Ed

AAa

b

c

a

ARRAA

KMTPMT

1

strcbcicitav[bw

(

h1

Journal of Photochemistry and Photobiology A: Chemistry 284 (2014) 49–54

Contents lists available at ScienceDirect

Journal of Photochemistry and Photobiology A:Chemistry

jo ur nal homep age: www.elsev ier .com/ locate / jphotochem

ffect of chemical parameters on the interaction between cationicyes and poly(acrylic acid)

nouar Ben Fradja, Ridha Lafia, Sofiane Ben Hamoudaa,∗, Lassaad Gzarac,hmed Hichem Hamzaouib, Amor Hafianea

Laboratory of Wastewater Treatment, CERTE, BP 273, Soliman 8020, TunisiaLaboratory of Valorisation of Materials, CNRSM, BP 95, Hammam-Lif 2050, TunisiaCenter of Excellence in Desalination Technology, King Abdulaziz University, Jeddah, Saudi Arabia

r t i c l e i n f o

rticle history:eceived 25 November 2013eceived in revised form 30 March 2014ccepted 5 April 2014vailable online 18 April 2014

a b s t r a c t

Being polymers and electrolytes, polyelectrolytes are widely used in many applications. In perspective ofdye removal from textile effluents, they have been used in coagulation–flocculation and to a lesser extentin polyelectrolyte enhanced ultrafiltration. To optimize the abovementioned process we need to study indetail the interaction of dye with polyelectrolyte in conditions near the industry reality. In this contextwe investigate herein the effect of chemicals additives, NaCl, surfactant, pH on the behavior of two model

eywords:ethylene blue

oluidine blueoly(acrylic acid)etachromatic complex

hermodynamic parameters

cationic dyes, methylene blue (MB) and toluidine blue (TB), with polyacrylic acid polymer (PAA). Usingspectrophotometric method it was found that the poly(acrylic acid) induced metachromasy in the dyesresulting by the blue shift of the absorbance confirming the formation of dye polymer complexes. Thestoichiometry of MB–PAA and TB–PAA complexes determined by the ratio method was found to be 2:1.The stability constant of the complexes at 298 K was found to be 5332 for MB–PAA and 4358 dm3 mol−1

for TB–PAA and the amount of additives inducing total destabilization of the complex were determined.© 2014 Elsevier B.V. All rights reserved.

. Introduction

The interaction between dyes and polyelectrolyte in aqueousolutions was largely investigated [1–3]. Studies on binding of dyeo different synthetic and natural polymers by absorbance, fluo-escence and circular dichroism experiments yielded significantontributions [4–6]. It is known that electrostatic and hydropho-ic interactions both contribute to the binding between oppositelyharges dyes and polyelectrolytes [7]. The possibility of utiliz-ng electrostatic interactions between anionic polyelectrolytes andationic dye molecules to foster aggregation has gathered a lot ofnterest in recent years due to its potential nanomaterial applica-ions [8]. The aggregation of dyes is accompanied by changes in thebsorbance and/or fluorescence spectrum compared to the indi-

idual monomeric molecules. According to Kasha’s exciton theory9], H-aggregates are spectroscopic entities that are characterizedy a blue-shifted absorption with respect to monomer absorption,hereas J aggregates present a red-shifted absorption band. The

∗ Corresponding author. Tel.: +216 79 325 750; fax: +216 79 325 802.E-mail addresses: anouar benfradj@yahoo.fr, anouarfradj@gmail.com

A.B. Fradj), sofianebenhamouda@yahoo.fr (S.B. Hamouda).

ttp://dx.doi.org/10.1016/j.jphotochem.2014.04.003010-6030/© 2014 Elsevier B.V. All rights reserved.

H and J-aggregates involve a parallel stacking of dye moleculesinto well-ordered fashion, in H-aggregate the molecules are alignedin face-to-face arrangement, while in J-aggregate the molecularalignment is edge-to-edge [10]. The strength of such molecularaggregation depends upon both the concentration and structureof the dye, ionic strength, solvent and other factors [11].

