Article pubs.acs.org/jced
Volumetric Properties of Sodium Lauroylsarcosinate in Aqueous Alcohol Solutions of Methanol, Ethanol, and 1‑Propanol Rais Ahmad Shah,† Oyais Ahmad Chat,†,‡ Ghulam Mohammad Rather,† and Aijaz Ahmad Dar*,†,§ †
Physical Chemistry Division, Department of Chemistry, University of Kashmir, Srinagar, J&K 190006, India Department of Chemistry, Government Degree College Pulwama, Pulwama, J&K 192301, India § Department of Chemistry and Chemical Biology, Rutgers: The State University of New Jersey, New Brunswick New Jersey 08901-8554, United States ‡
S Supporting Information *
ABSTRACT: The work attempts to gain an insight into the solution behavior of a biocompatible surfactant, sodium lauroylsarcosinate (SLS), in aqueous alcohol media at practically used concentrations of SLS (>CMC) where the solute−solute and solute−solvent interactions of surfactant aggregates are expected to be different from that between the solvent and the constituent monomers. The study of volumetric properties stresses the importance of hydrophilic and hydrophobic interactions operative between the SLS molecules and between SLS and the solvent. Moreover, it is interesting to observe how the dominance of electrostatic interactions fades and that of hydrophobic interactions rises as the concentration of SLS is progressively increased. Also, the study of standard apparent molar volumes, and the standard volumes of transfer offers a convenient way for accounting the differences between the alcohols which stems from their differing hydrophobicity.
1. INTRODUCTION Surfactants find applications in many industrial processes and everyday life as detergents, cosmetics, or personal hygiene products.1−6 In many applications, they are used as mixtures of different kinds of surfactants or surfactants with additives. Short chain alcohols are among the extensively studied additives used in surfactant systems.7−16 Alcohols may be considered as cosurfactants at lower concentrations because of their polar nature which allows them to intercalate between the surfactant head groups in the micellar shells, and as cosolvents at higher concentrations because of their ability to affect the solvent dielectric constants and the free energy change involved in the relocation of the surfactant hydrocarbon tails from the solvent to the aggregate core during aggregate formation.11,17 This intercalation results in a decrease in the micelle surface area per headgroup and an increase in the ionization of the micellized surfactant which is thought to affect the shape and the growth of the micelles.18 Because of the presence of both polar −OH and hydrophobic alkyl groups, alcohol molecules are expected to show distinctive interactions with water molecules. It is thought that through such interactions alcohol molecules rebuild the structure of water, which has a considerable bearing on the thermodynamic properties of the resulting aqueous alcohol solutions.19 Most of the studies on the alcohol−surfactant systems have mainly focused on the effect of the alcohols on the micellization of the surfactants. A prominent effect of the short chain alcohols on the critical micellization concentration (CMC) of the surfactants is known, with an inhibition of micellization being observed when short chain alcohols are present at concentrations © 2017 American Chemical Society
higher than their critical aggregation concentration (CAC). On the other hand, the effect of surfactants on the CAC of alcohols is almost nonexistent suggesting that the interaction between alcohol molecules in water is probably stronger than the interaction between alcohol and surfactant.20The effect of alcohols on surfactant micellization can be rationalized in terms of penetration power of alcohol molecules into the stern layer of micelles and the solvent modifying ability of alcohols, the relative magnitude of both of which depends on the concentration of the alcohol used.21,22 It is known that the volumetric properties serve as important tools which allow us to gain insight into the various solute−solute and solute−solvent interactions occurring in mixed systems.23 Although a lot of work has been done on short chain alcohol−surfactant systems, most of it concerns the effect of alcohols on the micellization process of conventional surfactants and surfactant mixtures.9,12,15,21,22 Nevertheless, there are a few instances in the literature where one comes across a study of short chain alcohol−surfactant systems involving commercial surfactants in which the effect of alcohols on the volumetric properties has been studied.24−27 Moreover, in many of their applications surfactants are used in concentrations higher than their CMC and therefore deserve attention. Sodium lauroylsarcosinate (SLS) is very popular in industrial and personal care applications because of its mild nature, good biodegradability, antimicrobial properties, and better stability toward hard water.28 Received: December 24, 2016 Accepted: July 28, 2017 Published: August 15, 2017 3015
DOI: 10.1021/acs.jced.6b01058 J. Chem. Eng. Data 2017, 62, 3015−3024
Journal of Chemical & Engineering Data
Article
3. RESULTS AND DISCUSSION Table 1 presents the density of water and aqueous alcohol solutions of various mass fractions of alcohol in the temperature range from 298.15 to 313.15 K. The density values are in close agreement as reported in the literature.24,25,29 The variation of density as a function of the concentration of SLS is given in Tables 2−5, respectively, for water, methanol (aq), ethanol (aq), and 1-propanol (aq) and plotted as Supporting Information
SLS can be used as component of cosmetics. It may also be used as an alternative to conventional surfactants in the mixture with short chain alcohols in applications such as lubrication, environmental remediation, microemulsion preparation, etc.10,21 It is therefore imperative to establish the effects of such and related compounds on the volumetric behavior of SLS. In view of this, we have studied the volumetric properties of SLS in aqueous solutions of methanol, ethanol, and 1-propanol in the post-CMC range of SLS28 in these systems.
