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Research ArticleThermodynamic and Spectroscopic Investigation of Interactionsbetween Reactive Red 223 and Reactive Orange 122 AnionicDyes and Cetyltrimethyl Ammonium Bromide (CTAB) CationicSurfactant in Aqueous Solution
Muhammad Irfan,1 Muhammad Usman,1 Asim Mansha,1 Nasir Rasool,1
Muhammad Ibrahim,2 Usman Ali Rana,3 Mohammad Siddiq,4 Muhammad Zia-Ul-Haq,5
Hawa Z. E. Jaafar,6 and Salah Ud-Din Khan3
1 Department of Chemistry, Government College University, Faisalabad 38000, Pakistan2Department of Environmental Sciences, Government College University, Faisalabad 38000, Pakistan3Deanship of Scientific Research, College of Engineering, King Saud University P.O. Box 800, Riyadh 11421, Saudi Arabia4Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan5The Patent Office, Karachi 74400, Pakistan6Department of Crop Science, Faculty of Agriculture, UPM, 43400 Serdang, Selangor, Malaysia
Correspondence should be addressed to Muhammad Usman; usm ca@yahoo.com and Hawa Z. E. Jaafar; hawazej@gmail.com
Received 2 April 2014; Revised 12 July 2014; Accepted 17 July 2014; Published 28 August 2014
Academic Editor: Kun Qiao
Copyright ยฉ 2014 Muhammad Irfan et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.
The present study describes the conductometric and spectroscopic study of the interaction of reactive anionic dyes, namely,reactive red 223 and reactive orange 122 with the cationic surfactant cetyltrimethyl ammonium bromide (CTAB). In a systematicinvestigation, the electrical conductivity data was used to calculate various thermodynamic parameters such as free energy (ฮ๐บ),enthalpy (ฮ๐ป), and the entropy (ฮ๐) of solubilization. The trend of change in these thermodynamic quantities indicates towardthe entropy driven solubilization process. Moreover, the results from spectroscopic data reveal high degree of solubilization, withstrong interactions observed in the cases of both dyes and the CTAB. The spontaneous nature of solubilization and binding wasevident from the observed negative values of free energies (ฮ๐บ๐ and ฮ๐บ๐).
1. Introduction
The study of dye/surfactant interaction is the source ofuseful information to understand several industrial pro-cesses, for example, solubilization processes to remove theorganic compounds from aqueous solution and the use ofsurfactants to assist dying processes in textile industry [1].Theefficient removal of loosely bound dyes from the substrate viasolubilization and the adsorption and fixation of dyes on asubstrate highly depend on the strength of binding betweendyes and the host as well as the extent of dye solubilizationin the surfactant containing solution [2]. By making use of
their polar as well as nonpolar moieties, the micelles pro-vide heterogeneous media to solubilize organic compoundsduring dye removal process [3]. In premicellar region, thesurfactantmonomers interact with the dyemolecules to formion association complexes, while in postmicellar region, thedyemolecules likely incorporate into themicelles [4]. In suchcases, the hydrophobic effect is the dominant factor to decidethe locus of additive within micelle. However, the effects ofelectrostatic interactions are not also too weak to be ignored[5].
Reactive dyes have reactive functional groups capableof forming covalent bond with substrate. Acidic and basic
Hindawi Publishing Corporatione Scientific World JournalVolume 2014, Article ID 540975, 8 pageshttp://dx.doi.org/10.1155/2014/540975
2 The Scientific World Journal
conditions are important for successful and rapid reactionof dyes with substrate [6]. Reactive dyes are most commonlyused in dyeing of cellulose like cotton or flax. They can alsobe applied on wool and nylon, where, in the latter case, theyare applied under weakly acidic conditions [7].
Earlier, we have reported the solubilization of somedrugs, that is, chloroquine diphosphate, quinacrine 2HCl,and pefloxacin mesylate [8โ10] by micellar solutions. Inthe present study, we report the detailed investigation ofthe interaction of reactive dyes, namely, reactive orange122 (RO122) and reactive red 223 (RR223) with cationicsurfactant cetyltrimethyl ammonium bromide (CTAB).
