Next Article in Journal
Physicochemical and Microstructural Analyses of Pepsin-Soluble Collagens Derived from Lizardfish (Saurida tumbil Bloch, 1795) Skin, Bone and Scales
Next Article in Special Issue
Some Remarkable Rheological and Conducting Properties of Hybrid PVC Thermoreversible Gels/Organogels
Previous Article in Journal
Application of Polyacrylic Hydrogel in Durability and Reduction of Environmental Impacts of Concrete through ANN
Previous Article in Special Issue
Bis-Pyridine-Based Organogel with AIE Effect and Sensing Performance towards Hg2+
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Gels
Volume 8
Issue 8
10.3390/gels8080469
gels-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Polymeric Hydrogelator-Based Molecular Gels Containing Polyaniline/Phosphoric Acid Systems

by
Yutaka Ohsedo
1,* and
Mayumi Sasaki
2
1
Division of Engineering, Faculty of Engineering, Nara Women’s University, Kitauoyahigashi-machi, Nara 630-8506, Japan
2
Graduate School of Human Centered Engineering, Nara Women’s University, Kitauoyahigashi-machi, Nara 630-8506, Japan
*
Author to whom correspondence should be addressed.
Gels 2022, 8(8), 469; https://doi.org/10.3390/gels8080469
Submission received: 14 July 2022 / Revised: 21 July 2022 / Accepted: 25 July 2022 / Published: 27 July 2022
(This article belongs to the Collection Recent Advances and Future Perspectives in Organogels and Organogelators Research)
Browse Figures
Versions Notes

Abstract

:
To expand the range of applications of hydrogels, researchers are interested in developing novel molecular hydrogel materials that have affinities for the living body and the ability to mediate electrical signals. In this study, a simple mixing method for creating a novel composite molecular gel is employed, which combines a hydrophilic conductive polymer, a polyaniline/phosphoric acid complex, and a polymer hydrogelator as a matrix. The composite hydrogel showed an improved gel-forming ability; more effective mechanical properties, with an increased strain value at the sol–gel transition point compared to the single system, which may be sufficient for paintable gel; and a better electrochemical response, due to the electrically conducting polyaniline component. These findings demonstrate the applicability of the new composite hydrogels to new potential paintable electrode materials.

Graphical Abstract

1. Introduction

Electrically conducting polymers have been actively researched and developed as active materials for thin-film electronic devices, taking advantage of their light weight and thin-film formation capabilities, which are the characteristics of organic polymers [1,2,3,4,5,6]. Additionally, good solubility or dispersity in solvents is important in preparing thin films of conductive polymers [1,2,3,4,5,6,7,8,9].
Polyaniline has long been known as an insoluble material, aniline black, and its use as an active material for functional electrodes continues to be actively investigated [10,11]. More recently, water-dispersed polyaniline particles have become useful materials with excellent maneuverability that can guarantee electronic and electrical conductivity after film formation [11,12]. On the other hand, water-soluble polyaniline, in which water-soluble functional groups have been introduced into the molecular structure of the polymeric main chain, is another useful material that exhibits electrical conductivity after film formation [1,11,13]. The above water-soluble or hydrophilic conductive polymers have a good affinity for hydrogels [14,15,16,17,18,19,20,21], which comprise new soft materials, and their successful complexation with the hydrogel matrix allows us to obtain a gel state that is difficult to obtain with a conductive polymer alone. Since this soft electron-conductive composite material is expected to have a high affinity for the living body, which is a hydrogel, it is expected to be used as a novel gel material for sensing devices and artificial skin in direct contact with the body.
Recently, molecular gels [22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37] composed of low-molecular-weight gelators (LMWGs) or polymer gelators [38,39,40] have received attention as advanced soft materials with functionalities such as stimuli responsiveness [37] and thixotropy [22,23,24,41] (mechanically induced reversible sol-to-gel and gel-to-sol transition behavior). Additionally, molecular gels composed of multicomponent LMWGs have been investigated to create molecular gels with new properties [42,43,44,45,46,47,48]. Previously, we employed a simple mixing method to create multicomponent molecular gels with improved properties, which were composed of LMWG homologs [29,30,49,50]. Additionally, by mixing the hydrogelator and synthetic clay, the composite hydrogels showed enhanced thixotropic behavior [51].
To develop novel gel materials that are expected to have an affinity with living organisms and that can mediate electrical signals, this study aimed to generate conductive molecular hydrogels by compositing hydrophilic conductive polymers through mixing, using a polymeric hydrogelator as a matrix to form the hydrogel material. Poly(sodium-3–sulfo-p-phenyleneterephthalamide) (NaPPDT) [52] was selected as a polymer hydrogelator (Scheme 1), as it is capable of creating various composite materials, such as LAPONITE® [53], a water-soluble silicate, and polyaniline/water-soluble polymer polyion complexes [54], with better gel properties. In this study, a hydrophilic conductive polymer complexed with phosphoric acid (PAPA, Scheme 1) was selected as the hydrophilic conductive polymer, as it enabled us to obtain water-soluble conductive polyaniline polymerized from aqueous aniline phosphoric acid solutions through oxidation. Polyaniline with phosphoric acid or phosphoric acid moiety as a dopant has been reported as a better combination for conducting polymers [18,55,56]. Molecular polymer hydrogels composed of NaPPDT and aqueous solutions of the polyaniline complex of PAPA (mixed-system molecular gels) were prepared, and their mechanical properties were evaluated to determine whether simple mixing can produce conductive molecular gel materials with an electrochemical response while maintaining the properties of the molecular gels. Such electrochemically active composite gels are expected to become a paintable electrode material, facilitating the fabrication of electrochemical devices such as glucose sensors on a variety of media, e.g., cloths or papers [18].

