The size effect of silica nanoparticles (SiO2) on thermal decomposition of poly(methylmethacrylate) (PMMA) was investigated by the controlled rate thermogravimetry. Thermal
degradation temperature of PMMA–SiO2 composites depended on both fraction and size of SiO2, the thermal degradation temperature of 23 nm (diameter) SiO2–PMMA (6.1 wt%) was 13.5 °C higher than that of PMMA. The thermal stabilities of 17 nm SiO2–PMMA (3.2 wt%) and 13 nm SiO2–PMMA (4.8 wt%) were 21 and 23 °C, respectively, higher than that of PMMA without SiO2. The degree of degradation improvement was increased linearly with the surface area of SiO2. The number of surface hydroxyl group in unit volume of SiO2 particle increased with increasing the specific surface area of SiO2, and the interaction between hydroxide group of SiO2 and carbonyl group of PMMA had an important role to improve the thermal stability of PMMA.
The enthalpies of precipitation of ZnS nanoparticles within water containing reversed micelles of sodium bis(2-ethylhexyl)
solfosuccinate, L-α phosphatidylcholine, tetraethyleneglycol-mono-n-dodecyl ether and didodecyldimethylammonium bromide as a function of the molar concentration ratioR (R=[water]/[surfactant]) were measured by calorimetric technique. The results indicate that the energetic state of ZnS nanoparticles
confined in the aqueous core of the reversed micelles is different from that in bulk water. Effects due to nanoparticle size,
adsorption of HS− ions on the nanoparticle surface and interactions between nanoparticles and water/surfactant interfaces are discussed.
Authors:Razwan Baber, Luca Mazzei, Nguyen T.K. Thanh, and Asterios Gavriilidis
Synthesis of silver nanoparticles (NPs) in an impinging jet reactor (IJR) was investigated due to its unique properties of efficient mixing and lack of channel walls which avoid fouling. Silver NPs were formed at room temperature by reducing silver nitrate with sodium borohydride in the presence of sodium hydroxide. Two types of ligand were used to stabilize the NPs, trisodium citrate, and polyvinyl alcohol (PVA). Weber number, the ratio between inertial forces and surface tension forces, is used to characterize flow in impinging jets. Flow regimes were investigated forWeber numbers in the range of 13–176. A liquid sheet/chain regime was identified at lowerWeber numbers (<90), and an unstable rim structure was identified at higherWeber numbers (>90). Mixing time was found to be in the range 1–7ms, using theVillermaux—Dushman reaction system and interaction by exchange with the mean mixing (IEM) model. Fastest mixing occurred at Weber number ca. 90. Using trisodium citrate as a ligand, NP size decreased from 7.9 ± 5.8 nm to 3.4 ± 1.4 nm when flow rate was increased from 32 mL/min to 72 mL/min using 0.5 mm jets, and from 6.4 ± 3.4 nm to 5.1 ± 4.6 nm when flow rate was increased from 20 mL/min to 32 mL/min using 0.25 mm jets. Using PVA as a ligand, NP size decreased from 5.4 ± 1.6 nm to 4.2 ± 1.1 nm using 0.5 mm jets and stayed relatively constant between 4.3 ± 1 nm and 4.7 ± 1.3 nm using 0.25 mm jets. In general, the size of the NPs decreased when mixing was faster.
Authors:S. Hosseini, A. Moghadassi, D. Henneke, and Ali Elkamel
Changes in the thermal conductivities of paraffin and mono ethylene glycol (MEG) as a function of β-SiC nanoparticle concentration
and size was studied. An enhancement in the effective thermal conductivity was found for both fluids (i.e., both paraffin
and MEG) upon the addition of nanoparticles. Although an enhancement in thermal conductivity was found, the degree of enhancement
depended on the nanoparticle concentration in a complex way. An increase in particle-to-particle interactions is thought to
be the cause of the enhancement. However, the enhancement became muted at higher particle concentrations compared to lower
ones. This phenomenon can be related to nanoparticles interactions. An improvement in the thermal conductivities for both
fluids was also found as the nanoparticle size shrank. It is believed that the larger Brownian motion for smaller particles
causes more particle-to-particle interactions, which, in turn, improves the thermal conductivity. The role that the base-fluid
plays in the enhancement is complex. Lower fluid viscosities are believed to contribute to greater enhancement, but a second
effect, the interaction of the fluid with the nanoparticle surface, can be even more important. Nanoparticle-liquid suspensions
generate a shell of organized liquid molecules on the particle surface. These organized molecules more efficiently transmit
energy, via phonons, to the bulk of the fluid. The efficient energy transmission results in enhanced thermal conductivity.
