Double layer (surface science)

In <a href="/facts/Surface_science/WTENdutJ">surface science</a>, a double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the <a href="/facts/Surface/0XA8ce89">surface</a> of an object when it is exposed to a <a href="/facts/Fluid/tMQ46Tmz">fluid</a>. The object might be a <a href="/facts/Solid/hj5UsXno">solid</a> particle, a <a href="/facts/Gas_bubble/99TogqIG">gas bubble</a>, a liquid <a href="/facts/Droplet/m4kuGAgH">droplet</a>, or a <a href="/facts/Porous_media/KTMRISJf">porous body</a>. The DL refers to two parallel layers of <a href="/facts/Electric_charge/xxsBfmlB">charge</a> surrounding the object. The first layer, the <a href="/facts/Surface_charge/p067lYHS">surface charge</a> (either positive or negative), consists of <a href="/facts/Ion/3bePpDna">ions</a> which are <a href="/facts/Adsorbed/ARH9peYM">adsorbed</a> onto the object due to <a href="/facts/Intermolecular_force/xIcFMvL7">chemical interactions</a>. The second layer is composed of ions attracted to the surface charge via the <a href="/facts/Coulomb_force/V0lR5NKv">Coulomb force</a>, electrically <a href="/facts/Electric-field_screening/hDR3NcJa">screening</a> the first layer. This second layer is loosely associated with the object. It is made of free ions that move in the fluid under the influence of <a href="/facts/Electromagnetism/oAkmALHT">electric attraction</a> and <a href="/facts/Thermal_motion/WUaJuMHU">thermal motion</a> rather than being firmly anchored. It is thus called the "diffuse layer".
<a href="/facts/Interface_(chemistry)/HnIAndVA">Interfacial</a> DLs are most apparent in systems with a large <a href="/facts/Surface-area-to-volume_ratio/lEl1rKLh">surface-area-to-volume ratio</a>, such as a <a href="/facts/Colloid/9EVucqND">colloid</a> or porous bodies with particles or pores (respectively) on the scale of <a href="/facts/Micrometres/7eDFxD2L">micrometres</a> to <a href="/facts/Nanometres/a98sjHyu">nanometres</a>. However, DLs are important to other phenomena, such as the <a href="/facts/Electrochemical/C0RUWpBH">electrochemical</a> behaviour of <a href="/facts/Electrode/251PaKX8">electrodes</a>.
DLs play a fundamental role in many everyday substances. For instance, <a href="/facts/Homogenized_milk/wDJBUHvy">homogenized milk</a> exists only because <a href="/facts/Fat/87HcP11s">fat</a> droplets are covered with a DL that prevents their <a href="/facts/Coagulation_(milk)/yqRzqk51">coagulation</a> into <a href="/facts/Butter/FqydR0dC">butter</a>. DLs exist in practically all <a href="/facts/Heterogeneous/y84KQJxl">heterogeneous</a> fluid-based systems, such as blood, paint, ink and ceramic and cement <a href="/facts/Slurry/erSTjthc">slurry</a>.
The DL is closely related to <a href="/facts/Electrokinetic_phenomena/JNhmz14r">electrokinetic phenomena</a> and <a href="/facts/Electroacoustic_phenomena/N7pFTbEx">electroacoustic phenomena</a>.

Double layer (surface science) open-in-new

Double layer (surface science)