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Ind. Eng.
Chem. Prod. Res. Dev..
VoI. 17, NO. 4. 1978
POLYMER COATINGS SECTION Microvoids as Pigments. A Review Jerome A. Seiner
Downloaded by UNIV OF NEBRASKA-LINCOLN on September 6, 2015 | http://pubs.acs.org Publication Date: December 1, 1978 | doi: 10.1021/i360068a005
P.P.G. rmistties, Coatings and Resins R8D Center. A l f i w Park, Pennsyhan.a 15101
This review encompasses the world literature on microvoids embedded in polymeric materials up to and including most of 1978. It includes sections on naturally occurring microvoid materials and all of the more important synthetic routes. These latter are discussed with regard to their applications. and examples of specificlaboratory preparations are included. Along with a section on light smilering characteristics there are 324
references. 1. Background a n d History of Microvoids
A. Introduction. Microvoids have had practical utility to man and nature for as long as life has existed on earth. It wasn't, however, until the early 1900's that man tried to produce materials containing microvoids for specific purposes, and until the 1960's that he was very successful a t that. Today microvoids are broadly incorporated into paints and coatings for enhanced opacification and reflectance properties. Additional reasons for utilizing microvoids are: heat reflectance, UV reflectance, optical brightness, density reduction, filters and membranes, battery separators, synthetic leathers, active ingredient carriers (controlled release films), carbonless carbon paper, electrodeposition primers, self-priming paints, and others. B. Natural Occurrence. Most whiteness which occurs in nature is due to the presence of microvoids and the interaction of interfaces between transparent materials and air. The reflection, refraction, and diffraction of radiation at these interfaces leads to overall diffuse reflectance from the outer surface. Examples of this natural reflectance include snow, sand, the white of a fried egg, sea foam, feathers, cliffs of Dover, pulverized sugar and salt, flour, lilies, and whipped cream. To scientists the absence of white pigments in snow has presented a challenge. Its whiteness (albedo or percent reflectance integrated over the visible spectrum) is measured to be as high as 90% ( I ) . Giddings and LaChapelle treated the important aspects of radiation theory in snow with respect to the influence of free water in lowering the alhedo and have derived an expression for the extent of ice to air and ice to water interfaces (2). Experimentally, Amhach measured radiation distribution in glacier ice (3). With similar techniques snow layers of random crystal orientation were supported on transparent plastic sheets and illuminated from below to permit measurement of albedo variation with thickness (4). Scientists have also long sought to duplicate the microvoid breathing properties of natural leather. It wasn't until the 1950's that man was able to make an artificial 0019-7890/78/1217-0302$01.00/00
Jerome A . Seiner received B.S. degrees from Carnegie Mellon Uniuersity in Chemical Engineering (1954) a n d Industrial Management (1960) a n d completed master's level studies in Macromolecular Science a t Case Western Reserue Uniuersity. He has been emdoved bv PPG In.~ dustries as a rpsmrch engineer and scic.ntiat since 1,954. H e hus .srrred os ,
