Effect of sodium chloride on the enhanced performance of chitosan-based ion actuator

doi:10.21203/rs.3.rs-3319679/v1

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Effect of sodium chloride on the enhanced performance of chitosan-based ion actuator

https://doi.org/10.21203/rs.3.rs-3319679/v1

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In this work, an actuate membrane and an electrode membrane were prepared by a sol-gel method. And then, they were physically pressed to form a chitosan-based ion actuator (CSIA). Importantly, the effect of sodium chloride on CSIA were investigated, the mechanical properties of CSIA were tested by establishing an output force test platform while testing its porosity. And, the electrochemical performance was tested by electrochemical workstation. At the end, the surface morphology and functional groups were measured by scanning electron microscopy and Infrared spectrogram, respectively. The results indicated that the sodium chloride mass ratio was the best at 0.4 % for CSIA. Its output force of mechanical properties could attain at 2.939 mN and the maximum porosity of 12.98 % at the same time. The specific capacitance of the electrochemical performance was up to 0.07719 F g^-1, and the minimum resistance reached 13.48 Ω. From the surface morphology and functional groups, the appropriate doping ratio of Nacl into CSIA was helpful for increasing the transport space of internal ions. The effective internal ion concentration and significantly reduced internal stress provided excellent performances under the appropriate voltage conditions. The doping of inorganic ion sodium chloride improved the internal electron transport efficiency of chitosan ion actuator, and it advanced the mechanical properties of the actuator. Hence the enhancement of Nacl output force in CSIA had a good significance for the development of inorganic salt ion strengthened ion actuator.

Sodium chloride

chitosan

doped

ion actuator

In the process of productivity development and technological innovation, traditional mechanical methods can no longer meet the current development trend of miniaturization, portability, intelligence and precision on account of their low efficiency and high energy consumption^[1–4]. Because of the advantages of light weight, low manufacturing cost, low actuating voltage, good flexibility and fast response speed, ion actuator had extremely important application potential in aerospace, underwater equipment, biomedicine, micro-robotics and other fields^[5–7]. In recent years, the researchers found that the actuate membrane materials including sodium alginate^[8], cellulose, chitosan^[9–12]. Due to their unique three-dimensional network structure and ability to retain a large amount of water, ion actuator had a wide range of applications in hydrogel artificial muscles^[13] including biomedical applications, drug carriers^[14–15], biosensors^[16], medical devices^[17], tissue engineering^[18], separation systems^[19–20], microfluidic systems^[21], microvalves^[22] and actuator^[23–24]. Chitosan (CS) was a product of natural chitin. Owing to its rich hydroxyl and amino groups, the chemical properties of CS were the more active. This was able to improve its strength, heat resistance, elastic modulus, electrical conductivity and other abilities through a variety of chemical modification reactions, while having good biocompatibility and biodegradable characteristics^[25].

According to the conductive mechanism, ion actuator was divided into inorganic salt ion conductive actuator and ionic liquid conductive actuator. The preparation methods of ion actuator were generally classified into two types. One of them was to put inorganic salts into an ionic solution formed by the formed hydrogel material, after that the ions penetrated into the hydrogel network to obtain ion actuator. And the other one was to use the one-pot method, which it added all raw materials including inorganic salt ions into the reaction system to form an ionic conductive hydrogel. Compared with traditional doping reagents, Nacl had the more reliable purity and raw material price advantages, and the process flow was relatively simple without complex side reaction impurities. However, ion actuator still had the problems of small mechanical properties and narrow doping improvement paths. At the meantime, the preparation of chitosan-based ion actuator (CSIA) by Nacl dissolved in gel solution had not been tested, and the effect of CSIA materials on the output performance and electrochemical performance of gel material actuator needed to be further studied.

Therefore, this work proposes to immerse ionic conductive hydrogels in inorganic salt ion solutions by physical doping process to just the proportion of inorganic salt Na⁺ ions. Then, the effect of sodium chloride on CSIA was studied by testing the mechanical properties, porosity, electrochemical properties, and surface morphology and functional group measurements.

