Another triboelectric series based on measuring the triboelectric charge density of materials was proposed by the group of Zhong Lin Wang. The triboelectric charge density of the tested materials was measured with respect to liquid mercury in a glove box under well-defined conditions, with fixed temperature, pressure and humidity. thumb|Cyclic triboelectric series example, illustrating that a linear approach does not work in practice It is known that this approach is too simple and unreliable. There are many cases where there are triangles: material A is positive when rubbed against B, B is positive when rubbed against C, and C is positive when rubbed against A, an issue mentioned by Shaw in 1914. This cannot be explained by a linear series; cyclic series are inconsistent with the empirical triboelectric series. Furthermore, there are many cases where charging occurs with contacts between two pieces of the same material. This has been modelled as a consequence of the electric fields from local bending (flexoelectricity).
Another triboelectric series based on measuring the triboelectric charge density of materials was proposed by the group of Zhong Lin Wang. The triboelectric charge density of the tested materials was measured with respect to liquid mercury in a glove box under well-defined conditions, with fixed temperature, pressure and humidity. thumb|Cyclic triboelectric series example, illustrating that a linear approach does not work in practice It is known that this approach is too simple and unreliable. There are many cases where there are triangles: material A is positive when rubbed against B, B is positive when rubbed against C, and C is positive when rubbed against A, an issue mentioned by Shaw in 1914. This cannot be explained by a linear series; cyclic series are inconsistent with the empirical triboelectric series. Furthermore, there are many cases where charging occurs with contacts between two pieces of the same material. This has been modelled as a consequence of the electric fields from local bending (flexoelectricity).