Confinement of linear polymers, surfactants, and particles between interfaces

The review addresses the effect of geometrical confinement on the structure formation of colloidal dispersions like particle suspensions, (non)micellar surfactant solutions, polyelectrolyte solutions and mixed dispersions. The dispersions are entrapped either between two fluid interfaces (foam film) in a Thin Film Pressure Balance (TFPB) or between two solid interfaces in a Colloidal Probe Atomic Force Microscope (Colloidal Probe AFM) or a Surface Force Apparatus (SFA). The oscillating concentration profile in front of the surface leads to an oscillating force during film thinning. It is shown that the characteristic lengths like the distance between particles, the distance between micelles, or the mesh size of the polymer network remain the same during the confining process. The influence of different parameters like ionic strength, molecular structure, and the properties of the outer surfaces on the structure formation are reported. The confinement of mixed dispersions might lead to phase separation and capillary condensation, which in turn causes a pronounced attraction between the two opposing film surfaces.