© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

9.2 Adhesion and Fluid Transport

An understanding of surface forces is an essential preliminary to any study of mechanisms of manipulation or locomotion. Such adhesive forces become important at the submicron scale where nanorobotic parts are meshing with and sliding against one another. Surface adhesion forces may cause tools, parts or workpieces to stick together. Surface forces may cause airborne or solvent-immersed nanodevices to adhere to container walls, to other dry or humid surfaces, or to each other possibly causing clumping. For a 1-micron object, the adhesive forces may exceed gravitational and inertial forces by a factor of 10⁶ or more. Capillary forces also are important in fluid transfers inside nanodevices, in fluid transfers between nanodevices or between nanodevices and their operating environment, and during nanodevice tasks requiring locomotion through, or limb/object manipulation in, a watery environment. Surface tension forces are especially relevant during locomotion missions requiring passage through air/water interfaces, as might occur in the lungs.

Bowling¹¹⁴⁶ classifies adhesive forces between objects into three categories. The first category includes long-range attractive interactions that may bring a particle to a surface and establish the adhesion contact area, such as van der Waals forces (Section 9.2.1), electrostatic forces (Section 9.2.2), and magnetic forces (Sections 4.7.2 and 5.4.1). A second category of forces are the interfacial reactions that help to define the adhesion area, most importantly the capillary forces arising from the establishment of liquid or solid bridges between particle and surface (Section 9.2.3), but also including other effects such as sintering (diffusion and condensation), diffusive mixing, mutual dissolution and surface alloying, which will not be considered further here. In the third category are very short-range interactions that may strengthen adhesion after an adhesive contact area has already formed; such forces include chemical bonds of all types and various noncovalent bonds such as hydrogen bonds that have already been described in Section 3.5.1.

The rest of this Section is concerned with the transport and manipulation of fluids. After a brief discussion of capillarity theory and the unique problems associated with nanotubular fluid flow (Section 9.2.4), this Section presents basic aspects of continuum fluid flow (Section 9.2.5), describes the problems of effervescence and crystallescence during offloading (Section 9.2.6), and concludes by examining various design issues in submicron-scale fluid pumping, plumbing, mixing, and containerization (Section 9.2.7).

Last updated on 20 February 2003