Apparent Molar Volume, Adiabatic Compressibility, and Critical

Article pubs.acs.org/jced

Apparent Molar Volume, Adiabatic Compressibility, and Critical Micelle Concentration of Flucloxacillin Sodium in Aqueous NaCl Solutions at Different Temperatures M. Roksana Khatun, M. Monirul Islam,* Farhana Rahman Rima, and M. Nazrul Islam Department of Chemistry, University of Rajshahi, Rajshahi 6205, Bangladesh ABSTRACT: Densities, ρ, and speeds of sound, u, of flucloxacillin sodium in water and aqueous NaCl solutions were measured at T = (298.15, 303.15, 308.15, 313.15, 318.15, and 323.15) K and atmospheric pressure using a high precision vibrating U-tube digital density and sound velocity analyzer (DSA 5000, Anton Paar, Austria). From the experimental data, apparent molar volume, ϕv, apparent molar adiabatic compressibility, ϕk, limiting apparent molar volume, ϕv0, limiting apparent molar adiabatic compressibility, ϕk0, and critical micelle concentration of flucloxacillin sodium were calculated. The limiting apparent molar volumes, ϕ0v , were used to calculate Hepler’s constant. The results were interpreted in terms of solute−solvent and solute−solute interactions and structure making/breaking ability of the solute in the aqueous environment.

1. INTRODUCTION The physicochemical interactions between a drug and functionally important molecules in a living organism1 may include ionic, covalent, charge transfer, hydrogen bonding, ion−dipole interactions, or hydrophobic hydration2 and are of great benefit for understanding the pharmacodynamics and pharmacokinetics3 of drugs. These interactions are tremendously useful for the migration and transformation of drugs or their metabolites that enter water via urine, fecal excretions, and so forth4 and contaminate the water. Because most of the biochemical processes occur in aqueous media, the studies on the physicochemical interactions in the aqueous phase through the volumetric and ultrasonic methods provides useful information in pharmaceutical5 and medicinal chemistry. The drug−water molecular interactions and their temperature dependence play an important role in the understanding of drug action6,7 at the molecular level. Such results are also helpful for predicting the absorption of drugs, transport of drugs across biological membranes, and investigating the presence, migration, and transformation of the drugs in the environment. Flucloxacillin sodium (FluNa), which is the sodium salt of flucloxacillin, is a narrow spectrum beta-lactam antibiotic of the penicillin class. It is used in the treatment of bacterial infections caused by susceptible, usually Gram-positive, organisms. The microbiological activity of beta-lactam antibiotics largely depends on the stability of the beta-lactam ring structure.8 The beta-lactam ring structure of FluNa is shown in Figure 1. The stability of beta-lactam ring structures and biomolecules is greatly influenced by the chemical species, such as electrolytes,9,10 glucose, urea, and so forth, present in body fluids. Taboada et al.11 investigated aggregation properties of FluNa in water and aqueous NaCl by light-scattering and NMR techniques, but there is no report on the physicochemical © XXXX American Chemical Society

Figure 1. Structure of FluNa.

properties of FluNa in water or aqueous electrolyte solvents. With this view, the volumetric and ultrasonic investigation of FluNa in water and aqueous electrolyte solutions is undertaken. In this study, NaCl is considered only because of its utmost contribution as an electrolyte in extracellular fluid12 of the human body compared to other ions, such K+, Mg+, Ca+, HCO3−, and HPO4−. The extent of Na+ is ∼92 % of total positive ions, and that of Cl− is ∼68 % of total negative ions. To deliberate the interactions between FluNa and electrolytes, the densities, ρ, and speeds of sound, u, of FluNa in water and aqueous NaCl solutions were measured at T = (298.15, 303.15, 308.15, 313.15, 318.15, and 323.15) K and atmospheric pressure. From these data, various parameters, such as apparent molar volumes, ϕv, apparent molar adiabatic compressibility, ϕk, their corresponding limiting parameters, and critical micelle concentrations were Received: April 5, 2015 Accepted: November 4, 2015

A

DOI: 10.1021/acs.jced.5b00317 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

solute−solvent and solute−solute interactions. The density and speeds of sound data are used to calculate ϕv and ϕk using the relations ρ − ρ0 M ϕv /m3 mol −1 = 2 − ρ mρρ0 (1)

computed. The experimental results and derived parameters together with their discussion are presented in this paper.

2. EXPERIMENTAL DETAILS 2.1. Materials. FluNa (purity, mass fraction of >0.99) obtained from Beximco Pharmaceuticals Limited, Bangladesh, and sodium chloride (purity, mass fraction of >0.995) obtained from Loba Chemie Pvt. Ltd., India were used in this study. The specifications of the chemicals used in this study are given in Table 1.

ϕk /m3 mol −1 Pa−1 =

βs /Pa−1 =

Table 1. Specifications of the Chemicals purity declared by supplier

chemical name

molar mass/kg·mol−1

flucloxacillin sodium (FluNa) sodium chloride (NaCl)

0.475855

mass fraction, ≥ 0.990

0.058442

mass fraction, ≥ 0.995

− ρβs0 βρ s 0 mρρ0

+

βsM 2 ρ

1 ρu 2

(2)

(3)

−1

where m/mol kg is the molality of FluNa in binary or ternary solutions, ρ/kg m−3 and βs/Pa−1 are the density and adiabatic compressibility, respectively, of FluNa in water (binary solutions) or in aqueous NaCl solutions (ternary solutions), ρ 0/kg m −3 and β s0/Pa −1 are the density and adiabatic compressibility, respectively, of water or aqueous NaCl solutions, and M2/kg mol−1 is the molar mass of FluNa. The standard combined uncertainties in various parameters, such as molality, apparent molar volume, apparent molar adiabatic compressibility, and so forth, are calculated using their corresponding error equations. The general form of the error equation is given by

origin Beximco Pharmaceuticals Limited, Bangladesh Loba Chemie Pvt. Ltd., India

2.2. Measurement of Density and Speeds of Sound. Freshly prepared redistilled and degassed water (specific conductance < 10−6 S cm−1) was used for the preparation of solutions. The solutions were prepared in molality by weighing on a balance (Mettler Toledo, B204-S, Switzerland) having a precision of ± 0.0001 g. The uncertainties in the molality of solutions are within ± 2·10−5 mol kg−1. The densities, ρ, and speeds of sound, u, of the solutions were simultaneously and automatically measured using a density and sound velocity analyzer (DSA 5000, Anton Paar, Austria). A density check or an air/water adjustment was performed at 20 °C with triply distilled, degassed water and with dry air at atmospheric pressure. Before each series of measurements, the density and sound velocity analyzer was calibrated with redistilled and degassed water in the experimental temperature range. Both the density and speeds of sound are extremely sensitive to temperature, so it was controlled to ± 1·10−3 K by a built-in Peltier device. The sensitivity of the instrument corresponds to a precision in density and speeds of sound measurements of 1·10−3 kg m−3 and 1·10−2 m s−1. The uncertainty of the density and speeds of sound estimates was found to be within ± 5·10−3 kg m−3 and ± 5·10−2 m s−1, respectively. 2.3. Measurement of Conductivity. Approximately 35 aqueous solutions of FluNa within the concentration range (0.02 to 0.19) mol kg−1 were prepared from a 0.4216 mol kg−1 stock solution by appropriate dilution. The solution was transferred to a conductivity cell and kept in the water thermostat for 15−20 min to attain the working temperature. The temperature of the water bath was controlled with a precision of ± 0.1 °C by a thermostat (INSREF, Chennai-58, India). The conductivity of the solution was then recorded repeatedly by a digital multi range conductivity meter (JENWAY Model-4520, England). The conductivity meter was calibrated with (0.001, 0.01, and 0.1) M potassium chloride solution.

ΔY =

⎛ ∂y ⎞2 ⎞2 ⎛ ∂y Δx n⎟ ⎜ Δx1⎟ + ·······+⎜ ⎠ ⎝ ∂x1 ⎝ ∂x n ⎠

(4)

where Δx1, Δx2...Δxn are standard errors associated with the independent variables x1, x2 • • • xn, respectively. The obtained values of ϕv along with their standard uncertainties are presented in Table 3. The ϕv values of FluNa in water and aqueous NaCl solutions of different concentration are also graphically represented in Figure 2. From the data, it is observed that ϕv values of FluNa increase with an increase in temperature and with an increase in the concentration of FluNa but decrease with an increase in the concentration of NaCl. The calculated ϕk values, including the standard uncertainties for FluNa in water and aqueous NaCl solutions at different temperatures, are reported in Table 4. The ϕk values of FluNa in water and aqueous NaCl solutions are also graphically represented in Figure 3. The ϕk values are negative at low temperatures and a low concentration of FluNa. These become less negative or even positive with an increase in temperature and with an increase in concentration of FluNa. However, the magnitude of ϕk values increases with the increase in the concentration of NaCl. From Figures 2 and 3, it is discernible that ϕv and ϕk increase linearly with the increase in concentration of FluNa with the appearance of a definite break point. The break point is quite significant and has almost the same magnitude as that observed in the conductivity versus molality curve of aqueous FluNa solutions as shown in Figure 4. The break points were used to evaluate the critical micelle concentration (CMC) of FluNa in water and aqueous NaCl solutions. 3.2. Limiting Apparent Molar Quantities and CMCs. The variation of ϕv and ϕk with the molalities of FluNa are represented by the piece-wise linear model

3. RESULTS AND DISCUSSION 3.1. Apparent Molar Quantities. The measured densities, ρ, and speeds of sound, u, of FluNa in water and aqueous NaCl solutions at different concentration are presented in Table 2 as a function of the molality of FluNa and temperature. The apparent molar volume, ϕv, and apparent molar adiabatic compressibility, ϕk, are very useful parameters in the understanding of

when m < X ⎫ ⎪ ⎬ 0 y = y + b1X + b2(m − X ) when m ≥ X ⎪ ⎭ y = y 0 + b1m

B

(5)



Article

Table 2. Experimental Density, ρ, and Speeds of Sound, u, of FluNa in Water and Aqueous NaCl Solutions at Different Temperatures and Atmospheric Pressurea 298.15 K