Table 2. Density (ρ) of Different Concentrations of Aqueous Sodium Lauroylsarcosinate Solutions at Various Temperatures at Pressure P = 0.085 MPaa
2. EXPERIMENTAL SECTION 2.1. Materials. Sodium lauroylsarcosinate (purity ≥ 98%) was purchased from MP Biomedicals, France. Methanol (purity ≥ 99.9%), ethanol (purity ≥ 99.9%), and 1-propanol (purity ≥ 99.8%) were from Merck Millipore, India, and were used as such. (see Supporting Information for sample description in Table S1) All the solutions were prepared in triply distilled water. Alcohol−water mixed solutions with mass fraction (w) of alcohol equal to 0.04 ± 0.01, 0.08 ± 0.01, and 0.16 ± 0.01 were prepared by thoroughly shaking the two components and keeping still for 24 h to allow the air bubbles to escape before attempting to prepare the solutions with sodium lauroylsarcosinate. A weighed amount of sodium lauroylsarcosinate was dissolved in water and in the alcohol−water solvent system of a given mass fraction of alcohol to obtain the surfactant solutions of known molality (0.02 ± 0.001 mol·kg−1 to 0.09 ± 0.001 mol·kg−1). 2.2. Methods. To obtain volumetric properties of sodium lauroylsarcosinate in water and water−alcohol solutions, density measurements were carried with an Anton Paar vibrational tube densitometer DMA-4500, in which the sample density is a function of the oscillation frequency when the tube vibrates under the assumption that the sample volume between the oscillation modes is constant. The instrument was calibrated with degassed triply distilled water. The accuracy of the thermometer and the density measurements were ±0.01 K and ±0.00005 g/cm3, respectively. The uncertainty in density measurements was obtained by performing three replicate measurements and was found to be ±0.0005 g/cm3.
ρ/g cm−3 [SLS]/mol·kg 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
308.15 K
313.15 K
water
0.99729
0.99246
methanol ethanol 1-propanol
0.98997 0.99013 0.99059
methanol ethanol 1-propanol
0.98292 0.98390 0.98546
methanol ethanol 1-propanol
0.96942 0.97257 0.97364
0.99590 0.99427 w = 0.04 0.98862 0.98703 0.98879 0.98724 0.98914 0.98749 w = 0.08 0.98147 0.97991 0.98243 0.98077 0.98386 0.98213 w = 0.16 0.96761 0.96592 0.97069 0.96860 0.97145 0.96908
308.15 K
313.15 K
0.99667 0.99699 0.99732 0.99761 0.99796 0.99827 0.99859 0.99888
0.99504 0.99533 0.99567 0.99593 0.99627 0.99656 0.99688 0.99714
0.99318 0.99348 0.99380 0.99406 0.99441 0.99470 0.99495 0.99527
ρ/g cm−3
ρ/g cm 303.15 K
303.15 K
0.99813 0.99842 0.99873 0.99903 0.99943 0.99967 1.00007 1.00037
Table 3. Density (ρ) of Sodium Lauroylsarcosinate as a Function of Its Molality and Temperature in Methanol− Water System at Different Mass Fractions (w) of Methanol at Pressure P = 0.085 MPaa
−3
298.15 K
298.15 K
a Standard uncertainties u are u(P) = 2 kPa, u(ρ) = 0.0005 g/cm3, u(T) = 0.01 K, u([SLS]) = 0.001 mol·kg−1.
