±6.26E–04)
Compound
 Glycine + water 288.15 0.1191 (±1.13E–04) 0.0365 (±1.59E–04) 0.0077 (±2.16E–04)
296.15 0.1162 (±1.34E–04) 0.0401 (±7.65E–05)
304.15 0.1274 (±5.07E–05) 0.0192 (±5.58E–04)
312.15 0.1848 (±3.77E–04) −0.0745 (±2.72E–03)
320.15 0.1235 (±7.97E–05) 0.0468 (±7.78E–05)
 Alanine + water 288.15 0.0832 (±6.04E–04) 0.1655 (±1.11E–03) 0.0242 (±2.56E–04)
296.15 0.2526 (±2.02E–04) 0.0406 (±4.82E–04)
304.15 0.2391 (±1.38E–04) 0.0092 (±8.83E–04)
312.15 0.2906 (±3.83E–04) −0.0611 (±1.78E–03)
320.15 0.1852 (±1.19E–04) 0.1158 (±4.76E–04)
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Substituting equation (4) into the following Jones–Dole [21] equation one obtains

graphic file with name 706_2010_402_Article_Equa.gif

or

graphic file with name 706_2010_402_Article_Equ5.gif 5

Eliminating the contributions due to the ionic interaction from both sides we obtain

graphic file with name 706_2010_402_Article_Equ6.gif 6

Thus, at a given concentration (C), the coefficient B can be interpreted in terms of a competition between these specialized viscosity effects. The charged cations strongly orient with water molecules and in fact are believed to have a primary sheath of firmly attached molecules which moves with them as a kinetic entity [39]. ∆η E will therefore be large because the ion plus primary sheath can be visualized as a single entity. It is also probable that, at room temperature, water molecules beyond this inner layer are oriented to some extent, giving positive ∆η A. The sum ∆η E + ∆η A will not outweigh the decrement due to ∆η D, because it is thought to be small for these ions and the fixed outward-pointing hydrogen atoms fit reasonably well into the tetrahedral water structure. Thus, in this case of ions, ∆η E + ∆η A ≫ ∆η D, and the B coefficient is large and positive. The sign of Inline graphic, i.e., the first derivative of the viscosity coefficient of B with respect to temperature, which corresponds to structure-making or structure-breaking properties of solutes, was determined [40]. The values of Inline graphic are presented in Table 7.

For glycine, alanine, and DTAB in aqueous solutions the values of Inline graphic are positive, which corresponds to structure-breaking behavior [41]. Although glycine and alanine have high values of B, the simplest amino acids are classified as structure breakers [33, 42, 43]. It is seen that Inline graphic is negative for DTAB in aqueous amino acid solutions, which indicates that DTAB acts as a structure maker in the aqueous amino acid solvent system [44].

The viscosity coefficient A represents the ion–ion interactions coupled with the size and shape effect of the solute and to some extent solute–solvent interactions. In this study, irregular variation in the values of A was found, which may be due to

  1. Incomplete dissociation and ion association of electrolyte in aqueous and in aqueous amino acid solvent, and

  2. The size of ions which differ in degree of hydration or solvation [45].

The decrease of A with rising temperature is probably due to greater thermal agitation and reduction of attractive forces between the ions. The increase in A value can be explained by the interpenetration effect, which brings the ions closer together [46]. It is found that more A coefficient values are negative for DTAB in aqueous glycine solutions than in aqueous alanine solutions. This indicates that DTAB has less solute–solute interaction in the aqueous glycine solvent system. On the other hand the viscosity coefficient D also represents the solute–solute interaction, but it is related to nonelectrolyte solutions. In aqueous glycine and alanine solutions, the coefficient D shows negative values at 312.15 K (Table 7). The negative D contributions indicate that amino acid–amino acid interactions are decreased compared with amino acid–water interactions.

The thermodynamic properties of glycine, alanine, and DTAB in aqueous and DTAB in aqueous amino acid solutions were calculated at the mentioned temperatures using the Nightingale and Benck [47] and Eyring equations [48] and are shown in Tables 8, 9, and 10. The ∆G # value is positive for all the studied systems. The positive free energy of activation for viscous flow can be interpreted with the help of the Furth model [49], which states that the kinetic species involved in forming cavities or holes in the liquid medium are given by the work required in forming the hole against surface tension of the solution. The solute–solvent interaction, interstitial incorporation, and hydrophilic hydration interaction render the binary and ternary aqueous systems more structured. This is reflected in the positive ∆G # value.

Table 8.

