Particle size control tuning

In any case, the ability to tune their luminescence characteristics by particle size control, combined with relatively high quantum yields, narrow fluorescence emission, very broad absorption spectra and photostability provide new solutions to many of the problems associated with traditional luminescence sensors and hold a strong promise for a completely new set of analytical applications with QDs.18... 

In 2000, Sun and co-workers succeeded in synthesis of monodispersed Fe/Pt nanoparticles by the reduction of platinum acetylacetonate and decomposition of Fe(CO)5 in the presence of oleic acid and oleylamine stabilizers [18]. The Fe/Pt nanoparticle composition is readily controlled, and the size is tunable from 3 to 10 nm in diameter with a standard deviation of less than 5%. For practical use, we developed the novel symthetic method of FePt nanoparticles by the polyol reduction of platinum acetylacetonate (Pt(acac)2) and iron acetylacetonate (Fe(acac)3) in the presence of oleic acid and oleylamine stabilizers in di- -octylether [19,20]. The Fe contents in FePt nanoparticles can be tuned from 23 to 67atomic%, and the particle sizes are not significantly affected by the compositions, retaining to be 3.1 nm with a very narrow size distribution, as shown in Figure 6. 

Fig. 4 PIC dye nanoparticles prepared by the ion-association method. (1) Particle size distributions (determined by the dynamic light scattering technique) and the corresponding electron micrographs of the dye nanoparticles. The average diameter can be controlled by tuning the molar ratio of TPB- to PIC+ (=[TPB-]/[PIC+]. With an increase in the molar ratio, the average diameter decreased. (2) Absorption spectra of PIC nanoparticles in aqueous solution with different sizes (125 and 64 nm in diameter), exhibiting size-dependent peak shift of the 0-0 band. The spectrum of the aqueous PIC-Br monomer solution is also shown...

These studies indicate that the charge transfer at the metal-oxide interface alters the electronic structure of the metal thin film, which in turn affects the adsorption of molecules to these surfaces. Understanding the effect that an oxide support has on molecular adsorption can give insight into how local environmental factors control the reactivity at the metal surface, presenting new avenues for tuning the properties of metal thin films and nanoparticles. Coupled with the knowledge of how particle size and shape modify the metal s electronic properties, these results can be used to predict how local structure and environment influence the reactivity at the metal surface. 

Within the process itself, there are several factors that can affect the quality and consistency of the final extract. These include the particle size of the raw material, the extraction time, the extraction temperature and the solvent used. The difference between these variables and those in the raw materials section is that, to a greater or lesser extent, they can be controlled by the manufacturer, so that an extract is produced as consistently as possible, using these variables to fine-tune the final extract to meet the customer s requirements. The effect that each of each of these controllable parameters has on the final extract is discussed in the following paragraphs. 

The earlier works were performed in trioctylphosphine oxide (TOPO). Wakefield et al. (1999a,b) reported the synlhesis of Tb203 and EU2O3 nanocrystals through a colloidal precipitation method. The RCI3 methanol solution was added to TOPO and a controlled amoimt of NaOH methanol solution was added later to initiate the precipitation. The dehydrating properties of the alcohol result in the formation of oxide, not hydroxides. The obtained NPs are covered with TOPO and the size could be controlled by tuning the ratio of solvents. However, the particle size distribution is still broad. 

Using the so-called two-step process [15, 16], polymer nanoparticles are first synthesized via emulsion polymerization. The size of the resulting nanoparticles can be tuned by a simple process parameter and covers a range of about 30-400 nm. In a second step these nanoparticles are used to coat microbubbles in a controlled bubble formation process. The nanoparticles migrate to the surface of the bubbles (this is related to the interface activity of hydrophobic nanoparticles in general) and build a monolayer around the bubbles. Consequently, the size of the nanoparticles determines the shell thickness of the final microcapsules. Additionally, a carefully chosen nanoparticle concentration regime results in a certain microcapsule size distribution. In principle, particle sizes in the range of 0.5-10 jum can be adjusted and the microcapsule size distributions are ex-... 

The size of the particles could be tuned by simply controlling the flow rates of the disperse phase and continuous phase. This approach has been adopted to fabricate microparticles of gels [80, 81], polymers [13, 82, 83], and inorganic materials with designed physical and chemical properties. 

The control of nanoparticle morphology becomes a very important aspect, since morphology profoundly influences the material performance. As a longterm goal the development of synthesis schemes able to control particle size, shapes, and composition independently from one another is very important, in order to allow tuning of nanocomposite properties. 

With such mixers it is desirable that the impeller speed is variable so that the mixer can be tuned to the process requirements. It is also important that the size of the coating particle be controlled within as smalt a size spectrum as possible. 

Preparation of iron oxide magnetic nanoparticles and their encapsulation with polymers in W/0, i.e. inverse microemulsion polymerization, was also applied by O Connor et al. [167]. Inverse microemulsion polymerization was used to prepare submicron hydrophilic magnetic latex containing 5-23 wt% iron oxide. AM and crosslinker MBA were added to an aqueous suspension of previously synthesized iron oxide nanoparticles (6 wt%) this aqueous phase was dispersed in a aerosol OT (sodium l,4-bis(2-ethylhexoxy)-l,4-dioxobutane-2-sulfonate) (AOT)-toluene solution to form a W/O microemulsion, followed by polymerization with AIBN or V-50 as initiator. The particle size (80-180nm)was controlled by tuning the concentration of the water-soluble crosslinker agent as well as the amount of surfactant with respect to water [168]. 

Historically, QDs were first synthesized in glass matrices where the slow difiusion of precursors provided some measure of size control. In the last couple of decades, colloidal techniques have advanced to the point that parameters such as precursor reactivity, temperature, surfactants etc. can be independently tuned to control and regulate nanocrystal formation. This enables the synthesis of high quality solvent dispersible particles that may be further processed using simple wet-chemical methods. Qne of the earliest techniques employed to achieve this is known as the arrested precipitation method where the semiconductor growth is arrested after the... 

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