Polymer Surface Layer Research Articles

The Effect of Polymer Binder on the Electrochemical Performance of Si/C Anodes

Silicon with its theoretical capacity of 4200 mAh/g is an attractive alternative to graphitic carbon in lithium ion batteries.[1] However, silicon suffers from poor passivating behavior in organic electrolytes electrolyte side reactions, which both result in large irreversible capacity loss and gradual electrolyte consumption with a lithium inventory shift in the Li-ion cell. Furthermore, large crystallographic volume changes (~320%) occur during cycling, which leads to particle decrepitation, particle isolation, and electrode delamination. This has negative impact on the interfacial stability and the composite electrode mechanical integrity. To assure electronic connectivity and mechanical integrity of the composite Si/C electrode during extended charge-discharge cycles, the polymer binder needs to exhibit unique physic-chemical properties. Therefore it is essential to understand the basic properties and the polymer binder and its effect on the electrochemical performance of Si/C anodes. Chemical changes in polymer binders during cycling are carefully monitored and evaluated. Thin films (20 nm) of binder polymers like, polyacrylic acid lithium salt (PAALi), poly-1,1-difluroethane (PVdF) and poly(1-pyrenemethyl methacrylate) (PPY), are spin coated onto B-doped Si (100) wafers, which reproduce the thickness of the polymer films in the composite Si electrode if the polymer coats the Si particles uniformly. Electrochemical studies provide information about Li+ doping, possible polymer reduction, interfacial reactions and surface layer formation. The surface chemistry at the electrolyte side as well as the substrate/binder interphase is carefully analyzed and evaluated. These basic phenomena are then linked with the Si/C electrode electrochemical performance and electrode/cell life. This study also focuses on the determination of the mechanical properties of various binders before and with cycling. Stress-strain curves, indentation measurements and adhesion tests give information about properties needed to withstand the large volume changes during cycling. Furthermore, possible chemical deterioration of binders and possible its adverse effects on adhesion, crack initiation, growth, and particle delamination are monitored. These results can be used to develop and/or select effective binder candidates, which can lead to more efficient Si-based high-energy Li-ion battery systems. Acknowledgements This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, under the Applied Battery Research for Transportation (ABR) Program and Award Number DE-EE0006443. [1] T. D. Hatchard, J. R. Dahn, Journal of the Electrochemical Society 2004, 151, A838.

Effects of direct fluorination on space charge accumulation in HTV silicone rubber

HTV silicone rubber (SiR), due to its better electrical insulation, elasticity, temperature resistance, is used in cable accessories for HVDC cables. The space charge, formed under dc stress in SiR, would distort the local electric field, and furtherly influence the characteristics of partial discharge and accelerate the insulation aging. Direct fluorination, as a solution to change the chemical component, could alter the electrical properties of the polymer surface layer. This paper focuses on the effect of the fluorination on the space charge accumulation in HTV SiR. In this investigation, the samples were fluorinated at 25 ° using a F2/N2 mixture gas with 20 % F2 by volume at 0.05 MPa for 10, 20, 30 and 40 minutes. The space charge behavior of the fluorinated samples was observed by PEA method and the trap level distribution was obtained by modified isothermal discharge current (MIDC) test. The results indicated that the fluorination for 20 minutes effectively suppressed the space charge injection in SiR. However, excessive fluorination (over 30 minutes) brought in abundant deep traps, and led to significant amount of space charge accumulation in the bulk of polymer. As a consequence, the appropriate fluorination has significant effect on the space charge accumulation in HTV SiR and has a potential application for inner insulation in premolded accessories of HVDC cable.

Hydrophilicity improvement of silicone rubber by interpenetrating polymer network formation in the proximal layer of polymer surface

A novel method composed of an interpenetrating polymer network (IPN) formation reaction in aqueous solution was developed to improve the hydrophilicity of silicone rubber (SR) substrate. This solution phase method is compatible, simple, and convenient for some sensitive biomedical applications of SR devices because of using water as reaction solvent instead of harmful chemicals. In this work, a sequential interpenetrating polymer network formation in the proximal layer of SR surface, using poly(2-hydroxyethyl methacrylate) (PHEMA), as the second network was conducted so that led to actually surface modification resulting in an improved hydrophilicity. The modified surfaces were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) to assess the wettability, chemical composition and morphology of the surface modified PDMS. The results indicated that the surface modification method offered a novel and facile approach to improve the hydrophilicity of SR without altering its bulk properties. This method could be suitable for biomedical applications because of using water as a monomer solvent and polymerization medium.

