Reversible Switching between Hydrophilic and Hydrophobic Superparamagnetic Iron Oxide Microspheres via One-Step Supramolecular Dynamic Dendronization: Exploration of Dynamic Wettability

Abstract

We describe the use of hydrophobic poly(aryl ether) dendrons to peripherally functionalize hydrophilic amine-containing superparamagnetic iron oxide microspheres (SPIO-NH2) in one step via imine formation. The reversible formation of imine bonds in the absence/presence of water renders dynamic control of the hydrophilicity and hydrophobicity of the microspheres (SPIO-Gn). The dynamic nature of the imine-containing dendronized microspheres (SPIO-Gn) can be "fixed" by locking the reversible 2,6-diiminopyridyl moieties with metal cations (Zn2+, Co2+, and Ni2+) to afford kinetically stable dendronized microspheres (SPIO-Gn-M). Isolation of these microspheres is facilitated by convenient magnetic separation by an externally applied magnetic field. Characterization of these novel organic-inorganic hybrid microspheres has been performed by various techniques using UV/visible absorption and Fourier transform infrared spectroscopies, transmission electron microscopy, thermogravimetric analysis, and a vibrating sample magnetometer. We have demonstrated the stability and reversible switching of hydrophilicity/hydrophobicity by contact-angle measurements. In particular, the hydrophilic SPIO-NH2 microspheres demonstrated a contact angle of 42 +/- 2 degrees when a drop of water was added to a SPIO-NH2-coated mica surface. On the other hand, the hydrophobic SPIO-Gn-M dendronized microspheres demonstrated a contact angle of 85 +/- 2 degrees , an observation that involves an increase of the contact angle of over 40 degrees . Furthermore, when a drop of water was placed on a dynamic SPIO-Gn-coated mica surface, the contact angle of the water droplet decreased in time. Comparatively, the rate of decrease of the contact angle is H2O > 1% Co(OAc)2/H2O > N,N'-dimethylformamide/H2O (1:1).

Different synthetic pathways of nanoparticle-cored dendrimers (NCDs): Effects on the properties and their application as redox active centers

“…The spectrum of APS does not present any band in the studied range, while the dendron's spectrum presents a pronounced absorbance band at 237 nm ( λ max ) and a shoulder located at 325 nm. Neither the unmodified NPs nor NPs‐APS show any absorbance bands and only indicate the scattering of light and a noticeable spectral noise, likewise in the case of functionalized magnetite microspheres reported by Leung et al In contrast, the spectra of dendronized NPs (all three NCD systems) are similar to the spectrum of the free dendron since the mentioned absorbance bands are seen, although they appear remarkably blue‐shifted to λ max ≤ 230 nm. NCD‐1 presents the lowest shifting ( λ max = 230 nm) whereas the λ max of NCD‐2 and NCD‐3 are out of the measured UV window (i.e., λ max < 200 nm).…”

Noble Metal-Iron Oxide Hybrid Nanomaterials: Emerging Applications

“…With the aim of increasing the loading amount of Au NPs on Fe 3 O 4 particles, ammonium‐functionalized Fe 3 O 4 @SiO 2 ‐ core/shell microspheres, with a shell thickness of ∼ 25 nm, were employed to investigate the immobilization efficiency. Figure a shows the TEM image of the Fe 3 O 4 @ SiO 2 ‐Au hybrids which were synthesized using the ammonium‐functionalized Fe 3 O 4 @SiO 2 ‐ microspheres (∼ 200 nm), self‐assembled electrostatically with citrate‐coated Au NPs (∼ 2 nm).…”

“…On the other hand, a core/shell hybrid structure Fe 3 O 4 @ SiO 2 ‐Ag with an Fe 3 O 4 core, a silica shell, and multiple Ag NP composite was synthesized . The preparation of Fe 3 O 4 @ SiO 2 ‐Ag nanospheres was conducted with ultrasonication using Fe 3 O 4 @SiO 2 ‐NH 2 as the template . In this process, the –NH 2 group served as a bridging adhesive between SiO 2 coating and Ag NPs.…”

“…The as‐synthesized SPIO‐polyacryate nano/microparticles, which exhibit magneto‐photonic properties, are relatively monodispersed. In particular, porous Fe 3 O 4 nanospheres, hollow Fe 3 O 4 nanospheres, Fe 3 O 4 nanospheres with mesoporous silica coating nanospheres, and hybrid nanowires/chains were synthesized successfully. Some of the structures possess spherical cores with uniform shell coatings, e.g., silica, carbon, polyaniline, and polydopamine, with controllable thicknesses, which require sophisticated, fine‐tuned synthetic procedures, which we have worked out in our laboratories.…”

Synthesis and characterization of surface-functionalized paramagnetic nanoparticles and their application to immobilization of α-acetolactate decarboxylase

“…Then, the product was collected by an external magnetic field and rinsed three times with ethanol. PMN Fe 3 O 4 @SiO 2 OH NPs were finally obtained by 24 h drying under vacuum condition at room temperature [21][22][23].…”