Layered organosilicate nanoparticles with liquidlike behavior

Spectroscopic Investigation of Entropic Canopy-Canopy Interactions of Nanoparticle Organic Hybrid Materials

Nanoparticle organic hybrid materials (NOHMs) are self-suspended liquid-like nanoparticle-based functional materials consisting of a surface-functionalized inorganic nanocore and oligomeric or polymeric chains. They often exhibit complex intermolecular and intramolecular interactions among their constituents, resulting in versatile physicochemical characteristics that range from glassy solids to solvent-free nanoparticle fluids. A variety of applications involving NOHMs have been investigated thus far, including thermal management fluids, lubricants, magnetic fluids, nanocomposites, electrolytes, water treatment and biomass pretreatment chemicals, and CO₂ capture solvents. In particular, NOHMs have recently been recognized as a promising CO₂ capture and utilization medium. To capture CO₂ more effectively, a variety of specific functional groups of strong chemical affinity to CO₂ can be added to the polymeric canopy (enthalpic contribution), and various steric considerations induced by attractive/repulsive interactions among the nanocores and canopies can be introduced (entropic contribution). These occur while maintaining negligible vapor pressure and enhanced thermal stability. Here, we investigated the canopy dynamics of NOHMs with different-sized SiO₂ nanocores, aiming to reveal the hidden nature of the entropic interaction occurring in NOHMs. Pulse-field gradient nuclear magnetic resonance spectroscopy (with ¹H) was employed to investigate the canopy dynamics of the NOHMs synthesized using 7, 12, and 22 nm SiO₂ particles, and these results were compared with those from a ternary mix of all three sizes of SiO₂ nanocores. The self-diffusion coefficient and thermal diffusivity were also evaluated.

Composite proton exchange membranes produced using chitosan and kaolin solvent-free fluid

In this study, composite membranes produced by combining both biopolymer chitosan (CS) and kaolin solvent-free fluid (kaolin-SF) were used as substitutes for the electrolyte membranes in direct-methanol fuel cells. To improve the interfacial morphologies between organic and inorganic substances, kaolin-SF was prepared using the ion exchange method. Subsequently, kaolin-SF of various doping proportions was mixed with CS crosslinked with sulfuric acid to produce thin membranes. The results of heat exhaustion and scanning electron microscope image analysis indicated that kaolin-SF was successfully doped into the CS polymer substrates, and this addition enhanced the thermal stability and mechanical properties of the CS polymer substrates. As long as the concentration of kaolin-SF was below 5 wt.%, the water absorption rate and proton conductivity of the CS/kaolin-SF composite membranes increased along with the kaolin-SF content. These results indicate that CS/kaolin-SF composite membranes are suitable for practical applications.

PU nanocomposites from bifunctional nanoparticles: impact of liquid interphase on mechanical properties

The Fe₃O₄@Poly(1,4-butanediol)/polyurethane nanocomposite is a highly interphase-dependable material with unique characteristics. Firstly, the nanoparticle's organic shell allows simple fabrication of very well dispersed nanocomposites and the incorporation of extremely high amounts of nanoparticles (NP) into the polymer matrix. Secondly, both chemical and physical aspects of the nanoparticles determine the material's mechanical behavior. The chemical functionality of the organic layer - free hydroxyl groups at the end of the tethered chains - ensures the material's stiffening through covalent bonds with the matrix, while being at molten state provides high flexibility and deformability yet maintaining mechanical resistance. As a result, nanocomposites at the low concentration region show increased elastic modulus and tensile strength and slight increase in total strain, while highly concentrated nanocomposites show reduction of elastic modulus and tensile strength and roughly double the total strain. The combination of the chemical and physical functionalities ensures high compatibility between nanoparticles and matrix and allows the production of highly concentrated - above 90% in weight - nanocomposites as a cohesive and flexible material, instead of a brittle wafer. This bifunctionality effect is unprecedented and the results open a wide range of new possibilities in the tailoring of functional nanomaterials for all sorts of applications in materials science.

