Two Dimensional Self-assembly

Interestingly, in both approaches the two-dimensional arrangement undergoes sooner or later similar phase transitions as illustrated in Fig. 9.3. 

While for LB-layers, the molecules have to be organized by means of compression prior to deposition of the monolayer at the air-water interface, the self-organization process into SAMs follows similar pathways by itself This requires sufli- 

By now a broad range of SAMs on various substrates are available. For an overview on SAM systems several comprehensive reviews [1-4] as well as the reference book by A. Ulman are available [5]. In Tab. 9.1 a list of examples is given [5, 6, 33]. 

The process of formation of SAMs on the various substrates strongly depends on the nature of all three moieties of the surface active molecule. If a suitable mesogen is chosen, the affinity of the head group toward the substrate determines the kinetics of the physisorption and chemisorption as well as the stability of the resulting layer. 

Among the SAM systems listed in Tab. 9.1, those based on silanes on silica and thiols on (noble) metals represent the majority of the reported accounts. In the following some specific properties of these two systems will be outlined. 

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Figure 17 Three examples of two dimensional self-assembly based on one structure, hexagons. In the insets the bold sides indicate hydrophobic faces and the thin sides indicate hydrophilic faces. The hexagons are floating at the perSfluor-odecalin-water interface. The array shown in (A) results when all the sides are equivalent and hydrophobic (B) and (C) show two of the arrays possible when the sides are differentiated...

SELF-ASSEMBLY AT INTERFACE (TWO-DIMENSIONAL SELF-ASSEMBLY)... 

Choi, I.S. Bowden, N. Whitesides, G.M. Macroscopic hierarchical, two-dimensional self-assembly. 23. 

Figure 3 Radiation-induced metal clusters, (a) Silver nanoclusters stabilized by PVA (10 nm). (b) STM imaging ofa single duster of the blue sol of silver oligomers Agd formed by y irradiation (n = 4). (c) Clusters ofAg, partially reduced by irradiation and then chemically developed by EDTA. (100 nm large and 15 nm thick), (d) TEM bright-held Image ofNi , PVA clusters (5 nm). (e) Two-dimensional self-assembled array of gold dusters (PVA) on mica with remarkable homodisperse size (5 nm). (f) Monocrystalline Pt nanotubes with CPCI (10 nm diameter and a few 100 nm long), (g) Pt nanorods with CTAB (3-4 nm thick and 20-40 nm long).

Nagayama, K. Two-dimensional self-assembly of colloids in thin liquid films. Coll. Surf. A, 109, 363, 1996. 

In this chapter, we have reviewed the two-dimensional self-assembly of oligothiophenes and polythiophenes on different surfaces and experimental conditions, as observed by high-resolution STM. This technique allows one to identify the bonding arrangements of molecules at surfaces, with molecular... 

MANY-BODY PHYSICS WITH COLD POLAR MOLECULES 12.4.1 Two-Dimensional Self-Assembled Crystals... 

Significant differences also apply when comparing more traditional supramolecular chemistry with surface-based approaches. Two differences are perhaps the most apparent. Firstly, the surface automatically acts as a two-dimensional barrier defining the nature of the self-assembly process. Secondly, the surface does not play a passive role in the two-dimensional self-assembly process. For the molecules to adsorb on the surface there is inherently an interaction between substrate and the molecule. Thus, it can be reasonably concluded that the adsorption process must influence the ability of the molecule to form supramolecular assemblies. This influence has been demonstrated for the PTCDI-melamine family of compounds on surfaces including Ag/Si(lll), Au(lll), graphene," and As the area of surface-based self-assembly continues to develop it is likely that the role of the surface is increasingly understood and exploited to control self-assembly. 

Fig. 1.7 Molecular structure of two-dimensionally self-assembling fullerene molecules...

Shinkai and Kanekiyo discuss the development of boronic acid-based supra-molecular systems. Supramolecular systems discussed include sugar-responsive gels, porphyrin-boronic acid, systems that exhibit guest-induced spectroscopic changes, two-dimensional self-assembly at the air-water interface, boronic acid-functionalized metal nanoparticles and boronic acid-appended polymers. 

Uemura, S. Aono, M. Komatsu, T. Kunitake, M. 2011. Two-dimensional self-assembled structures of melamine and melem at the aqueous solution-Au(l 11) interface. Langmuir 27 1336-1340. 

Rizis G, vande Ven TGM, Eisenberg A (2014) Raft formation by two-dimensional self-assembly of block copolymer rod micelles in aqueous solution. Angew Chem Int Ed 53 9000-9003... 

Even though the fast scanning calorimeters were developed for metal samples, they were also successfully applied to the melting of PE single crystals, phase transitions in two-dimensional self-assembled hexadecanethiol monolayers, and the glass transition in ultrathin spin-coated polymer films. Figure 15 shows typical curves for the glass transition in nanometer-thick polymer films. From these... 

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