Stages Of Nanoparticle Formation Research Articles

Internal Nanoparticle Structure of Temperature-Responsive Self-Assembled PNIPAM-b-PEG-b-PNIPAM Triblock Copolymers in Aqueous Solutions: NMR, SANS, and Light Scattering Studies

In this study, we report detailed information on the internal structure of PNIPAM-b-PEG-b-PNIPAM nanoparticles formed from self-assembly in aqueous solutions upon increase in temperature. NMR spectroscopy, light scattering, and small-angle neutron scattering (SANS) were used to monitor different stages of nanoparticle formation as a function of temperature, providing insight into the fundamental processes involved. The presence of PEG in a copolymer structure significantly affects the formation of nanoparticles, making their transition to occur over a broader temperature range. The crucial parameter that controls the transition is the ratio of PEG/PNIPAM. For pure PNIPAM, the transition is sharp; the higher the PEG/PNIPAM ratio results in a broader transition. This behavior is explained by different mechanisms of PNIPAM block incorporation during nanoparticle formation at different PEG/PNIPAM ratios. Contrast variation experiments using SANS show that the structure of nanoparticles above cloud point temperatures for PNIPAM-b-PEG-b-PNIPAM copolymers is drastically different from the structure of PNIPAM mesoglobules. In contrast with pure PNIPAM mesoglobules, where solidlike particles and chain network with a mesh size of 1-3 nm are present, nanoparticles formed from PNIPAM-b-PEG-b-PNIPAM copolymers have nonuniform structure with "frozen" areas interconnected by single chains in Gaussian conformation. SANS data with deuterated "invisible" PEG blocks imply that PEG is uniformly distributed inside of a nanoparticle. It is kinetically flexible PEG blocks which affect the nanoparticle formation by prevention of PNIPAM microphase separation.

Investigations of initial particle stages during spark discharge

The number of nanoparticle-based products on the market is expected to increase considerably during the coming decades. This forces the industry to have highly meticulous manufacturing of large amounts of nanoparticles using cheap and environmentally friendly methods. For the production of metal nanoparticles spark discharge generation is a promising route to fulfill these demands. The spark discharge generator can be easily scaled-up for mass production due to its simple design solely by placing several units in parallel. Before doing so, one first needs to optimize a single spark discharge generator unit. To optimize the spark discharge generator in a controlled way the first stage of nanoparticle formation needs to be understood. To improve this understanding we have constructed a customized nanoparticle sampler to enable sampling of the initial stages of particle formation for imaging in a TEM. In this article we present the design of the sampler and discuss optimal sampling parameters. We also present how the generation parameters can be tuned in order to affect the first stages of particle formation and hence the final nanoparticles.

Electroplasma method for the formation of metallic nanoparticles of a given size

A nanoparticle formation mechanism is proposed for three versions of spark discharge generation in a system with a liquid electrode. Three stages of nanoparticle formation are revealed, and their stable states for the system under study are determined. A physicomathematical model is developed, and it shows that the particle size can be controlled by changing the initial salt solution concentration and the parameters of the discharge system.

Kinetics and mechanism of the interaction between HAuCl4 and rutin

The kinetics and mechanism of the reaction of HAuCl4 with rutin and the size of the resulting gold nanoparticles have been studied by UV-vis, FTIR, and surface-enhanced Raman spectroscopy (SERS), atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). The reaction includes the formation of a rutin complex with HAuCl4 and its decomposition yielding Au atoms. The gold nanoparticles result from Au ions and atoms at the second stage. This stage can be described in terms of a second order kinetic equation. The rate constant and Gibbs energy of the second stage of nanoparticle formation have been determined.

Effect of active impurities on the condensation of nanoparticles from supersaturated carbon vapor in the combined laser photolysis of C3O2 and H2S

The effect of active H2S, HS·, and atomic hydrogen impurities on the condensation of highly supersaturated carbon vapor obtained in the combined laser photolysis of a mixture of C3O2 and H2S diluted with argon was studied. The concentrations of carbon vapor, HS·, and atomic hydrogen obtained in the laser photolysis of the mixture were determined using the absorption cross sections of C3O2 and H2S molecules measured in this work and the measured amount of absorbed laser radiation. The time profiles of the sizes of growing nanoparticles synthesized in C3O2 + Ar and C3O2 + H2S + Ar mixtures were measured using the laser-induced incandescence (LII) method. An improved LII model was developed, which simultaneously took into account the heating and cooling of nanoparticles and the temperature dependence of the thermophysical properties of nanoparticles, as well as the cooling of nanoparticles by evaporation and thermal emission. The size distributions of carbon nanoparticles formed in the presence and absence of active impurities were determined with the use of a transmission electron microscope. The final average size of carbon nanoparticles was found to decrease from 12 to 9 nm upon the addition of H2S to the system, whereas the rate of nanoparticle growth decreased by a factor of 3, and the properties of nanoparticles changed. In particular, the translational energy accommodation coefficient for Ar molecules at the surface of carbon nanoparticles was found to decrease from 0.44 to 0.30. A comparison of the calculated total carbon balance at the early stage of nanoparticle formation with experimental data demonstrated that the reaction C + H2S → HCS· + H, which removes a portion of carbon vapor from the condensation process, has a determining effect on the carbon balance in the system. It was found that HS· and atomic hydrogen affect the carbon balance in the system only slightly. Thus, the experimentally observed decrease in the rate of nanoparticle growth and in the sizes of nanoparticles can be explained by a decrease in the concentration of free carbon upon the addition of H2S molecules to the system.