In situ formation of surface-functionalized ionic calcium carbonate nanoparticles with liquid-like behaviours and their electrical properties

This paper reports a new route to synthesize calcium carbonate (CaCO₃)-based nanoscale ionic materials (NIMs) via an in situ formation method to form the CaCO₃ nanoparticles with a polysiloxane quaternary ammonium salt (PQAC) corona (PQAC-CaCO₃ nanoparticles), followed by an ionic exchange reaction to fabricate a poly(ethylene glycol)-tailed sulfonate anion (NPEP) canopy. The chemical compositions and structures of the CaCO₃-based NIMs synthesized in this work were confirmed by Fourier-transform infrared spectroscopy and solid-state ¹³C NMR spectroscopy. Transmission electron microscopic observation indicated that the CaCO₃-based NIMs presented a rhombohedral shape with a well-defined core-shell structure, and they also obtained an NPEP canopy with a thickness of 4-6 nm. X-ray powder diffraction investigation confirmed that the CaCO₃ inner core had a calcite crystalline structure, whereas the NPEP canopy was amorphous. The NPEP canopy was found to show a characteristic crystallization-melting behaviour in the presence of the ion bonding with PQAC-CaCO₃ nanoparticles according to the characterization of differential scanning calorimetry. Thermogravimetric analysis indicated that the CaCO₃-based NIMs achieved a high content of NPEP canopy as well as an improvement in thermal stability owing to the ion-bonding effect. Most of all, the CaCO₃-based NIMs demonstrated a liquid-like behaviour above the critical temperature in the absence of solvent. Moreover, the CaCO₃-based NIMs also showed a relatively high electrical conductivity with a temperature dependency due to the ionic conductive effect. This work will provide a more feasible and energy-saving methodology for the preparation of CaCO₃-based NIMs to promote their industrialization and extensive applications.

Enhanced viscoelastic property of iron oxide nanoparticle decorated organoclay fluid under magnetic field

Stable hydrophobic nanocomposites of magnetic nanoparticles and clay are prepared by the self-assembly of magnetite (Fe₃O₄) nanoparticles on surfaces of exfoliated clay platelets. Due to the attractive interaction between hydrophobic groups, oleic acid coated nanoparticles are strongly attached to the surface of cetyl trimethylammonium cation coated clay platelets in organic media. Crystal structure and magnetic property of composite particles are examined using electron microscopy, x-ray diffractometer and vibration sample magnetometer. In addition, composite particles are dispersed in mineral oil and rheological properties of composite particle suspensions are characterized using steady-state and oscillatory measurements. Magnetite nanoparticle decorated organoclay forms a tunable network in mineral oil. When a magnetic field is applied, the composite particle fluid exhibits higher storage modulus and maintains a solid-like property at larger strain. Our results show that the viscoelastic property of the magnetite nanoparticle decorated organoclay fluid is controlled by applying external magnetic field.

Functionalized alginate with liquid-like behaviors and its application in wet-spinning

Alginate is a kind of marine-derived plant polysaccharide with useful properties including inherent flame-retardancy and biocompatibility, yet poor flowability and low processing efficiency induced by high viscosity impede its further industrial applications. In this study, PEG-substituted tertiary amines were adapted to functionalize alginate with different molecular weight via acid-base reaction to improve the flowability. Based on alginate with low molecular weight, alginate fluids exhibited excellent flowability at room temperature in the absence of solvent. For alginate with high molecular weight, gelatinous precipitated phase exhibited significant shear-thinning properties and higher solid content despite lack of solvent-free flowability, which was applied to wet-spinning. The alginate fibers exhibited increased tensile strength by 104% and elongation at break by 132% compared with conventional alginate fibers, and the spinning efficiency was significantly improved. The proposed strategy is expected to extend to highly efficient processing of other polysaccharides to obtain high-performance biomedical materials.

Solid polymer electrolyte based on ionic bond or covalent bond functionalized silica nanoparticles

This article reports a solid polymer electrolyte based on ionic bond or covalent bond functionalized silica nanoparticles for lithium ion batteries.

