Formation Of Short Chains Research Articles

Crystallinity in polymer electrolyte membranes used in H2 generators: Degradation mechanism from the perspective of recycling

Methanol-based electrolysis can be a prospective alternative for the reduction of energy consumption. Developing highly durable methanol-based electrolysers with small CO2 release can help achieve cheaper hydrogen. Further, to arrive at a circular economy in H2, recycling the precious components would play a major role. Several studies on catalyst recycling have overshadowed the need for recycling the proton exchange membrane. Membrane, which forms 25% of the device cost, need to be studied for its degradation and optimizing the operating parameters of the device have a big role to play in establishing recycling. Our previous studies concluded that the change in crystallinity of membrane from fuel cell was closely related to membrane properties. Herein, for the first time, we have correlated the crystallinity of the membrane retrieved from an electrochemical methanol-reformer to its degradation mechanism. The average crystallinity on the anode and cathode sides was observed to be increased drastically compared to a fuel cell. As observed from Fourier Transform Infrared Spectroscopy (FTIR), the presence of sulfonic acid anhydrides was considered one of the reasons for this increase in crystallinity. X-ray photoelectron spectroscopy (XPS) showed that carbon peaks in the side chain was devoid of α-OCF2, –CF3, indicating severe degradation. The probability of finding a degraded area on the anode side of the scanned recycled membrane was 88% and 55% for the cathode side. The severe degradation of amorphous side chains and formation of short chains had considerably increased the crystallinity. The disparity in the intensity of degradation on the anode and cathode sides of the membrane was confirmed by the percentage of crystallinity and XPS studies. Further, the severity of degradation on either side of the membrane from methanol-based Proton Exchange Membrane electrolysers makes them difficult for further reuse in hydrogen-based energy systems.

Potential risk from and prevention of phytoplankton outbreaks in blocking the cooling water system in a nuclear power plant on the Southeast China coast

The invasion or aggregation of marine biota in coastal waters has become a common problem, threatening the safety of cooling water systems in the context of environmental and climate changes. However, studies on issues of coastal nuclear power plants from the view of marine ecology have mostly focused on the thermal effluent, entrainment effect on organisms, residual chlorine, radioactivity, etc. There is a lack of information on the safety of cooling water systems in nuclear power plants blocked by marine biota. Based on field and historical datasets, this study screened phytoplankton species that may potentially block the cooling water system of the Fuqing nuclear power plant on the Southeast China coast, identified the phytoplankton risk and a risk calendar, and established a catalog of risk phytoplankton species for the cooling water system. The screening criteria were simultaneously required as follows: (1) particle size of cells or group >2000 μm; (2) phytoplankton bloom or aggregation events occurred in surrounding areas; (3) and species abundance maintained at >0.5×105 cells/L in the surrounding area. Nine high-risk species were screened out that can easily form colonies, clusters, and groups, including Thalassiosira diporocyclus, Thalassiosira subtilis, Noctiluca scintillans, Phaeocystis globosa, Pseudo-nitzschia pungens, Pseudo-nitzschia delicatissima, Skeletonema costatum, Skeletonema dohrnii, Paralia sulcata. Due to small cells or the formation of short chains, some dominant phytoplankton species, even those with advantages in abundance and occurrence, had difficulty threatening the reliability of cooling water systems in nuclear power plants. The outbreak of different phytoplankton species varied daily, and the risk of blockage was highest from April to July. The biological characteristics, ecological mechanisms underlying outbreaks of high-risk phytoplankton species are reviewed and discussed, suggesting a high degree of temporal and spatial variability of blockage risk. Finally, main prevention and control measures used against high-risk phytoplankton species are provided to imply new ideas and methods for nuclear power plants. These strategies have very important practical and scientific significance.

Reconfiguring nanostructures in magnetic fluids using pH and magnetic stimulus for tuning optical properties

In this paper, we demonstrate tuning the optical properties of magnetic fluids through pH and magnetic field control. The role of reconfigurable nanostructures in the temporal and switching behavior of transmitted light is also studied. An oil-in-water magnetic nanoemulsion with an average diameter of 200 nm, containing Fe3O4 superparamagnetic nanoparticles of 10 nm average diameter, is used in this study. To make the emulsion pH reconfigurable, the droplets are covered with a weak polyelectrolyte, poly (acrylic acid). The swelling of the PAA molecules, due to ionization of the carboxylic acid groups, resulted in an increase in adlayer thickness at increase in pH. The change in transmitted intensity is found to scale linearly with the applied magnetic field strength, and at higher fields, the formed structures took more time to reconfigure themselves after the removal of magnetic field. At a pH 5, the increase in transmitted light intensity is seen even at a very low magnetic field strength due to the lower interdroplet spacing. On the contrary, at pH 9, the interdroplet spacing between the emulsion drops were large, due to the extension of PAA molecules, which led to a weaker magnetic interaction between the droplets and formation of shorter chains, where a lower transmission is seen due to multiple scattering. A straight-line pattern was observed in the transmitted intensity, due to the scattering of light from linear chains that are aligned perpendicular to the light propagation direction. Bridging of polymer covered surfaces was seen at pH 3, due to hydrogen bonding between PAA molecules. Our results show that tuning optical properties of magnetic emulsion (switching between transparent and opaque states) is possible through pH control. Our findings open up new opportunities to develop optical devices and accessing of diverse structures by tuning pH and magnetic field.

