Investigation of the Orientation of CTA + Ions in the Interlayer of CTAB PillaredMontmorillonite

e orientation of CTA in the interlayer of organic pillared montmorillonite prepared by adding different amounts of surfactant corresponding to the CEC of the pristine clay mineral has been studied using X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectra. Morphology of the samples was examined by scanning electron microscopy (SEM). e results are supported by the measurements of zeta potentials and contact angles of pristine clay and organoclay samples. From the XRD results, a series of arrangement models of CTA in the interlayer of montmorillonite have been proposed as lateral-bilayer, pseudotrilayer, paraffin-type-monolayer and pseudotrilayer, paraffin-type-bilayer and pseudotrilayer for 0.5, 1, 1.5, and 2.0 CEC, respectively. FTIR spectrum and contact angle measurements of pristine montmorillonite and organoclays indicated the incorporation of surfactant and the changing of hydrophility in the different OMts.is study demonstrates that not only the arrangement model of surfactant, but also the morphology of organoclay strongly depends on the surfactant packing density within the montmorillonite interlayer space. In addition, it can be also proposed that, the magnitude of surface charge or its distribution on clay mineral might be an important factor for expansion characteristics of organoclay.


Introduction
Modi�cation of clay mineral surfaces by adsorption of organic compounds has been largely studied in the literature."Organoclay minerals" (also called "bentonite") were initially used for their rheological properties, but their most recent application is as �ller for a polymer, in order to modify its mechanical, thermal, or barrier properties.Organomontmorillonites (OMts) have found wide applications in organic pollution control �elds because of their excellent adsorption capacity towards hydrophobic organic compounds [1][2][3][4][5][6].Understanding microstructure of this kind of organoclays is of high importance for clarifying their adsorption characteristics and improving their adsorption efficiency.In the past decades, structural characteristics of OMt have been extensively investigated.e structural characteristics, such as basal spacing, surface area, porous structure, and arrangement models of organic cations, have been reported in numerous publications [7][8][9][10][11][12][13][14][15][16].Based on the obtained structural information, the potential correlation between microstructure and adsorption characteristics of organoclays has been proposed in several reports [1,[17][18][19][20][21][22][23][24].Chen et al. [5] indicated that as the arrangement model of organic cations evolves from �at-monolayer to �at-bilayer, to pseudotrilayer, then to paraffin-monolayer and �nally to paraffinbilayer with the increase of their loading amounts, the alkyl chains will �rst form strong adsorbed organic �lm and then gradually transfer to weak partition organic phase.
For this purpose, smectites are the clay minerals mainly used a�er surfactant modi�cation, as �ller in clay-polymer nanocomposites [25].e smectites are layered inorganic phyllosilicates where the layers of about 1 nm are held apart mainly by electrostatic forces.Montmorillonite is one of the most common smectites, which is widely used in a range of applications because of its high cation exchange capacity, swelling capacity, high surface areas, and resulting strong adsorption.ere are two natural varieties of montmorillonite: sodium montmorillonite having a high swelling capacity in water and calcium montmorillonite with slight swelling capacity.e ability to cation exchange in the interlayer space determines the most interesting property of this material which can be used as a �ller for nanocomposites showing unique mechanical properties [26].Consequently, smectites have found many applications in the �elds of cosmetic, catalysis, adsorption, and so forth.e general approach to improve the different mechanical and thermal properties involves the mixing of a polymer with traditional �llers like talc, glass �bers, calcium carbonate, and so forth.Recently, great efforts have been paid on synthesis and application of inorganic-organic clay complexes [27][28][29][30][31].Wu et al. [29] found that modifying inorganic pillared montmorillonites with surfactant could greatly improve their sorbing capacity to phenol.By preadsorption of organic molecules (amines) between the clay layers prior to pillaring with aluminium precursor, it was possible to increase the microporosity of the obtained materials [30].However, up to now, there are few studies on the interlayer structure and surface properties of the importance for the synthesis and applications.e aim of this study is to investigate the microstructure of CTAB-Mt complexes and the effect resulted from the premodi�ed surfactant loadings.is study provides some new insights in the synthesis of inorganic-organic clay complexes and the interlayer structure of the resulting materials.It is important for well understanding the structure and properties of inorganic-organic clays and their applications.

