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Research Articles

Depth-Sensing Nanoscale Deformation Experiments in Polymer Nanocomposites

[+] Author and Article Information
R. D. K. Misra

e-mail: dmisra@louisiana.edu
Center for Structural and Functional Materials,
University of Louisiana at Lafayette,
P.O. Box 44130,
Lafayette, LA 70504-4130

1Corresponding author.

Manuscript received February 15, 2012; final manuscript received August 14, 2012; accepted manuscript posted August 23, 2012; published online January 22, 2013. Assoc. Editor: John Lambros.

J. Appl. Mech 80(2), 021011 (Jan 22, 2013) (8 pages) Paper No: JAM-12-1072; doi: 10.1115/1.4007434 History: Received February 15, 2012; Revised August 14, 2012; Accepted August 23, 2012

There is currently a trend toward increased usage of polymeric materials as functional materials because they are likely to experience force in the nanometer range. Thus, we describe here nanoindentation experiments in a polymer nanocomposite system with different nanoclay content and compare with the pristine counterpart. A Berkovich nanoindenter was used to conduct nanoscale deformation experiments using a load of 1–5 mN. The nanoindentation contact properties of relevance to functional applications notably hardness, modulus, and adhesion forces were studied. The addition of 8 wt% of nanoclay to high density polyethylene led to an increase in the indentation hardness by ∼30% and modulus by 25%. Furthermore, using load-displacement plots, the adhesion force between the indenter tip and the material's surface was measured. The adhesion force that is related to the stickiness of the surface was observed to decrease on the introduction of nanoclay in the polymer because of an increase in hardness and modulus of the nanocomposite, leading to a decrease in the area of interaction between the indenter tip and the probed surface. The resistance to nanoindentation of the nanocomposite is explained in terms of a shift in von Mises stress from the surface to the subsurface in the nanocomposite.

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Figures

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Fig. 1

Schematic of the penetration of polymer chains between the individual silicate layers during melt compounding. During this process the clay layers are delaminated. This is referred as intercalation.

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Fig. 2

Transmission electron micrographs showing (a) uniform distribution of clay and (b) intercalation of clay in high density polyethylene (HDPE)-4 wt.% clay nanocomposite

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Fig. 3

Scanning electron micrographs of (a) high density polyethylene (HDPE) and (b) high density polyethylene-4 wt.% clay nanocomposite illustrating the macromolecular structure. The presence of clay in the nanocomposite refines the microstructure (reduces the crystal size) because of geometrical confinement.

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Fig. 4

Stress-strain plots for HDPE and HDPE-clay nanocomposites

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Fig. 5

Load-displacement plots for HDPE and a detailed view of adhesion force regime

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Fig. 6

Load-displacement plots for HDPE-4 wt.% clay composite and a detailed view of adhesion force regime

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Fig. 7

Load-displacement plots for HDPE-8 wt.% clay composite and a detailed view of adhesion force regime

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Fig. 8

Experimentally observed maximum displacement during nanoindentation experiment as a function of % clay content

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Fig. 9

Adhesion force as a function of peak load for high density polyethylene (HDPE) and their nanocomposites. The adhesion force is the tensile force required to bring the indenter tip to the initial position.

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Fig. 10

Nanoindentation hardness profiles of HDPE as a function of clay loading content

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Fig. 11

Nanoindentation modulus profiles of HDPE as a function of clay loading content

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Fig. 12

Nanoindentation modulus and nanoindentation hardness of polyethylene and its nanocomposites as a function of clay loading content obtained from the depth range of 3000–4000 nm

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Fig. 13

(a) Transmission electron micrograph of the cross-sectional view of surface damaged HDPE; (b) TEM micrographs of the cross-sectional view of a HDPE-clay nanocomposite

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