Elastic behavior of adsorbed single compact chains

Elastic behaviors of short single two-dimensional compact chains adsorbed on the attractive surface are investigated in this paper by using the enumeration calculation method. In our model a single compact chain is fixed with one of its end at a position above the impenetrable surface, and then it is pulled away from the attractive surface slowly through elastic force acting. We investigate the chain size and shape of adsorbed compact chains, such as mean-square end-to-end distance per bond 〈R²〉/N mean-square radii of gyration per bond 〈S²〉_x/N and 〈S²〉_y/N, shape factors 〈δ〉, and fraction of adsorbed monomers f_a in order to illuminate how the size and shape of adsorbed compact chains change during the process of tensile elongation. Especially for strong attraction interaction there are some special behaviors in the chain size and shape during this process. If there exits adsorption interaction, single compact chain is first almost pulled down to the adsorption surface and then moves in the direction of force until to leave the adsorption surface. These changes become more obvious with strong adsorption interaction. Our calculation can show this elastic process of adsorbed compact chains visually and simply. On the other hand, some thermodynamics properties are also studied here. We use average energy per bond, average Helmholtz free energy per bond, elastic force f and energy contribution to elastic force f_u to study the elastic behavior of adsorbed single compact chains in the process of tensile elongation. Elastic force f has a long plateau during the tensile elongation for strong adsorption interaction, which agrees well with experimental and theoretical ones. These investigations can provide some insights into the elastic behaviors of adsorbed protein chains.     

Direct prediction of HP sequences of compact polymer chains from elastic force

In this paper, a new method is proposed to predict HP sequences of compact polymer chains from elastic force based on the PERM (pruned-enriched-Rosenbluth method) simulation. Two different HP sequences are selected here, and we let them pass through a nanopore after acting of elastic force, which only allow single but not double strands to pass. Some thermodynamics properties of compact polymer chains are investigated during the translocation process, such as average Helmholtz free energy 〈A〉, average energy per bond 〈U〉, and average contact energy per bond 〈U_c〉. We find that the curves of them change non-monotonously with different steps, which inversely can be used to distinguish H and P accurately. The most important parameter of them is elastic force f because it can be measured directly using single-molecule force spectroscopy (SMFS) in experiment. Through recording and comparing force-extension curves, we can determine the HP sequences accurately. This method is also applied to determine DNA sequence directly, and to study the contact interactions in proteins and the protein folding.     

Effects of temperature on elastic behavior of short compact polymers

In this paper, we study further to explore the effects of temperature on the elastic behavior of short compact polymers. Average conformations and thermodynamics statistical properties at various temperatures T are calculated here. Different chain lengths N and elongation ratio λ are also considered simultaneously. From the plots of f and f_U vs. elongation ratio at low temperature, we can know that compact polymers are more close to the native states. With temperature decreasing deeply, polymer chains have the tendency to form globular structures. The results are concluded from: the ratio of 〈L₁²〉/〈L₂²〉 increase abruptly with temperature decreasing at low temperature, and both characteristic ratio 〈R²〉/Nb² and average energy per bond 〈U〉 decreases abruptly with temperature decreasing at low temperature, here L₁², and L₂² are the eigenvalues of the radius of gyration tensor S (L₁²≤L₂²). We also analyze the relationship between the heat capacity C_V and temperature T for different chain lengths in the process of tensile elongation. The coil-to-globule transition temperature T_c can be estimated from the location of the peak on the heat capacity plot as a function of temperature. The plots of 〈R²〉 as a function of chain length N at different temperatures are also shown, and the correlation 〈R²〉∼N^α is obtained at T>T_c or T<T_c, while at T=T_c, the plots are irregular, here α depends on temperature and elongation ratio simultaneously. Elastic force (f), energy contribution to elastic force (f_U), and the ratio f_U/f are also discussed at various temperatures. These investigations may provide some insights into elastic behaviors of compact polymers at different temperatures, especially at low temperature.     

