Morphological investigation of synthetic poly(amic acid)/cerium oxide nanostructures.
Nanotechnology, a field of science and technology, which concerned to the structures at dimensions between 1 and 100 nm showed great interest in recent years [1, 2]. Nanoscale organization with different shapes and sizes displayed unusual properties rather than the traditional one , Nowadays, new application areas of nanostructures are created in creative fields such as electronics, sensors, and biotechnology , Polymer nanocomposites (NC)s are commonly defined as the combinational material composed of a polymer matrix and additives which have at least one dimension in the nanometer scale. The additives can be one-dimensional, two-dimensional (2D), or three-dimensional (3D) . In NCs, the properties of inorganic parts such as rigidity and high thermal stability came together with the special characteristics of organic polymer parts like flexibility, ductility, and processability , In NCs, the polymers can be reinforced by different nanostructures such as metals , metal oxides , clays , nanotubes , and so forth , Optimization of particle characteristics in the nanoscale has opened a thrilling research field in the areas of nanotechnology and NCs . One of the challenging subjects in the field of NCs is the circumstance of the bonding between the nanofillers and the polymeric media. The performance of the NC in actual applications depends on to the adhesion strength between the dispersed nanostructures and the continuous polymer phase [13-15], Due to the incompatible nature of the inorganic substrate with the organic polymers, phase separation and agglomeration of fine filler particles may be occurred . Inorganic nanoparticles (NPs) are frequently modified by organic molecules such as silane coupling agents with the aim of the improvement in compatibility of two dissimilar phases . It has been proven that the surface modification technique is a very effective way to eliminate the agglomeration of nanostructures [18, 19]. As an example, Abdolmaleki et al.  used the [gamma]-methacryloxypropyltrimethoxysilane (KH570) as the silane coupling agent for improving the dispersion properties of zinc oxide NPs in optically active poly(amide-imide)s. Abdolmaleki et al. concluded that the surface modification of NPs with KH570 effectively hindered the unfavorable aggregation of NPs in NCs. Also, Shen et al.  used 3-aminopropyltriethoxysilane (APS) to modify magnetite NPs. The presented results by this team showed that the modified NPs have a good dispersion and stability parameters in aqueous fluids. Zhang et al.  also modified ceria NPs with APS in aqueous system. The dispersion stability of ceria NPs was considerably improved due to the introduction of aliphatic units on the surface of NPs. It is helpful to know that, Ce[O.sub.2], as an abrasive, has been used in glass chemical mechanical polishing (CMP) for many times. Lately, ceria NPs have become very imperative in silicon oxide CMP and shallow trench isolation CMP, due to their good elimination selectivity, high polishing efficiency, and themial properties ,
Polycondensation polymers have been considered as appropriate matrices for preparing advanced composites. In addition, synthesis of the thermally stable polymer is an attractive field in polymer science due to the existence of thermostable units in polymer main or side chains [24-26], Among the different polycondensation polymers, suitable for industrial applications such as microelectronic, membrane, electrically conductive adhesives, polyimide (PI) has received a great attention due to their thermal and chemical stability and low dielectric constant [27-30], However, the adhesion of different materials directly to the PIs is usually poor due to the inertness of PI surfaces. Failure in correct embedding of fillers into PI matrix will usually cause the consequent coatings to be poorly adhered [31-33], The most suitable intermediate of PI for use in composite technology are polyamic acids (PAA) [34-36]. The PAAs are easily processed rather than PIs. Also other representative benefits are as follows: (i) thermooxidative stability, (ii) reduction of thermal expansion, (iii) increase in modulus, and (iv) reduction in moisture uptake .
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Among the different kinds of phenol containing compounds, macromolecules with phenolic units showed great interest [38-41], Investigations of the redox behavior of polymer compounds by means of electrochemical techniques have the potential for providing valuable insights into the physical properties of these compounds. Hydroxyl group in phenol structure can be oxidized at a suitable potential in electrochemical process [41-43], Therefore, based on the structure of the designed polymers, the physical and chemical properties of macromolecules like inherent viscosity have shown relationship with electrochemical behavior , The electrochemical techniques could be applied as flattering analyses in these groups of macromolecules.
