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Friccohesity

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Physicochemical Properties of Dodecyltrimethylammonium Bromide (DTAB) and SodiumDodecyl Sulphate (SDS) Rich Surfactants in Aqueous Medium, At T ¼ 293.15, 298.15, and 303.15 K K. M. Sachin, Sameer Karpe, Man Singh, and Ajaya Bhattarai* cationic surfactants together can produce interesting microstructures not formed by the pure components (e.g., vesicles and or rod-like micelles) and can dramatically decrease the concentration at which liquid crystalline phases form.[5] There are important physicochemical aspects that need intensive attention for understanding both the fundamental and application prospects[6,7]; such as, formations of aggregations and their dependence on environmental factors (temperatures and additives, etc.), their thermodynamics of formation, counter ion binding, aggregation numbers, etc. Bagheri et al.[8] have been studied the physicochemical properties (hydrophobicity, cloud point, Kraft point, etc.) of mixed surfactants. Das et al.[9] have been reported amphiphilic chemical structure, the surfactant has a preference toward interfacial adsorption at low concentration region; whereas above a critical concentration, it self-aggregates to form assembled structure whose size, shape, and an average number of amphiphile per aggregated structure depend on the amphiphile concentration and other physicochemical parameters like temperature, the presence of salt. Lakra et al.[10] have been reported physicochemical properties of single and binary mixtures have been determined by various techniques like conductivity, surface tensiometry, potentiometric, spectroscopic methods, etc. In last few years, mixed surfactants have received especial attention due to their high efficiency of solubilization, dispersion, suspension, and transportation abilities.[11–13] Song et al.[14] have been reported physicochemical properties and surface tension prediction of mixed surfactant systems: Triton X-100 with dodecylpyridinium bromide and Triton X-100 with sodium dodecylsulfate. And more other research studies have been done likes extensive reports exist in the literature on studies of the different combination of mixed surfactant system viz. cationic-cationic,[15,16] nonionic-nonionic,[15–17] anionic-cationic,[18,19] anionic-nonionic,[15,20] and cationic-nonionic.[20,21] Ionic/nonionic surfactant mixtures are important from fundamental as well as application point of view as they exhibit highly nonideal behavior on mixing and also their behavior can be complementary in the mixed micelle causing the critical concentration concentration (cmc) to decrease.

The physicochemical properties of Dodecyltrimethylammonium Bromide (DTAB) and Sodium Dodecylsulfate (SDS) rich surfactants in aqueous medium have been studied by surface tension, viscosity, density, and sound velocity at T ¼ 293.15, 298.15, and 303.15 K. The DTAB concentration varies from 0.0001 to 0.03 mol L1 in the presence of 0.01 mol L1 SDS and the SDS concentration varies from 0.001 to 0.015 mol L1 in the presence of 0.005 mol L1 DTAB, so that the concentrations of cationic (DTAB-rich) and anionic (SDS-rich) solutions are taken in the ratio of 3:1. The density (ρ) and sound velocity (μ) data are used for calculating apparent molar volume (Vϕ), friccohesity (σ), isentropic compressibility (Ks,ϕ), surface tension (γ), and viscosity (η). These parameters reveals that the relative solute-solvent and solute-solute interactions of SDS-DTAB and DTAB-SDS in an aqueous medium with the help of physicochemical properties (PCPs).

1. Introduction Catanionic surfactant systems have unique physiochemical properties that are different from those of their individual constituents, including lower critical aggregation concentrations and higher surface activities, which are important for detergency applications.[1,2] The interactive behavior of cationic and anionic surfactants in the aqueous medium is of numerous importance for basic science and technological applications.[3] Catanionic surfactant systems have also been used as semi-permanent wall coatings for fused silica capillaries[4] in capillary electrophoresis (CE) applications or as pseudo-stationary phases in micellar electro kinetic chromatography (MEKC). The mixer of two anionic and K. M. Sachin, S. Karpe, M. Singh School of Chemical Sciences Central University of Gujarat Gandhinagar, Gujarat, India A. Bhattarai Department of Chemistry M. M. A. M. C Tribhuvan University Biratnagar, Nepal E-mail: [email protected]

