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• The novel functional microgels (PNI-MSPC) were synthesized, which exhibited thermo-sensitivity, redox actuatable size and fluorescence. • The PNI-MSPC microgels can be used as the fluorescent sensor for ultrasensitive and selective detection of MnO 4 − anions in aqueous solution. • The limit of detection for MnO 4 − anions was about 25 nM with a fast response time of 5 min and a linear concentration range of 0–50 μM. The novel functional microgels, namely PNI-MSPC microgels, were fabricated via surfactant free emulsion polymerization (SFEP) by using N -isopropylacrylamide (NIPAm) as the monomer and a home-designed dichlorinated 1,1′-di[4-(vinyl)benzyl]-4,4′-pyridinium salt (MSPC2+.2Cl−) as the cross-linker. The PNI-MSPC microgels exhibited not only thermo-sensitivity but also redox actuatable hydrodynamic diameter and fluorescence properties. The PNI-MSPC microgels were successfully applied as the fluorescent sensor for ultrasensitive and selective detection of trace MnO 4 - anions in aqueous solutions. The presence of MnO 4 - anions led to the significant fluorescence quenching of the PNI-MSPC microgels with a fast response time of 5 min. The limit of detection (D L) for MnO 4 - anions can reach 25 nM with a linear concentration range of 0–50 μM. The co-existence of 16 other species of anions or 17 species of metal ions did not interfere with the detection of trace MnO 4 - anions in aqueous solutions. The potential applications of the PNI-MSPC microgels for sensing trace MnO 4 - anions in real world samples were also validated. [ABSTRACT FROM AUTHOR]

[Display omitted] • MXene@Fe 3 O 4 @PNA reduce the COF of water from 0.559 to 0.218, the wear volume decreased by 78.7%. • The excellent lubricating properties are attributed to the tribofilm and hydration layer. • MXene@Fe 3 O 4 @PNA can be heated to 73.1 °C and 123 °C in water and dry state under infrared light. Improving the tribological performance of water via designing nanomaterials as lubricant additive has garnered mounting interest. In this work, the poly-(N-isopropylacrylamide) microgel is grafted onto Fe 3 O 4 nanoparticles surface (Fe 3 O 4 @PNA) via free radical polymerization. Then, the Fe 3 O 4 @PNA can self-anchored on the MXene nanosheets via hydrogen bonding interaction to obtain MXene@Fe 3 O 4 @PNA composite. The as-prepared MXene@Fe 3 O 4 @PNA can effectively reduce friction and wear when used as a water-based lubricant additive. Compared with pure water, the average coefficient of friction (COF) and wear volume decrease by 61% and 78.7%, respectively. The lubrication mechanism was analyzed by focused ion beam technique-TEM (FIB-TEM) and X-ray photoelectron spectroscopy (XPS). The outstanding tribological performance of MXene@Fe 3 O 4 @PNA is attributed to the synergistic lubrication effect of MXene and Fe 3 O 4 @PNA. Interlayer shear of MXene and spherical Fe 3 O 4 @PNA can make MXene@Fe 3 O 4 @PNA play a full role of sliding friction and rolling friction mechanism, which can induce tribo-chemical reactions to form a protective film on the contact area of the friction pair. In addition, the hydrophilic groups of the MXene@Fe 3 O 4 @PNA can adsorb a large number of water molecules and form a hydration layer, reducing the agglomeration of nanosheets and acting as a boundary lubrication film. Moreover, the as-prepared MXene@Fe 3 O 4 @PNA exhibit excellent photothermal conversion performance in both underwater environment and dry state. Based on this characteristic, infrared light can be collected efficiently and stored quickly. Then, convert and utilize it. Therefore, the multifunctional MXene@Fe 3 O 4 @PNA has a broad application prospect as a water-based intelligent lubrication additive. [ABSTRACT FROM AUTHOR]

A highly selective and sensitive optical sensor was developed to colorimetric detect trace Fe3+ ions in aqueous solution. The sensor was the sulfasalazine (SSZ) functionalized microgels (SSZ-MGs), which were fabricated via in-situ quaternization reaction. The obtained SSZ-MGs had hydrodynamic radius of about 259 ± 24 nm with uniform size distribution at 25 °C. The SSZ-MG aqueous suspensions can selectively and sensitively response to Fe3+ ions in aqueous solution at 25 °C and pH of 5.6, which can be quantified by UV-visible spectroscopy and also easily distinguished by the naked eye. Job’s plot indicated that the molar binding ratio of SSZ moiety in SSZ-MGs to Fe3+ was close to 1:1 with an apparent association constant of 1.72 × 104 M−1. A linear range of 0−12 μM with the detection limit of 0.110 μM (0.006 mg/L) was found. The obtained detection limit was much lower than the maximum allowance level of Fe3+ ions in drinking water (0.3 mg/L) regulated by the Environmental Protection Agency (EPA) of the United States. The existence of 19 other species of metal ions, namely, Ag+, Li+, Na+, K+, Ca2+, Ba2+, Cu2+, Ni2+, Mn2+, Pb2+, Zn2+, Cd2+, Co2+, Cr3+, Yb3+, La3+, Gd3+, Ce3+, and Bi3+, did not interfere with the detection of Fe3+ ions.

