Silicate Condensation Research Articles

Vertical Alignment of Liquid Crystals Over a Functionalized Flexible Substrate

A simple and effective approach for vertical alignment of liquid crystals (LCs) over a functionalized transparent flexible substrate is described. Surface characterization of this commercially available plastic substrate through X-ray photoelectron spectroscopy (XPS) and attenuated total reflection infrared spectroscopy (ATR-IR) indicated that cellulose acetate is main component of the transparent substrate. This substrate was chemically functionalized with a suitable LC compound. A trimethoxysilane terminated new rod-shaped mesogen is synthesized and covalently attached to the pre-treated film through silane condensation reaction. LC functionalization of the polymer film is confirmed through contact angle (CA), atomic force microscopy (AFM), XPS and ATR-IR spectroscopy studies. Versatility of the LC modified flexible substrates for the alignment of bulk LC sample at substrate-LC interface was assessed for nematic (N) and smectic A (SmA) phases. Remarkably, LC functionalized cellulose acetate films were found to be highly efficient in assisting a perfect homeotropic alignment of LCs (for both, a room temperature N and a high temperature SmA phase) over the entire area of the LC sample under observation indicating their superior aligning ability in comparison to their unmodified and octadecyltrimethoxysilane (OTS) modified counterparts. The demonstrated method of surface modification of flexible polymer film is easy, surface modified substrates are stable for several months, retained their aligning ability intact and more importantly they are reusable with maximum delivery.

Equilibrium chemistry down to 100 K

We have introduced a fast and versatile computer code, GGCHEM, to determine the chemical composition of gases in thermo-chemical equilibrium down to 100 K, with or without equilibrium condensation. We have reviewed the data for molecular equilibrium constants, kp(T), from several sources and discussed which functional fits are most suitable for low temperatures. We benchmarked our results against another chemical equilibrium code. We collected Gibbs free energies, ΔGf⊖, for about 200 solid and liquid species from the NIST-JANAF database and the geophysical database SUPCRTBL. We discussed the condensation sequence of the elements with solar abundances in phase equilibrium down to 100 K. Once the major magnesium silicates Mg2SiO4[s] and MgSiO3[s] have formed, the dust to gas mass ratio jumps to a value of about 0.0045 which is significantly lower than the often assumed value of 0.01. Silicate condensation is found to increase the carbon to oxygen ratio (C/O) in the gas from its solar value of ~0.55 up to ~0.71, and, by the additional intake of water and hydroxyl into the solid matrix, the formation of phyllosilicates at temperatures below ~400 K increases the gaseous C/O further to about 0.83. Metallic tungsten (W) is the first condensate found to become thermodynamically stable around 1600–2200 K (depending on pressure), several hundreds of Kelvin before subsequent materials such as zirconium dioxide (ZrO2) or corundum (Al2O3) can condense. We briefly discuss whether tungsten, despite its low abundance of ~2 × 10−7 times the silicon abundance, could provide the first seed particles for astrophysical dust formation.

Mechanically Robust and Thermally Stable Colorful Superamphiphobic Coatings.

Colorful super anti-wetting coatings are receiving growing attention, but are challenging to invent. Here, we report a general method for preparing mechanically robust and thermally stable colorful superamphiphobic coatings. A composite of palygorskite (PAL) nanorods and iron oxide red (IOR) was prepared by solid-state grinding or hydrothermal reaction, which was then modified by hydrolytic condensation of silanes to form a suspension. Superamphiphobic coatings were prepared by spray-coating the suspension onto substrates. The superamphiphobicity depends upon the surface microstructure and chemical composition, which are controllable by the PAL/IOR concentration and the solid-state grinding time. The colorful coatings show excellent superamphiphobicity with high contact angles and low sliding angles for water and various organic liquids of low surface tension, e.g., toluene and n-decane. The coatings also feature high mechanical, chemical and thermal stability, which is superior to all the reported colorful super anti-wetting coatings. Moreover, superamphiphobic coatings of different colors can be prepared via the same procedure using the other metal oxides instead of IOR. We believe the colorful superamphiphobic coatings may find applications in many fields like anti-climbing of oils and restoration of cultural relics, as the coatings are applicable onto various substrates.

