Translocation of compact polymer chains through a nanopore

We perform dynamical Monte Carlo simulation to study the forced translocation of compact polymer chains in three-dimensional lattices. The chains are driven through a nanopore connecting two infinite channels by an external field. The scaling properties of average translocation time τ and translocation time distribution (TTD) are studied. The effects of contact energy (?_C), electric field strength (E), and nanopore width (L) on the scaling exponent (α) of average translocation time τ ∼ N^α and the TTD are investigated. For the scaling behavior of τ ∼ N^α, we have found that there is no crossover behavior with weak field strength when the nanopore width is one lattice spacing, which is less than average bond length, while crossover behaviors are observed for larger nanopore widths. The scaling exponent α also depends on contact energy ?_C and electric field strength E. For the TTD, it shifts from the Gaussian to a right-skew distribution with the electric field E increasing for short chains; while for long chains, multi-peak distributions are observed. As a primary and simple model, compact polymer chains are extensively used to capture the structure and thermodynamic properties of proteins, therefore we can investigate the protein translocation by simulating compact chain translocation, and this study will be useful for exploring the complex translocation behaviors of proteins.     

Homogenized model of environmental barrier coatings for evaluation of energy release rate

For efficient calculation of energy release rate (ERR) for interface cracks in environmental barrier coatings (EBCs) with a columnar layer, we propose a simple and versatile homogenization method of the columnar layer. The columnar layer consisting of a number of fine columns is modeled as an anisotropic homogenized layer whose elastic properties are isotropic in the plane perpendicular to the layer thickness direction. The homogenization was achieved by a finite element method (FEM) analysis for a single columnar model to obtain elastic parameters that characterize the homogenized layer. For validation of the homogenization method, we conduct an FEM analysis for a typical EBC structure and obtain the ERRs of an interface crack with various crack length and columnar size. We demonstrate that the homogenization method provides estimation of ERR with a good accuracy on the safer side, which is advantageous for EBC structure design. In addition, the method can reduce the calculation time by more than 50%. From these results, we conclude that the proposed homogenization method can be applied generally for estimation of ERR in EBCs with a columnar layer.     

Kinetics of diffusion of a pollutant from a recycled polymer through a functional barrier: Recycling plastics for food packaging

Recycled polymers containing a pollutant can be used for food packaging if the food is protected by a functional barrier made of virgin polymer. The mathematical treatment of the diffusion of pollutant through the packaging is established when the diffusivity is constant and when there is no transfer through the packaging-food interface. A functional barrier not only reduces but also delays migration during a lag phase. An increase in the relative thickness of the functional barrier dramatically increases its efficiency. Practical examples are presented. The difficulties of control of migration through functional barriers are pointed out. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 597–607, 1997     

Effect of operating conditions on energy efficiency for a small passive direct methanol fuel cell

Energy conversion efficiency was studied in a direct methanol fuel cell (DMFC) with an air-breathing cathode using Nafion 117 as electrolyte membrane. The effect of operating conditions, such as methanol concentration, discharge voltage and temperature, on Faradic and energy conversion efficiencies was analyzed under constant voltage discharge with quantitative amount of fuel. Both of Faradic and energy conversion efficiencies decrease significantly with increasing methanol concentration and environmental temperature. The Faradic conversion efficiency can be as high as 94.8%, and the energy conversion efficiency can be as high as 23.9% if the environmental temperature is low enough (10 °C) under constant voltage discharge at 0.6 V with 3 M methanol for a DMFC bi-cell. Although higher temperature and higher methanol concentration can achieve higher discharge power, it will result in considerable losses of Faradic and energy conversion efficiencies for using Nafion electrolyte membrane. Development of alternative highly conductive membranes with significantly lower methanol crossover is necessary to avoid loss of Faradic conversion efficiency with temperature and with fuel concentration.     

