Micellization behaviour of surface active N-alkyl pyridinium dodecylsulphate task-specific ionic liquids in aqueous solutions

Colloids and Surfaces A 529 (2017) 203–209

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Micellization behaviour of surface active N-alkyl pyridinium dodecylsulphate task-specific ionic liquids in aqueous solutions

MARK

⁎

Rohit L. Vekariyaa,b, , Nadavala Siva Kumarc a b c

Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, Vietnam Department of Chemical Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia

G RA P H I C A L AB S T R A C T

A R T I C L E I N F O

A B S T R A C T

Keywords: Ionic liquids Surface active properties Micellization Small angle neutron scattering

The synthesis and spectroscopic characterization of task-specific ionic liquid (TSIL) and its surface active properties are depicted in this study. The detailed synthesis protocol for CnPyCl (n = 4, 6, 8) along with CnPyDs are discussed. The physical properties of ILs including their solubility in various organic solvent are given. The synthesized ILs is characterized by 1H NMR, IR, MS and thermal methods From the TGA analysis, it found that the stability is increases by replacing anion (Cl−) by dodecylsulphate of ILs. The CnPyDs has very limited solubility in water, therefore they are making stable micelles and their geometry and size is determined by Small Angle Neutron Scattering (SANS) measurements. We have demonstrated that micellar behaviour of TSIL in water by SANS and surface tension measurements.

1. Introduction Recently, ionic liquids (ILs) appeared in the literature as a new class of solvents. They are considered as designer solvents owing to the quasiinfinite numbers of possible cations and anions combination that can be envisioned. In the early 1910, Walden [1] first mentioned that ethyl ammonium nitrate was liquid at room temperature. After almost a century, such compounds have undergone a massive success which has built up only over the last two decades [2–8]. They offer several advantages over traditional molecular solvents including negligible vapour pressure, properties modulations, easy access etc. As ILs are ⁎

molten salt which are in liquid state at room temperature, it composed of cation and anion. Mostly, the cationic centre involves a positively charged nitrogen or phosphorus which are based on ammonium, sulphonium, phosphonium, imidazolium, pyridinium, picolinium, pyrrolidinium, thiazolium, oxolium or pyrazolium cations [9]. Anions that form room temperature ILs are usually weakly basic inorganic or organic compounds that have a diffuse or protected negative charge. The common anions used so far in ILs are; AlCl3−, PF6−, BF4−, SbF6− alkyl substituted sulphate/phosphate/sulphonates, mesylate (CH3SO3−), tosylate (CH3PhSO3−), trifluoro acetate (CF3CO2−), acetate (CH3CO2), thiocynate (SCN−), triflate (CF3SO3−), borates, carbonates etc.

Corresponding author at: Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam. E-mail address: [email protected] (R.L. Vekariya).

http://dx.doi.org/10.1016/j.colsurfa.2017.05.083 Received 2 May 2017; Received in revised form 27 May 2017; Accepted 28 May 2017 Available online 03 June 2017 0927-7757/ © 2017 Elsevier B.V. All rights reserved.

Colloids and Surfaces A 529 (2017) 203–209

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Scheme 1. Reaction scheme for synthesis and modification of TSIL.

UV, MS etc. Due to poor solubility of CnPyDs (ILs) in water the micellar association behaviour and micelle size and shape were characterized by surface tension and SANS methods.

