Liquid corner films in channels or pores of polygonal cross-section are known to have a strong impact on evaporation with a much faster evaporation compared to a tube of circular cross section. The aim of this work is to study the interplay between colloidal particles, development of the corner films and evaporation in a micro channel from a combination of visualization experiments with fluorescent particles and numerical simulations. It is shown that the triple line pinning along the corner films due to particle accumulation in the films leads to the thinning of the corner films. As a result of the film thinning, evaporation is slower in the presence of particles compared to pure water. The identification of such an evaporation reduction mechanism at pore scale shed new light on the phenomenon of reduced evaporation in porous media due to the presence of colloidal particles reported in previous works.