Shape-controlled bridged silsesquioxanes: hollow tubes and spheres

A new approach for the morphological control of bridged silsesquioxanes has been achieved by the hydrolysis of silylated organic molecules bearing urea groups. The urea groups are responsible for the auto-association of the molecules through intermolecular hydrogen-bonding interactions. The self-assembly leads to supramolecular architectures that have the ability to direct the organization of hybrid silicas under controlled hydrolysis. The hydrolysis of the chiral diureido derivatives of trans-(1,2)-diaminocyclohexane 1 under basic conditions has been examined. The solid-state NMR spectra ((29)Si and (13)C) showed the hybrid nature of these materials with wholly preserved S-C bond covalent bonds throughout the silicate network. Hybrid silicas with hollow tubular morphologies were obtained by the hydrolysis of the enantiomerically pure compounds, (R,R)-1 or (S,S)-1, whereas the corresponding racemic mixture, rac-1, led to a hybrid with ball-like structures. The tubular shape is likely to result from a combination of two phenomena: the auto-association abilities and a self-templating structuration of the hybrid materials by the organic crystalline precursor. Electronic microscopy techniques (SEM and TEM) gave evidence for the self-templating pathway. The formation of the ball-like structures occurs through a usual nucleation growth phenomenon owing to a higher solubility of the corresponding crystals in the same medium.     

Particle growth of hybrid materials followed by dynamic light scattering

The hydrolysis of distannylated compounds in which the tin atoms are linked by an organic spacer has been studied under microemulsion conditions using dynamic light scattering and infrared spectroscopy. The experiments provided evidence that the growth of hybrid material particles occurs in the aqueous phase, outside the organic phase of the microemulsion. The growth rates of the particles were found to be strongly dependent on the nature of the spacers, a polymethylene chain inducing the fastest process. This different behavior was explained by a slower condensation process rather than a slower hydrolysis. The high surface areas measured for the hybrid materials could be explained by a possible coating of the hybrid particles by surfactant molecules, thus preventing either their growth or their aggregation.     

Lamellar bridged silsesquioxanes: self-assembly through a combination of hydrogen bonding and hydrophobic interactions

The synthesis of four bis(trialkoxysilylated) organic molecules capable of self-assembly--(EtO)3Si(CH2)3NHCONH-(CH2)n-NHCONH(CH2)3Si(OEt)3 (n = 9-12)--associating urea functional groups and alkylidene chains of variable length is described. These compounds behave as organogelators, forming supramolecular assemblies thanks to the intermolecular hydrogen bonding of urea groups. Whereas fluoride ion-catalysed hydrolysis in ethanol in the presence of a stoichiometric amount of water produced amorphous hybrids, acid-catalysed hydrolysis in an excess of water gave rise to the formation of crystalline lamellar hybrid materials through a self-organisation process. The structural features of these nanostructured organic/inorganic hybrids were analysed by several techniques: attenuated Fourier transformed infrared (ATR-FTIR), solid-state NMR spectroscopy (13C and 29Si), scanning and transmission electron microscopy (SEM and TEM) and powder X-ray diffraction (PXRD). The reaction conditions, the hydrophobic properties of the long alkylidene chains and the hydrogen-bonding properties of the urea groups are determining factors in the formation of these self-assembled nanostructured hybrid silicas.     

Adsorption of cationic surfactants and subsequent adsolubilization of organic compounds onto cellulose fibers

Cationic surfactants with different hydrophobic chain length were adsorbed onto cellulose fibers in an aqueous medium. The adsorption isotherms exhibited three characteristic regions which were interpreted in terms of the mode of aggregation of the surfactant molecules at the solid–liquid interface. The hydrophobic layers were used as a reservoir to trap various slightly water soluble organic molecules. A quantitative study of these phenomena suggested typical partition behavior of the organic solutes between the aqueous phase and the surfactant layer. The surfactant chain length (from C12 to C18) was shown to play an important role in terms of the capacity to retain the organic solute and the capacity increased with the number of carbon atoms.     

