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Abstract to“Interfacial colloidal particle films andtheir structure formation”; a licentiate thesis, whichwill be presented by Sandra Rödner in Q2, 29 November 2002at 13.00. Colloidal particles can be made to organise themselves intoordered arrays. These colloidal structures acquire interestingand useful properties, not only from their constituentmaterials but also from the spontaneous emergence of mesoscopicorder that characterises their internal structure. Orderedarrays of colloidal particles, with lattice constants rangingfrom a few nanometers to a few microns, have potentialapplications as optical computing elements and chemicalsensors, and also has an important influence on the mechanicalproperties and optical appearance of paint films and papercoatings. The control of colloidal structure formation starts with theparticle interactions (attractive or repulsive) and colloidaldynamics, which is the topic of this thesis. To enable adetailed understanding of the different factors that controlthe formation of dense 2D colloidal films, a method forstructural characterisation was developed. The degree of orderin the hexagonal close-packed structure, displayed by thecolloidal films, was characterised by the size of ordereddomains and by the distribution of pore sizes. The size ofordered domains was obtained from the pair distributionfunction, and the distribution of pores from a Delaunaytriangulation procedure. These methods are based on theparticle positions in the film, which were determined by lightmicroscopy and processed digital images. The two methods were used to study the effect of particleinteractions on the structure of colloidal monoparticulatefilms, formed at the air-liquid interface. The size of theordered domains decreased exponentially with increasing bondstrength, while the pore density increased. The transfer andsubsequent drying of the formed film on a solid substrateinduced structural changes; the capillary forces transformedsmall pores into triangular order while some of the largervoids and cracks increased in size. The structural features of colloidal monolayers, formed bydrying a dilute silica suspension on a substrate, wereinvestigated. Addition of small amounts of salt resulted indrastic changes of the particle film structure. The size of theordered domains decreased exponentially with increasing amountsof added salt (0-2.9% NaCl/Silica ratio), with a simultaneousincrease of the concentration of large defects. This suggeststhat loss of colloidal stability and onset of particle adhesionto the substrate inhibit rearrangement and ordering. Theevaporation rate was controlled by varying the relativehumidity during drying. Colloidal monolayers with the largestordered domains and the lowest concentration of stacking faultswere formed at an intermediate humidity (55% RH). The rearrangement process during drying of dilute silicasuspensions was followed in detail by studying the changes inthe structural features during growth of colloidal monolayers.Low crystal growth rate promoted the transition of squarelattice domains to a hexagonal close-packed structure. Additionof salt to the electrostatically stabilised dispersionincreased the formation of square structured regions at thecrystal-suspension interface, due to increasing adhesion to thesubstrate. The loss of colloidal stability inhibited therearrangement process, resulting in higher concentrations ofsquare lattice domains at large distances from the crystal edgecompared to systems without added salt. / NR 20140805

Yes / The properties of nitrogen centres acting either as hydrogen-bond or Brønsted acceptors in solid molecular acid–base complexes have been probed by N 1s X-ray photoelectron spectroscopy (XPS) as well as 15N solid-state nuclear magnetic resonance (ssNMR) spectroscopy and are interpreted with reference to local crystallographic structure information provided by X-ray diffraction (XRD). We have previously shown that the strong chemical shift of the N 1s binding energy associated with the protonation of nitrogen centres unequivocally distinguishes protonated (salt) from hydrogen-bonded (co-crystal) nitrogen species. This result is further supported by significant ssNMR shifts to low frequency, which occur with proton transfer from the acid to the base component. Generally, only minor chemical shifts occur upon co-crystal formation, unless a strong hydrogen bond is formed. CASTEP density functional theory (DFT) calculations of 15N ssNMR isotropic chemical shifts correlate well with the experimental data, confirming that computational predictions of H-bond strengths and associated ssNMR chemical shifts allow the identification of salt and co-crystal structures (NMR crystallography). The excellent agreement between the conclusions drawn by XPS and the combined CASTEP/ssNMR investigations opens up a reliable avenue for local structure characterization in molecular systems even in the absence of crystal structure information, for example for non-crystalline or amorphous matter. The range of 17 different systems investigated in this study demonstrates the generic nature of this approach, which will be applicable to many other molecular materials in organic, physical, and materials chemistry. / EPSRC, Sanofi-Aventis

