Contrary Hydration Behavior of <i>N</i>-Isopropylacrylamide to its Polymer, P(NIPAm), with a Lower Critical Solution Temperature

Ono, Yousuke; Shikata, Toshiyuki

doi:10.1021/jp068954k

Cited by 110 publications

(193 citation statements)

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“…29,30 They cannot be observed in the selected frequency range as in characteristic relaxation processes. However, conductivity related phenomena like the drift motion of charge carriers (DC-conductivity) and/or interfacial polarization effects such as Maxwell-Wagner-Sillars (MWS) polarization can be detected.…”

Section: Resultsmentioning

confidence: 99%

“…It allows investigations of the molecular structure by taking the molecular mobility and/or the conductivity as a probe. 27 Ono and Shikata 28,29 applied dielectric spectroscopy at high frequencies (1.6 Â 10 6 Hz to 1.6 Â 10 11 Hz) in order to study the hydration and molecular dynamics of linear pNIPAM in aqueous solutions at temperatures between 6 C and 39 C. The temperature dependence of the (de)hydration behaviour of the monomer NIPAM and the polymer pNIPAM was investigated by analyzing the dynamics of water molecules hydrated to the solute. The relaxation processes of linear pNIPAM and solvent molecules as a function of polymer concentration and type of solvent have been studied by Nakano et al 30 Dielectric spectroscopy was applied in a frequency range from 4 Â 10 4 Hz to 2 Â 10 10 Hz at a temperature of 25 C. Two relaxation processes could be detected due to the fluctuations of the polymer segments (MHz range) and the solvent molecules (GHz range).…”

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confidence: 99%

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Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

2012

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

2012

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“…The simulated network shown schematically in Figure 9a and atomistically in Figure 9b is similar to that identified in the experimental studies of Ono and Shikata. 25 Note that this network between two adjacent monomers comprises five water molecules. which is in good agreement with the experimentally reported value in ref 25. In addition to the conformation shown in Figure 9, we also observe another conformation of water-polymer network (shown in Figure 10).…”

Section: Resultsmentioning

confidence: 99%

Role of Solvation Dynamics and Local Ordering of Water in Inducing Conformational Transitions in Poly(N-isopropylacrylamide) Oligomers through the LCST

et al. 2012

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Conformational transitions in thermo-sensitive polymers are critical in determining their functional properties. The atomistic origin of polymer collapse at the lower critical solution temperature (LCST) remains a fundamental and challenging problem in polymer science. Here, molecular dynamics simulations are used to establish the role of solvation dynamics and local ordering of water in inducing conformational transitions in isotactic-rich poly(N-isopropylacrylamide) (PNIPAM) oligomers when the temperature is changed through the LCST. Simulated atomic trajectories are used to identify stable conformations of the water-molecule network in the vicinity of polymer segments, as a function of the polymer chain length. The dynamics of the conformational evolution of the polymer chain within its surrounding water molecules is evaluated using various structural and dynamical correlation functions. Around the polymer, water forms cage-like structures with hydrogen bonds. Such structures form at temperatures both below and above the LCST. The structures formed at temperatures above LCST, however, are significantly different from those formed below LCST. Short oligomers consisting of 3, 5, and 10 monomer units (3-, 5-, and 10-mer), are characterized by significantly higher hydration level (water per monomer ~ 16). Increasing the temperature from 278 to 310 K does not perturb the structure of water around the short oligomers. In the case of 3-, 5-, and 10-mer, a distinct coil-to-globule transition was not observed when the temperature was raised from 278 to 310 K. For a PNIPAM polymer chain consisting of 30 monomeric units (30-mer), however, there exist significantly different conformations corresponding to two distinct temperature regimes. Below LCST, the water molecules in the first hydration layer (~12) around hydrophilic groups arrange themselves in a specific ordered manner by forming a hydrogen-bonded network with the polymer, resulting in a solvated polymer acting as hydrophilic. Above LCST, this arrangement of water is no longer stable, and the hydrophobic interactions become dominant, which contributes to the collapse of the polymer. Thus, this study provides atomic-scale insights into the role of solvation dynamics in inducing coil-to-globule phase transitions through the LCST for thermo-sensitive polymers like PNIPAM.

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Section: ■ Introductionmentioning

confidence: 92%

“…6 for amide groups of low mass compounds. 13 The positive n H values for these compounds definitely reveal that these polar groups with DN values higher than 18 are hydrophilic because of the formation of hydrogen bonds between the polar groups and water molecules.There exist other types of water-soluble compounds possessing highly polar groups with dipole moments greater than 3.0 D. Although nitro compounds, such as nitro methane (MeNO 2 ) and nitro ethane (EtNO 2 ) bearing a nitro group (NO 2 ) with the large dipole moment of 3.4 D, but a low DN value of 3−4, are water-soluble, 1-nitropropane (PrNO 2 ) only slightly larger than EtNO 2 possesses a low water solubility of 0.17 M. 14 Very recently, dielectric spectroscopic measurements have revealed that the hydration number of the NO 2 group is n H = 0. 14 Then, the relatively high water solubility of MeNO 2 and EtNO 2 are not caused by the hydration effect of the NO 2 group.…”

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Dangling OH Vibrations of Water Molecules in Aqueous Solutions of Aprotic Polar Compounds Observed in the Near-Infrared Regime

Sagawa

Shikata

2015

J. Phys. Chem. B

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Near-infrared (NIR) absorption spectrum measurements over a frequency range from 4000 to 12000 cm(-1) were employed to investigate the effects of the presence of solute compounds to vibrational modes of water molecules in aqueous solutions of some aprotic hydroneutral polar compounds with large dipole moments, such as nitro compounds and nitriles. The obtained NIR spectra for the aqueous solutions were decomposed into three components: free water, solute, and water molecules affected by the presence of solutes. Newly determined NIR spectra of affected water molecules were well-described with at least four absorption modes observed at 7040, 6850, 6450, and 5640 cm(-1) for both the nitro compounds and nitriles. The highest frequency mode at 7040 cm(-1) possessing the strongest intensity was assigned to the first stretching overtone of affected water hydroxy (O-H) groups, which are nonhydrogen bonded to other water molecules and dangling. The second highest frequency mode at 6850 cm(-1) was assigned to the first stretching overtone of affected water O-H groups hydrated to other (free) water molecules. The third mode at 6400 cm(-1) was attributed to a combination mode of the fundamental stretching of O-H and the first overtone of the O-H bending mode of the affected water molecules. The lowest frequency mode at 5640 cm(-1) was assigned to the combination mode of the fundamental O-H stretching mode, the fundamental O-H bending mode, and the hindered rotational (libration) mode of the affected water molecules. Because absorption intensities of the third and lowest frequency modes for water molecules affected by the solutes depended on the sizes of alkyl groups of polar solutes, these two modes possibly result from the contribution of hydrophobic hydration effects.

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Contrary Hydration Behavior of N-Isopropylacrylamide to its Polymer, P(NIPAm), with a Lower Critical Solution Temperature

Cited by 110 publications

References 10 publications

Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

Role of Solvation Dynamics and Local Ordering of Water in Inducing Conformational Transitions in Poly(N-isopropylacrylamide) Oligomers through the LCST

Dangling OH Vibrations of Water Molecules in Aqueous Solutions of Aprotic Polar Compounds Observed in the Near-Infrared Regime

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