Thermo-responsiveness of poly( N , N -diethylacrylamide) polymers at the air–water interface: The effect of a hydrophobic block

• Published in: Journal of colloid and interface science Vol. 327; no. 1; pp. 129 - 137
• Main Authors: Gonçalves da Silva, Amélia M.P.S., Lopes, Sónia I.C., Brogueira, Pedro, Prazeres, Telmo J.V., Beija, Mariana, Martinho, José M.G.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01-11-2008; Elsevier
• Subjects: Chemistry; Colloidal state and disperse state; Copolymers; Exact sciences and technology; General and physical chemistry; Interfaces; LB films; Lower critical solution temperature (LCST); Poly( [formula omitted]-diethylacrylamide); Surface physical chemistry; Thermo-responsive polymers; Interfaces; Thermo-responsive polymers; Copolymers; Poly( N , N -diethylacrylamide); LB films; Lower critical solution temperature (LCST); Water; Gas liquid interface; Critical property; Monolayer; Atomic force microscopy; Poly(N,N-diethylacrylamide); Stability; Film; Lower critical solution température (LCST); Polymer; Hydrophobicity; Air water interface; Morphology; Diblock copolymer; Isotherm; Homopolymer; Critical temperature; Aggregate; Structure; Anchoring
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2008.08.011

The poly(
N
,
N
-diethylacrylamide) (h-PDEA) homopolymer and the poly(
N-decylacrylamide)-
b-PDEA (PDcA
11-
b-PDEA
231) diblock copolymer were studied in the range of 10 to 40 °C, at the air–water interface. The
π
–
A
isotherms of h-PDEA appear nearly invariant with temperature while the
π
–
A
isotherms of PDcA
11-
b-PDEA
231 deviate significantly to lower areas with the temperature increase evidencing the thermo-responsiveness of this diblock copolymer at the interface. For the copolymer, the limiting area per segment
versus temperature shows a break point around 29 °C, slightly lower than the lower critical solution temperature (LCST) of h-PDEA in water (31–33 °C). AFM images of LB monolayers transferred at 40 °C revealed for both polymers the presence of hydrophobic aggregates due to the conformational changes (collapse) of chains that occur at the LCST. Differences in the morphology of these aggregates, flat irregular structures for h-PDEA and round-shaped domains for PDcA
11-
b-PDEA
231, were related with the condensing effect of the hydrophobic block. The PDcA
11 block, anchoring the polymer to the interface, ensures a better stability and cohesion to the film and preserves the thermo-sensitivity of the h-PDEA at the interface.
Aggregates of variable size were observed at the air–water interface above the LCST of the PDcA
11-
b-PDEA
231 thermo-responsive copolymer.