The development of thermal nanoprobe methods as a means of characterizing and mapping plasticizer incorporation into ethylcellulose films

Purpose: The phase composition and distribution of ethylcellulose (EC) films containing varying amounts of the plasticizer fractionated coconut oil (FCO) were studied using a novel combination of thermal and mapping approaches.

Methods: The thermal and thermomechanical properties of films containing up to 30% FCO were characterized using modulated temperature differential scanning calorimetry (MTDSC) and dynamic mechanical analysis (DMA). Film surfaces were mapped using atomic force microscopy (AFM; topographic and pulsed force modes) and the composition of specific regions identified using nanothermal probes.

Results: Clear evidence of distinct conjugate phases was obtained for the 20–30% FCO/EC film systems. We suggest a model whereby the composition of the distinct phases may be estimated via consideration of the glass transition temperatures observed using DSC and DMA. By combining pulsed force AFM and nano-thermal analysis we demonstrate that it is possible to map the two separated phases. In particular, the use of thermal probes allowed identification of the distinct regions via localized thermomechanical analysis, whereby nanoscale probe penetration is measured as a function of temperature.

Conclusion: The study has indicated that by using thermal and imaging techniques in conjunction it is possible to both identify and map distinct regions in binary films.