Micelles molecular motion

In liquid crystals or LC-glasses one looks for orientational order and an absence of three-dimensional, long-range, positional order. In liquid crystals, large scale molecular motion is possible. In LC-glasses the molecules are fixed in position. The orientational order can be molecular or supermolecular. If the order rests with a supermolecular structure, as in soap micelles and certain microphase separated block copolymers, the molecular motion and geometry have only an indirect influence on the overall structure of the material. 

Like the triplet-state lifetimes of the photosensitizer, the bimolecular quenching constants with oxygen are also affected by the presence of micelles. The experimentally determined quenching constants for the para-substituted TPPs in micelles (5.9 X lO M s ) were smaller than in cyclohexane (1. 9 X 10 M s ) despite the longer triplet-state lifetimes in micelles. A possible reason for the smaller rate constants in micelles is restricted molecular motion of the porphyrins within the micelles due to porphyrin-micelle interaction [7]. This suggestion agrees with NMR relaxation measurements, which clearly reveal that the porphyrins in micelles are less mobile than in organic... 

These have thus far included studies of the following systems proteins, microemulsions, colloids, copolymers, micelles, liposomes, fibrinogen, internal molecular motions, liquid interfaces, fatty acids, viruses, bacteria, vesicles, viscosity, lipids, motile cells, enzymes, lipoprotein, polyelectrolytes, spores, liquid crystals, glass transmissions, sols, microgels, soot, blood plasma, nanoparticles, swelling latex, gene delivery, and intravenous fat emulsions. 

In comparison with the polymer bound sensitizers, the i micelle does not emit excimer emission. Furthermore, LCV is incorporated in micelle so that the loss of molecular motion in molecular aggregate state is not a serious drawback. However, side reaction of anthracene presumably photooxygenation at the 9, 10 position of anthracene is accelerated in micellar system. Results are summarized in Table 3. 

Chemical-shift measurement has proven to be useful in determining cmc, surfactant chain conformation, and the extent of water penetration into micelle. Menger [39] found that as many as three methylene groups of an alkyl chain near the head group are hydrated in a micelle. Relaxation times are related to translational and rotational molecular motions. These also can give us informa-... 

Lindman and co-workers [21-23] demonstrated that the organisation and structure of microemulsions can be elucidated from self-diffusion measurements of all the components (using pulse-gradient or spin-echo NMR techniques). Within a micelle, the molecular motion of the hydrocarbon tails (translational, reorientation and chain flexibility) is almost as rapid as in a liquid hydrocarbon. In a reverse micelle, water molecules and counter ions are also highly mobile. 

Increasing temperature for ionic surfactants usually opposes micellization due to enhanced molecular motion that reduces p. For oxyethylene-containing nonionics, temperature causes the association number to increase up to the cloud point, when phase separation occurs because polyoxyethylene becomes insoluble in water. The cloud point decreases with decreasing oxyethylene (E) chain length indeed, surfactants of the type CmE (Section 4.2) with n < 4 are insoluble in water and so the system is always phase separated. As the association number increases with temperature, the solvent quality for oxyethylene becomes worse, causing the corona to shrink. A compensation between the increase in p and a decrease in corona size results in an approximately constant overall micellar radius. 

DOPPN 125 ph.>25 Can be used to trap radicals in micelles. " Very poorly soluble in water and gives very broad EPR lines due to slow molecular motion. " ... 

Recent studies indicate that like the surfactant monomers themselves, the solubilized molecules are not rigidly fixed in the micelle but have a freedom of motion which is dependent to some extent on the solubilization site. In fact, as discussed in Chapter 3, solubilized probes are used as indicators of the fluidity of their micellar micro-environment. In particular, a decrease in the polarization of the fluorescent radiation from fluorescent probes located in the micellar core is indicative of the molecular motion of these probes. Similarly, tumbling of solubilized nitroxide probes proceeds at a more rapid rate than can be accounted for by simple rotation of the micelle itself indicating that the solubilized probe undergoes dynamic motion within the micelle. Such motion produces a characteristic hyperfine pattern on e.s.r. spectra. 

Mesoscale simulations model a material as a collection of units, called beads. Each bead might represent a substructure, molecule, monomer, micelle, micro-crystalline domain, solid particle, or an arbitrary region of a fluid. Multiple beads might be connected, typically by a harmonic potential, in order to model a polymer. A simulation is then conducted in which there is an interaction potential between beads and sometimes dynamical equations of motion. This is very hard to do with extremely large molecular dynamics calculations because they would have to be very accurate to correctly reflect the small free energy differences between microstates. There are algorithms for determining an appropriate bead size from molecular dynamics and Monte Carlo simulations. 

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