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Research Papers

Graphene Oxide Colloidal Suspensions as Cutting Fluids for Micromachining—Part II: Droplet Dynamics and Film Formation

[+] Author and Article Information
Bryan Chu

Department of Mechanical Aerospace and
Nuclear Engineering,
Rensselaer Polytechnic Institute,
110 8th Street,
Troy, NY 12180
e-mail: chub3@rpi.edu

Johnson Samuel

Assistant Professor
Department of Mechanical Aerospace
and Nuclear Engineering,
Rensselaer Polytechnic Institute,
110 8th Street,
Troy, NY 12180
e-mail: samuej2@rpi.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received May 7, 2015; final manuscript received July 14, 2015; published online August 21, 2015. Assoc. Editor: Sangkee Min.

J. Micro Nano-Manuf 3(4), 041003 (Aug 21, 2015) (9 pages) Paper No: JMNM-15-1032; doi: 10.1115/1.4031136 History: Received May 07, 2015; Revised July 14, 2015

Part II of this paper is focused on studying the droplet spreading and the subsequent evaporation/film-formation characteristics of the graphene oxide colloidal solutions that were benchmarked in Part I. A high-speed imaging investigation was conducted to study the impingement dynamics of the colloidal solutions on a heated substrate. The spreading and evaporation characteristics of the fluids were then correlated with the corresponding temperature profiles and the subsequent formation of the residual graphene oxide film on the substrate. The findings reveal that the most important criterion dictating the machining performance of these colloidal solutions is the ability to form uniform, submicron thick films of graphene oxide upon evaporation of the carrier fluid. Colloidal suspensions of ultrasonically exfoliated graphene oxide at concentrations < 0.5 wt.% are best suited for micromachining applications since they are seen to produce such films. The use of thermally reduced (TR) graphene oxide suspensions at concentrations < 0.5 wt.% results in nonuniform films with thickness variations in the 0–5 μm range, which are responsible for the fluctuations seen in the cutting force and temperatures. At concentrations ≥ 0.5 wt.%, both the TR and ultrasonically exfoliated graphene oxide solutions result in thicker and nonuniform films that are detrimental for machining results. The findings of this study reveal that the characterization of the residual graphene oxide film left behind on a heated substrate may be an efficient technique to evaluate different graphene oxide colloidal solutions for cutting fluids applications in micromachining.

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Figures

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Fig. 1

(a) Experimental setup for single-droplet impingement study, (b) front view, and (c) top view

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Fig. 2

Characteristic temperature profile of a 0.2 wt.% TR500 droplet with insets showing droplet shape. (Note: R1—spreading regime; R2—pinning regime; and R3—receding regime.)

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Fig. 3

Numerical metrics for comparing temperature profiles: (a) characteristic temperature difference and (b) duration of regimes

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Fig. 4

Characteristic temperature profile of a 1.0 wt.% US GOP solution

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Fig. 5

Characteristic trend seen in droplet height and contact angle measurements during the pinning regime of a 0.5 wt.% TR500 GOP solution

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Fig. 6

Trends for multiplicative coefficients αh and αθ

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Fig. 7

Trends for decay coefficients βh and βθ

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Fig. 8

Droplet evaporation behavior in the receding regime (top view)

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Fig. 9

Representative graphene oxide film profile scans. (Note: The origin is the center of the circular residue patch.) (a) TR GOPs at concentrations < 0.5 wt.%, (b) TR GOPs at concentrations ≥ 0.5 wt.%, (c) ultrasonically exfoliated GOPs at concentrations < 0.5 wt.%, and (d) ultrasonically exfoliated GOPs at concentrations ≥ 0.5 wt.%.

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Fig. 10

Relative-frequency curves for thickness distribution. (Note: The x-axis in (d) is longer than the others.) (a) TR GOPs at concentrations < 0.5 wt.%, (b) TR GOPs at concentrations ≥ 0.5 wt.%, (c) ultrasonically exfoliated GOPs at concentrations < 0.5 wt.%, and (d) ultrasonically exfoliated GOPs at concentrations ≥ 0.5 wt.%.

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Fig. 11

Hypothesized nature of the GOP films deposited at the tool–workpiece interface: (a) TR GOPs at concentrations < 0.5 wt.%, (b) TR GOPs at concentrations ≥ 0.5 wt.%, (c) ultrasonically exfoliated GOPs at concentrations < 0.5 wt.%, and (d) ultrasonically exfoliated GOPs at concentrations ≥ 0.5 wt.%

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Fig. 12

Digital images of the clearance and rake face of the turning tool showing GOP film formation at 100 °C (scale bar = 120 μm): (a) dry tool—no cutting fluid, (b) TR GOPs < 0.5 wt.%, (c) TR GOPs ≥ 0.5 wt.%, (d) US GOPs < 0.5 wt.%, and (e) US GOPs ≥ 0.5 wt.%

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