Vibration-assisted surface micropatterning for controlled wettability modification of aluminum and PVDF thin films

초록

Surface modification techniques are crucial for controlling wettability in various industrial applications. This study presents a novel vibration-assisted micropatterning method for thin film surface modification utilizing resonant droplet dynamics. The technique employs controlled vertical vibrations (5-15 kHz, up to 3.5 mu m) applied to precisely placed deionized water droplets (volume range: 50 pL to 0.5 mu L) on aluminum (6 mu m) and PVDF (6 mu m) thin films to create permanent localized surface micropatterns through stress concentration mechanisms at the droplet contact line. The technique achieved significant wettability modifications with measurable contact angle changes, as validated through static contact angle measurements: contact angles decreased from 75 degrees to 60 degrees on aluminum surfaces and increased from 95 degrees to 110 degrees on PVDF surfaces. Frequency response analysis on aluminum substrates using laser Doppler vibrometer revealed characteristic resonance shifts: upward frequency shift (+ 2%) upon droplet placement due to increased effective tension, followed by downward shift (- 2%) after pattern formation indicating local stiffness reduction due to plastic deformation. Scanning electron microscopy and atomic force microscopy revealed the formation of micropatterns with feature sizes as small as 50 mu m on both substrate types, with pattern depths ranging from 2 mu m on PVDF to 10 mu m on aluminum surfaces. Finite element analysis using COMSOL Multiphysics on demonstrated stress concentration mechanisms at the droplet contact line, where localized stresses exceed material yield strength (276 MPa for aluminum) to induce permanent surface deformation. The critical load for plastic deformation was estimated as 0.8-1.2 mN for typical droplet contact areas. The wettability changes follow composite-drop model for aluminum and PVDF surfaces, with solid fraction determining the final contact angle. This vibration-assisted technique offers advantages over conventional methods: no chemical reagents, simple equipment, ambient processing conditions, and scalability potential. The method demonstrates promise for surface engineering applications in electronics, automotive, and biomedical industries where controlled wettability modification is essential.

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