USE OF ATOMIC-FORCE MICROSCOPE FOR THE MEASUREMENTS OF HYDROPHOBIC FORCES BETWEEN SILANATED SILICA PLATE AND GLASS SPHERE

An atomic force microscope (AFM) was used to measure the short- and long-range hydrophobic forces between a silanated glass sphere and silica plate. The hydrophobicity was controlled by depositing different amounts of octadecyltrichlorosilane (ODTCS) and trimethylchlorosilane (TMCS). The forces measured with TMCS-coated surfaces using the AFM are comparable to those obtained previously using other techniques. The force vs distance curves can be fitted by both exponential and power laws. The measured hydrophobic forces increase with contact angle, perhaps the most convenient measure of hydrophobicity. Adsorption of ODTCS results in the formation of molecular clusters (or domains), whose size remains relatively constant in the range of advancing contact angles (95-115-degrees) studied in the present work. The charge or the dipole moment associated with those domains may be reponsible for the observed long-range hydrophobic forces.