▁on ▁the ▁unders ide ▁of ▁a ▁text ured ▁substr ate , ▁which ▁can ▁be ▁im aged ▁using ▁a ▁high ▁resolution ▁C CD ▁camera . ▁An ▁autom ated ▁system ▁allows ▁for ▁til ting ▁the ▁substr ate ▁and ▁anal ys ing ▁the ▁images ▁for ▁the ▁calculation ▁of ▁adv ancing ▁and ▁re ced ing ▁contact ▁angles . ▁ ▁The ▁dynamic ▁sess ile ▁drop ▁method ▁ ▁The ▁dynamic ▁sess ile ▁drop ▁is ▁similar ▁to ▁the ▁static ▁sess ile ▁drop ▁but ▁requires ▁the ▁drop ▁to ▁be ▁modified . ▁A ▁common ▁type ▁of ▁dynamic ▁sess ile ▁drop ▁study ▁determ ines ▁the ▁largest ▁contact ▁angle ▁possible ▁without ▁increasing ▁its ▁solid – liqu id ▁inter fa cial ▁area ▁by ▁adding ▁volume ▁dynamically . ▁This ▁maximum ▁angle ▁is ▁the ▁adv ancing ▁angle . ▁Volume ▁is ▁removed ▁to ▁produce ▁the ▁smallest ▁possible ▁angle , ▁the ▁re ced ing ▁angle . ▁The ▁difference ▁between ▁the ▁adv ancing ▁and ▁re ced ing ▁angle ▁is ▁the ▁contact ▁angle ▁h yst er esis . ▁ ▁Dynamic ▁Wil hel my ▁method ▁ ▁A ▁method ▁for ▁calculating ▁average ▁adv ancing ▁and ▁re ced ing ▁contact ▁angles ▁on ▁sol ids ▁of ▁uniform ▁geometry . ▁Both ▁sides ▁of ▁the ▁solid ▁must ▁have ▁the ▁same ▁properties . ▁W et ting ▁force ▁on ▁the ▁solid ▁is ▁measured ▁as ▁the ▁solid ▁is ▁imm ers ed ▁in ▁or ▁with dra wn ▁from ▁a ▁liquid ▁of ▁known ▁surface ▁t ension . ▁Also ▁in ▁that ▁case ▁it ▁is ▁possible ▁to ▁measure ▁the ▁equilibrium ▁contact ▁angle ▁by ▁applying ▁a ▁very ▁controlled ▁v ibration . ▁That ▁method ology ,