Self-assembled layers

The power of optical spectroscopies is that they are often much better developed than their electron-, ion- and atom-based counterparts, and therefore provide results that are easier to interpret. Furtlienuore, photon-based teclmiques are uniquely poised to help in the characterization of liquid-liquid, liquid-solid and even solid-solid interfaces generally inaccessible by other means. There has certainly been a renewed interest in the use of optical spectroscopies for the study of more realistic systems such as catalysts, adsorbates, emulsions, surfactants, self-assembled layers, etc. 

Steiner U B, Cased W R, Suter U W, Rehahn M and Rau I U 1994 Self-assembled layers of substituted poly(p-phenylene)s on gold and copper Langmuir 10 1164-70... 

In a separate study using the JKR technique, Chaudhury and Owen [48,49] attempted to understand the correlation between the contact adhesion hysteresis and the phase state of the monolayers films. In these studies, Chaudhury and Owen prepared self-assembled layers of hydrolyzed hexadecyltrichlorosilane (HTS) on oxidized PDMS surfaces at varying degrees of coverage by vapor phase adsorption. The phase state of the monolayers changes from crystalline (solidlike) to amoiphous (liquid-like) as the surface coverage (0s) decreases. It was found that contact adhesion hysteresis was the highest for the most closely packed... 

Self-Assembled Layers, Langmuir-Blodgett Layers, and Liquid Crystals... 

FIG. 8 Si02 AFM image of six bilayers in situ self-assembled layer-by-layer films of polypyrrole coated with Si02 and poly(styrene sulfonate). 

FIG. 16 SEM pictures of self-assembled layers of particles Ic after different dipping times t (concentration 3 mg/mL T = 23.5°C pH = 5.8). (From Ref. 98, with permission from Elsevier, Amsterdam.)... 

FIG. 17 Plot of normalized surface coverage C of self-assembled layer of particles Ic vs. dipping time of substrate for different concentrations of the latex dispersion (T = 23.5°C, pH = 5.8). 

Peter LM, Rdey DJ, TuU EJ, Wijayantha KGU (2002) Photosensitization of nanocrystalline Ti02 by self-assembled layers of CdS quantum dots. Chem Commun 10 1030-1031... 

Peter LM, Wijayantha KGU, Rdey DJ, Waggett JP (2003) Band-Edge Tuning in Self-Assembled Layers of Bi2S3 Nanoparticles Used To Photosensitize NanocrystaUine Ti02. J Phys Chem B 107 8378-8381... 

Switzer, J. A., Maune, B. M., Raub, E. R. and Bohannan, E. W. (1999) Negative differential resistance in electrochemicaDy self-assembled layered nanostructures. J. Phys. Chem. B, 103, 395-398. 

Fig. 8.14 TEM images showing (A) self-assembled layers of individual myoglobin molecules wrapped by condensed oligomers of AMP (B) top view of single sheet showing ordered superstructure of the hydrophobic organoclay wrapped myoglobin molecules.

Lee et al. utilized the self-assembled layer of thiol group-modified protein A for the oriented immobilization of antibodies [64], An increased binding capacity was further observed. As another illustrative instance, a protein A-based orientation-controlled immobilization strategy for antibodies was proposed for the fabrication of a QCM immunosensor using nanometer-sized gold particles and amine-terminated PPF [65], Moreover, in recent years, there has emerged another oriented immobilization... 

J.S. Li, Z.S. Wu, H. Wang, G.L. Shen, and R.Q. Yu, A reusable capacitive immunosensor with a novel immobilization procedure based on 1,6-hexanedithiol and nano-Au self-assembled layers. Sens. Actuators B 110, 327-334 (2005). 

P.K.H. Ho, M. Granstrom, R.H. Friend, and N.C. Greenham, Ultrathin self-assembled layers at the ITO interface to control charge injection and electroluminescence efficiency in polymer light-emitting diodes, Adv. Mater., 10 769-774, 1998. 

The motivations for the study of biomolecules immobilised on surfaces, briefly outlined above, also provide an explanation for the increased popularity of microscopy-based techniques. Indeed, while for single molecule and self-assembled layers the use of microscopy techniques is obvious, the commercial biodevices are increasingly micro- and even nanoscale devices. 

In the formation of self-assembled layer, one can distinguish three steps [131, 132]. The first step lasts for several seconds and obeys chemisorption and formation... 

Also, self-assembled layers of functionalized oKgo(cyclohexylidene) molecules on Au(lll) electrodes have been studied... 

Starodub NF, Pirogova LV, Demchenko A, Nabok AV (2005) Antibody immobilization on the metal and silicon surface. The use of self-assembled layer and specific receptors. Bioelectrochem 66 111-115... 

Langmuir and Langmuir-Blddgett Films and Other Self-assembling Layers... 

Surface tension of self-assembled layers from hydrolyzed silane solutions... 

Figure 15.19 Light induced topochemical polymerisation of a diacetlyene self-assembled layer on HOPG.26...

Surfactants at Interfaces. Somewhat surprisingly, the successes described above in the in-situ studies of protein adsorption have not inspired extensive applications to the study of the adsorption of surfactants. The common materials used in the fabrication of IREs, thalliumbromoiodide, zinc selenide, germanium and silicon do, in fact, offer quite a range in adsorption substrate properties, and the potential of employing a thin layer of a substance as a modifier of the IRE surface which is presented to a surfactant solution has also been examined in the studies of proteins. Based on the appearance of the studies described below, and recent concerns about the kinetics of formation of self-assembled layers, (108) it seems likely that in-situ ATR studies of small molecules at solid - liquid interfaces ("wet" solids), will continue to expand in scope. 

Determination of lateral periodicities in the self-assembled layer is an important goal in surface analysis. 2D surface crystal structures are best studied with low energy electrons, since their escape depth, contrary to X-rays, is basically limited to the top-most atomic layers. Consequently, LEED has become the most important method in surface monolayer crystallography. However, single-crystalline substrates are required. Via this technique, 2D supramolecular chiral lattice structures on single crystal surfaces had already been observed in 1978 [19]. 

An interesting phenomenon in water-oil-amphiphile systems is the presence of self-assembled arrays of amphiphiles (surfactants) called micelles. From 1948 to 1950, Philip Alan Winsor reported that upon simple mixing (i.e., without the need for high shear conditions), oil, water, and amphiphiles yielded clear, macro-scopically homogeneous single phases which he termed type IV systems (Winsor, 1948, 1950). The term microemulsion was introduced later by Jack H. Shulman, a Columbia University chemistry professor, to denote these thermodynamically stable optically isotropic, transparent oil-water-amphiphile dispersions (Shulman et al., 1959). Type IV systems contain small droplets of one liquid dispersed within the other, with a self-assembled layer of surfactant molecules (micelles) along the interface between the two phases. The spontaneous self-assembly of the micelle is driven by the thermodynamic tendency to minimize the surface tension between the water and the oil in the presence of the amphiphile (Hoar and Shulman, 1943). 

Figure 19-2. Schematic overview of the type of apparatus used to investigate the desorption of ions and neutral species induced by electron impact on thin molecular and bio-organic films. In the case of thin DNA films, they are formed outside vacuum by lyophilization on a metal substrate or as a self-assembled layer. The films are placed on the multi-sample holder in the load-lock chamber. From there, they can be transferred one by one to the main chamber for analysis...

The self assembled layer-by-layer of polyeleetrolytes on CNTs previously funetionalized was also proposed [71]. CNTs were synthesized on a grid for TEM by CVD using metallic catalysts. The negative eharges were originated onto the surfaee of earbon nanotubes by adsorbing a pyrene derivative. 

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