Particles, hybrid

Mellors, J.S., Jorgenson, J.W. (2004). Use of 1.5-pm porous ethyl-bridged hybrid particles as a stationary-phase support for reversed-phase ultrahigh-pressure liquid chromatography. Anal. Chem. 76, 5441-5450. 

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. 

Template core-shell particles with cores comprised mainly of poly(glycidyl methacrylate) (GMA) and shells consisting mainly of PNIPAM and amino or thiol-functionalized have been used for the synthesis of Au NPs. The obtained hybrid particles exhibited a reversible color change from red to purple, which originated from the surface plasmon resonance of gold nanoparticles and was temperature-dependent in the range 25-40 °C [96] (Scheme 3.15). 

The polyurethane (PU) can be considered an environment-friendly material because the urethane bond resembles the amide bond, which implies possible biodegradability. It can be used in various elastomer formulations, paints, adhesives for polymers and glass, and artificial leather as well as in biomedical and cosmetic fields. Polyurethane spheres were prepared from 20/40% of PU prepolymer solution in xylene [91]. PU droplets were formed in water with the SPG membrane of different pore size (1.5-9.5 pm) and then polymerized to form the final microspheres. Finally, spherical and solid PU particles of 5 pm were obtained after the removal of the solvent. In another study, Ma et al. reported the formation of uniform polyurethane-vinylpolymer (PUU-VP) hybrid microspheres of about 20 pm, prepared using SPG membranes and a subsequent radical suspension polymerization process [92], The prepolymers were solubilized in xylene and pressed through the SPG membrane into the continuous phase containing a stabilizer to form uniform droplets. The droplets were left for chain extension at room temperature for some hours with di- and triamines by suspension polymerization at 70 °C for 24h. Solid and spherical PU-VP hybrid particles with a smooth surface and a higher destructive strength were obtained. 

The use of a polymer species as a way to control diffusion to the inside of mesoporous silica was also employed by Lopez and coworkers.67 In this work the researchers polymerized iV-isopropyl acrylamide on mesoporous silica by atom transfer radical polymerization, and took advantage of the changes the polymer experiences upon thermal treatment. The authors discovered that the hybrid material could take up more fluorescein than nonfunctionalized material at temperatures above 45°C. At that temperature the polymer is in a collapsed hydrophobic state and partially covers the negatively charged surface of silica that otherwise repels the negatively charged fluorescein dye. At temperatures below 30°C the polymer exists in a hydrated state in which the chains are expanded. Interestingly, the fluorescein loaded hybrid particles were... 

With the concept of nanoreactors one can take advantage of an additional mode control for the design of nanoparticles where both thermodynamic aspects as well as shear history enter the particle size and the inner structure of the latexes or hybrid particles. The polymerization in such nanoreactors takes place in a highly parallel fashion, i.e., the synthesis is performed in 1018-102° nanocompartments per liter that are separated from each other by a continuous phase. In miniemulsion polymerization, the principle of small nanoreactors is realized as demonstrated in Fig. 1. 

TEM and ultracentrifuge results showed (see Fig. 16) that this process results in effective encapsulation of the carbon with practically complete yield only rather small hybrid particles, but no free carbon or empty polymer particles, were found. It has to be stated that the hybrid particles with high carbon contents do not possess spherical shape, but adopt the typical fractal structure of carbon clusters, coated with a thin but homogeneous polymer film. The thickness of the monomer film depends on the amount of monomer, and the exchange of monomer between different surface layers is - as in miniemulsion polymerization - suppressed by the presence of an ultrahydrophobe. 

The main downside of silica-based sorbents is pH compatibility they are stable only at pH values from 2 to 8 at lower pH, the H3O+ ions catalyze the hydrolysis of the alkyl ligand at higher pH, the nucleophilic attack of Si-O bonds by OH results in the erosion of the silica surface. The formation of Si(OH)4 is signaled by a back pressure increase. Recently the chemical resistance of the silica particles has been improved by hybrid particle technology. Organic moieties such as ethyl groups were inserted close to the particle surfaces and columns stable between pH 1 and 12 under ultra-high pressure (1000 bar) were produced. 

Various papers on hybrid mini emulsion polymerization have used alkyd [98, 99], polyester [100] or polyurethane [101] as both the costabihzer and a component of the hybrid particle. Since most of these materials were added far in excess of the levels normally used as costabihzers, it is not surprising that they are effective. 

