Silicon

High molecular weight copolymers, referred to as polysilalkylene siloxanes or hybrid silicones, were prepared using anionic ROP of 1,1,3,3,14,14,16,16-octamethyl-2,15-dioxa-1,3,14,16-tetrasilacyclohexacosane (II) and octamethylcyclotetrasiloxane (D4) mixtures. The resultant gum-like polymers were characterized by 1H NMR, 13C NMR, 29Si NMR, FTIR, GPC, TGA and FTIR. It was determined that the resultant polymers possessed a ratio of alkylene to dimethylsiloxane units similar to that expected from the original monomer ratio. Number averaged molecular weights ranged from 111,000 to 160,900 g/mol in yields of 75% to 78%. In addition, the thermal stability of the poly(decanylene-co-dimethylsiloxane)s were similar to that of the homopolymer based on II. KeywordsPolysilalkylenesiloxane–Poly(decanylene-co-dimethylsiloxane)–Hybrid silicone–Copolymer

Metal-oxo-colloids have been prepared using tetraethoxysilane (TEOS) oligomers with titanium tetra-i-propoxide (TIP) or titanium (di-i-propoxide) bis(acetylacetonate) (TIA) precursors. Transmission electron microscopy (TEM), FTIR, UV-Vis, and photoluminescence spectroscopy were used to investigate the composition, the size, and optical properties of the Si/Ti core–shell colloids. The presence of hetero-bonded silicate structure (Si–O–Ti) was indicated by FTIR spectroscopy. The size of Si/TIP system ranged from 55 to 120nm and Si/TIA system ranged from 220 to 250nm. The TEM data indicated that the size of colloids can be controlled by the TIP or TIA content. The Si/Ti system exhibited strong absorption in the UV-range, yet had excellent optical transmittance in the visible range. The Si/Ti systems exhibited a photoluminescence emission at 329nm. KeywordsSilica-Colliod-Sol–Gel-Photoluminescence

Infrared absorption spectroscopy measurements for a number of Na-borosilicate glasses containing AgBr and Cu2O were carried out in order to elucidate the structure of these glasses and the forms in which the transition metal ions exist in it. The raw materials used were of chemically pure grade and were finely pulverized. The temperature of the melting was 1,450°C for 2h and the samples were then annealed at 480°C. The prepared glasses studied were then heat treated at 600°C for 1h and cooled inside the furnace. The absorption measurements in the Infrared region of the spectrum were recorded in range of (4,000–400) cm−1 using a Jacso FT-IR 300E Infrared spectrophotometer for all glasses studied. The experimental results obtained showed characteristic variations of the position and intensity of the absorption bands with the glass composition. The effect of the different transition metal oxides on the deformation of the groups present was investigated. KeywordsSodium borosilicate glasses–Transition metal oxides–Silver bromide–Cuprous oxide–Photochromic glasses–Infrared spectra

A study was made in the present investigation on siloxane containing tetraglycidyl epoxy nanocomposites in order to determine their suitability for use in high performance applications. The synthesis of the siloxane tetraglycidyl epoxy resin denoted as ‘E’ was done and it was characterized by Fourier Transform Infrared (FT-IR) spectra and 1H, 13C Nuclear Magnetic Resonance (NMR) spectra. Nanoclay and polyhedral oligomeric silsesquioxanes (POSS)-amine nanoreinforcements denoted as N1 and N2 were incorporated into the synthesized epoxy resin. Curing was done with diaminodiphenylmethane (DDM) and bis (3-aminophenyl) phenylphosphine oxide (BAPPO) curing agents denoted as X and Y respectively. The mechanical, thermal, flame retardant and water absorption behaviour of the epoxy nanocomposites were studied and the results are discussed. KeywordsEpoxy resin–Thermal stability–Flame retardancy–Limiting oxygen index–Mechanical properties

The effects of precursor structure and polycondensation conditions on the properties of hybrid nanoparticles synthesized from organo-trimethoxysilanes were studied. Hybrid nanoparticles containing groups capable of forming hydrogen bonds were synthesized from functional derivatives of 3-aminopropyltrimethoxysilane. For the synthesis of phenylurea-functionalized organosilica nanoparticles different approaches to nanoparticle preparation were used. It was shown that the nature of the functional groups (proton-donor or proton-acceptor) affects the aggregation of silica nanoparticles. Also, the difference in behavior of nanoparticles prepared using surface modification and polycondensation was demonstrated for different pH, ionic strength and solvent polarity. As a result, by changing the pH of the solutions, it is possible to shift the aggregation pattern of these nanoparticles, such as the size of the initially formed aggregates. KeywordsSilica–Colloid–Nanoparticle–Aggregation

Quantum mechanical DFT calculations of the model methyl and silyl esters of simple thiophosphorus acids are presented which help to predict some structural features and reactivity aspects of these reactants. Their applicability in organophosphorus chemistry is discussed. KeywordsSilyl esters of thiophosphoric acids–Silyl esters of thiophosphinic acids–Structure–Reactivity–DFT calculations

