X-ray diffraction to probe the kinetics of ice recrystallization inhibition

Understanding the nucleation and growth of ice is crucial in fields ranging from infrastructure maintenance, to the environment, and to preserving biologics in the cold chain. Ice binding and antifreeze proteins are potent ice recrystallization inhibitors (IRI), and synthetic materials that mimic this function have emerged, which may find use in biotechnology. To evaluate IRI activity, optical microscopy tools are typically used to monitor ice grain size either by end-point measurements or as a function of time. However, these methods provide 2-dimensional information and image analysis is required to extract the data. Here we explore using wide angle X-ray scattering (WAXS/X-ray powder diffraction (XRD)) to interrogate 100's of ice crystals in 3-dimensions as a function of time. Due to the random organization of the ice crystals in the frozen sample, the number of orientations measured by XRD is proportional to the number of ice crystals, which can be measured as a function of time. This method was used to evaluate the activity for a panel of known IRI active compounds, and shows strong agreement with results obtained from cryo-microscopy, as well as being advantageous in that time-dependent ice growth is easily extracted. Diffraction analysis also confirmed, by comparing the obtained diffraction patterns of both ice binding and non-binding additives, that the observed hexagonal ice diffraction patterns obtained cannot be used to determine which crystal faces are being bound. This method may help in the discovery of new IRI active materials as well as enabling kinetic analysis of ice growth

Unprecedented phase transition sequence in the perovskite Li0.2Na0.8NbO3

Funding for this research was provided by: EPSRC (award No. EP/L505079/1).We demonstrate the existence of a novel phase transition sequence in the perovskite Li0.2Na0.8NbO3 at elevated temperature. The rare Glazer tilt system, a+a+c-, is observed in both polar and centrosymmetric polymorphs. The perovskite Li0.2Na0.8NbO3 is shown, by powder neutron diffraction, to display a unique sequence of phase transitions at elevated temperature. The ambient temperature polar phase (rhombohedral, space group R3c) transforms via a first-order transition to a polar tetragonal phase (space group P42mc) in the region 150 – 300 °C; these two phases correspond to Glazer tilt systems a-a-a- and a+a+c-, respectively. At 500 °C a ferroelectric – paraelectric transition takes place from P42mc to P42/nmc, retaining the a+a+c- tilt. Transformation to a single-tilt system, a0a0c+ (space group P4/mbm), occurs at 750 °C, with the final transition to the aristotype cubic phase at 850 °C. The P42mc and P42/nmc phases have each been seen only once previously in perovskite crystallography, in both cases in compositions prepared at high pressure.Publisher PDFPeer reviewe

Highly selective continuous flow hydrogenation of cinnamaldehyde to cinnamyl alcohol in a Pt/SiO2 coated tube reactor

A novel continuous flow process for selective hydrogenation of α, β-unsaturated aldehyde (cinnamaldehyde, CAL) to the unsaturated alcohol (cinnamyl alcohol, COL) has been reported in a tube reactor coated with a Pt/SiO2 catalyst. A 90% selectivity towards the unsaturated alcohol was obtained at the aldehyde conversion of 98.8%. This is a six-fold improvement in the selectivity compared to a batch process where acetals were the main reaction products. The increased selectivity in the tube reactor was caused by the suppression of acid sites responsible for the acetal formation after a short period on stream in the continuous process. In a fixed bed reactor, it had a similar acetal suppression phenomenon but showed lower product selectivity of about 47–72% due to mass transfer limitations. A minor change in selectivity and conversion caused by product inhibition was observed during the 110 h on stream with a turnover number (TON) reaching 3000 and an alcohol production throughput of 0.36 kg gPt −1 day−1 in the single tube reactor. The catalysts performance after eight reaction cycles was fully restored by calcination in air at 400◦C. The tube reactors provide an opportunity for process intensification by increasing the reaction rates by a factor of 2.5 at the reaction temperature of 150◦C compared to 90◦C with no detrimental effects on catalyst stability or product selectivity

Crystallographic and optical study of PbHfO3 crystals

The symmetry of the intermediate high-temperature phase of PbHfO3 has been determined unambiguously to be orthorhombic using a combination of high-resolution X-ray diffraction and birefringence imaging microscopy measurements of crystal plates. While lattice parameter measurements as a function of temperature in the intermediate phase are consistent with either orthorhombic or tetragonal symmetry, domain orientations observed in birefringence imaging microscopy measurements utilizing the Metripol system are only consistent with orthorhombic symmetry with the unit cell in the rhombic orientation of the pseudocubic unit cell

In situ X‐ray scattering of the crystallisation of basic magnesium chlorides using a laboratory instrument

A method for in situ monitoring of the crystallisation of basic magnesium chlorides using a laboratory-based SAXS (small angle X-ray scattering)/ WAXS (wide angle X-ray scattering) instrument is demonstrated. By simultaneous acquisition of SAXS/WAXS, time-resolved particle size and phase evolution information was obtained for crystallisation of Mg3Cl(OH)5 ⋅ 4 H2O. Comparison of SAXS and WAXS data provides new mechanistic insights into the formation of this material, from long-range crystallographic order to nanoscale particle size, highlighting the information laboratory instruments can provide

