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DOI: 10.1016/j.jmrt.2019.02.003
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Available online 16 April 2019
Influence of silica nanoparticles incorporated with chitosan/polyacrylamide polymer nanocomposites
Laila Hussein Gaaboura,b,
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a Physics Department, Faculty of Science, University of Jeddah, Jeddah, Saudi Arabia
b Physics Department, Faculty of Science, Jeddah University, Jeddah, Saudi Arabia
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Nanocomposite films based on chitosan (Cs) and polyacrylamide (PAM) embedded with silica nanoparticles (SiO2) were prepared. The films were studied and characterized using different techniques. The X-ray diffraction revealed the presence of the semi-crystalline nature of Cs/PAM blend. No peaks characterizing pure SiO2 were observed due to the masking effect of the Cs/PAM blend matrix resulting of the low amount of SiO2. The main characteristic IR-bands to the vibrational groups for Cs/PAM were observed. No changes in the position of IR bands were seen after incorporation of SiO2 nanoparticles. The UV–vis spectra showed an absorption band at 253nm with a sharp absorption edge which indicates the semi-crystalline nature of Cs/PAM matrices. The spectra optical parameters were measured and characterized as a function of photon energy. The value of optical energy gap (Eg) was estimated using indirect transition model and explained due to local cross-linking in the amorphous regions of Cs/PAM. The plot of dielectric loss and dielectric constant ε′ and ε″ with the frequency was gradually decreased with the increase of the frequency and reaches to constant values at higher frequencies due to polarization effects. The plot of real impedance (Z′) with imaginary impedance Z″ gives a perfect semicircle correlated to Debye behavior.

Cs/PAM blend
Silica nanoparticles
Dielectric modulus
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Blending between two or more polymers is very important to obtain a new material with new wide applications [1]. The decision for polymer blends can permit simpler molding and great handling of the nanocomposites as per their optical, mechanical, electrical and attractive practices. The expansion of nanomaterials to the polymer gives well mechanical properties and warm solidness with novel functionalities that rely upon capacity bunch in the polymer, the concoction structure between the polymer and nanomaterials, the shape and size the nanomaterials [9]. Nanocomposites based polymer or polymer blend with nanomaterials have consideration because of their one of kind properties rising out of the blend of these materials. The got nanocomposites show improved, optical, mechanical, thermal, electrical and optoelectronic properties [2].

Chitosan (Cs) is a biodegradable material available in nature which it is obtained from deacetylation (the removal of an acetyl group) of chitin. Chitosan is consisting of amine and hydroxyl groups (NH2 and OH) [3–6]. Low thermal and mechanical stability of chitosan is a major drawback and it enhanced by the addition of nanofillers to obtain new nanocomposite materials [7,8]. At the point when chitosan is mixed with other polymers, the miscibility between the polymers is an extremely critical factor particularly for a mechanical property of the blend [9,10].

Polyacrylamide (PAM) is normal linear water-soluble that demonstrates the nontoxicity and great biocompatibility [11,12]. The PAM is additionally conceivable to advantageously alter their mechanical, synthetic, and biophysical properties. The PAM is utilized in huge number applications including water illumination, waste water treatment, oil recuperation, agriculture and biomedical applications. The blends between polyacrylamide with other polymers are studied [13–16].

Silica nanoparticles (silicon dioxide, SiO2) are progressed practical materials utilized broadly as added to rubbers, plastics, and polymers because of their high particular surface region, dispersion, purity, and easy to use [17,18]. Silica has recently attracted significant attention for its uses in a wide range of emerging applications. The point of the present work is to explore the changes of the structural, optical, and electrical properties of pure Cs/PAM and Cs/PAM blend incorporated with various amounts for silica nanoparticles (SiO2).

2Experimental work

The low molecular weight of chitosan (Cs, C18H35N3O13) and powder of polyacrylamide (PAM, (C3H5NO)n) were supplied from Sigma-Aldrich. The amount of chitosan (40%) and polyacrylamide (60%) were dissolved in distilled water with acetic acid (2wt.%). Both the polymers were homogeneously mixed using a magnetic stirrer at 50°C about 12h. The solution of nanosilica (SiO2) was added to the blend solution using the concentrations 0.15, 0.3, 0.6 and 0.9wt.% stirring about 2h. The final solutions were dried at 40°C for 2 days. The thickness of the obtained films is in the range of 80μm.