Material.
Montmorillonite is used in this study, a commercial sample of bentonite of Çankırı deposit in Turkey was obtained from Karakaya A. Ş. Mineral Company, Ankara, Turkey.e sample was air-dried, sieved and distribution of particle size determined using ASTM Standard sieves.e results are given in   the clay sample was determined by Rigaku RIX-3000 Xray �uorescence spectrometry (Rigaku Corporation, Tokyo, Japan) and the results are presented in Table 2.
XRD measurements of the raw and organoclay samples were performed using Rigaku 2200D/Max-IIIC (Rigaku Corporation, Tokyo, Japan) powder diffractometer equipment with CuK radiation (   Å) source at 30 kV, 10 mA and at scan rate of 2 ∘ in min unit, and a scan range from 2 ∘ to 10 ∘ .X-ray diffraction patterns of the samples are given in Figure 2.
e XRD and the chemical analysis revealed that clay was a Na-montmorillonite (Na-Mt).
e cation-exchange capacity (CEC) of the clay is determined by the ammonium acetate method [32] as 107 meq/100 g.Cetyltrimethylammonium bromide (CTAB), a cationic surfactant also known as hexadecyltrimethylammonium bromide, was used as the modi�er.With a long hydrocarbon chain, CTAB were purchased from Merck and used without further puri�cation (Figure 1).All chemicals used in this study were obtained from Merck.
FT-IR spectra of all samples were run on a Perkin Elmer Model 1600 FT-IR spectrophotometer using KBr pellets.
Surface morphologies of the pristine montmorillonite and organoclay samples were examined by a Philips XL 30 SFEG model scanning electron microscope (SEM) operating at 24 kV.
e zeta potential measurements of solid particles in suspensions were carried out by using a Zeta Meter 3.0+ (Zeta-Meter, Inc., Staunton, VA, USA) at the unadjusted pHs.
e static contact angle measurement was performed using a CAM-101 optical contact angle analyzer (KSV Instruments, Finland).For this purpose, a pellet was prepared under 1.06 ton/cm 2 pressure, using 0.6 g organoclay sample.e contact angles were measured by using goniometer, which used a water drop of 6 L and took Young-Laplace equation into account at solid-liquid interface.

