ramé-hart Newsletter

                   

January 2025
 

Fabrics designed to repel water, such as those used in outdoor gear or rainwear, rely heavily on high contact angles, also known as superhydrophobicity. A high contact angle indicates that water beads up and rolls off the fabric instead of soaking in, a feature often achieved by coating the fabric with hydrophobic materials or structuring its surface to mimic the lotus effect.¹

Water droplet resting on the surface of a superhydrophobic fabric

In contrast, sportswear and performance textiles are engineered for low contact angles with water. This ensures that moisture spreads quickly across the fabric’s surface, enabling rapid evaporation and keeping the wearer dry and comfortable. Researchers in Hong Kong have developed a superhydrophilic fabric which, in addition to providing ultra fast liquid transportation, can output electrical energy.²

High contact angles also help prevent liquids like coffee or wine from seeping into the fabric, making stain-resistant textiles possible. This is particularly useful in home furnishings and clothing.

Fabrics that combine water-resistance with breathability, such as Gore-Tex, achieve a delicate balance of contact angle optimization. The microstructure of such materials allows water vapor (from sweat) to pass through while repelling liquid water.

There are some challenges in measuring contact angle on fabrics and textiles. Many textiles are porous, causing liquid droplets to penetrate the material instead of resting on the surface. This makes traditional contact angle measurements less reliable. Likewise, fabrics often have rough or irregular surfaces, which can distort the apparent contact angle by creating multiple points of contact for the liquid droplet. Unlike rigid materials, fabrics are soft and can deform under the weight of the liquid droplet, altering the contact angle. Some fabrics are treated with coatings or finishes that may wear unevenly, leading to variability in contact angle measurements.

Using a ramé-hart goniometer with DROPimage software can help accurately determine the contact angle, even on rough or porous surfaces. For fabrics with high porosity or roughness, the tilting plate method—measuring the angle at which a droplet begins to slide—can provide insights into wettability beyond static contact angle measurements. This can be done with any ramé-hart instrument with a manual or Automated Tilting Base.

Additionally, modifying the traditional sessile drop method to account for liquid absorption over time can yield more meaningful data for porous textiles. Ensuring consistent fabric tension and surface treatment during measurements can reduce variability and improve accuracy. By using optional ramé-hart Film Clamps, the fabric sample can be secured flat on the stage with uniform tension for more repeatable output data.

ramé-hart Model 590 Goniometer / Tensiometer equipped with Automated Tilting Base and Automated Dispensing System for measuring equilibrium contact angle as well as advancing and receding contact angle and roll-off angle

Measuring advancing and receding contact angles—which represent the maximum and minimum angles a liquid droplet makes as it spreads or retracts—can provide a more comprehensive picture of wettability, with their difference (contact angle hysteresis) offering insights into surface uniformity and liquid adhesion, critical factors for designing functional fabrics. The ramé-hart Automated Tilting Base is especially useful for this task although the add/remove volume method can also be used with the ramé-hart Automated Dispensing System. 

Understanding and measuring the contact angle is critical in the design and optimization of functional fabrics and textiles. Whether the goal is to create waterproof rainwear, moisture-wicking athletic gear, or stain-resistant upholstery, the contact angle offers a direct link between material properties and performance. By addressing the unique challenges of measuring contact angle on fabrics, researchers and manufacturers can continue to innovate, ensuring that the textiles of tomorrow meet the evolving demands of consumers.

Notes
¹ For a more detailed discussion of hydrophobic fabrics, see this article.
² See https://doi.org/10.1016/j.nanoen.2024.109919 

Carl Clegg
Director of Sales
Phone 973-448-0305
www.ramehart.com
Contact us