Hydrophobic hexamethyldisilazane

AT-cut, 9 MHz quartz-crystal oscillators were purchased from Kyushu Dentsu, Co., Tokyo, in which Ag electrodes (0.238 cm2) had been deposited on each side of a quartz-plate (0.640 cm2). A homemade oscillator circuit was designed to drive the quartz at its resonant frequency both in air and water phases. The quartz crystal plates were usually treated with 1,1,1,3,3,3-hexamethyldisilazane to obtain a hydrophobic surface unless otherwise stated [28]. Frequencies of the QCM was followed continuously by a universal frequency counter (Iwatsu, Co., Tokyo, SC 7201 model) attached to a microcomputer system (NEC, PC 8801 model). The following equation has been obtained for the AT-cut shear mode QCM [10] ... 

Specific properties of polysilanes have been linked to the method of synthesis.35 For example, in the case of anionic polymerization of poly[l-(6-methoxy-hexyl)-l,2,3-trimethyldisilanylene] a new type of chromism was induced in the polysilane film by the difference in the surface properties of substrates and was termed a surface-mediated chromism. The polysilane exhibited thermochromism with an absorption maximum at 306 nm at 23°C, but <15°C a band at 328 nm began to appear. A monolayer of the polysilane was transferred onto both a clean hydrophilic quartz plate and a hydrophobic one treated with hexamethyldisilazane by the vertical dipping method. With the hydrophobic plate, a broad UV absorption at 306 nm is obtained, whereas the absorption on a hydrophilic plate shifts to 322 nm. The conformation of the polysilane is preserved by hydrogen bonding between the silica surface and the ether section of the substituent on the hydrophilic plate. The polysilane is attached to the hydrophobic surface only by van der Waals forces, and this weaker interaction would not sustain the thermodynamically unstable conformational state that is attained on the water surface. 

Hydroxyethyl methacrylate Human immunodeficiency virus 1,1,1,3,3,3,-Hexamethyldisilazane Hydrophobically modified polycationic dextran Heteronuclear multiple quantum correlation High performance liquid chromatography Herpes simplex virus... 

The most important representative of the silazanes is hexamethyldisilazane, which is utilized in large quantities for the introduction of protective groups in the synthesis of pharmaceuticals and for hydrophobizing fillers, in particular silicates. It can be easily produced by reacting trimethylchlorosilane with ammonia ... 

The catalytic activity of Ti-MCM-48 catalysts may be improved by increasing the hydrophobic character of the surface by a silylation post-treatment with hexamethyldisilazane (HDMS) as silylating agent. In this way the poisoning of the catalysts is noticeably decreased. The silylation procedure led to the transformation of silanols, Si(OSi)3(OH), into Si(OSi)3[OSi(CH3)3], which was confirmed by Si-MAS-NMR and diffuse reflectance (DR) UV-Vis spectroscopies. 

Noteworthy, a remarkable increase in the activity of Ti-containing mesoporous catalysts was obtained by anchoring trimethylsilyl groups on the silanols, which led to an increase of the hydrophobicity of the surface [15,16]. In this paper we report on peculiar aspects of the preparation and characterisation of mesoporous Ti-fimctionalised MCM-48 silicas. The spectroscopic and catalytic properties of Ti-MCM-48 catalysts upon a post treatment of silylation with hexamethyldisilazane (HDMS) as silylating agent, are also reported. 

The organic surfactant molecules can be removed by calcination or extraction of the as-synthesized material. The walls of the obtained mesoporous solid consist of partially condensed silica. They carry silanol groups which can be used to modify the pore walls, e.g. by trimethylsilylation with hexamethyldisilazane (hydrophobization) or phenylsilylation with phenyltrimethoxysilane (functionalization). 

H2000 and SKS300 are hexamethyldisilazane-treated highly hydrophobic fumed silica H2000 was desagglomerated (and milled/classified in addition). 

