Self-assembling of tetradecylammonium chain on swelling high charge micas (na-mica-3 and na-mica-2): Effect of alkylammonium concentration and mica layer charge

1 Self-assembling of tetradecylammonium chain on 1 swelling high charge micas (Na-Mica-3 and Na-2 Mica-2): Effect of alkylammonium concentration 3 and mica layer charge 4 M. Carolina Pazos,1 Agustín Cota,2 Francisco J. Osuna, 3 Esperanza Pavón,3,4 María D. Alba*,3 5 1 Escuela de Ciencias Químicas, Universidad Pedagógica y Tecnológica de Colombia UPTC. 6 Avda. Central del Norte, Vía Paipa,Tunja, Boyacá, Colombia. 7 2 Laboratorio de Rayos-X. Centro de Investigación, Tecnología e Innovación de la Universidad 8 de Sevilla (CITIUS), Universidad de Sevilla. Avda. Reina Mercedes, 4, 41012 Sevilla, Spain. 9 3 Instituto Ciencia de los Materiales de Sevilla (ICMS), Consejo Superior de Investigaciones 10 Científicas-Universidad de Sevilla, Avda. Américo Vespucio, 49, 41092 Sevilla, Spain. 11 4 Centers for the Development of Nanoscience and Nanotechnology, CEDENNA, 9170124 12 Santiago, Chile. 13 14 KEYWORDS. Organomica, hydrophobicity, alkylammonium, cation exchange capacity, 15 swelling high-charged micas. 16 17 2 ABSTRACT. A family of tetradecylammonium micas is synthesized using synthetic swelling 18 micas with high layer charge (NanSi8-nAlnMg6F4O20·XH2O, where n= 2 and 3) exchanged with 19 tetradecylammonium cations. The molecular arrangement of the surfactant is elucidated on the 20 basis of XRD patterns and DTA. The ordering conformation of the surfactant molecules into the 21 interlayer space of micas is investigated by IR/FT, 13C, 27Al and 29Si MAS NMR. The structural 22 arrangement of the tetradecylammonium cation in the interlayer space of high-charge micas is 23 more sensitive to the effect of the mica layer charge at high concentration. The surfactant 24 arrangement is found to follow the bilayer-paraffin model for all values of layer charge and 25 surfactant concentration. However, at initial concentration below the mica CEC a lateral 26 monolayer is also observed. The amount of ordered conformation all-trans is directly 27 proportional of the layer charge and surfactant concentration. 28 29 30 3 INTRODUCTION 31 The term organoclays (OC) denotes a family of hydrophobic materials, obtained by modifying 32 clays and clay minerals with various organic compounds through intercalation processes and 33 surface grafting.1,2,3,4,5 Organoclays have important practical applications, notably as adsorbents 34 of organic pollutants6,7,8,9 and as components in the formation of clay polymer 35 nanocomposites2,10,11,12. A large volume of literature has been accumulated over the past two 36 decades on various aspects of OC research, including i) synthesis and characterization4,13,14; ii) 37 surface properties and stability4,13,14; iii) production of clay-based nanocomposites10,11,12,15; and 38 iv) synthesis of novel materials using the OC as precursors16,17. 39 A more recent development that has attracted much interest is the organo-functionalization of a 40 new family of swelling high-charged micas.18,19,20 Those synthetic micas have a charge density 41 similar to brittle micas but with a higher swelling capacity, higher crystallinity and controllable 42 composition.21,22,23 In this way, those synthetic micas overcome some limitations of the natural 43 clay minerals to be used as host materials. 