Dependence of nanomechanical modification of polymers on plasma-induced cross-linking
- Department of Mechanical Engineering, University of California, Berkeley, California 94720 (United States)
The nanomechanical properties of low-density polyethylene (LDPE) modified by inductively coupled, radio-frequency Ar plasma were investigated by surface force microscopy. The polymer surface was modified under plasma conditions of different ion energy fluences and radiation intensities obtained by varying the sample distance from the plasma power source. Nanoindentation results of the surface stiffness versus maximum penetration depth did not reveal discernible differences between untreated and plasma-treated LDPE, presumably due to the small thickness of the modified surface layer that resulted in a substrate effect. On the contrary, nanoscratching experiments demonstrated a significant increase in the surface shear resistance of plasma-modified LDPE due to chain cross-linking. These experiments revealed an enhancement of cross-linking with increasing ion energy fluence and radiation intensity, and a tip size effect on the friction force and dominant friction mechanisms (adhesion, plowing, and microcutting). In addition, LDPE samples with a LiF crystal shield were exposed to identical plasma conditions to determine the role of vacuum ultraviolet (VUV) and ultraviolet (UV) radiation in the cross-linking process. The cross-linked layer of plasma-treated LDPE exhibited much higher shear strength than that of VUV/UV-treated LDPE. Plasma-induced surface modification of the nanomechanical properties of LDPE is interpreted in the context of molecular models of the untreated and cross-linked polymer surfaces derived from experimental findings.
- OSTI ID:
- 20884972
- Journal Information:
- Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 1 Vol. 101; ISSN JAPIAU; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
ADHESION
CROSS-LINKING
CRYSTALS
FAR ULTRAVIOLET RADIATION
FRICTION
LAYERS
LITHIUM FLUORIDES
MICROSCOPY
MOLECULAR MODELS
PENETRATION DEPTH
PLASMA
POLYETHYLENES
RADIOWAVE RADIATION
SHEAR PROPERTIES
SUBSTRATES
SURFACE FORCES
SURFACE TREATMENTS
THICKNESS