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A series of highly dispersed Ho2O3–Yb2O3/SiO2 nanocomposites was synthesized using a liquid-phase method and examined using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron microscopy (TEM), Scanning Electron Microscopy (SEM), and photon correlation spectroscopy (PCS). X-ray fluorescence spectrometry (XRF) confirmed a similar amount of weight percentage of Ho, Yb and Si oxides in the prepared samples. Samples HoYbSi1 (Ho2O3:Yb2O3:SiO2 = 0.5:10:89.5, wt. %), HoYbSi2 (Ho2O3:Yb2O3:SiO2 = 1:10:89, wt. %) and HoYbSi3 (Ho2O3:Yb2O3:SiO2 = 2:10:88, wt. %) calcined at 550 °C are amorphous. TEM and SEM analysis confirm a sphere-like morphology with a quite homogeneous size and shape. As compared with the initial silica, the agglomerated particles of nanocomposites in the aqueous medium are in the range from 200 to 850 nm according to PCS data. The effect of anionic polyacrylic acid (PAA) adsorption on fumed silica (SiO2) and Ho2O3–Yb2O3/SiO2 nanocomposite surfaces on suspension stability was studied. The turbidymetry method was used to monitor the initial silica and triple nanooxides suspensions stability as a function of time.

In this paper, we focus on fabrication and physicochemical properties investigations of silica–multiwalled carbon nanotubes/poly(dimethylsiloxane) composite coatings deposited on the glass supports activated by cold plasma. Air or argon was used as the carrier gas in the plasma process. Multiwalled carbon nanotubes were modified with poly(dimethylsiloxane) in order to impart their hydrophobicity. The silica–multiwalled carbon nanotubes/poly(dimethylsiloxane) nanocomposite was synthesized using the sol–gel technique with acid-assisted tetraethyl orthosilicate hydrolysis. The stability and the zeta potential of the obtained suspension were evaluated. Then, the product was dried and used as a filler in another sol–gel process, which led to the coating application via the dip-coating method. The substrates were exposed to the hexamethyldisilazane vapors in order to improve their hydrophobicity. The obtained surfaces were characterized by the wettability measurements and surface free energy determination as well as optical profilometry, scanning electron microscopy, and transmittance measurements. In addition, the thermal analyses of the carbon nanotubes as well as coatings were made. It was found that rough and hydrophobic coatings were obtained with a high transmittance in the visible range. They are characterized by the water contact angle larger than 90 degrees and the transmission at the level of 95%. The X-ray diffraction studies as well as scanning electron microscopy images confirmed the chemical and structural compositions of the coatings. They are thermally stable at the temperature up to 250 °C. Moreover, the thermal analysis showed that the obtained composite material has greater thermal resistance than the pure nanotubes.

The presented study deals with the fabrication of highly stable and active nanobiocatalysts based on Candida antarctica lipase B (CALB) immobilization onto pristine and poly(dimethylsiloxane) modified MWCNTs. The MWCNTs/PDMS nanocomposites, containing 40 wt.% of the polymer with two molecular weights, were successfully synthesized via adsorption modification. The effect of PDMS chains length on the textural/structural properties of produced materials was studied by means of the nitrogen adsorption–desorption technique, Raman spectroscopy, and attenuated total reflectance Fourier transform infrared spectroscopy. P-MWCNTs and MWCNTs/PDMS nanocomposites were tested as supports for lipase immobilization. Successful deposition of the enzyme onto the surface of P-MWCNTs and MWCNTs/PDMS nanocomposite materials was confirmed mainly using ATR-FTIR spectroscopy. The immobilization efficiency, stability, and catalytic activity of the immobilized enzyme were studied, and the reusability of the produced biocatalytic systems was examined. The presented results demonstrate that the produced novel biocatalysts might be considered as promising materials for biocatalytic applications.

