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Synthesis and Properties of Nonionic Surfactants fromRosin-Imides Maleic Anhydride AdductAyman M. Atta a , Ahmed M. Ramadan b , K. A. Shaffei b , Amal M. Nassar a , N. S. Ahmed a &Mohamed Fekry ba Egyptian Petroleum Research Institute, Petroleum Application Department , Nasr City,Cairo, Egyptb Helwan University, Faculty of Science, Chemistry Department , Helwan, Cairo, EgyptPublished online: 22 Jul 2009.

To cite this article: Ayman M. Atta , Ahmed M. Ramadan , K. A. Shaffei , Amal M. Nassar , N. S. Ahmed & Mohamed Fekry(2009) Synthesis and Properties of Nonionic Surfactants from Rosin-Imides Maleic Anhydride Adduct, Journal of DispersionScience and Technology, 30:7, 1100-1110, DOI: 10.1080/01932690802597806

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Synthesis and Properties of Nonionic Surfactants fromRosin-Imides Maleic Anhydride Adduct

Ayman M. Atta,1 Ahmed M. Ramadan,2 K. A. Shaffei,2

Amal M. Nassar,1 N. S. Ahmed,1 and Mohamed Fekry21Egyptian Petroleum Research Institute, Petroleum Application Department,Nasr City, Cairo, Egypt2Helwan University, Faculty of Science, Chemistry Department, Helwan, Cairo, Egypt

Ester-adduct derivatives of rosin were synthesized by reacting rosin with polyethylene glycol 600(PEG 600) or 2000 (PEG2000) and maleic anhydride (MA) at elevated temperature. Thesederivatives were evaluated for acid number, FTIR spectroscopy, molecular weight (Mw), andpolydispersity. The derivatives were soluble in organic solvents; aqueous solubility was pH dep-endent. Rosin-imides were synthesized from a rosin ester-maleic anhydride adducts. It wascondensed with diaminobutane or triethylene tetramine to obtain rosinimides. This imide wasetherified by reaction with PEG in the presence of b,b0-dichlorodiethyl ether as a linking agentand NaOH as a catalyst. The surface properties of the prepared surfactants were determinedby measuring the surface tension at different temperatures. The surface tension, critical micelleconcentration and surface activities were determined at different temperatures. Surface para-meters such as surface excess concentration (Cmax), the area per molecule at interface (Amin),and the effectiveness of surface tension reduction (pCMC) were determined from the adsorptionisotherms of the prepared surfactants. Some thermodynamic data for the adsorption process werecalculated and are discussed.

Keywords Adsorption, polyethylene glycol, rosin derivatives, surface activity, thermo-dynamic parameters

INTRODUCTION

Gum rosin, which contains approximately 90% rosinacids and its isomers, is obtained from the exudation ofpine trees. Rosin acids are monocarboxylic acids basedon alkylated hydrophenanthrene nuclei. They have tworeactive sites—one being the carboxylic acid group andthe other being the latent conjugated unsaturation centre.These reactive sites can be used for further modificationof the rosin molecule to convert it to a monomer or varioussuitable intermediates to be used for the synthesis of poly-mers. Various types of polymers from rosin have beenreported in the literature. Rosin has also been polymerizedor dimerized using its reactive sites. Copolymers have beenprepared from rosin or rosin derivatives with vinyl mono-mers. Copolyimides,[1] polyurethanes,[2] polyesters,[3–5]

and epoxy resins,[6,7] from rosin have also been reported.Water-soluble synthetic polymers are a family of materi-

als that have been developed commercially and studiedscientifically at an accelerating pace in recent years. Partly,

this is a reflection of the increasing diversity in theapplications of water-soluble polymers in mineral proces-sing, water-treatment, oil-recovery and surfactants. Sur-factants or amphiphilic monomers are used together withpolymers in a wide range of applications. In areas asdiverse as detergents, paints, paper coatings, food andpharmacy, formulations usually contain a combination ofa low molecular weight surfactant and a polymer whichmay or may not be highly surface active. Amphiphilicpolymers consisting of hydrophilic and hydrophobic partshave become the subject of numerous studies on theirsolutions, solid state, and surface properties. Many watersoluble polymers, because of their amphipathic structureand surface activity, are used as surface active agents.The study of the surface and thermodynamic propertiesare important both for basic research and for industrialapplications.[8–12] In previous work, nonionic oil solublesurfactants were prepared from rosin acid and used asflow improver of petroleum crude oil.[13] The present workdeals with synthesis of water soluble nonionic surfactantsfrom rosin acid adducts with diamine followed by etherifi-cation with different molecular weights of poly(ethyleneglycol), PEG, in presence of b,b0-dichlorodiethyl etherand sodium hydroxide as a catalyst. The thermodynamics