Structural changes of layered alkylsiloxanes during the reversible melting-solidification process

Through various in situ analyses, we have revealed the structural changes that occur during the reversible melting-solidification process of layered alkylsiloxanes (CnLSiloxanes) with carbon numbers (n) of 18 and 16. In situ high-resolution solid-state (13)C nuclear magnetic resonance (NMR) analysis at controlled temperatures indicates drastic conformational changes of the long alkyl chains during the melting-solidification process. A (13)C NMR signal at 33 ppm, which shows the highest intensity at room temperature (RT), is assigned to an inner methylene group with an all-trans conformation. As the temperature increases, the 33-ppm signal intensity decreases while the signal intensity at 30.5 ppm simultaneously increases. The 30.5 ppm signal is assigned to an inner methylene group with a trans-gauche conformation. Subsequently, upon cooling, the signal at 33 ppm recovers, even after CnLSiloxanes have melted. In situ X-ray diffraction measurements at controlled temperatures reveal that the ordered arrangement of the long alkyl chains becomes disordered with elevating temperatures and reordered upon cooling to RT. In situ high-resolution solid-state (29)Si NMR analysis shows that the melting-solidification process progresses without any structural change in siloxane sheets of the CnLSiloxanes. Thus, the in situ analyses show that disordering of the long alkyl chains causes the CnLSiloxanes to melt. Because the majority of long alkyl chains are packed again in the ordered arrangement with the all-trans conformation upon cooling, the CnLSiloxanes are reversibly solidified and the CnLSiloxane structure is recovered.

Interfacial and bulk nanostructure of liquid polymer nanocomposites

Liquid polymer nanocomposites (l-PNCs) have been prepared using silica nanoparticles with diameters of 15 nm (l-PNC-15) and 24 nm (l-PNC-24), and Jeffamine M-2070, an amine-terminated ethylene oxide/propylene oxide (PEO/PPO, ratio 31/10) copolymer. Jeffamine M-2070 was used as the host liquid in which the particles were suspended and was also grafted onto the particle surface to prevent aggregation. The grafting density of Jeffamine M-2070 on the particle surfaces was ∼0.75 chains nm(-2). When the total polymer content (surface layer + host) was greater than ∼30 wt %, the PNC was a liquid, while at lower polymer volume fractions the PNC was solid. In this work, the bulk and surface structures of l-PNCs with ∼70 wt % polymer and 30% silica are characterized and compared. Small-angle neutron scattering (SANS) was used to probe the bulk structure of the l-PNCs and revealed that the particles are well-dispersed with minor clustering in l-PNC-15 and substantial clustering in l-PNC-24. This is attributed to stronger van der Waals attractions between particles due to the larger particle size in l-PNC-24. Corresponding effects were revealed using tapping mode atomic force microscopy (TM-AFM) at the l-PNC-air interface; clustering was minimal on the surface of l-PNC-15 but significant for l-PNC-24 droplets. In regions of the l-PNC where the particles were well-dispersed, the spacing between particles is consistent with their volume fractions. This is the first time that the distribution of polymer and particles within l-PNCs has been imaged in situ.

A functionalized phosphonate-rich organosilica layered hybrid material (PSLM) fabricated through a mild process for heavy metal uptake

A phosphonate-rich organosilica layered hybrid material (PSLM) made of 3-(trihydroxysilyl)propyl methylphosphonate, monosodium salt, as the single silica source, has been obtained from its aqueous solution through a xerogel process and mild thermal aging. The method is simple, affording bulk quantities of powdered PSLM in a single-step. The hybrid is stable in water and possesses a high content of phosphonate groups fixed on the solid matrix. In addition, PSLM shows good thermal stability, which exceeds 300°C in air. The material was characterized using SEM, TEM, XRD, FT-IR and TGA techniques. Potentiometric titrations show that PSLM bears high-surface density of phosphonate groups (3 mmol g(-1)). As a result, the material displays high metal uptake capacity for heavy metal ions such as Cu(2+) (2.72mmolg(-1)), Pb(2+) (1.67 mmol g(-1)) and Cd(2+) (1.00 mmol g(-1)) at neutral pH values e.g. the pH of natural waters. Detailed theoretical modeling using a Surface Complexation Model combined with Electron Paramagnetic Resonance (EPR) spectroscopy shows that the surface distribution of surface bound Cu(2+) ions is rather homogeneous e.g. copper-binding phosphonate sites are arranged in average distances 5-8Å.

