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No / Despite a tendency to undergo solution-mediated polymorphic transformation, the dissolution behaviour of the metastable FI (triclinic) polymorph of the pharmaceutical compound carbamazepine (CBZ) was investigated using in situ optical microscopy. Experiments were performed at an undersaturation where single crystals of the metastable FI polymorph dissolved. Dissolution in different solvents was investigated at a constant undersaturation. Separately the sublimation of FI was examined and additionally the dissolution was observed at undersaturations where the more stable FIII polymorph crystallized. The results show that both the dissolution and sublimation of FI occur primarily in the direction of the a-axis of the FI crystal structure where the CBZ molecules are found to stack in this direction. The order for the dissolution rate of FI was acetonitrile ≥ methanol > ethanol. The order of the dissolution rates in each of the solvents is inversely correlated to the viscosity and the binding energy of the solvents with the (100) surface of FI in each of the solvents. This suggests that the rate determining step for the dissolution may be either the diffusion or the detachment of CBZ molecules from the surface of FI. A notable difference in dissolution behaviour is also observed at undersaturations where the more stable FIII polymorph nucleates and grows. / SFI

Yes / Polymorphism, crystal shape and solubility of 1,4-dihydroxyanthraquinone (quinizarin) have been investigated in acetic acid, acetone, acetonitrile, n-butanol and toluene. The solubility of FI and FII from 20 °C to 45 °C has been determined by a gravimetric method. By slow evaporation, pure FI was obtained from n-butanol and toluene, pure FII was obtained from acetone, while either a mixture of the two forms or pure FI was obtained from acetic acid and acetonitrile. Slurry conversion experiments have established an enantiotropic relationship between the two polymorphs and that the commercially available FI is actually a metastable polymorph of quinizarin under ambient conditions. However, in the absence of FII, FI is kinetically stable for many days over the temperature range and in the solvents investigated. FI and FII have been characterized by infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission and ordinary powder X-ray diffraction (PXRD) at different temperatures. The crystal structure of FII has been determined by single-crystal XRD. DSC and high-temperature PXRD have shown that both FI and FII will transform into a not previously reported high-temperature form (FIII) around 185 °C before this form melts at 200–202 °C. By indexing FIII PXRD data, a triclinic P[1 with combining macron] cell was assigned to FIII. The solubility of quinizarin FI and FII in the pure organic solvents used in the present work is below 2.5% by weight and decreases in the order: toluene, acetone, acetic acid, acetonitrile and n-butanol. The crystal shapes obtained in different solvents range from thin rods to flat plates or very flat leaves, with no clear principal difference observed between FI and FII. / SFI; Swedish Research Council

No / The solution-mediated polymorphic transformation from Form II to Form III 2-oxo-1-pyrrolidine acetamide (piracetam) was investigated in seven organic solvents over the temperature range of 5–50 °C. The transformation rate increased as a function of temperature, agitation, and the solubility of piracetam in the host solvent. However, this trend was reversed in 2-propanol. Molecular modeling demonstrated that 2-propanol forms interactions with piracetam molecules in solution stronger than those formed by other solvents, thereby retarding the nucleation and growth of FIII(6.525) during the transformation in this solvent. / SFI