Fig. 3. Protein composition of Sulfolobus 50S ribosomal subunits. The primary RNA-binding proteins are evidenced as black spots. The solid arrows indicate proteins found in the low-temperature reconstitution intermediate and in the 42S hybrid particles obtained from the reaction between Sulfolobus TP 50 and either E. coli or H. mediterranei 23 S RNA. The open arrows indicate proteins found in the 42S hybrid particles but not in the low-temperature reconstitution intermediate.

Within each of the two classical domains, bacteria and eucarya, reciprocal combinations of ribosomal subunits from distantly related organisms yield synthetically active hybrid ribosomes [174-176], In contrast, formation of hybrid particles from eucaryal and bacterial ribosomal subunits appears to be subject to severe constraints [174], One case of hybrid monosome formation from subunits of bacterial E. coli) and eucaryal ribosomes Artemia salina) has been reported by Boublik et al. [177] hybrid ribosomes (73S), however, were assembled only from Artemia 40S subunits and E. coli SOS subunits, and only at levels (30mM) considerably higher -about twofold - than those (ISIS mM) normally required for poly(U)-directed poly(Phe) synthesis in both bacterial and eucaryal cell-free systems. 

Unlike the early assembly proteins, the proteins and/or the rRNA domains involved in the late assembly reactions of bacterial and archaeal SOS ribosomes appear to share little structural homology this is indicated by the inability of the hybrid particles to bind additional proteins and to complete the assembly process, regardless of the environmental conditions employed [103]. 

Scheme 3 Synthetic path to produce stable PVFA-co-PVAm/silica hybrid particles...

Table 1 Thickness of PVFA-co-PVAm layers adsorbed on to silicon wafers, determined by AFM, and IEP, determined by pH-dependent electrokinetic measurements in aqueous KC1 solution (10—3 mol L-1) using PVFA-co-PVAm/silica hybrid particles...

Both dyes have been to be found suitable as surface polarity indicators for organically functionalized silica particles [83, 84]. In contrast to dye 1 the steric demand of the substituents in the 2- and 6-positions of the pheno-late moiety prevent penetration of the dye 2 molecules through the organic layer towards the silica surface. Therefore, solutions of dye 2 in 1,2-dichlor-oethane or toluene seem very suitable as a probes to study the surface polarity of organically functionalized/silica hybrid particle [83]. 

As expected, the influence of the content of amino groups of the adsorbed PVFA-co-PVAm molecules on the polarity of the hybrid particles surface is fairly strong. Figure 5 shows the surface polarity parameters ET (30) as function of the amino content of the polymer component of PVFA-co-P VAm/sili-ca hybrid materials. 

Fig. 5 (a) Dependence of Ex (30) values of several PVFA-co-PVAm/silica hybrid particles on the amino content in the PVFA-co-PVAm copolymer ET (30) values were determined from solvatochromic experiments using the adsorption of dye 2 from 1,2-dichlor-oethane (open circles), and toluene (filled circles) (b) Ej (30) values compared with the IEP values of several PVFA-co-PVAm/silica hybrid particles. ET (30) values were determined from solvatochromic experiments using the adsorption of dye 2 from 1,2-dichlor-oethane (open circles), and toluene (filled circles). IEP data were determined by means of pH-dependent electrokinetic experiments in aqueous 10-3 mol L-1 KCl solution... 

According to the symmetric acid-base theories, an increase of the basicity of the surface should cause a decrease of its acidity [86]. Hence, the increase of the p values should correspond to reduced Ex (30) values of the hybrid surface, because the silica surfaces HBD groups are involved in the adsorption process. Consequently, an inverse dependence of the Ex (30) on IEP values is expected. This is qualitatively shown in Fig. 5 for several PVFA-co-PVAm/silica hybrid particles. 

To fix the adsorbed PVFA-co-PVAm layers irreversibly, cross-linking reactions with bifunctional or multifunctional reagents were carried out on the surface of solid PVFA-co-PVAm/hybrid particles. The cross-linking reactions were performed as two-step synthesis. In the first step PVFA-co-PVAm was... 

Fig. 6 Solid-state 13C CP MAS NMR spectra of PVFA-co-PVAm-95/silica hybrid particles (Mn=400,000 g mor1) (a) before cross-linking, and (b) after cross-linking with BICDPM, (c) virtual structure of a BICDPM-functionalized PVFA-co-PVAm network cut out and assignment of the signals in the 13C CPMAS NMR spectra...

---