PVP core-shell nanocomposites

Journal Pre-proofs Novel Formation Mechanism of Ag/PANI/PVP Core-Shell Nanocomposites Shawkat Salameh Gasaymeh, Noura Nayef ALmansoori PII: DOI: Reference:

S2211-3797(18)33308-4 https://doi.org/10.1016/j.rinp.2019.102882 RINP 102882

To appear in:

Results in Physics

Received Date: Revised Date: Accepted Date:

9 December 2018 12 December 2019 12 December 2019

Please cite this article as: Gasaymeh, S.S., ALmansoori, N.N., Novel Formation Mechanism of Ag/PANI/PVP CoreShell Nanocomposites, Results in Physics (2019), doi: https://doi.org/10.1016/j.rinp.2019.102882

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Novel Formation Mechanism of Ag/PANI/PVP Core-Shell Nanocomposites 1Shawkat

Salameh Gasaymeh, 1Academic Support Department, Abu Dhabi Polytechnic - Abu Dhabi - UAE. 2Noura Nayef ALmansoori, 2Electrical Engineering Department, United Arab Emirate University – UAE

1Corresponding

author: [email protected]

ABSTRACT Recently, polymer-inorganic nanocomposites core shells have attracted great attention as new materials because of their novel mechanical, electrical, and optical properties. In this article, we report a simultaneous synthesis of polyaniline (PANI) nanoparticles and Silver (Ag) nanoparticles to form Ag/PANI nanocomposite core-shell embedded in polyvinilpirrolidone (PVP) by using hybrid chemical and gamma-irradiation oxidation process of aniline and reduction of Ag ions, respectively in the presence of dodecylbenzenesulphonic acid (DBSA). The mechanism of formation of Ag/PANI/PVP core-shell is proposed in this article. In addition, the effects of gamma-dose and Ag ions concentration on structural, and optical, properties of the nanocomposites PVP/PANI/Ag coreshell were carefully examined. The structural and morphological studies show the presence of PANI with regular granular nanostructure as a shell with a diameter of 20 nm and Ag nanoparticles with spherical shape as a core and diameter less than 10 nm. The average particle size of my modified Ag/PANI nanoparticles decreased with increasing dose and decreasing of precursor concentration due to increase of nucleation process over aggregation process during gamma irradiation. The UVVisible Spectroscopy, Scanning Electron Microscopy (SEM) and the TEM showed appreciated result of formation Ag/PANI which is going to be discussed in current studies. Keyword: Silver, Ag, PANI, PVP, Ag/PANI, nanoparticles, Polyaniline, Core-shell, nanocomposites. Introduction Conducting polymers are conjugated chain of organic compounds that display special properties such as electric conductivity, electroluminescence, photoconductivity and lazing, similar to metals because of the present of large carrier concentrations of extended π-electrons, known as polarons, which allow charge mobility along the backbone of the polymer chain, which ordinary plastics or insulated polymers do not. Their electrical conductivities are comparable with metals but polymers have many advantages, such as being lightweight, resistance to corrosion, flexibility, and low cost. Conducting polymers are finding numerous applications in television sets, cellular telephones, displays, light emitting diodes, solar cells, batteries, actuators, sensors, electromagnetic shielding, and microelectronic devices [1–3]. In addition, the conductivity of conducting polymers can change over several orders of magnitude in response to changes like in pH and redox potential of their environment as discussed by [15-23]. Amongst the family of conducting polymers, polyaniline (PANI) has been of particular interest due to its controllable electrical conductivity, high absorption coefficients in the visible light, interesting redox properties, chemical stability, relatively high conductivity, easy polymerization, and low cost of monomer [24-29]. The synthesis of PANI has been mostly accomplished by oxidation of aniline through chemical [30], electrochemical [31], photolysis [32] and [33] or radiation [34-36] methods. One of the requirements for polymers to exhibit good conductivity is the existence of πelectrons, which overlaps along the conjugated chain to form π-conjugated band. Fig. 1 shows the monomeric units of some of several families of conducting and semiconducting polymers and of the well-studied conducting polymers, i.e., transpolyacetylene [t-(CH)x], the leucoemeraldine base (LEB),

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emeraldine base (EB) and pernigraniline base (PNB) form of polyaniline PANI, polypyrrole (PPy), polythiophene (PT), poly(p-phenylene) (PPP), and poly(p-phenylene vinylene) (PPV).

