Adsorption of PEO-PPO-PEO Triblock Copolymers with End-Capped Cationic Chains of Poly(2-dimethylaminoethyl methacrylate)

We study the adsorption of a symmetric triblockcopolymer of ethylene oxide, EO, and propylene oxide, PO, end-capped with quarternized poly(2-dimethylaminoethylmethacrylate), DMAEMA (DMAEMA24 EO132PO50EO132 DMAEMA24). Light scattering and tensiometry are used tomeasure the relative size of the associated structures and surfaceexcess at the air liquid interface. The adsorbed amount, theamount of coupled water, and the viscoelasticity of the adsorbedpolymer layer are measured on hydrophobic and hydrophilicsurfaces (polypropylene, cellulose, and silica) by using quartz crystal microgravimetry (QCM) and surface plasmon resonance(SPR) at different ionic strengths and temperatures. The results of the experiments are compared with those obtained afteradsorption of the uncharged precursor copolymer, without the cationic end-caps (EO132PO50EO132). DMAEMA24 EO132PO50-EO132 DMAEMA24 possesses higher affinity with the negatively charged silica and cellulose surfaces while the unchargedcopolymer adsorbs to a larger extent on polypropylene surfaces. In this latter case, adsorption increases with increasing solutionionic strength and temperature. Adsorption of EO132PO50EO132 on silica surfaces has little effect on the water contact angle (WCA),while adsorption ofDMAEMA24 EO132PO50EO132 DMAEMA24 increases theWCA of silica to 32 , indicating a large density ofexposed PPO blocks upon adsorption. After adsorption of EO132PO50EO132 and DMAEMA24 EO132PO50EO132 DMAEMA24on PP, the WCA is reduced by ≈14 and ≈28 , respectively, due to the exposed hydrophilic EO and highly water-solubleDMAEMA segments on the surfaces. The extent of surface coverage at saturation at the polypropylene/liquid interfaces (≈31 and40 nm2/molecule obtained byQCMand SPR, respectively) is much lower, as expected, when compared with results obtained at theair/liquid interface, where a tighter packing is observed. The percentage of water coupled to the adsorbed cationic polymer decreaseswith solution ionic strength. Overall, these observations are ascribed to the effects of electrostatic screening, polymer hydrodynamicsize, and solvency.

Publication year: 2011
Authors: Xiaomeng Liu†, Arja-Helena Vesterinen§, Jan Genzer‡, Jukka V. Seppälä§, and Orlando J. Rojas*†∥
Affiliations:
† Department of Forest Biomaterials and ‡ Department of Chemical & Bimolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States
Faculty of Chemistry and Materials Sciences, Department of Biotechnology and Chemical Technology, Aalto University, P.O. Box 16100, FI-00076 Aalto, Finland
Faculty of Chemistry and Materials Sciences, Department of Forest Products Technology, Aalto University, P.O. Box 16300, FI-00076, Aalto, Finland
Published in: Langmuir, 2011, Vol. 27 (16), p. 9769–9780
DOI: 10.1021/la201596x

MP-SPR KEYWORDS

adsorption cellulose hydrophilic hydrophobic ionic strength polypropylene QCM silica SPR surface temperature water amount
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