Effect of Flory-Huggins Interaction Parameter of Block Copolymers on the Shape of Block Copolymer Particles

Systematic modulation of shape-anisotropy of block copolymer (BCP) particles is of great importance in tuning their shape-dependent properties. Herein, we investigate the effect of Flory-Huggins interaction parameter (χ) on the shape of BCP particles. Four different poly(styrene-b-butadiene) (PS-b-PB), poly(styrene-b-dimethylsiloxane) (PS-b-PDMS), poly(styrene-b-(4-vinylpyridine)) (PS-b-P4VP), and poly(dimethylsiloxane-b-(2-vinylpyridine)) (PDMS-b-P2VP) with different χ values but similar degree of polymerization (N) were used to produce two different anisotropic BCP particles (i.e., striped ellipsoidal particles and convex-lens particles). Lamellae-forming BCPs with higher χ assembled into ellipsoidal particles with more elongation. In particular, the aspect ratio (AR) of PDMS-b-P2VP ellipsoidal particles increased more than 3-fold over PS-b-PB. Similarly, cylinder-forming BCPs with higher χ assembled into flatter convex lens-like particles, resulting in an increase in AR greater than 10. Fine-tuning of shape anisotropy depending on χ was supported with theoretic calculation of particle free energy.