1 research outputs found
Temporal Evolution of Optical Gradients during Drying in Cast Polymer Solutions
The development of optical anisotropy
gradient as a result of solvent
evaporation for polyÂ(amide–imide) (PAI) solution in dimethylacetamide
(DMAc) was investigated for the first time. Experiments were carried
out using real-time optical measurement with spectral birefringence
technique coupled with off-line optical techniques such as the Abbe
refractometer and optical compensator method. We have shown that drying
process induces temporal evolution of nonuniform out-of-plane birefringence
profile through the thickness direction while in-plane birefringence
remained zero. The highest birefringence was observed at the substrate–solution
interface at early stages of drying. Beyond a critical time, the formation
of highly oriented layer was observed at the air–solution interface.
This oriented layer progresses through the thickness direction as
the solvent concentration is disproportionately reduced in these regions.
Abbe refractometer results confirmed the anisotropy is preserved at
longer drying times, the air–solution interface birefringence
becoming higher compared to the substrate–solution interface.
Overall, observations obtained by real-time measurement system agreed
with off-line measurements