44 Dodecylammonium and octadecylammonium have been successfully intercalated in the 45 interlayer space of a whole family of synthetic high-charge mica. In all case, a paraffin-type 46 bilayer structure was observed with a tilt angle between 51º and 65º.19,20 However, the structural 47 arrange of alkylammonium in the interlayer space for the lowest chain length (12 vs 18 carbon 48 atoms) was more sensitive to the mica charge because the adsorbed amount of alkylammonium 49 was slightly less than the cation exchange capacity of mica. In the case of the highest chain 50 length (18 vs 12 carbon atoms), alkylammonium was adsorbed by: exchange reaction and on the 51 surface by hydrophobic interaction.20 52 4 Many studies have been performed to analyze the effect of alkyl chain length,24,25,26,27 the 53 species of cationic surfactant28,29, and its concentration30,31,32 on the d-spacing and the alkyl chain 54 arrangements on organoclays. Among them, the most important factor was found to be the 55 surfactant concentration. Lagaly33 reported that the surfactant package on clay minerals changes 56 from a lateral monolayer to a lateral bilayer, and, finally to a pseudotrimolecular layer or a 57 paraffin-type monolayer depending on the nature of surfactant and layered silicate. Later on, also 58 the d-spacing was found to increase with the increment on the surfactant concentration, allowing 59 the alkyl chains to adopt a paraffin-type bilayer with a tilting angle of 35° at a surfactant 60 concentration higher than its exchange capacity (CEC).34 Moreover, this alkyl chain arrangement 61 but with a larger tilting angle (60°) has also been reported in KNiAsO4.35 However, the effect of 62 surfactant concentration on the hydrophobicity, d-spacing and alkyl chain arrangement of 63 modified swelling high-charged micas has not been analyzed yet. 64 Thus, the aim of this work is to evaluate the arrangement and interlayer properties of different 65 swelling high charge micas, Na-Mica-n (n is the layer charge; n=2 and 3), as a function of 66 alkylammonium concentration and mica layer charge. Based on our previous work,20 67 tetradecylammonium has been chosen, it has an carbon chain length between the 12 and 18 as 68 previously analyzed, to satisfy the 0.5-10 CEC of the micas. 69 70 EXPERIMENTAL DETAILS 71 a. Materials. Na-Mica-n (n=2 and 3) were synthesized using the NaCl-melt method following 72 a similar procedure to that described by Alba et al.23 Their structural formulae are Nan[Si8- 73 nAln]Mg6O20F4·zH2O,where n represent the charge per unit cell (n=2 and 3) and z is the number 74 of water molecules. The starting materials employed were SiO2 (Sigma; CAS no. 112945-52-5, 75 5 99.8% purity), Al(OH)3 (Riedel-de Haën; CAS no. 21645-51-2, 99% purity), MgF2 (Aldrich; 76 CAS no. 20831-0, 98% purity), and NaCl (Panreac; CAS no. 131659, 99.5% purity). 77 Stoichiometric proportions of reactants were weighed and mixed in an agate mortar. The molar 78 ratio between the reactants were (8-n)SiO2:(n/2)Al2O3:6MgF2:(2n)NaCl. It was added twice the 79 amount of NaCl to ensure the complete charge balance with Na+ cation into the interlayer 80 space.36 The optimal amount of mixture reaction for grinding was up to 2 g per batch during 30 81 min for ensuring the homogeneity of the mixture in an agate mortar. The heat treatments were 82 carried out in a closed Pt crucibles at 900 ºC during 15 h using a heating rate of 10 ºC·min-1. The 83 product was washed with distilled water and the solid was separated by filtration, dried at room 84 temperature and then ground in the agate mortar. 