PVC-MnO2的制备及其对锂离子的吸附行为

MnCO3和Li2CO3经高温煅烧合成Li4Mn5O12,再与聚氯乙烯(PVC)和N,N-二甲基甲酰胺溶液混合,干燥、酸洗后制得粒径3?4 mm的多孔球形PVC?MnO2锂离子筛,用其吸附Li离子. 结果表明,PVC?MnO2吸附Li离子的反应符合Langmuir方程和拟二级动力学方程,吸附焓变为0.358 kJ/mol,吸附反应为吸热反应,Li离子最高吸附量可达23.4 mg/g.     

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.     

Zn2+-imprinted porous polymer beads: Synthesis,structure, and selective adsorption behavior for template ion

Zn²⁺-imprinted polymer was synthesized in porous spherical forms via a self-assembled complex between 2,2′-bipyridyl/4-vinylpyridine complexant/functional monomer and Zn²⁺ template ion. Diameters of particles ranged from 250 to 550 μm to enlarge the surface area and thus enhance the adsorption capacity. The presence/absence of the template ion in the preparation of the imprinted polymer was confirmed by EDX spectroscopy, and the physical structure of the particles was investigated using ESEM and BET analysis. The particle and the pore size were controlled by the cross-linker/monomer feed ratio. The adsorption capacity of the imprinted polymers was 210.61 μmol g^?1 for Zn²⁺, while those for Cu²⁺, Ni²⁺, and Pb²⁺, were 37.92 μmol g^?1, 33.02 μmol g^?1, and 9.70 μmol g^?1, respectively. This big discrepancy of the adsorption capacities illustrates the excellent separation selectivity of the imprinted polymers. The adsorption capacity decreased significantly at pH below 4.5, as the polymers are easily protonated. The imprinted particles lost only 10 % of their adsorption ability after 10 repeated uses.     

A study of adsorption behavior of 2,4-Dichlorophenoxyacetic Acid onto various GACs

Adsorption and desorption of 2,4-dichlorophenoxyacetic acid (2,4-D) onto granular activated carbon (GAC) were studied to get basic information on their removal from aqueous solution. Single species adsorption equilibria of 2,4-D dissolved in water have been measured using F400, SLS103, and WWL. Equilibrium capacity increased with decreasing pH. The magnitude of adsorption capacity of 2,4-D was the order of F400> SLS103>WWL. Kinetic parameters were measured in a batch adsorber to analyze the adsorption rate of 2,4-D. The internal diffusion coefficients were determined by comparing the experimental concentration curve with that predicted from the surface diffusion model (SDM) and Pore diffusion model (PDM). The linear driving force approximation (LDFA) model was used to simulate isothermal adsorption behaviors in a fixed bed adsorber and successfully simulated experimental adsorption breakthrough behavior under various operation conditions. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

Phase behavior of semicrystalline polymer blends

The phase behavior of the semicrystalline polymer blend composed of isotactic polypropylene (iPP) and linear low density polyethylene (PE) was studied using small angle X-ray scattering (SAXS) and optical microscopy (OM). Based on the random phase approximation, the iPP/PE interaction parameter, χ, was obtained, and used to construct the iPP/PE phase diagram. The χ values reported in this study are lower than the χ values for deuterium-labeled moieties, measured by small angle neutron scattering (SANS). The predicted phase diagram has upper critical solution temperature (UCST) behavior with a critical temperature of 143 °C for the molecular weights used in this study. OM was used to locate cloud points and the results are consistent with the predicted phase diagram. Since iPP melts above the critical point, care was taken to distinguish phase separation from iPP crystallization by studying the kinetics of iPP crystallization, and the iPP crystallization was discerned from dewetting. In PE-rich blends, the iPP crystallization was suppressed and no dewetting was observed.     

