**3. Properties of PVA/Ag nanocomposites**

## **3.1. Mechanical properties**

From the experimental and theoretical approaches that deal and explain the behavior of the nanocomposites, the insertion of the nanoparticles into polymer matrices is the direct reason to obtain nanocomposite materials with higher mechanical properties. There are many techniques to determine the mechanical parameters of the polymer/metal nanocomposites such as tensile, compression and shear stress techniques. From the stress-strain curve, the mechanical parameters including Young's modulus, elongation at break, stress yield, tensile strength and compressive strength were determined. The interfaces between the nanoparticles surface and polymer matrix (called the interfacial or boundary region) exhibit the nanocomposites local properties different than that of the bulk or traditional composites.

to a semi-crystalline state. The behavior of true stress-strain curve can be divided into three distinct lines. The first stage is the linear part and called the elastic strain following Hooke's law. The increase in the slope of this stage is attributed to the increase in the density of Ag nanoparticles. The second stage shows the starting of the neck formation. The length of this stage decreases with raising the content of Ag nanoparticles. Accordingly, the crystals of the isotropic PVA begin to be oriented in this deformation stage under the tensile stress. Also, it is clear that Young's modulus raises as the amount of Ag nanoparticles increases. This may be illustrated on the assumption that the introduction of metals in the polymer chain increases the density of the materials which leads to a decrease in lattice strain under external mechanical stress (where the introduction of silver nanoparticles in the PVA leads to the increase in the intra-molecular forces, creating a charge transfer complex which inhibits the molecules of PVA from sliding over each other. This may describe the raise of Young's modulus). The increase in the concentration of Ag nanoparticles causes shifts in the neck region to low strain side and the neck formation appears by increasing the concentration of Ag nanoparticles. These results can be explained by the fact that the increase of silver nanoparticles concentration causes an increase in the intra-intermolecular forces inside the polymer. This increase demonstrates itself by the shift of the formed neck to low strain

**Figure 6.** (left side) the stress-strain behaviors, (right side) the optical absorption spectra for prepared samples (pure PVA (a) and 0.2, 0.4, 0.8 and 1.5 wt.% of Ag nanoparticles take a label (b1–b4)) [23]. Copyright 2014. Reused with permission

Polymer/Noble Metal Nanocomposites http://dx.doi.org/10.5772/intechopen.79016 55

Chatterjee et al. [32] doped the PMMA/block copolymer with the Ag (from 0.16 to 0.65 wt.%) and then studied the storage moduli for this nanocomposite film. They documented the increment in both the storage and loss moduli of nanocomposite as the Ag concentration raise. This behavior was explained on the basis of the attraction forces (van der Waals forces) between the PVA and the Ag nanoparticles, and huge surface area to volume ratio of the Ag nanoparticles. Also, Deka et al. [33] recorded enhancement in the mechanical parameters such as Young's modulus, tensile strength, elongation at break, impact resistance and Shore A hardness of the

appearance on its gradual side.

from Elsevier Ltd.

One of the most important and major factors that affect the mechanical behavior of the polymer/metal nanocomposite is the concentration of the metal nanoparticles and the preparation method. Experiments showed that the mechanical parameters of the polymer/metal nanocomposites are strongly altered by these two parameters. Given facts showed that Young's modulus was found to be 2.2 [31] and 4.6 GPa [23] at approximately the same concentration of Ag nanoparticles 1 wt.% for the PVA/Ag nanocomposites, but with different experimental procedures. Also, it increased with raising the Ag nanoparticles content by using the same experimental procedures for the same nanocomposite. We believed that this increment in Young's modulus and the reduction in the elongation at break is assigned to the growth in the intra- and intermolecular hydrogen bonding due to the increase in the content of the Ag nanoparticles and then higher the cross-linking level in the nanocomposite. So, the increasing Young's modulus behavior and the decrease in the behavior of the elongation at break take place.

