Siloxane Rings Research Articles

Effect of ceria and zirconia nanoparticles on mechanical behavior of nanocomposite hybrid coatings

Epoxy-silica based hybrid nanocomposite coatings have been developed with different organicinorganic contents by sol–gel process. Various ratios of ceria and zirconia colloidal dispersions as inorganic nanoparticles are uniformly distributed in the hybrid sol. The hybrid sols are prepared by hydrolysis and condensation of 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethylorthosilicate (TEOS) in acidic solution using bisphenol A (BPA) and 1-methyl-imidazol (MI). A thin layer of each sol is coated on a micro-glass slide and 1050 aluminum alloy as substrates. The effect of alkoxysilane precursors (i.e. TEOS and GPTMS) and inorganic to organic molar ratio are investigated. Nanoindentation and dynamic mechanical analysis (DMA) performed to characterize the mechanical properties of the coatings in nanorange scale. It is revealed that all hybrid nanocomposite coatings had appropriate flexibility and strong interfacial interaction with the aluminum alloy substrate. It is proposed that the ceria and zirconia nanoparticles can be bonded to the surrounding of siloxane ring which can be induced high restriction in polymeric chain mobility in dynamic mechanical analysis. Nanoindentation tests showed that by increasing the inorganic phase in the nanocomposite, both elastic modulus and hardness increase, especially they are very intense in the higher levels of inorganic content.

Monomolecular Siloxane Film as a Model of Single Site Catalysts.

Achieving structurally well-defined catalytic species requires a fundamental understanding of surface chemistry. Detailed structural characterization of the catalyst binding sites in situ, such as single site catalysts on silica supports, is technically challenging or even unattainable. Octadecyltrioxysilane (OTOS) monolayers formed from octadecyltrimethoxysilane (OTMS) at the air-liquid interface after hydrolysis and condensation at low pH were chosen as a model system of surface binding sites in silica-supported Zn(2+) catalysts. We characterize the system by grazing incidence X-ray diffraction, X-ray reflectivity (XR), and X-ray fluorescence spectroscopy (XFS). Previous X-ray and infrared surface studies of OTMS/OTOS films at the air-liquid interface proposed the formation of polymer OTOS structures. According to our analysis, polymer formation is inconsistent with the X-ray observations and structural properties of siloxanes; it is energetically unfavorable and thus highly unlikely. We suggest an alternative mechanism of hydrolysis/condensation in OTMS leading to the formation of structurally allowed cyclic trimers with the six-membered siloxane rings, which explain well both the X-ray and infrared results. XR and XFS consistently demonstrate that tetrahedral [Zn(NH3)4](2+) ions bind to hydroxyl groups of the film at a stoichiometric ratio of OTOS:Zn ∼ 2:1. The high binding affinity of zinc ions to OTOS trimers suggests that the six-membered siloxane rings are binding locations for single site Zn/SiO2 catalysts. Our results show that OTOS monolayers may serve as a platform for studying silica surface chemistry or hydroxyl-mediated reactions.

Molecular Simulation of Cesium Adsorption at the Basal Surface of Phyllosilicate Minerals

AbstractA better understanding of the thermodynamics of radioactive cesium uptake at the surfaces of phyllosilicate minerals is needed to understand the mechanisms of selective adsorption and help guide the development of practical and inexpensive decontamination techniques. In this work, molecular dynamics simulations were carried out to determine the thermodynamics of Cs+ adsorption at the basal surface of six 2:1 phyllosilicate minerals, namely pyrophyllite, illite, muscovite, phlogopite, celadonite, and margarite. These minerals were selected to isolate the effects of the magnitude of the permanent layer charge (⩽2), its location (tetrahedral vs. octahedral sheet), and the octahedral sheet structure (dioctahedral vs. trioctahedral). Good agreement was obtained with the experiments in terms of the hydration free energy of Cs+ and the structure and thermodynamics of Cs+ adsorption at the muscovite basal surface, for which published data were available for comparison. With the exception of pyrophyllite, which did not exhibit an inner-sphere free energy minimum, all phyllosilicate minerals showed similar behavior with respect to Cs+ adsorption; notably, Cs+ adsorption was predominantly inner-sphere, whereas outer-sphere adsorption was very weak with the simulations predicting the formation of an extended outer-sphere complex. For a given location of the layer charge, the free energy of adsorption as an inner-sphere complex varied linearly with the magnitude of the layer charge. For a given layer charge location and magnitude, adsorption at phlogopite (trioctahedral sheet structure) was much less favorable than at muscovite (dioctahedral sheet structure) due to electrostatic repulsion between adsorbed Cs+ and the H atom of the OH- ion directly below the six-membered siloxane ring cavity. For a given layer charge magnitude and octahedral sheet structure, adsorption to celadonite (octahedral sheet layer charge) was favored over adsorption to muscovite (tetrahedral sheet layer charge) due to the increased distance to the surface K+ ions and the decreased distance to the O atom of the OH- ion directly below the surface cavity.