85 b. Preparation of tetradecylammonium micas. The organomicas were prepared by a cation-86 exchange reaction between the micas and variable concentration of tetradecylammonium salt to 87 satisfy the 0.5, 1, 2, 3 or 10 times the cation exchange capacity (CEC) of Na-Mica-n. Thus, the 88 primary amine was dissolved in an equivalent amount of HCl (0.1 M) and the resulting mixture 89 stirred for 3 h at 80 °C. The tetradecylammonium dispersion was then mixed with 0.6 g of Na-90 Mica-n and stirred for 3 h at 80 °C. After adding hot deionized water, the mixture was stirred for 91 30 min at 50 °C and then the dispersion was centrifuged at 10,000 r.p.m. for 20 minutes. The 92 product was dissolved in a hot ethanol-water mixture (1:1) and stirred for 1 h at 50 ºC and then 93 centrifuged.13 The precipitate was dried at room temperature. The sample will be named as C14-94 Mica-n-m; where n is the interlayer charge 2 or 3 and m is the initial concentration of the 95 tetradecylammonium salt (m=0, 0.5, 1, 2, 3 and 10 CEC). The samples C14-Mica-n-0 96 corresponds to the as-synthesized sample Na-Mica-n. 97 6 c. Techniques. Simultaneous TG/DTA measurements were performed at the Departamento de 98 Cristalografía, Mineralogía y Química Agrícola (University of Seville, Spain) using a NETZSCH 99 (STA 409 PC/PG) instrument which is equipped with a Pt/Pt-Rh thermocouple for direct 100 measurement of the temperature at the sample/reference crucible from room temperature up to 101 900 °C (heating rate: 10 °C·min–1) in an atmosphere of N2. Approximately 150 mg of sample 102 was used and the DTA reference was pure aluminum oxide. 103 X-ray diffraction (XRD) patterns were obtained at the CITIUS X-ray laboratory (University of 104 Seville, Spain) on a Bruker D8 Advance instrument equipped with a Cu K radiation source 105 operating at 40 kV and 40 mA. Diffractograms were obtained in the 2 range of 1–70° with a 106 step size of 0.05° and a step time of 3.0 s. 107 FTIR spectra were recorded in the range 4000–300 cm–1 by the Spectroscopy Service of the 108 ICMS (CSIC-US, Seville, Spain), as KBr pellets, using a Nicolet spectrometer (model 510P) 109 with a nominal resolution of 4 cm–1. 110 Single-pulse (SP) MAS-NMR experiments were recorded on the samples where the 111 tetradecylammonium concentration were the lowest and the highest because they should exhibit 112 appreciable differences at short-range order, C14-Mica-n-m (n=2 and 3; m=0.5 and 10 CEC), the 113 C14-Mica-n-2 was also measured for comparison with previous works19,20. The measurements 114 were carried out on the Spectroscopy Service of the ICMS (CSIC-US, Seville, Spain) using a 115 Bruker DRX400 spectrometer equipped with a multinuclear probe. Powdered samples were 116 packed into 4-mm zirconia rotors and spun at 10 kHz. 27Al MAS NMR spectra were acquired at 117 a frequency of 104.26 MHz, using a pulse width of 0.92 μs (π/2 pulse length = 9.2 μs) and a 118 delay time of 0.1 s. 23Na MAS NMR spectra were recorded at 105.84 MHz with pulse widths of 119 2.0 μs (π/2 pulse length=12.0 μs) and a delay time of 0.1 s. 29Si MAS NMR spectra were 120 7 acquired at a frequency of 79.49 MHz, using a pulse width of 2.7 μs (π/2 pulse length = 7.1 μs) 121 and a delay time of 3 s. 13C MAS NMR spectra were recorded at 104.26 MHz with proton 122 decoupling, a pulse width of 2.5 μs (π/2 pulse length = 7.5 μs) and a delay time of 2 s. The 123 chemical shift values are reported in ppm with respect to 0.1 M AlCl3 solution for 27Al, 0.5 M 124 NaCl solution for 23Na and tetramethylsilane for 29Si and 13C. 125 126 RESULTS AND