Ag nanowire-based nanocomposites for interconnects of flexible/wearable electronics

With the recent increasing interest in wearable/stretchable electronics, there are concentrated efforts to develop a material system for flexible/stretchable interconnects that can endure severe mechanical deformations. The most widely used strategy to fabricate stretchable interconnects is to form polymer composites by embedding conductive fillers such as metal particles or metal nanowires into the elastomeric polymer matrix. The conductive fillers can form a percolated network in the polymer matrix, which enables the polymer composites to serve as conductors. Because of the elastomeric properties of the polymer matrix, the composites could withstand mechanical strain while maintaining the conductive properties until the percolation in the network of the conductive fillers is lost below the critical percolation threshold above which conduction can start. The volumetric deformation of the polymer matrix under severe mechanical strain causes disconnection of the percolated network, which results in the degradation of conductivity. Since the loss of percolation is highly dependent on the mechanical properties of the polymer matrix, the development of a stretchable polymer matrix that is high compatible with the conductive fillers is urgently needed. Please click Additional Files below to see the full abstract

Assessment of percolation threshold simulation for individual and hybrid nanocomposites of carbon nanotubes and carbon black

Modeling electrical conductivity of polymer composites with conductive fillers has great applicability to predict conductive materials behavior. In this study, the electrical behavior of simple and hybrid systems prepared from Carbon Black (CB) and Carbon Nanotubes (CNT) was studied. There have been few advances reported in the literature regarding the modeling of hybrid systems, which motivated the development of this study. More specifically, a program was developed with the intention to describe the electric percolation threshold and the effect of synergism between the conductive fillers. Simulation was performed using the Monte Carlo method and Fortran programming language, considering concentration and geometry of conductive fillers to the system in two dimensions. Finally, simulation results were compared with the experimental results and this method proved to be effective in predicting the systems percolation threshold, being an important contribution to predict material behavior, which allows reducing the number of samples to be prepared in an experimental study20616381649CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQsem informaçã

Stretchable electronics for artificial skin

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Thermal conductivity of filled RTV compounds

Sealant materials with high thermal conductivity, and electrically nonconductive were studied for applications. Alumina and other thermally conductive fillers were examined for room temperature vulcanizing (RTV) use. The guarded hot plate apparatus, and its operation are described, and results of the thermal conductivity tests are discussed. It was found that magnesium oxide is significantly better than aluminum oxide as a filler enhancing the thermal conductivity of RTV. Recommendations for future studies are included

Mechanical And Thermal Properties Of Thermally Conductive Fillers Filled Polypropylene Composites

The current study was carried out to investigate the effect of various fillers for example (such as) carbon nanotube (MWNT), synthetic diamond (SD), boron nitride (BN) and copper (Cu) on the properties of polypropylene (PP) composites. This composite was compounded using two roll mill mixing method and the filler content was loaded from 1 to 4 volume %. It was observed that the PP/SD, PP/BN and PP/Cu exhibited maximum tensile strength at 2 volume % and a reduction trend can be observed after 2 volume %. Scanning electron microscopy (SEM) was used to examine the fractured structure of the composites, and it was observed that agglomeration increased as the filler loading increased. Thermal conductivity, thermal stability, coefficient of thermalexpansion (CTE) and storage modulus of the composites were improved by addition of fillers in PP. Among these four fillers, MWNT showed greater potential in improving thermal properties of PP composites. In the second series, the effects of hybrid filler (MWNT/SD and MWNT/BN) in PP composites were studied. The results showed that the thermal conductivity, thermal stability, coefficient of thermal expansion and storage modulus of the hybrid composites were improved if compared to single fillers composites. However, the tensile and flexural properties of hybrid composites were noted to be lower than the single composites. In the third series, the improvements in the compounding were carried out by using two compounding methods; planetary ball mill and two roll mill. Enhancement in strength, stiffness, thermal conductivity and storage modulus of the composites has been observed in this system. Nevertheless, the thermal stability was found to be reduced as the two compounding methods were used in the fabrication process

Developing the knowledge-based human resources that support the implementation of the National Dual Training System (NDTS): evaluation of TVET teacher's competency at MARA Training Institutions

