Generalized Theoretical Study of the Effect of Molecular Bond Optical Tensor Components on the Mean-Squared Optical Anisotropy ⟨γ²⟩ of Model Bead-Spring Linear Homopolymer Chains

Abstract

The conformationally averaged mean-squared optical anisotropy ⟨γ²⟩ of homopolymer chains under the theta solution condition is simulated using a rotational isomeric state (RIS) scheme with a generalized optical tensor description based on model bead-spring macromolecules. The effect of torsion angle values, number of minimum energy torsion states, probability (statistical weights) of the conformational states, and values of the components of the polarizability tensor for the bead are studied in this manner for the first time. Chains having either one or two interdependent rotatable bonds in the repeat unit are simulated. We find that under certain conditions of the relative orientations and values of the optical polarizability components with regards to the plane of the backbone bond angle, a higher probability for the gauche (less extended) conformation actually leads to a higher value of the optical anisotropy. In other cases, in conjunction with expectations from known experimental results, the optical anisotropy decreases with an increase in the probability of the gauche conformational state consistently over the range of values. We observe that, in most cases, higher values of the difference in the polarizability components lead to higher values of the chain optical anisotropy.

Keywords:

• conformations
• homopolymer
• optical anisotropy
• polarizability
• rotational isomeric state theory