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Colloids and Surfaces A: Physicochem. Eng. Aspects 462 (2014) 153–161

Contents lists available at ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

journa l h om epage: www.elsev ier .com/ locate /co lsur fa

ffect of ionic liquids on microstructures of micellar aggregatesormed by PEO–PPO–PEO block copolymer in aqueous solution

ohit L. Vekariyaa, Debes Rayb, Vinod K. Aswalb, Puthusserickal A. Hassanc,aurabh S. Sonia,∗

Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388 120, Gujarat, IndiaSolid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, Maharashtra, IndiaChemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, Maharashtra, India

i g h l i g h t s

Aqueous mixed systems ofPluronics® (F127) with variouspyridinium based ILs were studied.Size and shape for micelles of F127in aqueous solutions of ILs were mea-sured by SANS and DLS.The interactions between PEO/PPOwith ILs were checked by 1H NMR andviscosity.Upon addition of ILs, an enhancementin CMC and reduction in micellar sizeof F127 were found.Effect of alkyl chain length, headgroup, anions and concentration ofILs has been discussed.

g r a p h i c a l a b s t r a c t

r t i c l e i n f o

rticle history:eceived 29 April 2014eceived in revised form 28 August 2014ccepted 30 August 2014vailable online 16 September 2014

a b s t r a c t

Effect of ionic liquids (ILs) viz. pyridinium, picolinium and imidazolium halide on the micellization and thestructure of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblockcopolymer, F127 in aqueous solution has been studied by small angle neutron scattering (SANS) anddynamic light scattering (DLS) measurements. The interaction information between ILs and PEO/PPO hasbeen explored by using 1H NMR and viscosity measurements. The micellar structural parameters areobtained as a function of variation in alkyl chain length, cationic head group and concentrations of ILs by

eywords:lock copolymeroom temperature ionic liquidluronicsicellization

ANSiscosity

fitting the SANS data with model composed of core–shell form factor and a hard sphere structure factorof interaction. Addition of ILs is found to decrease the micellar core radius, aggregation number and hardsphere radius of F127 micelles. The effect of concentration, chain length and head groups of ILs also havebeen studied.

© 2014 Elsevier B.V. All rights reserved.

∗ Corresponding author. Tel.: +91 2692 226858x216; fax: +91 2692 236475.E-mail addresses: soni b21@yahoo.co.in, saurabhavna@gmail.com (S.S. Soni).

ttp://dx.doi.org/10.1016/j.colsurfa.2014.08.030927-7757/© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Amphiphilic poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide), (PEO–PPO–PEO) triblock copolymers are knownas Pluronics® or polaxamer or symperonics (ICI). These inter-esting types of amphiphilic block copolymers are commercially

1 : Phys

a[apwyumoabooabTrind[ssaaahPutcb

iflc[ipbea

ua[bgmsfs

b[m(acoabaCoc

a maximum output power of 2 W. The average decay rate was

54 R.L. Vekariya et al. / Colloids and Surfaces A

vailable in a variety of molecular weights and PEO/PPO ratios1]. The hydrophobic/hydrophilic character of the copolymer inqueous solution can be altered by varying the solution tem-erature or modifying the solvent properties, hence they areidely used in many industrial formulations [2,3]. In recent

ears, the scope of their application is much broader as theysed in nanoparticles synthesis [4,5], gene delivery [6], as poly-er gel electrolyte [7,8], as templating agents [9], etc. Majority

f these applications are associated with the micelles, thosere formed in aqueous solution and therefore, micellization oflock copolymers has attracted great attention [10]. In aque-us media, above the critical micellization temperature (CMT)r above the critical micellization concentration (CMC) they selfssociate into micelles with a hydrophobic core containing POlocks surrounded by outer shell of the hydrated EO blocks [3].he interesting feature of Pluronics is they self assembled inich micro-crystalline phases. It is well known that copolymersnteract with classical surfactants such as anionic, cationic andonionic. The Pluronic F127 with aqueous solutions of sodiumodecyl sulphate [10], tertradecyltrimethylammonium bromide11] and hexaethylene glycol mono-n-dodecyl ether [12] weretudied. The addition of salts and conventional cationic and anionicurfactants has a strong effect on the micellization, cloud pointnd CMT [13]. Hecht et al. [14,15] have reported that very smallmounts of NaDS interfered with the micelle formation of F127nd when the concentration of added NaDS was sufficientlyigh the micellization of F127 was completely suppressed [16].luronics–cetyltrimethylammonium bromide (CTAB) supramolec-lar assemblies, in which the hydrophobic chains of CTAB occupyhe hydrophobic core of the Pluronics micelle while the positivelyharged head groups reside at the micellar core–shell interface haseen studied by Sing et al. [17].

Ionic liquids (ILs) received great attention, because of theirntriguing properties like negligible vapour pressure, negligibleammability, excellent chemical and thermal stability, electro-hemical window and stability over a broad temperature range18–20]. Due to these interesting properties, ILs have been widelyn use in the areas of organic synthesis, catalyst, electrochemistry,olymer electrolyte, etc. Among all reported ILs, due to higheriodegradability, IL composed of alkyl pyridinium cation with vari-ty of anions are used in various applications including as surfacective agent [21,22].

In recent years, ILs in combination with polymers have also beensed as reaction media for polymer synthesis [23], supported cat-lyst [24], polymer electrolyte membrane [25], metal ion removal26], as an electrolyte in dye sensitized solar cell [27], lithium ionatteries [28], etc. Moreover, very recently, water based polymerel electrolyte received much attention because of the environ-ental and safety issues [29]. In view of these, it is necessary to

tudy the effect of ILs, their interactions and location of cation/anionragments in micelles of amphiphilic block copolymers in aqueousolutions.

