I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[20409]
Open Access
Abstract: Water quality parameters such as salt content and various pH environments can alter the stability of gels as well as their rheological properties. Here, we investigated the effect of various concentrations of NaCl and different pH environments on the rheological properties of TEMPO-oxidised cellulose nanofibril (OCNF) and starch-based hydrogels. Addition of NaCl caused an increased stiffness of the OCNF:starch (1:1 wt%) blend gels, where salt played an important role in reducing the repulsive OCNF fibrillar interactions. The rheological properties of these hydrogels were unchanged at pH 5.0 to 9.0. However, at lower pH (4.0), the stiffness and viscosity of the OCNF and OCNF:starch gels appeared to increase due to proton-induced fibrillar interactions. In contrast, at higher pH (11.5), syneresis was observed due to the formation of denser and aggregated gel networks. Interactions as well as aggregation behaviour of these hydrogels were explored via ζ-potential measurements. Furthermore, the nanostructure of the OCNF gels was probed using small-angle X-ray scattering (SAXS), where the SAXS patterns showed an increase of slope in the low-q region with increasing salt concentration arising from aggregation due to the screening of the surface charge of the fibrils.
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Mar 2021
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[17580]
Abstract: Surface hydrophobization of cellulose nanomaterials has been used in the development of nanofiller reinforced polymer composites and formulations based on Pickering emulsions. Despite well known effect of hydrophobic domains on self assembly or association of water soluble polymer amphiphiles, very few studies have addressed the behavior of hydrophobized cellulose nanomaterials in aqueous media. In this study, we investigate the properties of hydrophobized cellulose nanocrystals (CNCs) and their self assembly and amphiphilic properties in suspensions and gels. CNCs of different hydrophobicity were synthesized from sulfated CNCs by coupling primary alkylamines of different alkyl chain lengths (6, 8 and 12 carbon atoms). The synthetic route permitted the retention of surface charge, ensuring good colloidal stability of hydrohobized CNCs in aqueous suspensions. We compare surface properties (surface charge, Zeta potential), hydrophobicity (water contact angle, microenvironment probing using pyrene fluorescence emission) and surface activity (tensiometry) of different hydrophobized CNCs and hydrophilic CNCs. Association of hydrophobized CNCs driven by hydrophobic effects is confirmed by X ray scattering (SAXS) and autofluorescent spectroscopy experiments. As a result of CNC association, CNCs suspensions/gels can be produced with a wide range of rheological properties depending on the hydrophobic/hydrophilic balance. In particular, sol gel transitions for hydrophobized CNCs occur at lower concentrations then hydrophilic CNCs and more robust gels are formed by hydrophobized CNCs. Our work illustrates that amphiphilic CNCs can complement associative polymers as modifiers of rheological properties of water based systems.
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Jan 2020
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[163641]
Open Access
Abstract: A novel mechanism of heat-triggered gelation for oxidised cellulose nanofibrils (OCNF) is reported. We demonstrate that a synergistic approach combining rheology, small-angle X-ray scattering (SAXS) and saturation transfer difference NMR (STD NMR) experiments enables a detailed characterisation of gelation at different length scales. OCNF dispersions experience an increase in solid-like behaviour upon heating as evidenced by rheological studies, associated with enhanced interfibrillar interactions measured using SAXS. Interactions result in an increased fibrillar overlap and increased population of confined water molecules monitored by STD NMR. By comparison, cationic cellulose nanofibrils (produced by reaction of cellulose with trimethylglycidylammonium chloride) were found to be heat-unresponsive.
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Sep 2018
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I11-High Resolution Powder Diffraction
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Gerardo
Algara-Siller
,
Nikolai
Severin
,
Sam
Chong
,
Torbjörn
Björkman
,
Robert
Palgrave
,
Andrea
Laybourn
,
Markus
Antonietti
,
Yaroslav Z.
Khimyak
,
Arkady V.
Krasheninnikov
,
Jürgen P.
Rabe
,
Ute
Kaiser
,
Andrew I.
Cooper
,
Arne
Thomas
,
Michael J.