2. Results and Discussion

PAPA was prepared from an oxidative polymerized aniline in phosphoric acid aqueous solution, and, after purification through dialysis, it yielded a polyaniline complex aqueous solution (PAPA aq.) with a dark greenish color. The concentration of PAPA aq. was fixed at 1.0 wt% in the dry weight standard of PAPA. A mixture of NaPPDT/PAPA was produced using a vortex mixer (Figure 1), with varied compositions of 1.0 wt% NaPPDT hydrogel aqueous solution and 1.0 wt% PAPA aqueous solution. The gel formation ability of the composite gels was evaluated using the vial inversion method. After mixing, the concentration of NaPPDT became 0.5 wt%, which showed a liquid state in its single solution (Figure 1a), and the composite hydrogel NaPPDT/PAPA 1/1 (w/w) exhibited a gel state (Figure 1b). Since the composite hydrogel NaPPDT/PAPA with the composition 1/2 (w/w) did not show a gel state, the following measurements were performed to analyze only the composite hydrogel NaPPDT/PAPA 1/1 (w/w). The composite hydrogels maintained their homogeneous gel state for at least 1 year.
To investigate the NaPPDT/PAPA composite’s hydrogel state, a qualitative evaluation of the mechanical properties of the gels was performed with rheometric measurements (Figure 2a,b). By applying the frequency sweep to the gels (Figure 2a), the existence of the pseudo plateau, where the magnitude of the modulus showed that the storage modulus (G′) > the loss modulus (G″), proved that gelation had occurred, as has been shown in other organic polymer gels [57]. By increasing the stress on the gels (Figure 2b), G′ and G″ demonstrated the transition from the gel state (G′ > G″) to the sol state (G′ < G″) over the intersection of G′ and G″. The results of the composite hydrogel also confirmed the gel state and the formation of a softer and more tenacious hydrogel than the corresponding NaPPDT hydrogel, evidenced by the shift in the value and cross point of G′ and G″, as also indicated for the other mixed composite hydrogels composed of LAPONITE® [53] or polyaniline/water-soluble polymer complex with NaPPDT [54].
Additionally, as shown in Figure 2c and Figure 3, the composite hydrogel NaPPDT/PAPA 1/1 (w/w) showed thixotropic behavior similar to the NaPPDT hydrogel in a single component. This may suggest that mixing NaPPDT with PAPA improves the gel-forming abilities of the polymer hydrogelator NaPPDT, as previously shown in the other composite hydrogels [45,46]. The quantitative data on the composite hydrogel’s thixotropic behavior were also measured by step-shear measurements after repeatedly applying a large deformation force and resting (Figure 2c). It was demonstrated that after applying the deformation force, there was a repeated recovery from the sol state (G’ < G”) to the gel state (G’> G”) at the same rate each time in this system [58]. Recovery from gel to sol took 1 min using the inversion method but only a few tens of seconds using rheometry, since we were observing the behavior in a tiny space with a gap of 0.5 mm. The obtained results for the NaPPDT hydrogel and the composite hydrogel suggested that the thixotropic behavior of the composite hydrogel was the same as that of the NaPPDT hydrogel, whereas adding PAPA enhanced the gel properties of the composite hydrogel and softened the obtained composite.
Scanning electron microscopy (SEM) was performed for freeze-dried samples of PAPA aq. and hydrogels (xerogels) to closely observe the composite hydrogel microstructure. As shown in Figure 4, while the composite’s components were in the order of dozens of nanometers of fiber, the components of the PAPA particles were aggregated in the order of micrometers, and the components of the NaPPDT displayed porous wrinkled networks also in the order of micrometers [52]. The structure of the composite xerogel seemed to comprise a network of components (fibers) that were finer than those of the freeze-dried PAPA and NaPPDT xerogel. This may suggest that the presence of PAPA prevents the aggregation of the NaPPDT polymer chains from creating thicker network components. This suppression of NaPPDT aggregation may be related to the increased strain value of the sol–gel transition, as the mesh density is enhanced while the overall polymer concentration is diluted and the gel becomes soft. Although the freeze-drying process may influence the maintenance of the gel state network structure by drying-induced aggregation and ice growth [59], these SEM images nevertheless reflect the difference in the network structure of a native network of gels.
The electrical conductivity of the composite hydrogel was determined to explore its potential application as an electroactive material in electrochemical devices. As polyanilines show their electric conductivity in the doping state, the doping state of PAPA was checked by investigating the existence of doping (the existence of radical cation species) with the UV-vis spectrum of the NaPPDT/PAPA composite hydrogel (Figure 5). The absorption band of the composite, ranging from 650 to 900 nm, was a typical band of doped polyaniline derivatives and was attributed to the emeraldine-oxidized state of polyanilines [60,61]. It is suggested that the electronic environment of PAPA was changed by the existence of NaPPDT, and this result showed some interaction between PAPA and NaPPDT (unfortunately, no specific peaks or shifts were observed in the FT-IR measurements).
By applying the four-probe method of electronic conductivity measurement to the NaPPDT/PAPA 1/1 (w/w) composite hydrogels, we found that the electronic conductivity was 2.5 × 10−5 S cm−1, which is within the range of semiconducting polymers and superior to our previous gelator/polyaniline composite hydrogel [54]. Although this value is relatively low for conducting polymers due to the existence of pure water, and it is in the same range of conductivity as the composite hydrogels consisting of NaPPDT and polyaniline ion complexes [54], it maintains a sufficient current for the electrochemical process, as was shown in poly(N-vinylcarbazole) with a conductivity of 10−6 S cm−1, which functioned as an electroactive and electrode-active material [62,63].
Finally, the electrochemical response of the composite gels was examined to verify the potential electrochemical properties of the NaPPDT/PAPA composite hydrogels in a thin-layer cell. Before the electrochemical measurements, it was observed that the gel state was stable, as shown in Figure 6, and the NaPPDT/PAPA hydrogel solubility in water was suppressed in NaCl electrolyte aqueous solution, indicating a pseudo-chemically reversible electrochemical process of recycling potential sweeps (Figure 7). As shown in Figure 7, whereas the NaPPDT gel showed smaller and inert electrochemical responses, the NaPPDT/PAPA 1/1 (w/w) composite hydrogel in a thin-layer cell as a working electrode showed an oxidation peak at 0.60 V in the anodic oxidation process and a corresponding smaller reduction peak at −0.30 V in the cathodic oxidation process, attributed to the electrochemical response of the polyaniline complex in the composite hydrogel. These electrochemical processes were similar to those of a typical polyaniline film, as seen in the literature [61,64]. These results demonstrate that the composite gels may become potentially paintable and thixotropic electrode-active materials for electrochemical devices. To utilize the paintable and thixotropic properties of the composite gels, further electrochemical evaluation of the composite gel electrode is required.