填充聚合物的流变行为探讨

对炭黑、无机物质、纤维填充聚合物的流变行为分别进行了讨论。初步探讨了影响填充聚合物流变性能的因素,并概括了其流变特性和粘弹性质。     

Conformational properties and elastic behavior of protein-like lattice polymers

The interior conformations and elastic behaviors of protein-like lattice polymers in the process of tensile elongation are investigated by means of Monte Carlo method and the (310) hybrid lattice model. Here (HHPPHPP)_x sequence of protein-like polymer chains is adopted. It is found that three types of contacts, i.e. HH-, PP- and HP-contact, have different behavior in the process of elongation. Second structures of protein-like chains, i.e. helical, coil and expanded structures, have distinct characteristic in our simulation. The average energy, the Helmholtz free energy and elastic force are also investigated at different temperature. Moreover, and 〈δ^*〉 as a function of elongation ratio carefully reflect the shape change in the process of tensile elongation, and the snapshots of contact maps can directly explain the interior conformation change of protein-like chains, therefore, here we give some discussions about the shape and the snapshots of contact maps. These investigations may provide some insights into the elastic behavior of protein-like chains.     

Impact of channel wall hydrophobicity on through-plane water distribution and flooding behavior in a polymer electrolyte fuel cell

Through-plane liquid accumulation, distribution and transport inside polymer electrolyte fuel cell (PEFC) components were analyzed as a function of channel wall hydrophobicity with the use of high-resolution neutron imaging. Neutron images were taken with polytetrafluoroethylene (PTFE) coated and uncoated flow channel walls. Anode to cathode liquid distribution was analyzed for each case at low and high current conditions over 20 min of operation. The form and amount of liquid water inside the channels and diffusion media (DM) were compared for hydrophobically coated channels and hydrophilic channels, and a primary liquid transport-flooding mechanism is suggested for each case. The location and value of maximum water storage in DM at low and high current operation were analyzed and slopes of water mass versus distance curve were calculated to compare the significance of capillary liquid flow and phase-change-induced flow within the diffusion media. A significant effect of CL|MPL and MPL|DM interfaces on liquid transport and flooding is found through the analysis of micro-porous layer (MPL) water content and saturation profile along the CL|MPL and MPL|DM interface region.     

Nonionic surfactants adsorption onto activated carbon. Influence of the polar chain length

The adsorption of a nonionic surfactants series characterized by a different length of the hydrophilic tail on an activated carbon has been studied over a wide concentration range. Adsorption isotherms show two steps limited by the critical micelle concentration (c.m.c.) of the surfactants. The adsorption extension depends on the oxyethylenic chain length, in such way that the amount adsorbed decreases with increasing the chain length, although the effect is much lower for the longest polar chains. In the concentration range below the c.m.c. of the surfactants, the molecules are adsorbed by direct interactions with the activated carbon surface, but with different configuration of the polyoxyethylene chain (POE) directed to the aqueous phase. For concentrations above the c.m.c., the adsorption takes place by the interactions between the adsorbed surfactants molecules and differences related to the length of the hydrophilic chain are also found.     

Curie temperature of a ferromagnetic polymer chain model

Phase transition of a self‐avoiding walking polymer chain with spatial nearest neighbor ferromagnetic Ising interaction on the simple cubic lattice is investigated using Metropolis dynamic Monte Carlo technique. Magnetic susceptibility χ is determined from the Brillouin function and from the linear response of magnetization to external magnetic field in small field region. We find the later is better, though both are in consistent with each other at high temperatures. The magnetic susceptibility χ can be expressed using the Curie law and thus the Curie temperature θ is estimated. The chain length dependent Curie temperature θ of the chain model can be well fitted as θ = 1.40 ? 4.0 × n^?0.619 based on the finite‐size scaling law. The transition temperature for an infinite long chain θ(∞) = 1.40J/k_B and the exponent ? = 0.619 are in agreement with our previous study ( 19 ). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 969–973, 2006     

主链型液晶高分子改善聚丙烯熔体高速挤出的流变行为

采用恒速型双毛细管流变仪研究了主链型热致液晶对无规共聚聚丙烯(PPR)熔体高速挤出流变性能的影响.PPR熔体螺纹状畸变是由口模入口区的应力集中效应和横向环流造成的;利用原位成纤法制备PPR/热致液晶聚合物(TLCP)试样,TLCP在拉伸场中明显取向,随拉伸速率增大,取向程度先增大后减小;取向的TLCP明显减弱熔体挤出物...     