The X-ray pattern is recorded on a PANalytical X’Pert PROXRD analyzer with filtered Cu Kα radiation (λ=1.54056Å) working at 30kV acceleration and 10mA currents of the X-ray tube. The FT-IR spectra are recorded on Nicolet iS10, USA spectrometer having a resolution 4cm−1 in the wave number range 4000–400cm−1 to examine their structure. Ultraviolet–visible (UV–vis) absorption spectra of polymer films are recorded using (V-570 UV/VIS/NIR, JASCO) in the wavelength range 195–900nm. The AC electrical studies are done in a frequency range from 10−1 to 107Hz, using Novocontrol Technologies Broadband Dielectric Spectroscopy. All the measurements are done in an evacuated system to eliminate the effect of moisture.

3Results and discussion3.1X-ray diffraction analysis

The X-ray spectra for chitosan/polyacrylamide (Cs/PAM) blend with the ratio 40/60wt.% of Cs and PAM, respectively, and CS/PAM doped with 0.15, 0.3, 0.6 and 0.9wt.% of silica nanoparticles (SiO2) are shown in Fig. 1. The spectrum of SiO2 (insert in Fig. 1) reveals an amorphous broad peak with Bragg angle at 2θ=21.75° agrees with JCPDS data (card No. 01-086-1561) [19].

Fig. 1.

The X-ray diffraction of pure SiO2, the chitosan/polyacrylamide (Cs/PAM) blend and CS/PAM doped with 0.15, 0.3, 0.6 and 0.9wt.% of silica nanoparticles (SiO2).


For pure Cs/PAM, there are two fundamental broad peaks are observed: the first peak is founded at about 2θ=13° and the second peak is clear at about 2θ=20°, ascribed to the anhydrous crystalline conformation of chitosan. Likewise, a peak at 2θ=10° is watched ascribed to the discrepancy between these diffraction angles might be credited to the difference of degree of deacetylation of the Cs/PAM blend and the samples processing. It is noticed that the diffraction peaks of the regenerated chitosan film are broadened, which is ascribed to the partial reorganization of the crystalline part inside the polymer during the formation of the blend film. When a little of SiO2 is added to Cs/PAM blend, the absence of the main peaks of SiO2 in the nanocomposite films may be because of the masking effect of Cs/PAM blend matrix resulting from the small contents of SiO2.

3.2FT-IR spectroscopy

The FT-IR absorption spectra for chitosan/polyacrylamide (Cs/PAM) blend with the ratio 40/60wt.% of Cs and PAM, respectively, and CS/PAM doped with 0.15, 0.3, 0.6 and 0.9wt.% of silica nanoparticles (SiO2) in the range of 4000–400cm−1 are shown in Fig. 2. The spectrum of the pure SiO2 shows the IR bands at 3437 and 1630cm−1 are ascribed to stretching and bending mode of OH groups, respectively [20]. The presence of small shoulder observed at 3246cm−1 is due to stretching mode of SiOH groups inside SiO2 structure. The presence of the broad band is seen at nearly 1111cm−1 and a small shoulder ≈1188cm−1 is ascribed to the asymmetric mode of SiOSi groups [21]. The absorption broad band is observed between 3300 and 3500cm−1 which describe OH stretching mode [22]. The bands at 1103cm−1 and at 945cm−1 are due to asymmetric and symmetric modes for SiO and SiOH, respectively [23].

Fig. 2.

The FT-IR absorbance spectra of the chitosan/polyacrylamide (Cs/PAM) blend and CS/PAM doped with 0.15, 0.3, 0.6 and 0.9wt.% of silica nanoparticles (SiO2).


For the spectrum of pure Cs/PAM blend, a broad band is clear seen at 3430cm−1 for PAM is ascribed to NH2 groups [24]. The band at 2929cm−1 is due to CH2 group and the two bands at 1629cm−1 and 1775cm−1 are described to CO modes. The strong band at 1402cm−1 is assigned to CH2 scissoring mode and the band 1132cm−1 is assigned to CO mode.

The bands for chitosan are assigned as: the broad band at nearly 3450–3200cm−1 is due to OH and NH groups and the band at 1633cm−1 is assigned to CO for acetyl group (amide-I) and amide-II group is seen at 1539cm[25]. The bands at 1406cm−1 and at 1066cm−1 are due to OH bending and to CO groups, respectively [26]. The small band at 1255cm−1 is assigned to COC group. There are no changes in the position of vibrational bands after incorporation of SiO2 nanoparticles. Scheme 1 shows the possible probability to an interaction between the Cs/PAM blend and the blend with silica nanoparticles.

