Thermodynamic Properties of Poly(ethenol) with and without Sodium

Jun 17, 2013 - But the viscosity increases with an increase of SDS concentration when surfactant SDS concentration is larger than CAC value mainly due...
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Thermodynamic Properties of Poly(ethenol) with and without Sodium Dodecyl Sulfate by Viscosity, Surface Tension, and Dynamic Light Scattering Feng Yang and Mingtan Hai* School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, PR China ABSTRACT: We investigate the thermodynamic properties of a water-soluble polymer poly(ethenol) (PVOH) with and without ionic surfactant sodium dodecyl sulfate (SDS) by viscosity, surface tension, and dynamic light scattering (DLS) measurements at 298 K. The viscosity, refractive index, and hydrodynamic radius values of polymer PVOH aqueous solutions without surfactant SDS increase with increasing PVOH concentration, but the surface tension of PVOH aqueous solution decreases with increasing PVOH concentration. For SDS+PVOH aqueous solutions, both viscosity and surface tension values decrease with an increase of SDS concentration when SDS concentration is lower than the critical aggregation concentration (CAC) of SDS+PVOH aqueous solutions, and the relative minimum viscosity value indicated the shrinkage of the polymer PVOH chain resulting in the formation of compact structure at the binding site of SDS+PVOH. But the viscosity increases with an increase of SDS concentration when surfactant SDS concentration is larger than CAC value mainly due to the extension of PVOH chains. We obtain the CAC value of SDS+PVOH aqueous solutions from the corresponding SDS concentration at the first minimum value of both surface tension and hydrodynamic diameter. The CAC value is much smaller than the critical micelle concentration (CMC) of SDS which indicated the strong interaction strength between ionic surfactant SDS and water-soluble polymer PVOH due to the large negative value of Gibbs free energy change.

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INTRODUCTION Poly(ethenol) not only is nontoxic and fully degradable but also has excellent film forming, emulsifying, and adhesive properties, and it is widely used as a continuous phase to generate monodisperse water/oil/water (w/o/w) emulsion as templates to generate monodisperse polymersome or liposomes by glasscapillary microfluidics.1,2 The aqueous solutions containing PVA prevent the coalescence of double emulsion droplets. It is important to study the thermodynamic properties of PVOH with and without surfactant, and further study the interaction between PVOH and SDS. It is highly desired to investigate the thermodynamic properties and further study the interaction between ionic surfactant and the water-soluble polymer. The formation of micelle−polymer complexes by surfactants and water-soluble polymer and the interaction between surfactants and polymers are extensively documented due to their widespread commercial applications and theoretical studies.3−5 Viscosity,6 ESR,7,8 dynamic light scattering, fluorescent probing9, and surface tension10 methods are most widely used to study the thermodynamic property as well as the interaction between surfactants and polymers. For the SDS and polyacrylamide (PAM) system, the addition of a water-soluble polymer PAM to SDS7 would decrease the viscosity value to the minimum value at the binding site of SDS+PAM due to the contraction of © XXXX American Chemical Society

polymer chains and the formation of a more compact structure. Our previous studies7 have confirmed that the addition of polymers to the surfactant solution could definitely decrease the critical micelle concentration (CMC) of surfactants resulting in the strong interaction between surfactant and polymer, and the polymer−surfactant complexes are formed along the polymer chains at a critical aggregation concentration (CAC) of surfactant and polymer. For the surfactant and polymer aqueous system, the CAC value is generally considered to measure the binding interaction strength between surfactant and polymer; a lower CAC than CMC value of the surfactant indicates the interaction strength between the surfactant and polymer is very strong. In this paper, we investigate the thermodynamic properties of water-soluble polymer PVOH aqueous solution either alone or with ionic surfactant SDS by viscosity, refractive index, surface tension, electrical conductivity, and dynamic light scattering methods, and provide more understanding of the interaction between PVOH and SDS. We also evaluate the effect of either PVOH concentration or SDS concentration on the thermodynamic properties including viscosity, surface tension, electrical Received: March 11, 2013 Accepted: June 5, 2013