Association behaviour and surface activity of amphiphiliclock copolymers and ILs are very well documented in literature21,22,30,31]. Some reports are available on self-assembly and

icellization behaviour of amphiphilic block copolymer in an ILwhere ILs were used as a solvent) [32,33]. But very few literaturesre available on effect of IL on aggregation behaviour of triblockopolymers in aqueous medium. To the best of our knowledge,nly two reports on the effect of ILs on Pluronic micelles are avail-ble in literature [34,35]. Zheng et al. [34] reported aggregationehaviour of Pluronic P104 in presence of 1-butyl-3-methyl imid-

zolium bromide (BmimBr) in aqueous solution. The variation ofMT, CMC and interaction between hydrophobic part (butyl groupf the Bmim+) cation with PO block of triblock copolymer werearried out using FTIR, FFTEM, DLS and NMR spectroscopy. Very

icochem. Eng. Aspects 462 (2014) 153–161

recently, Parmar et al. [35] studied interaction between 1-alkyl-3-methyl imidazolium tetrafluroborate and Pluronic P103 in aqueoussolutions using DLS, SANS and NMR studies. From the selectiveNOESY NMR spectrum, they indicated that there is an interactionbetween butyl chain of cation and PO group of P103 micelles. Bothof these reports are based on the imidazolium based ILs and as faras we aware, no other reports are available on detailed SANS anal-ysis as a function of concentrations, cationic head groups and alkylchain length on pyridinium cation of ILs on micelles of F127 blockcopolymer in water. The aim of the present study is to make cor-relation between variation of concentration, alkyl chain length andcation of IL and micellization of Pluronic F127 in aqueous solutions.

In this paper we report the results on the aggregation behaviourof a block copolymer, Pluronic F127 [(EO)97(PO)69(EO)97] in pres-ence of various ILs in aqueous media as studied by SANS, DLS, NMRand viscosity measurements. SANS and DLS studies were used todetermine the size and shape of F127 micelles under the influenceof ILs. From NMR analysis, interactions of ILs with micellar core(PPO block) and shell (PEO block) were determined. Effects of headgroups, alkyl chain length of cations, anions and concentration of ILson micellization of F127 in aqueous solution have been discussed.

2. Experimental

2.1. Chemicals and materials

Pluronic F127 (EO97PO69EO97) with average molecular weight12,600 g mol−1 was purchase from the Sigma–Aldrich, India andused as received. All ILs were prepared by the procedure reportedin literature [18,22,36,37] and were characterized by 1H NMR, TGA,IR methods. All ILs were stored at 60 ◦C in vacuum prior to useand the water content was measured by Karl-fisher analysis whichfound less than 0.05% in all ILs. The structures, molecular weight,and CMC of synthesized ILs are given in Table 1. Aqueous solutionsof Pluronic and ILs were prepared by weight using an analyticalbalance in degasse Millipore grade distilled water. For SANS andNMR measurements samples were prepared in D2O (>99% purity,Sigma–Aldrich).

2.2. Methods

2.2.1. Small angle neutron scattering (SANS)SANS measurements were carried out on micellar solutions of

F127 triblock copolymer in presence of various types of ILs. TheSANS measurements were performed using a fixed geometry SANSinstrument with a sample-to-detector distance of 1.8 m at DHRUVAreactor, Trombay, India [41]. This spectrometer makes use of a BeOfiltered beam which provides a mean wavelength of 5.2 A and hasa wavelength resolution of about 15%. The angular distribution ofthe scattered neutrons is recorded using a 1 m long one dimensionaldetector. The accessible wave transfer, q range of this instrumentis 0.015–0.35 A−1. The solutions were held in a 0.5 cm path lengthUV-grade quartz sample holder with tight fitting Teflon stopperssealed with parafilm. The theoretical approach for analysis of SANSdistribution curves is given in supporting documents.

2.2.2. Dynamic light scattering (DLS)DLS measurements of the solutions were performed using a

Malvern 4800 autosizer employing a 7132 digital correlator. Thelight source was an argon ion laser operated at 514.5 nm with

obtained by analyzing the electric field autocorrelation functiong1(�) vs. time data using a modified cumulants method. Thedata were analyzed as per the theory and equation reportedelsewhere [42].

R.L. Vekariya et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 462 (2014) 153–161 155

Table 1Molecular weight, CMC and structure of ILs.

Entry Materials Mol. wt. (g mol−1) CMC (mM) Structures of ILs

1 C4PyCl 176.6 600 [38], 900 [21]

2 C6PyCl 199.7 800 [21]

3 C8PyCl 227.5 180 [21]

4 C8PyBr 272.2 180 [22]

5 C8PyI 319.2 188 [39]

6 C8MimCl 230.7 234 [40]

7 C8�mPicCl 229.0 170 [21]

8 C8�mPicCl 229.0 175 [21]

2

seaa

2

havmcaew

3

3

itwp

.2.3. Nuclear magnetic resonance (NMR)All NMR experiments were conducted on a Bruker Avance 400

pectrometer at a Larmor frequency of 400.13 MHz for protonquipped with a microprocessor controlled gradient unit and anctively shielded z-gradient coil. All samples were prepared in D2Ond TMS was used as an internal standard.

.2.4. ViscosityThe viscosity measurements were carried out using an Ubbel-

ode suspended level capillary viscometer. The viscometer waslways suspended vertically in a thermostat at 30 ± 0.1 ◦C. Theiscometer was cleaned and dried every time before each measure-ent. The flow time for constant volume of solution through the

apillary was measured with a calibrated stopwatch. The flow timelways exceeds 170 s and thus no kinetic corrections were consid-red. The copolymer solutions that showed Newtonian behaviourere all considered for measurements with capillary viscometer.

. Results and discussion

.1. SANS measurements

We have performed SANS studies on 10% (w/v) F127 to exam-

ne the role of various ILs on its micellar structure. Fig. 1(a) showshe SANS data obtained for 10% (w/v) F127 aqueous solutionsith varying C8PyCl concentrations at 30 ◦C. A strong correlationeak was observed in micellar aqueous solution of 10% (w/v) F127

without IL. The micellar parameters; core radii (Rc), hard sphereradii (RHS), volume fraction (�), polydispersity (�) and aggregationnumber (Nagg) obtained by fitting of the data based on sphericalcore–shell micelles are reported in Table 2 with error bars uncer-tainty. It was checked that a pure core model gives poor fits, withsignificantly larger chi-squared (�2) values which justifies the useof a complete core–shell model. The micellar parameters includingcore radius obtained from SANS measurements in D2O are in goodagreements with those reported by Ganguly et al. for 10% (w/v)F127 micelles [43]. Upon addition of IL (C8PyCl), correlation peakshifts towards high q region of the scattering curve indicating thatthe correlation between micelles becomes weak for F127 which isbecause of increase in number density of micelles. But the observedreduction in magnitude of d�/d concurs that the demicellizationof F127 micelles may occur in presence of IL. Due to hydrophilicnature of F127, the extent of hydration is high in presence of IL,which leads to reduction in micellar size and increasing correlationbetween micelles. The micellar volume fraction of the 10% (w/v)F127 solution slightly decreases or almost remains constant in thepresence of ILs (Table 2), and such an observation at fixed copoly-mer concentration can occur only because of an increase in thedegree of hydration in the F127 micelles.

