cedes ▁from ▁previously ▁wet ▁surface , ▁contact ▁angle ▁h yst er esis ▁can ▁also ▁arise ▁if ▁the ▁solid ▁has ▁been ▁alter ed ▁due ▁to ▁its ▁previous ▁contact ▁with ▁the ▁liquid ▁( e . g ., ▁by ▁a ▁chemical ▁reaction , ▁or ▁absor ption ). ▁Such ▁alter ations , ▁if ▁slow , ▁can ▁also ▁produce ▁meas ur ably ▁time - dependent ▁contact ▁angles . ▁ ▁Effect ▁of ▁rough ness ▁to ▁contact ▁angles ▁Sur face ▁rough ness ▁has ▁a ▁strong ▁effect ▁on ▁the ▁contact ▁angle ▁and ▁w ett ability ▁of ▁a ▁surface . ▁The ▁effect ▁of ▁rough ness ▁depends ▁on ▁if ▁the ▁dro ple t ▁will ▁wet ▁the ▁surface ▁gro ov es ▁or ▁if ▁air ▁po ckets ▁will ▁be ▁left ▁between ▁the ▁dro ple t ▁and ▁the ▁surface . ▁ ▁If ▁the ▁surface ▁is ▁w ett ed ▁hom ogene ously , ▁the ▁dro ple t ▁is ▁in ▁W enz el ▁state . ▁In ▁W enz el ▁state , ▁adding ▁surface ▁rough ness ▁will ▁enh ance ▁the ▁w ett ability ▁caused ▁by ▁the ▁chem istry ▁of ▁the ▁surface . ▁The ▁W enz el ▁correlation ▁can ▁be ▁written ▁as ▁ ▁where ▁ θ m ▁is ▁the ▁measured ▁contact ▁angle , ▁ θ Y ▁is ▁the ▁Young ▁contact ▁angle ▁and ▁r ▁is ▁the ▁rough ness ▁ratio . ▁The ▁rough ness ▁ratio ▁is ▁defined ▁as ▁the ▁ratio ▁between ▁the ▁actual ▁and ▁project ed ▁solid ▁surface ▁area . ▁ ▁If ▁the ▁surface ▁is ▁w ett ed ▁heter ogene ously , ▁the ▁dro ple t ▁is ▁in ▁Cass ie - B