Please use this identifier to cite or link to this item:
https://hdl.handle.net/10316/10447
DC Field | Value | Language |
---|---|---|
dc.contributor.author | Rebelo, L. P. N. | - |
dc.contributor.author | Visak, Z. P. | - |
dc.contributor.author | Sousa, H. C. de | - |
dc.contributor.author | Szydlowski, J. | - |
dc.contributor.author | Azevedo, R. Gomes de | - |
dc.contributor.author | Ramos, A. M. | - |
dc.contributor.author | Najdanovic-Visak, V. | - |
dc.contributor.author | Ponte, M. Nunes da | - |
dc.contributor.author | Klein, J. | - |
dc.date.accessioned | 2009-07-02T08:24:39Z | - |
dc.date.available | 2009-07-02T08:24:39Z | - |
dc.date.issued | 2002-02-26 | - |
dc.identifier.citation | Macromolecules. 35:5 (2002) 1887-1895 | en_US |
dc.identifier.issn | 0024-9297 | - |
dc.identifier.uri | https://hdl.handle.net/10316/10447 | - |
dc.description.abstract | Aqueous solutions of a copolymer derivative of a polyacrylamide showed very interesting behavior, that in which the system evolves from one kind of double criticality (pressure−hypercritical point) to another (temperature−hypercritical point) as polymer molecular weight decreases. While in the neighboring region of the former point one expects a change from contraction to expansion upon mixing with increasing pressure; in the latter, mixing should be accompanied by a change in the sign of the excess enthalpy as temperature increases. L−L equilibria studies were performed in a wide range of (T, p) experimental conditions (300 < T/K < 460, 0 < p/bar < 700). Poly(N-isopropylacrylamide), usually called PNIPAAM, and its copolymer derivative poly(N-isopropylacrylamide/1-deoxy-1-methacrylamido-d-glucitol), herein referred to as CP, were investigated for several chain lengths and compositions. An He/Ne laser light scattering technique was used for the determination of cloud-point (T, p, x) conditions. The experimental results were used to assist in the determination of computed values at temperatures beyond experimental accessibility, which are obtained by the application of a modified Flory−Huggins model. The model also estimates the excess properties of these solutions. Because of the intrinsic self-associating nature of these systems, all studied solutions show a lower critical solution temperature (LCST). Both modeling results and H/D isotope substitution effects suggest also the existence of upper critical solution temperatures (UCST) and therefore closed-loop-type phase diagrams. However, these upper-temperature branches are experimentally inaccessible. Pressure effects are particularly interesting. For a low-MW CP, experimental data display a tendency toward a reentrant T−p locus, which supports the conjecture that these systems are inherently of the closed-loop type. In the cases of PNIPAAMs and high-MW CPs, the T−p isopleths show extrema. The copolymer aqueous solutions under study in this work model a single chemical system where pressure−hypercritical behavior evolves to a temperature−hypercritical one as the chain length decreases. | en_US |
dc.language.iso | eng | en_US |
dc.publisher | American Chemical Society | en_US |
dc.rights | openAccess | eng |
dc.title | Double Critical Phenomena in (Water + Polyacrylamides) Solutions | en_US |
dc.type | article | en_US |
dc.identifier.doi | 10.1021/ma011533a | - |
item.openairecristype | http://purl.org/coar/resource_type/c_18cf | - |
item.grantfulltext | open | - |
item.openairetype | article | - |
item.languageiso639-1 | en | - |
item.fulltext | Com Texto completo | - |
item.cerifentitytype | Publications | - |
crisitem.author.researchunit | CIEPQPF – Chemical Process Engineering and Forest Products Research Centre | - |
crisitem.author.parentresearchunit | Faculty of Sciences and Technology | - |
crisitem.author.orcid | 0000-0002-2629-7805 | - |
Appears in Collections: | FCTUC Eng.Química - Artigos em Revistas Internacionais |
Files in This Item:
File | Description | Size | Format | |
---|---|---|---|---|
Double Critical Phenomena in (Water + Polyacrylamides).pdf | 135.91 kB | Adobe PDF | View/Open |
SCOPUSTM
Citations
63
checked on Aug 26, 2024
WEB OF SCIENCETM
Citations
1
57
checked on Aug 2, 2024
Page view(s) 50
496
checked on Aug 27, 2024
Download(s)
391
checked on Aug 27, 2024
Google ScholarTM
Check
Altmetric
Altmetric
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.