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Gels
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New Era in the Volume Phase Transition of Gels II
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New Era in the Volume Phase Transition of Gels II

A special issue of Gels (ISSN 2310-2861). This special issue belongs to the section "Gel Chemistry and Physics".

Deadline for manuscript submissions: closed (31 March 2023) | Viewed by 3770

Special Issue Editors

Prof. Dr. Masayuki Tokita

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Guest Editor
Department of Physics, Graduate School of Science, Kyushu University, Fukuoka 819-0395, Japan
Interests: gel; phase transition; critical phenomena; sol-gel transition; phase separation; morphogenesis
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Masahiko Annaka

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Guest Editor
Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka 819-0395, Japan
Interests: gels; polyethylene glycols; neutron scattering
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Gerald S. Manning

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Guest Editor
Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ 08854-8087, USA
Interests: gels; polyelectrolytes; bubbles and droplets; osmosis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

It is now well recognized that the discovery of the volume phase transition of gels in 1978, by Toyoichi Tanaka, marked the beginning of a new era in the science and technology of gels. Following this finding, many new phenomena related to the volume phase transition of gels have been found and discussed, one by one, in terms of the theory of the volume phase transition of gels. The theory of the volume phase transition of gels, which was proposed in the early stage of these studies, is constructed on the basis of analogy with the liquid–gas transition of a van der Waals gas, where the gas phase and the liquid phase correspond to the swelling state and the collapsed state of gel, respectively. This theory adequately demonstrates the universality of the volume phase transition of the gel and can be easily understood by a general audience. Consequently, such a depiction of the volume phase transition of the gel has been widely disseminated. From a scientific point of view, however, it is clearly an oversimplification. The crucial point is that the gel consists of a polymer network and solvent. In other words, the gel usually consists of at least two components, a solute and a solvent. On the other hand, the van der Waals gas is a single-component system consisting only of gas molecules. Moreover, the solute, that is, the polymer network, cannot dissolve into the solvent freely because the polymers are connected by crosslinks to form a network. These points may appear trivial but are the essence of gels. Although many aspects of the volume phase transition of gel have been clarified so far, many phenomena are still left unsolved. We believe it is time to revisit the volume phase transition of gels in marking a possible second beginning of a new era in the science of gels. We look forward to the submission of new results on the volume phase transition of gels. The submission of both theoretical and experimental studies is welcome.

Prof. Dr. Masayuki Tokita
Prof. Dr. Masahiko Annaka
Prof. Dr. Gerald S. Manning
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Gels is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • volume phase transition of gels
  • swelling behaviors of gels
  • phase equilibrium of gels
  • chemical and/or physical studies related to the volume phase transition of gels

Published Papers (3 papers)