The practical application of non-photochemical laser-induced nucleation (NPLIN) to continuous flow was investigated. Supersaturated aqueous solutions were screened with a 5 ns pulsed laser (532 nm 44 MW cm-2) for NPLIN activity. Upon irradiation succinic acid nucleated at S20 = 4.3 and adipic acid at S20 = 2.0 - 3.0. NPLIN activity is reported for the first time in nicotinic acid (S20 = 2.6 - 3.0). No overall pattern was observed of chemical structure on NPLIN activity. From inorganic compounds similarly screened, ammonium chloride (S20 = 1.04 - 1.20) was identified as most suitable for further tests. It was shown to have an increase of NPLIN crystals with higher supersaturation from 13 at S = 1.038 to 252 at S = 1.135. A quadratic increase in number of crystals with increased laser power. The effects of NPLIN upon ammonium chloride are diminished upon filtration through a 0.2 μm poly (ether sulfone) filter, reducing the number of crystals from 350 to 10 per 70 mJ pulse (25 MW cm-2). The use of NPLIN in continuous flow was demonstrated from the first time. A S23 = 1.1 solution of aqueous ammonium chloride in flow produced crystals when irradiated by 10 pulses s-1 of a 1064 nm 6 ns laser. When the laser was stopped, crystals were no longer produced and the system returned to flowing supersaturated solution. Lab scale apparatus for continuous NPLIN experiments was developed. A design involving a re-dissolution step and loop flow was constructed for both laminar and slug-flow regimes. Nucleation of ammonium chloride (S = 1.1) was demonstrated in both systems. Repeatable NPLIN experiments were hindered by spontaneous nucleation. Spontaneous nucleation in flow was observed around areas where supersaturated solution passed from one component to another. Spontaneous nucleation was also observed upon cooling (25 to 10 °C). Filtration was observed to both suppress NPLIN and spontaneous nucleation in flow.

The goal of this work is to provide a detailed description of the freezing mechanism in gold clusters. This is accomplished by using constrained Monte Carlo simulations combined with parallel tempering algorithms to evaluate the free energy barriers for various temperatures with respect to crystalline order parameters on a 456 atom cluster. <p>Our simulation results help us to challenge the usual assumption of classic nucleation theory where nucleation starts at the center of a cluster, showing instead that nucleation is favored by freezing started at the surface. We study simplistic phenomenological models for surface freezing and find that the three phase contact line free energy term must be included in order to properly describe the features of the free energy barriers. <p>Furthermore, we propose an alternative free energy parameter with which we are able to identify a kinetic spinodal temperature where the nucleation barrier disappears and find that the critical cluster size remains finite at the limit of stability of the fluid phase. This result is supported by Molecular Dynamics simulations.

The goal of this work is to provide a detailed description of the freezing mechanism in gold clusters. This is accomplished by using constrained Monte Carlo simulations combined with parallel tempering algorithms to evaluate the free energy barriers for various temperatures with respect to crystalline order parameters on a 456 atom cluster. <p>Our simulation results help us to challenge the usual assumption of classic nucleation theory where nucleation starts at the center of a cluster, showing instead that nucleation is favored by freezing started at the surface. We study simplistic phenomenological models for surface freezing and find that the three phase contact line free energy term must be included in order to properly describe the features of the free energy barriers. <p>Furthermore, we propose an alternative free energy parameter with which we are able to identify a kinetic spinodal temperature where the nucleation barrier disappears and find that the critical cluster size remains finite at the limit of stability of the fluid phase. This result is supported by Molecular Dynamics simulations.

Nucleation of ice crystals in the atmosphere often occurs through heterogeneous freezing processes facilitated by an atmospheric aerosol that acts as the ice nuclei (IN). Depending on ambient conditions and aerosol composition, heterogeneous nucleation will occur through one of several mechanisms including the contact and immersion freezing mechanisms. Through a series of contact freezing experiments, we have characterized the ability of aerosols composed of volcanic ash, soot, and peat soil, to act as ice nuclei (IN) as a function of temperature. The immersion freezing ability of the ash particles has also been measured. In these studies, an optical microscope apparatus equipped with a cooling stage and a digital camera was used to observe the freezing events. For each experiment, a particular IN was placed in contact with the surface, or immersed in the bulk, of an ultra pure water droplet. The droplet was then subjected to freezing-melting cycles resulting in 25 independent measurements of the freezing temperature of the droplet. In the volcanic ash experiments, we observed contact freezing at warmer temperatures than immersion freezing. As contact freezing IN, the peat was the most effective with an average contact freezing temperature of -10.5 �C, followed by volcanic ash (-11.2 �C), and then soot (-25.6 �C). In addition, we have used classical nucleation theory to identify the contact parameters and nucleation rates for the compositions explored.

