Molecular simulation on penetrants diffusion at the interface region of organic-inorganic hybrid membranes

Detailed atomistic structures of blend (class I) and chemical tethered (class II) poly vinyl alcohol (PVA)-silica hybrid membranes were constructed to investigate the diffusion behavior of small molecules at the interfacial region. Stronger interaction between PVA and silica, as well as more appropriate interfacial morphology which was evaluated by interchain distance, chain mobility and free volume were found in class II hybrid membranes due to the presence of covalent bonds. The effects of interfacial morphology on diffusion behavior of small molecules including benzene and cyclohexane were tentatively explored, and found that diffusion coefficients were closely related to fraction of free volume (FFV). Subsequently, the diffusion selectivity was calculated by the ratio of FFV probed by benzene and cyclohexane molecules. Hopefully, this study will offer some important qualitative insight into the transport phenomena within organic-inorganic hybrid membranes.     

Modeling of branching density and branching distribution in low-density polyethylene polymerization

Low-density polyethylene (ldPE) is a general purpose polymer with various applications. By this reason, many publications can be found on the ldPE polymerization modeling. However, scission reaction and branching distribution are only recently considered in the modeling studies due to difficulties in measurement and computation of scission effect and branchings of polymer. Our previous papers [Kim, D.M., et al., 2004. Molecular weight distribution modeling in low-density polyethylene polymerization; impact of scission mechanisms in the case of CSTR. Chemical Engineering Science 59, 699-718; Kim, D.M., Iedema, P.D., 2004. Molecular weight distribution modeling in low-density polyethylene polymerization; impact of scission mechanisms in the case of a tubular reactor. Chemical Engineering Science, submitted for publication] are concerned with the scission reaction during ldPE polymerization and its effect on molecular weight distribution (MWD) of ldPE for various reactor types. Here we consider branching distributions as a function of chain length for CSTR and tubular reactor processes. To simultaneously deal with chain length and branching distributions, the concept of pseudo-distributions is used, meaning that branching distributions are described by their main moments. The computation results are compared with properties of ldPE samples from a CSTR and a tubular reactor. Number and weight average branchings and branching density increase as chain length increases until the longest chain length. The concentrations of long chain branching (LCB) are close to those of first branching moment in both CSTR and tubular reactor systems. The branching dispersity, a measure for the width of the branching distribution at a certain chain length, has the highest value at shorter chain length and then monotonously decreases approaching to 1.0 as chain length increases. Excellent agreements in branching dispersities between calculation with branching moments and prediction with assumption of binomial distribution for a tubular reactor and CSTR processes show that the branching distribution follows a binomial distribution for both processes.     

Onsager coefficients for binary mixture diffusion in nanopores

This paper presents a critical appraisal of current estimation methods for the Onsager coefficients L₁₁, L₂₂, and L₁₂ for binary mixture diffusion inside nanopores using pure component diffusivity data inputs. The appraisal is based on extensive sets of molecular dynamics (MD) simulation data on L_ij for a variety of mixtures in zeolites (MFI, AFI, TON, FAU, CHA, DDR, MOR, and LTA), carbon nanotubes (CNTs: armchair and zig-zag configurations), titanosilicates (ETS-4), and metal-organic frameworks (IRMOF-1, CuBTC). The success of the L_ij predictions is crucially dependent on the estimates of the degree of correlations in molecular jumps for different guest-host combinations; these correlations are captured in Maxwell-Stefan approach by the exchange coefficients ?_ij. Three limiting scenarios for correlation effects have been distinguished; for each of these scenarios appropriate expressions for the L_ij are presented. For CNTs, correlation effects are dominant and the interaction factor, defined by , is close to unity. For cage-type zeolites such as LTA, CHA, and DDR with narrow windows separating cages, correlation effects are often, but not always, negligibly small and the assumption of uncoupled diffusion, i.e., α₁₂=0, is a reasonable approximation provided the occupancies are not too high. In other cases such as zeolites with one-dimensional channel structures (AFI, TON), intersecting channels (MFI), cage-type zeolite with large windows (FAU), ETS-4, CuBTC, and in IRMOF-1, it is essential to have a reliable estimation of the ?_ij; MD simulations underline the wide variety of factors that influence the ?_ij.We also highlight two situations where estimations of the L_ij fail completely; in both cases the failure is caused due to segregated adsorption. In adsorption of CO₂-bearing mixtures in LTA and DDR zeolites, CO₂ is preferentially lodged at the narrow window regions and this hinders the diffusion of partner molecules between cages. The second situation arises in MOR zeolite that has one-dimensional channels connected to side pockets. Some molecules such as methane, get preferentially lodged in the side pockets and do not freely participate in the molecular thoroughfare. Current phenomenological models do not cater for segregation effects on mixture diffusion.     

