Kaustav Goswami

Dielectric properties of ultraviolet cured poly(dimethyl siloxane) sub-percolative composites containing percolative amounts of multi-walled carbon nanotubes

In this study a new method of multi-walled carbon nanotube (MWCNT) incorporation was employed in the preparation of ultraviolet (UV) curable MWCNT-filled poly(dimethyl siloxane) (PDMS) composites. The composites were designed to contain amounts of MWCNT above the percolation threshold, without becoming conductive. Ultrasonicated and dispersed MWCNTs were co-precipitated together with an excess of short chain α,ω-vinyl terminated PDMS with a deficient amount of thiol-crosslinker and a photoinitiator (2,2-dimethoxy-2-phenylacetophenone, DMPA) into MeOH. The entire mixture was UV irradiated, resulting in a layer of hyperbranched PDMS forming around the MWCNTs. This MWCNT mixture was added to a hyperbranched long chain PDMS to provide concentrations of MWCNT of 0.33%, 0.66% and 1%, and a fully crosslinked system was obtained in a final photochemical curing. Rheology of the composites showed a moderate decrease in storage modulus (G′) across the entire frequency range in line with an increasing amount of MWCNT, thus demonstrating that the rheological percolation threshold was not reached throughout the concentration range. Dielectric spectroscopy measurements showed an increase in permittivity in line with an increasing MWCNT content as well as the desired frequency-dependent conductivity for all samples. The composites showed moderate dielectric breakdown strength of 48 V μm−1 at 0.33 wt% MWCNT, which decreased throughout the samples to 20 V μm−1 at 1 wt%. Temperature-dependent AC conductivity studies revealed that an increase in the sample temperature could explain the premature breakdown observed for those composites with higher MWCNT loading.

UV-cured, platinum-free, soft poly(dimethylsiloxane) networks.

To overcome the drawbacks exhibited by platinum-catalyzed curing of silicones, photoinitiated thiol-ene cross-linking of high-molecular-weight poly(dimethylsiloxane) (PDMS) prepolymers has been investigated as a pathway to novel soft PDMS networks, based on commercially available starting materials was developed. Through a fast and efficient two-step cross-linking reaction highly flexible PDMS elastomers were prepared.

Synthesis and characterization of UV photocrosslinkable hydrogels with poly(N-vinyl-2-pyrrolidone): Determination of the network mesh size distribution

ABSTRACT Hydrogels of poly(n-vinyl-2-pyrrolidone) were produced by UV irradiation of aqueous solutions of the polymer in presence of hydrogen peroxide, used as initiator. The mechanical and the nanostructural properties of the gels were characterized by a combination of experimental techniques including rheology, low field nuclear magnetic resonance spectroscopy (LF-NMR), and small angle X-ray scattering. Different irradiation doses as well as polymer and initiator concentrations were tested in the characterization. The study elucidates the relationship between different methods to estimate the mesh size of the gel polymeric network. Moreover, a novel correlation model was developed based on Chui and Scherer theories for the interpretation of LF-NMR dataset of polymer solutions and networks. GRAPHICAL ABSTRACT

Silicone resembling poly (propylene glycol) interpenetrating networks based on no pre-stretch as basis for electrical actuators

Elastomers currently used as transducers have not been designed with this specific application in mind and there is therefore a need for new target engineered materials to bring down driving voltages and increase actuator performance. A proposed method of optimization involves the development of new types of interpenetrating polymer networks (IPNs) to be used as dielectric elastomer (DE) transducers. This work demonstrates the use of polypropylene glycol (PPG) as a novel DE material. The IPNs formed were shown to exhibit excellent thermal stability and mechanical properties including lower tendency for viscous dissipation with higher dielectric permittivity compared to state of the art polydimethylsiloxane (PDMS) materials.