Article pubs.acs.org/jced
Surface Tension, Viscosity, and Refractive Index of Sodium Dodecyl Sulfate (SDS) in Aqueous Solution Containing Poly(ethylene glycol) (PEG), Poly(vinyl pyrrolidone) (PVP), and Their Blends Ram Singh,† Suvarcha Chauhan,† and Kundan Sharma*,‡ †
Department of Chemistry, H. P. University, Shimla 171005, India Department of Chemistry, Govt. Degree College Paonta Sahib affiliated to Himachal Pradesh University, Shimla (H.P.) 173 025, India
‡
S Supporting Information *
ABSTRACT: Taking into consideration the importance of the polymer− surfactant system, in present manuscript we discuss the intermolecular interactions present in solution containing sodium dodecyl sulfate (SDS) in six different solvent concentrations of polymer and their mixtures in their mass ratio [1 g of PEG (m1), 0.8:0.2 PEG/PVP (m2), 0.6:0.4 PEG/PVP (m3), 0.4:0.6 PEG/PVP (m4), 0.2:0.8 PEG/PVP (m5), and 1 g of PVP (m6) in 100 mL of distilled water] having a molal concentration corresponding to 1.66 mmol·kg−1, 1.38 mmol·kg−1, 1.10 mmol·kg−1, 0.81 mmol·kg−1, 0.53 mmol·kg−1, and 0.25 mmol·kg−1, respectively. It suffices to mention here that the concentration (molality) corresponds to the total polymer content in the solution. All of the measurements were carried out at three different temperatures, that is, 293.15, 303.15, and 313.15 K. The whole experiment was carried out with techniques like surface tension, viscosity, and refractive index measurements. Different parameters of relevance like surface excess (Γmax), minimum area per molecule at air−water interface (Amin), relative viscosity (ηr), viscous relaxation time (τ), and limiting dielectric constant (ε∞), and so forth have been evaluated from surface tension, viscosity, and refractive index measurements. This persistence of the surface tension (γ) beyond the critical micelle concentration (CMC) appears to suggest that the aggregate formation in the presence of the PEG or PVP or their blends is sufficiently large. The close approximated value of relative viscosity to the unity implies that the conformational changes in the polymer are minimal. The refractive index measurements further reveal that the overall polarizability of the studied systems increases with an increase in the amount of polymer in the solution.
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INTRODUCTION The study of the interactions present between the polymers with surfactants in aqueous solution gives rise to the formation of the associated complex. This analysis of the complexes formed depends on the molecular properties of the polymer and the surfactant. In general, the mutual presence of polymer and surfactant molecules alters the rheological properties of solutions. Due to a variety of molecular structures, polymer and surfactant, when mixed together forming a complex in aqueous solution, display a wide array and remarkable influence on the properties of the system.1 Therefore, the study of these interactions present in such a system has been the subject of prime research for the researcher for the last three decades.2−6 There are two different pictures of polymer−surfactant system: (i) one describing interaction in terms of association or binding of a surfactant to the polymer and (ii) second, in terms of micellization of the surfactant on or near the polymer chain. The micelle sizes are similar to and without polymer present, whereas aggregation numbers are similar or slightly lower than those of micelles forming in the absence of polymer. When a surfactant is added to an aqueous solution of polymer having © XXXX American Chemical Society
hydrophobic segments, then due to a hydrophobic effect, it would become thermodynamically favorable for the surfactant to adsorb to polymer or even to form aggregates with a hydrophobic portion of the polymer.7−10 Poly(vinyl pyrrolidone) (PVP) used in the present study is synthesized by the free-radical addition polymerization consequently developed a history of extraordinary human compatibility and safety. It has a comb-like structure with amide groups on alternate carbon and is resonance-stabilized by delocalization of the carbonyl electrons through the amide bond.1 PVP homopolymer operatrd in personal care products as a viscosifying and emulsion stabilizing polymer.11,12 Poly(ethylene glycol) (PEG) is highly flexible, and its hydrophilicity can improve the solubility in water. The nontoxicity, nonimmunogenicity, and biocompatibility as well as solubility in water and in many organic solvents make it an Received: November 23, 2016 Accepted: June 15, 2017
A
DOI: 10.1021/acs.jced.6b00978 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
