scholarly journals Swelling Effects on the Conductivity of Graphene/PSS/PAH Composites

Nanomaterials ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 3280
Author(s):  
Tianbao Zhao ◽  
Ruyi Yang ◽  
Zhi Yang
Keyword(s):  
Mass Fraction ◽  
Water Mass ◽  
Microphase Separation ◽  
Water Molecules ◽  
Layer By Layer ◽  
Polyelectrolyte Multilayer ◽  
Styrene Sulfonate ◽  
Assembly Technique ◽  
Dynamics Simulations ◽  
Lubrication Effect

Graphene/poly-(sodium-4-styrene sulfonate)(PSS)/poly-(allylamine hydrochloride) (PAH) composite is a frequently adopted system for fabricating polyelectrolyte multilayer films. Swelling is the bottleneck limiting its applications, and its effects on the conductivity is still controversial. Herein, we report successful swelling of a graphene/PSS/PAH composite in a vapor atmosphere, and the relation with the mass fraction of water is uncovered. The composite was prepared via a layer-by-layer assembly technique and systematically characterized. The results indicated that the average thickness for each bilayer was about 0.95 nm. The hardness and modulus were 2.5 ± 0.2 and 68 ± 5 GPa, respectively, and both were independent of thickness. The sheet resistance decreased slightly with the prolongation of immersion time, but was distinct from that of the water mass fraction. It reduced from 2.44 × 105 to 2.34 × 105 ohm/sq, and the change accelerated as the water mass fraction rose, especially when it was larger than 5%. This could be attributing to the lubrication effect of the water molecules, which sped up the migration of charged groups in the polyelectrolytes. Moreover, molecular dynamics simulations confirmed that a microphase separation occurred when the fraction reached an extreme value owing to the dominated interaction between PSS and PAH. These results provide support for the structural stability of this composite material and its applications in devices.

Driving Forces and Transportation Efficiency in Water Transportation Through Single-Walled Carbon Nanotubes

2012 ◽  
Vol 3 (2) ◽  
Author(s):  
Meng Zi Sun ◽  
Wen Hui Duan ◽  
Quan Wang ◽  
Martin Dowman ◽  
Jayantha Kodikara
Keyword(s):  
Molecular Dynamics ◽  
Water Molecule ◽  
Driving Force ◽  
Environmental Temperature ◽  
Water Mass ◽  
Driving Forces ◽  
Channel Length ◽  
Water Molecules ◽  
Water Transportation ◽  
Dynamics Simulations

Based on the concept of an energy pump, water transportation in a carbon nanotube (CNT) is studied by molecular dynamics simulations. The influences of CNT pretwist angle, water mass, environmental temperature, CNT diameter, CNT channel length, and CNT channel restrain condition on driving force and transportation efficiency are investigated. It is found that in order to initiate the transportation, the pretwist angle must be larger than certain threshold, 80 deg, for the case of one water molecule in a restrained (8,0) CNT. Furthermore, driving force decreases with increasing water mass and it is more efficient to transport multiple water molecules than one water molecules. The water molecule is found to have higher degrees of collisions in a (8,0) CNT in elevated environmental temperature. By comparing three CNT channel lengths, the channel length of 19.80 nm is identified as a faster and more efficient transporter in an unrestrained (8,8) CNT. Finally, molecular dynamics (MD) simulation indicates that a water molecule can only be transported below 300 K in an unrestrained (8,8) CNT due to the large friction caused by severely deformed channel and the Brownian motion.

Control of DNA incorporation into nanoparticles with poly(L-lysine) multilayers

2008 ◽  
Vol 86 (12) ◽  
pp. 1085-1094 ◽  
Author(s):  
Annie C Dorris ◽  
Kimberly L Douglas ◽  
Maryam Tabrizian ◽  
Christopher J Barrett
Keyword(s):  
Cell Uptake ◽  
Layer By Layer ◽  
Polyelectrolyte Multilayer ◽  
Flat Surfaces ◽  
Bulk Film ◽  
Vis Spectroscopy ◽  
Assembly Technique ◽  
Resultant Effect ◽  
Ph Conditions ◽  
Dna Incorporation