The experimentally measured thermal conductivities of the suspensions were compared to a variety of models. None of the models
proved to adequately predict the thermal conductivities of the nanoparticle suspensions.
lunar samples from Apollo 11, 12 and 16 missions were personally examined. The thickness of the adsorbed liquid layers (adsorption capacity) and adsorbate–adsorbente interactions (desorption energy) on the lunar nanoparticles can be assessed by means of
Authors:Stéphanie Etienne, C. Becker, D. Ruch, B. Grignard, G. Cartigny, C. Detrembleur, C. Calberg, and R. Jerome
Silica nanoparticles of various sizes have
been incorporated by melt compounding in a poly(methyl methacrylate) (PMMA)
matrix to enhance its thermal and mechanical properties. In order to improve
nanoparticles dispersion, PMMA grafted particles have been prepared by atom
transfer radical polymerization (ATRP) from well-defined silica nanoparticles.
This strategy was expected to ensure compatibility between both components
of the PMMA nanocomposites. TEM analysis have been performed to evaluate the
nanosilica dispersion whereas modified and non-modified silica/PMMA nanocomposites
thermal stability and mechanical properties have been investigated by both
thermogravimetric and dynamical mechanical analysis.
Magnetic nanoparticles were prepared by a wet chemical method. Precursors of MFe2O4 (M = Co, Mn, Zn) were prepared from a mixture of metal chloride and metasilicate nonahydrate aqueous solutions. The precipitates
obtained in the wet chemical method were calcined to obtain MFe2O4 nanoparticles encapsulated by amorphous SiO2. The blocking temperatures TB’s were between 20 and 320 K, in this temperature range, the anisotropy energy of the particles decreased below their thermal
energy. TB increased with the particle size. In order to clarify the nanoparticle formation process, differential thermal analysis and
thermogravimetric (TG-DTA) measurements were performed for the as-prepared samples.
Authors:Elena Parfenyuk, Galina Kulikova, and Irina Ryabinina
Human serum albumin (HSA) adsorbed onto silica nanoparticles modified by 3-aminopropyltriethoxysilane (APTES) and polyethyleneimine
(PEI) was investigated by differential scanning calorimetry, IR spectroscopy, and photon correlation spectroscopy. The structural
alterations of the protein molecules induced from adsorption process were estimated on the basis of temperatures of denaturation
transition (Td) of the protein in free (native) and adsorbed form. It was found that adsorption of the protein onto the APTES-modified silica
nanoparticles results in an increase in the temperature of denaturation transition from 42 to 47.4 °C. HSA adsorbed onto the
PEI-modified silica nanoparticles unfolds extensively.
Authors:M. Kanemaru, Y. Shiraishi, Y. Koga, and N. Toshima
Summary Recently, we have reported a noble method of preparing Ag/Rh bimetallic nanoparticles with a pseudo-core/shell structure. We simply mix the dispersions of poly(N-vinyl-2-pyrrolidone)(PVP)-protected Ag and Rh nanoparticles in solution at room temperature. We found that the mixture of dispersions forms bimetallic nanoparticles in a pseudo-core/shell structure on standing. We call this process the ‘self-assembling’ or ‘self-organizing’. In this study we seek for a thermodynamic driving force for this process by determining the enthalpy of the interaction among three pairs of nanoparticles by isothermal titration calorimetry (ITC). The results indicate that the interaction between each pair is strongly exothermic, and that among the pairs studied here the strength of the exothermic interaction is in the order of Ag/Pt<Ag/Pd<Ag/Rh.