On the other hand, polyelectrolytes have been utilized in manyapplications. In water treatment, polyelectrolytes serve as floc-culants to remove particles, colloids and soluble contaminants[12,13]. They may assist the ultrafiltration membrane for the reten-tion of organics of low molecular weight and ions from wastewaterin PEUF process [14,15]. In the case of dye effluents treatmentthe type of interaction between polyelectrolyte and dye will bedeterminant in the efficiency of those processes. As the effluentis complex the effect of many kind of additive present in waste-water may affect the dye polymer interaction. Furthermore as theUV–vis spectrum of dye is sensitive to its environment it becomesdifficult to analyze it with accuracy. For these reason we plan in the

present study to investigate the effect of physicochemical parame-ters on the interaction between two cationic dyes chosen as modelcationic dyes and polyacrylic acid (PAA) as anionic polyelectrolyte.TB and MB, two thiazine dyes, have similar chemical structuresbut differ by their partition coefficients (P), the TB coefficient is

50 A.B. Fradj et al. / Journal of Photochemistry and Photobiology A: Chemistry 284 (2014) 49–54

blue,

aohstttopo

2

2

i(TFcSc

2

sawtalwdurttr

3

3

dr

MB–PAA. The same procedure was repeated for TB–PAA. Accordingto Fig. 3, the stoichiometry of the two complexes was found to be 2:1which indicates that the binding takes place on alternate anionicsites [22].

4 0 0 5 0 0 6 0 0 7 0 0 8 0 0

0 .0

0 .2

0 .4

0 .6

0 .8

W a v e le n g th (n m )

Abs

orba

nce

(a.u

.)

P /D = 0 P /D = 0 .2 P /D = 0 .5 P /D = 1 P /D = 1 .2 P /D = 1 .5 P /D = 2 P /D = 3 P /D = 5P /D = 1 0P /D = 1 5P /D = 2 0P /D = 3 0

(a)

0 .0

0 .1

0 .2

0 .3

0 .4

0 .5

Abs

orba

nce

(a.u

.)

P / D = 0 P / D = 0 . 2 P / D = 0 . 5 P / D = 1 P / D = 1 . 2 P /D = 1 .5 P / D = 2 P / D = 3 P / D = 5P / D = 1 0P / D = 1 5P / D = 2 0P / D = 3 0

(b)

Fig. 1. Molecular structure of (a) methylene

lmost 3-fold higher than that of MB [16]. The metachromatic effectf polyacrylic on cationic dyes has been demonstrated [17,18],owever to our knowledge there is no in the literature an exten-ive study on the effect of chemical additives on the behavior ofhe dye–polyelectrolyte system. Therefore, the present experimen-al study will be done by changing the initial concentration ofhe poly(acrylic acid), the concentrations of sodium chloride andf cetylpyridinium chloride and pH. Thereafter, thermodynamicarameters of interaction �G, �H and �S and the binding constantf complexes will be evaluated at different temperatures.

. Experimental

.1. Materials

Methylene blue and toluidine blue, two cationic phenoth-azine dyes, were purchased from Fluka. Polyacrylic acid (PAA)MW = 100,000 g mol−1, 35 wt.%) was provided by Sigma–Aldrich.he chemical structures of the three compounds are shown inig. 1. Hydrochloric acid, sodium chloride, sodium hydroxide andetylpyridinium chloride C16H33Pyr+Cl− (CPC), were provided byigma–Aldrich. All the chemicals were used without further purifi-ation. Distilled water was used for solution preparation.

.2. UV–vis spectroscopy

The UV–vis spectra were acquired on aqueous MB and TB dyesolutions with a Perkin Elmer Lambda 25 spectrophotometer, with

matched pair of cuvettes of 1 cm path length. The temperatureas always maintained at 25 ± 0.1 ◦C except when we studied

he influence of temperature. The stoichiometry of poly(acryliccid)–dye complex was determined using the ratio method as fol-ows: increasing amounts of polyelectrolyte (0–6 ml, 1 × 10−3 M)

ere added to a fixed volume of dye solution (2 ml, 1 × 10−4 M),ye in different sets of experiments and the total volume was madep to 10 ml by adding distilled water. Absorbance measured at Am

efers to the absorbance of the monomeric band and at AM refers tohe absorbance of metachromatic band. The ratio Am/AM was plot-ed against the poly(acrylic acid) concentration/dye concentrationatio [P]/[D].

