I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[16500]
Abstract: Simultaneous synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS) was used to follow the crystalline morphology evolution of poly-L- lactic acid (PLLA) during uniaxial deformation at various draw temperatures (Td). The mechanical behaviour of PLLA, was found to be strongly dependent on Td. 2D SAXS/WAXS data taken during the draw showed that at low Tds cavitation and voiding occurred and the initial crystallites underwent ‘overdrawing’ where they slip and are partially destroyed. SEM confirmed that surface voiding and cavitation had occurred at Td = 60 and 65 °C but was absent at higher Tds. During the draw, no long-range macromolecular lamellar structure was seen in the SAXS, but small crystallites of the disordered α′ crystal form of PLLA were observed in the WAXS at all Tds. The PLLA samples were then step annealed in a second processing stage (post-draw) to develop the oriented crystalline lamellar structure and increase the amount of the stable α crystalline form. SAXS/WAXS data showed that a highly oriented lamellar stack macrostructure developed on annealing, with increased crystallite size and crystallinity at all Tds. Furthermore, step annealing drove the crystalline transition in all samples from the disordered α′ crystal form to the stable α crystal form. Therefore, varying pre- and post-processing parameters can significantly influence the mechanical properties, orientation, crystalline morphology and crystal phase transition of the final PLLA material.
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Apr 2020
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[20409]
Abstract: Through charge-driven interfacial complexation, we produced millimetre-sized spheroidal hydrogels (SH) with a core-shell structure allowing long term stability in aqueous media. The SH were fabricated by extruding, drop-wise, a cationic cellulose nanofibril (CCNF) dispersion into an oppositely charged polyacrylic acid (PAA) bath. The SH have a solid-like CCNF-PAA shell, acting as a semi-permeable membrane, and a liquid-like CCNF suspension in the core. Swelling behaviour of the SH was dependent on the osmotic pressure of the ageing media. Swelling could be supressed by increasing the ionic strength of the media as this enhanced interfibrillar interactions and thus strengthened the outer gel membrane. We further validated a potential application of SH as re-usable matrixes for glucose oxidase (GOx) entrapment, where the SH work as “microreactors” from which substrate and product are freely able to migrate, through the SH shell whilst avoiding enzyme leakage.
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Feb 2020
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B21-High Throughput SAXS
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Abstract: Polymerisation-induced self-assembly (PISA) has become widely recognised as a versatile and efficient strategy to prepare well-defined diblock copolymer nanoparticles in a range of solvents. In this article, we report the synthesis of anionic, sterically-stabilised, sulfonate-functional diblock copolymer nanoparticles via PISA using a reversible addition–fragmentation chain-transfer (RAFT) polymerisation formulation. Anionic poly(potassium 3-sulfopropyl methacrylate) (PKSPMA) macromolecular chain-transfer agents (macro-CTAs) were synthesised via RAFT solution polymerisation followed by chain-extension with benzyl methacrylate (BzMA) in alcohol/water mixtures to form PKSPMA–PBzMA nanoparticles. The influence of solvent quality on the formation of these nanoparticles was investigated by judiciously changing the alcohol/water ratio, the alcohol co-solvent (ethanol or methanol) and relative copolymer composition. The resulting diblock copolymer nanoparticles were analysed by dynamic light scattering (DLS), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and aqueous electrophoresis. The results demonstrated that nanoparticles with controllable diameters for a fixed copolymer composition can be prepared by altering the co-solvent composition. More specifically, when using different ratios of ethanol/water or methanol/water, the nanoparticle diameter can be tuned from approximately 20 to 200 nm with fixed copolymer composition. This indicates that the solvency of both the stabiliser and core-forming block has a marked impact on both the aggregation of polymer chains during self-assembly and the resulting nanoparticles. Additionally, these nanoparticles remain colloidally stable and highly anionic over a wide pH range from 4 to 10, as judged by aqueous electrophoresis.
