TY - JOUR
T1 - Effect of surfactants on the thermoresponse of PNIPAM investigated in the brush geometry
AU - Gresham, Isaac J.
AU - Willott, Joshua D.
AU - Johnson, Edwin C.
AU - Li, Peixun
AU - Webber, Grant B.
AU - Wanless, Erica J.
AU - Nelson, Andrew R.J.
AU - Prescott, Stuart W.
N1 - Publisher Copyright:
© 2022 Elsevier Inc.
PY - 2023/2
Y1 - 2023/2
N2 - Hypothesis: Anionic surfactants have been reported to interact with poly(N-isopropyl acrylamide) (PNIPAM), suppressing its thermoresponse. Scattering and NMR studies of the anionic sodium dodecylsulfate (SDS) system propose that the PNIPAM-surfactant interaction is purely hydrophobic. However, prior phenomenological investigations of a range of surfactant identities (anionic, cationic, nonionic) show that only anionic surfactants affect the thermoresponse and conformation of PNIPAM, implying that the hydrophilic head–group also contributes. Crucially, the phenomenological experiments do not measure the affinity of the tested surfactants to the polymer, only their effect on its behaviour. Experiments: We study the adsorption of six surfactants within a planar PNIPAM brush system, elucidating the polymer conformation, thermoresponse, and surfactant adsorption kinetics using ellipsometry, neutron reflectometry (NR), optical reflectometry and the quartz crystal microbalance technique. NR is used to measure the distribution of surfactants within the brush. Findings: We find that only anionic surfactants modify the structure and thermoresponse of PNIPAM, with the greater affinity of anionic surfactants for PNIPAM (relative to cationic and nonionic surfactants) being the primary reason for this behaviour. These results show that the surfactant head–group has a more critical role in mediating PNIPAM-surfactant interaction than previously reported. Taking inspiration from prior molecular dynamics work on the PEO-surfactant system, we propose an interaction mechanism for PNIPAM and SDS that reconciles evidence for hydrophobic interaction with the observed head–group-dependent affinity.
AB - Hypothesis: Anionic surfactants have been reported to interact with poly(N-isopropyl acrylamide) (PNIPAM), suppressing its thermoresponse. Scattering and NMR studies of the anionic sodium dodecylsulfate (SDS) system propose that the PNIPAM-surfactant interaction is purely hydrophobic. However, prior phenomenological investigations of a range of surfactant identities (anionic, cationic, nonionic) show that only anionic surfactants affect the thermoresponse and conformation of PNIPAM, implying that the hydrophilic head–group also contributes. Crucially, the phenomenological experiments do not measure the affinity of the tested surfactants to the polymer, only their effect on its behaviour. Experiments: We study the adsorption of six surfactants within a planar PNIPAM brush system, elucidating the polymer conformation, thermoresponse, and surfactant adsorption kinetics using ellipsometry, neutron reflectometry (NR), optical reflectometry and the quartz crystal microbalance technique. NR is used to measure the distribution of surfactants within the brush. Findings: We find that only anionic surfactants modify the structure and thermoresponse of PNIPAM, with the greater affinity of anionic surfactants for PNIPAM (relative to cationic and nonionic surfactants) being the primary reason for this behaviour. These results show that the surfactant head–group has a more critical role in mediating PNIPAM-surfactant interaction than previously reported. Taking inspiration from prior molecular dynamics work on the PEO-surfactant system, we propose an interaction mechanism for PNIPAM and SDS that reconciles evidence for hydrophobic interaction with the observed head–group-dependent affinity.
KW - 2024 OA procedure
KW - Polymer brushes
KW - Responsive polymers
KW - Sodium dodecylsulfate
KW - Surfactants
KW - poly(N-isopropylacrylamide)
UR - http://www.scopus.com/inward/record.url?scp=85141919876&partnerID=8YFLogxK
U2 - 10.1016/j.jcis.2022.10.071
DO - 10.1016/j.jcis.2022.10.071
M3 - Article
C2 - 36395740
AN - SCOPUS:85141919876
SN - 0021-9797
VL - 631
SP - 260
EP - 271
JO - Journal of colloid and interface science
JF - Journal of colloid and interface science
ER -