Received 13 January 2008; accepted 5 February 2008.Address correspondence to Ayman M. Atta, Egyptian Petro-

leum Research Institute, Petroleum Application Department, NasrCity 11727, Cairo, Egypt. E-mail: khaled_00atta@yahoo.com

Journal of Dispersion Science and Technology, 30:1100–1110, 2009

Copyright # Taylor & Francis Group, LLC

ISSN: 0193-2691 print=1532-2351 online

DOI: 10.1080/01932690802597806

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and surface properties of the synthesized monomers andtheir corresponding polymers are another objective ofthis work.

EXPERIMENTAL

Materials

All materials were used without further purification.Rosin were heated at 150�C for 4 hours then heated at200�C for 30 minutes in nitrogen atmosphere to isomerizerosin acids to leveopimaric acid, then it were separated bycrystallization from the cold acetone solution of commer-cial rosin. Rosin acids with acid number 183mg KOH.g�1

and melting point 167�C was obtained from a commercialrosin. The separation of the rosin acids from rosin wascarried out to increase the yield and to remove terpens,which have the ability to react with maleic anhydride.Maleic anhydride (MA), triethylene tetramine (TETA),diaminobutane (DAB), b,b0-dichlorodiethyl ether, zinc dust,poly (ethylene glycol) having molecular weights 600 and2000 designated as PEG 600 and PEG 2000, ptoluene,and sodium hydroxide were supplied from AldrichChemicals Co. (USA) and used as received. N,N-dimethyl-formamide (DMF) was analytical grade and purchasedfrom Aldrich.

Monomer Synthesis

Preparation of Rosin Ester-Maleic Anhydride Adducts(RMPEG)

Rosin (1mol) was placed in a glass reactor and heated to220�C on a heating bath. PEG 600 (1.1mol) or PEG 2000(1.1mol) was mixed with this molten mass using a glassstirrer. The temperature of the mixture was maintained at240�C till the completion of reaction. Zinc dust (0.5%)was added as catalyst. Acid number of the mixture at every1-hour interval indicated fate of reaction and the insignifi-cant difference between the two successive acid numbersconfirmed its completion. Further, the melt was allowedto cool to 140�C. MA (1 mole) was added to this meltand the reaction was continued for 1 hour. The moltenmass was poured on steel plates, allowed to solidify,powdered, washed thoroughly with water, and air dried.To confirm the changes in material characteristics, rosinwas treated under similar conditions without addition ofany reactants and treated as reference.

Rosin PEG ester-maleic anhydride adducts withPEG600 or PEG 2000 can be designated as RE-MA1 orRE-MA2, respectively.

Preparation of Rosin-Imides (RI)

Rosin-imides (RI) may be prepared as follows: TETA orDAB (15mmol) was diluted in 6ml of DMF in a flaskfitted with a water condenser with a drying tube, a

thermometer and an N2 purge tube. RE-MA1 or RE-MA2 (10mmol), was dissolved in 10ml of DMF and thesolution added to the diamine solution dropwise at 80�Cwith stirring. During addition, the temperature of the reac-tion mixture was raised to 135�C and kept there for 2hours. DMF. With water formed during imidization, wasremoved by distillation while fresh dry DMF was addedto the reaction mixture continuously. This procedure con-tinued for 2 hours when the reaction mixture was pouredinto excess water. The precipitate was filtered, washed thor-oughly with water and then with diethylether to removeunreacted RE-MA1 or RE-MA2 and TETA or DAB. Itwas finally dried at 40�C under vacuum. The monomersproduced with TETA and DAB were designated as RIT-1 or RIT-2 and RID-1, or RID-2, respectively. RID-1,RIT-1, RID-2, and RIT-2 monomers were a light brownpowders; yields were 85, 90, 88 and 95%; melting pointswere 90, 65, 110 and 78�C and nitrogen contents were calc.2.64; found 2.55, calc. 5.01; found 5.22, calc. 1.92; found1.88 and calc. 3.70; found, 3.75, respectively.