303.15 K

m/mol kg−1

ρ/kg m−3

u/m s−1

ρ/kg m−3

u/m s−1

0.00000 0.03508 0.05711 0.07305 0.09335 0.11419 0.13434 0.14801 0.16752 0.18122

997.035 1003.210 1007.005 1009.683 1013.038 1016.416 1019.680 1021.891 1025.016 1027.164

1496.98 1502.99 1506.38 1508.61 1511.24 1513.65 1515.81 1517.20 1518.92 1520.06

995.633 1001.740 1005.492 1008.141 1011.460 1014.804 1018.038 1020.229 1023.328 1025.459

1509.41 1514.78 1517.82 1519.87 1522.21 1524.41 1526.39 1527.61 1529.21 1530.21

0.00000 0.02314 0.04870 0.05579 0.07082 0.08281 0.09840 0.12511 0.14248 0.15416 0.16619 0.17241

998.068 1002.207 1006.632 1007.830 1010.338 1012.307 1014.820 1019.153 1021.928 1023.767 1025.648 1026.677

1498.87 1502.97 1506.97 1507.98 1509.97 1511.44 1513.38 1516.17 1517.71 1518.63 1519.48 1519.90

996.654 1000.746 1005.121 1006.306 1008.786 1010.734 1013.221 1017.510 1020.257 1022.078 1023.941 1024.960

1511.26 1514.92 1518.50 1519.40 1521.20 1522.54 1524.28 1526.76 1528.13 1528.94 1529.69 1530.06

0.00000 0.01231 0.02544 0.03458 0.05003 0.06427 0.07582 0.08572 0.09020 0.10723 0.12426 0.14153 0.14865 0.16880

999.427 1001.677 1004.010 1005.609 1008.237 1010.583 1012.529 1014.174 1014.882 1017.700 1020.435 1023.178 1024.273 1027.392

1501.10 1503.39 1505.65 1507.10 1509.35 1511.40 1512.90 1514.11 1514.65 1516.46 1518.07 1519.44 1519.96 1521.15

997.998 1000.229 1002.540 1004.125 1006.732 1009.059 1010.991 1012.625 1013.327 1016.124 1018.841 1021.565 1022.652 1025.751

1513.43 1515.45 1517.46 1518.75 1520.74 1522.59 1523.92 1524.99 1525.47 1527.07 1528.49 1529.70 1530.16 1531.22

0.00000 0.00518 0.00985 0.01696 0.02025 0.02721 0.03778 0.04384 0.05315 0.06695 0.08100 0.10051 0.11835 0.13936

1001.162 1002.130 1002.991 1004.276 1004.858 1006.082 1007.882 1008.913 1010.515 1012.869 1015.221 1018.456 1021.345 1024.686

1503.82 1504.84 1505.73 1507.04 1507.62 1508.78 1510.44 1511.36 1512.76 1514.71 1516.54 1518.78 1520.58 1522.33

999.715 1000.675 1001.527 1002.800 1003.377 1004.590 1006.376 1007.403 1008.990 1011.326 1013.660 1016.871 1019.739 1023.056

1516.05 1516.95 1517.73 1518.89 1519.40 1520.43 1521.90 1522.73 1523.99 1525.72 1527.37 1529.38 1531.00 1532.60

0.00000 0.01089 0.02099 0.02876 0.03894

1002.990 1005.027 1006.838 1008.167 1009.863

1506.43 1508.64 1510.50 1511.84 1513.39

1001.523 1003.548 1005.347 1006.669 1008.357

1518.55 1520.48 1522.11 1523.29 1524.65

308.15 K ρ/kg m−3

313.15 K

u/m s−1

Water + FluNa 994.014 1520.14 1000.055 1524.93 1003.766 1527.64 1006.387 1529.45 1009.671 1531.56 1012.982 1533.52 1016.183 1535.26 1018.354 1536.40 1021.426 1537.75 1023.540 1538.69 Water + 0.0251 M NaCl 995.026 1521.94 999.074 1525.19 1003.402 1528.36 1004.575 1529.17 1007.029 1530.76 1008.956 1531.95 1011.417 1533.49 1015.664 1535.67 1018.385 1536.85 1020.189 1537.56 1022.035 1538.19 1023.045 1538.51 Water + 0.0586 M NaCl 996.357 1524.03 998.567 1525.81 1000.856 1527.58 1002.426 1528.71 1005.009 1530.47 1007.317 1532.12 1009.233 1533.28 1010.853 1534.22 1011.550 1534.65 1014.324 1536.04 1017.020 1537.28 1019.724 1538.32 1020.804 1538.72 1023.881 1539.62 Water + 0.1021 M NaCl 998.056 1526.54 999.006 1527.33 999.850 1528.02 1001.111 1529.03 1001.683 1529.48 1002.884 1530.38 1004.653 1531.67 1005.675 1532.43 1007.248 1533.54 1009.564 1535.06 1011.877 1536.52 1015.062 1538.30 1017.908 1539.74 1021.198 1541.17 Water + 0.1483 M NaCl 999.851 1528.93 1001.861 1530.61 1003.647 1532.03 1004.959 1533.05 1006.636 1534.24

C

318.15 K

323.15 K

ρ/kg m−3

u/m s−1

ρ/kg m−3

u/m s−1

ρ/kg m−3

u/m s−1

992.197 998.174 1001.846 1004.440 1007.691 1010.968 1014.137 1016.289 1019.335 1021.432 + FluNa 993.201 997.207 1001.491 1002.652 1005.081 1006.989 1009.424 1013.631 1016.328 1018.117 1019.948 1020.950 + FluNa 994.523 996.710 998.976 1000.530 1003.087 1005.368 1007.267 1008.871 1009.561 1012.310 1014.982 1017.662 1018.733 1021.784 + FluNa 996.208 997.148 997.983 999.232 999.798 1000.990 1002.741 1003.748 1005.301 1007.594 1009.886 1013.041 1015.862 1019.126 + FluNa 997.991 999.982 1001.755 1003.061 1004.721

1529.23 1533.46 1535.86 1537.48 1539.37 1541.12 1542.68 1543.65 1544.93 1545.70

990.195 996.110 999.746 1002.313 1005.531 1008.775 1011.913 1014.047 1017.068 1019.148

1536.77 1540.50 1542.62 1544.06 1545.71 1547.30 1548.68 1549.54 1550.62 1551.40

988.021 993.877 997.477 1000.019 1003.204 1006.417 1009.525 1011.641 1014.637 1016.699

1542.86 1546.11 1547.97 1549.23 1550.70 1552.07 1553.29 1554.04 1555.00 1555.68

1530.99 1533.85 1536.66 1537.37 1538.78 1539.82 1541.19 1543.07 1544.09 1544.69 1545.22 1545.48

991.192 995.159 999.402 1000.551 1002.957 1004.848 1007.257 1011.429 1014.104 1015.880 1017.697 1018.691

1538.50 1541.02 1543.48 1544.10 1545.34 1546.24 1547.44 1549.07 1549.94 1550.45 1550.90 1551.12

989.012 992.942 997.146 998.285 1000.670 1002.543 1004.929 1009.069 1011.725 1013.488 1015.294 1016.281

1544.56 1546.75 1548.88 1549.42 1550.48 1551.25 1552.30 1553.68 1554.41 1554.83 1555.19 1555.37

1533.02 1534.59 1536.14 1537.14 1538.68 1540.12 1541.11 1541.90 1542.26 1543.41 1544.41 1545.22 1545.52 1546.15

992.506 994.669 996.911 998.448 1000.977 1003.230 1005.109 1006.696 1007.379 1010.100 1012.748 1015.401 1016.464 1019.486

1540.48 1541.86 1543.23 1544.10 1545.45 1546.69 1547.53 1548.19 1548.50 1549.43 1550.21 1550.82 1551.03 1551.44

990.317 992.455 994.671 996.190 998.690 1000.913 1002.772 1004.340 1005.016 1007.706 1010.328 1012.954 1014.007 1016.999

1546.50 1547.71 1548.90 1549.66 1550.82 1551.89 1552.59 1553.15 1553.40 1554.15 1554.75 1555.18 1555.33 1555.56

1535.45 1536.15 1536.75 1537.64 1538.04 1538.83 1539.97 1540.64 1541.61 1542.94 1544.20 1545.71 1546.93 1548.10

994.181 995.111 995.936 997.171 997.731 998.911 1000.643 1001.634 1003.170 1005.437 1007.703 1010.824 1013.615 1016.843

1542.85 1543.46 1544.00 1544.78 1545.13 1545.82 1546.82 1547.39 1548.23 1549.35 1550.40 1551.63 1552.58 1553.46

991.983 992.902 993.717 994.940 995.496 996.660 998.366 999.342 1000.858 1003.098 1005.338 1008.423 1011.183 1014.379

1548.81 1549.35 1549.82 1550.50 1550.80 1551.41 1552.28 1552.76 1553.48 1554.42 1555.28 1556.26 1556.99 1557.60

1537.76 1539.24 1540.48 1541.37 1542.42

995.954 997.926 999.680 1000.974 1002.618

1545.09 1546.38 1547.47 1548.26 1549.16

993.747 995.697 997.431 998.710 1000.335

1550.98 1552.12 1553.07 1553.75 1554.53



Article

Table 2. continued 298.15 K m/mol kg−1

ρ/kg m−3

u/m s−1

303.15 K ρ/kg m−3

u/m s−1

0.05405 0.07537 0.09110 0.10230 0.11580 0.12430 0.13891 0.14930 0.16416

1012.402 1015.960 1018.542 1020.347 1022.497 1023.839 1026.112 1027.694 1029.968

1515.69 1518.72 1520.71 1522.01 1523.44 1524.26 1525.53 1526.34 1527.28

1010.890 1014.432 1017.004 1018.803 1020.946 1022.283 1024.547 1026.127 1028.394

1526.73 1529.44 1531.24 1532.42 1533.72 1534.48 1535.66 1536.43 1537.33

0.00000 0.01170 0.02011 0.02921 0.03987 0.05117 0.06124 0.08113 0.10904 0.13080 0.14222 0.15134

