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

Abstract

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.

Recent Applications of Ionic Liquids in the Sol-Gel Process for Polymer–Silica Nanocomposites with Ionic Interfaces

“…In this process, the selection of the silica domains growth mechanism (i.e., monomer-cluster or cluster-cluster) is an important factor for good filler dispersion. It was found that the tendency of forming smaller silica domains in cluster-cluster mechanism makes it more favorable for the homogeneous nanocomposite formation [4,[6][7][8]111]. Also the non-hydrolytic approach provides slower nanosilica growth, thus facilitating better structure and morphology control [8,112].…”

“…These materials constitute a new family of thermally-resistant structurally-ordered solids that can be exploited in areas like electrochemistry [21,91,92], catalysis [93,94], biocatalysis, optics, sensors [85], electrorheological fluids [95][96][97] and nanocomposites preparation [4,[6][7][8][9]11]. …”

“…It has been shown that both, the ex situ application of pre-formed sol-gel silica-IL hybrids in melted thermoplastics [6] and in situ formation in thermosets [4,[7][8][9][10] or water soluble polymers [11] improve significantly thermo-mechanical properties of polymer matrices. In those systems ILs act There are two main IL classes that differ by the synthesis type, which involve the proton transference (protic ILs) or an alquilation process (aprotic ILs).…”

“…However, it is known that the structural behavior of the original solution also determines the polycondensation and network formation in the sol-gel process [2]. Further, a series of studies were performed applying and investigating the influence of different ILs from the first moments of the reaction, allowing further particle structure control [3][4][5]8,60] 6 ]) resulted in highly distinct morphologies, depending on anion applied. Moreover, further extracting the ILs exposed the ordered porous silica structures formed ( Figure 5) [60].…”

“…However, it is known that the structural behavior of the original solution also determines the polycondensation and network formation in the sol-gel process [2]. Further, a series of studies were performed applying and investigating the influence of different ILs from the first moments of the reaction, allowing further particle structure control [3][4][5]8,60]. It was observed initially that the use of ILs with 1-ethylene glycol monomethyl ether-3-methylimidazolium [C3OMIm] cation associated to different anions ([BF4], methanesulfonate [MeSO3], and hexafluorophosphate [PF6]) resulted in highly distinct morphologies, depending on anion applied.…”