Preparation of the Organoclays
. e synthesis of surfactant modi�ed montmorillonites was performed as in the following procedure: 50 g montmorillonite was �rst dispersed in distilled water and stirred for 10 h at stirring speed of 200-250 rpm to swell and to form homogeneous liquor, into which then a desired amount of cetyltrimethylammonium bromide (CTAB) was slowly added.e concentrations of surfactants were 0.5, 1.0, 1.5, and 2.0 times CEC of montmorillonite, respectively.e mixture was stirred for 1 h, then stirring was stopped and the resulting organomontmorillonite (OMt) was �ltered and washed with distilled water for several times to remove excess salts, dried at 90 ∘ C, ground and sieved.e single basal spacing of the organomontmorillonite with surfactant/CEC = 0.5 (0.5 CEC-OMt) is 1.83 nm.is peak corresponds to an interlayer opening of 0.87 nm (aer subtraction of the silicate layer thickness value of 0.96 nm) and is the main re�ection in the sample 0.5 CEC which is approximate to the height of lateral bilayer (0.81 nm).e organic ion arrangement can be considered as lateral bilayer.e possible arrangement model of the lateral bilayer is that the protrudent methyl inserts into cavity between organic cations or into the hexagonal hole of basal oxygen plane [13,33,34].Consequently, the alkyl chains may come close together and arrange in LB model.So, the height of LB model depends on the height of the double layers of alkyl chains rather than that of the cation end of CTA + .e added surfactant/CEC ratio from 0.5 to 1 increases to the opening of the interlayers spaces by 0.1766 nm.e observed peak at 2.0066 nm for 1.0 CEC indicates that there is an interlayer spacing of 1.0466 nm in height.e height of the two layer of CTA + in a bilayer-mirror-image arrangement is just 1.02 nm which equals the interlayer spacing corresponding to the peak at 2.0066 nm.But, considering the repulsive force between cations, the probability for this kind of arrangement is little.Pseudotrilayer arrangement may explain well the basal re�ection at 2.0066 nm.Brindley and Moll [35], Beneke and Lagaly [36] reported the arrangement model of alkyl chains with mutual interlocking, in which the parallel packing of the chains was presumed that a -CH 2 group of one chain laies between two such groups of neighbouring chains.In this case, the height of the bilayer with interlocking chains should be smaller than that without interlocking chains [37].But, according to our results, the fact that interlayer basal spacing value of 1.0466 nm indicates the presence of CTA + ions connected with dispersive interactions to tail parts of CTA + ions apart from pseudotrilayer arrangement of CTA + ions.is result is supported by the increasing value of zeta potential (+25 mV).e main peak of the organomontmorillonite with surfactant/CEC = 1.5 (1.5 CEC-OMt) has a basal spacing of 2.148 nm followed by a large shoulder centered at about 2.848 nm.is indicates a lack of the homogeneous interlayer opening due to the different interlayer expansions.e reason is that the amount of added surfactant is low compared to the CEC of the clay mineral and that not all charge balancing cations are replaced by the surfactant cations.Both nonexchanged inorganic cations (hydrated Na + ) and organic cations (cationic surfactant) are present, perhaps within the same interlamellar space [24].e peak at the 2.148 nm (d 002 ) shows that the arrangement model of CTA + ions in the interlayer of montmorillonites is pseudotrilayer.e fact that the basal space distance is larger than the basal spacing distance required for pseudo trilayer shows that the CTA + ions connected with CTA + ions due to the dispersive interactions.e zeta potential measurements also support this result.e shoulder peak (d 001 ) on the le side of the d 002 peak shows a new arrangement of CTA + ions between layers of clay other than the pseudo trilayer model.e maximum value of this peak (d 001 ) is 2.848 nm, and CTA + ions between the clay layers have settled with a paraffinic monolayer arrangement.

Assignment
Frequency, cm e XRD patterns of 2.0 CEC-OMt show a well-organized structure, with a narrow �rst higher intensity peak at 4.2037 nm and with a second peak at 2.0066 nm corresponding to para�nic bilayer and pseudo trilayer arrangement, respectively.is indicates that the amount of added surfactant has a direct effect on the interlayer expansion of smectites.e surfactant chains lie parallel to each other in a paraffin-type structure at a certain angle with the silicate layers.For 2.0 CEC-OMt, the d 001 basal spacing (4.2037 nm) corresponds to a con�guration of C 16 chains almost perpendicular to the clay layer [24].A value of 4.2037 nm is obtained for a theoretical basal distance of OMt assuming a trans conformation of the chain in the interlamellar space.
In summary, by adding increasing amount of surfactant, several ranges of paraffin-like structures occur (i) <3 nm till 1.5 CEC and (ii) >4 nm aer the CEC with highly ordered assembly.ere is probably an intermediate con�guration where the chains are not perpendicular to the layers with enough free lateral spaces allowing the chains to adopt different orientations leading to highest entropy.With the increase of the concentration of pillaring reagent, the stack density of organic cations in the interlayer space increases and the arrangement of organic cations changes.e heterogeneity of charge on various layers may be the crucial factor for different arrangements coexisting.Tamura and Nakazawa [38] proposed that the basal spacing of 3.98 nm should be attributed to the PB model and the a PB (between the alkyl chain and basal surface) was 30 ∘ .In the analogous study, Beneke and Lagaly [36] pointed out that long alkyl chain (n > 16) alkylammonium arranged in a paraffinic bilayer model and the basal spacing reached 4.0 nm.e occurrence of the basal spacing of 4.2037 nm in our study implies that CTA + ions should be arranged in the paraffinic bilayer model and the a PB > 30 ∘ [34].e peak at 2.0066 nm corresponds to pseudo trilayer arrangement.On the other hand, the measurements of zeta potential support that there are bounded CTA + ions through dispersive interactions to the tails of CTA + ions in paraffinic bilayer arrangement between the clay layers.