3. Conclusions

In conclusion, the simple mixing of a water-soluble electronically conducting polyaniline complex PAPA and the polymeric hydrogelator NaPPDT produced a new composite molecular hydrogel with improved gelation ability and thixotropic behavior, although no individual component exhibited these gel properties in the same concentration regions. The new composite hydrogel showed the retention of the gel state in an electrolyte solution and electronic conductivity in a semiconducting region, which proves the applicability of electroactive materials in electrochemical devices. The NaPPDT/PAPA 1/1 (w/w) composite hydrogels demonstrated electrochemical responses owing to the polyaniline complex in an aqueous electrolyte. These results showed that composite hydrogels might be suitable for new potential paintable electrode materials. A detailed examination of the electrochemical properties of the composite hydrogels for glucose sensors is ongoing.

4. Materials and Methods

NaPPDT (Mn = 10,000) was synthesized according to the literature procedures [52,65,66]. Aniline (99%, Wako Pure Chemical Industries, Ltd., Tokyo, Japan) was used without further purification. All other chemicals were purchased from Wako Pure Chemical Industries, Ltd. and used without further purification. Water was deionized with an Elix UV 3 Milli-Q integral water purification system (Nihon Millipore K.K., Tokyo, Japan). Glucose oxidase from Aspergillus niger (Type VII, lyophilized powder, ≥100,000 units/g solid (without added oxygen)) was purchased from Sigma-Aldrich and used as received.
The water-soluble polyaniline complex (PAPA) was prepared via the oxidative polymerization of aniline with potassium persulfate (APS, electrophoresis grade) in the presence of phosphoric acid (PA). Firstly, in a sample tube, 470 mg aniline (5.00 mmol) and 1.65 g PA (15.00 mmol) were dissolved in 2 mL of Triton-X-100 1 wt% aqueous solution (solution A). In another sample tube, 582 mg APS (2.50 mmol) was dissolved in 2 mL of Triton-X-100 1 wt% aqueous solution (solution B). Solutions B and A were placed in a refrigerator (5 °C) for 5 min, and then solution B was added to solution A in an ice bath (10 °C) and allowed to react for 10 min without stirring. The mixed solution immediately turned black/green and solidified. The mixed solution was left to stand at room temperature for 24 h and then placed in a Fisherbrandt regenerated cellulose dialysis tube (molecular weight cut off: 3500 Da, Fisher Scientific and wexer lifescience Co.,Ltd., Tokyo, Japan) with pure water. The concentrated PAPA aqueous solution after dialysis was prepared (based on the weight of the solution after it was dried) so that the dry matter weight was 1.0 wt% in the aqueous solution. Unfortunately, the dried samples from the PAPA dispersion were insoluble in D2O and DMSO-d6, so the chemical structure could not be measured by NMR measurements.
Elemental analysis result for PAPA was performed with YANACO CHN CORDER MT-5 (organic trace element analyzer, YANACO technicalscience, Co., Ltd., Tokyo, Japan). Elemental analysis result for PAPA: Found: C, 62.38; H, 4.37; N, 11.95 (1st measurement) and Found: C, 62.61; H, 4.40; N, 11.95 (2nd measurement). From the elemental analysis of PAPA, the molar mass ratio of the aniline moiety (An: -NHC6H4-) to the phosphate moiety (PA: P=O(OH)3), taking into account the presence of bound water, yields the following ratio: An/PA/H2O = 100/25/5 = 20/5/1 (C, 61.85; H, 5.09; N, 12.02).
The preparation of NaPPDT/PAPA composite hydrogels was done as follows: at first, 1.0 wt% NaPPDT hydrogel was made by mixing NaPPDT solid and pure water and rest for one day at room temperature. Then 1.0wt% PAPA aq. was added to the 1.0 wt% NaPPDT gel at room temperature and mixed by use of a vortex genie (Scientific Industries, Inc., Bohemia, New York, NY, USA). Before measurements, the mixed composite hydrogels were rested for 30 min.
