Temperature Induced Volume-Phase Transitions in Surface-Tethered Poly( N -isopropylacrylamide) Networks
2008; American Chemical Society; Volume: 41; Issue: 3 Linguagem: Inglês
10.1021/ma071438n
ISSN1520-5835
AutoresAjay Vidyasagar, Jarosław Majewski, Ryan Toomey,
Tópico(s)Advanced Polymer Synthesis and Characterization
ResumoThe swelling behavior of a surface-tethered poly(N-isopropylacrylamide) (polyNIPAAm) network in D2O was characterized with neutron reflection and compared to the demixing behavior of linear poly(NIPAAm) in solution. The surface-tethered network was fabricated by cross-linking a 250 Å thick film of a copolymer comprised of NIPAAm and 3 mol % methacroylbenzophenone. As the temperature was varied between 15 and 29 °C, the thickness of the poly(NIPAAm) network in aqueous solution decreased gradually from 1100 to 750 Å. In this regime, the network lay entirely in the single phase region of the phase diagram for linear poly(NIPAAm). At approximately 30 °C, the network entered the two-phase region of the phase diagram and collapsed along the tie line to a thickness of 339 Å. Above 30 °C, the thickness of the network adjusted to the binodal curve of the phase diagram. The agreement between the swelling discontinuity in the surface-tethered network and the two-phase region of uncross-linked poly(NIPAAm) suggests that confinement does not alter the miscibility gap of poly(NIPAAm). With the use of a temperature, T, and polymer volume fraction, φ, Flory interaction parameter, χ(T,φ), that is tabulated from the demixing data of the linear poly(NIPAAm), the swelling behavior of the surface-tethered network could be modeled using the mean-field Flory−Rehner theory modified for uniaxial swelling.
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