Thermal reproducibility and voltage stability of carbon black/multiwalled carbon nanotube and carbon black/SnO2‐Sb coated titanium dioxide filled silicone rubber heaters

Flexible heaters were prepared by extruding platinum‐catalyzed silicone rubber (SR) compound with carbon black (CB)/multiwalled carbon nanotube (MWNT) and CB/SnO₂‐Sb coated titanium dioxide (TiO₂). MWNT with average particle length of 20 μm and acicular shaped TiO₂ with average particle length of 1.7 μm were selected. Thermal aging and mechanical deformation stability were compared for SR/CB, SR/CB/MWNT, and SR/CB/TiO₂ composites system. During thermal aging, conductor resistivity decreased because of the toughening effect of SR matrix. When 1 wt % of MWNT and TiO₂ were added into SR/CB compound, the deformation stability increased significantly. Thermal reproducibility and voltage stability of the extruded heaters were also investigated by applying AC voltage of 220 V. The heaters containing MWNT exhibited poor thermal reproducibility and voltage stability compared with heater containing TiO₂ or unfilled. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Resistivity and Thermal Reproducibility of the Carbon Black and SnO2/Sb Coated Titanium Dioxide Filled Silicone Rubber Heaters

Summary: Flexible heaters were prepared by extruding platinum‐catalyzed silicone rubber compound with electroconductive carbon black (CB) and SnO₂/Sb coated titanium dioxide (TiO₂). Two types of acicular‐shaped TiO₂ with average particle sizes of 1.7 and 5.2 µm, and two types of spherical‐shaped TiO₂ with average particle sizes of 0.3 and 2.5 µm were selected. Thermoelectric switching phenomena were investigated for the silicone rubber/CB/TiO₂ system. Positive temperature coefficient (PTC) was significant when the acicular filler was added rather than spherical ones. Resistivity change and thermal reproducibility of the extruded heaters were also investigated by applying periodically AC voltage of 220 V. The heaters containing acicular‐shaped TiO₂ exhibited excellent electrical reproducibility.

Scanning electron micrograph of the fractured surface of the extruded composites.     

Preparation of positive‐temperature coefficient heaters using platinum‐catalyzed silicone rubber

Various output heaters were extruded with acetylene black–filled platinum‐catalyzed silicone rubber. The resistivity–temperature behavior of extruded heaters exhibited a positive‐temperature coefficient (PTC) effect without any negative‐temperature coefficient (NTC) effect. Resistivity and thermal reproducibility of the extruded heaters were investigated during heating and cooling cycles at an applied voltage of 220 V. These heaters initially showed poor reproducibility of resistivity during the repeated cycles and this effect increased significantly as the acetylene black content decreased. PTC effect and electrical reproducibility were improved significantly during the thermal ageing process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1611–1617, 2004     

The correlativity of positive temperature coefficient effects in conductive silicone rubber

A thorough study on the positive temperature coefficient (PTC) effects of conductive silicone rubber was made. Various conductive silicone rubbers with apparent differences in PTC anomalies (defined as the ratio of peak resistivity to room temperature resistivity) were chosen. The correlation between the size of the PTC anomaly and both the thermal expansion coefficient of conductive silicone rubber and the interaction between silicone rubber and carbon black (CB) were found. The effects of cross‐linking on the temperature effect of resistivity of conductive silicone rubber were also studied. The results testify the important role of the interaction between silicone rubber and CBs in the temperature effect of resistivity of conductive silicone rubber. Copyright © 2005 Society of Chemical Industry     

Novel heat‐conductive composite silicone rubber

The silicone rubber with good thermal conductivity and electrical insulation was obtained by taking vinyl endblocked polymethylsiloxane as basic gum and thermally conductive, but electrically insulating hybrid Al₂O₃ powder as fillers. The effects of the amount of Al₂O₃ on the thermal conductivity, coefficient of thermal expansion (CTE), heat stability, and mechanical properties of the silicone rubber were investigated, and it was found that the thermal conductivity and heat stability increased, but the CTE decreased with increasing Al₂O₃ fillers content. The silicone rubber filled with hybrid Al₂O₃ fillers exhibited higher thermal conductivity compared with that filled with single particle size. Furthermore, a new type of thermally conductive silicone rubber composites, possessing thermal conductivity of 0.92 W/mK, good electrical insulation, and mechanical properties, was developed using electrical glass cloth as reinforcement. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2478–2483, 2007     

Correlation of electrical and swelling properties with nano free‐volume structure of conductive silicone rubber composites

