posted on 2018-08-22, 11:01authored byMichael Svärd, Renuka K. Devi, Dikshitkumar Khamar, Donal Mealey, Dominic Cheuk, Jacek Zeglinski, Åke C. Rasmuson
Molecular clustering and solvent–solute interactions in isopropanol solutions of fenoxycarb have been
thoroughly and systematically investigated by dynamic light scattering, small-angle X-ray scattering, and
nanoparticle tracking, supported by infrared spectroscopy and molecular dynamics simulations. The
existence of molecular aggregates, clusters, ranging in size up to almost a micrometre is clearly
recorded at undersaturated as well as supersaturated conditions by all three analysis techniques. The
results systematically reveal that the cluster size increases with solute concentration and time at
stagnant conditions. For most concentrations the time scale of cluster growth is of the order of days. In
undersaturated solutions the size appears to eventually reach a maximum value, higher the higher the
concentration. Below a certain concentration threshold clusters are significantly smaller. Clusters are
found to be smaller in solutions pre-heated at a higher temperature, which offers a possible explanation
for the so-called ‘‘history of solution’’ effect. The cluster distribution is influenced by filtration through
membranes with a pore size of 0.1 mm, offering an alternative explanation for the ‘‘foreign particle-catalysed
nucleation’’ effect. At moderate concentrations larger clusters appear to be sheared into smaller ones, but the
original size distribution is rapidly re-established. At higher concentrations, although still well below solubility,
the cluster size as well as solute concentration are strongly affected, suggesting that larger clusters contain at
least a core of more organized molecules not able to pass through the filter.
History
Publication
Physical Chemistry Chemical Physics;20, pp. 15550-15559