Formation of the terrestrial planets in the solar system around 1 au via radial concentration of planetesimals

Context. No planets exist inside the orbit of Mercury and the terrestrial planets of the solar system exhibit a localized configuration. According to thermal structure calculation of protoplanetary disks, a silicate condensation line (~1300 K) is located around 0.1 au from the Sun except for the early phase of disk evolution, and planetesimals could have formed inside the orbit of Mercury. A recent study of disk evolution that includes magnetically driven disk winds showed that the gas disk obtains a positive surface density slope inside ~1 au from the central star. In a region with positive midplane pressure gradient, planetesimals undergo outward radial drift. Aims. We investigate the radial drift of planetesimals and type I migration of planetary embryos in a disk that viscously evolves with magnetically driven disk winds. We show a case in which no planets remain in the close-in region. Methods. Radial drifts of planetesimals are simulated using a recent disk evolution model that includes effects of disk winds. The late stage of planet formation is also examined by performing N-body simulations of planetary embryos. Results. We demonstrate that in the middle stage of disk evolution, planetesimals can undergo convergent radial drift in a magnetorotational instability (MRI)-inactive disk, in which the pressure maximum is created, and accumulate in a narrow ring-like region with an inner edge at ~0.7 au from the Sun. We also show that planetary embryos that may grow from the narrow planetesimal ring do not exhibit significant type I migration in the late stage of disk evolution. Conclusions. The origin of the localized configuration of the terrestrial planets of the solar system, in particular the deficit of close-in planets, can be explained by the convergent radial drift of planetesimals in disks with a positive pressure gradient in the close-in region.

Copper-loaded nanocellulose sponge as a sustainable catalyst for regioselective hydroboration of alkynes

It is desirable for catalyst supports to be biodegradable, easily-modifiable, and possessing high surface area. In this work, thiolated nanocellulose sponge was prepared from hydrolytic silane condensation of cellulose nanofibrils (CNF) and used as a green support to immobilize copper cations via in situ CuII to CuI reduction and complexation. The sponge featured high porosity (90.5%) and low density (29.4 mg/cm3) with regular morphology. The sponge easily recovered 94% of its original shape in water after experiencing 80% deformation under stress of 95 kPa. When used in catalyzing hydroboration of alkynes, excellent conversion and up to 99% regioselectivity were achieved with the copper-loaded sponge. The sponge-supported catalysts worked well in the absence of additional ligands, had a broad substrate scope, and retained 93% of their activity after six catalytic cycles. This simple and scalable strategy offers an efficient route for immobilizing metal catalysts on porous supports.

A Self-consistent Cloud Model for Brown Dwarfs and Young Giant Exoplanets: Comparison with Photometric and Spectroscopic Observations

Abstract We developed a simple, physical, and self-consistent cloud model for brown dwarfs and young giant exoplanets. We compared different parametrizations for the cloud particle size, by fixing either particle radii or the mixing efficiency (parameter f sed), or by estimating particle radii from simple microphysics. The cloud scheme with simple microphysics appears to be the best parametrization by successfully reproducing the observed photometry and spectra of brown dwarfs and young giant exoplanets. In particular, it reproduces the L–T transition, due to the condensation of silicate and iron clouds below the visible/near-IR photosphere. It also reproduces the reddening observed for low-gravity objects, due to an increase of cloud optical depth for low gravity. In addition, we found that the cloud greenhouse effect shifts chemical equilibrium, increasing the abundances of species stable at high temperature. This effect should significantly contribute to the strong variation of methane abundance at the L–T transition and to the methane depletion observed on young exoplanets. Finally, we predict the existence of a continuum of brown dwarfs and exoplanets for absolute J magnitude = 15–18 and color = 0–3, due to the evolution of the L–T transition with gravity. This self-consistent model therefore provides a general framework to understand the effects of clouds and appears well-suited for atmospheric retrievals.

Shielding of Enzymes on the Surface of Graphene-Based Composite Cellular Foams Through Bioinspired Mineralization.

Immobilization of enzyme on the surface of graphene-based composite cellular foams (GCCFs) is commonly prone to acquire stable and ultrahigh loading of enzymes and fast transport of substrates during the catalytic process. In this chapter, we reported a method of preparing GCCFs through combination of redox assembly and biomimetic mineralization with in situ enzyme immobilization. Briefly, GCCFs were first prepared through redox assembly of graphene oxide (GO) nanosheets enabled by polyethyleneimine (PEI). The cationic PEI in the resultant reduced GO/PEI (rGO/PEI) cellular foams acted as the mineralization-inducing agent could catalyze the condensation of silicate to form silica (biomimetic silicification) on the reduced graphene oxide (rGO) surface, where enzyme (with penicillin G acylase as model enzyme) is in situ entrapped and shielded within the silica network. Enzymes could be stably resided on the surface of GCCFs without any leaching against a broad range of pH values (3.5-10.0). GCCFs show a three-dimensional (3D) porous structure, which facilitates the fast transfer of substrate and, thereby, leads to desirable catalytic activity. Combined with the monolithic feature, GCCFs exhibit ease of recyclability and superior thermal/recycling stabilities during the catalytic synthesis of 6-aminopenicillanic acid (6-APA, an important pharmaceutical intermediate) compared to free enzyme and enzyme adsorbed on rGO/PEI cellular foams.