Infrared Spectra of the Montmorillonite and Organoclay
Samples.Vibrational spectroscopy has been extensively used for probing the conformation in amine chain assemblies.Infrared spectroscopic studies have led to detailed correlation of the spectra with structural features such as chain conformation, chain packing, and even speci�c conformational sequences [8,39,40].
Fourier Transform Infrared (FTIR) spectra of the previously dried samples were recorded on a Pelkin-Elmer Spectrum-One instrument.Each sample was �nely ground with oven-dried spectroscopic grade KBr and pressed into a disc.All samples were oven-dried at 120 ∘ C to remove physisorbed water.en, the spectra were recorded at resolution between 400 and 4000 cm −1 .e FTIR spectra of pristine clay and the modi�ed clay samples by adsorption of cethyltrimethylammonium bromide (CTAB) based on cation exchange capacity (CEC) of clay are shown in Figure 3 and all the important absorption bands and their assignments are listed in Table 4.As shown in Figure 3, though the different OMts (Figure 3) shows the peaks of the pristine clay, new characteristic peaks appear at 2931.17 cm −1 -2855.75cm −1 , at 2924.2 cm −1 -2851.49cm −1 at 2919.77 cm −1 -2850.57cm −1 and at 2918.98 cm −1 -2850.24cm −1 corresponding to the -CH 2 asymmetric, (_as(CH 2 )) and -CH 2 symmetric (_s(CH 2 )) stretching vibrations for 0.5 CEC, 1.0 CEC, 1.5 CEC and 2.0 CEC, respectively [41].ese peaks absent in the IR spectrum of the pristine Mt indicate the incorporation (or the presence) of the surfactant in the different OMts.As the peaks are very narrow, we can compare the variation of their intensity instead of their peak area in order to estimate the increase of adsorbed amount of surfactant.e intensity increases with increasing initial surfactant content, indicating the intercalation of higher amount of surfactant in the montmorillonite with increasing initial amount.For CEC values between 0.5 and 1, the linear increase of the intensity with the amount of surfactant added is steeper than between 1 and 2 CEC.e �rst part, till 1 CEC, corresponds to a linear direct cationic exchange of the exchangeable Na + cation by the cationic surfactant.e second part, in excess of the CEC, deviates from the previous linearity and corresponds to an adsorption of surfactant on the external surface, followed by adsorption in the interlamellar space, by lateral chain-chain surfactant interactions.
Previous studies [10,42] indicated that the ordered conformation of the alkyl chains in the con�ned system showed a strong dependence on amine concentration and orientation.In relatively high concentration range, the con�ned amine chains adopt an essential all-trans-conformation and the frequency of the asymmetric CH 2 stretching absorption band locates at a relatively low frequency.However, in the relatively low amine concentration range, the frequency shis signi�cantly to higher frequency and the con�ned amine chains adopt a large number of gauche conformations.Only when the chains are highly ordered (all-trans-conformation), the narrow absorption bands appear around 2918 (_as(CH 2 )) and 2850 cm −1 (_s(CH 2 )) in the infrared spectrum.If conformational disorder is included in the chains, their frequencies shi upward, depending upon the average content of gauche conformers.
As shown in Figure 3 and Table 4 the frequency shied signi�cantly to low wavenumber, indicating more transconformational molecules introduced into alkyl chain with the increase of surfactant loading.
Kung and Hayes [10] �gured out the relative shis of -CH 2 vibrational energies can be used to assess the relative hydrophobic properties of the loaded surfactant, with lower energies (lower wave number) re�ecting a more structured and hydrophobic environment.e results obtained in this study re�ect that the degree of the hydrophobic properties may be increased with the increment of surfactant loading.At relatively high surfactant loading, most hydration cations were exchanged by surfactant cations, resulting in a decrease of the hydration water content and a surface property change from hydrophilic to hydrophobic.In this case, water molecules are difficult to be introduced into clay interlayer space and the gallery height is impossible to be expanded [40].
e infrared absorption bands between 1480 and 1440 cm −1 , due to the methylene scissoring modes, are quite similar to the methylene rocking modes at 800-700 cm −1 in the position and shape of the bands (shown in Figure 3).In the spectra of pristine Mt, doublets at 1478 and 1442 cm −1 corresponds to the scissoring modes and those at 797.47 and 779.18 cm −1 to the rocking modes, respectively.e splitting of the -CH 2 scissoring and rocking bands is due to the intermolecular interaction between the two adjacent hydrocarbon chains in a perpendicular orthorhombic subcell [43,44] and further requires an all-trans-conformation for its detection [45].As shown from Figure 3, when the alkyl intercalated into montmorillonite, a broad band at 1478 cm −1 splits with the increase of surfactant loading as described in the literature [15] for 1.0 CEC, 1.5 CEC, and 2.0 CEC.For the -CH 2 rocking modes, with the increase of surfactant loading, two well-resolved vibration bands at 797 and 778 cm −1 were observed, similar to -CH 2 scissoring.is phenomenon is similar to those descriptions in previous researches [46].According to above results, it could be said that splitting of the methylene scissoring and rocking modes not only relates with surfactant loading, but also relates with the con�guration of the used surfactants.
Spectral hydration features in montmorillonite have been attributed to the structural OH in the octahedral layer, water adsorbed on the clay external surfaces, and water adsorbed in the interlayer regions.e character of these interlayer water molecules is greatly dependent on the moisture level and the interlayer cation [40].
e spectra display more obvious absorption band at 3620 cm −1 due to the OH stretching vibrations of structural OH groups and the frequency is independent on the surfactant loading which is consistent with the result reported in the literature [40].In the region of 3100-3500 cm −1 , the spectra show a broad band around 3400 cm −1 corresponding to the overlapping symmetric _ 1 (H-O-H) and asymmetric _ 3 (H-O-H) stretching vibrations, and a shoulder around 3250 cm −1 due to an overtone (2 2 ) of the bending model [10,24,40].As seen in Table 4, the frequency of the band around 3444 cm −1 gradually shis to the lower frequency with the increase of surfactant loading.e H-O-H bending vibration shis signi�cantly from 1642 cm −1 (pristine Mt) to low frequency of 1640.09cm −1 (0.5 CEC-OMt), of 1638.01 cm −1 (1.0 CEC-OMt), of 1637.21 cm −1 (1.5 CEC-OMt), and of 1633.37 cm −1 (2.0 CEC-OMt).When the surfactants intercalated into the gallery of montmorillonites, the water bounded directly to the hydrated cations was removed with the replacement of the hydrated cations by surfactant cations.erefore, the detected absorption bands are mainly attributed to adsorbed water molecules especially at high surfactant loading.Simultaneously, with the intercalation of surfactants, the surface property of montmorillonite is modi�ed� that is, the hydrophilic surface of montmorillonite has been changed to hydrophobic.Hence, H 2 O is not easy to be adsorbed by organomontmorillonite [40].Zeta potential measurements support these results.
When the surfactant intercalated into interlayer space of montmorillonites, the frequency of the Si-O stretching band in the tetrahedral network was changed.As seen from Figure 3, for the pristine montmorillonite, the band in the region of 950-1100 cm −1 corresponding to stretching vibration of Si-O group splits into a sharp band at 1033 cm −1 with a shoulder around 1088 cm −1 attributed to perpendicular Si-O stretching [40].However, for the organo-montmorillonites, the change of the band shape and its frequency strongly depends on the surfactant loading.As seen in Figure 3, frequencies of the Si-O stretching bands observed at the 1101 cm −1 and at the 1018,43 cm −1 for the pristine Mt shied with a surfactant loading.For the organoclays prepared from CTAB with a low surfactant loading the shoulder at ca. 1101 cm −1 is markedly reduced.With the increase of surfactant loading, the shoulder band shied to low frequency, from 1101 cm −1 to 1088 cm −1 for 0.5 OMt, to 914.73 cm −1 for 1.0 OMt.When further increasing the surfactant loading, the frequency almost kept unchanged for 1.5 CEC-OMt and 2.0 CEC-OMt (to 918 cm −1 for 1.5 OMt and to 914 cm −1 for 2.0 OMt).Aer the intercalation of CTAB, the band at the 1018.43 cm −1 shied to 1000.38 cm −1 , to 1036 cm −1 , to 1029 cm −1 and to 1022 cm −1 for 0.5 CEC-OMt, 1.0 CEC-OMt, 1.5 CEC-OMt and 2.0 CEC-OMt, respectively.is is coincident with that reported in the previous studies [10,[47][48][49][50]. e intercalation of CTAB (as cation, or a neutral molecule) into the interlayer space is accompanied by a marked interlayer swelling, during which a perpendicular sorbate orientation is reached.In this way, the interlayer distance is markedly increased, the orientation of the SiO 4 tetrahedral is changed, most probably towards a better ordered arrangement and more marked manifestation of the perpendicular Si-O vibrations.Xi et al. [51] proposed that the signi�cant changes in Si-O stretching band suggest that there is an interaction between the surfactant molecules and siloxane (Si-O) surface.us, the changes of Si-O stretching band are attributed to an increase of the interaction between the surfactant and silicate surfaces.

