Monolayer mixtures

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 influence of CHL and Q3P on film morphology in monolayer mixtures with DPPC has been studied. Monolayers of DPPC as well as it mixtures tvith cholesterol, transferred by HP method, showed a molecularly smooth structure of uniform thickness. The addition of Q3P or CHL to DPPC, as investigated by AFM phase measurements, showed that a marked phase separation occurs in DPPC/Q3P mixtures or DPPC/SM/CHL films at small concentration of the alcohols, proving raft domain formation in the case of DPPC/SM/CHL films. 

Fadeev, A. Y. McCarthy, T. J., Binary monolayer mixtures modification of nanopores in silicon-supported tris(trimethylsiloxy)silyl monolayers, Langmuir 1999, 15, 7238-7243... 

The reaction of THF (tetrahydrofuran) with Li was studied. THF adsorbed on deposited Li films with partial dissociation, yielding less than a monolayer mixture of THF and dissociated products on the surface. It was observed that Li diffused into Ag above room temperature. The electron beam in AES and x-rays in XPS caused severe damage to THF. 

H. You, S.C. Fain, Jr., S. Satija, and L. Passell. Observation of Two-Dimensional Compositional Ordering of a Carbon Monoxide and Argon Monolayer Mixture Physisorbed on Graphite. Phys. Rev. Lett. 56 244 (1986). 

The properties of monolayers of the cyclodepsipeptide, valinomydn (Fig. 4.12) have been the subject of recent investigations. Ries and Swift [105] have determined a molecular area of 3.70 nm from extrapolations of pressure-area isotherms for monolayers of valinomydn from which they infer a horizontal orientation of molecules within the monolayer. Mixtures of valinomydn and cholesterol (which has a vertical orientation in monolayers) have been investigated in view of their similarity to biological membranes and the possibility of their use as models for naturally occurring membranes. Monolayers of valinomydn are also of interest because of the ability of valinomycin to stimulate the transport of ions across mitochondrial and red blood cell membranes [106]. Several workers have studied the interaction of electrolytes with valinomycin monolayers [106-108]. These studies have shown a specific interaction of... 

The ability to contrast match the air with a mixture of water and heavy water makes neutron reflectivity an attractive technique [180,181], Under these contrast conditions the scattering arises from the monolayer alone and combining... 

There has been extensive activity in the study of lipid monolayers as discussed above in Section IV-4E. Coexisting fluid phases have been observed via fluorescence microscopy of mixtures of phospholipid and cholesterol where a critical point occurs near 30 mol% cholesterol [257]. 

As mentioned in Section IX-2A, binary systems are more complicated since the composition of the nuclei differ from that of the bulk. In the case of sulfuric acid and water vapor mixtures only some 10 ° molecules of sulfuric acid are needed for water oplet nucleation that may occur at less than 100% relative humidity [38]. A rather different effect is that of passivation of water nuclei by long-chain alcohols [66] (which would inhibit condensation note Section IV-6). A recent theoretical treatment by Bar-Ziv and Safran [67] of the effect of surface active monolayers, such as alcohols, on surface nucleation of ice shows the link between the inhibition of subcooling (enhanced nucleation) and the strength of the interaction between the monolayer and water. 

A logical division is made for the adsorption of nonelectrolytes according to whether they are in dilute or concentrated solution. In dilute solutions, the treatment is very similar to that for gas adsorption, whereas in concentrated binary mixtures the role of the solvent becomes more explicit. An important class of adsorbed materials, self-assembling monolayers, are briefly reviewed along with an overview of the essential features of polymer adsorption. The adsorption of electrolytes is treated briefly, mainly in terms of the exchange of components in an electrical double layer. 

Fig. XV-9. Fluorescence micrograph of the stripe patterns observed in a monolayer from a mixture of PA and SP-Bi-25 (20% by weight peptide) on a buffered saline subphase at 16 C and zero surface pressure. (From Ref. 55.)...

