Sonoelectrochemical (20 kHz) production of platinum nanoparticles from aqueous solutions

The present work describes the production of platinum nanoparticles from aqueous chloroplatinic solutions in the presence of low-frequency high-power ultrasound (20 kHz) on titanium alloy electrodes. The production of this new type of Pt nanoparticles was performed galvanostatically at (298 ± 1) K using a newly designed experimental set-up and ‘sonoelectrode’ producing ultrasonic pulses triggered and followed immediately by short applied current pulses. From galvanostatic studies, it was shown that Pt mean grain size ranging from 11 to 15 nm was produced. Morphological and structural studies of the produced nanoparticles were performed by TEM, SEM, XRD and SAED and showed that Pt nanoaggregates were predominantly formed, with no redissolution of the nanoaggregates. Globular clusters had a mean size ranging between 100 and 200 nm which in turn aggregated and built complex structures.     

Sonoelectrochemical (20 kHz) production of Co<Subscript>65</Subscript>Fe<Subscript>35</Subscript> alloy nanoparticles from Aotani solutions

This paper describes the production of alloy nanoparticles of Co:Fe ratio 65:35 from Aotani solutions in the presence of high power ultrasound (20 kHz). The production of this new type of alloy nanoparticles was performed potentiostatically and galvanostatically at (298 ± 1) K using a newly designed experimental set-up i.e. a ‘sonoelectrode’ producing short applied current pulses triggered and followed immediately by ultrasonic pulses. It was shown that cathode efficiencies decreased with increasing current densities and high nanoparticle yields were obtained at low current densities. Morphological and structural studies of the produced nanoparticles were performed by TEM, SEM, XRD, and SAED, and showed that the strongly aggregated Co₆₅Fe₃₅ alloy nanoparticles were predominantly formed, with prevalent body-centered cubic bcc crystalline structure; no redissolution of the nanoaggregates was observed and no separate Fe and Co metallic nanoparticles were produced sonoelectrochemically. The experimental value of the lattice parameter for bcc Co–Fe alloy was 2.85 Å and was in excellent agreement with literature values.     

Sono-electrodeposition (20 and 850 kHz) of copper in aqueous and deep eutectic solvents

This paper reports the effects of ultrasound at different frequencies and powers upon the electrodeposition of copper(II) chloride in aqueous potassium chloride and in glyceline 200 (a deep eutectic solvent - DES) on Pt electrodes in the potential range for copper deposition and dissolution. It is shown that the deposition of copper in both solvents is greatly affected by ultrasound at the two frequencies of 20 and 850 kHz employed. Limiting current densities were obtained in both solvents under sonication at 20 and 850 kHz and a 10-fold and 5-fold increase in currents in aqueous potassium chloride and glyceline 200 compared to silent conditions was observed respectively. The difference in viscosity of water (KCl) and glyceline 200 was found to be a crucial parameter in the evaluation of limiting current densities.     

Block copolymer synthesis and chain extension from TEMPO‐terminated chains formed by ultrasonic chain scission

Long poly(ethyl methacrylate) (M_n = 2,300,000) and polystyrene (M_n = 1,200,000) chains were subjected to ultrasonic scission in the presence of a radical scavenger, 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO). This procedure yielded polymers with lower molecular weights and TEMPO terminal units. Application of these polymers in stable radical mediated polymerization of styrene resulted in chain extension and block copolymers, depending on the precursor polymer. Block copolymer formation was evidenced by NMR measurement, and chain extension was shown by GPC analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1950–1953, 2000     

General treatment of polymer crystallization kinetics—Part 1. A new macrokinetic equation and its experimental verification

A new macrokinetic equation of the autocatalytic type is proposed to describe the polymer crystallization process. The derived equation is compared with the known Avrami equation. It is shown to be consistent with the results of isothermal experiments.     

