SURFACE TEXTURING TO IMPROVE HYDROPHOBICITY AND MOISTURE RESISTANCE OF POLYMERS.

Abstract

Polymer degradation due to prolonged exposure to moisture environments is a major concern for applications where long-term durability is needed. This deterioration over time could be delayed by improving the hydrophobic properties of polymers. While many surface modification techniques have been developed over the years, in-depth understanding of the effects of surface modification on hydrophobicity and long-term durability of polymers still awaits significant learning. This study investigates the influence of surface modification, specifically, surface texturing on polymer hydrophobicity by introducing various texture types and geometries on Ultrahigh Molecular Weight Polyethylene (UHMWPE) and High Density Polyethylene (HDPE) surfaces. Hydrophobicity is evaluated by the contact angle measurements using DI water and bovine serum. The results show that introduction of surface textures significantly increases the contact angle, and, thereby, improving the hydrophobicity. Contact angle of textured HDPE surfaces increases to a maximum of 156.7° in DI water and 160.8° in bovine serum for square protrusions, compared to 104.7° and 108.6° in DI water and bovine serum, for smooth surfaces, respectively. For UHMWPE, textured surfaces achieve a maximum contact angle of 157.3° in DI water and 159.8° in bovine serum for hemispherical protrusions, compared to the smooth surface values of 98.4° in DI water and 104.0° in bovine serum. This improvement in hydrophobicity, achieved by introducing surface textures, significantly improves the resistance to moisture absorption in polymers, specifically in HDPE, with textured surfaces showing a moisture absorption of less than 1.5% compared to the smooth surface moisture absorption of 4.5%, over 90 days of immersion in DI water. A wetted surface fraction ratio is proposed to describe the relationship between surface texture and wetting of the polymer surfaces using transition state modeling approach, as this approach provides more in-depth insights on the relationship compared to the conventional Cassie-Baxter and Wenzel models. The study provides guidelines for enhancing hydrophobicity and moisture resistance, and, therefore, long-term durability of polymers used in biomedical, automotive, aerospace, electronics, and household applications.