Abstract
The control of nanostructuration of graphene and graphene related materials (GRM) into self-assembled structures is strictly related to the nanoflakes chemical functionalization, which may be obtained via covalent grafting of non-covalent interactions, mostly exploiting π-stacking. As the non-covalent functionalization does not affect the sp2 carbon structure, this is often exploited to preserve the thermal and electrical properties of the GRM and it is a well-known route to tailor the interaction between GRM and organic media. In this work, non-covalent functionalization of graphite nanoplatelets (GnP) was carried out with ad-hoc synthesized pyrene-terminated oligomers of polylactic acid (PLA), aiming at the modification of GnP nanopapers thermal properties. PLA was selected based on the possibility to self-assemble in crystalline domains via stereocomplexation of complementary poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) enantiomers. Pyrene-initiated PLLA and PDLA were indeed demonstrated to anchor to the GnP surface. Calorimetric and X-ray diffraction investigations highlighted the enantiomeric PLAs adsorbed on the surface of the nanoplatelets self-organize to produce highly crystalline stereocomplex domains. Most importantly, PLLA/PDLA stereocomplexation delivered a significantly higher efficiency in nanopapers heat transfer, in particular through the thickness of the nanopaper. This is explained by a thermal bridging effect of crystalline domains between overlapped GnP, promoting heat transfer across the nanoparticles contacts. This work demonstrates the possibility to enhance the physical properties of contacts within a percolating network of GRM via the self-assembly of macromolecules and opens a new way for the engineering of GRM-based nanostructures.
Highlights
Graphene and graphene-related materials (GRM) are one of the most intensively explored nanoparticles family in materials science owing to their superior properties (Geim and Novoselov, 2007; Gómez-Navarro et al, 2007; Lee et al, 2008; Stoller et al, 2008; Balandin and Nika, 2012)
We report a facile approach to promote polylactic acid (PLA) SC formation onto the surface of GnP, exploiting the denser chain packing in the SC structure (Anderson and Hillmyer, 2006; Xu et al, 2006) to modify the physical properties of the contact between graphite nanoplatelets
The poly(L-lactic acid) (Pyr-L) and Pyr-D synthesized by the ring-opening polymerization of L-lactide and D-lactide using Pyr-OH as initiator have been first characterized for their molar masses
Summary
Graphene and graphene-related materials (GRM) are one of the most intensively explored nanoparticles family in materials science owing to their superior properties (Geim and Novoselov, 2007; Gómez-Navarro et al, 2007; Lee et al, 2008; Stoller et al, 2008; Balandin and Nika, 2012). Graphene oxide (GO), reduced graphene oxide (RGO), multilayer graphene (MLG), and Stereocomplexation of Poly(Lactic Acid)s on GnP graphite nanoplatelets (GnP) attracted a wide research attention in the last decade (Ferrari et al, 2015) Their peculiar mechanical, electrical and thermal properties make GRM ideal platforms for the construction of sophisticated nanostructured systems, which fabrication requires precise control of graphene chemistry, including chemical modifications with specific functional groups (Rodriguez-Perez et al, 2013). In this field, the organic functionalization of GRM has led to the manufacturing of high-performance multifunctional graphene-based materials where covalent and non-covalent bonding provides bridges between adjacent layers (Meng et al, 2013; Wan et al, 2018). Non-covalent functionalization of GRM may be exploited to tailor interfaces between nanoplatelets and the surrounding organic media or to control interfaces within GRM networks
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