The effect of cationic, non-ionic and amphiphilic surfactants on the intercalation of bentonite

Surfactant-clay interactions are key for the development of new clay applications and inorganic-organic nanocomposites. Bentonite, with montmorillonite as the principal clay mineral constituent, was modified with varying concentrations of hexadecethyltrimethylammonium chloride (HDTMA), as a reference cationic surfactant, polypropylene glycol (PPG) 1200 and 2000, as non-ionic surfactants, and lecithin and Topcithin®, as amphiphilic phospholipid surfactants, according to the cation exchange capacity (CEC). The modified bentonites were characterised by X-ray diffraction, thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectrometry, specific surface area and pore volume. Three intercalation regions have been identified depending on the surfactant. The non-ionic surfactant caused only a crystalline expansion of bentonite interlayers, while the cationic surfactant induced an osmotic intercalation. The amphiphilic lecithin derivatives intercalated more extensively with the bentonite matrix. The TGA and the FTIR spectra showed that, at lower concentrations, the PPGs and HDTMA adopted a disordered conformation that required more energy to degrade, while at higher concentrations, the surfactants were ordered in the interlayer space of the bentonite. The lecithin derivative surfactant had a greater thermal and conformation stability. The specific surface area reduced with increasing surfactant concentrations. This study highlights the effect of surfactant type on the interlayer space of montmorillonite in the perspective of developing novel clay functions. © 2013.

Energy scattering in weakly non-linear systems.

The Chinese Tam-Tam exhibits non-linear behavior in its vibro-acoustic response. The frequency content of the response during free, unforced vibration smoothly changes, with energy being progressively smeared out over a greater bandwidth with time. This is used as a motivating case for the general study of the phenomenon of energy cascading through weak nonlinearity. Numerical models based upon the Fermi-Pasta-Ulam system of non-linearly coupled oscillators, modified with the addition of damping, have been developed. These were used to study the response of ensembles of systems with randomized natural frequencies. Results from simulations will be presented here. For un-damped systems, individual ensemble members exhibit cyclical energy exchange between linear modes, but the ensemble average displays a steady state. For the ensemble response of damped systems, lightly damped modes can exhibit an effective damping which is higher than predicated by linear theory. The presence of a non-linearity provides a path for energy flow to other modes, increasing the apparent damping spectrum at some frequencies and reducing it at others. The target of this work is a model revealing the governing parameters of a generic system of this type and leading to predictions of the ensemble response.