Detection Orthogonality in Macromolecular Separations: Role of the On-Line Viscometer in Characterizing Polymers at Conditions of Spectroscopic Invisibility

Much has been written over the last two decades about the advantages of separation orthogonality for the characterization of complex polymers and blends, and of the additive and synergistic benefits of combining various physical and chemical detection methods in the determination of molar mass, chemical heterogeneity, dilute solution conformation, etc. Less attention has been paid to the complementarity of detection methods that are truly orthogonal to each other with respect to a given property. A common, yet particularly different type of macromolecular liquid chromatography detector is the on-line viscometer, as its measurement principle is based on hydrodynamic transport properties, thus separating it from the large variety of spectroscopically based detectors. Here, we explore how the on-line viscometer can provide insights into the size-exclusion chromatographic analysis of individual homopolymer samples and of blends, even in cases where no response is observed with commonly employed detectors such as on-line refractometry and static and quasi-elastic light scattering, i.e., when analyses are conducted at conditions of spectroscopic invisibility.