Topography over chemistry: Achieving tunable hydrophobicity on polymethyl methacrylate via ultraviolet picosecond and near-infrared nanosecond laser ablation

Precise control of polymethyl methacrylate (PMMA) wettability is critical for applications in microfluidics, biomedical implants, and optical devices. Conventional modification methods often rely on chemical treatments, which can lack precision and introduce contamination. This study presents a clean, non-contact alternative using laser ablation. A systematic comparison of ultraviolet (UV) picosecond and near-infrared (NIR) nanosecond lasers reveals that laser wavelength and the resulting surface topography, not chemical alteration, is the decisive factor in wettability control. UV laser irradiation produces finely textured, hydrophobic surfaces with water contact angles (WCAs) up to 120.2°, whereas NIR laser treatment induces thermal damage, leading to hydrophilic surfaces with WCAs as low as 62.6°. Comprehensive characterization with FTIR, XPS, and Raman confirms no detectable chemical changes, underscoring a purely physical modification mechanism. COMSOL® Multiphysics simulations elucidate the underlying processes: UV laser photochemical ablation enables precise micro-structuring, while NIR laser photothermal effects cause melting and irregular topography. Dynamic contact angle measurements and a preliminary aging study confirm the stability and topography-dominated nature of the wetting states. This work establishes UV picosecond laser ablation as cost-effective, single-step, chemistry-free, scalable method for achieving tunable and stable hydrophobic PMMA surfaces, offering a superior solution for precision manufacturing of advanced polymeric devices. • Laser ablation controls PMMA wettability via surface topography. • UV-picosecond laser creates hydrophobic surfaces (>120° CA). • NIR-nanosecond laser yields hydrophilic surfaces (