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<p>The wettability of a surface can be tuned by introducing micro- and nano-textures on the surface or by modifying its chemistry, leading to various properties such as self-cleaning, drag reduction, anti-biofouling, and capillary suction. Surfaces with these properties have a variety of applications, such as consumer products, aerospace components, and medical devices. However, achieving cost-effective manufacturing of both highly wettable and highly non-wettable surfaces remains a significant challenge. This work attempts to enhance the inherent wettability of originally hydrophobic as well as originally hydrophilic polymeric surfaces by making a negative of micro-textures on a mold insert via femtosecond laser ablation, followed by replication via injection molding. The impact of the pitch (center-to-center distance) of micro-textures and surface chemistry on the resulting wettability is investigated. For this purpose, micro-textures are made at a pitch of 20, 30, 40, 50, and 60&#xa0;µm, and replication is performed with two polypropylene (PP) grades: the first being a standard PP exhibiting hydrophobic properties and the second a special grade with hydrophilic properties The influence of nanoscale laser-induced periodic surface structures (LIPSS) on wettability is assessed. Lastly, two-component (2K) injection molding is performed with both polymers using a separate non-textured mold insert for the wettability tuning on the same product. The results show that for the hydrophobic PP, a pitch of 20 and 30&#xa0;µm results in the water droplet being in the Cassie-Baxter regime, hence showing superhydrophobicity. An increase in the pitch of micro-textures decreases the water contact angle (CA) and increases the contact angle hysteresis (CAH), indicating a transition from the Cassie-Baxter to the Wenzel regime. For the textured superhydrophilic PP, the complete spreading of water droplets occurs, which is quantified in terms of capillary flow speed as a function of micro-pillar pitch. In this case, the pitches of 20 and 30&#xa0;µm result in complete water spreading within 2.5 and 5&#xa0;s, respectively. It demonstrates that topographical variation can control the dynamic wettability of a superhydrophilic surface regardless of its surface chemistry. Anisotropic wettability is achieved due to the presence of groove-shaped LIPSS on the replicated polymer, showing different CA in directions parallel and perpendicular to the direction of grooves. Fourier-transformed infrared spectroscopy (FTIR) of samples reveals the presence of hydroxyl and carbonyl functional groups on the highly hydrophilic PP, leading to superwetting. The results from 2K injection molding demonstrate that wettability control from hydrophilic to hydrophobic is efficiently achievable using this approach.</p>

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Development of extreme wettable/non-wettable polymeric surfaces through injection molding replication of femtosecond laser-induced micro and nano textures

  • 期刊论文

  • 发表日期：

    2025年10月8日

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  • Mian Monib ur Rehman,
  • Tim Evens,
  • Pol Vanwersch,
  • Albert Van Bael,
  • Sylvie Castagne

摘要

The wettability of a surface can be tuned by introducing micro- and nano-textures on the surface or by modifying its chemistry, leading to various properties such as self-cleaning, drag reduction, anti-biofouling, and capillary suction. Surfaces with these properties have a variety of applications, such as consumer products, aerospace components, and medical devices. However, achieving cost-effective manufacturing of both highly wettable and highly non-wettable surfaces remains a significant challenge. This work attempts to enhance the inherent wettability of originally hydrophobic as well as originally hydrophilic polymeric surfaces by making a negative of micro-textures on a mold insert via femtosecond laser ablation, followed by replication via injection molding. The impact of the pitch (center-to-center distance) of micro-textures and surface chemistry on the resulting wettability is investigated. For this purpose, micro-textures are made at a pitch of 20, 30, 40, 50, and 60 µm, and replication is performed with two polypropylene (PP) grades: the first being a standard PP exhibiting hydrophobic properties and the second a special grade with hydrophilic properties The influence of nanoscale laser-induced periodic surface structures (LIPSS) on wettability is assessed. Lastly, two-component (2K) injection molding is performed with both polymers using a separate non-textured mold insert for the wettability tuning on the same product. The results show that for the hydrophobic PP, a pitch of 20 and 30 µm results in the water droplet being in the Cassie-Baxter regime, hence showing superhydrophobicity. An increase in the pitch of micro-textures decreases the water contact angle (CA) and increases the contact angle hysteresis (CAH), indicating a transition from the Cassie-Baxter to the Wenzel regime. For the textured superhydrophilic PP, the complete spreading of water droplets occurs, which is quantified in terms of capillary flow speed as a function of micro-pillar pitch. In this case, the pitches of 20 and 30 µm result in complete water spreading within 2.5 and 5 s, respectively. It demonstrates that topographical variation can control the dynamic wettability of a superhydrophilic surface regardless of its surface chemistry. Anisotropic wettability is achieved due to the presence of groove-shaped LIPSS on the replicated polymer, showing different CA in directions parallel and perpendicular to the direction of grooves. Fourier-transformed infrared spectroscopy (FTIR) of samples reveals the presence of hydroxyl and carbonyl functional groups on the highly hydrophilic PP, leading to superwetting. The results from 2K injection molding demonstrate that wettability control from hydrophilic to hydrophobic is efficiently achievable using this approach.