Especies de palmas utilizadas en SSP

In order to achieve oxidation stability of the copper particles embedded in a UV- cured acrylic crosslinked films. Based on the data available in literature15, 50,238,241,256,257 _{we have tried to in-situ synthesized copper metal particles in the}

presence of polymer capping agents. In this work, 0.5%(w/w) PVP and 0.2%(w/w) pyrrole were used as the polymeric capping agents and added to the polymeric formulation containing 1wt% CuCl2, 5wt% benzophenone and 2wt% diethanol

amine. We investigated the effect of the presence of pyrrole and PVP on the photochemical formation of copper particles, their stability against oxidation with the help of UV-vis spectra.

0 0.1 0.2 0.3 0.4 0.5 0.6 420 470 520 570 620 670 720 770 820 870 A b so rb a n c e Wavelength (nm)

1%Cu salt after 2 hrs

0.5% Cu salt after 2 hrs

5.5.3.1

Effect of pyrrole on the stabilization of Cu-NPs embedded

in a polymer matrix

For the stabilization of metal colloids in a polymeric matrix, the UV-crosslinked films were prepared by dissolving 1wt% CuCl2 and 5wt% benzophenone in a few drops of

ethanol, 1g PEGDA was added and 2wt% diethanol amine was added at the end. 0.2 %( w/w) pyrrole with respect to PEGDA was added and mixed well with the help of ultraturax for 2mins. With the addition of pyrrole in a CuCl2-amine complex, green

color turns to black as shown in Figure 71(a-b). The films of 100 µ were subjected to UV irradiation under nitrogen at intensity of 45mW.cm-2 _{for the necessary time to}

get cured.

Figure 71 Change in color observed (a) CuCl2-amine coordination complex in PEGDA, (b) in

the presence of 0.2 %( w/w) pyrrole, (c) Freshly prepared crosslinked film in the presence of 0.2 %( w/w) pyrrole

The crosslinked film obtained after UV-irradiation was red in color as shown in Figure 71-c. The deep red color of the film can be attributed to the formation of copper particles, as previously observed for the UV-irradiation CuCl2-amine

coordination complex. However, for the confirmation of the formation of copper nanoparticles, UV-crosslinked films were subjected to the UV-vis spectra. Spectra in

Figure 72 show a single absorption peak at around 575 nm.

5.5.3 Stabilization of UV-crosslinked films against oxidation

To monitor the stability of copper particles in air, we measured the absorption of the cross-linked film embedded with Cu-NPs after regular intervals of time. The UV-vis spectra of freshly prepared film and after exposing it to ambient atmosphere for different intervals of time are shown in Figure 72. The decrease in intensity can be easily observed with the increase in time of exposure to open atmosphere. A red shift in wavelength was observed from 575 nm for the freshly prepared film, to 578 nm after exposure in air for 1 hr. After being exposed to air for 2 and 3 hrs respectively, absorption spectrum was shifted towards 579 nm. Usually with the increase in particle size, absorption peak shifts towards higher wavelength.

Figure 72 UV-vis spectra of the cross linked films containing 1%CuCl2, 5%PI, and 2% DEA in

the presence of 0.2% pyrrole after regular intervals of time

However, after being exposed to air for 4 hrs, no peak observed. This could be due to the oxidation of copper particles to copper oxide (І) nanoparticles since the similar optical behavior of copper oxide (І) nanoparticles have been reported by Halin et al.300 0 0.2 0.4 0.6 0.8 1 400 450 500 550 600 650 700 750 800 A b so rb a n c e Wavelength (nm) Py after 1 hr after 2 hr after 3 hr after 4 hrs

5.5.3.2

Effect of PVP on the stabilization of Cu-NPs embedded in

a polymer matrix

Investigation of the contemporary acrylic resin crosslinking reaction and in-situ preparation of copper particles was carried out in the presence of PVP as a polymer capping agent. In order to obtain UV-cured acrylic crosslinked films, 1wt% CuCl2 and

5wt% benzophenone were dissolved in a few drops of ethanol, 1g PEGDA was added and 2wt% diethanol amine was added at the end. 0.5 %( w/w) PVP with respect to PEGDA was added and mixed well with the help of ultraturax for 5 mins. With the addition of PVP in a CuCl2-amine complex, green color turns to blue as shown in

Figure 73(a-b)

The films of 100 µ were subjected to UV irradiation under nitrogen at intensity of 45mW.cm-2_{. A deep red colored film was obtained after irradiating the sample for}

10mins. In a similar way, stability of copper particles obtained in the presence of 0.5 %( w/w) PVP was measured after regular intervals of time. The UV-vis spectra in

Figure 74 clearly show a strong absorption band at around 575 nm for the freshly prepared film, which confirms the formation of copper particles. However, the intensity of absorption band decreases with the increase in time of contact with air. The UV-cross linked film containing PVP as a stabilizer show a stable position of absorbance peak at around 575 nm even after 2 hrs of exposure. However, a red shift to 576 nm and 578 nm was observed after exposing for 3 hrs and 4 hrs respectively.

5.5.3 Stabilization of UV-crosslinked films against oxidation

Figure 73 Change in color observed (a) CuCl2-amine coordination complex in PEGDA, (b) in

the presence of 0.5 %( w/w) PVP, (c) Crosslinked film in the presence of 0.5 %( w/w) PVP,

Figure 74 UV-vis spectra of the cross linked films containing 1%CuCl2, 5%PI, and 2% DEA in

the presence of 0.5% PVP after regular intervals of time

(a) (b) (c) 0 0.2 0.4 0.6 0.8 1 400 450 500 550 600 650 700 750 800 A b so rb an ce Wavelength (nm) PVP after 1 hr after 2 hr after 3 hr after 4 hr after 6 hr

After being exposed to air for 6 hrs no absorption spectra was recorded. This straight line after observed after few hours of exposure to air could be due to the oxidation of copper particles to copper oxide (І) nanoparticles since the similar optical behavior of copper oxide (І) nanoparticles have been reported by Halin et al.300

The absorption spectra shown in Figure 68 and Figure 70 clearly indicates that the photochemical formation of copper nanoparticles is possible independent of the presence of stabilizers and also the obtained Cu-NPs are only stable for an hour in an ambient atmosphere. In-situ formation of copper nanoparticles along with the cross- linking of the acrylic resin in the presence of pyrrole and PVP can be observed clearly from the absorption spectra shown in Figure 72 and Figure 74 respectively. The results show that copper nanoparticles can be successfully prepared and stabilized against oxidation by photoreducing copper precursor in an acrylic resin in the presence of stabilizers by one step photochemical method. Although Cu particles obtained in the presence of 0.2wt%pyrrole and 0.5wt% PVP persisted against oxidation, but for only few hours in an atmospheric condition.

Conclusions and Future Work

Chapter 6

Conclusions

And

Future Work