Phase transitions in the system poly(N-isopropylacrylamide)/water and swelling behaviour of the corresponding networks

Afroze, Fatema; Nies, Erik; Berghmans, Hugo

doi:10.1016/s0022-2860(00)00559-7

Cited by 314 publications

(454 citation statements)

References 18 publications

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“…Its physical origin can be traced back to the particular thermodynamic properties of PNIPAM/water mixtures. From their experimental study of the phase diagram of PNIPAM in solution in water, Afroze et al [37] have shown that the measured coexistence curve could be reproduced semi-quantitatively by modifying the usual Flory-Huggins free energy of mixing in order to account for a concentration dependence of the interaction parameter, χ ef f (φ), which characterizes the difference of interaction energies in the mixture. Such a φ-dependence can be attributed to monomer/solvent hy-drogen bonds [38].…”

Section: Resultsmentioning

confidence: 99%

“…This quantitative discrepancy is likely to result from the fact that SCF theory uses the empirical form of χ ef f determined by Afroze [12,37], which accounts only semi-quantitatively for the PNIPAM/water phase diagram. Such quantitative differences between theory and experiments call for further studies of this phase diagram in order to determine more accurately the φ-dependence of χ ef f , or, alternatively, for the use of data obtained on brushes, such as those presented here, to deduce χ ef f (φ) from confrontation with theory.…”

Section: Resultsmentioning

confidence: 99%

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The Conformation of Thermoresponsive Polymer Brushes Probed by Optical Reflectivity

2016

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We describe a microscope-based optical setup that allows us to perform space-and time-resolved measurements of the spectral reflectance of transparent substrates coated with ultrathin films. This technique is applied to investigate the behavior in water of thermosensitive polymer brushes made of poly(N-isopropylacrylamide) grafted on glass. We show that spectral reflectance measurements yield quantitative information about the conformation and axial structure of the brushes as a function of temperature. We study how molecular parameters (grafting density, chain length) affect the hydration state of a brush, and provide one of the few experimental evidence for the occurrence of vertical phase separation in the vicinity of the lower critical solution temperature of the polymer. The origin of the hysteretic behavior of poly(N-isopropylacrylamide) brushes upon cycling the temperature is also clarified. We thus demonstrate that our optical technique allows for in-depth characterization of stimuli-responsive polymer layers, which is crucial for the rational design of smart polymer coatings in actuation, gating or sensing applications.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

The Conformation of Thermoresponsive Polymer Brushes Probed by Optical Reflectivity

2016

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“…It was previously demonstrated that the LCST transition of copolymers of 2-ethyl-2-oxazoline (EtOx) and 2-n-propyl-2-oxazoline (PropOx) is almost as robust as the LCST transition of the most studied polymer poly(N-isopropylacrylamide) with regard to concentration and pH dependence while the reversibility of the poly(2-oxazoline) phase transition is even better [30]. It should be noted however that PNIPAM exhibits type II LCST behavior [31] and PEtOx exhibits type I LCST behavior [32], resulting in an increased molar mass dependence for the LCST of PEtOx. The thermal transition of poly(2-i-propyl-2-oxazoline) (i-PropOx) is reversible when cycled, but upon prolonged heating above the phase transition temperature crystallization occurs causing irreversible precipitation since the melting temperature of the crystals (almost 200 °C ) is far beyond the boiling point of water [33,34].…”

Section: Introductionmentioning

confidence: 99%

Temperature Induced Solubility Transitions of Various Poly(2-oxazoline)s in Ethanol-Water Solvent Mixtures

et al. 2010

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Abstract:The solution behavior of a series of poly(2-oxazoline)s with different side chains, namely methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, heptyl, octyl, nonyl, phenyl and benzyl, are reported in ethanol-water solvent mixtures based on turbidimetry investigations. The LCST transitions of poly(2-oxazoline)s with propyl side chains and the UCST transitions of the poly(2-oxazoline)s with more hydrophobic side chains are discussed in relation to the ethanol-water solvent composition and structure. The poly(2-alkyl-2-oxazoline)s with side chains longer than propyl only dissolved during the first heating run, which is discussed and correlated to the melting transition of the polymers.

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“…Also,  is the interaction parameter of the network which is a function of temperature and the polymer volume fraction for the temperature sensitive PNIPAM hydrogel. In addition, 0 A , 0 B , 1 A and 1 B are material parameters adopted for the experiments reported by Afroze et al [37]. Using swelling constraint, equation (6), the total free energy density is:…”

Section: Model Descriptionmentioning

confidence: 99%

Study of swelling behavior of temperature sensitive hydrogels considering inextensibility of network

Mazaheri

2018

Scientia Iranica

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In this work, the equilibrium swelling of temperature sensitive hydrogel networks is studied with an emphasis on the chain locking of the network. Using Gent model for elastic part of free energy and modifying the mixing part of the free energy, a continuous model is developed which consider inextensibility of the network chains and has a good agreement with the experimental data particularly for smaller values of crosslinking density of the network and larger values of the swelling ratio. After validating the modified model, it is employed for the studying the inhomogeneous swelling of a spherical shell on a hard core both analytically and numerically.The analytical solution is used for validating the numerical method. Finally, the inhomogeneous swelling of a bilayer beam with an active temperature sensitive hydrogel is investigated and the results are presented. The obtained results show the importance level of considering the chain locking in swelling of the network in the applied problems.

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Phase transitions in the system poly(N-isopropylacrylamide)/water and swelling behaviour of the corresponding networks

Cited by 314 publications

References 18 publications

The Conformation of Thermoresponsive Polymer Brushes Probed by Optical Reflectivity

The Conformation of Thermoresponsive Polymer Brushes Probed by Optical Reflectivity

Temperature Induced Solubility Transitions of Various Poly(2-oxazoline)s in Ethanol-Water Solvent Mixtures

Study of swelling behavior of temperature sensitive hydrogels considering inextensibility of network

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