1.10 mmol·kg−1 (m3), 0.81 mmol·kg−1 (m4), 0.53 mmol·kg−1 (m5), and 0.25 mmol·kg−1 (m6), respectively. The solutions thus obtained were stirred (with 1500 rpm) for about 30 min with a magnetic stirrer before being subjected to measurements. The SDS concentration was varied over the range (1−16 mmol·kg−1) in aqueous polymer solutions and their blends covering pre- and post-micellar regions in the same way as in the conductivity measurements.21 Viscosity and Surface Tension. Viscosity and surface tension measurements were carried out using a Man Singh Survismeter. It is an inexpensive device for measuring viscosity and surface tension of the solution simultaneously (calibration no. 06070582/1.01/C-0395, NPL, Govt. of India)22,23 supplied by Spectro Lab Equipment’s Pvt. Ltd. (India). The Survismeter was periodically cleaned by treating with chromic acid and distilled water and finally washed with alcohol and dried in an oven for 3−4 h. After drying, the Survismeter was filled with a fixed volume of the test solution. The temperature of the Survismeter was maintained constant to ∼ ±0.15 K. The average deviation of 2−3 measurements of a single concentration of a solution did not exceed ±0.03 s. The efflux time for viscosity measurements was in between 300−395 s; therefore, no kinetic energy correction was made.24 However, the viscometer was calibrated before use with DMSO and MeOH (both of A.R. Grade) at 298.15 K using the viscosity coefficient (ηo = 0.8903 cP and density do = 997.070 kg m−3) for water.25 The viscosity of liquid was determined by the following formula:
ideal choice for various biological, chemical, biomedical, and pharmaceutical applications.13,14 On the other hand, surfactants or surface-active agents are characterized by its tendency to adsorb at the surface or interface. This adsorption behavior can be attributed to the solvent nature and to the chemical structure for surfactants that combine both a polar and a nonpolar (amphiphilic) groups into a single molecule.15 The ability of surfactants to radically vary surface and interfacial properties provides the means to apply surfactants, in wettability, detergency, mineral and petroleum processing, biological systems, personal care products, foods, and crop protection, and so forth.16−19 It is, therefore, proposed to investigate the effect of different polymers, namely, polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) and their blends on anionic surfactant, sodium dodecyl sulfate (SDS), in aqueous solutions at different temperatures.
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EXPERIMENTAL SECTION Materials and Methods. Poly(ethylene glycol) (PEG). PEG with a molecular weight of 6000 (L.R. grade) was obtained from SD. Fine Chem. Pvt. Ltd. (India). Poly(vinyl pyrrolidone) (PVP). PVP with a molecular weight of 40000 (A.R. grade) was purchased from Calbiochem (Germany). Sodium Dodecyl Sulfate (SDS). SDS of analytical grade was obtained from HIMEDIA (India). However, a pure sample of SDS was obtained by giving the additional treatment as reported in literature.20 The chemical sample specification and the mass fraction purity have been presented in Table 1.
η = η0[(td)/(t0d0)]
where η = viscosity of the solution, η0 = viscosity of the solvent, to = flow time of the solvent, t = solution flow time, d = density of solution, and d0 = density of solvent. The viscosity coefficients of DMSO and MeOH were found to be 2.000 and 0.555 cP, respectively. These experimental values were found to be in good agreement with the literature values (1.99 and 0.543 cP) at 298.15 K.26,27 The entire work was concerned solely with relative viscosities and was determined by using eq 2 as
Table 1. Specification and Mass Fraction Purity of Chemical Samples Used in the Experiment chemical name poly(ethylene glycol) (PEG) poly(vinyl pyrrolidone) (PVP) sodium dodecyl sulfate (SDS) a
source SD. Fine−Chem. Pvt. Ltd. (India) Calbiochem (Germany) HiMedia (India)
purification method
mass fraction purity
none
0.98a
none
0.97a
crystallization
0.99
(1)
ηr = η /η0 = (td)/(t0d0)
(2)
where t0, d0, and η0 refer to the flow time, density, and viscosity of solvents and t and d of the solution, respectively. The calibration of the Survismeter was carried out by measuring the surface tension of DMSO and MeOH at 298.15 K. The γ value of these solvents was determined by using eq 3 as
Declared by supplier.
Distilled Water. Water, being the main solvent, was calibrated before use with the standard procedure as follows. About 1000 mL of pure water was collected from the Millipore distillation unit. This sample was subjected to further distillation on acidified KMnO4 over a ∼ 750 mm of Hg long fractionating column. Different fractions of the distilled water were collected, and their conductivity, κ (S cm−1), and pH were determined. The sample of κ value