. Results and discussion

.1. Effect of polymer concentration

In aqueous solution, MB exhibits a band at 665 nm and a shoul-er at 612 nm which are assigned to monomeric and dimeric forms,espectively. Toluidine blue presents only one band at 623 nm

(b) toluidine blue and (c) poly(acrylic acid).

indicating the presence of only monomeric form. The addition ofincreasing amounts of poly(acrylic acid), as shown in Fig. 2a andb, caused the decrease of absorption at maximum wavelength forboth dyes followed by the appearance of new band at 598 nm inthe case of MB and at 566 nm in the case of TB. This indicates that anew metachromatic complexes were formed between cationic dyesand the anionic polyelectrolyte [17–19]. The large hypsochromicshift for MB (67 nm) and for TB (57 nm) were also attributed tothe formation of dye H-aggregates [20,21]. As a consequence of thehigher local concentration near the polyanion, the dyes self aggre-gate by means of aromatic–aromatic interaction forming H-typeaggregates at substantially low dye concentrations.

To determine the stoichiometry of poly(acrylic acid)–dye com-plex, a plot of Am/AM versus polymer/dye [P]/[D] ratio was made for

4 0 0 5 0 0 6 0 0 7 0 0 8 0 0

W a v e l e n g t h ( n m )

Fig. 2. Absorption spectra of dye in presence of PAA at various P/D ratios: (a) methy-lene blue and (b) toluidine blue.

A.B. Fradj et al. / Journal of Photochemistry and Photobiology A: Chemistry 284 (2014) 49–54 51

0 1 2 3 4 50 .8

1 .2

1 .6

2 .0

2 .4 M B - P A A T B - P A A

Am

/AM

3

ebidpircFp1picdfr

Fi

P /D

Fig. 3. Stoichiometry for MB–PAA and TB–PAA complexes.

.2. Effect of NaCl

The self-association of ionic dyes in aqueous solution can benhanced by the addition of inorganic salt. This behavior maye due to the increase of the screening factor and/or to the

ncrease of effective dielectric constant [23]. The effect of NaCl onye–polyelectrolyte is more complicated as NaCl may affect also theolyelectrolyte conformation [24]. The absorption spectra of dyes

n presence of polyelectrolyte were studied at NaCl concentrationanged from 10−5 M to 1 M and at fixed dye and polyelectrolyteoncentrations equal, respectively, to 2 × 10−5 M and 4 × 10−4 M.ig. 4a and b shows that the absorbance of metachromatic com-lex increases slightly as function of NaCl concentration up to0−4 M. At NaCl concentration of 10−2 M, the monomer band reap-ears at 665 nm and 623 nm for MB–PAA and TB–PAA, respectively,

ndicating the beginning of disaggregation of dye. At medium salt

oncentrations from 10−1 M to 1 M the metachromatic band totallyisappeared while the absorbance of monomeric band increasedor both cationic dyes. The molar concentration of NaCl required toeverse metachromasy was found to be about 10−2 M of PAA–dye

ig. 4. Absorption spectra of (a) MB–PAA complex and (b) TB–PAA complex at var-ous concentration of NaCl.

·

Fig. 5. Effect of NaCl concentration on reversal metachromasy for MB–PAA andTB–PAA complexes.

complexes (Fig. 5). It seems that Na+ cations present in solution athigh concentration compared to that of dye occupy the negativelycharged binding sites of polyelectrolyte thus reducing electrostaticattraction between the site and dye molecules. The decrease ofmetachromatic complex stability with added NaCl salt is a typi-cal behavior of systems where long-range electrostatic interactionbetween dye and polyelectrolyte is the main force [25]. Polystyre-nesulfonate (PSS) a polyelectrolyte having aromatic groups directlyattached to the negatively charged sulfonate groups shows a lowdependence of the interaction on the ionic strength [26]. In thiscase aromatic–aromatic interaction short-range is the main driv-ing force. Also, the authors found that a high concentration of NaClis not sufficient to remove the dye bound from the polyelectrolytehaving hydrophobic character.

