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Effects of Hydrophobic Modification and Electrostatic Interactions on the Association Behavior in Aqueous Solutions of Poly(vinyl alcohol). A Pulsed Field Gradient NMR Study
Author(s) -
Andersen Peder Oscar,
Marstokk Olav,
Nyström Bo,
Walderhaug Harald
Publication year - 2001
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/1521-3935(20010501)202:8<1457::aid-macp1457>3.0.co;2-k
Subject(s) - vinyl alcohol , pulsed field gradient , aqueous solution , diffusion , polymer , self diffusion , chemistry , polymer chemistry , thermal diffusivity , chemical physics , chemical engineering , thermodynamics , organic chemistry , physics , self service , marketing , business , engineering
The dynamics of dilute and semi‐dilute aqueous solutions of unmodified poly(vinyl alcohol) (PVA) and of hydrophobically modified anionic PVA with two different degrees of hexadecyl substitution (HM‐PVA1 and HM‐PVA2) is studied by means of pulsed field gradient NMR (PGSE‐NMR). The spin‐echo decays for solutions of PVA are well portrayed by a stretched exponential, except at the highest concentration. In this case, as well as for the dilute and semi‐dilute solutions of the hydrophobically modified polymers, the echo decay can initially be described by a stretched exponential (fast self‐diffusion) followed by a single exponential (slow self‐diffusion). The appearance of a bimodal echo decay indicates the existence of two populations of diffusing species with different self‐diffusivity. The emergence of the slow self‐diffusion mode, is probably related to the formation of large association structures. Both the width of the distribution of fast self‐diffusion coefficients and the sizes of the association complexes are larger for the hydrophobically modified samples than for PVA. The results suggest that both the size and the cluster size distribution are affected by polymer concentration and hydrophobicity of the polymer. The influence of hydrophobicity, and polymer concentration dependencies of the fast and the slow self‐diffusion coefficient are significantly different. The diffusion behaviors at high salinity for the charged hydrophobically modified polymers indicate that the clusters contract due to screening of the electrostatic interactions.