Induction time experiments, spectroscopic and calorimetric analysis, and molecular modeling were used to probe the influence of solvent on the crystal nucleation of fenoxycarb (FC), a medium-sized, flexible organic molecule. A total of 800 induction times covering a range of supersaturations and crystallization temperatures in four different solvents were measured to elucidate the relative ease of nucleation. To achieve similar induction times, the required thermodynamic driving force, RT ln S, increases in the order: ethyl acetate < toluene < ethanol < isopropanol. This is roughly matched by the order of interfacial energies calculated using the classical nucleation theory. Solvent–solute interaction strengths were estimated using three methods: solvent–solute enthalpies derived from calorimetric solution enthalpies, solvent–solute interactions from molecular dynamics simulations, and the FTIR shifts in the carbonyl stretching corresponding to the solvent–solute interaction. The three methods gave an overall order of solvent–solute interactions increasing in the order toluene < ethyl acetate < alcohols. Thus, with the exception of FC in toluene, it is found that the nucleation difficulty increases with stronger binding of the solvent to the solute.

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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 μm, 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.

Crystallization experiments performed with highly supercooled solutions produced highly pure (>99 wt %) and highly crystalline mesocrystals of curcumin from impure solutions (∼22% of two structurally similar impurities) in one step. These mesocrystals exhibited a crystallographic hierarchy and were composed of perfectly or imperfectly aligned nanometer-thick crystallites. X-ray diffraction and spectroscopic analysis confirmed that the spherulites are a new solid form of curcumin. A theoretical hypothesis based on particle aggregation, double nucleation, and repeated secondary nucleation is proposed to explain the spherulite formation mechanism. The experimental results provide, for the first time, evidence for an organic molecule to naturally form spherulites without the presence of any stabilizing agents. Control experiments performed with highly supercooled pure solutions produced spherulites, confirming that the formation of spherulites is attributed to the high degree of supercooling and not due to the presence of impurities. Likewise, control experiments performed with a lower degree of supercooling produced impure crystals of curcumin via classical molecular addition mechanisms. Collectively, these experimental observations provide, for the first time, evidence for particle-mediated crystallization as an alternate and efficient method to purify organic compounds.

The blend-based polymer electrolyte consisting of poly (vinyl chloride) (PVC) and poly (ethylene glycol) (PEG) as host polymers and lithium perchlorate (LiClO 4 ) as the complexing salt was studied. An attempt was made to investigate the effect of TiO 2 concentration in the unplasticized PVC-PEG polymer electrolyte system. The XRD and FTIR studies confirm the formation of a polymer-salt complex. The conductivity results indicate that the incorporation of ceramic filler up to a certain concentration (15 wt.%) increases the ionic conductivity and upon further addition the conductivity decreases. The maximum ionic conductivity 0.012×10 −4 S cm −1 is obtained for PVC-PEG-LiClO 4 -TiO 2 (75-25-5-15) system. Thermal stability of the polymer electrolyte is ascertained from TG/DTA studies.