Analysis of the pH and Thermo-Responsive Behavior of a Series of Amino (Meth)Acrylate Polymer Brushes on Silicon Substrates By in-Situ Ellipsometry and AFM Measurements

Stimuli responsive polymers have potential use in a wide range of applications, from nanometer-scale drug delivery to flow control in microfluidic devices.  In this study, surface-confined atom transfer radical polymerization (ATRP) or single electron transfer living radical polymerization (SET-LRP) were used to synthesize a series of surface-grafted poly(amino (meth)acrylate) brushes from silicon/gold substrates that were pre-modified with silane self-assembled monolayers (SAMs).  The following polymers were synthesized and characterized: poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), poly(2-(dimethylamino)ethyl acrylate) (PDMAEA), poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA), and poly(2-(tert-butylamino)ethyl methacrylate) (PTBAEMA). In-situ spectroscopic ellipsometry studies were performed using a temperature-controlled liquid cell to collect dynamic and equilibrium data at different pH/ionic strength conditions.  Multilayer models were generated based on a general-oscillator (Genosc) dispersion model that accounted for the polymer, initiator, and silane SAM layers.  In-situ atomic force microscopy (AFM) measurements were collected at different pH and temperature conditions using a liquid cell. AFM scans were used to determine any phase transition or aggregation behavior of the grafted polymers in response to pH and temperature changes. In addition to examining the structure-property relationships for a series of surface-tethered pH and temperature responsive poly(amino (meth)acrylates) brushes, a novel Genosc model for evaluating optical constants of surface-tethered polymer brushes is described.