Mechanism of formation of macrocyclic siloxanes with a benzimidazole fragment by reaction of benzimidazole with 1,3-bis(iodomethyl)-1,1,3,3-tetramethyldisiloxane

The formation of macrocyclic polysiloxane system containing a benzimidazole fragment by reaction of benzimidazole with 1,3-bis(iodomethyl)-1,1,3,3-tetramethyldisiloxane was studied at the B3LYP/6-31G(d,p) level of theory. The calculations showed that expansion of siloxane ring involves thermodynamically controlled insertion of four silanone molecules generated by thermal decomposition of the complex derived from the initial siloxane and hydrogen triiodide.

Diversity of monomeric dioxo chromium species in Cr/silicalite-2 catalysts: A hybrid density functional study

The present paper deals with the theoretical characterization of the dioxo Cr species exchanged into the silicalite-2 structure via hybrid density functional theory with cluster models to represent the active site. The molecular models range from a simple mono silicon atom ring to more complex Cr–siloxane rings of 7T atoms. The common B3LYP and M06 density functionals were used for the calculations. The results indicate that the chemical hardness increases from a complex ring to a simple geminate type. Overall, the QTAIM calculations point to intermediate ionic–covalent nature of the Cr–oxygen bonds. An excellent correlation is found between the positive eigenvalue of the Hessian at the bond critical point with the CrO bond distance. Whereas the enthalpy change on the exchange reaction alters from −20.3 to 56.1kcal/mol at the M06/6-311+G∗ level, the binding energy lies in a shorter range of 907.5–926.6kcal/mol. As concluded from the Gibbs free energy changes on the exchange reaction with both of the methods, only the clusters of 4T size or larger would be formed spontaneously. However, M06 predicts ∼13% stronger bindings for the Cr ion. Overall, the electronic properties depend upon both the SiOCrOSi aperture size and the local configuration of the matrix. Furthermore, a fivefold coordination of Cr is accompanied with a lower ionization potential, a longer CrO distance, and a less negative charge on the terminal O atoms.

Cyclic Silanols with Long Alkyl Chains

Facile synthesis of cyclotrisiloxanetriols ((RSi(OH)O)3; R = hexyl and octyl) bearing a relatively unusual six-membered siloxane ring was accomplished by taking advantage of long alkyl chains. The ...

Surficial Siloxane-to-Silanol Interconversion during Room-Temperature Hydration/Dehydration of Amorphous Silica Films Observed by ATR-IR and TIR-Raman Spectroscopy.

Silica has been frequently studied using infrared and Raman spectroscopy due to its importance in many practical contexts where its surface chemistry plays a vital role. The majority of these studies have utilized chemical-vapor-deposited films in vacuo after high-temperature calcination. However, room-temperature hydration and dehydration of thin silica particle films has not been well characterized in spite of the importance of such films as substrates for polymer and surfactant adsorption. The present study has utilized ATR-IR spectroscopy and thin silica particle films exposed to varying humidity to clearly show reversible conversion between surface siloxanes and hydrogen-bonded silanols without the need for semiempirical peak deconvolution. The IR spectra from corresponding hydration experiments on deuterated silica films has confirmed the vibrational mode assignments. The variation of humidity over silica films formed from silica suspensions of differing pH gave IR spectra consistent with the change in the relative populations of siloxide to silanol surface groups. In addition, total internal reflection Raman spectroscopy has been used to provide further evidence of room-temperature dehydroxylation, with spectral evidence for the presence of three-membered siloxane rings when films are dehydrated under argon. The confirmation of room-temperature siloxane-to-silanol interconversion is expected to benefit understanding in many silica surface chemical contexts.