The aggregation number (Nagg) is defined as the number of block

copolymer molecules per micelle and is given by,

Nagg = 4�(RC )3

3nPOVPO(1)

156 R.L. Vekariya et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 462 (2014) 153–161

Table 2Core radius (Rc), polydispersity (�), hard sphere radius (RHS), volume fraction (�) and aggregation number (Nagg) for 10% (w/v) F127 solutions with and without ILs at 30 ◦C.

System Rc (nm) � RHS (nm) � Nagg

F127 3.0 ± 0.2 0.58 9.1 ± 0.4 0.24 19 ± 2Effect of concentration of C8PyClF127 + 200 mM C8PyCl 2.4 ± 0.2 0.64 7.8 ± 0.4 0.23 10 ± 2F127 + 400 mM C8PyCl 2.1 ± 0.1 0.60 6.5 ± 0.3 0.20 6 ± 1

Effect of alkyl chain length on cationic head group (CnPyCl, n = 4, 6, 8)F127 + 200 mM C4PyCl 2.6 ± 0.2 0.74 9.1 ± 0.4 0.22 12 ± 2F127 + 200 mM C6PyCl 2.5 ± 0.2 0.74 8.8 ± 0.4 0.23 11 ± 2F127 + 200 mM C8PyCl 2.4 ± 0.2 0.64 7.8 ± 0.4 0.23 10 ± 2

Effect of cationic head groupsF127 + 200 mM C8PyCl 2.4 ± 0.2 0.64 7.8 ± 0.4 0.23 10 ± 2F127 + 200 mM C8�mPicCl 2.4 ± 0.2 0.47 7.5 ± 0.4 0.22 10 ± 2

3

8

wo(e

aC2It(cm4fRoovrom

bbPitTfsiCiFfrha6rUaaohcc[

F127 + 200 mM C8�mPicCl 2.2 ± 0.2 0.7F127 + 200 mM C8MimCl 2.4 ± 0.1 0.4

here VPO is the volume of one PPO monomer, nPO is the numberf PPO monomers per block (for F127, nPO = 69). The Nagg for 10%w/v) F127 in D2O is ∼19, closer to the value reported by Gangulyt al. for 10% (w/v) F127 micelles in D2O [43].

When the micellar parameters for 10% (w/v) F127 micelles inqueous solutions in absence and presence of aqueous solution of8PyCl are compared, it is observed that Rc decreases from 3.0 to.5 and 2.1 nm for 200 mM and 400 mM of C8PyCl, respectively.t is worth to mention that the concentrations of IL selected forhis study were just above their CMC values at desire temperatureTable 1), moreover, it is documented [21] that even up to 1000 mMoncentration of these ILs are not making very well organizedicelles. Surprisingly, RHS decreases upon addition of 200 mM and

00 mM of C8PyCl. Along with Rc and RHS, a rise in the volumeraction, � is also observed. The concomitant decrease of Nagg andc is consistent with the decrease in micellar volume. From thesebservations one can conclude that C8PyCl favours the apparitionf smaller micelle but with a higher number density, so the overallolume fraction of all the hard spheres is almost constant. This iseflected in the values of RHS (Table 2) and in Fig. 1(a), the shiftingf correlation peak positions to higher q values indicates that theean intermicellar distance decreases upon addition of IL (C8PyCl).The small micelles with a large part of the surfactant hydropho-

ic chains in contact with the solvent are unfavourable in D2Oecause the interfacial tension between water and hydrophobicPO chains is high. The addition of C8PyCl to D2O reduces thenterfacial tension between hydrophobic chains and the solvent sohat the formation of smaller micelles becomes more favourable.herefore, due to high hydration, the micellization becomes lessavourable and leads to decrease in core radius, Nagg, since a betterolvent environment for both PEO and PPO blocks of copolymers available. The effect of alkyl chain length of pyridinium cation,nPyCl (n = 4, 6, 8) on the structure of F127 micelles has been

nvestigated at 30 ◦C. Fig. 1(b) shows the SANS data for 10% (w/v)127 micelle in 200 mM CnPyCl aqueous solutions. It can be seenrom the figure that with the addition of C4, C6 and C8PyCl, drasticeduction in intensity along with peak shifting towards higher q,as been observed, i.e. micelles of F127 is undergo size reductionnd increase in the number density in presence of CnPyCl (n = 4,, 8). The increase in the number density of micelles is probablyesponsible for the observed decrease in Rc, RHS (see Table 2).pon addition of CnPyCl, the high degree of hydration of shellnd PPO/PEO interface occurs which ultimately reduce the Rc

nd facilitate the de-micellization and reduction of overall sizef micelles. The decrease in core radius might be because of

ydration of PPO/PEO interface due to presence of pyridiniumations which ultimately push the PPO chain further inside theore. These results are opposite to the one reported by Zheng et al.34] with P104 [(PEO)27–(PPO)61–(PEO)27] in aqueous solution of

7.7 ± 0.3 0.23 7 ± 26.6 ± 0.3 0.34 10 ± 2

1-butyl-3-methyl imidazolium bromide (BmimBr). However,authors reported the growth of P104 micelles when the concen-tration of BmimBr was above 1.232 mol/L, while almost no changein CMT or micellar growth was observed for lower concentrationof BmimBr. The higher concentration of IL (BmimBr) favours thedehydration of PEO shell and resulted into overall growth in themicellar size. The concentration (1.232 mol/L or 1232 mM) ofBmimBr that induced such growth in micellar size is much higherthan the concentration (i.e. 200 mM and 400 mM) used in our study.The observed reverse trend implies that the amount of IL usedin our case is not sufficient to persuade dehydration of micelles,therefore, no expansion in micellar dimension was observed. More-over, variation in nature of cationic head groups (organic moiety)as well as % PEO units in block copolymers may also be responsiblefor such type of discrepancies in the micellar parameters.

