STUDIES OF SURFACE AND INTERFACE SEGREGATION IN POLYMER BLENDS BY SECONDARY ION MASS-SPECTROMETRY

Dynamic secondary ion mass spectrometry (SIMS) has recently been employed to obtain high resolution depth profiles in polymer blend thin films and is now regarded as a key probe of surface and interfacial segregation in these systems. Segregation phenomena strongly impact blend properties such as adhesion, friction and weatherability. The strengths and limitations of the SIMS polymer profiling technique are described and contrasted with the complementary techniques of forward recoil elastic scattering (FRES) and neutron reflectivity (NR). The procedures developed for sample preparation and data acquisition are discussed. Experimental results for the effect of incident O2+ energy and angle on depth resolution and sputtering rate in polystyrene (PS) are presented. Ongoing SIMS studies of model blend systems are described: Segregation from dPS (deuterated)/PS blends to vacuum and Si interfaces is examined as a function of the molecular weight of the blend components and preparation of the Si substrate, revealing the importance of long range interactions. Similar behaviour in an acrylonitrile blend is demonstrated. The surface segregation profiles in the immiscible blend PBrS (polybromostyrene)/PS are discussed for samples annealed in the one and two phase regions. The conformation of carboxy terminated PS and dPS chains grafted to the Si oxide interface in a melt is studied as a function of grafting density, temperature, and matrix molecular weight. Diffusion of homopolymer dPS in a crosslinked PS matrix is examined and the observed diffusion coefficients are in good agreement with calculated values using rubber elasticity theory. Interdiffusion of PS/PS bilayer samples annealed above the glass transition temperature is studied. Trapped oxygen at the original bilayer interface is observed, indicating UV crosslinking of the individual film surfaces.