Effect of Siloxane Ring Strain and Cation Charge Density on the Formation of Coordinately Unsaturated Metal Sites on Silica: Insights from Density Functional Theory (DFT) Studies

Amorphous silica (SiO2) is commonly used as a support in heterogeneous catalysis. However, because of the structural disorder and temperature-induced change of surface morphology, the structures of silica-supported metal catalysts are difficult to determine. Most studies are primarily focused on understanding the interactions of different types of surface hydroxyl groups with metal ions. In comparison, the effect of siloxane ring size on the structure of silica-supported metal catalysts and how it affects catalytic activity is poorly understood. Here, we have used density functional theory (DFT) calculations to understand the effect of siloxane ring strain on structure and activity of different monomeric Lewis acid metal sites on silica. In particular, we have found that large siloxane rings favor strong dative bonding interaction between metal ion and surface hydroxyls, leading to the formation of high-coordinate metal sites. In comparison, metal–silanol interaction is weak in small siloxane rings, resulting in low-coordinate metal sites. The physical origin of this size dependence is associated with siloxane ring strain, and a correlation between the metal–silanol interaction energy and the ring strain energy has been observed. In addition to ring strain, the strength of the metal–silanol interaction also depends on the positive charge density of the cations. In fact, a correlation also exists between metal–silanol interaction energy and charge density of several first-row transition and post-transition metals. The theoretical results are compared with the extended X-ray absorption fine structure (EXAFS) data of monomeric Zn(II) and Ga(III) ions grafted on silica. The molecular level insights of how metal ion coordination on silica depends on siloxane ring strain and cation charge density will be useful in the synthesis of new catalysts.

Effect of “Reducible” Titania Promotion on the Mechanism of H-Migration in Pd/SiO2 Clusters

Industrial catalysts, consisting of metal species dispersed on a porous surface, are typically prepared by hydrogen treatment at high temperatures, and the migration of hydrogen constitutes the key elementary reaction that mediates the metal-support interactions and the generation of active catalytic sites. A detailed modeling of these processes is challenging especially for systems involving disordered surfaces. A debated issue is the role of the support “reducibility” on the mechanism of H-spillover processes. Transition-metal oxides such as titania significantly improve the activity and selectivity of catalysts supported on “non-reducible” oxides, such as silica, particularly in hydrogenation and dehydrogenation processes. To gain insight into the mechanism of H-migration in disordered catalysts and nano-particles, a comprehensive DFT-analysis of the potential energy surfaces is carried out for the transfer of H-atoms from a palladium-tetramer catalyst to a silica-support, represented by a substituted siloxane ring, doped with “reducible” titania. The H-migration to non-stoichiometric supports occurs via both a direct and H 2 -assisted transfer of H-atoms when the metal-catalyst is anchored to the non-bonding oxygen atoms of the support (defect sites). The calculations revealed that the transfer to different types of supports proceeds through identical pathways but significantly different barriers. The titania-promotion, as well as the addition of dihydrogen ligands to the catalyst, decreases the direct and H 2 -assisted H-migration barriers. Due to the extended transition state structures, the H2-assisted mechanism provides access to more distant and hindered active centers, and thus can account for the “bottleneck” particle-to-particle (along grain boundaries) transport of hydrogen atoms. The H-migration to titania-promoted stoichiometric (defect-free) supports generates intermetallic Pd-Ti bonds, in contrast to the pristine silica-based catalysts, which do not form analogous bonds between palladium and silicon centers of the support.

Kinetics and Mechanism of the Oxidation of Cyclic Methylsiloxanes by Hydroxyl Radical in the Gas Phase: An Experimental and Theoretical Study.

