Self-assembly experimental systems

The shape and size of self-assembled micellar systems depend on the conditions for a given system. Changes can be induced, e.g., by addition of cosurfactant or salt or by high surfactant concentrations. An aqueous solution of cetyltrimethylammonium chloride (CTAC) exhibits a transition from spherical micelles to elongated cylinders upon addition of chlorate anions, which is shown, for instance, by a strong increase in viscosity [25]. This system was experimentally studied by TRLQ, with results in good agreement with theory, as shown in Fig. 4. 

The focus of this article is based on experimental results obtained and reported by members of our research group in recent years, on the use of self-assembled chemical systems, particularly microemulsions, in some areas involved in modem petroleum industry [21-39]. After initial presentation on some historical aspects that led to the development of this work, we aim to cover the following main subject areas ... 

A number of experimental fluorescence studies of specific self-assembling copolymer systems will be described in the next chapter. 

Tailoring block copolymers with three or more distinct type of blocks creates more exciting possibilities of exquisite self-assembly. The possible combination of block sequence, composition, and block molecular weight provides an enormous space for the creation of new morphologies. In multiblock copolymer with selective solvents, the dramatic expansion of parameter space poses both experimental and theoretical challenges. However, there has been very limited systematic research on the phase behavior of triblock copolymers and triblock copolymer-containing selective solvents. In the future an important aspect in the fabrication of nanomaterials by bottom-up approach would be to understand, control, and manipulate the self-assembly of phase-segregated system and to know how the selective solvent present affects the phase behavior and structure offered by amphiphilic block copolymers. 

For technological applications it is highly desirable to be able to design self-assembling systems to have particular physico-chemical properties under a given set of experimental conditions. Using computer simulation, it is possible to construct an atomistic model of tapes, ribbons and fibrils to study all of the interatomic interactions within the system in a quantitative manner. Figure 13 shows atomistic... 

DD can be monitored by a variety of experimental techniques. They involve thermodynamic, dilatometric, and spectroscopic procedures. Molecular dynamics (MD) simulations also become applicable to self-assembled systems to some extent see the review in Ref. 2. Spectroscopic methods provide us with molecular parameters, as compared with thermodynamic ones on the macroscopic level. The fluorescence probing method is very sensitive (pM to nM M = moldm ) and informs us of the molecular environment around the probes. However, fluorescent molecules are a kind of drug and the membrane... 

The ability of block copolymers to self-assemble into organized microdomain (MD) structures when the thermodynamic repulsion between the constituents is high enough seems to be fairly well understood. This is particularly true in the case of amorphous diblock copolymers where phase diagrams for particular systems have been successfully predicted and experimentally proven [1-5]. 

The polymer self-assembly theory of Oosawa and Kasai (1962) provides valuable insights into the nature of the nucleation process. The polymerization nucleus is considered to form by the accretion of protomers, but the process is highly cooperative and unfavorable. Indeed, this is strongly suggested by the observation that thousands of actin or tubulin protomers are found in F-actin and microtubule structures if nucleation of self-assembly were readily accomplished and highly favorable, the consequence would be that many more fibers of shorter polymer length would be observed. The Oosawa kinetic theory for nucleation permits one to obtain information about the size of the polymerization nucleus if two basic assumptions can be satisfied in the experimental system. First, the rate of nuclei formation is assumed to be proportional to the loth power of the protomer concentration with io representing the number of protomers required to create the nucleus. Second, the treat-... 

For many applications such as catalysis and possible functional devices, SAMs are simply too thin, the organized structure not flexible enough or the sterical situation within the layer too confined in order to incorporate a desired function or respond to changes in the environment in a dynamic and reversible way. One approach to increase the layer thickness of well-ordered self-assembled stractures of up to 100 nm is the formation of SAM and LB multilayers by means of consecutive preparation steps (Fig. 9.1 (3)) [5, 108]. This strategy was successfully applied by several research groups, but requires the constant intervention of the experimenter to put one type of monomolecular layer on top of the other. The dynamic behavior of the layer is limited by the crystal-like organization of the system and the extreme confinement of all surface-bonded molecules. Hence, surface... 

Figure 6.5 shows experimental data relating to the self-assembly of sodium K-carrageenan, as induced by cooling in the presence of 0.1 M NaCl, and occurring simultaneously with the coil-to-helix transition for the same polysaccharide (Semenova et al., 1988). In what follows we consider this system in some detail. 

It should be noted that the development of such polymer systems is stimulated by existing experimental works. In particular, the experimental methods of preparation of nanometer-sized hollow-sphere structures have been suggested [58-63] because of their possible usage for encapsulation of molecules or colloidal particles. The preparation of hollow-sphere structures, generally, is based on self-assembling properties of block copolymers in a selective solvent, i.e., on the formation of polymer micelles with a nanometersized diameter. Further cross-finking of the shell of the micelle and photodegradation [64] of the core part produce nanometer-sized hollow cross-linked micelles. 

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