Organophilic Silica Research Articles

The effect of inorganic particles on the breakdown strength and mechanical properties ofEVA‐based composites

AbstractEthylene‐vinyl acetate (EVA) copolymer was melt‐blended with different inorganic particles, such as alumina trihydrate (ATH), montmorillonite‐based organoclay (CLO15A) and organophilic silica (R202) to produce (nano)composites with outstanding electrical breakdown strength. The composites loaded with different amount of particles were characterized by dielectric, rheological, morphological and mechanical properties. The addition of the particles resulted in an increase of electrical breakdown strength, whose results depend on the nature and amount of filler. The addition of 1%–5% of ATH resulted in an increase of 50% of this property. Similar results were observed for the composites loaded with 7% of CLO15A and R202. All composites displayed low values of dielectric constant and dielectric loss, which is interesting for insulator applications. The presence of the filler did not exert great influence on the rheological properties of the composites, thus keeping the good processability of EVA matrix. Finally, the composites containing the organoclay presented the best mechanical response.

Effect of microcrystalline and nanocrystals cellulose fillers in materials based on PLA matrix

The aim of this work was to compare the effects of microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC) addition on the properties of PLA matrix. The CNC were obtained by acid hydrolysis of the MCC. Both MCC and CNC were separately incorporated in PLA at ratios of 3, 5 and 7 wt%. In some compositions, organophilic silica (R972) was added to improve the cellulose-matrix compatibility. The properties of the materials were evaluated by FTIR, XRD, NMR and mechanical tests. Functional groups and crystalline structure of MCC and CNC were determined by FTIR and XRD, respectively. NMR T1H values showed that films containing CNC presented better interfacial interaction than those containing MCC, and indicated that R972 acts as compatibilizer. MCC and CNC acted as nucleating agents for PLA crystallization and there was an improvement in the mechanical performance of materials with the addition of CNC.

Development and properties evaluation of bio‐based PLA/PLGA blend films reinforced with microcrystalline cellulose and organophilic silica

The preparation and properties of hybrid materials based on poly(lactic acid)/poly(lactic acid‐co‐glycolic acid) (PLA/PLGA) blends using microcrystalline cellulose (MCC) and organophilic silica (R972) as fillers have been investigated. Hybrid materials were manufactured by solution casting using chloroform as solvent to prepare films. R972 was incorporated in a ratio of 3 wt%, and MCC was added in ratios of 3, 5, or 7 wt% with respect to the weight of the polymeric matrix. Films were prepared with only MCC addition or with MCC and R972 combined. Properties of the films were evaluated by X‐ray diffraction (XRD), nuclear magnetic resonance, differential scanning calorimetry (DSC) and mechanical property measurements. The results show that each filler, when added individually or in combination, affects the structure and final properties of the films differently. MCC acts as a nucleating agent for the crystallization of the polymeric matrix. An increase in the MCC content increased the crystallinity of the films. This effect became more pronounced with silica addition. The domain distribution curves showed PLA/PLGA blends to be homogeneous, which was further confirmed by DSC. An improvement in the mechanical performance was observed with MCC addition, especially when silica was added together with cellulose. POLYM. ENG. SCI., 57:464–472, 2017. © 2016 Society of Plastics Engineers.

Development of biopolymer/cellulose/silica nanostructured hybrid materials and their characterization by NMR relaxometry

The objective of this study was to investigate the preparation and properties of hybrid materials composed of poly(lactic acid) (PLA) and poly(lactic acid)/poly(lactic-co-glycolic acid) (PLA/PLGA) blends employing cellulose nanocrystals (CNCs) and/or organophilic silica (R972) as nanoparticles. The CNCs were obtained by acid hydrolysis of commercially available microcrystalline cellulose (MCC). The materials were produced in film form by solution casting. Organophilic silica was incorporated at a ratio of 3 wt.%, and CNCs were added at ratios of 3 wt.% and 5 wt.% in relation to the weight of the polymer matrix. Two series of films were obtained. The first was prepared using only PLA as the matrix, and the second was obtained using blends of PLA and PLGA. The properties of the films were evaluated by X-ray diffractometry, nuclear magnetic resonance, Fourier-transform infrared spectroscopy and measurement of mechanical properties. The results revealed that each nanoparticle, whether added individually or combined with the other type of nanoparticle, induced different final material properties. Cellulose nanocrystals can act as nucleating agents for the crystallization of PLA. There was an improvement in the mechanical performance of films with the addition of CNCs. Further, the incorporation of silica combined with CNCs resulted in the generation of films with the strongest mechanical properties. The results of this study indicate that silica decreases the surface tension between PLA-cellulose and PLA/PLGA-cellulose.

