Browsing by Author "Ratan Kumar Dey"

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Aligned Proton-Conducting Graphene Sheets via Block Copolymer Supramolecular Assembly and Their Application for Highly Transparent Moisture-Sensing Conductive Coating
(Wiley-Blackwell, 2019) Soumili Daripa; Koomkoom Khawas; Santanu Das; Ratan Kumar Dey; Biplab Kumar Kuila
Here, we have demonstrated a well-defined strategy to prepare highly sulphonated reduced graphene oxide (S-rGO) sheets via non-covalent modification of rGO with water soluble rod-coil conjugated block copolymer poly(3-hexylthiophene)-block-poly(4-styrenesulfonic acid) (P3HT-b-PSSA) carrying a long PSSA block. S-rGO sheets are highly water soluble and its aqueous solution can be used to fabricate highly transparent conductive thin film coating on versatile smooth substrate surfaces like glass, indium tin oxide (ITO), quartz and flexible PET. The successful anchoring of sulfonic acid group on rGO surface via non-covalent modification by P3HT-b-PSSA was confirmed and analyzed by FTIR and XRD study. The bulk morphology of S-rGO reveals sheet like morphology where individual sheets are aligned with each other in a parallel arrangement through intercalation of PSSA chains driven by block copolymer self- assembly. AFM image of the thin film also supports nice parallel alignment of S-rGO sheets of average thickness ∼100 nm on substrate surface. S-rGO sample shows very high water uptake (∼91% in comparison to its initial weight) and proton conductivity 0.5 S/cm after water vapor exposure for 1 hour. Such high proton conductivity is due to the synergy of alignment of graphene sheets with a continuous network of proton conducting nanochannels created by block copolymer microphase separation on the rGO surface. Nyquist plot with two semicircles suggested the presence of grain boundaries in the sample. I−V measurement of transparent thin film device fabricated from S-rGO sheets shows linear behavior with systematic increase of current on increasing water vapor exposure time. The block copolymer device shows well correlated, systematic and reversible resistance change with relative humidity (RH) confirming its efficient sensing capability towards moisture. We believe that high proton conductivity and interesting, reversible moisture sensitive electrical property of this material will be useful in fabricating transparent and flexible moisture sensors, flexible electronics, moisture induced energy storage, fuel cell, biological applications and others. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Highly Water-Soluble Rod–Coil Conjugated Block Copolymer for Efficient Humidity Sensor
(Wiley-VCH Verlag, 2019) Koomkoom Khawas; Soumili Daripa; Pallavi Kumari; Santanu Das; Ratan Kumar Dey; Biplab Kumar Kuila
In this report, the preparation of highly water-soluble rod–coil conjugated block copolymer poly(3-hexylthiophene)-b-polystyrenesulfonic acid (P3HT-b-PSSA) is demonstrated using a facile method with its moisture sensing properties. The block copolymer synthesis method comprises Kumada catalyst transfer polymerization and atom transfer radical polymerization from a bifunctional initiator followed by sulfonation of polystyrene using moderate reaction conditions. The polymerization results in the synthesis of well-defined block copolymers with controllable block length. The successful synthesis of the block copolymer is studied by NMR and FTIR spectroscopy while optical and structural properties of the block copolymer are investigated using UV–vis, photoluminescence spectroscopy, XRD, and FESEM. In water, the block copolymer shows aggregated structure with crystalline core formed by rod-like P3HT chain with absorption maxima at 558 nm, whereas in solid state the absorption maxima is blue shifted to 548 nm. The proton conductivity of the block copolymer P3HT-b-PSSA with ≈91% of PSSA (by weight) is measured from impedance study, and the values for bulk and grain conductivities are 5.25 × 10−4 and 4.66 × 10−6 S cm−1, respectively, at room temperature. The as-synthesized block copolymer shows a very high water uptake with maximum ≈80% in comparison with its initial weight. The I–V measurement of the device made from block copolymer shows nonlinear, rectifying characteristic and the current increases with increase of relative humidity (RH%). The block copolymer device shows well-correlated systemic and reversible resistance change with RH both in doped and undoped state. It is believed that the interesting and highly reversible moisture-sensitive electronic properties of this block copolymer will be useful for the fabrication of moisture-sensitive polymer-based flexible electronic devices. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim