NMR Self-Diffusion of Associative Polymers in Aqueous Solution: The Influence of the Hydrocarbon End-Chain Length on the Polymer Transport Dynamics in Single- and Two-Component Mixtures
✍ Scribed by S. Abrahmsén-Alami; P. Stilbs
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 144 KB
- Volume
- 189
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
tonian behavior at low shear rates with shear thinning only 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 of the polymer and when the collective cluster diffusion