No / This study investigates the influence of length scale effects (micro- and macro-injection molded parts) and mold temperature on the epitaxial growth and morphological characteristics in injection-molded bars of isotactic polypropylene (iPP)/high-density polyethylene (HDPE) blends. After preparing the blends with an iPP content of 70 wt% via melt extrusion, the injection-molded bars were formed using both micro and conventional injection molding. Samples were subsequently prepared from the moulded components to allow investigation of the internal morphology using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and polarized light microscopy (PLM). The results indicated that the matching of micro scale and appropriate mold temperature was most favorable for epitaxial crystallization. The micro-parts had a large fraction of shear layer compared with macro-parts. The SEM observations showed that the shear layer of the former consisted of a highly oriented shish-kebab structure. Moreover, the effects of different methods of injection molding on the morphological characteristics of the micro-parts and macro-parts in different layers were elucidated in detail using PLM and SEM.

No / There is considerable interest, both fundamental and technological, in understanding how additives and impurities influence nucleation, and in being able to modulate nucleation in a predictable way using designer auxiliary molecules. Notable applications involving auxiliaries include the control of nucleation in proteins, inhibition of urinary stone formation, inhibition of ice formation in living tissues during cryoprotection, prevention of blockages in oil and gas pipelines due to wax precipitation, and gas hydrate formation. Despite the immense interest, our understanding of how these molecules exert their effect is still rudimentary, partially because the molecular level processes involved are inaccessible to experiment. We have investigated mechanisms of action of nucleation additives and have derived explicit rules for designing additive molecules for modulating crystal nucleation. The mechanisms of action and the design features have been derived using molecular simulation of simple model systems. Our studies reveal that an effective nucleation inhibitor should have a strong interaction with the solute and have a structure that is able to disrupt the periodicity characterizing the emerging nucleus. Disruption can be achieved by steric effects resulting from structural differences between the additive and solute molecules, the additive possessing extensive degrees of freedom, or via a strong energetic interaction with the solute. Additive molecules that have an amphiphilic character and end up at the solute/solvent interface can inhibit, retard or promote nucleation depending on their specific structure and interactions with the solute and solvent and the given supersaturation, and these specific features and the link with the supersaturation will be discussed. These findings will help to rationalize the mechanisms of action of known nucleation inhibitors and modulators. They will also serve as a framework for rationally identifying or designing additive molecules for either inhibiting or promoting nucleation in specific systems.

no / In this feature article we will focus on the issues relating to the crystal growth of co-crystals, with a particular emphasis on drug development. The initial focus of this perspective is on the relevant literature examples that may be able to inform our understanding with regards co-crystal crystallisation and the allied supramolecular concepts. The second part of this perspective contains selected examples from our own work, which add to the literature perspective. Topics include; nucleation templates, in situ synchrotron XRD studies, solid-state synthesis through mixing and screening strategies.

Ternary crystalline complexes consisting of both salts and ionic co-crystals have been created through the crystallisation of the binary co-crystal 3,5-dinitrobenzoic acid–4-(dimethylamino)benzoic acid with group 1 or ammonium cations. The size and charge density of the cation can be used to adjust the protonation level and local geometry of the acid pair. The selectivity and coordination geometry of the chaperone cation may be further adjusted by the inclusion of a crown ether to reduce the number and location of potential binding sites.

yes / 2D materials such as graphene, LAPONITE® clays or molybdenum disulfide nanosheets are of extremely high interest to the materials community as a result of their high surface area and controllable surface properties. While several methods to access 2D inorganic materials are known, the investigation of 2D organic nanomaterials is less well developed on account of the lack of ready synthetic accessibility. Crystallization-driven self-assembly (CDSA) has become a powerful method to access a wide range of complex but precisely-defined nanostructures. The preparation of 2D structures, however, particularly those aimed towards biomedical applications, is limited, with few offering biocompatible and biodegradable characteristics as well as control over self-assembly in two dimensions. Herein, in contrast to conventional self-assembly rules, we show that the solubility of polylactide (PLLA)-based amphiphiles in alcohols results in unprecedented shape selectivity based on unimer solubility. We use log Poct analysis to drive solvent selection for the formation of large uniform 2D diamond-shaped platelets, up to several microns in size, using long, soluble coronal blocks. By contrast, less soluble PLLA-containing block copolymers yield cylindrical micelles and mixed morphologies. The methods developed in this work provide a simple and consistently reproducible protocol for the preparation of well-defined 2D organic nanomaterials, whose size and morphology are expected to facilitate potential applications in drug delivery, tissue engineering and in nanocomposites. / University of Warwick, Materials GRP, EPSRC, The Royal Society, ERC