Effect of LiCl on electrospinning of PAN polymer solution: theoretical analysis and experimental verification

Polyacrylonitrile(PAN) is used to study the effect of surface charge on electrospinning by adding LiCl. The theoretical analysis shows that the relationship between radius r of jet and the axial distance z from nozzle follows an allometric law in the form r∼z^−0.5 in case of full surface charge, and the scaling exponent becomes larger for partly charged fibers in electrospinning.     

Hydrodynamics of power-law fluids in trickle-flow reactors: Mechanistic model, experimental verification and simulations

A fully predictive one-dimensional mechanistic model was developed for describing the hydrodynamics of power-law fluids in trickle-bed reactors. The model is a generalization of the slit approach to the case of non-Newtonian fluids obeying Ostwald-deWaele rheological behavior. Without recourse to adjustable parameters, the proposed model enabled prediction of the experimental values of (i) total two-phase total pressure drop and total liquid holdup in the trickle flow regime, (ii) frictional pressure drop in single-phase flows through packed beds, and (iii) total liquid holdup in gravity driven liquid downflow and stagnant gas through packed beds. Parametric simulations guided by knowledge of the behavior of highly viscous Newtonian liquids in trickle beds highlighted the capability of the model in the simulation and design of trickle flow operation using power-law fluids.     

Role of entanglements and bond scission in high strain-rate deformation of polymer gels

A key factor that limits the practical implementation of polymer gels is low gel toughness. Here, we present coarse-grained molecular dynamics simulations of the effects of solvent molecular weight on the toughness of entangled and non-entangled polymer gels in the ballistic impact regime. Our results demonstrate that higher molecular weight solvents enhance gel toughness, and that mechanical properties including strength and toughness can be influenced by bond scission. Further, we find a remarkable two-step gel fracture mechanism on the molecular level: network chains undergo scission first (and well before fracture), followed by scission of solvent chains. For strain rates greater than inverse relaxation time of the solvent, long, highly entangled solvent chains provide fracture resistance even after the network chains break by effectively increasing the number of chains that must be broken as a crack propagates.     

Surface modification of poly(vinyl chloride) using high intensity ultrasound

The use of high intensity ultrasound to promote a number of reactions at the surface of solid poly(vinyl chloride) is reported. Substitution reactions involving a range of compounds, including dyes, can rapidly be carried out from aqueous solution under labile conditions. Sonochemically enhanced treatment with strong aqueous base produces dehydrochlorination even at room temperature to produce a thin layer of conjugated material at the surface which can then be grafted with a number of compounds. Some speculation as to the mechanistic features of the process as well as its potential utility is made. © 1999 Society of Chemical Industry     

溶剂对分子印迹聚合物分子识别能力的影响：实验研究与计算量子化学分析

以茶碱为印迹分子，甲基丙烯酸为功能单体，二甲基丙烯酸乙二醇酯为交联剂，以氯仿、二甲基亚砜和四氢呋喃为溶剂，合成了分子印迹聚合物并测定了其对茶碱分子的识别能力，实验结果显示，在氯仿中合成的MIPs的分子识别性能最佳.综合Scatchard分析吸附行为、¹H NMR测定氢键以及量子化学中的密度泛函计算印迹分子和单体分子的溶剂化能等方法，研究聚合反应的溶剂体系对于印迹聚合物分子识别能力的影响及其作用机制.计算结果显示：采用与印迹分子和单体相互作用力较弱的溶剂体系所合成的印迹聚合物具有较高的分子识别性能.这与¹H NMR分析结果和吸附测定实验结果具有一致性.上述结果表明，溶剂对于分子印迹聚合物的分子识别性能具有重要的影响，而计算量子化学分析对于分子印迹介质合成时的溶剂体系选取和优化具有很好的指导作用.     