A

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was measured by using dynamic and static light scattering ALV/DLS/SLS-5000 compact geniometer system. For the ALV-compact goniometer system, a special extended temperature range cell housing is now available that allows sample temperatures from −35 to 250 °C to be used. High performance DLS and SLS in cylindrical cuvettes with outer diameter as small as 10 mm allows measurement of the hydrodynamic radius using a sample volume as small as 1.0 mL. The hydrodynamic diameter measurement range is from 0.1 nm to 1 μm. The decay constant is rewritten as a function of the particles and is related by Brownian motion to the diffusivity by Γ = −Dq2, q = (4πn/λ) sin(θ/2) with q2 reflecting the distance the particle travels. The diffusivity can be determined by the Stokes−Einstein equation D = kT/(6πηr) (k, Boltzmann Constant; T thermodynamic temperature; η viscosity; r hydrodynamic radius). The decay constant is experimentally determined and diffusivity is determined based on the refractive index, wavelength (488 nm or 633 nm He−Ne laser) and angle (90°). So the hydrodynamic radius can be determined based on the Stokes−Einstein equation as r = kT/ 6πηD, which is related to the thermodynamic temperature T, refractive index, and viscosity. Hydrodynamic radius and polydispersity index as well as particle size distribution can be obtained from the DLS measurement with all ALV-goniometer systems using a comprehensive software tool available for the alignment of the instrument (ALV-WinAlignment software). The combined expanded uncertainty U of the hydrodynamic radius with level of confidence 0.98 is about 0.02.

conductivity, and hydrodynamic diameter values of PVOH or the SDS+PVOH aqueous solutions. The interaction strength between surfactant SDS and water-soluble polymer PVA based on the thermodynamic properties of the complex system is discussed and evaluated.

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EXPERIMENTAL SECTION Materials. Ultrapurified sodium dodecyl sulfate (SDS) (minimum purity of 99.5 %), sodium chloride (ACS reagent minimum 99.0 %), and poly(ethenol) (PVOH) with molecular mass (13000 to 23000) g·mol−1, (87 to 89) % hydrolyzed (minimum purity of 99.0 %) were purchased from SigmaAldrich and used without further purification. Table 1 provides Table 1. Source and Purity Chemical Information chemical name sodium dodecyl sulfate sodium chloride poly(ethenol)

source

initial mole fraction purity

purification method

Sigma-Aldrich

≥ 0.995

none

Sigma-Aldrich Sigma-Aldrich

≥ 0.990 ≥ 0.990

none none

information about the source and purity of the chemicals used. Double distilled water with a resistivity value of 18.2 MΩ·cm−1 at 298.15 K was acquired from a Milli-Q system (Millipore corporation, USA). Methods. The viscosity measurements of SDS, PVOH, SDS + (0.010, 0.030, 0.050) g·g−1 PVOH aqueous solutions in a water bath were carried out at 298 K by using U-shaped glass capillary viscometer. The temperature of the water bath for the viscosity measurement was controlled by IKA RCT basic within (298 ± 1) K. Both 0.01 mol·kg−1 NaCl solution and pure water were used to calibrate the viscometer at 298 K as described in our previous works.6 The combined expanded uncertainty U of the viscosity measurement with level of confidence 0.99 is about 0.01. The surface tension values of SDS + (0.010, 0.030) g·g−1 PVOH aqueous solutions were measured at (298 ± 1) K by using Sigma Force tensiometer 700/701 (KSV Instrument). This instrument measures the static surface tension and interfacial tension of liquids by using a Du Nouy ring in either push or pull mode. Ultrapure water was used to calibrate the tensiometer at 298 K. The surface tension measuring range is from (1 to 2000) mN·m−1 with displayed resolution 0.001 mN·m−1. The combined expanded uncertainty U of surface tension measurement with level of confidence 0.99 is about 0.01. The refractive index of PVOH aqueous solutions with and without SDS was measured at (298 ± 1) K by using a refractometer (Fisher Scientific Co.). The refractometer was calibrated by ultrapure water at (298 ± 1) K before the refractive index measurement of the samples was performed. The combined expanded uncertainty U of the refractive index with level of confidence 0.995 is about 0.005. The electrical conductivity of PVOH aqueous solutions was measured at (298 ± 1) K by using VWR SB80PC SympHony. The instrument was calibrated by conductivity standard solutions at 298 K. The combined expanded uncertainty U of the electrical conductivity with level of confidence 0.98 is about 0.02. The hydrodynamic radius and polydispersity index of PVOH aqueous solutions with or without SDS at (298.15 ± 0.10) K

