Microstructures monolayer structure

A section through the phase prism at constant surfactant concentration ( Shinoda-cut ) is particularly illustrative. This shows the interrelation between the temperature-dependence and the dependence on the water-to-oil ratio. By choosing the surfactant concentration to be slightly above 0, one obtains a phase behaviour that is illustrated schematically in Figure 17.4. This section contains a rich variety of microstructures, e.g. the microemulsion phase which has a surfactant monolayer structure and the lamellar phase and the sponge phase which both have a bilayer... 

The enthalpy effect of rod packing influences the microstructures at the air- water interface. The copolymer with the long rods, forms a cylindrical structure in the monolayer due to the bigger enthalpy decrease. Copolymer, with the middle-sized rods, will form micellar structure in the monolayer by self - assembly. Copolymer... 

The special property of surfactants in solution is that they associate into a monolayer or sheetlike structure with the water-soluble moieties (hydrophilic heads) on one side of the sheet and water-insoluble moieties on the other side [8], These sheetlike structures provide the building blocks for a rich variety of fluid microstructures, which, depending on thermodynamic... 

Micellar solutions are isotropic microstructured fluids which form under certain conditions. At other conditions, liquid crystals periodic in at least one dimension can form. The lamellar liquid crystal phase consists of periodically stacked bilayers (a pair of opposed monolayers). The sheetlike surfactant structures can curl into long rods (closing on either the head or tail side) with parallel axes arrayed in a periodic hexagonal or rectangular spacing to form a hexagonal or a rectangular liquid crystal. Spherical micelles or inverted micelles whose centers are periodically distributed on a lattice of cubic symmetry form a cubic liquid crystal. 

We have found that the microstructural changes and stress response of our model protein monolayer to uniaxial compression is very sensitive to the nature of the particle-particle interactions. The structural differences of the same systems at equilibrium are much less obvious. These findings suggest that the validation of simulation models by comparing their qualitative behavior under large-deformation compression (expansion) with the experimental results is likely to be more powerful than the comparison of just the equilibrium properties of the adsorbed films. 

In the case of in-use stiction, it is hypothesized that moisture from the environment (relative humidity) comes in contact with the MEMS structural surfaces. If, during operation, these structures come in contact, the moisture can cause a temporary bond that, like release stiction, can then become permanent with time. To reduce in-use stiction, three basic techniques have been attempted. The first is to use a hermetic seal around the microstructure to eliminate the possibility of moisture encountering the structure. Secondly, the use of techniques to minimize the work of adhesion has been employed. Specifically, Houston et al. have used ammonium fluoride to reduce the work of adhesion on surface micromachined structures [59, 60]. Lastly, various coatings and/or surface treatments have been used on the microstructure to eliminate the chance of contact between two surfaces that have the prevalence to stick (e.g., polysilicon and silicon, each material with a native oxide). The University of California, Berkeley has pioneered techniques of using self-assembled layer monolayer coatings to minimize in-use stiction [18, 25, 59, 61]. Also, other researchers have used fluorocarbon coatings to minimize the in-use stiction [62-64]. 

We have previously reported [9] our study on the microstructure of TRS 10 - 410 + isobutanol system using freeze fracture electron microscopy and NMR spectroscopy. The results clearly showed the formation of lamellar structures in the NaCl concentration in the range of 1.2 to 2%. It appears from the present study that the lamellar structure is more effective in reducing coefficient of friction and protecting the metal surface against wear as compared to spherical micelles or adsorbed monolayer of surfactant on metal surface. Presumably the lamellar structures orient parallel to the metal surface, and hence reduce the coefficient of friction as well as protect the surface against wear. 

In principle, we can distinguish (for surfactant self-assemblies in general) between a microstructure in which either oil or water forms discrete domains (droplets, micelles) and one in which both form domains that extend over macroscopic distances (Fig. 7a). It appears that there are few techniques that can distinguish between the two principal cases uni- and bicontinuous. The first technique to prove bicontinuity was self-diffusion studies in which oil and water diffusion were monitored over macroscopic distances [35]. It appears that for most surfactant systems, microemulsions can be found where both oil and water diffusion are uninhibited and are only moderately reduced compared to the neat liquids. Quantitative agreement between experimental self-diffusion behavior and Scriven s suggestion of zero mean curvature surfactant monolayers has been demonstrated [36]. Independent experimental proof of bicontinuity has been obtained by cryo-electron microscopy, and neutron diffraction by contrast variation has demonstrated a low mean curvature surfactant film under balanced conditions. The bicontinuous microemulsion structure (Fig. 7b) has attracted considerable interest and has stimulated theoretical work strongly. 

It was suggested [284] that the perforated lamellar phase may form via the growth of branched and multiconnected threadlike micelles. Interconnection of threadlike micelles reduces the overall curvature of the monolayer making up the micelles and thereby reflects a preference for microstructures of decreasing curvature [119]. The suggested morphological sequence for the system cetylpyridinium chloride-hexanol-brine is spheres, small disks, long capped cylinders, branched cylinders, perforated bilayers, smooth bilayers, loose network of connected bilayers (foamlike structure), and multiphasic domain [284]. 

The earliest molecular monolayer was made by sorption and covalent bonding of chemicals to electrode surfaces however, limitations exist in the ability to control the structural and dynamic aspects of the immediate microscopic environment of the immobilized chemicals. SAMs that form spontaneously at solid/liquid interfaces have attracted much attention lately as it provides a unique technique for controlling the properties of solid surfaces. SAMs on electrodes give the platform needed for probing the relationship between the microstructure on the electrode surface and macroscopic electrochemical responses, which reach the top level of the molecular monolayer CMEs. 

In summary, our results have demonstrated that a colloidal monolayer can be used as a flexible template to create ordered nano-structured arrays. Combining it with other techniques, a series of ordered nano-structured arrays with centimeter size could be easily fabricated on many different substrates. These nano-structured arrays are of surface roughness on the nano- and micro-scales, or similar to the microstructure of lotus leaves. Our results have demonstrated that such micro/nano-structured arrays, not only of insulators and semiconductors but also of metals, display morphology-dependent wettability. Significant enhancement of both hydrophobicity and hydrophilicity can be achieved by fabricating special surface micro/nano-structure on any material. This means that we can also realize tunable and controllable wettability of surface of any material by designing the proper surface structure. From this study, it can thus be expected that the nano-devices based on our nano-structured arrays would be waterproof and self-cleaning, in addition to their special device functions. 

Figure 1 (A) Schematic section through a chemically microstructured TSG sample after pCP with reactive DSU, formation of a HUT SAM and immobilization of proteins. Primary amines of proteins react with the end groups of the DSU crosslinker (11, ll -dithio-bis(succinimi-dylundecanoate), Fig. 1C bound DSU (thiolate form) with the formation of an amide bond. (B) Schematic section through a microstructured silicon/gold structure after pCP, etching the gold, titanium and silicon, removal of the etch-resistant monolayer, formation of a reactive monolayer and finally reaction with protein.

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