Effect of polymer chain scission on photodegradation behavior of polystyrene/multi‐wall carbon nanotube composite

To clarify an effect of polymer chain scission on a polystyrene (PS)/multi‐wall carbon nanotube (MWNT) composite photodegradation, a relationship between the change of molecular weight and photodegradation behavior was studied. The MWNT loading brought about severe PS chain scission and led to the increase of the low molecular weight (less than 10⁵) fraction. The increase of the fraction was not proportional to the loading amount and showed the minimum at the 2% loading. The strange behavior was due to a rheological effect bringing about a decrease of shear stress in the composite preparation. An unsaturated end group was produced by the chain scission and became the photodegradation initiator leading to auto‐oxidation and crosslink reactions. The MWNT scavenged radical species and worked as an antioxidant. The coexistence of the unsaturated end group and MWNT made the photodegradation behavior complicated. However, the MWNT radical scavenging ability was considerably poor, and the MWNT had little ability to inhibit the photodegradation initiation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40362.     

The devolatilization of polyimide fiber composites: Model and experimental verification

A one-dimensional devolatilization model is developed for autoclave processing of themroplastic polyimide, graphite-reinforced, composites. The model rests on the assumption that continous gas passages are formed during processing due to partical crystallization of the polymer in the course of polymerization. Both DSC and optica microscopy indicate that crystallinity develops in the Avimid-III polyimide resin during polymerization, which in turn facilitates formation of cracks. These cracks heal upon removal of volatiles and polymer melting. Model-Calculated temperature profiles in the laminate during polymerization, and the predicted removal rates of volatile species (water, ethanol, NMP) are compared to experimental miniautoclave data for the DuPont Avimid K-III/IM6 system. Good agreement is obtained when the volumetric mass transfer coefficient required by the model is assumed to vary proportionally to the inverse of the changing resin viscosity. The model allows the investigation of desired cure cycle parameters for different laminate thicknesses.     

Comment on “Simulation and experimental verification of the filtration and filter cake compression model”

Comment on “Simulation and experimental verification of the filtration and filter cake compression model” by Kocurek and Palica [Kocurek, J., Palica, M., 2005. Simulation and experimental verification of the filtration and filter cake compression model. Powder Technology 159 (1) 17-26.].     

Modelling and experimental verification of cellulose substitution kinetics

Cellulose and starch derivatives are often prepared by substitution reactions to the hydroxyl groups (OH-2, OH-3 and OH-6) of the corresponding anhydroglucose units. A general kinetic model for the substitution of cellulose and starch was developed. The model assumes different reactivities of the hydroxyl groups and a decrease in the reactivity as the substitution proceeds. Both phenomena are taken into account in the model. The model predicts the detailed distribution of the different mono (2, 3, 6)-, di (23, 26, 36)—and trisubstituted (236) units as a function of the reaction time. The classical Spurlin distribution is obtained as a special case of the general model. Numerical strategies were developed for the solution and computer simulation of the model. Simulation results were shown to be valid for various reactivity ratios of the hydroxyl groups. The modelling concept was verified with experimental data obtained for carboxymethylation of cellulose. It should be emphasized, however, that the same general approach is also applicable in studies of any hemicelluloses or oligo- or monosaccharides. The detailed data, which revealed the non-uniform reactivities of the different hydroxyl groups and the decline of the substitution rate with time, were successfully described by the mathematical model.     

Modeling and verification of fluid-responsive polymer pumps for microfluidic systems

The fundamental principles necessary to create and model a pump for microfluidic systems using fluid-responsive polymer particles are described. The pump is “activated” by the addition of water to the particles, which induces a significant particle volume expansion and pushes a stored fluid from an adjacent reservoir at a predicted flow rate. Two particle systems were investigated to examine how polymer properties affect the rate and amount of fluid delivered. Poly (acrylic acid) (PAA) particles obtained from Pampers^® diapers yield the best micropump swelling characteristics for delivering fluid at pressures above 1100 Pa, whereas the softer potassium-neutralized PAA particles from Aldrich are best only at lower pressures. The maximum flow rates produced by the Pampers^®and Aldrich particles with minimal backpressure are 0.5 and of PAA, respectively. The experimental results demonstrate good agreement with an analytical model describing equilibrium and dynamic polymer swelling coupled with pressure-driven flow through cylindrical channels under conditions in which gel-blocking was not important. Fluid-responsive polymer micropumps could provide an inexpensive and lightweight method for driving fluid flow in microfluidic and other applications.     