Nanoparticles coated with DNA and poly(L-lysine) (PLL) were prepared using a layer-by-layer assembly technique under various solution conditions. Both the level of DNA loading into the materials, the rate and the extent of DNA released from films upon degradation were controlled by varying the pH of polyelectrolyte assembly solutions. To determine optimal conditions for DNA loading, analogous films assembled on flat surfaces were prepared under various pH conditions. Using UV–vis spectroscopy and thin-film ellipsometry, it was found that the extent of DNA incorporation could be varied by more than a factor of two, and that the highest loading was obtained for films built using a combination of DNA and poly(L-lysine) solutions of pH = 4 and pH = 7, respectively. The layers coated onto the silica nanoparticles permitted the surface charge to be characterized by zeta potential electrophoresis. Furthermore, the acid–base dissociation constant measured for PLL on the outermost layer of the DNA/PLL film showed that the pKa of PLL can be shifted by more than three units. Film degradability was investigated via the exposure of films assembled under different pH conditions to α-chymotrypsin. The fraction of DNA released from degraded films can also be increased by a factor of three when films are built under conditions of pH = 4 for the DNA solution. The resultant effect on the transfection ability of pEGFP-N1/PLL coated particles was then measured, and results suggest that the control achieved over the bulk film properties also extends to a strong influence on cell uptake and transfection.Key words: polyelectrolyte multilayer, DNA incorporation, enzymatic degradation, nanoparticles, gene therapy.

Stabilization of starch-based microgel-lysozyme complexes using a layer-by-layer assembly technique

2017 ◽  
Vol 214 ◽  
pp. 213-217 ◽  
Author(s):  
Bao Zhang ◽  
Yi Pan ◽  
Hanqing Chen ◽  
Tengfei Liu ◽  
Han Tao ◽  
...  
Keyword(s):  
Layer By Layer ◽  
Layer By Layer Assembly ◽  
Assembly Technique ◽  
Layer Assembly

scholarly journals Electrical Breakdown Mechanism of Transformer Oil with Water Impurity: Molecular Dynamics Simulations and First-Principles Calculations

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 123
Author(s):  
Bin Cao ◽  
Ji-Wei Dong ◽  
Ming-He Chi
Keyword(s):  
Molecular Dynamics ◽  
Thermal Diffusion ◽  
First Principles ◽  
Electrical Breakdown ◽  
Transformer Oil ◽  
Water Molecules ◽  
Conducting Channel ◽  
Breakdown Mechanism ◽  
Water Impurity ◽  
Dynamics Simulations

Water impurity is the essential factor of reducing the insulation performance of transformer oil, which directly determines the operating safety and life of a transformer. Molecular dynamics simulations and first-principles electronic-structure calculations are employed to study the diffusion behavior of water molecules and the electrical breakdown mechanism of transformer oil containing water impurities. The molecular dynamics of an oil-water micro-system model demonstrates that the increase of aging acid concentration will exponentially expedite thermal diffusion of water molecules. Density of states (DOS) for a local region model of transformer oil containing water molecules indicates that water molecules can introduce unoccupied localized electron-states with energy levels close to the conduction band minimum of transformer oil, which makes water molecules capable of capturing electrons and transforming them into water ions during thermal diffusion. Subsequently, under a high electric field, water ions collide and impact on oil molecules to break the molecular chain of transformer oil, engendering carbonized components that introduce a conduction electronic-band in the band-gap of oil molecules as a manifestation of forming a conductive region in transformer oil. The conduction channel composed of carbonized components will be eventually formed, connecting two electrodes, with the carbonized components developing rapidly under the impact of water ions, based on which a large number of electron carriers will be produced similar to “avalanche” discharge, leading to an electrical breakdown of transformer oil insulation. The water impurity in oil, as the key factor for forming the carbonized conducting channel, initiates the electric breakdown process of transformer oil, which is dominated by thermal diffusion of water molecules. The increase of aging acid concentration will significantly promote the thermal diffusion of water impurities and the formation of an initial conducting channel, accounting for the degradation in dielectric strength of insulating oil containing water impurities after long-term operation of the transformer.

scholarly journals Origin and control of ionic hydration patterns in nanopores

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Miraslau L. Barabash ◽  
William A. T. Gibby ◽  
Carlo Guardiani ◽  
Alex Smolyanitsky ◽  
Dmitry G. Luchinsky ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Distribution Functions ◽  
Water Molecules ◽  
Surrounding Water ◽  
Ionic Hydration ◽  
Hydration Shells ◽  
Water Layers ◽  
Dynamics Simulations ◽  
And Control

AbstractIn order to permeate a nanopore, an ion must overcome a dehydration energy barrier caused by the redistribution of surrounding water molecules. The redistribution is inhomogeneous, anisotropic and strongly position-dependent, resulting in complex patterns that are routinely observed in molecular dynamics simulations. Here, we study the physical origin of these patterns and of how they can be predicted and controlled. We introduce an analytic model able to predict the patterns in a graphene nanopore in terms of experimentally accessible radial distribution functions, giving results that agree well with molecular dynamics simulations. The patterns are attributable to a complex interplay of ionic hydration shells with water layers adjacent to the graphene membrane and with the hydration cloud of the nanopore rim atoms, and we discuss ways of controlling them. Our findings pave the way to designing required transport properties into nanoionic devices by optimising the structure of the hydration patterns.

