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Gels
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Recent Advances in Thermoreversible Gelation
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Recent Advances in Thermoreversible Gelation

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 2024) | Viewed by 8848

Special Issue Editors

Prof. Dr. Fumihiko Tanaka

E-Mail Website
Guest Editor
Department of Polymer Chemistry, Kyoto University, Kyoto 615-8510, Japan
Interests: gels; thermoreversible gelation; polymer phase separation; cross-linking; hydrogen bonding; associating polymers; rheology of transient networks
Prof. Dr. Chi Wang

E-Mail Website
Guest Editor
Department of Chemical Engineering, National Cheng Kung University, Tainan 70401, Taiwan
Interests: electrospinning; polymer processing; polymer nano-composites; rheology; polymer nanofibers

Special Issue Information

Dear Colleagues,

Thermoreversible gelation is a transition from a sol state to a gel state in solutions of functional molecules, which can be reversed by tuning thermal conditions and external stimuli. Formed gels are three-dimensional polymer networks with non-covalent physical cross-links, which can break and recombine in response to the system parameters such as temperature, concentration, pH, ionic charges, and also to the environmental parameters such as pressure, shear flow, elongation, light, salts, enzymes, antigens, etc. Most gels in nature are thermoreversible gels. They have unique dynamic properties as soft materials, and hence have been noted as one of the most interesting subjects in materials science. This Special Issue focuses on the fascinating gelation transition of polymer solutions, and provides a comprehensive overview of the current state of research on the thermoreversible gelation with original papers and reviews on the most fundamental aspects to recent diverse applications of these exciting materials.

Potential topics include, but are not limited to, the following:

  • Thermoreversible gelation as a phase transition;
  • Interfering with phase separation;
  • Structure and dynamics of the reversible cross-links;
  • New methods of reversible cross-linking;
  • Gelation time necessary for network formation;
  • Gelation in mixed solvents;
  • Rheology and flow properties as transient polymer networks;
  • Fracture and self-healing;
  • Large-scale structure and non-uniformity of the networks;
  • Modeling and computations of thermoreversible gelation.

Prof. Dr. Fumihiko Tanaka
Prof. Dr. Chi Wang
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 2100 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

  • thermoreversible gelation;
  • reversible cross-linking;
  • phase separation;
  • gelation time;
  • mixed solvents;
  • transient polymer networks;
  • associating polymers;
  • ion binding;
  • self-healing

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Published Papers (5 papers)