The present study focuses on finding a correlation between the positron annihilation parameters of silicone rubber polydimethylsiloxane (PDMS) composites loaded with different conductive fillers and their swelling and electrical properties. Four types of conductive fillers have been used in this study, i.e., carbon black (CB), graphite (G), copper, and nickel powders. The investigated swelling parameters for PDMS composites such as the maximum degree of swelling Q_m%, the penetration rate, P, and consequently the diffusion coefficient, D, decreased with increasing the filler content due to the reduction of the size of free‐volume, which could be observed through a decrease of the probability of ortho‐positronium (o‐Ps) formation I₃, that has been measured by the positron annihilation spectroscopy (PALS). Accordingly, a positive correlation has been found of 76.78% and 61.1% between Q_m% and the o‐Ps lifetime τ₃, representing the size of free‐volume for the CB and G filled composites, respectively. It is worthwhile, mentioning that the CB filled composites exhibit relatively low values of P, D, and Q_m% as compared to the G filled composites due to the difference in the physical properties of the filler, particle size, surface area as well as the tendency of the filler particles to make aggregates. On the other hand, the variation of the diffusion coefficient with the relative fractional free‐volume F_r is found in good agreement with the Fujita's free‐volume theory. On the other hand, the electrical conductivity increases with increasing the conductive filler content. Positive temperature coefficient of conductivity (PTCC) behavior is detected, except for the composite containing 20 or 25 phr CB, which showed a metallic behavior. Besides, CB filled PDMS composites exhibit higher electrical conductivity as compared to the composites filled with the other three fillers. The electrical conductivity ln (σ) is positively correlated with the probability of free annihilation of positrons at interfaces I₂, thus suggesting an increase in the electron density with the filler content. The activation energy of conduction, E_a, decreases with the increase in the loading of conductive filler. Moreover, it was noticed that E_a varies with the filler type, the values of E_a increase as the particle size of the filler increases. Finally, a correlation between the free‐volume V_f, determined by PALS with the DC electrical conductivity ln(σ) is found to be in accordance with Miyamoto and Shibayma model. POLYM. COMPOS., 34:2105–2115, 2013. © 2013 Society of Plastics Engineers     

Effects of oxidation and particle shape on critical volume fractions of silver‐coated copper powders in conductive adhesives for microelectronic applications

The effects of oxidation and particle shape on critical volume fractions of silver‐coated copper powders in conductive adhesives are investigated. Silver‐coated copper powders with spherical and flake‐shaped particles were oxidized at temperatures of 30°C, 175°C and 240°C for two hours and dispersed in an epoxy matrix. As silver‐coated copper powders are oxidized at 30°C and 175°C, the critical volume fractions of the conductive adhesives are slightly affected by oxidation and particle shape at these temperatures. As the oxidation temperature approaches 240°C, the critical volume fractions of the conductive adhesives are strongly affected by oxidation temperature and particle shape, owing to the formation of oxides such as Cu₂O on the surface of silver‐coated copper powder—Cu diffuses from the interior to the surface of silver‐coated copper powder and reacts with the oxygen in the air. Silver‐coated copper powder with flake‐shaped particles shows lower critical volume fractions in conductive adhesives than silver‐coated copper powder with spherically shaped particles. Polym. Eng. Sci. 44:2075–2082, 2004. © 2004 Society of Plastics Engineers.     

Thermally conductive silicone rubber reinforced with boron nitride particle

Thermally conductive silicone rubber used as elastomeric thermal pad is successfully developed with boron nitride powder as conductive filler. The effects of content and particle size of filler on the thermal conductivity and mechanical property of silicone rubber are investigated. The results indicate that the use of hybrid boron nitride with three different particle sizes at a preferable weight ratio gives silicone rubber better thermal conductivity compared with each boron nitride with single particle size at the same total filler content. Furthermore, scanning electron microscopy, differential scanning calorimeter, thermogravimetric, etc., are used to characterize the morphology, curing behavior, thermal stability, and coefficient of thermal expansion (CTE) of the silicone rubber composites. POLYM. COMPOS., 28:23–28, 2007. © 2007 Society of Plastics Engineers     

An investigation on flowability and compressibility of AA 6061100 − x-x wt.% TiO2 micro and nanocomposite powder prepared by blending and mechanical alloying

