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2006-2010, BEng in Bio-materials Science and Engineering, Beijing University of Chemical Technology;
2010-2011, MSc in Polymer Technology, Loughborough University;
2012-2015, PhD in Materials Science and Engineering;
2015-2016, Research Associate in Loughborough University;
2016-present, Research Fellow in University of Leeds.
Graphene and its composites;
Lab Teaching and MSc Modules
(2016) “Heterogeneous distribution of entanglements in a nonequilibrium polymer melt of UHMWPE: Influence on crystallization without and with graphene oxide”, Macromolecules. 49.19: 7497-7509.
DOI: 10.1021/acs.macromol.6b01173, Repository URL: http://eprints.whiterose.ac.uk/105514/
© 2016 American Chemical Society. In the past, studies have been performed to follow chain dynamics in an equilibrium polymer melt using low molar mass polymers. Here we show that in linear ultrahigh molecular weight polyethylene entanglements formed during or after polymerization are influencing differently the overall chain topology of the polymer melt. When a disentangled UHMWPE sample is crystallized under isothermal conditions after melting, two endothermic peaks are observed. The high temperature peak is related to the melting of crystals obtained on crystallization from the disentangled domains of the heterogeneous (nonequilibrium) polymer melt, whereas the low melting temperature peak is related to the melting of crystals formed from entangled domains of the melt. On increasing the annealing time in melt, the enthalpy of the lower melting temperature peak increases at the expense of the high melting temperature peak due to the transformation of the disentangled nonequilibrium melt into the entangled equilibrium one. However, independent of the equilibrium or nonequilibrium melt state, the high melting temperature peak is observed when the disentangled samples are left to isothermally crystallize at a specific temperature, although with a decrease in bulk crystallinity. A commercial (entangled) sample, instead, shows both shift in the position of the melting temperature peak and drop in crystallinity. To ascertain that entanglements are the cause for the observed difference, experiments are performed in the presence of reduced graphene oxide (rGON): the melting response of disentangled UHMWPE crystallized from its heterogeneous melt state remains nearly independent of the annealing time in melt. This observation strengthens the concept that in the presence of a suitable filler, chain dynamics is arrested to an extent that the nonequilibrium melt state having lower entanglement density is retained.
(2016) “Influence of reduced graphene oxide on the rheological response and chain orientation on shear deformation of high density polyethylene”, Polymer (United Kingdom). 87: 8-16.
© 2016 Elsevier Ltd. All rights reserved. The rheological response of high density polyethylene/reduced graphene oxide nanoplatelets (HDPE/rGON) composites, and the influence of rGON on chain orientation and crystallization behavior after shear flow are investigated. Melt rheology reveals the presence of s trong interaction between polymer chains and the filler. Above 4.0 wt % of the filler concentration, the terminal region of frequency sweep shows changes in the linear viscoelastic properties of the composites. In particular, at these high concentrations the cross-over frequency at which the transition from predominantly elastic to viscous behavior occurs significantly shifts to lower values, indicating the formation of a solid-like percolated network. A drop in G′ at high frequency (100 rad/s) is observed in the presence of the filler, and the storage modulus shows minima at filler concentration between 2.0 and 4.0 wt %. The influence of chain-filler interaction on chain orientation, and subsequent crystallization behavior after application of shear is followed by time resolved WAXD/SAXS. The orientation of the crystalline domains was quantified by the Herman's orientation factor that supports the presence of strong chain-filler interaction. The Deborah number of reptation and retraction suggests that during the applied non-linear shear, polymer chains in the composites experience mild stretch that is not significant enough to induce crystallization at the high temperature (136 °C). However, restriction imposed by the filler on the chain mobility is pronounced enough to preserve oriented state that causes anisotropy in crystallization on cooling. The enhanced orientation with increasing filler content is conclusively attributed to the strong chain-filler interaction.
(2015) “Unique rheological response of ultrahigh molecular weight polyethylenes in the presence of reduced graphene oxide”, Macromolecules. 48.1: 131-139.
© 2014 American Chemical Society. The paper addresses the difference in electrical conductivities and rheological properties between two nanocomposites of reduced graphene oxide nanosheets (rGON) with commercial ultrahigh molecular weight polyethylene (C-PE) and a low-entanglement-density UHMWPE synthesized under controlled conditions (Dis-PE). It has been found that composites made with Dis-PE can reach conductivities at least 100 times higher than those made with C-PE on doing thermal treatment at lower temperatures. However, the difference in the electrical conductivity diminishes when both sets of samples are given a high temperature treatment. This phenomenon is attributed to the difference in morphology of the polymer matrices, for example, grain boundaries between the nascent particles. Furthermore, rheological analyses of the two sets of UHMWPE/rGON nanocomposites conclusively demonstrate differences in the interaction between polyethylene chain segments of the disentangled UHMWPE and rGON, compared to the entangled commercial UHMWPE. Both composites show minima in the storage modulus at a specific graphene composition. The strong interaction of polyethylene chains with the filler inhibits disentangled UHMWPE to achieve the thermodynamic equilibrium melt state, whereas in the commercial sample, having a broader molar mass distribution, the higher adhesion probability of the long chains to the graphene surface lowers the elastic modulus of the polymer melt. Correlation between the percolation threshold for electrical conductivity and rheological response of the composites has also been discussed.
(2016) Composite material of uhmwpe and graphene and process for manufacturing thereof.
The present invention pertains to a process for the manufacture of a composite wherein the process comprises the following steps: i) graphene is exfoliated, ii) ultra high molecular weight polyethylene (UHMWPE) is combined with the exfoliated graphene, wherein the UHMWPE has an elastic shear modulus in the plateau region of at most 1.4 MPa and a Mw/Mn ratio of at most 15 and the amount of graphene is 0.5 to 5 wt% based on the combined dry mass of the UHMWPE and the graphene, and the invention also pertains to composites and materials comprising said composites.
Research Projects & Grants
Influence of reduced graphene oxide on the rheological response and chain orientation on shear deformation of high density polyethylene K Liu, E Andablo-Reyes, N Patil, DH Merino, S Ronca, S Rastogi; Polymer 87, 8-16
Composite material of uhmwpe and graphene and process for manufacturing thereof; Kangsheng LIU, S. Rastogi, Y. DESHMUKH, S. RONCA; EP Patent WO2016005504 (A1)
‘Disentanglement’ of polyethylene chains in the presence of graphene Kangsheng Liu, E. Andablo-Reyes, S. Ronca, S. Rastogi Abstract Book of Annual European Rheology Conference, 14
Stabilisation of non-equilibrium melt in a linear polyethylene in the presence of reduced graphene oxide nanoplatelets