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Research

22 pages, 551 KiB  
Article
Dipole Theory of Polyzwitterion Microgels and Gels
by Murugappan Muthukumar
Gels 2024, 10(6), 393; https://doi.org/10.3390/gels10060393 - 11 Jun 2024
Cited by 1 | Viewed by 1063
Abstract
The behavior of polyzwitterions, constituted by dipole-like zwitterionic monomers, is significantly different from that of uniformly charged polyelectrolytes. The origin of this difference lies in the intrinsic capacity of polyzwitterions to self-associate intramolecularly and associate with interpenetrating chains driven by dominant dipolar interactions. [...] Read more.
The behavior of polyzwitterions, constituted by dipole-like zwitterionic monomers, is significantly different from that of uniformly charged polyelectrolytes. The origin of this difference lies in the intrinsic capacity of polyzwitterions to self-associate intramolecularly and associate with interpenetrating chains driven by dominant dipolar interactions. Earlier attempts to treat polyzwitterions implicitly assume that the dipoles of zwitterion monomers are randomly oriented. At ambient temperatures, the dipolar zwitterion monomers can readily align with each other generating quadrupoles and other multipoles and thus generating heterogeneous structures even in homogeneous solutions. Towards an attempt to understand the role of such dipolar associations, we present a mean field theory of solutions of polyzwitterions. Generally, we delineate a high-temperature regime where the zwitterion dipoles are randomly oriented from a low-temperature regime where quadrupole formation is significantly prevalent. We present closed-form formulas for: (1) Coil-globule transition in the low-temperature regime, the anti-polyelectrolyte effect of chain expansion upon addition of low molar mass salt, and chain relaxation times in dilute solutions. (2) Spontaneous formation of a mesomorphic state at the borderline between the high-temperature and low-temperature regimes and its characteristics. A universal law is presented for the radius of gyration of the microgel, as a proportionality to one-sixth power of the polymer concentration. (3) Swelling equilibrium of chemically cross-linked polyzwitterion gels in both the high temperature and low-temperature regimes. Addressing the hierarchical internal dynamics of polyzwitterion gels, we present a general stretched exponential law for the time-correlation function of gel displacement vector, that can be measured in dynamic light scattering experiments. The present theory is of direct experimental relevance and additional theoretical developments to all polyzwitterion systems, and generally to biological macromolecular systems such as intrinsically disordered proteins. Full article
(This article belongs to the Special Issue Recent Advances in Thermoreversible Gelation)
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13 pages, 3710 KiB  
Article
UCST-Type Thermoresponsive Sol–Gel Transition Triblock Copolymer Containing Zwitterionic Polymer Blocks
by Akifumi Kawamura, Ryogo Takahashi and Takashi Miyata
Gels 2024, 10(5), 288; https://doi.org/10.3390/gels10050288 - 24 Apr 2024
Viewed by 1720
Abstract
Thermoresponsive sol–gel transition polymers are of significant interest because of their fascinating biomedical applications, including as drug reservoirs for drug delivery systems and scaffolds for tissue engineering. Although extensive research has been conducted on lower critical solution temperature (LCST)-type sol–gel transition polymers, there [...] Read more.
Thermoresponsive sol–gel transition polymers are of significant interest because of their fascinating biomedical applications, including as drug reservoirs for drug delivery systems and scaffolds for tissue engineering. Although extensive research has been conducted on lower critical solution temperature (LCST)-type sol–gel transition polymers, there have been few reports on upper critical solution temperature (UCST)-type sol–gel transition polymers. In this study, we designed an ABA-type triblock copolymer composed of a poly(ethylene glycol) (PEG) block and zwitterionic polymer blocks that exhibit UCST-type thermoresponsive phase transitions. A sulfobetaine (SB) monomer with both ammonium and sulfonate (–SO3) groups in its side chain or a sulfabetaine (SaB) monomer with both ammonium and sulfate (–OSO3) groups in its side chain was polymerized from both ends of the PEG block via reversible addition–fragmentation chain-transfer (RAFT) polymerization to obtain PSB-PEG-PSB and PSaB-PEG-PSaB triblock copolymers, respectively. Although an aqueous solution containing the PSB-PEG-PSB triblock copolymer showed an increase in viscosity upon cooling, it did not undergo a sol-to-gel transition. In contrast, a sol-to-gel transition was observed when a phosphate-buffered saline containing PSaB-PEG-PSaB was cooled from 80 °C to 25 °C. The PSaB blocks with –OSO3 groups exhibited a stronger dipole–dipole interaction than conventional SB with –SO3 groups, leading to intermolecular association and the formation of a gel network composed of PSaB assemblies bridged with PEG. The fascinating UCST-type thermoresponsive sol–gel transition properties of the PSaB-PEG-PSaB triblock copolymer suggest that it can provide a useful platform for designing smart biomaterials, such as drug delivery reservoirs and cell culture scaffolds. Full article
(This article belongs to the Special Issue Recent Advances in Thermoreversible Gelation)
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13 pages, 3729 KiB  
Article
Gelation upon the Mixing of Amphiphilic Graft and Triblock Copolymers Containing Enantiomeric Polylactide Segments through Stereocomplex Formation
by Yuichi Ohya, Yasuyuki Yoshida, Taiki Kumagae and Akinori Kuzuya
Gels 2024, 10(2), 139; https://doi.org/10.3390/gels10020139 - 9 Feb 2024
Viewed by 1812
Abstract
Biodegradable injectable polymer (IP) systems that form hydrogels in situ when injected into the body have considerable potential as medical materials. In this paper, we report a new two-solution mixed biodegradable IP system that utilizes the stereocomplex (SC) formation of poly(l-lactide) [...] Read more.