Table 1. Density (ρ) of Water and Aqueous Alcohol Solutions at Various Mass Fractions (w) of Alcohol in the Temperature Range of 298.15 to 313.15 K at Pressure P = 0.085 MPaa solvent media
−1
0.98522 0.98542 0.98562 0.97812 0.97885 0.98012 0.96368 0.96640 0.96684
a
[SLS]/mol·kg−1
298.15 K
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.99179 0.99212 0.99241 0.99275 0.99305 0.99340 0.99367 0.99403
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.98415 0.98447 0.98473 0.98502 0.98534 0.98564 0.98585 0.98619
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.97046 0.97056 0.97062 0.97068 0.97077 0.97083 0.97092 0.97099
303.15 K w = 0.04 0.99050 0.99079 0.99106 0.99141 0.99168 0.99203 0.99226 0.99260 w = 0.08 0.98277 0.98305 0.98329 0.98355 0.98384 0.98408 0.98433 0.98460 w = 0.16 0.96855 0.96863 0.96870 0.96877 0.96887 0.96897 0.96901 0.96909
308.15 K
313.15 K
0.98904 0.98928 0.98946 0.98972 0.98990 0.99012 0.99034 0.99056
0.98705 0.98735 0.98764 0.98798 0.98823 0.98856 0.98883 0.98918
0.98100 0.98125 0.98152 0.98175 0.98203 0.98227 0.98252 0.98281
0.97917 0.97942 0.97967 0.97990 0.98017 0.98045 0.98065 0.98094
0.96662 0.96672 0.96678 0.96683 0.96691 0.96699 0.96704 0.96711
0.96455 0.96460 0.96462 0.96465 0.96467 0.96471 0.96474 0.96476
a
Standard uncertainties u are u(P) = 2 kPa, u(ρ) = 0.0005 g/cm3, u(T) = 0.01 K, u(w) = 0.01.
Standard uncertainties u are u(P) = 2 kPa, u(ρ) = 0.0005 g/cm3, u(T) = 0.01 K, u(w) = 0.01, u([SLS]) = 0.001 mol·kg−1. 3016
DOI: 10.1021/acs.jced.6b01058 J. Chem. Eng. Data 2017, 62, 3015−3024
Journal of Chemical & Engineering Data
Article
Table 4. Density(ρ) of Sodium Lauroylsarcosinate as a Function of Its Molality and Temperature in Ethanol−Water System at Different Mass Fractions (w) of Ethanol at Pressure P = 0.085 MPaa
Table 5. Density(ρ) of Sodium Lauroylsarcosinate as a Function of Its Molality and Temperature in 1-Propanol− Water System at Different Mass Fractions (w) of 1-Propanol at Pressure P = 0.085 MPaa
ρ/g cm−3 [SLS]/mol·kg−1
298.15 K
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.99158 0.99185 0.99211 0.99239 0.99268 0.99289 0.99324 0.99346
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.98512 0.98545 0.98574 0.98611 0.98644 0.98681 0.98706 0.98742
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.97360 0.97389 0.97414 0.97444 0.97474 0.97502 0.97529 0.97559
303.15 K w = 0.04 0.99021 0.99046 0.99074 0.99096 0.99125 0.99143 0.99175 0.99196 w = 0.08 0.98365 0.98398 0.98426 0.98457 0.98492 0.98527 0.98553 0.98584 w = 0.16 0.97166 0.97192 0.97220 0.97248 0.97278 0.97304 0.97331 0.97363
308.15 K
ρ/g cm−3 [SLS]/mol·kg−1
313.15 K
0.98863 0.98884 0.98906 0.98932 0.98958 0.98976 0.99001 0.99025
0.98675 0.98696 0.98718 0.98742 0.98767 0.98786 0.98811 0.98830
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.99183 0.99211 0.99240 0.99280 0.99315 0.99340 0.99372 0.99412
0.98193 0.98220 0.98250 0.98281 0.98311 0.98345 0.98371 0.98402
0.98000 0.98024 0.98055 0.98085 0.98114 0.98142 0.98169 0.98199
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.98629 0.98648 0.98672 0.98702 0.98728 0.98746 0.98776 0.98798
0.96947 0.96978 0.97007 0.97036 0.97063 0.97100 0.97126 0.97156
0.96710 0.96746 0.96770 0.96804 0.96830 0.96863 0.96894 0.96927
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.97422 0.97438 0.97450 0.97465 0.97476 0.97492 0.97505 0.97517
a
Standard uncertainties u are u(P) = 2 kPa, u(ρ) = 0.0005 g/cm3, u(T) = 0.01 K, u(w) = 0.01, u([SLS]) = 0.001 mol·kg−1.
