CHAPTER 5: A COMPUTATIONAL TOOLBOX FOR EXAMINING THE EFFICIENCY OF
5.3. MODEL DEVELOPMENT
5.6.3. Gel-Trapping technique
A 2.0 wt% solution of phytagel was made up by dissolving in water at 80oC with vigorous stirring, and then left to cool to 50°C with light stirring, until no bubbles remained in the system. This solution was placed in a Petri dish and n-hexadecane at 50°C was layered on top. 100 µl of a 1.0 wt% hematite particle suspension in isopropanol was injected at the oil-water interface by syringe, and the Petri dish was left to cool for 30 minutes at room temperature until the aqueous phase gelled. The oil layer was gently removed by pipette and replaced by a Sylgard 184 elastomer at a mass ratio of 9:1 PDMS:curing agent ratio, which had previously been degassed in a vacuum. The liquid PDMS was gently poured over the gel surface and left to cure for 2 days at room temperature. At this point the PDMS layer was peeled from the hydrogel surface and immersed in hot water for two minutes to remove any residual phytagel.
Squares of PDMS (1cm x 1cm) were cut before cleaning in boiling deionized water for 2 minutes. Atomic force microscopy (AFM) images were obtained using an Asylum Research MFP-3D (Santa Barbara, USA) in AC mode using AC240TS cantilevers (Olympus). SEM samples were prepared by sputter-coating PDMS squares with platinum at a 45° angle. An operating voltage of 15 kV was used, calculated to give a surface thickness of 5 nm. Imaging was performed at a 14.1° angle with respect to the plane of the interface on a Zeiss Supra 55VP SEM, operated at 10 kV. Particle sizes were averaged over 100 isolated particles. A simple trigonometric correction factor was applied when measuring particle height in order to account for the tilt of the stage.
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5.7.
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