Dynamic/compositional heterogeneity

Creep Rate Spectroscopy for a Discrete Analysis of the Glass Transition Anomalies and Dynamic/Compositional Heterogeneity in Complex Polymer... 

Estimation of Copolymer Composition Distribution. A copolymer is normally polydisperse not only in molar mass but also in chain composition. A combination of static and dynamic LLS can be used to estimate its composition distribution. Consider a copolymer sample consisting of monomers A and B and suppose that the copolymer species i is characterized by the molar mass M and the weight fraction wpSMi)). Assume that for a given M, there is no further composition heterogeneity. For a given copolymer in solvents 1 and 2, eq (12) applies (43,44)... 

Creep rate spectroscopy study of the PCN-PTMG hybrid networks [148,151] demonstrated most distinctly the complicated, heterogeneous nature of glass transition dynamics in these systems providing the detailed information on this problem. Not only the dynamic heterogeneity (Tg plurality) but also the compositional heterogeneity and dynamics/nanostructure interrelationships were found for these amorphous networks. 

In the new hierarchical structures of liquid crystal composite systems, this dynamic heterogeneity has a close relationship with the structure and dynamics of the composite. Even in the well-known micro-phase-separated structure of surfactants and in the mesoscale structures of polymer solutions, polymer blends, gels, and colloidal suspensions, molecular aggregates and polymer chain networks have a characteristic timescales, which are completely different from the surrounding medium, and thus static and dynamic spatial heterogeneity appears. 

Dispersion Characteristics The chief characteristics of gas-in-liquid dispersions, like those of hquid-in-gas suspensions, are heterogeneity and instabihty. The composition and structure of an unstable dispersion must be obsei ved in the dynamic situation by looking at the mixture, with or without the aid of optical devices, or by photographing it, preferably in nominal steady state photographs usually are required for quantitative treatment. Stable foams may be examined after the fact of their creation if they are sufficiently robust or if an immobilizing technique such as freezing is employed [Chang et al., Ind. Eng Chem., 48, 2035 (1956)]. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

Early studies of ET dynamics at externally biased interfaces were based on conventional cyclic voltammetry employing four-electrode potentiostats [62,67 70,79]. The formal pseudo-first-order electron-transfer rate constants [ket(cms )] were measured on the basis of the Nicholson method [99] and convolution potential sweep voltammetry [79,100] in the presence of an excess of one of the reactant species. The constant composition approximation allows expression of the ET rate constant with the same units as in heterogeneous reaction on solid electrodes. However, any comparison with the expression described in Section II.B requires the transformation to bimolecular units, i.e., M cms . Values of of the order of 1-2 x lO cms (0.05 to O.IM cms ) were reported for Fe(CN)g in the aqueous phase and the redox species Lu(PC)2, Sn(PC)2, TCNQ, and RuTPP(Py)2 in DCE [62,70]. Despite the fact that large potential perturbations across the interface introduce interferences in kinetic analysis [101], these early estimations allowed some preliminary comparisons to established ET models in heterogeneous media. 

The dynamic mechanical behavior of most homogeneous and heterogeneous solid and molten polymeric systems or composite formulations can be determined by DMA. These polymeric systems may contain chemical additives, including fillers, reinforcements, stabilizers, plasticizers, flame retardants, impact modifiers, processing aids, and other chemical additives, which are added to the polymeric system to impart specific functional properties and which could affect the process-ability and performance. 

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