Transferred onto solid substrates

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

Well organized Langmuir-Blodgett (LB) films have been obtained from mixtures of a push-pull carotenoid and co-tricosenoic acid as shown in 7. These mixed films exhibit a very good cohesion, with an area of about 25 A2 per carotenoid molecule. They can easily be transferred onto solid substrates. Examination by UV-visible linear dichroism measurements confirms that the carotenoid chains are oriented perpendicularly to the surface of the substrate in card-packed aggregates, in which the polyenic chains interact via excitonic coupling, as indicated by the large hypsochromic shift of the tc-tc transition (20). 

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. 

The absorbance vs. wavelength spectra of films transferred onto solid substrates were obtained using a Shimadzu UV-260 spectrophotometer. The scan rate of all spectra was 180 nm/min and the slit width was 2 nm. All spectra were obtained at room temperature (20°-25°C). 

We have tried to stabilize freely-suspended films in two ways a) by transfer onto solid substrates and b) by using polymeric liquid crystals. 

The construction of fullerene ultrathin films with an ordered structure is of interest from both a fundamental and practical point of view [20-22]. Geo alone and amphiphilic fullerene derivatives form mono-layers at the air-water interface and these monolayers can be transferred onto solid substrates [23-27]. The authors [28-38] and others [39-43] have been interested in combining fullerene chemistry and the... 

The original work carried out by Langmuir was the ability to form and transfer monolayers of fatty acid, ester and alcohol monolayers onto solid substrates. Several years later, Katherine Blodgett showed that multilayer films can also be formed and transferred onto solid substrates. The ability to transfer layers of organic material from a liquid phase, typically water, to a solid substrate allows the careful construction of ordered layer structures at a molecular level... 

The composite subphase mentioned above is the key factor for the stable rare earth complex monolayers at air/liquid interface. During monolayer transfer process, it is found that the monolayers are too rigid to transfer onto solid substrates. The conventional film-forming molecule AA with a long aliphatic chain was mixed with them in the spreading solution in a molar ratio of 1 1. The obtained mixed LB films emitted homogeneous intense fluorescence. So the use of a fatty acid AA is the key factor for the monolayer transfer during LB film fabrication. 

Lu et al. used calix[4]arene derivatives with two ammonium (25) or guanidinium functionalities (26) at opposite sides of the lower rim to form stable monolayers. Inside the layer the amphiphiles are orientated orthogonal to the air-water interface (Fig. 24.10). With their cationic moieties immersed in the water phase the calixarene derivatives are able to recognize nucleotides in the subphase. The properties of the monolayer along with the recognition potential for 5 -AMP and 5 -GMP were analyzed at the film balance by means of surface pressure-area tz-A) isotherms and relaxation experiments as well as UV, CD, TR-IR spectra and X-ray photoelectron spectra. Due to their strong molecular interactions nucleotides can even be transferred onto solid substrates along with the monolayers. The... 

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. 

Transfer experiments of the Langmuir films onto solid substrates and the preparation of LB films were investigated for 43. The deposition of films of 43 occurred regularly on quartz sHdes or silicon wafers with a transfer ratio of 1 0.05. The diblock structure of dendrimer 43 also appeared crucial for efficient transfers of the Langmuir films in order to obtain well-ordered multilayered LB films. Effectively, the transfer of the Langmuir films of the dendrimer 42 with the small polar head group was found to be difficult with a transfer ratio of about... 

Fig. 9.1 A schematic illustration of surface coatings with their typical thickness ranging from angstroms to micrometers. Selected are monomolecular layers fabricated by the transfer of Langmuir-Blodgett (LB) films onto solid substrates (1) self-assembled monolayers (SAMs) (2) multilayers thereof (3) polymer-...

Monolayers 2D, 3D depends on trough Spreading of water-insoluble surfactants, in an organic solvent, onto the surface of clean water Days Parties grown under monolayers could be transferred to solid substrates at any stage of their growth 104,105... 

Monolayers can be transferred layer-by-layer onto solid substrates such as silicon wafers or mica by the Langmuir-Blodgett2 (LB) technique [620,621] (reviews Refs. [622-625]). This is shown schematically in Fig. 13.13. 

Figure 13.13 Langmuir-Blodgett transfer of organic monomolecular layers from water onto solid substrates.

Langmuir films prepared at air/water interface are transferred on solid substrates and LB firms are constructed. The morphologies of the LB films and their molecular arrangements depend on the characters of hydrophilic and hydrophobic moieties of amphiphiles and the affinity of the moieties to the substrates. Transition of molecular arrangement in LB films of third generation amphiphilic PAMAM dendrimers with dodecyl terminal groups was elucidated [77]. The LB films were transferred by horizontal lifting onto hydrophobic silicon wafers and were devoted to their structural characterization. Since silicon wafers are ahead treated (that is, oxidized) by an aqueous solution of... 

Typical LB films are constructed through transferring monolayers of amphiphilic molecules at the air-water interface onto solid substrates [8,12,13]. The amphiphilic molecules are first dissolved in an organic solvent that is immiscible with water, spread on a water surface, and compressed by decreasing the area in which the molecules are confined, to form a monolayer at the air-water interface. Then the monolayer is transferred onto a solid substrate by moving the substrate vertically or horizontally. This procedure allows us to obtain ultrathin films with the struc-... 

Efforts to stabilize BLMs by the use of polymerizable lipids have been successful, but the electrochemical properties of these membranes were greatly compromised and ion channel phenomena could not be observed [21]. Microfiltration and polycarbonate filters, polyimide mesh, and hydrated gels have been used successfully as stabilizing supports for the formation of black lipid films [22-25] and these systems were observed to retain their electrical and permeability characteristics [24]. Poly(octadec-l-ene-maleic anhydride) (PA-18) was found to be an excellent intermediate layer for interfacing phospholipids onto solid substrates, and is sufficiently hydrophilic to retain water for unimpeded ion transfer at the electrode-PA-18 interface [26]. Hydrostatic stabilization of solventless BLMs has been achieved by the transfer of two lipid monolayers onto the aperture of a closed cell compartment however, the use of a system for automatic digital control of the transmembrane pressure difference was necessary [27]. 

Monolayer or sequential monolayer modifications of electrodes are performed using either the Langmuir-Blodgett (L-B) technique, in which the monolayer is formed at an air-water interface and transferred onto solid electrode substrates, or the self-assembly method directly from the solution. 

In order to improve the packing symmetry and reduce the defect concentration, many attempts were made to prepare monolayers or multilayers of near-monodis-perse nanoparticles. In a straightforward approach, monolayers could be prepared almost defect-free on a water surface, and transferred via microcontact printing onto solid substrates [86] (Figure 5.58). 

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