Remarks on the simulation of Cl electrosorption on Ag(1 0 0) reported in Electrochimica Acta 50 (2005) 5518

Some problems in connection with the simulation of Cl electrosorption on Ag(1 0 0) reported in Electrochimica Acta 50 (2005) 5518 are discussed.It is concluded, that although the electrostatic model could be correct, the results of the simulation can be hardly reconciled with the experimental data owing to the contradictions discussed in the present paper.     

Reply to “Remarks on the simulation of Cl electrosorption on Ag(1 0 0) reported in Electrochimica Acta 50 (2005) 5518”

We reply to the remarks by Láng and Horányi [G.G. Láng, G. Horányi, Electrochim. Acta (2006), doi:10.1016/j.electacta.2006.07.009] on the meaning of the notion of “electrosorption valency” used by Abou Hamad et al. [I. Abou Hamad, S.J. Mitchell, Th. Wandlowski, P.A. Rikvold, G. Brown, Electrochim. Acta 50 (2005) 5518]. It is concluded that, contrary to the assertion of Láng and Horányi, the magnitude of the current in the external circuit upon adsorption of an ion of charge ze with partial charge transfer is indeed given by an electrosorption valency γ such that |γe|<|ze|. We believe the conclusion of Láng and Horányi to the contrary is the result of an excessively severe charge-neutrality requirement.     

Application of the Monte Carlo simulation method to the investigation of peculiar free‐radical copolymerization reactions: Systems with both reactivity ratios greater than unity (rA > 1 and rB > 1)

With a Monte Carlo simulationmethod, copolymer properties have been thoroughly studied, and the influence of the reactivity ratios and feed composition has been taken into consideration. Instantaneous alterations of the copolymer composition and copolymer heterogeneity, which is also called a randomness parameter, have been examined with data obtained from the simulation at each stage of the copolymerization reaction. The results prove the azeotropic behavior of copolymerization reactions in which both reactivity ratios are greater than unity, although some special reactivity ratio combinations ignore the azeotropic behavior. The copolymer composition reaches an azeotrope point at the end of the copolymerization reaction when the copolymerization is an azeotropic reaction. In addition, the randomness parameter takes its maximum value at the azeotrope point when reactivity ratio r_A is equal to reactivity ratio r_B. Finally, increasing the reactivity ratios causes no change in the trend of copolymer composition/feed composition curves when r_A is equal to r_B. However, the curves produced with larger r_A and r_B values show more fluctuations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Monte Carlo simulation of molecular motion and phase transition in poly(ethylene) crystal

Conformational properties of a chain and a phase transition in poly(ethylene) crystal are studied by extending a previous Monte Carlo calculation for a chain in a cylindrical crystalline potential. The crystalline potential is here estimated from van der Waals interactions between one CH₂ group of a chain and its six neighbouring chains. Firstly, conformational disorders of the chains of various chain length are examined, and a definite dependence of the chain conformation on its length is demonstrated. Secondly, the behaviour of the chain at atmospheric pressure is simulated, where the modes of molecular motions and the associated disorders in conformation are clarified as a function of temperature. Thirdly, the phase transition at high temperature and pressure, from orthorhombic phase to hexagonal one, is simulated by assuming a proper molecular field for the chain. All these calculations show the present Monte Carlo calculation to have a wide variety of applications in the studies of polymer crystals.     

Monte Carlo simulation of gas phase polymerization of 1,3‐butadiene. Part II: Kinetics optimization and confirmation

Studies on the deactivations and initiations of gas phase polymerizations of 1,3‐butadiene have been achieved by Monte Carlo simulation. Initiation and deactivation control the reaction before and after the peak of the polymerization rate, respectively. The influence of polymerization temperature has been studied. Monte Carlo modeling of polymerization kinetics and mechanism was confirmed by the agreement of experimental data and simulation results of polymerizations run with a temporary evacuation of monomer. The balance of catalysts and active chains is established by both initiation and chain transfer reactions with cocatalyst, which causes a ‘pseudo‐stability’ stage. © 2003 Society of Chemical Industry     

Modeling of fractionation in CRYSTAF using Monte Carlo simulation of crystallizable sequence lengths: Ethylene/1‐octene copolymers synthesized with single‐site–type catalysts

Monte Carlo simulation was used to model the fractionation process in crystallization analysis fractionation (CRYSTAF). Five poly(ethylene/1‐octene) samples synthesized with a single‐site–type catalyst were used to verify the simulation results. It was proposed that the fractionation mechanism be controlled by the crystallization of the longest ethylene sequence in each chain. Good agreement between experimental and simulation results verified the validity of the proposed fractionation mechanism. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2200–2206, 2001     

Oxygen sites active in H-abstraction at a Cu(110)-O surface: Comparison of a Monte Carlo simulation with imide formation studied by XPS and VEELS

A Monte Carlo simulation of the development of the topographic structure of the Cu(110)-O overlayer has provided quantitative data for the distribution of different oxygen sites during formation of the overlayer. Those oxygen atoms present at the ends of copper-oxygen chains are shown to be able to account for the observed activity of the overlayer in imide formation through H-abstraction from ammonia. The Monte Carlo simulation also mimics closely features of the Cu(110)-O system observed by scanning tunnelling microscopy.     