2. Parameters Calculated
2.1. Calculation of Thermodynamic Parameters. Free energyof solubilization (ฮ๐บ) was calculated using the followingequation;
ฮ๐บ = (2 โ ๐ฝ) ๐ ๐ ln๐CMC. (1)
In (1), ๐ฝ is the degree of dissociation; ๐ is the general gasconstant having value โผ8.314 Jmolโ1 Kโ1; ๐ is the absolutetemperature;๐CMC is CMC in term of mole fraction. Here, ๐ฝcan be calculated from the ratio of the slopes of postmicellarand premicellar regions of conductivity-concentration plotusing following equation:
๐ฝ =๐2
๐1. (2)
In (2), ๐1 and ๐2 represent the slopes of the straight lines inthe premicellar and postmicellar region, respectively.
The value of enthalpy of solubilization can be obtainedfrom the following equation [8โ15]:
ฮ๐ป = โ2.3 (2 โ ๐ฝ) ๐ ๐2[๐ (log๐CMC)
๐๐]๐
. (3)
In (3), the factor ๐(log๐CMC)/๐๐was obtained from the slopeof straight line plotted between log(๐CMC) and๐.The entropyof micellization can be calculated by the following equation:
ฮ๐ =ฮ๐ป โ ฮ๐บ
๐. (4)
2.2. Calculation of Partition and Binding Parameters. Par-titioning of dye molecules between aqueous and micellarmedia is governed by partition law. Partition coefficient isdetermined by differential absorbance method reported byKawamura et al. [12]:
1
ฮ๐ด=
1
๐พ๐ฮ๐ดโ (๐ถ๐ + ๐ถ๐๐๐ )+1
ฮ๐ดโ. (5)
In (5), ๐ถ๐ is concentration of dye in molโ dmโ3 and ๐ถ๐๐๐
represents ๐ถ๐ -CMC๐, in the same units. Here, CMC๐ is CMCof CTAB in water and ๐ถ๐ is total surfactant concentrationin molโ dmโ3. ฮ๐ด is differential absorbance, and ฮ๐ดโ repre-sents its value at infinity.๐พ๐ is partition constant having value
in dm3/mol. The dimensionless quantity partition coefficient๐พ๐ฅ is obtained as ๐พ๐ฅ = ๐พ๐๐๐ค, where ๐๐ค is number of molesof water per dm3.
The value of standard free energy change for the transferof additive from aqueous to micellar phase was calculatedusing the following relation:
ฮ๐บ๐ = โ๐ ๐ ln๐พ๐ฅ. (6)
In (6), ๐ is the general gas constant and ๐ is absolutetemperature. Later, the binding constant was calculated byusing the following quantitative approach:
๐ถ๐ ๐ถ๐
ฮ๐ด=๐ถ๐
ฮ๐๐+1
๐พ๐ฮ๐๐. (7)
In (7), ๐ถ๐ represents the concentration of dye, while ๐ถ๐ indicates the surfactant concentration. In addition, ฮ๐ด rep-resents differential absorbance; ฮ๐ is difference of absorptioncoefficient; ๐ is path length, while ๐พ๐ stands for the bindingconstant [12โ14].
The value of standard free energy change of binding wascalculated using the following relation:
ฮ๐บ๐ = โ๐ ๐ ln๐พ๐. (8)
3. Materials and Method
3.1. Materials and Preparation of Solution. Specific con-ductivities were measured with WTW inoLab Cond 720(Germany). This instrument can measure the electrical con-ductivity in the range of 0.01 ๐S to 199.9mS with an accuracyof ยฑ0.5% ยฑ 2 and temperature control accuracy of โผ ยฑ0.5 K.The electrode used has cell constant โผ0.98 cmโ1 and wascoated with platinum black to avoid the polarization effect.The conductivities weremeasured over the temperature rangeโผ293Kโ323K with the increment of 10 K. The electrode wascalibrated using KCl(aq) over the appropriate concentrationrange.
All absorption spectra of the sample were measuredon Hitachi UV-2800 spectrophotometer in the UV-visiblerange. The cells used were square cuvettes having 1.0 cm inthickness with the slit width of โผ1.0 nm. In simple UV/visibleabsorption spectra, distilled water was kept at the referenceside, while, in the differential UV/visible spectroscopy, dyesolution was adopted as reference. In both cases, dye-surfactant-water ternary solution was taken in the samplecell.
4. Results and Discussion
4.1. Conductometric Studies. Theelectrical conductivitymea-surement is a reliable and sensitive way to detect CMCand to calculate thermodynamic parameters. In practice, asharp change in the conductivity of amphiphilic solution isusually observed after reaching CMC. The results from theconductivity-concentration plot (Figure 1) display an evidentdecrease in the slope, after reachingCMCprimarily due to thereasons that (1) micelles are less mobile and (2) concentrationof free ions in the solution decreases.
