(95i) Examining the Effects of Surfactants on the Structural and Mechanical Properties of a Thermoresponsive Polymer Brush
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Engineering Sciences and Fundamentals
Solid-Liquid Interfaces
Monday, November 11, 2019 - 10:00am to 10:15am
Layers
of densely-tethered polymers (polymer brushes) are of interest due to their
unique lubricating, antifouling, and/or biocompatible properties, which stem
from their diffuse ‘brushy’ conformation. When these brushes are constructed
from stimuli-responsive polymers their properties can be modulated via a
stimulus-induced conformational change. These responsive systems enable
advanced interface design, and as such it is important that their behaviour in
complex environments be understood. This
work explores the interactions between a range of surfactants and a
poly(N-isopropylacrylamide) (PNIPAM) brush layer, using a combination of
ellipsometry, Neutron Reflectometry (NR) and quartz crystal microbalance
techniques to quantify the structure of the layer and the location of the surfactant
within the interface. We investigate the mechanical implications of the
presence of surfactant by subjecting the brush to a confining force and
measuring its conformation with NR. As part of this work, new modelling
techniques for the analysis of NR data from diffuse interfaces and the
quantification of uncertainty within NR experiments were developed.
Figure
1: Schematic of (a) different modes of surfactant swelling and (b) embedded
surfactant increasing the resistance to confinement. A
rich surfactant-specific behaviour is observed and is found to be headgroup
dependent, consistent with prior work on other PNIPAM architectures. Those
surfactant species that do interact are found to swell the brush layer, even at
concentrations well below the CMC. We show that the mechanism behind this
response is the adsorption of surfactant micelles along the polymer chain,
decorating the ordinarily neutral PNIPAM with charges. We report that these
charges modify the mechanical properties of the brush, assisting it in
resisting confinement. These findings elucidate the nature of the
surfactant-NIPAM interaction, giving hints as to the mode of surfactant binding
and revealing a method for modifying the mechanical properties of a brush
layer.
of densely-tethered polymers (polymer brushes) are of interest due to their
unique lubricating, antifouling, and/or biocompatible properties, which stem
from their diffuse ‘brushy’ conformation. When these brushes are constructed
from stimuli-responsive polymers their properties can be modulated via a
stimulus-induced conformational change. These responsive systems enable
advanced interface design, and as such it is important that their behaviour in
complex environments be understood. This
work explores the interactions between a range of surfactants and a
poly(N-isopropylacrylamide) (PNIPAM) brush layer, using a combination of
ellipsometry, Neutron Reflectometry (NR) and quartz crystal microbalance
techniques to quantify the structure of the layer and the location of the surfactant
within the interface. We investigate the mechanical implications of the
presence of surfactant by subjecting the brush to a confining force and
measuring its conformation with NR. As part of this work, new modelling
techniques for the analysis of NR data from diffuse interfaces and the
quantification of uncertainty within NR experiments were developed.
Figure1: Schematic of (a) different modes of surfactant swelling and (b) embedded
surfactant increasing the resistance to confinement. A
rich surfactant-specific behaviour is observed and is found to be headgroup
dependent, consistent with prior work on other PNIPAM architectures. Those
surfactant species that do interact are found to swell the brush layer, even at
concentrations well below the CMC. We show that the mechanism behind this
response is the adsorption of surfactant micelles along the polymer chain,
decorating the ordinarily neutral PNIPAM with charges. We report that these
charges modify the mechanical properties of the brush, assisting it in
resisting confinement. These findings elucidate the nature of the
surfactant-NIPAM interaction, giving hints as to the mode of surfactant binding
and revealing a method for modifying the mechanical properties of a brush
layer.