Silane monolayer

In choosing a SAM system for surface engineering, there are several options. Silane monolayers on hydroxylated surfaces are an option where transparent or nonconductive systems are needed. However, trichlorosilane compounds are moisture-sensitive and polymeri2e in solution. The resulting polymers contaminate the monolayer surface, which occasionally has to be cleaned mechanically. CarboxyUc acids adsorb on metal oxide, eg, AI2O2, AgO through acid—base interactions. These are not specific therefore, it would be impossible to adsorb a carboxyUc acid selectively in the presence of, for example, a terminal phosphonic acid group. In many studies SAMs of thiolates on Au(lll) are the system of choice. 

Instabihty in the wettabiUty behavior of OH surfaces was noticed when OH-terminated silane monolayers were exposed to hydrophobic solvents, such as CCI4 (175). Similarly, monolayers of 11-hydroxyundecane-thiol (HUT), HO—(CH2)2] SH, on Au(lll) surfaces have been found to undergo surface reorgani2ation by exposure to ambient atmosphere for a few hours (328). After that, the water contact angle reached a value of ca 60°, and only ca 25% of... 

In general, the silanization of hydroxyl-terminated substrates such as silica or glass is an effective method which is used quite often for chemical modification of the substrate surface for immobilization of biomolecules. The main focus for silanization procedures is once again the examination of the self-organizing silane-monolayers. The properties of the monolayer depend on the chemical structure of the silanization reagent, the density of silanol-groups which are available on the surface and the physical surface structure on a nano-scale level. 

In general, the formation of monolayers with silanization reagents requires a precise reaction scheme regarding humidity, the selection of solvents, temperature, and reaction time. Often, not enough consideration is given to these factors. As a result a number of authors concluded that the reproducibility of homogeneous silane-monolayers is insufficient, that their stability in aqueous solution is limited, or that they are prone to the formation of multilayers. 

Removal of reversibly adsorbed (physisorbed) cyanine-dye molecules, D, led to skeletonized, SA silane monolayers having pinholes in the shape of D (Fig. 18) [185]. Such pinholes can, in turn, serve as templates for similarly shaped guest molecules. This approach opens the door for molecular recognition and device construction based on molecular recognition [186-190]. The idea relies upon the construction of a well-packed, SA monolayer from a mixture of OTS molecules and a solvent removable guest species. Removal of the guest molecules leaves pinholes with precise dimensions which only accept molecules with... 

Although it was postulated earlier that silane monolayers covalently bound to substrates possessing dangling OH groups could be formed by the... 

Gate sites in silane monolayers on tin (IV) oxide electrodes have also been studied for resistometric gas-phase sensing [117]. 

When the toner is loaded with pyrogenic silica particles, these appear as isolated protrusions at the surface (Fig. IB-D). Depending on the modification, the diameters of the protrusions range between 50 and 200 nm. When HMDS is used as the silylation reagent, a silane monolayer is fbrmed. In this case the diameter of the particles is ca. 100 nm. Such particles are adsmbed mainly as isolated aggregates to the toner surface (Fig. IB). PDMS-modified particles seem to coat almost the entire toner particle (Fig. 1C). Their topographical diameter is doubled conq)aied to that of the HMDS-coated particles. This can be explained by the formation of a polymer-like PDMS layer. HMDS/PDMS-coated silicas appear only as isolated protrusions with a diameter up to 250 nm (Fig. ID). 

Figure 6.12 The mobility of deuterated silane monolayers on silical gel can be studied by solid state deuterium NMR spectroscopy. The degree of coating as well as the environment can be modified. The above models summarize the results. These modified silica surfaces are the most simple models for receptors of apolar molecules. The unique advantage of these probes is the large quantity of monolayer in a small volume.

J.D. LeOrange, J.L. Markham and C.R. Kurkijan, Effects of surface hydration on the deposition of silane monolayers on silica, Langmuir, 9, 1749-1753 (1993). 

This patterned substrate was exposed to plasma for removal of the monolayer (Fig. 10.5d). The resist pattern was used as the mask for plasma ashing. After this process, photo-resist was removed and the amino silane monolayer was formed on the exposed clean oxide layer (Fig. 10.5e). 

Baseline spectra were taken on 5 NOSA resonators and parallel silicon wafers after surface functionalization. A film thickness of 3.11 nm corresponds to the molecular thickness of native oxide, amine-terminated silane monolayer, and glutaraldehyde functionalization, each of which contributes 1 mn to total film thickness. Since the field at the sensor surface exhibits an exponential decay, the growth of the pofyelectrol5fte multilayer and the resulting effect on resonance shift were fit to an exponential model as shown in Fig. 2. 

Plasma treatment of PDMS followed by adsorption of self-assembled silane monolayers has enabled us to controllably modify the surface energy of elastomer surfaces as described in the section on the Johnson, Kendall, and Roberts approach to deriving the surface free energy of solids. A similar treatment of silicon substrates has produced a useful, low—hysteresis model substrate for contact angle study. There are three types of PDMS contact angle substrates usually studied fluids baked or otherwise chemisorbed on solids such as glass or metals cross-linked coatings on flexible substrates, such as paper or plastic film PDMS elastomer surfaces. 

An ideal substrate would be smooth, rigid (i.e. a polished metal), coated with an ultra-thin PDMS layer anchored by a well-understood and controllable chemistry. This has been achieved by taking semi-conductor silicon wafers which have a thin oxidized silica layer which can be treated by a self-assembling silane monolayer, such as vinyl terminated alkyltrichlorosilane. This can then be reacted with SiH-containing PDMS this hydrosilylation reaction is well-understood and the random substitution of such SiH groups along a PDMS chain has been well established by NMR studies. The low hysteresis surface that can be obtained in this manner is illustrated by the data in Table 4. 

The degree of silanization and thereby the water wettability is controlled by the exposure time, the amount of silane used, and importantly the concentration of water. Water has a big influence on the mechanism of the silane monolayer formation and structural properties. In the absence of water submonolayers with only one siloxane bond binding can be formed. Water promotes the hydrolysis of the remaining SiCl groups on the initial immobilized silane layer enabling another silanization reaction yielding enhanced silane density. However excess water leads to uncontrolled silane... 

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