[4,8,10–16]. Because of wide range of available cations and anions approximately 1018 anion-cation combinations exist and cover large number of applications in nanotechnology [17], biology [18], electrochemisty [19], industry [20], environmental [21] and agriculture sectors [22]. The tuneability of combinations of cations and anions and the possibility to achieve modification of the cation or/and the anion part offers variety to ILs with targeted properties, e.g. the hydrophilicity/ hydrophobicity, balance or flexibility, viscosity of ILs etc. In view of this, the development of novel TSIL and their synthetic procedure plays a vital role. Bonhote et al. [23] reported synthesis of hydrophobic, dialkylimidazolium bis(triflyl) amides and dialkylimidazolium nonafluorobutane sulphate by reacting the corresponding halide or triflate with Lithium bis(triflyl) amide LiNTf2 or potassium nonafluorobutanesulphonate in aqueous solution. In 1999, Seddon and his Co-workers [24] synthesized [C2Mim][BF4] by metathesis reaction of the corresponding chloride or bromide with sodium tetrafluroborate in propanone. However, they encounter a problem in the separation of sodium halide from resultant IL because of the slight solubility of the later in propanone. Fuller et al. overcome this problem by carrying out metathesis reaction of [C2Mim] [Cl] with ammonium tetrafluoroborate in propanone with high purity [25]. The water solubility of ILs is very much dependent on both the cation and anion. Generally, water solubility decreases with increasing the alkyl chain length on the cation. The common anions like BF4, PF6, NTf2 are also known for introducing hydrophobicity of the ILs. Seddon et al. [24] earlier discussed the metathesis reaction of halide salt with HBF4 in water followed by extraction into dichloromethane yielding improved purity depending upon the alkyl chain length (n) on the imidazolium cation. For example, for n = 6–10, the IL separates as a dense liquid where as for chain length n > 10, a solid separates from the aqueous reaction mixture. In case of hydrophobic anions PF6, BF4, NTf2 etc. certain precautions are necessary. The hydrophobic ILs with PF6 anion are sparingly soluble in water but when used in water based applications like metal ion extraction etc., PF6 may undergo hydrolysis to produce HF and PO43− [26], while miscibility of ILs based on BF4, depends on the length of the alkyl chain or the temperature of the system. Apart from all the above mentioned problems with anions, the cost of the hydrophobic IL with PF6, BF4, NTf2 etc. is quite high compare to other ILs [27]. In view of the emerging importance of benign and environmental friendly ILs, here in this paper we explore the synthesis of TSILs based on N-alkyl pyridinium cation with dodecylsulphate as the halogen free anion. The main advantage with sodium dodecylsulphate (SDS) over other alkyl sulphate which is made from synthetic alcohol, SDS is a naturally derived surfactant made from the whole natural coconut. The applications of this TSIL in various fields such as shape directing agent in silver nanoparticles synthesis [28] and other applications are still under experiments in our laboratory. In this study, ILs containing alkyl chain on pyridinium cation with dodecylsulphate anion is synthesized by metathesis reaction of halide (Cl−) of N-alkyl pyridinium chloride. These ILs were characterized by spectroscopic methods like NMR, IR,

2. Experimental 2.1. Materials and methods The N-alkyl chloride (99%) and Sodium dodecylsulphate (99%) were purchased from Sigma-Aldrich, India. All solvents were of analytical grade and used as received. Milli-Q grade water was used for the preparation of aqueous solutions. For NMR and SANS measurements D6-Acetone and D2O (> 99.9%) respectively were obtained from Merck. The synthesized ILs was characterized by IR (ABB FTIR, Canada), 1H-NMR (400 MHz, Brucker Scientific, Switzerland) and Mass spectroscopy (Thermo scientific, USA). The TGA data were obtained at a heating rate of 5 °C/min on a TGA-DTA instrument (TA instruments model 5000/2960 thermogravimetric analyser, USA). UV–vis spectra were recorded on a UV-160A spectrophotometer (Shimadzu Corporation, Japan) in water and methanol. The surface tension measurements with an uncertainty of ± 0.03 mNm−1 were made using wilbemy plate method through a surface tensiometer (Data Physics, Germany, Model DCAT-ll). 2.2. Synthesis of TSIL N-alkyl pyridinium dodecylsulphate (CnPyDs) In order to get desired IL, first pyridine was used as a starting material and reacted with N-alkyl chloride. SDS was then added to replace the chloride ions with dodecylsulphate anion forming the desired IL (Scheme 1). In the first step, 0.05 mol (3.96 g) Pyridine and 0.05 mol of N-alkyl chloride (4.65 g of N-butyl chloride, 6.01 g of N-hexyl chloride and 7.45 g of N-octyl chloride) were placed in two necked round bottom flask and stirred thoroughly while heating at 70 °C for 20 h under N2 atmosphere. The resulting viscous liquid was cooled to room temperature washed several times with small portion (20 ml × 3) of ethyl acetate to remove unreacted starting material and dried under vacuum for 5–7 h. In second step, N-alkyl pyridinium dodecylsulphate (CnPyDs), IL was synthesized from the metathesis reaction between SDS and N-alkyl pyridinium chloride (CnPyCl) in acetone under mild heating. The ILacetone mixture was filtered to remove sodium chloride (NaCl) and the filtrate was vacuum dried at 75 ± 0.1 °C. The resultant products are semi solid light yellow to brown waxy type material (Fig. 1) which have partial solubility in water (∼0.01–0.05% w/v). The chemical structures and molecular weight of synthesized ILs including SDS is given in Table 1. The solubility of synthesized ILs in various organic solvents is listed in Table S1 (supporting information). No major problems were encountered during the synthesis of these ILs and in most cases > 90% yields were obtained. Once synthesised, the compounds were identified and characterised using a range of techniques, in order to verify that the product of synthesis correspond 204