3.3. Effect of pH

One of the most important factors in the interaction of cationic

dye with polyanion is the pH of solution. The initial pH value wascontrolled by the addition of dilute hydrochloric acid or sodiumhydroxide solutions. Fig. 6a and b shows the visible spectra of aque-ous methylene blue and toluidine blue solutions, respectively, in

Fig. 6. Absorption spectra of (a) MB–PAA complex and (b) TB–PAA complex at var-ious pH solutions.

52 A.B. Fradj et al. / Journal of Photochemistry and Photobiology A: Chemistry 284 (2014) 49–54

Fi

tf3ptt5emttptmp

3

dtTTitwMaspbdTccmt

tion (CD), L is the optical path length of the solution, εD and εDP arethe respective molar extinction of dye and dye bound to polyelec-trolyte, Kc is the binding constant. The value of binding constantKc was then obtained from the slope and intercept of the plot ofCD.CP/(A − A0) against CP shown in Fig. 9a and b, respectively. From

·

ig. 7. Absorption spectra of (a) MB–PAA complex and (b) TB–PAA complex at var-ous concentration of CPC.

he presence of poly(acrylic acid) at P/D = 20 and at pH rangingrom 2 to 11. Fig. 6a shows that in the range of pH from 2 to.65, there is no change in the methylene blue spectra. At theseH, the polymer is mainly in the acid form (pKa = 4.28) [27] andherefore it does not interact with the dye. For pH superior to 4.42he absorbance of monomer decreases and a new band appears at98 nm due to the formation of complex between dye and poly-lectrolyte mainly in anionic form. At pH = 10.86, the absorbance ofonomer form increases again indicating that electrostatic interac-

ion is weakened. Similar changes in the spectra were observed onhe interaction of methylene blue with polyacrylamide and sodiumolyacrylate [28]. Fig. 6b shows the same trends for toluidine blue,he monomer form decreases when pH increases and a metachro-

atic complex appearing at 566 nm for pH 4.37. At pH = 11.23 theeak of monomer reappears.

.4. Effect of surfactant

The effect of surfactant on the absorption spectra of cationicyes in presence of polyelectrolyte was studied at dye and polyelec-rolyte concentrations of 2 × 10−5 M and 4 × 10−4 M, respectively.he concentration of surfactants varied from 10−7 M to 10−1 M.he absorbance of metachromatic complex increases slightly uponncreasing (CPC) concentration up to 10−4 M. Fig. 7a and b showshat for CPC concentration from 5 × 10−4 to 10−1 M maximumavelength moves abruptly to 665 and 632 nm in the case ofB–PAA and TB–PAA complexes, respectively, signifying the dis-

ggregation of the dye. It seems that cationic surfactant formstrong complex with anionic polymer which induces the dis-lacement of dye polymer complex equilibrium. The associationetween polyelectrolyte and oppositely charged surfactants isriven by both electrostatic and hydrophobic interactions [29,30].

he strong interaction between the charged group leads to a bulkomplexation above a surfactant concentration called the criti-al aggregation concentration (CAC) which is several orders ofagnitude below CMC of surfactant of pure solution. The concen-

ration of CPC required to reverse metachromasy was found to be

·

Fig. 8. Effect of CPC concentration on reversal metachromasy for MB–PAA andTB–PAA complexes.

5 × 10−4 mol L−1 for both complex as shown in Fig. 8. This value islower than CMC of CPC surfactant which is 9 × 10−4 M [31]. Similarresults for reversal of metachromasy in presence of surfactant arereported by Nandini et al. in the case of Alginate/Azure B system[32].

