Silicate Surface Research Articles

Irreversible adsorption of atmospheric helium on olivine: A lobster pot analogy

This study reports new experimental results that demonstrate that large amounts of atmospheric helium may be adsorbed onto the surfaces of olivine grains. This behavior is surface-area-related in that this contamination preferentially affects grains that are smaller than 125μm in size. One of the most striking results of our study is that in vacuo heating at 900°C for 15min is not sufficient to completely remove the atmospheric contamination. This suggests that the adsorption of helium may involve high-energy trapping of helium through irreversible anomalous adsorption. This trapping process of helium can thus be compared to a “lobster pot” adsorption: atmospheric helium easily gets in, but hardly gets out. While this type of behavior has previously been reported for heavy noble gases (Ar, Kr, Xe), this is the first time that it has been observed for helium. Adsorption of helium has, until now, generally been considered to be negligible on silicate surfaces. Our findings have significant implications for helium and noble gas analysis of natural silicate samples, such as for cosmic-ray exposure dating or noble gas characterization of extraterrestrial material. Analytical procedures in future studies should be adapted in order to avoid this contamination. The results of this study also allow us to propose an alternative explanation for previously described matrix loss of cosmogenic 3He.

Fluorescence Properties of Perylene and Pyrene Dyes Covalently Linked to 6H-SiC(0001) and Silicate Surfaces

The functionalization of wide bandgap semiconductors and insulators with self-assembled layers of polycyclic aromatic hydrocarbons (PAHs) has gained major attention due to various potential applications such as sensors, in molecular electronics, or in solar cells and organic light-emitting diodes. Their fluorescence properties depend among others on the spatial arrangement and aggregation of the molecules on the surface. In the present study, silane linkers of different length and conjugation were employed to functionalize silicon carbide and silicate surfaces with two PAHs. High-resolution X-ray photoemission spectroscopy (XPS) ascertained the degree of functionalization, supported by attenuated total reflection Fourier transform infrared spectroscopy and contact angle measurements. The homogeneity of the functionalized layers was evaluated by fluorescence microscopy. Using ultraviolet excitation, both a blue and a broad band fluorescence emission extending from 500 nm to beyond 600 nm were observed. Lif...

Effects of inorganic surface treatment on water permeability of cement-based materials

The permeability of the cement-based materials can be used as an important indicator of their durability. Surface treatment is a simple way to reduce permeability and improve durability of cement-based materials. This paper studied the effects of fluosilicate and sodium silicate surface treatments on the permeability of cement-based materials using the Autoclam water permeability and water absorption testing method. The experimental results showed that both fluosilicate and sodium silicate surface treatments could effectively reduce the permeability of cement-based materials. However, fluosilicate worked within the first 28days after treatment, while sodium silicate showed more obvious effect at later ages. Autoclam water permeability index exhibited an exponential relationship with the water absorption of the cement-based materials. In addition, mercury intrusion porosimetry result suggested that these inorganic surface treatment agents could reduce the porosity of surface layer of cement-based materials.

Safety evaluation of liposomal nanohybrid cerasomes and their application in the release of 10-hydroxycamptothecin

Cerasomes, a novel type of organic–inorganic liposomal nanohybrid with a silicate surface, has attracted a great deal of attention as a perfect substitute for liposomes due to its good morphological stability.

Does Fe2+ in olivine-based interstellar grains play any role in the formation of H2? Atomistic insights from DFT periodic simulations

Using periodic DFT-D2 methods, atomistic simulations of interstellar H adsorption and H2 formation on a (010) Fe-containing olivine surface are presented. At variance with the (010) Mg2SiO4 surface and key to these processes are the large Fe/H interaction energies, suggesting that olivine surfaces are good reservoirs of H atoms for subsequent recombination to form H2.

Molecular Dynamics Simulations of the Initial Adsorption Stages of Fibrinogen on Mica and Graphite Surfaces.

Fibrinogen, a blood glycoprotein of vertebrates, plays an essential role in blood clotting by polymerizing into fibrin when activated. Upon adsorption on material surfaces, it also contributes to determine their biocompatibility and has been implicated in the onset of thrombosis and inflammation at medical implants. Here we present the first fully atomistic simulations of the initial stages of the adsorption process of fibrinogen on mica and graphite surfaces. The simulations reveal a weak adsorption on mica that allows frequent desorption and reorientation events. This adsorption is driven by electrostatic interactions between the protein and the silicate surface as well as the counterion layer. Preferred adsorption orientations for the globular regions of the protein are identified. The adsorption on graphite is found to be stronger with fewer reorientation and desorption events and shows the onset of denaturation of the protein.