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to the IL expected. The outcome of such characterisation is presented in the next section. 2.3. Spectral characterization of synthesized TSILs 2.3.1. 1-Butyl-pyridinium chloride (C4PyCl) 1 H NMR (400 MHz, D2O, TMS): δH: 8.79 (t, 2H, NCHCHCHCH), 8.48 (t, 1H, NCHCHCH), 8.01 (d, 2H, CHNCH), 4.54 (t, 2H, NCH2CH2), 1.91 (p, 2H, NCH2CH2), 1.29 (sext, 2H, NCH2CH2CH2), 0.85 (t, 3H, NCH2CH2CH2CH3) (Fig. S1). FTIR (neat liquid) ν/cm−1: 3387 (due to moisture), 3063 (might be due to aromatic CeH stretching) 2922-2878 (aliphatic CeH stretchin), 1636-1489 (due to CeC multiple band stretching), 1404 (due to aromatic CeN vibration), 1173-918 (due to CeN stretching), 771-679 (due to CeH bending of aromatic substitution of five adjacent hydrogen atom) (Fig. S2). Fig. 1. Physical appearances of synthesized TSILs, (a) SDS, (b) C8PyCl, (c) C8PyDs.

2.3.2. 1-Butyl-pyridinium dodecylsulphate (C4PyDs) 1 H NMR (400 MHz, d-Acetone, TMS): δH 9.35 (t, 2H, NCHCHCHCH), 8.72 (t, 1H, NCHCHCH), 8.27 (d, 2H, CHNCH), 4.89 (t, 2H, NCH2CH2), 3.86 (t, 2H, eOCH2), 1.49 (p, 24H, (CH2)12), 0.95 (t, 6H, (CH3)2) (Fig. S3). FTIR (neat waxy material) ν/cm−1: 3425 (due to moisture), 3063 Table 1 Chemical structure, abbreviation and molecular weight of synthesized TSILs. Entry

ILs

1.

Abbreviation

Mol. wt (gm mol−1)

C4PyCl

171.6

C6PyCl

199.7

C8PyCl

227.5

C4PyDs

401.2

C6PyDs

429.2

C8PyDs

457.2

SDS

288.1

N-Butyl pyridinium chloride 2.

N-Hexyl pyridinium chloride 3.

N-Octyl pyridinium chloride 4.

N-Butyl pyridinium dodecylsulphate 5.

N-Hexyl pyridinium dodecylsulphate 6.

N-Ocyl pyridinium dodecylsulphate 7.

Sodium dodecylsulphate

205

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Fig. 3. Surface tension curves for SDS, C8PyCl and CnPyDs (n = 4, 6, 8) at 30 °C.

6H, (CH3)2) (Fig. S8). FTIR (neat waxy material) ν/cm−1: 3425 (due to moisture), 3070 (might be due to aromatic CeH stretching), 2924-2854 (aliphatic CeH stretching), 1636-1489 (due to CeC multiple band stretching), 1373 (due to aromatic CeN vibration), 1180-1041 (due to R-SO3−), 1180856 (due to CeN stretching), 764-725 (due to CeH bending of aromatic substitution of five adjacent hydrogen atom). (Fig. S9). ES-MS: m/z 429.20 (Fig. S10). 2.4. Theoretical approach to SANS For a monodispersed system particle, the coherent differential scattering cross-section dΣ/dΩ can be written as [29–32]

dΣ / dΩ = nm Vm2 (ρm − ρs )2P (q) S (q) + B

(1)