DISCUSSIONS 127 a. Adsorption in the interlayer space of organomicas: Hydrophobicity and stability. To 128 investigate the structure and properties of the tetradecylammonium molecules adsorbed onto Na-129 Mica-n, the adsorbed amount of the organic cations are monitored by TG.37,38,39 Table 1 shows 130 the content of water and surfactant obtained from the analysis of the TG curves, where the 131 amount of interlayer water is determined from the weight loss in the temperature range of 25–132 170 °C and the amount of the adsorbed tetradecylammonium molecules is determined from the 133 weight loss between 170 and 900 °C.40 134 The amount of adsorbed tetradecylammonium is higher in C14-Mica-3 than in C14-Mica-2, 135 thus, the main adsorption may occur by cation exchange, and this adsorption is proportional to 136 the initial concentration of alkylammonium. In C14-Mica-n-m (m<2), tetradecylammonium is 137 adsorbed in less amount than their CEC (ca. 0.60 CEC for m=0.5 and ca. 0.95 CEC for m=1). At 138 m≥2 the alkylammonium cations adsorption exceeds the mica exchange capacity and this excess 139 is stabilized by van der Waals interactions between alkyl chains. 41,42,43,44 This excess is only 140 slightly higher than the CEC for C14-Mica-3-m, for m=2 and 3, but is five time higher than CEC 141 for m=10. The alkylammonium concentration necessary to satisfy the layer charge is higher for 142 8 C14-Mica-3 and, thus, the packing density is higher and the van der Waals interactions between 143 alkyl chains are favored. 144 DTG analysis (Figure 1) suggests two distinct states for the intercalated surfactant molecules: 145 (i) the first one is associated to the thermal decomposition of intercalated alkylammonium, with 146 stronger interaction, and, thus, requires a higher temperature (442 ºC) to decompose45,46, and, (ii) 147 the second one is due to the presence of ion-pair alkylammonium ions,20 with weaker interaction, 148 whose decomposition temperature is slightly lower (ca. 350 ºC). For m=0.5 only the 149 decomposition at the higher temperature is observed and agrees with the adsorption of surfactant 150 of ca. 60 % of their CEC (Table 1). As the initial concentration of alkylammonium increases the 151 decomposition at lower temperature is more relevant and becoming the dominant process for 152 C14-Mica-3-10. 153 Mica surface properties can be altered from hydrophilic to organophilic by the exchange of the 154 hydrated Na+ interlayer cation by an organic one,47 and consequently causing a drastic 155 diminishing of the water content. Thus, whereas the water content on Na-Mica-n-0 is found to be 156 between 3.17 and 3.63 molecules per unit cell; it decreases on C14-Mica-n-m due to the 157 replacement of Na+ for the organic cations favoring the hydrophobic character of the interlayer 158 space (Table 1). For m≤1, a gradual decrease of interlayer water with alkylammonium 159 concentration is observed, being in concordance with an increasing in the exchange of inorganic 160 cations by the organic ones. However, for m≥2, the amount of water slightly increases with 161 alkylammonium concentration due to that is adsorbed not only by cation exchange reaction but 162 also by ionic pair which could adsorb some water molecules in the hydrophilic head of the 163 cationic surfactant. 