Ordered hybrids from template-free organosilane self-assembly

Despite considerable achievements over the last two decades, nonporous organic-inorganic hybrid materials are mostly amorphous, especially in the absence of solvothermal processes. The organosilane self-assembly approach is one of the few opportunities for creating a regular assembly of organic and inorganic moieties. Additionally, well-established organosilicon chemistry enables the introduction of numerous organic functionalities. The synthesis of periodically ordered hybrids relies on mono-, bis-, or multisilylated organosilane building blocks self-assembling into hybrid mesostructures or superstructures, subsequently cross-linked by siloxane Si-O-Si condensation. The general synthesis procedure is template-free and one-step. However, three concurrent processes underlie the generation of self-organized hybrid networks: thermodynamics of amphiphilic aggregation, dynamic self-assembly, and kinetically controlled sol-gel chemistry. Hence, the set of experimental conditions and the precursor structure are of paramount importance in achieving long-range order. Since the first developments in the mid-1990s, the subject has seen considerable progress leading to many innovative advanced nanomaterials providing promising applications in membranes, pollutant remediation, catalysis, conductive coatings, and optoelectronics. This work reviews, comprehensively, the primary evolution of this expanding field of research.

Nanocomposites with Liquid-Like Multiwalled Carbon Nanotubes Dispersed in Epoxy Resin without Solvent Process

Liquid-like multiwall carbon nanotubes (MWNTs) were prepared with as-received carboxylic MWNTs-COOH and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO) through hydrogen bonding. The sample has liquid-like behavior above 58°C. The MWNTs content is 26.6 wt%. The liquid-like MWNTs nanofluids were incorporated into epoxy matrix with solvent-free process and dispersed well. When the liquid-like MWNTs nanofluids content is up to 1 wt%, the impact toughness of the nanocomposite is 153% higher than the pure epoxy matrix.

Water in the formation of biogenic minerals: peeling away the hydration layers

Minerals of biogenic origin form and crystallize from aqueous environments at ambient temperatures and pressures. The in vivo environment either intracellular or intercellular, contains many components that modulate both the activity of the ions which associate to form the mineral, as well as the activity and structure of the crowded water. Most of the studies about the mechanism of mineralization, that is, the detailed pathways by which the mineral ions proceed from solution to crystal state, have been carried out in relatively dilute solutions and clean solutions. These studies have considered both thermodynamic and kinetic controls. Most have not considered the water itself. Is the water a passive bystander, or is it intimately a participant in the mineral ion densification reaction? A wide range of experiments show that the mineralization pathways proceed through a series of densification stages with intermediates, such as a "dense liquid" phase and the prenucleation clusters that form within it. This is in contrast to the idea of a single step phase transition, but consistent with the Gibbs concept of discontinuous phase transitions from supersaturated mother liquor to crystal. Further changes in the water structure at every surface and interface during densification guides the free energy trajectory leading to the crystalline state. In vertebrates, mineralization takes place in a hydrated collagen matrix, thus water must be considered as a direct participant. Although different in detail, the crystallization of calcium phosphates, as apatite, and calcium carbonates, as calcite, are mechanistically identical from the viewpoint of water.

Self-organized poly(n-octadecylsilsesquioxane) films via sol-gel photopolymerization

We describe a novel solvent- and water-free sol-gel process for n-octadecyltriclorosilane (C(18)H(37)SiCl(3)) film catalyzed by photogenerated Brönsted acids. Driven by hydrophobic van der Waals interactions, a photoinduced self-assembly process occurs to afford a long-range ordered lamellar mesostructure, characterized by X-ray diffraction and transmission electron microscopy. Real-time Fourier transform IR spectroscopy was instrumental to probe the fast hydrolysis kinetics and assess the change of conformational behavior of the alkyl chains during UV irradiation. A unique combination of different solid-state NMR techniques ((29)Si, (13)C, (1)H) provided an insight into the supramolecular organization of this hybrid film.

