Conductivity Evaluation of Smart Hydrogels composed of Polyacrylamide-Polyaniline
Rajeshwari Jaiswal, Reena Bhadani
Department of Chemistry, Ranchi Women’s College, Ranchi University, Ranchi.
*Corresponding Author E-mail: rajeshwarijaiswal06@gmail.com
ABSTRACT:
Electro active composite system as hydrogels was prepared from non-conducting polymer and conducting polymer combined together. This type of composite hydrogels has both properties of hydrogel and conducting polymer representing a new material. Polyacrylamide hydrogels was prepared by polymerizing acrylamide (5 mole/L) in an aqueous solution of (NH4)2S2O8(0.20 mole/L) containing a crosslinker N,N’ methylene bisacrylamide (0.2 mole/L) in a test tube at 40oc for 24 hours. After polymerization, the cross linked polymer was isolated from the tube in a long cylindrical shape which was cut into pieces in one cm in length. After getting it washed repeatedly to remove the soluble materials and then dried at room temperature for 48 hours. The hydrogel, so formed, was soaked in an aqueous solution of aniline hydrochloride (1 mole/L) solution to allow the monomer to diffuse inside the hydrogel networks. When 0.25 mole/L FeCL3- an oxidant was added to the solution, the polyaniline was formed inside the porous structure of hydrogel. The resulting hybrid polymer was taken out from polymerizing mixture which was thoroughly washed and dried. The sample appeared deep dark green colour. The average surface resistance (Inverse representation of conductivity) of the sample was estimated about 103 Ohm. Another oxidant like Fe2(SO4)3 gives almost the same results. The reproducibility of conductivity value is poor because it is very difficult to form uniform distribution of the conducting polymer throughout in the hydrogel networks.
Polymeric hydrogels, notably in their three-dimensional forms, typically exhibit brittleness and lack electrical conduction properties. The intrinsic softness and high water content of polyacrylamide hydrogels, which are composed of cross-linked hydrophilic polymer chains, often restrict their usage in more advanced applications1,2,3. Overcoming the challenge to synthesize hydrogels that are both electrically conductive and mechanically robust represents a significant scientific pursuit. In our research, we have engineered composite hydrogels based on polyacrylamide (PAM) that demonstrate promising electrical conductivity4,5.
This study delineates a two-step methodology for the fabrication of an electrically conductive, superabsorbent hydrogel composed of polyacrylamide and polyaniline 6,7. We present a composite hydrogel with exceptional electrical conductivity (>3505S/cm) that can transmit direct current efficiently while retaining its softness and deformability8,9.
Initially, a superabsorbent polyacrylamide hydrogel was synthesized with remarkable water swelling capabilities (500g water/g polyacrylamide)10,11. Subsequently, polyaniline was incorporated into this pre-formed hydrogel network via a straightforward oxidative polymerization process, varying in extent based on specific synthesis conditions. The resulting conductive hydrogels displayed electrical resistance values ranging from 100-1000 ohm/cm2, contingent on the doping electrolyte utilized12.
Mineral particles were successfully integrated within the polyacrylamide hydrogel network (PAAm) by soaking in a radical monomer solution. This process was followed by using a free radical solution polymerization method13. Aniline monomer was similarly integrated into the PAAm composite hydrogel network, and polymerization was carried out at room temperature. We measured the electrical conductivity of the hydrogels with a multimeter, revealing that the newly prepared semi-interpenetrating polymer network (S-IPN) exhibited a conductivity of 1.1x10-4 S/ cm-1 14. This S-IPN hydrogel system also underwent swelling experiments in water.
The promising attributes of these hydrogels suggest a range of potential applications. Nevertheless, current levels of electrical conductivity (<100 S cm-1) remain insufficient for digital circuit integration and bioelectronic applications, thus directing ongoing efforts to enhance the conductivity of these hydrogel systems15.
MATERIALS AND METHODS:
Materials:
The foundational monomers for crafting the conductive hydrogel composite included Acrylamide (AM), Aniline, Pyrrole, and Theophylline. Oxidizing and initiating agents such as Ammonium Persulfate (APS), Potassium Persulfate (KPS), Ferric Chloride (FeCl3), Cupric Chloride (CuCl2), and Nitrogen Dioxide (NO2) gas were employed. N,N'-Methylenebisacrylamide (MBA) served as the crosslinking agent. Double distilled water was utilized for all experimental procedures.
Synthesis of Polyacrylamide (PAM) Hydrogel:
The polymerization process of acrylamide was initiated with 2.5grams of acrylamide monomer, utilizing 20 grams of ammonium persulfate as the initiator and 0.65 grams of N,N'-methylenebisacrylamide as the crosslinking agent, all dissolved in 50ml of distilled water. This reaction yielded polyacrylamide hydrogel after a designated period. Subsequently, the gel was extracted and steeped in a 0.4ml molar hydrochloric acid solution for 24hours, followed by immersion in a 0.5 molar ammonium persulfate solution for an additional 24 hours.
1 2
3 4
Fig 1: Preparation of conducting hydrogel
Conductivity Measurement:-
The electrical conductivity of the hydrogel composite was determined using the equation:
P = R x L / A
where P represents resistivity, R indicates resistance, L is the length of the film (cm), and A is the cross-sectional area of the film (cm²).