Development and characterization of hybrid materials based on biodegradable PLA matrix, microcrystalline cellulose and organophilic silica

The goal of this work was to investigate the production and properties of hybrid materials based on poly(lactic acid) (PLA), employing microcrystalline cellulose (MCC) and organophilic silica (R972) as fillers. The composites were obtained by solution casting to form films. Each nanoparticle was incorporated at 3 wt. %, relative to the polymer matrix. In this experiment, four films were obtained (PLA, PLA/MCC, PLA/R972 and PLA/MCC/R972). The films properties were evaluated by X-ray diffractometry, nuclear magnetic resonance, Fourier transform infrared spectroscopy and mechanical properties. The results showed that each nanoparticle, added individually or both combined, had different effect on the final properties of the films. Microcrystalline cellulose can act as nucleating agent for the crystallization of PLA. Silica promoted an increase in rigidity, due to the strong intermolecular forces, while MCC addition promoted an increase in the molecular mobility of the polymeric chains. The PLA/MCC/R972 film showed the highest crystallinity degree and tensile modulus. This film presented a T1H value between both values found for PLA/MCC and PLA/R972 films. The results indicated that silica R972 could promote a decrease of the surface tension between PLA and cellulose.

Development of hybrid nanocomposites based on PLLA and low-field NMR characterization

Hybrid nanocomposite based on poly(L-lactic acid) (PLLA) employing silica (A200) and organophilic silica (R972), natural clay (NT-25) and two types of organoclay (S4 and S7) were prepared by the solution casting method. Each nanoparticle type was incorporated at two ratios (3 and 5%) relative to the polymer matrix. The nanocomposites formed were evaluated by X-ray, thermal resistance and molecular dynamic analysis, using proton spin-lattice relaxation time. The results showed that each nanoparticle type acted independently of the polymer/nanoparticle ratio in the new material. Both silica types promoted an increase in rigidity, due to the strong intermolecular forces. The natural clay did not cause any significant change in the molecular mobility of the nanocomposites, probably due to the non-affinity of the chemical structure. Therefore, both organoclays were better dispersed in the polymeric matrix, allowing good intermolecular interaction and, consequently, exfoliated and intercalated nanocomposites were formed.

Soft glassy rheology model applied to stress relaxation of a thermoreversible colloidal gel

Measurements of the stress relaxation modulus of a thermoreversible colloidal gel are compared with the predictions of the soft glassy rheology (SGR) model of Sollich and co-workers [Sollich et al., Phys. Rev. Lett. 78, 2020–2023 (1997); Sollich, Phys. Rev. E 58, 738–759 (1998); Fielding et al., J. Rheol. 44, 323–369 (2000)] in the linear and nonlinear regimes. The material is a 20% volume fraction suspension of organophilic silica (diameter=80nm) dispersed in the organic solvent tetradecane that gels below the critical temperature of T=23°C. We perform measurements in which prior deformation history and slip are carefully controlled. The linear stress relaxation modulus shows a significant dependence on waiting time, tw. SGR model predictions are applied to linear step strain measurements for a range of tw to assign a best fit estimate of the noise temperature, x=1.05±0.01. We then test predictions of the SGR model for the nonlinear stress relaxation modulus, G(t−tw,tw;γo), based on the linear determinat...