疏水性杂化分子筛的控制合成及催化应用

以乙基三乙氧基硅烷和甲基三乙氧基硅烷为有机硅源, 分别通过转动和静态干胶转化法一步合成出乙基和甲基功能化杂化分子筛并对其进行了表征. 通过对合成路线、 有机基团碳链长度、 凝胶配比等的调变, 实现了对杂化分子筛疏水性的有效调控, 合成出水接触角为124°的疏水性杂化分子筛. 以疏水性杂化分子筛为载体制备的Ru负载催化剂在催化苯酚加氢反应中表现出优异的催化性能, 这归因于疏水/亲油的催化剂表面有利于苯酚分子在催化剂表面的富集进而促进反应的进行.     

Insights into the self-directed structuring of hybrid organic-inorganic silicas through infrared studies

Fourier transform infrared (FTIR) spectroscopy has been used to probe the organization of the organic fragments in lamellar bridged silsesquioxanes with organic substructures based on alkylene chains of various lengths and urea groups [O1.5Si(CH2)3NHCONH(CH2)nNHCONH(CH2)3SiO1.5] (n = 6, 8-12). The structure and intermolecular interactions (hydrophobic and H-bonding) of these well-defined self-structured hybrid silicas are discussed in relation to their powder X-ray diffraction patterns. The degree of structural order is determined by the length and parity of the alkylene spacer. A concomitant enhancement in the degree of condensation of the inorganic component and a decrease in the strength of the hydrophobic interactions between the organic components are demonstrated. The strength and directionality of the H-bonding are directly correlated to the crystalllinity of the organic-inorganic hybrid materials.     

IPS mode investigation of liquid crystal alignment on organic hybrid overcoat layer via ion beam irradiation

The nematic liquid crystal alignment capability and electro‐optical (EO) performance characteristics of in‐plane switching (IPS) cells were first demonstrated on organic hybrid overcoat layers via ion beam irradiation. Usually the organic hybrid overcoat is used as the material for making a plate alignment layer in a colour filter process. To characterise the organic hybrid overcoat layer, we analysed the surface composition of the organic hybrid overcoat by X‐ray photoelectron spectroscopy. The results show that the intensity of C = O and C–O bonding undergoes a change corresponding to the changes in energy of the ion beam exposure. Moreover, EO performance characteristics of IPS cells on the organic hybrid overcoat layer via ion beam irradiation were observed to have similar characteristics to the polyimide.     

Hybrid Surfactant Systems with Inorganic Constituents

Surfactants are molecules of enormous scientific and technological importance, which are widely used as detergents, emulsifiers, and for the preparation of diverse nanostructures. Their fascinating ability to form self‐organized structures, such as micelles or liquid crystals, originate from their amphiphilic architecture—a polar head group linked to a hydrophobic chain. While almost all known surfactants are organic, a new family of surfactants is now emerging, which combines amphiphilic properties with the advanced functionality of transition‐metal building blocks, for example, redox or catalytic activity and magnetism. These hybrid surfactants exhibit novel self‐organization features because of the unique size and electronic properties of the metal‐containing entities.     

含氟高分子/SiO2杂化疏水材料的制备及涂层表面性质

采用自由基溶液聚合与溶胶-凝胶法相结合的方法制备了含氟高分子/SiO2杂化疏水材料.通过甲基丙烯酸十二氟庚酯(FA)与乙烯基三乙氧基硅烷(VTES)共聚合成了含氟硅共聚物(PFAS),进一步通过原硅酸乙酯(TEOS)与PFAS共聚物溶液共水解缩聚制备了具有含氟侧基的碳碳主链高分子和硅氧网络的含氟高分子/SiO2杂化疏水材料.研究结果表明,SiO2组分含量提高可以显著增加杂化材料薄膜的涂敷厚度,改善其耐久性能,而对杂化材料疏水性能的影响不大.     

Out‐of‐Water Constitutional Self‐Organization of Chitosan–Cinnamaldehyde Dynagels

An investigation of the constitutional adaptive gelation process of chitosan/cinnamaldehyde ( C / Cy ) dynagels is reported. These gels generate timely variant macroscopic organization across extended scales. In the first stage, imine‐bond formation takes place “in‐water” and generates low‐ordered hydrogels. The progressive formation of imine bonds further induces “ out‐of‐water” increased reactivity within interdigitated hydrophobic self‐assembled layers of Cy , with a protecting environmental effect against hydrolysis and that leads to the stabilization of the imine bonds. The hydrophobic swelling due to Cy layers at the interfaces reaches a critical step when lamellar self‐organized hybrids are generated (24 hours). This induces an important restructuration of the hydrogels on the micrometric scale, thus resulting in the formation of highly ordered microporous xerogel morphologies of high potential interest for chemical separations, drug delivery, and sensors.     

