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Cononsolvency of the responsive polymer poly(N-isopropylacrylamide) in water/methanol mixtures: a dynamic light scattering study of the effect of pressure on the collective dynamics

  • The collective dynamics of 25 wt% poly(N-isopropylacrylamide) (PNIPAM) solutions in water or an 80:20 v/v water/methanol mixture are investigated in the one-phase region in dependence on pressure and temperature using dynamic light scattering. Throughout, two dynamic modes are observed, the fast one corresponding to the relaxation of the chain segments within the polymer blobs and the slow one to the relaxation of the blobs. A pressure scan in the one-phase region on an aqueous solution at 34.0 °C, i.e., slightly below the maximum of the coexistence line, reveals that the dynamic correlation length of the fast mode increases when the left and the right branch of the coexistence line are approached. Thus, the chains are rather swollen far away from the coexistence line, but contracted near the phase transition. Temperature scans of solutions in neat H2O or in H2O/CD3OD at 0.1, 130, and 200 MPa reveal that the dynamic correlation length of the fast mode shows critical behavior. However, the critical exponents are significantly larger than the value predicted by mean-field theory for the static correlation length, ν = 0.5, and the exponent is significantly larger for the solution in the H2O/CD3OD mixture than in neat H2O.

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Document Type:Article
Author:Bart-Jan NiebuurORCiD, André DeyerlingORCiD, Nicole Höfer, Alfons SchulteORCiD, Christine M. PapadakisORCiD
Parent Title (English):Colloid and Polymer Science
First Page:1269
Last Page:1279
Year of first Publication:2022
Release Date:2023/02/23
Impact:02.434 (2021)
Funding Information:Deutsche Forschungsgemeinschaft (DFG) for funding (Pa771/22–1).
DDC classes:600 Technik, Medizin, angewandte Wissenschaften / 660 Technische Chemie
Open Access:Open Access
Signature:INM 2022/032
Licence (German):License LogoCreative Commons - CC BY - Namensnennung 4.0 International