Fig. 1. Chemical structures of some monomer units of several electronic conjugated polymers Handful of published articles has showed that conducting polymers have special properties that are interesting of the point of view of this new technology. Conjugated polymers are good materials to be employed in the fabrication of molecular electronic devices because they have properties that can be controlled by external parameters. The charge carriers in conjugated polymers are a fundamental part of this new technological search. Conductive polymers may be classified into four categories [37]. The first category is the polymer composites, in which the conductivity is caused by filling the conventional insulating polymers with powder of conductive materials, such as metal or carbon powders. The conductivity of these composites is due to the conductive particles that are in contact with each other, while the polymer is acting as a binder. The second category is the ionic organic polymers, in which the electrical conduction is caused by ions of inorganic salts introduced into the polymers. The third group is the redox polymers, which contain immobilized electroactive centers such as sulfonic group SO3- dopants, which are not in contact with each other but are capable of exchanging charges i.e. protons (H+) by hopping mechanism. The fourth category is a new class of polymers known as intrinsically conducting polymers derived from conjugated polymers where a high degree of overlapping of the molecular orbitals permits the formation of molecular structure defects that allow free movement of π-electrons throughout the lattice under the influence of an electric field. Dopants are chemical oxidants or reductants incorporated into conducting polymer by means of radiation, chemical, electrochemical and/or at the time of synthesis [38]. Increased doping can lead to increase conduction, via the creation of more mobile charges, and the maximum doping levels achievable vary for different conducting polymers and different dopants. These charges lead also to the relaxation of the geometry of the polymer to a more energetically favored conformation. Oxidation (anionic doping/p-type) generates a positively charged conducting polymer and an associated anion, while reduction (cationic/n-type) generates a negatively charged conducting polymer and an associated cation. These processes are illustrated below in equations 1 and 1, where M and A are any cation and anion, respectively and P represents a polymer [38].

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𝑃 + 𝑀𝐶𝑙𝑂4 → 𝑃 + 𝐶𝑙𝑂4― + 𝑀 + 𝑃 + 𝑁𝑎𝐴 →𝑁𝑎 + 𝑃 ― + 𝐴 ―

(Oxidation) (Reduction)

1 2

The chemical polymerization principle can be expressed by simple oxidation of aniline monomer with an oxidant agent FeCl3 as illustrated by the following equation. + ― ] 𝐶4𝐻4𝑁𝐻 + [2.25𝑛𝐹𝑒𝐶𝑙3]𝑛 →[𝐶4𝐻3𝑁0.25 +2𝑛𝐻𝐶𝑙 + 𝐹𝑒𝐶𝑙2(𝐻2𝑂) + 𝐶𝑙0.25 [𝑚𝑜𝑛𝑜𝑚𝑒𝑟 = 𝑎𝑛𝑖𝑙𝑖𝑛𝑒, 𝑑𝑜𝑝𝑎𝑛𝑡 = 𝐹𝑒𝐶𝑙3, 𝑜𝑥𝑖𝑑𝑎𝑛𝑡 = 𝐹𝑒𝐶𝑙3, 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 = 𝐻2𝑂]

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However, since the 17 century, stained glass windows have been used throughout Europe, especially for decorative windows of cathedrals, which were made from nanoparticles of gold. Implantation studies commenced in the 1970s with Ag, Cu and Au implants into silica and glass to produce characteristic optical absorption bands [39]. At that time the precipitation of absorption, bands were described in terms of scattering theory of metallic colloids. Current terminology now favors the use of ‘nanotechnology’ to emphasize the more complete aspects of the physical and chemical processes and their potential applications. The effects of particle morphology (size and shape), metal dispersion, concentration, and the host medium for the metal nanoparticles on the electronic properties have been reported [40]. The favorable nanoparticles compounds, which have been used in preparing polymer nanoparticles, are in the form of nitrate, such as silver nitrate and gold nitrate [34]. However, silver nitrate is a chemical compound with a chemical formula AgNO3 shown in Fig. 2. This nitrate of silver is the light sensitive ingredient in photographic film and is a corrosive compound. Soluble silver salts tend to be very toxic to bacteria and other lower life species. The compound notably stains the skin giving a blackening colour, which is made visible after exposure to sunlight. Silver nitrate is one of the significant compounds in the field of industries due to its potential characteristics such as wider response to electromagnetic radiations i.e. optical properties in addition to electronic, magnetic and catalysis [41]. It has been used in wider applications as conductive ink, thick film pastes, adhesive for electronic compounds [42] and photonic and photographic applications [43]. The characteristics of silver nitrate are has a molecular weight of 169.87, boiling point 444 oC, melting point 212 oC as crystal structure rhombic, decomposed by heat to give Ag, NO2 and O2.