3.5. Determination of interaction parameters

3.5.1. Binding constantThe binding constant of dye–polyelectrolyte complex can be

determined using the Rose–Drago equation [33]:

CDCP

A − A0= 1

KcL(εDP − εD)+ CP

L(εDP − εD)(1)

where A is the absorbance of the complex measured at metachro-matic band using different set of solutions containing varyingamounts of polyelectrolyte solution (CP) in a fixed dye concentra-

·

Fig. 9. Plots of CD·CP /A − A0 against CP for (a) MB–PAA and (b) TB–PAA complexes.

A.B. Fradj et al. / Journal of Photochemistry and Photobiology A: Chemistry 284 (2014) 49–54 53

Table 1Thermodynamic parameters of interaction for MB–PAA and TB–PAA complexes.

Complex Temperatures (K) Kc (dm3 mol−1) �G (kJ mol−1) �H (kJ mol−1) �S (kJ mol−1 K−1)

MB–PAA

298 5332 −21.261

−24.307 −0.0102308 3895 −21.171313 3341 −21.115318 2875 −21.055

−20.761

−21.897 −0.00381−20.727−20.707−20.685

ToovWhh

3

tIp

�e

�

l

�

c(a

tratatt

TB–PAA

298 4358

308 3275

313 2856

318 2499

able 1, it is observed that, as temperature increases, the valuef the binding constant decreases for both complexes. From thebtained results, we note that the growth of temperature is unfa-orable to the interaction between the dye and the polyelectrolyte.e note also that the stability constants of MB–PAA complex are

igher than those of TB–PAA which may be related to the moreydrophobic character of TB versus MB.

.5.2. Thermodynamic parametersAs mentioned above the interaction between dye and polyelec-

rolyte may be composed by hydrophobic and electrostatic forces.n order to elucidate the nature of interaction, thermodynamicarameters were calculated.

The Gibbs free energy �G, the enthalpy �H and the entropyS reported in. Table 1 were determined by using the following

quations:

G = −RT ln Kc (2)

n Kc = −�H

RT+ C (Vant’ Hoff equation) (3)

G = �H − T�S (4)

�G calculated directly from Eq. (1), �H determined graphi-ally by plotting ln Kc against 1/T according to Vant’ Hoff equationFig. 10) and �S obtained from the slope of the curve �G = f(T)ccording to Eq. (3) (Fig. 11).

The negative value of �G decreased with increasing tempera-ure for both complexes MB–PAA and TB–PAA, indicating that theeaction is spontaneous at a lower temperature (Table 1). The neg-tive value of �H indicates that the reaction is exothermic and

he negative �S means that hydrophobic interactions do not play

major role in the interaction between the dye and the polyelec-rolyte [34], and as a consequence electrostatic interaction playshe major role in the cationic dye–poly(acrylic acid) interaction.

Fig. 10. Vant’ Hoff plot for MB–PAA and TB–PAA complexes.

Fig. 11. Variation of free energy versus temperature for MB–PAA and TB–PAA com-plexes.

4. Conclusion

The study of the effect of NaCl, pH, surfactant on the inter-actions between cationic dyes with poly(acrylic acid) have beeninvestigated by UV–vis spectrometry. The spectra changes uponaddition of polyelectrolyte, in absence of any additives, indicatedthat complexes entities were formed. This induced the formation ofdye H-aggregates as showed by the hypsochromic shift absorptionobtained. The stoichiometry of dye–polyelectrolyte complexes,evaluated by the molar ratio method, is 2:1 which indicated thatthe binding takes place on alternate anionic sites. The additionof amount of sodium chloride salt, H+ ions and cetylpyridiniumchloride surfactant induced changes in the spectra showing clearlythe destabilization of complex. This indicated that the interac-tion between the dyes and polyelectrolyte is mainly electrostatic.The negative value of entropy and the more affinity for MB thanTB confirm this assertion. These finding may find applications inthe control of retention or release of dye in the polyelectrolyteenhanced ultrafiltration and flocculation processes.

References

[1] E.S. Dragan, I.A. Dinu, Interaction of dis-azo dyes with quaternizedpoly(dimethylaminoethyl methacrylate) as a function of the dye structure andpolycation charge density, J. Appl. Polym. Sci. 112 (2009) 728–735.