Evaluation of Electrical Conductivity
Electrical conductivity assessments were conducted on both the hydrogel slices and the polyaniline (PANI) infused PAM hydrogel. Measurements were executed utilizing a multimeter, carefully placing the probes on the opposite circular faces of the hydrogel specimen. The surface resistance obtained inversely correlates with the electrical conductivity of the material.
Subsequent experimentation involved systematic variation of the monomer, initiator, crosslinker, and aniline concentrations to observe their respective influences on the hydrogel's electrical conductivity.
RESULT AND DISCUSSION:
Table 1: Effects of concentration of various constituents of the composite gels on conductivity (Surface Resistance)
|
AM Concentration (g) |
Surface Resistance of PAM Hydrogel (K Ω) |
Surface Resistance of PANI impregnated hydrogel (K Ω) |
Other Ingredients |
|
2 |
192 |
40 |
MBA – 0.2g APS – 0.5 g AN – 10 millimole in 0.5M HCI |
|
3 |
182 |
21 |
|
|
4 |
154 |
15.1 |
|
|
5 |
141 |
6.4 |
Fig 1: Effects of concentration of various constituents of the composite gels on conductivity (Surface Resistance)
Effects of Concentration of Monomers
Impact of Acrylamide Concentration on Conductivity:
The effect of varying acrylamide (AA) concentrations on the matrix's conductivity or surface resistance was investigated. Acrylamide content was incrementally raised from 2g to 5g, with corresponding surface resistance measurements detailed in Table 1. Findings indicate a systematic reduction in surface resistance concurrent with increased AA levels, which in turn enhance the polyacrylamide (PAM) concentration within the matrix. This augmentation provides a greater number of COO- ions along the macromolecular chains, thus bolstering the matrix's electrical conductivity by promoting electron transfer along the PANI chains. Additionally, a higher PAM presence augments the rate of PANI impregnation, which correlates with the noted uptick in conductivity, thereby reducing surface resistance.
Table 2: Effects of concentration of various constituents of the composite gels on conductivity (Surface Resistance)
|
BAM Concentration (g) |
Surface Resistance of PAM Hydrogel (K Ω) |
Surface Resistance of PANI impregnated hydrogel (K Ω) |
Other Ingredients |
|
0.05 |
180 |
41.2 |
AM – 5g APS – 0.20g AN – 10 millimole in 0.5M HCI |
|
0.10 |
151 |
22.2 |
|
|
0.15 |
142 |
16.0 |
|
|
0.20 |
135 |
10.1 |
|
|
0.25 |
120 |
10.1 |
Fig 2: Effects of concentration of various constituents of the composite gels on conductivity (surface Resistance)
The data presented in Table 2 unequivocally demonstrates that’s surface resistance diminishes sharply-indicative of heightened conductivity-with an elevated MBA concentration ranging from 0.05g to 0.2g. This trend is attributed to the densification of the network structure at increasing crosslinker concentrations, leading to a more compact network that facilities electron flow and thus enhances conductivity, However, surpassing an optimal crosslinker threshold result in a plateau in conductivity gains, as the gel network achieves maximum compactness beyond which no future conductivity enhancement is observed.
Table 3: Effects of concentration of various constituents of the composite gels on conductivity (surface Resistance)
|
Aniline conc, in (ml) |
Surface Resistance of PAM Hydrogel (KΩ) |
Surface Resistance of PANI impregnated hydrogel (KΩ) |
Other Ingredients |
|
5 |
196 |
16.2 |
AM-5 gm APS – 0.2 g MBA – 0.2 g HCI – 0.5M solution |
|
10 |
180 |
9.0 |
|
|
15 |
162 |
6.1 |
|
|
20 |
154 |
5.2 |
Fig 3: Effects of concentration of various constituents of the composite gels on conductivity (surface Resistance)
Conductivity Variation with Aniline Concentration:
Conductivity improvement (or surface resistance reduction) is observed with progressive increases in aniline (AN) solution concentration. This trend is readily explicable: higher AN concentration within the matrix avails a larger population of aniline molecules for polymerization, which consequently heightens the degree of impregnation and, thus, elevates the conductivity of the composite hydrogels.
Fig.4 Representation of surface resistance with variable concentration of monomer, crosslinker, aniline.
We can observe a noticeable change in surface resistance (conductivity) as we examine the variation of concentration changes of monomer, crosslinker, and initiator in the hydrogel matrix. Specifically, a decrease in resistivity may be the consequence of conductivity in the hydrogel network due to an increase in monomer, crosslinking agent, and aniline (conducting monomer).
CONCLUSION:
The electrically conducting polymers have been synthesized with conductivities as nearly with the magnitude of less than metal. The conductivity of some doped polyaniline are measured in addition with its higher stability and durability which is an excellent candidate for study. Doped polyacrylamide was synthesized and its electrical resistivity was experimentally measured with the variable addition of monomer, crosslinker and initiator. These conducting polymers have many potential applications such as protective finishes, organic solar cells show yet another trend for their future application.
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Received on 20.03.2025 Revised on 31.03.2025 Accepted on 08.04.2025 Published on 14.04.2025 Available online from April 18, 2025 Asian J. Research Chem.2025; 18(2):67-70. DOI: 10.52711/0974-4150.2025.00010 ©A and V Publications All Right Reserved
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