Fig. 2. The chemical structure of the silver nitrate compound In general, there are four classes of metallic nanoparticles, i.e. metallic nanoparticles island, metallic nanoparticles embedded in dielectrics, metallic coated dielectric nanoparticles, and quantum dots. These nanoparticles exhibit strong UV-Vis absorption bands, which can lead to the brilliant colors. Solution-based metallic nanoparticles utilize surface plasmon resonance principle, whereby when the nanoparticles are in close proximity, they able to interact electromagnetically through a dipole-dipole coupling mechanism [44]. Several different methods for the controlled synthesis of silver nanoparticles have been developed including electrospraying liquid metals, ion implantation, gas phase condensation, chemical reduction, ultrasound irradiation, UV-irradiation, and ionizing radiation methods [45]. Some aspects of the synthesis will be discussed in this section.

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In this article, the UV-vis spectra analyses are described in detail, in which the absorption peaks at 320-350 nm (π-π* transition) and at 380-420 nm (polaron band) [1] and [2] and [47]. Absorption peak at around the 800 nm (polaron band) [46] and [1] for polyaniline emeraldine salt (PANI ES) state. All these absorption bands are observed in our entire Ag/PANI core-shell nanocomposites at a certain parameter, which indicates PANI (ES), is formed. Furthermore, the peak at 580-600 nm (exciton transition of the quinoid ring) [1], appears only at zero irradiation doses or/and zero DBSA, which indicates the insulator PANI (EB), is formed. The UV-vis absorption spectroscopy was used to observe the changes in the entire nanocomposites samples as prepared at different parameters. Further, the UV-visible absorption spectra prove the proposed formation mechanism discussed herein this study. Experimental Method Materials The materials used for preparing the samples in this work dodecylbenzenesulphonic acid (DBSA, 98 %, Aldrich) and polyvinilpirrolidone (PVP Mw = 10, Aldrich), aniline monomer (Aniline, 99.8%, Aldrich) was distilled and stored in the refrigerator, silver nitrate (AgNO3, 98 %, Aldrich), and ammonium persulfate (APS, 98 %, Aldrich) were used as received. Isopropyl alcohol (IPA) was used as radical scavenger in all samples. Deionized water was prepared in the laboratory and used through this study. Preparation of Composites: Ag/PANI core-shell nanocomposite has been synthesized by using hybrid chemical and γirradiation oxidation process of aniline monomer. For this purpose, procedures were done in a clean room, with appropriate amount of DBSA and PVP were dissolved in deionized water and maintained under vigorous stirring and heating (70˚C) until a homogeneous solution was obtained then cooled to room temperature and kept in a refrigerator and labeled (A). The use of PVP in Ag/PANI samples with the AgNO3 solution to prevent the process of agglomeration and distortion during as well as after, γ-irradiation [48] and [49]. Aniline was mixed in deionized water, maintained under vigorous stirring for half an hour, and then kept in a refrigerator to be used, denoted as (B). An appropriate amount of AgNO3 was mixed in deionized water, maintained under vigorous stirring for half an hour, and then kept in dark room to be used, denoted as (C). APS was dissolved in deionized water separately, maintained under vigorous stirring for half an hour, and then kept in the refrigerator, denoted as (D). Isopropyl alcohol was used in all samples which eventually changed into isopropyl radicals under the effect of the gamma ray that served as scavenger for the hydroxyl and hydrogen radicals (OH• and H•) as going to be discussed in this study. The preparation steps are presented in Table 1. Table 1 The preparation steps of Ag/PANI/PVP core-shell nanoparticles

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THE FOLLOWING SOLUTIONS WERE PREPARED AS:

THE PROCEDURES WERE DONE AS FOLLOWING:

[A]: DBSA + PVP + Deionized water heated (70 ℃) under vigorous stirring (30 min) [B]: Aniline + Deionized water under vigorous stirring (30 min) [C]: AgNO3 + Deionized water under vigorous stirring (30 min) [D]: APS + Deionized water under vigorous stirring (30 min) [E]: 5 ml of IPA

[A] + [B] under vigorous stirring (30 min) + [C] under vigorous stirring (20 min) + [D] Drop wise under vigorous stirring (5 min) + [E] Drop wise under vigorous stirring (5 min) All the above procedures done in dark room