[2] L. D’Ilario, I. Francolini, A. Martinelli, A. Piozzi, Insight into the heparin–toluidine blue (C.I. Basic Blue 17) interaction, Dyes Pigm. 80 (2009) 343–348.

[3] E.G. Mamchits, I.R. Nasimova, E.E. Makhaeva, A.R. Khokhlov, Effect of polyelec-trolytes on aggregation of a cyanine dye, Poly. Sci. 48 (2006) 91–96.

[4] S.S. Carrasco, J.G. Delcros, A.A.M. García, F.S. Jiménez, F.J. Ramírez, Studyby optical spectroscopy and molecular dynamics of the interaction ofacridine–spermine conjugate with DNA, Biophys. Chem. 133 (2008) 54–65.

[5] Y.Z. Zhang, X. Xiang, P. Mei, J. Dai, L.L. Zhang, Y. Li, Spectroscopic studies on theinteraction of Congo Red with bovine serum albumin, Spectrochim. Acta A 72(2009) 907–914.

[6] K. Yurekli, E. Conley, R. Krishnamoorti, Effect of laponite and a nonionic poly-

mer on the absorption character of cationic dye solutions, Langmuir 21 (2005)5825–5830.

[7] S. Gadde, E.K. Batchelor, A.E. Kaifer, Controlling the formation of cyanine dyeH- and J-aggregates with cucurbituril hosts in the presence of anionic polyelec-trolytes, J. Chem. Eur. 15 (2009) 6025–6031.

5 and Ph

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[tions, Spectrochim. Acta A 74 (2009) 1025–1030.

4 A.B. Fradj et al. / Journal of Photochemistry

[8] I. Willerich, T. Schindler, F. Grohn, Effect of polyelectrolyte architectureand size on macroion–dye assemblies, J. Phys. Chem. B 115 (2011) 9710–9719.

[9] M. Kasha, H.R. Rawls, M.A. El-Bayoumi, The exciton model in molecular spec-troscopy, Pure Appl. Chem. 11 (1965) 371–392.

10] H. Yao, T. Isohashi, K. Kimura, Electrolyte-induced mesoscopic aggregation ofthiacarbocyanine dye in aqueous solution: counterion size specificity, J. Phys.Chem. B 111 (2007) 7176–7183.

11] B. Boruah, P.M. Saika, R.K. Dutta, Spectrophotometric of the monomer–dimerprocess of C.I. Basic Blue 9 in aqueous polymer–surfactant system, Dyes Pigm.85 (2010) 16–20.

12] A.Y. Zahrim, C. Tizaoui, N. Hilal, Coagulation with polymers for nanofiltrationpretreatment of highly concentrated dyes: a review, Desalination 266 (2011)1–16.

13] A.K. Verma, R.R. Dash, P. Bhunia, A review on chemical coagulation/flocculationtechnologies for removal of colour from textile wastewaters, J. Environ. Man-age. 93 (2012) 154–168.

14] X. Tan, N.N. Kyaw, W.K. Teo, K. Li, Decolouration of dye-containing aqueoussolutions by the polyelectrolyte-enhanced ultrafiltration (PEUF) process usinga hallow fiber membrane module, Sep. Purif. Technol. 52 (2006) 110–116.

15] S. Mondal, H. Ouni, M. Dhahbi, S. De, Kinetic modeling for dye removal usingpolyelectrolyte enhanced ultrafiltration, J. Hazard. Mater. 229–230 (2012)381–389.

16] M.N. Usacheva, M.C. Teichert, M.A. Biel, The role of the methylene blue andtoluidine blue monomers and dimers in the photoinactivation of bacteria, J.Photochem. Photobiol. B 71 (2003) 87–98.

17] M.K. Pal, S. Basu, Polyelectrolyte chromotropes in metachromacy, Makromol.Chem. 27 (1958) 69–79.

18] P. Mukerjee, A.K. Ghosh, P. Mukerjee, A.K. Ghosh, The effect of urea on methy-lene blue, its self-association, and interaction with polyelectrolytes in aqueoussolution, J. Phys. Chem. 67 (1963) 193–197.