scholarly journals Encapsulation of Phase Change Materials Using Layer-by-Layer Assembled Polyelectrolytes

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Qiangying Yi ◽  
Gleb B. Sukhorokov ◽  
Jin Ma ◽  
Xiaobo Yang ◽  
Zhongwei Gu
Keyword(s):  
Phase Change ◽  
Phase Change Materials ◽  
Low Cost ◽  
Sodium Dodecyl ◽  
Layer By Layer ◽  
Latent Heat Storage ◽  
Good Thermal Stability ◽  
Lbl Assembly ◽  
Acid Sodium Salt ◽  
Assembly Technique

Phase change materials absorb the thermal energy when changing their phases (e.g., solid-to-liquid) at constant temperatures to achieve the latent heat storage. The major drawbacks such as limited thermal conductivity and leakage prevent the PCMs from wide application in desired areas. In this work, an environmentally friendly and low cost approach, layer-by-layer (LbL) assembly technique, was applied to build up ultrathin shells to encapsulate the PCMs and therefore to regulate their changes in volume when the phase change occurs. Generally, the oppositely charged strong polyelectrolytes Poly(diallyldimethylammonium chloride) (PDADMAC) and Poly(4-styrenesulfonic acid) sodium salt (PSS) were employed to fabricate multilayer shells on emulsified octadecane droplets using either bovine serum albumin (BSA) or sodium dodecyl sulfate (SDS) as surfactant. Specifically, using BSA as the surfactant, polyelectrolyte encapsulated octadecane spheres in size of ∼500 nm were obtained, with good shell integrity, high octadecane content (91.3% by mass), and good thermal stability after cycles of thermal treatments.

scholarly journals Optimal Relabeling of Water Molecules and Single-Molecule Entropy Estimation

Biophysica ◽  
2021 ◽  
Vol 1 (3) ◽  
pp. 279-296
Author(s):  
Federico Fogolari ◽  
Gennaro Esposito
Keyword(s):  
Single Molecule ◽  
Degrees Of Freedom ◽  
Water Molecules ◽  
Maximum Information ◽  
Nearest Neighbours ◽  
Biomolecular Simulations ◽  
Solvent Molecules ◽  
Solvation Entropy ◽  
Dynamics Simulations ◽  
Internal Degrees Of Freedom

Estimation of solvent entropy from equilibrium molecular dynamics simulations is a long-standing problem in statistical mechanics. In recent years, methods that estimate entropy using k-th nearest neighbours (kNN) have been applied to internal degrees of freedom in biomolecular simulations, and for the rigorous computation of positional-orientational entropy of one and two molecules. The mutual information expansion (MIE) and the maximum information spanning tree (MIST) methods were proposed and used to deal with a large number of non-independent degrees of freedom, providing estimates or bounds on the global entropy, thus complementing the kNN method. The application of the combination of such methods to solvent molecules appears problematic because of the indistinguishability of molecules and of their symmetric parts. All indistiguishable molecules span the same global conformational volume, making application of MIE and MIST methods difficult. Here, we address the problem of indistinguishability by relabeling water molecules in such a way that each water molecule spans only a local region throughout the simulation. Then, we work out approximations and show how to compute the single-molecule entropy for the system of relabeled molecules. The results suggest that relabeling water molecules is promising for computation of solvation entropy.

Multilayer composite beads constructed via layer-by-layer self-assembly for lysozyme controlled release

RSC Advances ◽  
2014 ◽  
Vol 4 (46) ◽  
pp. 24369-24376 ◽  
Author(s):  
Jiemin Zhao ◽  
Xiaoping Wang ◽  
Yanshen Kuang ◽  
Yufeng Zhang ◽  
Xiaowen Shi ◽  
...  
Keyword(s):  
Controlled Release ◽  
Self Assembly ◽  
Cross Linking ◽  
Layer By Layer ◽  
Multilayer Composite ◽  
Composite Beads ◽  
Assembly Technique ◽  
Positively Charged

Alginate (ALG)–lysozyme (LZ) beads were fabricated by a cross-linking process. Negatively charged ALG and positively charged LZ were alternately deposited on the positively charged ALG–LZ beads via a layer-by-layer (LBL) self-assembly technique.

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