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Feb 2020
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[21776]
Abstract: Polymerisation-induced self-assembly (PISA) is widely recognised to be a powerful platform technology for the rational synthesis of diblock copolymer nano-objects. RAFT alcoholic dispersion polymerisation is an important PISA formulation that has been used to prepare block copolymer spheres, worms and vesicles. In this study, we have utilised the RAFT dispersion polymerisation of lauryl methacrylate (LMA) using a poly(N-(2-methacryloyloxy)ethyl pyrrolidone) (PNMEP) stabiliser in order to prepare vesicles with highly deformable membranes. More specifically, a PNMEP28 precursor was chain-extended with LMA in an 80 : 20 w/w ethanol–water mixture to produce a series of PNMEP28-PLMAx diblock copolymer nano-objects (Mw/Mn ≤ 1.40; LMA conversions ≥98% in all cases, as indicated by 1H NMR spectroscopy). Differential scanning calorimetry studies confirmed that the membrane-forming PLMA block had a relatively low glass transition temperature. Transmission electron microscopy and small angle X-ray scattering were used to identify copolymer morphologies for these highly asymmetric diblock copolymers. A mixed sphere and vesicle morphology was observed when targeting x = 43, while polydisperse vesicles were obtained for x = 65–151. Slightly smaller vesicles with lower mean aggregation numbers and thicker membranes were obtained when targeting higher PLMA DPs. A minor population of sheet-like lamellae was observed for each target copolymer composition, with lamellar stacking leading to a structure peak in the scattering patterns recorded for PNMEP28-PLMA129 and PNMEP28-PLMA151. Bearing in mind potential industrial applications, RAFT chain-end removal strategies were briefly explored for such PNMEP28-PLMAx vesicles. Thus, 96% of dithiobenzoate chain-ends could be removed within 3 h at 50 °C via LED irradiation of a 7.5% aqueous dispersion of PNMEP28-PLMA87 vesicles at a wavelength of 405 nm. This appears to be an attractive method for RAFT chain-end removal from diblock copolymer nano-objects, particularly those comprising highly hydrophobic cores.
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Jan 2020
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[9490, 10237]
Abstract: Binary mixtures of anionic and non-ionic macromolecular chain transfer agents (macro-CTAs) are utilized in order to rationally design diblock copolymer nanoparticles with tunable morphologies and anionic character via pseudo-living radical polymerization. More specifically, poly(methacrylic acid) (PMAA) and poly(glycerol monomethacrylate) (PGMA) macro-CTAs are pre-mixed prior to reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA). This strategy facilitates the formation of PHPMA-based diblock copolymer spheres, worm-like micelles and vesicles via polymerization-induced self-assembly (PISA). The presence of the anionic PMAA stabilizer block has a dramatic impact on the resulting copolymer morphology, particularly if the degree of polymerization (DP) of the PMAA stabilizer chains is longer than that of the PGMA. Two phase diagrams have been constructed to investigate the effect of the relative proportion and molar mass of the two macro-CTAs. Such a systematic approach is essential for the reproducible synthesis of pure worm-like micelles, which occupy relatively narrow phase space. The rheological behavior of a series of soft, free-standing worm gels is investigated. Finally, such gels are examined as model matrices for the growth of biomimetic calcite crystals and the role of the anionic PMAA stabilizer chains in directing crystal growth is evaluated.
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Aug 2019
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[8065]
Abstract: Uniform, periodic and ordered iron oxide nanopatterns can be generated by selective metal ion inclusion into microphase separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin films. After solvent mediated metal ion inclusion into the PEO block, an ultraviolet-Ozone (UVO) treatment was used to remove the polymer and oxidize the metallic ions to their oxides. This paper provides an in-depth study of the UVO processing steps as a function of exposure time. Surface wettability, topography, morphology, compositional and interfacial changes were analysed by contact angle measurement, microscopic and spectroscopic techniques through the UVO treatment. It was found that the UVO treatment initially cross-links the polymer network followed by oxidation and removal of the polymer simultaneously. It was also found that if short UVO exposure times are used, a post calcination treatment can be used to generate similar patterns. The iron oxide nanopatterns created due to strong coordination bond between metallic ions and free electron pairs of O atoms in the PEO and these interactions are responsible for the final pattern mimicking the original self-assembled BCP morphology. The film thicknesses, surface roughness, the size/shape of the iron oxides and patterns, the amount of residual polymers were also investigated regarding the UVO exposure time.
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Apr 2019
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[16500]
Abstract: The mechanical behaviour, crystalline and macromorphology structure development during uniaxially deformation and annealing of poly-L- lactic acid (PLLA), with varying strain rate and draw temperatures, (Td) above Tg, have been investigated using Small- and wide-angle X-ray scattering (SAXS/WAXS), microscopy, thermal and mechanical techniques. The mechanical behaviour of PLLA, was strongly dependent on Td where embrittlement and eventual failure were observed as Td was increased, during uniaxial drawing of the amorphous polymer. This was mirrored in the bulk surface morphology where crazing, microvoiding and cavitation occurred with increasing Td. SAXS/WAXS data showed that strain-induced crystallization occurs on drawing, but crystallite orientation decreased with increasing Td, due to chain relaxation at temperatures ≥30 oC above Tg. However, no long-range oriented lamellar macromorphology was observed post-draw directly and only developed in the samples that were step annealed at temperatures above Td. Also, the disordered α’ crystal form was observed post-draw at Td between 60 – 80 oC, whereas Td ≥ 90 oC, resulted in the ordered α crystal form directly. However, on annealing at temperatures of ≥110 oC, the α’- α crystal transition ensued and in all samples, an oriented lamellar macromorphology developed. Therefore, Td and post-draw annealing, have a significant influence on the mechanical properties, crystallinity and crystalline phase transformation in PLLA, which in-turn, affects the polymers medical and industrial applications.
