title: Effect of hydrogen-bonding complexation on the interfacial behavior of poly(isoprene)-b-poly(ethylene oxide) and poly(isoprene)-b-poly(acrylic acid) Langmuir monolayers.
abstract: The effect of hydrogen-bonding complexation on the interfacial behavior of poly(isoprene)-b-poly(ethylene oxide) (PI-b-PEO) diblock copolymer at the air-water interface has been investigated by Langmuir balance and neutron reflectivity. PI-b-PEO forms Langmuir monolayers with PI as the anchoring block. Introduction of a second diblock, poly(isoprene)-b-poly(acrylic acid) (PI-b-PAA) yields PI-b-PEO/PI-b-PAA mixed layers with interfacial behavior that is pH-dependent. At pH 10.0 and 5.7, the compression (pi-A) isotherms exhibit three regions that are characteristic of PEO-type tethered layers, (i) a low-pressure 2-D "pancake" region (region I), (ii) a pseudoplateau where PEO segments desorb and are immerse in the subphase (region II), and (iii) a steep pressure rise region commonly considered as the "brush" regime (region III). At pH 2.5, on the other hand, the pi-A isotherm shows only two regions, (I) and (III). This novel behavior is attributed to hydrogen-bonding complexation between the undissociated carboxylic acids and the PEO, forming very compact layers. It appears that desorption of PEO segments is hindered as a consequence of this complexation. Furthermore, no brush-like structure is observed in region III of the isotherml; thus, the steep rise in surface pressure in this case arises primarily from interactions of the anchoring block. The hydrogen-bonded complex of PI-b-PEO/PI-b-PAA monolayers thus shows enhanced surface stability.
authors.affiliation: The Hefei National Laboratory for Physical Sciences at Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Dinghai
authors.initials: D
authors.lastname: Xie
authors.forename: Camila A
authors.initials: CA
authors.lastname: Rezende
authors.forename: Guangming
authors.initials: G
authors.lastname: Liu
authors.forename: Stergios
authors.initials: S
authors.lastname: Pispas
authors.forename: Guangzhao
authors.initials: G
authors.lastname: Zhang
authors.forename: Lay-Theng
authors.initials: LT
authors.lastname: Lee