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RESULTS AND DISCUSSION Viscosity of SDS Solution at 298 K. The relationship between the viscosity of the SDS aqueous solutions and SDS concentration at 298 K is listed in Table 2 and presented in

Table 2. The Viscosity (η) of SDS Aqueous Solutions at 298 Ka mSDS/mmol·kg−1

η/mPa·s

0 4.0 6.0 7.0 8.0 8.5 10.0 12.0 16.0 20.0 32.5

0.890 0.897 0.929 0.928 0.925 0.920 0.925 0.931 0.937 0.955 0.983

Abbreviations: mSDS, SDS molar concentration; η, viscosity. The relative standard uncertainty u is ur(mSDS) = ± 0.1 mmol·kg−1, ur(T) = ± 1 K, and ur(η) = ± 0.001 mPa·s. a

Figure 1. Figure 1 exhibits three distinctive stages. At the first stage, the viscosity of SDS aqueous solutions increases insignificantly with increasing SDS concentration. At the second stage, the value decreases to a minimum viscosity value with increasing SDS concentration. At the last stage, the viscosity increases remarkably with increasing SDS concentration. The obtained relative minimum viscosity value, as in our previous work,6 corresponds to the critical micelle concentration (CMC) value of surfactant SDS solutions. The formation of SDS free micelles would definitely decrease the B

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Figure 1. The viscosity η of SDS aqueous solutions as a function of SDS concentration mSDS at temperature T = 298 K.

Figure 2. The viscosity η and surface tension γ of polymer PVOH aqueous solutions as a function of polymer PVOH concentration CP at temperature T = 298 K.

fluidity and increase the viscosity of SDS aqueous solutions. The obtained CMC value of SDS aqueous solution at 298 K is 8.5 mmol·kg−1 which agrees well with our previous studies from the previous surface tension and ESR measurements6,7,11 for SDS aqueous solutions at 298 K. Viscosity, Surface Tension, Refractive Index, Electrical Conductivity and Hydrodynamic Diameter of PVOH Aqueous Solutions at 298 K. For the water-soluble polymer PVOH aqueous solutions, molecules are associated through intermolecular hydrogen bonds. The relationship between the values of viscosity, surface tension, refractive index, hydrodynamic radius, and polymer PVOH concentration without SDS at 298 K are listed in Table 3 and presented in Figure 2 Table 3. The Viscosity (η), Surface Tension (γ), Refractive Index (n), Hydrodynamic Radius, and Polydispersity Index of PVOH Solutions at Different Concentrations at 298 Ka CP/g·g−1

η/mPa·s

γ/mN·m−1

n

r/nm

PDI

0 0.010 0.030 0.040 0.050 0.100

0.890 1.172 2.191 2.961 3.70 12.721

71.90 44.49 42.67 42.30 42.16 41.04

1.3332 1.3359 1.3370

0.3 ± 0.1 5.3 ± 4.0 6.7 ± 4.6

0.22 0.43 0.47

1.3390 1.3470

7.7 ± 5.2 13.6 ± 9.9

0.47 0.51

Figure 3. The refractive index n and the hydrodynamic radius r as a function of polymer PVOH concentration CP at temperature T = 298 K.