Gelation ability and thixotropic behavior were evaluated by the vial inversion method (a method in which a vial containing gel is inverted and judged to be a gel state if it does not drip). In evaluating thixotropic behavior, if it recovered from a sol to a gel when it was broken with a vortex gene to form a sol and inverted after standing for a certain time (If it is not recovered and sol, it will drip).
SEM image measurements were carried out using a SU-8000 scanning electron microscope (Hitachi High-Technologies Corporation, Tokyo, Japan) at 1.0 kV. The freeze-dried sample or freeze-dried hydrogels (xerogels) were measured on a conductive tape on the brass SEM stage. The samples were coated with a spattering of Pt (10 nm-thick) to add electrical conductivity.
Rheological measurements were performed using an MCR-301 rheometer (Anton Paar Japan K.K., Tokyo, Japan) with a parallel plate (8 mm diameter) at a gap of 0.50 mm at 25 °C. The frequency sweeps were carried out with γ of 0.01 %. The strain sweeps were carried out with a constant angular frequency of 1 rad s−1. The repeated step-shear measurements were carried out with a normal strain with an amplitude of 0.01% and frequency of 1 Hz and a large strain with a shear rate of 3000 s−1 for 0.1 s.
Measurements of the absorbance of a 0.4 mm thick polymer or hydrogel sample between slide glasses with overlapped Kapton films (0.4 mm thickness) as a spacer and PAPA aq. in a quartz cuvette with a light path length of 1.0 mm were performed using a measurement system consisting of a spectrometer HR4000 (Ocean Optics, Inc., Tokyo, Japan), UV-VIS-NIR light source DH-200-BAL (Mikropack GmbH), and variable attenuator FVA-UV (Ocean Optics, Inc., Tokyo, Japan) controlled by PC software OPwave (Ocean Photonics, Tokyo, Japan). The measurement system was constructed by Ocean Photonics.
The electronic conductivity of the composite hydrogel was evaluated with a four-probe method using an interdigitated array electrode (BAS Inc., Tokyo, Japan), a digital multimeter 34401a (KEYSIGHT TECHNOLOGIES, Santa Rosa, CA, USA) and (ADC CORPORATION, Saitama, Japan), a digital multimeter GDM 8255 (Good Will Instrument Co., Ltd., New Taipei City, Taiwan), and a DC power supply U8001 A (30 V/3 A, KEYSIGHT TECHNOLOGIES, Santa Rosa, CA, USA). An interdigitated array electrode for the four-probe method was placed on a cool plate CP-085 (SANSYO, Co., Ltd., Tokyo, Japan) at 25 °C. The current value between the inner electrodes was measured when a DC voltage was applied between the outer electrodes of the four terminals, and the resistance of the gel sample was calculated from the distance between the electrodes and the electrode area. We placed the gel on the electrode, and after an ionic current of the composite hydrogel was settled, the electronic conductivity of the hydrogel was measured.
For electrochemical measurement using an electrochemical analyzer ALS model 6271E (BAS Inc., Tokyo, Japan), the composite gel or NaPPDT gel was sandwiched between an indium–tin–oxide electrode (10 ohm/square) and a glass slide via spacers (overlapped Kapton films: 0.4 mm thickness) to form a thin-layer cell (active area: 9 mm × 10 mm). The protruded gel that formed during the fabrication of the cell was wiped off. Cyclic voltammetry for the thin-layer cell made with the gel immersed in NaCl aq. (0.1 mol dm−3) was conducted with platinum wire and Ag/AgCl (3 mol dm−3) as the counter and reference electrodes, respectively. To prepare for future electrochemical measurements, measurements were made on a composite gel containing 1 wt% glucose oxidase.

Author Contributions

Conceptualization, Y.O.; investigation, Y.O. and M.S.; writing—original draft preparation, Y.O.; writing—review and editing, Y.O. and M.S.; supervision, Y.O.; funding acquisition, Y.O. All authors have read and agreed to the published version of the manuscript.

Funding

This research was partly funded by JSPS KEKENHI, grant numbers 15K05610 and 19K05634. A part of this work was supported by Nissan Chemical Industries, Ltd.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Acknowledgments

