Transport Mechanism Of Molecules Research Articles

A systematic review of the molecular simulation of hybrid membranes for performance enhancements and contaminant removals

Number of research on molecular simulation and design has emerged recently but there is currently a lack of review to present these studies in an organized manner to highlight the advances and feasibility. This paper aims to review the development, structural, physical properties and separation performance of hybrid membranes using molecular simulation approach. The hybrid membranes under review include ionic liquid membrane, mixed matrix membrane, and functionalized hybrid membrane for understanding of the transport mechanism of molecules through the different structures. The understanding of molecular interactions, and alteration of pore sizes and transport channels at atomistic level post incorporation of different components in hybrid membranes posing impact to the selective transport of desired molecules are also covered. Incorporation of molecular simulation of hybrid membrane in related fields such as carbon dioxide (CO2) removal, wastewater treatment, and desalination are also reviewed. Despite the limitations of current molecular simulation methodologies, i.e., not being able to simulate the membrane operation at the actual macroscale in processing plants, it is still able to demonstrate promising results in capturing molecule behaviours of penetrants and membranes at full atomic details with acceptable separation performance accuracy. From the review, it was found that the best performing ionic liquid membrane, mixed matrix membrane and functionalized hybrid membrane can enhance the performance of pristine membrane by 4 folds, 2.9 folds and 3.3 folds, respectively. The future prospects of molecular simulation in hybrid membranes are also presented. This review could provide understanding to the current advancement of molecular simulation approach in hybrid membranes separation. This could also provide a guideline to apply molecular simulation in the related sectors.

Tunable sieving of small gas molecules using horizontal graphene oxide membrane

Graphene oxide membrane (GOM) has attracted extensive attraction as a molecular sieve for the separation of water, ions, and gases. However, Å-level control of the GOM interlayer spacing for separating the specific size of gas molecule is difficult and the vertical transport mechanism of molecules through the GOM is highly complex because of the existence of several possible pathways. Here we fabricated GOMs with different Å-scale interlayer spacing through heat treatment and made them allow horizontal entrance and transport of gas molecules. The GOMs with angstrom channels exhibited superior performance in permeance in horizontal mode and moderate selectivity for H2/CO2 and He/CO2 by tuning the sieving size of the channels. Molecular dynamics (MD) simulations reveal that the precisely controlled interlayer spacing plays a primary role as a molecular sieve indeed, but increased graphitic area, a result of heat treatment, also affects observed selectivity. Our results provide insight into the transport mechanism of gas molecules through GO nanochannel, which has not been accurately identified due to its complex behavior and suggest the possibility of studying nanochannels as effective vehicle for separating molecules precisely.

Elucidating Ultrafast Molecular Permeation through Well-Defined 2D Nanochannels of Lamellar Membranes.

Lamellar membranes with well-defined 2D nanochannels show fast, selective permeation, but the underlying molecular transport mechanism is unexplored. Now, regular robust MXene Ti3 C2 Tx lamellar membranes are prepared, and the size and wettability of nanochannels are manipulated by chemically grafted hydrophilic (-NH2 ) or hydrophobic (-C6 H5 , -C12 H25 ) groups. These nanochannels have a sharp difference in mass transfer behavior. Hydrophilic nanochannels, in which polar molecules form orderly aligned aggregates along channel walls, impart ultrahigh permeance (>3000 L m-2 h-1 bar-1 ), which is more than three times higher than that in hydrophobic nanochannels with disordered molecular configuration. In contrast, nonpolar molecules with disordered configuration in both hydrophilic and hydrophobic nanochannels have comparable permeance. Two phenomenological transport models correlate the permeance with the mass transport mechanism of molecules that display ordered and disordered configuration.

Elucidating Ultrafast Molecular Permeation through Well‐Defined 2D Nanochannels of Lamellar Membranes

AbstractLamellar membranes with well‐defined 2D nanochannels show fast, selective permeation, but the underlying molecular transport mechanism is unexplored. Now, regular robust MXene Ti3C2Tx lamellar membranes are prepared, and the size and wettability of nanochannels are manipulated by chemically grafted hydrophilic (−NH2) or hydrophobic (−C6H5, −C12H25) groups. These nanochannels have a sharp difference in mass transfer behavior. Hydrophilic nanochannels, in which polar molecules form orderly aligned aggregates along channel walls, impart ultrahigh permeance (>3000 L m−2 h−1 bar−1), which is more than three times higher than that in hydrophobic nanochannels with disordered molecular configuration. In contrast, nonpolar molecules with disordered configuration in both hydrophilic and hydrophobic nanochannels have comparable permeance. Two phenomenological transport models correlate the permeance with the mass transport mechanism of molecules that display ordered and disordered configuration.