Zeta Potential and Contact Angle Measurements of the Montmorillonite and Organoclay Samples
. e values of zeta potential and contact angle of pristine montmorillonite and organoclays were measured.e variation zeta potential and contact angel depending on CEC ratio are given in Figure 4.As shown from Figure 4, there are linear increase in the zeta potential values as it increased the CEC ratio and it reaches to maximum value at 2.0 CEC.e observed increase in the the contact angle values of organoclay samples by comparison pristine montmorillonite reaches to maximum value at 1.0 CEC, thereaer relative decrease observed in these values for 1.5 CEC and 2.0 CEC.e value of zeta potential shied to positive value with the increase of the CEC ratio.e signi�cant increase appeared up to 1.0 CEC, then relative increase carried out for other CEC ratios.Depending on the contact angle value is quite low for pristine Mt, it can be said that diffusion trend of water to the spaces between the layers is extremely high, and water molecules penetrated to the basal area bond with silicate oxygen by hydrogen bonding.As a result, hydrated cations in a basal area improve wetting properties of the montmorillonite.e values of zeta potential and contact angle in 0.5 OMt sample increased twice in respect of pristine montmorillonite.It was understood from these results that the interactions between CTA + ions and the negative centers on the montmorillonite surface occur through weak and electrostatic interactions and CTA + ions in basal space tend to orientate interval surface as parallel and lateral interactions appear as reciprocal.e increase in contact angle supports this result.Namely, CTA + ions tended as parallel and laterally interacted have negatively changed the wetting characteristic of clay and the existence tendency of water molecules in basal region.FTIR spectra (Figure 3) show that creating an effective dipole-dipole interaction and hydrogen bonding are trends of organoclay samples according to pristine Mt sample decreased.
e zeta potential value of 1.0 CEC-OMt samples has reached a very high and a positive value.In parallel, a signi�cant increase in the value of contact angle has appeared.e conversion of zeta potential from negative value to positive value indicated that the orientation of CTA + ions at interface is changed from parallel to perpendicular.But the fact that the zeta potential value is greater than zero indicated the presence of dispersive interactions between parts of tails of the adsorbed CTA + ions in basal space of montmorillonite and of the attached CTA + ions partly as a horizontal.Despite the positive charge in the basal spaces of montmorillonite layers, it is a fact that the value of contact angle is signi�cantly large (the changes of Si-O stretching band supports this result) showing that the tendency of diffusion of water is reduced by the hydrophobic tail parts of CTA + ions.e considerable increase in the zeta potential value of 1.5 CEC-OMt sample has pointed completely vertical orientation.XRD observations (Figure 2) clearly indicate that formed structures similar to the situation at 1.0 CEC-OMt.Pseudotrilayer structure at 1.5 CEC-OMt sample reveals also the vertically oriented paraffinic monolayer structure depending on the increased concentration of CTA + ions.e electrostatic interactions due to high CTA + ion concentration at 1.5 CEC-OMt leads to emergence of paraffinic monolayer orientation primarily with the support of the vertical and horizontal dispersion interactions between the tails.ere-aer, the rest of the CTA + ions from the paraffinic oriented CTAB molecules leads to an adsorption of similar structure at 1.0 CEC-OMt sample.
It was seen that the measured zeta potential value in the case of 2.0 CEC-OMt is extremely large and the contact angle value was relatively low than that of the other samples.is situation has pointed to the transformation of some of CTA + ions between the layers of Mt from the paraffinic monolayer structure to the paraffinic bilayer structure.Extremely high and positive value of zeta potential and also the fact that the distance determined from the XRD measurements (Table 3) is relatively large expose the reciprocal semimicelle formation.Due to the requirement of being away from as possible between similar charges this formation leads to a partial expansion at the basal distance.Aer this stage, decrease in concentration gradient leads to the transformation of the structure to pseudotrilayer structure.

