Double Critical Phenomena in (Water + Polyacrylamides) Solutions
Autor(a) principal: | |
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Data de Publicação: | 2002 |
Outros Autores: | , , , , , , , |
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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Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
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7160 |
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 |
format |
article |
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 |
eu_rights_str_mv |
openAccess |
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) instname:Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informação instacron:RCAAP |
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Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informação |
instacron_str |
RCAAP |
institution |
RCAAP |
reponame_str |
Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
collection |
Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
repository.name.fl_str_mv |
Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) - Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informação |
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