The design study is composed of two parts. In this work, as part one, PAA was prepared as a new intermediate matrix for application in fabrication of hybrid NCs, and the second part included the PI NCs. In this work, PAA films were designed, fabricated, and characterized for the first time and then the related NCs were prepared. We attempt to investigate the effect of PAA and PI matrix structure on to the properties of the NCs, and also the influences of intermediate technology in the properties of final NCs were inspected. Therefore, a new series of PAA/cerium oxide hybrids was fabricated by sonochemical assisted synthesis by using surface treatment technology for enhancing the compatibility of NPs and matrix in interfacial regions. Moreover, the properties of the PAA/Ce[O.sub.2] hybrids are characterized by a number of techniques including Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and atomic force microscopy (AFM) analyses.
Nano CeC[O.sub.2] powder was achieved from Neutrino with average particle sizes of 35-45 nm. N. N-dimethylacetamide and N-mcthyl-2 pyrrolidone (NMP) were dried over BaO, then distilled in vacuum. The hexadecyltrimethoxysilane (HDTMS), and benzene-1,2,4,5-tetracarboxylic dianhydride (PMDA) were obtained from Merck Chemical and were used as gained without further purification.
Infrared spectra of the samples were recorded at room temperature in the range of 4000-400 [cm.sup.-1], on FTIR Rayleigh (WQF-510) spectrophotometer. The spectra of solids were obtained using KBr pellets. The vibrational transition frequencies are reported in wavenumbers ([cm.sup.-1]). Band intensities are assigned as weak (w), medium (m), strong (s), and broad (br). The ([sup.1]H NMR, 500 MHz) spectrum was recorded by using a Bruker (Germany) DRX-600 instrument at room temperature in dimethylsulphoxide-[d.sub.6] (DMSO-[d.sub.6]). Multipilicities of proton resonance were designated as singlet (s), doublet (d), and multiplet (m). Inherent viscosities were measured by a standard procedure using a Cannon-Fenske routine viscometer (Germany) at the concentration of 0.5 g/dL at 25[degrees]C. TGA is performed with a Mettler TA4000 at a heating rate of 10[degrees]C/min from 25[degrees]C to 800[degrees]C under argon atmosphere. The XRD pattern was acquired by using a [D.sub.8]ADVANCE, Bruker. The diffractograms were measured for 20, in the range of 10-80[degrees], using Cu K[alpha] incident beam ([lambda] = 1.51418 [Angstrom]). The dispersion morphology of the NPs on PAA matrix was observed using FE-SEM [HITACHI (S-4160)]. AFM topographic pictures were obtained using digital multimode instruments Compact Frame, Bruker. A transmission electron microscope (ZEISS EM900 operating at 50 kV) was used to observe the morphology of NCs.
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The 3,5-diamino-N-(4-hydroxyphenyl) benzamide  was produced according to our earlier studies. In the case of nitrogen atom containing polymers, such as polyamides, Pis, and polyureas, one of the main elements is an amine structure. Therefore, design of the diamine containing compound in polymer synthesis has great attention. The purpose of application of 3,5-diamino-N-(4-hydroxyphenyl)benzamide (1) as the diamine in the production of polymer in this study was to introduce the pendent benzamide groups in the side chains of polymer for increasing the flexibility beside the maintenance of the thermal stability of the macromolecular chains. FT1R and [sup.1]H NMR spectroscopic techniques were used to identify the structures of the PAA. The PAA (3) was synthesized by low temperature solution reaction of the diamine compound (1) with PMDA (2) in dry NMP and was illustrated in Scheme 1. The polycondensation reaction of the diamime (1) was successively carried out in a flask by adding dropwise a 3,5-diamino-N-(4-hydroxyphenyl) benzamide (0.25 mmol) solution into PMDA (0.25 mmol) in NMP (6 mL) under a nitrogen flow at room temperature, followed by further stirring for 48 h to achieve a viscous PAA solution. Then the viscous liquid was precipitated in 20 mL of methanol. PAA powder was obtained in high yield and its inherent viscosity value is 0.34 dL [g.sup.-1].