**Figure 6** explains as follows: the true stress-strain curve is changed after the addition of Ag nanoparticles in the PVA that show a transformation from a rubber-like of the PVA polymer

to this fact, the reactivity of the plane {100} to interact with PVA is larger than the reactivity of the plane {111} with PVA. So, there is a large difference in reactivity between the two surfaces of Ag nanorods. Consequently, the PVA coated the plane {100} of the Ag nanorods and completely blocked Ag nanorods from growing. On the other hand, the PVA partially coated the plane {111} of the Ag and also PVA partially blocked the Ag nanorods from growing along this direction as shown in **Figure 5**. This investigation confirms that the PVA macromolecule

Yonghong et al. [27] successfully prepared the polyacrylamide/gold (PAM/Au) nanocomposites by γ (gamma)-irradiation in an ethanol system. In a similar way, Krkljes et al. [28] prepared the PVA/gold nanocomposites via the gamma irradiation, in situ method. Also, Ali et al. [29] recently used the gamma irradiation to prepare the PVA/copper nanocomposites, with the obtained copper size ranging from 13.9 to around 19 nm. Graeser et al. [30] used gamma irradiation to reduce Ag + ions in the presence of polyvinylpyrrolidone (PVP) to pro-

From the experimental and theoretical approaches that deal and explain the behavior of the nanocomposites, the insertion of the nanoparticles into polymer matrices is the direct reason to obtain nanocomposite materials with higher mechanical properties. There are many techniques to determine the mechanical parameters of the polymer/metal nanocomposites such as tensile, compression and shear stress techniques. From the stress-strain curve, the mechanical parameters including Young's modulus, elongation at break, stress yield, tensile strength and compressive strength were determined. The interfaces between the nanoparticles surface and polymer matrix (called the interfacial or boundary region) exhibit the nanocomposites local

One of the most important and major factors that affect the mechanical behavior of the polymer/metal nanocomposite is the concentration of the metal nanoparticles and the preparation method. Experiments showed that the mechanical parameters of the polymer/metal nanocomposites are strongly altered by these two parameters. Given facts showed that Young's modulus was found to be 2.2 [31] and 4.6 GPa [23] at approximately the same concentration of Ag nanoparticles 1 wt.% for the PVA/Ag nanocomposites, but with different experimental procedures. Also, it increased with raising the Ag nanoparticles content by using the same experimental procedures for the same nanocomposite. We believed that this increment in Young's modulus and the reduction in the elongation at break is assigned to the growth in the intra- and intermolecular hydrogen bonding due to the increase in the content of the Ag nanoparticles and then higher the cross-linking level in the nanocomposite. So, the increasing Young's modulus

**Figure 6** explains as follows: the true stress-strain curve is changed after the addition of Ag nanoparticles in the PVA that show a transformation from a rubber-like of the PVA polymer

interacts with the Ag plane {100}, which is stronger than the Ag plane {111}.

duce the PVP/Ag nanocomposites.

**3.1. Mechanical properties**

54 Nanocomposites - Recent Evolutions

**3. Properties of PVA/Ag nanocomposites**

properties different than that of the bulk or traditional composites.

behavior and the decrease in the behavior of the elongation at break take place.

**Figure 6.** (left side) the stress-strain behaviors, (right side) the optical absorption spectra for prepared samples (pure PVA (a) and 0.2, 0.4, 0.8 and 1.5 wt.% of Ag nanoparticles take a label (b1–b4)) [23]. Copyright 2014. Reused with permission from Elsevier Ltd.

to a semi-crystalline state. The behavior of true stress-strain curve can be divided into three distinct lines. The first stage is the linear part and called the elastic strain following Hooke's law. The increase in the slope of this stage is attributed to the increase in the density of Ag nanoparticles. The second stage shows the starting of the neck formation. The length of this stage decreases with raising the content of Ag nanoparticles. Accordingly, the crystals of the isotropic PVA begin to be oriented in this deformation stage under the tensile stress. Also, it is clear that Young's modulus raises as the amount of Ag nanoparticles increases. This may be illustrated on the assumption that the introduction of metals in the polymer chain increases the density of the materials which leads to a decrease in lattice strain under external mechanical stress (where the introduction of silver nanoparticles in the PVA leads to the increase in the intra-molecular forces, creating a charge transfer complex which inhibits the molecules of PVA from sliding over each other. This may describe the raise of Young's modulus). The increase in the concentration of Ag nanoparticles causes shifts in the neck region to low strain side and the neck formation appears by increasing the concentration of Ag nanoparticles. These results can be explained by the fact that the increase of silver nanoparticles concentration causes an increase in the intra-intermolecular forces inside the polymer. This increase demonstrates itself by the shift of the formed neck to low strain appearance on its gradual side.

