Here, we report a new class of hybrid nanoparticles (NPs) that are self-supporting and display viscous flow behavior in the absence of solvent, yet convert to a purely inorganic material on heating. Hairy nanoparticles (HNPs) composed of silica nanoparticle cores (10−20 nm diameter) and preceramic poly(1,1-dimethylpropylsilane) (l-PCS) brushes were synthesized via a grafting-from approach utilizing hydrosilylation chemistry. The l-PCS polymer brush was grown from the nanoparticle core by anchoring the Pt(0) Karstedt's catalyst to Si−H groups functionalized on the silica surface. The resulting l-PCS-based HNPs were easily dispersed in a variety of organic solvents, displaying Newtonian rheological behavior at low weight percent solvent loadings, while neat HNPs displayed relatively low viscosities. The Krieger−Dougherty equation was used to evaluate viscosity trends as related to corona size, with the corona size being determined through dynamic light scattering. Thermally cured HNPs were successfully converted to SiO 2 /SiC nanocomposites, as evidenced by X-ray diffraction and attenuated total reflection (ATR)-Fourier transform infrared (FTIR). These unique preceramic HNPs hold considerable promise as a route to high-temperature materials, offering enhanced processability and compositional tailorability compared to neat resins.
Lamellar
block copolymers based on polymeric ionic liquids (PILs) show promise
as electrolytes in electrochemical devices. However, these systems
often display structural anisotropy that depresses the through-film
ionic conductivity. This work hypothesizes that structural anisotropy
is a consequence of surface-induced ordering, where preferential adsorption
of one block at the electrode drives a short-range stacking of the
lamellae. This point was examined with lamellar diblock copolymers
of polystyrene (PS) and poly(1-(2-acryloyloxyethyl)-3-butylimidazolium
bis(trifluoromethanesulfonyl)imide) (PIL). The bulk PS–PIL
structure was comprised of randomly oriented lamellar grains. However,
in thin PS–PIL films (100–400 nm), the lamellae were
stacked normal to the plane of the film, and islands/holes were observed
when the as-prepared film thickness was incommensurate with the natural
lamellar periodicity. Both of these attributes are well-known consequences
of preferential wetting at surfaces. The ionic conductivity of thick
PS–PIL films (50–100 μm) was approximately 20×
higher in the in-plane direction than in the through-plane direction,
consistent with a mixed structure comprised of randomly oriented lamellae
throughout the interior of the film and highly oriented lamellae at
the electrode surface. Therefore, to fully optimize the performance
of a block copolymer electrolyte, it is important to consider the
effects of surface interactions on the ordering of domains.
Incorporating dynamic bonds into polymers enables static thermosets to be transformed into active materials, possessing the reprocessability of thermoplastics while maintaining the bulk properties of fully crosslinked networks. This new class of materials, termed covalent adaptable networks (CANs), has helped bridge the gap between traditional thermosets and thermoplastics. Here, epoxy-based adaptable networks were synthesized by combining a diepoxide monomer with an oligosiloxane prepolymer containing aminopropyl groups, which crosslink irreversibly, and silanolate end-groups, which participate in dynamic bonding. Two separate diepoxide crosslinkers were used to give a range of soft to stiff materials with a Young’s modulus varying from 12 MPa to 2.2 GPa. This study documents how the thermal and mechanical properties (e.g., glass transition temperature and modulus) are affected by compositional changes in these silanolate networks. Dynamic bonding also results in self-healing properties, offering the ability to repair structural polymers and composites. When combined with tunable mechanical properties, self-healing capabilities make these materials well-suited to be sustainable alternatives for many traditional thermosets. For example, we demonstrated the ability to weld a stiff epoxy thermoset to a dissimilar soft material, a feature traditional epoxies do not permit.
Graphical abstract
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