Concentration dependence of activation parameters for viscous flow of glycine in aqueous solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

Conc. m (mol kg−1) Free energy ∆G # (kJ mol−1) ∆S # (J mol−1 K−1) ∆H # (kJ mol−1 K−1)
288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
0.0499 9.4346 8.9878 8.5807 8.1951 7.8485 22.3979 15.8745
0.1003 9.4573 9.0067 8.5953 8.2083 7.8572 22.7845 16.0085
0.1501 9.4662 9.0240 8.6141 8.2343 7.8799 22.2375 15.8621
0.1997 9.5000 9.0410 8.6350 8.2526 7.9003 22.5068 15.9671
0.2504 9.5075 9.0606 8.6512 8.2685 7.9211 22.1468 15.8746
0.2998 9.5199 9.0794 8.6744 8.3065 7.9402 21.6264 15.7401
0.3486 9.5528 9.0983 8.6933 8.3324 7.9762 21.3803 15.6934
0.3985 9.5664 9.1178 8.7071 8.3195 7.9752 22.1618 15.9377
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Table 9.

Concentration dependence of activation parameters for viscous flow of DTAB in aqueous solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

Conc. m (mol kg−1) Free energy ∆G # (kJ mol−1) ∆S # (J mol−1 K−1) ∆H # (kJ mol−1 K−1)
288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
0.0005 9.4424 9.2390 9.0182 8.8527 8.7107 23.3540 16.1548
0.0010 9.4371 9.2335 9.0319 8.8437 8.7031 23.4297 16.1750
0.0015 9.4371 9.2388 9.0392 8.8300 8.7021 23.6858 16.2524
0.0020 9.4342 9.2798 9.0511 8.8311 8.6924 24.2968 16.4466
0.0025 9.4322 9.2735 9.0491 8.8201 8.6885 24.4082 16.4754
0.0030 9.4408 9.2724 9.0742 8.8328 8.6952 24.2627 16.4415
0.0034 9.4309 9.2479 9.0246 8.8652 8.7322 22.4694 15.8934
0.0040 9.4375 9.2519 9.0642 8.8419 8.7175 23.2975 16.1475
0.0080 9.4397 9.2562 9.0218 8.8465 8.7160 23.4363 16.1833
0.0100 9.4481 9.2684 9.0449 8.8606 8.7198 23.4995 16.2148
0.0130 9.4588 9.2908 9.0356 8.8463 8.7094 24.4922 16.5165
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Table 10.

Concentration dependence of activation parameters for viscous flow of DTAB in 0.25 m glycine aqueous solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

Conc. m (mol kg−1) Free energy ∆G # (kJ mol−1) ∆S # (J mol−1 K−1) ∆H # (kJ mol−1 K−1)
288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
0.0005 9.5362 9.3481 9.1830 8.9732 8.8681 21.3961 15.65952
0.0010 9.5585 9.3623 9.1817 8.9880 8.8462 22.4744 15.99311
0.0015 9.5495 9.3749 9.1707 8.9850 8.8251 22.9400 16.12851
0.0020 9.5492 9.3859 9.1913 8.9966 8.8270 22.8369 16.10609
0.0025 9.5560 9.3752 9.1680 9.0040 8.8312 22.7247 16.06876
0.0030 9.5724 9.3616 9.1813 8.9829 8.8266 23.3615 16.26074
0.0035 9.5482 9.3640 9.1730 8.9755 8.8463 22.3963 15.9635
0.0040 9.5620 9.3603 9.1752 8.9807 8.7807 24.1954 16.50107
0.0080 9.5649 9.3636 9.1788 8.9636 8.8186 23.6350 16.33571
0.0099 9.5687 9.3650 9.1996 8.9669 8.8279 23.4604 16.29143
0.0130 9.5861 9.3705 9.2215 8.9734 8.8397 23.5893 16.34311
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It is seen that the ∆G # value of glycine in aqueous solutions increases very slowly with increasing solute concentration and decreases with increasing temperature (Fig. 7). The slow increase in ∆G # for aqueous amino acid solutions indicates that the structure-destroying property is decreased with increasing solute concentration. Similar structure-making results have been reported by other authors as well [32, 50–52]. For aqueous DTAB solutions, overall decrease of ∆G # is shown with increasing solute concentrations at all studied temperatures. This indicates that DTAB acts as a structure breaker for the water system (Fig. 9).

Fig. 7.

Fig. 7

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Free energy of activation versus molality of glycine in aqueous solutions at different temperatures

Fig. 9.

Fig. 9

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Free energy of activation versus molality of DTAB in 0.25 m aqueous glycine solutions at different temperatures

For DTAB in aqueous glycine solutions, there is an overall increase of ∆G # with increasing DTAB concentration (Figs. 8, 9). This indicates that DTAB acts as a structure maker for H2O–amino acid solvent systems. The change may be attributed to the fact that ∆G # controls the rate of flow, which is governed by the slowest step in the fluid process. Similar structure-making results for electrolytes have been reported by other authors earlier [49, 53–55].