Mechanism of heterogeneous catalytic ozonation of p-chloronitrobenzene in aqueous solution with iron silicate dried at different temperatures

The degradation efficiencies of p-chloronitrobenzene (pCNB) in aqueous solution by processes employing ozone alone and ozone/iron silicates based on iron silicates dried at 60, 250, 600, or 800°C were investigated. The results demonstrated that iron silicate dried at 60°C possessed better catalytic capacity for the ozonation of pCNB than that dried at higher temperatures owing to increased concentrations of hydrogen peroxide (H2O2) and the formation of hydroxyl radicals (⋅OH). Adsorption of pCNB on the surface of iron silicate exhibited no remarkable influence on the degradation efficiency of pCNB. An increase in the drying temperature was found to slightly increase the adsorption ability and significantly reduce the catalytic activity of the iron silicate. Because of the formation of a new crystalline phase, the catalytic activity of iron silicate dried at 800°C was the lowest. The results of the mechanism analysis suggest that Fe2O3, FeOOH, and silicato-iron(III) surface complexes are the dominant components of catalytic activity in the iron silicate catalytic ozonation of pCNB. Moreover, the surface hydroxyl groups of the iron silicate determine the initiation of ⋅OH from ozone decomposition.

Fine CuO anisotropic nanoparticles supported on mesoporous SBA-15 for selective hydrogenation of nitroaromatics

SBA-15 modified with APTMS (3-aminopropyl trimethoxysilane) having pore diameter (∼8nm) has been synthesized and impregnated with 1–10wt.% Cu using Cu(NO3)2 as a metal source followed by calcination at 350°C. As-prepared CuO/ap-SBA-15 powder showed changes in the color from white for bare SBA-15 to light green due to formation of anisotropic CuO nanoparticles that exhibited a characteristic plasmon absorption band at 359 and 747nm. TEM studies showed a change in the morphology of CuO NPs as a function of increased Cu loading. Moreover, well dispersed CuO nanospheres (∼5–6nm) and nanorods (aspect ratio ∼11–20nm) having monoclinic crystal phase were observed within the mesoporous channels of SBA-15. Elemental mapping studies confirmed uniform distribution of CuO nanoparticles on the surface of SBA-15. An increase in surface area was also observed from 694m2g−1 for SBA-15 to 762m2g−1 for 10wt.% Cu loading probably due to the deposition of excess of CuO nanoparticles on the outer siliceous surface. The catalytic activity also increased with Cu loading and 10wt.% CuO/ap-SBA-15 catalyst displayed the highest catalytic activity for the reduction of m-chloronitrobenzene and m-nitrotoluene with 83% and 100% selectivity for m-chloroaniline and m-aminotoluene respectively.

Kinetic Studies of Reactions of Hydroxyporphyrins on Silicate Surface

The condensation reaction of hydroxyporphyrin with the surface silanol groups on silicate glass proceeded in the solid state. Kinetics of the reaction was analyzed by two parallel first order reactions, i.e., a double exponential equation. Introduction of long alkyl chains to hydroxyporphyrin accelerated the condensation, where the slower phase of the reaction was accelerated. If we assume that the rate limiting step in the slower phase is the reorientation of the molecule, long alkyl groups accelerated the molecular motion. Tertiary alcohol reacted slower than primary alcohol, and the much less fraction of faster phase can account for the slower reaction. The result implies that the tertiary alcohol structure inhibit the formation of preorganized structure for the condensation reaction.

Influences of Dilute Organic Adsorbates on the Hydration of Low-Surface-Area Silicates.