All samples of our composition are presented in Table 2. The preparation of samples was done by adding B to A and kept under vigorous stirring for half an hour in order to get homogeneous solution and then C was added to them followed by D then the addition of IPA drop wise in five minutes. The samples were bubbled with nitrogen while the solution was under magnetic stirring for half an hour. The quantity of PVP, IPA and water were 0.3 g, 5 ml and 200ml, respectively in all samples. In addition, the molar ratio of aniline/APS is constant for all samples. The mixture of aqueous solution of PVP/aniline /DBSA/APS/AgNO3 was irradiated with γ-radiation at various doses up to 50-kGy in step of 10-kGy The use of this method leads to clear transparent green solution, which can be directly applied on different substrates. Table 2 Shows the measurements used to prepare Ag/PANI/PVP core-shell nanocomposites those synthesized with different parameters Sample no.

DBSA (g)

Aniline (g)

APS (g)

AgNO3

γ- Dose (kGy)

1

0

1.5

2.17

0.4

40

2

5

0.5

0.75

0.4

40

3

8

2.5

3.6

0.1

10

4

8

2.5

3.6

0.1

20

5

8

2.5

3.6

0.1

30

Results and discussion Formation Mechanism of Ag/PANI Core-Shell Nanocomposites It has become clear that, gamma irradiation induced technique is an appropriated method for preparation of monometallic or bimetallic nanoparticles because of its powerful to produce fully reduced and highly pure metallic nanoparticles, free from by-products and reducing agents [1] and

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[2]. Nuclear radiation is ionizing, which on passage through matter, gives positive ions, free electrons, and free radicals and excited molecules [35], [36] and [45]. Ionization of γ-irradiation involves the transfer of sufficient energy to a bound electron located in an atomic or molecular orbital of the irradiated material that the electron becomes free. The solvated and the ejected free electrons produced during gamma-ray irradiation in colloidal solutions can reduce the metal ions into zero-valent metal atoms without using reducing agents or catalysts and their consequent side reactions [1] and [35]. However, during polymerization of aniline into PANI by γ-irradiation employing AgNo3, the photon excites aniline monomer and the silver nitrate that Ag+ behaves as an electron acceptor and as a result Ag* is reduced and the aniline monomer is oxidized. Gamma irradiation offers sufficient energy that interacts with the hydrated aqueous samples by photoelectric absorption, Compton scattering, and pair production which causes the formation of ― secondary electrons by Compton scattering that induce among others hydraed electron (𝑒 𝑎𝑞 ). The • • hydroxyl and hydrogen radicals (OH and H ), induced in radiolysis of water are also strong reducing agents in aqueous colloidal solution which can be presented in Equation (4) [45]. In addition, the following electron-induced chemical reactions and disintegration processes can be initiated in a mixture of AgNO3 and PVP solution presented in Equation (5) [45]. 𝑛𝐻2𝑂

𝛾 ― 𝑟𝑎𝑦 ― ― ―→

― 𝑒𝑎𝑞 , 𝐻•, 𝑂𝐻•, 𝐻2,, 𝐻3𝑂 + , 𝐻2𝑂2…. 𝑒𝑡𝑐

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𝛾 ― 𝑟𝑎𝑦

𝐴𝑔𝑁𝑂3 ― ― ―→ 𝐴𝑔 + +𝑁𝑂3―

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The released electrons interact with silver ions Ag+ to form silver nanoparticles Ag. For the Ag+ ions, the electron capture cross section is high and, therefore, a large number of neutral (Ag0) silver atoms can be produced in the solution through the following Equation (6), [45]. The neutral Ag0 atoms can encounter the excess Ag+ ions and produce Ag2+ species, which progressively leads to the formation of silver nanoparticles in the solution as given in Equations (7 and 8). ― 𝐴𝑔 + + 𝑒𝑎𝑞 →𝐴𝑔0

𝐴𝑔0 +𝐴𝑔 + → 𝐴𝑔2+ 𝐴𝑔𝑛 ― 1 +𝐴𝑔 + →𝐴𝑔𝑛+

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The polymerization process of aniline involves the photolysis of the nitrate ions (NO3-), instead of Ag+ ions in the early stage of irradiation process. The first stage involves the photon decomposition of NO3- from AgNO3 for the polymerization of the aniline monomer. In the second stage, the Ag+ in the solution oxidizes the remaining oligomers, dimers or tetramers because of its low oxidation potential compared to the aniline monomers and consequently, more and more radiation and DBSA doping method produces composites of Ag/PANI core-shell via competing process between the oxidation and the reduction by single step process. In the oxidation process, in which aniline, APS, DBSA and PVP under the influence of γ-irradiation cause bond scission that leads to polymerization and high protonation of PANI, i.e. protonation of N+ of aniline molecules by SO3–. While in reduction process, radiation-induced electrons reduce silver ions Ag+ to silver Ag nanoparticles as discussed above for Ag/PANI/PVP and as presented in Fig. 3.

