In this study, the structure, electrical and thermal properties of ten polymer compositions based on polylactic acid (PLA), low-cost industrial graphene nanoplates (GNP) and multi-walled carbon nanotubes (MWCNT) in mono-filler PLA/MWCNT and PLA/GNP systems with 0–6 wt.% filler content were investigated. Filler dispersion was further improved by combining these two carbon nanofillers with different geometric shapes and aspect ratios in hybrid bi-filler nanocomposites. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy exhibited uniform dispersion of nanoparticles in a polymer matrix. The obtained results have shown that for the mono-filler systems with MWCNT or GNP, the electrical conductivity increased with decades. Moreover, a small synergistic effect was observed in the GNP/MWCNT/PLA bi-filler hybrid composites when combining GNP and CNT at a ratio of 3% GNP/3% CNT and 1.5% GNP:4.5% CNT, showing higher electrical conductivity with respect to the systems incorporating individual CNTs and GNPs at the same overall filler concentration. This improvement was attributed to the interaction between CNTs and GNPs limiting GNP aggregation and bridging adjacent graphene platelets thus, forming a more efficient network. Thermal conductivity increases with higher filler content; this effect was more pronounced for the mono-filler composites based on PLA and GNP due to the ability of graphene to better transfer the heat. Morphological analysis carried out by electron microscopy (SEM, TEM) and Raman indicated that the nanocomposites present smaller and more homogeneous filler aggregates. The well-dispersed nanofillers also lead to a microstructure which is able to better enhance the electron and heat transfer and maximize the electrical and thermal properties. The obtained composites are suitable for the production of a multifunctional filament with improved electrical and thermal properties for different fused deposition modelling (FDM) 3D printing applications and also present a low production cost, which could potentially increase the competitiveness of this promising market niche.

Imidazolium ionic liquids (ILs) have the capacity to exert multiple functions as additives for the formation of epoxy-silica nanocomposites, via the simultaneous sol-gel process and epoxy network build-up. This study addresses the effect of ILs on the reinforcement of tensile properties in rubbery epoxy-silica nanocomposites, allowing property tailoring. The use of ILs together with the coupling agent 3-glycidyloxypropyltrimethoxysilane (GTMS) created a synergic action between physical and chemical interfacial bonding, enabling an increase in toughness without a considerable loss of stiffness. The best tensile property balance was obtained with IL 1-triethylene glycol monomethyl ether-3-methylimidazolium methanesulfonate and GTMS. The rubbery nanocomposite produced was remarkably both stiffer and tougher than the unmodified epoxy-silica system, displaying ca. 6 times higher modulus and tensile strength as well as more than 10 times higher energy to break.

Carboxylic-functionalyzed task-specific imidazolium ionic liquids (carboxylic-IL) presented selective high reactivities with epoxy-functionalized compounds, even in highly complex epoxy-silica nanocomposite systems. The carboxylic-IL induced the in situ covalent bonding with epoxy based materials and tuning the nanocomposites' filler-matrix interphase when applied either via hydrolytic or non-hydrolytic sol-gel process. Structural modifications in the carboxylic-IL allowed fine morphology control and promoted the formation of well dispersed silica nanodomains. This approach resulted in nanocomposites with improved mechanical properties, without negative effect on the glass transition temperature, for both rubbery and glassy epoxy-silica nanocomposite systems with a very small IL content (~0.2 wt.-%). The best properties were achieved with the application of IL 1-carboxypropyl-3-methylimidazolium chloride, which produced toughness increase of more than 7 times for the rubbery and almost twice for the glassy epoxy systems, when compared to their ILfree equivalents. These easy and quick procedures to produce imidazolium functionalized materials have the potential to open a broad range of new conductive, responsive, smart and tune-reinforced materials. Fig. 9 Time dependent FTIR spectra of the reaction between PGE and C3H6CO2HMImCl. Curves represent measurements at 30 min, 1 h, 5 h, 24 h and 48 h. Scheme 1 Sumary of characteristics of the epoxy-silica formed via hydrolytic and non-hydrolytic sol-gel process in the presence of IL.Scheme 2 Schematic representation of the interphase compositions depending on the IL applied, based on a sequence of covalent and physical bonds.

This work presents a detailed investigation about the influence of a complementary set of imidazolium ionic liquids ([NTf 2 ]) in the preparation of hydrolytic sol-gel silica wet gels and xerogels, providing insights into their hierarchical structures, morphologies of primary particles and aggregation domains. The reported IL decreased dramatically the gelation time (up to *500 times), evolving the systems to transparent or opalescent wet gels with distinct consistencies, or silica powders. Characterization of the obtained silica xerogels was performed by transmission and scanning electron microscopy, atomic force microscopy, X-ray diffraction, small-angle X-ray scattering and thermogravimetric analysis. In general, the IL allowed controlling the silica particle size, color, compactness, structures and morphology. The xerogels showed homogenous and ordered structures (spherical or triangular) of different sizes and with distinct microporosities, depending on the IL applied. These results highlight the key role of IL in the sol-gel silica synthesis with controlled properties, which can be further tuned for specific applications by changing small process parameters.Electronic supplementary material The online version of this article (