No abstract

Nitroaromatic 2,4-dinitroanisole (DNAN) was used as a model compound for the study of surface-poisoning effects in crystallization. In addition to the expected solvent effect, it was found that the concentration of solutions and presence of additives control the formation of polymorphs and forms. In some cases, aromatic and/or nitro-containing additives interact with DNAN, probably competing with intrinsic intermolecular interactions that allow the formation and growth of DNAN crystals. It was also found that singlecrystal-to-single-crystal phase transitions take place between two β forms and from the β form to the α form. This β-to-α transformation is most probably possible because of a similarity between the two crystal structures. Hence, the barrier for this transformation is rather low. Nevertheless, the formation of α-DNAN in the typically β morphology introduces strain in the crystals, causing defects. It was also found that the orientations of the molecules against the unit cell faces for the two α forms (blocks and needles) are markedly different.

No abstract

Today the standard treatment for wastewater is secondary treatment. This procedure cannot remove salinity or some organic micropollutants from water. In the future, a tertiary cleaning step may be required. An attractive solution is membrane processes, especially nanofiltration (NF). However, currently available NF membranes strongly reject multivalent ions, mainly due to the dielectric effect. In this work, we present a new method for preparing NF membranes, which contain negatively and positively charged domains, obtained by the combination of two polyelectrolytes with opposite charge. The negatively charged polyelectrolyte is provided in the form of particles (polystyrene sulfonate (PSSA), d ~300 nm). As a positively charged polyelectrolyte, polyethyleneimine (PEI) is used. Both buildings blocks and glycerol diglycidyl ether as crosslinker for PEI are applied to an UF membrane support in a simple one-step coating process. The membrane charge (zeta potential) and salt rejection can be adjusted using the particle concentration in the coating solution/dispersion that determine the selective layer composition. The approach reported here leads to NF membranes with a selectivity that may be controlled by a different mechanism compared to state-of-the-art membranes.