1. INTRODUCTION:

Superabsorbent polymers like polyacrylamide (PAM) are known for their distinctive three-dimensional (3D) crosslinked network structures, which enable them to absorb and retain large quantities of water. Once hydrated, these materials form stable hydrogels, and the absorbed water remains largely unaffected by external pressure. Initially introduced in agriculture and personal hygiene products (such as diapers) over thirty years ago, their exceptional water retention capability has since found applications across multiple fields.

Recently, there has been growing interest in utilizing superabsorbent polymers in more advanced applications-including as components in conductive materials, biomaterials, sensors, drug-release systems, and even electromagnetic wave-absorbing materials^1,2. To meet the evolving demands of these applications, researchers have employed various chemical strategies such as modification, grafting, and copolymerization to produce multifunctional superabsorbent materials. Despite this progress, limited studies have specifically focused on composite hydrogels derived from superabsorbent polymers. Conducting hydrogels offer several advantages-including high conductivity, stability in colloidal form, cost-effectiveness, and ease of synthesis-which make them promising candidates for use in technologies like fuel cells, supercapacitors, dye-sensitized solar cells, and rechargeable lithium batteries^3,4. This research aims to develop a novel porous conducting composite hydrogel by combining PANI and PAM in an acidic environment. While numerous studies have explored hydrogels formed from various combinations of crosslinked matrices (such as PAM, PAA, polyacrylates, PVA, and biopolymers) and conductive polymers (like PANI, PPy, PEDOT, and PTh), the field still offers substantial room for new developments.⁵ Interestingly, many of these materials share similar physicochemical behaviors, which provides a solid foundation for analyzing their observed performance and mutual effects in composites. Electrically conducting polymers (ECPs), such as polyaniline (PANI), polypyrrole (PPy), and polythiophene (PTh), have gained significant attention due to their unique electrical, electrochemical, and optical properties. These macromolecules—also referred to as conjugated polymers—exhibit inherent semiconducting behavior due to their delocalized π-electron systems. Among them, PANI stands out for its environmental stability, affordability, and versatile synthesis techniques.^6,7 Like other ECPs, PANI can exist in various oxidation and protonation states, offering different electrical and optical properties. However, its poor solubility in organic solvents poses challenges for processing and integration into systems. Typically, PANI is synthesized through the polymerization of aniline in an acidic medium.⁸ Recent studies have explored how polymerization conditions influence the molecular weight of PANI and have proposed novel mechanisms to explain the shape and aggregation behavior of its nanoparticles.⁹

1.1 Electrically Conducting Hydrogels: Electrical conductivity is a critical feature in hydrogels designed for biological and biomedical applications. Electrically conductive hydrogels are widely used in areas such as electroactive cell scaffolds, flexible sensors for health monitoring, wearable electronics, and electrically-triggered drug delivery systems. These hydrogels can be engineered using three main strategies: incorporating conductive polymers, enhancing the ionic conductivity of the aqueous phase, or embedding conductive materials into the hydrogel matrix. Conductive polymers like polypyrrole(PPy), polyaniline(PANI), and PEDOT are often used due to their delocalized π-electron systems, which allow for efficient electron transport. Although these polymers cannot form hydrogels on their own, they are combined with supporting polymers that provide hydrophilicity and mechanical strength. Alternatively, conductivity can be improved by increasing the ionic content of the hydrogel or by adding conductive materials such as carbon nanotubes, graphene, metal microwires, or nanoparticles to form continuous conductive networks. These approaches enable the development of hydrogels that are both electrically functional and biologically compatible for a range of smart, responsive medical technologies.

2. EXPERIMENTAL:

2.1 Materials: All chemicals used in this study were of analytical grade and were utilized without any further purification. The materials included acrylamide (AM), aniline (AN), hydrochloric acid (HCl), potassium persulfate (KPS), ammonium persulfate (APS), cupric chloride (CuCl₂), ferric chloride (FeCl₃), N,N′-methylenebisacrylamide (MBA), and concentrated nitric acid (HNO₃). Throughout the synthesis process, distilled water was used as the solvent to ensure purity and consistency.