Molecular dynamics simulations for nitridation of organic polymer surfaces due to hydrogen-nitrogen ion beam injections

Interaction of organic polymer surfaces with energetic reactive ions during etching processes by hydrogen-nitrogen plasmas has been investigated microscopically with the use of classical molecular dynamics (MD) simulations. Especially examined in the present study are interactions of atomic-nitrogen, molecular-nitrogen, or ammonia beams with a polyparaphenylene (PPP) surface and the resulting surface modification. It has been observed in the simulations that, when reactive atomic-nitrogen (N) beams are injected into a PPP surface, a carbon nitride layer with carbon-nitrogen bonds of higher bond orders (i.e., bonds containing π bonds) tend to be formed and it also acts as a source of carbon-nitride clusters for sputtered species. This observation is consistent with the fact that excessive supply of nitrogen to a carbon nitride film makes the film structurally weak as nitrogen atoms tend to break up carbon chains. On the other hands, when ammonia (NH₃) beams are injected, carbon-nitrogen single bonds (i.e., σ bonds only) are more likely to be formed since hydrogen atoms would efficiently terminate π bonds should they be formed.     

Applications of fullerene beams in analysis of thin layers

Molecular dynamics computer simulations have been employed to model ejection of particles from Ag{1 1 1} metal substrate and thin benzene overlayer bombarded by fullerene cluster projectiles. The sputtering yields are analyzed depending on the size (from C₂₀ up to C₅₄₀) and the kinetic energy (5-20 keV) of a projectile. It has been found that for clean metal substrate bombarded by 15 keV projectiles the maximum ejection is stimulated by the impact of the C₆₀ cluster. However, the size of the cluster projectile maximizing the yield depends on the kinetic energy of the cluster, shifting towards larger clusters as the impact energy increases. For a thin benzene overlayer, the yield increases monotonically with the size of the cluster within investigated range of fullerene projectiles and kinetic energies.     

Effect of Oxime Ether Incorporation in Acyl Indole Derivatives on PPAR Subtype Selectivity

Compounds that simultaneously activate peroxisome proliferator‐activated receptor (PPAR) subtypes α and γ have the potential to effectively treat dyslipidemia and type 2 diabetes (T2D) in a single pharmaceutically active molecule. The frequently observed side effects of selective PPARγ agonists, such as edema and weight gain, were expected to be overcome by using additive PPARα activity, leading to dual PPARα/γ agonists with balanced activity for both subtypes. Herein we report the discovery, synthesis, and optimization of a new series of α‐ethoxyphenylpropionic acid bearing 5‐ or 6‐substituted indoles. The incorporation of oxime ethers on the carbonyl portion of the benzoyl group can bring the PPARα/γ potency ratio equal to or slightly greater than one, as is the case for compounds 20 c and 21 a . Compound 20 c shows high efficacy in an ob/ob mouse model of T2D and dyslipidemia, similar to that of rosiglitazone and tesaglitazar, but with a significant increase in body weight gain. In contrast, compound 21 a , less potent as a dual PPARα/γ activator than 20 c , showed an interesting pharmacological profile, as it elicits a decrease in body weight relative to reference compounds.     

一种基于接触力分析进行对接的控制策略

为实现空间机械臂在舱体表面爬行过程中机械臂末端与指定对接口的对接任务,设计了一种针对整体对接过程的控制策略。首先根据接触点的个数对可能出现的接触情况进行分类,然后根据六维力传感器传递的实时接触力数据进行接触力分析,确定不同接触力数据对应的不同对接情况,并针对不同类型的对接情况设计对应的对接控制策略。该整体控制策略简单明了,易于工程实现。     

Design schemes and comparison research of the end-effector of large space manipulator

The end-effector of the large space manipulator is employed to assist the manipulator in handling and manipulating large payloads on orbit.Currently,there are few researches about the end-effector,and the existing end-effectors have some disadvantages,such as poor misalignment tolerance capability and complex mechanical components.According to the end positioning errors and the residual vibration characters of the large space manipulators,two basic performance requirements of the end-effector which include the capabilities of misalignment tolerance and soft capture are proposed.And the end-effector should accommodate the following misalignments of the mechanical interface.The translation misalignments in axial and radial directions and the angular misalignments in roll,pitch and yaw are ±100 mm,100 mm,±10°,±15°,±15°,respectively.Seven end-effector schemes are presented and the capabilities of misalignment tolerance and soft capture are analyzed elementarily.The three fingers-three petals end-effector and the steel cable-snared end-effector are the most feasible schemes among the seven schemes,and they are designed in detail.The capabilities of misalignment tolerance and soft capture are validated and evaluated,through the experiment on the micro-gravity simulating device and the dynamic analysis in ADAMS software.The results show that the misalignment tolerance capabilities of these two schemes could satisfy the requirement.And the translation misalignment tolerances in axial and radial directions and the angular misalignment tolerances in roll,pitch and yaw of the steel cable-snared end-effector are 30mm,15mm,6°,3° and 3° larger than those of the three fingers-three petals end-effector,respectively.And the contact force of the steel cable-snared end-effector is smaller and smoother than that of the three fingers-three petals end-effector.The end-effector schemes and research methods are beneficial to the developments of the large space manipulator end-effctor and the space docking mechanism.     

Effect of organic groups on hydrogen adsorption properties of periodic mesoporous organosilicas

We investigate the hydrogen adsorption properties of periodic mesoporous organosilicas (PMOs) and focus, in particular, on how these properties are affected by diverse organic groups embedded in the walls. PMOs with π electrons on the pore surface adsorb more hydrogen molecules per unit area and have a higher isosteric heat of hydrogen adsorption (Q_st). The number of adsorbed hydrogen molecules per unit area correlates well with the density of organic groups on the pore surface. We attribute the high Q_st to the high polarizability of organic groups with π electrons, which enhances the dispersion force. The molecular order of organic groups affects the adsorption-site affinity to hydrogen molecules as well as the location of adsorption sites. For phenylene-bridged PMOs with crystal-like pore walls, Q_st decreases rapidly with increasing hydrogen loading, which indicates two types of adsorption sites with different affinities to hydrogen molecules: one is an exposed CH bond and the other is a siloxane bond. However, Q_st for phenylene-bridged PMOs with amorphous pore walls exhibits a moderate slope, which might be caused by the random order of organic groups; this results in several types of adsorption sites with various affinities.     

Synthesis and structure of AlPO4-9: An unacquainted member in the family of microporous aluminophosphates

In the family of microporous aluminophosphate, AlPO₄-9 is one of the members reported first in 1982. However, its structure and characteristics have not been known up to now, and this makes it a special member. In the present work, AlPO₄-9 has been synthesized using piperazine as the structure-directing agent and the mixture of H₂O and EG as the solvent. Structure refinement from single crystal X-ray diffraction data shows that AlPO₄-9 is a material with the composition of C₂H₇Al_5.50NO₂₅P₆. It crystallizes in the monoclinic space group C2/c (No: 15), with a = 24.230(5) Å, b = 14.026(5) Å and c = 16.197(3) Å, β = 119.87(4)°, V = 4773(2) Å³, Z = 8. The open-framework of AlPO₄-9 is built of alternating corner-sharing PO₄ tetrahedra and AlO₄ tetrahedra (AlO₆ octahedra) to construct a curved one-dimensional 8-ring channel system running along [1 0 1]. Meanwhile, the strict alternative of PO₄ tetrahedra and AlO₄ tetrahedra (AlO₆ octahedra) results in a negative framework in AlPO₄-9. Thermal stability has been determined on a thermal analyzer and by calcination. It reveals that AlPO₄-9 framework is thermally stable and has a potential to be a catalytic material.