Faculty Publications
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Item Investigation on electromechanical properties of solid silicone rubber composites with conductive carbon filler(Trans Tech Publications Ltd ttp@transtec.ch, 2019) Manohar Shankar, B.S.; Kulkarni, S.M.Dielectric elastomers belonging to the class of electro-active polymers are promising materials for electromechanical transduction. They are used as actuators, capacitive sensors and energy harvesters. In the present study solid silicone rubber-super conducting carbon black composites are prepared through compression moulding process and evaluated for their mechanical and dielectric properties. Electromechanical sensitivity is estimated and discussed using Taguchi orthogonal arrays for the factors, such as content of active filler and curing agent, mixing time in roll mill, curing temperature. Permittivity of the composites increased 6 times when compared with the sample without active filler. Electromechanical sensitivity of the composite improved 2 fold, thus highlighting that this approach could lead to development of newer dielectric elastomer transducer materials. © 2019 Trans Tech Publications Ltd, Switzerland.Item Experimental investigation on dielectric properties of composites using Taguchi technique(Elsevier Ltd, 2020) Manohar Shankar, B.S.; Mathias, K.A.; Kulkarni, S.M.Flexible composites find applications as dielectric elastomers. These composites are used as actuators and sensors. Solid silicone rubber-conductive filler composites are promising candidates for above applications. They are fabricated using compression moulding and evaluated for their dielectric properties, using Taguchi design of experiments. The influence of factors such as filler and curing agent loading, mixing time, curing temperature on the dielectric properties are presented. Permittivity increased to 14.1 and dielectric loss increased to 1.27 for the conductive filler loading of up to 12 parts per hundred rubber, while still being in insulator regime. © 2019 Elsevier Ltd. All rights reserved.Item Influence of filler and processing parameters on the mechanical properties of dielectric elastomer composites(Elsevier Ltd, 2020) Manohar Shankar, B.S.; Mathias, K.A.; Kulkarni, S.M.Dielectric elastomer composites are used as actuators and sensors. They convert electrical energy directly into mechanical energy and vice versa. Conductive and dielectric fillers are added to elastomers in order to improve its permittivity, thereby altering its mechanical properties. This study investigates the effect of conductive filler and processing parameters on the mechanical properties of dielectric elastomer composites fabricated using solid silicone rubber as matrix and ketjenblack as conductive filler using compression moulding process. The processing parameters such as amount of curing agent, mixing time and curing temperature also influence the mechanical properties. Maximum values of Young's modulus, density and shore A hardness recorded were 25.2 MPa, 1210 kg/m3 and 86 for the present study. © 2019 Elsevier Ltd. All rights reserved.Item Influence of filler on dielectric properties of silicone rubber particulate composite material(Elsevier Ltd, 2020) Mathias, K.A.; Hiremath, H.; Manohar Shankar, B.S.; Kulkarni, S.M.This paper deals with the development of silicone rubber particulate composites filled with strontium titanate to improve dielectric properties of neat silicone rubber. The composite material is prepared by a solution casting method with three different volume percentages of the filler. The composite samples prepared are tested for dielectric properties as per standards. The influence of filler on dielectric properties of composite material is studied by testing for dielectric permittivity, loss tangent, and ac conductivity. The dielectric permittivity experimentally obtained is compared with the available empirical models. The dielectric permittivity, loss tangent, and ac conductivity of silicone rubber composite increased with the increase of volume percentage of strontium titanate. Compared to neat silicone rubber the dielectric permittivity, loss tangent, and ac conductivity of the silicone rubber composite filled with 10% volume of strontium titanate is increased by 66%, 117%, and 267% respectively. Further, the empirical models confirmed that dielectric permittivity obtained is within the limit. The microscopic study reveals that the improved dielectric properties attributed to the stronger bond between the silicone rubber and the strontium titanate particles. © 2019 Elsevier Ltd. All rights reserved.Item Modelling the electromechanical sensitivity of silicone composites using response surface methodology(IOP Publishing Ltd, 2021) Manohar Shankar, B.S.; Kulkarni, S.M.Dielectric elastomers are used for sensor and actuator applications. These materials convert voltage applied directly into strain through Maxwell stress. An important parameter in the determination of voltage induced strains is electromechanical sensitivity. This paper presents an approach to establish the model for predicting the electromechanical sensitivity of silicone dielectric elastomer composites using the response surface methodology. Two-factor and two-level, face-cantered composite design is used for experimentation. The parameters which affect the electromechanical sensitivity are selected as superconducting