Some observations on determining the size of pores in paper

Abstract

The various methods which have been used to determine the size of pores in paper are briefly reviewed. These are of three general types: (a) methods based on rate of efflux of fluids; (b) methods based on rate of rise of liquids in vertical strips; (c) methods based on the capillary pressure involved in penetration by liquids. A new method is outlined, which takes advantage of the fact that the coefficient of slip of air in viscous flow through paper is a function of pressure. From the Meyer equation, the average effective pore radius is evaluated in terms of the air permeability values at two pressures. It is only necessary to determine the air permeability at two different pressures of an identical area of paper. Experimental values for two such air-permeability determinations on each of five papers, and the resulting values calculated for the average effective pore radius, are tabulated. CONTENTS Page I. Methods available ____ _________ ____________ ______________________ _ 435 1. Introduction _____ ______ _____ _______________________ _______ 435 2. Tacit definition ___________________ __________ _________ ______ 436 3. The microscope as an aid ______ _____ ________________ ____ ____ 436 4. Methods based on rate of efflux of fluids ______________________ 437 5. Methods based on rate of ascent of liquid in strips ___________ __ 437 6. Methods based on capillary pressure ________ ___ _____ __________ 438 7. Other data and methods _________ __________ ________ _________ 438 II. Anewmethod ________ ____ ____________________ _____ __________ ____ 439 1. Origin of the method _________________ ______________ ______ __ 439 2. Slip coefficient _______________________ ____________ ____ ______ 439 3. Equation for pore radius __ ______________________________ ____ 440 4. Experimental values ___ __ _____ __________ __________ ___ __ ___ __ 440 5. Concluding remarks ________ ____ ______ __________ ____________ 441 III. References _____ ________________ _________________________________ 442