Development and Optical Properties of Cadmium Sulfide and Cadmium Selenide Nanoparticles in Amphiphilic Block Copolymer Micellar-like Aggregates

CdS and CdSe nanoparticles were prepared in organic solvents using as templates inverse amphiphilic block copolymer micellar aggregates, which were induced by cadmium complexation. Amphiphilic block copolymers utilized in this work include poly(sulfonated styrene-block-tert-butylstyrene) (SPS−PtBS) and poly(styrene-block-sulfonated isoprene) (PS−SPI). Copolymers with different compositions and molecular weights were synthesized by anionic polymerization high-vacuum techniques and postpolymerization selective sulfonation reactions. Cadmium acetate was used as the cadmium precursor and thioacetamide or H2Se as the sulfur or selenium source, respectively. The nanostructured organic−inorganic hybrid materials were characterized in solution and in thin films by light scattering, UV−vis and fluorescence spectroscopy, infrared and Raman vibrational spectroscopy, and transmission electron microscopy (TEM). The influence of composition and molecular weight of block copolymers on the properties of nanoparticles was investigated at all stages of nanoparticle formation. It was shown that well-defined CdS and CdSe semiconductor nanoparticles with controllable sizes and optical properties can be formed by judicious choice of the experimental conditions following the suggested preparation protocol.

Electronic excitations and optical response of metal nanocomposites under heavy ion implantation

The optical transmission and ion-induced luminescence under implantation of copper ions into quartz glass (a-SiO2) have been measured to study the processes of formation of copper nanoparticles. It is shown that in situ measurements are more informative in comparison with the ordinary approach—investigation of the properties of ion-implanted nanocomposites only after implantation. A series of experiments was performed to prove that the ion-induced luminescence band at 545–550 nm is due to Cu+ ions dissolved in a-SiO2. The combined use of in situ optical techniques makes it possible to monitor the states of implanted copper (metal nanoparticles and dissolved atoms) by the change in the optical absorption near the surface plasmon resonance of nanoparticles and by the intensity of ion-induced luminescence of Cu+ states in solid solution. It is shown that the optical bands of defects, dissolved copper, and nanoparticles can be separated within a simple linear approximation. Near the surface plasmon resonance and defect bands, ion-induced transient optical absorption has been revealed. The transient optical absorption near the surface plasmon resonance is explained by the temperature effect. The relationship between the electronic excitation, radiation-induced optical response, and the kinetics of nanoparticle formation is analyzed. Several stages of nanoparticle formation have been established: accumulation of implanted copper in solid solution, nucleation of nanoparticles, coalescence, growth of nanoparticles, and saturation of nanocomposites.

Electronic excitation and optical responses of metal-nanoparticle composites under heavy-ion implantation

Measurements of optical transmission and ion-induced photon emission (IIPE) during implantation of copper ions into silica glass (a-SiO2) have been combined in order to study formation of Cu nanoparticles. It has been shown that in situ measurements are more advantageous than conventional experimental approaches of examining the properties of ion-implanted nanocomposites solely after implantation. Series of experiments have been done to prove that the band of IIPE at 545–550 nm originates from Cu+ solutes in a-SiO2. The combination of in situ optical techniques provides means of monitoring Cu nanoparticles and Cu solutes via the optical absorption in the range of the surface-plasmon resonance (SPR) of nanoparticles and the IIPE of Cu+ solutes. It has been shown that a simple linear approximation can be used to separate optical bands of defects, Cu solutes, and nanoparticles. Ion-induced transient optical absorption has been found in the ranges of SPR and defect bands. The transient optical response in the range of SPR has been tentatively attributed to a thermomodulation effect. We analyze relationships between electronic excitation, radiation-induced optical responses, and kinetics of nanoparticle formation. Several stages of nanoparticle formation have been distinguished: accumulation of Cu solutes, precipitation of Cu atoms, coalescence, growth of nanoparticles, and saturation of nanocomposites.

Quasi-two-dimensional or hcp palladium nanoparticles with host-guest interaction prepared at room temperature

Quasi-two-dimensional palladium nanoparticles with an average lateral dimension of 7 nm have been prepared by reduction of a PdCl2 graphite intercalation compound precursor by lithium-diphenylide in tetrahydrofuran at room temperature. Selected-area electron diffraction patterns provide evidence that the palladium nanoparticles are hcp single-crystal particles. Owing to the template effect of the graphite lattice, the lattice parameter of palladium was found to have a strong relation with the graphite, and a 3a graphite superstructure was inferred. The palladium structure is rotated by 30o with regard to the carbon host lattice. Raman spectroscopy on this sample showed that a charge transfer between carbon and palladium occurs. The sample can be considered as a common Pd-graphite intercalation compound with palladium nanoparticles as guest. This behaviour is different from palladium nanoparticles prepared by hydrogen reduction at higher temperatures from the same precursor material. These particles may represent an early stage of nanoparticle formation.