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Feb 2018
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B21-High Throughput SAXS
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Diamond Proposal Number(s):
[12411]
Abstract: We report on the self-assembly behavior of poly(2-methyl-2-oxazoline)–block–poly(2-octyl-2-oxazoline) comprising different terminal perfluoroalkyl fragments in aqueous solutions. As reported previously [Eur. Polym. J., 2017, 88, 645-655] such polyphiles can form a plethora of nanostructures depending of the composition and on the way of preparation. Here we report, for the first time, detailed information on the internal structure of the nanoparticles resulting from the self-assembly of these copolymers. Small-angle neutron and x-ray scattering (SANS/SAXS) experiments unambiguously prove the existence of polymersomes, wormlike micelles and their aggregates in aqueous solution. It is shown that increasing content of fluorine in the poly(2-oxazoline) copolymers results in a morphological transition from bilayered or multi-layered vesicles to wormlike micelles for solutions prepared by direct dissolution.
In contrast, nanoparticles prepared by dialysis of a polymer solution in a non-selective organic solvent against water are characterized by SAXS method. The internal structure of the nanoparticles could be assessed by fitting of the scattering data, revealing complex core-double shell architecture of spherical symmetry. Additionally, long range ordering is identified for all studied nanoparticles due to the crystallization of the poly(2-octyl-2-oxazoline) segments inside the nanoparticles.
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Jan 2018
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B21-High Throughput SAXS
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Manuel
Hartweg
,
Charlotte J. C.
Edwards-gayle
,
Elham
Radvar
,
Dominic W. P.
Collis
,
Mehedi
Reza
,
Michael
Kaupp
,
Jan
Steinkönig
,
Janne
Ruokolainen
,
Robert
Rambo
,
Christopher
Barner-kowollik
,
Ian W.
Hamley
,
Helena S.
Azevedo
,
C. Remzi
Becer
Diamond Proposal Number(s):
[15778]
Abstract: Monodisperse sequenced peptides and peptoids present unique nano-structures based on their self-assembled secondary and tertiary structures. However, the generation of peptide and peptoid hybrid oligomers in a sequence-defined manner via Ugi multicomponent reaction has not yet been studied. Herein, we report a synthetic strategy that enables both the modification of peptides as well as the generation of sequence-defined peptide-peptoid hybrid structures. Our synthetic methodology rests on the fusion of solid phase peptide synthesis with Ugi multicomponent reactions. We evidence that a diversity of chemical functionalities can be inserted into peptides or used in the design of peptide-peptoid hybrids exploiting a wide functional array including amines, carboxylic acids, hydrocarbons, carbohydrates as well as polymers, introducing a sequence-defined synthetic platform technology for precision peptoid hybrids.
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Dec 2017
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Abstract: In this work, fire inhibition performance of four flame retardant formulations of brominated flame retardant (BFR: GreenArmor®), antimony(III) oxide (Sb2O3) and high impact polystyrene (HIPS) is reported. The standard Underwriters Laboratory (UL 94) vertical burn test was applied for assessing the flame retardancy of a variety of polymer blends. A formulation having 13.3 wt% GreenArmor®, 4 wt% Sb2O3 and 82.7 wt% HIPS, named sample D, successfully passed the flame test and was rated V-0. The other formulations with deficient composition exhibited low flame retardancy, as expected. The X-ray grating interferometry method is introduced for probing the 3D internal structures across the burnt UL 94 flame retarded polymer blend formulations to present the detailed mechanisms of flame retardancy. The X-ray images revealed several features for the formulation (sample D) that passed the UL 94 test: heat-induced dissolution of BFR and Sb2O3 residual particles, formation of gas bubbles inside the burnt polymer test bar, deflation of gas bubbles in a char layer through a microcrack, and thick char layer development, defined by the Br and Sb concentration profile to a depth of 100–220 μm. Also, the X-ray images show clear differences between formulations that pass and fail the UL 94 test. X-ray grating interferometry imaging is proposed as a novel technique for assessment of new generation flame retardants.
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Apr 2017
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