Thermodynamic and Conformational Analysis of Chiral Block Copolymers in the Disordered State

Block copolymers with one chiral block have emerged as promising candidates for materials with novel properties like photonic bandgaps and negative refractive index. Thermodynamic insights into the self-assembly of these materials is of great interest as it would allow more facile access to these highly desirable materials. Experimental studies attempting to understand the self-assembly of these chiral polymers have yielded intriguing results – despite identical structural properties of the chiral lamellar structure, the chiral molecules exhibit a decrease in the order-disorder temperature when compared to the achiral counterparts. Thus, altering the molecular shape alters the entry point of these novel phases possessing sought after properties. Employing a combination of free energy perturbation and thermodynamic integration in a particle-based simulation model, we are able to quantify the free energy, entropy, and enthalpy to yield a highly accurate quantification of these unresolved thermodynamics by measuring the effects of increasing the chirality of one block in the block copolymer melt. When tying these contributions with varying topology metrics two distinct regimes were found - a compressed regime which corresponds to recent discussions in the literature, and a novel elongated regime.The insights generated from this study suggests that the development of new chiral materials in the elongated regime could exhibit novel mechanical properties.