Etherification of RIAAT and RIAAD

In a 250ml three-necked flask fitted with condenser,mechanical stirrer, and thermometer the RIT-1 or RIT-2and RID-1 or RID-2 monomers (0.1 mole), b,b0-dichlorodiethyl ether (0.2 mole), PEG (0.2 mole), NaOH (0.4 mole)and DMF (100ml) were added together with stirring. Thereactants were agitated and slowly heated to a temperatureof 170�C. The reaction mixture was maintained at thistemperature for 5 hours. The progress of the reactionwas evaluated by determine the NaCl content thatincreases gradually to reach a constant value at the endof the reaction. The product was treated with an equalvolume of saturated NaCl solution and neutralized withdilute HCl. Then the reaction mixture was filtered to getrid of the solid NaCl precipitate then the product was driedfrom DMF under vacuum.

Measurements

The acid values of the synthesized resins were deter-mined by the conventional acetic anhydride=pyridinemethod.[14] The acid numbers were determined by titrationof resin solution in acetone against 0.1N of methanolicKOH in the presence of phenolphthalein.

The monomers were characterized by elemental(nitrogen) analysis.

Inherent viscosity measurement, were performed with0.5% (w=v) solutions in DMF solvent at 303K usingUbbelhode viscometer. Dynamic Viscosity of resins wasdetermined with a Brookfield, Model DV-111 viscometerat different temperatures.

Infrared spectra of the prepared compounds wererecorded in polymer=KBr pellets using Mattson-Infinityseries FTIR Bench Top 961.

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1HNMR spectra of prepared resins were recorded on a270MHz spectrometer W-P-270 and Y Brulker usingCDCl3 solvent. Molecular weights of epoxy resins weredetermined by using a Muffidetector GPC Waters 600-Eequipped with Styragel column.

Cloud points of 2% of the prepared surfactant aqu-eous solutions were determined visually by testing thetemperature at which turbidity was observed. We alsonoted the temperature at which turbidity disappeared oncooling. The average of the three results was taken as thecloud point of the system.

The surface tension measurements of the preparedsurfactants were carried out at different molar concentra-tions and different temperatures (289K, 308K, 318K,and 328K) by using platinum tensiometer. The surfacetension was determined using a Kruss K-12 tensiometer.

RESULTS AND DISCUSSION

The reaction of an acid with an alcohol to form esterand water is reversible that leads to formation of impureproducts. Products with high ester yield can be obtainedeither by using catalysts or by use of one of the reactingcomponents in large excess or by removal of water. In viewof this, it may be noted that the reaction temperature in thecurrent scheme spontaneously removed any water moleculeand the reaction continued till the complete conversion ofPEG 600 or PEG 2000 into esters of resin acid. Additionof zinc granules significantly increased the reaction rate.These esters were soft at room temperature and difficultto handle. However, addition of maleic anhydride impro-ved the physical characteristics of the products. Thesequence of reaction taking levopimaric as model compo-nent is given in Figure 1. The physicochemical propertiesof rosin and the derivatives are illustrated in Table 1. In

the present study, the color of the derivatives changed fromyellow to reddish brown with replacing PEG 2000 insteadof PEG 600. The concentration of PEG 600 in the reactionmixture proportionally converted resin acids into estersand exhibited reciprocal relationship with the acid number.As the concentration of PEG 2000 or PEG 600 in thereactant mixture increases, more of the resin acids areconverted into PEG ester of higher molecular weights.Therefore the average molecular weight of the derivatives

FIG. 1. Scheme of synthesis of RE-MA adducts.

TABLE 1Physicochemical properties of rosin and adduct

Appearance Rosin RE-MA1 RE-MA2

Color Paleyellowsolid

Yellowsolid

Reddishbrownsolid

Melting point(�C)

167 45–47 50–55

Molecularweighta

303 (1.13) 820 (1.3) 2450 (1.4)

Acid number(mg KOH)

183 57.71 88.19

PH of 1%suspension

5.81 6.12 6.02

Solubility Insoluble inwater Solublein acetone

Soluble inwater andacetone

Soluble inwater andacetone

aValues in parenthesis indicate polydispersity (Mw=Mn).

FIG. 2. Scheme of synthesis of ERID and ERIT surfactants.