Table 4. The Electrical Conductivity (κ) of Polymer PVOH Aqueous Solutions at Different Polymer Concentration (Mass Fraction Cp) at 298 Ka

Abbreviations: Cp, polymer PVOH concentration; η, viscosity; γ, surface tension; n, refractive index; r, hydrodynamic radius; PDI, polydispersity index. The relative standard uncertainties are polymer concentration ur(Cp) = ± 0.002 g·g−1, viscosity ur(η) = ± 0.001 mPa·s, surface tension ur(γ) = ± 0.01 mN·m−1, relative standard uncertainty of refractive index ur(n) = ± 0.0005, hydrodynamic radius ur(r) = ± 0.1 nm. a

and Figure 3. The electrical conductivity of PVOH aqueous solutions as a function of polymer concentration (mass fraction) at 298 K is listed in Table 4 and presented in Figure 4. The values of viscosity, electrical conductivity, and refractive index all increase with increasing PVOH concentration, but the surface tension of PVOH aqueous solutions decreases with increasing polymer PVOH concentration mainly due to the emulsifying property of PVOH. The electrical conductivity of water increases with increasing temperature,12,13 but the electrical conductivity of 0.100 g·g−1 PVOH aqueous solutions decreases with increasing temperature which is listed in Table 5 and presented in Figure 5. The electrical conductivity tendency

Cp/g·g−1

κ/μs·cm−1

ur(κ)/μs·cm−1

0 0.010 0.020 0.050 0.070 0.100

3.4 98.4 194.5 693.0 901.2 1206.0

0.2 1.5 2.8 4.0 4.8 5.7

a Abbreviations: Cp, polymer concentration; κ, electrical conductivity. The relative standard uncertainty of polymer concentration ur(Cp) = ± 0.002 g·g−1 and ur(T) = ± 1 K.

of PVOH aqueous solutions is opposite to pure water mainly due to the typical behavior of a polyelectrolyte of PVOH. The hydrodynamic diameter of PVOH aqueous solution and the hydrophobic interaction increase remarkably with increasing polymer PVOH concentration. C

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Table 6. The Viscosity/Polymer Concentration (η/CP) Ratio of SDS + (0.010, 0.030, 0.050) g·g−1 PVOH Aqueous Solutions vs SDS Concentrations at 298 Ka

Figure 4. The electrical conductivity κ as a function of polymer PVOH concentration CP at temperature T = 298 K.

Table 5. The electrical conductivity (κ) of polymer 0.10 g·g−1 PVOH aqueous solutions at different temperaturea T/K

κ/μs·cm−1

ur(κ)/μs·cm−1

296.95 297.05 297.15 297.25 297.45 298.15

1220.0 1218.0 1216.0 1213.1 1206.0 1184.0

1.2 1.5 1.3 1.6 1.6 1.8

mSDS/mmol·kg−1

CP/g·g−1

(η/CP)/mPa·s·g·g−1

0 0 0 5.0 5.0 5.0 20.0 20.0 20.0 25.0 25.0 25.0 50.0 50.0 50.0

0.010 0.030 0.050 0.010 0.030 0.050 0.010 0.030 0.050 0.010 0.030 0.050 0.010 0.030 0.050

117.0 73.2 76.0 118.1 83.1 98.0 121.1 100.2 104.3 125.1 106.1 114.0 139.1 135.0 151.2

a

Abbreviations: mSDS , SDS molar concentration; Cp , PVOH concentration; η, viscosity. The relative standard uncertainties are polymer concentration ur(Cp) = ± 0.002 g·g−1, viscosity ur(η/Cp) = ± 1.0 mPa·s·g·g−1, SDS concentration ur(mSDS) = ± 0.1 mmol·kg−1 and ur(T) = ± 1 K.