M 1000 − (ρ − ρ0 ) ρ mρρ0
303.15 K w = 0.04 0.99042 0.99069 0.99099 0.99138 0.99166 0.99193 0.99226 0.99257 w = 0.08 0.98469 0.98491 0.98517 0.98545 0.98570 0.98591 0.98617 0.98644 w = 0.16 0.97201 0.97217 0.97236 0.97255 0.97269 0.97290 0.97306 0.97321
308.15 K
313.15 K
0.98877 0.98899 0.98930 0.98962 0.98997 0.99020 0.99052 0.99077
0.98680 0.98708 0.98734 0.98771 0.98801 0.98826 0.98857 0.98882
0.98283 0.98305 0.98331 0.98358 0.98382 0.98403 0.98426 0.98451
0.98077 0.98099 0.98123 0.98152 0.98175 0.98199 0.98220 0.98247
0.96967 0.96981 0.96998 0.97013 0.97026 0.97043 0.97058 0.97071
0.96717 0.96732 0.96748 0.96761 0.96773 0.96790 0.96804 0.96816
a
Standard uncertainties u are u(P) = 2 kPa, u(ρ) = 0.0005 g/cm3, u(T) = 0.01 K, u(w) = 0.01, u([SLS]) = 0.001 mol·kg−1.
(Figures S1 to S4). As is evident, at constant temperature the density of the aqueous and aqueous alcohol solutions of SLS increases linearly with surfactant concentration. Such behavior has also been previously reported.24 Both the mass fraction of alcohol and temperature are found to affect the solution densities of SLS solutions. Keeping the temperature constant, the density values of SLS solutions decrease with decreasing relative permittivity of the aqueous alcohol solutions (increasing mass fraction of alcohol). An increase in temperature on the other hand decreases the solution density. The calculation of apparent molar volume, Vφ, is very important in order to gain an insight about the solute−solute interactions, as its values are explicitly dependent on the solvent environment around the solute particles.29 Apparent molar volumes, Vφ, for SLS (aq) and alcohol (aq)−SLS solutions at various temperatures have been obtained using the relation:30 Vφ =
298.15 K
hydrophilic groups, the effect on the volumetric properties is therefore expected to be quite complex because it is likely to be governed by a subtle balance of the effects of the hydrophobic and hydrophilic groups on the solvent.23 Also since it is known that the solute−solute interactions in a solution can be ignored at infinite dilution, the values of infinite dilution apparent molar volume, also called as the standard partial molar volume, Vφ0, have been evaluated by fitting the Vφ data to the Redlich−Rosenfeld−Meyer equation derived from the Debye−Huckel limiting law in order to gain an insight into solvent−solute interactions:31 Vφ = Vφ 0 + A(m)1/2 + Bm
(2)
where A is the Debye−Huckel limiting slope, reflecting the volumetric and the dielectric properties of the solvent and B is the empirical constant. V0φ depends on relative permittivity of the solvent, size and charge of ions, pressure, and temperature. The constant B takes care of the deviations from the Debye− Huckel limiting law in terms of interactions between the solvation shells.31 In aqueous alcohol solutions of SLS, ion−ion interactions among the head groups of SLS, ion−hydrophobic interactions between the headgroup of one SLS molecule and the hydrophobic tail of another SLS molecule, and hydrophobic− hydrophobic interactions among the hydrophobic tails of SLS are
(1)