Immobilization of Polymeric Luminophor on Nanoparticles Surface.

Polymeric luminophors with reduced toxicity are of the priorities in the production of lighting devices, sensors, detectors, bioassays or diagnostic systems. The aim of this study was to develop a method of immobilization of the new luminophor on a surface of nanoparticles and investigation of the structure of the grafted layer. Monomer 2,7-(2-hydroxy-3-methacryloyloxypropoxy)naphthalene (2,7-NAF.DM) with luminophoric properties was immobilized on silica and carbon nanotubes in two ways: mechanical mixing with previously obtained polymer and by in situ oligomerization with chemisorption after carrier’s modification with vinyl groups. The attached polymeric (or oligomeric) surface layer was studied using thermal and spectral techniques. Obtained results confirm the chemisorption of luminophor on the nanotubes and silica nanoparticles at the elaborated synthesis techniques. The microstructure of 2,7-NAF.DM molecules after chemisorption was found to be not changed. The elaborated modification approach allows one to obtain nanoparticles uniformly covered with polymeric luminophor.

The influence of particle distribution and interphase on the thermal expansion coefficient of particulate composites by the use of a new model

In this work, the thermal expansion coefficient (CTE) of a composite containing spherical particles surrounded by an inhomogeneous interphase embedded in an isotropic matrix is evaluated by means of a new model. The thermomechanical properties of the interphase are formulated as continuous radial functions. It is assumed that this third phase developed between the polymeric matrix and the filler particles contains both areas of absorption interaction in polymer surface layers onto filler particles as well as areas of mechanical imperfections. It can be said that the concept of boundary interphase is a useful tool to describe quantitatively the adhesion efficiency between matrix and particles and that there is an effect of this phase on the thermomechanical properties of the composite. The thickness and volume fraction of this phase were determined from heat capacity measurements for various filler contents. On the other hand, it is assumed that the particle arrangement (distribution) which can be considered as an influence of neighboring inclusions and their interaction should affect the thermomechanical constants of the composite. The theoretical predictions were compared with experimental results as well as with theoretical values from expressions obtained from other workers and they were found to be in satisfactory agreement.

Study of NaCl permeability through a non-porous polypropylene film

The possibility of NaCl permeation through a polymeric matrix of polypropylene membranes was studied. A non-porous polypropylene film, which was assembled in a flat sheet module, separates a saturated solution of NaCl from pure water. The changes of water composition were determined by the application of ion chromatography and measurements of the electric conductivity. The studies were carried out for 4 years, and the permeation of salt through the polypropylene film from the feed to pure water was not observed over this period. In the first month the results of studies were affected by the impurities, which were introduced to pure water from the installation walls. Moreover, the electrical conductivity of water was also enhanced by adsorption of components from the ambient air. The used polypropylene film demonstrated a high resistance to polymer degradation. SEM observations revealed that the film was free from micropores and cracks after 4 years of studies. The DSC examinations demonstrated only slight changes in the polymer crystallinity. FTIR spectra recorded for a new film and film assembled in the module were similar. The XPS studies did not demonstrated the presence of NaCl in the surface layer of polymer on the side of brine flow. Moreover, a significant change of material hydrophobocity did not take place over the period studied. A dynamic wetting angle measured for a new film amounted to 103–106° and was decreased to 95° on the water side and to 84° on the brine side after 4 years of contact of the polymer with water and a saturated NaCl solution, respectively.

Solid-material-based coupling efficiency analyzed with time-of-flight secondary ion mass spectrometry

The coupling behavior of a microparticle embedded amino acid active-ester into a Poly(ethylene glycol)methacrylate-film, synthesized onto a silicon wafer by a grafting from approach, is characterized using dynamic time-of-flight secondary ion mass spectrometry (ToF-SIMS) to analyze the 3d distribution of the amino acids in the polymer film. Besides standard solid phase peptide synthesis, employing solubilized amino acids in a solvent, we used solid polymer microparticles, incorporating the amino acids. These microparticles were especially designed for a new technique to produce high-density combinatorial peptide microarrays: upon heating, the particles become viscous, which releases the embedded amino acids to diffuse and couple to the surface. In the scope of the development of this new particle-based application, ToF-SIMS is used to analyze a complex chemically modified polymer surface layer. Due to depth profile measurements, it is possible to investigate the particle-based coupling reaction not only on the surface, but also into the depth of the PEGMA film.

