Titanate hydrophobicity

Highly porous silica gel served as a support for the TADDOL moiety derived from inexpensive and readily available i-tartaric acid, which provided access to htanium-based Lewis acid catalysts (Heckel, 2000). Such entihes are employed successfully for enantioselective reactions. TADDOLs were covalently attached to the trimethyl-silyl-hydrophobized silica gel, controlled-pore glass (CPG) at about 300 m2 g-1, at a loading of 0.3-0.4 mmol gl (Heckel, 2002). In a carefully monitored mulh-step immobilization procedure, the TADDOLs were titanated to yield dichloro-, diisopropyl-, or ditosyl-TADDOLates. These catalysts were employed in dialkylzinc addihon to benzaldehydes and diphenyl nitrone addihon to 3-crotonyloxazolidinone, a [3+2] cycloaddition. 

Typically, titanate-treated inorganic fillers or reinforcements are hydrophobic, organophilic, and organofunctional and, therefore, exhibit enhanced dispersibility and bonding with the polymer matrix. When used in filled polymer systems, titanates claim to improve impact strength, exhibit lower viscosity, and enhance the maintenance of mechanical properties during aging. 

ER fluids are typically are suspensions of 1- to 100- um particles of cornstarch, silica, calcium titanate, or other semiconductors at volume fractions of0.05-0.50 in a hydrophobic liquid, such as mineral oil or com oil. For an electric field E of 50-5000 V/mm, the particles form chains that span the gap between the field-generating electrodes (see... 

Fig. 4. Dielectric loss master curves obtained by horizontal shifting from data measured on CaC03 billed polyethylene samples stored in atmospheres of different relative humidi-ties. Left Data obtained on mechanical mixtures containing 10, 30 and 50 wt% titanate treated (hydrophobized) Ca-...

The functional site (1) of the titanate molecule is associated with coupling, dispersion, adhesion, and hydrophobicity effects. These effects are also related to the method of application of the titanate on the filler surface as discussed below. 

Surface treatment is another value-added step that can improve the performance of kaolin. Since the filler is naturally very hydrophilic due to its hydroxyl groups, a treatment can be applied to render its surface hydrophobic or organophilic. These surface-modified kaolins are useful especially in plastics and rubber industries, where they improve adhesion and dispersion and hence act more effectively as functional fillers. Silanes, titanates, and fatty adds as discussed in Chapters 4-6, respectively, may be used to modify the surface charaderistics of either hydrous or calcined kaolins, promoting dea lomeration, often lower viscosities, and improved mechanical and eledrical properties. 

For the deposition of titanium dioxide the substrate is exposed to a 5% (v/v) solution of titan-tetrabutoxide in isopropanol. First the titanium forms phenolates on the hydrophilic areas. When this solution is exposed to air the titanium alkoxide starts to hydrolyze and titanium dioxide is deposited at the hydrophilic parts of the substrate. If this process happens to fast because of high humidity or good air exchange above tte reaction mixture the conqilete surfiaie will be covered with titanium dioxide. But because of the bad interaction between the hydrophobic parts and titanium dioxide it is possible to remove die excess titanium dioxide by sonification. The titanium tUoxide at the hydrophobic parts of the surface is much more resistant against this substrate treatment (Figure 6). 

As shown in Table 3.16, the whiskers modified with OTS have lower surface energy, lower polar component, and better hydrophobic and lipophilic properties than untreated whiskers. The dispersive component ratio of potassium titanate whiskers modified with OTS to OTS molecules is much closer to the dispersion value of the -CH2- group rather than the -CH3-group, which indicates that the whisker surface modified with... 

Table 3.17 shows the adsorption work and interfacial tension of potassium titanate whiskers before and after modification with OTS with water and benzene. After modification with OTS, the adsorption work of modified whiskers to oil is lower than to water, and the interfacial tension of whiskers to water increases while that to oil is close to zero. These prove that whiskers treated with OTS have more typical hydrophobicity and lipophilicity. 

Of the various mineral fillers used, calcium carbonate (CaCO ) is one of the most common, due mainly to its availability in readily usable form and low cost [76]. However, the incompatibility of its high energetic hydrophilic surface with the low-energy surface of hydrophobic polymers, e.g., polyethylene (PE) and polypropylene (PP), is a particular problem. For this and other reasons, the surface of calcite is often rendered organophilic by a variety of surface modifiers such as silanes, titanates, phosphates, and stearic acid. 

Microbeads also dififer because of their surface finish. The typical surface of these beads is highly hydrophilic, because of the presence of hydroxyl groups. The hydroxyl groups are frequently reacted with silanes, titanates, or zirconates, which contain an organic part. This organic part remains oriented out of the surface (the inorganic part reacts with the bead surface). This reactive treatment changes properties of the surface, which becomes hydrophobic and, as such, more compatible with the polymeric matrix. 

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