Influence of Side Chain Length on Linear and Nonlinear Rheological Behaviors of Poly(3-alkylthiophene) Networks

The present article describes the creation of uniformly distributed (polyalkylthiophene) (P3AT) networks with various alkyl side chains. Modulations of optical, structural, morphological, and rheological characteristics caused by the alteration of the length of the alkyl side chain in P3AT aggregates have been investigated thoroughly by temperature-dependent UV-visible studies, powder X-ray diffraction, and atomic force microscopy (AFM) studies. At a low polymer concentration, all P3ATs form networks and reveal their rheological properties. The current study describes the influence of the alkyl side chain microstructure on two important behaviors of P3AT networks under small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS)─via rheology. Industrially relevant and uncommon large deformation mechanisms caused by the "strain stiffening and shear thinning" of these P3AT networks have been explored herein. Nonlinear stress waveforms have been analyzed using Lissajous-Bowditch curves, Fourier transform (FT) rheology, and FT coupled with Chebyshev polynomials based stress decomposition within the MITlaos framework. The FT coupled techniques allow us to extract user-friendly measurements under limiting conditions (γ → 0, γ → γ_max) and to estimate parameters such as S, T, G₁^', G_M^', G_L^', η₁^', η_M^', and η_L^'. The breakdown and effect of aggregated networks in response to the applied deformation and time scale create a "rheological fingerprint" (Pipkin space). Additionally, the sequence of physical processes (SPP) has been utilized to gain a clearer understanding of the intracyclic yielding and rheological behavior. Our findings provide quantitative insight into the type and extent of aggregation, crystallinity, and nonlinear rheological features for low concentration P3AT networks in anisole solvent.