Internal Stresses during Film Formation of Polymer Latices

Abstract

The lateral stresses that latex dispersions undergo upon forming films have been investigated by an optical lever technique. Dilational lateral stress induced by capillary pressure, tensile stress caused by the uniaxial shrinkage imposed by the substrate, and stress relaxation on longer time scales were observed. Failure of film formation because of cracking events was reflected in irregular substrate deflection. The stress evolution in pigment-filled paints below the critical pigment volume concentration displayed two maxima in tensile stress which we associate with a separation of time scales between the drying of polymeric binder and the particle rearrangement to eliminate voids.