carbon black (SCCB) and barium titanate (BT). Response surface methodology is used to derive second-order quadratic model with interactions. Investigation showed that SCCB has more significant effect than parameter BT, on controlling the electromechanical sensitivity of these composites. Maximum electromechanical sensitivity for these composites was found at around ≤ 4 parts per hundred weight fractions for both the parameters. © Published under licence by IOP Publishing Ltd.Item Influences of dielectric and conductive fillers on dielectric and mechanical properties of solid silicone rubber composites(Springer London, 2019) Manohar Shankar, B.S.; Kulkarni, S.M.Dielectric elastomers are materials being used for electromechanical transduction applications. Their electromechanical response depends on permittivity, Young’s modulus and electric breakdown strength. A factor that limits its application is high operating voltages that can be reduced through improvement in permittivity. One of the methods is by incorporating high permittivity fillers into polymer matrix to obtain dielectric–dielectric composites (DDC).These composites show high permittivity at the cost of reduced flexibility. An alternative solution is development of composites by incorporating organic or inorganic conductive fillers into polymer matrix. These composites show high permittivity with high dielectric loss and low breakdown strength. To overcome both the above limitations both dielectric and conductive fillers are incorporated into dielectric polymer matrix to obtain conductor–dielectric composites (CDC). In this study, high temperature vulcanized solid silicone rubber as matrix has been used to prepare DDC composites with barium titanate (BT) filler and CDC composites with both BT as dielectric and ketjenblack as conductive fillers, using Taguchi design of experiments. The effect of factors such as amount of fillers and curing agent, mixing time in roll mill and curing temperature on the dielectric and mechanical properties are reported. Lichtenecker model predicts the permittivity of the DDC composite more accurately. For the CDC composites permittivity increased by 390%, effective resistivity decreased by 80%, Young’s modulus increased by 368% and Shore A hardness increased by 90% as compared to those of reference matrix. Important interaction effects are observed among both the fillers that are uniformly dispersed without any aggregation. © 2019, Iran Polymer and Petrochemical Institute.Item Influence of conductive and dielectric fillers on the relaxation of solid silicone rubber composites(Institute of Physics Publishing helen.craven@iop.org, 2019) Manohar Shankar, B.S.; Hiremath, S.; Kulkarni, S.M.Flexible dielectrics possessing high permittivity and low loss are desirable for many electromechanical transduction applications. Solid silicone rubber composites are promising materials for electromechanical applications. These composites are fabricated using high-temperature vulcanization process, with various amounts of conductive, dielectric and conductor-dielectric filler and processing parameters. Dielectric and conductivity relaxations of these composites are investigated using dielectric spectroscopy in the 20 Hz-2 MHz frequency range at room temperature. Dielectric relaxations of dielectric filler composites show different behaviour compared to conductive and conductive - dielectric filler composites even with the same filler loading. All composites show increased permittivity at lower frequencies. The maximum permittivity of 46, 5.8 and 46 at 20 Hz was attained for the conductive, dielectric and conductive-dielectric composites respectively at similar filler loadings. The composites follow the AC universality law with exponents in the range of 0.82 to 1.02. The conductive filler is more reinforcing than dielectric filler as seen from the variation of Young's modulus with filler type. Uniform dispersion of fillers is observed for all the three composites. © 2019 IOP Publishing Ltd.Item Effect of ketjenblack and barium titanate on the piezoresistive behaviour of silicone rubber particulate composites(IOP Publishing Ltd, 2021) Manohar Shankar, B.S.; Hiremath, H.; Kulkarni, S.M.In the present study, silicone rubber reinforced with ketjenblack and barium titanate were fabricated using high temperature compression molding method. These particulate composites are characterized for piezoresistive sensitivity. Ketjenblack and barium titanate are the conducting and dielectric fillers in the high temperature vulcanized silicone rubber matrix. The effects of ketjenblack and barium titanate fillers, filler loading, amount of curing agent, curing temperature and mixing time on the piezoresistive properties of these composites were investigated. The piezoresistive sensitivity recorded maximum values of 3.7(10-3) (kPa)-1 for dielectric and dielectric-conductive composites. The linear variation of normalized resistance change was observed for change in pressure up to 20 kPa. The dielectric composite sensitivity increases with reduction in dielectric filler and curing agent loadings, increasing with mixing time and curing temperature. The piezoresistive sensitivity for dielectricconductive composites depends on ketjenblack and barium titanate filler loading. These composites demonstrate interaction effects among the factors. © 2021 The Author(s). Published by IOP Publishing Ltd.