{HEAD ~ An oil repellent layer} is applied to {TAIL ~ either the surface portion} having grooves thereon or its opposing surface in the vicinity of the narrower gap 
{ HEAD ~ An oil repellent layer } is applied to { TAIL ~ either the surface portion } having grooves thereon or its opposing surface in the vicinity of the narrower gap
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH