Sebastian Barwich - Academia.edu (original) (raw)
Papers by Sebastian Barwich
Journal of Materials Chemistry A, 2013
In this work two dimensional graphene flakes were used to prepare new electrolytes for dye sensit... more In this work two dimensional graphene flakes were used to prepare new electrolytes for dye sensitized solar cells (DSSCs). Small amounts (up to 3 wt%) of graphene nanoflakes were suspended into the ionic liquid (IL) 1-propyl-3-methyl imidazolium iodide (PMII) to produce new electrolytes. The use of these electrolytes in DSSCs resulted in more than twenty five times improvement of the solar cell efficiency.
Soft Matter, 2015
For a wide range of applications of graphene suspensions, a thorough understanding of their rheol... more For a wide range of applications of graphene suspensions, a thorough understanding of their rheological properties is crucial. We probe the microstructure of dense suspensions of micron-sized, few-layer, defect-free graphene platelets by measuring their viscoelastic properties at various concentrations up to 39 mg ml À1 . We propose a model to relate the yield strain to the mesh size of the microstructure as a function of volume fraction f. From the yield stress measurements we infer the typical bond energy (z20 k B T) and f dependence of the bond number density. These results allow us to express the steady shear viscosity for Peclet number Pe < 10 in terms of the platelet dimensions, bond energy and f using a relaxation ansatz.
Nanoscale, 2015
In this work we have used melt-processing to mix liquid-exfoliated boron-nitride nanosheets with ... more In this work we have used melt-processing to mix liquid-exfoliated boron-nitride nanosheets with PET to produce composites for gas barrier applications. Sonication of h-BN powder, followed by centrifugationbased size-selection, was used to prepare suspensions of nanosheets with aspect ratio >1000. The solvent was removed to give a weakly aggregated powder which could easily be mixed into PET, giving a composite containing well-dispersed nanosheets. These composites showed very good barrier performance with oxygen permeability reductions of 42% by adding just 0.017 vol% nanosheets. At low loading levels the composites were almost completely transparent. At higher loading levels, while some haze was introduced, the permeability fell by ∼70% on addition of 3 vol% nanosheets. † Electronic supplementary information (ESI) available. See
The Journal of Physical Chemistry C, 2013
We have demonstrated a simple method to pretreat graphite powder resulting in a significant reduc... more We have demonstrated a simple method to pretreat graphite powder resulting in a significant reduction in the time required to produce dispersions of solvent-exfoliated graphene. Sonication of graphite in either stabilizing solvents such as NMP or nonstabilizing solvents such as water results in significant breakage of graphite flakes and considerable exfoliation to give graphene. As expected, much of the graphene produced is stable indefinitely in NMP. Surprisingly, however, in the water-based samples unaggregated graphene was observed up to 26 h after sonication with complete sedimentation only observed after 70−130 h. In both cases, removal of the solvent resulted in a powder consisting of broken graphite flakes and reaggregated graphene. For both water and NMP pretreatments, this powder could be very easily redispersed by sonication in NMP to give good quality, defect-free graphene nanosheets. However, the concentration achievable after a given resonication time depended strongly on the pretreatment solvent and time. Redispersion of NMP-pretreated powder occurred much faster with concentrations of 1 mg/mL achieved after only 1 min resonication. This pretreatment technique will facilitate both the storage and transportation of liquid exfoliated graphene.
Nature Materials, 2014
To progress from the laboratory to commercial applications, it will be necessary to develop indus... more To progress from the laboratory to commercial applications, it will be necessary to develop industrially scalable methods to produce large quantities of defect-free graphene. Here we show that high-shear mixing of graphite in suitable stabilizing liquids results in large-scale exfoliation to give dispersions of graphene nanosheets. X-ray photoelectron spectroscopy and Raman spectroscopy show the exfoliated flakes to be unoxidized and free of basal-plane defects. We have developed a simple model that shows exfoliation to occur once the local shear rate exceeds 10 4 s −1 . By fully characterizing the scaling behaviour of the graphene production rate, we show that exfoliation can be achieved in liquid volumes from hundreds of millilitres up to hundreds of litres and beyond. The graphene produced by this method performs well in applications from composites to conductive coatings. This method can be applied to exfoliate BN, MoS 2 and a range of other layered crystals. † A full list of authors and a liations appears at the end of the paper. NATURE MATERIALS | ADVANCE ONLINE PUBLICATION | www.nature.com/naturematerials 1
Journal of Materials Chemistry A, 2013
In this work two dimensional graphene flakes were used to prepare new electrolytes for dye sensit... more In this work two dimensional graphene flakes were used to prepare new electrolytes for dye sensitized solar cells (DSSCs). Small amounts (up to 3 wt%) of graphene nanoflakes were suspended into the ionic liquid (IL) 1-propyl-3-methyl imidazolium iodide (PMII) to produce new electrolytes. The use of these electrolytes in DSSCs resulted in more than twenty five times improvement of the solar cell efficiency.