The SEM measurement was performed at the Research Center for Materials and Energy Devices of the Fukuoka Institute of Technology (FIT-ME). The author is indebted to the Service Center of the Elementary Analysis of Organic Compounds, Kyushu University for elemental analysis.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Reynolds, J.R.; Thompson, B.C.; Skotheim, T.A. Handbook of Conducting Polymers, 4th ed.; CRC Press: Boca Raton, FL, USA, 2019. [Google Scholar]
  2. Chandrasekhar, P. Conducting Polymers, Fundamentals and Applications, 2nd ed.; Springer International Publishing: Cham, Switzerland, 2018. [Google Scholar]
  3. Rahman, M.A.; Kumar, P.; Park, D.-S.; Shim, Y.-B. Electrochemical Sensors Based on Organic Conjugated Polymers. Sensors 2008, 8, 118–141. [Google Scholar] [CrossRef]
  4. Rahman, M.M.; Ahammad, A.J.S.; Jin, J.-H.; Ahn, S.J.; Lee, J.-J. Electrochemical DNA Hybridization Sensors Based on Conducting Polymers. Sensors 2015, 15, 3801–3829. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  5. Khan, A.; Jawaid, M.; Khan, A.A.P.; Asiri, A.M. Electrically Conductive Polymers and Polymer Composites: From Synthesis to Biomedical Applications; Wiley-VCH: Weinheim, Germany, 2018. [Google Scholar]
  6. Le, T.H.; Kim, Y.; Yoon, H. Electrical and Electrochemical Properties of Conducting Polymers. Polymers 2017, 9, 150. [Google Scholar] [CrossRef] [PubMed]
  7. Nezakati, T.; Seifalian, A.; Tan, A.; Seifalian, A.M. Conductive Polymers: Opportunities and Challenges in Biomedical Applications. Chem. Rev. 2018, 118, 6766–6843. [Google Scholar] [CrossRef] [PubMed]
  8. Ibanez, J.G.; Rincón, M.E.; Gutierrez-Granados, S.; Chahma, M.; Jaramillo-Quintero, O.A.; Frontana-Uribe, B.A. Conducting Polymers in the Fields of Energy, Environmental Remediation, and Chemical-Chiral Sensors. Chem. Rev. 2018, 118, 4731–4816. [Google Scholar] [CrossRef]
  9. Namsheer, K.; Rout, C.S. Conducting Polymers: A Comprehensive Review on Recent Advances in Synthesis, Properties and Applications. RSC Adv. 2021, 11, 5659–5697. [Google Scholar] [CrossRef]
  10. Zare, E.N.; Makvandi, P.; Ashtari, B.; Rossi, F.; Motahari, A.; Perale, G. Progress in Conductive Polyaniline-Based Nanocomposites for Biomedical Applications: A Review. J. Med. Chem. 2020, 63, 1–22. [Google Scholar] [CrossRef]
  11. Beygisangchin, M.; Rashid, S.A.; Shafie, S.; Sadrolhosseini, A.R.; Lim, H.N. Preparations, Properties, and Applications of Polyaniline and Polyaniline Thin Films—A Review. Polymers 2021, 13, 2003. [Google Scholar] [CrossRef]
  12. Pecher, J.; Mecking, S. Nanoparticles of Conjugated Polymers. Chem. Rev. 2010, 110, 6260–6279. [Google Scholar] [CrossRef]
  13. Jaymand, M. Recent progress in chemical modification of polyaniline. Prog. Polym. Sci. 2013, 38, 1287–1306. [Google Scholar] [CrossRef]
  14. Ma, Z.; Shi, W.; Yan, K.; Pan, P.; Yu, G. Doping engineering of conductive polymer hydrogels and their application in advanced sensor technologies. Chem. Sci. 2019, 10, 6232–6244. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  15. Hassan, M.H.; Vyas, C.; Grieve, B.; Bartolo, P. Recent Advances in Enzymatic and Non-Enzymatic Electrochemical Glucose Sensing. Sensors 2021, 21, 4672. [Google Scholar] [CrossRef] [PubMed]
  16. Ghosh, S.; Inganäs, O. Conducting Polymer Hydrogels as 3D Electrodes: Applications for Supercapacitors. Adv. Mater. 1999, 11, 1214–1218. [Google Scholar] [CrossRef]
  17. Åsberg, P.; Inganäs, O. Hydrogels of a conducting conjugated polymer as 3-D enzyme electrode. Biosens. Bioelectron. 2003, 30, 199–207. [Google Scholar] [CrossRef]
  18. Pérez-Madrigal, M.M.; Estrany, F.; Armelin, E.; Díaz, D.D.; Alemán, C. Towards Sustainable Solid-State Supercapacitors: Electroactive Conducting Polymers Combined with Biohydrogels. J. Mater. Chem. A 2016, 4, 1792–1805. [Google Scholar] [CrossRef] [Green Version]
  19. Pan, L.; Yu, G.; Zhai, D.; Lee, H.R.; Zhao, W.; Liu, N.; Wang, H.; Tee, B.C.K.; Shi, Y.; Cui, Y.; et al. Hierarchical Nanostructured Conducting Polymer Hydrogel with High Electrochemical Activity. Proc. Natl. Acad. Sci. USA 2012, 109, 9287–9292. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  20. Zhai, D.; Liu, B.; Shi, Y.; Pan, L.; Wang, Y.; Li, W.; Zhang, R.; Yu, G. Highly Sensitive Glucose Sensor Based on Pt Nanoparticle/Polyaniline Hydrogel Heterostructures. ACS Nano 2013, 7, 3540–3546. [Google Scholar] [CrossRef]