Most LB-forming amphiphiles have hydrophobic tails, leaving a very hydrophobic surface. In order to introduce polarity to the final surface, one needs to incorporate bipolar components that would not normally form LB films on their own. Berg and co-workers have partly surmounted this problem with two- and three-component mixtures of fatty acids, amines, and bipolar alcohols [175, 176]. Interestingly, the type of deposition depends on the contact angle of the substrate, and, thus, when relatively polar monolayers are formed, they are deposited as Z-type multilayers. Phase-separated LB films of hydrocarbon-fluorocarbon mixtures provide selective adsorption sites for macromolecules, due to the formation of a step site at the domain boundary [177]. 

Electroless reactions must be autocatalytic. Some metals are autocatalytic, such as iron, in electroless nickel. The initial deposition site on other surfaces serves as a catalyst, usually palladium on noncatalytic metals or a palladium—tin mixture on dielectrics, which is a good hydrogenation catalyst (20,21). The catalyst is quickly covered by a monolayer of electroless metal film which as a fresh, continuously renewed clean metal surface continues to function as a dehydrogenation catalyst. Silver is a borderline material, being so weakly catalytic that only very thin films form unless the surface is repeatedly cataly2ed newly developed baths are truly autocatalytic (22). In contrast, electroless copper is relatively easy to maintain in an active state commercial film thicknesses vary from <0.25 to 35 p.m or more. 

FIG. 1 Self-assembled structures in amphiphilic systems micellar structures (a) and (b) exist in aqueous solution as well as in ternary oil/water/amphiphile mixtures. In the latter case, they are swollen by the oil on the hydrophobic (tail) side. Monolayers (c) separate water from oil domains in ternary systems. Lipids in water tend to form bilayers (d) rather than micelles, since their hydrophobic block (two chains) is so compact and bulky, compared to the head group, that they cannot easily pack into a sphere [4]. At small concentrations, bilayers often close up to form vesicles (e). Some surfactants also form cyhndrical (wormlike) micelles (not shown). 

The other class of phenomenological approaches subsumes the random surface theories (Sec. B). These reduce the system to a set of internal surfaces, supposedly filled with amphiphiles, which can be described by an effective interface Hamiltonian. The internal surfaces represent either bilayers or monolayers—bilayers in binary amphiphile—water mixtures, and monolayers in ternary mixtures, where the monolayers are assumed to separate oil domains from water domains. Random surface theories have been formulated on lattices and in the continuum. In the latter case, they are an interesting application of the membrane theories which are studied in many areas of physics, from general statistical field theory to elementary particle physics [26]. Random surface theories for amphiphilic systems have been used to calculate shapes and distributions of vesicles, and phase transitions [27-31]. 

In the latter the surfactant monolayer (in oil and water mixture) or bilayer (in water only) forms a periodic surface. A periodic surface is one that repeats itself under a unit translation in one, two, or three coordinate directions similarly to the periodic arrangement of atoms in regular crystals. It is still not clear, however, whether the transition between the bicontinuous microemulsion and the ordered bicontinuous cubic phases occurs in nature. When the volume fractions of oil and water are equal, one finds the cubic phases in a narrow window of surfactant concentration around 0.5 weight fraction. However, it is not known whether these phases are bicontinuous. No experimental evidence has been published that there exist bicontinuous cubic phases with the ordered surfactant monolayer, rather than bilayer, forming the periodic surface. 

Fig. 6. Phase diagram for the binary mixture of terminally polar mesogens showii the reentrant nematic (N), monolayer (Ai), partially bilayer (Ad) and two-dimensional (C) phases (Lobko et al. [47])...

Both compound I and a mixture of the two derivatives M70 (70% 1 30% II) display the usual monolayer smectic Aj phase on cooling down from the isotropic liquid. At lower temperatures the particular smectic phases (X and X ) showing polar behaviour have been observed [78]. The smectic X phase in... 

For below one monolayer the deposit may consist of an inhomogeneous mixture of a bare substrate and clusters approximately one monolayer thick. The state with the lowest chemical potential is represented by a line through the origin and tangent to the E[N) curve near the first local minimum, at Ni Nq. The slope of this tangent defines a chemical potential Thus, as N is increased from 0 to the fraction of the sub-... 

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

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... 

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