pH and Thermo-Responsive Behavior of Amino (Meth)Acrylate Polymer Brushes on Silicon Substrates By in-Situ Ellipsometry and Atomic Force Microscopy

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) and single electron transfer living radical polymerization (SET-LRP) were used to synthesize a series of surface-grafted poly(amino (meth)acrylate) brushes from silicon substrates that were pre-modified with silane self-assembled monolayers (SAMs).  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) were synthesized and characterized using in-situ techniques.  In-situ spectroscopic ellipsometry studies were performed using a temperature-controlled liquid flow cell to collect dynamic and equilibrium data under various pH/ionic strength conditions.  Multilayer models were generated based on a Gaussian general-oscillator (GenOsc) dispersion model that accounted for the polymer, initiator, and silane SAM layers.  In-situ atomic force microscopy (AFM) measurements were also collected under different pH and temperature conditions using a liquid cell. AFM was used to identify changes in the polymer brush structure, including phase separation/aggregation behavior changes. In addition to measuring thickness changes, response rates, and stimuli conditions for these surface-tethered pH and temperature responsive poly(amino (meth)acrylates) brushes, for the first time application of the GenOsc model to evaluate the optical constants of surface-tethered polymer brushes is presented.