Argon gas cluster fragmentation and scattering as a probe of the surface physics of thermoset polymers

Surface and thin films are important in modern technologies and there is growing demand for their characterization. Secondary ion mass spectrometry (SIMS) is universally used for extracting information on the chemical composition of surfaces. This study shows that it can provide information about the physical (mechanical) properties of thermoset polymer surfaces. The intensities of backscattered Arn+ clusters were measured upon 10 keV Ar3000+ gas cluster ion bombardment of polymer films. Tyrosol diaminodiphenylmethane based benzoxazine thermosets with different curing cycles were used. The intensity ratios Ar2+/(Ar2++Ar3+) and Ar2+/(Ar2++Ar4+) were highly sensitive to the physical changes of the thermoset coating surfaces as a function of their curing cycle and of temperature. These intensity ratios provide direct access to the surface transition temperature TT (related to the bulk glass transition Tg), and show a dependence on the curing degree below and above TT. Moreover, we discuss the influence of surface contamination and clusters induced roughness on the measured values. Our results suggest that contamination has a dramatic influence on the intensity of backscattered Arn+ clusters, while that of roughness appears to be minor. This study constitutes a step forward towards a quantitative assessment of the mechanical properties of polymer coating surfaces using SIMS