COALESCED CORE SHELL LATEX FILMS UNDER ELONGATION IMAGED BY ATOMIC-FORCE MICROSCOPY/

Atomic force microscopy has been used to image deformed latex films. T he films were made from core/shell latex particles having a soft shell and a hard core so that when the films were formed, the continuous ph ase was composed of the shell polymer in which the hard cores formed l ong range hexagonal orderings. Upon small amounts of film elongation, linear necklaces of core particles, perpendicular to the elongation di rection, were observed at the surface of the films. This observation, which is mainly due to matrix deformation and has been analyzed theore tically in the companion paper (preceding paper in this issue), can be easily understood. When the film is elongated, it becomes thinner in the direction perpendicular to the elongation; as a result, the core p articles are pushed together in the direction perpendicular to the elo ngation, whereas, at the same time, the core particles are pulled apar t along the direction of elongation. However, as the elongation increa ses further, AFM images show that, besides the matrix deformation proc ess, another deformation mechanism, which is a geometrical rearrangeme nt of the core particles, appears. The response of the film to the str ain is then characterized by the appearance of breaks in the linear ne cklace of core particles, which now form zigzags or chevrons. Such a g eometrical rearrangement of the core particles was anticipated from th e failure of the theoretical analysis to account for the experimental strain-stress curves at large film elongations. Therefore, future theo retical analysis of the mechanical behavior at finite strain of coales ced core/shell latex films should take into account both deformation m echanisms.