New silane and siloxane compounds containing cyclic carbonate functional groups were synthesized and characterized. The compounds were prepared via two routes: hydrosilation of SiH containing siloxanes and alcoholysis of chlorosilanes with hydroxy-terminated oligoethers. The products were purified by distillation and solvent extraction and characterized using 1H, 13C, and 29Si NMR. Upon doping with lithium bis(oxolato)borate (LiBOB), the conductivities of the compounds were determined. These carbonate compounds themselves did not show promising conductivities. However, when used as additives to silicone-containing oligoether electrolytes, the conductivities of the resulting mixtures were increased by up to 35%. KeywordsSiloxane–Silane–Hydrosilation–Alcoholysis–Lithium battery–Ionic conductivity–Electrolyte–Poly(ethylene oxide)–Cyclic carbonate

Five silane blends were evaluated as experimental adhesion-promoter primers. First, five organosilane monomers (silicon esters), 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, tetrakis-(2-ethyloxyethoxy)silane and bis-[3-(triethoxysilyl)propyl]tetrasulfide, were diluted to 1% (v/v) and blended with a non-functional cross-linking silane, 1,2-bis-(triethoxysilyl)ethane (1%), in 95% ethanol. After activation, each blend was applied to silica-coated Ti coupons. A resin based on bis-phenol-A-diglycidyldimethacrylate was then bonded and photo-polymerized as stubs to the pretreated Ti coupons. Half of the specimens were stored in dry conditions and half were artificially aged by thermo-cycling. The primers containing 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltrimethoxysilane produced significantly higher shear bond strength values than the control silane, a standard pre-activated product used in clinical dentistry. KeywordsSilica-coating-Silica-Silane coupling agent-Silane monomer-Titanium

Three bifunctional silane coupling agent monomers and their blends with a cross-linking silane were investigated as six experimental adhesion-promoters in vitro. Three organosilane monomers, 3-methacryloxypropyltrimethoxysilane, styrylethyltrimethoxysilane, and 3-(N-allylamino)propyltrimethoxysilane, were prepared as 1% (v/v) primers and also blended with a cross-linking silane, 1,2-bis-(triethoxysilyl)ethane at 0.5% (v/v), in a 95:5 solution of ethanol in deionized water. The silanes were allowed to hydrolyze using formic acid as catalyst and were applied to a substrate of silica-coated Ti. The control was a pre-hydrolyzed silane coupling agent that is commonly used in dentistry. An experimental unfilled bis-phenol-A-diglycidyldimethacrylate/methylmethacrylate resin was bonded by photo-polymerization as stubs to the prepared Ti. Half of the specimens were artificially aged by wet thermo-cycling and half were stored in dry conditions in a desiccator. Storage conditions and the type of primer silane or blend significantly affected shear bond strength values. 3-Methacryloxypropyltrimethoxysilane, alone or blended, produced significantly higher shear bond strength values than the control, both after dry storage and after thermo-cycling. KeywordsFormic acid-Silica-coating-Silica-Silane coupling agent-Silane monomer-Titanium

Background Clinically, in dental practice the durability of zirconia adhesion is the key to successful long-term all-ceramic structures, e.g. fixed partial dentures (FPDs). Purpose To evaluate the effects of seven different surface conditioning methods on the shear bond strength of particulate filler resin composite cement bonded onto a zirconia surface. Methods Seven groups of zirconia each consisting of 14 specimens (n = 14) were made. The specimens were conditioned using various methods and embedded into acrylic cylinders with an acrylic polymer material to form substrates. The specimens were cleaned in an ultrasonic device for 300 s. Self-adhesive particulate filler resin composite stubs were added onto zirconia surfaces and photopolymerized for 40 s. The specimens were kept in distilled water for 24 h at room temperature and thermocycled 6,000 cycles (5 ± 1°C-55 ± 1°C). The shear bond strengths were measured with a crosshead speed of 1.0 mm/min and the data were analyzed by ANOVA. Results The shear bond strengths varied widely and ANOVA revealed significant differences between the groups (p < 0.001). Conclusions Tribochemical silicatization combined with silanization achieved the highest shear bond strength values.

In this study we have assessed the effect of long-term water storage at 37oC on silane-aided adhesion promotion. Five experimental silane blends were evaluated as adhesion-promoters. First, five functional organosilane monomers (silicon esters), 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, tetrakis-(2-methacryloxyethoxy)silane and bis-[3-(triethoxysilyl)propyl]tetrasulfide, were diluted to 1% (v/v) in 95% ethanol and blended with a non-functional cross-linking silane, bis-1,2-(triethoxysilyl)ethane (1%). A commercially available pre-activated silane product was used as the control. After activation by hydrolysis, each primer blend was applied to silica-coated Ti coupons. Stubs of experimental bis-phenol-A-diglycidyldimethacrylate (bis-GMA)-based resin were bonded by photo-polymerization onto the pretreated Ti coupons. Half of the specimens were stored in deionized water for 6months and half for 12months. The primer containing 3-acryloxypropyltrimethoxysilane and bis-1,2-(triethoxysilyl)ethane produced significantly higher shear bond strengths than the control silane and other experimental silane primers after both periods of storage. KeywordsSilica-coating-Silica-Silane coupling agent-Silane monomer-Titanium-Water-storage

Silica-bound aldehyde functional silane was used as a versatile bridge to attach porphyrin to the surface of silica and as a surface-bound free radical initiator to yield PMMA brushes. The aldehyde functionality is obtained by a simple ozonolysis of the surface-bound allylsilane, whereby the double bonds are oxidized in high yield to the desired aldehyde. Mono-amino porphyrin was attached to the silica surface under mild conditions via Schiff-base linkages, whilst anchored PMMA was obtained by free radical initiation using an aldehyde/redox free radical polymerization. FTIR and TGA data were used to determine and characterize the attachment to the silica surface.