No / We demonstrate that nanofiltration of aqueous glycine solutions has a pronounced effect on laser-induced nucleation. Two nucleation regimes were observed in nonfiltered, irradiated solutions under isothermal conditions: a rapid initial regime associated with laser-induced nucleation and a second much slower spontaneous nucleation regime. Filtration of the solutions prior to irradiation greatly suppressed the rapid regime, while the slow regime was similar regardless of filtration or irradiation, for all supersaturations studied. A clear effect of filtration on crystal polymorphism was also observed. Nonfiltered irradiated solutions at a lower supersaturation almost exclusively yielded the α-polymorph, while at higher supersaturations there was significant presence (∼40%) of the γ-polymorph. On the other hand, filtered solutions almost exclusively yielded the α-polymorph of glycine at all supersaturations studied. These surprising results challenge some established ideas about laser-induced nucleation, showing that previously reported laser-induced nucleation phenomena in glycine aqueous solutions can be effectively suppressed by filtration, so that the underlying mechanism is unlikely to be based on molecular scale interactions involving just the solute and the solvent alone. Instead, laser-induced nucleation in this system appears to be related to either colloidal scale solution clusters or foreign solid or molecular impurities that can be removed by nanofiltration.

Yes / We report the crystallization-driven self-assembly of diblock copolymers bearing a poly(L-lactide) block into cylindrical micelles. Three different hydrophilic corona-forming blocks have been employed: poly(4-acryloyl morpholine) (P4AM), poly(ethylene oxide) (PEO) and poly(N,N-dimethylacrylamide) (PDMA). Optimization of the experimental conditions to improve the dispersities of the resultant cylinders through variation of the solvent ratio, the polymer concentration, and the addition speed of the selective solvent is reported. The last parameter has been shown to play a crucial role in the homogeneity of the initial solution, which leads to a pure cylindrical phase with a narrow distribution of length. The hydrophilic characters of the polymers have been shown to direct the length of the resultant cylinders, with the most hydrophilic corona block leading to the shortest cylinders. / EPSRC and the University of Warwick, the Swiss National Science Foundation - Early Postdoc Mobility fellowship (Grant no PBNEP2-142949 to A.P.B.). The Warwick Research Development Fund. Some items of equipment funded by Birmingham Science City: Innovative Uses for Advanced Materials in the Modern World (West Midlands Centre for Advanced Materials Project 2), with support from Advantage West Midlands (AWM) and part funded by the European Regional Development Fund (ERDF).

No / Cocrystallization of modafinil, (1), and 1,4-diiodotetrafluorobenzene, (2), in toluene leads to the formation of a metastable modafinil channel hydrate containing an unusual hydrogen bonded dimer motif involving the modafinil molecules that is not seen in anhydrous forms of modafinil. Computational methodologies utilizing bias drift-free differential evolution optimization have been developed and applied to a series of molecular clusters and multicomponent crystals in the modafinil/water and modafinil/water/additive systems for the additive molecules (2) or toluene. These calculations show the channel hydrate is less energetically stable than the anhydrous modafinil but more stable than a cocrystal involving (1) and (2). This provides theoretical evidence for the observed instability of the channel hydrate. The mechanism for formation of the channel hydrate is found to proceed via templating of the modafinil molecules with the planar additive molecules, allowing the formation of the unusual hydrogen-bonded modafinil dimer. It is envisaged that the additive is then replaced by water molecules to form the channel hydrate. The formation of the channel hydrate is more likely in the presence of (2) compared to toluene due to the destabilizing effect of the larger iodine molecules protruding into neighboring modafinil clusters. / Science Foundation Ireland, IRCSET, UCC 2012 Strategic Research Fund

Yes / A green approach has been used for co-crystallization of non-congruent co-crystal pair of caffeine – maleic acid using water. Ultrasound is known to affect crystallization hence the effect of high power ultrasound on the ternary phase diagram has been investigated in detail using a slurry co-crystallization approach. A systematic investigation was performed to understand how the accelerated conditions during ultrasound assisted co-crystallization will affect different regions of the ternary phase diagram. Application of ultrasound showed considerable effect on the ternary phase diagram; principally on caffeine/maleic acid 2:1 (disappeared) and 1:1 co-crystal (narrowed) regions. Also, the stability regions for pure caffeine and maleic acid in water were narrowed in the presence of ultrasound, expanding the solution region. The observed effect of ultrasound on the phase diagram was correlated with solubility of caffeine and maleic acid and stability of co-crystal forms in water.

