Nanoparticles Preparation of Aniline and

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solution by copolymerization of acrylonitrile and aniline using KIO and benzoyl peroxide as an oxidant in the. 3 presence of various surfactants such as sodium ...

World Applied Sciences Journal 5 (2): 204-210, 2008 ISSN 1818-4952 © IDOSI Publications, 2008

Nanoparticles Preparation of Aniline and Acrylonitrile Copolymer Using Various Surfactants Mohsen Ghorbani and Hossein Eisazadeh Babol University of Technology, P.O. Box 484, Babol, Iran Abstract: Polyaniline/Polyacrylonitrile (PAn/PANr) copolymer was prepared in the aqueous/non-aqueous solution by copolymerization of acrylonitrile and aniline using KIO3 and benzoyl peroxide as an oxidant in the presence of various surfactants such as sodium dodecylbenzenesulfonate, poly(vinyl alcohol) and hydroxypropylcellulose. In this study, the PAn/PANr copolymer was characterized in terms of conductivity, morphology, yield, particle size and structure. The results indicate that the morphology, yield, particle size and conductivity of products are dependent on the type of surfactants. Also, the structure of obtained product was determined by FTIR spectroscopy.The results show that the intensity of peaks is dependent on the type of surfactant. Key words: Copolymer

Surfactant

Morphology

Conductivity

INTRODUCTION

Structure

conductivity of conducting polymers with the mechanical and optical properties of a matrix polymer such as poly(vinyl chloride) [13] or poly(vinyl alcohol) [14]. A process that was developed at the time took advantage of the aggregated character and consisted of forming colloidal dispersions or latex forms of conducting polymers [15,16]. Two methods have been used to produce stable dispersions. The first utilizes a dispersion polymerization route in which macroscopic precipitation is prevented by a thin, physically adsorbed outer layer of a suitable polymeric surfactant which acts as a steric stabilizer. The second consists of the synthesis of a graft copolymer in which one of the components is the steric stabilizer [16]. Macroscopic precipitation/flocculation takes place if the concentration of stabilizer is not sufficient. Chemical grafting (copolymers) of aniline onto the backbone of the polymeric surfactant is a novel way to obtain colloidal forms of this conducting polymer [15,16]. The chemical grafting technique offers the advantage, compared to physical adsorption, in the case of polypyrrole, of forming more stable materials in which desorption of the stabilizers does not take place. Suspension polymerization of aniline in the presence of dodecylbenzenesulfonic acid (DBSA) with styrenebutadiene-styrene (SBS) and without SBS was carried out and result indicate that DBSA acts simultaneously as a surfactant (emulsifier) and as a dopant [17,18]. Also

Polyaniline has attracted considerable attention because of its unique electrical, optical and electrooptical properties and its numerous potential applications [1]. One of the key problems related to the potential applications of polyaniline is its processability. Processability is an important requirement in conducting polymers for their possible commercial use. Since most of the conducting polymers are not processable, much of the efforts made in this field have been directed towards circumventing this problem. To solve this problem, various approaches have been tried, including addition of side groups to the polymer backbone [2], grafting of polymers to a non-conducting polymer [3], direct polymerization of intractable polymers into the final desired shape, making a composite of blend of conducting polymers [4,5] and copolymerization [6]. Extensive research has been directed toward the improvement of the processability of polyaniline by copolymerization with substituted aniline [7,8] or doping polyaniline with stable functionalized protonic acid [9,10]. The insolubility in common solvents and infusibility of conducting polymers, in general, make them poorly processable either by solution technique or by melt processing methods [11,12]. Several attempts have been made to overcome these problems, essentially by fabrication of composites, which combine the

Corresponding Author: Hossein Eisazadeh, Faculty of Chemical Engineering, University Technology of Babol, P.O. Box 484, Babol, Iran

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surfactant affect on the morphology (degree of crystalline order and orientation) [18]. Polyaniline which is soluble in common organic solvents have been synthesized by using organic acids of large molecular size or graft polymerization with polyaminostyrene [19]. Particle size and conductivity can be decreased by increasing the concentration of stabilizer [20,21]. These are related to the mass of insulating stabilizer adsorbed. The size and type of the dopant (anion) affect the morphology, size and electrical conductivity of resulting polymers [22,23]. The type and concentration of oxidant (dopant), type of protonic acids and additives affect the yield and electrical conductivity of polyaniline prepared chemically [24]. The polarity of the counterion plays an important role in the conductivity as well as in the chemical properties. Conductivity increases which small counterions are used [25]. The surfactants influence the physical properties (morphology, solubility) of the resultant polymer [26]. Foremost among the current commercial ventures are applications of conducting polymers in energy storage devices such as rechargeable batteries [27], electromagnetic interference (EMI) shielding [28], antistatic coatings [29], gas sensors [30], optical devices [31], etc. In this study, Polyaniline/Poly(acrylonitrile) copolymer was prepared in the aqueous/non-aqueous solution by copolymerization of acrylonitrile and aniline using KIO3 and benzoyl peroxide as an oxidant in the presence of various surfactants.

