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Thermodynamic behavior of polyelectrolytes with the lower critical solution temperature (LCST) phenomenon
Author(s) -
Casolaro Mario,
Barbucci Rolando
Publication year - 1996
Publication title -
polymers for advanced technologies
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.61
H-Index - 90
eISSN - 1099-1581
pISSN - 1042-7147
DOI - 10.1002/(sici)1099-1581(199611)7:11<831::aid-pat586>3.0.co;2-5
Subject(s) - lower critical solution temperature , polyelectrolyte , aqueous solution , polymer , poly(n isopropylacrylamide) , materials science , polymer chemistry , protonation , hydrophobic effect , chemical engineering , ionic bonding , copolymer , chemistry , organic chemistry , ion , engineering , composite material
A series of vinyl polymers with L‐valine and L‐leucine residues, and related copolymers with N‐isopropylacrylamide, were studied in aqueous solution at different temperatures (25, 30 and 35°C) and at two ionic strengths (0.01 M and 0.1 M NaCl). The protonation behavior revealed great differences between the polymers that were attributed to the size of the hydrophobic lateral group. Macromolecular shrinkage, occurring above a critical degree of protonation β, was related to hydrophobic forces outweighing the electrostatic repulsions between COO – groups. Low salt concentrations increased the electrostatic potential while high temperatures increased the hydrophobic interaction at lower β. The release of fewer water molecules structured around the polymer chain, responsible for the lower critical solution temperature phenomenon, revealed lower entropy changes at higher temperatures. The reversible configuration of graft polymer chains instantly responded to changes in pH and temperature, modifying the water filtration rates through the pores of cellulose membranes.