Gels | Special Issue : Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka

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Open AccessEditorial

Advancements in Gel Science—A Special Issue in the Memory of Toyoichi Tanaka

by Masayuki Tokita

Gels 2019, 5(3), 33; https://doi.org/10.3390/gels5030033 - 26 Jun 2019

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Abstract

It is a great pleasure for us to present a collection of recent papers that were submitted to the special issue of Gels, Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka [...] Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

Research

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20 pages, 2371 KiB

Open AccessArticle

Analysis of Heterogeneous Gelation Dynamics and Their Application to Blood Coagulation

by Toshiaki Dobashi and Takao Yamamoto

Gels 2018, 4(3), 59; https://doi.org/10.3390/gels4030059 - 9 Jul 2018

Cited by 7 | Viewed by 5124

Abstract

We present a scaling model based on a moving boundary picture to describe heterogeneous gelation dynamics. The dynamics of gelation induced by different gelation mechanisms is expressed by the scaled equation for the time taken for development of the gel layer with a [...] Read more.

We present a scaling model based on a moving boundary picture to describe heterogeneous gelation dynamics. The dynamics of gelation induced by different gelation mechanisms is expressed by the scaled equation for the time taken for development of the gel layer with a few kinetic coefficients characterizing the system. The physical meaning obtained by the analysis for a simple boundary condition from the standpoint of the phase transition shows that the time development of the gelation layer depends on whether the dynamics of the order parameter expressing the gelation of the polymer solution is fast or slow compared with the diffusion of the gelators in the heterogeneous gelation. The analytical method is used to understand the coagulation of blood from various animals. An experiment using systems with plasma coagulation occurring at interfaces with calcium chloride solution and with packed erythrocytes is performed to provide the data for model fitting and it is clarified that a few key kinetic coefficients in plasma coagulation can be estimated from the analysis of gelation dynamics. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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17 pages, 4926 KiB

Open AccessArticle

Dynamic Behaviors of Solvent Molecules Restricted in Poly (Acryl Amide) Gels Analyzed by Dielectric and Diffusion NMR Spectroscopy

by Hironobu Saito, Shunpei Kato, Keisuke Matsumoto, Yuya Umino, Rio Kita, Naoki Shinyashiki, Shin Yagihara, Minoru Fukuzaki and Masayuki Tokita

Gels 2018, 4(3), 56; https://doi.org/10.3390/gels4030056 - 22 Jun 2018

Cited by 9 | Viewed by 4737

Abstract

Dynamics of solvent molecules restricted in poly (acryl amide) gels immersed in solvent mixtures of acetone–, 1,4-dioxane–, and dimethyl sulfoxide–water were analyzed by the time domain reflectometry method of dielectric spectroscopy and the pulse field gradient method of nuclear magnetic resonance. Restrictions of [...] Read more.

Dynamics of solvent molecules restricted in poly (acryl amide) gels immersed in solvent mixtures of acetone–, 1,4-dioxane–, and dimethyl sulfoxide–water were analyzed by the time domain reflectometry method of dielectric spectroscopy and the pulse field gradient method of nuclear magnetic resonance. Restrictions of dynamic behaviors of solvent molecules were evaluated from relaxation parameters such as the relaxation time, its distribution parameter, and the relaxation strength obtained by dielectric measurements, and similar behaviors with polymer concentration dependences for the solutions were obtained except for the high polymer concentration in collapsed gels. Scaling analyses for the relaxation time and diffusion coefficient respectively normalized by those for bulk solvent suggested that the scaling exponent determined from the scaling variable defined as a ratio of the size of solvent molecule to mesh size of polymer networks were three and unity, respectively, except for collapsed gels. The difference in these components reflects characteristic molecular interactions in the rotational and translational diffusions, and offered a physical picture of the restriction of solvent dynamics. A universal treatment of slow dynamics due to the restriction from polymer chains suggests a new methodology of characterization of water structures. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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13 pages, 1345 KiB

Open AccessFeature PaperArticle

Propagation of Fatigue Cracks in Friction of Brittle Hydrogels

by Tetsuo Yamaguchi, Ryuichiro Sato and Yoshinori Sawae

Gels 2018, 4(2), 53; https://doi.org/10.3390/gels4020053 - 8 Jun 2018

Cited by 11 | Viewed by 5753

Abstract

In order to understand fatigue crack propagation behavior in the friction of brittle hydrogels, we conducted reciprocating friction experiments between a hemi-cylindrical indenter and an agarose hydrogel block. We found that the fatigue life is greatly affected by the applied normal load as [...] Read more.