164 9 The hydrophilic character of the interlayer space after the adsorption of different 165 concentrations of tetradecylammonium can be explained from the analysis of the 23Na MAS 166 NMR spectra (Figure 2). The 23Na MAS NMR spectra of C14-Mica-n-0 (Na-Mica-n) is 167 characterized by two signals one at 3.7 ppm due to sodalite48, and other at -10.1 ppm due to fully 168 hydrated exchangeable sodium49,50. When the initial concentration of the alkylammonium 169 increases the signal of interlayer sodium decreases, this effect is more evident as the layer charge 170 increases. It corroborates the increasing hydrophopic character of the interlayer space and that 171 the slightly increasing of water content observed for m≥2 (see Table 1) is due to water associated 172 at ionic pair tetradecylammonium. The interlayer sodium is completely replaced in C14-Mica-3-173 10 in good agreement with the extremely high content of adsorbed tetradecylammonium (Table 174 1). 175 b. Tetradecylammonium package on organomicas. The analysis of the 00l reflections of the 176 XRD patterns (Figure 3) can be shed a light on the long-range structural order of the 177 organomicas. The basal spacing of Na-Mica-n is 1.20 nm, which corresponds to Na+ in the 178 interlayer space surrounded by one water pseudomonolayer.23 The exchange reaction between 179 Na+ and the tetradecylammonium cation causes an increase in the basal spacing (d001). An unique 180 and well-ordered sequence of the 00l reflections is only observed for the C14-Mica-3-10, and that 181 corresponds to a basal spacing of 4.02 nm, an interlayer gallery height of 3.08 nm (Table 2), 182 compatible with paraffinic bilayer -type structures.51,52,53 Paul et al.54 observed that the surfactant 183 molecules adopt an arrangement that allow them to pack efficiently; therefore, the maximum 184 concentration of adsorbed tetradecylammonium in C14-Mica-3-10 could favor a high and ordered 185 packing which is reflected in a well-ordered sequence of the 00l reflections. However, in the 186 other C14-Mica-n-m, at least two 00l reflections sequences are observed. The splitting of the 00l 187 16 (13) Lagaly, G. Characterization of clays by organic compounds. Clay Miner. 1981, 16, 1–21. (14) Zhu, J.X.; He, H.P.; Guo, J.G.; Yang, D.; Xie, X.D. Arrangement models of alkylammonium cations in the interlayer of HDTMA+ pillared montmorillonites. Chin. Sci. Bull. 2003, 48, 368–372. (15) Lambert, J.F.; Bergaya, F. Smectites-Polymer Nanocomposites, Chapter 13.1, Handbook of Clay Science, In: Bergaya, F., Lagaly, G. (Eds.), 2nd edition. Developments in Clay Science, vol. 5A. Elsevier, 2013; pp. 699–706. (16) Bergaya, F.; Lagaly, G. Intercalation Processes of Layered Minerals, in Layered Mineral Structures and Their Application in Advanced Technology. Chapter 6 In: Brigatti, M.F., Mottana, A. (Eds.), EMU notes in Mineralogy, 2011, vol. 11, pp. 259–284. (17) Ishii, R.; Nakatsuji, M.; Ooi, K. Preparation of highly porous silica nanocomposites from clay mineral: a new approach using pillaring method combined with selective leaching. Micro. Meso. Mater. 2005, 79, 111–119. (18) Franklin, K.R.; Lee, E. Synthesis and ion-exchange properties of Na-4-mica. J. Mater. Chem. 1996, 6, 109-115. (19) Alba, M.D.; Castro, M.A.; Orta, M.M.; Pavón, E.; Pazos, M.C.; Valencia, J.S. Formation of Organo-Highly Charged Mica. Langmuir 2011, 27, 9711-9718. (20) Pazos, M.C.; Castro, M.A.; Orta, M.M.; Pavón, E.; Valencia, J.S.; Alba, M.D. Synthetic High-Charged Organomica: Effect of the Layer Charge and Alkyl Chain Length on the Structure of the Adsorbed Surfactants. Langmuir 2012, 28, 7325-7332. (21) Kodama, T.; Komarneni, S. Na-4-mica: Cd2+, Ni2+, Co2+, Mn2+ and Zn2+ ion exchange. J. Mater. Chem. 1999, 9, 533-539. 