|
|
|
Results and Discussions
UV-Spectroscopic studies of the interpolymer complex UV-spectrometer was used to verify the presence of doped PANi used in making the doped PANi/PCL interpolymer complexes. Prior to doping, UV-spectroscopy shows the characteristic peaks of pure PANi at approximately 315 and 625 nm (Chart 1). The 315 nm peak is due to the p ® p * transition of benzenoid amine structure of PANi while the 625 nm peak is a result of the excitation of the quinoid imine structure. Upon doping with PHBSA, a red shift was observed, with the characteristic peaks of doped PANi at 420 and 800 nm (Chart 1). |
|
The 420 nm peak was a result of doped benzenoid amine excitation while the 800 nm peak was due to the change from polaron to the bipolaron state. UV-vis spectroscopy was also performed on PCL and it shows the characteristic peak of PCL at about 270 nm. This peak is a result of the n ® p * excitation of the carbonyl functional group.
UV-spectroscopy was also performed on the blends. The UVs show that the blends do not contain the characteristic doped PANi peaks at 420 nm and 800 nm but contains the standard PCL peak at approximately 270 nm (Chart 2). However, peaks at 420 nm appear in the shoulders of 320 nm because the absorption coefficient of carbonyl functional group of PCL is very large compared to that of doped PANi's benzenoid amine. Therefore, PCL's energy absorption overwhelmed that of doped PANi in the 420 nm region. |
|
|
|
UV also reveals the existence of a new set of peaks ranging from 550 nm to 610 nm, depending on the blend composition. As the weight percentage of PANi composition increases, there appears to be a shift in these peaks, with a general trend of increasing wavelength as the PANi composition increases (from 20 wt% PANi and on)(Chart 3). The discovery of these new peaks can signify the first sign of an interpolymer interaction because the absorption peak may be a result of the hydrogen bond interaction between the PHBSA anion of the doped PANi and the oxygen atom of the carbonyl functional group of PCL (Figure 3). From the red shift observed between 20 wt% PANi and 80 wt%, it can be concluded that excitation in the interpolymer complex should be easier as the percentage of PANi composition increases. This is due to the fact that an increase in wavelength implies a decrease in energy because of the inverse relationship between the two. Therefore, as PANi concentration increases in the blend, it becomes increasingly easier to excite the electrons. |
|
|
|
Blends' Conductivity The conductivity of the polyblends was measured using the two-probe method. The conductivity of the polyblends was observed to be within the upper range of semiconductors, which ranges from 10-8 S/cm to 0 S/cm. Measurements showed that the blend's conductivity is between 10-4 and 10-3 S/cm, depending on the composition (Chart 4). These values are quite high because in all the polyblends studied in this experiment, PCL, a non-conductive polymer, is the dominant specie. With the addition of only 5 wt% PANi, the conductivity increased by a factor of over 10 |
|
|
|
X-ray diffraction spectroscopy X-ray diffraction spectroscopy was performed to study the effects PANi has on PCL's d-spacings. Through Bragg's Equation with a wavelength of 1.541838 Å, the d-spacings were calculated for the peaks A, B, and C (Chart 5). A comparison of the d-spacings shows that there is very little change in the d-spacing of the blends with respect to PCL. At peak A, the average d-spacing is approximately 4.15Å; at peak B, 4.02Å; and at peak C, 3.75Å. The d-spacings of pure PCL at peaks A, B, and C are 4.18Å, 4.04Å, and 3.79Å respectively. Thus, the addition of PANi to PCL did not alter PCL's crystalline configuration. |
|
|
|
Fourier Transform Infrared Spectroscopy (FTIR) FTIR was performed by Ciba Specialty Chemicals Corporation in Tarrytown, NY. A look at the FTIR of pure PCL shows the characteristic peak at 1724 cm-1 (Chart 6a). This absorption peak is from the vibrational movement or stretching of the carbonyl functional group of PCL. If there is a hydrogen bonding interaction between doped PANi and PCL, then the hydrogen bond will attract electrons from the p bonds of the carbonyl group at PCL. This will weaken the C==O double bond and causes a decrease in the bond's energy because of the lowering of the force constant k (Equation 1), which decreases the frequency, and therefore, decreases the carbonyl functional group's vibrational energy. |
|
Equation 1: This equation gives frequency ( n ) with respect to the force constant k, and the reduced mass number m . |
|
|
|
Since energy is inversely proportional to wavelength, as the energy of the C==O bond decreases, wavelength will increase. As a result, a decrease in wavenumber (1/wavelength) should theoretically be observed if there were an interpolymeric interaction. However, as can be seen from the blend's (40:60) FTIR, there is no shift in the 1724 cm-1 peak (Chart 6). Therefore, a hydrogen bonding interaction was not detected through the use of FTIR. |
|
|
|
DSC and TGA DSC was performed on the blends to study the glass transition (Tg) and melting (Tm) points. There does not appear to be a significant change in the melting points of the blends as PANi composition increases. The melting points measured are approximately that of pure PCL, which is about 55.5 oC (Chart 7). This further supports the conclusion made in x-rays spectroscopy that the addition of PANi does not affect the crystalline configuration of PCL since the melting points remain relatively constant for all samples. A single Tg point, that of PCL, was found at is approximately -58.68 oC. A second Tg point was not located due to the usual difficulties of detecting PANi's Tg point by DSC. Since the existence of two Tg points indicates phase separation, the homogeneity of the blends cannot be determined accurately through the use of DSC. However, from optical microscopy analysis, it is concluded that phase separation does exist in the blends. TGA was performed on pure PANi to find PANi's decomposition temperature. Data collected show that PANi decomposes at approximately 305 oC. The high decomposition indicates PANi's high thermal stability. In addition, this temperature also determines the upper limit of the temperature that PANi can be heated to without causing it to decompose. Thus, this result was taken into consideration upon performing DSC and hot stage heating. |
|
|
|
Optical Microscopy and Hot Stage heating The affects of heating on blends were studied using Mettler FP82 Hot Stage unit under Nikon Optiphot microscope. Prior to heating, doped PANi particles and PCL crystals were arranged haphazardly, without any well-defined pattern (Figure 6a). Upon heating, PANi begins to show ordered arrangements as PCL begins to melt. Connected pathways were formed between PANi particles, creating conductive "highways" for electrons to travel in when an electric current is applied across the sample (Figure 6b-c). As PCL is allowed to cool, the crystals hardened around these conductive pathways, forming dividers between the various lanes of the conductive "highways" (Figure 6d). Heating the samples shows that the intermolecular organization becomes more ordered, thus increasing the blends' relative homogeneity even though phase separation still exists. |
|
|