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Fig. 3.

A proposed mechanism of the formation of monolithic noble metal nanoparticles of Ag as a core with the formation of PANI nanoparticles as a shell to form Ag/PANI coreshell nanocomposites

In addition, irradiation not only can be used to dope polymers but also assumptions was made by [35,50-52], suggested that; irradiations cause a chemical changes in polymers, including cross linking, chain scission, formation of C=C, formation of alkyne groups, depletion of heteroatoms, e.g. N, S or O). The effect of γ-irradiation, neutron, ion or e-beams on polycarbonate is primarily chain scission. UV analysis by [1] have provided an evidence for the existence of three categories of compounds in heavy ion (128 MeV Ar9+) irradiated polycarbonate. The first one may form from intramolecular combination of the phenoxy–phenyl and phenoxy–phenoxy radical pairs. The second kind is formed by the reaction of the radical with a neighboring H, O or H2O molecule which may lead to chain ruptures and, as a result, a decrease in the molecular weight. These two categories may occur at low dose. The third one is formed by inter-molecular radical combination. This could occur at high dose, whereas at high doses the yield of the third category of compound is sufficiently high to control the process. This result will cause a decrease in the particle size due to the polymer scission, which end with better distribution as a nano scale particles as shown by our SEM analyses, and increase in their conductivity as shown by our conductivity measurements and reduce their energy band gap. Herein, this study I present additional data regarding this specific doping process in PANI composites, by using two doping techniques γ-irradiation and DBSA acid by single step. The binding energy of C-C bond is much stronger than C-H and C-OH bonds and thus, the effect of γ-irradiation on PVP polymer at low dose is likely to cause more bond scissions of C-H (binding energy 4.37 eV) and some C-OH side chain [1, 49,53-58]. At higher gamma irradiation doses, more C-OH covalent bond scissions are likely to be broken and leads to the formation of new bonds such as C=C and C=O of the aldehyde compounds [1, 59,60].

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The SEM and TEM Morphology of Ag/PANI Core-Shell Nanocomposites The synthesis of Ag nanoparticle of desired shape and size with uniform distribution within the matrix remain highly challenging. With this challenge at hand, an additional of Ag nanoparticles in a polymer composites induced by γ-radiation may give a positive influence on the particle sizes and distribution. Fig. 4 shows the Ag/PANI core-shell nanocomposite synthesized at 40-kGy. The TEM morphology shows a core of Ag nanoparticles with about 150 nm diameter synthesized at 30-kGy was homogeneously surrounded by PANI as a shell with thickness of 15 to 20 nm. In addition, the TEM result shows both PANI and Ag were distributed uniformly in PVP, the diameter of the homogeneously spherical Ag nanoparticles was estimated to be around 40 nm with smaller particle could be less than 10 nm for those synthesized at 40 and 50-kGy, respectively. This finding is in agreement with Shawkat and Saion [35, 36, and 45] who reported irregular granular structure of chemically synthesized PANI containing transition metal ions of nickel and cobalt. This indicates that the complexion of transition metal ions to PANI greatly change the aggregation state of PANI molecular chains. There have been reported that the diameters of the PANI nanoparticles polymerized chemically with hydrochloric acid were about 150 to 250 nm for PVA/PANI nanocomposites [61] and less than 100 nm for PVP/PANI nanocomposites [62]. This suggests that the type of binder determined the diameter of spherical PANI.

