Characterizing single chain nanoparticles (SCNPs): a critical survey†
We provide the results of a critical literature survey on the reported sizes of single chain polymer nanoparticles (SCNPs), an emerging class of functional nanomaterials with sub-30 nm diameters. Comparing different size evaluation techniques (DLS, 2D DOSY NMR, viscometry as well as microscopic techniques) by plotting the SCNPs’ estimated diameters, D, versus their measured (apparent) number average molecular weight, Mn, we demonstrate the vast data scatter that besets their analysis. We show that while relative reductions in measured diameter certainly indicate chain collapse, accurately describing the absolute size of SCNPs in solution remains a challenging task. Critically, conformation-size relationships emerge depending on the method used for size determination. We submit that the vast majority of reported sizes are only indicative of the relative size reduction during chain collapse and that absolute size determination approaches currently in use need to be further refined.