Stereocomplexation of Poly(Lactic Acid)s on Graphite Nanoplatelets: from Functionalized Nanoparticles to Self-Assembled Nanostructures

TL;DR

This study demonstrates that stereocomplexation of PLA enantiomers on functionalized graphite nanoplatelets enhances thermal transfer in nanostructured materials, enabling improved heat conduction through self-assembled crystalline domains.

Contribution

It introduces a novel non-covalent functionalization method using pyrene-terminated PLA oligomers to promote stereocomplexation on graphite nanoplatelets, improving thermal properties.

Findings

Stereocomplexation forms highly crystalline domains on nanoplatelets.

Enhanced heat transfer across nanoparticle contacts due to crystalline bridging.

Pyrene-terminated PLA effectively anchors to graphite surfaces.

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 {\pi}-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.