  21. Lu, Y.; He, W.; Cao, T.; Guo, H.; Zhang, Y.; Li, Q.; Shao, Z.; Cui, Y.; Zhang, X. Elastic, Conductive, Polymeric Hydrogels and Sponges. Sci. Rep. 2014, 4, 5792. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  22. Weiss, R.G.; Terech, P. Molecular Gels: Materials with Self-Assembled Fibrillar Networks; Springer: Dordrecht, The Netherlands, 2006. [Google Scholar]
  23. Guenet, J.-M. Organogels Thermodynamics, Structure, Solvent Role, and Properties; Springer International Publishing AG: Cham, Switzerland, 2016. [Google Scholar]
  24. Weiss, R.G.; Blair, D.L.; Toro-Vazquez, J.F.; Perez-Martinez, J.D.; Li, J.; Zhang, Z.; Liu, X.; Rubio-Magnieto, J.; Escuder, B.; Rogers, M.A.; et al. Corradini. In Molecular Gels, Structure and Dynamics; The Royal Society of Chemistry: London, UK, 2018. [Google Scholar]
  25. Dawn, A.; Shiraki, T.; Haraguchi, S.; Tamaru, S.; Shinkai, S. What Kind of “Soft Materials” Can We Design from Molecular Gels? Chem. Asian J. 2011, 6, 266–282. [Google Scholar] [CrossRef]
  26. Weiss, R.G. The Past, Present, and Future of Molecular Gels. What Is the Status of the Field, and Where Is It Going? J. Am. Chem. Soc. 2014, 136, 7519–7530. [Google Scholar] [CrossRef]
  27. Babu, S.S.; Praveen, V.K.; Ajayaghosh, A. Functional π-Gelators and Their Applications. Chem. Rev. 2014, 114, 1973–2129. [Google Scholar] [CrossRef] [PubMed]
  28. Rogers, M.A.; Weiss, R.G. Systematic Modifications of Alkane-Based Molecular Gelators and the Consequences to the Structures and Properties of Their Gels. New J. Chem. 2015, 39, 785–799. [Google Scholar] [CrossRef]
  29. Ohsedo, Y. Low-Molecular-Weight Organogelators as Functional Materials for Oil Spill Remediation. Polym. Adv. Technol. 2016, 27, 704–711. [Google Scholar] [CrossRef]
  30. Ohsedo, Y. Low-Molecular-Weight Gelators as Base Materials for Ointments. Gels 2016, 2, 13. [Google Scholar] [CrossRef] [PubMed]
  31. Yamanaka, M. Development of C3-Symmetric Tris-Urea Low-Molecular-Weight Gelators. Chem. Rec. 2016, 16, 768–782. [Google Scholar] [CrossRef]
  32. Amabilino, D.B.; Smith, D.K.; Steed, J.W. Supramolecular Materials. Chem. Soc. Rev. 2017, 46, 2404–2420. [Google Scholar] [CrossRef]
  33. Miao, R.; Peng, J.; Fang, Y. Molecular Gels as Intermediates in the Synthesis of Porous Materials and Fluorescent Films: Concepts and Applications. Langmuir 2017, 33, 10419–10428. [Google Scholar] [CrossRef]
  34. Weiss, R.G. Controlling Variables in Molecular Gel Science: How Can We Improve the State of the Art? Gels 2018, 4, 25. [Google Scholar] [CrossRef] [Green Version]
  35. Mayr, J.; Saldías, C.; Díaz Díaz, D. Release of Small Bioactive Molecules from Physical Gels. Chem. Soc. Rev. 2018, 47, 1484–1515. [Google Scholar] [CrossRef]
  36. Chivers, P.R.A.; Smith, D.K. Shaping and Structuring Supramolecular Gels. Nat. Rev. Mater. 2019, 4, 463–478. [Google Scholar] [CrossRef] [Green Version]
  37. Panja, S.; Adams, D.J. Stimuli Responsive Dynamic Transformations in Supramolecular Gels. Chem. Soc. Rev. 2021, 50, 5165–5200. [Google Scholar] [CrossRef] [PubMed]
  38. Lee, K.Y.; Mooney, D.J. Hydrogels for Tissue Engineering. Chem. Rev. 2001, 101, 1869–1880. [Google Scholar] [CrossRef] [PubMed]
  39. Wojtecki, R.J.; Meador, M.A.; Rowan, S.J. Using the Dynamic Bond to Access Macroscopically Responsive Structurally Dynamic Polymers. Nat. Mater. 2011, 10, 14–27. [Google Scholar] [CrossRef] [PubMed]
  40. Krieg, E.; Bastings, M.M.C.; Besenius, P.; Rybtchinski, B. Supramolecular Polymers in Aqueous Media. Chem. Rev. 2016, 116, 2414–2477. [Google Scholar] [CrossRef] [PubMed]
  41. Goodwin, J.; Hughes, R. Rheology for Chemists: An Introduction, 2nd ed.; Royal Society of Chemistry: Cambridge, UK, 2008. [Google Scholar]
  42. Cornwell, D.J.; Smith, D.K. Expanding the scope of gels —combining polymers with low-molecular-weight gelators to yield modified self-assembling smart materials with high-tech applications. Mater. Horiz. 2015, 2, 279–293. [Google Scholar] [CrossRef] [Green Version]
  43. Guenet, J.M. Hybrid Physical Gels from Polymers and Self-Assembled Systems: A Novel Path for Making Functional Materials. Gels 2018, 4, 35. [Google Scholar] [CrossRef] [Green Version]
  44. Draper, E.R.; Adams, D.J. How Should Multicomponent Supramolecular Gels Be Characterised? Chem. Soc. Rev. 2018, 47, 3395–3405. [Google Scholar] [CrossRef] [Green Version]
  45. Dasgupta, D.; Srinivasan, S.; Rochas, C.; Ajayaghosh, A.; Guenet, J.M. Hybrid Thermoreversible Gels from Covalent Polymers and Organogels. Langmuir 2009, 25, 8593–8598. [Google Scholar] [CrossRef]