Scheme 1.

The possible interaction between the Cs/PAM blend and the blend with silica nanoparticles.

3.3UV–visible spectra

The UV–visible spectra of pure Cs/PAM and Cs/PAM doped different contents nanosilica (SiO2) are shown in Fig. 3. The spectrum of Cs/PAM blend shows a small band at 253nm with a sharp absorption edge which indicates the semi crystalline structure of the Cs/PAM matrices. The new band at 313nm is observed after addition of SiO2 with the decrease in the UV–visible regions with shift toward longer wavelength. The red shift in the doped Cs/PAM blend confirms the complexation between the blend and SiO2. Also, it reflects the change in the value for the optical energy gap, which decreases because the occurrence changes in crystallinity inside Cs/PAM blend. The dramatic improvement in absorption is observed to be in coincidence with change of color of Cs/PAM films which the changes from transparent to off-white after addition of SiO2. The red shift is due to the quantum confinement effects and may be of the distribution of the SiO2 in the Cs/PAM matrices.

Fig. 3.

The UV–vis absorbance spectra of the chitosan/polyacrylamide (Cs/PAM) blend and CS/PAM doped with 0.15, 0.3, 0.6 and 0.9wt.% of silica nanoparticles (SiO2).


The investigation of the absorption spectra is a method to study and more data for the materials structure. The changes in the absorption radiation (lower to higher energy state) can decide kinds transitions of the electron. The optical energy gap (Eg) for direct and indirect transitions can be calculated by equations as following [27,28]:

The absorption coefficient (α) in term of absorbance becomes:

where hv is the photon energy, A is a constant, d is the sample thickness and n is 1/2 for allowed direct transition and is equal to 3/2 for forbidden direct transition.

The optical gap (Eg.) can be determined from extrapolation of the liner part from the plot between (αhν)n and the photon energy () as in Fig. 4. The estimated values of Eg are decreased from 4.49eV for Cs/PAM blend to 3.15eV for Cs/PAM–SiO2 nanocomposites. This decrease due to the interaction between the Cs/PAM and SiO2 that is the causes of localized states which generate an charge transfer complexes between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). The change in Eg values is due to cross-linking in the amorphous regions in the Cs/PAM and the increase in SiO2 cause an increase for localized states within the forbidden gap.

Fig. 4.

The (αhν)1/2 vs photon energy () for the chitosan/polyacrylamide (Cs/PAM) blend and CS/PAM doped with 0.15, 0.3, 0.6 and 0.9wt.% of silica nanoparticles (SiO2).

3.4The AC electrical studies3.4.1The dielectric properties

Fig. 5 displays the plot between the angular frequency Logω (where ω=2πf) with the dielectric constant (ε′) and Fig. 6 illustrates the relation between plot of dielectric loss (ε″) against Logω of pure Cs/PAM blend and the Cs/PAM embedded by 0.0, 0.15, 0.3, 0.6 and 0.9wt.% of SiO2 nanoparticles at room temperature.

Fig. 5.

The dielectric constant (ε′) depends on Log (ω) the chitosan/polyacrylamide (Cs/PAM) blend and CS/PAM doped with 0.15, 0.3, 0.6 and 0.9wt.% of silica nanoparticles (SiO2).

Fig. 6.

The dielectric los (ε″) depends on Log (ω) the Chitosan/Polyacrylamide (Cs/PAM) blend and CS/PAM doped with 0.15, 0.3, 0.6 and 0.9wt.% of silica nanoparticles (SiO2).


As we see in the two figures, the behavior of both ɛ′ and ɛ″ is decreased with the increase of frequency. This behavior is a general trend of dielectrics materials as a polymer that can be understood by polarization which created related to the ionic exchange of the number of ions by locally displacing in the applied field direction. The dielectric constant for the polymer is created due to the dipolar, electronic, ionic, and interfacial polarizations. At lowest frequency, there is a charge accumulation at the interface causing contributions for various interfacial polarizations are watched. The discussion of this behavior is that at a certain point, the space charges cannot support and comply with the outside field which causes a decrease in the polarization and there is no charge accumulation at the interface. At low frequencies, dielectric constant and dielectric loss depend on the presence of ion center type of polarization in the films and to the interfacial polarization. The dielectric constant is high at the low frequency that might be because of space charge polarization. It is because obstructing of charge carriers at the electrodes due to confinement to their movement at the interface. Likewise, we can observe the dielectric dispersion at low frequencies. The Debye equations give the complex permittivity related to free dipole oscillating in an alternating field is as follows [29]:

where ε∞ and εs are the dielectric constant at high frequency and limiting low frequency of dielectric constant, respectively, is the relaxation time (τ=RC) and i=−1.