Polymer composites are fast becoming a material in the manufacturing of automotive interior and exterior parts such as facias and dashboard components. Production of rigid structural foams are ideal because they reduce the overall weight as well as reduce the amount of material used to manufacture the part. Polymer-clay nanocomposites are a classification of materials containing a blend of polymer and a small weight percentage of nanoclay. These materials are currently of interest to automotive part manufacturers because they are known to deliver improved mechanical properties and increase foamability of a polymer. The current study investigates the changes in material properties and the foamability of a thermoplastic polyolefin (TPO)-clay nanocomposite as the degree of intercalation was varied. The TPO-clay nanocomposite was produced by melt blending TPO, nanoclay and maleic anhydride grafted polypropylene (MAHgPP) in a co-rotating twin screw extruder. The material was subjected to a multi-pass process to vary the degree of intercalation. Degree of intercalation was tracked by rheology, XRD and TEM micrographs. Part density, cell density and flexural modulus measurements were performed on foamed and non-foamed injection molded bars to observe changes in the foamability of the material. Material was also processed without clay and analyzed in the same manner. Through TEM and XRD analysis it was found that the degree of intercalation and delamination was varied with increasing number of passes. Rheological measurements showed that the TPO-clay nanocomposite underwent (beta)-scission and intercalation simultaneously. The changes in intercalation had a positive effect on the foamability of the TPO-clay nanocomposite. As well, the TPO-clay nanocomposite experienced an increase in flexural properties for both unfoamed and foamed parts compared to the TPO-PPgMAH blend; TPO-clay nanocomposite experienced a 44% and 23% increase in the flexural modulus for unfoamed and foamed parts respectively. Data also showed that there was a limit to the number of times the TPO-clay nanocomposite can be recycled before the foamability of the material begins to decrease, which was attributed to material degradation. / Thesis / Master of Applied Science (MASc)

Structures grown via self-assembly are a unique field in nanotechnology. The morphology of self-assembled structures is affected by the balance between kinetics and thermodynamics during growth. Hence structures with tailored morphologies and properties can be created with adjustments in growth conditions. In this thesis we study crystal nucleation and equilibration, for both real and model systems. The growth of thin bismuth films is investigated on three atomically flat surfaces; Mica, Molybdenum di Sulphide, and highly oriented pyrolitic graphite (HOPG). Films are grown under UHV conditions, and characterised using scanning electron microscopy and atomic force microscopy. For coverages of only a few monolayers, bismuth particles are found to aggregate into flat, isolated islands. Islands have characteristic heights and morphologies for each substrate. By altering the deposition flux and coverage, the island density and morphology can be manipulated. On HOPG substrates, planar islands grown at low flux are replaced by 1D structures at high temperature. These anisotopic structures result from an anisotropy in bond strengths at the crystal-vapour interface. Depositing Bi on HOPG substrates at low flux or high temperature conditions produces nanorods aligned (roughly) perpendicular to step edges on the graphite. The aspect ratios (ARs) of these 1D structures are found to increase as the deposition flux is lowered, or the substrate temperature is increased. The Arrhenius dependence of the AR is determined from experiment. A Kinetic Monte Carlo (KMC) model for high AR step-edge aggregates was developed, determining the likely growth mechanism for the nanorods. A scaling regime devised from the KMC results predicts the dependence of nanorod ARs on flux and temperature, and allows an estimation of the energy binding Bi dimers to the sides of nanorods. Thin films can also be grown via the self-assembly of atomic clusters. After deposition coalescence of clusters has implications for the film morphology, and properties. We use KMC simulations to investigate the coalescence of pairs of 3D atomic clusters (15000 to 130000 atoms in size) via lattice based surface diffusion. For early coalescence stages, the radius of the neck region connecting the two clusters is found to develop with a different powerlaw to classical theory. For later coalescence stages, when the nucleation of new atomic layers on facets of the cluster is required for further coalescence the temperature, cluster size, and cluster orientation all influence the coalescence. Equilibration times for clusters coalescing at high temperature are found to be limited by the dissociation of atomic layers.