κ is the electrical conductivity. The relative standard uncertainty of temperature ur(T) = ± 0.10 K.

a

Figure 6. The ratio between the viscosity and polymer concentration (η/CP) as a function of SDS concentration mSDS at temperature T = 298 K.

listed in Table 7 and presented in Figure 7 which exhibited two distinctive stages. At the first stage, the viscosity value first decreases unremarkably with an increase of SDS concentration. At such a low SDS concentration there is neither free SDS micelle nor SDS+PVOH complexes formation in aqueous solution. At the binging site, the formation of polymer− surfactant complexes would favor the polymer chains contraction which would lead to the formation of a more compact structure and yield the relative minimum viscosity. The SDS concentration at the relative minimum viscosity value corresponds to the CAC value of SDS+PVOH, it is 4.1 mmol·kg−1. After that stage, the viscosity values finally increase significantly with increasing SDS concentration when the SDS concentration is larger than the CAC value due to the formation of free SDS micelles and SDS+PVOH complexes in the aqueous solution. The formation of SDS+PVOH complexes and free SDS micelles would not only enhance the hydrophobic interaction between surfactant SDS and polymer PVOH but

Figure 5. The electrical conductivity κ of 0.10 g·g−1 PVOH aqueous solutions as a function of temperature.

Viscosity of SDS +PVOH Aqueous Solutions. The ratio (η/CP) of viscosity values of SDS + (0.010, 0.030, 0.050) g·g−1 PVOH aqueous solution with different SDS concentrations and PVOH concentration mass fraction (Cp) at 298 K are listed in Table 6 and shown in Figure 6. This ratio decreases remarkably with an increase of polymer concentration, but it increases remarkably with an increase of SDS concentration. The results confirm that both the SDS+PVOH complexes and SDS free micelles formation result in the increasing value of the solution viscosity. The increase of electroviscosity effect of SDS+PVOH aqueous solutions definitely indicated the typical behavior of a polyelectrolyte. The viscosity of SDS + 0.010 g·g−1 PVOH aqueous solutions at different SDS concentration at 298 K is D

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Table 7. The Viscosity (η) of SDS + 0.010 g·g−1 PVOH Aqueous Solutions at Different SDS Concentration at 298 Ka mSDS/mmol·kg−1 0 2.3 4.1 4.4 4.5 7.7 22.3 44.7 70.7

Table 8. The Surface Tension (γ) of SDS + (0.010, 0.0 30) g·g−1 PVOH Aqueous Solutions at Different SDS Concentration at 298 Ka γ/mN·m−1

η/mPa·s −1

1.170 1.197 1.121 1.160 1.171 1.180 1.209 1.424 1.809

mSDS/mmol·kg 0 2.3 2.6 2.7 3.4 4.1 4.4 4.6 4.8 5.0 5.9 6.2 6.6 7.5 8.1 8.8 9.6 15.7 20.3 44.7 70.7

a Abbreviations: mSDS, SDS molar concentration; η, viscosity. The relative standard uncertainties of ur(mSDS) = ±0.1 mmol·kg−1 and ur(η) = ± 0.001 mPa·s.

0.010 g·g

−1

PVOH

43.52 43.20 43.17 43.12 43.02 42.28 42.49 42.66 42.71 43.0 42.43 42.54 42.33 42.35 42.17 42.04 41.87 40.36 39.58 38.74 37.00

0.030 g·g−1 PVOH 42.67 41.05 40.84 41.44 41.77 41.84 41.71 42.14 42.47 42.48 42.52 42.44 42.57 42.43 42.44 42.00 41.60 40.22 39.21 38.17 36.83

a Abbreviations: mSDS, SDS molar concentration; γ, surface tension. The relative standard uncertainties SDS concentration ur(mSDS) = ± 0.1 mmol·kg−1, surface tension ur(γ) = ± 0.01 mN·m−1.