The ubiquitous presence of cyclic volatile methylsiloxanes (cVMS) in the global atmosphere has recently raised environmental concern. In order to assess the persistence and long-range transport potential of cVMS, their second-order rate constants (k) for reactions with hydroxyl radical ((•)OH) in the gas phase are needed. We experimentally and theoretically investigated the kinetics and mechanism of (•)OH oxidation of a series of cVMS, hexamethylcyclotrisiloxane (D3), octamethycyclotetrasiloxane (D4), and decamethycyclopentasiloxane (D5). Experimentally, we measured k values for D3, D4, and D5 with (•)OH in a gas-phase reaction chamber. The Arrhenius activation energies for these reactions in the temperature range from 313 to 353 K were small (-2.92 to 0.79 kcal·mol(-1)), indicating a weak temperature dependence. We also calculated the thermodynamic and kinetic behaviors for reactions at the M06-2X/6-311++G**//M06-2X/6-31+G** level of theory over a wider temperature range of 238-358 K that encompasses temperatures in the troposphere. The calculated Arrhenius activation energies range from -2.71 to -1.64 kcal·mol(-1), also exhibiting weak temperature dependence. The measured k values were approximately an order of magnitude higher than the theoretical values but have the same trend with increasing size of the siloxane ring. The calculated energy barriers for H-atom abstraction at different positions were similar, which provides theoretical support for extrapolating k for other cyclic siloxanes from the number of abstractable hydrogens.

Reactive Molecular Dynamics Simulations of Siliceous Solids Polycondensed from Tetra- and Trihydroxysilane

The chemical structure of siloxanes polycondensed from tetra- and trihydroxysilane monomers is investigated with reactive molecular dynamics. Solids of varying densities, ranging from porous gels to glasses are obtained through an iterative scheme in which silane is periodically added to the reacting system. It is found that tetrahydroxysilane forms denser solids, with smaller siloxane rings, and a greater concentration of siloxane bridges in comparison to trihydroxysilane, which produces networks of silsesquioxane clusters and sheets. The thermal treatment of solids produced from tetrahydroxysilane is modeled after drying, which leads to densification, and a reduction of porosity and silanol content. Dense solids with low silanol concentration are found to be less susceptible to shrinkage during thermal treatment.

Reduction of Acute Inflammatory Effects of Fumed Silica Nanoparticles in the Lung by Adjusting Silanol Display through Calcination and Metal Doping.

The production of pyrogenic (fumed) silica is increasing worldwide at a 7% annual growth rate, including expanded use in food, pharmaceuticals, and other industrial products. Synthetic amorphous silica, including fumed silica, has been generally recognized as safe for use in food products by the Food and Drug Administration. However, emerging evidence from experimental studies now suggests that fumed silica could be hazardous due to its siloxane ring structure, high silanol density, and "string-of-pearl-like" aggregate structure, which could combine to cause membrane disruption, generation of reactive oxygen species, pro-inflammatory effects, and liver fibrosis. Based on this structure-activity analysis (SAA), we investigated whether calcination and rehydration of fumed silica changes its hazard potential in the lung due to an effect on silanol density display. This analysis demonstrated that the accompanying change in surface reactivity could indeed impact cytokine production in macrophages and acute inflammation in the lung, in a manner that is dependent on siloxane ring reconstruction. Confirmation of this SAA in vivo, prompted us to consider safer design of fumed silica properties by titanium and aluminum doping (0-7%), using flame spray pyrolysis. Detailed characterization revealed that increased Ti and Al doping could reduce surface silanol density and expression of three-membered siloxane rings, leading to dose-dependent reduction in hydroxyl radical generation, membrane perturbation, potassium efflux, NLRP3 inflammasome activation, and cytotoxicity in THP-1 cells. The reduction of NLRP3 inflammasome activation was also confirmed in bone-marrow-derived macrophages. Ti doping, and to a lesser extent Al doping, also ameliorated acute pulmonary inflammation, demonstrating the possibility of a safer design approach for fumed silica, should that be required for specific use circumstances.

Reactivity of an Octanuclear Copper(I) Siloxide Compound – Isolation of a Copper(II) Oxo Compound with a Supertetrahedral Core

AbstractThe reactivity of the octanuclear copper(I) siloxide compound [L4Cu8], (1) (L2– = –OPh2SiOSiPh2O–), towards external substrates was tested. In the presence of N‐donor molecules like acetonitrile and propionitrile 1 decomposes with formation of cyclic siloxane rings. Contact with 2,2′‐bipyridine (bipy) leads to the formation of a mixed valent tricopper complex [L2Cu3(bipy)2], (3), which likely represents an intermediate of the disproportion of 1 to elemental copper and a mononuclear copper(II) complex [LCu1(bipy)], (2), which was isolated and characterized as the final product. The addition of O2 to 1 leads to an unprecedented supertetrahedral copper(II) complex [L6Cu10(μ4‐O)4(MeCN)4], (4), that incorporates four μ4‐oxido ligands. The structural parameters for compounds 2–4 were elucidated by single‐crystal X‐ray crystallography.