In order to understand fatigue crack propagation behavior in the friction of brittle hydrogels, we conducted reciprocating friction experiments between a hemi-cylindrical indenter and an agarose hydrogel block. We found that the fatigue life is greatly affected by the applied normal load as well as adhesion strength at the bottom of the gel–substrate interface. On the basis of in situ visualizations of the contact areas and observations of the fracture surfaces after the friction experiments, we suggest that the mechanical condition altered by the delamination of the hydrogel from the bottom substrate plays an essential role in determining the fatigue life of the hydrogel. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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9 pages, 2032 KiB

Open AccessArticle

Irreversible Swelling Behavior and Reversible Hysteresis in Chemically Crosslinked Poly(vinyl alcohol) Gels

by Keiichiro Kamemaru, Shintaro Usui, Yumiko Hirashima and Atsushi Suzuki

Gels 2018, 4(2), 45; https://doi.org/10.3390/gels4020045 - 21 May 2018

Cited by 10 | Viewed by 4195

Abstract

We report the swelling properties of chemically crosslinked poly(vinyl alcohol) (PVA) gels with high degrees of polymerization and hydrolysis. Physical crosslinking by microcrystallites was introduced in this chemical PVA gel by a simple dehydration process. The equilibrium swelling ratio was measured in several [...] Read more.

We report the swelling properties of chemically crosslinked poly(vinyl alcohol) (PVA) gels with high degrees of polymerization and hydrolysis. Physical crosslinking by microcrystallites was introduced in this chemical PVA gel by a simple dehydration process. The equilibrium swelling ratio was measured in several mixed solvents, which comprised two-components: a good solvent (water or dimethyl sulfoxide (DMSO)), and a poor organic solvent for PVA. In the case of aqueous/organic solvent mixtures subjected to a multiple-sample test, the swelling ratio decreased continuously when the concentration of the organic solvent increased, reaching a collapsed state in the respective pure organic solvents. In the case of DMSO, starting from a swollen state, the swelling ratio rapidly decreased by between 15 and 50 mol % when the concentration of the organic compound increased in a single-sample test. To understand the hysteresis phenomenon, the swelling ratio was measured in a DMSO/acetone mixed solvent, starting from a collapsed state in acetone. The reversibility of swelling in response to successive concentration cycles between DMSO and acetone was examined. As a result, an irreversible swelling behavior was observed in the first cycle, and the swelling ratio in acetone after the first cycle became larger than the initial ratio. Subsequently, the swelling ratio changed reversibly, with a large hysteresis near a specific molar ratio of DMSO/acetone of 60/40. The microstructures were confirmed by Fourier transform infrared spectroscopy during the cycles. The irreversible swelling behavior and hysteresis are discussed in terms of the destruction and re-formation of additional physical crosslinking in the chemical PVA gels. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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12 pages, 4515 KiB

Open AccessArticle

Frozen State of Sephadex^® Gels of Different Crosslink Density Analyzed by X-ray Computed Tomography and X-ray Diffraction

by Norio Murase, Yuki Uetake, Yuki Sato, Kentaro Irie, Yohei Ueno, Toru Hirauchi, Toshio Kawahara and Mitsuhiro Hirai

Gels 2018, 4(2), 44; https://doi.org/10.3390/gels4020044 - 18 May 2018

Cited by 2 | Viewed by 4795

Abstract

Water in Sephadex^® (crosslinked dextran) gels is known to indicate different freezing behavior which is dependent on the density of the crosslinks, and water in a Sephadex^® G25 gel remains partially unfrozen during cooling and crystallizes during rewarming. The mechanism of [...] Read more.

Water in Sephadex^® (crosslinked dextran) gels is known to indicate different freezing behavior which is dependent on the density of the crosslinks, and water in a Sephadex^® G25 gel remains partially unfrozen during cooling and crystallizes during rewarming. The mechanism of anomalous ice crystallization during rewarming is still unclear. The objective of this study is to observe the ice grains that form in Sephadex^® beads and to comprehend their frozen state with a focus on the ice crystallization during rewarming. Sephadex^® beads containing 50 wt % water were prepared and used for the measurements. The observation of the ice grains was carried out by using synchrotron radiation-sourced X-ray CT (computed tomography). XRD (X-ray diffraction) analysis was also conducted to investigate the frozen state. As a result, ice grains that were larger than ~1 μm were hardly observed after the slow cooling of Sephadex^® beads, except in the G25 beads. However, at the occurrence of ice crystallization during rewarming, ice grains that were larger than 10 μm appeared in the G25 beads. Using XRD, it was found that small incomplete ice crystals were formed in G25 beads and the presence of glassy water was indicated in the gel. In conclusion, the size and distribution of ice grains that formed in Sephadex^® beads were different depending on the density of the crosslinks. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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13 pages, 1134 KiB