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Research

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18 pages, 3401 KiB  
Article
Physical Gels of Atactic Poly(N-isopropylacrylamide) in Water: Rheological Properties and As-Derived Spinodal Temperature
by Ya-Chen Chuang, Yu Wang and Chi Wang
Gels 2023, 9(4), 288; https://doi.org/10.3390/gels9040288 - 01 Apr 2023
Cited by 1 | Viewed by 1054
Abstract
Aqueous solutions of atactic poly(N-isopropylacrylamide) (a-PNIPAM) undergo complex phase transitions at 20–33 °C. In this temperature range, the a-PNIPAM solution exhibits a phase behavior of lower critical solution temperature at the binodal temperature (Tb) and physical gel formation at the [...] Read more.
Aqueous solutions of atactic poly(N-isopropylacrylamide) (a-PNIPAM) undergo complex phase transitions at 20–33 °C. In this temperature range, the a-PNIPAM solution exhibits a phase behavior of lower critical solution temperature at the binodal temperature (Tb) and physical gel formation at the gel temperature (Tgel). On slow heating of the one-phase solution containing linear a-PNIPAM chains, branched chains are gradually developed to proceed with the physical gelation before phase separation considering that Tgel < Tb. Thus, the phase separation temperature determined from the conventional approaches, either by turbidity to derive the Tb or by scattering to derive the spindal temperature (Ts) from the Ornstein–Zernike analysis, is strictly the transition temperature associated with the a-PNIPAM hydrogel (or highly branched chains newly developed at elevated temperatures), rather than the initial a-PNIPAM solution prepared. Herein, the spinodal temperatures of a-PNIPAM hydrogels (Ts,gel) of various concentrations were determined from rheological measurements at a heating rate of 0.2 °C/min. Analyses of the temperature dependence of loss modulus G″ and storage modulus G′ give rise to the Ts,gel, based on the Fredrickson–Larson–Ajji–Choplin mean field theory. In addition, the specific temperature (T1) above which the one-phase solution starts to dramatically form the aggregated structure (e.g., branched chains) was also derived from the onset temperature of G′ increase; this is because as solution temperature approaches the spinodal point, the concentration fluctuations become significant, which is manifested with the elastic response to enhance G′ at T > T1. Depending on the solution concentration, the measured Ts,gel is approximately 5–10 °C higher than the derived T1. On the other hand, Ts,gel is independent of solution concentration to be constant at 32.8 °C. A phase diagram of the a-PNIPAM/H2O mixture is thoroughly constructed together with the previous data of Tgel and Tb. Full article
(This article belongs to the Special Issue New Era in the Volume Phase Transition of Gels II)
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15 pages, 2180 KiB  
Article
Modeling the Phase Transition in Hydrophobic Weak Polyelectrolyte Gels under Compression
by Alexander D. Kazakov, Varvara M. Prokacheva, Oleg V. Rud, Lucie Nová and Filip Uhlík
Gels 2023, 9(3), 259; https://doi.org/10.3390/gels9030259 - 22 Mar 2023
Cited by 1 | Viewed by 1073
Abstract
One of the emerging water desalination techniques relies on the compression of a polyelectrolyte gel. The pressures needed reach tens of bars, which are too high for many applications, damage the gel and prevent its reuse. Here, we study the process by means [...] Read more.
One of the emerging water desalination techniques relies on the compression of a polyelectrolyte gel. The pressures needed reach tens of bars, which are too high for many applications, damage the gel and prevent its reuse. Here, we study the process by means of coarse-grained simulations of hydrophobic weak polyelectrolyte gels and show that the necessary pressures can be lowered to only a few bars. We show that the dependence of applied pressure on the gel density contains a plateau indicating a phase separation. The phase separation was also confirmed by an analytical mean-field theory. The results of our study show that changes in the pH or salinity can induce the phase transition in the gel. We also found that ionization of the gel enhances its ion capacity, whereas increasing the gel hydrophobicity lowers the pressure required for gel compression. Therefore, combining both strategies enables the optimization of polyelectrolyte gel compression for water desalination purposes. Full article
(This article belongs to the Special Issue New Era in the Volume Phase Transition of Gels II)
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Review

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16 pages, 557 KiB  
Review
Phase Transition of Gels—A Review of Toyoich Tanaka’s Research
by Masayuki Tokita
Gels 2022, 8(9), 550; https://doi.org/10.3390/gels8090550 - 30 Aug 2022
Cited by 1 | Viewed by 1269
Abstract
In 70’s, the extensive studies about the gel science has begun with the discovery of the volume phase transition of gel at the physics department of Massachusetts Institute of Technology. After the discovery of the volume phase transition of gel, the phenomenon was [...] Read more.
In 70’s, the extensive studies about the gel science has begun with the discovery of the volume phase transition of gel at the physics department of Massachusetts Institute of Technology. After the discovery of the volume phase transition of gel, the phenomenon was extensively studied and advanced by the discoverer, the late Professor Toyoichi Tanaka, who deceased on 20 May 2000 in the halfway of his research. In this paper, we would like to review his research to clarify his deep insight into the science of gels. Full article
(This article belongs to the Special Issue New Era in the Volume Phase Transition of Gels II)
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