The fluid control mechanism of bionic structural heterogeneous composite materials and its potential application in enhancing pump efficiency

Studies have shown that the structure of dolphin skin controls fluid media dynamically. Gaining inspiration from this phenomenon, a kind of bionic structural heterogeneous composite material was designed. The bionic structural heterogeneous composite material is composed of two materials: a rigid metal base layer with bionic structures and an elastic polymer surface layer with the corresponding mirror structures. The fluid control mechanism of the bionic structural heterogeneous composite material was investigated using a fluid–solid interaction method in ANSYS Workbench. The results indicated that the bionic structural heterogeneous composite material’s fluid control mechanism is its elastic deformation, which is caused by the coupling action between the elastic surface material and the bionic structure. This deformation can decrease the velocity gradient of the fluid boundary layer through changing the fluid–solid actual contact surface and reduce the frictional force. The bionic structural heterogeneous composite material can also absorb some energy through elastic deformation and avoid energy loss. The bionic structural heterogeneous composite material was applied to the impeller of a centrifugal pump in a contrast experiment, increasing the pump efficiency by 5% without changing the hydraulic model of the impeller. The development of this bionic structural heterogeneous composite material will be straightforward from an engineering point of view, and it will have valuable practical applications.

A new model for the influence of particle arrangement and interphase on the stiffness of particulate composites

ABSTRACTIn this work, the stiffness of a composite containing spherical particles surrounded by an inhomogeneous interphase embedded in an isotropic matrix is evaluated. The elastic constants of the interphase are modeled as continuous radial functions. It is assumed that this third phase developed between the polymeric matrix and the filler particles contains both areas of absorption interaction in polymer surface layers onto filler particles and areas of mechanical imperfections.It can be said that the concept of boundary interphase is a useful tool to describe quantitatively the adhesion quality between matrix and particles and that there is an effect of this phase on the thermomechanical properties of the composite. The thickness and volume fraction of this phase were determined from heat capacity measurements for various filler contents.On the other hand, it is assumed that the particle arrangement (distribution) and their interactions should affect the thermomechanical constants of the composite.The theoretical predictions were compared with experimental results as well as with other theoretical values derived from expressions given in the literature and in some cases, they were found to be in a reasonable agreement.

Degradation of Co3O4 anode in rechargeable lithium-ion battery: a semi-empirical approach to the effect of conducting material content

A large amount of conducting materials has typically been blended with transition metal oxides (MxOy, M = Fe, Co, Ni, Cu), and their electrochemical properties as the anode in lithium-ion batteries have been studied. Here, we report that a higher content of the conducting material results in poorer cycling stability of Co3O4. From the analysis of the cumulative irreversible capacity loss, a high content of conducting material is proven to promote irreversible electron consumption for the growth of a polymeric surface layer which is the origin of degradation. Furthermore, its formation is mathematically modeled on the basis of the Butler–Volmer relation. From the physical parameters of the polymeric surface layer determined by fitting the model to the experimental data, the degradation mechanism of Co3O4 is discussed.

Accelerated weathering of wood–polypropylene composite containing carbon fillers

The effect of freeze-thaw weathering on the tensile properties, and accelerated weathering with xenon-arc light on the color stability and the tensile properties of co-extruded wood–polypropylene composite loaded with different carbon fillers, such as carbon black, graphite, expandable graphite, carbon nanotubes, and carbon fibers is studied. The results showed that carbon fillers prevented the composites from the fading during xenon-arc light weathering. Almost all types of composites showed the reduced tensile properties after the weathering so that during xenon-light treatment, the tensile strength decline for 10–22% and modulus for 9–25%; during freeze-thaw cycling reduction was 3–21% for the strength and 4–20% for the modulus. Scanning electron microscopy analysis revealed deterioration of the polymer surface layer in all xenon-light weathered composites.

Hydrophobicity, surface charge and DC flashover characteristics of direct-fluorinated RTV silicone rubber

Silicone rubber (SiR), as a basic insulating material, is widely used in insulators for HVDC transmission lines. The prominent characteristics of the SiR coating are the hydrophobicity and the hydrophobicity recovery, which can suppress the development of leakage currents and dry-band discharges, and prevent the flashover incidents. Fluorination is a method to change the chemical component of the surface layer of polymers, which could induce the corresponding change in hydrophobicity and some electrical properties, thus influencing the dc surface flashover characteristics. Room temperature vulcanized (RTV) SiR samples were fluorinated in a stainless reaction vessel at about 298K (25°C) using a F2/N2 mixture with 12% F2 by volume and 0.05 MPa (500 mbar) for respectively 5, 10, 15 and 20 minutes. The hydrophobicity of samples with different fluorination time was measured by the static contact angle tests after corona aging. The variation of hydrophobicity with the lapse of time was recorded. DC flashover tests in different conditions were carried out between two plane electrodes on top of the material sample. The flashover voltage was found to be associated with the surface hydrophobicity status of samples. Obtained results showed the effects of the fluorination on the surface charge, hydrophobicity performance and dc flashover voltage. It is suggested that the appropriate fluorination can improve surface hydrophobicity and suppress surface charge accumulation, thus raising the dc flashover voltage.