A systematic study of the dynamics of chain formation in electrorheological fluids

We report a systematic study of the dynamics of chain formation in electrorheological fluids using Brownian dynamics simulations. The parameters of the system such as applied electric field, polarizability, dipole moment, friction coefficient, and number density are expressed in reduced units and changed in a wide range in order to map the system’s behavior as a function of them. We define time constants obtained from bi-exponential fits to time dependence of various physical quantities such as dipolar energy, diffusion constant, and average chain length. The smaller time constant is associated with the formation of shorter chains (pairs, triplets, and so on), while the larger time constant is associated with the formation of longer chains in the regime of those that overarch the simulation cell. We use the approximation that the dipole moments are induced by the applied electric field only, as usual in the literature. However, we report preliminary results for the case when particle–particle polarization is also possible.

Dynamic numerical simulations of magnetically interacting suspensions in creeping flow

The equations governing the motion of N magnetic particles suspended in a viscous fluid at low Reynolds and finite Stokes numbers are solved by direct numerical simulations for different Péclet numbers. The Langevin dynamics simulations include all dipole–dipole magnetic interactions for force and torque. An external applied magnetic field and near field interactions represented by contact and repulsion forces are also considered. Repulsive forces are modeled using a variation of the screened-Coulomb type potential. The initial particle distribution is an ergodic ensemble in which each member consists of N mutually impenetrable spheres whose centers are randomly distributed in a prismatic cell of volume V with wall boundaries. The stability of the proposed numerical method and its convergence in calculating some relevant macroscopic properties of the magnetic suspension are carefully examined. The simulations are used to investigate structure transition from an isotropic random distribution of particles to other structures in the presence of an external magnetic field and magnetic particle–particle interactions. The simulations show dimmers and short chain formation in the suspension space at low volume fraction. When the volume fraction is increased long chains and thin anisotropic structures may be observed along the magnetic field direction. The numerical method is also used to calculate the steady state equilibrium magnetization, and accurate results are obtained for different particle volume fractions ϕ in agreement with Oϕ3 asymptotic theories. The method presented is able to consider up to 3000 particles with accuracy and computational efficiency. Typical configurations and particle trajectories are also shown and discussed from a physical point of view.

Kinetics and mechanism of benzyl para-chlorophenyl ketone oxidation

The oxidation of benzyl para-chlorophenyl ketone in chlorobenzene at 100°C occurs through the formation of short chains. Non-peroxide reaction products (1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone, para-chlorobenzyl, benzaldehyde, and para-chlorobenzoic acid) are formed not only by the transformation of hydroperoxide (1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone) but also (or solely) through the recombination of α-ketoperoxyl radicals with or without chain termination. α-Hydroperoxide decomposes predominantly through a heterolytic route to form para-chlorobenzoic acid and benzaldehyde. Benzaldehyde and 1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone undergo radical chain oxidation in the reaction medium to form benzoic acid (benzaldehyde), para-chlorobenzyl, and benzoic and para-chlorobenzoic acids (1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone). The homolytic decomposition of α-hydroperoxy ketone and α-hydroxy-α-hydroperoxy ketone causes the self-acceleration of the process and affords 1-(4-chlorophenyl)-2-hydroxy-2-phenyl-1-ethanone or, to a lesser extent, benzaldehyde and para-chlorobenzoic acid (α-hydroperoxy ketone). para-Chlorobenzoic acid substantially accelerates the heterolytic decomposition of α-hydroxy-α-hydroperoxy ketone and the oxidation of benzyl para-chlorophenyl ketone with peroxy acids to ester according to the Baeyer-Villiger mechanism. The rate constants of the main steps of the process and kinetic parameters are calculated by solving the inverse kinetic problem.

Mechanisms of initial alloy formation for Pd on Cu(100) studied by STM.

The nucleation and growth of Pd alloys on Cu(100), up to the ordered c(2\ifmmode\times\else\texttimes\fi{}2) structure have been studied using scanning tunneling microscopy. Atomically resolved images at low Pd coverages (0.20 ML) show protrusions, located in the lattice sites of the substrate, that are attributed to individual Pd atoms. A pair- correlation plot shows that there is a strong tendency for them to be located in second-nearest-neighbor positions, resulting in the formation of short chains along the [001] and [010] directions. As the coverage increases, the chains converge to form a c(2\ifmmode\times\else\texttimes\fi{}2) structure, with the squeezed-out Cu atoms nucleating into Cu islands. The Cu islands also form over the alloyed regions, with the result that more than the previously reported 0.5 ML of Pd is required to form the c(2\ifmmode\times\else\texttimes\fi{}2) structure with second-layer growth initiated before a perfect c(2\ifmmode\times\else\texttimes\fi{}2) structure is formed.

Pivalolactone, 1 interchange reactions with polypivalolactone

AbstractEster interchange, alcoholysis, and acidolysis of polypivalolactone (PPVL) were studied by melting PPVL with bisphenol diacetates, 1, 4‐butanediol, or aromatic diacids. Interchange of PPVL with the diacetates and the diol occured readily, in particular in the presence of a titanium catalyst. Melting PPVL with 10 mol‐% of bisphenol‐Adiacetate in the presence of 0,5 wt.% tetrabutylorthotitanate resulted in an incorporation of 33% of the diacetate in the polymer chains, whereas the logarithmic viscosity number decreased by 81%. The ester interchange was suggested to proceed by an initial cleavage of ester bonds in the polymer chain of PPVL, resulting in the formation of shorter chains, followed by a reaction between the newly formed ester end‐groups and initially present hydroxyl chain ends. The acidolysis of PPVL with the diacids proved to be less effective; in the case of the acidolysis of PPVL with 10 mol‐% isophthalic acid, less than 1% of the diacid was incorporated in the polymer chains and a decrease in the logarithmic viscosity number of only 22% was found. Both the high stability of the ester bond in PPVL towards acids in general and the heterogeneity of these systems were supposed to cause the behaviour of PPVL with respect to acidolysis. The results concerning the interchange reactions with PPVL were compared with studies on other polyesters.