DOI: 10.1002/masy.201700034

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Bhattarai et al.[22] have been reported anionic/cationic binary systems display the strongest synergisms in both such as reduction in surface tension and in mixed micelle formation.[23] Wang et al.[24] have been reported on the adsorption layer of catanionic mixtures possesses higher dilational elasticity and viscosity because of the coulombic attraction between molecules.[25] Also, Wang et al.[24] have been reported on the catanionic surfactant mixtures can form stable vesicles in the bulk solution.[26–28] Alexandrova et al.[29,30] have found that the mixed surfactants of tetradecyltrimethylammonium bromide (C14TAB) and sodium alkyl sulphonates induced lower contact angles on silica as compared to the pure C14TAB due to the strong initial adsorption of surfactant complexes at the airsolution interface, followed by the adsorption at the silica interface. Maiti et al.[31] have assumed into consideration of formation of an ion-pair amphiphile (IPA) by the interaction between cetylpyridinium chloride (CPC) and sodium dodecylsulfate (SDS), and studied their transformation into coacervates, micelles, precipitates, vesicles, and other phases in solution. Nong et al.[32] have studied cationic and anionic active groups, show excellent physical and chemical properties, such as mild functionality, low toxicity, foam stability, and are easily soluble in water. Dozens of reports regarding mixing of cationic and anionic amphiphiles have been reviewed in the literature.[33–39] In this regard, Hubbard and Abbott have discussed the bilayer formation on mixing cationic bolaform surfactants with either sodium dodecylsulfate or sodium tetradecyl sulfate in aqueous solutions by using small angle neutron scattering measurements.[33] Wang et al.[40] have been studied, including cationic/ anionic,[41–48] cationic/cationic,[49] cationic/nonionic,[50] anionic/nonionic,[51] and zwitterionic/anionic[52] mixed surfactant systems. Qi et al.[53] have been reported the surfactants are much followed to efficiently remediate soils contaminated by hydrophobic organic compounds. They generally dissolved and diluted surfactants into the water, sufficiently blended them with soils, dried the soils by air, and made a measurement of water-stable aggregation or tensile strength at last. Hines[54] describes the recent advances in the theoretical evaluation of micellization in mixed surfactant systems. The mixing of surfactants in a formulation may also have other advantages, such as lowering the Kraft temperature and increasing the cloud point of the system.[55] Study of the variations in the selfdiffusion coefficient and viscosity with the changing concentration of CTAB to SDS in the cationic-rich and anionic-rich regions revealed a phase transitions nanostructures from microstructures (vesicles) to nanostructures (mixed micelle).[56] So far our knowledge, there is very little work reported in the literature which deals with the studies of anionic and cationic surfactant mixtures in non-aqueous solvents[57–58] and few work has been done on the effect of the medium.[59–62,22] In this paper, we reported the results of physicochemical parameters on anionic (SDS-rich) and cationic (DTAB-rich) mixtures of DTAB and SDS in an aqueous mediumat T ¼ 293.15, 298.15, and 303.15 K.

2. Experimental Section The chemicals used in the experiments were purchased from Sigma–Aldrich; the details are mentioned in Table 1. Due to the

Macromol. Symp. 2018, 379, 1700034

Table 1. Name of chemicals used in this work. Name of chemicals

Puritya)

Mw

Source

CAS No.

DTAB

99%

308.34

Sigma–Aldrich, USA

1119-94-4

98%

288.37

Sigma–Aldrich, USA

151-21-3

SDS

DTAB, dodecyltrimethyl ammonium bromide; SDS, sodium dodecyl sulfate. Purity as provided by suppliers.

a)

hygroscopic nature of DTAB and SDS, they were stored in P2O5 filled vacuum desiccator. Milli-Q water was used for the preparation of the solutions at T ¼ 293.15, 298.15, and 303.15 K. The DTAB was recrystallized several times until no minimum in the surface tension-concentration plot was observed and its cmc agreed with the literature value.[63] The SDS was recrystallized several times for purification till the minimum in the surface tension-concentration plot was observed. The aqueous solutions of purified and unpurified samples of SDS exhibited a minimum in the surface tension versus log C plot (C, the concentration of SDS). The minimum in the plot of γ versus log C for SDS is considered as due to the presence of highly surface-active dodecyl alcohol molecules.[64] Dodecyl alcohol may be present as an impurity in the supplied sample of SDS or it may be produced in the SDS solution by its hydrolysis. The cmc of SDS is taken to be the concentration of SDS corresponding to the minimum in the plot of γ versus log C and it is equal to 8.10 mmol kg1 in the absence of any added electrolyte at 298.15 K. This value is in good agreement with the cmc values of SDS obtained from conductance (8.10 mmol kg1).[65] The densities (ρ) were measured by Anton Paar DSA 5000 M density meter, with 0.001 K temperature controlled by a built-in Peltier device, with 0.00005 g cm3 accuracy. The instrument was calibrated with Milli-Q water and dried air at 25 C. The reported densities were an average of three repeated measurements with 0.00004 g cm3 repeatability. The viscosity, surface tension, and friccohesity were measured with Borosil Mansingh Survismeter[66,67] (cal.no. 06070582/1.01/C-0395, NPL, India) through viscous flow time (VFT) and pendant drop number (PDN) methods, respectively. The temperature was controlled by Lauda Alpha KA 8 thermostat with 0.05 K. After attaining a thermal equilibrium, VFT was recorded with an electronic timer of 0.01 s accuracy, while the PDN was counted with an electronic counter. The Survismeter was washed with Milli-Q water followed by acetone and was absolutely dried before measurements. The reported viscosity and surface tension are average values of three repeated measurements with 0.00002 kg m1 s1 and 0.03 mN m1 combined uncertainties in viscosity and surface tension, respectively. For both anionic (SDS-rich) and cationic (DTAB-rich) solutions were used in the ratio of 3:1 of SDS:DTAB and DTAB:SDS, respectively. The surface tension and viscosity measurements were determined with Borosil Man Singh Survismeter[66,67] at T ¼ 293.15, 298.15, and 303.15 K. Each experiment was repeated several times until good reproducibility was achieved. Several readings were noted and tabulated. The tabulated surface tension (γ) and log C (i.e., C is the surfactant concentration) plotted and the cmc values were calculated.