Effect of surface modification on starch biopolymer wettability

The main goal of this paper was to determine wettability properties of native starch and starch modified by antibacterial solution of chitosan or lysozyme as a function of temperature and/or after plasma treatment. Contact angles for polar water (and formamide) and nonpolar diiodomethane on glass plates covered with starch film before and after gelatinization (25 °C, 37 °C and 60 °C) were measured. The surface free energy of solid (gel) was determined from the advancing and receding contact angles of these probe liquids, using the contact angle hysteresis model (CAH). The plasma treatment was immediately followed by a sharp decrease of contact angle. In the course of ageing the contact angle also decreased due to the reorientation of polar groups into the surface layer of polymer. Also a sharp decrease in negative values of WS takes place which indicates more hydrophilic character of starch after plasma treatment. The same was after lysozyme modification but to a smaller extent. The opposite trend of changes was visible after chitosan solution treatment. The surface characterization was observed by FTIR measurements and surface topography from the profilometer images and such measurements well support the contact angle results. The arrangement of temperature, plasma treatment or biological modification can lead to improvement of starch surface wettability and stability. The obtained results open up possibilities of starch application in food, paper and packaging industries as well as in pharmacy.

Effect of surface modification on starch/phospholipid wettability

Abstract The objective of this work was to determine surface properties of biopolymer film as a function of temperature and/or after plasma treatment with the aim of further wettability tests and biocompatibility. The examined biopolymers were native starch and starch modified by solution of PC (phosphatidylcholine). Contact angles for polar water (and formamide) and nonpolar diiodomethane on the glass plates covered with starch film before and after gelatinization (25 °C, 37 °C and 60 °C) were measured for the base and plasma modified film. The surface free energy of solid (gel) was determined from the advancing and receding contact angles of these probe liquids, using the contact angle hysteresis model (CAH). The plasma treatment was immediately followed by a sharp decrease of contact angle and in the course of ageing the contact angle also decreased due to the reorientation of polar groups into the polymer surface layer. To depict better changes in hydrophilic/hydrophobic character of the starch surface before and after modification the work of water spreading, W S was calculated. A sharp decrease in negative values of W S takes place which indicates more hydrophilic character of starch surface after modification. Surface morphology and roughness were studied by optical profilometer and FTIR measurements which confirm the contact angle results. It was also proved that a combination of input treatment parameters led to improvement of biopolymer wettability and provided possibilities of starch application where uniform thin films are required.

Accelerated and Natural Weathering of Wood-Polypropylene Composites Containing Pigments

In general, wood-polymer composites are vulnerable to weathering factors such as UV radiation, moisture, freeze-thaw action. Weathering can cause discoloration, chalking, dimensional change, and loss of mechanical properties of wood-polymer composites. This comparative study was focused on weatherability of wood–polypropylene composites made with and without pigments. Two types of inorganic pigments were applied: carbon black master-batch and synthetic iron oxide. Wood-polypropylene composite made without pigment was used as a reference. Also, composites prepared with addition of wollastonite were tested. The composite samples were exposed to outdoor weathering and in a parallel the accelerated UV weathering was conducted in xenon weathering chamber for the 2000 hours. The colour change was estimated by spectrophotometric method, and the change of Charpy impact strength after weathering was determined. The surface morphology was studied with scanning electron microscopy (SEM). The addition of pigments decreased the lightness of non-weathered composites. The change of lightness and total colour change of weathered composites were affected a lot by type of pigment and method of weathering. As, expected wood-polypropylene composite made with carbon black showed the best results in colour stability of composites exposed to weathering. SEM showed that accelerated weathering in the xenon chamber caused more significant changes in the morphology of the polymer surface layer of the composites than outdoor weathering. Charpy impact strength of all studied composites was found to retain after 2000 hours of outdoor weathering, although accelerated weathering caused significant reduction of Charpy impact strength of these composites.

