Relationship between the Continually Expanded Interlayer Distance of Layered Silicates and Excess Intercalation of Cationic Surfactants

Abstract

Excess intercalation of cationic surfactants into Na+-montmorillonites (MMTs) was investigated in organically modified silicates (OMSs), synthesized with MMTs and octadecylammonium chloride (OAC) by systematically varying the surfactant loading level from 0.625 to 1, 1.25, 1.56, 2, and 2.5 with respect to the cation exchange capacity (CEC) of MMTs. Wide-angle X-ray diffraction and thermogravimetric analysis results indicated that the continuous increase of interlayer distances came from the entering of surfactants into the interlayer of MMTs. Excess surfactants were extracted with a Soxhlet apparatus, which showed two kinds of intercalation states of surfactants in the interlayer when the surfactant loading level was beyond the CEC. Fourier transform infrared spectroscopy and differential scanning calorimetry were used to explore the microstructures of OMSs. It was found that the surfactants arranged more orderly as the loading level increased and the excess surfactants piled up in the interlayer together with counterions, forming a sandwiched surfactant layer. On the basis of the results, the layer structures of OMSs and the mechanism by which the surfactants entered the interlayer were expounded: surfactant cations entered the interlayer through cation exchange reactions and were tightly attracted to the silicate platelet surfaces when the surfactant loading level was below the CEC; however, excess cationic surfactants entered the interlayer together with counterions through hydrophobic bonding and formed a sandwiched layer in the interlayers, leading to a continuous increase of the interlayer distance, when the surfactant loading level was beyond the CEC.

Characterization of organic phases in the interlayer of montmorillonite using FTIR and 13C NMR

“…This reflects that, even in the sample HM5.0CEC with the most ordered conformation and highest surfactant loading level, the local molecular environment is different from that of the crystalline. Meanwhile, we can find that ΔδC 16 is bigger than ΔδC 15 , indicating that there is much mobility for C 16 than that for C 15 . This provides the supporting evidence for the proposal that the tail of alkyl chain is movable even in higher packing density of the intercalated surfactants [4].…”

“…Figure 1 displays the C-H stretching vibration of the infrared spectrum (3300-2700 cm -1 ) of the CTMAB/Montmorillonite hybrids with different surfactant loading levels. The bands at ~2920 cm -1 and ~2850 cm -1 correspond to CH 2 asymmetric stretching mode (ν as (CH 2 )) and symmetric stretching mode (ν s (CH 2 )), respectively [8,15]. With the increase of the surfactant loading level and interlayer packing density, ν as (CH 2 ) shifts from 2926 to 2919 cm -1 and ν s (CH 2 ) shift from 2854 to 2850 cm -1 for the specimen from HM0.2CEC to HM5.0CEC (Table 1).…”

The interlayer swelling and molecular packing in organoclays

“…The swelling of clay minerals, e.g., sodium montmorillonite, upon the exchange of interlayer metal cations with organic surfactant cations (commonly alkyl ammoniums) has been extensively studied since the 1940s [1][2][3][4][5][6][7][8][9][10][11]. It is generally accepted that the extent of swelling depends on the length of the alkyl chain and the cation-exchange capacity (CEC) of the clay.…”

Characterization of cetylpyridinium bromide-modified montmorillonite incorporated cellulose acetate nanocomposite films

“…The organoclay shows characteristic band of MMT and surfactant. However, bands associated to C-H vibrations of methylene groups of alkyl chain from surfactant between 3000-2800 cm -1 (asymmetric and symmetric stretching) and 1520-1440 cm -1 (bending) have been recognized as the most important bands to confirm the organoclay formation [29][30][31]. The rest of signals from synthesized organoclays are according with vibrational bands characteristic of the clays, such as 3630 cm -1 (Al-OH stretching), 3427 cm -1 (-OH stretching from interlayer water), 1638 cm -1 (-OH bending from absorbed water), 1048 cm -1 (Si-O stretching), 917 cm -1 (Al-Al-OH bending), 522 cm -1 (Si-O-Al bending), and 463 cm -1 (Si-O bending) [29,30,32,33].…”