2.1 Experimental and reagent

Force measurement software (FA1004) was produced by Shanghai Shangping Instrument Co., Ltd (Shanghai, China). Vacuum drying oven (DZF-6050) was produced by Shanghai sead Instrument Co., Ltd (Shanghai, China). Electrochemical workstation (CHI760E) was produced by Shanghai Chenhua Instrument Co., Ltd. Infrared spectroscopy (FT-IR200) was produced by Tianjin Gangdong Technology Development Co., Ltd. Scanning electron microscope (S-240) was produced by Cambridge Instrument Company.

Chitosan (CS), sodium chloride (Nacl), acetic acid (HAC), Multi-walled carbon nanotubes (MCNT), Glycerol were provided by Shanghai Aladdin Bio-Chem Technology Co., Ltd (Shanghai, China). All chemicals were of analytic grade and used without treating further for purification and the deionized water was self-restraint.

2.2 Preparation of chitotan-based ion actuator

Chitosan-based ion actuator was a new type of responsive electronic material, mainly composed of electrode membranes and actuate membranes, and its detailed preparation was shown in Figure S1. The detailed preparation of Nacl-doped CSIA in this experiment was shown in Table S1.

2.3 Experimental setup

2.3.1 Output force and displacement test of CSIA

The force test platform was shown in Figure S2 (a), under the experimental test conditions of 300 s, voltage of 3 V and baud rate of 9600, the output force test of CSIA samples from S0-S5 was carried out, and the output force experimental test data of 6 groups were averaged. The deflection of CSIA on electrical stimulation was shown in Figure S2 (b).

Since the ion channel could improve the transmission ratio of charged ions inside the actuate membrane of CSIA, its mechanochemical characteristics and the porosity of the actuate membrane^[26]. The formula for calculating porosity was shown below.

$$P=\frac{{m}_{1}-{m}_{0}}{\rho \times V}\times 100 \% \left(1\right)$$

Where ${m}_{0}$ (g) was the constant mass of the actuate membrane. ${m}_{1}$ (g) was the mass weight. r (g.cm^− 3) was the density of absolute ethanol and $V$ (cm³) was the volume of the samples, respectively.

2.3.2 Electrochemical testing of CSIA

The electrochemical tests were tested by the electrochemical workstation, as shown in Figure S3 (a). The three-electrode system (Figure S3 (b)) was formed by using saturated calomel electrode as reference electrode and platinum electrode as auxiliary electrode and working electrode. The CHI760E was used for cyclic voltammetry (CV) test and electrochemical impedence spectroscopy (EIS) test. The volt-ampere characteristic was curve obtained by the actuate membranes at 20 mV s^− 1, 50 mV s^− 1, 100 mV s^− 1 scanning speeds. Because the clamping part of the electrochemical analyzer and the actuate membrane might had certain poor contact and the voltage instability when the instrument started, so the method of cyclic scanning was used to obtain three sets of voltammetry characteristic curve data at scanning speed. Calculating the area enclosed by the plotted figure, which was approximately the value of the integral part, and then it was brought into the specific capacitance formula^[27] to calculate the specific capacitance (Cp) of the material. The specific capacitance was calculated as follows.

$$Cp=\frac{A}{2({V}_{2}-{V}_{1}\times m\times k)} \left(2\right)$$

Among them, Cp was the specific capacitance. A was the scanning area. ${V}_{1}$ and ${V}_{2}$ were low and high potential, respectively. m was the sample quality and k was the scanning speed.

The equivalent circuit model was indicated in Figure S3 (c). It was used to study the electrochemical impedance data^[28].This analog circuit used ${R}_{s}$ to represent the resistance of the electrolyte solution, ${R}_{ct}$ to denote the charge transfer resistance, ${C}_{d}$ to show the electric double-layer capacitance, and ${W}_{o}$ to represent the open potential. Data fitting was performed using Z-view software. The reverse extension of the data in the figure was connected to the x-axis, and its intercept was the measured resistance value.

2.3.3 Morphology and functional group testing of CSIA

The surface morphology of S0-S5 of the CSIA sample was microscopic by high-resolution scanning electron microscope (SEM). By Fourier transform, the infrared spectrum in the range of 4000 − 400 cm^− 1 was marked with potassium bromide (KBr) particles to study the chemical molecular structure and physical doping reaction of the actuate membrane.

3.1 Effect of Nacl on the mechanical properties of CSIA

The output force and time curves of different CSIA samples were shown in Fig. 1(a), from which it could be concluded that from S0 to S4, with the increase of the doping ratio of Nacl, the maximum output force of the CSIA sample S4 reached 2.939 mN, which was 3.4 times higher than that of the control group S0. With the doping ratio continuously increased, the output force decreased to 0.3020 mN for S5 sample, and it reached 54.72% of S0. This showed at an appropriate amount Nacl doping, it had a certain optimization of the network structure of the actuate membranes of CSIA, this could improve the ion transfer rate inside the actuate membranes, thereby the output force of the CSIA was improved, but an excessive doping would change the arrangement frame of the internal structure of the actuate of CSIA, it weakened its performance, leading to serious deformation bubbling and energy loss in the sample during the electrical stimulation response.

The relationship between the maximum output force of the sample CSIA and the porosity of the actuate membranes were shown in Fig. 1(b), the trend of the two sets of data were the similar, with the increase of Nacl doping ratios, the change trend of porosity and output force increased first, and the porosity of actuate membranes CSIA of Nacl-doped reached the maximum at S4, and the maximum attained 12.98%, The lowest of porosity decreased at S5. This showed that Nacl had a certain optimization of the internal three-dimensional network structure of CS, which could improve the ion transfer rate inside the actuate membranes of CSIA, but over Nacl cross-linking doping would lead to beyond ion blockage inside the actuate membranes, the water content of the actuate membranes would decrease, and the CSIA would lose water and harden, resulting in the greater internal stress during deflection, thereby it weakened the output force. The performance parameters of CSIA were detailed in Table S2.

Researchers^[29] showed that the deflection mechanism of the ion actuator aceration mechanism of the cellulose backbone was that under the action of electric field, the charge was injected into the cathode and the anode to form an electric double layer. The positively charged cation –NH₃⁺ was bound by the polymer CS backbone and was fixed with the action of Van der Waals force. The anion –CH₃COO⁻ moved towards the anode side of the electrode, and accumulates with increasing concentration over time, while the cation moved in the direction of the cathode. Based on above, the cathodic deflection of the actuator on a weakly acidic solution biogel was used, and this cathodic deflection phenomenon was mainly the result of internal ion movement.

As shown in Fig. 1(c), the CS molecule contained a large amount –NH₂, in the aqueous acetic acid solution, the backbone chain hydrolysis of CS, many free amino groups on the internal ions bind H⁺ in the solution, so that chitosan became –NH₃⁺ polyelectrolyte, while the remaining anions were in a free state to dissolve –CH₃COO⁻ of CS. As shown in Fig. 1(d), in the CSIA actuate membranes after Nacl doping, Na⁺ ions were concentrated near the cathode electrode membrane, because the ion radius of Na⁺ ions (0.97Å) was less than –CH₃COO⁻ ion radius (4.50 Å), so when the concentration on both sides accumulated to a certain amount, the ion concentration difference on both sides was inside the actuate membranes under the action of Van der Waals force to make the surface of the electrode showing stress and bending strain. Since the ionic radius of the anion was significantly larger than the ionic radius of the cation, the volume difference of the actuate membranes was generated, so that actuator exhibited cathodic deflection. When voltage was applied across the electrode, ion migration changed from the previous disordered state to ordered. The ion migration rate enhanced. Then, the ion concentration gradient was quickly established, which correspondingly reduced the resistance of the actuator membrane and enhanced the internal ion concentration and mechanical properties of the ion actuator sample.