1005.194 1007.404 1008.914 1010.458 1012.157 1013.825 1015.217 1018.211 1022.401 1025.568 1027.197 1028.479

1509.42 1511.90 1513.50 1515.08 1516.72 1518.22 1519.29 1521.71 1524.79 1526.78 1527.67 1528.31

1003.704 1005.894 1007.389 1008.918 1010.601 1012.252 1013.627 1016.608 1020.764 1023.909 1025.524 1026.793

1521.40 1523.57 1524.98 1526.38 1527.84 1529.19 1530.18 1532.46 1535.30 1537.16 1538.01 1538.63

0.00000 0.01246 0.02115 0.03095 0.03661 0.05263 0.06815 0.07500 0.08635 0.10204 0.12102 0.13373 0.15065

1007.115 1009.509 1011.028 1012.652 1014.061 1015.779 1017.632 1018.322 1019.447 1021.525 1024.000 1025.617 1027.722

1511.76 1514.49 1516.20 1517.90 1519.30 1520.88 1522.37 1522.88 1523.48 1525.04 1526.65 1527.59 1528.65

1005.605 1007.975 1009.479 1011.086 1012.480 1014.182 1016.014 1016.697 1017.834 1019.897 1022.353 1023.958 1026.049

1523.60 1525.98 1527.49 1528.99 1530.25 1531.68 1533.09 1533.59 1534.31 1535.78 1537.31 1538.22 1539.27

308.15 K ρ/kg m−3

313.15 K

u/m s−1

Water + 0.1483 M NaCl 1009.160 1536.07 1012.681 1538.45 1015.239 1540.01 1017.029 1541.05 1019.161 1542.19 1020.491 1542.85 1022.744 1543.89 1024.318 1544.56 1026.575 1545.35 Water + 0.2047 M NaCl 1002.014 1531.63 1004.184 1533.52 1005.665 1534.75 1007.177 1535.97 1008.845 1537.24 1010.483 1538.43 1011.843 1539.29 1014.814 1541.38 1018.939 1543.91 1022.061 1545.58 1023.663 1546.36 1024.924 1546.93 Water + 0.2543 M NaCl 1003.899 1533.69 1006.244 1535.75 1007.733 1537.07 1009.323 1538.38 1010.701 1539.48 1012.386 1540.74 1014.196 1542.00 1014.870 1542.46 1016.018 1543.21 1018.064 1544.54 1020.501 1545.94 1022.093 1546.78 1024.167 1547.77

ρ/kg m−3 + FluNa 1007.224 1010.719 1013.260 1015.038 1017.158 1018.481 1020.722 1022.288 1024.535 + FluNa 1000.138 1002.288 1003.755 1005.255 1006.908 1008.532 1009.880 1012.841 1016.939 1020.040 1021.632 1022.883 + FluNa 1002.010 1004.329 1005.803 1007.376 1008.737 1010.403 1012.190 1012.855 1014.013 1016.041 1018.456 1020.034 1022.091

318.15 K

323.15 K

u/m s−1

ρ/kg m−3

u/m s−1

ρ/kg m−3

u/m s−1

1544.04 1546.11 1547.47 1548.36 1549.34 1549.90 1550.79 1551.36 1552.01

1005.089 1008.547 1011.062 1012.823 1014.922 1016.231 1018.451 1020.002 1022.228

1550.55 1552.30 1553.42 1554.15 1554.93 1555.37 1556.04 1556.46 1556.90

1002.771 1006.187 1008.673 1010.414 1012.489 1013.783 1015.978 1017.511 1019.711

1555.69 1557.15 1558.06 1558.63 1559.24 1559.56 1560.04 1560.33 1560.58

1540.35 1542.02 1543.10 1544.18 1545.30 1546.35 1547.13 1549.06 1551.36 1552.91 1553.64 1554.18

998.089 1000.220 1001.672 1003.160 1004.800 1006.410 1007.750 1010.686 1014.754 1017.832 1019.410 1020.654

1547.58 1549.05 1549.99 1550.94 1551.91 1552.83 1553.49 1555.18 1557.18 1558.52 1559.16 1559.62

995.872 997.983 999.422 1000.898 1002.526 1004.124 1005.458 1008.356 1012.392 1015.442 1017.008 1018.244

1553.40 1554.69 1555.51 1556.33 1557.16 1557.94 1558.48 1559.86 1561.49 1562.55 1563.04 1563.40

1542.29 1544.12 1545.29 1546.45 1547.44 1548.57 1549.71 1550.14 1550.95 1552.21 1553.56 1554.40 1555.40

999.952 1002.245 1003.703 1005.258 1006.600 1008.249 1010.010 1010.666 1011.831 1013.840 1016.232 1017.796 1019.834

1549.44 1551.06 1552.09 1553.11 1553.99 1554.98 1555.99 1556.37 1557.16 1558.32 1559.57 1560.36 1561.32

997.725 999.991 1001.432 1002.969 1004.293 1005.923 1007.656 1008.303 1009.428 1011.408 1013.766 1015.307 1017.317

1555.18 1556.62 1557.53 1558.43 1559.19 1560.04 1560.90 1561.23 1561.84 1562.83 1563.91 1564.58 1565.39

Standard uncertainties, u, are u(ρ) = 5·10−3 kg m−3, u(u) = 5·10−2 m s−1, u(T) = 0.001 K and standard combined uncertainty, uc, in molality are uc(m) ≤ 2·10−5 mol kg−1. a

where y stands for ϕv or ϕk, m and X are molality and CMC, respectively, y0 indicates the limiting parameter at infinite dilution ϕ0v or ϕ0k , b refers to the experimental slope Sv or Sk, and subscripts 1 and 2 refer to pre- and post-CMC region, respectively. The values of the fitting parameters along with their standard uncertainties are listed in Table 5. The ϕ0v values of FluNa are graphically shown in Figure 5(a) against the concentration of NaCl at different temperatures. It is observed that the ϕ0v values are positive and increase with increasing temperature, which gives an insight that there exists strong solute−solvent interactions that are facilitated at higher temperatures. Furthermore, the ϕ0v values decrease with the increase in concentration of NaCl, which is the signature of the existence of strong interactions between solute and cosolute in the mixtures. According to the specific structure and properties of FluNa, the plausible interactions between FluNa and NaCl can be classified as (a) ion−ion interactions between COO− ions produced from the ionization of FluNa and Na+ of NaCl and ion−ion interactions between Na+ of FluNa and Cl− of NaCl, (b) ion−hydrophilic interactions between Na+ of NaCl and the

hydrophilic groups of FluNa, such as O, N, F, Cl, and S, and (c) ion−hydrophobic interactions between Na+ of NaCl and the hydrophobic groups of FluNa, such as alkyl groups and a benzene ring. The cosphere overlap model13 developed by Friedman and Krishnan suggests that the interaction of type (a) and (b) contributes positively to ϕ0v , whereas type (c) makes a negative contribution to ϕ0v . The negative change in the ϕ0v values with the increase in concentration of NaCl implies that the ion− hydrophobic interaction surpasses the ion−ion and ion− hydrophilic interactions. The ϕ0k values of FluNa are also graphically illustrated in Figure 5(b) against the concentration of NaCl at different temperatures. It is seen that the ϕ0k values are negative at low temperatures, and the magnitudes of ϕ0k values decrease with the increase in temperature and even become positive in magnitude at higher experimental temperatures. The negative ϕ0k values indicate that the water molecules surrounding FluNa are less compressible than that present in bulk and decrease in magnitude or become positive at elevated temperature, which may be attributed to the melting of rigid hydration structures around the D



Article

Table 3. Apparent Molar Volume, ϕv, of FluNa in Water and Aqueous NaCl Solutions at Different Temperatures and Atmospheric Pressure ϕv/10−6 m3 mol−1 m/mol kg

−1

298.15 K

303.15 K

0.03508 0.05711 0.07305 0.09335 0.11419 0.13434 0.14801 0.16752 0.18122

298.36 298.66 299.29 299.99 300.69 300.86 300.83 300.80 300.92

± ± ± ± ± ± ± ± ±

0.10 0.06 0.05 0.04 0.03 0.02 0.02 0.02 0.02

300.50 300.81 301.42 302.10 302.75 302.87 302.81 302.74 302.83

± ± ± ± ± ± ± ± ±

0.10 0.06 0.05 0.04 0.03 0.02 0.02 0.02 0.02

0.02314 0.04870 0.05579 0.07082 0.08281 0.09840 0.12511 0.14248 0.15416 0.16619 0.17241

295.99 297.69 298.19 299.17 299.88 300.82 301.22 301.45 301.65 301.84 301.54

± ± ± ± ± ± ± ± ± ± ±

0.15 0.07 0.06 0.05 0.04 0.03 0.03 0.02 0.02 0.02 0.02

298.21 299.88 300.36 301.33 302.02 302.91 303.28 303.49 303.67 303.84 303.54

± ± ± ± ± ± ± ± ± ± ±

0.15 0.07 0.06 0.05 0.04 0.03 0.03 0.02 0.02 0.02 0.02

0.01231 0.02544 0.03458 0.05003 0.06427 0.07582 0.08572 0.09020 0.10723 0.12426 0.14153 0.14865 0.16880

292.53 294.38 295.34 297.21 299.00 299.19 299.47 299.94 300.03 300.55 300.96 301.29 301.82

± ± ± ± ± ± ± ± ± ± ± ± ±

0.29 0.14 0.10 0.07 0.05 0.04 0.04 0.04 0.03 0.03 0.02 0.02 0.02

294.23 296.17 297.11 298.92 300.67 300.83 301.07 301.54 301.60 302.09 302.47 302.80 303.30

± ± ± ± ± ± ± ± ± ± ± ± ±

0.29 0.14 0.10 0.07 0.05 0.04 0.04 0.04 0.03 0.03 0.02 0.02 0.02

0.00518 0.00985 0.01696 0.02025 0.02721 0.03778 0.04384 0.05315 0.06695 0.08100 0.10051 0.11835 0.13936

288.42 289.51 291.21 292.12 293.46 295.86 296.59 296.95 297.36 297.96 298.48 299.12 299.84

± ± ± ± ± ± ± ± ± ± ± ± ±

0.66 0.35 0.21 0.18 0.13 0.09 0.08 0.06 0.05 0.04 0.04 0.03 0.03

290.12 291.39 293.08 293.97 295.29 297.60 298.21 298.60 298.98 299.56 300.05 300.67 301.36

± ± ± ± ± ± ± ± ± ± ± ± ±

0.66 0.35 0.21 0.17 0.13 0.09 0.08 0.06 0.05 0.04 0.04 0.03 0.03

0.01089 0.02099 0.02876 0.03894 0.05405 0.07537 0.09110

287.99 291.11 293.99 296.93 298.52 299.49 300.08

± ± ± ± ± ± ±

0.32 0.16 0.12 0.09 0.07 0.05 0.04

289.24 292.41 295.24 298.11 299.54 300.49 301.05

± ± ± ± ± ± ±

0.32 0.16 0.12 0.09 0.07 0.05 0.04

308.15 K

Water

Water

Water

Water

Water + FluNa 302.61 ± 0.10 302.92 ± 0.06 303.51 ± 0.05 304.17 ± 0.04 304.79 ± 0.03 304.90 ± 0.02 304.81 ± 0.02 304.71 ± 0.02 304.76 ± 0.02 + 0.0251 M NaCl 300.33 ± 0.15 301.98 ± 0.07 302.44 ± 0.06 303.39 ± 0.05 304.08 ± 0.04 304.96 ± 0.03 305.28 ± 0.03 305.47 ± 0.02 305.64 ± 0.02 305.78 ± 0.02 305.48 ± 0.02 + 0.0586 M NaCl 296.14 ± 0.29 298.07 ± 0.14 299.00 ± 0.10 300.78 ± 0.07 302.48 ± 0.05 302.60 ± 0.04 302.84 ± 0.04 303.29 ± 0.04 303.33 ± 0.03 303.79 ± 0.03 304.14 ± 0.02 304.45 ± 0.02 304.92 ± 0.02 + 0.1021 M NaCl 292.23 ± 0.66 293.41 ± 0.35 295.04 ± 0.20 295.89 ± 0.17 297.22 ± 0.13 299.51 ± 0.09 300.00 ± 0.08 300.38 ± 0.06 300.74 ± 0.05 301.32 ± 0.04 301.78 ± 0.04 302.37 ± 0.03 303.04 ± 0.02 + 0.1483 M NaCl 290.79 ± 0.32 293.94 ± 0.16 296.76 ± 0.12 299.58 ± 0.09 300.83 ± 0.07 301.76 ± 0.05 302.30 ± 0.04 E

313.15 K

+

+

+

+

304.70 305.00 305.58 306.21 306.81 306.90 306.79 306.65 306.68 FluNa 302.40 304.01 304.47 305.41 306.08 306.96 307.25 307.40 307.55 307.67 307.36 FluNa 298.24 300.12 301.04 302.80 304.54 304.62 304.84 305.29 305.30 305.72 306.05 306.35 306.78 FluNa 294.38 295.56 297.10 297.95 299.15 301.45 302.06 302.51 302.83 303.35 303.78 304.32 304.94 FluNa 292.74 295.68 298.31 301.24 302.49 303.38 303.87

318.15 K

323.15 K

± ± ± ± ± ± ± ± ±

0.10 0.06 0.05 0.04 0.03 0.02 0.02 0.02 0.02

306.78 307.03 307.61 308.23 308.82 308.90 308.76 308.58 308.59

± ± ± ± ± ± ± ± ±

0.10 0.06 0.04 0.04 0.03 0.02 0.02 0.02 0.02

308.80 309.04 309.61 310.23 310.81 310.87 310.71 310.50 310.49

± ± ± ± ± ± ± ± ±

0.09 0.06 0.04 0.04 0.03 0.02 0.02 0.02 0.02

± ± ± ± ± ± ± ± ± ± ±

0.15 0.07 0.06 0.05 0.04 0.03 0.03 0.02 0.02 0.02 0.02

304.38 305.96 306.43 307.34 307.99 308.89 309.12 309.25 309.37 309.47 309.15

± ± ± ± ± ± ± ± ± ± ±

0.15 0.07 0.06 0.05 0.04 0.03 0.03 0.02 0.02 0.02 0.02

306.30 307.86 308.31 309.20 309.85 310.76 310.93 311.02 311.12 311.19 310.86

± ± ± ± ± ± ± ± ± ± ±

0.15 0.07 0.06 0.05 0.04 0.03 0.02 0.02 0.02 0.02 0.02

± ± ± ± ± ± ± ± ± ± ± ± ±

0.29 0.13 0.09 0.07 0.05 0.04 0.04 0.04 0.03 0.03 0.02 0.02 0.02

300.46 302.29 303.21 304.96 306.74 306.80 307.01 307.44 307.42 307.80 308.11 308.38 308.80

± ± ± ± ± ± ± ± ± ± ± ± ±

0.29 0.13 0.09 0.07 0.05 0.04 0.04 0.04 0.03 0.03 0.02 0.02 0.02

302.80 304.62 305.54 307.26 309.08 309.11 309.32 309.73 309.71 310.04 310.32 310.57 310.95

± ± ± ± ± ± ± ± ± ± ± ± ±

0.29 0.13 0.09 0.07 0.05 0.04 0.04 0.04 0.03 0.03 0.02 0.02 0.02

± ± ± ± ± ± ± ± ± ± ± ± ±

0.65 0.34 0.20 0.17 0.13 0.09 0.08 0.06 0.05 0.04 0.03 0.03 0.02

296.56 297.84 299.37 300.20 301.33 303.62 304.34 304.76 305.07 305.59 305.99 306.51 307.11

± ± ± ± ± ± ± ± ± ± ± ± ±

0.65 0.34 0.20 0.17 0.13 0.09 0.08 0.06 0.05 0.04 0.03 0.03 0.02

298.97 300.27 301.62 302.33 303.59 306.04 306.82 307.25 307.53 308.01 308.37 308.85 309.39

± ± ± ± ± ± ± ± ± ± ± ± ±

0.65 0.34 0.20 0.17 0.13 0.09 0.08 0.06 0.05 0.04 0.03 0.03 0.02

± ± ± ± ± ± ±

0.32 0.16 0.12 0.09 0.07 0.05 0.04

294.73 297.74 300.31 303.21 304.59 305.47 305.95

± ± ± ± ± ± ±

0.32 0.16 0.12 0.09 0.07 0.05 0.04

297.02 300.04 302.60 305.49 306.98 307.85 308.30

± ± ± ± ± ± ±

0.32 0.16 0.12 0.09 0.07 0.05 0.04



Article

Table 3. continued ϕv/10−6 m3 mol−1 m/mol kg−1

298.15 K

303.15 K

0.10230 0.11580 0.12430 0.13891 0.14930 0.16416

300.58 301.12 301.43 302.01 302.50 302.92

± ± ± ± ± ±

0.03 0.03 0.03 0.02 0.02 0.02

301.53 302.05 302.35 302.92 303.38 303.78

± ± ± ± ± ±

0.03 0.03 0.03 0.02 0.02 0.02

0.01170 0.02011 0.02921 0.03987 0.05117 0.06124 0.08113 0.10904 0.13080 0.14222 0.15134

285.74 289.24 293.50 298.48 303.86 308.33 310.57 311.87 312.89 313.42 313.85

± ± ± ± ± ± ± ± ± ± ±

0.30 0.18 0.12 0.08 0.06 0.05 0.04 0.03 0.02 0.02 0.02

287.59 291.13 295.37 300.32 305.68 310.18 312.19 313.46 314.43 314.95 315.40

± ± ± ± ± ± ± ± ± ± ±

0.30 0.18 0.12 0.08 0.06 0.05 0.04 0.03 0.02 0.02 0.02

0.01246 0.02115 0.03095 0.03661 0.05263 0.06815 0.07500 0.08635 0.10204 0.12102 0.13373 0.15065

282.41 288.96 294.49 283.48 307.54 317.03 321.59 327.67 328.56 329.41 330.02 330.86

± ± ± ± ± ± ± ± ± ± ± ±

0.29 0.16 0.11 0.10 0.06 0.04 0.04 0.03 0.03 0.02 0.02 0.02

284.46 290.95 296.46 285.55 309.40 318.86 323.39 329.15 330.00 330.83 331.43 332.25

± ± ± ± ± ± ± ± ± ± ± ±

0.28 0.16 0.11 0.10 0.06 0.04 0.04 0.03 0.03 0.02 0.02 0.02

308.15 K

313.15 K

Water + 0.1483 M NaCl + FluNa 302.75 ± 0.03 304.30 303.26 ± 0.03 304.77 303.55 ± 0.03 305.04 304.11 ± 0.02 305.55 304.54 ± 0.02 305.97 304.93 ± 0.02 306.31 Water + 0.2047 M NaCl + FluNa 289.47 ± 0.30 291.37 293.00 ± 0.18 294.91 297.32 ± 0.12 299.12 302.19 ± 0.08 303.97 307.46 ± 0.06 309.20 311.97 ± 0.05 313.68 313.74 ± 0.04 315.24 314.97 ± 0.03 316.43 315.93 ± 0.02 317.36 316.45 ± 0.02 317.86 316.87 ± 0.02 318.30 Water + 0.2543 M NaCl + FluNa 286.61 ± 0.28 288.88 293.01 ± 0.16 295.16 298.50 ± 0.11 300.60 287.70 ± 0.10 289.94 311.36 ± 0.06 313.44 320.79 ± 0.04 322.84 325.31 ± 0.04 327.34 330.75 ± 0.03 332.47 331.58 ± 0.03 333.28 332.38 ± 0.02 334.06 332.97 ± 0.02 334.63 333.77 ± 0.02 335.41

318.15 K

323.15 K

± ± ± ± ± ±

0.03 0.03 0.03 0.02 0.02 0.02

306.36 306.80 307.07 307.56 307.97 308.30

± ± ± ± ± ±

0.03 0.03 0.03 0.02 0.02 0.02

308.69 309.12 309.38 309.85 310.25 310.57

± ± ± ± ± ±

0.03 0.03 0.03 0.02 0.02 0.02

± ± ± ± ± ± ± ± ± ± ±

0.30 0.18 0.12 0.08 0.06 0.05 0.04 0.03 0.02 0.02 0.02

293.23 296.84 300.96 305.74 310.94 315.34 316.89 318.03 318.94 319.45 319.86

± ± ± ± ± ± ± ± ± ± ±

0.30 0.18 0.11 0.08 0.06 0.05 0.04 0.03 0.02 0.02 0.02

295.20 298.76 302.80 307.49 312.64 316.93 318.67 319.75 320.66 321.16 321.54

± ± ± ± ± ± ± ± ± ± ±

0.30 0.18 0.11 0.08 0.06 0.05 0.04 0.03 0.02 0.02 0.02

± ± ± ± ± ± ± ± ± ± ± ±

0.28 0.16 0.11 0.10 0.06 0.04 0.04 0.03 0.03 0.02 0.02 0.02

291.18 297.39 302.81 292.33 315.59 325.01 329.48 334.32 335.10 335.87 336.42 337.18

± ± ± ± ± ± ± ± ± ± ± ±

0.28 0.16 0.11 0.10 0.06 0.04 0.04 0.03 0.03 0.02 0.02 0.02

293.60 299.75 305.12 294.78 317.85 327.29 331.74 336.83 337.60 338.34 338.88 339.62

± ± ± ± ± ± ± ± ± ± ± ±

0.28 0.15 0.10 0.10 0.06 0.04 0.04 0.03 0.03 0.02 0.02 0.02

Figure 2. (a) Variation of ϕv with the concentration of FluNa at T = (■, 298.15; ●, 303.15; ▲, 308.15; ⧫, 313.15; ×, 318.15; and *, 323.15) K. (b) The ϕv values of FluNa in m = (□, 0.000; ○, 0.0251; △, 0.0586; ▽, 0.1021; ◇, 0.1483; left-facing triangle, 0.2047; and right-facing triangle, 0.2543) M aqueous NaCl solutions at 298.15 K. The solid lines represent the fitting values according to eq 5. F



Article

Table 4. Apparent Molar Adiabatic Compressibility, ϕk, of FluNa in Water and Aqueous NaCl Solutions at Different Temperatures and Atmospheric Pressure ϕk/10−14 m3 mol−1 Pa−1 m/mol kg

−1

298.15 K

303.15 K

0.03508 0.05711 0.07305 0.09335 0.11419 0.13434 0.14801 0.16752 0.18122

−4.86 −4.39 −3.99 −3.52 −3.03 −2.65 −2.42 −2.07 −1.83

± ± ± ± ± ± ± ± ±

0.24 0.15 0.12 0.09 0.07 0.06 0.06 0.05 0.05

−3.50 −3.10 −2.79 −2.35 −1.94 −1.62 −1.41 −1.12 −0.90

± ± ± ± ± ± ± ± ±

0.24 0.14 0.11 0.09 0.07 0.06 0.06 0.05 0.05

0.02314 0.04870 0.05579 0.07082 0.08281 0.09840 0.12511 0.14248 0.15416 0.16619 0.17241

−5.38 −4.54 −4.30 −3.80 −3.43 −3.08 −2.47 −2.07 −1.81 −1.53 −1.43

± ± ± ± ± ± ± ± ± ± ±

0.36 0.17 0.15 0.12 0.10 0.09 0.07 0.06 0.05 0.05 0.05

−3.96 −3.22 −3.01 −2.59 −2.27 −1.95 −1.41 −1.05 −0.81 −0.57 −0.48

± ± ± ± ± ± ± ± ± ± ±

0.36 0.17 0.15 0.12 0.10 0.08 0.07 0.06 0.05 0.05 0.05

0.01231 0.02544 0.03458 0.05003 0.06427 0.07582 0.08572 0.09020 0.10723 0.12426 0.14153 0.14865 0.16880

−6.14 −5.53 −5.11 −4.42 −3.97 −3.66 −3.40 −3.26 −2.82 −2.37 −1.90 −1.71 −1.17

± ± ± ± ± ± ± ± ± ± ± ± ±

0.68 0.33 0.24 0.17 0.13 0.11 0.10 0.09 0.08 0.07 0.06 0.06 0.05

−4.59 −4.08 −3.72 −3.09 −2.72 −2.45 −2.21 −2.09 −1.70 −1.30 −0.89 −0.72 −0.25

± ± ± ± ± ± ± ± ± ± ± ± ±

0.67 0.32 0.24 0.16 0.13 0.11 0.10 0.09 0.08 0.07 0.06 0.05 0.05

0.00518 0.00985 0.01696 0.02025 0.02721 0.03778 0.04384 0.05315 0.06695 0.08100 0.10051 0.11835 0.13936

−7.06 −6.77 −6.37 −6.15 −5.71 −5.06 −4.80 −4.53 −4.15 −3.75 −3.21 −2.71 −2.12

± ± ± ± ± ± ± ± ± ± ± ± ±

1.60 0.84 0.49 0.41 0.30 0.22 0.19 0.16 0.12 0.10 0.08 0.07 0.06

−5.44 −5.13 −4.79 −4.59 −4.21 −3.64 −3.44 −3.22 −2.89 −2.55 −2.08 −1.65 −1.14

± ± ± ± ± ± ± ± ± ± ± ± ±

1.57 0.82 0.48 0.40 0.30 0.21 0.18 0.15 0.12 0.10 0.08 0.07 0.06

0.01089 0.02099 0.02876 0.03894 0.05405 0.07537 0.09110

−7.31 −6.49 −5.89 −5.07 −4.48 −3.89 −3.45

± ± ± ± ± ± ±

0.75 0.39 0.29 0.21 0.15 0.11 0.09

−5.59 −4.86 −4.34 −3.61 −3.17 −2.67 −2.31

± ± ± ± ± ± ±

0.74 0.38 0.28 0.21 0.15 0.11 0.09

308.15 K

Water

Water

Water

Water

Water + FluNa −2.31 ± 0.23 −1.96 ± 0.14 −1.67 ± 0.11 −1.30 ± 0.09 −0.93 ± 0.07 −0.63 ± 0.06 −0.47 ± 0.05 −0.19 ± 0.05 −0.02 ± 0.04 + 0.0251 M NaCl −2.70 ± 0.35 −2.03 ± 0.17 −1.86 ± 0.14 −1.47 ± 0.11 −1.19 ± 0.10 −0.90 ± 0.08 −0.42 ± 0.06 −0.09 ± 0.06 0.12 ± 0.05 0.34 ± 0.05 0.42 ± 0.05 + 0.0586 M NaCl −3.25 ± 0.65 −2.78 ± 0.32 −2.45 ± 0.23 −1.90 ± 0.16 −1.58 ± 0.12 −1.34 ± 0.11 −1.13 ± 0.09 −1.02 ± 0.09 −0.68 ± 0.07 −0.32 ± 0.06 0.04 ± 0.06 0.20 ± 0.05 0.62 ± 0.05 + 0.1021 M NaCl −3.98 ± 1.54 −3.73 ± 0.81 −3.39 ± 0.47 −3.22 ± 0.39 −2.86 ± 0.29 −2.35 ± 0.21 −2.23 ± 0.18 −2.03 ± 0.15 −1.74 ± 0.12 −1.44 ± 0.10 −1.04 ± 0.08 −0.66 ± 0.07 −0.22 ± 0.06 + 0.1483 M NaCl −4.09 ± 0.73 −3.44 ± 0.38 −2.94 ± 0.27 −2.31 ± 0.20 −1.94 ± 0.15 −1.52 ± 0.10 −1.20 ± 0.09 G

313.15 K

+

+

+

+

−1.21 −0.91 −0.66 −0.35 −0.02 0.23 0.38 0.60 0.77 FluNa −1.55 −0.98 −0.82 −0.48 −0.22 0.03 0.48 0.77 0.96 1.16 1.23 FluNa −2.09 −1.64 −1.35 −0.85 −0.54 −0.31 −0.11 0.00 0.32 0.66 1.01 1.16 1.56 FluNa −2.79 −2.50 −2.20 −2.06 −1.74 −1.28 −1.15 −0.97 −0.70 −0.43 −0.05 0.29 0.71 FluNa −2.88 −2.27 −1.82 −1.24 −0.92 −0.53 −0.24

318.15 K

323.15 K

± ± ± ± ± ± ± ± ±

0.23 0.14 0.11 0.09 0.07 0.06 0.05 0.05 0.04

−0.25 0.01 0.22 0.52 0.79 1.01 1.14 1.34 1.46

± ± ± ± ± ± ± ± ±

0.23 0.14 0.11 0.09 0.07 0.06 0.05 0.05 0.04

0.65 0.87 1.05 1.30 1.55 1.74 1.86 2.03 2.13

± ± ± ± ± ± ± ± ±

0.22 0.14 0.11 0.08 0.07 0.06 0.05 0.05 0.04

± ± ± ± ± ± ± ± ± ± ±

0.35 0.16 0.14 0.11 0.10 0.08 0.06 0.06 0.05 0.05 0.05

−0.58 −0.04 0.11 0.41 0.65 0.88 1.28 1.54 1.71 1.89 1.95

± ± ± ± ± ± ± ± ± ± ±

0.34 0.16 0.14 0.11 0.10 0.08 0.06 0.06 0.05 0.05 0.05

0.35 0.83 0.96 1.25 1.47 1.67 2.03 2.26 2.41 2.58 2.62

± ± ± ± ± ± ± ± ± ± ±

0.34 0.16 0.14 0.11 0.09 0.08 0.06 0.06 0.05 0.05 0.05

± ± ± ± ± ± ± ± ± ± ± ± ±

0.64 0.31 0.23 0.16 0.12 0.10 0.09 0.09 0.07 0.06 0.06 0.05 0.05

−1.05 −0.66 −0.38 0.08 0.39 0.61 0.80 0.90 1.21 1.54 1.87 2.02 2.40

± ± ± ± ± ± ± ± ± ± ± ± ±

0.64 0.31 0.23 0.16 0.12 0.10 0.09 0.09 0.07 0.06 0.06 0.05 0.05

−0.12 0.26 0.51 0.95 1.25 1.46 1.63 1.73 2.03 2.34 2.66 2.79 3.15

± ± ± ± ± ± ± ± ± ± ± ± ±

0.63 0.31 0.23 0.16 0.12 0.10 0.09 0.09 0.07 0.06 0.06 0.05 0.05

± ± ± ± ± ± ± ± ± ± ± ± ±

1.52 0.80 0.46 0.39 0.29 0.21 0.18 0.15 0.12 0.10 0.08 0.07 0.06

−1.65 −1.47 −1.17 −1.03 −0.74 −0.31 −0.16 0.01 0.28 0.55 0.92 1.26 1.66

± ± ± ± ± ± ± ± ± ± ± ± ±

1.51 0.79 0.46 0.38 0.29 0.21 0.18 0.15 0.12 0.10 0.08 0.07 0.06

−0.73 −0.52 −0.24 −0.10 0.16 0.58 0.74 0.91 1.17 1.43 1.79 2.12 2.51

± ± ± ± ± ± ± ± ± ± ± ± ±

1.50 0.79 0.46 0.38 0.28 0.20 0.18 0.15 0.12 0.10 0.08 0.07 0.06

± ± ± ± ± ± ±

0.72 0.37 0.27 0.20 0.14 0.10 0.09

−1.76 −1.22 −0.82 −0.26 0.06 0.45 0.73

± ± ± ± ± ± ±

0.71 0.37 0.27 0.20 0.14 0.10 0.08

−0.85 −0.31 0.09 0.62 0.97 1.35 1.63

± ± ± ± ± ± ±

0.71 0.37 0.27 0.20 0.14 0.10 0.08



Article

Table 4. continued ϕk/10−14 m3 mol−1 Pa−1 m/mol kg−1

298.15 K

303.15 K

0.10230 0.11580 0.12430 0.13891 0.14930 0.16416

−3.14 −2.77 −2.53 −2.13 −1.84 −1.43

± ± ± ± ± ±

0.08 0.07 0.07 0.06 0.05 0.05

−2.05 −1.73 −1.54 −1.20 −0.96 −0.61

± ± ± ± ± ±

0.08 0.07 0.06 0.06 0.05 0.05

0.01170 0.02011 0.02921 0.03987 0.05117 0.06124 0.08113 0.10904 0.13080 0.14222 0.15134

−7.89 −7.04 −6.13 −5.07 −3.95 −2.94 −2.18 −1.44 −0.87 −0.57 −0.33

± ± ± ± ± ± ± ± ± ± ±

0.70 0.40 0.28 0.20 0.16 0.13 0.10 0.07 0.06 0.06 0.05

−6.08 −5.34 −4.54 −3.60 −2.61 −1.72 −1.14 −0.52 −0.03 0.23 0.43

± ± ± ± ± ± ± ± ± ± ±

0.68 0.40 0.27 0.20 0.16 0.13 0.10 0.07 0.06 0.06 0.05

0.01246 0.02115 0.03095 0.03661 0.05263 0.06815 0.07500 0.08635 0.10204 0.12102 0.13373 0.15065

−8.45 −7.34 −6.19 −7.55 −3.62 −1.80 −0.99 0.24 0.64 1.12 1.44 1.87

± ± ± ± ± ± ± ± ± ± ± ±

0.65 0.38 0.26 0.22 0.15 0.12 0.11 0.09 0.08 0.07 0.06 0.05

−6.55 −5.58 −4.55 −5.88 −2.29 −0.69 0.03 1.03 1.37 1.78 2.05 2.42

± ± ± ± ± ± ± ± ± ± ± ±

0.63 0.37 0.26 0.22 0.15 0.12 0.11 0.09 0.08 0.07 0.06 0.05

308.15 K

313.15 K

Water + 0.1483 M NaCl + FluNa −0.97 ± 0.08 −0.03 ± 0.08 −0.70 ± 0.07 0.22 ± 0.07 −0.53 ± 0.06 0.37 ± 0.06 −0.23 ± 0.06 0.64 ± 0.06 −0.02 ± 0.05 0.83 ± 0.05 0.29 ± 0.05 1.11 ± 0.05 Water + 0.2047 M NaCl + FluNa −4.51 ± 0.67 −3.28 ± 0.66 −3.84 ± 0.39 −2.65 ± 0.38 −3.10 ± 0.27 −1.97 ± 0.26 −2.24 ± 0.20 −1.18 ± 0.19 −1.35 ± 0.15 −0.36 ± 0.15 −0.54 ± 0.13 0.38 ± 0.13 −0.10 ± 0.10 0.71 ± 0.10 0.43 ± 0.07 1.17 ± 0.07 0.85 ± 0.06 1.53 ± 0.06 1.07 ± 0.06 1.72 ± 0.05 1.25 ± 0.05 1.87 ± 0.05 Water + 0.2543 M NaCl + FluNa −4.87 ± 0.62 −3.64 ± 0.62 −4.01 ± 0.37 −2.83 ± 0.36 −3.08 ± 0.25 −1.96 ± 0.25 −4.34 ± 0.21 −3.17 ± 0.21 −1.02 ± 0.15 −0.06 ± 0.15 0.43 ± 0.11 1.29 ± 0.11 1.08 ± 0.10 1.89 ± 0.10 1.91 ± 0.09 2.55 ± 0.09 2.19 ± 0.08 2.79 ± 0.08 2.54 ± 0.06 3.08 ± 0.06 2.78 ± 0.06 3.27 ± 0.06 3.09 ± 0.05 3.53 ± 0.05

318.15 K

323.15 K

0.93 1.17 1.32 1.59 1.77 2.04

± ± ± ± ± ±

0.08 0.07 0.06 0.06 0.05 0.05

1.83 2.06 2.21 2.47 2.65 2.91

± ± ± ± ± ±

0.08 0.07 0.06 0.06 0.05 0.05

−2.20 −1.57 −0.96 −0.21 0.56 1.26 1.55 1.96 2.29 2.46 2.60

± ± ± ± ± ± ± ± ± ± ±

0.66 0.38 0.26 0.19 0.15 0.13 0.09 0.07 0.06 0.05 0.05

−1.23 −0.64 −0.05 0.67 1.40 2.07 2.41 2.80 3.12 3.28 3.41

± ± ± ± ± ± ± ± ± ± ±

0.65 0.38 0.26 0.19 0.15 0.12 0.09 0.07 0.06 0.05 0.05

−2.53 −1.76 −0.94 −2.10 0.85 2.12 2.69 3.25 3.44 3.69 3.85 4.06

± ± ± ± ± ± ± ± ± ± ± ±

0.61 0.36 0.25 0.21 0.14 0.11 0.10 0.09 0.07 0.06 0.06 0.05

−1.59 −0.83 −0.05 −1.14 1.68 2.91 3.45 4.06 4.24 4.45 4.60 4.80

± ± ± ± ± ± ± ± ± ± ± ±

0.61 0.36 0.24 0.21 0.14 0.11 0.10 0.09 0.07 0.06 0.06 0.05

Figure 3. (a) Variation of ϕk with the concentration of FluNa at T = (■, 298.15; ●, 303.15; ▲, 308.15; ⧫, 313.15; ×, 318.15; *, 323.15) K. (b) The ϕk values of FluNa in m = (□, 0.00; ○, 0.0251; △, 0.0586; ▽, 0.1021; ◇, 0.1483; left-facing triangle, 0.2047; and right-facing triangle, 0.2543) M aqueous NaCl solutions at 298.15 K. The solid lines represent the fitting values according to eq 5. H



Article

FluNa molecule. However, the ϕ0k values become more negative with the increase in concentration of NaCl, indicating the clustering of water through the enhancement of hydrogen bonding. According to Frank and Wen,14 ions having low-charge density are surrounded by more randomly distributed monomeric water molecules compared to bulk rather than orderly arranged water molecules. The water molecules in the monomeric form are more compressible. The hydrophilic groups of FluNa, such as O, N, F, Cl, and S, possess weak partial charges and the interaction of type (b) is responsible for relaxing monomeric water molecules to bulk, where they are reorganized to cluster, giving a negative contribution to ϕ0k values. It is also reported15 that aromatic rings are well-accommodated in aqueous electrolyte solution rather than pure water, which also leads to a decrease in ϕ0k. Progressively negative ϕ0k values with increasing concentration of NaCl may be attributed to dominating the interaction of type (b) and good fitting of the aromatic ring in aqueous NaCl solution. The calculated CMC values for FluNa are graphically represented in Figure 6 as a function of NaCl molality and temperature. Comparison of the CMC values of FluNa with

Figure 4. Conductivities of aqueous FluNa solutions as a function of molality of FluNa at 295.15 K.

Table 5. Fitting Parameters of eq 5 for ϕv and ϕk against the Molalities of NaCl at Different Temperatures and Atmospheric Pressurea ϕv/10−6 m3 mol−1 m

ϕ0v

Sv1

ϕk/10−14 m3 mol−1 Pa−1 X

0.0000 0.0251 0.0586 0.1021 0.1483 0.2047 0.2543

297.11 ± 0.17 294.55 ± 0.13 291.11 ± 0.15 287.31 ± 0.07 284.48 ± 0.15 280.11 ± 0.11 275.52 ± 0.37

30.7 ± 2.2 64.3 ± 1.9 122.8 ± 4.6 227.9 ± 3.2 322.4 ± 5.4 461.5 ± 2.9 613.4 ± 7.7

0.1209 ± 0.0064 0.1009 ± 0.0033 0.0640 ± 0.0019 0.0403 ± 0.0005 0.0423 ± 0.0005 0.0643 ± 0.0004 0.0850 ± 0.0009

0.0000 0.0251 0.0586 0.1021 0.1483 0.2047 0.2543

299.30 ± 0.16 296.82 ± 0.13 292.85 ± 0.17 289.13 ± 0.10 285.79 ± 0.15 282.03 ± 0.11 277.61 ± 0.37

29.7 ± 2.0 62.7 ± 1.9 122.8 ± 5.1 227.4 ± 4.6 319.6 ± 5.6 460.0 ± 2.7 609.5 ± 7.7

0.1198 ± 0.0057 0.1008 ± 0.0034 0.0631 ± 0.0020 0.0395 ± 0.0007 0.0418 ± 0.0005 0.0639 ± 0.0004 0.0845 ± 0.0009

0.0000 0.0251 0.0586 0.1021 0.1483 0.2047 0.2543

301.46 ± 0.15 298.96 ± 0.13 294.78 ± 0.17 291.22 ± 0.08 287.38 ± 0.16 283.99 ± 0.09 279.76 ± 0.36

28.8 ± 1.8 61.7 ± 1.9 121.5 ± 5.1 221.8 ± 3.6 316.9 ± 5.8 457.1 ± 2.4 606.2 ± 7.6

0.1204 ± 0.0051 0.1007 ± 0.0033 0.0626 ± 0.0020 0.0392 ± 0.0005 0.0412 ± 0.0005 0.0634 ± 0.0003 0.0840 ± 0.0009

0.0000 0.0251 0.0586 0.1021 0.1483 0.2047 0.2543

303.59 ± 0.14 301.04 ± 0.12 296.90 ± 0.17 293.41 ± 0.09 289.39 ± 0.11 285.94 ± 0.09 282.01 ± 0.35

27.8 ± 1.8 60.8 ± 1.8 119.5 ± 5.0 214.2 ± 4.1 305.6 ± 4.2 453.2 ± 2.2 603.1 ± 7.3

0.1207 ± 0.0048 0.1011 ± 0.0031 0.0633 ± 0.0020 0.0404 ± 0.0006 0.0418 ± 0.0004 0.0629 ± 0.0003 0.0835 ± 0.0009

0.0000 0.0251 0.0586

305.68 ± 0.16 303.04 ± 0.12 299.12 ± 0.16

27.0 ± 2.0 59.9 ± 1.8 118.0 ± 4.8

0.1214 ± 0.0051 0.1011 ± 0.0031 0.0640 ± 0.0019

Sv2 298.15 K 0.9 ± 3.7 9.7 ± 3.0 26.8 ± 1.2 33.7 ± 1.0 40.3 ± 1.1 46.7 ± 2.1 48.9 ± 8.7 303.15 K −1.3 ± 3.4 8.4 ± 3.0 25.1 ± 1.4 32.5 ± 1.4 38.8 ± 1.1 45.4 ± 2.1 47.6 ± 8.7 308.15 K −3.3 ± 3.2 7.0 ± 2.9 23.3 ± 1.4 31.3 ± 1.1 37.5 ± 1.2 44.4 ± 1.8 46.3 ± 8.6 313.15 K −5.1 ± 3.0 5.1 ± 2.9 21.5 ± 1.4 29.2 ± 1.3 34.9 ± 0.8 43.3 ± 1.6 45.1 ± 8.3 318.15 K −7.0 ± 3.4 3.4 ± 2.8 19.7 ± 1.3 I

ϕ0k

Sk1

X

Sk2

−5.69 ± 0.02 −6.15 ± 0.02 −6.69 ± 0.01 −7.39 ± 0.01 −8.17 ± 0.01 −9.09 ± 0.03 −9.83 ± 0.07

23.3 ± 0.24 33.1 ± 0.36 45.6 ± 0.26 61.4 ± 0.40 79.7 ± 0.25 100.4 ± 0.83 118.3 ± 1.49

0.1190 ± 0.0037 0.0807 ± 0.0015 0.0534 ± 0.0005 0.0408 ± 0.0004 0.0423 ± 0.0001 0.0642 ± 0.0007 0.0848 ± 0.0011

17.56 ± 0.40 22.58 ± 0.15 26.76 ± 0.07 28.01 ± 0.12 27.70 ± 0.05 26.57 ± 0.62 25.33 ± 1.70

−4.22 ± 0.02 −4.62 ± 0.02 −5.09 ± 0.01 −5.70 ± 0.01 −6.35 ± 0.01 −7.04 ± 0.02 −7.77 ± 0.06

19.9 ± 0.29 28.8 ± 0.37 39.8 ± 0.26 54.7 ± 0.55 70.3 ± 0.34 86.8 ± 0.40 104.4 ± 1.24

0.1182 ± 0.0057 0.0799 ± 0.0019 0.0528 ± 0.0005 0.0393 ± 0.0005 0.0409 ± 0.0002 0.0639 ± 0.0004 0.0838 ± 0.0010

15.29 ± 0.50 20.20 ± 0.15 23.63 ± 0.07 24.09 ± 0.17 23.21 ± 0.07 21.92 ± 0.30 21.59 ± 1.41

−2.94 ± 0.02 −3.29 ± 0.02 −3.69 ± 0.01 −4.24 ± 0.01 −4.78 ± 0.01 −5.47 ± 0.04 −5.99 ± 0.05

17.6 ± 0.25 25.8 ± 0.34 35.8 ± 0.21 50.5 ± 0.34 63.5 ± 0.31 80.8 ± 0.93 94.6 ± 1.12

0.1220 ± 0.0050 0.0795 ± 0.0019 0.0514 ± 0.0004 0.0371 ± 0.0003 0.0401 ± 0.0002 0.0619 ± 0.0009 0.0828 ± 0.0010

13.21 ± 0.43 18.16 ± 0.14 21.03 ± 0.06 21.00 ± 0.06 20.25 ± 0.06 19.23 ± 0.69 18.40 ± 1.27

−1.76 ± 0.02 −2.07 ± 0.02 −2.49 ± 0.01 −3.00 ± 0.02 −3.51 ± 0.01 −4.18 ± 0.02 −4.67 ± 0.05

15.1 ± 0.21 22.4 ± 0.31 32.8 ± 0.31 46.6 ± 1.05 58.4 ± 0.31 74.4 ± 0.41 87.8 ± 1.00

0.1212 ± 0.0051 0.0819 ± 0.0023 0.0517 ± 0.0008 0.0365 ± 0.0009 0.0398 ± 0.0002 0.0613 ± 0.0004 0.0814 ± 0.0009

11.48 ± 0.36 16.41 ± 0.13 20.07 ± 0.08 19.48 ± 0.19 18.42 ± 0.06 16.48 ± 0.30 15.22 ± 1.14

−0.73 ± 0.02 −1.06 ± 0.02 −1.42 ± 0.01

13.3 ± 0.24 20.8 ± 0.32 30.0 ± 0.21

0.1223 ± 0.0059 0.0809 ± 0.0023 0.0533 ± 0.0006

9.70 ± 0.42 14.70 ± 0.13 19.23 ± 0.06



Article

Table 5. Continued ϕv/10−6 m3 mol−1 m

ϕ0v

Sv1

ϕk/10−14 m3 mol−1 Pa−1 X

0.1021 0.1483 0.2047 0.2543

295.67 ± 0.11 291.42 ± 0.11 287.86 ± 0.06 284.31 ± 0.35

212.3 ± 5.0 304.3 ± 3.9 449.3 ± 1.6 600.9 ± 7.4

0.0409 ± 0.0008 0.0423 ± 0.0004 0.0628 ± 0.0002 0.0830 ± 0.0009

0.0000 0.0251 0.0586 0.1021 0.1483 0.2047 0.2543

307.71 ± 0.16 304.97 ± 0.12 301.46 ± 0.16 298.02 ± 0.10 293.72 ± 0.11 289.98 ± 0.06 286.73 ± 0.35

26.7 ± 2.0 59.2 ± 1.8 117.6 ± 4.7 210.9 ± 4.3 303.9 ± 3.9 440.6 ± 1.5 598.7 ± 7.4

0.1215 ± 0.0050 0.1013 ± 0.0029 0.0642 ± 0.0019 0.0421 ± 0.0007 0.0428 ± 0.0004 0.0634 ± 0.0002 0.0836 ± 0.0009

Sv2 318.15 K 28.1 ± 1.6 33.8 ± 0.8 42.2 ± 1.2 43.9 ± 8.4 323.15 K −8.5 ± 3.4 1.2 ± 2.8 18.0 ± 1.3 25.9 ± 1.3 32.6 ± 0.8 41.1 ± 1.1 42.8 ± 8.4

ϕ0k

Sk1

X

Sk2

−1.87 ± 0.00 −2.34 ± 0.01 −3.12 ± 0.03 −3.50 ± 0.05

41.3 ± 0.16 53.3 ± 0.25 72.9 ± 0.91 82.8 ± 0.95

0.0391 ± 0.0002 0.0406 ± 0.0002 0.0600 ± 0.0006 0.0806 ± 0.0009

19.09 ± 0.05 17.94 ± 0.05 14.46 ± 0.36 12.67 ± 1.08

0.23 ± 0.02 −0.09 ± 0.02 −0.47 ± 0.01 −0.92 ± 0.01 −1.42 ± 0.01 −1.97 ± 0.03 −2.51 ± 0.05

11.5 ± 0.24 18.8 ± 0.27 28.3 ± 0.20 39.9 ± 0.30 52.3 ± 0.20 66.3 ± 0.75 79.9 ± 0.99

0.1260 ± 0.0066 0.0832 ± 0.0027 0.0539 ± 0.0006 0.0397 ± 0.0004 0.0414 ± 0.0001 0.0620 ± 0.0008 0.0816 ± 0.0010

8.38 ± 0.41 13.06 ± 0.20 18.22 ± 0.05 18.53 ± 0.09 17.60 ± 0.04 14.24 ± 0.56 11.47 ± 1.12

Units are m/mol kg−1, ϕ0v /10−6 m3 mol−1, Sv1 (or Sv2)/10−6 kg m3 mol−2, ϕ0k/10−14 m3 mol−1 Pa−1, Sk1 (or Sk2)/10−14 kg m3 mol−2 Pa−1, and X/mol kg−1.