After studying the effect of concentration and alkyl chain lengthon cationic head groups, we measured 10% (w/v) F127 micellarsolutions in presence of various cationic head groups (keeping com-mon alkyl chain length and anion) using SANS. Fig. 1(c) shows SANSdata for the 10% (w/v) F127 aqueous solution in presence of 200 mMof C8YCl [Y = pyridinium, ˇ-picolinium (3-methyl pyridinium), �-picolinium (4-methyl pyridinium) and imidazolium] at 30 ◦C. Themicellar parameters obtained by fitting the data are reported inTable 2. In case of ˇ- and �-picolinium chloride, it shows similartrends in the reduction of core radius and thus the size of micelles.The F127 micelles, � values decreases with various pyridiniumbased cationic head groups. In case of imidazolium based cationichead group (C8MimCl), correlation peak is shifted to higher q andintensity of curve reduces compare to pure F127 micelles in D2O.Fig. 1(c) shows that, extent of enhancement in the volume fractionof micelles increases compared to pyridinium based IL. Moreover,due to the presence of two heteroatoms (N) in imidazole moiety,the degree of hydration is more compared to the single heteroatombased pyridinium cation. The higher hydration, enhancement inshell thickness as well as polydispersity of micelle, ultimately leadsto disfavour condition for micellization.

3.2. Dynamic light scattering (DLS)

DLS studies on the effect of various ILs on the 5%(w/v) F127copolymers solutions have been carried out. Figs. S1 and S2 (sup-porting information) portrait the graphs of correlation functiong1(�) vs time (�s) and average relaxation time g1(�) vs. concentra-tion of ILs respectively. The observed initial negative slope in Fig.S1(c) indicates that the micelles of F127 in presence of I− anions

are smaller in size and so they diffuse faster compared to the otheranions, like Cl− and Br−, which are diffuse slowly.

A systematic decrease in relaxation time with the concentra-tion of ILs having various anions, cations and the chain length

R.L. Vekariya et al. / Colloids and Surfaces A: Phys

100

101

102

F12 7 F127 + 20 0 mM C8PyCl F127 + 40 0 mM C8PyCl

dΣΣ/dΩΩ

, cm

-1

(a)

100

101

102

F12 7 F127 + 20 0 mM C4PyCl F127 + 20 0 mM C6PyCl F127 + 20 0 mM C8PyCl

dΣΣ/dΩΩ

, cm

-1

(b)

1.010.0

100

101

102

F12 7 F127 + 200 mM C8PyCl F127 + 200 mM C8MimCl F127 + 200 mM C8PyββmPicCl F127 + 200 mM C8γγmPicCl

dΣΣ/dΩΩ,, c

m-1

q, Å-1

0.3

(c)

Fig. 1. SANS data for 10% (w/v) F127 under variation of: (a) concentration of C8PyCl,(a

wsCte

R

and a penetration of protons into a nonpolar or polar medium

b) alkyl chain length on IL, (c) cationic head groups of ILs in D2O at 30 ◦C (solid linesre the theoretical fits to the experimentally measured data).

as observed in Fig. S2, which reveals the reduction in micellarize. The diffusion coefficients for all the system were obtain fromONTIN analysis and the obtained diffusion coefficients were usedo calculate hydrodynamic radius, using following Stoke–Einsteinquation.

h = KBT

6�DO(2)

icochem. Eng. Aspects 462 (2014) 153–161 157

where Rh is the hydrodynamic radius, KB is the Boltzmann constant, is the viscosity of solvent at temperature T and D0 is the diffusioncoefficient. Fig. 2 represents the variation in Rh for 5% (w/v) F127as a function of concentration of various ILs.

For 5% (w/v) F127 aqueous solution in absence of IL has Rh value11 nm at 30 ◦C which is in agreement with the literature valueof 10.0 nm [44]. Upon addition of 25 mM C8PyCl, no appreciablechange in Rh is observed. As concentration of C8PyCl increases from25 mM to 100 mM, the extent of decrease in the micelle dimensionwas observed which is confirmed by narrowing of the scatteringintensity and its shift to shorter radius (Fig. S3).

In case of 100 mM CnPyCl (n = 4, 6, 8), the reduction in Rh of F127micelle is observed. For shorter chain length, C4PyCl and C6PyCl,the average hydrodynamic radius slightly lowers, size distributionbecomes asymmetric (right skewed) and the width of distribu-tion increases. This suggests that the polydispersity of micellesincreases upon the addition of C4PyCl and C6PyCl, while for C8PyClthe narrowing in size distribution was observed along with the sizereduction in F127 micelles. Fig. 2 indicates variation in Rh as a func-tion of halide ion in C8PyX (X = Cl−, Br−, I−). The order for extent ofdecrease in average Rh is Cl− < Br− < I−, which is opposite to theeffect of alkali halide salts on the micelles of amphiphilic blockcopolymer. This might be because of presence of alkyl ammoniumcation in IL, which may overcome the ‘salting in’ and ‘salting out’ability of halide ions. An imidazolium cationic head group has pro-nounced effect in the reduction of micellar size compared to othersubstituted pyridinium based ILs (Fig. 2(b)).

All the results suggest the micelle undergoes reduction in sizekeeping spherical geometry which is also observed in SANS analy-sis using hard sphere core–shell model. An imidazolium cationichead group has pronounced effect in the reduction of micellescompared to other substituted pyridinium based ILs. Surprisinglyexcept C8PyCl and C8�mPicCl, all other ILs are narrowing the sizedistribution which indicates that the micelles become monodis-persed along with almost constant micellar volume fractions. Theseresults are in consistent with the SANS study.

3.3. NMR measurements

To obtain the information concerning the detailed interactionsites between ILs and different moieties of the block copolymerspecies and to understand the molecular level mechanism of theeffect of ILs on the micellization of PEO–PPO–PEO block copoly-mers, 1H nuclear magnetic resonance (NMR) measurements werecarried out. 1H NMR spectra of 10% (w/v) F127 in D2O along withpure ILs and their mixture were taken at 25 ◦C (Figs. S4–S7). Accord-ing to the spectra, the singlet at ∼1.10 ppm is attributed to protonsof PO CH3 groups and the additional broad peaks at 3.34–3.48 ppmand sharp peak at ∼3.64 ppm belong to the protons of PO CH2groups and EO CH2 groups, respectively. The signal ∼4.80 ppmis the residual signal of HDO, these assignments are in good agree-ments with reported values [45,46].

