Deciphering the Effect of Polymer-Assisted Doping on the Optoelectronic Properties of Block Copolymer-Anchored Graphene Oxide

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• 作者：Nabasmita Maity ; Atanu Kuila ; Arun K. Nandi
• 刊名：Langmuir
• 出版年：2017
• 出版时间：February 14, 2017
• 年：2017
• 卷：33
• 期：6
• 页码：1460-1470
• 全文大小：587K
• ISSN：1520-5827

文摘

Doping facilitates the tuning of band gap, providing an opportunity to tailor the optoelectronic properties of graphene in a simple way, and polymer-assisted doping is a new route to combine the optoelectronic properties of graphene with the properties of a polymer. In this endeavor, a linear diblock copolymer, polycaprolactone-block-poly(dimethyl aminoethyl methacrylate) (PCL₁₃-b-PDMAEMA₁₁₇) (GPCLD) is grafted from the graphene oxide (GO) surface via consecutive ring opening and atom transfer radical polymerization. GPCLD is characterized using proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy, atomic force microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and Raman spectroscopy. The phase transition behavior of the GPCLD solution with varying temperature and pH is monitored using fluorescence spectroscopy and dynamic light scattering. Temperature-dependent ¹H NMR spectra at pH 9.2 indicate the influence of temperature on the interaction between GPCLD and solvent (water) molecules causing the phase separation. Fluorescence spectra at pH 4 and 9.2 give the evidence of localized p- and n-type doping of graphene assisted by the pendent PDMAEMA chains. In the impedance spectra of GPCLD films, the Nyquist plots vary with pH; at pH 4, they exhibit a semicircle at higher frequencies and a spike at lower frequencies; at pH 7.0, the spike is replaced by an arc; and at pH 9.2, the semicircle at higher frequencies vanishes and only a spike is noticed, all of these suggesting different types of doping of graphene at different pH values. The dc-conductivity also varies with pH and temperature because of the different types of doping. The current (I)–voltage (V) property of GPCLD at different pH values is very unique: at pH 9.2, an interesting feature of negative differential resistance (NDR) is observed; at pH 7, the rectification property is observed; and at pH 4, again the NDR property is observed. The temperature-dependent I–V property at pH 7 and 9.2 clearly indicates a signature of doping, dedoping, and redoping because of the change in the interaction of GO with the grafted polymer arising from coiling and decoiling of polymer chains.