2.2 Synthesis of Hydrogel: The synthesis of the polyacrylamide hydrogel began by dissolving 1 gram of acrylamide monomer, three drops of concentrated HNO₃, and 0.2 grams of MBA (serving as a crosslinking agent) in 50 mL of distilled water. This mixture was allowed to undergo polymerization, leading to the formation of the polyacrylamide hydrogel over a specific period. Once the gel was formed, it was removed from the reaction environment and soaked in 0.4mL of aniline hydrochloride solution for 24 hours. The entire synthesis was carried out at a controlled temperature of 60°C. To study the effects of formulation parameters, multiple hydrogel samples were prepared with varying concentrations of monomer, crosslinker, and initiator, as described in the subsequent sections.

2.3 Preparation of Nanocomposites: The most widely adopted method for integrating polyaniline (PANI) into crosslinked polyacrylamide (cPAM) hydrogels involves in situ polymerization of aniline within the hydrogel network-a straightforward and effective technique. Initially, the hydrogel is synthesized via free radical polymerization of acrylamide in the presence of a bifunctional crosslinker containing vinyl groups. The process is typically initiated through a redox system, often employing concentrated HNO₃, which promotes the formation of a nanoporous hydrogel structure. In some cases, highly porous or "superporous" cPAM hydrogels can also be fabricated. These hydrogels may be shaped into thin films, fibers, or particles before being combined with PANI. After hydrogel formation, aniline is absorbed into the matrix, and upon swelling, the gel interacts with the oxidizing agent, triggering the polymerization of PANI within the network.

3. RESULTS AND DISCUSSION:

3.1 Characterization of Hydrogels: A variety of analytical techniques were employed to evaluate key properties of the hydrogels, including swelling behavior, mechanical strength, pore structure, mesh size, water distribution (both bound and free), chemical composition, and bond interactions. These characterization efforts are essential for gaining insight into the underlying mechanisms of hydrogel formation, guiding structural control, and tailoring the material's physical and functional properties for targeted applications. To determine the defining physical and chemical features of the hydrogels, a combination of methods was used-such as rheological analysis, scattering techniques, strength testing, compositional analysis, and microscopic imaging. These tools provide complementary data that together form a comprehensive understanding of the material. However, each technique has inherent limitations, including challenges related to sample preparation, resolution constraints, data variability, and overall measurement precision. Due to the complex nature of hydrogels such as their high-water content, low solid fractions, and variable mesh dimensions–no single technique can capture the complete structural profile. Factors like heterogeneous composition, fluctuating binding interactions, and dynamic mechanical behavior make thorough characterization particularly challenging.

3.2 Physical appearance: Figure a,b and c,d shows native and PANI-impregnated gels respectively, demonstrating PANI's incorporation into the polymer gel matrix. The images (fig a,b) show that the native gel is semi-transparent, whereas (fig c,d) the impregnated gel is dark-green, indicating the presence of PANI within the matrix.


a	b

c	d

Fig. 1:

3.3. The repeatability of data: All measurements were repeated at least three times, and the average value was used to report the results. The experimental errors were consistently under 1%.

FESEM Analysis:

The figure displays the shape of an air-dried hydrogel. The 3D image clearly depicts a porous surface in clean, dry PAM hydrogel. However, in Fig. 6, a pore channel was partially filled with a spherical grain PANI molecule, showing that the PANI was trapped within the pore of the polyacrylamide hydrogel. Again, PAM-PANI hydrogel had a surface roughness value (Rmax) of 1um at the start of polymerization (Fig. 5), but a different surface morphology was observed with a Rmax value of 200 nm at the end of polymerization (Fig. 1), confirming that polyaniline is trapped inside the hydrogel network. As the number of scans in electro polymerization rose, the production of polyaniline became more homogenous within the pores of the polyacrylamide hydrogel, and hence roughness may be proportional to the thickness of the PANI. Interestingly, the corresponding phase image (Fig. 7) revealed a three-dimensional network structure on the sample's surface. In the PAM-PANI system, the light phase represented PANI, while the dark phase represented polyacrylamide. These occurrences could be caused by the creation of conducting PAM doped PANI inside the pores of polyacrylamide hydrogel with no crosslinking (physical or chemical) between them. The appearance of a black phase indicated that some sections of the polyacrylamide pore remained empty or filled with fluid. This could explain why the PAM-PANI hydrogel retained its swellability. Hydrogels' dynamic swelling behavior is influenced by both penetrant diffusion and crosslinked polymer chains. To confirm the effect of nanoparticles on the microstructure of hydrogels, FESEM of clear and nanoparticle-stacked hydrogels were analyzed, as shown in Fig. 3. Analysis was performed using field emission scanning and electron microscopy (FESEM) with minimal modifications. FESEM was used to evaluate the surface characteristics of hydrogels. Polyacrylamide incorporating polyaniline microparticles has a micro porous structure with an average pore diameter of less than 1µm. Polyaniline nanoparticles facilitated burst release by modifying polymeric complexes and altering release mechanisms. The FESEM picture magnifications were performed at the range between 2.0KX to 100KX. Apparently, stacking nanoparticles altered the surface morphology of the clear hydrogel. The arrangement of nanoparticles in the clear hydrogel reveals clear structures through gel interaction. Nanofillers form similar structures when integrated into a blank matrix, particularly in magnetic nanocomposites. Adding nanoparticles to hydrogels alters their porosity. Fig. 3 shows that nanoparticles are successfully distributed throughout the hydrogel structure.

PANI Impregnation and Its Influence on Composite Components:

In this investigation, aniline (AN) was used as the monomer for polyaniline (PANI) formation. For polymerization to occur within the hydrogel network, the aniline molecules must first diffuse into the polymer matrix. To facilitate this, AN was dissolved in hydrochloric acid to form aniline hydrochloride, producing cationic species. The positively charged nature of these species means their diffusion into the hydrogel is primarily governed by electrostatic interactions and the matrix's swelling behaviour. While the hydrogel matrix is hydrophilic and aniline is hydrophobic, hydrophobic/hydrophilic interactions play a minimal role in the diffusion process. Instead, electrostatic forces—particularly those between the ionic species of aniline and the polar segments of the polyacrylamide (PAM) matrix—seem to be the primary driving mechanism. PANI incorporation occurs as the hydrogel film swells in the aniline hydrochloride solution, followed by in situ polymerisation within the matrix. The extent of aniline absorption and subsequent PANI formation is strongly influenced by the hydrogel’s chemical makeup. The presence of PAM enhances electrostatic interaction, which supports deeper diffusion of AN molecules. Therefore, modifying the hydrogel components' concentration directly impacts the PANI impregnation level, as discussed below.

Effect of Acrylamide (AM) Concentration:

To assess how acrylamide concentration affects PANI loading, the amount of AM was varied from 1 gram to 5 grams while keeping all other parameters constant. Results shown in Table 1 indicate that higher concentrations of PAM lead to more significant PANI impregnation. This effect is likely due to the ionic nature of PAM, which promotes inter-chain repulsion within the matrix. As the polymer chains repel each other, the network becomes more open, allowing increased penetration of aniline molecules. Consequently, this enhances the level of PANI incorporated into the hydrogel. As more PANI is impregnated, the electrical resistivity of the original PAM hydrogel decreases while the conductivity of the resulting composite hydrogel increases.

Table 1: Variation of acrylamide content in surface resistance

AM Concentration (in gm)	Surface Resistance of PAM Hydrogel (in M^-1Ω^-1)	Surface Resistance of PANI Hydrogel (in M^-1Ω^-1)	Concentration of aniline and HCl (in ml)
1	0.065	4.02	9:1
2	0.089	2.66	9:1
3	0.125	1.95	9:1
4	0.147	1.87	9:1
5	0.178	1.62	9:1

Table 1 shows variation of surface resistance of PAM hydrogel with variable concentration of AM.

