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1. Dynamics of ionic liquids in the presence of polymer-grafted nanoparticles

   https://doi.org/10.1039/c9nr04204k  

   Liu, Siqi; Liedel, Clemens; Tarakina, Nadezda V.; Osti, Naresh C.; Akcora, Pinar (October 2019, Nanoscale)

   null (Ed.)

   We incorporated polymer-grafted nanoparticles into ionic and zwitterionic liquids to explore the solvation and confinement effects on their heterogeneous dynamics using quasi-elastic neutron scattering (QENS). 1-Hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIM-TFSI) mixed with deuterated poly(methyl methacrylate) (d-PMMA)-grafted nanoparticles is studied to unravel how dynamic coupling between PMMA and HMIM-TFSI influence the fast and slow diffusion characteristics of the HMIM + cations. The zwitterionic liquid, 1-butyl-3-methyl imidazole-2-ylidene borane (BMIM-BH 3 ) is critically selected and mixed with PMMA-grafted nanoparticles for comparison in this work as its ions do not self-dissociate and it does not couple with PMMA through ion-dipole interactions as HMIM-TFSI does. We find that long-range unrestricted diffusion of HMIM + cations is higher in well-dispersed particles than in aggregated particle systems, whereas the localized diffusion of HMIM + is measured to be higher in close-packed particles. Translational diffusion dynamics of BMIM-BH 3 is not influenced by any particle structures suggesting that zwitterions do not interact with PMMA. This difference between two ionic liquid types enables us to decouple polymer effects from the diffusion of ionic liquids, which is integral to understand the ionic transport mechanism in ionic liquids confined in polymer-grafted nanoparticle electrolytes. 

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2. Ion Channels in Sulfonated Copolymer-Grafted Nanoparticles in Ionic Liquid

   https://doi.org/10.1039/D2SM00725H  

   Li, Ruhao; Han, Yuke; Akcora, Pinar (June 2022, Soft Matter)

   The use of ionic liquids as solvent for polymers or polymer-grafted nanoparticles provides an exciting feature to explore electrolyte-polymer interaction. 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIm-TFSI) holds specific interactions with the polymer through ion-dipole or hydrogen bonding. For this work, poly(methyl methacrylate)-b-poly(styrene sulfonate) (PMMA-b-PSS) copolymer-grafted Fe3O4 nanoparticles with different sulfonation levels (~4.9-10.9 mol% SS) were synthesized and their concentration dependent ionic conductivities were reported in acetonitrile and HMIm-TFSI/acetonitrile mixture. We found that conductivity enhancement with the particle concentration in acetonitrile was due to the aggregation of grafted particles, hence sulfonic domain connectivity. The ionic conductivity was found to be related to the effective hopping transfer within ionic channels. To the contrary, the conductivity decreased or remained constant with increasing particle concentration in HMIm-TFSI/acetonitrile. This result was attributed to the ion coupling between ionic liquid and copolymer domains. 

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3. Polymer-Encapsulated ionic liquids as lubricant additives in non-polar oils

   https://doi.org/10.1016/j.molliq.2023.122089  

   Yan, Jieming; Mangolini, Filippo (August 2023, Journal of Molecular Liquids)

   While ionic liquids (ILs) have attracted much attention as potential next-generation lubricant additives, their implementation in oil formulations has been hindered by their limited solubility in hydrocarbon fluids and corrosivity. Here, we encapsulate an oil-insoluble IL that has been studied in lubrication science, namely 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HMIM][TFSI]), within poly(ethylene glycol dimethacrylate-buytl methacrylate copolymer) (poly(EGDM-c-BMA)) microshells using a mini-emulsion polymerization process. The synthesized poly(EGDM-c-BMA)-encapsulated [HMIM][TFSI] microparticles are shown to be dispersible in a non-polar, synthetic oil (i.e., poly-α-olefin). Tribological experiments indicated that the microcapsules act as an additive reservoir that reduces friction by releasing the encapsulated IL at the sliding interface following the mechanical rupture of the polymer shell. X-ray photoelectron spectroscopy (XPS) measurements provided evidence that [HMIM][TFSI] does not tribochemically react on steel surfaces to create a reaction layer, thus suggesting that this IL reduces friction by generating a solid-like, layered structure upon nanoconfinement at sliding asperities, as proposed by previous nanoscale studies. The results of this work do not only provide new insights into the lubrication mechanism of ILs when used as additives in base oils in general, but also establish a new, broadly-applicable framework based on polymer encapsulation for utilizing ILs or other compounds with limited solubility as additives for oil formulations. 

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

   https://doi.org/10.1002/adfm.201905168  

   Kubiak, Joshua_M; Macfarlane, Robert_J (August 2019, Advanced Functional Materials)

   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. 

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5. Film Thickness Dependence of Surface and Internal Morphology Evolution in Polymer-Grafted Nanocomposites

   https://doi.org/10.1021/acs.macromol.4c00854  

   Zhang, Aria C; Ohno, Kohji; Composto, Russell J (July 2024, Macromolecules)

   This study investigates the interplay between film thickness and the surface and internal morphologies in polymer nanocomposite (PNC) films. The PNC is 25 wt.% poly(methyl methacrylate)-grafted silica nanoparticles (NPs) in poly(styrene-ran-acrylonitrile) annealed in the two-phase region. At greatest confinement (120 nm), NP surface density remains constant and lateral phase separation is inhibited upon annealing. For thicker films (240 nm to 1400 nm), surface density increases with time before approaching ca. 740 NP/μm2, consistent with 2D random close packing. Moreover, lateral domain growth exhibits a dimensional crossover as thickness increases from 𝑡 to , consistent with domain coalescence. Water contact angles 1/2 𝑡1/3 decrease upon annealing in agreement with the lateral domain composition. For thickest films (1400 nm to 4000 nm), a morphology map summarizes the distinct internal arrangements of NPs: disordered aggregates, continuous vertical pillars, discrete vertical pillars, isolated domains, and random networks. This study of PNC films provides guidance for controlling surface and bulk structure which can lead to improved barrier, mechanical and transport properties. 

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