Hybrid dispersion Initiator

When the process is carried out according to Method la it may be assumed that the kind of initiating system (water-soluble initiator or redox system) does not have any significant effect on the morphology of hybrid dispersion particles since the polymerisation proceeds mainly on the surface of DPUR particles and monomer droplets and in the micelles of emulsifier. In the case of water-soluble initiator (potassium persulphate) the polymerisation starts in water where the ion-radicals are formed from the monomer molecules dissolved in water. These ion-radicals can diffuse to DPUR particles, monomer droplets and emulsifier micelles. After this happens the system will consist of ... 

Method of Hybrid Dispersion Synthesis and Kind of Initiating System... 

The results of investigations of the effect of method of hybrid dispersion synthesis (la, lb, 2 or 3 - see Section 3.2) on the properties of dispersions as well as of films and coatings made from them are presented in Tables 6.9 to 6.11 (dispersions prepared using water-soluble initiator) and in Tables 6.12 to 6.14 (dispersions prepared using redox initiating system). In all dispersions the chemical structure of the polyurethane-urea and acrylic/styrene polymer component was the same (see relevant tables in Section 6.5.2). All the dispersions contained a similar low level (2-3.6%) of NMP. 

Particle size distribution and zeta potential of a typical hybrid dispersion obtained using a water-soluble initiator are presented in Figures 6.17 and 6.18, respectively. 

Table 6.9 Properties of hybrid dispersions of the same chemical composition prepared according to different methods using a water-soluble initiator (K S O ) ... 

Figure 6.17 Particle size distribution for a typical polyurethane-urea-acrylic/styrene hybrid dispersion synthesised in this study (MDPUR-ASD 97 from Table 6.7 prepared according to method 2 using a water-soluble initiator).

The DSC thermogram of the film obtained from a typical hybrid dispersion obtained using redox initiator is presented in Figure 6.22. 

Properties of hybrid dispersions prepared according to the different methods (la, lb and 2 - see Section 6.3.2) and based on the same polyol (PTMG 2000), but differing in the presence or absence of double bonds in the polyurethane-urea part of the hybrid, as well as of films and coatings made of them, are presented in Tables 6.21 and 6.22. All dispersions have a similar low level (2.0-3.3%) of coalescent and have the same structure of the acrylic/styrene part of the hybrid. Redox initiator was used in the synthesis of dispersions according to the method 2, and in all other dispersions presented in these tables a water-soluble initiator was applied. 

The properties of hybrid dispersion prepared according to two different methods (la and 3 - see Section 3.2) and having the same chemical composition and differing only in the chemical structure of the acrylic/styrene polymer component are presented in Tables 6.24 to 6.26. All dispersions were synthesised using a water-soluble initiator. Dispersions prepared according to method la did not contain any coalescent while dispersions prepared according to method 3 contained 11.6% of NMP. 

The morphology of particles of hybrid dispersion synthesised according to method 2 using water-soluble and redox initiators is presented in Figures 6.32 and 6.33, respectively. Both pictures show both the single particles and the coalesced particles to demonstrate what happens to the particle morphology in the process of film formation. White colour represents the polyurethane-urea part of the hybrid. 

Figure 6.32 Morphology of particles of hybrid polyurethane-urea-acrylic/styrene hybrid dispersion prepared according to method 2 (See Section 6.3.2) using water-soluble initiator (MDPUR-ASD 97). Micrograph was taken using TEM. Both single particle and coalesced particles are shown. Reproduced with permission from Professor A. E. Czalych, Institure of Chemical Physics of the Russian Academy of Sciences, Moscow.

When the properties of hybrid dispersions having the same composition but prepared according to different methods using water-soluble and redox initiator (Tables 6.9 and 6.12) are compared with the properties of starting DPUR and ASD (Tables 6.1 and 6.4) it can be noted that ... 

From a practical point of view it is very important that, regardless of the type of initiator and method of synthesis, the films made from hybrid dispersions are transparent (this proves that their structure is quite uniform), strong, elastic and resistant to water (very good resistance) and organic solvents (good resistance). 

In the specific case of silica nanoparticles-pH EMA hybrid materials, the synthesis relies on obtaining a fine dispersion of silica nanoparticles (with a mean diameter of 7nm) in HEMA monomers (liquid phase). When a homogeneous solution is obtained, a free radical initiator is added at a concentration based on the weight of the monomer mixture. After the initiator dissolution, the solution can be poured into molds or between two glass plates to obtain monoliths or uniform films, respectively, after being cured at temperatures around 60-85 °C for several hours. 

Three different combinations are possible depending upon the number of orbitals involved in the hybridization. The four existing outer electrons of the carbon atom (two in the 2s orbital and one in each of the 2px and 2py orbitals) are initially dispersed, one in each of the available orbitals (2s, 2px,... 

Owing to the simphcity and versatility of surface-initiated ATRP, the above-mentioned AuNP work may be extended to other particles for their two- or three-dimensionally ordered assemblies with a wide controllabiUty of lattice parameters. In fact, a dispersion of monodisperse SiPs coated with high-density PMMA brushes showed an iridescent color, in organic solvents (e.g., toluene), suggesting the formation of a colloidal crystal [108]. To clarify this phenomenon, the direct observation of the concentrated dispersion of a rhodamine-labeled SiP coated with a high-density polymer brush was carried out by confocal laser scanning microscopy. As shown in Fig. 23, the experiment revealed that the hybrid particles formed a wide range of three-dimensional array with a periodic structure. This will open up a new route to the fabrication of colloidal crystals. 

Flotation-washing (hybrid) processes involve flotation de-inking followed by further washing processes. The latter are intended to remove fine particles of ink that were not removed by the flotation step. In this case the dispersants are usually added after the pulper but before the washing, so that any ink not initially floated will be emulsified and removed during the washing process [767]. 

Macroscopic solvent effects can be described by the dielectric constant of a medium, whereas the effects of polarization, induced dipoles, and specific solvation are examples of microscopic solvent effects. Carbenium ions are very strong electrophiles that interact reversibly with several components of the reaction mixture in addition to undergoing initiation, propagation, transfer, and termination. These interactions may be relatively weak as in dispersive interactions, which last less than it takes for a bond vibration (<10 14 sec), and are thus considered to involve "sticky collisions. Stronger interactions lead to long-lived intermediates and/or complex formation, often with a change of hybridization. For example, onium ions are formed with -donors. Even stable trityl ions react very rapidly with amines to form ammonium ions [41], and with water, alcohol, ethers, and esters to form oxonium ions. Onium ion formation is reversible, with the equilibrium constant depending on the nucleophile, cation, solvent, and temperature (cf., Section IV.C.3). 

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