Aligned Proton‐Conducting Graphene Sheets via Block Copolymer Supramolecular Assembly and Their Application for Highly Transparent Moisture‐Sensing Conductive Coating

Abstract

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 selfassembly. 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. IÀ 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.

Efficient Moisture-Induced Energy Harvesting from Water-Soluble Conjugated Block Copolymer-Functionalized Reduced Graphene Oxide

“…The protons also can diffuse freely throughout the material from a high density side to a low density side through a continuous proton-conducting channel. The microphase separation of the block copolymer anchored on the RGO surface creates oriented nanochannels (pore diameter of 5–20 nm, as supported by FESEM, Figure b) filled with sulfonic acid groups, and proton transport occurs through these channels . During desorption of water molecules, the free H + will again drift back and recombine with the unmovable −SO 3 – ion, which hence induces a reverse potential or current.…”

“…The microphase separation of the block copolymer anchored on the RGO surface creates oriented nanochannels (pore diameter of 5−20 nm, as supported by FESEM, Figure 4b) filled with sulfonic acid groups, and proton transport occurs through these channels. 27 During desorption of water molecules, the free H + will again drift back and recombine with the unmovable −SO 3 − ion, which hence induces a reverse potential or current. When all the free H + will have combined to the unmovable −SO 3 − ions, any potential difference would not be observed between the two electrodes.…”

“…It has been revealed that the efficiency of such energy-harvesting devices strongly depends on the agile regulation of oxygen content and interaction of oxygen-rich GO and water molecules, which finally tune the properties and functions of the materials and devices. ,, Despite the oxygen functionalities, the large internal resistance of GO due to its structural defects compared to that of pristine graphene results in an unsatisfactory and low power density . Therefore, to avoid such a drawback, a supramolecular approach by noncovalent modification of graphene is an elegant way to introduce a large amount of oxygen-containing functional groups on the graphene surface with fewer structural defects for developing a moisture-harvesting device. Other important challenges related to these devices are the rigid working conditions (such as a large humidity change within a second), the complex experimental configuration, , and in most cases, the energy generators not being able to store the energy harvested. , …”

Two-Dimensional Nanomaterials for Moisture-Electric Generators: A Review

“…In this study, the hydrophilic BCP, [poly(3hexythiophene)-block-poly (4-styrenesulfonic acid] (P3HT-b-PSSA) was anchored on the surface of rGO. 90,91 It was found that insertion of PSSA chains to the rGO sheets helps achieve a good alignment between the adjacent rGO layers. Also, the surface of the graphene sheets is homogeneously covered by the BCP to introduce the porous nanochannels, which was a result of microphase separation from the noncovalently bonded BCP.…”

Fluoride Induced Dual Mode Moisture Detection in Organic Solvents, Food, and Agricultural Materials using Benzothiazole Based Azo Dye Sensor

“…as a common impurity. [4,5] In most industrial processes, maintaining dry conditions is imperative because water contaminants can deteriorate the quality of products. Moreover, trace quantity of water can greatly affect the selectivity, product yield and efficiency of many chemical reactions.…”