Competitive adsorption of dilute quantities of certain organic molecules and water at silicate surfaces strongly influence the rates of silicate dissolution, hydration, and crystallization. Here, we determine the molecular-level structures, compositions, and site-specific interactions of adsorbed organic molecules at low absolute bulk concentrations on heterogeneous silicate particle surfaces at early stages of hydration. Specifically, dilute quantities (∼0.1% by weight of solids) of the disaccharide sucrose or industrially important phosphonic acid species slow dramatically the hydration of low-surface-area (∼1 m(2)/g) silicate particles. Here, the physicochemically distinct adsorption interactions of these organic species are established by using dynamic nuclear polarization (DNP) surface-enhanced solid-state NMR techniques. These measurements provide significantly improved signal sensitivity for near-surface species that is crucial for the detection and analysis of dilute adsorbed organic molecules and silicate species on low-surface-area particles, which until now have been infeasible to characterize. DNP-enhanced 2D (29)Si{(1)H}, (13)C{(1)H}, and (31)P{(1)H} heteronuclear correlation and 1D (29)Si{(13)C} rotational-echo double-resonance NMR measurements establish hydrogen-bond-mediated adsorption of sucrose at distinct nonhydrated and hydrated silicate surface sites and electrostatic interactions with surface Ca(2+) cations. By comparison, phosphonic acid molecules are found to adsorb electrostatically at or near cationic calcium surface sites to form Ca(2+)-phosphonate complexes. Although dilute quantities of both types of organic molecules effectively inhibit hydration, they do so by adsorbing in distinct ways that depend on their specific architectures and physicochemical interactions. The results demonstrate the feasibility of using DNP-enhanced NMR techniques to measure and assess dilute adsorbed molecules and their molecular interactions on low-surface-area materials, notably for compositions that are industrially relevant.

Hard X-ray photoelectron spectra (HXPES) of bulk non-conductor vitreous SiO2: Minimum linewidths and surface chemical shifts

Hard X-ray photoelectron spectra (2200eV to 5000eV photon energies) have been obtained for the first time on a bulk non-conductor, vitreous SiO2, on a high resolution (E/ΔE of 10,000) synchrotron beamline at the Canadian Light Source (CLS). To minimize charging and differential charging, the SiO2 was coated with very thin layers (0.5 to 1.5nm) of Cr metal. The O 1s linewidth obtained at 2500eV photon energy was 1.26eV—the minimum linewidth for SiO2—and in good agreement with that obtained at 1486eV on a Kratos Axis Ultra spectrometer equipped with a magnetic charge compensation system. The Si 1s linewidth of 1.5eV, somewhat broader than that previously obtained at 1486eV on the Si 2p3/2 line of 1.16eV, is mainly due to the much larger inherent Si 1s linewidth (0.5eV) compared to the inherent Si 2p linewidth (<0.1eV). Both linewidths are dominated by the large final state vibrational broadening previously described.The Cr coating produces surface monolayers of interfacial Cr “suboxide” (Cr-subox), Cr metal, and a surface Cr oxide (Cr-surfox). Cr-subox (SiOCr) gives rise to the weak near-surface Si 1s peak, while both oxides give rise to both the weak surface O 1s peak and the Cr 2p oxide peak. Both the O 1s and Si 1s surface peaks are shifted by ∼2eV relative to the large bulk Si 1s and O 1s peaks. The weak Si 1s and O 1s surface peaks along with the Cr 2p oxide peak decrease in intensity greatly as the photon energy increases, due to an increase in inelastic mean free path (IMFP) in SiO2 from 27Å at 1486eV to 90Å at 5000eV. The decrease in intensity of these surface peaks is consistent with the theoretical IMFP's in the literature. The intensity of the weak O 1s and Si 1s peaks, along with the Cr 2p oxide peak, shows that the surface structure gives close to monolayer amounts of Cr-subox, Cr metal, and Cr-surfox. These high-energy spectra should be very useful in the future for bulk analysis of the O species in non-conducting silicate glasses, or surface analysis on non-conducting silicate surfaces and bulk as a function of photon energy.

Kinetic Studies of Reactions of Hydroxyporphyrins on Silicate Surface

Construction of the monolayer film of semiconductive and redox-active porphyrins on the metal oxides such as silicate or titanates attracts interests for possible applications of the process in fabricating organic electronic devices, organic catalysts, and organic-inorganic hybrid materials. Porphyrins bearing linker functional groups such as hydroxy or bromo groups in the peripheral meso-phenyl groups were reacted with the surface silanol groups of silicate glass at 80 to 240 oC in a solid-solid reaction to obtain the monolayer film of porphyrin on the silicate glass. The rates of the reaction were determined by visible spectroscopic studies and they decreased in the order: primary alcohol > primary bromide ~ tertiary alcohol. In addition to the structures of the linker groups, melting points of porphyrins also affect the reactivity of the porphyrin. Porphyrins with long alkyl chains reacted faster than those without long alkyl chains, because the long alkyl groups would facilitate molecular motion to reach the transition state of the reaction. Hydrolysis of the porphyrin monolayer prepared from primary alcohol in 1 M aq. HCl at 50 oC proceeded in a similar rate to that prepared from tertiary alcohol. Base catalyzed hydrolysis in 1 M aq. NH3 at 30 oC of the porphyrin monolayer prepared from tertiary alcohol proceeded 20 times slower than that prepared from the primary alcohol. In the literature, it is well established that the hydrolysis of the silicate ester bond proceeds via the Si-O bond cleavage, since the silicon atom can form a penta-coodinated structure, and much more reactive than carbon atom toward a substitution reaction. Hydrolysis of the porphyrin monolayer prepared from the tertiary alcohol in H2 18O afforded 18O-labelled tertiary alcohol, indicating that there was a covalent bond between the porphyrin and silicate glass, and the C-O bond was cleaved in the acid catalyzed hydrolysis reaction of the tertiary alkyl silicate ester on the silicate glass.

