EFFECT OF DISSOLVED-GAS AND SALT ON THE HYDROPHOBIC FORCE BETWEEN POLYPROPYLENE SURFACES

The hydrophobic interaction between polypropylene surfaces in NaCl solutions has been measured using a modified atomic force microscope (AFM). An attractive force of 30 nm range was measured. This is of much shorter range than that reported for Langmuir-Blodgett deposited surfactant films on mica. Removal of the gases dissolved in dilute NaCl solutions was found to reduce the range of the interaction. Increased NaCl concentration up to 1 M has little or no effect on the range of the interaction, within experimental error. The results have implications for the mechanism of the long range hydrophobic interaction.