Where nm denotes the number density of micelles, ρm and ρs are the scattering length densities of the micelles and the solvent respectively. P(q) is the single particle intra-particle form factor, S(q) is the interparticle structure factor and B is a constant term that represents the incoherent scattering background which is mainly due to the hydrogen in the sample. The above expression can be simplified for non-interacting micelles (i.e. for the dilute solution the interparticle structure factor S(q) ∼1)

Fig. 2. UV–vis spectra of synthesized TSILs in, methanol (a) and water (b).

(might be due to aromatic CeH stretching) 2924-2854 (aliphatic CeH stretching), 1636-1489 (due to CeC multiple band stretching), 1373 (due to aromatic CeN vibration), 1173-1041 (due to R-SO3−), 1180849 (due to CeN stretching), 779-687 (due to CeH bending of aromatic substitution of five adjacent hydrogen atom). (Fig. S4). ES-MS: m/z 401.00 (Fig. S5).

dΣ / dΩ = nm Vm2 (ρm − ρs )2P (q) + B

2.3.3. 1-Hexyl-pyridinium chloride (C6PyCl) 1 H NMR (400 MHz, D2O, TMS): δH: 8.84 (t, 2H, NCHCHCHCH), 8.53 (t, 1H, NCHCHCH), 8.06 (d, 2H, CHNCH), 4.59 (t, 2H, NCH2CH2), 1.97 (p, 2H, NCH2CH2), 1.23 (sext, 6H, NCH2CH2CH2CH2CH2), 0.77 (t, 3H, NCH2CH2CH2CH2CH2CH3) (Fig. S6). FTIR (neat liquid) ν/cm−1: 3394 (due to moisture), 3063 (might be due to aromatic CeH stretching) 2932-2862 (aliphatic CeH stretching), 1636-1489 (due to CeC multiple band stretching), 1404 (due to aromatic CeN vibration), 1173-926 (due to CeN stretching), 779-679 (due to CeH bending of aromatic substitution of five adjacent hydrogen atom) (Fig. S7).

P (q) =

(2)

The particle form factor P(q) depends on the shape and size of the micelles. Expression for P(q) corresponding to different geometrical shapes are known [33,34]. In particular, P(q) for an ellipsoidal(i) P(q) for an ellipsoidal shape; 1

∫

[P (q, μ)]2 dμ (3)

0

3(sin x − x cos x ) x3

(4)

x = q [a2μ2 + b2 (1 − μ2 )]1/2

(5)

P (q, μ) =

where, a and b are the semi minor and semi major axis of the ellipsoidal micelle, μ is the cosine of the angle between the major axis and wave vector transfer q. (ii) for cylinder of radius, R and length, L = 2l, π

P (q) =

2.3.4. 1-Hexyl-pyridinium dodecylsulphate (C6PyDs) 1 H NMR (400 MHz, d-Acetone, TMS): δH 9.34 (d, 2H, NCHCHCHCH), 8.76 (t, 1H, NCHCHCH), 8.25 (d, 2H, CHNCH), 4.90 (t, 2H, NCH2CH2), 3.91 (t, 2H, eOCH2), 1.29 (p, 28H, (CH2)14), 0.86 (t,

2

∫ 0

sin2 (qlcosβ ) 4J12 (q, R, sinβ ) sinβdβ q2l2cos 2β q2R2sin2β

(6)

where, β is the angle between the axis of the cylinder and bisectrix, and J1 is the Bessel function of order unity. The radius R, and length l are 206

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Table 2 Surface active parameters obtained from surface tension for SDS, C8PyCl and CnPyDs (n = 4, 6, 8) at 30 °C. System