Abstract: The electrophoretic mobility of thermosensitive poly(N-isopropylacrylamide) (PNIPAM) microgels, functionalized to contain the same bulk carboxylic acid content using acrylic acid (AA), methacrylic acid (MAA), vinylacetic acid (VAA) and acrylamide hydrolyzed in situ (H-AM), is fit to the soft particle mobility model developed by Ohshima. Good model fits were achieved for experimental mobility data as a function of both ionic strength and temperature. The model deconvolutes the underlying contributions to soft particle mobility, identifying large morphology differences between microgels with similar absolute mobility values (i.e. AA-NIPAM and VAA-NIPAM). The differences in the predicted morphologies can be correlated to the physical properties of the carboxylic acid-containing comonomers and independent light scattering data. Theoretical softness models significantly overestimate the best-fit softness of the microgels but give reasonable estimates of how the softness changes as a function of temperature. Based on simultaneous comparisons of the best-fit softness, volumetric charge density, mobility, and particle size profiles, functionalized microgels appear to deswell primarily through a consecutive core-shell mechanism. [Copyright &y& Elsevier]

As a micro-/nano-sized hydrogel, polymeric microgel not only has three-dimensional (3D) molecular networks but also displays the small-size effect, which has been widely used in various fields, such as drug nanocarrier, photonic crystal, functional coating, and aqueous lubrication. In this work, a photothermal lubricating coating was prepared using polymeric/inorganic hybrid microgels and its surficial friction was deliberately modulated by the remote irradiation of near-infrared (NIR) light. Specifically, a photothermal hybrid microgel, Fe 3 O 4 @poly( N -isopropylacrylamide- co -polyacrylic acid) (Fe 3 O 4 @PNA), was first fabricated and then sprayed onto poly(ethyleneimine) (PEI)-modified substrate to form a lubricating microgel coating. At room temperature, this microgel coating was hydrophilic and achieved good hydration lubrication with relatively low friction. After the introduction of NIR light, the photothermal microgel coating converted light energy into heat energy for increasing its own temperature rapidly. Due to the thermosensitive PNA shell, the wettability of the coating was transformed to hydrophobicity above the lower critical solution temperature (LCST), resulting in a remarkable increase in friction. In other words, the surficial friction of this microgel coating could be reversibly modulated using NIR light. This work expands the application scope of microgels in the field of aqueous lubrication and introduces the functional microgels into making the smart lubricating coating for the first time. This basic research in the field of friction control may provide an efficient strategy for the design of interfacial sensing, controlled transmission, and intelligent manipulator.

A highly selective and sensitive optical sensor was developed to colorimetric detect trace Fe3+ ions in aqueous solution. The sensor was the sulfasalazine (SSZ) functionalized microgels (SSZ-MGs), which were fabricated via in-situ quaternization reaction. The obtained SSZ-MGs had hydrodynamic radius of about 259 ± 24 nm with uniform size distribution at 25 °C. The SSZ-MG aqueous suspensions can selectively and sensitively response to Fe3+ ions in aqueous solution at 25 °C and pH of 5.6, which can be quantified by UV-visible spectroscopy and also easily distinguished by the naked eye. Job's plot indicated that the molar binding ratio of SSZ moiety in SSZ-MGs to Fe3+ was close to 1:1 with an apparent association constant of 1.72 × 104 M−1. A linear range of 0–12 μM with the detection limit of 0.110 μM (0.006 mg/L) was found. The obtained detection limit was much lower than the maximum allowance level of Fe3+ ions in drinking water (0.3 mg/L) regulated by the Environmental Protection Agency (EPA) of the United States. The existence of 19 other species of metal ions, namely, Ag+, Li+, Na+, K+, Ca2+, Ba2+, Cu2+, Ni2+, Mn2+, Pb2+, Zn2+, Cd2+, Co2+, Cr3+, Yb3+, La3+, Gd3+, Ce3+, and Bi3+, did not interfere with the detection of Fe3+ ions. [ABSTRACT FROM AUTHOR]