The Scientific World Journal 3
0.6 0.8 1.0 1.2 1.4 1.6
100
150
200
250
300
Cs ร 10โ3 (molยทkgโ1)
๐ (๐
Sยทcm
โ1)
(a)
0.6 0.8 1.0 1.2 1.4 1.6180
200
220
240
260
280
300
Cs ร 10โ3 (molยทkgโ1)
๐ (๐
Sยทcm
โ1)
CMC = 1.078 ร 10โ3 mol kgโ1
(b)
Figure 1: (a) Plots of electrical conductivity versus concentration of CTAB in presence of reactive orange 122 at 298K (black square), 308K(red circle), 318 K (blue triangle), and 328K (purple triangle). (b) Plot of electrical conductivity versus concentration of CTAB in the presenceof reactive orange 122 at 298K.
Table 1: The data of critical micelle concentrations (CMC), enthalpy of micellization (ฮ๐ป), free energy of micellization (ฮ๐บ), entropy ofmicellization (ฮ๐), and degree of dissociation (๐ฝ) for aqueous solution ofCTAB in the presence of reactive orange 122 at different temperatures.
๐
(K)CMC(mM)
ฮ๐ป
(kJmolโ1)ฮ๐บ
(kJmolโ1)ฮ๐
(JKโ1molโ1) ๐ฝ
298 1.10 3.56 โ46.14 166.75 0.28308 1.078 3.78 โ47.54 166.60 0.29318 1.04 3.91 โ47.77 162.50 0.34328 1.01 4.08 โ48.50 160.32 0.37
When CTAB molecules dissociate in the premicellarregion in water, a dynamic equilibrium is usually establishedbetween the undissociated and dissociated molecules asfollows;
CTABโโ CTA+ + Bโ (9)
In postmicellar region an electrical double layer is oftenformed around the micelle due to the adsorption of counterions, where, positive charge is developed at themicelle surfacedue to unequal distribution of charges between the aqueousandmicellar phases. According to Sternโsmodel, the electricaldouble layer has two parts: (1) a layer of strongly held ionsadsorbed onto the micellar surface called Stern layer and(2) a diffused layer of counter ions. In such a case, theelectrical potential rapidly drops first within the Stern layerand gradually in diffused layer [14].
The plots of electrical conductivity of CTAB in thepresence of reactive orange 122 at various temperatures areshown in Figure 1 while similar plots for reactive red 223are shown in supplementary Figure S1 available online athttp://dx.doi.org/10.1155/2014/540975.
Table 1 outlines the data of critical micelle concentra-tions (CMC), enthalpy of micellization (ฮ๐ป), free energyof micellization (ฮ๐บ), entropy of micellization (ฮ๐), and
degree of dissociation (๐ฝ) for aqueous solution of CTAB inthe presence of reactive orange 122 at different temperatures.The CMC value of pure CTAB is 1.0mM. Reactive orange 122causes slight increase in CMC of CTAB due to its structurebreaking effect. RO122 has relatively more rigid structurebecause it has four fused rings; therefore it is difficult to adjustits molecules in micelle; thus its orientation is more likelyin outer portion of micelle close to micelle water interface.Such fashion of adsorption of drug molecules increases workof micellization by producing less increase in entropy, thusmaking micellization less convenient and increasing CMC.RR223 on the other hand has less rigid structure; thus itadjusts more easily in micelle, thus decreasing repulsionbetween ionic heads of micelle, making micellization easy,and decreasing the CMC value of surfactant [5, 8โ10].
From Table 1, the observed continuous decrease in theCMC values with increasing temperature can be explained bythe greater degree of hydrophobic dehydration compared tothe hydrophilic dehydration. In addition, the changing trendsin other thermodynamic parameters such as the large nega-tive value of ฮ๐บ indicates toward the spontaneous nature ofmicellization, while, the positive values ofฮ๐ andฮ๐ป suggestthat the micellization was entropy driven process. Literaturesuggests that the enthalpy change (ฮ๐ป) during micellizationis a combined effect of the changes in enthalpies that arose
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Table 2: The data of critical micelle concentrations (CMC), enthalpy of micellization (ฮ๐ป), free energy of micellization (ฮ๐บ), entropy ofmicellization (ฮ๐), and degree of dissociation (๐ฝ) for aqueous solution of CTAB in the presence of reactive red 223 at different temperatures.