Optimizing Cu(II) luminescent nanosensors by molecular engineering of the indicator dye and the encapsulation process

This paper describes the preparation of silica nanoparticles doped with a molecularly engineered luminescent Ru(II) complex for the selective determination of Cu(II) ions in aqueous media. Initially, three novel indicator dyes, namely [Ru(phen)2(L)]2+, where L is either hmpi (2-(1H-imidazo[4,5-f]-1,10-phenanthrolin-2-yl)-4-methoxyphenol), haip (1-(4-hydroxy-3-(1H-imidazo[4,5-f]-1,10-phenanthrolin-2-yl)phenyl)ethanone), or btym (N,N'-(2,2'-bipyridine-4,4'-diyl)bis(2-(thymin-1-yl)acetamide)), were synthesised, characterised and their response to metal ions was evaluated. The [Ru(phen)2(haip)]2+ complex demonstrated to be selective to Cu(II), so that it was embedded in 20-nm silica nanoparticles, synthesised by the Stöber method. The maximum sensitivity of the luminescent nanosensor was obtained when the indicator dye was incorporated 8h after the beginning of the 10-h silane condensation process, because interaction with the metal ions improves when the encapsulated luminophore molecules are closer to the nanoparticle outermost surface The nanosensor showed selective response to Cu(II) in the presence of Zn(II), Hg(II), Pb(II), Ni(II), Cd(II) and Fe(II) ions in 50mM phosphate buffer at pH 8.0, with a limit of detection of 0.30μmolL−1, RSD values lower than 3.0%, and a response time <30s. The nanosensor was applied to the determination of Cu(II) in mineral and tap waters spiked with 5.0 and 7.0μmolL−1 of the analyte, with recoveries from 88 to 110%.

Wired-up wash and go

Flexible Electronics A range of approaches have emerged for making flexible electronics and for their inclusion into textiles and fabrics. One challenge common to all those approaches is to make the conducting fibers robust enough to survive extensive usage, including the need to wash the fabrics on a regular basis. Le Floch et al. address that challenge by combining a hydrogel that provides flexibility, a hygroscopic salt that enables ionic conduction at fixed humidity, and an outer coating of butyl rubber to retain the water level of the hydrogel. A silane condensation reaction makes it possible to dip-coat the butyl rubber coating. Cyclical stretching of the fibers in a detergent solution and several machine washing cycles caused little change in the fiber conductivity. ACS Appl. Mater. Interfaces 10.1021/acsami.7b07361 (2017).

Effects of the Planetary Temperature on the Circumplanetary Disk and on the Gap

Abstract Circumplanetary disks (CPDs) regulate the late accretion to the giant planet and serve as the birthplace for satellites. Understanding their characteristics via simulations also helps to prepare for their observations. Here we study disks around 1, 3, 5, and 10 M Jup planets with 3D global radiative hydrodynamic simulations with sub-planet peak resolution and various planetary temperatures. We found that as the 1 M Jup planet radiates away its formation heat, the circumplanetary envelope transitions to a disk between and 4000 K. In the case of 3–10 M Jup planets, a disk always forms. The temperature profile of the CPDs is very steep, the inner 1/6th is higher than the silicate condensation temperature, and the entire disk is higher than the water freezing point, making satellite formation impossible in this early stage (&lt;1 Myr). Satellites might form much later and first in the outer parts of the disk, migrating inwards later on. Our disk masses are 1, 7, and 20 for the 1, 3, 5, and 10 M Jup gas giants, respectively, and we provide an empirical formula to estimate the subdisk masses based on the planet- and circumstellar disk (CSD) mass. Our finding is that the cooler the planet, the lower the temperature of the subdisk, and the higher the vertical influx velocities. The planetary gap is also both deeper and wider. We also show that the gaps in 2D and 3D are different. The subdisk eccentricity increases with and violently interacts with the CSD, making satellite-formation less likely when .

Chitosan-doped-hybrid/TiO2 nanocomposite based sol-gel coating for the corrosion resistance of aluminum metal in 3.5% NaCl medium

The study outlines the role of chitosan, a biopolymer on corrosion behavior of Hy/nano-TiO2 based sol-gel coating over aluminum metal. In this study organic-inorganic hybrid sols were synthesized through hydrolysis and condensation of 3-glycidoxypropyltrimethoxy silane (GPTMS), tetraethoxysilane (TEOS) and titanium (IV) isopropoxide (TIP) in acidic solution. Chitosan was doped into sol-gel matrix and self-assembled over aluminum substrate. The resultant chitosan-doped-Hy/nano-TiO2 sol-gel coating was characterized by Fourier Transform Infrared (FT-IR) spectra, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Energy-Dispersive X-ray Spectroscopy (EDX) analyses. The as-tailored aluminum substrate was evaluated for corrosion resistance in neutral medium. The protection ability of these coatings was evaluated by electrochemical impedance studies (EIS) and potentiodynamic polarization (PP) measurements in 3.5% NaCl medium. The EIS and PP results showed that chitosan-doped- Hy/nano-TiO2 sol-gel coating exhibited better protection from corrosion than the undoped Hy/TiO2 nanocomposite coating.

Multilayered polyion complexes with dissolvable silica layer covered by controlling densities of cRGD-conjugated PEG chains for cancer-targeted siRNA delivery

Surface functionalization of nanoparticles is a crucial factor for nanoparticle-mediated drug and nucleic acid delivery. Particularly, the density of targeting ligands on nanoparticle significantly affects the affinity of nanoparticles to specific cellular surface (or receptor) through the multivalent binding effect. Herein, multilayered polyion complexes (mPICs) are prepared to possess varying densities of cyclic RGD peptide (cRGD) ligands for cancer-targeted small interfering RNA (siRNA) delivery. A template PIC is first prepared by mixing siRNAs with homo catiomers of N-substituted polyaspartamide bearing tetraethylenepentamine (PAsp(TEP)) in aqueous solution, followed by silica-coating through silicate condensation reaction. Then, silica-coated PICs (sPICs) are further covered with block catiomers of PAsp(TEP) and poly(ethylene glycol) (PEG) equipped with cRGD ligand. Successful preparation of targeted mPICs is confirmed from the changes in size and ζ-potential and the elemental analysis by transmission electron microscopy. Notably, the number of cRGD ligands per mPIC is regulated by altering the silicate concentration upon preparation of sPICs, which is confirmed by fluorescence correlation spectroscopy using fluorescent-labeled block catiomers. Ultimately, the targeted mPICs with a higher number of cRGD ligands demonstrate more efficient cellular uptake in cultured cancer cells, leading to enhanced gene silencing activity.

Rare event simulations reveal subtle key steps in aqueous silicate condensation.

A replica exchange transition interface sampling (RETIS) study combined with Born-Oppenheimer molecular dynamics (BOMD) is used to investigate the dynamics, thermodynamics and the mechanism of the early stages of the silicate condensation process. In this process, two silicate monomers, of which one is an anionic species, form a negatively charged five-coordinated silicate dimer. In a second stage, this dimer can fall apart again, forming the original monomers, or release a water molecule into the solution. We studied the association and dissociation reaction in the gas phase, and the dissociation and water removal step in the aqueous phase. The results on the aqueous phase dissociation suggest two possible mechanisms. The breakage of the bond between the intermediate oxygen and the five-coordinated silicon is sometimes accompanied by a proton transfer. After dissociation into silicate monomers, the anionic monomer is either the previously four-coordinated silicon or the previously five-coordinated silicon depending on whether the hydrogen transfer occurs or not. Our results show that the mechanism of proton transfer is highly predominant. Water removal simulations also show two possible mechanisms distinguished by the proton transfer reaction path. Proton transfer can occur either via a direct or via a water mediated reaction step. The calculations reveal that although both mechanisms contribute to the water removal process, the direct proton transfer is slightly favorable and occurs roughly in six out of ten occasions.

Monolithic biocatalytic systems with enhanced stabilities constructed through biomimetic silicification-induced enzyme immobilization on rGO/FeOOH hydrogel

In this study, we present a green and facile method of utilizing biomimetic silicification to trigger enzyme immobilization on the surface of the rGO/FeOOH hydrogel for constructing stable monolithic biocatalytic systems. In brief, the rGO/FeOOH hydrogel is firstly prepared through metal ion-induced reduction/assembly of graphene oxide (GO) nanosheets, which is then utilized to adsorb cationic polyethyleneimine (PEI). This cationic PEI, as the mineralization-inducing agent, catalyzes the condensation of silicate to form silica (biomimetic silicification) on the rGO surface, where enzyme is simultaneously entrapped. The resultant rGO/FeOOH/silica hydrogel shows an extraordinary three-dimensional (3D) porous structure. The silica content on the rGO surface can be facilely tailored through changing the silica precursor concentration. Combined with monolithic macroscale of the rGO/FeOOH/silica hydrogel, the acquired monolithic biocatalytic systems display easy recyclability and elevated pH/thermal/recycling/storage stabilities during the catalytic production of 6-aminopenicillanic acid (6-APA) in comparison to enzyme in free form and enzyme adsorbed on rGO/FeOOH hydrogel. Notably, the activity can be retained up to 93.3% of its initial activity after 11 reaction cycles for our biocatalytic systems.

Dynamic atmospheres and winds of cool luminous giants

High spatial resolution techniques have given valuable insights into the mass loss mechanism of AGB stars, which presumably involves a combination of atmospheric levitation by pulsation-induced shock waves and radiation pressure on dust. Observations indicate that Al$_2$O$_3$ condenses at distances of about 2 stellar radii or less, prior to the formation of silicates. Al$_2$O$_3$ grains are therefore prime candidates for producing the scattered light observed in the close vicinity of several M-type AGB stars, and they may be seed particles for the condensation of silicates at lower temperatures. We have constructed a new generation of Dynamic Atmosphere & Radiation-driven Wind models based on Implicit Numerics (DARWIN), including a time-dependent treatment of grain growth & evaporation for both Al$_2$O$_3$ and Fe-free silicates (Mg$_2$SiO$_4$). The equations describing these dust species are solved in the framework of a frequency-dependent radiation-hydrodynamical model for the atmosphere & wind structure, taking pulsation-induced shock waves and periodic luminosity variations into account. Condensation of Al$_2$O$_3$ at the close distances and in the high concentrations implied by observations requires high transparency of the grains in the visual and near-IR region to avoid destruction by radiative heating. For solar abundances, radiation pressure due to Al$_2$O$_3$ is too low to drive a wind. Nevertheless, this dust species may have indirect effects on mass loss. The formation of composite grains with an Al$_2$O$_3$ core and a silicate mantle can give grain growth a head start, increasing both mass loss rates and wind velocities. Furthermore, our experimental core-mantle grain models lead to variations of visual and near-IR colors during a pulsation cycle which are in excellent agreement with observations.

Zeolite Beta Formation from Clear Sols: Silicate Speciation, Particle Formation and Crystallization Monitored by Complementary Analysis Methods.

The formation of silicate nanoaggregates (NAs) at the very early stages of precursor sols and zeolite beta crystallization from silicate nanoparticles (NPs) are investigated in detail using a combination of different analysis methods, including liquid-state 29 Si, 27 Al, 14 N, and 1 H NMR spectroscopy, mass spectrometry (MS), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy at cryogenic temperatures (cryo-TEM). Prior to hydrothermal treatment, silicate NAs are observed if the Si/OH ratio in the reaction mixture is greater than 1. Condensation of oligomers within the NAs then generates NPs. Aluminum doped into the synthesis mixtures is located exclusively in the NPs, and is found exclusively in a state that is fourfold connected to silicate, favoring their condensation and aggregation. These results are in agreement with general trends observed for other systems. Silicate NAs are essential intermediates for zeolite formation and are generated by the aggregation of hydrated oligomers, aluminate, and templating cations. Subsequent further intra-nanoaggregate silicate condensation results in the formation of NPs. 1 H and 14 N liquid NMR as well as diffusion ordered spectroscopy (DOSY) experiments provide evidence for weakly restricted rotational and translational mobility of the organic template within NAs as a consequence of specific silicate-template interactions. NAs thus appear as key species in clear sols, and their presence in the precursor sol favors silicate condensation and further crystallization, promoted either by increasing the Si/OH ratio or by heating.