17 (22) Park, M.; Lee, D.H.; Choi, C.I.; Kim, S.S.; Kim, K.S.; Choi, J. Pure Na-4-mica: Synthesis and Characterization. Chem. Mater. 2002, 14, 2582-2589. (23) Alba, M. D.; Castro, M. A.; Naranjo, M.; Pavón, E. Hydrothermal Reactivity of Na-n-Micas (n = 2, 3, 4) Chem. Mater. 2006, 18, 2867-2872. (24) Yilmaz, N.; Yapar, S. Adsorption properties of tetradecyl- and hexadecyl trimethylammonium bentonites. Appl. Clay Sci. 2004, 27, 223–228. (25) Calderon, J.U.; Lennox, B.; Kamal, M.R. Thermally stable phosphonium-montmorillonite organoclays. Appl. Clay Sci. 2008, 40, 90–98. (26) Chen, H.; Zhou, L.M.; Jiang, X.H.; Lu, F.; Zhou, Y.F.; Yin, W.M.; Ji, X.Y. Modification of montmorillonite surfaces using a novel class of cationic gemini surfactants. J. Coll. Inter. Sci. 2009, 332, 16–21. (27) Frost, R.L.; Xi, Y.F.; He, H.P. Modification of the surfaces of Wyoming montmorillonite by the cationic surfactants alkyl trimethyl, dialkyl dimethyl, and trialkylmethyl ammonium bromides. J. Coll. Inter. Sci. 2007, 305, 150–158. (28) Duchet-Rumeau, J.; Livi, S.; Pham, T.N.; Gerard, J.F. A comparative study on different ionic liquids used as surfactants: Effect on thermal and mechanical properties of high-density polyethylene nanocomposites. J. Coll. Inter. Sci. 2010, 349, 424–433. (29) Tiwari, R.R.; Khilar, K.C.; Natarajan, U. Synthesis and characterization of novel organomontmorillonites. Appl. Clay Sci. 2008, 38, 203–208. (30) Lagaly, G. Inorganic layer compounds. Die Naturwissenschaften 1981, 68, 82–88. (31) Wen, X.; He, H.; Zhu, J.; Jun, Y.; Ye, C.; Deng, F. Arrangement, conformation, and mobility of surfactant molecules intercalated in montmorillonite prepared at different pillaring 18 reagent concentrations as studied by solid-state NMR spectroscopy. J. Coll. Inter. Sci. 2006, 299, 754–760. (32) Xi, Y.F.; Frost, R.L.; He, H.P.; Kloprogge, T.; Bostrom, T. Modification of Wyoming montmorillonite surfaces using a cationic surfactant. Langmuir 2005, 21, 8675–8680. (33) Lagaly, G. Interaction of alkylamines with different types of layered compounds. Sol. State Ionics 1986, 22, 43–51 (34) Yui, T.; Yoshida, H.; Tachibana, H.; Tryk, D.A.; Inoue, H. Intercalation of polyfluorinated surfactants into clay minerals and the characterization of the hybrid compounds. Langmuir 2002, 18, 891–896. (35) Beneke, K.; Lagaly, G. The Brittle Mica-Like KNiAsO4 and its Organic Derivatives. Clay Miner. 1982, 17, 175–183. (36) Esfandiari, A.; Nazokdast, H.; Rashidi, A. S.; Yazdanshenas, M. E. Review of polymerorganoclay nanocomposites. J. Appl. Sci. 2008, 8, 545-561. (37) Osman, M. A.; Seyfang, G.; Suter, U. W. Two-Dimensional Melting of Alkane Monolayers Ionically Bonded to Mica. J. Phys. Chem. B 2000, 104, 4433-4439. (38) Osman, M. A.; Suter, U. W. Surface Treatment of Calcite with Fatty Acids: Structure and Properties of the Organic Monolayer. Chem. Mater. 2002, 14, 4408-4415. (39) Osman, M. A.; Ploetze, M.; Suter, U. W. Surface treatment of clay minerals — thermal stability, basal-plane spacing and surface coverage. J. Mater. Chem. 2003, 13, 2359-2366. (40) Xie, W.; Gao, Z.; Pan, W. P.; Hunter, D.; Singh, A.; Vaia, R. Thermal Degradation Chemistry of Alkyl Quaternary Ammonium Montmorillonite. Chem. Mater. 2001, 13, 2979- 2990. 19 (41) Narine, D. A.; Guy, R. D. Interactions of some large organic cations with bentonite in dilute aqueous systems. Clays Clay Miner. 