Mixing physical methods

The synthesis of bimetallic nanoparticles is mainly divided into two methods, i.e., chemical and physical method, or bottom-up and top-down method. The chemical method involves (1) simultaneous or co-reduction, (2) successive or two-stepped reduction of two kinds of metal ions, and (3) self-organization of bimetallic nanoparticle by physically mixing two kinds of already-prepared monometallic nanoparticles with or without after-treatments. Bimetallic nanoparticle alloys are prepared usually by the simultaneous reduction while bimetallic nanoparticles with core/shell structures are prepared usually by the successive reduction. In the preparation of bimetallic nanoparticles, one of the most interesting aspects is a core/shell structure. The surface element plays an important role in the functions of metal nanoparticles like catal5dic and optical properties, but these properties can be tuned by addition of the second element which may be located on the surface or in the center of the particles adjacent to the surface element. So, we would like to use following marks to inscribe the bimetallic nanoparticles composed of metal 1, Mi and metal 2, M2. 

Despite the utility of the physical methods described above, characterization of entities on the nanometer scale is still a problem. Well-mixed nanoparticles are not necessarily completely homogeneous, and one metal may preferentially segregate to the nanoparticle surface. Subtle differences in surface stoichiometries are presently extremely difficult to quantitatively evaluate with spectroscopy, even when the metal of interest has an intense surface plasmon. 

In liquids, the most commonly used methods are electrical conductivity (18, 19), light absorption, fluorescence (30) and chemical methods based on the color change of an indicator under the influence of an instantaneous reaction (21, 22). The spatial resolution of physical methods (optical, electrical microprobes) is about 100 ym (19) so that these are well suited to macromixing studies but cannot compete with chemical methods for the study of mixing at the molecular scale. An original method based on the continuous injection of radioactive tracers in an industrial mixer has also been proposed (23). In gases, concentration fluctuations have been measured using a catalytic wire (24). 

Phthalocyanines 84 and 85 substituted with six optically active alkyl chains and one chiral diol have been synthesized by mixed cyclization of the two corresponding phthalonitriles [72], The self-organizing properties of these compounds in chloroform solution and thin film have been studied by a range of spectroscopic and physical methods. Both compounds show split Q-band absorptions at 678 and 694 nm in chloroform, and the emission (at 696 nm) is red-shifted compared with that of a non-diol-containing analog. Upon addition of 0.5% methanol, the absorption at 694 nm... 

The standard chemical activation procedure is similar to the physical method of activation. That is, the dried raw material is crushed and sieved to the desired size fraction. Afterward, the obtained powdered material is mixed with a concentrated solution of a dehydrating compound subsequently, this blend is dried and heated under inert... 

Physical methods are of limited effectiveness for separating the phases in cement clinker because of the intimate scale on which the latter are mixed however, Yamaguchi and Takagi (Yl) had some success with the use of dense liquids. Some concentration of the ferrite phase can be effected by magnetic separation (M35,Y1). 

Other physical methods often used include measurements of polarimetry, infrared (see Infrared Spectroscopy) and Raman (see Raman Spectroscopy) spectroscopy, conductivity, and colligative properties such as depression of the freezing point, solubility, and reaction kinetics. These topics and the extensive work carried out on mixed and polynuclear complexes is discussed in many of the books to which reference has aheady been made. ... 

The limit of stability of the crystal framework at different extents of Ni ion exchange of type A molecular sieve is shown by means of electron microscopy, differential thermal analysis, and x-ray diffraction. The data obtained from catalytic studies are in accord with the results of physical methods, showing preservation of the molecular sieve properties after reduction of the Ni ions. Metallic Ni aggregates on the external surface of the zeolite. In the dehydrogenation of cyclohexane and the hydrogenolysis of n-hexane, type A molecular sieve shows the properties of metallic Ni on an inert support. When NiNaA is mixed mechanically with CaY, a typical bifunctional catalyst is obtained. 

