Browsing by Subject "Graphene Oxide"

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    Analysis of Bacterial Adhesion with Graphene Oxide-Modified PES Ultrafiltration Membranes
    (2019-06) Wuolo-Journey , Karl
    Given its potent biocidal properties, graphene oxide (GO) holds promise as a building block of anti-microbial surfaces, with numerous potential environmental applications. Nonetheless, the extent to which GO-based coatings decrease bacterial adhesion propensity, a necessary requirement of low-fouling surfaces, remains unclear. AFM-based single-cell force spectroscopy (SCFS) was used to show that coatings comprising GO nanosheets bonded to a hydrophilic polymer brush, mitigate adhesion of Pseudomonas fluorescens cells, while preserving GO’s intrinsic biocidal activity. This work demonstrated the simultaneous biocidal and low-adhesion GO coatings by grafting poly(acrylic acid) (PAA) to polyethersulfone (PES) substrates via self-initiated UV polymerization, followed by edge-tethering of GO to the PAA chains through amine coupling. The chemistry and interfacial properties of the unmodified PES, PAA-modified (PES-PAA), and GO-modified PES (PES-GO) substrates were demonstrated using ATR-FTIR, Raman spectroscopy, contact angle goniometry, and AFM to confirm the presence of PAA and covalently bonded GO on the substrates. Using SCFS, it was shown that peak adhesion force distributions for PES-PAA (with mean adhesion force F ̅Peak = -0.13 nN) and PES-GO (F ̅Peak = -0.11 nN) substrates were skewed towards weaker values compared to the PES control (F ̅Peak = -0.18 nN). The results show that weaker adhesion on PES-GO was due to a higher incidence of non-adhesive (repulsive) forces (45.9% compared to 22.2% over PES-PAA and 32.3% over PES), which result from steric repulsion allowed by the brush-like GO-PAA interface.
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    Graphene Oxide - Towards A Comprehensive Characterization Scheme
    (2015-09) Ismail, Issam
    Graphene oxide (GO) is a near-2D material derived via oxidation of graphite and exploited in nanocomposites and optoelectronics. Following a literature review, the modified Tour-Dimiev (MTD) method was singled out for making GO, with the introduction of modifications tailored towards producing large sheets by starting with a large graphite size, tuning the oxidation conditions, employing temperature control and a modified wash routine. The product was characterized using wide-angle x-ray diffraction, x-ray photoelectron and Raman spectroscopy, revealing near completeness of graphite conversion, high oxygen content of GO and a comparable degree of defects to literature reports on the same. We imaged MTD-GO via fluorescence quenching microscopy (FQM) and atomic force microscopy (AFM). We compared the analytical capabilities of the image analysis software ImageJ with MATLAB, introducing several MATLAB subroutines to mitigate image analysis issues. We image-analyzed MTD-GO, concluding that GO size and thickness are statistically uncorrelated and described by lognormal and normal distributions respectively. We demonstrated that AFM captures small particles better than FQM, and that these two techniques can be combined to obtain a complete picture of polydisperse sample size distributions. Next, we modeled polydisperse dilute dispersions of oblate spheroids and discs in shear, uniaxial and biaxial extension using microhydrodynamic models found in the literature. We used the shear model to fit experimental shear data on a number of serially diluted sheet dispersions to obtain the dimensions and distributions thereof. The systems analyzed were MTD-GO, commercial GO before and after sonication, and a literature dataset on aqueous layered double hydroxides. Finally, we conducted novel Langmuir trough experiments with MTD-GO to understand the mechanisms surrounding the air-water interfacial assembly of GO. We were able to successfully transfer our films from the air-water interface onto a simple and versatile substrate such as surface-treated glass. We correlated film morphology in situ using Brewster Angle Microscopy and ex situ through FQM imaging of Langmuir-Blodgett-coated glass slides, to the pressure-area isotherm. We established that film packing occurs at low surface pressures. Finally, we showed that GO shows weak, pH-dependent intrinsic surface activity.