1981, 29, 205-212. (42) Rosen, M. J. Surfactants and Interfacial Phenomena; ed. John Wiley & Sons, New York, 1999 (43) Tahani, A.; Karroua, M.; van Damme, H.; Levitz, P.; Bergaya, F. Adsorption of a Cationic Surfactant on Na-Montmorillonite: Inspection of Adsorption Layer by X-Ray and Fluorescence Spectroscopies. J. Colloid Interface Sci. 1999, 216, 242-249. (44) Ijdo, W. L.; Pinnavaia, T. J. Staging of Organic and Inorganic Gallery Cations in Layered Silicate Heterostructures. J. Solid State Chem. 1998, 139, 281-289. (45) Onal, M. Examination of some commercial sorptive organobentonites. Turk. J. Chem. 2007, 31, 579-588. (46) Yariv, S. The role of charcoal on DTA curves of organo-clay complexes: an overview. Appl. Clay Sci. 2004, 24, 225-236. (47) Jaynes, W. F.; Boyd, S. A. Clay Mineral Type and Organic Compound Sorption by Hexadecyltrimethylammonium-Exchanged Clays. Soil Sci. Soc. Am. J. 1991, 55, 43-48. (48) Johnson, G.M.; Mead, P. J.; Dann, S. E.; Weller, M. T. Multinuclear MAS NMR studies of sodalitic framework materials. J. Phys. Chem. B 2000, 104, 1454-1463. (49) Zeng, Z.; Matuschek, D.; Studer, A.; Schwicker, C.; Pöttgen, R.; Eckert, H. Synthesis and characterization of inorganic-organic hybrid materials based on the intercalation of stable organic radicals into a fluoromica clay. Dalton Trans. 2013, 42, 8585-8596. (50) Casal, B.; Aranda, P.; Sanz, J.; Ruiz-Hitzky, E. Interlayer adsorption of macrocycliccompounds (crown-ethers and cryptands) in 2/1 phyllosilicates .2. Structural features. Clay Miner. 1994, 29, 191-203. 20 (51) Brindley, G. W. Complexes of primary amines with montmorillonite and vermiculite. Clay Miner. 1965, 6, 91-96. (52) Johns, W. D.; Sen Gupta, P. K. Vermiculite-alkyl ammonium complexes. Am. Mineral. 1967, 52, 1706-1724. (53) Brindley, G.W.; Hofmann R.W. Orientation and packing of aliphatic chain molecules on montmorillonite: in Clays and Clay Minerals, Proc. 9th Natl. Conf. West Lafayette, Indiana, 1960, Ada Swineford, ed., Pergamon Press, New York, 1962, 546-556. (54) Paul, D.R.; Zeng, Q.H.; Yu, A.B.; Lu, G.Q. The interlayer swelling and molecular packing in organoclays. J. Coll. Inter. Sci. 2005, 292, 462-468. (55) Lagaly, G.; Weiss, A. Arrangement and orientation of cationic tensides on silicate surfaces. 3. Paraffin-like structures in alkylammonium layer-silicates with an average layer load (vermiculite). Kolloid Z. Z. Polym. 1970, 238, 485-&. (56) Fornes, T.D.; Yoon, P.J.; Hunter, D.L.; Keskkula, H.; Paul, D.R. Effect of organoclay structure on nylon 6 nanocomposite morphology and properties. Polymer 2002, 43, 5915-5933. (57) Casal, H.L.; Mantsch, H.H.; Cameron, D.G.; Snyder, R.G. Interchain vibrational coupling in phase-II(hexagonal) n-alkanes J. Chem. Phys. 1982, 7, 2825-2830. (58) Venkataraman, N.V.; Vasudevan, S. Conformation of methylene chains in an intercalated surfactant bilayer. J. Phys. Chem. B 2001, 105, 1805-1812. (59) Weers, J.G.; Scheuing, D.R. Fourier Transform Infrared Spectroscopy in Colloidal and Interface Science, in: D.R. Scheuing (Ed.), ACS Symposium Series 447, American Chemical Society,Washington, DC, 1990; p. 87. (60) Li, Z.; Jiang, W.T.; Hong, H. An FTIR investigation of hexadecyltrimethylammonium intercalation into rectorite. Spectrochim. Acat A. 2008, 71, 1525-1534. 21 (61) Wang, L.Q.; Liu, J.; Exarhos, G.J.; Flanigan, K.Y.; Bordia, R. Conformation Heterogeneity and Mobility of Surfactant Molecules in Intercalated Clay Minerals Studied by Solid-State NMR. J. Phys. Chem. B. 2000, 104, 2810-2816. (62) Vaia, R. A.; Teukolsky, R. K.; Giannelis, E. P. Interlayer Structure and Molecular Environment of Alkylammonium Layered Silicates. Chem. Mater. 