This work investigates the relationships between the components of powders, namely, the powder surface morphology, the flow characteristics and the compressibility of low-energy (microcomposite) and high-energy (nanocomposite) ball milled powders of Al 6061 alloy reinforced with TiO₂ particles. The morphology of the above powder as the function of reinforcement and the milling time was studied by using the scanning electron microscope (SEM). The changes in powder characteristics such as the apparent density, tap density, true density and flow rate were examined by the percentage of reinforcement and milling time. The cohesive nature of the powder was also investigated in terms of Hausner ratio and Kawakita plot. Further, the particle/agglomerate size of low-energy and high-energy ball milled powders was explained by the laser particle size analyzer. X-ray peak broadening analysis was used to determine structural properties of mechanically alloyed powders. The compressibility behavior was examined by the compaction equation proposed by Panelli and Ambrosio Filho to investigate the deformation capacity of the powder. The compressibility behavior, namely, the densification parameter (A) of the microcomposite powder (irregular morphology) was decreased significantly with increasing TiO₂ content due to the disintegration of TiO₂ particles and the cluster formation followed by its agglomeration. The compressibility behavior, namely, the densification parameter (A) of the nanocomposite powder (equiaxed and almost spherical) was decreased slowly with increasing TiO₂ content due to work hardening on the matrix powder. With increased milling time, the compressibility behavior of AA 6061-10 wt.% TiO₂ composite powders increased up to 30 h of milling due to embedding of TiO₂ particles with matrix and changes in powder morphology and finally decreased after 40 h due to work hardening effect.     

Surface modification of silicone rubber by ion beam assisted deposition (IBAD) for improved biocompatibility

We studied the preparation of antimicrobial silicone rubbers of improved interfacial strength, which could be formed with the ion beam assisted deposition (IBAD) technique for coating metallic or inorganic materials (silver (Ag), Copper (Cu), and Hydroxyapatite(HAp)/TiO₂) on the silicone surface. Those coating materials provide high product safety as well as outstanding antimicrobial activity. The deposition methodology is composed of pre‐etching with oxygen gas, vaporizing the coating materials, and post‐treatment with Ar ion. With the evaporation of the coating materials, the Ar beam was focused on the substrate to assist deposition. It was found out that the ion assisting depositions in the IBAD process give a prominent enhancement in adhesion between silicone rubbers and coatings of Ag and Cu. The HAp/TiO₂ coating layer was easily dissolved in aqueous saline solution. All deposited layers display high antimicrobial activities against Staphlococcus aureus (ATCC 6538) and Escherichia coil (ATCC 25,922), showing 99.9% reduction of bacteria, respectively. In a cytotoxicity test, the Ag and HAp/TiO₂ coated silicone shows a decrease of cytotoxicity, while the Cu coating leads to a slight increase of cytotoxicity. The result on the surface modifications of silicone rubber will be employed in further study for applications of medical or rehabilitation devices. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1095–1101, 2005     

炭黑/铝银粉填充导电硅橡胶的性能研究

以炭黑和铝银粉为导电填料,通过溶液共混法制备出导电硅橡胶试样。研究了炭黑/铝银粉对导电硅橡胶导电性能和压阻特性的影响。结果表明,当炭黑含量一定时,随着铝银粉含量的不断增加,导电硅橡胶的电阻先减小后增大;当填料含量一定时,随着压力的不断增加,导电硅橡胶的压阻特性曲线先逐渐下降后趋于稳定;当炭黑含量为30 %（质量分数,下同）、铝银粉含量为3 %时,导电硅橡胶的导电性最好,压阻特性范围也变大。     

Highly efficient photocatalytic degradation of methylene blue using carbonaceous WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> composites

Recent improvements in the performance of photocatalysts made it possible to tackle pollution through environment friendly methods. This study investigates the modification of the photocatalytic activity of TiO₂ by employing WO₃ and conductive polymers, namely, polyaniline (Pani) and polypyrrole (Ppy). Basing on our previous improvement of TiO₂ using a conductive polymer and activated carbon (AC), this study determines the activated carbon forms of TiO₂. The prepared composites are characterized using X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, Brunauer–Emmet–Teller, and UV–Vis spectroscopy. The specific surface area of the mesoporous composites is as follows: WO₃/TiO₂·AC (Pani) > WO₃/TiO₂·AC (Ppy) > WO₃/TiO₂·Pani > WO₃/TiO₂·Ppy (127 > 98 > 68 > 44 m² g^?1), which exhibited a similar trend to the photocatalytic performances (100 > 95 > 91 > 72 % conversion rate). This result could be attributed to higher porosity, surge of charge separation, and photo-responding range extension induced by the synergistic effect of WO₃, conducting polymers, and TiO₂ in the samples.     

