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27 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I22-Small angle scattering & Diffraction	Determination of reaction kinetics by time-resolved small-angle X-ray scattering during polymerization-induced self-assembly: direct evidence for monomer-swollen nanoparticles Guoxing Liao , Matthew J. Derry , Andrew J. Smith , Steven P. Armes , Oleksandr Mykhaylyk Angewandte Chemie International Edition DOI: 10.1002/anie.202312119 Diamond Proposal Number(s): [14892, 15525, 24680] Open Access Show Abstract ▼ Abstract: The kinetics of heterogeneous polymerization is determined directly using small-angle X-ray scattering (SAXS). This important advance is exemplified for the synthesis of sterically-stabilized diblock copolymer nanoparticles by reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) in mineral oil at 90 °C. The principle of mass balance is invoked to derive a series of equations for the analysis of the resulting time-resolved SAXS patterns. Importantly, there is a continuous change in the X-ray scattering length density for the various components within the reaction mixture. This enables the volume fraction of unreacted BzMA monomer to be calculated at any given time point, which enables the polymerization kinetics to be monitored in situ directly without relying on supplementary characterization techniques. Moreover, SAXS enables the local concentration of both monomer and solvent within the growing swollen nanoparticles to be determined during the polymerization. The analysis reveals that the instantaneous rate of BzMA polymerization is proportional to the local monomer concentration within the nanoparticles. In principle, this powerful new time-resolved SAXS approach should be applicable to other heterogeneous polymerization formulations.	Nov 2023
I22-Small angle scattering & Diffraction	In situ small-angle X-ray scattering studies during the formation of polymer/silica nanocomposite particles in aqueous solution A. Czajka , G. Liao , O. O. Mykhaylyk , S. P. Armes Chemical Science 519 DOI: 10.1039/D1SC03353K Diamond Proposal Number(s): [21776] Open Access Show Abstract ▼ Abstract: This study is focused on the formation of polymer/silica nanocomposite particles prepared by the surfactant-free aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) in the presence of 19 nm glycerol-functionalized aqueous silica nanoparticles using a cationic azo initiator at 60 °C. The TFEMA polymerization kinetics are monitored using 1H NMR spectroscopy, while postmortem TEM analysis confirms that the final nanocomposite particles possess a well-defined core–shell morphology. Time-resolved small-angle X-ray scattering (SAXS) is used in conjunction with a stirrable reaction cell to monitor the evolution of the nanocomposite particle diameter, mean silica shell thickness, mean number of silica nanoparticles within the shell, silica aggregation efficiency and packing density during the TFEMA polymerization. Nucleation occurs after 10–15 min and the nascent particles quickly become swollen with TFEMA monomer, which leads to a relatively fast rate of polymerization. Additional surface area is created as these initial particles grow and anionic silica nanoparticles adsorb at the particle surface to maintain a relatively high surface coverage and hence ensure colloidal stability. At high TFEMA conversion, a contiguous silica shell is formed and essentially no further adsorption of silica nanoparticles occurs. A population balance model is introduced into the SAXS model to account for the gradual incorporation of the silica nanoparticles within the nanocomposite particles. The final PTFEMA/silica nanocomposite particles are obtained at 96% TFEMA conversion after 140 min, have a volume-average diameter of 216 ± 9 nm and contain approximately 274 silica nanoparticles within their outer shells; a silica aggregation efficiency of 75% can be achieved for such formulations.	Oct 2021
