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1. Confinement Effects on the Magnetic Ionic Liquid 1-Ethyl-3-methylimidazolium Tetrachloroferrate(III)

   https://doi.org/10.3390/molecules27175591  

   Burba, Christopher M. ; Chang, Hai-Chou ( September 2022 , Molecules)

   Confinement effects for the magnetoresponsive ionic liquid 1-ethyl-3-methylimidazolium tetrachloroferrate(III), [C2mim]FeCl4, are explored from thermal, spectroscopic, and magnetic points of view. Placing the ionic liquid inside SBA-15 mesoporous silica produces a significant impact on the material’s response to temperature, pressure, and magnetic fields. Isobaric thermal experiments show melting point reductions that depend on the pore diameter of the mesopores. The confinement-induced reductions in phase transition temperature follow the Gibbs–Thomson equation if a 1.60 nm non-freezable interfacial layer is postulated to exist along the pore wall. Isothermal pressure-dependent infrared spectroscopy reveals a similar modification to phase transition pressures, with the confined ionic liquid requiring higher pressures to trigger phase transformation than the unconfined system. Confinement also impedes ion transport as activation energies are elevated when the ionic liquid is placed inside the mesopores. Finally, the antiferromagnetic ordering that characterizes unconfined [C2mim]FeCl4 is suppressed when the ionic liquid is confined in 5.39-nm pores. Thus, confinement provides another avenue for manipulating the magnetic properties of this compound. 

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2. Sub-nanometer confinement enables facile condensation of gas electrolyte for low-temperature batteries

   https://doi.org/10.1038/s41467-021-23603-0  

   Cai, Guorui ; Yin, Yijie ; Xia, Dawei ; Chen, Amanda A. ; Holoubek, John ; Scharf, Jonathan ; Yang, Yangyuchen ; Koh, Ki Hwan ; Li, Mingqian ; Davies, Daniel M. ; et al ( June 2021 , Nature Communications)

   Confining molecules in the nanoscale environment can lead to dramatic changes of their physical and chemical properties, which opens possibilities for new applications. There is a growing interest in liquefied gas electrolytes for electrochemical devices operating at low temperatures due to their low melting point. However, their high vapor pressure still poses potential safety concerns for practical usages. Herein, we report facile capillary condensation of gas electrolyte by strong confinement in sub-nanometer pores of metal-organic framework (MOF). By designing MOF-polymer membranes (MPMs) that present dense and continuous micropore (~0.8 nm) networks, we show significant uptake of hydrofluorocarbon molecules in MOF pores at pressure lower than the bulk counterpart. This unique property enables lithium/fluorinated graphite batteries with MPM-based electrolytes to deliver a significantly higher capacity than those with commercial separator membranes (~500 mAh g⁻¹vs. <0.03 mAh g⁻¹) at −40 °C under reduced pressure of the electrolyte.

    

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3. Surface Chemical Functionalization to Achieve Extreme Levels of Molecular Confinement in Hybrid Nanocomposites

   https://doi.org/10.1002/adfm.201903132  

   Wang, Can ; Isaacson, Scott G. ; Wang, Yucheng ; Lionti, Krystelle ; Volksen, Willi ; Magbitang, Teddie P. ; Chowdhury, Mithun ; Priestley, Rodney D. ; Dubois, Geraud ; Dauskardt, Reinhold H. ( June 2019 , Advanced Functional Materials)

   Polymer confinement is realized in hybrid nanocomposites where individual polymer molecules are confined by a nanoporous matrix to dimensions less than the molecular size of the polymer. Here it is shown that by functionalizing the interior pore surfaces of a nanoporous organosilicate matrix, the pores can be filled with polystyrene molecules to achieve extreme levels of molecular confinement not previously possible. This provides opportunities for unique thermal and mechanical properties. It is shown that pore surface functionalization markedly impacts the polymer mobility during polymer infiltration by affecting the polymer–pore surface interaction, addressing the challenge of filling high‐molecular‐weight polymer molecules into nanoscale‐confined spaces. This allows for achieving extreme levels of molecular confinement with the loss of interchain entanglement and extensive polymer elongation along the pore axis. The glass transition temperature of the polymer is suppressed compared to bulk polymer melt, and is significantly affected by the polymer–surface interaction, which changes the polymer segmental mobility. The polymer–surface interaction also affects the interfacial polymer–pore sliding shear stress during polymer pullout from the nanopores, markedly affecting the fracture resistance of the nanocomposite.

    

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4. Kinetics of nanoconfined benzyl methacrylate radical polymerization

   https://doi.org/10.1002/pol.20230332  

   Zhai, Chunhao ; Koh, Yung P. ; Vogt, Bryan D. ; Simon, Sindee L. ( February 2024 , Journal of Polymer Science)

   The effect of nanoconfinement on the kinetics of benzyl methacrylate radical polymerization is investigated using differential scanning calorimetry. Controlled pore glass (CPG), ordered mesoporous carbons, and mesoporous silica are used as confinement media with pore sizes from 2 to 8 nm. The initial polymerization rate in CPG and mesoporous silica increases relative to the bulk and increases linearly with reciprocal pore size; whereas, the rate in the carbon mesopores decreases linearly with reciprocal pore size; the changes are consistent with the rate being related to the ratio of the pore surface area to pore volume. Induction times are longer for nanoconfined polymerizations, and in the case of CPG and carbon mesopores, autoacceleration occurs earlier, presumably due to the limited diffusivity and lower termination rates for the confined polymer chains. The molecular weight of the polymer synthesized in the nanopores is generally higher than that obtained in the bulk except at the lowest temperatures investigated. The equilibrium conversion under nanoconfinement decreases with decreasing temperature and with confinement size, exhibiting what appears to be a floor temperature at low temperatures.

    

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5. Capillary filling dynamics of polymer melts in a bicontinuous nanoporous scaffold

   https://doi.org/10.1063/5.0184427  

   Kong, Weiwei ; Neuman, Anastasia ; Zhang, Aria C ; Lee, Daeyeon ; Riggleman, Robert A ; Composto, Russell J ( January 2024 , The Journal of Chemical Physics)

   Polymer infiltrated nanoporous gold is prepared by infiltrating polymer melts into a bicontinuous, nanoporous gold (NPG) scaffold. Polystyrene (PS) films with molecular weights (Mw) from 424 to 1133 kDa are infiltrated into a NPG scaffold (∼120 nm), with a pore radius (Rp) and pore volume fraction of 37.5 nm and 50%, respectively. The confinement ratios (Γ=RgRp) range from 0.47 to 0.77, suggesting that the polymers inside the pores are moderately confined. The time for PS to achieve 80% infiltration (τ80%) is determined using in situ spectroscopic ellipsometry at 150 °C. The kinetics of infiltration scales weaker with Mw, τ80%∝Mw1.30±0.20, than expected from bulk viscosity Mw3.4. Furthermore, the effective viscosity of the PS melt inside NPG, inferred from the Lucas–Washburn model, is reduced by more than one order of magnitude compared to the bulk. Molecular dynamics simulation results are in good agreement with experiments predicting scaling as Mw1.4. The reduced dependence of Mw and the enhanced kinetics of infiltration are attributed to a reduction in chain entanglement density during infiltration and a reduction in polymer–wall friction with increasing polymer molecular weight. Compared to the traditional approach involving adding discrete particles into the polymer matrix, these studies show that nanocomposites with higher loading can be readily prepared, and that kinetics of infiltration are faster due to polymer confinement inside pores. These films have potential as actuators when filled with stimuli-responsive polymers as well as polymer electrolyte and fuel cell membranes.

    

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