Nanomechanics of confined polymer systems

Abstract

Polymers anchored to surfaces play an important role in nature and technology, and regulate diverse interfacial phenomena in areas such as tribology and colloidal stability. Polymers grafted to surfaces at high density form elongated “brushes” with characteristic lengths much larger than free coils in solution. These brushes can reduce interfacial friction and wear as well as impart fouling resistance to surfaces. In light of these functionalities it is important to understand the behaviour of surface-grafted polymers at the molecular and nanoscopic level. An emerging area of interest are polymers attached to nanopores. Theoretical studies predict interesting morphologies and dynamics of such confined brushes in and around nanopores, but nanopore environments have been difficult to study experimentally. In this thesis a unique polymer-functionalized nanopore-like experimental system is presented, functionalized with poly(ethylene glycol) (PEG). Atomic force microscopy (AFM) is employed to probe the PEG brushes with nanometre spatial precision and sub-nanonewton force sensitivity, revealing novel dynamics depending on the local grafting position of PEG with respect to the nanopore geometry. Further, AFM is used together with fluorescence microscopy to show how polymer–protein interactions can be used together with the anti-fouling property of PEG to sort specific biomolecules from complex biological fluids to nanoscale targets. This shows a way how to confer biological recognition and specificity to synthetic nanoscale systems which is important for biosensing and bioseparation applications.