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is coincident with the concentration of PEG 2000 or PEG600. Polydispersity values of all derivatives nearer to oneindicated uniformity of the reaction product.

The synthesis of RID and RIT may be schematicallyrepresented in Figure 2. The products were found to besoluble only in highly polar solvents such as dimethyl for-mamide, dimethyl sulfoxide, m-cresol etc. RID and RITwere characterized nitrogen analysis as described in theexperimental section. Elemental analysis indicates goodagreements between the experimental and theoreticalvalues. This reveals that the method of synthesis and pur-ification were performed successfully. The FTIR spectraof the derivatives are given in Figure 3. The characteristic

IR bands of the rosin imides are observed near 1725 cm�1

and 1785 cm�1, 725 cm�1 for the cyclic imide group. Thepeak for the olefinic double bond appears at 1625 cm�1.The broad band at 3300–3400 cm�1 is due to the stretchingvibration of N–H system present in the amide group.However, in addition to these two peaks, the IR spectraof all the derivatives show C¼O stretching at 1740 cm�1

suggesting formation of ester.[15] These results suggestedPEG 2000 or PEG 600 and MA react with rosin acids toform ester-adduct product.

No significant changes were observed in the materialcharacteristic when rosin was treated under similar con-ditions. While the color of the product changed from

FIG. 3. IR spectra of (a) RE-MA1 and (b) E1RID-1.

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pale yellow to reddish brown, the acid number and mole-cular weight remained the same; IR spectra was superimposable with untreated rosin. The pH of 1% suspensionof derivatives shows an increasing trend with the PEGmolecular weight in the derivatives. The conversion ofcarboxylic acid group into ester might be the reason forthis change.

Etherification of Rosin-Imides with PEG

Nonionic rosin imide polymeric surfactants were pre-pared from the etherification of RID and RIT monomersby using b,b0-dichloro diethyl ether and PEG 600 andPEG 2000 as reported in experimental section. The etheri-fied products of RID and RIT with PEG 600 and PEG2000 can be designated as E1RID-1, E2RID-2, E1RIT-1,and E2RIT-2, respectively. The numbers 1 and 2 can beattributed to PEG 600 and PEG 2000, respectively. Ether-ification of rosin imide with polyethylene having molecularweight 600 and 2000 g=mol in presence of DCDE to pro-duce nonionic polymeric surfactants was represented inFigure 2. The strategy of synthesis is based on preparationof polymeric surfactants having different hydrophile-lipophile balance to study effect of surfactant structureon its properties. Accordingly, the scheme of synthesis isclassified to prepare eight different groups of nonionicpolymeric surfactants. The first group is based on synthesisof RID monomer with different molecular weights of PEG.The second group is derived from esterification of RIT toincrease hydrophilicity of prepared surfactants. The Physi-cochemical characterization of the prepared PEG 600 andPEG 2000 surfactants were listed in Table 2. IR and 1H-NMR spectra were used to illustrate the structure of theprepared surfactants. 1H-NMR spectra of E1RID-1 andE2RIT-2 were selected and represented in Figure 4. IRspectrum of E1RID-1 was represented in Figure 2. It wasobserved that the spectra of all derivatives are nearly iden-tical. The stretching bands at 3450 cm�1 for OH areobserved in all spectra. On the other hand, IR analysiswas used to confirm the etherification of amine at two ends.In this respect, it was observed in all spectra the disappear-ance one of two sharp bands at 3350 cm�1 for NH and

appearance of new band at 1540 cm�1for C–N stretchingvibration of the tertiary amine. The 1HNMR spectra ofetherified RID and RIT monomers with PEG 600 andPEG 2000 were selected to illustrate the structure of themodified surfactants as represented in (Figure 4). The pro-tons of oxyethylene units at d¼ 3.6 ppm, �OH proton ofPEG and N-(CH2CH2)n-N at 4.3 ppm are observed inthe spectra of all surfactants. Signal of methylene (CH2)n,appear as an intense broad band at d¼ 1.35 was used toassign the incorporation of aliphatic diamines in thestructure of the prepared surfactants.

