Experimental determination of self-diffusivities through a polymer network for single components in a mixture (original) (raw)
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Journal of Colloid and Interface Science, 1997
This paper presents diffusion studies of two ''model'' associative at relatively high shear rates. polymers (hydrophobically end-capped poly(ethylene oxide)) (AP) Numerous investigations with various techniques have differing in end-group length, a factor of great significance in the been carried out on AP systems to obtain information about transport rate of APs in aqueous solution. An increase in endthe association mechanism, aggregate size, and solution group length was found to reduce the self-diffusion coefficient. As structure (1-13). It is now generally accepted that the rheoexpected, it also greatly influences the onset of aggregation, as monilogical characteristics of APs originate from assembly of tored by static fluorescence, and the phase behavior. The longer the their hydrophobic end groups into micelle-like aggregates hydrocarbon end group, the lower the critical aggregation concenat low concentrations and a gradual formation of network tration and the lower the cloud point of the polymer solution; i.e., the structures at higher concentrations. For aqueous solutions of lower critical solution temperature decreases. In line with oscillatory relaxation results obtained by T. Annable et al. (J. Rheol. (N.Y.) 37, sufficiently low-molecular-weight APs (M W õ 6000) at high 695 (1993)), the data of the present paper show that AP transport in concentrations this network structure can also become highly equimolar mixtures of the two APs is characterized by two-compoordered into a cubic array (10-11). nent behavior over a wide range of semidilute polymer concentra-During the AP aggregation process the transport mechations. The diffusion of the polymer is therefore judged to be molecunism gradually changes from overall cluster diffusion to diflarly determined in this concentration region; i.e., the polymers fusion of individual AP molecules. This action has been diffuse independently within a network structure. The dynamic found to result in a distribution of self-diffusion coefficients hydrophobic domains, keeping the network together, are considered (D i) that changes with polymer content (7-9, 12-13). At to be mixed, containing end groups of both lengths. We also find that low polymer concentrations there is a significant distribution the cloud point temperature of these mixed solutions are situated of D i due to a broad cluster size distribution. between those of the single component solutions following a two-The aim of the present study is primarily to explore the state relation. ᭧ 1997 Academic Press influence of the hydrocarbon end group on the overall poly-Key Words: associative polymer (AP); associative thickener mer dynamics, i.e., the self-diffusion coefficient and its dis-(AT); end-group length; hydrocarbon chain length; cloud point tribution. Previous studies show that the transport rate in temperature (CPT); NMR; self-diffusion; static fluorescence; cac; activation energy; molecular transport. aqueous solution of relatively polydisperse commercial type APs, containing isocyanate groups, is significantly affected by the length of the hydrocarbon end group (8-9). This study complements previous work by using several methods 137
Dependence of the solvent diffusion coefficient on concentration in polymer solutions
Macromolecules, 1993
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Membranes
In many applications of hydrated, dense polymer membranes—including fuel cells, desalination, molecular separations, electrolyzers, and solar fuels devices—the membrane is challenged with aqueous streams that contain multiple solutes. The presence of multiple solutes presents a complex process because each solute can have different interactions with the polymer membrane and with other solutes, which collectively determine the transport behavior and separation performance that is observed. It is critical to understand the theoretical framework behind and experimental considerations for understanding how the presence of multiple solutes impacts diffusion, and thereby, the design of membranes. Here, we review models for multicomponent diffusion in the context of the solution-diffusion framework and the associated experiments for characterizing multicomponent transport using diffusion cells. Notably, multicomponent effects are typically not considered when discussing or investigating tr...
A PFG-NMR Study of Restricted Diffusion in Heterogeneous Polymer Particles
Journal of Colloid and Interface Science, 2001
The diffusion resistance to monomers during heterogeneous polymerization of polyolefin particles may have a significant effect on the observed activity. This diffusivity is, in general, unknown. To gain more information on this diffusion resistance in such systems, PFG-NMR has been used to measure the diffusion of organic solvents in various systems of porous polymer particles. In such systems the complex morphology and geometry demands careful analysis of the PFG-NMR attenuation curve. In this study, effects from restricted diffusion, domains having different diffusivity, and internal magnetic field gradients are expected. Thus, the obtained diffusivities have to be considered carefully, and a way to analyze the data taking these effects into account is presented.
Diffusion Coefficient Matrix in Nonionic Polymer−Solvent Mixtures
Journal of Physical Chemistry B - J PHYS CHEM B, 2001
Recent predictive equations for evaluating the value of diffusion coefficients, developed for two hard spheresolvent systems, have been extended to n-hard-sphere-solvent systems. This model has been used to predict the diffusion behavior of nonionic polymer-solvent mixtures as a first-order function of volume fraction from the knowledge of the distribution function. Hence, the entire diffusion matrix for polydisperse systems, which include both main-and cross-term diffusion coefficients, has been built up for the first time. The main-terms diffusion coefficients D ii are mostly affected by the variation in viscosity. The magnitude of the cross-term diffusion coefficients D ij is strictly related to the abundance and diffusivity of solute i and to the molecular volume corresponding to solute j. The predicted diffusion coefficients have been used to calculate the apparent, average diffusion coefficients, which are compared with the experimental values measured by the Gouy interferometry method in the case of the poly(ethylene glycol) homologous series. The agreement between the calculated and experimental Gouy parameters is good. The cross-term diffusion coefficients are found to be significant in the calculation of the apparent diffusion coefficient for a polydisperse solute. Some comments on the study of ternary systems containing a polydisperse solute are done.