Functional perovskite hybrid of polyacetylene ammonium and lead bromide: Synthesis, light emission, and fluorescence imagining

A highly photoresponsive perovskite hybrid containing an electroactive organic component (H1) was fabricated. A disubstituted polyacetylene (PA) with a hidden amino functionality (P3) was synthesized, hydrolysis and quaternization of which afforded the desired PA ammonium salt (P5). Mixing P5 with lead bromide readily yielded H1, which was stable, soluble, and film-forming. The inorganic framework induced the polymer chains to align in an ordered fashion, which helped to populate the chain segments with long conjugation lengths. The hybrid emitted a blue light (457 nm) in a high quantum yield (62%), thanks to the enhanced electronic conjugation, the weakened interaction between the layer-segregated chains, and the efficient energy transfer from the inorganic sheets to the organic layers. P3 exhibited a half-discharge time as short as approximately 0.7 s, representing the first example of an efficient photoconductive disubstituted PA. While stable to normal light illumination, H1 was rapidly bleached upon exposure to high-power UV irradiation, enabling facile generation of two-dimensional luminescent photopatterns. After the UV irradiation, the emissions of P9 and P9/H12 were enhanced and weakened, respectively, proving that the inorganic perovskite framework works as a photocatalyst for accelerating the bleaching process of the conjugated PA chains.     

Structure of Hybrid Silica Gels Incorporated with Hydrophobic Dye Molecules

Hybrid gels incorporated with functional organic molecules are interesting for their physical properties and microstructures as well as their potential applications. Organic-inorganic hybrid silica gels incorporated with hydrophobic organic dye were prepared by hydrolysis of phenyltriethoxysilane (PhTES) and tetraethoxysilane (TEOS) in ethanol solution containing organic dye, pyrene or rhodamine-B (RB). The structure of the gels were investigated by mean of IR absorption spectra and UV-visible absorption/fluorescence spectra. The xerogel prepared from the solution of [PhTES]/[PhTES + TEOS] < 0.3 was stable, and the incorporated dyes hardly dissolved into ethanol. Si-Ph bond increased with increasing PhTES content in the precursor solutions. The UV-visible absorption spectra of the gels incorporated with RB show increase in the amount of dimer with increasing Ph-content. The fluorescence spectra for the gels incorporated with pyrene show that the hydrophobic dye is preferentially incorporated as monomers when the amount of Ph-group in the gels increases in contrast with hydrophilic RB. It is also suggested that the hydrophobic dye is preferentially incorporated into gels as monomers when the gelation rate is low.     

Tunable porosity in bridged organosilicas using self-organizing precursors

Functionalized, mesoporous organosilicas with tunable porosity were prepared by a direct and simple approach from rationally designed precursors, combining the function of a network builder and a porogen in one molecule. The precursors are synthesized using a dual hydroboration reaction, fulfilling the criteria of "click-chemistry", first on an ethylene-bridged organosilica and then on a long-chain alkene. Thus, in the final molecule the boron atom connects the sol-gel precursor (the bridged organosilica) with the porogen (the long-chain alkene). The so-prepared precursors do self-organize when hydrolysis of their inorganic moiety takes place via an aggregation of their organic side chains into hydrophobic domains. The length of the attached chain influences the size of the hydrophobic domain and thus, after a condensation-aminolysis sequence, the finally observed porosity of the organosilicas. Depending on chain length micro- to mesoporous materials with average pore sizes from 1.5 to 4.1 nm (for attached pentene to hexadecene chains) are observed. Furthermore, the boron entity enables the subsequent introduction of various functional groups into the pore walls of the organosilica networks. Amine or hydroxyl functionalities can be easily introduced, dependent on the experimental conditions used during the borane cleavage and extraction step. The accessibility of these functionalities can be proven by a significant metal adsorption onto the functional organosilica walls.     