Synthesis of monodisperse fluorescent core-shell silica particles using a modified Stöber method for imaging individual particles in dense colloidal suspensions

Core-shell silica particles, with a diameter of 1.5 μm, containing a dye fluorescein isothiocyanate (FITC), are synthesized by the hydrolysis and condensation of tetraethylorthosilicate (TEOS). Sodium dodecyl sulfate (SDS) is added to synthesize fluorescent core particles with the diameter of approximately 1 μm. In the addition of SDS, the surface charge reduced by counterions (Na +) of the surfactant leads to a higher degree of aggregation of the primary particles and the formation of larger secondary particles. The particle growth kinetics confirms the aggregation growth model for the synthesis of monodisperse silica particles, and also shows the dependence of final particle size on colloidal stability resulting from the addition of SDS. Light and X-ray scattering data reveal that the final particles have compactly packed structures with smooth surfaces. The seeded growth technique is then used to form a silica shell layer on the fluorescent core. The added amount of water and NH 4OH has significant effects on shell formation. Finally, the final core-shell silica particles are modified by chemisorption of octadecanol at the surface to be dispersed in organic solvents. Octadecyl-coated silica particles are sterically stabilized in silica index-matching solvents such as chloroform and hexadecane to directly image separate particles using confocal microscopy. In chloroform, the organophilic silica particles disperse well, whereas in hexadecane they form a volume-filling gel structure at room temperature.

Hydrocarbon dispersion of nanospherical silica by a sol–gel process. 2. Alkoxysilane copolymerization

The preparation of hydrocarbon dispersions of nanospherical silica–silicone hybrids by copolymerization of tetraethoxysilane (TEOS) and alkylethoxysilanes such as methyltriethoxysilane (MTEOS) and dimethyldiethoxysilane using a sol–gel process was investigated. Particles completely dispersible in hexane with a diameter in the range 10–24 nm were obtained by means of TEOS and MTEOS copolymerization, using ethanol or methanol as a solvent and a terminator. The solubility of the nanospheres was shown to be dependent on the molar ratio of water to silicon, the reaction time, the terminator concentration as well as the stirring condition. The hexane-dispersible particles have hydroxyl and methyl groups on the surface. A higher conversion of organophilic silica–silicon nanoparticles was attained using trimethylchlorosilane as a terminator and a water-to-silicon molar ratio close to 9.

Biochemical evolution. I. Polymerization On internal, organophilic silica surfaces of dealuminated zeolites and feldspars.

Catalysis at mineral surfaces might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and photochemical gas reactions. Many ideas are implausible in detail because the proposed mineral surfaces strongly prefer water and other ionic species to organic ones. The molecular sieve silicalite (Union Carbide; = Al-free Mobil ZSM-5 zeolite) has a three-dimensional, 10-ring channel system whose electrically neutral Si-O surface strongly adsorbs organic species over water. Three -O-Si tetrahedral bonds lie in the surface, and the fourth Si-O points inwards. In contrast, the outward Si-OH of simple quartz and feldspar crystals generates their ionic organophobicity. The ZSM-5-type zeolite mutinaite occurs in Antarctica with boggsite and tschernichite (Al-analog of Mobil Beta). Archean mutinaite might have become de-aluminated toward silicalite during hot/cold/wet/dry cycles. Catalytic activity of silicalite increases linearly with Al-OH substitution for Si, and Al atoms tend to avoid each other. Adjacent organophilic and catalytic Al-OH regions in nanometer channels might have scavenged organic species for catalytic assembly into specific polymers protected from prompt photochemical destruction. Polymer migration along weathered silicic surfaces of micrometer-wide channels of feldspars might have led to assembly of replicating catalytic biomolecules and perhaps primitive cellular organisms. Silica-rich volcanic glasses should have been abundant on the early Earth, ready for crystallization into zeolites and feldspars, as in present continental basins. Abundant chert from weakly metamorphosed Archaean rocks might retain microscopic clues to the proposed mineral adsorbent/catalysts. Other framework silicas are possible, including ones with laevo/dextro one-dimensional channels. Organic molecules, transition-metal ions, and P occur inside modern feldspars.

A novel technique for preparing organophilic silica by water-in-oil microemulsions

A novel technique to prepare ultramicro spherical silica particles containing vinyl groups on their surfaces is presented. This process is a combination of the sol-gel technique and the water-in-oil microemulsion technique in which hydrolysis and condensation of TEOS [Si(OEt)4] and MPS (trimethoxysilylpropylmethacrylate) take place. Spherical silica particles with a size range from 20 to 70 nm were obtained and the surface concentrations of the double bonds per nm2 were from 4 to 7.

