Synthesis and Characterization of Phosphonated Graphene Oxide and Sulfonated Poly(styrene-isobutylene-styrene) Composite
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.438
Synthesis and Characterization of Phosphonated Graphene Oxide and Sulfonated Poly(styreneisobutylene-styrene) Composite Membranes Eduardo Ruiz-Colón, David Suleiman Chemical Engineering Dept., University of Puerto Rico, Mayagüez, PR 00681-9000
Abstract
Graphene oxide (GO) and its phosphonated analogue (pGO) have been incorporated into sulfonated poly(styrene-isobutylene-styrene) (SO3H SIBS) to generate membranes with enhanced water retention. The polymer nanocomposite membranes (PNMs) were prepared per SIBS sulfonation level (i.e., 38, 61, and 90 mole %), filler type (i.e., GO and pGO) and filler loading (i.e., 0.1, 0.5 and 1.0 wt.%). FT-IR and TGA confirmed the functionalization and incorporation of the fillers into SO3H SIBS. No significant changes were observed in the thermal stability or FTIR spectra of the PNMs after addition of the fillers. Dissimilar behaviors were observed for the water absorption capabilities (i.e., swelling ratio and water uptake) after incorporation of the fillers. The nanofillers enhanced the water absorption of the sulfonated polymer, possibly due to interconnections between the ionic groups. Therefore, the PNMs could not only potentially function as proton exchange membranes (PEMs) for several applications such as direct methanol fuel cells (DMFCs).
INTRODUCTION In recent years, graphene and its derivatives have gained increasing attention due to their excellent properties and variety of applications [1–5]. Out of all the commonly known derivatives, graphene oxide (GO) is one of the most utilized in fuel cells mainly because the material has a large surface area containing a variety of oxygenated functional groups (i.e., hydroxyl, ether, carboxylic acid, among others) that act as hydrophilic groups that facilitate proton conduction; also, the two-dimensional layer facilitates proton conduction through the formation of hydrogen-bonded channels [1]. GO has been extensively studied as organic filler to a variety of polymer matrices as a mean of improving or modifying the properties of the polymers for different applications including fuel cells [6–8]. The most common modification of GO is sulfonation but phosphonic acid is another protogenic functionality that could be more effective in improving the performance of polymer matrices than sulfonic acid due to its higher degree of self-dissociation and hydrogen bonding, chemical and thermal stability, and lower acidity [9–11]. SO3H SIBS has attracted attention as an alternative material due to its low cost and well-defined morphology [12]. Sulfonation of SIBS incorporates ionic groups into the polymer matrix, that enhances the transport properties through the
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material [13,14]. However, the performance of SO3H SIBS decreases
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