TABLE OF CONTENTS In the study of color imaging, it is always helpful to model the underlying physics as much as we can. This often means that some basic understanding of material structures is required. In this section we will give a brief description of the composition and structure of several major classes of common materials: water, minerals, ceramics, metals, glass, polymers, plants, and animals. Books on materials science (e.g., [217, 853]) can be consulted for further details.
A water molecule consists of two hydrogen atoms bonded to one oxygen atom. The oxygen hydrogen bond length is about 0.096 nm, and the angle between the two oxygen hydrogen bonds is 101.52 . The attractive forces between water molecules, in both the liquid and solid states, are mainly provided by hydrogen bonds. The positive charge on a hydrogen atom of one water molecule is attracted to the negative charge on an oxygen atom of another water molecule. The two hydrogen bonds and the two covalent (oxygen hydrogen) bonds form an approximate tetrahedron. This symmetry is found in ice crystals. However, in liquid water at room temperature, a molecule oscillates within a surrounding cage of other molecules for about 4 ps, before jumping out of this position and into an adjacent cage [217, p. 89]. Water molecules can spontaneously break up to form H + and OH ? at a rate of 2.5 10 ?5 per second, resulting in a concentration of H + (and also OH ?
