Abstract
Cationic and anionic block copolymer worms are prepared by polymerization-induced self-assembly via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion copolymerization of 2-hydroxypropyl methacrylate and glycidyl methacrylate (GlyMA), using a binary mixture of a nonionic poly(ethylene oxide) macromolecular RAFT agent and either a cationic poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) or an anionic poly(potassium 3-sulfopropyl methacrylate) macromolecular RAFT agent. In each case, covalent stabilization of the worm cores was achieved via reaction of the epoxide groups on the GlyMA repeat units with 3-mercaptopropyltriethoxysilane. Aqueous electrophoresis studies indicated a pH-independent mean zeta potential of +40 mV and −39 mV for the cationic and anionic copolymer worms, respectively. These worms are expected to mimic the rigid rod behavior of water-soluble polyelectrolyte chains in the absence of added salt. The kinetics of adsorption of the cationic worms onto a planar anionic silicon wafer was examined at pH 5 and was found to be extremely fast at 1.0 w/w % copolymer concentration in the absence of added salt. Scanning electron microscopy (SEM) analysis indicated that a relatively constant worm surface coverage of 16% was achieved at 20 °C for adsorption times ranging from just 2 s up to 2 min. Furthermore, the successive layer-by-layer deposition of cationic and anionic copolymer worms onto planar surfaces was investigated using SEM, ellipsometry, and surface zeta potential measurements. These techniques confirmed that the deposition of oppositely charged worms resulted in a monotonic increase in the mean layer thickness, with a concomitant surface charge reversal occurring on addition of each new worm layer. Unexpectedly, two distinct linear regimes were observed when plotting the mean layer thickness against the total number of adsorbed worm layers, with a steeper gradient (corresponding to thicker layers) being observed after the deposition of six worm layers.
Highlights
Following seminal work by Decher,[1−3] layer-by-layer (L-b-L) deposition of oppositely charged polyelectrolytes has become increasingly popular for the convenient preparation of functional multilayers at either planar surfaces or colloidal interfaces under exceptionally mild conditions.[4−8] In essence, the L-b-L technique involves alternately immersing the desired substrate into successive aqueous solutions of anionic and cationic polyelectrolytes with intermediate washing steps.[9]
A PEO113 macro-Chain Transfer Agents (CTAs) is instead prepared via esterification of a hydroxy-capped poly(ethylene oxide) (PEO) methyl ether using 4-cyano-4-(2-phenylethanesulfanylthiocarbonyl)sulfanylpentanoic acid (PETTC).[67]
Kinetic studies indicated that the electrostatic adsorption of cationic worms from an aqueous solution onto a clean bare anionic planar silicon wafer was complete within just a few seconds at 20 °C, the final surface coverage achieved for this first layer was only 16% as determined by ImageJ analysis
Summary
Following seminal work by Decher,[1−3] layer-by-layer (L-b-L) deposition of oppositely charged polyelectrolytes has become increasingly popular for the convenient preparation of functional multilayers at either planar surfaces or colloidal interfaces under exceptionally mild conditions (e.g., aqueous solution, neutral pH, and ambient temperature).[4−8] In essence, the L-b-L technique involves alternately immersing the desired substrate into successive aqueous solutions of anionic and cationic polyelectrolytes with intermediate washing steps.[9]. The mean square error (MSE) of this measurement was relatively low at 1.40, which validates the data fit for the experimental ψ and Δ values against the native oxide model within the CompleteEASE modeling software (MSE values of less than 2 indicate satisfactory fits to the model used).[85] Second, the kinetics of cationic worm adsorption onto a clean silicon wafer (1.0 w/w %, pH 5, 20 °C, and no added salt) was monitored via ellipsometry to determine the dry worm layer thickness.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
