NMR cryoporometry:: A novel method for the investigation of the pore structure of paper and paper coatings

Many of the properties that paper coatings are designed to modify are determined to varying degrees by the nature of the pore space that interweaves the consolidated matrix. It is therefore highly useful to characterize the pore size distribution of paper coatings. Commonly used methods include mercury porosimetry, image analysis of scanning electron micrographs, and stain imbibition. Here, we describe a method, NMR cryoporometry, which is novel in its application to pores in paper and paper coating and is particularly suitable for measuring small pore sizes in the range of 1 to 100 nm. Such pore sizes are difficult to access with other techniques. The method is based on the principle of the freezing and melting temperature suppression of fluids entrapped within pores. A general outline of the technique is given, and an example of a cryoporometry measurement on a coated paper sample is described.