Origin of Carbon Nanotubes Induced Poly(l-Lactide) Crystallization: Surface Induced Conformational Order

PEG-Grafted Graphene/PLLA Nanocomposites: Effect of PEG Chain Length on Crystallization Kinetics of PLLA

Poly-l-lactic acid (PLLA) nanocomposites containing graphene oxide (GO), modified with different chain lengths of poly(ethylene glycol) (PEG) (400, 2000, and 10 000 g/mol), were prepared by solution casting. The effect of the PEG chain length and nanoparticle content (0.5, 1, and 1.5 wt %) on the nucleation, crystal growth rate, and overall crystallization rate, under isothermal conditions, was then evaluated. The results showed that, in samples containing GO modified with 400 g/mol of PEG, the nucleation density increased as a function of a modified nanoparticle concentration. In the case of the samples containing GO modified with PEG of a molar mass of either 2000 or 10 000 g/mol, the nucleation density exhibited a maximum at a concentration of 1 wt %. Furthermore, the addition of graphene oxide modified with poly(ethylene glycol) of a molar mass of 2000 g/mol resulted in the largest nucleation, fastest crystal growth, and highest overall crystallization rate, for all concentrations. The results were explained in light of the steric hindrance between the modified nanoparticles.

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

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.

The Effect of Grafting Density on the Crystallization Behaviors of Polymer Chains Grafted onto One-Dimensional Nanorod

The crystallization behaviors of five polymer chain systems grafted on a nanorod and the corresponding effect of grafting density were investigated by dynamic Monte Carlo simulations. The segment density near the interfacial regions, the number of crystallites, and the mean square radius of gyration (<Rg2>) increase with increasing grafting density, which are beneficial to the enhancement of crystallizability. Meanwhile, the crystalline morphology is greatly influenced by grafting density and polymer-nanorod interaction. For the grafted system with 52 chains, a nanohybrid shish-kebab (NHSK) structure is formed, when the polymer-nanorod interaction (Eb/Ec) is -0.4. For the system with 128 chains, a NHSK structure is formed, when Eb/Ec is -1.0. For the system with 252 chains, NHSK structure cannot be formed. The findings in this work can supply important theoretical reference for the design, preparation, and application of polymer nanocomposites.

Stereocomplex formation in mixed polymers filled with two-dimensional nanofillers

Nanosheets promote the formation of stereocomplex crystallites due to the heterogeneous nucleation of mixed polymer chains on filler surfaces.

Epitaxial crystallization of precisely bromine-substituted polyethylene induced by carbon nanotubes and graphene

Epitaxial crystallization of precisely bromine-substituted polyethylene induced by carbon nanotubes and graphene.

Insight into the role of bound water of a nucleating agent in polymer nucleation: a comparative study of anhydrous and monohydrated orotic acid on crystallization of poly(l-lactic acid)

The bound water of orotic acid and its dehydration transition play a negative role in nucleation effects on PLLA crystallization.

Polymer crystal nucleation with confinement-enhanced orientation dominating the formation of nanohybrid shish-kebabs with multiple shish

An unexpected NHSK structure with multiple shish is observed. The aligned fillers act as multiple shish and the polymer crystal lamellae form kebabs.

Graphene oxide induced isotactic polypropylene crystallization: role of structural reduction

Nucleation ability of reduced GO was enhanced by the removal of oxygenic groups and the partial recovery of sp² carbon network.

Molecular dynamics simulation of melting and crystallization processes of polyethylene clusters confined in armchair single-walled carbon nanotubes

The confined interaction is important to understand the melting and crystallization of polymers within single-wall carbon tube (SWNT). However, it is difficult for us to observe this interaction. In the current work, the structures and behaviors of melting and crystallization for polyethylene (PE) clusters confined in armchair single-walled carbon nanotubes ((n,n)-SWNTs) are investigated and examined based on molecular dynamics (MD) simulations. The nonbonded energies, structures, Lindemman indices, radial density distributions, and diffusion coefficients are used to demonstrate the features of melting phase transition for PE clusters confined in (n,n)-SWNTs. The chain end-to-end distance (R(n)) and chain end-to-end distribution are used to examine the flexibility of the PE chain confined in SWNT. The global orientational order parameter (P2) is employed to reveal the order degree of whole PE polymer. The effect of polymerization degree on melting temperature and the influence of SWNT chirality on structure of PE cluster are examined and discussed. Results demonstrate that within the confined environment of SWNT, PE clusters adopt novel co-axial crystalline layer structure, in which parallel chains of each layer are approximately vertical to tube axis. The disordered-ordered transformation of PE chains in each layer is an important structural feature for crystallization of confined PE clusters. SWNTs have a considerable effect on the structures and stabilities of the confined PE clusters.

A free radical assisted strategy for preparing functionalized carbon nanotubes as a highly efficient nucleating agent for poly(l-lactide)

Schematic illumination of the fabrication of the CNT-OEG via free radical polymerization.

Novel polymorphism behavior of poly(butylene adipate) in its nanocomposites with carbon nanofibers

Carbon nanofibers prominently enhance the formation of α-form crystal poly(butylene adipate) at low temperature and lead to a novel plateau phenomenon of α-form crystal content in their composites through specific CH–π interactions.