3.2 Effect of Nacl on the electrochemical performance of CSIA

The electrochemical performance of CSIA with different doping ratios was tested by cyclic voltammetry, and the cyclic voltammetry characteristic curves at different scanning speeds were shown in Fig. 2(a-c), taking the specific capacitance at 50 mV s^− 1 scanning speed as an example, with the increase of the doping rate of Nacl, the specific capacitance of the actuate membranes firstly increased to S4 and then decreased to S5. Specifically, the specific capacitance of CS was up to 0.07719 F g^− 1 in S4, which was 1.58 times higher than that of 0.0299 F g^− 1 of the capacitance of CSIA S0. The specific capacitance value indicated the efficiency of ion migration in the sample to a certain extent, which might be due to the over crosslinking of the CSIA of the Nacl doped to interrupt the channel of ion migration in the actuate membranes, making its internal structure dense and uniform, thereby affecting the ion migration rate. In addition, the specific capacitance trend of the actuate membranes under different doping ratios and different scanning speeds were shown in Fig. 2(d, e). The specific capacitance of the actuate membranes gradually decreased as the scanning rate increased, which indicated that the scanning speed increase rate was faster than the area increases ratios of the CV curve. Finally, the relationship between the resistance of the actuate membrane and the specific capacitance was shown in Fig. 2(f). The two generally showed an inverse ratio, in the experimental group of S4. The specific capacitance reached the maximum, the resistance reached the minimum, which corresponded to the output force of S4, reflecting that the smaller the resistance, the larger the specific capacitance, the better the mechanical properties of the corresponding ion actuator.

The relationship between the real resistance and virtual reactance of the CSIA actuate membranes were shown in Fig. 3(a, b), and it could be seen that there was a good linear relationship between them. The line obtained by linear fitting intersects the x-axis, and the abscissa value of the intersection point was the resistance value of the actuate membrane of CSIA^[30]. The resistance of the actuate membranes of CSIA were shown in Fig. 3(c). The resistance of the CSIA sample ${R}_{s}$ could reflect the conductivity of the sample to a certain extent, taking 0.1-100000 Hz as an example, the resistance of the CSIA actuate membranes showed a trend of first decreasing and then increasing, in which the resistance of the actuate membrane at S4 was 13.48 Ω, which was 4.937% lower than that of the control group of S0. This showed that the CSIA sample achieved a better conductive effect at S4 and appropriate Nacl cross-linking doping could improve the electrochemical performance of the CSIA, while excessive doping would intensify and change the molecular structure arrangement inside the actuate membrane of CSIA.

This causes the ion channels to become clogged and crowded, increasing the resistance, and decreasing the electrochemical performance of CSIA.

3.3 Effect of Nacl on the surface morphology and functional groups of CSIA

3.3.1 Electron microscopy scan of CSIA

The micromorphology of the substrate surface and the side section under doped samples of CSIA S0-S5 were shown in Fig. 4. It could be seen from Fig. 4(a-f) that the surface of the CSIA actuate membranes in the control group were smooth, and with the increase of Nacl doping ratio, the particle size and roughness of the surface of the actuate membranes began to gradually increase. The particle size and roughness of CSIA increased significantly at S5. In addition, the interface change between the electrode membranes and the actuate membranes of the CSIA doped with Nacl was shown in Fig. 4(g-i). After observation and comparison, it was found that the undoped CSIA was in smooth contact, while the interface of the CSIA doped with Nacl had an obvious three-dimensional physical cross-network structure. This showed that the doping of Nacl had obvious changes to the internal structure of CSIA, which might be helpful to the performance of CSIA, but excessive doping would also be counterproductive.