four point probe method was used to measure the volume resistivity of conducting polymer films. Reagents and Standard Solutions: Materials used in this study were aniline (extra pure >99%, d=1.02 g cm 3, Merck), hydroxypropylcellulose (HPC, M w=10 6) from Aldrich, sodium dodecylbenzenesulfonate (DBSNa) from Loba chemie, poly(vinyl alcohol) (PVA, Mw=72000), acrylonitrile (d=0.8 g cm 3), sulfuric acid, potassium iodate, benzene and benzoyl peroxide from Merck. All reagents were used as received without further purification, unless stated otherwise. Distilled deionized water was used throughout this work. Aniline was purified by simple distillation. Copolymer Preparation: The reaction was carried out in aqueous/non-aqueous media at room temperature for 6 hours. The optimal conditions for copolymer formation are summarized in Table 1. In a typical experiment, 1 mL aniline monomer was added to a stirred aqueous/non-aqueous solution of 100 mL (water/benzene,75/25% v/v) of sulfuric acid 0.5 M containing 1 g of KIO3, 2 g of benzoyl peroxide and 0.2 g one of the surfactants respectively. After few minutes 3 mL acrylonitrile monomer was added to stirred aqueous/non-aqueous solution. After 6 hours, Polymer was filtered and to separate the oligomers and impurities, product was washed several times with deionized water and then dried in room temperature. RESULTS AND DISCUSSION

MATERIALS AND METHODS

Effect of surfactant type on the conductivity and yield of PAn/PANr copolymer: It is well established that the charge transport properties of conjugated polymers strongly depend on the processing parameters [32]. Polyaniline (PAn) has a reactive N-H group in a polymer

Instrumentation: A magnetic mixer model MK20, digital scale model FR 200, scanning electron microscope (SEM) model XL30 and fourier transform infrared (FTIR) spectrometer model shimadzu 4100 were employed. The

Table 1: Optimal preparation conditions and type of surfactant on the conductivity and yield of product Yield of 4.26 gram monomers Type of surfactant

Electrical

Type and concentration

Concentration

(aniline + acrylonitrile) to

Pan/PANr

Particle

conductivity

of oxidant (g L 1)

of surfactant (g L 1)

copolymer (g)

yield (%)

size(nm)

(S cm 1)

20

2.05

48

381

0.41×10-3

20

2.35

55

417

0.23×10-3

20

2.35

55

371

3.5×10-3

-

2.53

59

550

6.1×10-3

Dodecylbenzenesulfonate sodium KIO3=10 Benzoyl peroxide=20 Hydroxypropylcellulouse

KIO3=10 Benzoyl peroxide=20

Poly(vinyl alcohol)

KIO3=10

-

KIO3=10

Benzoyl peroxide=20 Benzoyl peroxide=20

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Fig. 1:

Scanning electron micrograph of PAn/PANr in aqueous/non-aqueous (water/benzene) media. Reaction conditions: (KIO3 = 10 g L–1 , benzolyl peroxide =20 g L–1 , aniline monomer 10.75×10 mol L–2 , acrylonitrile monomer 60.98×10–2 mol L–1 , volume of solution 100 mL (75/25% v/v), reaction time 6 hours at room temperature)

Fig. 2:

Scanning electron micrograph of PAn/PANr in aqueous/non-aqueous (water/benzene) media. Reaction conditions: (KIO3 =10 gL–1 , benzolyl peroxide =20 gL–1 , aniline monomer 10.75×10–2 mol L–1 , acrylonitrile monomer 60.98×10–2 mol L–1 , sodium dodecylbenzenesulfonate =2 gL–1 , volume of solution 100 mL (75/25 % v/v), reaction time 6 hours at room temperature)

Fig. 3:

Scanning electron micrograph of PAn/PANr in aqueous/non-aqueous (water/benzene) media. Reaction conditions: (KIO3 =10g L–1 , benzolyl peroxide =20gL–1 , aniline monomer 10.75×10–2 molL–1 , acrylonitrile monomer 60.98×10–2 mol L–1 , hydroxypropylcellulose=2gL–1 , volume of solution 100 mL (75/25% v/v), reaction time 6 hours at room temperature) 206