In order to understand the mechanism, the interaction andlocation of IL in micelle of block copolymers, we monitor thechange in chemical shift for PO CH3, PO CH2 , PO CH , EO CH2and terminal CH3 of alkyl chain on cationic head group of ILs. Theobserved change in the chemical shift for above mentioned protonsare depicted in Table 3. When 200 mM C8PyCl is added to F127micelles, the chemical shift of PO CH2 , PO CH3 and EO CH2protons experience a slight downfield shift, while PO CH protonundergo sudden ∼0.07 ppm upfield shift. It is well known that thechemical shift is sensitive to the chemical nature of related protons

would possibly induce an upfield or downfield shift due to thechange in magnetic susceptibility of the protons [47,48]. A slightly(∼0.01 ppm) downfield shift, for EO CH2 , PO CH2, PO CH3

158 R.L. Vekariya et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 462 (2014) 153–161

Table 31H-NMR chemical shift (ıppm) values of EO CH2 , PO CH2 , PO CH , PO CH3 of F127 in presence and absence of a variety of ILs.

System EO CH2 signal(ıppm)

PO CH2 Signal(ıppm)

PO CH Signal(ıppm)

PO CH3 signal(ıppm)

Terminal CH3 of alkyl chain on cationof ILs (without polymer) (ıppm)

Effect of concentration of C8PyClF127 3.65 3.37 3.55 1.09 –F127 + 200 mM C8PyCl 3.66 3.38 3.47 1.09 0.75F127 + 400 mM C8PyCl 3.65 3.40 3.47 1.08 0.74

Effect of alkyl chain length on cationic head group (CnPyCl, n = 4, 6, 8)F127 3.65 3.37 3.55 1.09 –F127 + 200 mM C4PyCl 3.65 3.39 3.50 1.11 0.85F127 + 200 mM C6PyCl 3.65 3.38 3.48 1.10 0.75F127 + 200 mM C8PyCl 3.66 3.38 3.47 1.09 0.75

Effect of anions (C8PyX, X = Cl− , Br− , I−)F127 3.65 3.37 3.55 1.09 –F127 + 200 mM C8PyCl 3.66 3.38 3.47 1.09 0.75F127 + 200 mM C8PyBr 3.66 3.38 3.47 1.07 0.74F127 + 200 mM C8PyI 3.65 3.39 3.45 1.06 0.75

Effect of cationic head groupsF127 3.65 3.37 3.55 1.09 –F127 + 200 mM C8PyCl 3.66 3.38 3.47 1.09 0.75F127 + 200 mM C8MimCl 3.65 3.37 3.48 1.07 0.68F127 + 200 mM C8�mPicCl 3.65 3.38 3.46 1.08 0.73

3.47

N

ibfmoNiP

opsmahastccsuenmulCRy

truiwTBttd

F127 + 200 mM C8�mPicCl 3.65 3.38

ote: Concentration of F127 is 10% (w/v) and all samples were prepared in D2O.

ndicates that the local environment of PEO blocks as well as PPOlocks remains almost unchanged. However, a drastic upfield shiftor PO CH group indicates the experience of dehydration which

ay occur at the PPO/PEO interface due to the possible presencef hydrated alkyl chain of cationic head group of IL. Thus from 1HMR results, it seems that most PPO segment probably cannot

nteract directly with IL, therefore an indirect interaction betweenPO and IL is suggested.

It is expected that this trend will continue if concentrationf IL increases from 200 mM to 400 mM but surprisingly all therotons of PPO and PEO domain (except PO CH2 ) undergotrong upfield shift (near to the values obtained for pure F127icelles in D2O). This indicates that PPO blocks apparently form

hydrophobic environment, while EO CH2 experiences slightydrophobic environment because of the presence of alkyl chaint the PPO/PEO interface and PEO domain. Further, this can beupported by monitoring the chemical shift of EO CH2 as a func-ion of alkyl chain length on cationic head group. IL with shorterhain length (C4, -butyl) undergoes the maximum downfield shiftompared to C6 and C8PyCl. This strong effect is inferred to thetrong interaction between EO CH2 groups and water whichltimately deshields the CH2 protons of ethylene oxide moi-ties. As chain length of alkyl group increases, due to hydrophobicature, it reduces the interaction between water and EO seg-ents. As explained earlier for 200 mM and 400 mM C8PyCl, the

pfield shift of PO-CH protons can be justified. Thus, C4PyCl isess affecting the micellar dimension compared to the C6PyCl and8PyCl. Similar results were observed for the micellar parameters,c, RHS, Rh and volume fraction obtained from SANS and DLS anal-sis.

If Cl− anion of C8PyCl is replaced by Br− and I−, due to low elec-ronegativity and larger atomic size, I− is less hydrated, and as aesult more water is available to deshield EO CH2 and inducespfield shift compared to Cl−. An increase in hydration of PEO

nduces an enhancement for the hydrogen bonding structure inater as well as the hydration of the hydrophobic groups of PPO.

he increasing hydration of PPO with the addition of C8PyX (X = Cl−,

r−, I−) is eventually prevents the occurrence of micellization. Inhe micellar state, all of the hydrophobic groups are oriented insidehe micellar core, hence interaction between EO segments and ILominates over the hydrophobic group–ILs interaction.

1.07 0.73

In case of effect of cationic head groups, surprisingly ıppm val-ues of EO CH2 shifts towards upfield as methyl substitution isintroduced on pyridine cation (at 3 and 4 position). At the sametime, protons of PO CH2 and PO CH3 groups are also undergoingupfield shift. The observed upfield shift in PO CH2 and PO CH3 isthe manifestation of the reduction of contact between PPO blocksand water, thus forms a hydrophobic environment. For C8MimCl,interestingly ıppm values of PO CH3, PO CH2 and PO CH areshifted to upfield while EO CH2 is showing downfield shift. Anupfield shifting of all protons of PPO moieties indicates dehydra-tion of PPO domain which may enhance the size of micelles, butdue to extent of PEO hydration, de micellization and size reductionof micelles occur.

3.4. Viscosity measurements

The reduced viscosities for various concentrations of copolymersolutions in presence of ILs at various concentrations were deter-mined. The reduced viscosity (sp/C), versus concentration plots forF127 in presence and absence of ILs at 30 ◦C are shown in Fig. 3. Fromfigure it is revealed that, all plots are linear, behaviour of typical ofan uncharged polymer which follows, Huggins relation;

sp

C= [] + []2kHC (3)

where sp/C is the reduced viscosity and kH is the Huggins constant.The obtained values of [] and kH for F127 in presence of 200 mMILs solutions are given in Table 4.

The [] value, 0.225 dl g−1 for F127 in water is in good agree-ment with the literature value, 0.214 g dl−1 [49]. Upon addition ofILs, composed of various halides, chain length and cationic headgroups, a decrease in [] and an increase in kH compared to waterare observed. The decreased [] values indicate the demicellizationfacilitated by micellar hydration and better solvent quality of themixed water + ILs system and lead to decrease in size of sphericalmicelles.

Similar types of observation were reported for various Pluronic

block copolymers in presence of additives [50,51]. The fact thatkH values become higher or even more than unity in addition ofILs, indicates that the hydration effects strengthen the attractiveinteractions between the hydrophilic part of the block copolymer

R.L. Vekariya et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 462 (2014) 153–161 159

0 20 40 60 80 10 06

7

8

9

10

11

12R

h, n

m

Concen tration of IL, mM

F127 + C8PyCl F127 + C8PyBr F127 + C8PyI

(a)

0 20 40 60 80 1006

7

8

9

10

11

12

Rh,

nm

Conce ntration of I L, mM

F127 + C8PyCl F127 + C8γγmPicCl F127 + C8ββmPicCl F127 + C8MimCl

(b)

0 20 40 60 80 10 06

7

8

9

10

11

12

Rh,

nm

Conce ntration of I L, mM

F127 + C4PyCl F127 + C6PyCl F127 + C8PyCl

(c)

Fig. 2. Hydrodynamic radius, Rh vs. concentration of ILs for 5% (w/v) F127 withvarying conditions (a) effect of anions, (b) effect of head group (cations), (c) effectof alkyl chain length at 30 ◦C.

Fig. 3. Reduced viscosity of F127 aqueous solutions in presence of ILs: (a) effect ofconcentration (C8PyCl) and chain length, (b) effect of anion and (c) effect of cationichead groups at 30 ◦C.

160 R.L. Vekariya et al. / Colloids and Surfaces A: Phys

Table 4Intrinsic viscosity [], and Huggins constant, kH , for F127 in presence and absenceof ILs in aqueous solution at 30 ◦C.

Systems [] (dl g−1) kH

F127 0.225 0.68F127 + 200 mM C4PyCl 0.209 0.80F127 + 200 mM C6PyCl 0.195 0.92F127 + 200 mM C8PyCl 0.171 1.15F127 + 100 mM C8PyCl 0.182 1.04F127 + 200 mM C8PyBr 0.154 1.41F127 + 200 mM C8PyI 0.126 2.18F127 + 200 mM C8�mPicCl 0.193 0.90

mWoakfasm

4

dobdctmt1

ibtoPafihohcsawoC

A

pDan

A

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F127 + 200 mM C8�mPicCl 0.154 1.41F127 + 200 mM C8MimCl 0.111 2.99

olecules and solvent (water + ILs) media to a considerable extent.ith rise in concentrations or change in halide ions (from Cl < Br < I)

r cationic head groups of ILs, the above mentioned attractive inter-ction become dominant, as reflected from the enhanced values ofH. Due to this attractive interaction and high hydration, the inter-acial tension between hydrophobic PPO and solvent is weakennd leads to decrease in micellar size. Thus, viscosity data are alsoupporting the conclusion drawn from the SANS and DLS measure-ents.

. Conclusion

This study aims at a better understanding of the role of pyri-inium based ILs with F127 micelles. The isotropic micellar phasef 10% (w/v) F127 micelles with and without IL is well describedy interacting spherical micelles modelled using SANS. The SANSata give information about the evolution of the micellar form byhanging the alkyl chain length of cation head groups, concentra-ions and nature of cationic head groups of IL, when added to the

icellar aqueous solution of F127. The investigation on the interac-ion of ILs with F127 block copolymer has been carried out by usingH NMR spectroscopic method. The NMR results provide valuablenformation on the interaction sites of IL molecules with the tri-lock copolymer species particularly PEO and PPO. It was shownhat the C8PyCl molecules interact directly with the PEO moietiesf triblock copolymer whereas an indirect interaction betweenPO and IL has been observed. However, for the case of effect oflkyl chain length, halide ions and cationic head groups, the down-eld shift of the PPO blocks is possibly the result of an increase inydration of PEO blocks, which eventually prevents the occurrencef micellization and is also responsible for reduction in size. Theighest degree of de-micellization and volume fraction remainsonstant and was observed in case of C8MimCl. Viscosity resultshow the propensity in micellar size reduction upon addition of ILsnd hence intrinsic viscosity decreases. The sequence of ions holdsith regards to the effect of carbon chain length, anions and cations

n the size reduction of the micelles of copolymers, the trend is4PyCl < C6PyCl < C8PyCl and anion Cl− < Br− < I−.

cknowledgements

RLV and SSS are thankful to Chemistry Division of BARC forroviding the DLS measurement facility. The authors thank UGC-AE, Mumbai centre, for financial support (CSR-M-172). Authorsre also thankful to the Head, Chemistry Department for providingecessary facilities.

ppendix A. Supplementary data

Supplementary data associated with this article can beound, in the online version, at http://dx.doi.org/10.1016/j.colsurfa.014.08.030.

[

icochem. Eng. Aspects 462 (2014) 153–161

References

[1] Pluronic and Tetronic Block Copolymer Surfactants; Technical Brochure, BASFCorp., 1989.

[2] P. Holmqvist, P. Alexandridis, B. Lindman, Modification of the microstructurein block copolymer–water–oil systems by varying the copolymer compositionand the oil type: small-angle X-ray scattering and deuterium-NMR investiga-tion, J. Phys. Chem. B 102 (1998) 1149–1158.