The effect of various inorganic and organic additives as possible nucleating agents on the crystallisation behaviour of P. E. T. and the suosequent influence on the morphological and mechanical properties has been examined. Various methods of mixing(: the polymer and additive were investigated and a method involving the screw-Extrusion of the polymer and the additive was ultimately adopted. Crystallisation studies were carried out using differential scanning calorimetry under dynamic and isothermal modes. The results produced under conditions of isothermal crystallisation were analysed by means of a computer. Despite differences between batches of polymer all the additives with the exception of indigo produced a nucleating effect in the polymer as indicated by an increase in the rate of crystallisation compared with that of the base polymer. Two organo-metallic substances (sodium benzoate and sodium stearate) proved to be the most effective in this respect by decreasing the degree of supercooling of the polymer by 20 [degrees]. Morphological studies were carried out on isothermally crystallised samples, after etching and replication using a transmission electron microscope. A nodular structure whose dimensions were sensitive to both the nucleating agent and the temperature of crystallisation was observed. Mechanical testing of samples direct from the D. S. C. was carried out using a compression method. The breaking loads were found to vary with both the type of nucleating agent used and the crystallisation temperature chosen. A separate study involving the exanination of the resulting fracture surfaces by scanning electron microscopy revealed that a, high breaking load was associated with a fine discontinuous structure whereas lower breaking loads were characterised by a more continuous linear appearance. This implies a higher energy of fracture due to the increased surface area of the fracture surface of the former.

This study presents results on the use of ellipsometry as a novel probe for thin films of a diblock copolymer. Ellipsometry makes use of the change in polarisation induced upon reflection of light from a film covered substrate to enable calculation of the refractive index and thickness of the film. The infom1ation obtained in these measurements can be compared to differential scanning calorimetry, with the additional advantages that small sample volumes and slow cooling rates can be employed, and expansion coefficients can be determined. The work is presented in two parts; first crystallisation within the phase-separated domains is studied, then a morphological transition in the diblock ordering is characterised. By studying the temperature dependence of the film thickness and refractive index, crystallisation kinetics within very small volumes( 10^-10 L) of a poly (butadiene-b-ethylene oxide) diblock copolymer are measured. Through a comparison of two different PEO block lengths, a reduction in both the crystallisation and melting temperatures is demonstrated as the domain volume is decreased. Upon cooling, an additional transition is observed. We ascribe this to a morphological transition from a layer of ordered spheres to a lamellar layer at the substrate, which is consistent with a comparison between the data and simulated ellipsometry data. The sensitivity of ellipsometry makes it a well suited and versatile technique for probing thin film kinetics in diblock copolymers. / Thesis / Bachelor of Science (BSc)

No / The present study demonstrates the application of decision tree algorithms to the co-crystallization process. Fifty four (54) batches of carbamazepine–salicylic acid co-crystals embedded in poly(ethylene oxide) were manufactured via hot melt extrusion and characterized by powder X-ray diffraction, differnetial scanning calorimetry, and near-infrared spectroscopy. This dataset was then applied in WEKA, which is an open-sourced machine learning software to study the effect of processing temperature, screw speed, screw configuration, and poly(ethylene oxide) concentration on the percentage of co-crystal conversion. The decision trees obtained provided statistically meaningful and easy-to-interpret rules, demonstrating the potential to use the method to make rational decisions during the development of co-crystallization processes.

No description available.

No / Crystallization of an isotactic polypropylene (iPP) homopolymer and two propylene/ethylene random copolymers (RACO), induced by high-stress shear, was studied using in situ synchrotron wide-angle X-ray diffraction (WAXD) at 137 °C. The “depth sectioning” method (Fernandez-Ballester Journal of Rheology 2009, 53 (5), 1229−1254) was applied in order to isolate the contributions of different layers in the stress gradient direction and to relate specific structural evolution to the corresponding local stress. This approach gives quantitative results in terms of the specific length of fibrillar nuclei as a function of the applied stress. As expected, crystallization becomes faster with increasing stress—from the inner to the outer layer—for all three materials. Stress-induced crystallization in a RACO with 7.3 mol % ethylene content was triggered at only 1 °C below its nominal melting temperature. The comparison of iPP and RACO’s with 3.4 and 7.3 mol % ethylene monomer reveals the effect of ethylene defects on high-stress shear induced crystallization at 137 °C. It is found that, for a given applied stress, the specific nuclei length formed by flow increases with ethylene content—which is attributed to a greater high molecular weight tail. However, the linear growth rate is significantly reduced by the presence of ethylene comonomers and it is found that this effect dominates the overall crystallization kinetics. Finally, a time lag is found between development of parent lamellae and the emergence of daughter lamellae, consistent with the concept of daughter lamellae nucleated by homoepitaxy on the lateral faces of existing parent lamellae.