Rheological behavior of clay-nanoparticle hybrid-added bentonite suspensions: specific role of hybrid additives on the gelation of clay-based fluids

Two different types of clay nanoparticle hybrid, iron oxide nanoparticle clay hybrid (ICH) and Al(2)O(3)-SiO(2) nanoparticle clay hybrid (ASCH), were synthesized and their effects on the rheological properties of aqueous bentonite fluids in steady state and dynamic state were explored. When ICH particles were added, bentonite particles in the fluid cross-link to form relatively well-oriented porous structure. This is attributed to the development of positively charged edge surfaces in ICH that leads to strengthening of the gel structure of the bentonite susensions. The role of ASCH particles on the interparticle association of the bentonite fluids is different from that of ICH and sensitive to pH. As pH of ASCH-added bentonite suspensions increased, the viscosity, yield stress, storage modulus, and flow stress decreased. In contrast, at low pH, the clay suspensions containing ASCH additives were coagulated and their rheological properties become close to those of ICH added bentonite fluids. A correlation between the net surface charge of the hybrid additives and the rheological properties of the fluids indicates that the embedded nanoparticles within the interlayer space control the variable charge of the edge surfaces of the platelets and determine the particles association behavior of the clay fluids.

Canopy dynamics in nanoscale ionic materials

Nanoscale ionic materials (NIMS) are organic-inorganic hybrids in which a core nanostructure is functionalized with a covalently attached corona and an ionically tethered organic canopy. NIMS are engineered to be liquids under ambient conditions in the absence of solvent and are of interest for a variety of applications. We have used nuclear magnetic resonance (NMR) relaxation and pulse-field gradient (PFG) diffusion experiments to measure the canopy dynamics of NIMS prepared from 18-nm silica cores modified by an alkylsilane monolayer possessing terminal sulfonic acid functionality, paired with an amine-terminated ethylene oxide/propylene oxide block copolymer canopy. Carbon NMR studies show that the block copolymer canopy is mobile both in the bulk and in the NIMS and that the fast (ns) dynamics are insensitive to the presence of the silica nanoparticles. Canopy diffusion in the NIMS is slowed relative to the neat canopy, but not to the degree predicted from the diffusion of hard-sphere particles. Canopy diffusion is not restricted to the surface of the nanoparticles and shows unexpected behavior upon addition of excess canopy. Taken together, these data indicate that the liquid-like behavior in NIMS is due to rapid exchange of the block copolymer canopy between the ionically modified nanoparticles.

Energy transfer in ionic-liquid-functionalized inorganic nanorods for highly efficient photocatalytic applications

Energy transfer in self-assembled ionic liquids (ILs) and iron oxyhydroxide nanocrystals and the controlled surface chemistry of functionalized nanomaterials for photocatalytic applications are reported. Self-assembled ILs play the role of multifunctional materials in terms of constructing a well-designed nanostructure, controlling the surface chemistry, and triggering the energy transfer of functionalized materials. IL-functionalized beta-FeOOH nanorods show approximately 10-fold higher performances than those of commercial materials due to the synergistic effect of well-defined nanomaterials in diffusion-controlled reactions, specific interactions with target pollutants, and energy transfers in hybrid materials. In particular, the energy transfer in C(4)MimCl-functionalized beta-FeOOH nanorods enhances photocatalytic activity due to the generation of Fe(2+). The strategy described herein provides new insight into the rational design of functionalized inorganic nanomaterials for applications in emerging technologies.

Preparation of a panoscopic mimic diatom from a silicon compound

Inspired by biological design principles, a panoscopic mimic diatom was created by hierarchical self-assembly of reactive amphiphiles in a multiphase medium comprising hexadecane, ethanol, water, and hydrochloric acid. Through simple stirring at room temperature, mesolamellar macroporous capsules covering oil droplets were obtained in large quantity, which was confirmed by NMR spectroscopy, X-ray diffraction, scanning electron microscopy, and thermogravimetry. At the mesoscale, amphiphilic C(16)Si(OH)(3) assembled into bilayer lamellae through polycondensation, hydrophobic interaction, and H bonding. At the micrometer scale, the bilayer lamellae nucleated at the interface and grew into a polar phase, thus leading to delicate microcages or mimic diatoms. Moreover, the microcages tended to interconnect and fuse into a continuous coating at the centimeter scale, which provided hydrophobicity through the micropatterned surface. This paradigm for creating hierarchical materials with multiphases could lead to new "synthetic" material technologies and novel fascinating materials with anisotropic properties.