[3] P. Alexandridis, T.A. Hatton, Poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymer surfactants in aqueous solutions and atinterfaces: thermodynamics, structure, dynamics, and modeling, Colloids Surf.A 96 (1995) 1–46.

[4] T. Sakai, P. Alexandridis, Single-step synthesis and stabilization of metalnanoparticles in aqueous Pluronic block copolymer solutions at ambient tem-perature, Langmuir 20 (2004) 8426–8430.

[5] S.S. Soni, R.L. Vekariya, V.K. Aswal, Ionic liquid induced sphere-to-ribbon tran-sition in the block copolymer mediated synthesis of silver nanoparticles, RSCAdv. 3 (2013) 8398–8406.

[6] A. Kabanov, J. Zhu, V. Alakhov, Pluronic block copolymers for gene delivery,Adv. Genet. 53 (2005) 231–261.

[7] S.S. Soni, K.B. Fadadu, A. Gibaud, Ionic conductivity through thermoresponsivepolymer gel: ordering matters, Langmuir 28 (2012) 751–756.

[8] S.S. Soni, K.B. Fadadu, R.L. Vekariya, J. Debgupta, K.D. Patel, A. Gibaud, V.K. Aswal,Effect of self-assembly on triiodide diffusion in water based polymer gel elec-trolytes: an application in dye solar cell, J. Colloid Interface Sci. 425 (2014)110–117.

[9] A. Gibaud, D. Grosso, B. Smarsly, A. Baptiste, J.F. Bardeau, F. Babonneau,D.A. Doshi, Z. Chen, C.J. Brinker, C. Sanchez, Evaporation-controlled self-assembly of silica surfactant mesophases, J. Phys. Chem. B 107 (2003) 6114–6118.

10] Y. Li, R. Xu, S. Couderc, D.M. Bloor, E. Wyn-Jones, J.F. Holzwarth, Bind-ing of sodium dodecyl sulfate (SDS) to the ABA block copolymer PluronicF127 (EO97PO69EO97): F127 aggregation induced by SDS, Langmuir 17 (2001)183–188.

11] Y. Li, R. Xu, S. Couderc, D.M. Bloor, J.F. Holzwarth, E. Wyn-Jones, Binding oftetradecyltrimethylammonium bromide to the ABA block copolymer PluronicF127 (EO97 PO69 EO97): electromotive force, microcalorimetry, and light scat-tering studies, Langmuir 17 (2001) 5742–5747.

12] S. Couderc, Y. Li, D.M. Bloor, J.F. Holzwarth, E. Wyn-Jones, Interactionbetween the nonionic surfactant hexaethylene glycol mono-n-dodecyl ether(C12EO6) and the surface active nonionic ABA block copolymer Pluronic F127(EO97PO69EO97) – formation of mixed micelles studied using isothermal titra-tion calorimetry and differential scanning calorimetry, Langmuir 17 (2001)4818–4824.

13] P. Alexandridis, J.F. Holzwarth, Differential scanning calorimetry investigationof the effect of salts on aqueous solution properties of an amphiphilic blockcopolymer (poloxamer), Langmuir 13 (1997) 6074–6082.

14] E. Hecht, H. Hoffmann, Kinetic and calorimetric investigations on micelle for-mation of block copolymers of the poloxamer type, Colloids Surf. A 96 (1995)181–197.

15] E. Hecht, H. Hoffmann, Interaction of ABA block copolymers with ionic surfac-tants in aqueous solution, Langmuir 10 (1994) 86–91.

16] E.D. Goddard, K.P. Ananthapadmanabhan (Eds.), The Interactions of Surfactantswith Polymers and Proteins, CRC Press, Boca Raton, FL, 1993.

17] P.K. Singh, M. Kumbhakar, R. Ganguly, V.K. Aswal, H. Pal, S. Nath, Time-resolvedfluorescence and small angle neutron scattering study in Pluronics – surfactantsupramolecular assemblies, J. Phys. Chem. B 114 (2010) 3818–3826.

18] P. Wassercheid, T. Welton, Ionic Liquids in Synthesis, 2nd ed., Wiley-VCH,Weinheim, 2007.

19] D.A. Kotadia, S.S. Soni, Symmetrical and unsymmetrical Brønsted acidic ionicliquids for the effective conversion of fructose to 5-hydroxymethyl furfural,Catal. Sci. Technol. 3 (2013) 469–474.

20] D.A. Kotadia, S.S. Soni, Sulfonic acid functionalized solid acid: an alternativeeco-friendly approach for transesterification of non-edible oils with high freefatty acids, Monatsh. Chem. 144 (2013) 1735–1741.

21] N.V. Sastry, N.M. Vaghela, P.M. Macwan, S.S. Soni, V.K. Aswal, A. Gibaud, Aggre-gation behavior of pyridinium based ionic liquids in water – surface tension,1H NMR chemical shifts, SANS and SAXS measurements, J. Colloid Interface Sci.371 (2012) 52–61.

22] A. Cornellas, L. Perez, F. Comelles, I. Ribosa, A. Manresa, M.T. Garcia, Self-aggregation and antimicrobial activity of imidazolium and pyridinium basedionic liquids in aqueous solution, J. Colloid Interface Sci. 355 (2011) 164–171.

23] P. Kubisa, Ionic liquids in the synthesis and modification of polymers, J. Polym.Sci. A: Polym. Chem. 43 (2005) 4675–4683.

24] P. Snedden, A.I. Cooper, K. Scott, N. Winterton, Cross-linked polymer–ionicliquid composite materials, Macromolecules 36 (2003) 4549–4556.

25] M.A.B.H. Susan, T. Kaneko, A. Noda, M. Watanabe, Ion gels prepared by in situradical polymerization of vinyl monomers in an ionic liquid and their charac-terization as polymer electrolytes, J. Am. Chem. Soc. 127 (2005) 4976–4983.

26] A.P. de los Rios, F.J. Hernandez-Fernandez, L.J. Lozano, S. Sanchez, J.I. Moreno,C. Godinez, Removal of metal ions from aqueous solutions by extraction withionic liquids, J. Chem. Eng. Data 55 (2010) 605–608.

27] F.S. Freitas, J.N. de Freitas, B.I. Ito, M.A. De Paoli, A.F. Nogueira, Electrochemi-cal and structural characterization of polymer gel electrolytes based on a PEOcopolymer and an imidazolium-based ionic liquid for dye-sensitized solar cells,ACS Appl. Mater. Interface 1 (2009) 2870–2877.