Initiation of chain and thermal explosions by the reactor surface. Criterion for the participation of branching chains in a thermal explosion

The combustion of hydrogen and silane is studied. It is established that the chain initiation reaction on quartz in the zone of hydrogen and silane combustion is manifested as an autocatalytic reaction which is able to initiate a chain explosion and participate in the initiation of a thermal explosion. It is shown that in the case of an oxyhydrogen gas, the assumption of a branching-chain nature of the third limit is inconsistent with Semenov’s law, which includes double exponential dependences of the chain reaction rate on time and temperature. A criterion for the participation of branching chains in complex processes is proposed based on the presence or absence of short delays of a thermal explosion (≈1 sec). According to the criterion, the explosion of an oxyhydrogen gas at atmospheric pressure with delays markedly exceeding 1 sec proceeds without the participation of branching chains and is consistently explained by the joint action of autocatalytic processes on the reactor wall and gas-phase processes. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 44–51, September–October, 2007.     

New methodologies for separating glass transitions from energy of film formation in polystyrene latexes

Polystyrene latexes were synthesized to study water evaporation details, and to separate the energy of film formation from the glass transition temperature. Three experimental techniques were employed in the present work to study the formation of polystyrene latex films: standard differential scanning calorimetry (DSC), modulated DSC, and the Mahr method applied to modulated DSC. High-resolution thermogravimetric analysis (TGA) was used to study the water evaporation. The TGA experiments revealed evaporation curves consistent with the notion of surface tension and tortuosity effects being the controlling factors. The method of Mahr was combined with the new software package for DSC to provide an improved method of separating the glass transition of polystyrene from its surface tension-based free energy of film formation. The result was that the films formed under the extremely mild conditions employed had 30–70% of their surfaces obliterated by interfacial adhesion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1763–1768, 1999     

一种新的利用LNG冷能的回收油田伴生气凝液的工艺

A novel process to recovery natural gas liquids from oil field associated gas with liquefied natural gas (LNG)cryogenic energy utilization is proposed.Compared to the current electric refrigeration process,the proposed process uses the cryogenic energy of LNG and saves 62.6%of electricity.The proposed process recovers ethane, liquid petroleum gas(propane and butane)and heavier hydrocarbons,with total recovery rate of natural gas liquids up to 96.8%.In this paper,exergy analysis and the energy utilization diagram method(EUD)are used to assess the new process and identify the key operation units with large exergy loss.The results show that exergy efficiency of the new process is 44.3%.Compared to the electric refrigeration process,exergy efficiency of the new process is improved by 16%.The proposed process has been applied and implemented in a conceptual design scheme of the cryogenic energy utilization for a 300 million tons/yr LNG receiving terminal in a northern Chinese harbor.     

Mechanisms of ionic conductivity for zwitterionic polymers

In this work, ionic conductivity data of zwitterionic polymers are compared with predictions of the random free-energy barrier model for a.c. conduction in disordered solids. It is shown that conductivity follows a long range delocalized diffusion of charge carriers within an equally probable distribution of free-energy barriers. Accordingly, it follows time–temperature superposition, expressed as a master curve for the normalized conductivity as a function of the non-dimensional frequency. The dielectric behaviour is dominated by ionic conductivity, and results suggest a process of quasi-ideal conduction of the ion carriers, consistent with a large value of the dielectric relaxation time characteristic of delocalized conduction processes. It is further remarked that alternative interpretations to the conduction behaviour in these polymers can also be given by other theories and models.     

Discrete particle simulations for flow of binary particle mixture in a bubbling fluidized bed with a transport energy weighted averaging scheme

Flow behavior of small and big particles with the same particle density in a bubbling fluidized bed is modeled by a combined approach of discrete particle method and computational fluid dynamics (CFD-DPM). The collision time of a collision pair is computed by a quartic equation in which the effect of acceleration due to the different diameters is considered. A transport energy weighted averaging approach is proposed to determine the local gas velocity at a particle. The fluidization behavior of binary mixture differing in size is experimentally and numerically studied in the gas bubbling fluidized bed. The distributions of mass fraction of small and big particles along the bed height are simulated, and the profiles of the mean particle diameters of binary mixture are determined. The numerical results are in agreement with experimental data. The distributions of granular temperature, stresses, and shear viscosities of small and big particles are compared.