Bojdys
Diamond Proposal Number(s):
[7040]
Abstract: Graphitic carbon nitride has been predicted to be structurally analogous to carbon-only graphite, yet with an inherent bandgap. We have grown, for the first time, macroscopically large crystalline thin films of triazine-based, graphitic carbon nitride (TGCN) using an ionothermal, interfacial reaction starting with the abundant monomer dicyandiamide. The films consist of stacked, two-dimensional (2D) crystals between a few and several hundreds of atomic layers in thickness. Scanning force and transmission electron microscopy show long-range, in-plane order, while optical spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations corroborate a direct bandgap between 1.6 and 2.0 eV. Thus TGCN is of interest for electronic devices, such as field-effect transistors and light-emitting diodes.
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Jul 2014
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I11-High Resolution Powder Diffraction
I19-Small Molecule Single Crystal Diffraction
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C.
Martí-Gastaldo
,
D.
Antypov
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M. E.
Briggs
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P. A.
Chater
,
P. V.
Wiper
,
Gary
Miller
,
Y. Z.
Khimyak
,
G. R.
Darling
,
N. G.
Berry
,
M. J.
Rosseinsky
,
J. E.
Warren
Diamond Proposal Number(s):
[7036]
Abstract: Porous materials are attractive for separation and catalysis—these applications rely on selective interactions between host materials and guests. In metal–organic frameworks (MOFs), these interactions can be controlled through a flexible structural response to the presence of guests. Here we report a MOF that consists of glycyl–serine dipeptides coordinated to metal centres, and has a structure that evolves from a solvated porous state to a desolvated non-porous state as a result of ordered cooperative, displacive and conformational changes of the peptide. This behaviour is driven by hydrogen bonding that involves the side-chain hydroxyl groups of the serine. A similar cooperative closure (reminiscent of the folding of proteins) is also displayed with multipeptide solid solutions. For these, the combination of different sequences of amino acids controls the framework's response to the presence of guests in a nonlinear way. This functional control can be compared to the effect of single-point mutations in proteins, in which exchange of single amino acids can radically alter structure and function.
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Feb 2013
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I11-High Resolution Powder Diffraction
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Kyriakos
Stylianou
,
Jeremy
Rabone
,
Sam
Chong
,
Romain
Heck
,
Jayne
Armstrong
,
Paul V.
Wiper
,
Kim E.
Jelfs
,
Sergey
Zlatogorsky
,
John
Bacsa
,
Alec G.
Mclennan
,
Christopher P.
Ireland
,
Yaroslav Z.
Khimyak
,
K. Mark
Thomas
,
Darren
Bradshaw
,
Matthew J.
Rosseinsky
Abstract: The reaction between Zn and a pyrene-based ligand decorated with benzoate fragments (H(4)TBAPy) yields a 2D layered porous network with the metal coordination based on a paddlewheel motif. Upon desolvation, the structure undergoes a significant and reversible structural adjustment with a corresponding reduction in crystallinity. The combination of computationally assisted structure determination and experimental data analysis of the desolvated phase revealed a structural change in the metal coordination geometry from square-pyramidal to tetrahedral. Simulations of desolvation showed that the local distortion of the ligand geometry followed by the rotation and displacement of the pyrene core permits the breakup of the metal-paddlewheel motifs and the formation of ID Zn-O chains that cross-link adjacent layers, resulting in a dimensionality change from the 2D layered structure to a 3D structure. Constrained Rietveld refinement of the powder X-ray diffraction pattern of the desolvated phase and the use of other analytical techniques such as porosity measurements, C-13 CP MAS NMR spectroscopy, and fluorescence spectroscopy strongly supported the observed structural transformation. The 3D network is stable up to 425 degrees C and is permanently porous to CO2 with an apparent BET surface area of 523(8) m(2)/g (p/p degrees = 0.02-0.22). Because of the hydrophobic nature, size, and shape of the pores of the 3D framework, the adsorption behavior of the structure toward p-xylene and m-xylene was studied, and the results indicated that the shape of the isotherm and the kinetics of the adsorption process are determined mainly by the shape of the xylene isomers, with each xylene isomer interacting with the host framework in a different manner.
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Dec 2012
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I11-High Resolution Powder Diffraction
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Abstract: Poly(triazine imide)—a 2D layered network—can be obtained as an intercalation compound with halides from the ionothermal condensation of dicyandiamide in a eutectic salt melt. The gallery height of the intercalated material can be tuned via the composition of the eutectic melt and by post-synthetic modification. Here, we report the synthesis of poly(triazine imide) with intercalated bromide ions (PTI/Br) from a lithium bromide and potassium bromide salt melt. PTI/Br has a hexagonal unit-cell (P63cm (no. 185); a = 8.500390(68) Å, c = 7.04483(17) Å) that contains two layers of imide-bridged triazine (C3N3) units stacked in an AB-fashion as corroborated by solid-state NMR, FTIR spectroscopy and high-resolution TEM. By comparison with a recently reported material PTI/Li+Cl−, prepared from a LiCl/KCl eutectic, the layer-stacking distance in the analogous bromide material was expanded from 3.38 Å to 3.52 Å – an exceptionally large spacing for an aromatic, discotic system (cf. graphite 3.35 Å). Subsequent treatment of PTI/Br with concentrated ammonium fluoride yields poly(triazine imide) with intercalated fluoride ions (PTI/F) (P63/m (no. 176); a = 8.4212(4) Å, c = 6.6381(5) Å) as a statistical phase mix with PTI/Br. Fluoride intercalation leads to a contraction of the gallery height to 3.32 Å, demonstrating that the gallery height is synthetically tuneable in these materials.
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Nov 2012
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[7040]
Abstract: Light-harvesting MOFs: A new porous porphyrinic metal–organic framework (MOF; see picture) was obtained by hydrothermal synthesis. The chemical and thermal stability of the material allows a postsynthetic insertion of zinc in the center of the porphyrin. The visible-light photocatalytic activity of this porphyrin-based material is shown for the sacrificial hydrogen evolution from water.
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Jul 2012
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I11-High Resolution Powder Diffraction
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Jeremy
Rabone
,
Yan-Feng
Yue
,
Sam
Chong
,
Kyriakos
Stylianou
,
John
Bacsa
,
Darren
Bradshaw
,
George
Darling
,
Neil
Berry
,
Yaroslav
Khimyak
,
Alexey
Ganin
,
Paul
Wiper
,
John
Claridge
,
Matthew
Rosseinsky
Diamond Proposal Number(s):
[1732]
Abstract: Porous materials find widespread application in storage, separation, and catalytic technologies. We report a crystalline porous solid with adaptable porosity, in which a simple dipeptide linker is arranged in a regular array by coordination to metal centers. Experiments reinforced by molecular dynamics simulations showed that low-energy torsions and displacements of the peptides enabled the available pore volume to evolve smoothly from zero as the guest loading increased. The observed cooperative feedback in sorption isotherms resembled the response of proteins undergoing conformational selection, suggesting an energy landscape similar to that required for protein folding. The flexible peptide linker was shown to play the pivotal role in changing the pore conformation.
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Aug 2010
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I11-High Resolution Powder Diffraction
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Abstract: The carboxylate ligand 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy)-based on the strongly fluorescent long-lifetime pyrene core-affords a permanently microporous fluorescent metal organic framework, [In2(OH)2(TBAPy)]·(guests) (1), displaying 54% total accessible volume and excellent thermal stability. Fluorescence studies reveal that both 1 and TBAPy display strong emission bands at 471 and 529 nm, respectively, upon excitation at 390 nm, with framework coordination of the TBAPy ligands significantly increasing the emission lifetime from 0.089 to 0.110 ms. Upon desolvation, the emission band for the framework is shifted to lower energy: however, upon re-exposure to DMF the as-made material is regenerated with reversible fluorescence behavior. Together with the lifetime, the emission intensity is strongly enhanced by spatial separation of the optically active ligand molecules within the MOF structure and is found to be dependent on the amount and chemical nature of the guest species in the pores. The quantum yield of the material is found to be 6.7% and, coupled with the fluorescence lifetime on the millisecond time scale, begins to approach the values observed for Eu(III)-cryptate-derived commercial sensors.
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Mar 2010
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