where M is the molar mass of SLS, m is the molality of the solute, and ρ and ρ0 are the densities of the solution and the solvent, respectively. It has been pointed out29 that when hydrophobic/hydrophilic solutes are dissolved in water, the density of the solvent in the immediate vicinity of the solute molecules changes. For amphiphillic molecules such as SLS having both hydrophobic as well as 3017
DOI: 10.1021/acs.jced.6b01058 J. Chem. Eng. Data 2017, 62, 3015−3024
Journal of Chemical & Engineering Data
Article
Table 6. Apparent Molar Volume, Vφ, of Sodium Lauroylsarcosinate in Water as a Function of Its Molality and Temperature at Pressure P = 0.085 MPaa Vφ/cm3 mol−1 [SLS]/mol·kg
−1
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 a
298.15 K
303.15 K
308.15 K
313.15 K
251.76 ± 0.25 256.04 ± 0.17 257.63 ± 0.12 258.76 ± 0.10 257.78 ± 0.08 259.39 ± 0.07 258.54 ± 0.06 258.99 ± 0.06
255.59 ± 0.25 257.69 ± 0.17 258.45 ± 0.12 259.68 ± 0.10 259.45 ± 0.08 259.85 ± 0.07 260.00 ± 0.06 260.44 ± 0.06
256.07 ± 0.25 259.18 ± 0.17 259.43 ± 0.12 261.17 ± 0.10 260.95 ± 0.08 261.50 ± 0.07 261.50 ± 0.06 262.17 ± 0.06
258.89 ± 0.25 260.84 ± 0.17 261.27 ± 0.12 262.72 ± 0.10 262.12 ± 0.08 262.55 ± 0.07 263.37 ± 0.06 263.19 ± 0.06
Standard uncertainties u are u(P) = 2 kPa. u(T) = 0.01 K, u([SLS]) = 0.001 mol·kg−1.
Table 7. Apparent Molar Volume, Vφ, of Sodium Lauroylsarcosinate in Methanol−Water Mixture as a Function of Its Molality and Temperature at Different Mass Fractions (w) of Methanol at Pressure P = 0.085 MPaa Vφ/cm3 mol−1
a
[SLS]/mol·kg−1
298.15 K
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
203.15 ± 0.25 222.76 ± 0.17 233.55 ± 0.13 238.97 ± 0.10 243.24 ± 0.08 245.52 ± 0.07 248.25 ± 0.06 249.32 ± 0.06
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
234.55 ± 0.25 244.63 ± 0.17 251.20 ± 0.13 254.48 ± 0.10 256.12 ± 0.08 257.57 ± 0.07 259.81 ± 0.06 260.03 ± 0.06
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
247.06 ± 0.26 261.91 ± 0.17 270.40 ± 0.13 275.48 ± 0.10 278.33 ± 0.09 280.81 ± 0.07 282.27 ± 0.06 283.63 ± 0.06
303.15 K w = 0.04 200.22 ± 0.25 222.28 ± 0.17 233.79 ± 0.13 239.01 ± 0.10 243.84 ± 0.08 246.09 ± 0.07 249.31 ± 0.06 250.52 ± 0.06 w = 0.08 231.16 ± 0.25 243.87 ± 0.17 251.24 ± 0.13 255.21 ± 0.10 257.31 ± 0.08 259.54 ± 0.07 261.07 ± 0.06 262.00 ± 0.06 w = 0.16 252.78 ± 0.26 266.63 ± 0.17 273.81 ± 0.13 278.11 ± 0.10 280.43 ± 0.09 282.07 ± 0.07 284.12 ± 0.06 285.22 ± 0.06
308.15 K
313.15 K
193.70 ± 0.25 219.77 ± 0.17 234.32 ± 0.13 241.37 ± 0.10 247.44 ± 0.08 251.16 ± 0.07 253.93 ± 0.06 256.08 ± 0.06
203.16 ± 0.25 224.17 ± 0.17 234.90 ± 0.13 240.26 ± 0.10 245.37 ± 0.08 247.80 ± 0.07 250.39 ± 0.06 251.46 ± 0.06
242.39 ± 0.25 252.55 ± 0.17 257.08 ± 0.13 260.60 ± 0.10 262.05 ± 0.08 263.67 ± 0.07 264.73 ± 0.06 265.07 ± 0.06
244.83 ± 0.25 254.33 ± 0.17 259.05 ± 0.13 262.28 ± 0.10 263.70 ± 0.08 264.54 ± 0.07 266.22 ± 0.06 266.44 ± 0.06
266.05 ± 0.26 274.94 ± 0.17 280.46 ± 0.13 283.98 ± 0.10 285.77 ± 0.09 287.05 ± 0.07 288.41 ± 0.06 289.22 ± 0.06
257.38 ± 0.26 271.18 ± 0.17 278.88 ± 0.13 283.28 ± 0.10 286.40 ± 0.09 288.31 ± 0.07 289.87 ± 0.06 291.21 ± 0.06
Standard uncertainties u are u(P) = 2 kPa, u(T) = 0.01 K, u(w) = 0.01, u([SLS]) = 0.001 mol·kg−1.