The present study reports the preparation and characterization of silica-based immobilization matrices for the purpose of metal accumulation using immobilized cyanobacterium Nostoc calcicola. Silica gel was prepared using aqueous sodium silicate and colloidal silica. Calcium alginate (CAG) beads were coated with silica using sodium silicate solutions. Microscopy observations and TTC tests confirmed that the immobilized cells were intact and viable. Ultrastructural studies with electron microscopy revealed a membrane thickness of approximately 10μm around the CAG and the silica gel to be of mesoporous nature. BET surface area of silica gel-immobilized N. calcicola was 160m2g−1. The porous volume and average pore diameter were 0.40cm3g−1 and ca. 100Å, respectively, as calculated using the BJH model. Studies on silica-coated calcium alginate immobilized cells showed that these were superior to the uncoated CAG beads in terms of mechanical strength and metal accumulation. The silica matrices were found to be stable for repeated cycles of metal removal and with commonly used eluants for desorption processes. These matrices have potential applications in immobilization of industrially important biocatalysts. KeywordsBioencapsulation-Hybrid materials-Silica gel-Bioremediation-Cyanobacteria

Introduction One major problem in the photovoltaic industry is the high price of refined solar grade silicon. In this research, a new method for refining metallurgical grade silicon to solar grade silicon is investigated. Methods The main steps include alloying with copper, solidification, grinding and gravity separation. Results A metallography study showed the presence of only two microconstituents, mainly pure silicon dendrites and Cu3Si intermetallic. Chemical analysis revealed a several times higher impurity level in the Cu3Si intermetallic than in the pure silicon; furthermore, the amount of nine elements in the refined silicon is reduced below the ICP detection limit. Discussion The acquired results showed that the suggested method is efficient in removing impurities from the metallurgical grade silicon with great potential for further development.

Metals and their alloys have been widely used in all aspects of science and engineering. However the science of nanotechnology is driving newer demands and requirements for better performance of existing materials and also at a higher level of precision. This is naturally presenting complicated demands on the surface of these metals with a need for surface modification. Self Assembled Monolayers (SAMs) are nanosized coatings that present the most efficient method of carrying out surface modification. Alkylsilanes are silicon based SAMs which are compatible with the majority of metals and alloys. These nanocoatings can serve primary functions such as surface coverage, etch protection and anti corrosion, along with a host of other secondary chemical functions because of their amphiphilic nature. We present a brief introduction to surface modification of metals and alloys followed by a detailed description of silane based nanocoatings and their applications in technology. Then a look at the engineering aspects of these coatings in terms of patterning techniques is presented along with a discussion of the applications of patterned SAMs. KeywordsSelf assembly-Surface modification-Self assembled monolayers (SAMs)-Alkylsilanes-Organosilanes-Patterning-Patterning techniques-Laser patterning

We report an elegant and simple method to fabricate silica films with controlled thickness and roughness using protein coated solid surfaces as substrates. Bovine serum albumin (BSA) and lysozyme having different inherent charges have been used as model proteins (templates) to fabricate silica films. The formation of silica films was achieved by immobilization of BSA and lysozyme on amine (poly(allylamine) (PAH), poly(ethyleneimine) (PEI) and octadecyl amine (ODA)), coated surfaces, followed by treatment with silica precursors (tetramethoxysilane) under environmentally benign conditions of pH and temperature. BSA adsorbs strongly on hydrophilic surfaces (PAH and PEI coated) via electrostatic interaction, while lysozyme shows greater affinity towards hydrophobic surfaces (ODA coated) via largely hydrophobic interactions. The thickness (12–60nm) and roughness of the films (1.30–3.75nm) could be tuned by varying the amount of the adsorbed proteins on the amine-coated surfaces. This simple route to prepare silica films of controlled thickness could have potential application in membrane fabrication, biomedical devices, biosensors and next generation electronic components. KeywordsSilica-BSA-Lysozyme-Thickness-Tuneable-Roughness