Two mixtures, sand and water, and table salt and water, are shown in Figure 3-12a. You know water to be a colorless liquid. Sand is a grainy solid that does not dissolve in water. When sand and water are mixed, the two substances are in contact, yet each substance retains its properties. The sand and water have not reacted. Just by looking at the sand-water mixture in beaker A, it is easy to see each separate substance. Some mixtures, however, may not look like mixtures at all. The mixture of table salt and water in the beaker labeled B is colorless and appears the same as pure water. How can you determine if it is a mixture If you were to boil away the water, you would see a white residue. That residue, shown in Figure 13-12b, is the salt. Thus, the colorless mixture actually contained two separate substances. The salt and the water physically mixed but did not react and were separated by the physical method of boiling. 

The chemical methods for the preparation of nanomaterial could be categorized as either template-directed or template-free. The template synthesis methods commonly used for the production of one-dimensional nanostructured PANI are further subdivided into hard template (physical template) synthesis and soft template (chemical template) synthesis approach according to the solubility of the templates in the reaction media. Non-template routes for the synthesis of one-dimensional nanostructured PANI such as rapid-mixing reaction method, radiolytic synthesis, interfacial polymerization, and sonochemical synthesis have also been reported [56], Other approaches like combined soft and hard template synthesis are also known. An overview of hard-template, soft-template, and template-free procedures are presented in the following paragraphs. 

This study is a continuation of our previous investigations, in which the aggregation phenomena of surfactant molecules (amphiphiles) in aqueous media to form micelles above the critical micelle concentration (c.m.c.) has been described based on different physical methods (11-15). In the current literature, the number of studies where mixed micelles have been investigated is scarcer than for pure micelles (i.e., mono-component). Further, in this study we report various themodynamlc data on the mixed micelle system, e.g., ci H25soi4Na (NaDDS) and sodium deoxycholate (NaDOC), enthalpy of micelle formation (by calorimetry), and aggregation number and second virial coefficient (by membrane osmometry) (1 6). 

As mentioned in Sect. 2.2.1.3 [33], we proposed that a trace amount of /3-phase, induced by the use of an electron-deficient moiety (TAZ) as an end-capper for PFO, can improve device performance to give a better blue purity. Following the idea of /3-phase formation, we further proposed a novel simple physical method to generate /3-phase at a content of up to 1.32% in a PFO film spin-coated on a substrate (the remaining part is amorphous phase) by immersing it in a mixed solvent/non-solvent (tetrahydrofuran/methanol) for a few seconds [45]. The device based on PFO with 1.32% / -phase (ITO/PEDOT PSS/emitting polymer/CsF/Al) has a dramatically enhanced device efficiency and an improved blue-color purity of 3.85 cd A-1 (external quantum efficiency, 3.33%) and CIE of x+y = 0.283 (less than the limit of... 

In the physical methods the mixing of an additive, which differs in temperature, concentration or density (refraction index) from the vessel contents, is foUowed by measuring the temperature, the electrical conductivity, the pH-value or by Schlieren optics. Other methods worthy of mention are ... 

A problem, different in nature, that needs additional attention refers to the characterization of the active centers involved in adsorption and catalytic processes and particularly to the estimation of the number of metallic centers and the exposed surface in supported and unsupported perovskites. A number of chemical and physical methods have been used for metals and oxides, and those based on selective chemisorption of probe molecules seem to be the most promising for this purpose (307). However, while considerable progress has been made for supported metals, no method has been accepted for oxides. This has been caused by the comparatively complex nature of these latter compounds where oxide ions and metal ions of different oxidation states may be present. As probe molecules, O2, CO, and NO were the most frequently used (307) the 02 chemisorption presents the problems inherent to any method based on gas adsorption at low temperatures (a large fraction of physisorbed gas accompanying the chemisorption). On the other hand, its symmetric character renders this molecule unamenable to study by IR spectroscopy. Nonetheless, this method has been used with some success by Weller et al. (308-310) on simple oxides, and its possible application to perovskites and other mixed oxides should be explored. Previous chemisorption work... 

How did chemists greet the new tool made suddenly available to them towards the mid-1950s Their obvious alacrity was tinged with ambivalence. Chemists of the old school did not always embrace the new situation that they were dependent on young upstarts, called NMR specialists . They retrained themselves. They had to. In addition, they had to contend with the shadow cast by physics, which obscured the cherished notion of the autonomy of chemistry, of its non-reducibility to physics. The mixed feeling expressed itself in a catch phrase of those times, physical methods . 

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