Poly(ethylene oxide) grafted silica nanoparticles: efficient routes of synthesis with associated colloidal stability

Temperature-Insensitive Nonpolar Suspensions of Polyoxyethylene Alkyl Ether-Grafted Silica Nanoparticles

Nonpolar suspensions of organically modified particles exhibit a strong temperature sensitivity owing to the high-temperature-induced desorption/decomposition and the low-temperature-induced disorder/order conformational transition of the modifiers. This strong temperature sensitivity limits their applications, such as lubricants and oil-based drilling fluids, which require the suspensions to operate over a wide temperature range (e.g., 0-200 °C). We hypothesize that the introduction of a flexible ethylene oxide (EO) chain into the modifiers can disrupt the low-temperature-induced ordered conformation to improve the stability of the nonpolar suspensions. In this article, nonpolar suspensions with temperature insensitivity in the range of 5-160 °C were obtained via the covalent modification of silica NPs and the introduction of EO chains into the modifier molecules. Here, octadecyl-grafted silica NPs (C18-SiO2) and polyoxyethylene alkyl ether-grafted silica NPs (AEOn-SiO2) were synthesized and subsequently dispersed in mineral oil. The rheological properties of each suspension at different temperatures were evaluated, and the thermal stability of AEOn-SiO2 in mineral oil was investigated along with the conformational changes of the grafted chains. In the temperature range of 5-160 °C, the apparent viscosity and gel strength of the C18-SiO2 suspension changed dramatically, whereas the AEOn-SiO2 suspensions exhibited constant rheological properties over this temperature range. This temperature insensitivity of AEOn-SiO2 suspensions is attributed to the excellent thermal stability of AEOn-SiO2 in mineral oil and the disordered conformation of the EO chains upon cooling. This study provides a novel approach to preparing temperature-insensitive nonpolar suspensions, which have potential applications in the petroleum and lubricant industries.

AMP coated SERS NanoTags with hydrophobic locking: Maximizing brightness, stability, and cellular targetability

Developing innovative surface-enhanced Raman scattering (SERS) nanotags continues to attract significant attention due to their unparalleled sensitivity and specificity for in vitro diagnostic and in vivo tumor imaging applications. Here, we report a new class of bright and stable SERS nanotags using alkylmercaptan-PEG (AMP) polymers. Due to its amphiphilic structure and a thiol anchoring group, these polymers strongly absorb onto gold nanoparticles, leading to an inner hydrophobic layer and an outer hydrophilic PEG layer. The inner hydrophobic layer serves to "lock in" the Raman reporter molecules adsorbed on the particle surface via favorable hydrophobic interactions that also allow denser PEG coatings, which "lock out" other molecules from competitive binding or adsorbing to the gold surface, thereby providing superior colloidal and signal stability. The higher grafting densities of AMP polymers compared to conventional thiolated PEG also led to dramatic increases in cellular target selectivity, with specific-to-nonspecific binding ratios reaching beyond an order of magnitude difference. Experimental evaluations and theoretical considerations of dielectric polarization and light scattering indicate that the hydrophobic layer provides a more favorable dielectric environment with less plasmon dampening, greater particle scattering efficiency, and increased Raman reporter polarizability. Accordingly, SERS nanotags with AMP polymer coatings are observed to be considerably brighter (∼10-fold). Furthermore, the AMP-coated SERS nanotag's increased intensity and avidity can boost cellular detection sensitivity by nearly two orders of magnitude.

New Crosslinked Single-Ion Silica-PEO Hybrid Electrolytes

New single-ion hybrid electrolytes have been synthetized via an original and simple synthetic approach combining Michael addition, epoxidation, and sol-gel polycondensation. We designed an organic PEO network as a matrix for the lithium transport, mechanically reinforced thanks to crosslinking inorganic (SiO_1.5) sites, while highly delocalized anions based on lithium vinyl sulfonyl(trifluoromethane sulfonyl)imide (VSTFSILi) were grafted onto the inorganic sites to produce single-ion hybrid electrolytes (HySI). The influence of the electrolyte composition in terms of the inorganic/organic ratio and the grafted VSTFSILi content on the local structural organization, the thermal, mechanical, and ionic transport properties (ionic conductivity, transference number) are studied by a variety of techniques including SAXS, DSC, rheometry, and electrochemical impedance spectroscopy. SAXS measurements at 25 °C and 60 °C reveal that HySI electrolyte films display locally a spatial phase separation with domains composed of PEO rich phase and silica/VSTFSILi clusters. The size of these clusters increases with the silica and VSTFSILi content. A maximum ionic conductivity of 2.1 × 10^-5 S·cm^-1 at 80 °C has been obtained with HySI having an EO/Li ratio of 20. The Li⁺ ion transfer number of HySI electrolytes is high, as expected for a single-ion electrolyte, and comprises between 0.80 and 0.92.

Dynamics of Polymer Chains in Poly(ethylene oxide)/Silica Nanocomposites via a Combined Computational and Experimental Approach

The dynamics of polymer chains in poly(ethylene oxide)/silica (PEO/SiO₂) nanoparticle nanohybrids have been investigated via a combined computational and experimental approach involving atomistic molecular dynamics simulations and dielectric relaxation spectroscopy (DRS) measurements. The complementarity of the approaches allows us to study systems with different polymer molecular weights, nanoparticle radii, and compositions across a broad range of temperatures. We study the effects of spatial confinement, which is induced by the nanoparticles, and chain adsorption on the polymer's structure and dynamics. The investigation of the static properties of the nanocomposites via detailed atomistic simulations revealed a heterogeneous polymer density layer at the vicinity of the PEO/SiO₂ interface that exhibited an intense maximum close to the inorganic surface, whereas the bulk density was reached for distances ∼1-1.2 nm away from the nanoparticle. For small volume fractions of nanoparticles, the polymer dynamics, probed by the atomistic simulations of low-molecular-weight chains at high temperatures, are consistent with the presence of a thin adsorbed layer that exhibits slow dynamics, with the dynamics far away from the nanoparticle being similar to those in the bulk. However, for high volume fractions of nanoparticles (strong confinement), the dynamics of all polymer chains were predicted slower than that in the bulk. On the other hand, similar dynamics were found experimentally for both the local β-process and the segmental dynamics for high-molecular-weight systems measured at temperatures below the melting temperature of the polymer, which were probed by DRS. These differences can be attributed to various parameters, including systems of different molecular weights and nanoparticle states of dispersion, the different temperature range studied by the different methods, the potential presence of a reduced-mobility PEO/SiO₂ interfacial layer that does not contribute to the dielectric spectrum, and the presence of amorphous-crystalline interfaces in the experimental samples that may lead to a different dynamical behaviors of the PEO chains.

One-Step Preparation of Highly Stable Copper-Zinc Ferrite Nanoparticles in Water Suitable for MRI Thermometry

Superparamagnetic ferrite nanoparticles coated with a polymer layer are widely used for biomedical applications. The objective of this work is to design nanoparticles as a magnetic resonance imaging (MRI) temperature-sensitive contrast agent. Copper-zinc ferrite nanoparticles coated with a poly(ethylene glycol) (PEG) layer are synthesized using a one-step thermal decomposition method in a polymer matrix. The resulting nanoparticles are stable in water and biocompatible. Using Mössbauer spectroscopy and magnetometry, it was determined that the grown nanoparticles exhibit superparamagnetic properties. Embedding these particles into an agarose gel resulted in significant modification of water proton relaxation times T 1, T 2, and T 2* determined by nuclear magnetic resonance measurements. The results of the spin-echo T 2-weighted MR images of an aqueous phantom with embedded Cu0.08Zn0.54Fe2.38O4 nanoparticles in the presence of a strong temperature gradient show a strong correlation between the temperature and the image intensity. The presented results support the hypothesis that CuZn ferrite nanoparticles can be used as a contrast agent for MRI thermometry.