This paper focuses on the improvement of hydrophicility and water content of poly(dimethylsiloxane) (PDMS) by bonding a hydrophilic macromer, hydroxyl-terminated linear poly(ethylene glycol) (PEG), into a highly hydrophobic macromer, hydroxyl-terminated linear PDMS to prepare amphiphilic conetworks (APCNs) with the crosslinkers, tetraethoxysilane (TEOS) and bis[(3-methyldimethoxysilyl)propyl]-polypropylene oxide (BMPPO), which also functioned as a compatibilizer. Fourier transform infrared results clearly demonstrated the occurrence of the hydrolysis reactions between the terminal hydroxyl groups on the terminal of the two polymer chains and the alkoxy groups in TEOS and BMPPO. Differential scanning calorimetry results and X-ray diffraction obviously showed the presence of the two phases in the conetworks. The contact angle (CA) indicated the wettability of the conetworks increased in the surfaces, that is, CA values decreased significantly from 105° in PDMS to 55° in the PEG/PDMS APCN (10/1mol ratio), and the swelling degrees of the APCNs increased from ca. 0 to 60 % when the PEG/PDMS mol ratio was larger than 4/1. The APCNs with such high hydrophilicity and the good mechanical properties should be useful as biomaterials.

Montmorillonite modified with distearyldimethyl ammonium chloride (C18-QAC) (Nanofil-15) (NF15) was incorporated into polydimethylsiloxane-urea (silicone-urea, PSU) copolymers. PSU was obtained by the reaction of equimolar amounts of aminopropyl terminated polydimethylsiloxane (PDMS) oligomer (  = 3,200g/mol) and bis(4-isocyanatohexyl)methane (HMDI). A series of PSU/NF15 nanocomposites were prepared by solution blending with organoclay loadings ranging from 0.80 to 9.60% by weight, corresponding to 0.30 to 3.60% C18-QAC. Colloidal dispersions of organophilic clay (NF15) in isopropanol were mixed with the PSU solution in isopropanol and were subjected to ultrasonic treatment. Composite films were obtained by solution casting. FTIR spectroscopy confirmed that the organoclay mainly interacted with the urea groups but not with PDMS. XRD analysis showed that nanocomposites containing up to 6.40% by weight of organoclay had fully exfoliated silicate layers in the polymer matrix, whereas 9.60% loading had an intercalated structure. Physicochemical properties of nanocomposites were determined. PSU/NF15 nanocomposites displayed excellent long-term antibacterial properties against E. coli.

The tetrakis(arylethynyl)silanes 1–4 of which 2–4 are new compounds have been synthesized and determined by single crystal structure analysis to show their tetrahedral molecular geometries reflected in slightly disturbed S4 symmetry in the crystal lattices. The lattice structures are mainly determined by close packing effects while the interactions of π-stacking type or C–H···π contacts are rather secondary. A similar behaviour is found for the crystal structure of the comparative compound 5 with reference to 4 which lacks the ethynylene units. It is demonstrated that the given molecular constructions are distinguished by a high degree of tetrahedral persistency governing the packing structures.

One-dimensional (1D) silicon nanowires (SiNWs) were fabricated on a catalyst free Si (100) substrate using a thermal evaporation method. Based on a SVLS growth mechanism, the SiNWs obtained were 30-265 nm in diameter and 1.7 mu m to several tens of microns in length. It was found that the presence of graphite powder alone is enough to accomplish the growth. A systematic study of how the growth conditions, such as the Ar carrier gas flow rate, and the growth time effect was performed. The Photoluminescence (PL) of SiNWs was also investigated. The observed broad band is composed of an UV peak or band centered at 350 nm (3.54 eV) and a wide hemisphere curve over the green bluish region (430-550 nm). The theory behind these emissions is discussed.

We close this special issue of SILICON with a personal commentary on Biological and Bioactive Silicon Systems by the editor-in-chief of the journal SILICON and the guest co-editor of this special issue. KeywordsSilicon–Silica–Biosilica–Silicones

Silicon is one of the most important elements in the current age of the anthropocene. It has numerous industrial applications, and supports a high-tech multi-billion Euro industry. Silicon has a fascinating biological and geological cycle, interacting with other globally important biogeochemical cycles. In this review, we bring together both biological and geological aspects of the silicon cycle to provide a general, comprehensive review of the cycling of silicon in the environment. We hope this review will provide inspiration for researchers to study this fascinating element, as well as providing a background environmental context to those interested in silicon. KeywordsSilicon biogeochemistry-Geology-Biology-Carbon-Nitrogen-Phosphorus

In this contribution, we demonstrate the potential of combining bioinspired synthesis and continuous flow processing to generate functional materials with possible applications in catalysis, biocatalysis and photonic devices. Specifically, we have prepared invertase immobilized on silica while preserving its enzymatic activity. Furthermore, we present routes to synthesize silica and gold colloid composite materials (Au@SiO2) and demonstrate that the colloids retain their optical activity. KeywordsBiomimetic-Flow chemistry-Enzymes-Green chemistry

Inspired by Nature, biocatalysis and biotechnology have quickly become burgeoning fields in silicon chemistry. From cell cultures to isolated enzymes researchers are exploring the use of biological systems to affect chemical transformations at or near silicon atoms. This review will examine the history of biotechnology as it pertains to organosilicon compounds (i.e., compounds with one or more Si-C bonds) and provide some insights into future directions for the field.

