Sessile drop method：Kyowa Interface Science

Sessile drop method

Introduction

Generally, the smooth surface of a well-cleaned unused glass slide has good wettability with water. The water droplet spreads over the surface after contact with the glass slide, resulting in a low contact angle. Contaminations that adhere to the solid’s surface lower the adhesive forces between the glass and water, reducing its wetting properties. Contact angle measurements of water are an easy way to determine the condition of a solid’s surface.

Measurements and results

We prepared unused glass slides of an unopened package and exposed them to air in a non-clean room for four different periods, namely, 0, 24, 48, and 72 hours, respectively. Using the sessile drop method with our contact angle meter DMo-702, we investigated the relationship between the contact angle and exposure time. We used distilled water droplets with a volume of 1 uL, performed five measurements on each sample, and used the average contact angle to compare the influence on the wettability over time. The contact angle of water with the glass surface tends to be higher the longer their exposure to air (Table 1, Fig. 1). Examples of the captured images and contact analysis after each air exposure time show the different spreading behavior of the droplets (Fig. 2 to Fig. 5).

Exposure time to air [hours]	Average contact angle of distilled water [º]
0	2.9 ±0.4
24	9.4 ±0.9
48	16.6 ±1.9
72	23.0 ±0.8

Table 1 – The average contact angles on glass surfaces with different exposure times

Figure 2 – Example image of 0 hours of air exposure

Figure 3 – Example image of 24 hours of air exposure

Figure 4 – Example image of 48 hours of air exposure

Figure 5 – Example image of 72 hours of air exposure

Overall

We found that the glass plates exposed to air have higher contact angles than unused ones. It indicates that material surfaces are generally susceptible to atmospheric contamination, which can significantly impact solid surfaces’ wettability. Even with no apparent visual evidence of a change on the surface, a single drop of water can capture changes in surface conditions. The contact angle measurement is the perfect method to check the solid surface condition as it is fast, sensitive, reliable, reproducible, and easily comparable.
Our high-performance optical contact angle meter has various models with sophisticated designs for all customer’s needs. Optional accessories, such as a computer-controlled dispenser, temperature control devices, and an external tilting stage, allow the device to meet special needs.

Download the PDF here →