InterPore2026

Experimental Study on the Influence of Surfactants on Contact Angle and Evaporation of Single Droplets

21 May 2026, 15:35

1h 30m

Poster Presentation (MS06) Interfacial phenomena across scales Poster

Speaker

Dr Ayomikun Bello (Otto von Guericke University Magdeburg)

Description

Evaporation droplet is a complex process influenced by multiple factors, including temperature, airflow, and the presence of surface-active agents. While each of these parameters has been studied in isolation, their combined influence on evaporation behavior remains poorly understood. Surfactants such as sodium dodecyl sulfate (SDS) significantly reduce liquid surface tension and alter wetting, often affecting the dynamics of evaporation. This motivated the present work, which examines the evaporation of droplets with varying surfactant mass fractions under controlled airflow and temperature conditions.
Single droplet evaporation experiments were performed in a controlled chamber using droplets with surfactant mass fractions ranging from 0 to 0.5 wt.%. The experiments were carried out under airflow rates between 28 and 65 mL/min and at ambient temperatures of either 30°C or 45°C. Sessile water droplets deposited on a hydrophilic glass substrate were also tested to measure contact angles across the same range of surfactant mass fractions. High-resolution imaging and image analysis were used to track each droplet’s size and contact angle over time.
Our results showed that increasing the airflow significantly increased evaporation by enhancing vapor removal from the droplet surface. At the highest flow rate (65 mL/min), the total evaporation time was about 24% shorter than at the lowest flow rate. Likewise, raising the temperature from 30°C to 45°C nearly halved the evaporation time.
The addition of surfactant had a pronounced impact on droplet wetting and evaporation dynamics. Even a small surfactant amount (0.1 wt.%) reduced the initial contact angle from 57° (water) to 33°. At 0.3 wt.%, the initial contact angle dropped below 11°, resulting in an almost completely flat droplet. Pure water droplets typically evaporated in a pinned contact line mode, whereas the presence of surfactant caused an earlier transition to a spreading mode. At higher surfactant mass fractions (0.3-0.5 wt.%), the contact line depinned almost immediately and the droplet became essentially flat soon after deposition. In contrast, the pure water droplet maintained a finite contact angle until near the end of its evaporation.
This study highlights the interaction between surfactant chemistry and environmental conditions in controlling droplet evaporation and wetting behavior. The findings provide valuable insights for optimizing industrial processes that depend on controlled droplet evaporation.