I22-Small angle scattering & Diffraction	Shear-induced alignment of block copolymer worms in mineral oil Matthew Derry , Oleksandr Mykhaylyk , Steven P. Armes Soft Matter 283 DOI: 10.1039/D1SM01011E Diamond Proposal Number(s): [10237] Open Access Show Abstract ▼ Abstract: Poly(stearyl methacrylate)–poly(benzyl methacrylate) [PSMA–PBzMA] diblock copolymer worms were synthesized directly in mineral oil via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization at 90 °C. Free-standing gels were obtained from this polymerization-induced self-assembly (PISA) formulation when targeting PSMA13–PBzMA65 dispersions at 5% w/w to 20% w/w copolymer concentration. Gel permeation chromatography (GPC) studies indicated that almost identical copolymer chains were obtained in all cases, while transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies confirmed that highly anisotropic worms were formed with mean cross-sectional diameters of 11.9–13.1 nm. These worms undergo a thermoreversible worm-to-sphere transition on heating up to 150 °C. Rheological studies were conducted to characterize the shear rate- and concentration-dependent behaviour caused by this change in copolymer morphology, where the initial shear-thinning worm gels form spheres (i.e. a Newtonian fluid) on heating up to 150 °C. Complementary shear-induced polarized light imaging (SIPLI) experiments confirmed the formation of aligned linear worms under applied shear between 80 °C and 110 °C, with high-viscosity dispersions of branched worms being obtained at 20–60 °C and low-viscosity spheres being produced at 150 °C. This study informs the use of such block copolymer worms as rheology modifiers for non-polar oils, which is of potential interest for the automotive industry.	Sep 2021
I13-1-Coherence	X-ray ptychography with a laboratory source Darren Batey , Frederic Van Assche , Sander Vanheule , Matthieu N. Boone , Andrew J. Parnell , Oleksandr O. Mykhaylyk , Christoph Rau , Silvia Cipiccia Physical Review Letters 126 DOI: 10.1103/PhysRevLett.126.193902 Open Access Show Abstract ▼ Abstract: X-ray ptychography has revolutionized nanoscale phase contrast imaging at large-scale synchrotron sources in recent years. We present here the first successful demonstration of the technique in a small-scale laboratory setting. An experiment was conducted with a liquid metal-jet x-ray source and a single photon-counting detector with a high spectral resolution. The experiment used a spot size of 5 μ m to produce a ptychographic phase image of a Siemens star test pattern with a submicron spatial resolution. The result and methodology presented show how high-resolution phase contrast imaging can now be performed at small-scale laboratory sources worldwide.	May 2021
	Control of the aqueous solubility of cellulose by hydroxyl group substitution and its effect on processing Cate T. O'Brien , Tommi Virtanen , Sergii Donets , James Jennings , Olga Guskova , Anna H. Morrell , Matt Rymaruk , Leena Ruusuvirta , Juha Salmela , Harri Setala , Jens-Uwe Sommer , Anthony J. Ryan , Oleksandr Mykhaylyk Polymer 90 DOI: 10.1016/j.polymer.2021.123681 Show Abstract ▼ Abstract: Native cellulose is insoluble in water, despite the high number of hydrogen bonding sites per chain, as molecules preferably hydrogen bond to each other, preventing its use in industrial applications. The modification of cellulose has received considerable recent attention, motivated by the move away from conventional petroleum-based, water-soluble polymers, however, a systematic analysis of the effects of modification is rare. Herein a detailed study of hydroxypropyl (HP)- and (2-hydroxypropyl) trimethylammonium chloride-modified cellulose, with degrees of substitution (DS) determined by NMR, establishes modification-property relationships. TEM, small-angle X-ray scattering and rheology demonstrated that increasing DS gradually changes the aqueous solubility, resulting in the formation of different morphologies, including micron-sized aggregates, needle-like cellulose nanoparticles (CNPs) and solvated molecules. It was found that aqueous dispersions with DSHP of 50 %, assigned to a ‘sweet spot’ in cellulose modification, are suitable for the fiber formation. It is shown that this state of the material can be easily detected by rheo-optical methods based on birefringence. Using structural analysis, molecular dynamic simulation and fiber-spinning results, it is proposed that co-existing CNPs and cellulose molecules, interacting via H-bonding, form a network which orients under shear, acting as a precursor for the fiber formation from aqueous solutions.	Mar 2021
