Single Macromolecule Diffusion at the Interface of Responsive Polymer Thin Films

Macromolecule adsorption at polymer interfaces has been much explored, yet the interfacial dynamics is not. We employ fluorescence correlation spectroscopy (FCS) and single-molecule imaging to examine the translational dynamic processes of protein molecules at the responsive polymer interfaces. We use the Atom Transfer Radical Polymerization method to synthesize stimuli-responsive poly (N-isopropylacrylamide) (PNIPAM) brush layers over smooth initiator monolayer via Langmuir-Blodgett deposition with controllable graft density and brush layer thickness. We focus on the dynamics of human serum albumin (HSA) and lubricin proteins at the interface of PNIPAM brush-like thin films. The effects of PNIPAM brush thickness, grafting density, and surface hydrophobicity on protein interfacial diffusivity are investigated. We observe the strong coupling of the local macromolecular dynamics at the polymer thin film interfaces with the interfacial viscoelasicity of PNIPAM brush thin layers.