Fig. 8.

Fig. 8

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Free energy of activation versus molality of DTAB in aqueous solutions at different temperatures

The variations of entropy of activation (∆S #) with the concentration of binary and ternary systems are noted in Tables 8, 9, and 10. The ∆S # values for the flow process are positive in all cases but do not follow any specific pattern. It is also found that the values of ∆S # for DTAB in the aqueous glycine system are higher than those in the aqueous alanine system, indicating that in the aqueous alanine system the DTAB is more structured than in the aqueous glycine system [51]. This corresponds to the structure-breaking property of solute. The positive values of ∆H # indicate that positive work has to be done to overcome the energy barrier for the flow process. That is, viscous flow is not thermodynamically favored for the systems studied. According to Freemantle and Lawrence [32], the viscosity coefficient B is related to the difference in chemical potential for the flow of 1 mol of solute. The change in chemical potential values (∆μ #1 − ∆μ #0) indicates the solute–solvent interactions in the solution (shown in Tables 11, 12, 13). A positive and high value of (∆μ #1 − ∆μ #0) indicates strong interaction between ions and solvents, whereas a low and negative value of (∆μ #1 − ∆μ #0) indicates structure disorder [53]. Calculated values obtained from the B coefficient data for all systems studied are presented in Table 7. An examination of the data indicates that positive values of (∆μ #1 − ∆μ #0) are obtained for glycine and alanine in aqueous solutions, corresponding to strong solute–solvent interaction. For DTAB in aqueous solvent systems the values of (∆μ #1 − ∆μ #0) are negative at 296.15 K, indicating a weak interaction, and positive at 288.15, 304.15, 312.15, and 320.15 K, indicating a strong interaction between ion and solvent. For DTAB in amino acid solvent systems the values of (∆μ #1 − ∆μ #0) are positive at the studied temperatures, indicating a strong interaction between ion and solvent.

Table 11.

Change of chemical potential (∆μ #1 − ∆μ #0) for glycine in aqueous solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1)
0.0497 21.29 0.0497 21.56 0.0496 23.77 0.0494 32.50 0.0493 33.93
0.0998 21.22 0.0996 21.54 0.0994 23.70 0.0991 32.37 0.0988 29.09
0.1490 21.21 0.1488 21.51 0.1484 23.64 0.1480 32.22 0.1475 27.47
0.1978 21.18 0.1975 21.47 0.1971 23.59 0.1965 32.11 0.1959 26.62
0.2476 21.12 0.2471 21.43 0.2466 23.53 0.2458 31.99 0.2450 26.09
0.2958 21.06 0.2952 21.37 0.2946 23.47 0.2937 31.85 0.2928 25.69
0.3432 20.98 0.3426 21.31 0.3418 23.40 0.3408 31.71 0.3397 25.40
0.3915 20.93 0.3908 21.26 0.3899 23.34 0.3887 31.58 0.3875 25.17
0.4410 20.85 0.4401 21.21 0.4391 23.28 0.4378 31.46 0.4364 24.97
0.4891 20.79 0.4880 21.14 0.4868 23.20 0.4854 31.32 0.4838 24.79
0.5359 20.74 0.5347 21.11 0.5334 23.15 0.5319 31.21 0.5301 24.66
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Table 12.

Change of chemical potential (∆μ #1 − ∆μ #0) for DTAB in aqueous solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1)
0.0005 139.00 0.0005 −178.93 0.0005 21.19 0.0005 344.23 0.0005 153.19
0.0010 140.16 0.0010 −177.48 0.0010 22.17 0.0010 345.47 0.0010 154.80
0.0015 139.46 0.0015 −178.32 0.0015 21.56 0.0015 344.59 0.0015 154.21
0.0020 139.16 0.0020 −178.22 0.0020 21.54 0.0020 344.56 0.0020 154.42
0.0025 140.13 0.0025 −177.58 0.0025 22.37 0.0025 345.09 0.0025 155.19
0.0030 140.06 0.0030 −177.63 0.0030 22.31 0.0030 344.81 0.0030 155.09
0.0034 139.72 0.0034 −177.76 0.0034 22.31 0.0034 344.75 0.0034 155.20
0.0040 140.08 0.0040 −177.77 0.0040 22.34 0.0040 344.51 0.0040 155.19
0.0080 139.81 0.0080 −178.12 0.0079 22.42 0.0079 343.02 0.0079 155.01
0.0100 139.68 0.0099 −178.36 0.0099 22.39 0.0099 342.21 0.0099 154.83
0.0129 139.50 0.0129 −178.67 0.0129 22.45 0.0129 341.10 0.0128 154.69
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Table 13.

