Ricardo Keitel Donato

The multifunctional role of ionic liquids in the formation of epoxy-silica nanocomposites

This work addresses the use of ionic liquids (ILs) as additives for formation of epoxy-silica nanocomposites, via the simultaneous sol–gel process and epoxy network build-up. The application of different methylimidazolium based ILs allows controlling the silica structure and modifying interphase interaction, thus producing hybrids with diverse morphologies and improved mechanical properties. Both the anionic and cationic components of the ILs affected the hybrid formation and the final properties. The application of 1-decyl-3-methylimidazolium tetrafluoroborate ionic liquid together with HCl as an acid catalyst promotes both hydrolysis and condensation in the sol–gel process as well as the self-assembly ordering of the IL. This system produces a very fine hybrid morphology with well dispersed silica nanodomains and a significantly increased rubbery modulus due to physical crosslinking by the ordered domains of decyl-substituents.

Imidazolium salts as antifungal agents: strong antibiofilm activity against multidrug-resistant Candida tropicalis isolates

The in vitro activity of the imidazolium salt C16MImCl against planktonic and biofilm cells of multidrug‐resistant isolates of Candida tropicalis was evaluated, both in solution and applied on a commercial catheter surface. This was determined by inhibition and susceptibility assays of biofilm and planktonic cells. In both cases, C16MImCl prevented in vitro biofilm formation of C. tropicalis strains, including multidrug‐resistant ones. Outstanding performances were observed, even at extremely low concentrations. Furthermore, this is the first report of the antifungal lock property of C16MImCl, using a tracheal catheter as the test specimen to mimic a clinical in vivo condition. As such, C16MImCl has been identified as a promising antimicotic pharmaceutical candidate for the treatment of candidiasis infections.

Imidazolium Salts as Antifungal Agents: Activity Against Emerging Yeast Pathogens, Without Human Leukocyte Toxicity

This study demonstrates the excellent in vitro antifungal activity profile of imidazolium ionic liquids (ILs) against species of opportunistic human mycoses. Several ILs were identified as more effective and less harmful than commercially available antifungal medications. Frequently, emerging yeast pathogens are resistant against commercial antifungal agents and, as a consequence, this class of imidazolium ILs represents a promising breakthrough in their treatment.

Tunable reinforcement of epoxy-silica nanocomposites with ionic liquids

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.

Imidazolium salts with antifungal potential against multidrug-resistant dermatophytes.

To investigate the antidermatophytic action of a complementary set imidazolium salts (IMS), determining structure‐activity relationships and characterizing the IMS toxicological profiles.

Epoxy–silica nanocomposite interphase control using task-specific ionic liquids via hydrolytic and non-hydrolytic sol–gel processes

Carboxylic-functionalized task-specific imidazolium ionic liquids (carboxylic-ILs) presented selective high reactivities with epoxy-functionalized compounds, even in highly complex epoxy–silica nanocomposite systems. The carboxylic-ILs induced the in situ covalent bonding with epoxy based materials and tuning of the nanocomposites’ filler–matrix interphase when applied either via hydrolytic or non-hydrolytic sol–gel processes. Structural modifications in the carboxylic-ILs allowed fine morphology control and promoted the formation of well dispersed silica nanodomains. This approach resulted in nanocomposites with improved mechanical properties, without a 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 a toughness increase of more than 7 times for the rubbery and almost twice for the glassy epoxy systems, when compared to their IL-free equivalents. These easy and quick procedures to produce imidazolium functionalized materials have the potential to open up a broad range of new conductive, responsive, smart and tunable reinforced materials.

Ionic liquids as dynamic templating agents for sol-gel silica systems: synergistic anion and cation effect on the silica structured growth

This work presents a detailed investigation about the influence of a complementary set of imidazolium ionic liquids (IL: [C4MIm][BF4]–[C10MIm][BF4]–[C7O3MIm][BF4]–[C4MIm][NTf2]–[C10MIm][NTf2]–[C7O3MIm][NTf2]) 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.Graphical Abstract

Tailored high performance shape memory epoxy–silica nanocomposites. Structure design

High performance shape memory (SM) epoxy–silica nanocomposites have been synthesized. The structure of the corresponding SM polymer was designed on the basis of the determined relationships between structure, mechanical properties and SM performance. The recovery stress, as a crucial SM property of high performance systems, is governed by the material toughness while the efficiency of the SM performance is controlled by morphological homogeneity and viscoelastic behaviour of the polymer as well as by experimental conditions of the SM procedure. The nanocomposites were prepared by in situ generation of nanosilica in the epoxy matrix. A non-aqueous sol–gel procedure was applied and the ionic liquid (IL) was used in the synthesis as a multifunctional agent controlling morphology and mechanical properties. The effect of nanosilica, IL, crosslinking density of the epoxy network, physical crosslinking as well as the application of the concept of bimodal networks on SM performance was evaluated and discussed. Based on the knowledge of the corresponding relationships and structural effects the SM nanocomposite was synthesized showing the high recovery stress σr = 3.9 MPa or high deformability eb = 103%. The study contributed to the better understanding of the SM behaviour of polymers.

“Unrolling” multi-walled carbon nanotubes with ionic liquids: application as fillers in epoxy-based nanocomposites

This work describes a straightforward procedure for the preparation of graphene by opening multi-walled carbon nanotubes (CNT), using ionic liquids (IL) as lubricating and stabilizing agents. The sequential application of vacuum and sonication allows the successful opening and unrolling of the CNT, and the final nanocarbon morphology is IL-dependent. This enabled the preparation of epoxy-based nanocomposites with morphologically distinct carbon nanofillers. The CNT–IL mixtures and nanocomposites obtained were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy.

Biocompatible succinic acid-based polyesters for potential biomedical applications: fungal biofilm inhibition and mesenchymal stem cell growth

Herein, we present the intrinsic property of well-known polyesters [poly(alkene succinates)], as Candida albicans and Candida tropicalis biofilm inhibitors with potential to substantially reduce the incidence of device-associated infections in, e.g., indwelling catheters and sutures. These new biopolymer applications, either for manufacturing or coating medical devices, present innovative features such as: simple and cheap preparation, easy scaling-up, good mechanical and thermal resistance properties, and antibiofilm ability without any specific surface functionalization or antimicrobial agent encapsulation. Furthermore, the polyesters are shown to be highly biocompatible, promote human mesenchymal stem cell (hMSC) attachment and proliferation, inducing morphological changes, which are dependent on the polymer structural characteristics, making them promising candidates for materials in specialized medical devices and in the tissue engineering field.