1994, 6, 1017-1022. (63) Yu, X.; Zhao, L.; Gao, X.; Zhang, X.; Wu, N. The intercalation of cetyltrimethylammonium cations into muscovite by a two-step process: II. The intercalation of cetyltrimethylammonium cations into Li-muscovite. J. Solid State Chem. 2006, 179, 1525-1535. (64) He, H.; Frost, R. L.; Deng, F.; Zhu, J.; Wen, X.; Yuan, P. Conformation of Surfactant Molecules in the Interlayer of Montmorillonite Studied by 13C MAS NMR. Clays Clay Miner. 2004, 52, 350-356. (65) Engelhardt, G.; Michel, D. High Resolution Solid State NMR of Silicates and Zeolites. Ed. Wiley, New York. 1987. (66) Pavón, E.; Castro M.A.; Naranjo, M.; Orta, M.M.; Pazos, M.C.; Alba, M.D. Hydration properties of the synthetic high-charge micas saturated with different cations: An experimental approach. Amer. Miner. 2013, 98, 394-400. 22 Table 1. Water and tetradecylammonium contents of the C14-Mica-n-m (n=2 and 3) nm 25º-170º C 170º-900º C % mol H2O/ mol mica[b] %[a] mol C14/ mol mica[b] %CEC 2 0 6.6 3.17 0.9 - -- 0.5 2.2 1.30 24.7 1.20 60.0 1 0.1 0.07 34.7 1.90 95.0 2 0.3 0.21 39.4 2.30 114.8 3 0.4 0.28 40.2 2.36 118.2 10 0.3 0.23 44.9 2.83 141.6 3 0 7.3 3.63 1.2 - -- 0.5 3.5 2.40 34.1 1.90 63.4 1 0.0 0.00 44.3 2.84 94.7 2 0.3 0.26 51.2 3.65 121.7 3 0.3 0.25 50.7 3.59 119.5 10 0.7 1.46 87.1 15.18 506.1 [a] % weight loss of the dry samples [b] It has been calculated taking into account the unit cell formulae (C14)mNanm (Si8-nAln)Mg6O20F4; n=2 or 3 23 Table 2. Geometrical and Package Parameters of the C14-Mica-n-m (n=2 and 3) C14-Mica-2 C14-Mica-3 m 0.5 1 2 3 10 0.5 1 2 3 10 d001 (nm) 3.51i 2.48ii* 1.43iii 4.08i 2.65ii* 4.19i 3.06ii* 4.06i 3.14ii* 4.18i* 3.63ii* 3.13iii 2.40iv 3.50i* 2.56ii 1.34iii 4.05i* 2.99ii 2.66iii 4.18i* 3.06ii 4.05i* 3.49ii 3.01iii 4.02 h[a] (nm) 2.57 1.54* 0.49 3.14 1.71* 3.25 2.12* 3.12 2.20* 3.24* 2.69* 2.19 1.46 2.56* 1.62 0.40 3.11* 2.05 1.72 3.24* 2.12 3.11* 2.55 2.07 3.08 V[b] (nm3) 1.27 0.76* 0.24 1.55 0.84* 1.61 1.05* 1.54 1.09* 1.60* 1.33* 1.08 0.72 1.26* 0.80 0.20 1.54* 1.01 0.85 1.60* 1.05 1.54* 1.26 1.02 1.52 α[c] (º) 42.70 23.97* -- 55.94 26.82* 59.04 34.01* 55.41 35.48* 58.75* 45.22* 35.30 22.66 42.49* 25.31 -- 55.14* 32.74 26.99 58.75* 34.01 55.14* 42.29 33.10 54.36 [i-iv] from the [00l]i-iv planes of Figure 3 * from the most intense 00l reflection [a] h=d001-0.94 and it is the high of interlayer gallery [b] V=h·a·b (a=0.534 nm, b=0.925 nm) and it is the interlayer volume [c] h=2·[(nc-1)·0.126+0.131]·sinα; where α is the tilt angle of the alkylchain and nc is the number of carbon atoms in the alkyl chain (nc=14) 24 FIGURE CAPTIONS Figure 1. DTG curves of the C14-Mica-n-m (n=2 or 3 and m=0.5, 1, 2, 3 and 10 CEC) in the tetradecylammonium decomposition temperature range. Figure 2. 23Na MAS NMR spectra of the C14-Mica-n-m (n=2 or 3 and m=0, 0.5, 1, 2, 3 and 10 CEC). Figure 3. XRD patterns of the C14-Mica-n-m (n=2 or 3 and m=0, 0.5, 1, 2, 3 and 10 CEC). Figure 4. The methylene scissoring vibrational region of the IR/FT spectra of the C14-Mica-n-m (n=2 or 3 and m=0.5, 1, 2, 3 and 10 CEC). Figure 5. Internal methylene groups region of the 13C MAS NMR raw spectra (left) and deconvoluted spectra (right) of the C14-Mica-n-m (n=2 or 3 and m=0.5, 2 and 10 CEC). The light grey area corresponds to the trans configuration contribution (It) and the dashed light grey area corresponds to the trans-gauche configuration contribution (It-g). Figure 6. 29Si MAS NMR spectra of the C14-Mica-n-m (n=2 or 3 and m=0, 0.5, 2 and 10 CEC). Dashed line indicates the Q3(qAl) environments. 25 Figure 1