Chatterjee et al. [32] doped the PMMA/block copolymer with the Ag (from 0.16 to 0.65 wt.%) and then studied the storage moduli for this nanocomposite film. They documented the increment in both the storage and loss moduli of nanocomposite as the Ag concentration raise. This behavior was explained on the basis of the attraction forces (van der Waals forces) between the PVA and the Ag nanoparticles, and huge surface area to volume ratio of the Ag nanoparticles. Also, Deka et al. [33] recorded enhancement in the mechanical parameters such as Young's modulus, tensile strength, elongation at break, impact resistance and Shore A hardness of the polyurethane PU/Ag nanocomposites with the Ag nanoparticles concentration from 2.5 to 5 wt.%. Moreover, Young's and storage moduli of PVP/PU blend were enhanced by introducing the Ag nanowires in the matrix. However, the elongation at break decreased from 536% for neat PVP/PU to 304% for 1.5 vol.% of Ag-doped PVA/PU in the PVA/PU blend, and also the ultimate strength decreased from 12.7 for PVA/PU to 9.8 MPa for 1.5 vol.% of Ag [34]. Also, Papageorgiou et al. [35] determined the tensile mechanical parameters (Young's modulus, strain) and impact strength of the same polymer polystyrene (PS) doping with 3 wt.% of different nanofillers such as PS/Ag nanoparticles, PS/Cu nanofiber, PS/nano-diamond and PS/MWCNT nanocomposites (**Table 1**). By comparing the obtained data, it is shown that Young's modulus, elongation and impact strength in PS matrix containing the metal nanoparticles are better than the other nanocomposites containing the multiwall carbon nanotube MWCNT, and nanodiamond. The improvement and enhancement of the mechanical parameters by embedding metal nanoparticles was also reported in chitosan/Ag [36] and PVA/Ag [37] nanocomposites. As a result, the mechanical behavior of polymer matrices can be improved by dispersing the metal nanoparticles through the polymer and giving many benefits.

**1.** The dielectric constants for both the metal and its surrounding matrix;

**3.** The interface area, crossing point or the boundary between the particle and the surround-

Polymer/Noble Metal Nanocomposites http://dx.doi.org/10.5772/intechopen.79016 57

Metals in the nanoscale range allow to control the refractive index (RI) and the dispersion behavior of polymeric nanocomposites when inserted into the polymer matrix. The higher refractive index of nanocomposite materials obey these materials to a functional application in many fields such as optical and optoelectronic lab (lenses, optical filters, optical waveguides), and advanced technology such as solar cells, photodiodes, optical adhesives or antireflection films [38]. A large number of the metal nanoparticles can be inserted into the polymer matrix for boosting the refractive index of polymer nanocomposites. The refractive index of polymer/metal nanocomposites has a linear function with the density of the metal nanoparticles and the absorption coefficient. Either the increase in the refractive index or a decrease makes the polymer/metal nanocomposites very useful in many applications such as chemical and biosensors. Another important parameter, which very much influences the refractive index of the nanocomposites, is the isotropy or anisotropy of the metal nanoparticles in the polymer matrix. The anisotropy of the metal nanoparticles in the polymer matrix produces birefringence behavior; this means that the nanocomposites have two refractive

In recent years, the race to develop polymer/metal nanocomposite materials with microorganisms' resistance properties had been of a very significant value and considered an important key factor for inhibiting foodborne diseases and preventing or controlling bacteria and infections originating in a hospital (nosocomial infections) from growth. Marketing, the polymer/ metal nanocomposite product with the antibacterial properties is extremely used. The mechanism of the interaction between the polymer/metal nanocomposite and the bacteria is subse-

The antimicrobial effects showed in polymer/metal nanocomposites depend on three

**2.** Size, dimensions and shape of the particle;

**4.** The particles distribution in the surrounding matrix.

ing matrix;

indexes [39].

phenomena:

**3.3. Antibacterial properties**

quently summarized and is shown in **Figure 7**.

