Subphase pH effect on the interfacial behaviour of polybenzyl methacrylate-b-poly(dimethylamino)ethyl methacrylate diblockcopolymers at the air-water interface.

DOS SANTOS CLARO, P.C.; COUSTET, M. E.; CORTIZO, SUSANA; REQUEJO, F.G.; DÍAZ, C.; PIETRASANTA, LÍA I.; AZZARONI, O.

París

Conferencia; 14th International Conference on Organized Molecular Films (ICOMF14).; 2012

Many amphiphilic block copolymers can self-assemble at the air-water interface into variousmicrophase-separated structures, which are called surface micelles [1,2]. The hydrophobic blocksaggregate to form isolated structures of different shapes mainly depending on the block copolymercomposition, which are stabilized by surface-active hydrophilic blocks spread on the water surface.The surface micelles exhibit various shapes from circular micelles to large planar aggregates via rodshapedmicelles mainly depending on the relative size of the two blocks.In this work we investigated the effect of the pH and ionic strength on the monolayer formationand surface micellization behavior of polybenzyl methacrylate-b-poly(dimethylamino)ethylmethacrylate (PBzMA-b-PDMAEMA) diblock copolymers at the air-water interface by the surfacepressure ( ) vs. area (A) isotherm and the morphology of the Langmuir-Blodgett (LB) films.PBzMA-b-PDMAEMA diblock copolymers were synthesized by group transfer polymerization. Themolecular weight was determined by gas phase chromatography resulting in 4.7 kDa with apolydispersity of 1.2. The presence and nature of the different groups were determined by 1HNMR.Surface pressure vs. area isotherms were recorded using a KSV-5000 through at a constanttemperature of 24 °C. Langmuir films of the PBzMA-b-PDMAEMA were formed at the air-waterinterface by spreading a dilute polymer solution in chloroform (0.3 mg/ml). The pH of the subphasewas adjusted with HCl or NaOH and the ionic strength was kept constant with KCl. The surface filmwas compressed symmetrically at a constant speed of 10 mm/min. LB films were transferred ontodifferent substrates, keeping the surface pressure constant by compression. The LB films wereexamined by tapping mode AFM.We observed that the ionization of the hydrophilic block changes the solubility of the coronachain of the surface micelles and the electrostatic interaction between the ionized chains [3-5].Depending on the pH of the subphase, the solubility of the hydrophilic chains is modified, thereforechanging the area occupied by hydrophilic chains spread on the air-water interface [6]. These resultscan be applied to the creation of ?smart? interfaces, as well as chemical nanoactuators withswitchable properties. The combined use of block copolymers as ?smart? building blocks and the LBtechnique provides new opportunities to molecularly design hybrid assemblies with controllabletransport properties that can be used for a wide range of different applications.References[1] Zhu, J.; Eisenberg, A.; Lennox, R. B. J. Am. Chem. Soc. 113, 5583 (1991).[2] Seo, Y.; Paeng, K.; Park, S. Macromolecules 34, 8735 (2001)[3] Zhang, L. F.; Yu, K.; Eisenberg, A. Science 272, 1777 (1996).[4] Martin, T. J.; Prochazka, K.; Munk, P.; Webber, S. E. Macromolecules 29, 6071 (1996).[5] Gohy, J.-F.; Antoun, S.; Jerome, R. Macromolecules 34, 7435 (2001).[6] Chung, B.; Choi, M.; Ree, M.; Jung, J.C.; Zin, W.C.; Chang, T. Macromolecules 39, 684 (2006)