Interfacial phenomena in core–shell nanocomposites of PDMS adsorbed onto low specific surface area fumed silica nanooxides: Effects of surface modification (original) (raw)
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Journal of Applied Physics, 2020
Surface modification of model silica to enhance compatibility in nanocomposites has been widely studied. In addition to model spherical silica, several authors have investigated the impact of surface conditions on compatibility in commercial aggregated carbon black and silica. In this paper, dispersion is investigated for a series of nanocomposites produced from commercially modified fumed silica mixed with styrene butadiene rubber, polystyrene, and polydimethylsiloxane. Surface modification includes variation in surface hydroxyl content, siloxane, and silane treatment. Qualitatively, hydroxyl groups on the silica surface are considered incompatible with non-polar polymers, while methyl groups are compatible with oleophilic polymers. X-ray scattering was used to analyze the filler aggregate structure before and after dispersion, and the second virial coefficient was used to quantify nanodispersion. The content of surface moieties was determined from Fourier-transform infrared spectroscopy. It is observed that modified silica can display mean field or specific interactions as reflected by the presence of a correlation peak in x-ray scattering. For systems with specific interactions, a critical ordering concentration is observed related to the free energy change for structuring. A van der Waals model was used to model the second virial coefficient as a function of accumulated strain, yielding the excluded volume and an energetic term. The excluded volume could be predicted from the structural information, and the bound polymer layer was directly related to the surface methyl content, whereas the energetic term was found to synergistically depend on both the methyl and hydroxyl surface content.
Porous polymeric nanocomposites filled with chemically modified fumed silicas
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Porous copolymers have been prepared by suspension-emulsion polymerization of divinylbenzene with styrene or some methacrylic monomers: di(methacryloyloxymethyl)naphthalene, methacrylic ester of p,p′ -dihydroxydiphenylpropane diglycidyl ether, and dimethacrylglycolethylene in the presence and absence of chemically modified fillers (fumed silicas with grafted methyl and silicon hydride groups). The results of investigations of the unfilled and filled polymeric systems by IR and 13 C NMR spectroscopies combined with AFM are presented.
Polymer International, 2015
A series of novel addition cured polydimethylsiloxane (PDMS) nanocomposites with various amounts of nano-silica sol were prepared via hydrosilylation for the first time. The influence of various amounts of nano-silica sol on the morphology, thermal behavior, mechanical and optical properties of these PDMS nanocomposites was studied in detail. It was found that with an increment in the amount of nano-silica sol the reinforcing effect of the nano-silica sol on the thermal and mechanical properties of the PDMS nanocomposites was very noticeable compared with the reference material. The prominent improvements in resistance to thermal degradation and mechanical properties can probably be attributed to the strong interaction of PDMS chains and uniformly dispersed particles resulting from the nano-silica sol. However, the transparency of the PDMS nanocomposites slightly decreased with an increment in weight fraction of nano-silica, compared with that of PDMS composite without nano-silica (Sol-0), which can probably be ascribed to an increasing size of the aggregated particles in the PDMS nanocomposites. The optimum amount of nano-silica sol for preparing novel addition curing PDMS nanocomposites was about 15 wt%.
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Polymer, 2010
Silica nanoparticles having specific surface area (SSA) 50e300 m 2 g À1 were admixed into vinylterminated dimethylsiloxy monomer with a dual asymmetric centrifuge (planetary mixer) and cured to form PDMS-based nanocomposites containing up to 12 vol% SiO 2 . Thin sections of cured nanocomposites obtained by a cryostate-microtome were analyzed by TEM while small and ultra small angle X-ray scattering (U/SAXS) was used to determine nanocomposite structure: filler primary particle, aggregate (chemically or sinter-bonded particles) and agglomerate (physically-bonded particles) size as a function of mixing duration and filler concentration. More aggregated silicas with higher SSA exhibited denser crosslinking than less aggregated ones regardless of crosslinker content as determined by swelling nanocomposites in toluene at equal filler content. The nanocomposite strength was determined by tensile tests (Young's modulus and elongation at break). Consistent with "bound rubber" theory, the Young's modulus of the nanocomposites increased non-linearly with increasing filler volume fraction.
Revue Roumaine De Chimie, 2020
Poly (methyl methacrylate)/SiO2 nanocomposite membranes were made by simple solution mixing procedure, using three different solvents: Acetone, Acetonitrile and Chloroform. FT-IR studies confirm first the formation of H-bond between the matrix (PMMA) and the filler (SiO2). Second, the FT-IR peak of bound carbonyl groups was shifted by 9, 11cm and 19 cm in the samples prepared with Acetone, Acetonitrile and Chloroform, respectively. These peak shifts are related to the H-bond interaction strength. The strongest interaction between PMMA and SiO2 was presented in the nanocomposite prepared by Chloroform solvent. In addition, the Studio Software Solution “Material Studio 6.0” was used to calculate the surface interaction energy between the PMMA, SiO2 and solvent. The results of the simulation showed that the Chloroform molecule form the weakest surface interaction energy between both PMMA molecule and Silica particle, which facilitates creating strong interaction between them .The calcu...