Surface Activity of the Prepared Surfactants

Due to the presence of the hydrophobic effect, surfac-tant molecules adsorb at interfaces, even at low surfactantconcentrations. As there will be a balance between adsorp-tion and desorption (due to thermal motions), the inter-facial condition requires some time to establish. It is wellknown that the modification of Schiff base monomersyields different hydrophobicity, chain flexibility and solu-bility due to the difference of inter- and intramolecularinteractions. This difference in solubility is due to thedifference in hydrophil-lipophil balance (HLB) of thesurfactants. The HLB values were calculated by usingthe general formula for nonionic surfactants,[16,17] HLB¼[MH=(MHþML)]� 20, where MH is the formula weightof the hydrophilic portion of the surfactant molecule andML is the formula weight of the hydrophobic portion.HLB values of nonionic surfactants based on Schiff basemonomers were calculated and listed in Table 3. It isobvious that the HLB values of surfactants have low valuescan be attributed to the structure of surfactants is morehydrophobic surfactants. HLB is an important parametercharacterizing a surfactant that can indicate its appropriateapplications. Classical equations derived by Griffin andDavies were used to calculate the HLB number of surfac-tants,[17,18] however, these equations consider only thechemical compositions, and the effect of position isomer-ism is not taken into account. Because HLB is difficult todetermine experimentally, we instead used cloud point torepresent the hydrophile–lipophile balance. The cloud

TABLE 2Physicochemical properties of the prepared ERI surfactants

Nitrogen content (%) Molecular weigh GPC analysis (g=mol)Inherent viscosity

In DMF (0.5% W=V)at 30�C (dL=g)

Yields(wt %)Designation Calc. Found

Number average(Mn)

Weight average(MW)

E1RID-1 1.22 1.25 2310 2772 0.15 93E1RIT-2 2.38 2.44 2410 2892 0.18 90E2RID-2 0.80 0.83 3530 4236 0.32 85E2RIT-2 1.58 1.62 3610 4512 0.42 80

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point is the temperature below which a single phase ofmolecular or micellar solution exists; above the cloud pointthe surfactant loses sufficient water solubility and a cloudydispersion results.[19] Above this temperature, the surfac-tant also ceases to perform some or all of its normalfunctions. So cloud point can be used to limit the choiceof nonionic surfactants for application in certain processes.A suggestion was made to regard the cloud point in solu-tion of nonionic surfactant as a pseudophase inversion.For polyoxyethylene-type surfactant, the cloud point andthe phase inversion temperature (PIT) are directly corre-lated when surfactant alone is dispersed in water. PITis defined as the temperature at which the hydrophile–

lipophile property of surfactant just balances at the inter-face.[20] So for the polyoxyethylene-type surfactants, cloudpoint is related to the hydrophile–lipophile balance. Astudy on the effect of structural changes in the surfactantmolecule on its cloud point[21] indicates that, at constantoxyethylene content the cloud point is lowered due todecreased molecular weight of the surfactant and increas-ing length of the hydrophobic group.

The surface activity of surfactants can be determinedby measuring surface or interfacial tensions versus timefor a freshly formed surface. The micellization andadsorption of surfactants are based on the critical micelleconcentrations (CMC), which was determined by the

FIG. 4. 1HNMR spectra of (a) RE-MA1 and (b) E2RID-2 surfactants.

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surface balance method. The CMC values of the preparedpolymeric surfactants were determined at 298, 308K,318K, and 328K from the change in the slope of theplotted data of surface tension (c) versus the natural loga-rithm of the solute concentration and listed in Table 4.Some representative plots are illustrated in Figure 5. Thepresented plots and all other plots are used for estimatingsurface activity and confirming the purity of the studiedsurfactants. It is of interest to mention that all obtained

isotherms showed one phase, which is considered as anindication on the purity of the prepared surfactants. Thelisted data show that the CMC decreases with decreasingmolecular weight of PEG units and measuring tempera-ture for the investigated nonionic monomeric and poly-meric surfactants. The reduction in CMC values is dueto the decrease in the solubility of the surfactants. Thisbehavior may result from a coiling of polyethylene oxidechains due to the decrease in the solubility of the

TABLE 3Surface properties of the prepared ERI surfactants at different temperatures

Temperature (K)

Designation Surface property 298 308 318 328

E1RID-1 Cmax� 1010 (mol cm�2) 1.2 1.13 0.98 0.86Amin (nm2=molecule) 0.14 0.15 0.16 0.19Pcmc (mNm�1) 35 34.8 34.5 34.4CMC� 104 (g=mol) 3.7 2.7 2.3 1.5c cmc (mN=m) 37 36.2 35.5 34.6pC20 5.6 5.8 6.4 6.8

E2RID-2 Cmax� 1010 (mol cm�2) 0.826 0.902 0.721 0.775Amin (nm2=molecule) 0.200 0.184 0.230 0.214Pcmc (mNm�1) 25 32 32 33CMC� 104 (g=mol) 20.4 18.4 10.2 5.1c cmc (mN=m) 39 37 35 33pC20 4.2 5.06 5.20 5.50

E1RIT-1 Cmax� 1010 (mol cm�2) 1.34 1.27 1.24 1.2Amin (nm2=molecule) 0.12 0.13 0.13 0.14Pcmc (mNm�1) 29.6 27 26.5 30.1CMC� 104 (g=mol) 3 1.36 1.2 1.01c cmc (mN=m) 45.1 44 42.5 38.1pC20 4.37 4.94 5.11 5.21

E2RIT-2 Cmax� 1010 (mol cm�2) 1.49 1.01 1.41 1.63Amin (nm2=molecule) 0.111 0.163 0.117 0.101Pcmc (mNm�1) 31 30 33 31CMC� 104 (g=mol) 5.00 2.51 1.24 0.625c cmc (mN=m) 39 37 36 35pC20 4 4.2 4.4 5.5b

TABLE 4Thermodynamic parameters of micellization for the prepared surfactants

Thermodynamic Parameters at Different Temperatures (KJmol�1)

25�C 35�C 45�C 55�CDSmic

(KJmol�1K�1)Surfactants �DGmic DHmic �DGmic DHmic �DGmic DHmic �DGmic DHmic

E1RID-1 17.1 11.6 18.1 11.6 19 11.5 20 11.4 0.05E2RID-2 17.04 34.06 19.41 33.41 20.04 34.49 22.55 33.69 0.1715E1RIT-2 20.1 27.6 22.8 26.5 23.7 27.2 25.1 27.4 0.16E2RIT-2 20.53 56.31 23.02 56.41 25.59 56.41 28.27 56.31 0.2579

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ethoxylated surfactants. This behavior is obvious onlyover some EO ranges, as would be expected from theincrease in the hydrophilic character of the moleculeresulting from this change. In previous work[22–23] thisbehavior was explained on the basis of coiling of thepolyethylene oxide chains.

The direct determination of the amount of surfactantadsorbed per unit area of liquid-gas or liquid-liquidinterface, although possible, is not generally under takenbecause of the difficulty of isolating the interfacial regionfrom the bulk phase for purpose of analysis when the inter-facial region is small, and of measuring the interfacial areawhen it is large. Instead, the amount of material adsorbedper unit area of interface is calculated indirectly from sur-face or interfacial tension measurements. As a result, a plotof surface (or interfacial) tension as a function of equili-brium, concentration of surfactant in one of the liquidphases, rather than an adsorption isotherm, is generallyused to describe adsorption of this interface can readilybe calculated as surface excess concentration Cmax. Thesurface excess concentration of surfactant at the interfacemay therefore be calculated from surface or interfacialtension data by using the following equation:

Cmax ¼1

RT

�@c@ ln c

� �T

½1�

Where �@c@ ln c

� �Tis the slope of the plot of c versus ln c at

a constant temperature (T), and R is the gas constant inJmol�1K�1. The surface excess concentration at surfacesaturation is a useful measure of the effectiveness of adsorp-tion of surfactant at the liquid-gas or liquid-liquid interface,since it is the maximum value which adsorption can attain.

The Cmax values were used for calculating the minimumarea Amin at the aqueous-air interface. The area per mole-cule at the interface provides information on the degree ofthe packing and the orientation of the adsorbed surfactantmolecules, when compared with the dimensions of themolecule as obtained by use of models. From the surface

excess concentration, the area per molecule at interface iscalculated using Equation (2).

