Microstructures self-assembled

Green, P.W. Syms, R.R.A. Yeatman, E.M. Demonstration of three-dimensional microstructure self-assembly. J. Microelectromech. Syst. 1995, 4 (4), 170. 

Figure 16 Hierarchical microstructures self-assembled from A(BC)3 multiblock copolymer with xabI 200,/ac/1/= 250, and /bc/V= 500 (a) spheres-in-lamellae (b) cylinders-in-lamellae (c) lamellae-in-lamella (d) cylinders-in-cylinder and (e) spheres-in-sphere. From (a) to (e), the volume fractions of A blocks are 0.10,0.20,0.50,0.75, and 0.88, respectively. The blue, red, and green colors are assigned to A, B, and C blocks, respectively. Reprinted with permission from Wang, L. Lin, J. Zhang, L. Macromolecules Zno, 43(3), 1602-1609. ...

As materials chemistry has developed, it has come to pay more and more attention to that archetypal concern of materials scientists, microstructure. That concern came in early when the defects inherent in non-stoichiometric oxides were studied by the Australian. I.S. Anderson and others (an early treatment was in a book edited by Rabenau 1970), but has become more pronounced recently in the rapidly growing emphasis on self-assembly of molecules or colloidal particles. This has not yet featured much in books on materials chemistry, but an excellent recent popular account of the broad field has a great deal to say on self-assembly (Ball 1997). The phenomenon of graphoepitaxy outlined in Section 10.5.1.1 is a minor example of what is meant by self-assembly. 

Since multiple electrical and optical functionality must be combined in the fabrication of an OLED, many workers have turned to the techniques of molecular self-assembly in order to optimize the microstructure of the materials used. In turn, such approaches necessitate the incorporation of additional chemical functionality into the molecules. For example, the successive dipping of a substrate into solutions of polyanion and polycation leads to the deposition of poly-ionic bilayers [59, 60]. Since the precursor form of PPV is cationic, this is a very appealing way to tailor its properties. Anionic polymers that have been studied include sulfonatcd polystyrene [59] and sulfonatcd polyanilinc 159, 60]. Thermal conversion of the precursor PPV then results in an electroluminescent blended polymer film. 

In order to prevent the irrevisible adhesion of MEMS microstructures, several studies have been performed to alter the surface of MEMS, either chemically or physically. Chemical alterations have focused on the use of organosilane self-assembled monolayers (SAMs), which prevent the adsorption of ambient moisture and also reduce the inherent attractive forces between the microstructures. Although SAMs are very effective at reducing irreversible adhesion in MEMs, drawbacks include irreproducibility, excess solvent use, and thermal stability. More recent efforts have shifted towards physical alterations in order to increase the surface roughness of MEMS devices. 

Archibald, D.D. and Mann S. (1993) Template mineralization of self-assembled anisotropic lipid microstructures. Nature,... 

Molecular calculations provide approaches to supramolecular structure and to the dynamics of self-assembly by extending atomic-molecular physics. Alternatively, the tools of finite element analysis can be used to approach the simulation of self-assembled film properties. The voxel4 size in finite element analysis needs be small compared to significant variation in structure-property relationships for self-assembled structures, this implies use of voxels of nanometer dimensions. However, the continuum constitutive relationships utilized for macroscopic-system calculations will be difficult to extend at this scale because nanostructure properties are expected to differ from microstructural properties. In addition, in structures with a high density of boundaries (such as thin multilayer films), poorly understood boundary conditions may contribute to inaccuracies. 

The next three chapters (Chapters 9-11) focus on the deposition of nano-structured or microstructured films and entities. Porous oxide thin films are, for example, of great interest due to potential application of these films as low-K dielectrics and in sensors, selective membranes, and photovoltaic applications. One of the key challenges in this area is the problem of controlling, ordering, and combining pore structure over different length scales. Chapter 9 provides an introduction and discussion of evaporation-induced self-assembly (EISA), a method that combines sol-gel synthesis with self-assembly and phase separation to produce films with a tailored pore structure. Chapter 10 describes how nanomaterials can be used as soluble precursors for the preparation of extended... 

There is now a solid body of available knowledge to indicate that the general features of biopolymer self-assembly in bulk aqueous solutions can account for various detailed aspects of the stability, rheology and microstructure of oil-in-water emulsions (and foams) stabilized by the same kinds of biopolymers (Dickinson, 1997, 1998 Casanova and Dickinson, 1998 Dickinson et al., 1997, 1998 Semenova et al., 1999, 2006 van der Linden, 2006 Semenova, 2007 Ruis et al., 2007). In particular, the richness of the self-assembly and surface-active properties of the... 

Hence, from the previously described light-scattering study of caseinate self-assembly in solution, we can postulate that heating/cooling not only alters the nature and strength of the physical (hydrophobic) interactions between emulsion droplets covered by caseinate. It most likely also transforms the nanoscale structural characteristics of the protein network in the bulk and at the interface, thereby affecting the viscoelastic and microstructural properties of the emulsions. 

On the strength of all the examples presented in this chapter, the reader should be convinced that variations in self-assembly of food biopolymers in aqueous media can have an enormous influence on food colloid stability, rheology and microstructure. It therefore seems reasonable to infer that further study and understanding of the molecular mechanisms of self-assembly and interactions of biopolymers in aqueous solution should provide increased opportunities for the creation of new classes of structured soft materials with potential application for incorporation in a wide range of new food and pharmaceutical products. 

Ipsen, R., Otte, J., Qvist, K.B. (2001). Molecular self-assembly of partially hydrolysed alpha-lactalbumin resulting in strong gels with a novel microstructure. Journal of Dairy Research, 68, 277-286. 

Figure 18a,b displays SFM images of SV films that have been prepared from chloroform and from toluene solutions, respectively. The mixed pattern of featureless areas and round-shaped stripes in Fig. 18a can be identified as in-plane lamella and perpendicular-oriented lamellae, respectively. The microstructure prepared from toluene solutions (Fig. 18b) is attributed to P2VP micelles surrounded by the PS shell. The micelle morphology is a result of the SV self-assembly in a selective solvent [119], We have made use of this morphological difference to study the microstructure response to solvent uptake by block copolymer films. 

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