Colloidal solution formation

In addition to the preparation of Langmuir and Langmuir-Blodgett films, the use of self-assembly techniques also plays an important role in the formation of particle films. Both physisorption, as, for example, electrostatic adsorption of charged particles from colloidal solution, and chemisorption onto a substrate have been investigated. In Section V.A, electrostatic adsorption will be reviewed chemisorption is the subject of Section V.B. 

The formation of colloidal sulfur occurring in the aqueous, either alkaline or acidic, solutions comprises a serious drawback for the deposits quality. Saloniemi et al. [206] attempted to circumvent this problem and to avoid also the use of a lead substrate needed in the case of anodic formation, by devising a cyclic electrochemical technique including alternate cathodic and anodic reactions. Their method was based on fast cycling of the substrate (TO/glass) potential in an alkaline (pH 8.5) solution of sodium sulfide, Pb(II), and EDTA, between two values with a symmetric triangle wave shape. At cathodic potentials, Pb(EDTA)2 reduced to Pb, and at anodic potentials Pb reoxidized and reacted with sulfide instead of EDTA or hydroxide ions. Films electrodeposited in the optimized potential region were stoichiometric and with a random polycrystalline RS structure. The authors noticed that cyclic deposition also occurs from an acidic solution, but the problem of colloidal sulfur formation remains. 

Induced precipitation is a collective name for processes accompanying the formation of solid phase, such as occlusion, adsorption, compound formation, formation of isomorphous mixtures, mixed crystals, colloidal solutions, etc. In... 

The alkaline EG S5mthesis method is a very effective technology for the chemical preparation of unprotected metal and alloy nanoclusters stabilized by EG and simple ions. This method is characterized by two steps involving the formation of metal hydroxide or oxide colloidal particles and the reduction of them by EG in a basic condition. The strategy of separating the core formation from reduction processes provides a valid route to overcome the obstacle in producing stable unprotected metal nanoclusters in colloidal solutions with high metal concentrations. Noble metal and alloy nanoclusters such as Pt, Rh, Ru, Os, Pt/Rh and Pt/Ru nanoclusters with small particle... 

The generation of Oj in suspensions of ZnO containing Ag" ions, which has been known for a long time has again been studied in recent years 210,211) experiments on colloidal solutions have also been carried out in our laboratory. Hada et al. measured the quantum yield of silver formation as a function of Ag concentration They found that the quantum yield q> could be expressed as... 

The significant increases in the turbidity of AgN03 solution could be due to the formation of colloidal solution of silver as also reported earlier by other researchers [60]. As evident from our data (Table 9.1), the increase in the turbidity could either be due to the formation of AgOH from Ag+ or possibly Ag° particles. Upon the addition of NH3, the formation of [Ag(NH3)2]+ in water itself could also be possible. 

In the study of effects of ultrasound on the aqueous reactions of nickel, we found some interesting results, for example, the colloidal formation of Ni-DMG complex and degassing of NH3 during different experiments. When 25 ml of 0.001 M NiSC>4 solution was complexed with 5 ml of 1% dimethyl glyoxime (DMG) in faintly alkaline ammonia medium and sonicated for 30 minutes and compared with another set of 25 ml of complexed solution which was stirred mechanically, a colloidal solution of Ni-DMG complex was formed in sonicated condition. Particles of Ni-DMG complex did not settle even after keeping 3 1 h because of their smaller size, in sonicated solution, whereas in the unsonicated condition large particles of Ni-DMG complex settled down immediately. 

From the above, it could be observed that ultrasound broke down the agglomerated precipitate of Ni-DMG complex to very fine particles, resulting in the formation of colloidal solution of Ni-DMG complex in the presence of an ultrasonic held. The settlement of particles was slow in the sonicated sample than in control sample. However, in the normal reaction, green precipitate of nickel (II) hydroxide dissolved in the excess NH3 solution and formed deep blue solution of hexammi-nenickel(II) ions, as under ... 

X 10 cmr/s. Thus it appears that colloidal crystal formation bears further investigation as a source of extraordinarily slow diffusion coefficients in low salt polyelectrolyte solutions. 

For example, Au NPs functionalized with 15-crown-5-alkanethiol chemically recognize K+ from an aqueous matrix containing physiologically important cations, such as Li+, Cs+, NH4+, Mg2 1, Ca2+, and an excess amount of Na+. The colloidal solution changes from red to blue upon addition of K+ and this is due to the selective formation of Au NP aggregates [184] (Figure 3.18). 

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