Figure 7. The viscosity η of SDS + 0.010 g·g−1 PVOH aqueous solutions as a function of SDS concentration mSDS at temperature T = 298 K.

also reduce the electrostatic interaction between SDS and PVOH which would certainly increase the fluid resistance of the SDS+PVOH aqueous solutions. Surface Tension of SDS+PVOH Aqueous Solutions. Surface tension is one of the most important thermodynamic parameters for evaluating the property of liquids and liquids mixtures. The surface tension values of SDS + 0.010, 0.030 g·g−1 PVOH aqueous solutions at different SDS concentration at 298 K are listed in Table 8 and presented in Figure 8. The surface tension of polymer PVOH solutions without SDS decreases with an increase of polymer concentration mainly because of the emulsifying property of polymer PVOH. The surface tension values of SDS+PVOH aqueous solutions exhibit three different stages. At the first stage, the surface tension decreases remarkably with increasing SDS concentration mainly due to the lowing surface tension ability of the surfactant SDS. At the second stage, it increases unremarkably with increasing SDS concentration. At the last stage, it decreases with increasing SDS concentration. In the first stage, SDS concentration is so low that neither free SDS micelle nor SDS+PVOH complexes are formed in the aqueous solution, the surface tension decreased till the relative minimum surface tension value occurs. The SDS concentration at the relative minimum value corresponds to the CAC value of SDS+PVOH, it is 4.1 mmol·kg−1 which agrees well with that obtained from the viscosity measurement. At the last stage, since SDS

Figure 8. The surface tension γ of SDS + 0.010, 0.030 g·g−1 PVOH aqueous solutions as a function of SDS concentration mSDS at temperature T = 298 K.

concentration is much larger than the CAC, the formation of many SDS free micelles and SDS+PVOH complexes in aqueous solutions would not only induce the increase of hydrophobic interaction between surfactant SDS and polymer PVOH but also the decrease of the electrostatic interaction between SDS and PVOH, and at the same time would reflect the changes of surface tension values of SDS+PVOH aqueous solutions. Refractive Index and Hydrodynamic Radius of SDS +PVOH Aqueous Solutions. To obtain an accurate hydrodynamic diameter of the surfactant and polymer aqueous solutions, we measured the refractive index of the polymer solutions with and without surfactants at 298 K. The refractive E

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index of SDS + 0.010 g·g−1 PVOH aqueous solution at various SDS concentrations at 298 K is listed in Table 9 and presented

Table 10. The Hydrodynamic Radius r, Width and Polydispersity Index of SDS + 0.010 g·g−1 PVOH Aqueous Solutions at 298.15 Ka

Table 9. The Refractive Index n of SDS + 0.010 g·g−1 PVOH Aqueous Solutions at 298 Ka mSDS/mmol·kg−1

n

0 2.3 4.1 4.4 4.5 7.7 22.3 44.7 70.7

1.3359 1.3340 1.3329 1.3331 1.3339 1.3340 1.3351 1.3370 1.3375

mSDS/mmol·kg−1

r/nm

width/nm

PDI

0 2.3 4.1 4.4 4.5 7.7 22.3 44.7 70.7

7.2 7.1 4.9 5.5 8.0 9.0 13.3 18.4 23.1

4.9 4.9 3.0 3.7 5.3 5.0 9.2 13.9 17.2

0.47 0.46 0.41 0.42 0.45 0.42 0.47 0.57 0.55

a

Abbreviations: mSDS, SDS molar concentration; r, hydrodynamic radius; PDI, polydispersity index. The relative standard uncertainty ur(r) is ±0.1 nm and the relative standard uncertainties SDS concentration ur(mSDS) = ± 0.1 mmol·kg−1 and ur(T) = ± 0.1 K.

a

Abbreviations: mSDS, SDS molar concentration; n, refractive index. The relative standard uncertainties SDS concentration ur(mSDS) = ± 0.1 mmol· kg−1 and ur(n) = ± 0.0005.

