Micellar solutions dynamics

As a result of the micellar environment, enzymes and proteins acquire novel conformational and/or dynamic properties, which has led to an interesting research perspective from both the biophysical and the biotechnological points of view [173-175], From the comparison of some properties of catalase and horseradish peroxidase solubilized in wa-ter/AOT/n-heptane microemulsions with those in an aqueous solution of AOT it was ascertained that the secondary structure of catalase significantly changes in the presence of an aqueous micellar solution of AOT, whereas in AOT/n-heptane reverse micelles it does not change. On the other hand, AOT has no effect on horseradish peroxidase in aqueous solution, whereas slight changes in the secondary structure of horseradish peroxidase in AOT/n-heptane reverse micelles occur [176],... 

Investigation of water motion in AOT reverse micelles determining the solvent correlation function, C i), was first reported by Sarkar et al. [29]. They obtained time-resolved fluorescence measurements of C480 in an AOT reverse micellar solution with time resolution of > 50 ps and observed solvent relaxation rates with time constants ranging from 1.7 to 12 ns. They also attributed these dynamical changes to relaxation processes of water molecules in various environments of the water pool. In a similar study investigating the deuterium isotope effect on solvent motion in AOT reverse micelles. Das et al. [37] reported that the solvation dynamics of D2O is 1.5 times slower than H2O motion. 

Figure 9.13 Dynamic-light-scattering size distribution (angle 120°) of a CgPC reverse micellar solution, containing aqueous DNA solution, wq = 5. (a) 0.5 mg mD DNA (b) 4 mg ml DNA. In (b) three size distributions are plotted, referring to 15 min (—) 1 d (- -) 6 d (-0-) from the preparation of the micellar solution (from Ousfuri et al, 2005) i and iii are empty micelles ii and iv are DNA-containing micelles.

In dynamic light scattering (DLS), or photon correlation spectroscopy, temporal fluctuations of the intensity of scattered light are measured and this is related to the dynamics of the solution. In dilute micellar solutions, DLS provides the z-average of the translational diffusion coefficient. The hydrodynamic radius, Rh, of the scattering particles can then be obtained from the Stokes-Einstein equation (eqn 1.2).The intensity fraction as a function of apparent hydrodynamic radius is shown for a triblock solution in Fig. 3.4. The peak with the smaller value of apparent hydrodynamic radius, RH.aPP corresponds to molecules and that at large / Hs,Pp to micelles. 

This chapter is concerned with experiments and theory for semidilute and concentrated block copolymer solutions.The focus is on the thermodynamics, i.e. the phase behaviour of both micellar solutions and non-micellar (e.g. swollen lamellar) phases. The chapter is organized very simply Section 4.2 contains a general account of gelation in block copolymer solutions. Section 4.3 is concerned with the solution phase behaviour of poly(oxyethylene)-containing diblocks and tri-blocks. The phase behaviour of styrenic block copolymers in selective solvents is discussed in Section 4.4. Section 4.5 is then concerned with theories for ordered block copolymer solutions, including both non-micellar phases in semidilute solutions and micellar gels. There has been little work on the dynamics of semidilute and concentrated block copolymer solutions, and this is reflected by the limited discussion of this subject in this chapter. 

It is now well established that formation of hard or stiff gels is the result of association of micelles into cubic phases. The notation hard gel follows Hvidt and co-workers (Almgren et al 1995 Hvidt et al. 1994) and refers to a micellar solution with a dynamic elastic shear modulus G > 103Pa. The correlation between the formation of a cubic phase and the onset of plastic flow (i.e. formation of a gel with a finite yield stress) was first made for PS-PI solutions in... 

One of the most important features of micellar solutions from a chemical point of view is their ability to solubilize otherwise water insoluble molecules. The liquid-like apolar micellar interior acts as a solvent for apolar substances. The solubilized molecules are of course also in dynamic equilibrium with the aqueous environment and other micelles. The kinetics of the solubilizate exchange has been studied by ESR methods using nitroxide radicals with a significant water solubility278. These studies indicated that the exchange process is rapid, but a detailed picture did not emerge. 

The structure and dynamics of inverse (water in oil) micellar solutions and microemulsions are of interest because of the unique properties of the water core, the view that such micelles may serve as models of enzyme active sites, and the potential use of inverse micelles as hosts for enzymatic reactions (80-82). 