**3.** The inhibition was done by biofilms.

**3.4. Antibacterial mechanism of metal/polymer nanocomposites**

**1.** Metal ions that can release from the nanocomposites,

**2.** Nanocomposites can release metal nanoparticles from it.

#### **3.2. Optical properties**

For centuries, the polymer/metal nanocomposite is one of the most important classes of functional materials due to its useful optical properties, including light absorption, photoluminescence spectra and refractive index, and its applications. The size of metal particles and their allocation inside the polymer matrix are the two strongest parameters that the optical properties of these polymer/metal nanocomposites depend on them. Polymer/metal nanocomposites that consist of inorganic UV-absorbers and polymer have been of interest in many fields. The fingerprint behavior for all the noble metal nanoparticles is the unique absorption peak in the visible spectrum (**Figure 6**). This band called surface plasmon resonance (SPR) band is attributed to the excitation of the collective modes of motion of the electron cloud (plasmon excitation) at the boundary of the particle under the effect of the light electrical field. When the light falls with a definite frequency, the resonance takes place and results in an optical absorption, surface plasmon, plasma resonance absorption, plasmons or localized surface. Some factors exerted on this band position, width and intensity, are as follows:


**Table 1.** Mechanical properties of PS nanocomposites, data were collected from [35]. Copyright 2014. Elsevier Ltd. Reused with permission from Elsevier Ltd.


polyurethane PU/Ag nanocomposites with the Ag nanoparticles concentration from 2.5 to 5 wt.%. Moreover, Young's and storage moduli of PVP/PU blend were enhanced by introducing the Ag nanowires in the matrix. However, the elongation at break decreased from 536% for neat PVP/PU to 304% for 1.5 vol.% of Ag-doped PVA/PU in the PVA/PU blend, and also the ultimate strength decreased from 12.7 for PVA/PU to 9.8 MPa for 1.5 vol.% of Ag [34]. Also, Papageorgiou et al. [35] determined the tensile mechanical parameters (Young's modulus, strain) and impact strength of the same polymer polystyrene (PS) doping with 3 wt.% of different nanofillers such as PS/Ag nanoparticles, PS/Cu nanofiber, PS/nano-diamond and PS/MWCNT nanocomposites (**Table 1**). By comparing the obtained data, it is shown that Young's modulus, elongation and impact strength in PS matrix containing the metal nanoparticles are better than the other nanocomposites containing the multiwall carbon nanotube MWCNT, and nanodiamond. The improvement and enhancement of the mechanical parameters by embedding metal nanoparticles was also reported in chitosan/Ag [36] and PVA/Ag [37] nanocomposites. As a result, the mechanical behavior of polymer matrices can be improved

by dispersing the metal nanoparticles through the polymer and giving many benefits.

For centuries, the polymer/metal nanocomposite is one of the most important classes of functional materials due to its useful optical properties, including light absorption, photoluminescence spectra and refractive index, and its applications. The size of metal particles and their allocation inside the polymer matrix are the two strongest parameters that the optical properties of these polymer/metal nanocomposites depend on them. Polymer/metal nanocomposites that consist of inorganic UV-absorbers and polymer have been of interest in many fields. The fingerprint behavior for all the noble metal nanoparticles is the unique absorption peak in the visible spectrum (**Figure 6**). This band called surface plasmon resonance (SPR) band is attributed to the excitation of the collective modes of motion of the electron cloud (plasmon excitation) at the boundary of the particle under the effect of the light electrical field. When the light falls with a definite frequency, the resonance takes place and results in an optical absorption, surface plasmon, plasma resonance absorption, plasmons or localized surface. Some factors exerted on this band position, width and intensity,

**Polymer/metal nanocomposites Young's modulus (Gpa) Elongation (%) Impact strength (J/m)**

**Table 1.** Mechanical properties of PS nanocomposites, data were collected from [35]. Copyright 2014. Elsevier Ltd.

Ps 2.59 1.93 11.1 Ps/Ag 2.81 2.65 12.5 PS/Cu nanofibers 2.79 1.8 14.6 Ps/MWCNT 2.92 2.06 13.9 Ps/nanodiamond 3.1 2.34 11.7

**3.2. Optical properties**

56 Nanocomposites - Recent Evolutions

are as follows:

Reused with permission from Elsevier Ltd.


