Dielectric silicone elastomers with mixed ceramic nanoparticles

A ceramic material consisting in a zirconium dioxide-lead zirconate mixture has been obtained by precipitation method, its composition being proved by wide angle X-ray powder diffraction and energy-dispersive X-ray spectroscopy. The average diameter of the ceramic particles ranged between 50 and 100 nm, as revealed by transmission electron microscopy images. These were surface treated and used as filler for a high molecular mass polydimethylsiloxane-α,ω-diol (Mn = 450,000) prepared in laboratory, the resulted composites being further processed as films and crosslinked. A condensation procedure, unusual for polydimethylsiloxane having such high molecular mass, with a trifunctional silane was approached for the crosslinking. The effect of filler content on electrical and mechanical properties of the resulted materials was studied and it was found that the dielectric permittivity of nanocomposites increased in line with the concentration of ceramic nanoparticles

A METHOD TO ESTIMATE TEMPERATURE OF UNPROTECTED STEEL STRUCTURES IN A FIRE ROOM FOR PERFORMANCE BASED FIRE-PROOF DESIGN

To realize low-voltage dielectric elastomer actuators (DEAs) for artificial muscles, a high-permittivity elastomer and a related thin-film deposition technique must be selected. For polydimethylsiloxane, fillers or functionalized crosslinkers have been incorporated into the elastomer to improve dielectric properties. To produce elastomer layers nanometers thin, molecular beam deposition was introduced. We pursue the synthesis of a high-permittivity oligomer, namely a chloropropyl-functional, vinyl-terminated siloxane to be thermally evaporated and subsequent UV curing to form an elastomer. The synthesized oligomer exhibits dielectric permittivity enhanced by 33% and a breakdown increase of 26% with respect to the commercially available oligomer DMS-V05. Films 160 nm thin were fabricated after being evaporated under ultra-high vacuum conditions. Spectroscopic ellipsometery served for film growth monitoring. Using atomic force microscopy, the film surface morphology and mechanics were characterized after growth termination and subsequent curing. The Young's modulus of the elastomer corresponded to (1.8 ± 0.2) MPa and is thus a factor of two lower than that of DMS-V05. Consequently, the properties of the films prepared by the new elastomer can be quantified by the normalized figure of merit, which estimates to 4.6. The presented approach is an essential step toward the realization of low-voltage DEA for medical applications and beyond

Antibacterial Polysiloxane Polymers and Coatings for Cochlear Implants

Within this study, new materials were synthesized and characterized based on polysiloxane modified with different ratios of N-acetyl-l-cysteine (NAC) and crosslinked via UV-assisted thiol-ene addition, in order to obtain efficient membranes able to resist bacterial adherence and biofilm formation. These membranes were subjected to in vitro testing for microbial adherence against S. pneumoniae using standardized tests. WISTAR rats were implanted for 4 weeks with crosslinked siloxane samples without and with NAC. A set of physical characterization methods was employed to assess the chemical structure and morphological aspects of the new synthetized materials before and after contact with the microbiological medium

Synthesis, characterisation and antifungal activity of chemically and fungal-produced silver nanoparticles against Trichophyton rubrum

Aims To characterise and explore the potential in extracellular biosynthesis of silver nanoparticles (AgNPs) by Penicillium chrysogenum and Aspergillus oryzae and to investigate the antifungal effect of chemically vs. biologically synthesised AgNPs comparing with conventional antifungal drugs against Trichophyton rubrum. Methods and Results Chemically synthesised AgNPs (Chem-AgNPs) coated with polyvinylpyrrolidone (PVP) were synthesised by chemical reduction method with glucose in PVP aqueous solution. Biologically synthesised AgNPs (Bio-AgNPs) were produced from the extracellular cell-free filtrate of Penicillium chrysogenum MUM 03.22 and Aspergillus oryzae MUM 97.19. Among the commercial antifungal drugs terbinafine exhibited the lower MIC range values of 0.063 to 0.25 μg ml-1 for the clinical strains. Chem-AgNPs exhibited antifungal activity against all T. rubrum strains. Bio-AgNPs produced by the fungal cell-free filtrate of P. chrysogenum showed an antifungal activity higher than fluconazole but less than terbinafine, itraconazole and Chem-AgNPs. Conclusion The synthesis parameters in future works should be carefully studied to take full advantage of all the potential of filamentous fungi in the synthesis of AgNPs. Significance and Impact of the study: Bio-AgNPs could be used as antifungal agents, namely against dermatophytesThe authors thank Pedro Martins (Physics Department of University of Minho) for help in XRD analysis. The authors thank to SDBSWeb: http://sdbs.db.aist.go.jp (Japanese National Institute of Advanced Industrial Science and Technology). The authors thank the FCT Strategic Project PEst-OE/EQB/LA0023/2013. Nicolina Dias acknowledges the project 'Consolidating Research Expertise and Resources on Cellular and Molecular Biotechnology at CEB/IBB', RECI/BBB-EBI/0179/2012

Intrinsically Tuning the Electromechanical Properties of Elastomeric Dielectrics:A Chemistry Perspective

Dielectric elastomers have the capability to be used as transducers for actuation and energy harvesting applications due to their excellent combination of large strain capability (100–400%), rapid response (10−3 s), high energy density (10–150 kJ m−3), low noise, and lightweight nature. However, the dielectric properties of non‐polar elastomers such as dielectric permittivity ε r , breakdown strength E b , and dielectric loss ε ″, need to be enhanced for real world applications. The introduction of polar groups or structures into dielectric elastomers through covalently bonding is an attractive approach to ‘intrinsically’ induce a permanent polarity to the elastomers, and can eliminate the poor post‐processing issues and breakdown strength of extrinsically modified materials, which have often been prepared by incorporation of fillers. This review discusses the chemical methods for modification of dielectric elastomers, such as hydrosilylation, thiol‐ene click chemistry, azide click chemistry, and atom transfer radical polymerization. The effects of the type and concentration of polar groups on the dielectric and mechanical properties of the elastomers and their performance in actuation and harvesting systems are discussed. State‐of‐the‐art developments and perspectives of modified dielectric elastomers for deformable energy generators and transducers are provided

Evaluation of the BET theory for the characterization of meso and microporous MOFs

Surface area determination with the Brunauer–Emmett–Teller (BET) method is a widely used characterization technique for metal–organic frameworks (MOFs). Since these materials are highly porous, the use of the BET theory can be problematic. Several researchers have evaluated the BET method to gain insights into the usefulness of the obtained results and interestingly, their findings are not always consistent. In this review, the suitability of the BET method is discussed for MOFs that have a diverse range of pore widths below the diameters of N2 or Ar and above 20 Å. In addition, the surface area of MOFs that are obtained by implementing different approaches, such as grand canonical Monte Carlo simulations, calculations from the crystal structures or based on experimental N2, Ar, or CO2 adsorption isotherms, are compared and evaluated. Inconsistencies in the state‐of‐the‐art are also noted. Based on the current literature, an overview is provided of how the BET method can give useful estimations of the surface areas for the majority of MOFs, but there are some crucial and specific exceptions which are highlighted in this review