Development in the world of technical and vocational education and training (TVET) on an ongoing basis is a challenge to the profession of the TVET-teachers to maintain their performance. The ability of teachers to identify the competencies required by their profession is very critical to enable them to make improvements in teaching and learning. For a broader perspective the competency needs of the labour market have to be matched by those developed within the vocational learning processes. Consequently, this study has focused on developing and validating the new empirical based TVET-teacher competency profile and evaluating teacher’s competency. This study combines both quantitative and qualitative research methodology that was designed to answer all the research questions. The new empirical based competency profile development and TVET-teacher evaluation was based upon an instructional design model. In addition, a modified Delphi technique has also been adopted throughout the process. Initially, 98 elements of competencies were listed by expert panel and rated by TVET institutions as important. Then, analysis using manual and statistical procedure found that 112 elements of competencies have emerged from seventeen (17) clusters of competencies. Prior to that, using the preliminary TVET-teacher competency profile, the level of TVETteacher competencies was found to be Proficient and the finding of 112 elements of competencies with 17 clusters was finally used to develop the new empirical based competency profile for MARA TVET-teacher. Mean score analysis of teacher competencies found that there were gaps in teacher competencies between MARA institutions (IKM) and other TVET institutions, where MARA-teacher was significantly better than other TVET teacher. ANOVA and t-test analysis showed that there were significant differences between teacher competencies among all TVET institutions in Malaysia. On the other hand, the study showed that teacher’s age, grade and year of experience are not significant predictors for TVET-teacher competency. In the context of mastering the competency, the study also found that three competencies are classified as most difficult or challenging, twelve competencies are classified as should be improved, and eight competencies are classified as needed to be trained. Lastly, to make NDTS implementation a reality for MARA the new empirical based competency profile and the framework for career development and training pathway were established. This Framework would serve as a significant tool to develop the knowledge based human resources needed. This will ensure that TVET-teachers at MARA are trained to be knowledgeable, competent, and professional and become a pedagogical leader on an ongoing basis towards a world class TVET-education system

Studies On The Properties Of Conductive Particulate Fillers Filled Rubber Composites [TS1892. A636 2008 f rb].

The use conductive fillers on properties of rubber composites were studied. Three types of conductive filler has been used in this study i.e. aluminium, zinc and carbon black. Penggunaan pengisi-pengisi konduktif ke atas sifat-sifat komposit getah telah dikaji. Tiga jenis pengisi konduktif telah digunakan dalam kajian ini iaitu aluminium, zink dan hitam karbon

Advances on the pyroresistive behaviour of conductive polymer composite

PhDThe positive temperature coefficient (PTC) effect in conductive polymer composites (CPC) are still poorly understood with the thermal expansion of the polymer matrix accepted as the main cause. This thesis aims to study a model system able to explain the effect of the filler size and shape on the PTC behaviour of CPCs. Silver coated glass spheres and flakes are used as conductive fillers due to the ease in controlling uniform size and shape. In a controlled system it was demonstrated that the PTC intensity increases with increasing filler size and with decreasing filler content, both for conductive fillers. Combinations of different conductive fillers were investigated to explore the possibility to obtain both low percolation thresholds and high PTC intensities. Model systems in which at least one of the two conductive fillers is of relatively homogenous size and shape were used to facilitate unravelling some of the complicated relationships between (mixed) conductive fillers and the PTC effect. The PTC intensity of mixed fillers composites were dominated by the filler with the lowest PTC intensity, even at very low volume fractions. The PTC intensity was not only influenced by the conductive particle size but also by its size distribution. The effect of difference in linear coefficient of thermal expansion (CTE) of conductive fillers and polymer matrix based on a change in filler core on PTC behaviour was investigated. Damage to the particles due to the poor adhesion between the silver coating and the PMMA bead lead to the composite behaving like mixed filler composite. Hybrid polymers filled with silver coated glass flakes was also examined in order to enhance the PTC intensity. The PTC intensity of the composite increased with increasing PPE content but the negative temperature coefficient (NTC) effect was observed in all the composites