Application of an adsorption non-flow exergy function to an exergy analysis of a pressure swing adsorption cycle

Pressure swing adsorption (PSA) is a popular gas separation technology for the process industries and is commonly used for air separation, hydrogen purification, and isomer separation. In this study, we apply a second law analysis to this technology to identify sources of irreversibility in the process and, in particular, identify which steps in the PSA cycle are responsible for the major losses. Unlike previous exergy analyses, we derive and use expressions for the exergy of the adsorbed phase using adsorption thermodynamics. In this way, exergy loss (or entropy generation) within the adsorption cycle in each step is clearly identified. We illustrate the use of these exergy functions with the application of binary linear isotherm (BLI) theory to a four-step Skarstrom cycle. Major losses in the process are shown to be the exergy loss across the valve in the blowdown step, and feed compressor aftercooler losses. Feed repressurisation is shown to be more efficient than product repressurisation for the separation factor examined in this study since part of the feed gas is introduced at a low pressure. During the cycle, bed exergy loss during the feed step is significant, while there is no exergy loss in the adsorbent bed during the blowdown or purge steps. The exergy functions derived in this study can readily be applied to more complex PSA cycles and provide a basis for cycle design.     

Hydrogen adsorption/desorption behavior of multi-walled carbon nanotubes with different diameters

Multi-walled carbon nanotubes (MWNTs) with different mean outer diameters in the range of 13-53 nm, synthesized by the catalytic decomposition of hydrocarbons using a floating catalyst method, were purified and pretreated with the same procedure for volumetric hydrogen adsorption/desorption measurements. It was found that the hydrogen storage capacity of the purified and pretreated MWNTs was proportional to their diameter, and that hydrogen in all types of MWNTs measured could not be completely desorbed at room temperature and ambient pressure. A possible mechanism for the above behavior was proposed based on the results of cryogenic nitrogen adsorption analysis and high-resolution transmission electron microscopy observations. It was considered that small “carbon islands” might be the main hydrogen adsorption site in MWNTs. The effects of metal catalyst as well as an etched cavity on the surface of MWNTs on the hydrogen adsorption/desorption of MWNTs were also discussed.     

1,3,5-Triazine-pentaethylenehexamine polymer for the adsorption of palladium (II) from chloride-containing solutions

A triazine-hexamine (TAPEHA) polymer demonstrating high acid-resistance, good affinity to noble metals, and a high density of amine and triazine functional groups has been designed and synthesized. The obtained polymer was used as an adsorbent for the recovery of palladium (II) ions from chloride-containing solutions. Effects of pH, pCl, contact time, initial Pd(II) concentration, and temperature on adsorption were investigated and optimized by batch adsorption experiments. The pseudo second-order kinetic equation provides the best correlation for the process. While five isotherms were used, the nonlinear resolution of the Langmuir isotherm equation has been found to provide the closest fit to the equilibrium data. The monolayer adsorption capacity which is highest among literature is 517.2 mg/g. All thermodynamic parameters suggest that Pd(II) adsorption onto TAPEHA particles is a spontaneous, physisorptive, and exothermic process. The formation of TAPEHA and Pd-adsorbed TAPEHA has been characterized by FE-SEM, EDAX, XRD, and FTIR instrumentations. Adsorption of the negatively charged chloropalladium (II) species mostly takes place via ligand exchange mechanism. Ease of synthesis and low cost, coupled with highly efficient and rapid removal of Pd(II) ions, make TAPEHA an attractive adsorbent.