title: Network formation in graphene oxide composites with surface grafted PNIPAM chains in aqueous solution characterized by rheological experiments.
abstract: Poly N-isopropyl acrylamide (PNI) radically polymerized in aqueous solution in the presence of graphene oxide (GO) can significantly change the properties of the resulting solution from a regular polymer solution to a soft solid with a GO content of only 0.176 wt% (3 wt% with respect to PNI). However, these properties require the presence of both grafting and supramolecular interactions between polymer chains and hydrophilic groups on GO (-OH, -COOH), proven by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffraction and spectroscopy (XRD) and Raman spectra. While very low GO-contents (below 0.05 wt%) only lead to a labile structure, which can be disassembled by shear, higher contents yield composites with solid-like characteristics. This is clearly evident from the rheological behaviour, which changes significantly at a GO content around 0.15 wt%. Intensive shearing destroys the weak network, which cannot reform quickly at lower GO-concentrations, while at intermediate concentrations, restructuring is fast. GO-contents of 0.176 wt% lead to a material behaviour, which almost perfectly recovers from small deformations (creep and creep recovery compliance almost match) but larger deformations lead to permanent damage to the sample.
authors.affiliation: College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, PR China. fjstadler@szu.edu.cn.
authors.forename: Amin
authors.initials: A
authors.lastname: GhavamiNejad
authors.forename: Saud
authors.initials: S
authors.lastname: Hashmi
authors.forename: Han-Ik
authors.initials: HI
authors.lastname: Joh
authors.forename: Sungho
authors.initials: S
authors.lastname: Lee
authors.forename: Youn-Sik
authors.initials: YS
authors.lastname: Lee
authors.forename: Mohammad
authors.initials: M
authors.lastname: Vatankhah-Varnoosfaderani
authors.forename: Florian J
authors.initials: FJ
authors.lastname: Stadler
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D006108:Graphite / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry; D012212:Rheology; D012996:Solutions / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D014783:Viscosity; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D000180:Acrylic Resins; D010087:Oxides; D012996:Solutions; D014867:Water; C052970:poly-N-isopropylacrylamide; D006108:Graphite