Graph 1: represents the variation of surface resistance with variable amount of AM.

The Consequense of AN concentration:

The study examined how altering the concentration of AN (monomer) in 0.5 N HCl solution affected PANI impregnation within the polymer matrix. The concentration ranged from 9:1ml to 6:4 ml ratio of aniline and HCl, while the content of other gel components remained constant. Table 2-6 shows that PANI impregnation increases with increased AN content in the matrix, but declines beyond 8:2 ratio of aniline and HCl concentration. Increasing the concentration of AN, a PANI monomer, in the gel leads to increased polymerization and impregnation. This may explain the reported findings. Beyond a specific concentration of 8:2 (aniline and HCl), the decrease in PANI impregnation could be attributed to lower swelling in the AN hydrochloride solution. Higher ionic concentration (due to aniline hydrochloride ion) in the external solution may result in lower swelling, allowing for fewer AN molecule to be polymerized.

Table 2: represents the variation of surface resistance with varying concentration of Aniline: HCl (Hydrogel Composition AM-1 gm, BAM-0.2 g, conc. HNO₃-3 drops)

Composition of hydrogel	Surface Resistance of PAM hydrogel (in M^-1 Ω^-1)	Ratio of Aniline: HCl (In ml)	Surface Resistance of PANI hydrogel (in M^-1 Ω^-1)
AM-1 gm, BAM-0.2 gm, Conc. HNO₃-3 drops	0.065	6:4	4.17
		7:3	3.83
		8:2	3.69
		9:1	4.02

Graph 2: represents the variation of surface resistance with varying concentration of Aniline:HCl (Hydrogel Composition AM-1 gm, BAM-0.2 g, conc.HNO₃-3 drops)

Table 3: represents the variation of surface resistance with varying concentration of Aniline:HCl (Hydrogel Composition AM-2 gm, BAM-0.2 gm, conc.HNO₃-3 drops)

Composition of hydrogel	Surface Resistance of PAM hydrogel (in M^-1 Ω^-1)	Ratio of Aniline: HCl (In ml)	Surface Resistance of PANI hydrogel (in M^-1 Ω^-1)
AM-2 gm, BAM-0.2 gm, Conc. HNO₃-3 drops	0.089	6:4	3.77
		7:3	3.12
		8:2	2.65
		9:1	2.66

Graph 3: represents the variation of surface resistance with varying concentration of Aniline:HCl (Hydrogel Composition AM-2 gm, BAM-0.2 gm,conc.HNO₃-3 drops)

Table 4: represents the variation of surface resistance with varying concentration of Aniline:HCl (Hydrogel Composition AM-3 gm, BAM-0.2 gm, conc.HNO₃-3 drops)

Composition of hydrogel	Surface Resistance of PAM hydrogel (in M^-1 Ω^-1)	Ratio of Aniline: HCl (In ml)	Surface Resistance of PANI hydrogel (in M^-1 Ω^-1)
AM-3 gm, BAM-0.2 gm, Conc. HNO₃-3 drops	0.125	6:4	2.75
		7:3	2.25
		8:2	1.47
		9:1	1.95

Graph 4 represents the variation of surface resistance with varying concentration of Aniline:HCl (Hydrogel Composition AM-3 gm, BAM-0.2 g,conc.HNO₃-3 drops)

Table 5: represents the variation of surface resistance with varying concentration of Aniline:HCl (Hydrogel Composition AM-4 gm, BAM-0.2 gm,conc.HNO₃-3 drops)

Composition of hydrogel	Surface Resistance of PAM hydrogel (in M^-1 Ω^-1)	Ratio of Aniline : HCl (In ml)	Surface Resistance of PANI hydrogel (in M^-1 Ω^-1)
AM-4 gm, BAM-0.2 gm, Conc. HNO₃-3 drops	0.147	6:4	2.56
		7:3	2.01
		8:2	1.20
		9:1	1.87

