Cloud point silica

The adsorption of block and random copolymers of styrene and methyl methacrylate on to silica from their solutions in carbon tetrachloride/n-heptane, and the resulting dispersion stability, has been investigated. Theta-conditions for the homopolymers and analogous critical non-solvent volume fractions for random copolymers were determined by cloud-point titration. The adsorption of block copolymers varied steadily with the non-solvent content, whilst that of the random copolymers became progressively more dependent on solvent quality only as theta-conditions and phase separation were approached. 

The products obtained were analyzed for composition using high-performance liquid chromatography (HPLC) (LC -10AT Shimadzu, Kyoto, Japan), which consisted of a column (STR ODS-II, 25 cm in length x 4.6 mm in id Shinwa Chemical, Osaka, Japan) operated at 40°C at a flow rate of 1.0 mL/min with methanol as a carrier solvent. The column was packed with silica particles (5-pm particle diameter and 12-nm pore diameter). The cloud and pour points of the obtained biodiesel were then determined by a mini-cloud/pour point tester (Model MPC-102 Tanaka Scientific, Tokyo, Japan) based on ASTM D2500 for cloud point and ASTM D6749 for pour point (14). 

Fig. 10.38 Qualitative comparison between the theory and the experimental phase diagram (cloud points) for the PVA/PMMA polymer blend without fillers (filled diamonds) and with 10 wt% fumed silica (open squares). The two curves correspond to the spinodals calculated using equations. It is assumed that both PVA and PMMA had degrees of polymerization (N) 1,000 and that (pN) a + bT, with (a)-lO.O, (b) 0.026374. Finally, assumed that (F) 0.65. For the filled system, we took nanoparticle loading of 14 vol%, with the dimensionless particle radius (R) 20 (corresponding to the real- particle radius of 10 run) (Ginzburg 2005)...

Different procedures based on that chemistry and using FIA [183], SIA [166,184], MSFIA [185,186], and MCFIA [187] have been described. Most of them make use of online sample preparation, including micellar-assisted preconcentration (cloud point extraction (CPE)) or solid-phase extraction (SPE) [185,186,188]. To this end, either a microcolumn packed with Amberlite XAD-4 resin [185] or C18-modified silica material may be used. 

The first attempts to use interactive stationary phases for the separation of polyolefins started in 2003. Macko et al. used an isocratic separation system for PE-PP blends [136,137]. For the separation of the two polymers, TCB was used as a thermodynamically good solvent for both components and ethylene glycol monobutylether (EGMBE) as eluent. Dimethylsiloxane-modified silica gel was used as stationary phase. As a result, PE eluted almost irrespective of its molar mass under limiting conditions, while PP eluted in the SEC mode before the PE components. Resolution of this method, however, was rather poor and additionally limited by the poor solubility of the polyolefins. These results triggered some in-depth studies on the solubility of polyolefins in different solvents using cloud point titration [138] and the testing of zeolites as selective stationary phases [139-142]. 

The use of neutrons to study interfaces is still relatively new, but several studies have already been made which demonstrate the scope of the technique. By way of example, some data for polystyrene adsorbing to amorphous silica [94] are shown in Figure 13.6. The curves show a large difference between IS and 3S °C, which is associated with a rapid increase in adsorption as the temperature is decreased to 21 °C, which is the cloud point for the solution of deuterated polystyrene (molecular weight 390 (XX)) in a mixture of deuterated and proto-nated cyclohexane. 

The cloud point curves for unfilled poly(vinyl acetate) - poly(me-thyl methacrylate) mixtures and those filled with 10% of non-modified and silanized fumed silica show that curves for filled mixtures are situated at much lower temperature than those for unfilled material.It should be noted that the temperature of phase separation decreases sharply in the region where one alloy component has a predominant content. The addition of silane-treated fumed silica also results in a lower temperatures of phase separation. These effects were attributed to the difference in adsorption of both components at the interface with a solid and are connected with the asymmetry of interaction in the system. The phase separation temperature in this alloy also depends on the filler content (Figure 7.4). At the same time, the phase separation temperature depends on the ratio of components. This fact may be interpreted as indirect confirmation of the role of asymmetry of interactions, because increasing the filler content should affect the as5mimetry of the interactions and therefore have an... 

Spec determination at pH = 7.0 preconcentration of zinc by cloud point extraction of the complex and determination by ICP optic emission spectrometry Flow-injection solid phase spec X = 595 nm with TAN inunobilized on CIS-bonded silica... 

Figure 7.7 Influence of nanoparticles on the phase behavior of bina7 blends, (a) Chlorinated polyethylene (CE)/poly(ethylene vinyl acetate) (EVA) blend shows an upward shift in the cloud point curve upon addition of fumed silica [79] here, silica particles stabilize homogeneous...

In some applications nonionic - surfactants (- fatty alcohol ethoxylates), which show the phenomenon of a cloud point, are used. Above their cloud point they act as defoamers, but below they may even act as foam stabilizers. Another special d. is silica that is made hydrophobic by treating it with - fatty amines. All these ingredients are used in solid or liquid (emulsion) form, with emulsifier to enhance dispersion. 

---