World Appl. Sci. J., 5 (2): 204-210, 2008

Fig. 4:

Fig. 5:

Scanning electron micrograph of PAn/PANr in aqueous/non-aqueous (water/benzene) media. Reaction conditions: (KIO3 =10gL–1 , benzolyl peroxide =20gL–1 , aniline monomer 10.75×10–2 mol L–1 , acrylonitrile monomer 60.98×10–2 mol L–1 , poly(vinyl alcohol) =2gL–1 , volume of solution 100 mL (75/25 % v/v), reaction time 6 hours at room temperature)

(a)

(b)

(c)

(d)

FTIR spectra of (a)PAn/PANr copolymer without surfactant (b)DBSNa ,(c)HPC and (d) PVA were used as surfactant in aqueous/ non-aqueous (water/benzene) media

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chain flanked on either side by a phenylene ring, imparting a very high chemical flexibility. It undergoes protonation and deprotonation in addition to adsorption through nitrogen, which, having alone pair of electrons, is responsible for the technologically interesting chemistry and physics. The electrical conductivities of various copolymers produced under different reaction conditions were measured on pressed pellets of the copolymer powders. The electrical conductivity of compressed pellets was measured using four point probe method. The yield, particle size and electrical conductivity of copolymers using various surfactants are listed in Table 1. As can be seen the yield, particle size and electrical conductivity are dependent on the type of surfactant, because the surfactant, influence the rate of polymerization and also surfactants are adsorbed physically or chemically (graft copolymer) by the growing polymer [15,16,33,34].

For instance, PAn/PANr copolymer (without surfactant) shows the presence of characteristic absorption bands at 1558.81 cm 1 (C=C stretching vibration of the quinoid ring), 1478.53 cm 1 (stretching vibration of C=C of the benzenoid ring), 1299.82 cm 1 (C-N stretching vibration), 1129.06 cm 1 (C-H in-plane deformation), 809.93 cm 1 (C-H out-of-plane deformation). Furthermore, new peaks at 1686.22 cm 1 appear in the spectrum of PAn/PANr particles which are due to aniline/acrylonitrile units. The presence of the characteristic bands of the aniline/acrylonitrile unit brings a strong supporting evidence for the effective incorporation of this monomer (acrylonitrile) in the conjugated polymer (aniline). CONCLUSIONS In this study the characteristics of PAn/PANr copolymers such as conductivity, yield, morphology, particle size and structure were investigated using various surfactants in aqueous/non-aqueous media. It was apparent that, the type of surfactant has a considerable effect on the conductivity, morphology and particle size of resultant product which is probably due to the adsorption of surfactant. The SEM micrographs show that the type of surface active agent plays a major role on the surface morphology of products. For instance it is evident that using surfactant decreases the tendency to form agglomerates because surfactant prevent from gross aggregation of particles. Also surfactants influence the yield and electrical conductivity which is probably because of anionic and non-ionic adsorption to the copolymer particles. The structure of product was determined by FTIR spectrum. The results indicate that the intensity of peaks is dependent on the type of surfactant, presumably due to the interaction of surfactant and polyaniline.

Characterization of the PAn/PANr Copolymer: The morphology of copolymers was studied, using scanning electron microscope. As shown in Fig. 1-4, the size and homogeneity of particles are dependent on the type of surfactant. The type of surfactant is known to influence the rate of polymer formation, particle size, size distribution, morphology and homogeneity [21, 35, 36]. Adsorption of the surface active agent on the PAn particles is primarily due to the hydrophobic component in the surfactants, probably via a hydrogen bonding mechanism with the aniline N-H group (graft copolymer) [21]. PAn/PANr particles synthesized without surfactant is shown in Fig. 1. As can be seen in micrographs, the copolymers obtained using surfactants (DBSNa, HPC and PVA) exhibits spherical and rice-grains particles. It is apparent that using surfactant decreases the tendency to form agglomerates which leads to more homogeneous distribution, because surfactant prevent from gross aggregation of particles. As can see been in table, particle size decreases using various surfactants. Also the size of particles related to the type of surfactant. The structure of obtained product was determined by FTIR spectrum. The FTIR spectroscopy has provided valuable information regarding the formation of polyaniline composites. FTIR analysis has been done to identify the characteristic peaks of product. FTIR spectra in the 2500-500 cm 1 region, for Pan/PANr copolymer is shown in Fig. 5. As can be seen, the FTIR spectrum changes greatly and gradually as the copolymer is formed using various surfactants.

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