Fig. 4. TEM micrographs of Ag/PANI core-shell nanocomposites prepared at 30-kGy Furthermore, it is observed that the dark inner part (core) is mainly the compound of Ag nanoparticles with different shape and size, and the outer-coated surface (shell) is PANI with variable thicknesses depends on different parameters (gamma dose, aniline, and PVP). However, the TEM of three samples of Ag/PANI core-shell nanocomposites synthesized at same conditions but with different irradiation doses. It is obvious that the size of the Ag was decreased as the dose increased from around 100 nm for that sample synthesized at 30-kGy to 30 nm at 40-kGy and then to below 10 nm for that sample synthesized at 50-kGy. The lowering of aniline capping over Ag nanoparticles and the probable use of aniline molecules in the surface of Ag nanoparticles might be

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assigned as the reason for the changed the particle size. It seems that the smaller Ag nanoparticles aggregated into larger ones during polymerization because of lower capping of stabilizer on the Ag nanoparticles. In other word lowering the size of Ag nanoparticles in Ag/PANI core-shell nanocomposites was noticed on increasing of either the amount of aniline or/and γ-irradiation doses. The size was well controlled by the effect of γ- irradiation doses and aniline continents.

Fig. 5.

SEM micrographs of PANI nanoparticles polymerized at 40-kGy and 50-kGy

Moreover, in order to study the influence of γ-irradiation on the morphology, SEM micrographs of Ag/PANI/PVP core-shell nanocomposites synthesized at 20-kGy was taken. The result indicates that there was no significant change in the shape of the particles but larger particle size

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could be around 400 nm was observed as compared to those prepared at higher irradiation dose. A morphology consisting mainly of nanoparticles shown in Fig. with diameters around 100 and 10 nm, can be also obtained by selecting appropriate dopant conditions, in this case by increasing gamma dose from 40 to 50 kGy the particle size was decreased from 100 nm to 10 nm. We believe that during the irradiation a decrease in the particle size due to the polymer scission, which end with better distribution as shown in our SEM result (Fig. 5). In addition, the results show that higher concentrations of aniline enhance the yield of polymerization. It is important to note that the process of Ag/PANI nanostructure formation seems to occur as discussed above in the formation section. Furthermore, there is a big evidence of interactions between PANI and Ag as shown by the SEM micrographs of Ag/PANI core-shell nanocomposites due to the nature of their bonds is not conclusive. Ag nanoparticles are assumed to be deposited as a core among PANI nanoparticles as a shell to form core-shell as seen by TEM imaging. The interactions between Ag and PANI will be explain using UV–VIS absorption spectra, the present paper intends to analyze the existence of chemical bonds between PANI and Ag, proving the composite formation. The result shows that the effect of Ag on the morphology of PANI is very small which can be negligible. In addition, Fig. 6 represents the elemental mapping for Ag/PANI core-shell nanocomposites that synthesized at 20-kGy. The result clearly show the formation of Ag nanoparticles and shows the amount and the distribution of Ag in PANI nanoparticles, which is more evidenced for the formation Ag nanoparticales in PANI nanoparticles. The sizes of Ag nanoparticales cannot be detected by the SEM micrographs. Morphology data for composites of Ag/PANI core-shell nanocomposites are very limited by the SEM analyses. The red dotes in the same figure are Ag nanoparticles. This result could support the data from the TEM and give big evidence that Ag is formed by γ-irradiation techniques, which satisfies our objectives.

Fig. 6.

SEM mapping micrographs for the Ag nanoparticles in the Ag/PANI core shell synthesized at 10-kGy.

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Fig. 7.

EDX of Ag nanoparticles in Ag/PANI core-shell nanocomposites synthesized at 40 and 50-kGy. Jing has reported by chemically synthesized PANI nanoparticles of diameter ranging

between 50 and 100 nm deduced from the SEM morphology of Ag/PANI nanocomposites [68]. Using TEM image they found that the Ag nanoparticles have the mean diameter of about 20 nm warped inside the PANI nanoparticles. Thus, Ag nanoparticles become core of the PANI nanoparticles. They claimed that hydrogen bonding and electrostatic interaction between stabilizers capped Ag and PANI nanoparticles in the Ag/PANI nanocomposites. However, Fig. 7 shows the EDX peaks of Ag with different intensities prepared at different doses as presented on the figure. The higher intensity may attribute to more reduction of Ag from AgNO3 as dose goes higher. Comparing our results by this technique to others by different synthesis methodologies indicates that the conducting Ag/PANI core-shell nanocomposites prepared by the influence of γirradiation shows an excellent particle size and distribution. Further, an excellent environmental stability even after exposed in air above seven months as shown in SEM micrograph of Ag/PANI core-shell nanocomposites synthesized at 50-kGy shown above. Gamma-irradiation offers many advantages for the preparation of metal nanoparticles. This result shows the primaries reduced silver atoms then undergo further aggregation to progressively larger clusters.