Bone cement adhesion on ceramic surfaces - surface activation of retention surfaces of knee prostheses by atmospheric plasma versus thermal surface treatment

CoCrMo alloys are contraindicated for allergy sufferers. For these patients, uncemented and cemented prostheses made of titanium alloy are indicated. Knee prostheses machined from that alloy, however, may have poor tribological behaviour, especially in relation to UHMWPE inlays. Therefore, for knee replacement cemented high-strength oxide ceramic prostheses are suitable for allergy sufferers and in cases of particle-induced aseptic loosening. For adhesion of bone cement, the ceramic surface, however, only exposes inefficient mechanical retention spots as compared with a textured metal surface. Undercuts generated by corundum blasting which in the short-term are highly efficient on a CoCrMo surface are not possible on a ceramic surface due to the brittleness of ceramics. Textures due to blasting may initiate cracks which will weaken the strength of a ceramic prosthesis. Due to the lack of textures mechanical retention is poor or even not existent. Micromotions are promoted and early aseptic loosening is predictable. Instead silicoating of the ceramic surface will allow specific adhesion and result in better hydrolytic stability of bonding thereby preventing early aseptic loosening. Silicoating, however, presupposes a clean and chemically active surface which can be achieved by atmospheric plasma or thermal surface treatment. In order to evaluate the effectiveness of silicoating the bond strengths of atmospheric plasma versus thermal surface treated and silicate layered ZPTA surfaces were compared with "as-fired" surfaces by utilising TiAlV probes (diameter 6 mm) for traction-adhesive strength tests. After preparing samples for traction-adhesive strength tests (sequence: ceramic substrate, silicate and silane, protective lacquer [PolyMA], bone cement, TiAlV probe) they were aged for up to 150 days at 37 °C in Ringer's solution. The bond strengths observed for all ageing intervals were well above 20 MPa and much higher and more hydrolytically stable for silicate layered compared with "as-fired" ZPTA samples. Silicoating may be effective for achieving high initial bond strength of bone cement on surfaces of oxide ceramics and also suitable to stabilise bond strength under hydrolytic conditions as present in the human body in the long-term. Activation by atmospheric plasma or thermal surface treatment seems to be effective for activation prior to silicoating. Due the proposed silicate layer migration, micromotions and debonding should be widely reduced or even eliminated.

Polymerization of octamethylcyclotetrasiloxane between montmorillonite nanoplatelets initiated by surface anions

Research deals with the assessment of grafting of cyclosiloxanes onto organically modified montmorillonite (MMT) layers through anionic ring-opening polymerization (AROP) without additional catalyst or initiator. Pristine Na+-MMT was organically modified by systematically varying the hexadecyltrimethylammonium bromide (HDTMABr) loading level. X-ray diffraction and thermogravimetric analysis of differently modified MMTs (OMMTs) showed that HDTMABr cations that exchanged sodium cations were strongly attracted to the silicate platelet surfaces. Part of HDTMABr formed a sandwiched HDTMABr layer between organically modified silicate platelets. The obtained OMMTs were tested as initiator material for AROP of octamethylcyclotetrasiloxane (D4) in the bulk, since the D4 polymerization may be initiated by oxygen anions located on the silicate surfaces. The highest monomer conversion (91 % after 24 h at 80 °C) was observed when OMMT with HDTMABr amount equal to cation exchange capacity was used. At lower amounts of HDTMABr, the MMT was less organically modified and thus less compatible with D4. On the other hand, when the HDTMABr sandwiched layer was thicker, lower rates of polymerization were observed due to the hindered transport of monomer to silicate platelet surfaces. The active function of surface anions in MMT platelets in the initiation process was confirmed experimentally by varying the OMMT/D4 ratio. It was observed that monomer conversion increased with increasing OMMT/D4 ratio. The obtained composites were exfoliated. In the last part of the research, OMMT was added to the formulation for D4 emulsion polymerization, where HDTMABr was also used as an emulsifier. The obtained composite material had a significantly improved thermal stability.