PA A (3) FTIR ([cm.sup.-1]): 3619 (br), 3253 (br), 1668-1664 (br) 1601 (s), 1562 (s), 1511 (s), 1430 (s), 1365 (s), 1241 (s), 1112 (s). [sup.1]H NMR (500 MHz, DMSO-[d.sub.6], [delta], ppm): [delta]11.0 (s, 2H, COOH), 9.80 (s, 1H, NH), 9.65 (s, 1H, NH), 9.18 (s, 1H, OH), 8.22 (s, 2H, phenyl), 7.90 (m, 1H, phenyl), 7.52 (m, 2H, phenyl), 7.47 (m, 2H, phenyl), 6.83 (m, 2H, phenyl).
Building of Suiface Modified Ce[O.sub.2] NPs and PAA/Ce[O.sub.2] NCs
The most common technique for surface treatment of NPs is the application of commercial silane coupling agents or other organic molecules composed of alkoxysilane linkages using ultrasonic method in altered media . In the first step, Ce[O.sub.2] NPs were modified with HDTMS using ultrasonic assisted process. Ce[O.sub.2] NPs were dried out at 120[degrees]C in an oven for 48 h. Then the 0.20 g dried nano Ce[O.sub.2] was sonicated for 15 min in absolute ethanol, then 0.03 g HDTMS was added to the mixture and sonicated for 20 min . The product was separated and dried at 60[degrees]C for 24 h. The PAA was sonicated in ethanol for 20 min and then obtained colloidal solution was mixed with the appropriate amount of treated Ce[O.sub.2] NPs to make 4, 8, and 12 wt% based on the PAA content. The combination was sonicated for 4 h. At the final stage, the solvent was eliminated and the collected materials washed two times with ethanol and then dried at 80[degrees]C for 2 h.
RESULTS AND DISCUSSION
PAAs are the intermediate compounds in the syntheses of PIs. PAA can turn in to PI by chemical or thermal process. Due to the some difficulty in processing of the PI, the processing of some PAA in to the PI may be achieved in final application media. Therefore, synthesis and separation of PAA as intermediate in the production of final PI are very crucial. In this study, PAA (3) was synthesized by low temperature solution reaction of the diamine compound (1) with PMDA as the dianhydride (2) in NMP as solvent (Scheme 1). Formation of PAA was confirmed by FTIR and [sup.1]H NMR analyses. Distinctive absorption bands were observed in the region of 3600-3200 [cm.sup.-1] (-COOH, -OH, and -NH stretching), 1668-1664 [cm.sup.-1] (amide-I band, -C=0 stretching), 1562 [cm.sup.-1] (amide-II band, interaction between NH deformation and C-N stretching), and 1365 [cm.sup.-1] (C-N). The chemical structure of the new PAA was also confirmed by [sup.1]H NMR analysis (Fig. 1). A broad signal was identified at 11 ppm chemical shift. This signal was assigned to the protons from COOH groups which are included in the PAA. The signals at 9.80 and 9.65 ppm were assigned to the protons from NH groups of amide units presented from the benzamide structures and the new amide unit created from the reaction of the diamine (1) and the compound (2) in PAA structure. The signal at 9.18 ppm was allocated to the proton from OH group of bulky pendent unit. The aromatic protons were identified in the 6.83-8.22 ppm ranges. It seems that the designated macromolecule, due to the presence of carboxylic acid, phenolic units, and benzene rings, and existence of amide groups was prepared successfully and estimated that it showed good thermal stability and also may show steric hindrance effect between NPs for better dispersion in NCs structures.
FTIR spectroscopy was used to distinguish the functional units existing on the surface of ceria particles before and after the surface treatment. FTIR spectra of Ce[O.sub.2] NPs, HDTMS silane coupling agent, and surface modified NPs, were illustrated in our previous report , and the data were reported earlier. The weak stretching band of the -OH groups at 3449 [cm.sup.-1] suggests the presence of -OH groups on the surface of ceria particles before treatment. This band is considerably decreased and shifted to 3280 [cm.sup.-1] after modification by HDTMS, which may be clarified as -OH groups remained in the structure of ceria NPs. Surface treatment of Ce[O.sub.2] is a well-known approach to change the surface of NPs and therefore improve the interfacial adhesion in polymer/ceria NCs. As a result, when the aggregation of the NPs was diminished, the quality features of NCs were improved. Also all the NCs display the characteristic absorption peaks of C=0 stretching of amide units around 1650 [cm.sup.-1] It is also found that the absorption bands of Ce[O.sub.2] NPs gradually broaden with increasing Ce[O.sub.2] NPs contents. These results revealed the success in synthesizing the PAA/ Ce[O.sub.2] NCs (Table 1).