Reactive modeling of the initial stages of alkoxysilane polycondensation: effects of precursor molecule structure and solution composition.

Reactive molecular dynamics simulations were performed to study the polycondensation of alkoxysilane in solution with alcohol and water. The dynamic formation of siloxane clusters and rings was observed with simulation time. Two mechanisms for the growth of siloxanes were observed: monomer addition and cluster-cluster aggregation. The impacts of the alkoxysilane monomer chemical structure and solution composition on the rates of hydrolysis and condensation were explored. The polycondensation of different precursor alkoxysilane monomers (tetramethoxysilane, trimethoxysilane, methyltrimethoxysilane, or tetraethoxysilane) was modeled. The steric bulk of chemical groups attached to the monomer, such as silyl or alkoxy groups, were found to impact reaction rates. The influence of solution composition was investigated by simulating multiple systems with different concentrations of tetramethoxysilane, methanol, and water. Reactive molecular dynamics is used for the first time to study the polycondensation of alkoxysilanes, creating opportunities for future theoretical studies of the sol-gel process.

Strained surface siloxanes as a source of synthetically important radicals

The calcination of pure amorphous silica at temperatures up to 850 °C results in the formation of strained siloxane rings which are capable of undergoing homolytic cleavage to generate radicals when in the presence of an appropriate substrate.

Flexible cyclic siloxane core enhances the transfection efficiency of polyethylenimine-based non-viral gene vectors.

Transfection of nucleic acid molecules, large enough to interfere with the genetic mechanisms of active cells, can be performed by means of small carriers, able to collectively collaborate in generating cargocomplexes that could be involved in passive mechanisms of cellular uptake. The present work describes the synthesis, characterization, and evaluation of transfection efficacy of a conjugate molecule, which comprises a cyclic siloxane ring (2,4,6,8-tetramethylcyclotetrasiloxane, cD4 H) as the core, and, on average, 3.76 molecules of 2 kDa polyethyleneimine (PEI) as cationic branches, with an average molecular mass of 7.3 kDa. As demonstrated by in silico molecular modeling and dynamic simulation, the conjugate molecule (cD4 H-AGE-PEI) tends to adopt an asymmetric structure, specific for amphipathic molecules (confirmed by a log P value of -1.902 ± 0.06), that favors a rapid interaction with nucleic acids. The conjugate and the polyplexes with the pEYFP plasmid were proved to be non-cytotoxic, and capable of ensuring transfection yields better than 30%, on HEK 293T cell culture, superior to the value obtained using the SuperFect® reagent. We presume that the increased transfection efficacy originates in the ability of the conjugate to locally tightly encompass pDNA molecules by electrostatic interaction mediated by the short PEI branches, and consequently to expose the siloxane hydrophobic moiety, which decreases the interaction energy with the lipid layers.

Hierarchical superstructures from a star-shaped molecule consisting of a cyclic oligosiloxane with cyanobiphenyl moieties.

Unconventional star-shaped liquid crystals (abbreviated as SiLCs) were successfully synthesized by chemically connecting four cyanobiphenyl anisotropic mesogens to the periphery of a super-hydrophobic and ultra-flexible cyclic tetramethyltetrasiloxane ring with flexible hexyl chains. Based on the combined experimental techniques of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), solid-state carbon-13 ((13)C) nuclear magnetic resonance (NMR) spectroscopy and one-dimensional (1D) wide-angle X-ray diffraction (WAXD), it was found that the SiLC molecule exhibited the monotropic phase transition from a LC phase to a crystalline phase. The crystalline phase was only detected during slow heating processes above its glass transition temperature, while a LC phase was formed both during cooling and during heating processes. The hierarchical superstructures were identified from the structure-sensitive 2D WAXD of the macroscopically oriented SiLC film and confirmed by selected area electron diffraction (SAED) of the SiLC single crystals. The molecular packing symmetry in the monoclinic unit cell was further investigated by computer simulations on the real and reciprocal spaces. Macroscopically oriented SiLC hierarchical superstructures on the different length scales may provide the targeted physical properties, which can allow us to apply SiLC molecules in the fields of electro-optical devices and nonlinear optics.