Amin ¼ 1016

NCmax½2�

Where N is Avogadro’s number.The surface tension values at CMC were used to calcu-

late values of surface pressure (effectiveness). The effective-ness of surface tension reduction,PCMC¼ co� cCMC, whereco is the surface tension of water and cCMC is the surfacetension of solution at CMC,[24] was determined at differenttemperatures. The values of PCMC show that, the most effi-cient one is that which gives the greater lowering in surfacetension at the critical micelle concentration. The effective-ness increases with increasing the length of carbon chainin the hydrophobic moiety. Efficiency PC20 is determinedby the concentration (mol=L) capable to suppress the sur-face tension by 20 dyne=cm. The efficiency of the preparedsurfactants, listed in Table 3, increases with decreasingmolecular weight of PEG and with increasing temperatureIt was observed that the A min of surfactants based ondiamine butane is higher than that based on TETA surfac-tants. This can be attributed to the fact that, the nonionicsurfactants have aliphatic linear aliphatic hydrophobicgroups, the easier for packing at the interface, thus obs-tructing the main chain interaction at the interface; then,the molecule occupies a smaller area, i.e., adsorption thanthat based on TETA chain. Careful inspection of data,indicates that, Amin at the surface decreased with increasingthe temperature and this is due to increased dehydration ofthe hydrophilic group at higher temperature.

The effectiveness of surface tension reduction, gCMC, inthese compounds shows a steady increase with replacementof DIB instead of TETA diamine units. The effectiveness ofadsorption, however, may increase, decrease or show nochange with increase in the length of the PEG dependingon the orientation of the surfactant at interface. If surfac-tant is perpendicular to the surface in a close-packedarrangement, an increase in the length of the straight-chainhydrophobic group appears to cause no significant changein the number of moles of surfactant adsorbed per unitarea of surface at surface saturation.[25] This is because,the cross-sectional area occupied by the chain oriented per-pendicular to the interface does not change with increase inthe number of units in the chain. When the area of hydro-philic group is greater than that of the hydrophobic chain,the larger the hydrophilic group, the smaller the amountadsorbed at surface saturation. If the arrangement is pre-dominantly perpendicular but not close-packed, theremay be some increase in the effectiveness of adsorptionwith increase length of hydrophobic group, resulting fromgreater Van der Waals attraction and consequent closerpacking of longer chains.[26] However, if the orientation of

FIG. 5. Adsorption isotherms of E1RIT-1 at different temperatures.

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surfactant is parallel to the interface, when the hydropho-bic chain interacts strongly with the surface. For example,electron rich aromatic nuclei, the effectiveness of adsorp-tion may decrease with increase in the chain length, dueto increase the cross-sectional area of the molecule on thesurface. Thus saturation of the surface will be accom-plished by a smaller number of molecules.[27] Finally, wecan concluded that the replacement of DIB instead ofTETA increases the surface excess of molecule and conse-quently, decreases Amin of molecule at air=water interface.This behavior can be attributed to increment of hydropho-bic interaction at interface, which increases with increasinglength of hydrophobic moieties (DIB), which reflects onincreasing of surfactant concentration and consequentlydecreases area per molecule. It is evident that, the mini-mum area per molecule at air=water interface can contri-bute to the molecular area. Accordingly, the adsorptionof the surfactant molecules at air=water interface increasewith incorporation of DIB instead of TETA in the chemi-cal structure of the prepared surfactants.

Thermodynamic Parameters of Micellization ofPrepared Surfactants

The formation of micelles in aqueous solutions is gener-ally viewed as a compromise between the tendency for alkylchains to avoid energetically unfavorable contacts withwater and the desire for the polar parts to maintain contactwith the aqueous environment. There are two principallydifferent models for micelle structure. A mean densitymodel[28] is the most appropriate one for micelles consistingof a large core and a relatively thin corona, and starmodel[29] is the most appropriate for those having a smallcore from which long chains protrude to form a large cor-ona. The ability for micellization processes depends onthermodynamic parameters, (enthalpy DH, entropy DSand free energy DG) of micellization. Thermodynamicparameters of adsorption of the prepared nonionic surfac-tants were calculated and listed in Table 5. The thermo-dynamic parameters of micellization are the standard free

energies DGmic, enthalpies DHmic, and entropies DSmic, ofmicellization for nonionic surfactants.

DGmic ¼ RT ln CMC ½3�

ValuesofDSmicwereobtainedfromEquation(4)by invok-ing the values of DGmic at 298K, 308K, 318K, and 328K.

@DGmic

@T¼ �DSmic ½4�

In addition, DHmic, was calculated from DGmic andDSmic by applying Equation (5).