Change of chemical potential (∆μ #1 − ∆μ #0) for DTAB in 0.25 m aqueous glycine solutions at 288.15, 296.15, 304.15, 312.15, and 320.15 K

288.15 K 296.15 K 304.15 K 312.15 K 320.15 K
Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1) Molarity (∆μ #1 − ∆μ #0) (kJ mol−1)
0.0005 85.99 0.0005 68.44 0.0005 85.70 0.0005 55.76 0.0005 58.85
0.0010 61.61 0.0010 43.35 0.0010 61.53 0.0010 31.16 0.0010 33.83
0.0015 55.57 0.0015 37.94 0.0015 56.23 0.0015 25.52 0.0015 27.54
0.0020 55.48 0.0020 37.65 0.0020 55.79 0.0020 25.12 0.0020 27.25
0.0025 54.43 0.0025 36.66 0.0025 54.91 0.0025 24.19 0.0025 26.25
0.0030 52.51 0.0030 34.58 0.0030 52.67 0.0030 22.11 0.0030 24.08
0.0035 51.70 0.0035 34.01 0.0035 52.09 0.0035 21.35 0.0035 23.32
0.0040 52.27 0.0040 34.38 0.0040 52.59 0.0040 21.92 0.0040 23.84
0.0080 55.23 0.0080 37.38 0.0080 55.59 0.0080 25.07 0.0080 26.94
0.0099 54.54 0.0099 36.72 0.0099 54.93 0.0099 24.41 0.0098 26.33
0.0130 54.17 0.0130 36.31 0.0130 54.49 0.0130 23.99 0.0129 25.87
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However, for DTAB in the aqueous amino acid solvent system, the values of (∆μ #1 − ∆μ #0) decrease with increasing DTAB concentration. This indicates that the structure-disordering properties of DTAB increase in the amino acid solvent system.

Conclusions

The studies on the solution properties of dodecyltrimethylammonium bromide, glycine, and rac-alanine in aqueous solution and DTAB in amino acid solutions (glycine/alanine) reveal the following:

  1. DTAB + water: the behavior of DTAB in aqueous solution is temperature dependent. In premicellar region it appears to be a structure breaker for the water solvent system.

  2. Glycine/rac-alanine + water: glycine and rac-alanine in aqueous solutions exhibit similar behavior. Both of the solutes act as structure breakers at all studied temperatures (15–47 °C).

  3. DTAB + 0.25 m glycine/rac-alanine: DTAB in aqueous glycine solution acts as a structure maker in premicellar region at all temperatures studied.

Experimental

The surfactant dodecyltrimethylammonium bromide (DTAB, purity ≥98%) was purchased from Fluka, Switzerland; the reported critical micellar concentration (cmc) value of DTAB in water is close to 0.015 m at 25 °C. Glycine (mass fraction ≥0.99) and rac-alanine (mass fraction ≥0.99) were procured from Fluka chemical company, Switzerland. The chemicals were used without further purification. Supplied distilled water was redistilled and deionized by passing through two ion-exchange columns. The deionized water was distilled again in alkaline KMnO4 medium and was used for preparation of all solutions. Conductivity of this water was found to be 1.00 μS. The cmc of DTAB in water was determined from conductance measurements. The concentration dependence of molar conductivity of aqueous solutions of DTAB was observed. The molar conductivity decreases with increasing DTAB concentration and shows a sharp break in its value where micelles start to form, determined by extrapolating the molar conductivity data in the premicellar region to intersect with a straight line drawn through the data in the postmicellar region. The estimated cmc value thus obtained for DTAB is 1.5 × 10−2 mol kg−1 at 23 °C, in good agreement with the values reported earlier in literature [52, 56, 57].

An electric balance with accuracy of ±0.0001 g was used for weighing. Viscosities of various liquids were measured using a calibrated Ostwald-type viscometer. The flow time of liquids was recorded by a timer able to read up to 0.01 s. Temperature was controlled by a water thermostat with accuracy of ±0.1 °C. A densitometer (DSA-5000; Anton Paar, Austria) was used for density measurements.

Acknowledgments

The authors gratefully acknowledge the Department of Chemistry, University of Rajshahi, Rajshahi-6205, Bangladesh for providing necessary facilities and help when needed for the work.

Open Access

This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Contributor Information

Tapan Kumar Biswas, Phone: +88-0721-770059, FAX: +88-0721-750064, Email: tapankb@ru.ac.bd.

M. Entazul Huque, Email: emhuque@yahoo.com.

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