This study aimed to reveal the interaction between selfassembled multilayers and dye molecules in the environment, which is closely related to the multilayers' stable performance and service life. In this work, the pH-responsive poly (N-isopropylacrylamide-co-2-(dimethylamino) ethyl methacrylate) microgels were prepared by free-radical copolymerization and self-assembled with sodium alginate (SA) into multilayers by the layer-by-layer deposition method. Quartz crystal microbalance (QCM) and atomic force microscopy (AFM) results confirmed the construction of multilayers and the absorbed mass, resulting in a decrease in the frequency shift of the QCM sensor and the deposition of microgel particles on its surface. The interaction between the self-assembled SA/microgel multilayers and anionic dyes in the aqueous solution was further investigated by QCM, and it was found that the electrostatic attraction between dyes and microgels deposited on the QCM sensor surface was much larger than that of the microgels with SA in multilayers, leading to the release of the microgels from the self-assembled structure and a mass loss ratio of 27.6%. AFM observation of the multilayer morphology exposed to dyes showed that 29% of the microgels was peeled off, and the corresponding microgel imprints were generated on the surface. In contrast, the shape and size of the remaining self-assembled microgel particles did not change.

In this study, a composite multilayer film onto gold was constructed from two charged building blocks, i.e., negatively charged graphene oxide (GO) and a branched polycation (polyethylenimine, PEI) via layer-by-layer (LbL) self-assembly technology, and this process was monitored in situ with quartz crystal microbalance (QCM) under different experimental conditions. This included the differences in frequency (Δf) as well as the changes in dissipation to yield information on the absorbed mass and viscoelastic properties of the formed PEI/GO multilayer films. The experimental conditions were optimized to obtain a high amount of the adsorbed mass of the self-assembled multilayer film. The surface morphology of the PEI/GO multilayer film onto gold was studied with atomic force microscopy (AFM). It was found that the positively charged PEI chains were combined with the oppositely charged GO to form an assembled film on the QCM sensor surface, in a wrapped and curled fashion. Raman and UV-vis spectra also showed that the intensities of the GO-characteristic signals are almost linearly related to the layer number. To explore the films for their use in divalent ion detection, the frequency response of the PEI/GO multilayer-modified QCM sensor to the exposure of aqueous solutions solution of Cu2+, Ca2+, Zn2+, and Sn2+ was further studied using QCM. Based on the Sauerbrey equation and the weight of different ions, the number of metal ions adsorbed per unit area on the surface of QCM sensors was calculated. For metal ion concentrations of 40 ppm, the adsorption capacities per unit area of Cu2+, Zn2+, Sn2+, and Ca2+ were found to be 1.7, 3.2, 0.7, and 4.9 nmol/cm2, respectively. Thus, in terms of the number of adsorbed ions per unit area, the QCM sensor modified by PEI/GO multilayer film shows the largest adsorption capacity of Ca2+. This can be rationalized by the relative hydration energies.

Using chemically etched stainless steel mesh (SSM) as matrix, chitosan (CS) as the hydrophilic component and acrylamide as (AAm) monomer, the underwater superoleophobic membrane (PAAm/CS@SSM) for oil-water separation was prepared by free radical polymerization initiated by ultraviolet light. The composition, morphology, underwater oil contact angle, and structure of PAAm/CS@SSM were characterized by Fourier-transform infrared spectroscopy, x-ray powder diffraction, scanning electron microscopy, and confocal laser scanning microscopy. The underwater oil contact angles of PAAm/ CS@SSM could reach 154.5 . When the number of oil-water cycles reached 20 times, the oil-water separation efficiency of PAAm/CS@SSM was larger than 99%. When the oil-water ratio is 1:3, 1:2, 1:1, 2:1, 3:1, the oil-water separation flux of PAAm/CS@SSM was 2096.8, 4457.9, 4735.7, 5395.7, and 3606.9 LÁmÁ À2 Áh À1 , respectively. When oils are n-hexane, petroleum ether, vegetable oil, and liquid paraffin, the oil-water separation efficiency of PAAm/ CS@SSM was 99.0%, 97.7%, 97.2%, and 99.3%, respectively. After the wear resistance test, the PAAm/CS@SSM membrane still exhibited underwater super-oleophobicity (>150 ).

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