Self-Assembly of Block Copolymers in thin films

Abstract

Block copolymers are a unique class of polymers, in which two or more different polymer blocks are connected by covalent bonds. Because of the presence of different polymers in the single chain, block copolymers exhibit unique control over polymer properties. Furthermore, in the presence of external stimuli, block copolymer can phase separate into different morphologies depending upon the number of blocks and block ratio. The block copolymer morphologies in thin film can result in nanostructures ranging from 3 nm -100 nm. These nanostructures in thin films have applications in nanolithography, bit patterned media, filtration membranes, ion-conduction membrane, photonics etc. In this work, we have looked at self- assembly of triblock and diblock copolymers. Alloocimene-b-Isobutylene-b-Alloocimene (AIBA) is a unique thermoplastic elastomeric polymer, having interesting properties in the bulk. Despite the interesting properties of AIBA polymer in the block , very little is known about the phase separation behavior of AIBA in thin films. In this work. we have studied the morphology of phase separated AIBA triblock copolymer under the influence of temperature stimulus. We have successfully mapped out the different morphologies of AIBA polymer and compared it with the existing library of triblock copolymer morphology and simulation studies. On the other hand, controlling the alignment and orientation of diblock copolymers has been a challenge since the research on block copolymer thin films has started. In the second part of this work, we have successfully sandwiched between two neutral controlled the orientation of diblock copolymers surfaces. Additionally, we have aligned the BCPs by using the shear generated by elastomeric top pad during thermal gradient based Cold Zone Annealing process. Notably, the shear force during due to thermal expansion and contraction of elastomeric pad is much higher than mechanical shear, thus aligning the BCPs with a spread less than 5 degrees. We believe that this work possesses the potential of transitioning the use of block copolymers from lab scale to industrial scale for use in nanolithography and other applications.