2,4-Bis(trimethylsilyl) substituted n-pentasilane Me3SiSiMe(SiMe3)SiMe2SiMe(SiMe3)SiMe3 (1) has been prepared from Me2SiCl2 and (SiMe3)2SiMeK, and its solid state molecular structure has been determined by single crystal X-ray diffraction. By reaction of 1 with KOtBu and subsequent treatment of the resulting silyl anion with (MeO)2SO2, the novel hexasilane Me3SiSiMe(SiMe3)SiMe2SiMe2SiMe3 (2) has been synthesized. By again using the reaction sequence KOtBu/(MeO)2SO2, known n-pentasilane Me3SiSiMe2SiMe2SiMe2SiMe3 (3) has been prepared in a novel and very convenient way from 2. All silanes 1, 2, and 3 as well as the intermediate silyl anions obtained from 2 and 3 have been characterized by 29Si and 1H NMR spectroscopy, 1 and 2 by elemental analyses also. Raman spectra in the temperature range 210–370K of the pure liquids 1, 2 and 3 as well as of solutions in toluene (1 and 2) or cyclopentane (3) reveal that all of the silanes exist as mixtures of conformers. The symmetric SiSi stretch observed in the range 341 to 363cm-1 and possessing by far the largest Raman intensity of all SiSi stretching vibrations splits into five bands for 3 and two bands for 1 and 3. Quantum chemical DFT B3LYP/6–311G(d) calculations located 15 conformational minima for 2 with relative energies up to 19.9 kJmol-1, and five minima for 1 with relative energies up to 15.5 kJmol-1. Calculated SiSiSiSi torsion angles vary between 26.2° (smallest value found) and 179.3°, demonstrating the flexibility of backbones composed of silicon. KeywordsPentasilanes-Quantum chemical calculations-Raman spectroscopy-Conformations

In this paper we discuss and interpret the results of shear bond strengths achieved after the use of two silane coupling agents with isocyanato functionality, viz. 3-isocyanatopropyltrimethoxysilane and 3-isocyanatopropyltriethoxysilane. The silanes were used alone and also blended with a non-functional cross-linking silane on silicatized zirconia before light-curing of resin stubs on the surface, as described elsewhere in the first part of our study (see “Part I: Experimental”). A series of reaction mechanisms and conceptual diagrams are also presented. The reaction mechanisms illustrating the effect of adding a cross-linking silane into a silane blend, the silane hydrolysis and the behavior of two organofunctional groups (isocyanate and alkene) of silanes upon reaction with Rely X Unicem Aplicap resin-composite cement are discussed in detail. KeywordsBimolecular nucleophilic substitution (SN2) reaction-Transition state-Siloxane network-Free radical reaction-3-isocyanatopropyltriethoxysilane-3-isocyanatopropyltrimethoxysilane-Cycloaddition

In this study we have investigated the effects of the chain length of hydrolyzable groups in two isocyanato silane coupling agents, 3-isocyanatopropyltrimethoxysilane and 3-isocyanatopropyltriethoxysilane, on the shear bond strength of resin attached to silicatized zirconia. In addition, the effects of varying the silane concentration (at 0.1vol% and 1.0vol%) with or without the addition of a cross-linking silane (0.05vol% or 0.5vol% bis-1,2-(triethoxysilyl)ethane) were assessed. It was concluded that the use of the experimental primer of 3-isocyanatopropyltrimethoxysilane at either 0.1vol% or 1vol% with cross-linking silane resulted in significantly higher shear bond strengths than the use of primer without the cross-linking silane. KeywordsSilane-3-isocyanatopropyltrimethoxysilane-3-isocyanatopropyltriethoxysilane- bis-1,2-(triethoxysilyl)ethane)-3-methacryloxypropyltrimethoxysilane-Cross-linking-Hydrolyzable group-Zirconia

The conjugation of nanoparticles to carbon nanotubes (CNTs) involves various steps including premodification of the nanotubes, which is known to be a very tedious process and sometimes leads to a mixture of products. In this regard, a direct route to generate such conjugates is a worthwhile endeavor. In this paper, we report a novel, mild, one-pot, approach to a controlled and direct coordination of Pd nanoparticles (Pd NPs) onto the surface of single walled carbon nanotubes (SWNTs), without any pre-modification of the SWNTs surface. We also present detailed characterization of the SWNT-Pd NP hybrid systems using High Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive X-ray Spectroscopy (EDS), Mid-Infrared Spectroscopy (Mid-IR) and UV-Visible Spectroscopy (UV–vis) along with the stability studies of the nanoconjugates. KeywordsSingle Walled Carbon Nanotubes (SWNTs)–Pd-Nanoparticle–Nanosized metal–Tris[3-(trimethoxysilyl)propyl] Isocyanurate–Conjugates–Catalyst