XRD is an adaptable, nondestructive analytical method for identification and quantitative determination of different phases of compound present in powder and solid samples. Diffraction happens as waves interact with a regular solid sample structure whose repeat distance is about the same as the wavelength. The XRD characterization results for 8 wt% NC are depicted in Fig. 2. The XRD peaks, which correspond to the (111), (200), (220), and (311) basal diffraction of cubic phase with fluorite structure (Ref. JCPDS card 34-394) were exactly detected in obtained pattem [47, 48]. The NC containing 8 wt% of ceda NPs showed the most distinct peaks related to polymer matrix and indicated the existence of Ce[O.sub.2] crystal structure in the NC. Although the sample showed broad peak with moderate intensity related to the PAA structure, ceria NPs which dispersed in PAA matrix showed sharper peaks than PAA peak. All the diffraction peaks for PAA/Ce[O.sub.2] NC are in good agreement with the XRD peaks of pure Ce[O.sub.2] NPs and polymer matrix, indicating that the PAA/ Ce[O.sub.2] NC contains pure ceria NPs. Crystallite size of the cerium oxide samples may be obtained using the Debye-Scherrer equation. The Debye-Scherrer equation is used commonly in X-ray analysis of materials, predominantly powder diffraction of metal oxides. It relates the peak width of a precise phase of a material to the mean crystallite size of that material. It is quantitative equivalent of saying that the larger the material's crystallites are, sharper are the XRD peaks. According to the full width at half-maximum of the diffraction peaks, the average size of the particles are estimated to be about 66-68 nm, which is basically in agreement with that from the microscopic data.
Examination and investigation of the morphology of the polymer NCs by using microscopic instruments is, therefore, a crucial stage for understanding the morphological characteristics of the NPs and functional units of matrices in NCs structures. Figure 3 shows the FE-SEM microscopic image of pure PAA which is illustrated the spongy structure with crack forms in a few images. Also the nanoscale dispersion of 4, 8, and 12 wt% of ceria NPs in PAA matrix is considered with FE-SEM and illustrated in Fig. 4. As can be seen in Fig. 4, the nanoscale distribution of NPs in 4 wt% sample was observed, while increase in the percentage of NPs to 8 wt% caused to increase the crack containing structure in some place of matrix. Also as shown in Fig. 4c and d, particles of Ce[O.sub.2], having a crystal size of about 56 nm in NC 8 wt%, tend to be few agglomerated state. The nanostructure Ce[O.sub.2] with average particle sizes below 70 nm was obviously detected in all the samples. In fact, the silane coupling agent can perform barrier for aggregation between NPs. The steric interaction forces and van der Waals forces potentially created NCs with outstanding stability. The feature of stability mechanism of PAA NCs is displayed in Scheme 2. Due to the little or no holes in the structure of NCs, it can be concluded that, good interfacial adhesion between ceria NPs and PAA matrix existed.
The TEM micrographs of PAA/ceria NCs are shown in Fig. 5a-d (8 and 12 wt%). The dark spots in the bright field image imply the existence of small particles with well-developed dispersion properties in TEM images. The colored array in prepared figures (Fig. 5a and b for NC 8 wt% and Fig. 5c and d for NC 12 wt%) were used to distinguish the dispersion of NPs in polymer matrix. The average ceria NPs sizes in the structure of PAA/ceria 8 wt% and 12 wt% samples are 46 and 56 nm, respectively. Well-dispersed NPs are observed in the pictures of samples. These results showed that the ceria NPs sufficiently dispersed in PAA matrix. This occurrence may be caused by more hydroxyl and carboxyl groups being presented in the PAA structure as bonding sites between the macromolecules chains and the untreated position of inorganic ceria.
