Enthalpy-Driven Stabilization of Dispersions of Polymer-Grafted Nanoparticles in High-Molecular-Weight Polymer Melts

Competing Effects of Temperature and Polymer Concentration on Evolution of Re-entrant Interactions in the Nanoparticle-Block Copolymer System

An interesting evolution of the re-entrant interaction has been observed in an anionic silica nanoparticle (NP)-block copolymer (P85) dispersion due to mutually competing effects of temperature and polymer concentration. It has been demonstrated that a rise in the temperature leads to an evolution of attraction in the system, which interestingly diminishes on increasing the polymer concentration. Consequently, the system exhibits a re-entrant transition from repulsive to attractive and back to repulsive at a given temperature but with respect to the increasing polymer concentration, within a selected region of concentration and temperature. The intriguing observations have been elucidated based on the temperature/concentration-dependent modifications in the interactions governing the system, as probed by contrast-variation small-angle neutron scattering. The initial transition from the repulsive to attractive system is attributed to the temperature-driven enhancement in the hydrophobicity of the amphiphilic triblock copolymer (P85) adsorbed on nanoparticles. The strength and range of this attraction are found to be more than van der Waals attraction while relatively less than electrostatic interaction. At higher polymer concentrations, the saturation of polymer adsorption on nanoparticles introduces additional steric repulsion along with electrostatic interaction between their conjugates, effectively reducing the strength of the attraction. However, with a significant increase in temperature (>75 °C), the attraction again dominates the system, which eventually leads to the particle aggregation at all the measured polymer concentrations (>0.1 wt %). Our study provides useful inputs to develop smart NP-polymer composites having capabilities to respond to external stimuli such as temperature/concentration variation.

Structure and Evolution of Quasi-Solid-State Hybrid Electrolytes Formed Inside Electrochemical Cells

Solid-state electrolytes (SSEs) formed inside an electrochemical cell by polymerization of a liquid precursor provide a promising strategy for overcoming problems with electrolyte wetting in solid-state batteries. Hybrid solid-state polymer electrolytes (HSPEs) created by in situ polymerization of a conventional liquid precursor containing electrochemically inert nanostructures are of particular interest because they offer a mechanism for selectively reinforcing or adding new functionalities to the electrolyte-removing the need for high degrees of polymerization. The synthesis, structure, chemical kinetics, ion-transport properties and electrochemical characteristics of HSPEs created by Al(OTf)₃ -initiated polymerization of 1,3-dioxolane (DOL) containing hairy, nano-sized SiO₂  particles are reported. Small-angle X-ray scattering reveals the particles are well-dispersed in liquid DOL. Strong interaction between poly(ethylene glycol) molecules tethered to the SiO₂  particles and poly(DOL) lead to co-crystallization-anchoring the nanoparticles in their host It also enables polymerization-depolymerization processes in DOL to be studied and controlled. The utility of the in-situ-formed HSPE, is demonstrated first in Li|HSPE|Cu half cells, which manifest Coulombic efficiencies (CE) values approaching 99%. HSPEs are also demonstrated in solid-state lithium-sulfur-polyacrylonitrile (SPAN) composite full-cell batteries. The in-situ-formed Li|HSPE|SPAN cells show good cycling stability and thus provide a promising path toward all-solid-state batteries.

Dynamic Mixing Behaviors of Ionically Tethered Polymer Canopy of Nanoscale Hybrid Materials in Fluids of Varying Physical and Chemical Properties

An emerging area of sustainable energy and environmental research is focused on the development of novel electrolytes that can increase the solubility of target species and improve subsequent reaction performance. Electrolytes with chemical and structural tunability have allowed for significant advancements in flow batteries and CO₂ conversion integrated with CO₂ capture. Liquid-like nanoparticle organic hybrid materials (NOHMs) are nanoscale fluids that are composed of inorganic nanocores and an ionically tethered polymeric canopy. NOHMs have been shown to exhibit enhanced conductivity making them promising for electrolyte applications, though they are often challenged by high viscosity in the neat state. In this study, a series of binary mixtures of NOHM-I-HPE with five different secondary fluids, water, chloroform, toluene, acetonitrile, and ethyl acetate, were prepared to reduce the fluid viscosity and investigate the effects of secondary fluid properties (e.g., hydrogen bonding ability, polarity, and molar volume) on their transport behaviors, including viscosity and diffusivity. Our results revealed that the molecular ratio of secondary fluid to the ether groups of Jeffamine M2070 (λ_SF) was able to describe the effect that secondary fluid has on transport properties. Our findings also suggest that in solution, the Jeffamine M2070 molecules exist in different nanoscale environments, where some are more strongly associated with the nanoparticle surface than others, and the conformation of the polymer canopy was dependent on the secondary fluid. This understanding of the polymer conformation in NOHMs can allow for the better design of an electrolyte capable of capturing and releasing small gaseous or ionic species.

