Stability of monolayers

A drop of a dilute solution (1%) of an amphiphile in a solvent is typically placed on tlie water surface. The solvent evaporates, leaving behind a monolayer of molecules, which can be described as a two-dimensional gas, due to tlie large separation between tlie molecules (figure C2.4.3). The movable barrier pushes tlie molecules at tlie surface closer together, while pressure and area per molecule are recorded. The pressure-area isotlienn yields infonnation about tlie stability of monolayers at tlie water surface, a possible reorientation of tlie molecules in tlie two-dimensional system, phase transitions and changes in tlie confonnation. Wliile being pushed togetlier, tlie layer at... 

We studied the surface pressure area isotherms of PS II core complex at different concentrations of NaCl in the subphase (Fig. 2). Addition of NaCl solution greatly enhanced the stability of monolayer of PS II core complex particles at the air-water interface. The n-A curves at subphases of 100 mM and 200 mM NaCl clearly demonstrated that PS II core complexes can be compressed to a relatively high surface pressure (40mN/m), before the monolayer collapses under our experimental conditions. Moreover, the average particle size calculated from tt-A curves using the total amount of protein complex is about 320 nm. This observation agrees well with the particle size directly observed using atomic force microscopy [8], and indicates that nearly all the protein complexes stay at the water surface and form a well-structured monolayer. 

Shimomura and Kunitake have reported that stable monolayers and LB films were obtained by electrostatic interaction of water soluble anionic polymers with cationic amphiphiles [58]. This polyion-complexation was also a useful method for stabilization of monolayers of unstable [59] or water soluble anionic surfactants [60]. Mixtures of water soluble cationic and anionic surfactants (1 1) also formed stable Langmuir monolayers at the air/ water interface [60]. 

Paulini R, Frankamp BL, Rotello VM (2002) Effects of branched ligands on the structure and stability of monolayers on gold nanoparticles. Langmuir 18 2368-2373... 

An attempt to obtain a copper conrplex from 2,4-heneicosanedione directly on ionic subphase was undertaken. The properties of 2,4-heneicosandione and its copper complex are investigated by x-A isotherms at water subphase. Incorporation of metal atoms into 2,4-heneicosandione monolayer with chelate metallocomplex formation on ionic subphase has been proved by IR- and UV-spectroscopies. Stability of monolayer film depending on AFM tip effect or water presence was studied. 

Hsu IJ, Kimmel YC, Dai Y, Chen S, Chen JG (2012) Rotating disk electrode measurements of activity and stability of monolayer Pt on tungsten carbide disks for oxygtm reduction reaction. J Power Sources 199 46-52... 

The energetics and kinetics of film formation appear to be especially important when two or more solutes are present, since now the matter of monolayer penetration or complex formation enters the picture (see Section IV-7). Schul-man and co-workers [77, 78], in particular, noted that especially stable emulsions result when the adsorbed film of surfactant material forms strong penetration complexes with a species present in the oil phase. The stabilizing effect of such mixed films may lie in their slow desorption or elevated viscosity. The dynamic effects of surfactant transport have been investigated by Shah and coworkers [22] who show the correlation between micellar lifetime and droplet size. More stable micelles are unable to rapidly transport surfactant from the bulk to the surface, and hence they support emulsions containing larger droplets. 

If an ionic surfactant is present, the potentials should vary as shown in Fig. XIV-5c, or similarly to the case with nonsurfactant electrolytes. In addition, however, surfactant adsorption decreases the interfacial tension and thus contributes to the stability of the emulsion. As discussed in connection with charged monolayers (see Section XV-6), the mutual repulsion of the charged polar groups tends to make such films expanded and hence of relatively low rr value. Added electrolyte reduces such repulsion by increasing the counterion concentration the film becomes more condensed and its film pressure increases. It thus is possible to explain qualitatively the role of added electrolyte in reducing the interfacial tension and thereby stabilizing emulsions. 

