When {HEAD ~ the surface} is protected by an SiO2 film, there exist a large number of {TAIL ~ hydroxyl groups} 
When { HEAD ~ the surface } is protected by an SiO2 film , there exist a large number of { TAIL ~ hydroxyl groups }
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL