Confinement Effect on the Surface of a Metal–Organic Polyhedron: Tunable Thermoresponsiveness and Water Permeability

Abstract

Materials under space confinement can alter their physical and chemical properties, paving the way for new science and novel applications. Nanoparticles can enforce spatial constraints on the polymers densely grafted on their surfaces, which can effectively change polymers’ thermal/mechanical properties and finally lead to significant mechanical reinforcement for the obtained nanocomposites. Here, we describe the confinement effect that metal–organic polyhedron (MOPs), nanoparticles with monodispersed and ultrasmall sizes (∼2 nm), impose to the 24 poly­(N-isopropylacrylamide) (PNiPAM) chains grafted on their surface. The curved surface of the MOP brings unique confinement to the grafted PNiPAMs: the inner fraction of PNiPAM chains is under ultraconfinement, while the outer fraction is almost free. Suggested from small angle neutron scattering studies, the outer layer polymers stay hydrated and help solvate the nanocomposites in water, while the inner polymer layer prohibits the water penetration into MOP area and contributes to the high stability of the MOPs. Such a confinement effect further influences the thermoresponsiveness of PNiPAM–MOPs in solutions and enhances their efficiency for controlled separation and release of small molecules.

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

“…Ligand exchange dynamics among MOPs in their bulks. Originated from the hierarchically constrained dynamics of MOP ligands, [25][26] the ligand exchange on MOP surface demonstrates logarithmic kinetics, which is distinct from the ligand exchange kinetics of simple coordination complexes (usually first order reaction kinetics). [27][28] This finally enables the unique thermally activated polymer network dynamics rather than fast dynamics feature of that from simple coordination complex.…”

Model2SAS: software for small-angle scattering data calculation from custom shapes

“…In recent years, SAS has become a powerful tool in the study of porous NPs such as {Mo 132 } and metal-organic polyhedra (MOPs) (Fig. S1) (Yin et al, 2016;Zhang et al, 2019;Lai et al, 2020;Abourahma et al, 2001;Eddaoudi et al, 2001). Conventionally, the SAS data of these NPs are fitted by a coreshell model.…”

Metal–Organic Polyhedra as Building Blocks for Porous Extended Networks

“…[ 65 ] The same approach was later used by Yin et al using poly( N ‐isopropylacrylamide) ( PNiPAM ) as a polymeric chain instead of PEG. [ 66 ]…”

“…[65] The same approach was later used by Yin et al using poly(N-isopropylacrylamide) (PNiPAM) as a polymeric chain instead of PEG. [66] Hydrophobic shielding also has been used to modulate the permeability of water molecules into a MOP structure. [67] For example, Ghosh et al demonstrated that attaching hydrophobic moieties to the exposed surface of a cuboctahedral Cu-MOP enhanced its hydrolytic stability.…”