Charged colloidal particles in a charged wedge: do they go in or out?

Abstract

Using real-space microscopy experiments, theory and computer simulation, we study the behaviour of highly charged colloidal particles which are confined between two highly charged plates forming a wedge geometry. Under low salt conditions it is experimentally observed that colloidal particles accumulate in the cusp of a wedge to form dense fluid or crystalline ordered structures. This behaviour is found for various cell geometries, salt concentrations and gravitational strengths, and even stays stable when additional convection is present in the system. An effort is made to understand this effect qualitatively on the basis of linear screening theory. For a single macro-ion, linear screening theory predicts an attractive 'trapping' force close to the cusp of the range of the Debye-Hückel screening length. The attractive force diverges logarithmically with decreasing distance of the macro-ion from the wedge cusp, while at large distances the force is repulsive. The results of the linear screening theory are confirmed by computer simulations of the primitive electrolyte model with explicit co-and counterions.

Helicity in cylindrically confined Yukawa systems

“…Our model is realized for charged colloidal suspensions under cylindrical confinement (cf. [17][18][19][20][21][22][23][24][25][26]), for trapped dusty plasmas [27,28] and for charged supramolecular aggregates or molecular ions in nanotubes [29][30][31]. We also remark that microspheres explored in [5] are governed by soft interactions such that our work here might be relevant for the findings in ref.…”

Nonadditivity in the effective interactions of binary charged colloidal suspensions

“…The latter fulfils Newton's third law. For more technical details we refer the reader to [48,49,[53][54][55][56]. Then the distance r is varied and the force-distance curve F(r ) is gained.…”

Confined colloidal crystals in and out of equilibrium

“…Soft confinement, on the other hand, is described by a smooth external potential. An important example are charged glass plates which act as a soft confinement to charged colloids as described by an exponentially screened Coulomb interaction [31][32][33].…”