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 lo ng-range hydrophobic forces between a silanated glass sphere and silic a plate. The hydrophobicity was controlled by depositing different amo unts of octadecyltrichlorosilane (ODTCS) and trimethylchlorosilane (TM CS). The forces measured with TMCS-coated surfaces using the AFM are c omparable to those obtained previously using other techniques. The for ce 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 re sults 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 observe d long-range hydrophobic forces.