Probing model interstellar grain surfaces with small molecules

Temperature-programmed desorption and reflection-absorption infrared spectroscopy have been used to explore the interaction of oxygen (O2), nitrogen (N2), carbon monoxide (CO) and water (H2O) with an amorphous silica film as a demonstration of the detailed characterization of the silicate surfaces that might be present in the interstellar medium. The simple diatomic adsorbates are found to wet the silica surface and exhibit first-order desorption kinetics in the regime up to monolayer coverage. Beyond that, they exhibit zero-order kinetics as might be expected for sublimation of bulk solids. Water, in contrast, does not wet the silica surface and exhibits zero-order desorption kinetics at all coverages consistent with the formation of an islanded structure. Kinetic parameters for use in astrophysical modelling were obtained by inversion of the experimental data at sub-monolayer coverages and by comparison with models in the multilayer regime. Spectroscopic studies in the sub-monolayer regime show that the C–O stretching mode is at around 2137 cm−1 (5.43 μm), a position consistent with a linear surface–CO interaction, and is inhomogenously broadened as resulting from the heterogeneity of the surface. These studies also reveal, for the first time, direct evidence for the thermal activation of diffusion, and hence de-wetting, of H2O on the silica surface. Astrophysical implications of these findings could account for a part of the missing oxygen budget in dense interstellar clouds, and suggest that studies of the sub-monolayer adsorption of these simple molecules might be a useful probe of surface chemistry on more complex silicate materials.

FORMATION OF HYDROXYLAMINE ON DUST GRAINS VIA AMMONIA OXIDATION

The quest to detect prebiotic molecules in space, notably amino acids, requires an understanding of the chemistry involving nitrogen atoms. Hydroxylamine (NH$_2$OH) is considered a precursor to the amino acid glycine. Although not yet detected, NH$_2$OH is considered a likely target of detection with ALMA. We report on an experimental investigation of the formation of hydroxylamine on an amorphous silicate surface via the oxidation of ammonia. The experimental data are then fed into a simulation of the formation of NH$_2$OH in dense cloud conditions. On ices at 14 K and with a modest activation energy barrier, NH$_2$OH is found to be formed with an abundance that never falls below a factor 10 with respect to NH$_3$. Suggestions of conditions for future observations are provided.

Hydroxyl radical initiated oxidation of formic acid on mineral aerosols surface: a mechanistic, kinetic and spectroscopic study

Environmental context The presence of air-borne mineral dust containing silicates in atmospheric aerosols should be considered in any exploration of volatile organic compound chemistry. This work reports the mechanisms, relative energies and kinetics of free-radical reactions with formic acid adsorbed on silicate surface models. We find that silicate surfaces are more likely to act as a trap for organic radicals than to have a catalytic effect on their reactions. Abstract Heterogeneous reactions of atmospheric volatile organic compounds on aerosol particles may play an important role in atmospheric chemistry. Silicate particles are present in air-borne mineral dust in atmospheric aerosols, and radical reactions can be different in the presence of these mineral particles. In this work, we use quantum-mechanical calculations and computational kinetics to explore the reaction of a hydroxyl free radical with a formic acid molecule previously adsorbed on several models of silicate surfaces. We find that the reaction is slower and takes place according to a mechanism that is different than the one in the gas phase. It is especially interesting to note that the reaction final products, which are the formyl radical attached to the cluster surface, and a water molecule, are much more stable than those formed in the gas phase, the overall reaction being highly exothermic in the presence of the surface model. This suggests that the silicate surface is a good trap for the formed formyl radical. In addition, we have noted that, if a second hydroxyl radical approaches the adsorbed formyl radical, the formation of carbonic acid on the silicate surface is a highly exothermic and exergonic process. The carbonic acid molecule remains strongly attached to the surface, thus blocking CO2 formation in the formic acid oxidation reaction. The spectroscopic properties of the systems involved in the reaction have been calculated, and interesting frequency shifts have been identified in the main vibration modes.

Molecular dynamics modeling of carbon dioxide, water and natural organic matter in Na-hectorite.

