Double Critical Phenomena in (Water + Polyacrylamides) Solutions

Detalhes bibliográficos
Autor(a) principal: Rebelo, L. P. N.
Data de Publicação: 2002
Outros Autores: Visak, Z. P., Sousa, H. C. de, Szydlowski, J., Azevedo, R. Gomes de, Ramos, A. M., Najdanovic-Visak, V., Ponte, M. Nunes da, Klein, J.
Tipo de documento: Artigo
Idioma: eng
Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
Texto Completo: http://hdl.handle.net/10316/10447
https://doi.org/10.1021/ma011533a
Resumo: 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.
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spelling Double Critical Phenomena in (Water + Polyacrylamides) SolutionsAqueous 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.American Chemical Society2002-02-26info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/articlehttp://hdl.handle.net/10316/10447http://hdl.handle.net/10316/10447https://doi.org/10.1021/ma011533aengMacromolecules. 35:5 (2002) 1887-18950024-9297Rebelo, L. P. N.Visak, Z. P.Sousa, H. C. deSzydlowski, J.Azevedo, R. Gomes deRamos, A. M.Najdanovic-Visak, V.Ponte, M. Nunes daKlein, J.info:eu-repo/semantics/openAccessreponame:Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)instname:Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãoinstacron:RCAAP2021-10-13T08:13:39Zoai:estudogeral.uc.pt:10316/10447Portal AgregadorONGhttps://www.rcaap.pt/oai/openaireopendoar:71602024-03-19T20:59:19.636077Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) - Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãofalse
dc.title.none.fl_str_mv Double Critical Phenomena in (Water + Polyacrylamides) Solutions
title Double Critical Phenomena in (Water + Polyacrylamides) Solutions
spellingShingle Double Critical Phenomena in (Water + Polyacrylamides) Solutions
Rebelo, L. P. N.
title_short Double Critical Phenomena in (Water + Polyacrylamides) Solutions
title_full Double Critical Phenomena in (Water + Polyacrylamides) Solutions
title_fullStr Double Critical Phenomena in (Water + Polyacrylamides) Solutions
title_full_unstemmed Double Critical Phenomena in (Water + Polyacrylamides) Solutions
title_sort Double Critical Phenomena in (Water + Polyacrylamides) Solutions
author Rebelo, L. P. N.
author_facet Rebelo, L. P. N.
Visak, Z. P.
Sousa, H. C. de
Szydlowski, J.
Azevedo, R. Gomes de
Ramos, A. M.
Najdanovic-Visak, V.
Ponte, M. Nunes da
Klein, J.
author_role author
author2 Visak, Z. P.
Sousa, H. C. de
Szydlowski, J.
Azevedo, R. Gomes de
Ramos, A. M.
Najdanovic-Visak, V.
Ponte, M. Nunes da
Klein, J.
author2_role author
author
author
author
author
author
author
author
dc.contributor.author.fl_str_mv Rebelo, L. P. N.
Visak, Z. P.
Sousa, H. C. de
Szydlowski, J.
Azevedo, R. Gomes de
Ramos, A. M.
Najdanovic-Visak, V.
Ponte, M. Nunes da
Klein, J.
description 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.
publishDate 2002
dc.date.none.fl_str_mv 2002-02-26
dc.type.status.fl_str_mv info:eu-repo/semantics/publishedVersion
dc.type.driver.fl_str_mv info:eu-repo/semantics/article
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status_str publishedVersion
dc.identifier.uri.fl_str_mv http://hdl.handle.net/10316/10447
http://hdl.handle.net/10316/10447
https://doi.org/10.1021/ma011533a
url http://hdl.handle.net/10316/10447
https://doi.org/10.1021/ma011533a
dc.language.iso.fl_str_mv eng
language eng
dc.relation.none.fl_str_mv Macromolecules. 35:5 (2002) 1887-1895
0024-9297
dc.rights.driver.fl_str_mv info:eu-repo/semantics/openAccess
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dc.publisher.none.fl_str_mv American Chemical Society
publisher.none.fl_str_mv American Chemical Society
dc.source.none.fl_str_mv reponame:Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
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