Microviscosity probe size

As already discussed for molecular probes, the probe size plays a pivotal role for the analysis of polymer systems. Its size with respect to characteristic length scales of the investigated system determines the dynamics to be measured. For sufficiently large nanoparticles with diameters in the 100 nm range microviscosity can be... 

Microviscosity experiments using a molecular probe indicated a greater viscosity in micelles than in the bulk. The viscosity decreases rapidly up to go 10 and then decreases slowly as the micelle size increases. Additional studies using fluorescence probes revealed two different solvation rates inside the micelle. Zhong attributed the different solvation rates to water bound to the polar head group of AOT and bulk water inside the micelle (Zhong et al., 2002). This increased viscosity and extended solvation sphere limits the size of particles that can be synthesized using reverse micelles. 

When TRAMs are made on dispersed probes, tc will reflect the speed of rotation of the fluorophore [20,46,60,76], which can be related to the microviscosity of the medium. In the context of probing the structure of PMAA, the fluorescent dyes have been occluded in the hypercoiled conformation [46,60,76] allowing an estimate of the size of the rotating, solubilizing cluster to be derived from the resultant tc. Alternatively, if the fluorophore is covalently attached to the polyelectrolyte in the form of a label then, depending on its mode of attachment, information concerning motion of the chain ends [46,60,76], the backbone [26,88,112,113], and chain substituents [26,88] can be derived from tc. 

The diffusion studies described in the above sections pertain to water-continuous and bicontinuous microemulsions. Chen and Georges [34] were the first to study diffusion in oil-continuous microemulsions using steady-state microelectrode voltammetry. Ferrocene was used to probe diffusion in an SDS-dodecane-1-heptanol-water system. The diffusion coefficient of the hydrophobic probe indicated the microviscosity of the oil rather than the bulk viscosity of the microemulsion. Owlia et al. [36] reported diffusion coefficient measurements of water droplets in an Aerosol OT [AOT, bis(2-ethylhexyl)sulfosuccinate] microemulsion using a microelectrode. Water-soluble cobalt(II) corrin complex (vitamin Bi2r) was used in an oil-continuous microemulsion containing 0.2 M AOT, 4 M water buffered at pH 3, and isooctane. The apparent diffusion coefficient decreased with the probe concentration in accordance with Eq. (13) as shown in Fig. 6 [36]. The water droplet size was... 

The applications of the technique may be divided into two categories. In one the motion of the whole or part of the macromolecule may be measured, providing information concerning the size and diape of the species, internal flexibility, s -tion states, etc. In the other case the environment surrounding the macromolecule may be probed providing information concerning, for example, the microviscosity of lipid bilayers. Examples of both cases will be presented here. 

E. Madonia, P. L. San Biagio, M. U. Pahna, et al. Photon scattering as a probe of microviscosity and channel size in gels such as sickle haemoglobin. Nature, 302 (1983), 412 15. 

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