Disorder-to-Order Transition in Settling Suspensions of Colloidal Silica: X-ray Measurements

Dispersions of colloidal particles exhibit thermodynamic properties similar to those of molecular systems, including a hard sphere disorder-to-order transition. In experiments with organophilic silica in cyclohexane, gravity settling was used to concentrate the particles. With small particles the slow sedimentation permits rearrangement into the iridescent ordered phase, but larger particles form amorphous sediments instead. Scanning electron microscopy of the crystalline sediment indicates hexagonally closepacked layers. X-ray attenuation measurements reveal a discontinuity coincident with the observed boundary between iridescent and opaque regions. Sediments accumulating faster than the maximum rate of crystallization produce a glass, in accord with the classical theory for crystal growth.

Thermodynamic factors of the sol—gel transition I. Reversible coagulation of organophilic and hydrophilic colloids

The coagulation of alcoholic dispersions of organophilic silica (methylated aerosil) by water and coagulation of aqueous dispersions of hydrophilic silica (nonmodified aerosil) by the cationic surfactant cetylpyridinium bromide (CPB) is studied at low and high ionic strength of the medium. Both organophilic dispersions at small water concentrations and hydrophilic dispersions at small CPB concentrations are resistant to electrolyte coagulation. When the corresponding concentrations are sufficiently high, coagulation proceeds even in the absence of added salt. The critical water or CPB coagulation concentration increases on decreasing the ionic strength. All of the data, including the peculiar trends in coagulation rates and the reversibility tests, indicate that the stability-coagulation transition in the systems is thermodynamic rather than kinetic.

Preparation and characterization of spherical monodisperse silica dispersions in nonaqueous solvents

In two earlier papers (A. K. van Helden and A. Vrij,J. Colloid Interface Sci.76, 418 (1980);78, 312 (1980)) light-scattering measurements of organophilic silica dispersions were reported. The preparation of these dispersions is described here in more detail. Organophilic silica dispersions consisting of spherical particles of narrow size distribution were produced by a combination of two earlier described processes. First uniform silica particles were prepared by hydrolysis of ethylorthosilicate according to the method of W. Sto¨ber A. Fink, and E. Bohn (J. Colloid Interface Sci.26, 62 (1968)). Then these particles were rendered organophilic by a coating reaction with stearyl alcohol according to R. K. Iler's method (U. S. Patent 2,801,185). Stable dispersions with particle radius between 20 and 100 nm were prepared in various organic solvents, e.g., cyclohexane, n-octane, diethylether. The stability does not reduce upon storage in cyclohexane for more than 1 year. A range of systems is investigated with a number of common techniques in colloid research, e.g., electron microscopy, ultracentrifugation, static and dynamic light scattering. The results can be qualitatively explained in terms of an initially porous alcohol particle which is dehydrated to some extent in the coating reaction. At low concentrations especially in diethylether electrostatic repulsion seems to occur. At higher concentrations this effect is not observed (van Helden and Vrij,J. Colloid Interface Sci.78, 312 (1980)).

Static light scattering of concentrated silica dispersions in apolar solvents

Organophilic silica dispersions, containing spherical monodisperse particles up to concentrations of 80% (w/v) of silica, were studied with the (static) light-scattering method. Cyclohexane and chloroform were chosen as solvents in order to minimize the scattering intensity. The results were interpreted with fluid-state theories. In a large range of silica concentrations the osmotic compressibility as well as the scattering at finite angles could be described rather well with hard-sphere interactions. The hard-sphere radius was rather close to the hydrodynamic radius of the particle. At the highest particle concentrations the scattering intensity sharply increases for small scattering angles. This is attributed to formation of large dense clusters of primary particles.