Tables 6−9 and Figures 1−4 depict the variation of Vφ with SLS concentration for aqueous and alcohol (aq) solutions of SLS. As is evident, Vφ values are positive and increase rapidly with the concentrations of SLS at lower SLS concentrations, but tend to level off at higher SLS concentrations. When a hydrophobic or a hydrophilic solute is dissolved in a solvent, the solvent properties become considerably altered in the vicinity of the solute particle. Such a region of changed solvent property around the solute is called the cosphere. For an amphiphillic molecule such as an alcohol, with both hydrophilic and hydrophobic groups it is known that the cosphere on the −OH group of alcohol is considerably different from the cosphere on −CH2− or CH3(of the alkyl chain), which are more or less similar to each other.32 It is reported33 that the overlap of cospheres of two ionic
expected to occur. In addition to such interactions, the following four types of interactions are expected to be operative between SLS and short chain alcohols: (a) Hydrophobic interactions between the alkyl chain of SLS and that of the short chain alcohols which is expected to be least in the case of methanol due to its short alkyl chain length. (b) Hydrophobic−hydrophilic interactions between the hydrophobic chain of SLS and the −OH group of alcohols. (c) Ion−hydrophobic interactions between the ionic headgroup of SLS and hydrophobic chains of alcohols. (d) Ion−hydrophilic interactions between the ionic head groups of SLS and the −OH group of alcohols. 3018
DOI: 10.1021/acs.jced.6b01058 J. Chem. Eng. Data 2017, 62, 3015−3024
Journal of Chemical & Engineering Data
Article
Table 8. Apparent Molar Volume, Vφ, of Sodium Lauroylsarcosinate in Ethanol−Water Mixture as a Function of Its Molality and Temperature at Different Mass Fractions (w) of Ethanol in Ethanol−Water Mixture at Pressure P = 0.085 MPaa Vφ/cm3 mol−1 [SLS]/mol·kg
a
−1
298.15 K
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
222.05 ± 0.25 237.43 ± 0.17 245.34 ± 0.13 249.65 ± 0.10 252.32 ± 0.08 255.39 ± 0.07 255.87 ± 0.06 257.72 ± 0.06
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
234.90 ± 0.25 244.44 ± 0.17 250.22 ± 0.13 251.98 ± 0.10 253.82 ± 0.08 254.51 ± 0.07 256.57 ± 0.06 256.88 ± 0.06
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
246.97 ± 0.26 254.81 ± 0.17 259.76 ± 0.13 261.63 ± 0.10 262.85 ± 0.09 264.01 ± 0.07 264.99 ± 0.06 265.38 ± 0.06
303.15 K w = 0.04 223.79 ± 0.25 239.39 ± 0.17 246.38 ± 0.13 251.78 ± 0.10 254.16 ± 0.08 257.46 ± 0.07 258.11 ± 0.06 259.87 ± 0.06 w = 0.08 235.15 ± 0.25 244.73 ± 0.17 250.78 ± 0.13 253.75 ± 0.10 255.00 ± 0.08 255.87 ± 0.07 257.69 ± 0.06 258.49 ± 0.06 w = 0.16 250.54 ± 0.26 258.42 ± 0.17 261.79 ± 0.13 263.78 ± 0.10 264.72 ± 0.09 265.99 ± 0.07 266.78 ± 0.06 266.78 ± 0.06
308.15 K
313.15 K
225.57 ± 0.25 242.08 ± 0.17 250.05 ± 0.13 253.97 ± 0.10 256.57 ± 0.08 259.59 ± 0.07 260.93 ± 0.06 262.08 ± 0.06
228.95 ± 0.25 244.50 ± 0.17 251.98 ± 0.13 256.03 ± 0.10 258.53 ± 0.08 261.20 ± 0.07 262.40 ± 0.06 264.02 ± 0.06
238.57 ± 0.25 249.24 ± 0.17 253.74 ± 0.13 256.20 ± 0.10 257.99 ± 0.08 258.64 ± 0.07 260.17 ± 0.06 260.75 ± 0.06
239.45 ± 0.25 251.03 ± 0.17 254.94 ± 0.13 257.47 ± 0.10 259.30 ± 0.08 260.74 ± 0.07 261.93 ± 0.06 262.48 ± 0.06
256.32 ± 0.26 260.67 ± 0.17 263.34 ± 0.13 264.91 ± 0.10 266.29 ± 0.09 265.71 ± 0.07 266.74 ± 0.06 267.04 ± 0.06
265.93 ± 0.26 265.48 ± 0.17 268.44 ± 0.13 268.03 ± 0.10 269.16 ± 0.09 268.87 ± 0.07 268.90 ± 0.06 268.66 ± 0.06
Standard uncertainties u are u(P) = 2 kPa , u(T) = 0.01 K, u(w) = 0.01, u([SLS]) = 0.001 mol·kg−1.