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3. Results and Discussion 3.1. Density (ρ) The densities of cationic (DTAB-rich) and anionic (SDS-rich) surfactants with solvent as a function of their molarities at T ¼ 293.15, 298.15, and 303.15 K are summarized in Table 2 and illustrated in Figure 1. Scrutiny of this Table 2 reveals that the interaction behavior of these surfactants in an aqueous solution. On addition of SDS in aq-DTAB, the ρ value slightly decreased compared to water due to the weakening of intramolecular forces (IMF) and electrostatic interaction with lower internal pressure (IP). Further on increasing SDS concentration, the ρ value is increased with stronger IMF, ions interactions, and van der Waal forces. Hence, IMF seems to be a fundamental driving force, stronger is the IMF; greater is the IP with higher ρ value. Naturally, the density becomes an essential property to define the IP. Also cohesion, cohesion-adhesion become prominent activities in such liquid mixture which are explained friccohesity via surface energy or surface tension (γ) become the IP structurally affect the continuous cohesion force of the solvent as well as of liquid mixture. In light of such chemical activities in the chosen molecules becomes a packing factor, which influences the ρ of the medium. The ρ is molecular interaction, which explained by the ρ, γ, and η becomes complementary data Table 2. Density (ρ/103 kg m3) of anionic (SDS-rich) and cationic (DTAB-rich) surfactants in aqueous medium at T ¼ 293.15, 298.15, and 303.15 K. M/mol L1

293.15 K

298.15 K

303.15 K

Anionic (SDS-rich) 0.000096

0.998354

0.997774

0.995774

0.000240

0.998360

0.997773

0.995773

0.000480

0.998365

0.997784

0.995784

0.000672

0.998364

0.997781

0.995798

0.000792

0.998381

0.997783

0.995793

0.000960

0.998405

0.997177

0.995734

0.006011

0.998396

0.997429

0.995933

0.007200

0.998367

0.997376

0.995339

0.007920

0.998084

0.997083

0.995907

0.009000

0.998435

0.997435

0.995949

0.010800

0.998437

0.997362

0.996097

0.012000

0.998429

0.997362

0.996151

0.000864

0.998732

0.997583

0.996195

0.000960

0.998721

0.997460

0.996071

0.001536

0.998701

0.997480

0.996010

0.002016

0.998679

0.997458

0.996046

0.002496

0.998619

0.997558

0.996193

0.002976

0.998697

0.997592

0.996194

0.003264

0.997372

0.995980

0.995548

0.003600

0.998709

0.997529

0.996026

0.005040

0.998765

0.997595

0.996183

Cationic (DTAB-rich)