Sulfosuccinic acid-sulfonated polyether ether ketone/organo functionalized microporous zeolite-13X membrane electrolyte for direct methanol fuel cells

Impact of modified hydrophilic microporous zeolite namely 13X by introducing organo-sulfonic acid groups through silane condensation; and its dispersion in sulfosuccinic acid-sulfonated polyether ether ketone (SSA-sPEEK) to form a mixed matrix membrane for its application in direct methanol fuel cells is explored. Organo-sulfonic acid groups present in modified zeolite-13X serves for dual purpose by restricting methanol cross-over and also providing additional ion conducting groups for overall improvement of the performance. Crosslinking of sPEEK with SSA proves to be beneficial in providing stability to the matrix and also helps in enhancing the ionic conductivity. Characteristic properties like ion exchange capacity, water sorption, water-methanol mixture sorption and proton conductivity for these mixed matrix membranes have been investigated. DMFC comprising SSA-sPEEK-HSO3-zeolite-13X (80:20 ratio) mixed matrix membrane delivers peak power density of 130 mW/cm2, whereas peak power density of 73 mW/cm2 was obtained for DMFC comprising pristine sPEEK membrane at 70 °C. These indicate that SSA-sPEEK-HSO3-zeolite-13X mixed matrix membrane exhibit higher DMFC performance and lower methanol permeability in comparison with pristine sPEEK membrane.

Fossilized condensation lines in the Solar System protoplanetary disk

The terrestrial planets and the asteroids dominant in the inner asteroid belt are water poor. However, in the protoplanetary disk the temperature should have decreased below water-condensation level well before the disk was photo-evaporated. Thus, the global water depletion of the inner Solar System is puzzling. We show that, even if the inner disk becomes cold, there cannot be direct condensation of water. This is because the snowline moves towards the Sun more slowly than the gas itself. Thus the gas in the vicinity of the snowline always comes from farther out, where it should have already condensed, and therefore it should be dry. The appearance of ice in a range of heliocentric distances swept by the snowline can only be due to the radial drift of icy particles from the outer disk. However, if a planet with a mass larger than 20 Earth mass is present, the radial drift of particles is interrupted, because such a planet gives the disk a super-Keplerian rotation just outside of its own orbit. From this result, we propose that the precursor of Jupiter achieved this threshold mass when the snowline was still around 3 AU. This effectively fossilized the snowline at that location. In fact, even if it cooled later, the disk inside of Jupiter’s orbit remained ice-depleted because the flow of icy particles from the outer system was intercepted by the planet. This scenario predicts that planetary systems without giant planets should be much more rich in water in their inner regions than our system. We also show that the inner edge of the planetesimal disk at 0.7AU, required in terrestrial planet formation models to explain the small mass of Mercury and the absence of planets inside of its orbit, could be due to the silicate condensation line, fossilized at the end of the phase of streaming instability that generated the planetesimal seeds. Thus, when the disk cooled, silicate particles started to drift inwards of 0.7AU without being sublimated, but they could not be accreted by any pre-existing planetesimals.

Synthesis of Poly(ϵ-caprolactone) Grafted Poly(2-hydroxyethyl methacrylate) Functionalized Hydroxyapatite by RAFT and ROP

Poly(ϵ-caprolactone) grafted poly(2-hydroxyethyl methacrylate) functionalized hydroxyapatite (HAP@PHEMA-g-PCL) nanocomposites were synthesized by the combination of reversible addition fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP). The RAFT agent was anchored on the surface of hydroxyapatite nanocrystals (HAPs) through the silane condensation process of 3-chloropropyltrimethoxysilane followed by reaction with potassium xanthogenate. Poly(2-hydroxyethyl methacrylate) (PHEMA) was covalently functionalized on the surface of HAPs by RAFT polymerization. Then, poly(ϵ-caprolactone) (PCL) was grafted on HAPs by ROP based on the hydroxyl groups of PHEMA to afford HAP@PHEMA-g-PCL. The structure and composition of HAP@PHEMA-g-PCL nanocomposites were characterized by FT-IR, XRD, and TGA analyses. The morphology and formation of the polymer encapsulating HAPs were demonstrated from SEM and TEM images, while the 1H MNR analysis of the cleaved PHEMA-g-PCL confirmed the grafting.

Thermal and thermo-oxidative properties of the decahydro-closo-decaborate anion B10H10 2− in a silicate matrix

Using thermogravimetric analysis and differential scanning calorimetry in air and argon, we have studied the products of reactions between the B10H102− anion and water glass (WG) sodium silicates. The reaction products have the form of spatially branched supramolecular structures. Supramolecular structures of various compositions have been synthesized at initial WG/(Et3NH)2B10H10 reactant ratios of 70/30, 60/40, 50/50, and 40/60. In the range 20–600℃, we have studied the following processes in the WG/B10H102− systems: removal of adsorbed water (50–200℃), condensation of silicates containing silanol groups (200–300℃), and oxidation of the B10H102− anion in the silicate matrix (300–600℃). All three processes have been shown to depend on content.