Phase separation and physico-chemical processes at microscopic and macroscopic levels in MWCNT laden polymer blends...

We propose a unique contact-free droplet based architecture in which thermally induced instabilities can be used to precisely alter the phase separation behavior in a dynamically asymmetric polymer blend (solution of PS/PVME in toluene) by controlling the external heating rates and concentration of added nanoparticles (multi-walled carbon nanotube particles, MWCNTs). In addition, by tuning the heating rates, distinctly different macroscopic morphologies (hollow shell or globular mass) can be obtained as a final structure in such droplets. Furthermore, the process of separation is temporally aggravated by several orders (about 3-5 orders) as compared to the traditional bulk processing techniques (thin film of blends). Faster production rate and high throughput promise a new spray-based architecture for producing phase separated structures. Addition of MWCNTs in the polymer blend delays the separation phenomenon as it interacts with the polymers and alters the stability criteria. Furthermore, addition of nanoparticles also introduces a different mode of instability at higher external heating rates. Heat accumulation due to particles causes boiling of the solvent (toluene) trapped inside the droplet which leads to subsequent explosion of the entire droplet, in addition to the phase separation phenomena (at the microscopic level). Volumetric expansion due to bubble growth leads to the formation of a unique hollow structure which is distinctly different from the globular mass obtained at lower heating rates.