Open AccessArticle

Emergence of Wrinkles during the Curing of Coatings

by Michiko Shimokawa, Hikaru Yoshida, Takumi Komatsu, Rena Omachi and Kazue Kudo

Gels 2018, 4(2), 41; https://doi.org/10.3390/gels4020041 - 3 May 2018

Cited by 8 | Viewed by 4629

Abstract

Wrinkles often emerge on a paint layer when a second coat of paint is applied on an already-coated substrate. Wrinkle formation occurs when the first layer absorbs organic solvent from the second layer. We set up experiments to mimic the double-coating process, focusing [...] Read more.

Wrinkles often emerge on a paint layer when a second coat of paint is applied on an already-coated substrate. Wrinkle formation occurs when the first layer absorbs organic solvent from the second layer. We set up experiments to mimic the double-coating process, focusing on the interaction between a paint layer and an organic solvent. In the experiments, we investigated the characteristic wavelengths of the wrinkles and the time of wrinkle emergence. We employed a simple model to explain the wrinkle emergence and performed numerical simulations. The linear stability analysis of the model provides a relation between the wavelengths and the characteristic timescale that agrees reasonably well with our experimental data as well as numerical results. Our results indicate that compression of the layer due to swelling and delamination are both important factors in the formation of wrinkles. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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9 pages, 1086 KiB

Open AccessArticle

Temperature Dependence of Electrophoretic Mobility and Hydrodynamic Radius of Microgels of Poly(N-isopropylacrylamide)

by Yasuyuki Maki, Kentaro Sugawara and Daisuke Nagai

Gels 2018, 4(2), 37; https://doi.org/10.3390/gels4020037 - 20 Apr 2018

Cited by 11 | Viewed by 4650

Abstract

Electrostatic interactions in charged microgels, which are dominated by the microgel net charge, play a crucial role in colloidal stabilization and loading of small, charged molecules. In this study, the temperature dependences of electrophoretic mobility μ and hydrodynamic radius R_h were measured [...] Read more.

Electrostatic interactions in charged microgels, which are dominated by the microgel net charge, play a crucial role in colloidal stabilization and loading of small, charged molecules. In this study, the temperature dependences of electrophoretic mobility μ and hydrodynamic radius R_h were measured for a slightly ionized poly(N-isopropylacrylamide) (PNIPA) microgel in a dilute suspension. A decrease in R_h was observed in the temperature range between 30 °C and 35 °C, corresponding to the lower critical solution temperature of PNIPA, and an increase in |μ| was observed in a higher temperature range between 34 °C and 37 °C. The analysis based on electrophoresis theory for spherical polyelectrolytes indicated that the net charge of the microgel decreased as the microgel was deswollen. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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14 pages, 6951 KiB

Open AccessArticle

Process Variable Optimization in the Manufacture of Resorcinol–Formaldehyde Gel Materials

by Martin Prostredný, Mohammed G. M. Abduljalil, Paul A. Mulheran and Ashleigh J. Fletcher

Gels 2018, 4(2), 36; https://doi.org/10.3390/gels4020036 - 17 Apr 2018

Cited by 18 | Viewed by 5574

Abstract

Influence of process parameters of resorcinol–formaldehyde xerogel manufacture on final gel structure was studied, including solids content, preparation/drying temperature, solvent exchange, and drying method. Xerogels produced using a range of solids content between 10 and 40 w/v% show improved textural [...] Read more.

