A modification of the bubble-point method to determine the pore-mouth size distribution of porous materials

An important use of porous materials is as substrates for surface coatings. For such applications, it is often necessary to evaluate the pore-mouth size (or surface pore size) distribution of the substrates. Although this process can be carried out with microscopic techniques, convenient and more effective methods are lacking. Herein, we introduce a new way by modifying the conventional bubble-point method, which measures the size of the pore-throat (i.e., the narrowest position at a pore tunnel). When a liquid is added to the pore-mouth while a pore tunnel is being purged with a gas under pressure, the closure of the pore-mouth by the liquid depends on the gas pressure and the liquid capillary force at the pore-mouth. Such a force can be used to probe the pore-mouth size, while the closure of the pore mouth can be probed by gas flux variation. Our preliminary tests on the new method with model samples are promising, and the results are well supported by those obtained by SEM, metallography, and the conventional bubble-point method. Due to the convenience and effectiveness of this novel technique, we expect that the new method will be of wide use in the surface analysis of porous materials.