Mixing Mechanics: The importance of scale of scrutiny
How well blended is your powder mixture? How well is it even possible to mix it? In this column we'll talk about the nature of a good mixture.
Liquids and gases are mobile. Most liquids and gases have no structure, but powders do. Powders transfer stresses from one particle to the next to give them structure and less mobility than liquids and gases have. Even within powders, differences in structure and mobility can lead to incomplete mixing or segregated mixing. Figures 1a and 1b represent a combination of two ingredients with an equal number of particles (represented as dots). Figure 1a shows that the ingredients are completely segregated before they've been mixed. Figure 1b shows a perfectly ordered mix: The square outlines in Figure 1b each represent a 16-particle sample; no matter where the 4-particle by 4-particle square is drawn, the sample will have exactly 8 green and 8 blue particles.