Sneak Peak at the New Chapter About Surface Tension in the 6th Edition of IPMB

The first page of Chapter 2 about
surface tension in the sixth edition
of Intermediate Physics for
Medicine and Biology.

For those interested in a preview of the 6th edition of Intermediate Physics for Medicine and Biology, I want to tell you about a new chapter on surface tension. This is the new Chapter 2, following immediately after the chapter about mechanics. It is the shortest chapter in the book. Below is the first paragraph.

Many biological processes occur at the interface between air and water where surface tension is important. Section 2.1 introduces the concept of surface energy, and then Sect. 2.2 relates surface energy to surface tension. Section 2.3 reviews adhesion and cohesion, which indicate if water molecules are more attracted to each other or to an adjacent surface. Section 2.4 describes how surface tension can make water climb up a hollow tube, a process called capillary action. The Bond number is introduced in Sect. 2.5, a dimensionless number that characterizes the relative importance of gravity and surface tension. The ability of an animal to live on the water surface depends on the Bond number. Section 2.6 reviews microfluidics, a modern experimental technique in which fluids flow in tiny chambers where surface tension plays a central role.

I was particularly anxious to include microfluidics in IPMB. We did, although we don't go into much detail. Here is the final section of the chapter.

Scientists have begun performing experiments and analyses using microfluidics: small volumes of fluid (nanoliters) passing through tubes tens of microns wide. In microfluidics, the Reynolds number is small, so flow is laminar, which implies that mixing of different fluids is difficult and must occur by diffusion rather than convection (See Chap. 5). Microfluidic systems often rely on capillary action to pump fluid. When mixing immiscible liquids, surface tension causes droplets to form and the droplet radius is determined by the tube size and the capillary number, a dimensionless number that highlights the competition of viscosity and surface tension (see Problem 18 or Squires and Quake, 2005). 

Microfluidics is used for microanalysis of biomarkers, for cell biology where the tubes have a size similar to the size of single cells, and for drug development. It offers the possibility of analyzing samples rapidly and in parallel, using minute amounts of reagent. Whitesides (2006) discusses many of these applications in detail.

I hope you like it.