Lithium transport through a sol-gel derived LiMn2O4 film electrode: analyses of potentiostatic current transient and linear sweep voltammogram by Monte Carlo simulation

Lithium transport through a sol-gel derived LiMn₂O₄ film electrode was theoretically investigated by analyses of the potentiostatic current transient and the linear sweep voltammogram in consideration of the interactions between lithium ions by using Monte Carlo simulation. The anodic current transients experimentally measured on the film electrode ran with the slope of logarithmic current with logarithmic time flatter than −0.5 in the early stage, and then did in an upward concave shape in the time interval between t_T1 and t_T2. The linear sweep voltammograms experimentally measured on the film electrode showed two anodic peak currents I_p1 and I_p2 which increased linearly with scan rate v to the power of 0.66 and 0.70, respectively, (i.e. I_p1∝v^0.66 and I_p2∝v^0.70) at the scan rates higher than 0.5 mV s⁻¹. Moreover, the higher v was, the larger appeared the positive deviations of the first and second peak potentials E_p1 and E_p2 from the first and the second transition potentials E°_p1 and E°_p2, respectively, in the inverse derivative of the electrode potential curve. The current transients and the linear sweep voltammograms were analyzed in consideration of the interactions between lithium ions in the electrode by using the Monte Carlo simulation under two different constraints of the diffusion-controlled lithium transport and the cell-impedance-controlled lithium transport. The current transients and the linear sweep voltammograms, theoretically calculated under the cell-impedance-controlled constraint in consideration of the interactions between lithium ions, were in good agreement with the experimental results in shape. The disorder to order phase transition in the LiMn₂O₄ film electrode during the cell-impedance-controlled lithium transport at the potential jump and scan was discussed with the aid of the concentration profiles and the local cross-sectional snapshots of the configuration of lithium ions simulated by the Monte Carlo method.     

In situ X-ray analysis under controlled potential conditions: An innovative setup and its application to the investigation of ultrathin films electrodeposited on Ag(1 1 1)

An innovative setup to combine electrochemical and in situ surface X-ray diffraction (SXRD) measurements is described. This electrochemical cell has a different design from the other ones commonly used for X-ray diffraction studies. It allows the sample surface to stay always completely immersed into the solution under controlled potential conditions even during the SXRD measurements. The X-ray beam crosses the liquid (about 1 cm) and the cell walls. Because of the high X-ray energy, the beam attenuation is negligible and by an appropriate positioning of the detector arm slits it is possible to minimize the diffuse scattering induced by the liquid and cell walls in order to still detect the minima of the crystal truncation rods (CTRs). The liquid solution in the cell is managed by a special device, which allows the controlled exchange of the electrolyte solutions necessary in the electrochemical atomic layer epitaxy (ECALE) growth. The whole setup can be remotely controlled from outside the experimental hutch by a dedicated computer. As an example we report measurements on S layers deposited at underpotential on the Ag(1 1 1) surface, and on CdS films of increasing thickness.     

Artificially phase-separated binary self-assembled monolayers composed of 11-amino-1-undecanethiolate and 10-carboxy-1-decanethiolate on Au(1 1 1): A comparative study of two preparing methods

Two methods have been compared for preparing artificially phase-separated two-component SAMs on Au(1 1 1) composed of 11-amino-1-undecanethiolates (AUTe) and 10-carboxyl-1-decanethiolates (CDTe), which would form, thermodynamically, a homogeneously mixed binary SAMs. The first method starts with the formation of a phase-separated binary SAM of AUTe and 2-hydroxy-1-ethanethiolate (HETe) as a template of the artificially phase-separated SAM, followed by the selective desorption of HETe domains and succeeding filling of the vacancy with CDTe. The second method utilizes fluoren-9-ylmethyl N-(11-mercaptoundecyl) carbamate (FMUCe) instead of 11-amino-1-undecanethiol in preparing the template. After the filling with CDTe, the 9-fluorenylmethyloxycarbonyl (Fmoc) group is removed to obtain AUTe domains. Both methods yield artificially phase-separated binary SAMs having AUTe domains of tens nanometer across. The molecularly flat SAM surface with nanometer-scale domains of different acid-base and electrostatic properties are thus created. For preparing binary SAMs with a higher degree of phase separation, the second method is a better choice; a more clear-cut phase separation is achieved.