Immobilized lipase B from Candida antarctica was used to synthesize copolymers of poly(ε-caprolactone) (PCL) with α,ω-(dihydroxy alkyl) terminated poly(dimethylsiloxane) (PDMS). The reactions were carried out in toluene with a 1:2w/v ratio of the monomers to solvent at 70 ºC. The PCL−PDMS−PCL triblock copolymer composition was varied by changing the feed ratio of the reactants [CL]/[PDMS] (80:20; 60:40; 40:60; 20:80w/w, respectively). The enzymatically synthesized copolymers were characterized by GPC, FTIR, TGA, DSC and XRD. The successful synthesis of the copolymers was confirmed by the appearance of a single peak in all of the respective GPC chromatograms. An increased feed ratio of [CL]/[PDMS] produced an increase in the number-average molecular weight (Mn) of the copolymers from 4,400g mol−1 (20:80w/w of [CL]/[PDMS]) to 13,950g mol−1 (80:20w/w of [CL]/[PDMS]). The copolymers were shown by DSC and XRD to be semi-crystalline and the degree of crystallinity increased with an increase in the [CL]/[PDMS] feed ratio. The crystal structure in the copolymers was analogous to that of the PCL homopolymer. In enzymatic polymerization the recovery and reuse of the enzyme is highly desirable. When the lipase was recovered and reused for the copolymerization, higher molecular weight copolymers were obtained upon a second use. This appears to be due to an increased activity of the immobilized lipase following an opening up of the acrylic resin matrix in the organic medium. This improvement was not maintained for subsequent recycling of the lipase principally due to the disintegration of the acrylic resin matrix.

Multiwalled carbon nanotubes (MWCNTs) have been coated with silicon carbide (SiC) using polycarbosilane as precursor in order to improve their thermo oxidative stability. The polycarbosilane coated MWCNTs were heated to ~1300°C under an inert atmosphere to generate the SiC coating. X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy have confirmed the formation of SiC on the MWCNTs. The retention of the tubular structure of the MWCNTs has been confirmed by transmission electron microscopy. Thermogravimetric analysis has been performed to evaluate the thermo oxidative stabilities of coated and virgin MWCNTs. Sonication studies have shown that the mechanical strength of the MWCNTs was increased after coating with SiC. KeywordsPolycarbosilane-SiC-MWCNTs

The effect of sterically hindered carbosilane moieties, situated as end groups in telechelic oligodimethylsiloxanes, was investigated with respect to the mobility of silicon atoms in the main chain. The relaxation phenomena in such crowded systems were studied by DSC and NMR methods. Spin–lattice relaxation times T 1 (29Si NMR) of silicon atoms in the oligomer chain were estimated and related to the distance between a given siloxane unit and the carbosilane moiety. It was found that the mobility of terminal siloxane units has been substantially affected. However, in the long range, the effect does not to seem to outweigh the intrinsic flexibility of the siloxane bonds. KeywordsSiloxane–Carbosilane–Tris(trimethylsilyl)methane–Segmental mobility–Relaxation

Silica and carbon are naturally occurring in rice husks (RH) and these were used for the production of ceramic materials made of Si, C, N and O as the main constituents. The various “silicon-based” ceramics were produced from the thermal decomposition of rice husks and posterior heat treatment at temperatures varying from 1200–1450 °C under a pure nitrogen atmosphere. FeSO4 in various concentrations was introduced to the decomposed rice husk prior to the heat treatment. The formation of various Si/C/N/O ceramics in general and silicon nitride in particular, were studied with respect to the concentration of FeSO4 (4–10%) as well as temperature (1200–1450 °C). The formation of different phases were confirmed by XRD and FT-IR analysis. Morphology and surface properties of the products have been studied using SEM. The maximization of whiskers of the ceramic products was also studied through microstructural analysis. Elemental analysis of the whiskers product was analyzed through EDX. The chemical analysis of raw rice husk was also carried out. KeywordsSi-based ceramics-XRD-SEM-FT-IR-EDX-Microstructure-Rice husk

The sponge protein silicatein is the first enzyme that has been described to form an inorganic polymer (silica) from a monomeric precursor (tetraethoxysilane or orthosilicic acid). The models proposed for silicatein-mediated silica formation are mainly based on the use of synthetic substrates (hydrolytic cleavage of tetraethoxysilane to silanol compounds) or only consider the formation of less reactive silicic acid dimers (disilicic acid). Here we propose a new model for the catalytic mechanism of silicatein that leads to the formation of reactive, cyclic silicic acid species (trisiloxane rings and higher-membered siloxane rings) which easily promote the silica polycondensation reaction. KeywordsSilicatein–Silica formation–Polycondensation–Nucleophilic attack–Cyclic trisiloxane

A novel redox initiator system for carrying out the cationic polymerization of epoxide, oxetane and vinyl ether monomers has been developed. The redox couple is based on a triarylsulfonium salt as the oxidant with an organosilane as the reducing agent. The reaction between these two agents is markedly catalyzed by platinum and palladium complexes. Cationic polymerizations using this redox initiator system were carried out in a conventional manner with neat monomer or under solution conditions. This paper also describes the novel use of a two-component redox system in which the silane is delivered to the monomer sample in the vapor state. Optical pyrometry (infrared thermography) was employed as a convenient method with which to monitor the polymerizations. A study of the effects of variations in the structures of the triarylsulfonium salt, the silane and the type of noble metal catalyst were carried out. The use of this initiator system for carrying out commercially attractive cross-linking polymerizations for coatings, composites and electronic encapsulations is discussed. KeywordsRedox initiator-Cationic polymerization-Initiators-Epoxides-Organosilanes-Triarylsulfonium salts

