Mesostructures and properties of transparent block copolymer/silica nanocomposite monoliths

In this work, three different block copolymer/silica hybrid nanocomposite monoliths that possess mesostructured domains (hexagonal, cubic, and disordered) were prepared through the micellization of the block copolymer during the sol-gel process of a silica precursor. Transparent block copolymer/silica nanocomposite monoliths were obtained from the amphiphilic triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (EO₁₀₆PO₇₀EO₁₀₆, Pluronic F127), which we used to organize the polymerizing silica networks; the ratio between the block copolymer and silica was fixed at 60:40 (wt%). Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used to observe the mesostructural ordering. Temperature-dependent SAXS patterns of the cubic structured nanocomposites showed that the calcination process takes place at 210°C. The transmittances of the nanocomposite monoliths over the range of wavelengths from 400 to 800 nm was >85%. From rheological measurements at low frequency, it was found that the hexagonally structured monoliths had higher storage and loss moduli relative to the monoliths possessing cubic and disordered structures.     

Effect of postgrafted alkyl chains on the wettability of hydrophilic poly(amidoamine)-grafted nano-sized silica

In order to control the surface wettability of hyperbranched hydrophilic poly(amidoamine) (PAMAM)-grafted nano-sized silica, hydrophilic alkyl chain (C _n H_2n+1) with different chain lengths (n = 4, 8, 15) were postgrafted onto PAMAM-grafted silica by the reaction of terminal amino groups of PAMAM grafted on the silica surface with alkyl acid chlorides (C _n H_2n+1-COCl). The postgrafting of C _n H_2n+1-COCl increased with increasing PAMAM grafting and alkyl chain length of C _n H_2n+1-COCl. However, the terminal amino groups of PAMAM-grafted silica used for the postgrafting of C _n H_2n+1-COCl decreased with increasing chain length. This may be due to the steric hindrance between terminal amino groups of PAMAM-grafted silica and C _n H_2n+1-COCl: the steric hindrance is considered to increase with increasing chain length of C _n H_2n+1-COCl. The surface wettability was estimated by contact angle measurement for water and methanol wettability. As a result, it was found that contact angle and methanol wettability increased with increasing alkyl chain length of postgrafted C _n H_2n+1-COCl. The hyperbranched PAMAM-grafted silica readily dispersed in water and methanol because of the hydrophilic nature of grafted PAMAM, but it lost dispersibility in water and methanol due to postgrafting of hydrophobic chains.     

Formation of graphitic carbon nanofiber (GCNF)/silica gel composites using surface-functionalized GCNFs and sol-gel processing

Reaction of herring-bone graphitic carbon nanofibers (GCNFs) containing surface-bound acid chloride functional groups with 3-aminopropyl triethoxysilane (APTES) leads to amide condensation and formation of carbon nanofibers surface-derivatized with pendant Si—OEt and Si—OH functional groups, GCNF-[C(O)NH(CH₂)₃Si(OEt)(OH)₂] _x . Addition of these GCNFs containing covalently bound 3-amidopropylsilyl linker molecules to silica sol-gel formulations gives GCNF/silica xerogels as dry black powders. Covalent binding of the linker molecule across the GCNF/ceramic interface is indicated by intermediate formation of especially stable GCNF/silica sol dispersions and the isolation of uniformly black GCNF/silica xerogel powders. SEM micrographs reveal excellent wetting of the carbon nanofiber surface by the silica xerogel matrix, and the presence of amido-carbonyl groups is confirmed from infrared spectral data. TGA plots show mass losses consistent with dehydration of the gel matrix and thermal decomposition of linker molecules at elevated temperature.     

分子连接性指数与溶液吸附自由能的相关性

测定了硅胶自四氯化碳中吸附脂肪醇及活性炭自水中吸附芳香化合物的吸附等温线, 等温线均可用Langmuir方程描述。利用Langmuir参数计算了各体系的吸附标准自由能变化。计算了各种吸附质的分子连接性指数。各种分子的分子连接性指数与吸附标准自由能变化间有相关性, 并给出了相关方程, 同时作了初步的讨论。     

Silicas modified with silane pro-adhesive compounds - active fillers of rubbers

In order to improve filler-polymer interaction, a modification of the silica surface character was indispensable, from a hydrophilic to a partially or fully hydrophobic one. The changes were effected in the course of precipitation by modification of silica surface with silane coupling agents. The modified silicas obtained were tested in SBR rubber and appropriate strengthening parameters of the filled SBR vulcanizates were established.     

Polyurethane nano-composite with functionalized silica particle

Nano-size silica particles were functionalized with vinyl isocyanate and subsequently UV cured to synthesize polyurethane–silica nano-composites which were tested for mechanical, dynamic mechanical, cross-link density, contact angle and XPS. The modified silica provides composites with cross-links that are pinned at the surfaces and which effectively reinforce the materials mechanically as well as thermally.     

Quantum-chemical study on the mechanical behaviour of polydimethylsiloxane under deformation: interaction with fumed silica surfaces

Silicone elastomers filled by fumed silica reveal peculiar technical behaviour. Chemical modification of the silica surface is commonly used to control the rheological and mechanical properties of uncured and cross-linked silicone elastomers. To study the microscopic aspect of the problem, quantum-chemical (QCh) modelling in the framework of originally elaborated semiempirical techniques has been performed. The response of a silicone polymer fragment, interacting with a silica model cluster, to external stress is considered in terms of a mechanochemical reaction. The impact of silicone-water and silicone-modified filler interactions on stress-strain characteristics, i.e. Young's modulus, energy and force of deformation and tensile strength have been studied on a molecular level.     

Water at the interface modified silica filler-polydimethylsiloxane: quantum-chemical modelling

Intermolecular interactions determine the reinforcement of polydimethylsiloxane (PDMS) elastomers by fumed silica, and a water interlayer on the fumed silica/PDMS interface may act as a lubricant, decreasing the interaction energy and promoting the PDMS molecule motion over the filler surface. A quantum-chemical (QCh) modelling has been performed to study a microscopic aspect of water impact on the intermolecular interactions in the system. The results obtained for a series of superclusters simulating fragments of the real silica filler surface, both hydroxylated and silylated, interacting with five-member PDMS oligomer in presence of individual water molecules and of a 'water drop', of several H-bonded water molecules, are in good agreement with results from IGC adsorption experiments.     

Moisture effects on improved hydrolysis reaction for TESPT and TESPD-silica compounds

The moisture(55 wt%)-treated silica compounds, bis(triethoxysilylpropyl)disulfide (TESPD)/silica/carbon black (CB)/SBR and bis(triethoxysilylpropyl)tetrasulfide (TESPT)/silica/CB/SBR, have been processed in a batch mixer and they are investigated with respect to the alcohol residue level in silane, the processability, the vulcanization characteristics, and the mechanical properties. The alcohol level is low at the moisture treated compounds. The TESPD compounds show lower alcohol level than the TESPT ones on moisture treated and untreated compounds. The probe temperatures of the moisture treated compounds are lower than the drop temperature, while those of the untreated compounds are higher than the drop ones, respectively. The vulcanization properties of the compounds are changed by the moisture treatment and this improves the physical properties of the compounds. The moisture treatment on silica surface increases the hydrolysis reaction of the alkoxy silane and the hydrolyzed silane improved the coupling reaction with the hydroxyl group on silica surface during reactive batch processing. It also reduces the rate of temperature rise during batch mixing due to the latent heat of the moisture and the endothermic reaction between silica and silane. At the vulcanization stage, it seems to further increase the coupling reaction between silica and silane. The steric hindrance theory of an alkoxy silane (TESPT) has to be reconsidered with a large amount of moisture treated silica/TESPD/CB/S-SBR compound system.