Morphology and thermal transitions of low-molecular weight polydimethylsiloxane (PDMS) adsorbed onto carbon nanotubes (CNTs) and micrometric colloidal graphite sheets (CG) were studied employing SEM, isothermal nitrogen adsorption–desorption and calorimetry techniques. The CNTs were found to agglomerate forming voids between tubes of a broad range, while adsorption of the polymer from a solution results in the expected wrapping of CNTs by PDMS chains and, further, in filling of voids, as documented by SEM and by reduction in specific surface area, SBET. By employing three different thermal protocols in differential scanning calorimetry (DSC) measurements, namely, fast cooling, slow cooling and isothermal annealing of crystallization, direct and indirect filler effects on PDMS mobility (glass transition temperature, Tg, mobile amorphous fraction, MAF), crystallization temperature, Tc, and crystalline fraction (CF) were followed. Results were further evaluated in terms of the rigid amorphous fraction, RAF, and the respective contributions of crystals, RAFcrystal, and of filler-polymer interfaces, RAFfiller. CNTs were found to increase the rate and degree of crystallization of PDMS, while RAF seems to correlate with a previously proposed fraction of polymer ordered at the interface with CNTs for the uncrystallized samples and with CF for the semicrystalline samples. CG particles interact at a lesser extent with PDMS (less RAFfiller), while their presence results in suppression of rate and degree of crystallization (i.e. opposite effects than those of CNTs), so that contributions to RAF could be separated in that case. For both cases of filler, changes in RAF correlate well with those in the SBET value of initial particles. This result supports previous observations in nanocomposites based on PDMS of various low molecular weights adsorbed onto metal oxide nanoparticles with a wide range of SBET.

Ternary CeO 2 –ZrO 2 /SiO 2 nanocomposite oxides were synthesized by a liquid-phase method and subjected to thermal treatment at 550 °C. The physicochemical characterization of the obtained nanosized systems was carried out by various techniques, namely: X-ray diffraction (XRD), nitrogen adsorption–desorption, Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). The XRD measurements revealed the presence of cubic phase Zr 0.4 Ce 0.6 O 2 in CZS1 (CeO 2 :ZrO 2 :SiO 2 = 3:10:87) and CZS2 (CeO 2 :ZrO 2 :SiO 2 = 10:10:80) samples. The crystallinity of this phase slightly increased with increasing ceria content in nanocomposites. Raman spectra indicated the presence of oxygen vacancies in the case of CZS2 and an absence displacement of oxygen ions from their normal lattice positions in both of the samples. XPS data indicated a significant quantity of Ce 3+ ions present in the composites, which is greater in the CZS2 composite. In the case of CZS systems the TEM–HRTEM results showed well-dispersed nanosized Zr–Ce–oxides over the surface of amorphous SiO 2 . All the characterization techniques revealed that silica does not form any compounds with the dispersed Zr–Ce-oxides. The prepared materials were tested in catalytic reaction of CO oxidation in the presence of H 2 and it was shown that CZS2 system had better performance than CZS1 one.

Morphology, thermal transitions and molecular dynamics of polydimethylsiloxane (PDMS) adsorbed onto low specific surface area (25 m 2 /g) spherical-like titania (TiO 2 ) nanoparticles were studied employing adsorption–desorption nitrogen isotherms, morphology (SEM), calorimetry (DSC) and dielectric (BDS) techniques. The initial titania particles (crystallites of 40–140 nm in diameter) were found to aggregate forming voids of a broad range. PDMS was adsorbed in the interior of voids in aggregates and onto external surfaces of the aggregates. With nanoparticles content increasing an increase in the glass transition temperature, T g , is observed in DSC, accompanied by a broadening of the glass transition step and a decrease in the heat capacity step, Δ C p . According to BDS the interfacial polymer fraction is larger and exhibits slower dynamics ( α int relaxation) in the case of shorter PDMS chains (∼22 monomers/chain) as compared to longer chains (∼105 monomers/chain). Changes in the interfacial polymer fraction correlate well with changes in the specific surface area of the aggregates, as recorded by gas molecules adsorption–desorption, and with morphology (SEM). Comparison with previous results obtained with PDMS-based nanocomposites suggests that interfacial polymer fraction and dynamics are dominated by the concentration of polymer–particle contact points (increased for shorter chains due to more free chain ends), rather than by the strength of polymer–filler physical bonds.