Graph 5 represents the variation of surface resistance with varying concentration of Aniline:HCl (Hydrogel Composition AM-4 gm, BAM-0.2 gm,conc.HNO₃-3 drops)

Table 6 represents the variation of surface resistance with varying concentration of Aniline:HCl (Hydrogel Composition AM-5 gm, BAM-0.2 gm,conc.HNO₃-3 drops)

Composition of hydrogel	Surface Resistance of PAM hydrogel (in M^-1 Ω^-1)	Ratio of Aniline: HCl (In ml)	Surface Resistance of PANI hydrogel (in M^-1 Ω^-1)
AM-5 gm, BAM-0.2 gm, Conc. HNO₃-3 drops	0.189	6:4	2.40
		7:3	2.11
		8:2	1.73
		9:1	1.62

Graph 6: represents the variation of surface resistance with varying concentration of Aniline:HCl (Hydrogel Composition AM-5 gm, BAM-0.2 gm,conc.HNO₃-3 drops)

The Consequense of PAM:

To investigate the impact of PAM on matrix conductivity, electrical conductivity was tested at various AM concentrations ranging from 1gm to 5gm. Table 1 shows that conductivity steadily increases with increasing PAM level in the gel. enhancing the concentration of PAM leads to an increase in COO- groups along the macromolecular chain, enhancing electrical conductivity and facilitating electron conduction along the PANI chain. These findings are expected. The study found that as the concentration of PAM increased, so did the % impregnation of PANI also increases in the examined range contribute to the observed rise in conductivity.

The Consequence of PANI:

To study the impact of PANI content on matrix conductivity, aniline concentrations ranging from 9ml to 6ml were added to the gel feed mixture along with the proper amount of HCl(as described on table). Table 2,3,4,5,6 shows that raising the concentration of AN leads to higher conductivity. As the concentration of AN solution increases, more molecules are accessible for polymerization, leading to increased impregnation of the matrix.

4. CONCLUSION:

This work developed a novel PANI/PAM composite hydrogel. Several characterizations are done to determine the structure and morphology of the composite hydrogel, such as conductivity measurement (multimeter) and FESEM. The results demonstrate that the PANI/PAM hydrogel has PANI crystallization and a PAM porous framework structure. The PANI/PAM hydrogel has a electrical conductivity of 0.042 S/cm due to its 3D porous structure and interaction between PAM and PANI. Field emission scanning electron microscopy (FESEM) was used to study microscopic morphology and elemental composition. A FESEM was used to obtain an image of the PAAm-hydrogel in a wet condition. A portion of PAAm hydrogel was extracted from the container and then directly placed on a covered FESEM grid. The examination was conducted at a voltage of 5 kV, with a working distance of 5–10 m. The FESEM images of PAM and PANI are shown in fig.2 and 3 respectively. The findings of this study suggested that AN might be included into a hydrogel matrix system to improve the conductivity properties of PAM as a PANI. This study also demonstrated that incorporating aniline into the PAM hydrogel was possible by electrically activating the PANI, resulting in a specific spectrum of conductivity. The conductivity of the PAM rose linearly with increasing PANI concentration. The hydrogel composite exhibits cluster-like morphology, Polyaniline (PANI) particles aggregate and vary in size, ranging from 1μm to 200nm. PANI impregnation in composite hydrogels varies based on their chemical makeup. Increasing AM and AN concentration leads to increased PANI impregnation until a certain point, beyond which it declines. In contrast, increasing PAM concentration leads to increased impregnation but decreased conductivity. The electrical conductivity of composites varies depending on their composition. Conductivity increases with PAM concentration, but decreases as concentrations increase more. In the case of AN, conductivity continuously increases.

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Received on 03.04.2025 Revised on 18.04.2025

Accepted on 01.05.2025 Published on 19.06.2025

Available online from June 23, 2025

Asian J. Research Chem.2025; 18(3):155-162.

DOI: 10.52711/0974-4150.2025.00025

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