: Phys

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

R.L. Vekariya et al. / Colloids and Surfaces A

28] A. Lewantowski, A. Swiderska-Mocek, Ionic liquids as electrolytes for Li-ionbatteries – an overview of electrochemical studies, J. Power Source 194 (2009)601–609.

29] M. Armand, J.M. Tarascon, Building better batteries, Nature 451 (2008)652–657.

30] B. Chu, Z. Zhou, Physical chemistry of polyalkylene block copolymer surfactants,in: V.M. Nace (Ed.), Nonionic Surfactants, Surf. Sci. Ser., vol. 60, 1996, p. 67.

31] T. Perche, X. Auvray, C. Petipas, R. Anthore, E. Perez, I. Rico-Lattes, A. Lat-tes, Micellization of N-alkylpyridinium halides in formamide tensiometric andsmall angle neutron scattering study, Langmuir 12 (1996) 863–871.

32] A. Triolo, O. Russina, U. Keiderling, J. Kohlbrecher, Morphology of poly(ethyleneoxide) dissolved in a room temperature ionic liquid: a small angle neutronscattering study, J. Phys. Chem. B 110 (2006) 1513–1515.

33] S. Zhang, N. Li, L. Zheng, X. Li, Y. Gao, L. Yu, Aggregation behavior of Pluronictriblock copolymer in 1-butyl-3-methylimidazolium type ionic liquids, J. Phys.Chem. B 112 (2008) 10228–10233.

34] L. Zheng, C. Guo, J. Wang, X. Liang, S. Chen, J. Ma, B. Yang, Y. Jiang, H. Liu, Effect ofionic liquids on the aggregation behavior of PEO–PPO–PEO block copolymersin aqueous solution, J. Phys. Chem. B 111 (2007) 1327–1333.

35] A. Parmar, V.K. Aswal, P. Bahadur, Interaction between the ionic liquids 1-alkyl-3-methylimidazolium tetrafluoroborate and Pluronic® P103 in aqueoussolution: A DLS, SANS and NMR study, Spectrochim. Acta A 97 (2012) 137–143.

36] J. Bowers, C.P. Butts, P.J. Martin, M.C. Vergara-Gutierrez, R.K. Heenan, Aggre-gation behavior of aqueous solutions of ionic liquids, Langmuir 20 (2004)2191–2198.

37] K.R. Seddon, A. Stark, M. Torres, Influence of chloride, water, and organic sol-vents on the physical properties of ionic liquids, Pure Appl. Chem. 72 (2000)2275–2287.

38] T. Singh, A. Kumar, Aggregation behavior of ionic liquids in aqueous solutions:effect of alkyl chain length, cations, and anions, J. Phys. Chem. B 111 (2007)7843–7851.

39] E. Fisicaro, A. Ghiozzi, E. Pelizzetti, G. Viscardiv, P.L. Quagliotto, Effect of thecounterion on thermodynamic properties of aqueous micellar solutions of 1-(3,3,4,4,5,5,6,6,6-nonafluorohexyl) pyridinium halides: II. Apparent and partialmolar enthalpies and osmotic coefficients at 313 K, J. Colloid Interface Sci. 184(1996) 147–154.

[

[

icochem. Eng. Aspects 462 (2014) 153–161 161

40] C. Jungnickel, J. Luczak, J. Ranke, J.F. Fernandez, A. Muller, J. Thoming, Micelleformation of imidazolium ionic liquids in aqueous solution, Colloids Surf. A 316(2008) 278–284.

41] V.K. Aswal, P.S. Goyal, Small-angle neutron scattering diffractometer at Dhruvareactor, Curr. Sci. 79 (2000) 947–953.

42] J. Bhattacharjee, G. Verma, V.K. Aswal, A.A. Date, M.S. Nagarsenker, P.A. Hassan,Tween80 – sodium deoxycholate mixed micelles: structural characteriza-tion and application in doxorubicin delivery, J. Phys. Chem. B 114 (2010)16414–16421.

43] R. Ganguly, V.K. Aswal, Improved micellar hydration and gelation character-istics of PEO–PPO–PEO triblock copolymer solutions in the presence of LiCl, J.Phys. Chem. B 112 (2008) 7726–7731.

44] Y. Zhang, Y.M. Lam, W.S. Tan, Poly(ethylene oxide) - poly(propylene oxide) -poly(ethylene oxide) -g- poly(vinylpyrrolidone) : Association behavior in aque-ous solution and interaction with anionic surfactants, J. Colloid Interface Sci.285 (2005) 74–79.

45] J.H. Ma, C. Guo, Y.L. Tang, H.Z. Lin, 1H NMR spectroscopic investigations onthe micellization and gelation of PEO–PPO–PEO block copolymers in aqueoussolutions, Langmuir 23 (2007) 9596–9605.

46] J.H. Ma, C. Guo, Y.L. Tang, C. Lin, P. Bahadur, H. Liu, Interaction of urea withPluronic block copolymers by 1H NMR spectroscopy, J. Phys. Chem. B 111 (2007)5155–5161.

47] B.J. Kim, S.S. Im, S.G. Oh, Investigation on the solubilization locus of aniline-HCl salt in SDS micelles with 1H NMR spectroscopy, Langmuir 17 (2001) 565–566.

48] Y. Su, H. Liu, J. Wang, J. Chen, Study of salt effects on the micellization ofPEO–PPO–PEO block copolymer in aqueous solution by FTIR spectroscopy,Langmuir 18 (2002) 865–871.

49] P.R. Desai, N.J. Jain, R.K. Sharma, P. Bahadur, Effect of additives on the micelliza-tion of PEO/PPO/PEO block copolymer F127 in aqueous solution, Colloids Surf.A 178 (2001) 57–69.

50] N.J. Jain, A. George, P. Bahadur, Effect of salt on the micellization of PluronicP65 in aqueous solution, Colloids Surf. A 157 (1999) 275–283.

51] M. Desai, N.J. Jain, R. Sharma, P. Bahadur, Temperature and salt-induced mice-llization of block copolymers in aqueous solution, J. Surf. Deterg. 3 (2000)193–199.