Control over microphase separation and dielectric properties via para-fluoro thiol click reaction

Herein, we have reported the facile para-fluoro thiol click reaction to control microphase separation and the dielectric properties of poly(pentafluorostyrene-b-acrylic acid) copolymers. The block copolymer of pentafluorostyrene and acrylic acid was synthesized resulting in high block incompatibility by Nitroxide Mediated Polymerisation. By using the para-fluoro thiol reaction, 1-dodecanethiol was precisely clicked to block copolymers in various ratios. The microphase structures were observed in cylindrical geometry and their directionality was changed from parallel to perpendicular with increasing click ratio, besides domain size was recorded as low as 5.5 nm. The dielectric constant of the copolymers decreases with increasing click ratio due to the low dielectric constant of dodecane pendant groups and reaches κ=2.4 (at 1000 Hz). This study provides insights on one-step control over phase and dielectric properties by using a facile and very effective click reaction strategy that can simplify the fabrication of novel polymers for next-generation capacitor films for use in directed energy and advanced integrated circuits with smaller feature sizes

Selecting phthalocyanine polymorphs using local chemical termination variations in copper iodide

Copper(I) iodide (CuI) thin films are employed as a structural templating layer for the growth of metal-free phthalocyanine (H2Pc) thin films. Structural polymorphs are observed in X-ray diffraction patterns when microcrystalline CuI films exhibiting copper and iodine terminated grains are used. Each polymorph is nucleated from a single termination, and distinctive crystallite morphologies are observed for each

Well-defined polyacrylamides with AIE properties via rapid Cu-mediated living radical polymerization in aqueous solution : thermoresponsive nanoparticles for bioimaging

There is a requirement for the development of methods for the preparation of well-controlled polymers with aggregation-induced emission (AIE) properties. This requirement directed this current work towards a robust synthetic route, which would be applicable for preparation in water and the presence of many types of functional groups. Herein, aqueous Cu-mediated living radical polymerization (LRP) has been optimized to provide facile and rapid access to a diverse range of water-soluble AIE polymers at sub-ambient temperatures. Homo-, block and statistical copolymerization all proceeded to a near full monomer conversion (≥99%) within 1 or 2 h and exhibited narrow dispersity, even when DP was targeted up to 1000. This excellent control associated with this polymerisation technique and the high-end group fidelity achieved were further demonstrated by linear first order kinetics and successful in situ block copolymerization, respectively. Fine-tuning the monomer sequence and composition of poly(N-isopropylacrylamide) (PNIPAM) copolymers allows for different lower critical solution temperature (LCST) and fluorescent thermoresponsive nanoparticles, which spontaneously self-assembled to varying sizes in water as determined by a combination of techniques (DLS, SAXS and TEM). Additionally, the fluorescence intensity was demonstrated to depend on the polymer concentration, architecture of the side chains and temperature. Particularly, PNIPAM-containing polymers were resistant to reduction in thermo-induced emission. The good biocompatibility, photostability and high specificity make them promising candidates as lysosome-specific probes for application in bioimaging

Systematic modification of UiO‐66 metal‐organic frameworks for glucose conversion into 5‐hydroxymethyl furfural in water

Metal organic framework UiO‐66 is studied as an adaptable heterogeneous catalyst for glucose conversion. UiO‐66 was modified by; i) partial linker substitution, ii) particle size modulation and iii) linker defects. We studied the effect of crystallinity and functional groups on the glucose conversion and product yields. The main products are: i) fructose from the isomerisation of glucose, ii) mannose from the epimerisation of glucose and iii) 5‐hydroxymethyl furfural from the dehydration of fructose. We found that defective and nano crystalline UiO‐66 catalyst performs best for isomerisation. When 50 % of the linkers of UiO‐66 are replaced by a sulfonate‐containing linker, the catalyst shows higher isomerisation activity than other UiO‐66 catalysts. Naphthalene‐dicarboxylate linkers were introduced to induce hydrophobicity and this catalyst further increased isomerisation activity showing 31 % fructose selectivity. Finally, the promising catalysts were tested in a flow reactor and a bifunctional mixed linker catalyst possessing both hydrophobic and acidic functional groups is shown to be stable in a time‐on‐stream study

Polymerisation‐induced self‐assembly of graft copolymers

We report the polymerisation-induced self-assembly of poly(lauryl methacrylate)-graft-poly(benzyl methacrylate) copolymers during reversible addition-fragmentation chain transfer (RAFT) grafting from polymerisation in a backbone-selective solvent. Electron microscopy images suggest the phase separation of grafts to result in a network of spherical particles, due to the ability of the branched architecture to freeze chain entanglements and to bridge core domains. Small-angle X-ray scattering data suggest the architecture promotes the formation of multicore micelles, the core morphology of which transitions from spheres to worms, vesicles, and inverted micelles with increasing volume fraction of the grafts. A time-resolved SAXS study is presented to illustrate the formation of the inverted phase during a polymerisation. The grafted architecture gives access to unusual morphologies and provides exciting new handles for controlling the polymer structure and material properties