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which depict the IP, strength of IMF, coulombic attraction via dipole-dipole interaction (DDI) and dipole-induced interaction (DII). On increasing the temperature, the ρ value decreases an account of weakening of binding forces (BF) with increases kinetic energy (KE). Therefore, the SDS and DTAB both have the same tail part (C-12) except head part (Figure 2) in its molecular structure. However, the interaction affinity of DTAB is higher compared to SDS an aqueous medium. It depicts that the DTAB having three CH3 groups in its head part which strongly interact and stronger hydrogen bonding (HB) with the solvent medium. Initially, addition of 0.000096 to 0.012 mol L1 SDS to aq-DTAB the ρ decreased by 0.001, 0.004, 0.003%, respectively at T ¼ 293.15, 298.15, and 303.15 K. We measured ρ value below and above cmc, and found that on increasing SDS concentration below the cmc, the ρ value slightly decreased but at the cmc, the ρ value significantly decreased because at this concentration the maximum surfactant molecules involved in the micelles formation, which shows weaker electrostatic interaction (Figure 1). Nevertheless, above the cmc on increasing SDS concentration, the ρ value initially increases after that remains constant. Similar finding in addition of 0.000864 to 0.00504 mol L1 DTAB to aq-SDS, the ρ value increased by 0.0004, 0.0001, 0.0002%, respectively at T ¼ 293.15, 298.15, and 303.15 K. Further on increasing DTAB concentration, the ρ value increased due to stronger solute-solvent interaction with the solvent molecules. The moderate homogenization is reflected from its highest ρ values. On increasing DTAB concentration, below the cmc, the ρ value slightly increased and higher increased as compared to anionic (SDS-rich) system, and similar to cationic (DTAB-rich) at the cmc, the ρ value drastically decreased. However, above the cmc with increasing DTAB concentration, the ρ value increases and remains constant. These parameters likes ρ value and cmc both are depending on the nature as well as the concentration of surfactant. In the literature,[68] it has been quoted that cationic surfactants show a weaker primary (electrostatic/non-specific) interaction with protein as compared to anionic surfactants, which is related to steric hindrance of the positive charge carried by the polar head groups of these surfactants. 3.2. Apparent Molar Volume (Vϕ) Densities of anionic (SDS-rich) and cationic (DTAB-rich) mixed surfactant have been used to calculate the apparent molar volume Vϕ (Table S1, Supporting Information) with equation (1) is given below[69]: Vϕ ¼

1000 ρ0 ρ M þ ρ mρ0 ρ

ð1Þ

where m is molarity of solute, M is a molar mass of solute, while ρ0 and ρ are the densities of solvent and solution, respectively. The trend of Vϕ value is as anionic (SDS-rich) > cationic (DTABrich), which is reversed from density order. The Vϕ of anionic (SDS-rich) is higher compared to cationic (DTAB-rich) due to the dominance of ion–hydrophilic interactions (IHI) over ion– hydrophobic interactions (IHbI), IHI among > Nþ < and Br,

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Figure 1. Influence on ρ value of above and below the cmc of anionic (SDS-rich) (a) and cationic (DTAB-rich) (b) surfactant at 293.15 K (^), 298.15 K (&), and 303.15 K (Δ).

O, Naþ ions, and OH, Hþ dipoles of water contribute their shares to this interaction. These interactions could weaken electrostriction interactions and Van der Waal forces with increased Vϕ value. The IHbI occurs between alkyl chain length (ACL) of DTAB and SDS seems to be functional in orienting the molecular motions of interacting molecules. Thus, the stronger interactions with higher electrostriction decreased the Vϕ values.[70] Since aqueous solvent has efficiently dispersed the surfactant through interacting abilities of water due to their electrostatic forces, these forces align anionic (SDS-rich), cationic (DTAB-rich), and water as per their isotropic orientations and molecular force fractionalization. The water could enter in their structural interstitial and behave as their integral part.

of ion–hydrophilic interactions (IHI) over ion–hydrophobic interactions (IHbI) similar to SLSOI. Specifically, IHI among > Nþ < and Br, O, Naþ ions, and hydrophilic Hþ, OH dipoles of water contribute their shares to interactions. These interactions could weaken the water electrostriction, increasing V 0ϕ values. The IHbI occurs between ACL of DTAB, SDS with OH, and Hþ of water molecules seem functional orienting molecular motions of the interacting molecules. Thus, the stronger interactions with higher electrostriction decreased V 0ϕ values.[70] The Vϕ value for increasing concentration of cationic (DTAB-rich) and anionic (SDS-rich) surfactants in the aqueous system is decreased below and above the cmc, while at cmc the Vϕ value significantly increased due to decreased contraction with weaker IMF, lower IP, and weaker electrostatic interaction. On increasing the temperature, the Vϕ value increased due to the developed weaker binding forces with higher expansion.

3.3. Limiting Apparent Molar Volume (V 0ϕ ) The V 0ϕ and SV are plotted by Vϕ versus M cationic (DTAB-rich) and anionic (SDS-rich) mixtures using equation 2.[71] Vϕ ¼

V 0ϕ þ SV m þ S0V m2

ð2Þ

The V 0ϕ as intercept depicts solute-solvent interactions (SLSOI) and slope SV the solute-solute interaction (SLSLI). The positive V 0ϕ value (Table S2, Supporting Information) infers stronger, while negative values reflect weaker SLSOI. Also, the positive and negative SV values illustrate stronger and weaker SLSLI, respectively.[72] The positive V 0ϕ values indicate the dominance

3.4. Isentropic Compressibility (ks) and Apparent Molar Isentropic Compressibility (ks,ϕ) The ρ and sound velocity (μ) values were obtained for cationic (DTAB-rich) and anionic (SDS-rich) systems at T ¼ 293.15, 298.15, and 303.15 K. The results of ρ and μ are given in Table 3. Initially, inclusion of SDS in aq-DTAB, sound velocity (μ) increased and DTAB to aq-SDS the μ value slightly decreased. The μ provides information about solvent–solvent, ion–solvent, and ion–ion interactions.[73] On increasing the temperature, increased μ value (Table 3) depicting the reorientation of

Figure 2. Molecular structure of Anionic (SDS) and Cationic (DTAB) surfactant.

