Double critical phenomena in (water + polyacrylamides) solutions

L.P.N. Rebelo, Z.P. Visak, H.C. De Sousa, J. Szydlowski, R. Gomes De Azevedo, A.M. Ramos, V. Najdanovic-Visak, M.N. Da Ponte, J. Klein

Research output: Contribution to journalArticle

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.
Original languageEnglish
Pages (from-to)1887-1895
JournalMacromolecules
Volume35
Issue number5
DOIs
Publication statusPublished - 26 Jan 2002

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Polyacrylates
Water
Copolymers
Chain length
Temperature
Derivatives
Pressure effects
Sorbitol
Isotopes
Light scattering
Phase diagrams
Enthalpy
Polymers
Substitution reactions
Molecular weight
polyacrylamide
Lasers
Chemical analysis
poly-N-isopropylacrylamide

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Rebelo, L. P. N., Visak, Z. P., De Sousa, H. C., Szydlowski, J., Gomes De Azevedo, R., Ramos, A. M., ... Klein, J. (2002). Double critical phenomena in (water + polyacrylamides) solutions. Macromolecules, 35(5), 1887-1895. https://doi.org/10.1021/ma011533a
Rebelo, L.P.N. ; Visak, Z.P. ; De Sousa, H.C. ; Szydlowski, J. ; Gomes De Azevedo, R. ; Ramos, A.M. ; Najdanovic-Visak, V. ; Da Ponte, M.N. ; Klein, J. / Double critical phenomena in (water + polyacrylamides) solutions. In: Macromolecules. 2002 ; Vol. 35, No. 5. pp. 1887-1895.
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Rebelo, LPN, Visak, ZP, De Sousa, HC, Szydlowski, J, Gomes De Azevedo, R, Ramos, AM, Najdanovic-Visak, V, Da Ponte, MN & Klein, J 2002, 'Double critical phenomena in (water + polyacrylamides) solutions', Macromolecules, vol. 35, no. 5, pp. 1887-1895. https://doi.org/10.1021/ma011533a

Double critical phenomena in (water + polyacrylamides) solutions. / Rebelo, L.P.N.; Visak, Z.P.; De Sousa, H.C.; Szydlowski, J.; Gomes De Azevedo, R.; Ramos, A.M.; Najdanovic-Visak, V.; Da Ponte, M.N.; Klein, J.

In: Macromolecules, Vol. 35, No. 5, 26.01.2002, p. 1887-1895.

Research output: Contribution to journalArticle

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T1 - Double critical phenomena in (water + polyacrylamides) solutions

AU - Rebelo, L.P.N.

AU - Visak, Z.P.

AU - De Sousa, H.C.

AU - Szydlowski, J.

AU - Gomes De Azevedo, R.

AU - Ramos, A.M.

AU - Najdanovic-Visak, V.

AU - Da Ponte, M.N.

AU - Klein, J.

PY - 2002/1/26

Y1 - 2002/1/26

N2 - 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.

AB - 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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Rebelo LPN, Visak ZP, De Sousa HC, Szydlowski J, Gomes De Azevedo R, Ramos AM et al. Double critical phenomena in (water + polyacrylamides) solutions. Macromolecules. 2002 Jan 26;35(5):1887-1895. https://doi.org/10.1021/ma011533a