Mixed monolayers preparation

Figure 5. Microdroplet density measurements on gradients (squares) and mixed monolayers prepared by coadsorption (circles). The microdroplet density changes little with contact angle for homogeneously mixed monolayers however, it changes significantly with contact angle for a gradient.

The < 100 nm-scale phase separation on the gradient prepared in this approach is a unique feature that results from the two immersion steps, which involve a quenching of the adsorption of the first component followed by saturation with the second component. A mixed monolayer prepared in a similar way also revealed such phase separation, whereas a mixed monolayer prepared from coadsorption of two components from a mixed solution revealed homogeneously mixed monolayers on the same scale. These microstructural inhomogeneities will have an impact... 

Figure (a) AFM and (b) LFM image of the (NTS/FOETS) mixed monolayer prepared by the Langmuir method and (c) its height profile along the line as shown in (a). 

Bertilsson L and Liedberg B 1993 Infrared study of thiol monolayers assemblies on gold—preparation, oharaoterization, and funotionalization of mixed monolayers Langmuir 3 141-9... 

The ionized forms of polypeptides exhibit many characteristics in common therefore, we have studied them under various conditions. The most interesting observation is the transition of a polyelectrolyte brush found by changing the polyelectrolyte chain density. The brush layers have been prepared by means of the LB film deposition of an amphiphile, 2C18PLGA(48), at pH 10. Mixed monolayers of 2C18PLGA(48) and dioctadecylphos-phoric acid, DOP, were used in order to vary the 2C18PLGA(48) content in the monolayer. 

In a study of mixed monolayers of C60 and p-iert-butylcalix[8]arene, different isotherm behavior was obtained [256]. The surface pressure was observed to rise at a lower molecular area (1.00 nm molecule vs. 2.30 mn molecule in the prior study). Similar isotherms were observed whether a 1 1 mixture or a solution prepared by dissolving the preformed 1 1 complex was spread. The UV spectra of the transferred LB films appeared different than that of bulk C60. It was concluded that a stable 1 1 complex could be formed by spreading the solution either of the mixture or of the complex. This was confirmed in a later study by the same group that included separate spreading of the calixarene and the C60... 

In general, a preparation of mixed monolayer can be realized by either a kinetic control or a thermodynamic control (Figure 1, left). Kinetic control is based on a suggestion that for an initial deposition step the desorption rate is ignorable in comparison with the adsorption rate. In this case, the concentration ratio of the adsorbed species A and B on the surface corresponds to the ratio of products of their adsorption rate constant ( a or b) and concentration (Ca or Cb) A aCa/A bC b. The validity of the initial assumption on low desorption rate means that the total surface coverage obtained under kinetic control is essentially lower than 100%. This non-complete coverage does not disturb most of optical applications of the... 

Two azobenzene-linked amphiphiles were dissolved in chloroform and mixture solution with various molar ratio were prepared. The mixed monolayers of C180AZON02 and C180AZOCOOH were spread on a 10 4 M aq. BaCl2 solution... 

Deposition of the mixed monolayer. Deposition solutions were prepared by dissolving octadecylmercaptan [ClsSH] and the respective bipyridinium in a mixture of chloroform and methanol. The electrode was cleaned by heating it in a gas-air flame. After cooling, the electrode was immersed in the deposition solution for 15 - 30 minutes, withdrawn, and rinsed in clean methanol or chloroform. Qualitatively the most reproducible surface redox waves and lowest charging currents during cyclic voltammetry were obtained with a freshly-prepared deposition solution containing 50 mM CiaSH and 10 mM of the bipyridinium in a 1 1 volume ratio of chloroform and methanol. 

Ft partial and full monolayers have been deposited onto alternative metal particle cores. Brankovic, Wang, and Adzic found Ft spontaneously deposited onto hydrogen-reduced Ru particles at a surface coverage of 0.11 and 0.50. An alternative method of depositing Ft onto Fd, Fd alloy, and Au particles has been developed by Sasaki et al. and Zhang et al. This involves the deposition of a Cu overlayer by underpotential deposition followed by galvanic displacement by Ft. Complete monolayers of Ft have been claimed and the technique has been extended to preparation of mixed monolayers of Ft and other precious metals. ... 

The spreading solutions were prepared as follows CisDAO was dissolved in 45/5, the SODS in 25/25, the SDS in 40/10, benzene/ methanol mlxture. The concentrations of these solutions were 1.157xlO M. For mixed monolayers, mixtures at different volume ratio were made from stock solutions prior to spreading. The aqueous substrates used were unbuffered, and the experiments were performed in the presence of atmospheric CO2. Deionised-distilled water was used to prepare the substrate. 

The extensive studies of the behavior of mixed monolayers or bilayers of di-acetylenic lipids and other amphiphiles parallel to some degree the studies of dienoyl-substituted amphiphiles. Since the dienoyl lipids do not contain a rigid diacetylenic group in the middle of the hydrophobic chains, they tend to be miscible with other lipids over a wide range of temperatures and compositions. In order to decrease the lipid miscibility of certain dienoyl amphiphiles, Ringsdorf and coworkers utilized the well-known insolubility of hydrocarbons and fluorocarbons. Thus two amphiphiles were prepared, one with hydrocarbon chains and the other with fluorocarbon chains, in order to reduce their ability to mix with one another in the bilayer. Of course it is necessary to demonstrate that the lipids form a mixed lipid bilayer rather than independent structures. Elbert et al. used freeze fracture electron microscopy to demonstrate that a molar mixture of 95% DM PC and 5% of a fluorinated amphiphile formed phase-separated mixed bilayers [39]. Electron micrographs showed extensive regions of the ripple phase (Pb phase) of the DM PC and occasional smooth patches that were attributed to the fluorinated lipid. In some instances it is possible to... 

Our group pursued another approach of combining the properties of nanoparticles with chiral nematic liquid crystal phases. The idea was to decorate gold nanoparticles with chiral molecules known to be strong inducers of chiral nematic phases. To realize the idea, we prepared a series of alkylthiol-capped gold nanoparticles, either pure monolayer or mixed monolayer, with all or about every second of the alkylthiols end-functionalized with (5)-naproxen (e.g., 6 in Fig. 11) [349]. 

In this work we utilized FTIR methods to examine the SA monolayers on flat, polar solid surfaces prepared from nonpolar solutions. We used ATR and GI FTIR measurements to characterize the material and bonding of the S A monolayers, and used transmission and ATR FTIR to monitor the dynamics of the SA adsorption process. With reference to measurements on standard Langmuir-Blodgett monolayer samples, we were able to quantify the S A kinetic results. We also used fluorescence spectroscopy of incorporated pyrene probes in S A mixed monolayer films as a simple method for the determination of the relative adsorption and thermodynamic constants. 

Pyrene-labeled SA mixed monolayers were prepared by adsorption from solutions of the desired concentration of a particular fatty acid, along with a small fraction (1-5%) of the probe Py-C16. All solutions used were of total acid concentration of 5xl0 3M. 

Fluorescence Of Monolayers Containing Pyrene-Labeled Probes. A fluorescence probe method was also used as a complementary technique to study the thermodynamics of SA film formation. Mixed monolayers containing the fluorescence probe pyrene hexadecanoic acid, Py-C16, in host fatty acids of different lengths were prepared by adsoiption from solutions containing mostly the host fatty acid and a small fraction of Py-C16 (approximately 1 to 5 mol %). All monolayers were prepared under equilibrium adsoiption conditions. For fluorescence measurements only A1 substrate was used because when glass is used an impurity fluorescence from glass interferes with the pyrene fluorescence. 

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