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Table 3. Sound velocity (μ/m s1) of anionic (SDS-rich) and cationic (DTAB-rich) surfactants in aqueous medium at T ¼ 293.15, 298.15, and 303.15 K. M/mol L1

293.15 K

0.000096

1484.34

1510.42

1510.42

0.000240

1484.46

1510.50

1510.50

0.000480

1484.45

1510.58

1510.58

0.000672

1484.36

1498.39

1510.63

0.000792

1484.34

1498.47

1510.67

0.000960

1484.26

1498.53

1510.43

0.006011

1483.69

1498.19

1509.70

0.007200

1484.53

1497.92

1509.90

0.007920

1483.44

1497.91

1509.75

0.009000

1484.18

1498.16

1509.84

0.010800

1484.08

1498.12

1510.05

0.012000

1484.78

1498.69

1510.62

298.15 K

303.15 K

Anionic (SDS-rich)

Cationic (DTAB-rich) 0.000864

1484.67

1484.22

1508.26

0.000960

1484.52

1498.29

1512.12

0.001536

1484.43

1498.31

1510.16

0.002016

1484.49

1498.41

1510.19

0.002496

1484.18

1498.18

1510.04

0.002976

1484.09

1498.09

1510.01

0.003264

1484.10

1498.08

1509.93

0.003600

1484.15

1498.01

1509.82

0.005040

1483.73

1497.47

1509.32

molecular interactions prevailing in medium and wakening of binding forces with increases the oscillation and kinetic energy. On increasing surfactants concentrations the μ increased, due to increased compactness of the medium due to stronger solutesolute interaction and reorientation of ACL and different head groups of surfactants, inducing stronger HbHI with the solvent medium. The ρ and μ values are applied to calculate isentropic compressibility (ks) by Laplace-Newton using equation 3. The surfactant concentration dependence of these isentropic compressibility values are summarized in Table S3, Supporting Information. ks ¼

1 ρμ2

ð3Þ

where ks is isentropic compressibility, ρ is density and μ is sound velocity. The positive ks may be attributed to the breaking or stretching hydrogen bonds (HB) in the self-associated water or DDI between the water molecules. Generally, the ks increases with increase in temperature at fixed composition due to an increase in the thermal agitation which makes the solution more compressible.[74,75] The ks directly determines IP because of strong ion hydrophilic interaction which forms a high compact environment. The sound is a form of energy which is affected by interaction and in a vacuum is zero due to the demand of a

Macromol. Symp. 2018, 379, 1700034

medium. In pure solvent, only one form of interacting molecules is present but with the addition of surfactants, this interaction is broken which leads to the development of stronger ion-solvent interaction. Therefore, the compactness is increased and the system turns further compressed. Apparent molar isentropic compressibility (ks,ϕ) is calculated by using equation 4, illustrated in Figure 3. ks;ϕ ¼

ðks ρ0 k0s ρÞ ks M þ mρρ0 ρ

ð4Þ

where ρ0, ρ and k0s , ks are the density and isentropic compressibility of solvent and solution, respectively. The ks,ϕ values are positive at T ¼ 293.15, 298.15, and 303.15 K and compositions of cationic (DTAB-rich) and anionic (SDS-rich) although the values changed because of differences in their molar volume. This result depicts that there is strong interaction between solute and solvent molecules. The decrease and increase in ks,ϕ are mainly explained that changes with a structure which conducts to change in ultrasonic velocity. The variation of ks,ϕ in ionic aqueous mixtures shows that there is a distinct contraction upon mixing which in turn is dependent on the ionic size with strength. Its variation may be due to the formation of ion water hydration sphere and micelles. This clearly indicates that there is a significant interaction between the ions and water. The decrease ks,ϕ value also indicates a domination contribution from structure breaking effect in (water þ surfactant) by the stronger ion-dipole interaction (IDI). The limiting apparent molar isentropic compressibility k0s;ϕ is calculated by plotting graph of ks,ϕ versus m using equation 5.[76] ks;ϕ ¼ k0s;ϕ þ Sk m1=2 þ Bk m

ð5Þ

The k0s;ϕ furnished information related to SLSOI, while Sk and Bk related to SLSLI. The k0s;ϕ values are given in Table S4 (Supporting Information) and illustrated in Figure 3, the ks,ϕ values follow the order: anionic (SDS-rich) > cationic (DTABrich). The ks,ϕ values are higher depicting stronger SLSOI with weaker SLSLI engaging solute, solvent molecules with stronger interaction. On increasing the temperature, the compressibility is increased due to the weakening of binding forces.

3.5. Surface Tension (γ) The γ data for cationic (DTAB-rich) and anionic (SDS-rich) solution with solvent as a function of their molarities at T ¼ 293.15, 298.15, and 303.15 K are summarized in Table 4. The γ determines the participation of solvent with surfactants activities where the cohesive force (CF) or surface energy of solvent decreases to interact with DTAB and SDS. Stronger cationic (DTAB-rich) and anionic (SDS-rich) with solvent interactions reflect a weaker CF with disruption of HB network, with a lower γ value. A perusal of Table 4 reveals that the γ value for DTAB and SDS in aqueous medium decreased due to surfactant acts as a structure breaker[77] and disrupts the HB networking of the water molecules, lowering the γ. In general, on addition of 0.000096 to 0.012 mol L1 SDS in aq-DTAB the γ is

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Figure 3. Influence on Ks,ϕ of above and below the cmc of anionic (SDS-rich) (a) and cationic (DTAB-rich) (b) surfactant at T ¼ 293.15, 298.15, and 303.15 K.

quantitatively changed by 0.80, 0.93, 0.67% at T ¼ 293.15, 298.15, and 303.15 K, respectively. Similarly, addition of 0.00864 to 0.00504 mol L1DTAB in aq-SDS the γ decreased by 0.42, 1.86, 1.17% at T ¼ 293.15, 298.15, and 303.15 K, respectively. The γ values for cationic (DTAB-rich) and anionic (SDS-rich) with aqueous solution follows the order: anionic (SDSrich) > cationic(DTAB-rich). We calculated γ value below and above cmc, on increasing SDS concentration below cmc the γ value slightly decreases, while at the cmc the γ value drastically increased, while above cmc the γ increased and remains constant. On the other hand similar trend find in cationic

Table 4. Surface Tension (γ/mN m1) of anionic (SDS-rich) and cationic (DTAB-rich) surfactants in aqueous medium at T ¼ 293.15, 298.15, and 303.15 K. M/mol L1

293.15 K

298.15 K

303.15 K


55.19

50.81

50.58

0.000240

50.88

47.56

46.25

0.000480

50.08

46.01

45.16

0.000672

51.18

46.98

45.88

0.000792

49.42

45.15

45.02

0.000960

50.02

46.65

46.23

0.006011

54.78

50.89

49.52

0.007200

59.56

55.62

53.47

0.007920

60.05

56.16

54.27

0.009000

60.45

56.35

54.66

0.010800

60.85

56.56

54.89

0.012000

60.98

56.98

54.99

(DTAB-rich). Water has a unique aptitude to form a network of self-associated molecules by HB. The positive ions of surfactants being kosmotropes impose strong electrostatic governing of the close water molecules. Since the ions are highly hydrated, their presence increases the organization of water molecules by packing water molecules around themselves, increasing γ of water. In contrast to this, the negative ion, being chaotrope, induces entropic disordering of the HB in the network of selfassociated water molecules. Thus, they are pushed to the water/ air interface, because only there can the bulk water better organize their HB network, decreasing γ of water.[78] Therefore, negative ions of surfactants are positively adsorbed at the water/ air interface while, positive ions are negatively adsorbed at the water/air interface. Since the addition of DTAB and SDS to water quantitatively decreases their γ (Table 4), they all act as kosmotropes. However, surfactants developed a weaker CF with lower γ due to water repelling nature of hydrophobic ACL. The ACL with stronger hydrophobic interactions entropically destabilized the structured water, tending to a saturate surface force. It lowers the γ because of hydrophobic force neutralized the surface forces. Thus, the DTAB and SDS surfactant decreased the CF with lower γ value and higher η, leading to form stable emulsion. The cationic (DTAB-rich) and anionic (SDS-rich) surfactant producing variable trends at T ¼ 293.15, 298.15, and 303.15 K inferring their temperature dependent activity. So their surface approaching behavior is distinguished due to London dispersion force (LDF) and þ I (inductive) effect. Probably, ACL effect on the CF can be illustrated from the Brownian motion. The geographical approach to γ value decreased with ACL on weakening the CF at T ¼ 293.15, 298.15, and 303.15 K, respectively.

3.6. Viscosity (η)


33.52

29.52

29.28

0.000960

25.73

26.28

25.03

0.001536

25.08

21.92

20.2

0.002016

25.38

21.38

20.83

0.002496

22.02

19.02

18.85

0.002976

23.53

22.53

21.12

0.003264

32.47

31.61

28.42

0.003600

37.04

34.73

32.26

0.005040

38.59

38.07

35.61

Macromol. Symp. 2018, 379, 1700034

Viscosity is a flowing property of a liquid, which directly reflects the interacting strength of cationic (DTAB-rich) and anionic (SDS-rich) with in aqueous medium. Stronger interactions infer higher opposing or higher frictional force (FF) with higher η, whereas weaker interactions infer lower FF with η lower. The viscosities of cationic (DTAB-rich) and anionic (SDS-rich) with solvent as a function of their molalities are presented in Table 5. The impact of cationic (DTAB-rich) and anionic (SDS-rich) solutions of viscosities as a function of its molarities are summarized in Table 5. Viscosity is the transport property of a liquid depicting their structural behavior. The inclusion of DTAB

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Table 5. Viscosity (η/103 kg m1 s1) of anionic (SDS-rich) and cationic (DTAB-rich) surfactants in aqueous medium at T ¼ 293.15, 298.15, and 303.15 K. M/mol L1

293.15 K

298.15 K

303.15 K


1.3874

1.4977

0.9447

0.000240

0.5825

1.3366

0.9665

0.000480

0.9773

1.8338

0.9602

0.000672

0.6735

1.3149

0.8004

0.000792

0.6046

1.0878

1.1854

0.000960

0.3997

1.1334

1.0028

0.006011

0.3855

1.0501

1.1145

0.007200

0.4033

1.2981

1.1241

0.007920

0.4214

1.3663

1.4087

0.009000

0.3904

1.2836

1.3685

0.010800

0.6719

1.3674

1.1258

0.012000

0.4425

1.2520

2.3509

Cationic (DTAB-rich)

3.7. Friccohesity (σ)

0.000864

0.6443

2.6773

0.7479

0.000960

0.8693

3.0803

0.8052

0.001536

0.6974

3.1264

0.8230

0.002016

1.0801

3.0718

0.7772

0.002496

1.7717

3.9818

0.7636

0.002976

2.2603

7.4516

0.8126

0.003264

3.4454

2.5597

0.7883

0.003600

0.3978

1.2173

0.8836

0.005040

0.6824

3.4865

1.0707

in water the η decreased as compared to water, while 0.000096 to 0.012 mol L1 SDS in aq-DTAB, η increased. We calculated η below and above the cmc, on increasing SDS concentration below the cmc, the η value decreased. However, at the cmc, the η value increased and above the cmc, the η value decreased and remains constant. On addition of 0.000864 to 0.00504 mol L1 DTAB in aq-SDS η increased due to stronger IMF and stronger binding forces. Similarly, η trends find in cationic (DTAB-rich). The η values are as cationic (DTAB-rich) > anionic (SDS-rich) showed higher η because of their stronger interaction affinity with solvent molecules. The 0.000864 to 0.00504 mol L1 DTAB with aq-SDS, the η is decreased by 50.21, 8.61, and 0.89 % while, SDS 0.000096 to 0.012 mol L1 in aq-DTAB the η decreased by 19.85, 3.15, and 4.96% at T ¼ 293.15, 298.15, and 303.15 K, respectively. The weaker LDF causes weaker binding forces with lower IP and weaker HbHbI with η decreased. Thus, the hydrophilic and hydrophobic groups of surfactants are better solvated by the dipoles of water molecules, causing a compact philic phobic structure of surfactants, reproduced by cationic (DTAB-rich) > anionic (SDS-rich) η values. As the DTAB and SDS, their alkyl chain having CH2 groups provides an opportunity for the extensive intermolecular association, whereas CH2 groups, because of their hydrophobic interactions with dipoles of water, result in a solvent structure with

Macromol. Symp. 2018, 379, 1700034

higher η values. Such consequence increases with a different head group of DTAB and SDS groups resulting in η values, that is, the main element leading to enhancement of η in the presence of hydrophilic part and concentration DTAB and SDS. On increasing surfactants concentration with an aqueous medium, the increased η value depicts the development of the IMF of head group ions with solvent molecules where, water molecules are tetrahedrally arranged around ions with stronger water cluster. On the other hand, the η value of cationic (DTABrich) and anionic (SDS-rich) solutions decreases sharply on increasing temperatures. Therefore, the trend of η is complementary to other PCPs. For illustrate, on increasing temperature, the η and ρ values decreased whereas, the u values increased. This effect defends the generation of oscillatory effects within the system. At higher temperature, molecules gain high kinetic energy (KE), can overcome the strong IMF within the system, and can slip faster over one another. However, stronger interacting activities slow down the faster slipping of liquid laminar flow with higher η values.

The cohesive force (CF) is the IMF prevailing within similar solvent molecules generating a tendency to resist separation preventing solute distribution in liquids. It clearly distinguishes between binding forces, CF, and distribution with dispersing forces. The binding forces are explained by applying van der Wall forces of two similar molecules whereas dispersion forces of two dissimilar molecules defined by Boltzmann distribution theory. An analysis of ρ, γ, and η data explain that concentration of the surfactants increased the ρ, γ, and decreased η value. Since CF is weakened that allows the structured medium to surround solvent molecules, forming several reoriented complexes surrounded by a solvent that causes stronger binding forces. The dissimilar molecules together decreased CF by increasing FF. The friccohesity (σ) is a product of CF and FF within similar and dissimilar molecular mixtures, respectively and has a special significance to predict their mutual distribution. The FF and CF are mutually interrelated and such combination of forces or their product reflects a critical state of an interacting behavior of molecules. Therefore, σ of cationic (DTAB-rich) and anionic (SDS-rich) are given Table 6, is calculated by using Mansingh equation (6).[66] σ¼

η0 γ0

t n t0 n0

ð6Þ

where, (η0, γ0, t0, and n0) and (η, γ, t, and n) are viscosity, surface tension, viscous flow time, and pendant drop numbers of solvent and solution, respectively. The σ value is as cationic (DTABrich) > anionic (SDS-rich) due to the weakening of CF and increasing of FF. The σ values are higher for cationic (DTABrich) as compared to anionic (SDS-rich) within a stronger interconversion of CF to FF as comparatively more hydrophobic. For 0.000096–0.012 mol L1 SDS in aq-DTAB, the σ value decreased. Contrary to 0.000864–0.00504 mol L1 DTAB with aq-SDS, the σ value increased. The σ distinguishes the effect of hydrophobicity on a cumulative mode. It finds a dominance of

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Table 6. Friccohesity (σ/s m1) of anionic (SDS-rich) and cationic (DTAB-rich) in aqueous medium at T ¼ 293.15, 298.15, and 303.15 K.

stronger FF. The PCPs of anionic (SDS-rich) and cationic (DTAB-rich) mixtures in pure water at T ¼ 293.15, 298.15, and 303.15 K have been presented as a function of surfactant concentration.

M/mol L1

293.15 K

0.000096

0.038310

0.019823

0.012966

0.000240

0.015990

0.017793

0.028780

0.000480

0.027620

0.024976

0.016246

0.000672

0.018488

0.016999

0.010986

0.000792

0.016497

0.014509

0.035301

0.000960

0.013525

0.014603

0.016969

0.006011

0.022959

0.014011

0.033183

0.007200

0.019108

0.017088

0.026638

0.007920

0.016662

0.023041

0.029207

0.009000

0.016190

0.020058

0.021447

0.010800

0.021061

0.021474

0.033363

0.012000

0.026232

0.023132

0.046441

Keywords apparent molar isentropic compressibility, apparent molar volume, friccohesity, isentropic compressibility

298.15 K

303.15 K

Anionic (SDS-rich)


0.019415

0.047099

0.012407

0.000960

0.034125

0.060868

0.015628

0.001536

0.028087

0.074072

0.014178

0.002016

0.042991

0.074628

0.018126

0.002496

0.081272

0.108707

0.014926

0.002976

0.097044

0.171742

0.018689

0.003264

0.122465

0.040937

0.014392

0.003600

0.012453

0.017069

0.014941

0.005040

0.018107

0.059584

0.018837

HHbI and HbHbI over HHI, which results in efficient trapping of solvent with a net contraction and less friction. The increase in σ values with increase in DTAB concentration may be due to an effective interconversion of CF to FF at the cost of CF. On increasing the temperature the σ values decreased. Thus, the weaker SLS0I or binding forces occur with weaker FF between solute and solvent as well as weaker CF in solvent molecules with the solute.

4. Conclusion The experimental results for the density values are increased by increasing SDS and DTAB concentration, below the cmc due to stronger IMF and electrostatic interaction with apparent molar volume and apparent molar isentropic compressibility decreased. The density values are higher increased with cationic-(DTAB-rich) surfactant due to DTAB has the higher interacting ability with a solvent system compared to SDS. On increasing temperature, the density value decreases and sound velocity, apparent molar volume increases due to the weakening of binding forces, increases oscillation with increasing binding energy and weakening of IMF. The surface tension was found to be decreased initially with increasing the concentration of SDS/ DTAB mixtures in water. Friccohesity increases on increasing concentration of SDS/DTAB due to the weakening of CF and

Macromol. Symp. 2018, 379, 1700034

Supporting Information Supporting Information is available from the Wiley Online Library or from the author.

Acknowledgements Authors are thankful to the TWAS, Italy for providing opportunity to work in the Department of Chemical Sciences, Central University of Gujarat, Gandhinagar (India).

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