Application of principal component analysis-based two-dimensional correlation spectroscopy to characterization of order-disorder transition of polystyrene-block-poly(n-pentyl methacrylate) copolymer

Principal component analysis-based two-dimensional (PCA2D) correlation spectroscopy through eigenvalue manipulating transformation (EMT) of spectral data set was applied to temperature-dependent IR spectra of polystyrene-block-poly(n-pentyl methacrylate) (PS-PnPMA) for spectral selectivity enhancement. EMT technique which uniformly lowers the power of a set of eigenvalues associated with the original data highlights the subtle contributions from minor eigenvectors. Thus subtle differences in the thermal responses of PS-PnPMA, which are difficult to observe by conventional 2D correlation analysis, are accentuated much more strongly than the original data. A conclusion was reached on details of phase transition of PS-PnPMA which exhibited a closed-loop phase behavior bounded by a lower disorder-to-order transition (LDOT) and an upper order-to-disorder transition (UODT). We found that a disordered state at lower temperature is different from that at higher temperature.