Nano- and Microtechnology from A - Z: From Nanosystems to Colloids and Interfaces

D

Damping Rate Viscometer

See Oscillating Viscometer.

Danish Agar

See Furcellaran.

Darcy's Law

See Permeability.

Dark-Field Illumination

A kind of illumination for microscopy in which the illumination of a specimen is arranged so that transmitted light falls out of the optical path of the microscope and only light scattered by a dispersed phase is observed. It is used to detect the presence of dispersed species that are smaller than the resolving power of the microscope. Sometimes termed dark-ground illumination. A microscope using this principle is referred to as an ultramicroscope. Example: commonly used in particle microelectrophoresis. See also Bright-Field Microscopy, Zsigmondy, Richard Adolf (1865–1929).

Dark-Field Microscopy

Optical microscopy in which a dark-field condenser lens is used to focus a hollow cone of light on the specimen under observation, such that the illuminating light passes outside of the viewing path. When the light comes into contact with the specimen, some of the scattered light becomes observable through the microscope. The sample then appears bright against a dark background. Often used for transparent and semitransparent samples. Also used to observe colloidal dispersions of particles whose sizes are smaller than the microscope's limit of optical resolution (in this case sometimes termed ultramicroscopy). Although the particles themselves may be too small to resolve, it is usually possible to observe the light scattered by the particles. ...