Nonlinear viscoelastic response in two dimensions—numerical modeling and experimental verification

Recently we developed a nonlinear viscoelastic constitutive model which called the Phases Model (PHM) [10]. The main advantages of the PHM over existing nonlinear viscoelastic models are that it lends itself to simple, straightforward calibration of the material functions, and that it is naturally suitable to step-by-step computer simulation. In this paper we apply the PHM to two dimensional (2-D) situations. To this end, we've developed a 2-D finite difference code in cylindrical geometry which is based on the PHM. We demonstrate the validity of our modeling by applying the code to a 2-D set-up developed for this purpose. The 2-D specimen is in the form of a disc of the test material compressed between two rigid metal anvils by a velocity-controlled Instron machine. We monitor the response of the viscoelastic disc in terms of the overall axial force history, and the axial stress component at the disc center. We get good agreement between theory and experiment.     

Prediction and experimental verification of bubble and processing characteristics in blown‐film extrusion

Blown‐film modeling is useful to the flexible packaging industry for predicting process and bubble characteristics, such as freeze line height (FLH), bubble diameter, and film thickness. The use of a suitable rheological equation to describe material properties is critical in simulating the blown‐film process. In this article, we present an improved rheological constitutive equation, which incorporates more realistic parameters of stress and deformation properties of the materials by combining the Hookean model with the Phan‐Thien Tanner (PTT) model. The proposed PTT–Hookean model is aimed at enhancing the viscoelastic behavior of the melt during biaxial stretching in the blown‐film extrusion. Predictions of the blown‐film bubble characteristics and FLH obtained with the PTT–Hookean model agreed well with the experimental data of this study and previous studies with different materials and different die geometries. The justification for combining the Hookean model with the PTT model in the blown‐film process is also reported here. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Damage of unfilled crosslinked rubbers as the scission of polymer chains: Modeling and tensile experiments

This article develops a damage model for unfilled crosslinked rubbers based on the concept of scission of polymer chains. The model is built up on the well‐known Gent elastic potential complemented by a kinetic equation describing effects of polymer chain scission. The macroscopic parameters in the damage model are evaluated through the parameters for undamaged elastomer. Qualitative analysis of changing molecular parameters of rubbers under scission of polymer chains resulted in easy scaling modeling the dependences of these parameters on the damage factor. It makes possible to predict the rubber failure in molecular terms as mechanical devulcanization. The model was tested in tensile quasistatic experiments with both the monotonous loading and repeated loading–unloading. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

聚合物增韧方法及增韧机理

探讨了聚合物增韧方法及增韧机理,为材料的研制与开发提供新的思路和准则。     

Depolymerization and demetallation treatments of asphaltene in vacuum residue

The asphaltene fraction [hexane insoluble (HI)] of a vacuum residue (VR) was treated under ultrasonic irradiation at 40°C in THF or 150°C in 1-methyl naphthalene (1-MN) in the presence of an adsorbent composed of modified macro-reticular polystyrene resin. Such a treatment was found effective to convert the asphaltene into the hexane soluble (HS: maltene) without any hydrogen consumption. 61 and 72% of the HI was converted by the adsorption treatment at 40°C in THF and 150°C in 1-MN, respectively, to HS materials having lower molecular weights. About 65% of the metal contaminants in the original asphaltene remained with the newly formed maltenes after this treatment. Structural analyses of the asphaltene and maltene fractions before and after the treatment suggests decoagulation and/or depolymerization of the asphaltene into maltene, while the porphyrin moiety becomes soluble, being transformed to the maltene fraction. The roles of polar solvent, ultrasonic irradiation, and adsorbent are discussed based on the above results.