19] S. Dragan, L. Ghimici, M. Cristea, A. Airinei, Polyelectrolyte complexes. III.Binding characteristics of some polydentate anionic azo dyes to polycationswith N,N-dimethyl-2-hydroxypropylene ammonium chloride units in the main

chain, Acta Polym. 50 (1999) 260–266.

20] F.C. Spano, S. Siddiqui, Exciton–vibrational coupling in pinwheel aggregates of�-conjugated molecules, Chem. Phys. Lett. 314 (1999) 481–487.

21] C. Peyratout, E. Donath, L. Daehne, Electrostatic interactions of cationic dyeswith negatively charged polyelectrolytes in aqueous solution, J. Photochem.Photobiol. A 142 (2001) 51–57.

[

[

otobiology A: Chemistry 284 (2014) 49–54

22] R. Nandini, B. Vishalakshi, A study of interaction of cationic dyes with anionicpolyelectrolytes, Spectrochim. Acta A 75 (2010) 14–20.

23] J. Xiang, X. Yang, C. Chen, Y. Tang, W. Yan, G. Xu, Effects of NaCl on the J aggre-gation of two thiacarbocyanine dyes in aqueous solutions, J. Colloid. InterfaceSci. 258 (2003) 198–205.

24] Z. Adamczyk, A. Bratek, B. Jachimska, T. Jasinski, P. Warszynski, Structure ofpoly(acrylic acid) in electrolyte solutions determined from simulations andviscosity measurements, J. Phys. Chem. B 110 (2006) 22426–22435.

25] G. Masci, A. Barbetta, M. Dentini, V. Crescenzi, Spectroscopic investigation onpoly[bis(carboxylatophenoxy)] phosphazene polyelectrolyte interactions withcationic dyes in dilute aqueous solution, J. Macromol. Chem. Phys. 200 (1999)1157–1162.

26] I.M. Villoslada, R.A. Hermosilla, J.P. Fuenzalida, G.D.C. Pizarro, G. Tripailaf,O.G. Marambio, H. Nishide, Comparative study of the self-aggregationof rhodamine 6G in the presence of poly(sodium 4-styrenesulfonate),poly(N-phenylmaleimide-co-acrylic acid), poly(styrene-alt-maleic acid), andpoly(sodium acrylate), J. Phys. Chem. B 114 (2010) 11983–11992.

27] S. Li, Removal of crystal violet from aqueous solution by sorptioninto semi interpenetrated networks hydrogels constituted of poly(acrylicacid–acrylamide–methacrylate) and amylose, Bioresour. Technol. 101 (2010)2197–2202.

28] F.A. Chmilenko, I.V. Korobova, S.V. Nazarenko, Spectrophotometric determina-tion of polyacrylamide in aqueous solutions using cationic dyes, J. Anal. Chem.59 (2004) 124–128.

29] D. Langevin, Complexation of oppositely charged polyelectrolytes and surfac-tants in aqueous solutions. A review, Adv. Colloid Interfaces Sci. 147–148 (2009)170–177.

30] N. Jain, S. Trabelsi, S. Guillot, D. McLoughin, D. Langevin, P. Letellier, M. Turmine,Critical aggregation concentration in mixed solutions of anionic polyelec-trolytes and cationic surfactants, Langmuir 20 (2004) 8496–8503.

31] M.J. Rosen, Surfactant and Interfacial phenomena, 3rd ed., Wiley Interscience,Hoboken, New Jersey, 2004.

32] R. Nandini, B. Vishalakshi, A comparative study of polyelectrolyte–dye interac-

33] N.J. Rose, R.S. Drago, Molecular addition compounds of iodine. I. An absolutemethod for the spectroscopic determination of equilibrium constants, J. Am.Chem. Soc. 81 (1959) 6138.

34] P.D. Ross, S. Subramanian, Thermodynamics of protein association reactions:forces contributing to stability, Biochemistry 20 (1981) 3096–3102.