Biodegradable injectable polymer (IP) systems that form hydrogels in situ when injected into the body have considerable potential as medical materials. In this paper, we report a new two-solution mixed biodegradable IP system that utilizes the stereocomplex (SC) formation of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA). We synthesized triblock copolymers of PLLA and poly(ethylene glycol), PLLA-b-PEG-b-PLLA (tri-L), and a graft copolymer of dextran (Dex) attached to a PDLA-b-PEG diblock copolymer, Dex-g-(PDLA-b-PEG) (gb-D). We found that a hydrogel can be obtained by mixing gb-D solution and tri-L solution via SC formation. Although it is already known that graft copolymers attached to enantiomeric PLLA and PDLA chains can form an SC hydrogel upon mixing, we revealed that hydrogels can also be formed by a combination of graft and triblock copolymers. In this system (graft vs. triblock), the gelation time was shorter, within 1 min, and the physical strength of the resulting hydrogel (G′ > 100 Pa) was higher than when graft copolymers were mixed. Triblock copolymers form micelles (16 nm in diameter) in aqueous solutions and hydrophobic drugs can be easily encapsulated in micelles. In contrast, graft copolymers have the advantage that their molecular weight can be set high, contributing to improved mechanical strength of the obtained hydrogel. Various biologically active polymers can be used as the main chains of graft copolymers, and chemical modification using the remaining functional side chain groups is also easy. Therefore, the developed mixing system with a graft vs. triblock combination can be applied to medical materials as a highly convenient, physically cross-linked IP system. Full article
(This article belongs to the Special Issue Recent Advances in Thermoreversible Gelation)
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14 pages, 1340 KiB  
Article
Thermoreversible Gel-Dispersed Liquid Crystals
by Akihiko Matsuyama
Gels 2023, 9(12), 965; https://doi.org/10.3390/gels9120965 - 8 Dec 2023
Viewed by 1365
Abstract
A simple model is introduced to describe phase behaviours of binary mixtures of a thermoreversible gel and a low-molecular-weight liquid crystal (LC). We predict novel phase diagrams on the temperature–concentration plane, including sol–gel transition, nematic–isotropic phase transition, and phase separation. At high temperatures, [...] Read more.
A simple model is introduced to describe phase behaviours of binary mixtures of a thermoreversible gel and a low-molecular-weight liquid crystal (LC). We predict novel phase diagrams on the temperature–concentration plane, including sol–gel transition, nematic–isotropic phase transition, and phase separation. At high temperatures, the phase separation between the isotropic sol and gel phases appears. As the temperature decreases, we have the phase separation between nematic sol and isotropic gel phases, in which the nematic domains are dispersed in the isotropic gel phase. We suggest that thermoreversible gelation of reactive molecules mixed with LCs will become one of the new classes of polymer-dispersed liquid crystals. Full article
(This article belongs to the Special Issue Recent Advances in Thermoreversible Gelation)
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23 pages, 785 KiB  
Article
Thermoreversible Gelation with Supramolecularly Polymerized Cross-Link Junctions
by Fumihiko Tanaka
Gels 2023, 9(10), 820; https://doi.org/10.3390/gels9100820 - 15 Oct 2023
Cited by 1 | Viewed by 1678
Abstract
Structure and reversibility of cross-link junctions play pivotal roles in determining the nature of thermoreversible gelation and dynamic mechanical properties of the produced polymer networks. We attempt to theoretically explore new types of sol–gel transitions with mechanical sharpness by allowing cross-links to grow [...] Read more.
Structure and reversibility of cross-link junctions play pivotal roles in determining the nature of thermoreversible gelation and dynamic mechanical properties of the produced polymer networks. We attempt to theoretically explore new types of sol–gel transitions with mechanical sharpness by allowing cross-links to grow without upper bound. We consider thermoreversible gelation of the primary molecules R{Af} carrying the number f of low molecular weight functional groups (gelators) A. Gelators A are assumed to form supramolecular assemblies. Some examples are: telechelic polymers (f=2) carrying π–π stacking benzene derivatives at their both ends, and trifunctional star molecules (f=3) bearing multiple hydrogen-bonding gelators. The sol–gel transition of the primary molecules becomes sharper with the cooperativity parameter of the stepwise linear growth of the cross-links. There is a polymerization transition (crossover without singularity) of the junctions in the postgel region after the gel point is passed. If the gelator A tends to form supramolecular rings competitively with linear chains, there is another phase transition in the deep postgel region where the average molecular weight of the rings becomes infinite (Bose–Einstein condensation of rings). As a typical example of binary cross-links where gelators A and B form mixed junctions, we specifically consider metal-coordinated binding of ligands A by metal ions B. Two types of multi-nuclear supramolecular complexes are studied: (i) linear stacking (ladder) of the sandwich A2B units, and (ii) linear train of egg-box A4B units. To find the strategy towards experimental realization of supramolecular cross-links, the average molecular weight, the gel fraction, the average length of the cross-link junctions are numerically calculated for all of these models as functions of the functionality f, the concentration of the solute molecules, and the temperature. Potential candidates for the realization of these new types of thermoreversible gelation are discussed. Full article
(This article belongs to the Special Issue Recent Advances in Thermoreversible Gelation)
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