AFM technique was used to observe the dimension and distribution of ceria NPs in the PAA matrix at surface topographic pictures. Figure 6 shows the AFM micrographs for PAA/ceria NC 8 wt% in the noncontact mode of cantilever and in a 2D level. It is demonstrated in Fig. 6 that the protruded particles size of the ceria spherical form NPs with the particle-matrix morphology is in the range of 46-50 nm and also showed that the dark spots of the ceria NPs are uniformly distributed in the matrix surface. It is due to some physical bond formation, reduced macroscopic phase separation, and hence safeguarding of the ceria NPs in the matrix. In addition to giving a 2D projection of the sample topography, AFM illustrate the 3D measurements of the surface structure of NCs. In this study, the AFM image provides information about surface morphologies by using the two- and three-dimensions. AFM images were in use with around 3 [micro]m X 3 [micro]m scan area from the images. Figure 7 shows the 3D AFM images of surface topography of 8 wt% PAA/Ceria NC. From 3D 3 [micro]m X 3 [micro]m draw, it comes out from 3D 3 [micro]m x 3 [micro]m outline of expanded NC 8 wt% picture shows an episodic structure, and also the maximum particles projected from the surface was around 75 nm.
The roughness results obtained by this study are presented in Table 2 displaying measured values of roughness parameters of prepared 8 wt% NC. Beside the analyses results of NC 8 wt%, it can be seen that although there are different NCs investigated in the study with different loading of NPs, all the materials have comparable average surface roughness properties. The NC 4 wt% showed the moderate results of all the measurements on the samples, which can be confirmed by the uniform 2D AFM images. The difference between the highest peak and the lowest valley within the multiple models in the evaluation length (Rtm) was calculated and shown in Table 2.
In evaluating the fracture surface of materials, numerous methods have been used. Fractal geometry has been revealed to be a valuable tool in the arenas of science and engineering [49, 50]. Fractal dimension, D is the basic quantitative component of fractal geometry. The fractal dimension comprised Euclidean and non-Euclidean component. Euclidean section illustrates the level of irregularity of the object. The non-Euclidean component describes the level of irregularity of the object from its Euclidean geometry. In this work, the AFM microscopic data were used to analyze the fractal dimension. To calculate the fractal dimension (D) from AFM data, a software Gwyddion was used. Gwyddion is a free and open source software program to calculate the fractal dimension from AFM data , The four main techniques were (a) cube counting, (b) triangulation, (c) variance, and (d) power spectrum. Figure 8 illustrates the (a) cube counting, (b) triangulation, (c) variance, and (d) power spectrum graphs for NC 8 wt%. The obtained results for the NC 8 wt% profiles were 2.17, 2.22, 2.26, and 2.13, respectively. The obtained results denote that the structure of the surface of NC 8 wt% in some positions containing the level of irregularity, but it is not volume filling.
The existence of inorganic nanofillers in a polymer matrix normally lead to a minuscule strengthening of thermal decomposition properties with esteem to the polymer dependence on to the character of the matrix and the nanofiller . The thermal properties of PAA and NCs were investigated with TGA and derivative thermogravimetry (DTG) in an argon atmosphere at a heating rate of 10[degrees]C [min.sup.-1].
Figures 9 and 10 explain the TG/DTG and differential thermal analysis (DTA)/derivative differential thermal analysis (DDTA) curves of the nanohybrid materials for 8 wt% Ce[O.sub.2] NCs from room temperature to 800[degrees]C. Thermal stability of the NCs were measured based on [T.sub.5] (the degradation temperature of 5% weight loss) and [T.sub.10]) (the degradation temperature of 10% weight loss) of the NCs and char yield at 700[degrees]C. There are four steps in the thermograph of PAA and NCs: (1) removal of water and elimination of aliphatic units of coupling agents; (2) exclusion of bulky pendent units; (3) thermal imidization of PAA to PI, and (4) degradation of the main chain of the polymer matrix. It can be monitored that PAA and NCs begin to lose weights at about 200-300[degrees]C. Due to the presence of many carboxyl and phenolic units in the structure of PAA, its weight loss could be ascribed to the loss of water due to water uptake characters of PAA and elimination of aliphatic units inserted from HDTMS. The 5% weight loss temperatures of the NCs were established between 253 and 272[degrees]C. The char yields of NCs were obtained in the range of 54-612% at 700[degrees]C. Several degradation mechanisms involving acid-base or ionic interactions between surface groups of metal oxides and the polar groups of polymers have been reported in the literature . Due to the presence of diverse chemical bonds and different categories of functional units in the structure of PAA, physical and chemical interactions were achieved by prepared NPs. Hydrogen bonds between the pendent hydroxyl groups of PAA and the hydroxyl groups of oxides encourage interactions through the Lewis base sites of ceria. The strong ionic or covalent bonds would prime to support in the stabilization of the NC structure during thermal degradation. Interactions between amide and carboxylic acid groups and the Lewis acid groups of the cerium oxide may also intervene and deferral the depolymerization. To conclude, the increase of the thermal stability of PAA in the presence of ceria observed in TGA is attributed based on restriction of the polymer chain mobility due to the presence of different hydrogen bond interaction between the existing functional units in the structure of polymer and also related to the structural changes to thermal stable PI moieties during the thermal process and also interaction between the PI and ceria NPs in NCs structures due to the inorganic filler character of ceria. Table 3 shows the thermal stability properties of polymer matrix and prepared NCs.