Influence of process parameters of resorcinol–formaldehyde xerogel manufacture on final gel structure was studied, including solids content, preparation/drying temperature, solvent exchange, and drying method. Xerogels produced using a range of solids content between 10 and 40 w/v% show improved textural character up to 30 w/v% with a subsequent decrease thereafter. Preparation/drying temperature shows a minimal threshold temperature of 55 °C is required to obtain a viable gel structure, with minimal impact on gel properties for further thermal increase. Improving the solvent exchange method by splitting the same amount of acetone used in this phase over the period of solvent exchange, rather than in a single application, shows an increase in total pore volume and average pore diameter, suggesting less shrinkage occurs during drying when using the improved method. Finally, comparing samples dried under vacuum and at ambient pressure, there seems to be less shrinkage when using vacuum drying compared to ambient drying, but these changes are insubstantial. Therefore, of the process parameters investigated, improved solvent exchange seems the most significant, and it is recommended that, economically, gels are produced using a solids content of 20 w/v% at a minimum temperature of 55 °C, with regular solvent replenishment in the exchange step, followed by ambient drying. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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8 pages, 6674 KiB

Open AccessArticle

Effect of Gamma Ray Irradiation on Friction Property of Poly(vinyl alcohol) Cast-Drying on Freeze-Thawed Hybrid Gel

by Saori Sasaki, Seiji Omata, Teruo Murakami, Naotsugu Nagasawa, Mitsumasa Taguchi and Atsushi Suzuki

Gels 2018, 4(2), 30; https://doi.org/10.3390/gels4020030 - 29 Mar 2018

Cited by 13 | Viewed by 4786

Abstract

Poly(vinyl alcohol) (PVA) is a biocompatible polymer with low toxicity. It is possible to prepare physically cross-linked PVA gels having hydrogen bonds without using a cross-linking agent. The newly reported physically cross-linked PVA cast-drying (CD) on freeze-thawed (FT) hybrid gel has an excellent [...] Read more.

Poly(vinyl alcohol) (PVA) is a biocompatible polymer with low toxicity. It is possible to prepare physically cross-linked PVA gels having hydrogen bonds without using a cross-linking agent. The newly reported physically cross-linked PVA cast-drying (CD) on freeze-thawed (FT) hybrid gel has an excellent friction property, which is expected to be applied as a candidate material for artificial cartilage. Gamma ray sterilization for clinical applications usually causes additional chemical cross-linking and changes physical properties of gels. In this study, CD on FT hybrid gels were irradiated using gamma rays at a different dose rate and irradiance. The results showed the optimized irradiation conditions for gamma irradiated gels to retain excellent friction characteristics. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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13 pages, 646 KiB

Open AccessArticle

Dynamics of Spinodal Decomposition in a Ternary Gelling System

by Yutaro Yamashita, Miho Yanagisawa and Masayuki Tokita

Gels 2018, 4(2), 26; https://doi.org/10.3390/gels4020026 - 22 Mar 2018

Cited by 5 | Viewed by 5344

Abstract

The phase diagram and phase transitions of the ternary system of gelatin, water and poly(ethylene glycol) oligomers were studied as a function of the weight fraction of gelatin and the weight fraction and molecular weight of poly(ethylene glycol) oligomers. It was found that [...] Read more.

The phase diagram and phase transitions of the ternary system of gelatin, water and poly(ethylene glycol) oligomers were studied as a function of the weight fraction of gelatin and the weight fraction and molecular weight of poly(ethylene glycol) oligomers. It was found that both phase separation and the sol-gel transition occur in this ternary system. The relative position of the phase separation line and the sol-gel transition line depends on the weight fraction and the molecular weight of the poly(ethylene glycol) oligomer that coexists in the solution. All aspects of the phase diagram are sensitive to the molecular weight of the poly(ethylene glycol) oligomer. Since the phase separation line crosses the sol-gel transition line in the phase space that is created by the temperature and the weight fraction of gelatin, the phase space is typically divided into four regions, where each region corresponds to a definite phase. The transitions between mutual phases were studied using the light-scattering technique. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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6 pages, 646 KiB

Open AccessCommunication

A Simple Method of Interpretating the Effects of Electric Charges on the Volume Phase Transition of Thermosensitive Gels

by Hiroshi Maeda, Shigeo Sasaki, Hideya Kawasaki and Rie Kakehashi

Gels 2018, 4(1), 24; https://doi.org/10.3390/gels4010024 - 19 Mar 2018

Cited by 3 | Viewed by 3161

Abstract

Various apparently inconsistent experimental observations have been reported on the effects of electric charges on the volume phase transition of thermosensitive gels. A simple method of interpretating these results is presented. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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9 pages, 2259 KiB

Open AccessArticle

Effect of Sweeteners on the Solvent Transport Behaviour of Mechanically-Constrained Agarose Gels

by Isamu Kaneda

Gels 2018, 4(1), 23; https://doi.org/10.3390/gels4010023 - 16 Mar 2018

Cited by 5 | Viewed by 4253

Abstract

Investigating the solvent transport behaviour of edible gels is important because it is strongly related to flavour release. We previously reported the solvent transport behaviour of mechanically-constrained agarose gels. These studies clearly showed that agarose gels can be treated as soft porous bodies. [...] Read more.

