Antifogging Properties of Spinodal Porous Structures for Optical Application

For the optical applications of antifogging, equilibrium amounts of adsorbed water with humidity were measured on bulk glasses having spinodal pores of 4, 10, 15, 20, and 50 nm. The kinetics of adsorption toward a saturated state and desorbing reversely from the saturated state were investigated on a 15 nm sample that was etched sufficiently to suppress the influence of the silica gel left in the pores. To clarify the role of the pores, the relative humidity (RH) was transformed to Kelvin's diameter, φ. There were pronounced hysteresis loops in the adsorption amounts against humidity, in which adsorption occurred at higher humidities and desorption took place at humidities corresponding to sizes of pores confirmed by mercury intrusion porosimetry. On the basis of weather data in Tokyo, the antifogging coating having pores larger than 12 nm in size was proposed with an emphasis on the recovery of antifogging. Antifogging was further discussed in terms of the capabilities of adsorption related to the thickness of the porous layer and the kinetics of adsorption with a degree of supersaturation at RH100%.