SEM Analysis of the Montmorillonite and Organoclay
Samples.SEM images of Mt and OMt samples to determine the surface morphology were taken and these images are given in Figure 5.In the SEM image of Mt sample some phase separations are seen, cracks and generally as a heterogeneous surface morphology.As seen in the SEM image of 0.5 CEC-OMt sample, the particles went to a more compact structure, increased tendency to aggregation and cracks and other defects are greatly reduced according to the Mt pattern.It can be said that compact structure occurs with the lateral interactions of the hydrophobic tails of CTAB on the taktoid surfaces.However, having particles lateral bilayer structure and the fact that the negative value of zeta potential (−15 mV) are considered as a reason for the occurred sharp cracks in the resulting morphology.
Unlike the case of 0.5 CEC-OMt, three-dimensional enlargements took place and structure reminiscent of pseudo-three-layer structures the spherical aggregates formed in the 1.0 CEC-OMt sample and the presence of fractures and faults are observed as a result of the presence of charged groups.
As it is evident from the XRD observations of 1.5 CEC-OMt sample, the spherical aggregates are seen as a result of the planar structures which re�ected the structuring of paraf-�nic monolayer and pseudotrilayer of CTAB (it con�rmed the presence of two different structuring).
e presence of paraffinic bilayer orientation in the case of 2.0 CEC-OMt is clearly seen in the topography of the material.In addition, spherical but dispersed relatively homogeneously, but also be seen the traces of mainly pseudotriple layer orientation.

