Abstract
The adsorption of poly(N-isopropylacrylamide) (PNIPAM) at the air−solution interface has been studied as a function of temperature using surface tension measurements and specular neutron reflectivity. At temperatures below 25 °C, water is a good solvent for PNIPAM and surface tension measurements show that a saturated layer of polymer is formed at the air−solution interface at very low bulk polymer concentrations. Characterization by neutron reflectivity shows that the adsorbed layer consists of a thin monomer-rich zone followed by a more dilute zone which extends toward the bulk solution up to a thickness proportional to the radius of gyration of the polymer. At temperatures above 25 °C, the polymer adsorption increases gradually until around 28 °C, beyond which it increases very steeply. This is attributed to a decrease in solvent quality. In the adsorbed layer, the monomer-rich zone also increases steeply beyond 28 °C while the central more dilute zone increases only gradually over the entire range of temperature studied. At temperatures above the bulk solution cloud point around 33 °C, an inhomogeneous layer is formed which exhibits very slow kinetics to reach equilibrium. We attribute this to a possible “glassy” nature of the adsorbed layer or a possible existence of a surface gel.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.