  46. Nyrkova, I.; Moulin, E.; Armao, I.J.J.; Maaloum, M.; Heinrich, B.; Rawiso, M.; Niess, F.; Cid, J.-J.; Jouault, N.; Buhler, E.; et al. Supramolecular Self-Assembly and Radical Kinetics in Conducting Self-Replicating Nanowires. ACS Nano 2014, 8, 10111–10124. [Google Scholar] [CrossRef]
  47. Zoukal, Z.; Elhasri, S.; Carvalho, A.; Schmutz, M.; Collin, D.; Vakayil, P.K.; Ajayaghosh, A.; Guenet, J.M. Hybrid Materials from Poly(Vinyl Chloride) and Organogels. ACS Appl. Polym. Mater. 2019, 1, 1203–1208. [Google Scholar] [CrossRef]
  48. Talebpour, P.; Heinrich, B.; Gavat, O.; Carvalho, A.; Moulin, E.; Giuseppone, N.; Guenet, J.M. Modulation of the Molecular Structure of Tri-Aryl Amine Fibrils in Hybrid Poly[Vinyl Chloride] Gel/Organogel Systems. Macromolecules 2021, 54, 8104–8111. [Google Scholar] [CrossRef]
  49. Ohsedo, Y.; Watanabe, H.; Oono, M.; Tanaka, A. Mixing Enhancement Effect of Low-Molecular-Weight Organogelators for Thixotropic Organogel Creation. Chem. Lett. 2013, 42, 363–365. [Google Scholar] [CrossRef]
  50. Ohsedo, Y.; Oono, M.; Tanaka, A.; Watanabe, H. Mixing Induced Thixotropy of a Two-Component System of Alkylurea Organogelators Having Different Alkyl Chains. New J. Chem. 2013, 37, 2250–2253. [Google Scholar] [CrossRef]
  51. Ohsedo, Y.; Oono, M.; Saruhashi, K.; Watanabe, H.; Miyamoto, N. A New Composite Thixotropic Hydrogel Composed of a Low-Molecular-Weight Hydrogelator and a Nanosheet. RSC Adv. 2014, 4, 44837–44840. [Google Scholar] [CrossRef]
  52. Ohsedo, Y.; Oono, M.; Saruhashi, K.; Watanabe, H. A New Water-Soluble Aromatic Polyamide Hydrogelator with Thixotropic Properties. RSC Adv. 2015, 5, 82772–82776. [Google Scholar] [CrossRef]
  53. Ohsedo, Y.; Oono, M.; Saruhashi, K.; Watanabe, H.; Miyamoto, N. New Composite Thixotropic Hydrogel Composed of a Polymer Hydrogelator and a Nanosheet. R. Soc. Open Sci. 2017, 4, 171117. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  54. Ohsedo, Y.; Saruhashi, K.; Watanabe, H.; Miyamoto, N. Synthesis of an Electronically Conductive Hydrogel from a Hydrogelator and a Conducting Polymer. New J. Chem. 2017, 41, 9602–9606. [Google Scholar] [CrossRef]
  55. Amaya, T.; Sugihara, R.; Hata, D.; Hirao, T. Self-Doped Polyaniline Derived from Poly(2-Methoxyaniline-5-Phosphonic Acid) and Didodecyldimethylammonium Salt. RSC Adv. 2016, 6, 22447–22452. [Google Scholar] [CrossRef] [Green Version]
  56. Amaya, T.; Kurata, I.; Inada, Y.; Hatai, T.; Hirao, T. Synthesis of Phosphonic Acid Ring-Substituted Polyanilines via Direct Phosphonation to Polymer Main Chains. RSC Adv. 2017, 7, 39306–39313. [Google Scholar] [CrossRef] [Green Version]
  57. Kavanagh, G.M.; Ross-Murphy, S.B. Rheological Characterisation of Polymer Gels. Prog. Polym. Sci. 1998, 23, 533–562. [Google Scholar] [CrossRef]
  58. Dawn, A.; Kumari, H. Low Molecular Weight Supramolecular Gels Under Shear: Rheology as the Tool for Elucidating Structure–Function Correlation. Chem.–A Eur. J. 2018, 24, 762–776. [Google Scholar] [CrossRef]
  59. Aston, R.; Sewell, K.; Klein, T.; Lawrie, G.; Grøndahl, L. Evaluation of the Impact of Freezing Preparation Techniques on the Characterisation of Alginate Hydrogels by Cryo-SEM. Eur. Polym. J. 2016, 82, 1–15. [Google Scholar] [CrossRef] [Green Version]
  60. Huang, W.S.; MacDiarmid, A.G. Optical Properties of Polyaniline. Polymer 1993, 34, 1833–1845. [Google Scholar] [CrossRef]
  61. Watanabe, A.; Mori, K.; Iwasaki, Y.; Nakamura, Y.; Niizuma, S. Electrochromism of Polyaniline Film Prepared by Electrochemical Polymerization. Macromolecules 1987, 20, 1793–1796. [Google Scholar] [CrossRef]
  62. Shirota, Y.; Noma, N.; Kanega, H.; Mikawa, H. Preparation of an Electrically Conducting Polymer by the Electrolytic Polymerization of N-Vinylcarbazole. J. Chem. Soc. Chem. Commun. 1984, 7, 470–471. [Google Scholar] [CrossRef]
  63. Kakuta, T.; Shirota, Y.; Mikawa, H. A Rechargeable Battery Using Electrochemically Doped Poly(N-Vinylcarbazole). J. Chem. Soc. Chem. Commun. 1985, 9, 553–554. [Google Scholar] [CrossRef]
  64. Rubinstein, I.; Sabatani, E.; Rishpon, J. Electrochemical Impedance Analysis of Polyaniline Films on Electrodes. J. Electrochem. Soc. 1987, 134, 3078–3083. [Google Scholar] [CrossRef]
  65. Viale, S.; Best, A.S.; Mendes, E.; Jager, W.F.; Picken, S.J. A Supramolecular Nematic Phase in Sulfonated Polyaramides. Chem. Commun. 2004, 12, 1596–1597. [Google Scholar] [CrossRef]