Figure 10. The hydrodynamic radius r of SDS + 0.010 g·g−1 PVOH aqueous solutions as a function of SDS concentration mSDS at temperature T = 298.15 K.

Figure 9. The refractive index n of SDS + 0.010 g·g−1 PVOH aqueous solution as a function of SDS concentrations mSDS at temperature T = 298 K.

different SDS concentration at 298 K by DLS measurement is around 0.4. The Interaction Strength between Surfactant SDS and Polymer PVOH. The Gibbs energy change for the transfer of free micelle to the surfactant + polymer complex can be calculated using the following equation6,14

in Figure 9. The hydrodynamic radius of SDS + 0.010 g·g−1 PVOH aqueous solution at various SDS concentrations at 298.15 K is listed in Table 10 and shown in Figure 10. Both the refractive index and hydrodynamic diameter values of SDS +PVOH aqueous solutions show two distinct stages. At the first stage, the values decrease significantly with increasing SDS concentration. Neither free SDS micelles nor SDS+PVOH complexes are formed because of the low SDS concentration. The relative minimum refractive index value and hydrodynamic diameter value of SDS concentration occurs due to the formation of SDS+PVOH complexes. The SDS concentration at that site corresponds to the CAC value of SDS+PVOH aqueous solution, that is also 4.1 mmol·kg−1 which agrees very well with that obtained value from the viscosity and surface tension measurements. At the second stage, the refractive index and hydrodynamic diameter of SDS+PVOH aqueous solutions increases remarkably with an increase of SDS concentration, because many SDS+PVOH complexes and free SDS micelles are formed at higher SDS concentration. The polydispersity index of SDS + 0.010 g·g−1 PVOH aqueous solutions at

ΔGps = (1 + K )RT ln(CAC/CMC)

(1)

where K is the effective micellar charge fraction, which for SDS was found to be 0.85.11 The Gibbs energy change and interaction strength between the surfactant and the polymer can be conveniently measured by using eq 1. The smaller is the value of the CAC, the larger is the negative value of Gibbs energy change and the stronger is the interaction strength between SDS and PVOH. The obtained CAC value by viscosity for SDS + 0.010 g·g−1 PEG6 and SDS + 0.010 g·g−1 PVOH aqueous solutions at 298.15 K and the calculated Gibbs energy change ΔGps for the transfer of free SDS micelle to SDS+PVOH complexes according to eq 1 are listed in Table 11. ΔGps of the SDS+PVOH aqueous solution is a large negative value which indicated that the interaction between SDS and polymer PVOH is stronger than that between SDS and PEG. F

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(3) Goddard, E. D. Polymersurfactant interaction part II. Polymer and surfactant of opposite charge. Colloids Surf. 1986, 19, 301−329. (4) Fishman, M. L.; Elrich, F. R. Interactions of aqueous poly(Nvinylpyrrolidone) with sodium dodecyl sulfate. II. Correlation of electric conductance and viscosity measurements with equilibrium dialysis measurements. J. Phys. Chem. 1975, 89, 2740−2744. (5) Goddard, E. D. In Interactions of Surfactants with Polymers and Proteins; CRC Press: Boca Raton, FL, 1993. (6) Cao, M.; Hai, M. T. Investigation on the interaction between sodium dodecyl sulfate and polyethylene glycol by electron spin resonance, ultraviolet spectrum, and viscosity. J. Chem. Eng. Data 2006, 51, 1576−1581. (7) Hai, M. T.; Han, B. X.; Yan, H. K. Investigation on interaction between sodium dodecyl sulfate and polyacrylamide by electron spin resonance and ultraviolet spectrum. J. Phys. Chem. B 2001, 105 (21), 4824−4826. (8) Witte, F. M.; Engberts, J. B. F. N. ESR spin probe study of micelle−polymer complexes. Poly(ethylene oxide)- and poly(propylene oxide)-complexed sodium dodecyl sulfate and cetyltrimethylammonium bromide micelles. J. Org. Chem. 1988, 53, 3085−3088. (9) Zana, R.; Lianos, P.; Lang, J. Fluorescence probe studies of the interactions between poly(oxyethylene) and surfactant micelles and microemulsion droplets in aqueous solutions. J. Phys. Chem. 1985, 89, 41−44. (10) Hai, M. T.; Han, B. X.; Yan, H. K.; Han, Q. Y. Vapor pressure of aqueous solutions of polyacrulamide + sodium dodecyl sulfate with and without NaOH. J. Chem. Eng. Data 1998, 43 (6), 1056−1058. (11) Hai, M. T.; Han, B. X.; Yan, H. K. The solublization of npentane gas in sodium dodecyl sulfate-polyethylene glycol solutions with and without electrolyte. J. Colloid Interface Sci. 2003, 267, 173− 177. (12) Hayashi, M. Temperature-electrical conductivity relation of water for environmental monitoring and geophysical data inversion. Environ. Monit. Assess. 2004, 96, 119−128. (13) Jones, R. G. Measurements of the electrical conductivity of water. IEE Proc.-Sci. Meas. Technol. 2002, 149, 320−322. (14) Lu, J. R.; Marrocco, A.; Su, T. J.; et al. Adsorption of dodecyl sulfate surfactants with monovalent metal counterions at the air−water interface studied by neutron reflection and surface tension. J. Colloid Interface Sci. 1993, 158, 303−316.

Table 11. The value of CMC of SDS Aqueous Solution and the Value of CAC and ΔGps of SDS + 0.010 g·g−1 Poly(ethanol) Aqueous Solutions at Temperature T = 298 Ka. SDS −1

CMC/(mmol·kg ) CAC/(mmol·kg−1) ΔGps /(kJ·mol−1)

8.5

SDS+poly(ethanol)

SDS+PEG6

4.1b −3.33c

4.46,b −3.46c

b

a

Abbreviations: CMC, critical micelle concentration; CAC, critical aggregate concentration; ΔGps, Gibbs energy change. bThe relative standard uncertainty ur(CMC) is ±0.1 mmol· kg−1 and ur(CAC) is ±0.2 mmol·kg−1. cThe relative standard uncertainty ur(ΔGps) is ±0.02 kJ·mol−1.

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CONCLUSION We investigate the thermodynamic properties of a watersoluble polymer poly(ethenol) aqueous solution with and without ionic surfactant SDS as well as the interaction between SDS and PVOH by viscosity, surface tension, conductivity, and DLS measurements at 298 K. For PVOH aqueous solutions alone, the thermodynamic properties including viscosity, electrical conductivity, refractive index, and hydrodynamic diameter increase with increasing polymer concentration, but the surface tension of PVOH aqueous solutions decreases with increasing polymer concentration. Our results confirm that the values of viscosity, refractive index, and hydrodynamic radius of SDS+PVOH aqueous solutions first decrease with increasing SDS concentration and then increase with further increased SDS concentration. The obtained relative minimum viscosity value of SDS+PVOH aqueous solutions confirmed the shrinkage of the polymer PVOH chains at the binding site, and the viscosity increases with increasing SDS concentration when the SDS concentration is above the CAC, but the surface tension decreases significantly with increasing SDS concentration when SDS concentration is lower than the CAC. The interaction strength between SDS and PVOH is strong because of the lower CAC value and large negative value of Gibbs free energy change.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86 010 62334505. Fax: + 86 010 62333759. Funding

We are grateful to the Fundamental Research Funds for the Central Universities (No. FRF-BR-09−021B) and 863 (No. 2006AA03Z108) program of PR China for financial support. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to the Editors and reviewers for their valuable comments and suggestions. REFERENCES

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