The real part ε′ and the imaginary part are written as [30]:

From the two figures, it is observed that both the behavior of ε′ and ε″ gradually decrease with the increase of the frequency and it reaches to constant values at higher frequencies. Also, the two estimated values of ε′ and ε″ are very high at lower frequencies and it decreases with the increase of frequency due to because of polarization effects and because of the dipoles, not start to follow the field variety at higher frequencies. The plots of ɛ′ and ɛ″ as shown in the figures exhibit three regions over the frequency range. In the first region at very low frequencies (ω≪τ⇒ε′=εs˙). Then, the dipoles flow the field and the values of ɛ′ and ɛ″ decrease attributed to the dominant contribution of interfacial polarization effect. The second region (ω≤(1/τ)), the dipoles begin to lag the field and the relaxation process are occurs. At the last region (ω≫τ), the linearity of ɛ′ is tending to approach steady state which can be assigned to the high frequency limiting permittivity ɛ values of the polymers. When ωτ≪1, the estimated values ɛ′ of is equal to ɛs. Whereas the plot of ɛ″ has a little decrease it becomes very low. After adding silica nanoparticles to Cs/PAM blend, by increasing of the frequency, the dipole moment will not sufficient to rotate causing decrease of ɛ′ and approach to stable due to interfacial polarization. The decrease of ɛ″ with increases of the frequency is due to the origin of ɛ″ is the conduction losses.

3.4.2Complex impedance study

The collective plot of complex impedance Z* as a function of frequency can be applied to identify whether the long-range or short-range movement of charge carriers is dominant in the relaxation process. To Interpret the dielectric spectra, different formalism such as complex impedance Z* has been explored. The complex impedance can be evaluated from the following relation [31]:

where Z′ and Z″ are the real and imaginary part of the complex impedance, which described as [32]:

The plot (Cole–Cole diagram) between the real impedance (Z′) and the imaginary impedance Z″ for the samples is shown in Fig. 7. From the figure, the curves give a semicircular arc which deviate its movement with changes and variations occurring with increase of silica contents. The behavior of the semi-circular curve can be display and explain the kind of the electrical process existing in the samples where the impedance arc is bent to characterized by the formation of the curves. The intercept of semicircles with Z′-axis provides information on the type of electrical processes occurring in the prepared nanocomposites. The intersection with Zo axis represents the sample bulk resistance. The semicircles in the plot can be correlated with Debye type relaxation. The plots further show a decrease in impedance with the increase in silica content.

Fig. 7.

The complex variation plots (Z′ and Z″) for the chitosan/polyacrylamide (Cs/PAM) blend and CS/PAM doped with 0.15, 0.3, 0.6 and 0.9wt.% of silica nanoparticles (SiO2).


The blend of chitosan (Cs) and polyacrylamide (PAM) doped low concentrations of silica nanoparticles (SiO2) was prepared and investigated using different techniques. There are no peaks assigned to pure SiO2 was observed in X-ray spectra may be due to the masking effect of Cs/PAM blend matrix resulting from the low amount of SiO2. The FT-IR absorption spectra show the presence of the main characteristic bands of Cs/PAM polymer blend. No changes in the position of the IR bands after incorporation of SiO2 nanoparticles. The UV–vis absorption spectra were measured as a function of wavelength. The optical band gap (Eg) was calculated using the indirect transition (forbidden transition). It was found that, the optical values of Eg was decreased with the increasing of SiO2 due to local cross-linking within the amorphous regions inside Cs/PAM matrices. The electrical modules were investigated before and after adding the silica nanoparticles to Cs/PAM blend. With increase of frequency the value of ɛ′ is decreased and approach to stable due to interfacial polarization. The decrease of ɛ″ with increases of both the frequency attributed to the origin of ɛ″ is the conduction losses. At low content of SiO2, the onset of the semicircles indicates that the impedance is very high. The variation of real impedance (Z′) with imaginary impedance Z″ (imaginary) of the prepared was studied. This plot between Z′ and Z″ displays a series of semicircular arc which deviates its movement with changes and variations occurring with increase of SiO2.

Conflicts of interest

The author declares no conflicts of interest.

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