Multiscale Effects of Interfacial Polymer Confinement in Silica Nanocomposites
Macromolecules, 2015
Dispersing hydrophilic nanofillers in highly hydrophobic polymer matrices is widely used to tune the mechanical properties of composite material systems. The ability to control the dispersion of fillers is closely related to the mechanical tunability of such composites. In this work, we investigate the physical−chemical underpinnings of how simple end-group modification to one end of a styrene−butadiene chain modifies the dispersion of silica fillers in a polymer matrix. Using surface-sensitive spectroscopies, we directly show that polymer molecular orientation at the silica surface is strongly constrained for silanol functionalized polymers compared to nonfunctionalized polymers because of covalent interaction of silanol with silica. Silanol functionalization leads to reduced filler aggregation in composites. The results from this study demonstrate how minimal chemical modifications of polymer end groups are effective in modifying microstructural properties of composites by inducing molecular ordering of polymers at the surface of fillers.
European Polymer Journal, 2016
Morphology, glass transition and molecular dynamics of polydimethylsiloxane (PDMS) adsorbed onto three types of silica nanoparticles, namely St€ ober, fumed-pyrogenic, and silica gel, were studied employing scanning electron microscopy (SEM), isothermal nitrogen adsorptionedesorption, calorimetry (DSC) and broadband dielectric spectroscopy (BDS) techniques. The initial St€ ober particles (specific surface area S BET~2 40 m 2 /g) form a quite loose silica network with mainly textural pores of~12 nm in size. Fumed silica (S BET~2 60 m 2 /g) demonstrates denser aggregation and increased textural porosity (~11 nm), while silica gel (S BET~8 50 m 2 /g) exhibits tremendous intraparticle porosity (tubular-like pores of~6 nm). On adsorption of PDMS (at~20 and~30 wt%), the glass transition temperature (T g) decreases as compared to the bulk, while the glass transition step broadens. Results suggest loosened molecular packing of the polymer chains accompanied by a broadening of the range of relaxation times in the composites as compared to the neat polymer. On the other hand, the heat capacity step at glass transition is significantly suppressed in the composites, suggesting the formation of a rigid polymer fraction (RAF) at the interfaces with nanoparticles due to strong physical interaction (hydrogen bonding). RAF increases in the order St€ ober < fumed (A300) < silica gel, this increase following that of S BET , in agreement with results in previous work on silica/PDMS systems. Next to the segmental dynamics (a relaxation) of the bulk-like polymer related to the glass transition, BDS allowed the detection of a separate segmental-like relaxation of the polymer in the interfacial silica-PDMS zone. In terms of timescale the interfacial relaxation is almost identical for St€ ober and A300, and slightly faster for silica gel. Comparison of the results of the present work with previous results obtained with similar nanocomposites based on low molecular weight PDMS and silica, provides additional support to recently proposed 'S BET einterfacial dynamics' and 'chain packingepolymer dynamics' correlations.
Nanoscale research letters, 2017
SiO2@PDMS and CeO2-ZrO2-SiO2@PDMS nanocomposites were prepared and studied using nitrogen adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), measurements of advancing and receding contact angles with water, and microcalorimetry. The pore size distributions indicate that the textural characteristics change after oxide modification by poly(dimethylsiloxane) (PDMS). Composites are characterized by mainly mesoporosity and macroporosity of aggregates of oxide nanoparticles or oxide@PDMS nanoparticles and their agglomerates. The FT-IR spectra show that PDMS molecules cover well the oxide surface, since the intensity of the band of free silanols at 3748 cm(-1) decreases with increasing PDMS concentration and it is absent in the IR spectrum at C PDMS ≥ 20 wt% that occurs due to the hydrogen bonding of the PDMS molecules to the surface hydroxyls. SEM images reveal that the inter-particle voids are gradually filled and aggregates are re...
On the origins of silicate dispersion in polysiloxane/layered-silicate nanocomposites
2006
We report the first multi-system study of a layered-silicate dispersion in polysiloxane/layered-silicate nanocomposites. A variety of layered silicates (montmorillonite, synthetic fluoromica, laponite, and fluorohectorite) and cationic modifiers (single-, twin-, and triple-tailed surfactants with tails of varying lengths and both primary and quaternary head-groups) are combined to form organically modified layered silicates, which are then screened for compatibility with low-molecular-weight silanol-terminated poly(dimethylsiloxane) (PDMS). Promising combinations are then selected and studied in greater depth with respect to both molecular weight and polysiloxane end-group and substituent chemistry. We find that the PDMS backbone is generally incompatible with the layered silicates, regardless of modification type, and that dispersion in PDMS systems results from the presence of polar end-groups, a result unprecedented in the field of polymer nanocomposites. We go on to quantify the substituent effect, not only with respect to end-group chemistry, but taking into account changes in the polysiloxane backbone itself. For instance, in the absence of polar end-groups we observe dispersion in the case of poly(methylphenylsiloxane) but not poly(3,3,3trifluoropropylmethylsiloxane). Finally, we apply a new epoxy/amine PDMS curing chemistry to PDMS-nanocomposite production and show higher levels of layered-silicate dispersion than observed in comparable silanol-terminated PDMS-based systems. Our findings serve as an indication of what is necessary to achieve a layered-silicate dispersion in polysiloxane/ layered-silicate nanocomposites, and may indicate a more general approach for improving dispersion in systems where the polymer backbone is otherwise incompatible with the layered silicate.