Characterization of ion-irradiated poly-L-lactic acid using nano-cutting

Area of Science:

• Materials Science
• Surface Science
• Ion Beam Modification

Background:

• Poly-L-lactic acid (PLLA) is a biodegradable polymer with applications in biomedical fields.
• Understanding the effects of ion irradiation on PLLA's mechanical properties is crucial for its use in radiation environments.

Purpose of the Study:

• To investigate the impact of 150 keV He(+) ion irradiation on the mechanical strength and surface properties of PLLA.
• To quantify changes in density, surface morphology, and cutting resistance as a function of ion fluence.

Main Methods:

• Surface analysis using atomic force microscopy (AFM) and a surface texture/contour measuring instrument.
• Mechanical property evaluation via cutting strength (Σ) measurements derived from cutting resistance.
• Density estimation using positron annihilation γ ray Doppler broadening measurements.
• Analysis of ion projected range and Bragg peak depth.

Main Results:

• AFM revealed significant surface subsidence with increasing He(+) ion fluence.
• The averaged ion projected range increased from 1.1 μm to 4 μm with increasing fluence.
• Material density decreased from 1.27 g cm(-3) to approximately 0.6 g cm(-3) at a fluence of 3 × 10(15) He(+)/cm(2).
• Anisotropic changes in cutting resistance indicated increased normal strength and decreased lateral strength.

Conclusions:

• Irradiation resulted in substantial material loss, with only ~30% of the original weight remaining in the irradiated region.
• The observed density decrease and surface subsidence are key indicators of material degradation under He(+) ion exposure.
• The anisotropic mechanical response suggests a complex modification of PLLA's structural integrity at the nanoscale.