๐
(K)CMC(mM)
ฮ๐ป
(kJmolโ1)ฮ๐บ
(kJmolโ1)ฮ๐
(JKโ1molโ1) ๐ฝ
298 0.94 5.46 โ15.26 69.54 0.493308 0.87 5.72 โ15.75 69.72 0.515318 0.82 6.06 โ16.39 70.56 0.532328 0.815 6.36 โ16.69 70.27 0.553
460 480 500 520 540
0.00
0.05
0.10
0.15
0.20
0.25
A
Wavelength (nm)
(a)
460 480 500 5200.10
0.15
0.20
0.25
Pure dyeDye + 1.50 mM CTABDye + 1.44 mM CTABDye + 1.34 mM CTABDye + 1.25 mM CTAB
Dye + 1.21 mM CTABDye + 1.17 mM CTABDye + 1.14 mM CTABDye + 1.10 mM CTAB
Abs
orba
nce
Wavelength (nm)
(b)
Figure 2: (a) Simple UV/visible absorption spectra of pure reactive orange 122. (b) Simple UV/visible absorption spectra of reactive orange122 in the presence of different CTAB concentration (molโ dmโ3).
from hydrophobic interactions, electrostatic interactions,hydration of polar groups, and counter ion binding to themicelles [8โ16]. On the other hand, the positive values of ฮ๐are suggested to be due to the transfer of hydrophobic groupsof the surfactant from aqueous phase to micelle core. In theimmediate vicinity of hydrophobic groups, the strength ofhydrogen bonding betweenwatermolecules is relatively high.This in turn has a strong effect on the hydrophobic hydrationphenomenon, making it different from the usual solvent-solute interaction.The enhanced hydrogen bonding betweenwater molecules in the neighborhood of nonpolar parts leadsto the tightening of water structure around hydrophobicgroups. Hydrophobic hydration causes internal torsionalvibrations of chains to be restricted in the solution. Both ofaforementioned factors lead to the decrease in entropy ofsystem. The removal of hydrophobic groups from aqueousmedia is entropically favorable that causes the disruption ofhighly organized water structure and removal of mobilityconstraints on hydrocarbon chain [16โ23].
Tables 1 and 2 display various thermodynamic parameterscalculated for CTAB in presence of RO122 and RR223,respectively.
4.2. Simple Absorption Spectra. Figure 2 shows UV/visiblespectra of reactive orange 122 in the absence (a) andpresence of CTAB (b). In both cases, the dye showed anabsorption maximum at 490 nm. The effect of surfactantconcentration on dye solubilization was clearly observedfrom the shifts in the absorbance with varying CTAB con-centration (Figure 2(b)). This solubilization process can beexplained by the host guest relationship between the dyeand surfactant molecules, where anionic dye molecules areaccommodated within the micelles of cationic CTAB. Theincrease in absorbance with increasing CTAB concentration(Figure 3(a)) suggests that more dye molecules are gettingengaged into the micelle. Once the CMC is reached, nofurther increase in absorbance occurred, a possible cause ofwhich could be maximum incorporation of dye molecules
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6 8 10 12 140.10
0.12
0.14
0.16
0.18
0.20
0.22A
bsor
banc
e
Cs ร 10โ4 (molยทdmโ3)
CMC = 10.42 ร 10โ4 molยทdmโ3
(a)
1.00 1.05 1.10 1.15 1.20 1.25 1.30
1.90
1.95
2.00
2.05
2.10
2.15
2.20
(mM)Cs
ฮAร10
โ3
(b)
Figure 3: (a) Plot of simple absorbance of reactive orange 122 as a function of CTAB concentration. (b) Plot of differential absorbance ofreactive orange 122 as a function of CTAB concentration.
into the micelle. Formation of new micelles and incorpo-ration of dye molecules into these micelles do not let theabsorbance acquire constant value [24โ26]. Similar plots ofUV/visible spectrum of reactive red 223 with and withoutCTAB are given in Figure S2 (supplementary information).
It has been found that thewhen the dyemolecules interactwith the hydrophilic groups of surfactant, it leads to theshift in dimer โ monomer equilibrium toward monomer.In such a case, the structural environment of dye moleculeschanges with CTAB concentration till the CMC is reached,whereas in postmicellar region, no change in the environ-ment takes place [13, 15, 24, 25]. The incorporation of dyemolecules into micelles is facilitated because anionic dyes areattracted by cationic CTAB.