Table 9. Apparent Molar Volume, Vφ, of Sodium Lauroylsarcosinate in 1-Propanol−Water Mixture as a Function of Its Molality and Temperature at Different Mass Fractions (w) of 1-Propanol at Pressure P = 0.085 MPaa Vφ/cm3 mol−1 [SLS]/mol·kg−1
298.15 K
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
232.71 244.18 249.62 250.58 252.05 254.56 255.51 255.31
± ± ± ± ± ± ± ±
0.25 0.17 0.13 0.10 0.08 0.07 0.06 0.06
0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
254.78 262.45 264.95 265.18 266.00 267.76 267.50 268.21
± ± ± ± ± ± ± ±
0.25 0.17 0.13 0.10 0.08 0.07 0.06 0.06
0.02 0.03 0.04 0.05 0.06
270.59 275.11 278.42 279.74 281.33
± ± ± ± ±
0.26 0.17 0.13 0.10 0.08
303.15 K w = 0.04 230.91 ± 0.25 243.43 ± 0.17 248.88 ± 0.13 250.27 ± 0.10 253.05 ± 0.08 255.16 ± 0.07 255.95 ± 0.06 256.78 ± 0.06 w = 008 255.13 ± 0.25 261.78 ± 0.17 264.03 ± 0.13 264.93 ± 0.10 266.03 ± 0.08 267.40 ± 0.07 267.75 ± 0.06 267.90 ± 0.06 w = 0.16 272.20 ± 0.26 276.39 ± 0.17 277.66 ± 0.13 278.40 ± 0.10 279.77 ± 0.08 3019
308.15 K
313.15 K
231.19 245.47 250.25 252.89 254.09 256.71 257.49 258.88
± ± ± ± ± ± ± ±
0.25 0.17 0.13 0.10 0.08 0.07 0.06 0.06
236.66 247.22 252.98 254.11 256.06 258.17 258.95 260.24
± ± ± ± ± ± ± ±
0.25 0.17 0.13 0.10 0.08 0.07 0.06 0.06
262.27 266.70 267.83 268.28 269.07 270.08 270.55 270.67
± ± ± ± ± ± ± ±
0.25 0.17 0.13 0.10 0.08 0.07 0.06 0.06
265.34 268.92 270.16 269.82 270.62 271.03 271.71 271.52
± ± ± ± ± ± ± ±
0.25 0.17 0.13 0.10 0.08 0.07 0.06 0.06
271.18 276.64 278.54 280.10 281.48
± ± ± ± ±
0.26 0.17 0.13 0.10 0.08
285.71 286.20 286.16 286.76 287.33
± ± ± ± ±
0.26 0.17 0.13 0.10 0.08
DOI: 10.1021/acs.jced.6b01058 J. Chem. Eng. Data 2017, 62, 3015−3024
Journal of Chemical & Engineering Data
Article
Table 9. continued Vφ/cm3 mol−1 [SLS]/mol·kg−1 0.07 0.08 0.09 a
298.15 K
303.15 K
308.15 K
313.15 K
281.68 ± 0.07 282.34 ± 0.06 282.97 ± 0.06
w = 0.16 279.66 ± 0.07 280.23 ± 0.06 280.79 ± 0.06
281.83 ± 0.07 282.36 ± 0.06 283.00 ± 0.06
286.95 ± 0.07 287.06 ± 0.06 287.38 ± 0.06
Standard uncertainties u are u(P) = 2 kPa , u(T) = 0.01 K, u(w) = 0.01, u([SLS]) = 0.001 mol.kg−1.
