Abstract
We investigated the adsorption properties of the newly synthesized, hydrophobically functionalized polyelectrolyte (HF-PE), poly(4-styrenesulfonic-co-maleic acid) copolymer (PSS/MA). The hydrophobic alkyl side chains (C12 or C16) were incorporated into the polyelectrolyte backbone via the labile amid linker to obtain the soft HF-PE product with the assumed amount of 15% and 40% degree of grafting for every length of the alkyl chain, i.e., PSS/MA-g-C12NH2 (15% or 40%) as well as PSS/MA-g-C16NH2 (15% or 40%). In the present contribution, we determined both the effect of grafting density and the length of alkyl chain on adsorption at water/air and water/decane interfaces, as well as on top of the polyelectrolyte multilayer (PEM) deposited on a solid surface. The dependence of the interfacial tension on copolymer concentration was investigated by the pendant drop method, while the adsorption at solid surface coated by poly(diallyldimethylammonium chloride)/poly(styrene sulphonate) PEM by the quartz crystal microbalance with dissipation (QCM-D), attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) and contact angle analysis. We found that surface activity of the hydrophobized copolymer was practically independent of the grafting ratio for C16 side chains, whereas, for C12, the copolymer with a lower grafting ratio seemed to be more surface active. The results of QCM-D and FTIR-ATR experiments confirmed the adsorption of hydrophobized copolymer at PEM along with the modification of water structure at the interface. Finally, it can be concluded that the hydrophobically modified PSS/MA can be successfully applied either as the efficacious emulsifier for the formation of (nano)emulsions for further active substances encapsulation using the sequential adsorption method or as one of the convenient building blocks for the surface modification materials.
Highlights
Nowadays, polyelectrolytes as classical soft-matter materials are of particular interest because they can modify many substrates at any interface, functionalize them, and convert them into various compatible forms with many solvents
As a continuation of our studies on soft HF-PEs [6,20] in the present contribution, we report our findings on adsorption behavior of newly synthesized, hydrophobically functionalized polyelectrolyte (HF-PE), i.e., decorated along its backbone with alkyl chains (C12 or C16) via the labile amid linker with the assumed amount of 15% and 40% degree
The results demonstrate that unmodified poly(4-styrenesulfonic-co-maleic acid) copolymer (PSS/MA) polyelectrolyte has no surface activity up to high concentration (5000 ppm)
Summary
Polyelectrolytes as classical soft-matter materials are of particular interest because they can modify many substrates at any interface, functionalize them, and convert them into various compatible forms with many solvents. The AT-cut, piezoelectric, gold-coated quartz sensors (14-mm diameter, 4.95-MHz fundamental resonance frequency) (Q-Sense, Biolin Scientific, Gothenburg, Sweden) were washed with piranha solution (96% H2SO4: 30% H2O2, 2:1 (v/v); 5 min) and boiled in distilled water in 80 ◦C, thoroughly rinsed with distilled water and stream-dried with air They were immersed in the solution of polycation (PDADMAC) for 15 min and rinsed in a 0.15 M NaCl solution to remove weakly adsorbed chains of polyelectrolyte from the substrate surface. The substrate was immersed in the negatively charged solution (for 15 min) of polyanion (PSS) and rinsed (0.15 M NaCl), which led to the formation of the polyelectrolyte bilayer By repeating this deposition cycle, one can obtain multilayer coatings with the desired structure and thickness. The experiment was performed according to the methodology described in [35]
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