| The montmorillonite/alkylammonium complexes prepared by intercalation of cations of alkyl quaternary ammonium salts with long carbon chain(Nc>12)have satisfactory gelling and adsorption properties, which are used widely in rheological controlling of high grade paints and grease, adsorption of inorganic and organic pollutants and as precursors in the synthesis of polymer intercalated nanocomposites. Therefore, it is of great importance function to research of adsorption of alkylammonium in the montmorillonite interlayers, the structures and performances of montmorillonite/alkylammonium complexes, in order to prepare and apply new type compound mineral materials of montmorillonite/alkylammonium.Using purified montmorillonite as material, adsorption characteristics of alkylammonium in the montmorillonite interlayers, structures and gelling properties of montmorillonite/ alkylammonium complexes are studied systematically. Based on these results, application force and mechanism of adsorption reaction, the relation between structures and gelling properties of montmorillonite/alkylammonium complexes are clarified in this paper.Results of adsorption properties of long-chain alkylammonium cations in the montmorillonite interlayers indicate that fitting effects of Modified Langmuir adsorption model is the best among isothermal adsorption models. OTA has strong affinity to Na-Mont and the OTA adsorption ratio has reached nearly 100% at even lower dosage. Adsorption curve attains the plateau region when dosage of OTA increases equilibrium concentration, namely CMC. The adsorption laws are similar for alkylammoniums with different length and number of carbon chain. At a higher dosage, alkylammonium cations exhibit excessive adsorption characteristics in montmorillonite interlayers. The saturated adsorptive capacities of OTA,CTA,TTA and ODA are 1.85CEC,1.81CEC,1.70CEC and 1.64CEC respectively, exceed the percents of CEC value are 85%,81%,70% and 64%.In order to expose the application force and mechanism, the reaction kinetics and thermodynamics for the alkylammonium adsorption in the montmorillonite interlayers are explored systematically. Reaction kinetics behavior of isothermal adsorption fit in with a second order reaction kinetics equation. The adsorption of alkylammonium cations goes through two stages, including a quick adsorption at beginning and a fluctuation adsorption later. Reaction rate constants have great differences with application force of adsorption process. The results of adsorption thermodynamics show that OTA adsorption in the montmorillonite interlayers is a spontaneous, exothermic reaction, which exists Van der Waals forces, hydrophobic bond forces, hydrogen bond forces and dipole bond forces. Entropy increase is another driving force to promote adsorption. The amount of alkylammonium adsorbed in the montmorillonite interlayers decreases with increasing temperature, thus adsorption amount can be controlled by changing reaction temperature.According to methods of XRD, FTIR, DTA and TG analysis, the influencing factors on amontmorillonite/alkylammonium complexes'structure, including alkylammonium dosage, carbon structure, temperature, pH value and montmorillonite layer charge, are systematically studied. For WF Na-Mont., with the increase of alkylammonium dosage from 0.5CEC to 3.0CEC, the arrangement models for alkylammonium cations in the montmorillonite interlayers are as follows, monolayer→bilayer→pseudotrimolecularlayer→paraffin-type monolayer→micellar structure. In fact, the effect of OTA dosage is realized by changing alkylammonium adsorption amount of montmorillonite interlayers. FTIR analysises prove that the carbon chain configuration of alkylammonium cations can change from liquid-like to solid-like with the alkylammonium dosage and reaction time. The arrangement of alkyl ammonium cations are more orderly.Based on the research of influencing factors of gelling property and its variation laws of montmorillonite/alkylammonium complexes, major influencing factors are obtained, including modification conditions, the alkylammonium structure, montmorillonite layer charge, the alkylammonium adsorption amount and solvent system properties. High pH is favorable to OTA adsorbing on montmorillonite, and it is easier to form stable complex structure in alkaline condition than in acidic condition, in which gelling's viscosity is higher. Montmorillonite with high layer charge can not be well dispersed in water, which influences the alkylammonium cations adsorption, so it cannot form gel with preferable gelling properties, however, intercalation complex with larger basal spacing can be got. Excessive adsorption of alkylammonium produces disadvantage influence on montmorillonite/alkylammonium complexes gelling property. Stable structure and better gelling property are obtained when the OTA dosage is 1.1CEC. Gelling's viscosity is higher in the strong polar organic solvent system. As the polarity of benzene series solvents increases, the viscosity rises steeply. Addition of activators can improve the viscosity significantly, and the activation performance of ethanol as activator is better than methanol. |
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