A series of CeO2–ZrO2/SiO2 and TiO2–ZrO2/SiO2 nanocomposites was synthesized using a liquid-phase method and characterized using nitrogen adsorption–desorption, X-ray diffraction, thermogravimetry, XRF spectrometry, FTIR spectroscopy, SEM, particle size (D) distribution measured with QELS, zeta (ζ) potential and surface charge density (σ) methods. Structural characteristics (phase composition, average size of crystallites) of the materials affected by pre-heating were determined from the XRD data. Samples TiZrSi1 (TiO2:ZrO2:SiO2 = 3:10:87) and TiZrSi2 (10:10:80) calcined at 550 °С are amorphous. Samples CeZrSi1 (CeO2:ZrO2:SiO2 = 3:10:87) and CeZrSi2 (10:10:80) include a crystalline (Zr0.4Ce0.6)O2 phase. This finding is in a good agreement with SEM analysis. The crystallite size depends slightly on treatment temperature. The influence of changes in the phase composition, sizes and surface structure of particles, surface charge density and zeta potential in aqueous suspensions of nanocomposites is observed as a shift of the isoelectric point (pHIEP) and changes in the shape of σ and ζ curves vs. pH.

Fumed silica modified by hexamethyldisilazane [HDMS] and polydimethylsiloxane [PDMS] was dispersed in a polystyrene/chloroform solution. To increase adhesion between deposited silica layers and a glass surface, the latter was pretreated with air plasma for 30 s. The silica/polystyrene dispersion was deposited on the glass support using a spin coater. After deposition, the plates were dried in a desiccator for 24 h. Water advancing and receding contact angles were measured using the tilted plate method. The apparent surface free energy ( γ S ) was evaluated using the contact angle hysteresis approach. The surface topography was determined using the optical profilometry method. Contact angles changed from 59.7° ± 4.4 (at surface coverage with trimethylsilyl groups Θ = 0.14) to 155° ± 3.1 at Θ = 1. The value of γ S decreased from 51.3 ± 2.8 mJ/m 2 (for the sample at the lowest value of Θ ) to 1.0 ± 0.4 mJ/m 2 for the most hydrophobic sample. Thus, some systems with a high degree of modification by HDMS showed superhydrophobicity, and the sliding angle amounted to about 16° ± 2.1.

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-arranged and increase from 20 to 200 nm in size with the increasing polymer concentration. The highest hydrophobicity (contact angle θ = 140° at C PDMS = 20–40 wt%) is obtained for the CeO2–ZrO2–SiO2@PDMS nanocomposites. The heat of composite immersion in water shows a tendency to decrease with increasing PDMS concentration.

The behavior of water bound to silica/zirconia (2.4 wt.%) (at hydration of 50 mg/g) bare or with adsorbed poly(dimethylsiloxane) (PDMS) (5 wt.%) strongly changes in chloroform medium in comparison with air. PDMS and CDCl 3 stimulate an increase in size of water structures (clusters, domains) to reduce the contact area ( S uw ) between water and hydrophobic polymer or weakly polar solvent. Adsorbed water does not completely cover the oxide surface in air since the surface area in contact with unfrozen water is S uw = 63 m 2 /g at the specific surface area of 290 m 2 /g. The S uw value decreases by 5–10 times for samples with PDMS in the chloroform or chloroform–acetonitrile dispersion media.