Metals in the nanoscale range allow to control the refractive index (RI) and the dispersion behavior of polymeric nanocomposites when inserted into the polymer matrix. The higher refractive index of nanocomposite materials obey these materials to a functional application in many fields such as optical and optoelectronic lab (lenses, optical filters, optical waveguides), and advanced technology such as solar cells, photodiodes, optical adhesives or antireflection films [38]. A large number of the metal nanoparticles can be inserted into the polymer matrix for boosting the refractive index of polymer nanocomposites. The refractive index of polymer/metal nanocomposites has a linear function with the density of the metal nanoparticles and the absorption coefficient. Either the increase in the refractive index or a decrease makes the polymer/metal nanocomposites very useful in many applications such as chemical and biosensors. Another important parameter, which very much influences the refractive index of the nanocomposites, is the isotropy or anisotropy of the metal nanoparticles in the polymer matrix. The anisotropy of the metal nanoparticles in the polymer matrix produces birefringence behavior; this means that the nanocomposites have two refractive indexes [39].

#### **3.3. Antibacterial properties**

In recent years, the race to develop polymer/metal nanocomposite materials with microorganisms' resistance properties had been of a very significant value and considered an important key factor for inhibiting foodborne diseases and preventing or controlling bacteria and infections originating in a hospital (nosocomial infections) from growth. Marketing, the polymer/ metal nanocomposite product with the antibacterial properties is extremely used. The mechanism of the interaction between the polymer/metal nanocomposite and the bacteria is subsequently summarized and is shown in **Figure 7**.

#### **3.4. Antibacterial mechanism of metal/polymer nanocomposites**

The antimicrobial effects showed in polymer/metal nanocomposites depend on three phenomena:


**2.** By one of two ways (endocytosis or direct diffusion), the bacteria cell wall penetrates by

Polymer/Noble Metal Nanocomposites http://dx.doi.org/10.5772/intechopen.79016 59

**3.** There are three steps for the metal nanoparticles within (10 and 100 nm to penetrate the bacteria cell wall by endocytosis: sticking to the membrane, the metal nanoparticles warped by the membrane and finally the particle-lipid complex separates from the membrane. **4.** The hydrophobic or hydrophilic nature of the metal nanoparticles at 10 nm plays an important role. The metal nanoparticle penetrates the membrane of the bacteria cell wall,

if the interaction is strong, driven by its preference for the lipid head group or tail.

**5.** Side by side and at the same time with these above mechanisms, the ions were freed and released from the nanoparticles and also concurrently excite the effects linked with the

**1.** The metal nanoparticles move through the nanocomposite matrix toward the surface, so

**2.** The attachment of bacteria is altered, by reducing the cell surface hydrophobicity (CSH) via the surface of the metal nanoparticles. Also, the extracellular polymeric substances (EPSs) are reduced by the surface of the metal nanoparticles, which also take a role in

Recently, Fatema et al. [40] prepared the PVA/Ag nanocomposites by two methods: first, by water in oil (w/o) microemulsion and the second by the in situ method. The antibacterial efficiency was done against G- bacteria '*E. coli*' and G+ bacteria '*S. aureus,*' respectively, for the above nanocomposites. They observed that the (w/o) microemulsion films have antibacterial activity higher than the in situ films under the same test condition. Also, Espana-Sanchez et al. reported the treatment of polypropylene PP/Ag and PP/Cu nanocomposites surface by using the argon plasma [41]. They showed that the nanocomposites have a higher quality in the antibacterial efficiency versus, pathogenic, the human disease bacteria, because of the larger surface area of the metal nanoparticles and the raising of the hydrophilicity and the roughness of film surface. Also, the in situ route was used to prepare the polyethylene PE/Ag nanocomposites for antibacterial applications [42]. They recorded that the Ag ions were released from

the PE/Ag nanocomposites with larger Ag concentration higher than the neat PE.

