Nanofluidics is the scientific study of fluid motion over very small distances. Fluids can flow through microscopic tubes or pores that may be blocked if even large molecules get in the way. The distance at which electron charges are separated, called the Debye length, can be similar to the dimensions of such a small tube. When confined to small spaces that are a few nanometers wide, therefore, the physical properties of most fluids change. Scientific advances have enabled researchers to control the activity of fluids in structures such as carbon nanotubes, and even build microscopic devices in nanotechnology applications.
When electrifying a nanoscale surface, researchers can create an electrical double layer in a small hole or passage. The layer can stretch across the width of this space, which typically changes the properties of a fluid compared to how it acts in larger volumes. Charged particles called ions are sometimes used to control the direction of a liquid, especially when the particle charge is opposite to that of the pore wall.
Another property studied in nanofluidics is hydrodynamic radius, which typically characterizes the interaction of large molecules or polymers in relation to nanoscale properties of a liquid solution. Deoxyribonucleic Acid (DNA) is a relatively large molecule that carries genetic information, and which is often manipulated in biology. Along with large polymers, it can coil up into a shape that can block a small channel. Researchers sometimes add materials and coatings to nanofluidics structures that can prevent such blockages.
Nanofluidics researchers can also control membrane thicknesses, as well as pore size and spacing, especially in aluminum. Temperature, voltage, and acid application over certain periods of time generally help to process specific materials. Scientists can then use these to study how different fluids react inside. Liquid properties such as velocity, surface tension, and at what angle a fluid tends to contact a nanoscale surface are often studied.
A printing technique called photolithography can be used to manufacture structures used in nanofluidics. Single channels or arrays of them can be formed out of silicon, polymers, glass, as well as other man-made tubular materials. Scientists can use a fluids properties to control its movement, in a way that supports a type of switching for digital systems. Nanofluidics is also applied to building small transistors, optical arrays, and microchip-based medical diagnostic systems. Liquid interaction in nanofluidic circuitry can be incorporated into controls for water filtration and energy storage systems.