Is the solid electrolyte interphase in lithium-ion batteries really a solid electrolyte? Transport experiments on lithium bis(oxalato)borate-based model interphases

In order to improve the properties of the solid electrolyte interphase (SEI) on the graphite anode in lithium-ion batteries, different electrolyte additives are used, such as lithium bis(oxalate)borate (LiBOB), vinylene carbonate, and fluoroethylene carbonate. It is known that LiBOB increases the SEI resistance, but there is very little fundamental knowledge about the influence of LiBOB on the structure of the SEI as well as on ion and molecule transport mechanisms in the SEI. Here, we study SEIs grown at the interface between a planar glassy carbon electrode and battery electrolytes containing different amounts of LiBOB. The SEIs are characterized by a combination of FIB-SEM, AFM, electrochemical impedance spectroscopy and redox probe experiments. The transport of Li+ ions and of redox molecules becomes slower with increasing LiBOB concentration in the electrolyte, but like observed for a LiBOB-free electrolyte, the effective diffusion coefficients of Li+ ions and ferrocene molecules in the SEIs are virtually identical and show the same temporal evolution after voltammetric SEI formation. This gives strong indication that both Li+ ions and molecules are transported in the liquid electrolyte phase inside the pores of the SEI and thus challenges the common view of a solid-electrolyte-type Li+ transport mechanism in SEIs.

Creating Aptamers and Their Use in Resisitive Pulse Sensors

Resistive pulse sensors, RPS, are allowing the transport mechanism of molecules, proteins and even nanoparticles to be characterized as they traverse small channels. Here we present our recent advancement of the technique identifying key experimental designs for potential POC assays. The first assay utilized superparamagnetic beads, if the surfaces of the beads are modified with an aptamer, the frequency of beads (translocations/minute) through the pore can be related to the concentration of specific proteins in the solution. Herein, we have demonstrated the successful use of TRPS to observe the binding of two proteins, to their specific aptamers simultaneously. We then adapt the measurement strategy and demonstrate that the translocation times of particles can be used to infer the zeta potential to measure the change in zeta potential of DNA modified particles. By measuring the translocation times of DNA modified nanoparticles as a function of packing density, length, structure, and hybridisation time, we observe a clear difference in zeta potential using both mean values, and population distributions as a function of the DNA structure. Finally we present the first comparison between assays that use resistive pulses or rectification ratios on a tunable pore platform.

Particle-by-Particle Charge Analysis of DNA-Modified Nanoparticles Using Tunable Resistive Pulse Sensing.

Resistive pulse sensors, RPS, are allowing the transport mechanism of molecules, proteins and even nanoparticles to be characterized as they traverse pores. Previous work using RPS has shown that the size, concentration and zeta potential of the analyte can be measured. Here we use tunable resistive pulse sensing (TRPS) which utilizes a tunable pore to monitor the translocation times of nanoparticles with DNA modified surfaces. We start by demonstrating that the translocation times of particles can be used to infer the zeta potential of known standards and then apply the method to measure the change in zeta potential of DNA modified particles. By measuring the translocation times of DNA modified nanoparticles as a function of packing density, length, structure, and hybridization time, we observe a clear difference in zeta potential using both mean values and population distributions as a function of the DNA structure. We demonstrate the ability to resolve the signals for ssDNA, dsDNA, small changes in base length for nucleotides between 15 and 40 bases long, and even the discrimination between partial and fully complementary target sequences. Such a method has potential and applications in sensors for the monitoring of nanoparticles in both medical and environmental samples.

The role of viscosity on polymer ink transport in dip-pen nanolithography.

Understanding how ink transfers to a surface in dip-pen nanolithography (DPN) is crucial for designing new ink materials and developing the processes to pattern them. Herein, we investigate the transport of block copolymer inks with varying viscosities, from an atomic force microscope (AFM) tip to a substrate. The size of the patterned block copolymer features was determined to increase with dwell time and decrease with ink viscosity. A mass transfer model is proposed to describe this behaviour, which is fundamentally different from small molecule transport mechanisms due to entanglement of the polymeric chains. The fundamental understanding developed here provides mechanistic insight into the transport of large polymer molecules, and highlights the importance of ink viscosity in controlling the DPN process. Given the ubiquity of polymeric materials in semiconducting nanofabrication, organic electronics, and bioengineering applications, this study could provide an avenue for DPN to expand its role in these fields.

Effect of tacticity of PMMA on gas transport through membranes: MD and MC simulation studies

The effects of tacticity of poly methyl methacrylate (PMMA) on the morphology and size distribution of free volume and gas molecules transport through PMMA matrix were conducted by molecular simulation techniques. How the spatial structure of PMMA affects the glass transient temperature T g of stereoregular PMMA membranes and the solution and diffusion mechanisms in the stereoregular PMMA membranes were conducted by molecular simulation techniques and were compared with experimental data. The polymer chains conformation, gas diffusion mechanism, the time course of the accessible free volume, free volume size distribution, free volume morphology and glass transient temperature, in the various stereoregular PMMA were obtained by a molecular dynamics simulation technique, while the gas solubility in different stereoregular PMMA was calculated by a Monte Carlo technique. A comprehensive comparison of the physical and transport properties of the stereoregular PMMA membranes between simulated and experimental results are provided based on a microscopic interpretation of chain flexibility, free volume morphology and size distribution of free volume in the stereoregular PMMA membranes and gas molecule transport mechanisms through the stereoregular PMMA membranes.

Relationship between the microstructure and the water permeability of transparent gas barrier coatings

The relationship between the microstructure and the water vapor permeability of transparent barrier coatings on polymeric films has been studied by atomic force microscopy (AFM). The average grain size, d, and the surface pore fractal dimension, D s, of the different coatings were determined from the AFM images. It was observed that those films with low d and high D s values presented a low water vapor permeability whereas when either d was high or D s was low the water vapor permeability increased. These differences are explained on the basis of the different dependences of the two main water molecule transport mechanisms (Knudsen and the surface diffusion) on the coating microstructure.