While the v-a plots for ionized monolayers often show no distinguishing features, it is entirely possible for such to be present and, in fact, for actual phase transitions to be observed. This was the case for films of poly(4-vinylpyri-dinium) bromide at the air-aqueous electrolyte interface [118]. In addition, electrostatic interactions play a large role in the stabilization of solid-supported lipid monolayers [119] as well as in the interactions between bilayers [120]. 

Salmeron M, Liu G-Y and Ogletree D F 1995 Molecular arrangement and mechanical stability of self-assembled monolayers on Au(111) under applied load Force in Scanning Probe Methods ed H-J Guntherodt et al (Amsterdam Kluwer)... 

The growth of a well ordered fullerene monolayer, by means of molecular beam epitaxy, has been used for the controlled nucleation of single crystalline thin films. The quality and stability of molecular thin films has been shown... 

Organosilanes, such as trichlorosilanes or trimethylsilanes, can establish SA monolayers on hydroxylated surfaces. Apart from their (covalent) binding to the surface these molecules can also establish a covalent intennolecular network, resulting in an enlranced mechanical stability of the films (figure C2.4.11). In 1980, work was published on the fonnation of SAMs of octadecyltrichlorosilane (OTS) 11171. Subsequently, the use of this material was extended to the fonnation of multilayers 11341. 

Chemical stability. The chemical stability of SA films is of interest in many areas. However, tliere is no general mle for it. The chemical stability of silane films is remarkable, due to tlieir intennolecular crosslinking. Therefore, tliey are found to be more stable tlian LB films. Alkyltrichlorosilane monolayers provide stmctures tliat are stable to chemical conditions tliat most LB films could not stand. However, photopolymerized LB films also show considerable stability in organic solvents. 

Adechanical stahility. ChemisoriDtion to tire surface, intennolecular interactions and crosslinking between adjacent compounds—if possible—all contribute to tire resulting stability of tire monolayer film. Lateral force microscopy investigations revealed tliat tire mechanical stability towards lateral forces on tire nanometre scale is likely to be detennined by tire defect density and tire domain size on a nano- to micrometre scale [163, 1731. 

Aronoff Y G, Chen B, Lu G, Seto C, Schwartz J and Bernasek S L 1997 Stabilization of self-assembled monolayers of carboxylic acids on native oxides of metals J. Am. Chem. Soc. 119 259-62... 

The process of adsorption of polyelectrolytes on solid surfaces has been intensively studied because of its importance in technology, including steric stabilization of colloid particles [3,4]. This process has attracted increasing attention because of the recently developed, sophisticated use of polyelectrolyte adsorption alternate layer-by-layer adsorption [7] and stabilization of surfactant monolayers at the air-water interface [26], Surface forces measurement has been performed to study the adsorption process of a negatively charged polymer, poly(styrene sulfonate) (PSS), on a cationic monolayer of fluorocarbon ammonium amphiphilic 1 (Fig. 7) [27],... 

Changes in thermal stability and mass due to the formation of CdS nanoparticles in LB films were examined [180]. The LB films were formed onto gold-coated quartz oscillators from monolayers of arachidic acid or nonacosa-10,12-diynoic acid on CdCH containing subphases. The films were exposed to H2S gas until the mass change indicated complete conversion of Cd to CdS. The thermal stability of the H2S-treated films was reduced, with significant mass loss initiating at 55°C, compared to minimal mass loss in the untreated films up to at least 80°C under mild vacuum. The average CdS-particle size... 

The LB technique was chosen for covering the spheres because it was shown to provide enhanced thermal stability of many types of proteins in deposited layers (Nicolini et al. 1993, Erokhin et al. 1995, Antolini et al. 1995), which no other technique is able to achieve. Since only the upper protein layer is involved in the catalytic activity, no special attention was paid to check whether the deposited layer is a monolayer or multilayer. However, the samples were thoroughly washed to remove protein molecnles not bound covalently to the sphere surface, since during the functional test these molecules could contribute to the measured apparent catalytic activity. 

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