The embedding of noble metal nanoparticles as filler into organic polymer matrices gives superior thermal, electronic, optical and mechanical properties for the resulting polymer/ metal nanocomposite materials. The improvements and enhancement of the physical properties go with these materials to be used in different technical applications in many various

**4. Applications of polymer-metal nanocomposites**

the outer layer of the nanocomposite becomes much more active.

the metal nanoparticles.

ions release.

*3.4.3. Biofilm inhibition*

biofilm creation and growth.

**Figure 7.** Mechanisms for the antibacterial behavior of polymer/metal nanocomposites: (1) adsorption of bacteria on the polymer surface triggering the diffusion of water through the polymer matrix due to the medium surrounding the bacteria; (2) water with dissolved oxygen reaches the surface of embedded metal nanoparticles allowing dissolution or corrosion processes, and this way metal ions are realized; (3) metal ions reach the nanocomposite surface damaging the bacteria membrane; (4) afterward, metal ions can diffuse into the bacteria.

#### *3.4.1. Release of metal ions*


#### *3.4.2. Release of metal nanoparticles*

**1.** The metal nanoparticles via molecular interactions adhere to the bacteria surface and with the electrostatic forces.


#### *3.4.3. Biofilm inhibition*

*3.4.1. Release of metal ions*

58 Nanocomposites - Recent Evolutions

oxidation are generated by the metal ions.

bacteria membrane; (4) afterward, metal ions can diffuse into the bacteria.

*3.4.2. Release of metal nanoparticles*

the electrostatic forces.

**1.** The metal ions are released from the polymer/metal nanocomposites and reach the bacteria cell wall (the outer membrane) and denaturation of proteins in the bacterial membrane by their interaction with the sulfhydryl groups and amines and carboxyl groups in the peptidoglycan layer that found in N-acetylglucosamine and N-acetylmuramic acid.

**Figure 7.** Mechanisms for the antibacterial behavior of polymer/metal nanocomposites: (1) adsorption of bacteria on the polymer surface triggering the diffusion of water through the polymer matrix due to the medium surrounding the bacteria; (2) water with dissolved oxygen reaches the surface of embedded metal nanoparticles allowing dissolution or corrosion processes, and this way metal ions are realized; (3) metal ions reach the nanocomposite surface damaging the

**2.** The cell wall and membrane of the bacteria are destabilized or broken and subsequently

**3.** The released ions bind to DNA in the bacteria resulting in disorganized helical structures involved in cross-linking within and between nucleic acid strands; this leads to the cell not capable of reproducing. Also, the reactive oxygen species, lipid peroxidation and protein

**1.** The metal nanoparticles via molecular interactions adhere to the bacteria surface and with

disintegrated by these interactions, which is known as the bacteriolytic effect.


Recently, Fatema et al. [40] prepared the PVA/Ag nanocomposites by two methods: first, by water in oil (w/o) microemulsion and the second by the in situ method. The antibacterial efficiency was done against G- bacteria '*E. coli*' and G+ bacteria '*S. aureus,*' respectively, for the above nanocomposites. They observed that the (w/o) microemulsion films have antibacterial activity higher than the in situ films under the same test condition. Also, Espana-Sanchez et al. reported the treatment of polypropylene PP/Ag and PP/Cu nanocomposites surface by using the argon plasma [41]. They showed that the nanocomposites have a higher quality in the antibacterial efficiency versus, pathogenic, the human disease bacteria, because of the larger surface area of the metal nanoparticles and the raising of the hydrophilicity and the roughness of film surface. Also, the in situ route was used to prepare the polyethylene PE/Ag nanocomposites for antibacterial applications [42]. They recorded that the Ag ions were released from the PE/Ag nanocomposites with larger Ag concentration higher than the neat PE.
