Monolayer transfer

The other method of monolayer transfer from the air/water interface onto solid substrates is illustrated in Figure 2. This method is called the Langmuir-Schaefer technique, or horizontal lift. It was developed in 1938 by I. Langmuir and V. Schaefer for deposition of protein layers. Prepared substrate horizontally touches the monolayer, and the layer transfers itself onto the substrate surface. The method is often used for the deposition of rigid monolayers and for protein monolayers, hi both cases the apphcation of the Lang-muir-Blodgett method produces defective films. 

Deposited films are usually divided into three types, schematically shown in Figure 4, namely, X-, Y-, and Z-types. As it is clear from the figure, the Y-type is a cen-trosymmetrical one, while the X- and Z-types are polar ones, which differ only by the orientation of the head groups and hydrocarbon chains with respect to the substrate surface. Such a difference appears due to the fact that in some cases there is no monolayer transfer during upward or downward motion of the substrate in the case of LB deposition. In the case of the LS deposition, moreover, the layers always seem to be transferred in a polar... 

Fig. 3.5 Representation of a scheme of an experiment (upper set of drawings) and the obtained experimental results presented as AFM images (middle part) and cross-sectional profiles (bottom) that provides evidence of silica nucleation and shell formation on biopolymer macromolecules. Scheme of experiment. This includes the following main steps. 1. Protection of the mica surface against silica precipitation. It was covered with a fatty (ara-chidic) acid monolayer transferred from a water substrate with the Langmuir-Blodgett technique. This made the mica surface hydrophobic because of the orientation of the acid molecules with their hydrocarbon chains pointing outwards. 2. Adsorption of carbohydrate macromolecules. Hydrophobically modified cationic hydroxyethylcellulose was adsorbed from an aqueous solution. Hydrocarbon chains of polysaccharide served as anchors to fix the biomacromolecules firmly onto the acid monolayer. 3. Surface treatment by silica precursor. The mica covered with an acid mono-...

QCM measurements were carried out at air using AT-cut gold-coated quartz crystals with a resonant frequency of 9 MHz (5 mm-diameter, Seiko EG Q Seiko Instruments Inc). Prior to use, the quartz crystals were cleaned with water and ethanol. The frequency was measured before and after the monolayer transfer with the use of a Seiko EG G model 917 quartz crystal analyzer. 

Fig. 2. The ED patterns of the arachidic acid monolayers transferred onto (a) SiO and (b) siliconized substrates.

Figure 3 shows the Tsp dependences of logK (max) for stearic acid monolayer on the water surface and the ED patterns of the monolayer transferred onto the hydrophilic substrate at the surface pressure of 20 mN-m. The homogeneous monolayer was formed on the water surface at this magnitude of surface pressure. The ED patterns were taken at the same temperature as... 

In the case of X and Z-type films, the molecules are oriented in the same direction, and thus, the surface will be composed of carboxyl and methyl groups. On the other hand, in a Y-type film, the molecules in adjacent layers will be oriented in opposite directions, and the LB film surface will be composed of methyl groups. Of these three types of LB films, the one that has been studied is the Y-type, in which the monolayer transfer takes place both ways on each dipping and withdrawal... 

Langmuir-Blodgett (LB) films 2D, 3D depends on substrate dimensions Monolayers transferred to substrates Weeks to months Desired molecules could be intercalated into specified positions small particles could grow in situ or be placed between the layers 106,137... 

Monolayers can be transferred onto solid substrates by the Langmuir-Blodgett technique giving rise to mono- or multilayers which can even have thicknesses in the range of the wavelength of visible light. The multilayer quality often depends on the quality of the first monolayer transfer. 

Monolayer FOms Transferred to Solid Substrates. Historically, the spectroscopic investigation of monolayer physical structure has been performed on films transferred to solid substrates, usually through conventional L-B techniques. A wide variety of methods may then be employed in the study of these films. For example, ultraviolet, circular dichroism, and IR spectroscopy, as well as electron microscopy have been performed on monolayers transferred to quartz (for UV and CD), Ge (for IR), and mica (for EM). While much useful information has been obtained in the study of transferred monolayers, there is always a concern about whether the actual physical process of transfer from a gas-liquid to a gas-solid interface induces a change in the structure of the molecule. 

With the development of the external reflectance IR technique for observing monolayers in-situ at the A/W interface, we now have the ability, for the first time, to directly compare the structure of the monolayer film at the A/W interface with the monolayer transferred to a solid substrate. In order to determine whether these transfer artifacts occur for the DPPC monolayer, we have studied the structure of DPPC when transferred to Ge ATR crystals. Figure 6 is the pressure-area curve of the DPPC monolayer on which are indicated the points at which film transfer was made. Specific surface pressures of transfer were chosen in order to insure that transferred monolayers were studied in the LE, LE-LC and LC-SC regions, to provide a basis of comparison with the in-situ monolayers. 

Figure 6. The points along the pressure-area curve of DPPC at which monolayer transfers onto Ge ATR crystals were made.

Fig. 3. The %-A isotherms for the OTS, DDTS, FDOPTES, and FOETS mono-layers on the water surface at a subphase temperature of 293 K, as well as the AFM images and ED patterns of the monolayers transferred onto the substrate at the surface pressure of around 20 mN m 1.

The mode of monolayer transfer achieved depends on the polarity of the hydrophilic head of the amphiphile and the surface pressure. If monolayer transfer occurs on both the down stroke and the up stroke, head-to-head and tail-to-tail orientations of the monolayers are achieved (Fig. 4.34). This transfer mode is called Y-type, and the LB film obtained is called Y film. When the... 

SRGs have been recorded on LB films from an azopolymer, a polymethacrylate containing DR13 covalently attached, mixed with cadmium stearate, where the latter was employed to enhance monolayer transfer in the LB process. SRGs with a modulation depth of 50-60 nm were inscribed using the interference of two p-polarized beams, at 532 nm from a cw Nd YAG laser, with 180 mW/cm for 3 min (see Figure 14,22). Mendon a et alr ... 

Figure 3.67. AFM image of a dipalmitoylphosphatidylcholine (DPPC) monolayer transferred onto a quartz plate at a surface pressure of 30 mN m. On this hydrophilic substrate the phospholipids have their head groups on the surface. Therefore, the bright spots should correspond to the end-methyl groups of the DPPC hydrocarbon chains. This is corroborated by the finding that the area per bright spot (averaged over many images) corresponds to half of the value for the area per phospholipid molecule as found from the r(A) isotherm at 30 mN m. (Courtesy of X. Zhai and J.M. Kleijn" )...

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