Investigating the solvent transport behaviour of edible gels is important because it is strongly related to flavour release. We previously reported the solvent transport behaviour of mechanically-constrained agarose gels. These studies clearly showed that agarose gels can be treated as soft porous bodies. Herein, we investigated the effect of sweeteners on the solvent transport speed, which is an important issue in the food industry, using sucrose and xylitol. Sucrose caused a concentration-dependent reduction in solvent transport speed. One of the reasons for the effect is that the solvent to which sucrose was added reduced solvent flow speed within the porous agarose network. This finding provides valuable information for flavour release from compressed gels. Moreover, we found a similar effect for xylitol, which is a promising candidate for substituting sucrose in low-calorie foods. This study would provide basic knowledge for the development of a new type of low-calorie foods. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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13 pages, 2114 KiB

Open AccessArticle

Effect of Monomer Sequence along Network Chains on Thermoresponsive Properties of Polymer Gels

by Shohei Ida, Toru Kawahara, Hidekazu Kawabata, Tatsuya Ishikawa and Yoshitsugu Hirokawa

Gels 2018, 4(1), 22; https://doi.org/10.3390/gels4010022 - 10 Mar 2018

Cited by 12 | Viewed by 5844

Abstract

The effect of monomer sequence along the network chain on the swelling behavior of polymer gels should be clarified for the advanced control of swelling properties of gel materials. To this end, we systematically investigated the swelling properties of poly(acrylamide derivative) gels with [...] Read more.

The effect of monomer sequence along the network chain on the swelling behavior of polymer gels should be clarified for the advanced control of swelling properties of gel materials. To this end, we systematically investigated the swelling properties of poly(acrylamide derivative) gels with the same composition but different monomer sequence by utilizing two gel synthetic methods: copolymerization giving a random network and co-crosslinking giving a blocky network. Both of the copolymerization and the co-crosslinking gels were prepared from the combination of two of the three following monomers: hydrophilic N,N-dimethylacrylamide (DMAAm), hydrophobic N-n-butylacrylamide (NBAAm), and thermoresponsive N-isopropylacrylamide (NIPAAm) with various monomer compositions. The swelling measurement of the obtained gels showed totally different behaviors between the copolymerization and the co-crosslinking gels, even with the same monomer composition. The copolymerization gels had the average property from the two monomers, depending on monomer composition, because random monomer distribution changed the affinity of each network chain to water. On the other hand, the co-crosslinking gels behaved as if two components independently contributed to the swelling properties, probably due to the domain structure derived from two kinds of prepolymers. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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Review

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11 pages, 21265 KiB

Open AccessReview

Single Micrometer-Sized Gels: Unique Mechanics and Characters for Applications

by Miho Yanagisawa, Chiho Watanabe and Kei Fujiwara

Gels 2018, 4(2), 29; https://doi.org/10.3390/gels4020029 - 28 Mar 2018

Cited by 13 | Viewed by 5560

Abstract

Microgels—small gels of submicron to micron size—are widely used in food, cosmetics and biomedical applications because of their biocompatibility and/or fast response to external environments. However, the properties of “single” microgels have not been characterized due to limitations in preparation technologies and measurement [...] Read more.

Microgels—small gels of submicron to micron size—are widely used in food, cosmetics and biomedical applications because of their biocompatibility and/or fast response to external environments. However, the properties of “single” microgels have not been characterized due to limitations in preparation technologies and measurement methods for single microgels with sizes in the multi-micrometer range. The synthesis of multiple shapes of single microgels and their characterization are important for further functionalization and application of gel-based materials. In this review, we explain the recent advancements in microgel fabrication and characterization methods for single microgels. The first topic discussed includes the self-assembly methods for single microgel fabrication using physical phenomena such as phase separation, interfacial wetting and buckling instability. The second topic deals with methods for analyzing the mechanics of single microgels and the differences between their mechanical characteristics and those of bulk gels. The recent progress in the fabrication and characterization of single microgels will bring important insights to the design and functionalization of gel-based materials. Full article

(This article belongs to the Special Issue Advancements in Gel Science—A Special Issue in Memory of Toyoichi Tanaka)

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