Covalent functionalization of silica surface using "inert" poly(dimethylsiloxanes).

Methyl-terminated poly(dimethylsiloxanes) (PDMSs) are typically considered to be inert and not suitable for surface functionalization reactions because of the absence of readily hydrolyzable groups. Nevertheless, these siloxanes do react with silica and other oxides, producing chemically grafted organic surfaces. Known since the 1970s and then forgotten and recently rediscovered, this reaction provides a versatile yet simple method for the covalent functionalization of inorganic surfaces. In this work, we have explored the reactions of linear methyl-terminated and cyclic PDMS and bis-fluoroalkyl disiloxanes for the surface functionalization of mesoporous silica (Dpore ≈ 30-35 nm). The optimal reaction conditions included 24 h of contact of neat siloxane liquids and silica at 120-250 °C (depending on the siloxane). A study of the reactions of silicas with different extents of hydration demonstrated the critical role of water in facilitating the grafting of the siloxanes. The proposed reaction mechanism involved the hydrolysis of the adsorbed siloxanes by the Lewis acidic centers (presumably formed by water adsorbed onto surface defects) followed by the coupling of silanols to the surface to produce grafted siloxanes. For rigorously dehydrated silicas (calcination ∼1000 °C), an alternative pathway that did not require water and involved the reaction of the siloxanes with the strained siloxane rings was also plausible. According to FTIR and chemical analysis, the reactions of bis-fluoroalkyl disiloxanes and cyclic PDMS (D3-D5) produced covalently-attached monolayer surfaces, and the reactions of high-MM methyl-terminated PDMS produced polymeric grafted silicas with a PDMS mass content of up to 50%. As evidenced by the high contact angles of ∼130°/100° (adv/rec) and the negligible amount of water adsorption over the entire range of relative pressures, including saturation (p/p0 → 1), the siloxane-grafted porous silicas show uniform, high-quality hydrophobic surfaces. An overall comparison of siloxanes with classical silane coupling agents (i.e., silanes with readily hydrolyzable functionalities such as chloro, amino, etc.) demonstrated that the reactions of siloxanes produced surfaces of similar quality and, although requiring higher temperatures, used noncorrosive, less hazardous reagents, thereby providing an environmentally benign alternative to the chemical functionalization of metal oxide surfaces.

Insight into the structure of polymer–silica nano-composites prepared by vapor-phase

Using a new synthesis technique, in which mesoporous Amberlite XAD7HP resin beads swollen with TEOS were exposed to vapors of either (H2O+HCl) or (H2O+NH3), we obtained smooth, porous, mechanically stable silica gel spheres after burning out the sacrificial organic template. Combined N2 sorption, SEM, TEM, 29Si NMR, and Raman measurements were used to characterize the physical properties and molecular structures of the intermediate and final gels. Our atomically resolved TEM pictures provide the first visual demonstration of the presence of 3 to 6 member siloxane rings predicted by our Raman studies and other indirect methods. It is demonstrated that the physical appearance, morphology and porosity of the acid and base set gels are different from each other and also from those silica gels that were earlier polymerized from TEOS or Na-silicate saturated Amberlite XAD7HP with aqueous NH4OH or HCl solutions in liquid phase. We show that the different physical properties of the vapor-phase set gels are associated with different gelling rates at acidic and basic conditions, which generates molecular differences both in the intermediate and the final products.

Infrared and Raman spectroscopic characterization of some organic substituted hybrid silicas

Nine hybrid silicas bearing the organic substituent groups methyl, octyl, octadecyl, vinyl, phenyl, mercaptopropyl, isocyanatopropyl, chloropropyl and glycidoxypropyl were synthesized by an acid-catalyzed, hydrolytic sol–gel process. The resulting solid materials were characterized by their absorbance and attenuated total reflection (ATR) IR and Raman spectra. The latter technique proved to be particularly useful in the identification of the organic moieties in the hybrid silicas. The effect of the presence of the organic groups on the silica networks was also investigated – there were increases observed in both the SiOSi bond angles and bond lengths. Moreover, deconvolution of the IR-active antisymmetric SiOSi stretching bands permitted detection of the four- and six-membered siloxane rings present in the silicas. There proved to be a greater number of four-membered rings on the surfaces of the particles. Both IR and Raman spectroscopy proved to be invaluable in the characterization of these hybrid materials.