Soft Matter, 2015
For a wide range of applications of graphene suspensions, a thorough understanding of their rheol... more For a wide range of applications of graphene suspensions, a thorough understanding of their rheological properties is crucial. We probe the microstructure of dense suspensions of micron-sized, few-layer, defect-free graphene platelets by measuring their viscoelastic properties at various concentrations up to 39 mg ml À1 . We propose a model to relate the yield strain to the mesh size of the microstructure as a function of volume fraction f. From the yield stress measurements we infer the typical bond energy (z20 k B T) and f dependence of the bond number density. These results allow us to express the steady shear viscosity for Peclet number Pe < 10 in terms of the platelet dimensions, bond energy and f using a relaxation ansatz.
Nanoscale, 2015
In this work we have used melt-processing to mix liquid-exfoliated boron-nitride nanosheets with ... more In this work we have used melt-processing to mix liquid-exfoliated boron-nitride nanosheets with PET to produce composites for gas barrier applications. Sonication of h-BN powder, followed by centrifugationbased size-selection, was used to prepare suspensions of nanosheets with aspect ratio >1000. The solvent was removed to give a weakly aggregated powder which could easily be mixed into PET, giving a composite containing well-dispersed nanosheets. These composites showed very good barrier performance with oxygen permeability reductions of 42% by adding just 0.017 vol% nanosheets. At low loading levels the composites were almost completely transparent. At higher loading levels, while some haze was introduced, the permeability fell by ∼70% on addition of 3 vol% nanosheets. † Electronic supplementary information (ESI) available. See
The Journal of Physical Chemistry C, 2013
We have demonstrated a simple method to pretreat graphite powder resulting in a significant reduc... more We have demonstrated a simple method to pretreat graphite powder resulting in a significant reduction in the time required to produce dispersions of solvent-exfoliated graphene. Sonication of graphite in either stabilizing solvents such as NMP or nonstabilizing solvents such as water results in significant breakage of graphite flakes and considerable exfoliation to give graphene. As expected, much of the graphene produced is stable indefinitely in NMP. Surprisingly, however, in the water-based samples unaggregated graphene was observed up to 26 h after sonication with complete sedimentation only observed after 70−130 h. In both cases, removal of the solvent resulted in a powder consisting of broken graphite flakes and reaggregated graphene. For both water and NMP pretreatments, this powder could be very easily redispersed by sonication in NMP to give good quality, defect-free graphene nanosheets. However, the concentration achievable after a given resonication time depended strongly on the pretreatment solvent and time. Redispersion of NMP-pretreated powder occurred much faster with concentrations of 1 mg/mL achieved after only 1 min resonication. This pretreatment technique will facilitate both the storage and transportation of liquid exfoliated graphene.
Nature Materials, 2014
To progress from the laboratory to commercial applications, it will be necessary to develop indus... more To progress from the laboratory to commercial applications, it will be necessary to develop industrially scalable methods to produce large quantities of defect-free graphene. Here we show that high-shear mixing of graphite in suitable stabilizing liquids results in large-scale exfoliation to give dispersions of graphene nanosheets. X-ray photoelectron spectroscopy and Raman spectroscopy show the exfoliated flakes to be unoxidized and free of basal-plane defects. We have developed a simple model that shows exfoliation to occur once the local shear rate exceeds 10 4 s −1 . By fully characterizing the scaling behaviour of the graphene production rate, we show that exfoliation can be achieved in liquid volumes from hundreds of millilitres up to hundreds of litres and beyond. The graphene produced by this method performs well in applications from composites to conductive coatings. This method can be applied to exfoliate BN, MoS 2 and a range of other layered crystals. † A full list of authors and a liations appears at the end of the paper. NATURE MATERIALS | ADVANCE ONLINE PUBLICATION | www.nature.com/naturematerials 1