When the solid has a high affinity for water - in which case it is called hydrophilic (high energy e.g. glass)- water spreads. In the opposite case of hydrophobic (low energy e.g. teflon) surfaces, water does not spread but, instead, forms at equilibrium a spherical cap resting on the substrate with a 'contact angle'.
Infections such as trichomoniasis, gonorrhea, and Chlamydia (all STDs); and yeast infection can all cause vaginal discharge. Vaginal discharge can be associated with other symptoms such as burning or itching. Antibiotics are given for infections that cause vaginal discharge.
As the infection becomes more chronic, it may become yellowish-green or green in color. A yellow discharge may also be seen in immune reactions due to the presence of eosinophils. 1  Normal vaginal discharge may appear slightly yellowish when it comes in contact with air and is seen dried on undergarments.