Self-assembly techniques

The so-called self-assembly technique has its origin in 1946, when a paper was published by Bigelow et a] [116] and tluis is slightly younger tlian tlie LB teclmique. The autliors noted tliat a hydrophilic surface exposed to an amphiphilic compound dissolved in a non-polar solvent induces tlie amphiphilic material to fonn a monolayer on it. 

Herein the focus is on SAMs of trichlorosilanes and thiols. SAMs of carboxyUc acids are important as a connection between the LB and self-assembly techniques, but studies of their formation and stmcture have been relatively limited. SAMs of carboxyUc acids on AI2O2, AgO, and CuO have also been carried out (113—124). 

Monolayers of alkyl chains on siUcon are a significant addition to the family of SAMs. An abiUty to directly connect organic materials to siUcon allows a direct coupling between organic materials and semiconductors. The fine control of supedattice stmctures provided by the self-assembly technique offers a route for building organic thin films with, for example, electrooptic properties on siUcon. 

The advantage of the LB technique is that it allows systematic studies of 2-D organization, both before and after transfer from the air—water interface onto a soHd substrate. However, the coupling of 3-D self-organization of macromolecules in solution with organization at a soHd surface may best be achieved using the self-assembly technique. 

Mono- and Multilayers of Spherical Polymer Particles Prepared by Langmuir-Blodgett and Self-Assembly Techniques... 

In addition to the preparation of Langmuir and Langmuir-Blodgett films, the use of self-assembly techniques also plays an important role in the formation of particle films. Both physisorption, as, for example, electrostatic adsorption of charged particles from colloidal solution, and chemisorption onto a substrate have been investigated. In Section V.A, electrostatic adsorption will be reviewed chemisorption is the subject of Section V.B. 

Some research groups also tried to build up bi- and multilayers of latex particles by using self-assembly techniques [92-94,97]. Either the alternate adsorption technique outlined in Figure 14 was used, in which cationic and anionic particles are successively adsorbed, or a slightly modified version of successive adsorption of anionic particles and a cationic poly-... 

Schaeferling M., Schiller S., Paul H., Kruschina M., Pavlickova P., Meerkamp M., Giammasi C., Kambhampati D., Application of self-assembly techniques in the design of biocompatible protein microarray surfaces, Electrophoresis 2002 23 3097-3105. 

Oh, B. K., Lee, W., Lee, W. H., and Choi, J. W. (2003). Nano-scale probe fabrication using self-assembly technique and application to detection of Escherichia coli 0157 H7. Biotechnol. Bioprocess Eng. 8, 227-232. 

Varghese B, Cheong FC, Sindhu S, Yu T, Lim CT, Valiyaveettil S, Sow CH (2006) Size selective assembly of colloidal particles on a template by directed self-assembly technique. Langmuir 22 8248-8252... 

POEA), a conducting polymer. The measurements were carried out using both solution and polymer films deposited by the self-assembly technique (Paterno and Mattoso, 2001). Figure 16.21 presents the Raman spectra of FA, POEA, and POEA/ FA complexes in different concentrations of FA. 

The use of self-assembly techniques in molecular electronics has proven to be useful, as shown by the many publications cited. We expect the field to continue to develop and mature as researchers fine-tune their procedures and new methods are developed. Processes refined for the molecular electronics field will find applications in other nanotechnology areas the reverse will also be true. Thus, as it will be beneficial for those in the solid-state microelectronics field to look toward molecular electronics for solutions to their problems, it will also be beneficial for those in the field of self-assembled molecular electronics to look outside that narrow range of technology for potential solutions to their problems. The coming years will surely see many exciting developments. 

Novel microreactors with immobilized enzymes were fabricated using both silicon and polymer-based microfabrication techniques. The effectiveness of these reactors was examined along with their behavior over time. Urease enzyme was successfully incorporated into microchannels of a polymeric matrix of polydimethylsiloxane and through layer-bylayer self-assembly techniques onto silicon. The fabricated microchannels had cross-sectional dimensions ranging from tens to hundreds of micrometers in width and height. The experimental results for continuous-flow microreactors are reported for the conversion of urea to ammonia by urease enzyme. Urea conversions of >90% were observed. 

Continuous-flow microreactors were successfully fabricated by etching channels in silicon and immobilizing urease onto channel surfaces by a layer-by-layer self-assembly technique. Preliminary results show urea conversion. The potential advantages of this surface-coating technique in microreactors warrant continued investigation. 

We acknowledge Dr. Yuri Lvov at Louisiana Tech s Institute for Micromanufacturing for assistance in applying layer-by-layer self-assembly techniques. We also wish to thank the Department of Defense (DAAH04-96-1-0200) and the Louisiana Board of Regents (LEQSF [1999-02J-RD-A-24) for their support of this work. 

Thus far, methods of organizing small molecules into mono- and multilayers have been discussed. However, both LB and self-assembly techniques allow deposition of polymer films as well. Two approaches to preparing polymer films by LB method have been described. An amphiphilic polymer film can be... 

Both the molecular template and the self-assembly techniques presented above have limited control over the final shape of the solid, since this is generally obtained in the form of a powder, fibers, or thin films. It is possible, however, to control the shape and size of solids by combining the former techniques with techniques that restrict the volume in which the synthesis takes place. The final goal is to have control over the solids at the molecular as well as macroscopic level, in order to have in a single material properties emerging from several levels of scale. Such structures are referred to as hierarchical [2, 6]. 

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