The purpose of surface treatment (conditioning) methods on dental ceramics is to improve the retention and bonding between the enamel or the dentin and ceramic veneer, with the help of resin composite luting cements. These types of surface treatments include chemically altering the surface of ceramics with some specific acidic etchants followed by applying a silane coupling agent (silane). The silane currently used in dentistry is 3-methacryloxypropyltrimethoxysilane, a hybrid organic–inorganic trialkoxy ester monomer, which is diluted in an acidified water-ethanol solvent system. Such silane primers are said to be pre-hydrolyzed. Some oxide ceramics with high crystalline content, such as alumina and zirconia, cannot be easily etched with acid etchants. They should be silica-coated and silanized prior to bonding. A silane coupling agent should be applied after silica-coating to the ceramic surface to achieve chemical bonding and the optimal durable bond strength. KeywordsSilane coupling agent–Silane–Silica-coating–Hydrofluoric acid–Acid etchants–Zirconia

Frederic Stanley Kipping FRS is regarded as one of the founding fathers of silicon chemistry. In 57 research papers published between 1899 and 1944 he reported the first use of Grignard reagents to make alkylsilanes and arylsilanes and the prepartion of silicone oligomers and polymers. He coined the term ‘silicone’ in relation to these materials in 1904. His research formed the foundation for James Franklyn Hyde’s development of the first silicon based insulation materials at Corning Glass Works and then Dow Corning Corp., as well as inspiring Eugene G. Rochow’s work at General Electric Company in the development of the ‘direct method’ of silicone synthesis using silicon hydrides. Kipping was the first Sir Jesse Boot Professor of Chemistry at Nottingham University College and was married to Lily Holland whose sisters, Mina and Kathleen were married to two other prominent early 20th century British Chemists, William H. Perkin Jr. FRS and Arthur Lapworth FRS. This paper provides an insight into Professor Kipping’s life, personality and career. KeywordsKipping–Silicon–Silicone–Holland–Perkin–Lapworth–Nottingham–Hyde–Rochow

Comparison between the two main sol–gel/emulsion methods to prepare microparticles made of organosilica doped with a lipophilic molecule shows that entrapment only takes place starting from O/W emulsions. In this case, however, formation of spherical microcapsules, observed when the sol–gel polycondensation is carried out in a W/O microemulsion, does not take place. KeywordsMicroparticle–Sol–gel–Microencapsulation–Emulsion–Silica–Organosilica

During valve formation of the siliceous frustules of diatoms, bulk uptake of silicic acid and its subsequent transport through the cell is required before it can be deposited in the silica deposition vesicle (SDV). It has been assumed that transport takes place via silicon transporters (SITs), but if that were the case a control mechanism would have to exist for stabilization of the large amounts of reactive silicon species during their passage through the cell on the way to the SDV. There is, however, no reason to assume that classical silica chemistry does not apply at elevated levels of silicic acid, and therefore autopolymerization could reasonably be expected to occur. In order to find alternative ways of Si transport that correspond with the high speed of valve formation at the earliest stages of cell division we followed 31Si(OH)4 uptake in synchronously dividing cells of the diatoms Coscinodiscus wailesii, Navicula pelliculosa, N. salinarum, and Pleurosira laevis. The results were related to systematically derived mathematical models for a compartmental analysis of 5 possible uptake/transport pathways, including one involving SITs and one involving (macro)pinocytosis-mediated uptake from the extracellular environment. Our study indicates that the uptake of radioactive silicic acid matches best with the model that describes macropinocytosis-mediated silicon uptake. This process is well in line with the observed ‘surge uptake’ at the start of valve formation when the demand for silicon is high; it infers that in diatoms a pathway of uptake and transport exists in which SITs are not involved. KeywordsCompartmental analysis–Diatoms–Si-31–Valve formation–Silicon uptake

Crystalline Silicon-on-Sapphire (SOS) films were implanted with boron (B+) and phosphorous (P+) ions. Different samples, prepared by varying the ion dose in the range 1014–5 × 1015 and ion energy in the range 150–350keV, were investigated by the Raman spectroscopy, photoluminescence (PL) spectroscopy and glancing angle x-ray diffraction (GAXRD). The Raman results from dose dependent B+ implanted samples show red-shifted and asymmetrically broadened Raman line-shape for B+ dose greater than 1014 ions cm−2. The asymmetry and red shift in the Raman line-shape is explained in terms of quantum confinement of phonons in silicon nanostructures formed as a result of ion implantation. PL spectra shows size dependent visible luminescence at ∼1.9eV at room temperature, which confirms the presence of silicon nanostructures. Raman studies on P+ implanted samples were also carried out as a function of ion energy. The Raman results show an amorphous top SOS surface for sample implanted with 150keV P+ ions of dose 5 × 1015 ions cm−2. The nanostructures are formed when the P+ energy is increased to 350keV by keeping the ion dose fixed. The GAXRD results show consistency with the Raman results. KeywordsNanocrystalline materials-Phonon confinement-Raman spectra