Any porous substrate (filter paper, polyester textile) covered by the PP of hexa-methyldisilazane or the double layer of hexamethyldisilazane and n-hexane becomes the membrane selective for the water and hydrophobic liquids (Bankovic et al. 2004). 

Fumed silica, or fumed silicon dioxide, is produced by the vapor phase hydrolysis of silicon tetrachloride in an H2/O2 flame. The reactions are shovm in Chapter 19. Hydrophilic fumed silica bearing hydroxyl groups on its surface is produced by this process. Hydrophobic fumed silica is made by processing fumed hydrophilic silica through in-line hydrophobic treatments such as with silanes, siloxanes, silazanes, and so on [1]. Examples of different types of hydrophobic fumed silica coatings include DMDS (dimethyldichlorosilane), TMOS (trimethoxyoctylsilane), HMDS (hexamethyldisilazane). 

FIGURE 1.141 The H NMR spectra of water adsorbed on surfaces of modified silicas (a) SM4, (b) SMS, and (c) SM6 at different temperatures ( H signals of CHCI3 and tetramethylsilane [TMS] are shown). (Adapted with permission from Langmuir, 19, Gun ko, V.M., Turov, V.V., Bogatyrev, V.M. et al., Influence of partial hydrophobization of fumed silica by hexamethyldisilazane on interaction with water, 10816-10828, 2003e. Copyright 2003, American Chemical Society.)... 

The two signals, inclination and resonance frequency, are acquired simultaneously, but are independent of each other. They yield the stress and the mass (Fig. 9A). We deposited a water drop on a silicon cantilever hydrophobized with a monolayer of hexamethyldisilazane (HMDS). The initial contact angle was 80°. It decreased nearly linearly during evaporation, and was 70° at the end. Tlie initial contact radius was 33 im, and decreased nearly linearly during evaporation. At the end it was below 10 xm. At present, we can record the inclination curve with a temporal resolution of 0.1 ms between data points, and the frequency curve with 5 ms. The mass calculated from the resonance frequency of the cantilever and from video microscope images is similar (Fig. 9B), although the time resolution ( 5 ms) and the sensitivity ( 50 pg) is much... 

The LB film deposition was performed on a NIMA 622 alternating trough (NIMA Technology, Coventry, UK) equipped with a Wilhelmy plate surface pressure sensor. The spreading solutions were obtained by dissolving 0.9 mg/ml of substance in chloroform. The monolayers were formed by spreading 200 pi of the solution on the water subphase provided by a Milli-Q system (Millipore). The subphase temperature was held constant at 21 °C. The films were compressed with a constant barrier speed of 50 cm /min. Multilayers of 10 monolayers were deposited on cleaned silicon wafers that were hydrophobized by treatment with hexamethyldisilazane (HMDS) before the deposition. A target pressure of 28 mN/m and a dipper speed of 5 and 10 mm/min yielded an observed transfer ratio between 0.8 and 1 (Y-type transfer). 

The first way of modifying the surface hydrophilicity and hydrophobicity is to apply an ultrathin monolayer of chemical onto the surface. This is often referred to as a self-assembled monolayer (SAM). One example in photolithography is to coat hexamethyldisilazane (HMDS) onto the substrate surface to enhance the adhesion of PR. Another example is applying octa-decyltricholorosilane (OTS) onto a glass substrate to make it hydrophobic. 

Elowever, cellulose nanofillers have some disadvantages such as moisture absorption and poor compatibility with the hydrophobic polymer matrices [27, 28]. The use of nanocellulosic fillers is mostly limited to hydrosoluble polymers, latexes, or DMF-soluble polymers [12, 29, 30]. To overcome this problem, several methods were proposed recently, which involved the chemical modification of the cellulosic fillers [12, 30] with various chemical reagents such as acetic anhydride [31], alkenyl succinic anhydrides [32], chlorosilanes [33,34], or hexamethyldisilazane [35]. 

---