Fabrication of Graphene-Coated Silica Particles for Polymer Chromatography to Quantify Chemical Composition Distribution of Polyolefin Materials

As the most consumed synthetic polymers globally, polyolefins provide tunable performance at a low production cost. This tunability is achieved by modifying polymer molecular weight or branching characteristics, the latter of which can be quantified by chemical composition distribution (CCD). CCD can be measured using interaction-based techniques relying on graphite-based material as the stationary phase. Interaction-based techniques are classified as solvent gradient or thermal gradient according to the type of gradient that is used to enable the separation of polyolefins. High-temperature thermal gradient interactive chromatography (HT-TGIC) has been the preferred technique as it overcomes the detector shortcomings of solvent gradient interactive chromatography. This work focuses on the HT-TGIC technique and strives to improve the separation resolution by adopting improvements in the stationary-phase packing material. Resolution is greatest with a substrate consisting of nonporous and homogeneous, spherical particles. However, the synthesis of such material with naturally occurring graphite has been a challenge. Here, an innovative yet simple approach to make such particles is described. A core-shell particle with nonporous silica as the core and graphene nanopowder (GNP) as the shell provides this solution. This novel method does not require chemical modification of graphene or silica particles, which has been explored previously as a potential avenue. These core-shell particles were packed into columns and showed an increase in chromatographic performance and separation resolution versus the best HT-TGIC columns currently available.