  66. Viale, S.; Li, N.; Schotman, A.H.M.; Best, A.S.; Picken, S.J. Synthesis and Formation of a Supramolecular Nematic Liquid Crystal in Poly(p-Phenylene−sulfoterephthalamide)−H2O. Macromolecules 2005, 38, 3647–3652. [Google Scholar] [CrossRef]
Gels 08 00469 sch001 550
Scheme 1. Chemical structures of the polymer hydrogelator (NaPPDT) and water-soluble polyaniline complex (PAPA).
Scheme 1. Chemical structures of the polymer hydrogelator (NaPPDT) and water-soluble polyaniline complex (PAPA).
Gels 08 00469 sch001
Gels 08 00469 g001 550
Figure 1. Photos of gelation test: (a) NaPPDT aqueous solutions in vials, (b) 1.0 wt% NaPPDT/1.0 wt% PAPA aq. mixed in vials, and (c) 1.0 wt% PAPA aq.
Figure 1. Photos of gelation test: (a) NaPPDT aqueous solutions in vials, (b) 1.0 wt% NaPPDT/1.0 wt% PAPA aq. mixed in vials, and (c) 1.0 wt% PAPA aq.
Gels 08 00469 g001
Gels 08 00469 g002 550
Figure 2. Rheometric results of NaPPDT/PAPA hydrogel systems: (a) frequency sweep, (b) strain sweep, and (c) periodic step-shear test (a vibration of G” was observed in both samples, probably due to the vibration of gels while the measurements were taken).
Figure 2. Rheometric results of NaPPDT/PAPA hydrogel systems: (a) frequency sweep, (b) strain sweep, and (c) periodic step-shear test (a vibration of G” was observed in both samples, probably due to the vibration of gels while the measurements were taken).
Gels 08 00469 g002
Gels 08 00469 g003 550
Figure 3. Photos of thixotropic behavior of 1.0 wt% NaPPDT/1.0 wt% PAPA aq. 1/1 (w/w) in a vial: (left) before shaking (gel state), (center) immediately after shaking (sol state), and (right) after resting for 1 min.
Figure 3. Photos of thixotropic behavior of 1.0 wt% NaPPDT/1.0 wt% PAPA aq. 1/1 (w/w) in a vial: (left) before shaking (gel state), (center) immediately after shaking (sol state), and (right) after resting for 1 min.
Gels 08 00469 g003
Gels 08 00469 g004 550
Figure 4. Scanning electron microscopy (SEM) images of xerogels and the dried sample obtained from freeze-drying method: (a) NaPPDT xerogel prepared from the corresponding NaPPDT 1.0 wt% hydrogel, (b) dried sample of 1.0 wt% PAPA aq., (c) NaPPDT/PAPA composite xerogel prepared from the corresponding NaPPDT/PAPA 1/1 (w/w) composite hydrogel.
Figure 4. Scanning electron microscopy (SEM) images of xerogels and the dried sample obtained from freeze-drying method: (a) NaPPDT xerogel prepared from the corresponding NaPPDT 1.0 wt% hydrogel, (b) dried sample of 1.0 wt% PAPA aq., (c) NaPPDT/PAPA composite xerogel prepared from the corresponding NaPPDT/PAPA 1/1 (w/w) composite hydrogel.
Gels 08 00469 g004
Gels 08 00469 g005 550
Figure 5. The UV-vis absorption bands of 1.0 wt% NaPPDT, NaPPDT/PAPA 1/1 (w/w) composite hydrogel, and 1.0 wt% PAPA aq.
Figure 5. The UV-vis absorption bands of 1.0 wt% NaPPDT, NaPPDT/PAPA 1/1 (w/w) composite hydrogel, and 1.0 wt% PAPA aq.
Gels 08 00469 g005
Gels 08 00469 g006 550
Figure 6. Solubility test of the hydrogels using a lump of the NaPPDT/PAPA 1/1 (w/w) composite hydrogel in NaCl aq. after 1 week.
Figure 6. Solubility test of the hydrogels using a lump of the NaPPDT/PAPA 1/1 (w/w) composite hydrogel in NaCl aq. after 1 week.
Gels 08 00469 g006
Gels 08 00469 g007 550
Figure 7. Cyclic voltammograms of hydrogels in 0.1 NaCl aq.: NaPPDT/PAPA 1/1 (w/w) composite gel and 1.0 wt% NaPPDT gel (10 oxidation/reduction cycles, scan rate: 0.05 V s−1). The horizontal arrows indicate the direction of movement of the curve as the number of scans increases.
Figure 7. Cyclic voltammograms of hydrogels in 0.1 NaCl aq.: NaPPDT/PAPA 1/1 (w/w) composite gel and 1.0 wt% NaPPDT gel (10 oxidation/reduction cycles, scan rate: 0.05 V s−1). The horizontal arrows indicate the direction of movement of the curve as the number of scans increases.
Gels 08 00469 g007
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Ohsedo, Y.; Sasaki, M. Polymeric Hydrogelator-Based Molecular Gels Containing Polyaniline/Phosphoric Acid Systems. Gels 2022, 8, 469. https://doi.org/10.3390/gels8080469

AMA Style

Ohsedo Y, Sasaki M. Polymeric Hydrogelator-Based Molecular Gels Containing Polyaniline/Phosphoric Acid Systems. Gels. 2022; 8(8):469. https://doi.org/10.3390/gels8080469

Chicago/Turabian Style

Ohsedo, Yutaka, and Mayumi Sasaki. 2022. "Polymeric Hydrogelator-Based Molecular Gels Containing Polyaniline/Phosphoric Acid Systems" Gels 8, no. 8: 469. https://doi.org/10.3390/gels8080469

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop