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1. Confinement Effects in Dynamics of Ionic Liquids with Polymer‐Grafted Nanoparticles

   https://doi.org/10.1002/cphc.202200219  

   Liu, Siqi ; Li, Ruhao ; Tyagi, Madhusudan ; Akcora, Pinar ( June 2022 , ChemPhysChem)

   Ionic liquid mixed with poly(methyl methacrylate)-grafted nanoparticle aggregates at low particle concentrations was shown to exhibit different dynamics and ionic conductivity than that of pure ionic liquid in our previous studies. In this work, we report on the quasi-elastic neutron scattering results on ionic liquid containing polymer-grafted nanoparticles at the higher particle concentration. The diffusivity of imidazolium (HMIM + ) cations of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIM-TFSI) in the presence of poly(methyl methacrylate)-grafted iron oxide nanoparticles and the ionic conductivity of solutions were discussed through the confinement. Analysis of the elastic incoherent structure factor suggested the confinement radius decreased with the addition of grafted particles in HMIM-TFSI/solvent mixture, indicating the confinement that is induced by the high concentration of grafted particles, shrinks the HMIM-TFSI restricted volume. We further conjecture that this enhanced diffusivity occurs as a result of the local ordering of cations within aggregates of poly(methyl methacrylate)-grafted particles.
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.
3. Zwitterionic copolymer additive architecture affects membrane performance: fouling resistance and surface rearrangement in saline solutions

   https://doi.org/10.1039/C8TA11553B  

   Kaner, Papatya ; Dudchenko, Alexander V. ; Mauter, Meagan S. ; Asatekin, Ayse ( February 2019 , Journal of Materials Chemistry A)

   Membrane separations are simple to operate, scalable, versatile, and energy efficient, but their broader use is curtailed by fouling or performance decline due to feed component depositing on the membrane surface. Surface functionalization with groups such as zwitterions can mitigate the adsorption of organic compounds, thus limiting fouling. This can be achieved by using surface-segregating copolymer additives during membrane manufacture, but there is a need for better understanding of how the polymer structure and architecture affect the effectiveness of these additives in improving membrane performance. In this study, we aim to explore the impact of the architecture of zwitterionic copolymer additives for polyvinylidene fluoride (PVDF)-based membranes in fouling mitigation and ionic strength response. We prepared membranes from blends of PVDF with zwitterionic (ZI) copolymers with two different architectures, random and comb-shaped. As the random copolymer, we used poly(methyl methacrylate- random- sulfobetaine-2-vinyl pyridine) (PMMA- r -SB2VP) synthesized by free radical polymerization. The comb-shaped copolymer was synthesized by grafting SB2VP side-chains from a PVDF backbone by controlled radical polymerization. Membranes were fabricated from PVDF-copolymer blends containing up to 5 wt% ZI copolymer. Compared to the additive-free PVDF membrane, water permeance increased five-fold with 5 wt% addition of either copolymer. The comb copolymermore »additive led to better resistance to fouling by a saline oil-in-water emulsion and to simulated protein adsorption in Atomic Force Microscopy (AFM) force measurements. The additive architecture had a significant influence on how membranes respond to changes in feed salinity, which is known to affect intra- and inter-molecular interactions in zwitterionic polymers. The random copolymer containing membrane showed a small and mostly reversible decrease in its permeance with salinity. In contrast, the comb copolymer-containing membrane underwent a conformational reorganization in saline solutions that leads to an irreversible permeance decrease, increased zwitterionic group content on the membrane surface, and smoother surface topography. The higher mobility of the zwitterionic groups in the comb-shaped architecture facilitates reorganization of the zwitterionic side-chains in response to ionic strength. Overall, this study establishes a new approach for developing highly fouling resistant membranes and defines how the architecture of a zwitterionic copolymer additive impacts the ionic strength response and fouling resistance of the membrane.« less
4. Surface Enrichment of Polymer-Grafted Nanoparticles in a Miscible Polymer Nanocomposite

   https://doi.org/10.1021/acs.macromol.2c00839  

   Maguire, Shawn M. ; Demaree, John Derek ; Boyle, Michael J. ; Keller, Austin W. ; Bilchak, Connor R. ; Kagan, Cherie R. ; Murray, Christopher B. ; Ohno, Kohji ; Composto, Russell J. ( August 2022 , Macromolecules)

   We show that the polymer-grafted nanoparticles (NPs) initially welldispersed in a polymer matrix segregate to the free surface of a film upon thermal annealing in the one-phase region of the phase diagram because the grafted polymer has a lower surface energy than the matrix polymer. Using a combination of atomic force microscopy, transmission electron microscopy, and Rutherford backscattering spectrometry, the evolution of the poly(methyl methacrylate)-grafted silica NP (PMMA NP) surface excess in 25/75 wt % PMMA NP/poly(styrene-ranacrylonitrile) films is observed as a function of annealing time at 150 °C (T < TLCST). The temporal growth of the surface excess is interpreted as a competition between entropic contributions, surface energy differences of the constituents, and the Flory−Huggins interaction parameter, χ. For the first time in a miscible polymer nanocomposite mixture, quantitative comparisons of NP surface segregation are made with the predictions of theory derived for analogous polymer blends. These studies provide insight for designing polymer nanocomposite films with advantageous surface properties such as wettability and hardness and motivate the need for developing rigorous models that capture complex polymer nanocomposite phase behaviors.
5. Model hard ellipsoids: the practical matter of producing them.

   Hollingsworth, A. ; Chaikin, P.M. ; Kondic, L. ; Reich, A. ; Khusid, B. ( March 2020 , Bulletin of the American Physical Society)

   Model hard colloids have a great deal of relevance to physics and in particular the study of their phase behavior which can mimic that of simple atomic liquids and solids. "Nearly hard colloidal sphere" suspensions were formulated 35 years ago by the Ottewill group (Univ. of Bristol) and Imperial Chemical Industries Ltd., which were used by Pusey and van Megen in their seminal study of the phase behavior of hard-sphere colloids. We report on our efforts to reproduce and refine this benchmark polymer colloid, including the recent synthesis of hard ellipsoids for random and ordered packing studies in microgravity*. The custom-made samples are composed of linear polymer chains of poly(methyl methacrylate), functionalized with photo-crosslinkable moieties and fluorescent molecules. The resulting ellipsoidal shapes are about 1 micron in size and stabilized with surface-grafted poly(12-hydroxystearic acid) chains. The particles are dispersed in a refractive index matching fluid and particle aspect ratios vary from 1 to 4. * Launched March 2020 aboard SpaceX CRS-20 resupply service mission to the International Space Station. *NASA NNX13AR67G (NYU); NSF GOALI 1832291 (NYU); NSF GOALI 1832260 (NJIT)