Insight into the Supramolecular Architecture of Intact Diatom Biosilica from DNP‐Supported Solid‐State NMR Spectroscopy

Diatom biosilica is an inorganic/organic hybrid with interesting properties. The molecular architecture of the organic material at the atomic and nanometer scale has so far remained unknown, in particular for intact biosilica. A DNP‐supported ssNMR approach assisted by microscopy, MS, and MD simulations was applied to study the structural organization of intact biosilica. For the first time, the secondary structure elements of tightly biosilica‐associated native proteins in diatom biosilica were characterized in situ. Our data suggest that these proteins are rich in a limited set of amino acids and adopt a mixture of random‐coil and β‐strand conformations. Furthermore, biosilica‐associated long‐chain polyamines and carbohydrates were characterized, thereby leading to a model for the supramolecular organization of intact biosilica.     

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

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

Selective hydrolysis of oxazoline block copolymers

Block copolymers, composed of a hydrophobic block [poly(N-t-butylbenzoyl ethylenimine) or poly(N-lauroyl ethylenimine)] and a hydrophilic block [poly(N-propionyl ethylenimine)], synthesized by cationic ring-opening polymerization of 2-substituted Δ2-oxazolines, were selectively deacylated by acid hydrolysis. The hydrolysis process was monitored by using ¹H-NMR. The results show that the propionyl groups could be removed from the hydrophilic block of the polymer chain without touching the hydrophobic block, if appropriate reaction conditions were used.     

Epoxide Opening versus Silica Condensation during Sol–Gel Hybrid Biomaterial Synthesis

Hybrid organic–inorganic solids represent an important class of engineering materials, usually prepared by sol–gel processes by cross‐reaction between organic and inorganic precursors. The choice of the two components and control of the reaction conditions (especially pH value) allow the synthesis of hybrid materials with novel properties and functionalities. 3‐Glycidoxypropyltrimethoxysilane (GPTMS) is one of the most commonly used organic silanes for hybrid‐material fabrication. Herein, the reactivity of GPTMS in water at different pH values (pH 2–11) was deeply investigated for the first time by solution‐state multinuclear NMR spectroscopic and mass spectrometric analysis. The extent of the different and competing reactions that take place as a function of the pH value was elucidated. The NMR spectroscopic and mass spectrometric data clearly indicate that the pH value determines the kinetics of epoxide hydrolysis versus silicon condensation. Under slighly acidic conditions, the epoxy‐ring hydrolysis is kinetically more favourable than the formation of the silica network. In contrast, under basic conditions, silicon condensation is the main reaction that takes place. Full characterisation of the formed intermediates was carried out by using NMR spectroscopic and mass spectrometric analysis. These results indicate that strict control of the pH values allows tuning of the reactivity of the organic and inorganic moities, thus laying the foundations for the design and synthesis of sol–gel hybrid biomaterials with tuneable properties.     

Schiff bases between pyridoxal 5′-phosphate and dodecylamine. Kinetic study

We studied the formation and hydrolysis of the Schiff base of pyridoxal-5′ -phosphate (PLP) and n-dodecylamine (DOD) by kinetic methods and found the formation rate constants to be much larger than those reported for related systems. This can be ascribed to the occurrence of local concentration of charges in the vicinity of the carbinolamine, which stabilizes the corresponding transition state of the dehydration reaction. On the other hand, the hydrolysis rate constants of our system were considerably smaller as a result of the 12-atom hydrocarbon chain acting as a bulky hydrophobic rest protecting the imine bond from attack by water.     

A fluorine-containing hydrophobically associating polymer. I. Synthesis and solution properties of copolymers of acrylamide and fluorine-containing acrylates or methacrylates

Fluorine-containing hydrophobically associating polymers have been synthesized by copolymerization of acrylamide with a small amount of an acrylate or methacrylate having a fluorocarbon containing ester group. It was found that hydrophobic associations occurring between these fluorocarbon chains was stronger than the interactions of the corresponding hydrocarbon comonomers and depend on the length of the fluorocarbon chain. The rheological properties of the copolymer solutions were studied. The solutions were found to be highly pseudoplastic but the viscosity loss was completely reversible upon removal of shear. Evidence for hydrophobic association of the fluorocarbon groups was obtained by the dependence of the Brookfield viscosity on temperature, the addition of NaCl, and the addition of organic solvents, urea, and surfactants.