Figure 1. Apparent molar volume, Vφ, of SLS as a function of its molality in water at various temperatures at pressure 0.085 MPa.
groups leads to an increase in volume, whereas the overlap of cospheres of hydrophobic groups with that of either ionic or hydrophobic groups results in a net decrease in volume. Kumar et al.29 also observed a similar variation of Vφ with bile salt concentration in aqueous amino acid solutions which has been related to the dominance of electrostatic interactions between bile salts and amino acids at lower surfactant (bile salt) concentrations followed by the dominating hydrophobic interactions at higher surfactant concentrations. Similarly, the dominance of ion−ion interactions between the head groups of SLS is believed to be the reason for increase in Vφ at lower concentrations of SLS. The final constancy in the values of Vφ at higher SLS concentrations may therefore be due to the balance of volume changes produced by overlap between ionic− hydrophobic and hydrophobic−hydrophobic cospheres of SLS molecules. The values of Vφ0 for aqueous SLS, and aqueous−alcohol SLS solutions are shown in Table 10. As evident from the table, Vφ0 values are positive for all the three alcohols and increase with the alcohol mass fraction for methanol, ethanol, and 1-propanol at all temperatures indicating the presence of strong solute−solvent interactions which increase with the mass fraction of alcohol. Knowing the fact that the overlap of cospheres of two ionic or polar species leads to an increase in volume, and if both the species or at least one is hydrophobic, the overlap results in a decrease in volume, the positive Vφ0 values suggest the occurrence of ion−hydrophilic interactions between headgroup of SLS and the −OH groups of alcohols. However, as is clear from the Table 10, Vφ0 values in most of the cases for aqueous alcohol solutions are lower than in pure water suggesting that the strength of the ion−hydrophilic interactions is weaker in aqueous alcohol than in water. This seems to be plausible because the increased hydrophobicity of the aqueous alcohol medium in comparison to water allows for weaker ion− hydrophilic interactions. Driven by this logic alone, it may be easily concluded that the values for Vφ0 should decrease with the
Figure 2. Apparent molar volume, Vφ, of SLS as a function of its molality in aqueous methanol solutions at 0.085 MPa and various temperatures with methanol mass fraction being (A) 0.04, (B) 0.08, (C) 0.16.
mass fraction of the alcohol in aqueous alcohol media, which is contrary to the experimental observations. Furthermore, Vφ0 values should be lower in 1-propanol than in ethanol which in turn should be lower than in methanol because the length of the hydrophobic alkyl group decreases in that order. The seemingly contradicting experimental observations (Table 10) may be 3020
DOI: 10.1021/acs.jced.6b01058 J. Chem. Eng. Data 2017, 62, 3015−3024
Journal of Chemical & Engineering Data
Article
Figure 4. Apparent molar volume, Vφ, of SLS as a function of its molality in aqueous 1-propanol solutions at 0.085 MPa and at various temperatures with 1-propanol mass fraction being (A) 0.04, (B) 0.08, (C) 0.16.
Figure 3. Apparent molar volume, Vφ, of SLS as a function of its molality in aqueous ethanol solutions at 0.085 MPa and at various temperatures with ethanol mass fraction being (A) 0.04, (B) 0.08, (C) 0.16.
alcohols is expected to be caused by the alkyl group of the alcohols, which in the case of 1-propanol is least, and is highest in the case of methanol. Hence higher Vφ0 values are observed in 1-propanol than in ethanol which in turn is higher than in methanol. The standard volume of transfer ΔtV0 for SLS from water to aqueous alcohol solutions may be calculated by
rationalized in terms of reduction in electrostriction caused by the alkyl chains of alcohols. An increase in V0φ for poly(vinylpyrrolidone) in short chain alcohols with the length of alkyl chain (methanol < ethanol
