ABSTRACT
An approach for polymer-carbon nanotube (CNT) composite preparation is proposed based on a two-step supercritical fluid treatment. The first step, rapid expansion of a suspension (RESS) of CNTs in supercritical carbon dioxide, is used to de-bundle CNTs in order to simplify their mixing with polymer in solution. The ability of RESS pre-treatment to de-bundle CNTs and to cause significant bulk volume expansion is demonstrated. The second step is the formation of polymer-CNT composite from solution via supercritical antisolvent (SAS) precipitation. SAS treatment allows avoiding CNT agglomeration during transition from a solution into solid state due to the high speed of phase transition. The combination of these two supercritical fluid methods allowed obtaining a polycarbonate-multiwalled carbon nanotube composite with tensile strength two times higher compared to the initial polymer and enhanced elasticity.
ABSTRACT
Fully atomistic molecular dynamics simulations are employed to study impregnation of the poly(methyl methacrylate) (PMMA) matrix with carbamazepine (CBZ) in supercritical carbon dioxide. The simulation box consists of 108 macromolecules of the polymer sample with the polymerization degree of 100, 57 molecules of CBZ, and 242,522 CO2 molecules. The simulation is performed at 333 K and 20 MPa. It is found that by the end of the simulation, the CBZ uptake reaches 1.09 wt % and 50 molecules are sorbed by PMMA. The main type of interaction between PMMA and CBZ is hydrogen bonding between the carbonyl oxygen of PMMA and the hydrogen atoms of the CBZ NH2-group. At the polymer surface, CBZ exists not only in the molecular form, as inside the polymer and in the bulk solution, but also in the form of dimers and trimers. The energy of formation of the hydrogen-bonded complexes is estimated within ab initio calculations.
ABSTRACT
Molecular dynamics (MD) studies of hydrogen bonding (H-bonding) in liquid, sub- and supercritical methanol have been performed in a wide range of thermodynamic parameters of state, using various potential models and two H-bond criteria. It was shown that there is the universal correlation between the average number of H-bonds per molecule (n(HB)) and the mole fraction of H-bonded molecules (X(HB)) for the studied thermodynamic parameters of state. The same feature was observed for the correlations between fractions of molecules forming one (f1), two (f2), three (f3) H-bonds and X(HB). These correlations served to fit experimental Raman spectra of methanol recorded under sub- and supercritical conditions. The advantage of the approach used here is that f1, f2, f3 values have a clear physical meaning and are dependent on the values of state parameters.
