Polymer Brushes for Molecular Transport - Paul Braun Research ...

CHAPTER 3
PATTERNED POLY(N-ISOPROPYLACRYLAMIDE) BRUSHES ON SILICA
SURFACES
Published as: Tu, H.; Heitzman, C. E.; Braun, P. V. Patterned Poly(N-isopropyl-acrylamide)
Brushes on Silica Surfaces by Microcontact Printing Followed by Surface-Initiated
Polymerization, Langmuir 2004, 18, 8313.
3.1 Introduction
We are interested in building quasi two-dimensional “smart” and stable molecular
devices which are able to confine and regulate molecular diffusion, generate and conduct
molecular signals upon receiving external stimuli as well as provide templates for the growth of
biological molecules. In this study, we present our results on the patterning of poly(N-
isopropylacrylamide) (PNIPAAm), which was selected because it has the potential to be
responsive in aqueous environments near room temperature.
PNIPAAm is particularly interesting because it is biocompatible and thermoresponsive,
exhibiting a lower critical solution temperature (LCST) near room temperature.[1-6] Free
PNIPAAm chains in pure water undergo a sharp LCST phase transition at 32 ± 1-2 °C.[1] In
contrast, a broadened LCST transition was first predicted[7] and then observed for PNIPAAm
brushes.[8, 9] The general LCST behavior of end-grafted PNIPAAm is thought to be dependent
on the geometry of the substrate, the grafting density of the polymers, and the polydispersity of
the polymer.[7, 9-13]
Unpatterned PNIPAAm brushes have been grafted onto polystyrene culture dishes,[14]
latex or microgel particles,[8, 15] planar gold surfaces,[9, 13] gold nanoparticles,[10] planar
silica substrates,[12, 16, 17] and silica particles.[18, 19] Patterned PNIPAAm brushes have been
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