Optical Properties The UV–VIS absorption spectra of the transparent green filtered Ag/PANI nanoparticles suspension in Fig. 8 exhibits three absorption peaks: an absorption peak at 350 nm corresponding to the π-π* transition of the benzenoid ring and two absorption peaks at about 440 and 800 nm, which

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can be assigned to the polaron band transitions. This band at around the 800 nm was found to be sensitive to changes in the concentration of the dopants (AgNO3, DBSA, aniline and γ-dose). The characteristic peak of the Ag nanoparticles in Ag/PANI core-shell nanocomposites suspension appears at around 420 nm, which is caused by surface plasmon resonance due to Ag nanoparticles and for the π=π* electronic transition due to conducting PANI nanoparticles shows a shift to a higher wavelength as AgNO3 increasing. A slight increase in the wavelength of 420 nm indicates more reduction of AgNO3 to Ag nanoparticles as AgNO3 concentration increase. These surface Plasmon resonance bands of metal nanoparticles i.e. cloudy electromagnetic waves coupled with the CB electrons, are sensitive to their surrounding environment. The third band is 350-360 nm (π*π transition of the benzenoid rings) indicating that the PANI nanoparticles is in its ES form in Ag/PANI core-shell nanocomposites. The peak around the 800 nm shows a shift to a higher wavelength as the dose, DBSA and/or aniline increased and shifted to the shorter wavelengths due to the presence of Ag in the composites. The decrease in wavelength indicating fewer polymers was formed as we increase the AgNO3 concentration that means less conductive PANI is formed, but it is still in its ES form with less protonation of the PANI backbone, which in turn decreases the number of polarons due to the presence of Ag nanoparticles.

Fig. 8.

UV-VIS absorption spectra of solved and filtered Ag/PANI/PVP in chloroform

This result of characteristic peaks of our Ag/PANI core-shell nanocomposites at around 340, 420 and 800 nm appeared in the UV-vis spectra consistent with previous work [1] and [63-67] for PANI nanoparticles by different synthesis techniques using different dopants. Moreover, similar experimental results were achieved by using a photo-redox reaction by [32,68.69] and a chemical reaction by [67] and [70-74]. They reported that the peak at high conducting PANI-ES form is at 760 nm and above which indicates the protonation level of the polymer backbone. This surface plasmon resonance band of metal nanoparticles at 430 nm is sensitive to their surrounding environment. Further, the presence of Ag nanoparticles did not lead to big change in UV–vis absorption bands. This result of the UV–Vis absorption spectra is an evidence of the formation of Ag/PANI core-shell nanocomposite. The absorption spectra clearly indicate a systematic increase in the overall absorbance, which is in proportion to the electrical conductivity. Fig. 9A shows a linear increase in absorbance around the peak of 800 nm as the concentration of AgNO3 decreases in the Ag/PANI system.

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Fig. 9.

UV–VIS absorbance around 800 nm band of Ag/PANI core-shell nanocomposites at different (A): AgNO3 wt. %, (B): DBSA concentrations, (C): Aniline concentrations (D): γ-doses (kGy)

The reduction of AgNO3 will result in the formation of a short chain with a corresponding increase in the absorbance at around 420 nm. The increase in absorbance of the band peak of 420 nm might be attributed to a light scattering of silver nanoparticles as their concentration increases, with a decreasing chain growth of the polymer as was indicated by decreasing the absorbance around the peak of 800 nm as the concentration of silver increases. The increase in the AgNO3 concentration causes the decrease in their absorbance around the peak of 800 nm due to a less protonation of PANI nanoparticles in Ag/PANI core-shell and fewer polarons are formed due to the increase in the Ag nanoparticles in the composites. Fig. 9B, C and D shows the plot of the absorbance of the band at around 800 nm vs. the feed concentration of DBSA wt. %, γ-doses (kGy) and aniline wt. %, respectively. It is evident from the results that the absorbance exhibits a linear dependency at a given values of aniline wt. %, DBSA wt. % and γ-doses (kGy) similar to those of PANI nanoparticles. Thus, within these parameters PANI dispersions in Ag/PANI/PVP core-shell nanocomposites obey the Beer-Lambert law. This indicates that in the Beer-Lambert concentration limit, the real polymerization yield of the dispersions, similar to those of pure PANI nanoparticles. Furthermore, below these concentrations of aniline or/and DBSA the peak at around 800 nm disappears. This result means that the conductive type of PANI in Ag/PANI core-shell nanocomposite does not exist anymore, a similar result was obtained in the case of PANI nanoparticles that synthesized at low aniline wt. %, doses (kGy) or/and DBSA wt. %, as shown in Fig. 10.