Hydrolysis kinetics of soda lime silicate glass (SLS) with 75mol% SiO2 in different pH solutions was investigated. Fourier Transform Infrared (FTIR) spectroscopy was used to monitor and confirm the proposed corrosion mechanisms on the surfaces of prepared undoped (SLS) glass together with samples doped with one of the first 3d-transition metal oxides (TMO) (TiO2→CuO) when exposed to an aqueous solution for a short time period. The traditional proposed mechanism of silicate glass corrosion through ion exchange is analyzed in correlation with infrared reflectance vibrational spectra to confirm the suggested mechanism. The effects of transition metal oxides are followed and interpreted. KeywordsSoda lime silica glass-Transition metal-Corrosion-FTIR spectroscopy

Siloxanes with either methyl, cyclopentyl, or cyclohexyl groups were functionalized with methacrylate groups, then UV-cured using a free radical photo-initiator and a reactive diluent. Hexanediol dimethacrylate (0.1wt%) was used as the reactive diluent. After curing, the mechanical, the viscoelastic, the coating, and the release properties of the cured films were studied. In addition, the oxygen permeability and the X-ray diffraction scans were evaluated. The crosslink density reduced with increase in siloxane substituent size. The oxygen permeability was dependent on crosslink density, and increased with increasing substituent size. The increase in permeability, and thus free volume, was supported by X-ray studies which showed an increase in d-spacing with increasing alkyl size. The hardness, adhesion, and solvent resistance increased as the size of the substituent increased (methyl to cyclopentyl to cyclohexyl) in the siloxane backbone. The adhesion and re-adhesion forces increased with an increase in size of the backbone substituents. There was also an increase in the advancing and the receding contact angles with the increase in substituent size. KeywordsTelechelic-Viscoelastic properties-Fracture toughness-Release properties-Adhesion

Monolithic inorganic-organic hybrid materials have been synthesized via sol-gel processing of an ethylene glycol-modified ethane-bridged silane precursor in aqueous solution of the non-ionic block copolymer Pluronic™ P123. The influence of different sol compositions on the final gel structure was investigated in detail. The resulting materials consist of macroporous networks comprising periodically arranged mesopores, where the macropore size as well as the morphology of the material can be deliberately tailored by reducing the amount of the block copolymer template. The structure was investigated by small-angle X-ray scattering as well as scanning and transmission electron microscopy. Information on the porosity, surface area and pore size distribution were obtained from BET/BJH analysis and mercury intrusion measurements. For a more detailed insight into mechanism and kinetics of the mesostructure formation, in-situ SAXS experiments were carried out.

The effect of turbulence on several freshwater diatom taxa was investigated and our findings are described herein. We have compared diatom morphology in shallow natural systems that experience turbulence due to wind and in river/waterfall systems where turbulence is due to high flow rates. We have also introduced turbulence into diatom laboratory cultures by mechanical shaking and by forcing air into the media. In particular, we have studied diatoms in five independent environments or cultures: the freshwater diatoms Tabellaria and Eunotia in equatorial lakes experiencing extreme seasonal variability in depth; two freshwater diatom monocultures of Aulacoseira granulata var angustissima and Melosira varians in the laboratory; and a freshwater diatom community possessing equal amounts (by number) of elongated and non-elongated diatoms (mostly Nitzschia and mostly Cyclotella, respectively) in the laboratory. We have demonstrated the effect of turbulence on freshwater diatom frustule morphologies and, perhaps more importantly, the effect of turbulence on freshwater diatom species population after controlled perturbation of the organisms’ environment. It has been widely reported that symmetry is often preferred in biological evolution, however here we have observed a preference towards asymmetry for the survival of diatoms in the presence of environmental stress (in particular, turbulence). We also note that to date there have been no systematic attempts to manipulate diatom frustules using external stimuli. We therefore present a proof-of-concept study in order to demonstrate: (i) that diatom morphologies can be manipulated by controlled simple external triggers (chemical and physical) (ii) that population balance (i.e. natural selection) can be controlled via simple external triggers (chemical and physical). This approach could open up an entire new field of future studies wherein controlled environmental perturbations are used to manipulate the structure, form, growth and reproduction of biological species. KeywordsDiatoms-Biosilica-Silica-Turbulence-Natural selection

As a result of systematic studies of numerous polydi-n-alkylsilane order-disorder transitions using a combination of UV, Raman, IR as well as XRD methods some generalizations are made concerning the nature of these processes. A criterion is proposed for a given UV band assignment to a given polymer modification based not only on its λmax value but also on the band width, contour and temperature behaviour of these parameters. Three types of ordering possible for these polymers were shown not to be necessarily interrelated. Side chain “melting” does not inevitably lead to thermochromism while thermochromic structural transitions can occur within the same phase. KeywordsPolydi-n-alkylsilanes–Phase and structural transitions–Chain conformation–Thermochromism–UV, Raman and IR spectroscopy