3.3.2 Fourier transform infrared spectroscopy of CSIA

The FTIR spectra of CSIA sample S0-S5 was shown in Fig. 5. At 3376.79 cm^− 1 and 2929.28 cm^− 1, they matched to the telescopic vibration peaks of − OH and − NH₂, respectively. The flexural vibration peaks was caused by − CH₂ and − CH₃ group near 1566.79 cm^− 1 and 1411.96 cm^− 1.A tensile vibration peak was caused by − CH₂ − O−CH₂ group narrowing 1045.12 cm^− 1 and bending vibration of − CH₂ − O−CH₂ group neared 854.10 cm^− 1. From this group of functional groups, it could be preliminarily inferred that it was a functional group in the structure of CSIA, and the peaks of S1-S5 in the experimental group were basically the same as those in the control group, indicating that the CSIA of Nacl-doped had no significant effect on its functional groups.

In order to explore the effect of sodium chloride on the enhanced performance of chitosan-based ion actuator (CSIA), sodium chloride doped CSIA were prepared by sol-gel method. Therefore, the effect of sodium chloride on CSIA were investigated. The mechanical properties of CSIA were tested by establishing an output force test platform while testing its porosity. The electrochemical performance was measured by electrochemical workstation. And the surface morphology and functional groups were measured by scanning electron microscopy and Infrared spectrogram, respectively. Then, the result indicated that the sodium chloride mass ratio was the best at 0.4% for CSIA. Its output force of mechanical properties attained at 2.939 mN and the maximum porosity of 12.98% at the same time. The specific capacitance of the electrochemical performance was up to 0.07719 F g^− 1, and the minimum resistance reached 13.48 Ω. If the doping ratio of NaCl continued to increase, its output force, porosity and specific capacitance decreased to varying degrees. It turned out that over doping would block the internal three-dimensional structure of the CSIA, the ion channel would decrease, and the corresponding resistance would increase, resulting in a decrease in the output force performance. Through scanning electron microscopy, it showed that excessive doping of CSIA led to an increase in compactness and cracks between the surface and interface of membrane. The infrared showed that Nacl had no significant effect on the CSIA internal functional groups. The effective internal ion concentration and significantly reduced internal stress provided excellent performances under the appropriate voltage conditions. The doping of inorganic ion sodium chloride improved the internal electron transport efficiency of chitosan ion actuator, and advanced the mechanical properties of the actuator. This work was ultimately shown that the appropriate sodium chloride mass ratio had a great effect on the performance of CSIA. In future research work, the addition of glycerol to the experiment reduced the internal stress generated in the CSIA itself, and increasing the water content of CSIA enhanced the working life and storage conditions of the ion actuator.

Ethics approval

Ethical approval does not apply to this article.

Competing interests

The authors declare no competing interests.

Author contribution

A (Zhaoyang Cui) wrote the main manuscript text. B (Xiaoli Zhao) and C (Weikun Jia) provided technical guidances to author. D (Yueming Ren), E(Yanzhuo Lv) and F (Yan Xu) provided authors with thesis advices and guidances.

Funding

This work was supported by Key Laboratory of Engineering Bionics, Ministry of Education, Jilin University.

Availability of data and materials

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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No competing interests reported.

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Effect of sodium chloride on the enhanced performance of chitosan-based ion actuator

Status:

Version 1

Abstract

Figures

1 Introduction

2 Experiments

2.1 Experimental and reagent

2.2 Preparation of chitotan-based ion actuator

2.3 Experimental setup

2.3.1 Output force and displacement test of CSIA

2.3.2 Electrochemical testing of CSIA

2.3.3 Morphology and functional group testing of CSIA

3 Results and Discussion

3.1 Effect of Nacl on the mechanical properties of CSIA

3.2 Effect of Nacl on the electrochemical performance of CSIA

3.3 Effect of Nacl on the surface morphology and functional groups of CSIA

3.3.1 Electron microscopy scan of CSIA

3.3.2 Fourier transform infrared spectroscopy of CSIA

4 Conclusions

Declarations

Ethics approval

Competing interests

Author contribution

Funding

Availability of data and materials

References

Additional Declarations

Supplementary Files

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