CMC mol dm−3

Гmax × 1010 mol cm−2

a 1s Å2

SDS C8PyCl C8PyDs C6PyDs C4PyDs

8.2 × 10−3 0.193 1.0 × 10−5 6.1 × 10−5 1.2 × 10−4

2.8 1.8 2.4 2.5 2.6

58 94 70 67 64

± ± ± ± ±

0.2 0.3 0.3 0.3 0.3

± ± ± ± ±

5 2 3 3 3

γcmc mN m−1

pC20

πcmc mN m−1

ΔGmic KJ mol−1

38.1 33.2 26.8 35.9 38.1

2.6 1.9 4.3 3.9 3.5

32.5 37.4 43.8 34.7 32.5

-22.2 -14.2 -39.1 -34.6 -32.8

3. Results and discussions 3.1. UV–vis spectra of TSIL in water and methanol In the quest of understanding the change in optical properties of the products (ILs) compare to the chloride and sulphate forms, the absorbance behaviour of C8PyDs was examined. The UV–vis absorption spectra of 0.001 M C8PyCl, C8PyDs and SDS in the water and methanol were measured and are shown in Fig. 2. In figures, a strong absorption in the deep UV region 210–300 nm with decreasing trend towards visible region were observed for all ILs. The same results were observed for other ILs (C4PyCl, C6PyCl, C4PyDs and C6PyDs). (Figs. S11 and S12). Since all compounds have almost identical absorption pattern, one can conclude that the absorption centre must be the N-alkyl pyridinium cation. Results show that the replacement of chloride of CnPyCl by dodecylsulphate anion, retained the significant absorption in the UV region. Hence these unique optical properties are not due to anion effect but are attributed to the cationic pyridinium moiety of the TSILs. These results are consistent with the report made by Paul et al. [35] where they studied the imidazolium cation with halogen based ILs in PF6− and Cl− forms and found significant electronic absorption in the UV region.

Fig. 4. SANS curves for synthesized IL C8PyCl and SDS at 30 °C (line indicate best fit with model).

3.2. Thermogravimetric analysis (TGA) In general most of ILs have a high thermal stability and often begins to decompose around ∼200 °C. Here ILs, C8PyDs shows similar behaviour. TGA curves of C4PyCl and C6PyCl (Figs. S13 and S14), it was found that an initial ∼10% weight loss near to ∼100 °C occurs which is attributed to the removal of water. This might be because of hygroscopic nature of ILs. This weight loss was followed by a shouldering from 200–290 °C with complete decomposition of organic moiety. Thus in all three ILs, replacement of Cl ̄ anion in CnPyCl by dodecylsulphate anion induces enhancement in their thermal stability. The complete decomposition occurs at around 350 °C. These suggested that the C4PyDs and C6PyDs are more stable as compared to C4PyCl and C6PyCl. (Figs. S15 and S16).

Fig. 5. SANS curves for synthesized ILs; CnPyDs (n = 4, 6, 8) at 30 °C (line indicate best fit with model).

considered as fitting parameters in the calculations, the disk being a special case for a cylinder when l ≪ R. It can be shown that for a cylindrical particle, P(q) varies as 1/q in the q range of 1/l < q < 1/R, and as 1/q2 for disk-like particles in the q range of 1/R < q < 1/l.

3.3. Surface tension measurements The critical micelle concentration of CnPyDs along with SDS and C8PyCl is determined by surface tension method at 30 °C. The surface tension isotherms for C8PyCl, SDS and CnPyDs are shown in Fig. 3. The isotherms are not showing any minima around the CMC confirming that the samples are free from any unreacted impurities. The

Table 3 Parameters obtained from SANS measurements. C4PyDs

C6PyDs

C8PyDs

Disk R (nm) 98.5

L (nm) 7.1

R (nm) 100.7

L (nm) 2.1

R (nm) 102.0

L (nm) 6.3

207

SDS

C8PyCl

Ellipsoidal

Not fitted in any model

a (nm) 32

b (nm) 15

– –

– –

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association behaviour of C8PyCl and CnPyDs were carried using surface tension measurements. The micelles of CnPyDs are processing disk like geometry which was characterized by SANS analysis. In short, here we have developed economical and environmentally benign process for the preparation of novel fluoride free hydrophobic CnPyDs TSILs which could be a good substitute of costly, toxic PF6−, BF4− etc. anions based ILs.

appearance of clear inflection point in surface tension isotherm indicate that C8PyDs is making micelles and the obtained CMC values of C8PyDs very much lower to that of pure SDS as well as C8PyCl. Thus, from the surface measurements it is inferred that C8PyCl is making micelles at higher concentration, while C4PyCl and C6PyCl are not making micelles even at high concentration because of highly hydrophilic in nature. The surface active parameters obtained from surface tension measurements are given in Table 2.

Conflict of interest 3.4. Small angle neutron scattering analysis Author declares there is no conflict of interest regarding this publication.

The geometry of micelle formed by ILs was determined by SANS measurements. The SANS measurements were performed using a fixed geometry SANS instrument with a sample-to-detector distance of 1.8 m. This spectrometer makes use of a BeO filtered beam which provides a mean wavelength of 5.2 Å and has a wavelength resolution of about 15%. The angular distribution of the scattered neutrons is recorded using an indigenously built one-dimensional position-sensitive detector. The accessible wave transfer (q = 4πsin(0.5θ)/λ, where λ is the mean wavelength of the incident neutrons and θ is the scattering angle) range of this instrument is 0.015–0.35 Å−1. The solutions were held in a 0.5 cm path length UV-grade quartz sample holder with tight fitting Teflon stoppers sealed with parafilm. From solubility studies, it was found that C8PyDs is partially miscible in water while SDS and C8PyCl are highly soluble in water. Because of the dodecyl chain on sulphate anion, SDS tends to making micelles in H2O [36]. In view of this; we assume and confirm from ST measurements that CnPyDs is making micelles in water at 30 °C. In order to characterize the micelles of CnPyDs, SANS measurements were carried out along with SDS and C8PyCl at 30 °C. The SANS curves for SDS, C8PyCl and CnPyDs are depicted in Figs. 4 and 5 respectively. The experimental SANS profiles were analyzed using different geometries such as spherical, ellipsoidal, cylinder etc. and of these shapes, we could best fit the SANS data by considering ellipsoidal geometry of micelles. In case of C8PyCl, we could not fit the data to any structural model because it is not organized well micelles in water at 30 °C. The parameters obtained from the above SANS analysis are depicted in Table 3. Here it is worth to mention that CnPyCl are not making stable micelles, so we did not measured SANS spectra for C4PyCl and C6PyCl. It is revealed from the SANS curves as no clear scattering is observed in this case. Therefore, we were not able to fit the SANS curves of C8PyCl with any model. In case of SDS, the parameters obtained by ellipsoidal models are a = 32 nm and b = 15 nm. These parameters are in good agreement with the reported values [36]. From the a/b ratio, it is clear that SDS micelles are in non-spherical shape, while for CnPyDs we could not able to fit SANS curves with ellipsoidal geometry. The SANS curves could be reproduced with disk or cylindrical like geometry. In the SANS curve of CnPyDs, the correlation values increases by decreasing the scattering vector q and there is an absence of correlation peaks (S(q) = 1) (Eq. (2)). High l/R ratio (∼20) for CnPyDs confirms the elongation in the shape of micelle. Thus, replacement of Cl− by dodecylsulphate anion induced micellization in water. On the other side we can say that substitution of sodium cation of SDS by N-alkyl pyridinium cation produce stretching of semi major axis along one direction of ellipsoids and leads to disk like shape.