Molecular dynamics (MD) modeling of systems containing a Na-exchanged smectite clay (hectorite) and model natural organic matter (NOM) molecules along with pure H2O, pure CO2, or a mixture of H2O and CO2 provides significant new insight into the molecular scale interactions among silicate surfaces, dissolved cations and organic molecules, H2O and CO2 relevant to geological C-sequestration strategies. The simulations for systems containing H2O show the following results; (1) Na(+) does not bridge between NOM molecules and the clay surface at protonation states comparable to near neutral pH conditions. (2) In systems without CO2 the NOM molecules retain charge balancing cations and drift away from the silicate surface. (3) In systems containing both H2O and CO2, the NOM molecules adopt equilibrium positions at the H2O-CO2 interface with the more hydrophilic structural elements facing the H2O and the more hydrophobic ones facing the CO2. In systems with only CO2, NOM and Na(+) ions are pinned to the clay surface with the hydrophilic structural elements of the NOM pointed toward the clay surface. Dynamically, in systems with only CO2, Na(+) diffusion is nearly eliminated, and in systems with a thin water film on the clay surface diffusion perpendicular the surface is greatly reduced relative to the system with bulk water. Energetically, the results for the systems with only H2O show that hydration of the net charge neutral Na-NOM molecule outweighs the sum of its Coulombic and dispersive interactions with the net charge-neutral Na-clay particle and the interactions of the water molecules with the hydrophobic structural elements of the NOM. The aggregation of NOM molecules in solution appears to be driven not by Na(+) bridging between the molecules but by hydrophobic interactions between them. In contrast, for the systems with only CO2 the interaction between the Na-NOM molecules and the CO2 is outweighed by the interaction of NOM with the clay particle. With both H2O and CO2 present, the energetic interactions leading to the hydration of the Na-clay surface and the hydrophilic structural elements of the Na-NOM molecule and the hydrophobic interactions between the CO2 and the hydrophobic aromatic and aliphatic structural elements of the NOM can both be satisfied, leading to the Na-NOM molecules migrating away from the surface and residing at the H2O-CO2 interface. The MD results suggest some alternative explanations for the previously observed (23)Na NMR behavior of Na-hectorite at elevated temperatures and CO2 pressures.

Effects of nanoscopic-confinement on polymer dynamics.

The static and dynamic behavior of polymers in confinement close to interfaces can be very different from that in the bulk. Among the various geometries, intercalated nanocomposites, in which polymer films of ∼1 nm thickness reside between the parallel inorganic surfaces of layered silicates in a well-ordered multilayer, offer a unique avenue for the investigation of the effects of nanoconfinement on polymer structure and dynamics by utilizing conventional analytical techniques and macroscopic specimens. In this article, we provide a review of research activities mainly in our laboratory on polymer dynamics under severe confinement utilizing different polymer systems: polar and non-polar polymers were mixed with hydrophilic or organophilic silicates, respectively, whereas hyperbranched polymers were studied in an attempt to probe the effect of polymer-surface interactions by altering the number and the kinds of functional groups in the periphery of the branched polymers. The polymer dynamics was probed by quasielastic neutron scattering and dielectric relaxation spectroscopy and was compared with that of the polymers in the bulk. In all cases, very local sub-Tg processes related to the motion of side and/or end groups as well as the segmental α-relaxation were identified with distinct differences recorded between the bulk and the confined systems. Confinement was found not to affect the very local motion in the case of the linear chains whereas it made it easier for hyperbranched polymers due to modifications of the hydrogen bond network. The segmental relaxation in confinement becomes faster than that in the bulk, exhibits Arrhenius temperature dependence and is observed even below the bulk Tg due to reduced cooperativity in the confined systems.

Single Molecular Layer Adaption of Interfacial Surfaces by Cyclic Azasilane “Click-Chemistry”

ABSTRACTThe surfaces of inorganic substrates containing hydroxyl groups can be adapted to a variety of physical and chemical requirements by reaction with cyclic azasilanes. The moderately-strained ring structure of cyclic azasilanes containing adjacent Si and N atoms, along with the high oxophilicity of silicon, enables the high reactivity towards available hydroxyl groups on all siliceous surfaces investigated, including amorphous silica and borosilicate glass. The reaction occurs quantitatively at room temperature, requires no catalyst and has no byproducts. This investigation looks specifically at the reaction kinetics by means of DRIFT spectroscopy and quantifies extent of reaction by TGA. The less sterically-hindered the Si–N bond, the faster the reaction occurs. In all cases, the reaction is essentially complete in less than one minute. This study provides the first confirmation that the rate and extent of reaction without catalysis or byproducts of cyclic azasilanes conforms to the Sharpless requirements for “click chemistry” and can be deemed “click chemistry for surfaces.”