Modification of poly(tetrafluoroethylene) (PTFE) by trichlorosilane chemisorption to hydroxyl-modified (PTFE-OH) and silicate-modified (PTFE/SiO2) PTFE is reported. PTFE/SiO2 was prepared by exposure of PTFE-OH to SiCl4 vapor. XPS and contact angle analyses were consistent with the chemical composition of PTFE-OH and PTFE/SiO2. Chemisorption of trichlorosilanes from solution produced layers on PTFE-OH and PTFE/SiO2. The FTIR absorption intensity for these layers was consistent with monolayer formation. Monolayers with Br, CF3, CH3, CD3, and CH=CH2 terminal groups were prepared. Relative to deuterated hexadecyltrichlorosilane (DHTS) monolayers on PTFE-OH, higher contact angles were observed for DHTS monolayers on PTFE/SiO2 under a greater variety of deposition conditions. Reflectance FTIR indicated that the monolayers formed on PTFE-OH and PTFE/SiO2 exhibited crystalline-like order consistent with a well-ordered monolayer. Thermal annealing of the DHTS monolayers for several days at 125 degrees C did not produce any significant changes in water contact angles.