Alignment of Nanoplates in Lamellar Diblock Copolymer Domains and the Effect of Particle Volume Fraction on Phase Behavior

Polymer nanocomposites (PNCs) that employ diblock copolymers (BCPs) to organize and align anisotropic nanoparticles (NPs) have the potential to facilitate self-assembling hierarchical structures. However, limited studies have been completed to understand the parameters that guide the assembly of nonspherical NPs in BCPs. In this work, we establish a well-defined nanoplate system to investigate the alignment of two-dimensional materials in a lamellar-forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) BCP with domains oriented parallel to the substrate. Monodisperse gadolinium trifluoride rhombic nanoplates doped with ytterbium and erbium [GdF₃:Yb/Er (20/2 mol %)] are synthesized and grafted with phosphoric acid functionalized polyethylene glycol (PEG-PO₃H₂). Designed with chemical specificity to one block, the nanoplates align in the PMMA domain at low volume fractions (ϕ = 0.0083 and ϕ = 0.017). At these low NP loadings, the BCP lamellae are ordered and induce preferential alignment of the GdF₃:Yb/Er nanoplates. However, at high volume fractions (ϕ = 0.050 and ϕ = 0.064), the BCP lamellae are disordered with isotropically dispersed nanoplates. The transition from an ordered BCP system with aligned nanoplates to a disordered BCP with unaligned nanoplates coincides with the calculated overlap volume fraction, ϕ* = 0.051, where the pervaded space of the NPs begins to overlap. Two phenomena are observed in the results: the effect of lamellar formation on nanoplate orientation and the overall phase behavior of the PNCs. The presented research not only expands our knowledge of PNC phase behavior but also introduces a framework to further study the parameters that affect nanoplate alignment in BCP nanocomposites. Our ability to control anisotropic NP orientation in PNCs through self-assembling techniques lends itself to creating multifunctional materials with unique properties for various applications such as photovoltaic cells and barrier coatings.

Quantifying the dispersion quality of partially aggregated colloidal dispersions by high frequency rheology

An important parameter for the performance of nanomaterials is the degree by which the nanoparticles are dispersed in a matrix. Optical microscopy or scattering methods are useful to characterise the state of dispersion, but are not generally applicable to all materials. Electron microscopy methods are laborious in preparation and typically offer only quantitative information on a very local scale. In the present work we investigate how high frequency rheological measurements can be used for partially dispersed suspensions at intermediate to higher particle loadings, even for high viscous matrices. Although the contribution of the particles is particularly visible in the low frequency linear viscoelastic behaviour, a more direct relationship between rheological properties and degree of dispersion can be derived from the loss modulus in the high frequency limit. To this end, a home-built piezo shear rheometer is constructed to extend the frequency range typically accessible by commercial rotational rheometers. Measurements on spherical silica particles, with a varying degree of dispersion in low molecular weight PDMS, are used to demonstrate how high frequency rheometry can be used to quantify dispersion quality. The linear viscoelastic properties are compared to analytical scaling theories to demonstrate that a hydrodynamically dominated regime is reached. The dependence of the relative high frequency loss modulus on volume fraction is then compared to predictions of a hydrodynamic viscosity model for the derivation of a dispersion quality index. It is used to follow the evolution of the dispersion quality as a function of mixing time and consumed power.

Diameter-controlled Cu nanoparticles on saponite and preparation of film by using spontaneous phase separation

Cu nanoparticles have attracted much attention due to their optical, catalytic, and electrical properties.