Acknowledgement Dr. Rohit L. Vekariya thankful to Ton Duc Thang University (TDTUDEMASTED) for financial support. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.colsurfa.2017.05.083. References [1] P. Walden, Bull. Acad. Sci. St. Petersburg 1800 (1914) 405–422. [2] P. Wasserscheid, T. Welton, Ionic Liquid in Synthesis, 2nd ed., Wiley, New York, 2007. [3] O. Russina, W. Schroer, A. Triolo, Mesoscopic structural and dynamic organization in ionic liquids, J. Mol. Liq. 210 (2015) 161–163. [4] T.L. Greaves, C.J. Drummond, Protic ionic liquids: properties and applications, Chem. Rev. 108 (2008) 206–237. [5] V.I. Parvulescu, C. Hardcre, Catalysis in ionic liquids, Chem. Rev. 107 (2007) 2615–2665. [6] J. Ranke, S. Stolte, R. Stormann, J. Arning, B. Jastorff, Design of sustainable chemical products the example of ionic liquids, Chem. Rev. 107 (2007) 2183–2206. [7] F. Van Rantwijk, R.A. Sheldon, Biocatalysis in ionic liquids, Chem. Rev. 107 (2007) 2757–2785. [8] T. Welton, Room-temperature ionic liquids. Solvents for synthesis and catalysis, Chem. Rev. 99 (1999) 2071–2084. [9] B. Kirchner (Ed.), Ionic Liquids, vol. 290, Springer, Berlin, 2010. [10] J. Lunagariya, A. Dhar, R.L. Vekariya, Efficient esterification of n-butanol with acetic acid catalyzed by the Brönsted acidic ionic liquids: influence of acidity, RSC Adv. 7 (2017) 5412–5420. [11] B.C. Ranu, R. Jana, You have full text access to this content ionic liquid as catalyst and reaction Medium −a simple, efficient and green procedure for knoevenagel condensation of aliphatic and aromatic carbonyl compounds using a task-specific basic ionic liquid, Eur. J. Org. Chem. 2006 (2006) 3767–3770. [12] R.L. Vekariya, A. Dhar, J. Lunagariya, Synthesis and characterization of double −SO3H functionalized Brönsted acidic hydrogensulfate ionic liquid confined with silica through sol-gel method, Composite Interf. 24 (2017) 801–816. [13] R.L. Vekariya, Effects of cationic head groups of ionic liquid on micellization in aqueous solution of PEO-PPO-PEO triblock copolymer, J. Dis. Sci. Technol. 38 (2017) 1594–1599. [14] R.L. Vekariya, A review of ionic liquids: applications towards catalytic organic transformations, J. Mol. Liq. 227 (2017) 44–60. [15] H.S. Schrekker, M.P. Stracke, C.M.L. Schrekker, J. Dupond, Ether-functionalized imidazolium hexafluorophosphate ionic liquids for improved water miscibilities, Ind. Eng. Chem. Res. 46 (2007) 7389–7392. [16] Z. Du, E. Li, Y. Cao, X. Li, G. Wang, Synthesis of trisiloxane-tailed surface active ionic liquids and their aggregation behavior in aqueous solution, Colloids and Surfaces A: Physicochem Eng. Aspects 441 (2014) 744–751. [17] M. Palacio, B. Bhushan, A review of ionic liquids for green molecular lubrication in nanotechnology, Tribology Lett. 40 (2010) 247–268. [18] R. Patel, M. Kumari, A.B. Khan, Recent advances in the applications of ionic liquids in protein stability and activity: a review, Appl. Biochem. Biotechnol. 172 (2014) 3701–3720. [19] D. Wei, A. Ivaska, Applications of ionic liquids in electrochemical sensors, Analytica Chim. Acta 607 (2008) 126–135. [20] G. Durga, A. Mishra, Ionic liquids: industrial applications encyclopedia of inorg, Bioinorg. Chem (2016) 1. [21] N. Deng, M. Li, L. Zhao, C. Lu, S.L. de Rooy, I.M. Warner, Highly efficient extraction of phenolic compounds by use of magnetic room temperature ionic liquids for environmental remediation, J Hazard Mater. 192 (2011) 1350–1357. [22] I. Kilpelainen, H. Xie, A. King, M. Granstrom, S. Heikkinen, D.S. Argyropoulos, Dissolution of wood in ionic liquids, J. Agric. Food Chem. 55 (2007) 9142–9148. [23] P. Bonhote, A.P. Dias, N. Papageorgiou, K. Kalyanasundaram, M. Gratzel, Hydrophobic highly conductive ambient-temperature molten salts, Inorg. Chem. 35

4. Conclusions Here, we have shown the synthetic procedure for the preparation of CnPyDs from SDS and CnPyCl. The ILs are characterized by 1H NMR, thermal methods, IR and MS. From the TGA analysis we showed the C4PyDs and C6PyDs are more stable (upto ∼350 °C) as compared to C4PyCl and C6PyCl. Due to limited solubility, CnPyDs are making micelles in aqueous media while C8PyCl is not making organized micelle so we could not fit SANS data of C8PyCl with any model. The CMC and 208

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