There is a continuum of environment from the hydratedmicelle surface to the nonpolar core. The solubilizate may beadsorbed onto the surface and orientate itself near the surface(short penetration), or entrapped in the hydrocarbon core(deep penetration). Its polar and/or nonpolar groups interactselectively with the surfactant depending on its substituents.Initially the dye-surfactant complex is formed which is thenadsorbed onto the micellar surface and subsequently leadsto the reorientation of dye molecules into micelle. The longrange electrostatic forces and short range hydrophobic forcesact together in the formation of dye surfactant complex. Theformer bring molecules of dye and surfactant close to eachother, while the latter align their hydrophobic parts in parallelfashion:
D๐โ + S+ โโ DS (10)
With the passage of time, these complexes undergo self-aggregation (as given below) and consequently, increase inthe absorbance is witnessed in premicellar region:
๐ (DS) โโ (DS)๐ (11)
When the CMC is approached, all dye molecules arecompartmentalized in micelles as normal monomers, and atthis point the absorbance reaches to its limiting value:
(DS)๐ +Mโโ DM (12)
In (12), DM represents dye monomers that are intercalatedinto the micelles. Solubilization is a dynamic process, andsolubilizate may spend different residence time at differentlevels between the core and the surface. The imbalance ofhydrophilic and hydrophobic forces keeps the solubilizatesomehow dynamic in the micelle, thus giving random valuesof absorbance [4, 14, 26โ29]. The hydrophilic-hydrophobicforces influence the orientation of additive molecules at theinterface of micelle. In case of polar additives, this balance isprevalent for hydrophilic forces, and thus additive moleculesare oriented near the surface of micelle. For nonpolar addi-tives, however, the hydrophobic interactions are favored, andadditive molecules are deeply buried inside core of micelle[27, 28].
4.3. The Differential Spectroscopy. Differential spectroscopyis a useful tool to calculate the values of partition andbinding parameters. A continuous increase in the differentialabsorption of RO122 with increasing CTAB concentrationis indicative of the continuous intercalation of additivemolecules within the micelle [7โ11, 30]. Similar plots for RR223 are displayed in Figure S3 (supplementary information)for reference. Value of ฮ๐ด is zero in premicellar regionof Figure 3(b) and Figure S3(b) because solubilization takesplace in postmicellar region [30].
The partition coefficient is the ratio of concentration ofdyemolecules inmicelle to that in aqueous solution, whereas,the partitioning of dye molecules between the two phasesis governed by partition law. The partition coefficient ofsolubilizate between micellar and aqueous phase providesinformation about the extent of solubilization. The value of
6 The Scientific World Journal
2000 4000 6000 8000 10000 12000 14000450
465
480
495
510(ฮ
A)โ
1
(Cmos + Ca)โ1
(a)
1.00 1.04 1.08 1.12 1.16 1.202.58
2.61
2.64
2.67
2.70
2.73
(CsC
a/ฮ
A)ร
10โ6
(mM)Cs
(b)
Figure 4: (a) Relationship between (ฮ๐ด)โ1 and (๐ถ๐ + ๐ถ๐๐
๐ )โ1 for the calculation of partition coefficient (๐พ๐ฅ) for RO122/CTAB system. (b) Plot
for calculation of binding constant (๐พ๐) for RO122/CTAB system.
Table 3: The data of partition coefficient (๐พ๐ฅ), free energy ofpartition (ฮ๐บ๐ฅ), binding constant (๐พ๐), and the free energy ofbinding (ฮ๐บ๐) for reactive orange 122/CTAB system.
10โ6๐พ๐ฅ ฮ๐บ๐ฅ/(kJmolโ1) ๐พ๐/(dm3 molโ1) ฮ๐บ๐/(kJmolโ1)
4.30 โ37.84 300 โ14.1
Table 4: The data of partition coefficient (๐พ๐ฅ), free energy ofpartition (ฮ๐บ๐ฅ), binding constant (๐พ๐), and free energy of binding(ฮ๐บ๐) for reactive red 223/CTAB system.
10โ6๐พ๐ฅ ฮ๐บ๐ฅ/(kJmolโ1) ๐พ๐/(dm3 molโ1) ฮ๐บ๐/(kJ molโ1)
9.5 โ39.8 600 โ15.8
free energy of partition becomes more negative for morehydrophobic dye, which in turn is an indicator of the ease ofpenetration of the additives into the micelle. Figures 4(a) and4(b) display the plots for calculation of partition coefficientand binding constant for RO122, respectively. Similar plots forRR223 are given in Figure S4 (supplementary information).