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Fig. 10.

UV-visible absorption spectra of PANI nanoparticles dispersed in PVP prepared at different parameters as illustrated in the figure

In addition, the absence of the peak at the 800 nm in the case of modified PANI (Ag/PANI) core-shell nanocomposites indicates that there is a threshold amount of aniline and DBSA or indicates that the concentration limits the polymerization yield and product in which type of PANI to be. Hence, to get the conductive Ag/PANI we should follow the mentioned ratios with suitable irradiation doses. The absorbance ratio of bands at 330−350 and 760−820 nm (A /A ) reveals the extent of 800

350

protonation of the polymer backbone and the influence of the dopant (AgNO3, DBSA and γ-doses) on protonation. In the case of modified PANI nanocomposites (Ag/PANI core-shell) with different weight ratios of AgNO3. The absorbance ratio (A /A ) of Ag/PANI was found to be decreased from 800

350

1 for that sample synthesized with 0.7 wt. % of AgNO3 to 0.76 for that of 3.6 wt. % of AgNO3 as shown in the Fig. 11. The increase of AgNO3 exhibits a linear decrease in the absorbance ratio (A /A ) indicating that PANI in Ag/PANI core-shell is formed with less protonation as compared to 800

350

800

350

those synthesized with the addition of DBSA or/and gamma dose. The higher absorbance ratios (A /A ) of dopants for Ag/PANI core-shell indicate that it can effectively dope the polymer backbone. Moreover, the result shows an increase in the absorbance ratio (A800/A350) versus aniline wt. % and other dopants DBSA wt. % and γ-doses (kGy). The absorbance ratio (A800/A350) for Ag/PANI core-shell nanocomposites exhibits a linear increase with the increase of aniline wt. %, DBSA wt. % and/or γ-doses (kGy).

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Fig. 11.

Absorbance ratio at peaks around ~800 to ~350 nm (A /A ) vs. AgNO3 wt. %. 800

350

Conclusion Summarizing the above discussion, the synthesis by γ-ray could influence the formation of PANI nanoparticles and Ag nanoparticles that show a good distribution in PVP. In addition, the homo-dispersed ions of these Ag nanoparticles were reduced by those reductive particles of the aqueous electrons by γ-irradiation. There was a high concentration of Ag nanoparticles coated by PANI in the PVP for those samples irradiated at higher doses of Gamma. This result satisfies our objectives, which goes with full agreement with the proposed mechanisms discussed above. The UV-visible absorption spectra for Ag/PANI/PVP core-shell nanocomposites in all cases is an evidence that the intensity of the broad absorption band at around the 800 nm corresponding to doped PANI bipolaronic state increases with an increase of PANI content in the composites due to those mentioned parameters. The SEM and TEM, analysis show the size of PANI nanoparticles reduced from above 400 nm at 10-kGy to around 10 nm at 50-kGy with better distribution and no indicated influence of Ag nanoparticles on the morphology of PANI. It indicates that the Ag nanoparticles have a nucleation effect on the polymerization, leading to a homogeneous PANI shell around them. The morphology of nanocomposites (PANI) was found to be sphere-type at 19-wt percentage of aniline and 50-kGy. By combining the results of UV-vis absorption and the morphology analysis proposed that the interaction of Ag/PANI could be divided into three major interactions: (a) π-π stacking; (b) electrostatic interactions; and (c) hydrogen bonding. The interaction between polar groups (polymer charge carriers) and oxygenated groups results in the possible formation of ionic or coordinated complexes. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper

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Acknowledgments We wish to express our deepest gratitude to Dr. Ali Al Naqbi, Director, AD Poly., and Dr. Mufeed Batarseh, Head of the Program, Academic Support Department for their constant encouragement they have rendered towards this work. Ethics This article is original and contains unpublished material. The corresponding author confirms that all of the other authors have read and approved the manuscript and no ethical issues involved References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

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Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

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Highlights:

I affirm that the manuscript has been prepared in compliance with Results in Physics Journal Publication's instructions to authors and the content of this manuscript, or a major portion thereof, has not been published in a referred journal nor being submitted for publication elsewhere.

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