Contact Angle Measurement

How does surface roughness affect the contact angle?

M D Mali

Contact Angle: The angle at which liquid/vapor interface meets solid surface, measure of the ability of a liquid on a surface.

Whenever the adhesive forces are stronger than the cohesive forces between the surfaces, the contact angle is acute. The reverse case gives obtuse contact angles.

Contact angle depends on factors like temperature, humidity, solid surface roughness and static electricity etc.

Physical properties of interaction between solids and liquid like wettability, affinity, adhesiveness and repellency can be studied.

Being an aquatic plant and living in muddy habitats Lotus plants stay dirt-free without

using detergent and expending energy.

Designing And Procedure To find a surface-dependence of contact angle, we used

different surfaces of objects such as Iron sheet, aluminium foil, marble tile, sprite can, TLC and leaves of different plants.

Used PDMS to get the patterns of surface ; we transfer red patterns used technique of “Lithographic patterning of two dimensional structures”. By doing so, we avoided material dependence of contact angle.

Measured the contact angle of water droplet with the PDMS patterned surface. Water droplets of around 5μL were used. Images of the different patterns were taken using Goniometer.

Images of the surfaces were also taken at 10X resolution using microscope.

Results obtainedObject Contact Angle

Iron Sheet 103.218 Hydrophobic

Aluminium Foil 99.930 Hydrophobic

TLC 81.174 Hydrophilic

Marble Tile 90.029 -

Sprite Can 81.516 Hydrophilic

Leaf 1 65.692 Hydrophilic

Leaf 2 85.052 Hydrophilic

Glass Slide 65.824 hydrophilic

An attempt to establish a relation between surface roughness and contact angle is a very tricky one. But here we are!

In general, the hydrophobic surface has a more rough surface in the sense that the distance between two consecutive peaks are small. We suspect that this is smaller than the size of the water droplet, which is hence unable to sit on the surface.

The hydrophilic substances have larger interstitial spaces where the water droplets can fit comfortably.

Glass slide TLC (Aluminium) Leaf Sprite Can

Future Application•Water-proof paints•Better understanding of wettability can help improve efficiency of fuel cells•Construction of sticky surfaces•Design hydrophobic substances to improve food-packaging•Determine cleanliness of solid surfaces

PDMS, in its most general form, is hydrophobic. The observed surface trends might change if we use a more hydrophilic substance in our experiment.

Thankyou

REFERENCES

•Wikipedia•Asknature.org•Kandlikar and Steinke•Vinaykumar Konduru