Effect of Weathering on the Properties of Wood-Polypropylene Composites Containing Minerals

The effect of UV-exposure on the properties of wood-polypropylene composites containing mineral fillers weathered in natural and accelerated conditions was studied. The changes in the colour of the composites after weathering were evaluated by spectrophotometry, and the changes of Charpy impact strength were measured with an impact tester. The outdoor weathering compared to accelerated weathering resulted in a greater colour change of the reference composite and composites containing calcium carbonate and wollastonite. The talc-containing composite, having low susceptibility to moisture, showed a greater colour change in the accelerated weathering test. The accelerated weathering resulted in severe degradation of the polymeric surface layer of the composites. The impact strength of a weathered composite depends on the type of weathering and the properties of the filler.

Effect of surface fluorination on space charge behavior in multilayered polyimide films

In recent years, the multilayered polyimide films have been widely used in flexible Print-Circuit Board in order to reduce the thickness of the combination of the flexible Print-Circuit Board. The existence of space charge as a main reason for dielectric breakdown, has a great effect on breakdown characteristic. So it is important to study the space charge characteristics of the multilayered polyimide films. Fluorination can change the chemical component in surface layer of polymers and therefore can influence the charge injection from electrodes and affect the electrical properties of the surface layer. This paper presents a study aimed at clarifying the effect of fluorination on space charge behavior in multilayered polyimide films. Samples were fluorinated in a laboratory vessel at 328 K (55 °C) using a F 2 /N 2 mixture with 20% F 2 by volume and 0.05 MPa (500 mbar) for respectively 15, 30, 45 and 60 minutes. The surface chemical compositions of the films were characterized by attenuated total reflection infrared analysis. The space charge distributions in multilayered polyimide films were measured by using the pulsed electroacoustic (PEA) method. Obtained results showed that the space charge distribution of multilayered film stacking with five fluorinated samples was quite different from that of multilayered film stacking with five untreated samples. It is also suggested that the fluorination can significantly suppress the injection of space charge.

Use of the ultrasonic slow wave to identify pore closure caused by deposition of a polymeric surface layer

Use of the ultrasonic slow wave to identify pore closure caused by deposition of a polymeric surface layer

The mycological effect on morphological, electrochemical and redox properties of the polyaniline surface

Biofilm formation with eight different microscopic fungi on the polyaniline surface and its effect on the morphological, electrochemical and redox properties have been studied. The investigations on selected Chrysosporium merdarium and Rhizomucor pusillus fungi behavior were performed. Conspicuous difference in the oxidation level, redox activity and oxalate impurities at the polymer surface layer treated with Chrysosporium merdarium and Rhizomucor pusillus was confirmed. The electrochemical behavior of the modified electrode was characterized using the cyclic voltammetry technique. The chemical composition of treated surface was determined by X‐ray photoelectron spectroscopy. For the estimation of conductive polymer morphology and roughness, the method of optical and scanning probe microscopy was applied, which showed that the polyaniline surfaces treated with Chrysosporium merdarium are homogenous and smoother than the polyaniline surfaces treated with Rhizomucor pusillus. Water contact angle measurements confirmed the effect of microbial growth on the properties of the polyaniline surface. Copyright © 2013 John Wiley & Sons, Ltd.

Surface charge accumulation and decay on directfluorinated polyimide/Al2O3 nanocomposites

Polyimide film, as a special type of engineering plastic film, is a basic insulating material and is widely applied in the electrical and electronic industry. Addition of nanoparticles into polyimide can improve the insulating properties compared with undoped material. However, due to the change of the material structure, the trap characteristics and charge behavior are altered as a consequence. The existence of surface charge has a great effect on the breakdown characteristic and is the main reason leading to dielectric breakdown. Fluorination as change the chemical component in surface layer of polymers should give rise to the corresponding change in electrical properties of the surface layer thus influence the charge injection from electrodes when they are used as an insulator. This paper presents a study aimed at clarifying the effect of fluorination and nanoparticles on the surface charge accumulation and decay behaviors of fluorinated polyimide nanocomposite film. Samples were prepared by dispersing nano-scale Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> into polyimides with weight percentages of 0, 1, 3, 5 and 7 respectively. Then the samples were surface fluorinated in a laboratory vessel at about 328 K (55 °) using a F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> > mixture with 20% F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> by volume and 0.05 MPa (500 mbar) for 30 minutes. Corona charging tests were performed at room temperature with a relative humidity of 40%. The charge distribution was measured by means of an electrostatic voltmeter. The results show the dependence of the charge density as well as the charge decay rate upon the fluorination and nanoparticle concentration, varying as a function of the charge polarity and charging time. It is suggested that the fluorination can significantly improve the decay rate of the surface charge in polyimide films.