Polymeric systems become increasingly complicated and multifunctional if they involve a larger level of structural complexity. In the last couple of decades the level of interest has gradually shifted from the μm-scale to the nm-scale region, for instance, systems having at least one structural size below 100nm, e.g. nanocomposites. The physical properties of polymers such as crystallisation, tensile modulus, impact strength and viscosity are strongly influenced by the presence of additives in the polymer matrix. Semicrystalline polymers comprise nearly two-thirds of all synthetic polymers. These are processed to form films, fibers, and moulded articles using operations such as extrusion, moulding, fiber spinning, film blowing etc. During these processes, the polymer melt is subjected to complex and intense flow fields (shear or elongational) after which the polymer crystallises. The morphology of the semicrystalline polymer in the final product and subsequently its properties and quality, depend on the manner in which the polymer crystallises from the flowing melt. The subject is continuously driven by the quest to understand the molecular mechanism of flow induced crystallisation; nevertheless, the flow induced crystallisation in presence of nanofillers has received little attention. The thesis deals with the crystallisation studies of polymer molecules during shear in presence of nanofillers (viz. single walled carbon nanotube (SWCNT) and zirconia particle) having different aspect ratio. For this purpose, the polyethylene (PE) consisting of desired molar mass and molar mass distribution within the processing range is utilised. The morphology of semicrystalline polymer is revealed using time resolved X-ray scattering (SAXS/WAXS) techniques. The rheological aspects of polymer melt in presence of nanoparticles are manifested. In chapter 2, the effect of SWCNTs on the crystallisation kinetics of polymers has been studied with and without application of shear rate. The shear rate effect on the formation of shish-kebab structures in the polymer containing SWCNTs is investigated. The effect of shear rates on the stretching of long chains of PE is verified using the approach involving the use of Deborah number. The study reveals the significance of SWCNTs on crystallisation of PE. In chapter 3, the influence of zirconia nanoparticles on crystal orientation of polymers is studied. Enhanced crystallisation kinetics is observed due to presence of zirconia nanoparticles. Overall crystal orientation is improved as a result of zirconia nanoparticles in the polymer matrix. In chapter 4 of the thesis, the role of broad molecular weight distribution of PE in formation of oriented (shish-kebab) structures is demonstrated. The presence of nanoparticles of different aspect ratios and binding efficiency with polymer on the formation of highly oriented structures in the early stage crystallisation is verified. The study reveals the significant role of SWCNTs in shish-kebab structure formation as compared to zirconia nanoparticles. Further, the insight on the selective adsorption of polymer chains to the nanoparticles is provided. In chapter 5 of the thesis, the molecular interaction between polymer and nanoparticles under shear above the equilibrium point (T = 141.2°C) is investigated. The study reveals the major role of SWCNTs with high aspect ratio, in the stability of flow induced precursor (FIP) and formation of extended chain crystals, as a result of strong interaction with PE molecules. On contrary, the poor interaction of Zirconia particles having low aspect ratio, with PE molecules prohibits molecular chain extension.

The research described in this dissertation mainly covers the development of novel technologies for co-crystallisation along with the discovering of plumbagin co-crystal and thermodynamic interrelationship between the co-crystal polymorphs. Co-crystallisation is a fast growing field in the area of crystal design and has shown potential advantages in the field of pharmaceutical. Currently, many research groups are working on the development of new technologies for the synthesis of pure and stoichiometrically controlled co-crystals. In present study, three novel technologies have been developed for co-crystallisation, which include microwave assisted co-crystallisation, spherical crystallisation and microwave assisted sub-critical water processing. The microwave assisted co-crystallisation is a slurry based technology where, effects of drug solubility and dielectric properties of the solvent were investigated using caffeine / maleic acid as a model co-crystal pair. The mechanism of co-crystallisation under microwave irradiation has been proposed. The co-crystals of plumbagin with improved solubility were obtained with the coformers such as hydroquinone, resorcinol and urea using microwave assisted co-crystallisation technique. The spherical crystallisation technology was developed for co-crystallisation of carbamazepine / saccharin co-crystal pair and demonstrated its application for polymorphic control and as a potential technique for the purification of desired crystal form through surface energetic based separation. The thermodynamic interrelationship between Form I and Form II of carbamazepine / saccharin co-crystal was studied using different thermodynamic tests. The results obtained suggest that the carbamazepine / saccharin co-crystal polymorphs are monotropic. Microwave assisted sub-critical water processing has been explored as a green technology for the synthesis of co-crystals. Carbamazepine / saccharin co-crystal pair has been used as a model pair and effects of processing variables on the resulting crystal form and degradation of an API have been studied.