a

Figure 5. Plot of ϕ0v (a) and ϕ0k (b) of FluNa against the molalities of NaCl at T = (■, 298.15; □, 303.15; ●, 308.15; ○, 313.15; ▲, 318.15; and △, 323.15) K. Figure 6. CMC of FluNa obtained from ϕv (solid splines) and ϕk (dashed splines) as a function of NaCl concentration at T = (○, 298.15; □, 303.15; △, 308.15; ◇, 313.15; ×, 318.15; and *, 323.15) K. For better representation, the y-axis for CMC is offset by 0.00, 0.03, 0.06, 0.09, 0.12, and 0.15 at T = (298.15, 303.15, 308.15, 313.15, 318.15, and 323.15) K, respectively.

previously reported values determined by light scattering11,16 and NMR11 techniques in aqueous and aqueous NaCl solutions shows a close agreement. It is apparent from Figure 6 that the CMC values obtained from ϕv−m and ϕk−m data exhibit an analogous response to the concentration of NaCl. The CMC values decrease with increasing concentration of NaCl, reaching a minimum value and then increasing. The initial decrease of CMC with increasing concentration of NaCl is due to the minimization of electrostatic repulsion among the polar head groups, such as COO−, O, N, F, Cl, and S in the presence of NaCl. Afterwards, the micelle in the presence of excess NaCl may undergo transition of their size and shape from spherical to cylindrical. It is reported17 that, at elevated salt concentrations, solute molecules pack densely enough such that they effectively adopt a more cylindrical (rather than conelike) shape. Because the micelle with cylindrical shape involves more solute molecules than spherical ones, these are expected to form at higher solute concentrations. The values of Sv and Sk are shown in Figure 7 as a function of NaCl molalities at 298.15 K. The values of pre-CMC slopes

(Sv1 and Sk1) increase with the increase in concentration of NaCl at all experimental temperatures. Conversely, the values of postCMC slopes (Sv2 and Sk2) increase at higher rates up to 0.1483 M solution of NaCl; afterwards, Sv2 increases at a much slower rate and Sk2 decreases. It is worth mentioning that Sv1 and Sk1 give insight into the interactions between FluNA molecules, whereas Sv2 and Sk2 provide information about interactions between their micelles. The positive values of Sv1 and Sk1 indicate the strong specific interactions between the FluNa molecules, and their increase with the addition of NaCl may be attributed to the minimization of electrostatic repulsion between their charged head groups. The positive values of Sv2 and Sk2 also signify the J



Article

The limiting partial molar expansibility, ϕ0E, denoted as a partial derivative of limiting partial molar volume with respect to temperature, can be calculated using the B and C parameters described above following the relation ϕE0 = (∂ϕv0 /∂T )p = B + 2C(T − Tm)

(7)

The calculated values of ϕ0E are displayed in Table 6 together with the fitting parameters of eq 6. Hepler’s constant, (∂2ϕ0v /∂T2)p, provides more detailed information on the hydration interaction in terms of structure-making and -breaking capacity of the solute, which can be obtained easily from the equation dϕE0 /dT = (∂ 2ϕv0 /∂T 2)p = 2C

The calculated Hepler’s constants are listed in Table 6. Hepler24 argued that a positive (∂2ϕ0v /∂T2)p is associated with a structure making nature, whereas a negative (∂2ϕ0v /∂T2)p is associated with a structure braking nature. From Table 6, it is apparent that at all of the temperatures under investigation the values of (∂2ϕ0v /∂T2)p are negative for FluNa in aqueous and dilute aqueous NaCl solution and then become positive when the concentration of NaCl is increased. It could, therefore, be concluded that FluNa tends to act as a structure maker in water and dilute aqueous NaCl solution and as a structure breaker in moderate and concentrated aqueous NaCl solutions. The structure-making capacity of FluNa in water or dilute aqueous NaCl solutions is attributed to the coordination of water molecules around FluNa molecules through electrostriction, hydrophilic hydration, and hydrophobic hydration. When the concentration of NaCl is increased, the interactions between solute and cosolute become significant, and the electrostricted and hydrated water molecules around the ionic, hydrophilic, and hydrophobic groups are relaxed to bulk, and hence, FluNa shows structure-breaking behavior.

Figure 7. Experimental slopes of FluNa as a function of NaCl molality at 298.15K. The left (▲) and right (■) scales represent pre- and postCMC slopes, respectively. The represented slopes are obtained from ϕv (a) and ϕk (b).

strong specific interactions between micelles. However, the magnitude of post-CMC slopes is sufficiently smaller than the pre-CMC slopes. This is probably due to the bulky size of the micelles. The interactions between the micelles may happen through Cl− counterions. This type of interaction may result in the rapid increase of post-slopes up to 0.1483 M concentration of NaCl. In the proceeding concentration, the precise interpretation of the slow increase of Sv2 or decrease of Sk2 is difficult. However, there may be a transition of spherical micelles to other geometrical shapes.17−19 3.3. Limiting Apparent Molar Expansibility. The ϕ0v values are highly sensitive to temperature20 and can be regressed against the temperature using the equation21−23 ϕv0 = A + B(T − Tm) + C(T − Tm)2

(8)

4. CONCLUSIONS The densities and speeds of sound of FluNa in water and aqueous NaCl solutions are measured at six different temperatures and atmospheric pressure. From the measurements, apparent molar volumes, ϕv, apparent molar adiabatic compressibility, ϕk, limiting apparent molar volume, ϕ0v , limiting apparent molar adiabatic compressibility, ϕ0k, critical micelle concentration, and the experimental slope in the pre- and post-CMC regions are calculated. The ϕv0 values increase with an increase in temperature but decrease with an increase in the concentration of NaCl. The negative response of ϕ0v to the increasing concentration of NaCl is due to the dehydration of FluNa molecules by ion−ion, ion−hydrophilic, and ion−hydrophobic interactions taking place between FluNa and NaCl. The ϕ0k

(6)

where T is the given temperature in Kelvin, and Tm is the mean value of the studied temperature (here, Tm = 310.65 K). The coefficients A, B, and C were evaluated through polynomial fits and are summarized in Table 6.

Table 6. Fitting Parameters of eq 6 for ϕv, Limiting Apparent Molar Expansibilities, ϕ0E, and Values of Hepler’s Constant, (∂2ϕ0v /∂T2)p, of FluNa and in Water and Aqueous NaCl Solutions at Different Temperatures and Atmospheric Pressurea ϕ0E/(10−7 m3 mol−1 K−1)

a

m

A

B

C

298.15 K

303.15 K

308.15 K

313.15 K

318.15 K

323.15 K

(∂2ϕ0v /∂T2)p

0.0000 0.0251 0.0586 0.1021 0.1483 0.2047 0.2543

302.53 ± 0.01 300.01 ± 0.01 295.82 ± 0.02 292.29 ± 0.03 288.35 ± 0.04 284.94 ± 0.03 280.87 ± 0.01

42.44 ± 0.04 41.62 ± 0.06 41.50 ± 0.10 43.10 ± 0.20 37.20 ± 0.30 39.30 ± 0.20 44.80 ± 0.05

−0.77 ± 0.05 −1.61 ± 0.08 3.00 ± 0.20 2.40 ± 0.30 4.80 ± 0.50 0.60 ± 0.30 1.61 ± 0.07

4.44 ± 0.01 4.56 ± 0.02 3.41 ± 0.05 3.71 ± 0.08 2.50 ± 0.10 3.78 ± 0.08 4.08 ± 0.02

4.36 ± 0.01 4.40 ± 0.01 3.71 ± 0.03 3.95 ± 0.05 3.00 ± 0.08 3.84 ± 0.05 4.24 ± 0.01

4.28 ± 0.01 4.24 ± 0.01 4.00 ± 0.02 4.19 ± 0.03 3.48 ± 0.04 3.90 ± 0.03 4.40 ± 0.01

4.21 ± 0.01 4.08 ± 0.01 4.30 ± 0.02 4.43 ± 0.03 3.96 ± 0.04 3.96 ± 0.03 4.56 ± 0.01

4.13 ± 0.01 3.92 ± 0.01 4.60 ± 0.03 4.66 ± 0.05 4.44 ± 0.08 4.02 ± 0.05 4.72 ± 0.01

4.05 ± 0.01 3.76 ± 0.02 4.90 ± 0.05 4.90 ± 0.08 4.90 ± 0.10 4.08 ± 0.08 4.88 ± 0.02

−1.54 −3.22 5.94 4.76 9.58 1.20 3.22

Units are m/mol kg−1, A/10−6 m3 mol−1, B/10−8 m3 mol−1 K−1, C/10−9 m3 mol−1 K−2, and (∂2ϕ0v /∂T2)p/10−9 m3 mol−1 K−2. K



Article

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values become more negative with an increase in concentration of NaCl, indicating that the dehydration of FluNa occurs together with the clustering of water in the bulk. The critical micelle concentration first decreases and then increases with increasing concentration of NaCl. The decreasing critical micelle concentration with the increasing concentration of NaCl is attributed to minimization of electrostatic repulsion among the charged head groups, whereas the increase in CMC at higher NaCl concentration is likely due to the shape transition of the micelles from spherical to something else, such as a cylindrical rod. The calculation of Hepler’s constant showed that FluNa acts as a water structure maker in water and dilute aqueous NaCl solutions and as a breaker in concentrated aqueous NaCl solutions. In water or dilute aqueous NaCl solutions, the FluNa molecule is capable of coordinating water molecules around its ionic, hydrophilic, and hydrophobic groups, and enhances the water structure. In moderate or concentrated aqueous NaCl solutions, the interactions between FluNa and NaCl cause relaxation of the electrostricted and hydrated water molecules around the ionic, hydrophilic, and hydrophobic spheres to bulk, and overall decrease the water structure. The dehydration and micellization of FluNa in an aqueous environment in the presence of NaCl would be helpful for the pharmacological application of drugs.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to the Department of Chemistry, University of Rajshahi, Bangladesh for providing financial support and laboratory facilities to carry out this research work.

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REFERENCES

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