Abstract
Polymers of intrinsic microporosity (PIMs) are a group of polymers with molecular sieve behaviour due to their rigid, contorted macromolecular backbones. They show great potential in organophilic pervaporation, solvent-resistant nanofiltration and gas and vapour separations. However, they are susceptible to physical ageing, leading to a reduction in permeability over time. An improvement in membrane permeability, control over diffusion selectivity and a reduction of the effect of physical ageing is expected by adding graphene as a nanofiller.Little is experimentally known about how the material disperses in the polymer. Here we used Raman spectroscopy, scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) to study the composite membrane's structure. Our results show that both STEM and Raman spectroscopy are able to identify the presence of graphene-based material in the composite. We show that STEM, through medium angle annular dark field (MAADF) or EELS imaging, can be exploited to obtain information on the morphology and the thickness of the flakes. Our results indicate that there is strong re-agglomeration of initially exfoliated graphene in solution when forming the composite. This is expected to produce strong changes in the mechanical properties and the physical ageing of the membrane.
Highlights
Graphene is a two dimensional allotrope of sp2 bonded carbon atoms in a hexagonal honeycomb structure, or more a single layer of graphite [1]
In this work we demonstrate the first extensive characterisation of PIM-1/Graphene (PIM-1/Gr) composites using Raman spectroscopy and scanning transmission electron microscopy (STEM) imaging
We have demonstrated the first detailed characterisation of PIM-1/graphene composite membranes by using complementary techniques such as UVeVis spectroscopy, Raman spectroscopy, STEM imaging and EEL spectroscopy
Summary
Graphene is a two dimensional allotrope of sp bonded carbon atoms in a hexagonal honeycomb structure, or more a single layer of graphite [1]. Graphene has attracted great interest due to its remarkable properties, such as high charge mobility [2e4], thermal conductivity [5], and mechanical stability and elasticity [6]. Micro-mechanical exfoliation (MME) of graphite is a relatively simple and low cost method, but this process is not massscalable and not compatible with industrial needs [7]. Amongst several methods of graphene production, liquid-phase exfoliation (LPE) shows great potential as a mass-scalable and lowcost approach for industrial production [7e9]. Mixing a nano-level dispersion of graphene platelets in a polymer matrix is a simple and cost-effective method that can bring significant improvement to the properties of the polymer. The high surface-to-volume ratios, relatively low production cost, and the unique properties of graphene make this material very attractive as a filler for composites. Shin et al / Carbon 102 (2016) 357e366 concentrations (
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