An example drawn from Deitrick s work (Fig. 2) shows the chemical potential and the pressure of a Lennard-Jones fluid computed from molecular dynamics. The variance about the computed mean values is indicated in the figure by the small dots in the circles, which serve only to locate the dots. A test of the thermodynamic goodness of the molecular dynamics result is to compute the chemical potential from the simulated pressure by integrating the Gibbs-Duhem equation. The results of the test are also shown in Fig. 2. The point of the example is that accurate and affordable molecular simulations of thermodynamic, dynamic, and transport behavior of dense fluids can now be done. Currently, one can simulate realistic water, electrolytic solutions, and small polyatomic molecular fluids. Even some of the properties of micellar solutions and liquid crystals can be captured by idealized models [4, 5]. 

In Sections II and III, the crystal structure of rhodopsin is briefly reviewed and compared with the dynamic structure in micellar solutions and membranes as inferred from the biophysical methods mentioned above. A structural model of the cytoplasmic surface derived from solution NMR of peptides has been presented (Ifeagle et al., 1997 Katagadda et al., 2001), but this approach does not provide direct information on... 

The photolyses of dlbenzyl ketones in aqueous micellar solution have been shown to greatly enhance both geminate radical pair recombination and the enrichment of in recovered ketone compared to homogeneous solution. These observations have been attributed to the combined effects of the reduced dimensionality imposed by mlcelllzatlon and hyperflne induced intersystem crossing In the geminate radical pairs. This latter effect is the basis of Chemically Induced Dynamic Nuclear Polarization (CIDNP), a phenomenon which is well known in homogeneous solution. 

This review will focus on a variety of photochemical reactions which have been studied in micellar solutions, and will show how the micelle affects the outcome of these reactions. Photochemical reactions can be altered by solubilization into micellar solutions, such that the products or the relative yield of products can change relative to homogeneous solution. Furthermore, an increase or decrease in the dynamics or the efficiencies of photochemical reactions may also occur upon solubilization in micelles. 

This chapter deals almost exclusively with neat, or pure, diblock copolymer melts. Polymer blends are discussed in Chapter 9, micellar solutions in Chapter 12, and stabilized suspensions in Chapter 6. In the following, Section 13.2 briefly reviews the thermodynamics of block copolymers, and Section 13.3 describes the rheological properties and flow alignment of lamellae, cylinders, and sphere-forming mesophases of block copolymers. More thorough reviews of the thermodynamics and dynamics of block copolymers in the liquid state have been written by Bates and Fredrickson (1990 Fredrickson and Bates 1996). The processing of block copolymers and mechanical properties of the solid-state structures formed by them are covered in Folkes (1985). Biological applications are discussed in Alexandridis (1996). 

A micelle is a dynamic aggregation of any number of individual surfactant molecules, or monomers. Although the molecules are intertwined, they are in constant motion like those of a liquid. Thus, the interior of a micelle can be thought of as a separate phase and a micellar solution can be thought of as a microdispersion of that phase in water. If the micelle is considered to be a separate phase, it is then convenient to evaluate the solubilization capacity (k), in... 

The effect of alcohol concentration on the solubilization of brine has been studied in this laboratory (41). It was observed that there is an optimal alcohol concentration which can solubilize the maximum amount of brine and can also produce ultralow interfacial tension. The optimal alcohol concentration depends on the brine concentration of the system. The effect of different alcohols on the equilibrium properties and dynamics of micellar solutions has been studied by Zana (42). 

Koehler, R.D. Raghavan, S.R. Kaler, E.W. Microstructure and dynamics of wormlike micellar solutions formed by mixing cationic... 

Hirtzel, C.S. and Rajagopalan, R., in Micellar Solutions and Microemulsions Structure, Dynamics and Statistical Thermodynamics, Springer-Verlag, New York, 1990, chap. 7. 

Almgren M.A., Grieser F. and Thomas J.K., Dynamic and static aspects of solubilization of neutral arenes in ionic micellar solutions . J. American Chemistry Society., 121, 279-291. (1979)... 

Studies of diffusional phenomena have direct relevance to detergency processes. Experiments are reported which investigate the effects of changes in temperature on the dynamic phenomena, which occur when aqueous solutions of pure non-ionic surfactants contact hydrocarbons such as tetradecane and hexadecane. These oils can be considered to be models of non-polar soils such as lubricating oils. The dynamic contacting phenomena, at least immediately after contact, are representative of those which occur when a cleaner solution contacts an oily soil on a polymer surface. With Ci2E5 as non-ionic surfactant at a concentration of 1 wt.% in water, quite different phenomena were observed below, above, and well above the cloud point when tetradecane or hexadecane was carefully layered on top of the aqueous solution. Below the cloud point temperature of 31°C very slow solubilisation of oil into the one-phase micellar solution occurred. At 35°C, which is just... 

The dynamics of fluorescence emission of pyrene has been previously studied in homogeneous and micellar solutions using time-resolved fluorescence spectrometry (Demas,... 

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