A series of TiO2–ZrO2/SiO2 nanocomposites were synthesized using a liquid-phase method and characterized by various techniques, namely, nitrogen adsorption–desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, high-resolution transmission electron microscopy, and photon correlation spectroscopy (PCS). It was revealed that the component ratio and calcination temperature affect the phase composition of nanocomposites. Composites TiZrSi1 (TiO2:ZrO2:SiO2 = 3:10:87) and TiZrSi2 (10:10:80) calcined at 1100 °С demonstrate the presence of t-ZrO2 crystallites in TiZrSi1 and ZrTiO4 phase in TiZrSi2. The samples calcined at 550 °С were amorphous as it was found from XRD data. According to the Raman spectra, the bands specific for anatase are observed in TiZrSi2. According to XPS data, Zr and Ti are in the highest oxidation state (+4). Textural analysis shows that initial silica is mainly meso/macroporous, but composites are mainly macroporous. The particle size distributions in aqueous media showed a tendency of increasing particle size with increasing TiO2 content in the composites.

Two nanosilica A-300/zirconia (SZ) composites at zirconia content C ZrO 2 = 5 and 20 wt.% were synthesized using a wet impregnation method with zirconium acetylacetonate as a precursor. The specific surface area of SZ is larger than that of A-300 because zirconia is composed of nanoparticles (crystallites of 4 nm in average size at C ZrO 2 = 20 wt . % ) smaller than those of the initial silica ( d av ≈ 11 nm). A-300 and SZ modified by polydimethylsiloxane (PDMS at molecular weight 1700 and 7960) in amounts of 5, 10, 15, 20 and 40 wt.% remained in the powder state with aggregates of primary particles smaller than those of A-300. SZ is more hydrophilic than silica but PDMS/SZ is more hydrophobic (maximum hydrophobic at C PDMS 15–20 or 40 wt.%) than PDMS/A-300.

Composites based on fumed silica with surface hydrophobic groups were synthesized by chemical substitution of silanol groups' proton for trimethylsilyl (TMS) groups, adsorption of poly(dimethylsiloxane) (PDMS) and combined chemical-adsorption methods. Microcalorimetry measurements and values of the wetting contact angle with water (Θ) were obtained to investigate the hydrophobic properties of prepared materials. The hydrophilicity indexes (K h ) were determined from the relationship of heat of immersion in water Q w to non-polar decane Q d . The Θ and Q w demonstrated changes with increase of modification degree (d m ) for composites containing a monolayer of PDMS. All samples with excess of PDMS had high Θ (>110°) and relatively low Q w and K h . Composites modified with TMS groups demonstrated hydrophobic properties in accordance with K h at d m 0.7, whereas Θ > 90° is observed only for those samples with d m = 1.0. The different methods of synthesis may be applied based on the morphological characteristics and hydrophobicity of the samples.

Effects of silica and silica/titania nanoparticles on glass transition and segmental dynamics of poly(dimethylsiloxane) (PDMS) were studied for composites of a core-shell type using differential scanning calorimetry, thermally stimulated depolarization current, and dielectric relaxation spectroscopy techniques. Strong interactions between the filler and the polymer suppress crystallinity (Tc, Xc) and affect significantly the evolution of the glass transition in the nanocomposites. The segmental relaxation associated with the glass transition consists of three contributions, arising, in the order of decreasing mobility, from the bulk (unaffected) amorphous polymer fraction (a relaxation), from polymer chains restricted between condensed crystal regions (ac relaxation), and from the semi- bound polymers in an interfacial layer with strongly reduced mobility due to interactions with surface hydroxyls of silica and silica/ titania nanoparticles (a 0 relaxation). The evolution of surface affected CH3 groups, as well as the degree of interaction of PDMS mole- cules with surface hydroxyl groups as a function of treatment temperature, was assessed by Fourier transform infrared spectroscopy, thermogravimetry and differential thermal analysis. The effectiveness of silica/PDMS and silica/titania/PDMS nanocomposites as hydrophobic coatings was investigated by static contact angle measurements. It was shown that the presence of titania nanoparticles and adsorbed PDMS promotes the hydrophobic properties of the PDMS coating after treatment in the 80-650 � C range. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41154.