Molecular Dynamics Study of the Dispersion Stability and Fluidity of Porous Liquids with Different Canopy Structures

Abstract

Porous liquids (PLs) as a new class of materials have broad application prospects in many areas such as gas separation and storage, air separation, and homogeneous catalysis. Here, molecular dynamics simulations were used to advance the understanding of PLs with different canopy structures. PLs composed of hollow SiO 2 molecules, which were functionalized with polymer chains containing coronas and canopies to make them liquid at accessible temperatures, were quite different from pure SiO 2 nanoparticles. It was found that linear and long canopy structures were better for dispersion of PLs, which was mainly due to the steric hindrance effect instead of electrostatic (charge) repulsion. In addition, simulation results demonstrated that PLs with long and linear polymer chains tended to have smaller relative entanglement depth, which means lower viscosity and better fluidity. Moreover, to keep intrinsic pores empty, PLs should possess long and linear canopies.

Porous liquids – the future is looking emptier

“…The authors later included the pores of the porous liquids and examined the depth to which canopies of the grafted SiO 2 nanoparticles entered the pores. 70,71 Assessing suspension stability is specifically necessary when forming type III porous liquids from porous solids; solvent molecules must not only be excluded from the pores, they must stabilise the porous scaffolds. 41 Indeed, charge transfer from the alkyl chains of [P 6,6,6,14 ][Br] to the zeolite H-ZSM-5 upon alkyl chain penetration helps balance van der Waals forces and mitigates aggregation of the porous liquid in chloroform.…”

Practical considerations in the design and use of porous liquids

“…They also help keep the intrinsic pores empty more appropriately. 75 More importantly, nanospheres synthesis can be modified by different factors such as calcination temperature, surfactant concentration as well as micelle swelling agent concentration to be able to control the size of internal cavities and nanospheres along with the microporosity of the silica shell. Thus, the cavity accessibility can be adjusted.…”

“…They also help keep the intrinsic pores empty more appropriately. 75 More importantly, nanospheres synthesis can be modified by different factors such as calcination temperature, surfactant concentration as well as micelle swelling (c) electrostatic grafting of polymers on the surface of the hollow carbon nanospheres (reproduced with permission, 67 Copyright 2017, Wiley-VCH); (d) electrostatic grafting of polymers on the surface of ionic-liquid, porous, tetrahedral coordination cage (reproduced with permission, 65 Copyright 2020, Springer Nature); (e) anionic porous organic cage and dicyclohexano-18-crown-6 using a supramolecular complexation strategy (reproduced with permission, 66 Copyright 2020, Wiley-VCH); (f) electrostatic grafting of polymers on the surface of the Silicalite-1 Zeolite (reproduced, 79 Open access); and (g) electrostatic grafting of polymers on the surface of the anisotropic (directionally dependent) hollow-core and silica-shell nanorods (reproduced with permission, 81 Copyright 2019, RSC Pub).…”

Transforming Porous Silica Nanoparticles into Porous Liquids with Different Canopy Structures for CO2 Capture

“…Porous liquids (PLs) were first proposed by James and co-workers in 2007, which combined porosity with fluidity. As the novel class of materials, they deemed broad application prospects in gas sorption and separation. − PLs can be categorized into three types based on their characteristic. − Type I PLs were neat liquids that could not collapse or interpenetrate, − Type II PLs were porous molecule cages dissolving in steric solvents that were too bulky to enter the cavities, − and Type III PLs were microporous framework particles dispersed in steric solvents. − …”

“…Although several different kinds of PLs have been synthesized for gas capacity and separation, corresponding CO 2 sorption experiments were rarely performed. Herein, we first synthesized Type I PLs with the core of large porous silica nanoparticles (PSNs) rather than hollow silica nanoparticles, which had previously been theoretically demonstrated by molecular dynamics (MD) simulations. − Scanning electron microscopy (SEM), transmission electron microscopy (TEM), pore size analysis, Fourier transfer infrared (FT-IR) spectroscopy, and thermogravimetric analysis were performed for characterization, and the effects of temperature, pressure, and canopy structures on absorptivity were investigated.…”