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.
Yellow mucus discharge. Yellow mucus discharge after pregnancy could start out as red in color and then change to brown or yellow. This discharge could be what is called lochia and is a mixture of blood and sloughed off lining of the uterus. The discharge could last for a few weeks and becomes almost whitish towards the end.