Studies on the Surface Properties of the Organophilic Silica Gels through the Adsorption of Various Kinds of Vapors and the Heat of Immersion

The surface properties of the organophilic silica gels were investigated by the adsorption of argon at 77°K, of water vapour at 288°K and of n-heptane at 273°K and the heat of immegions of water and n-heptane, respectively, on the samples which the native silica gels were treated by methanol, ethanol, butanol, pentanol, hexanol, octanol, decanol, dodecanol and tetradecanol. The following results were confirmed:(1) Since the BET surface area of argon and of water on the native silica gel showed good agreement, and the one of argon on the activated carbon agreed with the one of n-heptane, the argon molecule could be adsorbed on both the organophilic and the hydrophilic surface.(2) The argon surface areas on the surface-treated samples showed remarkable decrease, increasing the carbon chain of alcohol. The water surface area showed remarkable decrease in comparison with the argon surface area on each sample.(3) The surface area from argon adsorption on the surface-treated silica gels showed the sum of the surface areas from water and from n-heptane, respectively.(4) The heat of immersion in water and n-heptane on the surface-treated silica gels were well-explained by using the respective surface areas from water and n-heptane.

Studies on the Surface Properties of the Organophilic Silica Gels through the Vapor Adsorption and the Heat of Immersiont

メタノール,エタノール,ブタノール,ペンタノール,ヘキサノール,オ久タノール,デカノール,ドデカノール,テトラデカノールで表面処理した親油性シリカゲルの表面特性を77rKアルゴン,288。K水蒸気,273rK%-ヘプタン吸着等温平衡および水,かヘプタンへの湿潤熱から検討した結果つぎのことが認められた。(1)未処理シリカゲルおよびメタノール,エタノール処理シリカゲルの水蒸気吸着等温線はB￡TIII型であるが,付着基炭素鎖の長い場合にはBETI型である。表面処理シリカゲルによる水蒸気吸着量は未処理シリカゲルのそれにくらべいちじるしく小さい。(2)未処理シリカゲルのアルゴン表面積は水蒸気表面積にほぼ等しく,ヘプタン表面積は分子の大きさの相違を考慮すれば妥当な値と認められる。アルゴン表面積は親油,親水性表面のいずれに対しても合理的な表面積を与える。(3)表面処理シリカゲルの水蒸気表面積とヘプタン表面積を加えたものはアルゴン表面積に等しい。(4)処理シリカゲルの表面は付着基による親油性表面と,未反応でかつ吸着点となり得る親水性表面からなり,また未反応であるが付着基でおおわれて吸着点となり得ない付着基に近接したシラノールが存在する。(5)処理シリカゲルのヘプタンへの湿潤熱は付着基炭素鎖の長くなるにつれて大きくなる。処理シリカゲルの水への湿潤熱とそれぞれの水蒸気表面積との間には直線関係が成立する。

Preparation of the Organophilic Silica Gels by the Surface-treatment through the Solution of Various Alcohols in Hydrocarbon

Preparation of the Organophilic Silica Gels by the Surface-treatment through the Solution of Various Alcohols in Hydrocarbon

Preparation of the Organophilic Silica Gels by the Surface-Treatment through the Solutions of Various kinds of Alcohols in Hydrocarbon, and their Physicochemical Properties

The surface of silica gels was treated by the following procedure; the silica gels were soaked into hexane solution of various kinds of alcohols, i. c. saturated and unsaturated, both of linear and branched chains, phenyl alcohols, etc. Several diols were made to be reacted upon by the respective alcohols in autoclave under high pressure and temperature, and then the solution vapours were blown out at or near the critical point of hexane. The silica gels were then washed by alcohol or benzene and hexane.The following results were confirmed.(1) These surface-treated silica gels were organophilic, except those which were treated by diol in the test of the preferable property of dispersion into the mixed media like water∼hexane.(2) The surface group of treated silica gels were assigned as the alcohoxy group through the elemental analysis and argon surface area and also the silica gel treated by the unsaturated alcohol still held the double bond in the surface group.(3) The silica gel showed the hydrophilicity after treatment with diol, since a hydroxyl group of diols are reacted upon by a silanol of the silica gel.(4) Silanols of the silica gel were not reacted upon by tertiary alcohols like tert-butanol or tert-pentanol.(5) The decrease of argon surface area after surface treatment was interpreted by the existence of the micropores covered by the surface group.