I22-Small angle scattering & Diffraction	Elastic flow instabilities and macroscopic textures in graphene oxide lyotropic liquid crystals Jacek K. Wychowaniec , Maria Iliut , Bartłomiej Borek , Christopher Muryn , Oleksandr O. Mykhaylyk , Steve Edmondson , Aravind Vijayaraghavan Npj 2d Materials And Applications 5 DOI: 10.1038/s41699-020-00193-x Diamond Proposal Number(s): [15478, 14948, 12950] Open Access Show Abstract ▼ Abstract: Graphene oxide (GO) forms a well-aligned lyotropic liquid crystal (LC) phase in aqueous dispersions at relatively low concentrations. Under a remarkably wide range of shear rates, we report hitherto unobserved shear-induced polarized light image patterns, a Maltese cross combined with shear banding, recorded in real time and in situ during rheological measurements. This is shown to be a result of elastic flow instabilities that manifest as a helical flow in alternating bands of left- and right-handed helices, arising from a combination of shear flow and Taylor-type vortex flow. The instability is observed for LCs formed from large aspect ratio GO particles owing to their unique viscoelastic properties, but not for smaller aspect ratio particles. This phenomenon coincides with rheopecty and anomalous small-angle X-ray scattering patterns under shear flow, which confirm the instabilities. The results presented here could lead to advanced control over macroscopic periodic alignment in technologically relevant dispersions of two-dimensional material particles.	Jan 2021
I22-Small angle scattering & Diffraction	Enthalpic incompatibility between two steric stabilizer blocks provides control over the vesicle size distribution during polymerization-induced self-assembly in aqueous media Deborah L. Beattie , Oleksandr O. Mykhaylyk , Steven P. Armes Chemical Science 45 DOI: 10.1039/D0SC01320J Diamond Proposal Number(s): [21776] Open Access Show Abstract ▼ Abstract: Over the past two decades, block copolymer vesicles have been widely used by many research groups to encapsulate small molecule drugs, genetic material, nanoparticles or enzymes. They have also been used to design examples of autonomous self-propelled nanoparticles. Traditionally, such vesicles are prepared via post-polymerization processing using a water-miscible co-solvent such as DMF or THF. However, such protocols are invariably conducted in dilute solution, which is a significant disadvantage. In addition, the vesicle size distribution is often quite broad, whereas aqueous dispersions of relatively small vesicles with narrow size distributions are highly desirable for potential biomedical applications. Alternatively, concentrated dispersions of block copolymer vesicles can be directly prepared via polymerization-induced self-assembly (PISA). Moreover, using a binary mixture of a relatively long and a relatively short steric stabilizer block enables the convenient PISA synthesis of relatively small vesicles with reasonably narrow size distributions in alcoholic media (C. Gonzato et al., JACS, 2014, 136, 11100–11106). Unfortunately, this approach has not yet been demonstrated for aqueous media, which would be much more attractive for commercial applications. Herein we show that this important technical objective can be achieved by judicious use of two chemically distinct, enthalpically incompatible steric stabilizer blocks, which ensures the desired microphase separation across the vesicle membrane. This leads to the formation of well-defined vesicles of around 200 nm diameter (size polydispersity = 13–16%) in aqueous media at 10% w/w solids as judged by transmission electron microscopy, dynamic light scattering and small-angle X-ray scattering.	Jun 2020
I22-Small angle scattering & Diffraction	Role of sheet-edge interactions in β-sheet self-assembling peptide hydrogels Jacek K. Wychowaniec , Andrew Smith , Cosimo Ligorio , Oleksandr O. Mykhaylyk , Aline F. Miller , Alberto Saiani Biomacromolecules DOI: 10.1021/acs.biomac.0c00229 Diamond Proposal Number(s): [12950, 15246] Open Access Show Abstract ▼ Abstract: Hydrogels’ hydrated fibrillar nature makes them the material of choice for the design and engineering of 3D-scaffolds for cell culture, tissue engineering and drug delivery applications. One particular class of hydrogels that has been the focus of significant research is self-assembling peptide hydrogels. In the present work we were interested in exploring how fibre-fibre edge interactions affect the self-assembly and gelation properties of amphipathic peptides. For this purpose we investigated two β-sheet forming peptides, FEFKFEFK (F8) and KFEFKFEFKK (KF8K), the latter one having the fibre edges covered by lysine residues. Our results showed that the addition of the two lysine residues did not affect the ability of the peptides to form β-sheet rich fibres provided that the overall charge carried by the two peptides was kept constant. It did though significantly reduce edge driven hydrophobic fibre-fibre associative interactions resulting in a reduced tendency for KF8K fibres to associate / aggregate laterally and form large fibre bundles and consequently network crosslinks. This effect resulted in the formation of hydrogels with lower moduli but faster dynamics. As a result KF8K fibres could be aligned only under high shear and at high concentration while F8 hydrogel fibres were found to align readily at low shear and low concentration. In addition F8 hydrogels were found to fragment at high concentration due to the high aggregation state stabilising the fibre bundles resulting in fibre breakage rather than disentanglement and alignment.	Apr 2020
