Polymer microviscosity

With further understanding how molecular rotors interact with their environment and with application-specific chemical modifications, a more widespread use of molecular rotors in biological and chemical studies can be expected. Ratiometric dyes and lifetime imaging will enable accurate viscosity measurements in cells where concentration gradients exist. The examination of polymerization dynamics benefits from the use of molecular rotors because of their real-time response rates. Presently, the reaction may force the reporters into specific areas of the polymer matrix, for example, into water pockets, but targeted molecular rotors that integrate with the matrix could prevent this behavior. With their relationship to free volume, the field of fluid dynamics can benefit from molecular rotors, because the applicability of viscosity models (DSE, Gierer-Wirtz, free volume, and WLF models) can be elucidated. Lastly, an important field of development is the surface-immobilization of molecular rotors, which promises new solid-state sensors for microviscosity [145]. 

Polymers dynamics of polymer chains microviscosity free volume orientation of chains in stretched samples miscibility phase separation diffusion of species through polymer networks end-to-end macrocyclization dynamics monitoring of polymerization degradation... 

We should first emphasize that viscosity is a macroscopic parameter which loses its physical meaning on a molecular scale. Therefore, the term microviscosity should be used with caution, and the term fluidity can be alternatively used to characterize, in a very general way, the effects of viscous drag and cohesion of the probed microenvironment (polymers, micelles, gels, lipid bilayers of vesicles or biological membranes, etc.). 

It implied that the motion of P P is suppressed by the microviscosity created by hydrophobic contracted polymer chain aggregation. On the other hand, the ryjda jj of PQ3P dissolved in PIPAAm-b-PBMA micelle solutions were markedly lowerthan those of PIPAAm solutions overthe entire temperature region owing to highly compact cores of aggregated PBMA chains. 

CARS-CS experiments have been reported in the low-concentration limit ((N) <<1) on freely diffusing submicron-sized polymer spheres of different chemical compositions using both the E-CARS [162, 163] and the polarization-resolved CARS [163] detection scheme for efficient nonresonant background suppression. These experiments have unambiguously demonstrated the vibrational selectivity of CARS-CS, the dependence of its ACF amplitude on the particle concentration, (N), the dependence of lateral diffusion time, Tp, on the sphere size, and the influence of the microviscosity on its Brownian motion. 

The sequence order and relative importance of elementary reactions in the process of chain oxidation depends markedly on temperature and microviscosity of a polymer medium. As some elementary reactions have different activation energies, the changes in temperature induce not only the changes in reaction rate but also in the composition of reaction products. 

Mader, K., Bittner, B., Li, Y., Wohlauf, W., and Kissel,T. (1998), Monitoring microviscosity and microacidity of the albumin microenvironment inside degrading microparticles from poly(lactide-coglycolide) (PLG) or ABA-triblock polymers containing hydropho-... 

The diffusion coefficients associated with translational motions when the radii of the diffusing radicals are not much larger than that of the solvent are expressed more accurately by D = kTI6nrr T (where r is the radius of the diffusing radical assuming a spherical shape and r (=yxr ) is the microviscosity. The value of /, the microfriction factor, can be calculated or taken equal to DsE/f exptb the ratio between the Stokes-Einstein diffusion coefficient (that considers van der Waals volumes, but not interstitial volumes) and the experimentally measured diffusion coefficient, Dexpti- As will be discussed later, these relationships appear to hold even in some polymer matrices. 

In addition probe interrogation of the matrix microviscosity has revealed an involvement of the polymer matrix in the photophysical behaviour of the triplet state of naphthyl chromophores and information germane to speculation over the existence of triplet excimers of naphthalene is discussed. 

The application of luminescence techniques to the study of macro-molecular behaviour has enjoyed an enormous growth rate in the last decade. The attraction of such methods lies in the degrees of both specificity and selectivity afforded to the investigator. Consequently the polymer may be doped or labelled at sufficiently low concentration levels of luminophore as to induce minimal perturbation of the system. Polarized photoselection techniques offer particular attraction in the study of relaxation phenomena both in solution and solid states. In principle, astute labelling can allow elucidation of the molecular mechanisms responsible for the macroscopic relaxations exhibited by the raacromolecular system. In addition, luminescent probes can address the microviscosity of their environment. 

Fluorescence studies of excimer formation in the probe give information regarding the microviscosity of the matrix. Unusually the probe seems to reflect the low frequency glass transition and caution must be applied in interpreting photophysical data obtained with such probes in terms of polymer relaxation mechanisms. 

Fluorescence spectroscopy has also been widely used for investigating microviscosity in carbohydrates,deformation of poly(vinyl alcohol),composition of rare-earth metal-containing polymers,crystallinity in polyolefins and... 

Figure 9. Concentration dependence of microviscosities and Brookfield viscosities of unneutralized type A polymer...

Figure 11, Concentration dependence of microviscosity and Brookfield viscosities of neutralized type B polymer...

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