Forming Covalent Crosslinks between Polymer‐Grafted Nanoparticles as a Route to Highly Filled and Mechanically Robust Nanocomposites

Abstract

Filler aggregation in polymer matrix nanocomposites leads to inhomogeneity in particle distribution and deterioration of mechanical properties. The use of polymer grafted nanoparticles (PGNPs) with polymers directly attached to the particle surfaces precludes aggregation of the filler. However, solids composed of PGNPs are mechanically weak unless the grafted chains are long enough to form entanglements between particles, and requiring long grafts limits the achievable filler density of the nanocomposite. In this work, long, entangled grafts are replaced with short reactive polymers that form covalent crosslinks between particles. Crosslinkable PGNPs, referred to as XNPs, can be easily processed from solution and subsequently cured to yield a highly filled yet mechanically robust composite. In this specific instance, silica nanoparticles are grafted with poly(glycidyl methacrylate), cast into films, and crosslinked with multifunctional amines at elevated temperatures. Indentation and scratch experiments show significant enhancement of hardness, modulus, and scratch resistance compared to non-crosslinked PGNPs and to crosslinked polymer films without nanoparticle reinforcement. Loadings of up to 57 wt% are achieved while yielding uniform films that deform locally in a predominantly elastic manner. XNPs therefore potentially allow for the formulation of robust nanocomposites with a high level of functionality imparted by the selected filler particles.

Electrochemically Active Red P/BaTiO3‐Based Protective Layers Suppressing Li Dendrite Growth for Li Metal Batteries

“…Hardness is a measure of the resistance against deformation, such as penetration. [ 22 ] The hardness of Red P CPL was remarkably similar to that of PVdF‐HFP CPL, despite the fact that Red P CPL contained red P particles. This indicates that the mechanical property of PVdF‐HFP CPL was negligibly changed by the addition of red P particles.…”

Polymer‐Grafted Nanoparticles as Single‐Component, High Filler Content Composites via Simple Transformative Aging

“…Silica nanoparticles were prepared via the Stöber method and then immediately functionalized with (2‐bromo‐2‐methyl)propionyloxyhexyltriethoxysilane (BHE) in the same flask as reported previously. [ 31 ] Particles were purified by repeated centrifugation and kept as a stock solution in anisole.…”

“…An alternative method for achieving high filler content while maintaining mechanical robustness is to use short polymer grafts that contain reactive groups capable of forming covalent interparticle cross‐links; previous work has demonstrated that doing so can enhance stiffness, hardness, and damage resistance in cross‐linked PGNP films, even at loadings of 40 vol% filler. [ 31 ] Similar work has demonstrated mechanical property enhancement after thermally generating cross‐links between short aliphatic capping groups. [ 32,33 ] While this covalent cross‐linking strategy is promising, these materials were processed by slow drying from solution due to the fragility of the material prior to cross‐linking, which limits the applicability of this approach to only thin films or coatings.…”

Ordered polymer composite materials: challenges and opportunities

“…To circumvent the abovementioned drawbacks, polymer grafts containing end-tethered supramolecular recognition groups with precise binding behavior have been employed in regulating the superstructures of NP assemblies. 197,[201][202][203][204] When compared with hydrophobic forces, supramolecular interactions with chemically accurate stoichiometry have several key advantages: (1) the binding strength between complementary recognition group pairs can be determined using small molecules as model systems; (2) the supramolecular recognition motifs can be designed independently from the polymer component, thereby significantly increasing the modularity of the nanocomposite building blocks; (3) the versatile nature of supramolecular binding groups can introduce multi-stimuli responsiveness into the assembly.…”

“…Preliminary evidence even suggests that such structures may possess unique and tunable optical, magnetic, or mechanical properties as a function of their structural organization. 203,204 In order to further develop the potential of NCTs for forming ordered nanocomposites, it is necessary to expand their viability to a wider array of both NCT chemical compositions (i.e., different polymers, NP cores, and supramolecular recognition groups) and assembly conditions. This will allow the preparation of different model systems for ordered nanocomposites, enabling the further study of structure-property relationships and the establishment of design rules for ordered nanocomposite materials with programmable properties.…”