Conclusions
Systematically investigating the basal spacing evolution of OMt during the intercalation of CTAB can provide novel insight to the microstructures of organo clays.e intercalated CTAB will continue its rearrangement within the interlayer space which can lead to increase of basal spacing value.e interlayer distance of the montmorillonite (OMt) and the packing density of CTA + in the interlayer increases with increased amounts of adsorbed surfactant, as con�rmed by XRD pattern.According to the obtained results from basal spaces in XRD patterns of organoclays, the organic ion possible arrangement model can be considered as lateral bilayer, pseudo-trilayer, paraffin-type monolayer and pseudo trilayer and paraffin-type bilayer and pseudo trilayer for 0.5, 1, 1.5, and 2.0 CEC, respectively.FTIR spectrum and contact angle measurements of pristine montmorillonite and organo clays indicated the incorporation of surfactant and the changing of hydrophility in the different OMts.is study demonstrates that not only the arrangement model of surfactant but also the morphology of organoclay strongly depends on the surfactant packing density within the montmorillonite interlayer space.In addition, it can be also proposed that the surface charge magnitude or its distribution on clay mineral might be an important factor for expansion characteristics of organoclay.

F 2 :
XRD patterns of the pristine montmorillonite and the different organo-clays.

T 4 :
Positions and assignments of the IR vibration bands observed in the range of 400-4000 cm −1 .

F 3 :
FTIR spectra of the pristine montmorillonite and the different organoclays.

F 4 :
e variation of zeta potential and contact angle depend on surfactant loading.

Table
. Chemical composition of