DHmic ¼ DGmic þ TDSmic ½5�

The thermodynamic parameters values of adsorption,DGad, DHad and DSad were calculated via Equations (6),(7), and (8), respectively.[30]

DGad ¼ RT ln CMC � 0:6023 PCMC Amin ½6�

@DGad

@ T¼ �DSad ½7�

DHad ¼ DGad þ TDSad ½8�

The values of DGmic, DHmic and DSmic for both nonionicand ionic surfactants are calculated and listed in Table 4.Analyzing the thermodynamic parameters of micellizationleads to the fact that micellization process is spontaneous(DGmic< 0). The data show that DGmic values are lessnegative with increasing the number of methylene group.This indicates that the increase of hydrophobic groupsdecreases the micellization process. This can be explainedon the basis of steric bulk structure leads to steric inhibi-tion of micellization.[31] On the other hand, the data revealthat �DGmic increases with increasing temperature from298K to 328K. The data listed in Table 4 show that DSmic

lues are all positive, indicating increased randomness in thesystem upon transformation of the nonionic surfactantmolecules into micelles or increasing freedom of the

TABLE 5Thermodynamic parameters of adsorption for the prepared surfactants

Thermodynamic parameters at different temperatures (KJmol�1)

298K 308K 318K 328K

Designation �DGad DHad �DGad DHad �DGad DHad �DGad DHad DSad

E1RID-1 22.5S�>> �7.6 24.1 �8.7 23.4 �7.5 24.1 �8.0 0.095E2RID-2 20.07 44.68 22.95 43.96 24.47 44.62 26.8 44.46 0.2173E1RIT-2 22.2 25.5 24.9 24.4 25.9 24.9 27.3 25.2 0.16E2RIT-2 22.61 125.7 25.98 127.3 27.92 130.3 30.17 133 0.4977

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hydrophobic chain in the nonpolar interior of the micellescompared to aqueous environment. The decrement of posi-tive DSmic value with dencreasing the chain length units inthe surfactant molecule has been observed and can beattributed to decrease molecular weight of hydrophobicgroup which leads to increasing the hydrogen bondsbetween water and PEG, which decrease freedom motionof surfactants. The dissolution of the oxyethylene unitshas been stated to be the major contributing factor to thepositive entropy of micellization in polyoxyethylenatednonionics. An alternative explanation is that there is lessrestriction on the motion of the surfactant molecule whenit is in the essentially water-free environment of the micellethan in the aqueous phase. This extends to both the hydro-phobic chain, which is in a hydrocarbon-like environmentin the interior of the micelle, and the adjacent part of thehydrophilic polyoxyethylene chain, which is freed, on theonly partially solvated micelle surface, from some of the res-trictions placed on it by hydrogen bonding to water molecu-les. This explanation, which assigns the change in entropy tothe solute rather than to the solvent, is consistent with there-evaluation of the concept[31] of entropy of solution.

The values of DGad, DHad and DSad for all nonionicsurfactants are calculated and listed in Table 5. All DGad

values are more negative than DGmic, indicating thatadsorption at the interface is associated with a decrease inthe free energy of the system. This may be attributed tothe effect of steric factor on inhibition of micellization morethan its effect on adsorption. The values of DSad are allpositive and have greater values than DSmic for nonionicsurfactants. This may reflect the greater freedom of motionof the hydrophobic chains at the planar air-aqueous solu-tion interface compared to that in the relatively crampedinterior beneath of the convex surface of the micelle. Thisindicates that the steric factor inhibits micellization morethan do adsorption for nonionic surfactants. On the otherhand, the positive values of DHad are much lower thanthe corresponding values of DHmic. This indicates that thedehydration—breaking of hydrogen bonds—at adsorptionis easier than at micellization. The negative values of DHad,determined for E1RID-1, indicate that more bonds

between polyoxyethylene chain oxygen and water moleculesare broken in the process of adsorption at the air aqueoussolution interface than in micellization.

CONCLUSIONS

The following conclusions can be extracted from theprevious discussion:

1. New nonionic water soluble rosin-imide surfactantshaving different HLB values were prepared.

2. E1RID-1 have negative DHad values. This indicates thatthe hydrogen bonds between water and PEG groups arebroken at adsorption more than at micellization.

3. All DGad values of surfactants are more negative thanDGmic, indicating that adsorption at the interface isassociated with a decrease in the free energy of thesystem.

4. The values of DSad are all positive and are greater thanDSmic for nonionic surfactants.

5. The prepared surfactants favor adsorption at interfacemore than micellization in bulk aqueous solution.

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