I22-Small angle scattering & Diffraction	Influence of an ionic comonomer on polymerization-induced self-assembly of diblock copolymers in non-polar media Gregory N. Smith , Sarah L. Canning , Matthew J. Derry , Oleksandr O. Mykhaylyk , Sarah E. Norman , Steven P. Armes Polymer Chemistry 11, 2605 - 2614 DOI: 10.1039/D0PY00101E Diamond Proposal Number(s): [17255] Show Abstract ▼ Abstract: A series of poly(stearyl methacrylate)–poly(benzyl methacrylate) (PSMA–PBzMA) diblock copolymer nano-objects has been synthesized via reversible addition–fragmentation chain-transfer (RAFT) dispersion polymerization in n-dodecane at 20 wt%. This polymerization-induced self-assembly (PISA) formulation was modified by the incorporation of an anionic monomer, tetradodecylammonium 3-sulfopropyl methacrylate ([NDod4]+[SPMA]−) into the oil-insoluble PBzMA block. According to the literature (M. J. Derry, et al., Chem. Sci., 2016, 7, 5078–5090), PSMA18–PBzMA diblock copolymers only form spheres using this formulation for any core degree of polymerization. Unexpectedly, incorporating just a small fraction (<6 mol%) of [NDod4]+[SPMA]− comonomer into the structure-directing block resulted in the formation of non-spherical diblock copolymer nano-objects, including pure worm-like and vesicular morphologies. However, only spherical micelles could be formed using a longer PSMA34 stabilizer. These diblock copolymer nano-objects were characterized by transmission electron microscopy, small-angle X-ray scattering, and dynamic light scattering. The bulky nature of the ionic comonomer appears to make it possible to avoid the kinetically-trapped sphere morphology. This study reveals a new approach for tuning the morphology of diblock copolymer nano-objects in non-polar media.	Apr 2020
I22-Small angle scattering & Diffraction	In situ SAXS studies during RAFT aqueous emulsion polymerization Emma E Brotherton , Fiona L. Hatton , Amy A. Cockram , Matthew J. Derry , Adam Czajka , Erik J. Cornel , Paul D. Topham , Oleksandr O. Mykhaylyk , Steven P Armes Journal Of The American Chemical Society DOI: 10.1021/jacs.9b06788 Diamond Proposal Number(s): [19852] Open Access Show Abstract ▼ Abstract: Polymerization-induced self-assembly (PISA) is a powerful platform technology for the rational and efficient synthesis of a wide range of block copolymer nano-objects (e.g. spheres, worms or vesicles) in various media. In situ small-angle X-ray scattering (SAXS) studies of RAFT dispersion polymerizations have previously provided detailed structural information during self-assembly (see M. J. Derry et al., Chem. Sci., 2016, 7, 5078-5090). However, conducting the analogous in situ SAXS studies during RAFT aqueous emulsion polymerizations poses a formidable technical challenge because the inherent-ly heterogeneous nature of such PISA formulations requires efficient stirring to generate sufficiently small monomer drop-lets. In the present study, the RAFT aqueous emulsion polymerization of 2-methoxyethyl methacrylate (MOEMA) has been explored for the first time. Chain extension of a relatively short non-ionic poly(glycerol monomethacrylate) (PGMA) precur-sor block leads to the formation of sterically-stabilized PGMA-PMOEMA spheres, worms or vesicles, depending on the pre-cise reaction conditions. Construction of a suitable phase diagram enables each of these three morphologies to be reproduc-ibly targeted at copolymer concentrations ranging from 10 to 30% w/w solids. High MOEMA conversions are achieved with-in 2 h at 70 °C, which makes this new PISA formulation well-suited for in situ small angle X-ray scattering (SAXS) studies using a stirrable SAXS reaction cell. This bespoke cell enables efficient stirring and hence allows in situ monitoring during RAFT emulsion polymerization for the first time. For example, the onset of micellar nucleation and subsequent evolution in particle size can be studied when preparing PGMA29-PMOEMA30 spheres at 10% w/w solids. When targeting PGMA29-PMOEMA70 vesicles under the same conditions, both the nucleation event and the subsequent evolution in the diblock co-polymer morphology from spheres to worms to vesicles are observed. These new insights significantly enhance our under-standing of the PISA mechanism during RAFT aqueous emulsion polymerization.	Jul 2019

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