In situ synthesis,fabrication and Rietveld refinement of the hydroxyapatite/titania composite coatings on 316 L SS

The development of Hydroxyapatite (HAP)/Titania (TiO₂) composite coatings on metallic implants have received a great deal of attention during the recent years owing to their superior advantages in biomedical applications. The present study has focused on the in situ formation of HAP/TiO₂ composite powders through aqueous precipitation technique. Five different HAP/TiO₂ composite powders of varied HAP to TiO₂ ratios has been synthesized in the present study and the results were compared with the stoichiometric HAP, Rutile TiO₂ and Anatase TiO₂ which also have been synthesized by adapting a similar synthetic procedure. All the synthesized powders have been analyzed using X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. Rietveld Refinement technique has been employed to generate quantitative information about the structural characteristics and phase content in all the powder samples. Further, the electrophoretic deposition (EPD) method has been employed to fabricate HAP/TiO₂ composite coatings on 316 L SS and the resultant coatings were analyzed for its quantitative structural characteristics. The results from the present investigation has confirmed that concentration of TiO₂ in the HAP/TiO₂ composites and heat treatment temperatures have played a major role in the degradation of HAP to β-Tricalcium phosphate and also in the conversion of Anatase to Rutile TiO₂ phase.     

Effect of Ti3C2Tx/Ag MXene fillers on the electrical conductivity of Ag-coated Cu conductive adhesives

In this paper, we prepared ECAs (electrical conductive adhesives) with high electrical conductivity by using Ag-coated copper powder and M − II (Ti₃C₂T_x/Ag powder) as conductive filler. M-Ⅰ (Ti₃C₂T_x) and M-Ⅱ were prepared by acid etching and hydrothermal methods, respectively, and the electrochemical properties of M-Ⅱ and the effects of different contents of M-Ⅱ on the conductivity of ECAs were investigated. M − II has a unique reticular structure which helps to create conductive pathways, and its high specific surface area provides a large number of active sites for charge storage, resulting in increased electrical conductivity. The experimental results show that the best conductivity is achieved when the M-Ⅱ powder content is 1.2%, with a volume resistivity of 4.84 × 10⁻⁶ Ω m, at which time the Ag-coated Cu powder content is 69.8%. It has been shown in many studies that only when Ag-coated copper powder content is 70%–80%, the resistivity reaches about 10⁻⁶ Ω m. This work showed that adding a small amount of M − II and reducing the amount of Ag-coated copper powder could maintain the high electrical conductivity of ECAs.     

Studies of nanocomposites based on carbon nanomaterials and RTV silicone rubber

The mechanical and electrical properties were investigated for nanocomposites based on carbon nanotubes (CNTs) and conductive carbon black (CB). Solution room‐temperature‐vulcanized silicone rubber was used as a matrix. Vulcanizates based on CNTs and CB was prepared by solution mixing. With the addition of 2 phr of CNTs to the rubber matrix, the Young's modulus increased by 272% and reached as high as ～706% at 8 phr, whereas the modulus increased only 125% for CB specimens at 10 phr. Similarly, the electrical properties at 5 phr content of CNT were ～0.7 kΩ against ～0.9 kΩ at 20 phr CB. The Kraus plot from equilibrium swelling tests shows that the high properties for CNT specimens are due to high polymer–filler interfacial interactions, the small particle size that improves the distribution of the filler in a highly exfoliated state, and high electrical connective networks among the filler particles. These improvements can especially influence medical products such as feeding tubes, seals and gaskets, catheters, respiratory masks and artificial muscles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44407.     

Photocatalytic activity of rubber sheet impregnated with TiO2 particles and its recyclability

The preparation of rubber sheet impregnated with titanium dioxide particles is presented. This method is simple and low cost based on the use of commercial TiO₂ powder directly mixing with rubber latex (60% HA) and distilled water. The morphology and roughness of the sheet surface increased with increasing amount of distilled water. Sheet impregnated with anatase (Imp-An) showed uniform, small grains with dense structure and well surface coverage more than one with P25 (Imp-P25). Their photocatalytic activities were evaluated using methylene blue (MB) as a model organic dye compound. These impregnated sheets could degrade MB solution under UV-light irradiation. Comparing with the commercial TiO₂ samples in powder form (anatase from Carlo Erba and Degussa P25) the efficiencies of photocatalytic degradation of MB fall in the decreasing order as: P25 (powder) > anatase (Carlo Erba) (powder) > Imp-An sheet > Imp-P25 sheet. However, the impregnated sheet has an advantage over the loose powder that the catalyst sheet can be recovered after used and can be reused.     

Macro- and microdispersion of carbon black in liquid silicone rubbers

Abstract

A correlation between the online during mixing measured conductance of carbon black (CB) filled silicone rubber and macrodispersion of CB determined by optical microscopy and microdispersion analysed by AFM has been established. The online conductance is a suitable tool to characterise the effect of technological parameters (e.g. rotor type, speed, mixing temperature) and material parameters (matrix viscosity, CB type and content) on the macro- and microdispersion directly during the mixing process. Thus, a modified method of the online conductance measurement can be used as the in-process method for monitoring the production process of electrical conductive polymer materials with low viscosity, e.g. liquid silicone rubbers.     

Effect of SiO2 and TiO2 nanoparticle on the properties of phenyl silicone rubber

Two types of nanoparticles TiO₂ and SiO₂ treated with silane coupling agents were incorporated into phenyl silicone rubber at a low concentration (≤1.0%) and cured by the room temperature vulcanized method. The results showed that treated TiO₂ or SiO₂ nanoparticles improved the ultraviolet (UV)‐shielding ability and enhanced the visible transmittance of the phenyl silicone rubber, compared with their respective untreated particles. Moreover, when comparing treated nanoparticles, TiO₂ was more responsible for augmenting the UV‐shielding ability of the phenyl silicone rubber, while SiO₂ played a more important role in increasing the transmittance of visible light. Low levels of nanoparticles reduced the dielectric constant of the nanocomposite; however, on reaching a critical concentration, increasing the nanoparticle content had the opposite effect. The thermal conductivity of nanocomposites increased linearly with the amount of treated nanoparticles, while SiO₂ nanocomposites exhibited better thermal conductivity than those of TiO₂. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42806.     

Sonocatalytic damage of bovine serum albumin (BSA) under ultrasonic irradiation by mixed TiO2/SiO2 powder

BACKGROUND: In order to effectively damage some biomolecules under ultrasonic irradiation, a mixed TiO₂/SiO₂ powder with high catalytic activity and selectivity was used as a sonocatalyst. RESULTS: The mixed TiO₂/SiO₂ powder heat treated at 450 °C for 30 min was adopted as a sonocatalyst and the damage to BSA molecules under ultrasonic irradiation was assessed. In addition, the effects of such variables as molar ratio of TiO₂ and SiO₂, treatment temperature and time, ultrasonic irradiation time, catalyst amount, solution acidity, ionic nature and strength, ultrasonic irradiation power and D₂O concentration on the damage to BSA molecules were studied by means of UV‐visible and fluorescence spectra. The results showed that the degree of damage was aggravated by an increase in ultrasonic irradiation time, catalyst amount, solution acidity, ultrasonic irradiation power and D₂O concentration, but was reduced by an increase in ionic strength. CONCLUSION: The results indicated that the mixed TiO₂/SiO₂ powder displayed higher activity and selectivity compared with nano‐sized TiO₂ and SiO₂ powders during the sonocatalytic damage of BSA. The extent of the damage decreased in the order TiO₂/SiO₂ > nano‐sized TiO₂ > nano‐sized SiO₂. These results are of great significance for applying sonocatalytic methods to treat tumours. Copyright © 2008 Society of Chemical Industry     

Synthesis and electrochemical properties of TiO2/nanodiamond nanocomposite

Undoped nanodiamond (ND) powders were coated with TiO₂ through two steps: firstly Ti lay was deposited by cycled vacuum-feeding chemical vapour deposition from gaseous TiCl₄/H₂, and secondly an oxidation treatment was carried out in air. The structure and the morphology of the TiO₂/ND composite were characterized by Raman spectrum and transmission electron microscopy. The electrochemical properties of the TiO₂/ND powder electrode in a solution containing [Fe(CN)₆]^3?/4? or NO₂^? were investigated. The results showed that a continuous coating consisting of Ti nanoparticles covered on ND particle after the deposition. The following oxidation at 500 °C resulted in the formation of anatase phase TiO₂ nanoparticles of about 10 nm. The electrochemical results confirmed that the TiO₂/ND powder electrode exhibited higher electrochemical activity than the pristine ND electrode, especially higher catalytic ability toward the oxidation of nitrite anions. Moreover, the TiO₂/ND powder electrode presented fast response towards nitrite oxidation with a detection limit of 0.55 µM and a linear range of 0.05 to 1.0 mM.