Table 3 displays the values of partition and bindingparameters for RO122/CTAB system. The significantly largevalue of๐พ๐ฅ (4.3 ร 10
6) implies large-scale transfer of the dyemolecules from the aqueous to micellar media, whereas thelarge negative value of ฮ๐บ๐ (โ37.84 kJmolโ1) is indicative ofthe spontaneous nature of partitioning. In the same way, thespontaneous nature of dye-surfactant binding process is alsoevident, as can be observed from the negative value of the freeenergy of binding (ฮ๐บ๐ = โ14.1 kJmolโ1) [3, 8โ10, 16, 28, 30โ32].
The values of various thermodynamic parameters forRR223/CTAB system are given in Table 4. Again, the valuesof ๐พ๐ฅ and ๐พ๐ were found to be quite high (9.5 ร 106 and 600,resp.) because solubilization and binding took place at largescale. It is also suggested that the large negative values of ฮ๐บ๐
and ฮ๐บ๐ (โ39.8 kJmolโ1 and โ15.8 kJmolโ1, resp.) are dueto spontaneous nature of partitioning and binding. Here, thenegative values of ฮ๐บ๐ and ฮ๐บ๐ are indicative of the stabilityof system [3, 8โ10, 16, 28, 30โ32].
Figures 5(a) and 5(b) show structure of reactive red 223and reactive orange 122 respectively while Figures 6(a) and6(b) showproposed locus of dyemolecules inmicelle.Micellesurface has positive charge while its core is nonpolar. Dyemolecules are incorporated inmicelle in such a way that theirnonpolar parts having aromatic rings will be buried insidenonpolar core of micelle while anionic heads will be attractedby cationic surface of micelle [8โ10, 12, 31, 32].
5. Conclusions
Thepresent study describes the thermodynamic and spectro-scopic investigation of the interactions that occur betweenthe selective anionic dyes (reactive orange 122 and reac-tive red 223) and the micellar media of CTAB (cationicsurfactant). The results from experimental data reveal thatthe CMC of CTAB in the presence of dyes decreases withincreasing temperature due to the preferable dehydrationof hydrophobic parts as compared to the hydrophilic ones.The trends of change in various thermodynamic parameterssuch as ฮ๐บ, ฮ๐ป, and ฮ๐ suggest that the process of dyesolubilization in the micellar media of CTAB is entropydriven and spontaneous. Moreover, the spectroscopic resultsdemonstrate high degree of solubilization and strong hostguest relationship between the dyes and surfactant, whereas,the negative values of ฮ๐บ๐ and ฮ๐บ๐ indicate spontaneousnature of solubilization and binding.
Conflict of Interests
The authors declare that there is no conflict of interests.
The Scientific World Journal 7
Reactive red 223
H3COCHN
NaO3S SO3NaSO3Na
OH
NN
N N
N N
N
ClH
SO2CH2CH2OSO3Na
H
(a)
Reactive orange122
SO3Na
OHN
N N
N N
NN
Cl
NaO3S
NaO3S
NaO3SOH2CH2CO2S
H
H
(b)
Figure 5
N
N NN
N
N
N
N
N
N
NNN
N
N
N
NN
N
Aqueous
Locus of RR223 in micelle
solution
Na+
+
+ + ++
+
+
+
+
+
+
+++
+
+
++
+
Brโ Brโ
Brโ
Brโ
Brโ
BrโBrโBrโBrโ
Brโ
Brโ
Brโ
Brโ
Brโ
HN
NN
NCl
NH
OH
NN
Brโ Brโ
Brโ
Brโ
Brโ
Na+
Na+
O S3
SCO 2CH 2O
H2SO 3
SO 3
SO 3
(a)
Locus of RO122 in micelle
N
NN
N
N NN
N
N
N
N
N
NNN
N
N
N
N
HN
N
N
N
Cl
HN
N NOH
NHO
Aqueous solution
Na+
Br
Br
Br
Br
Br
Br
BrBrBrBr
Br
Br
Br
Br
โ
โ
โ
โ
โ
โ
โโโ
โ
โ
โ
โ
โ
SO3CH2CH2OSO3
O S3
SO3
+
+
+
+
+ ++
+
+
+
+
+
+
+
+++
+
+
(b)
Figure 6
Acknowledgments
The paper is a part of M. Phil thesis of Mr. MuhammadIrfan. All authors contributed at various stages of planning,execution, and writing. The authors are thankful to Sandaldyestuff Faisalabad, Pakistan, for donation of dyes. U. A. Ranais thankful to the Deanship of Scientific Research at KingSaud University for its funding through the Research GroupProject no. RGP-VPP-345.
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