The char yields of the PAA/ceria NCs enhanced with increasing ceria NPs content. Increasing the char formation amounts can reduce the production of combustible vapors and hamper the thermal conductivity of samples. The char yield has been linked to the flame retardance factor; so, the flame retardancy of the NCs is encouraged. The limiting oxygen index (LOI) was used to investigate the flame retardant properties of the obtained NCs. The amounts of LOI was measured based on Van Krevelen and Hoftyzer equation .
LOI = 17.5 + 0.4 CR
where CR is the char yield.
The LOI values (36.7-42.3) revealed that the PAA and prepared NCs can be categorized as the self-extinguishing substances.
Cerium oxide NPs were successfully functionalized with silane coupling agent HDTMS. The functionalization resulted in uniform dispersion of the NPs during NC preparation process which resulted in strong repulsion between NPs and well interaction with matrix due to the organic backbone of the polymer. The fracture behavior of aliphatic functionalized ceria NCs shows a strong affinity of the ceria NPs to the matrix by observing the structures of NCs samples in different ceria percentage. These results could be monitored by different microscopic analysis data. The consequences of FTIR analyses were used to distinguish surface functional groups of ceria NPs, the grafting process of the silane coupling agent to the ceria NPs, clarify the structure of prepared PAA, and investigate the different interaction of NPs with polymer matrix by comparing the vibration behaviour of different bonding in NCs structures. Insertion of well-dispersed NPs reinforced PAA composites by monitoring thermal analysis results. The properties of the NCs were confidentially related to the content, dimension, and surface nature of ceria NPs dispersed in PAA medium. The enhancement of solid content of the NCs conducted to a higher thermal stability. Assessment of morphology investigating of PAA/ceria NCs notified that the nanostructure ceria with particles sizes in the range of 40-60 nm were dispersed homogeneously in NCs structures.
The authors thank Research Affairs Division University of Bonab, Bonab for partial financial support. Further financial support from National Elite Foundation (NEF), Iran Nanotechnology Initiative Council (INIC) is appreciatively acknowledged.
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Mehdi Hatami, (1) Bibi Faezeh Azarkar, (2) Mohammad Qandalee, (3) Hamed Hasanabadi (4)
(1) Polymer Research Laboratory, Department of Polymer Science and Engineering, University of Bonab, Bonab, Iran
(2) Chemistry Research Laboratory, Faculty of Science, Mashhad Branch, Islamic Azad University, Mashhad, Iran
(3) Department of Biology, Garmsar Branch, Islamic Azad University, Garmsar, Iran
(4) Young Researchers and Elite Club, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran
Correspondence to: M. Hatami; e-mail: Hatami@bonabu.ac.ir
Contract grant sponsor: Research Affairs Division University of Bonab, Bonab and National Elite Foundation (NEF), Iran Nanotechnology Initiative Council (INIC).
TABLE 1. FTIR analyses results for surface modification Ce[O.sub.2] NPs, PAA, and NCs. Compound FTIR (KBr) [cm.sup.-1] Modified Ce[O.sub.2] 3280(br), 2894(s), 2733(s), 1374(w), 1406(w), 1178(w), 1125(m), 1007(m), 885(m), 686(w), 550(s) PAA 3847(w), 3734(br), 36l9(w), 3253(br), 1646(s), 1562(br), 1511(s), 1430(m), 1365(m), 1241(w), 1112(m) NC 4 wt% 3755(w), 3264(br), 3078(w), 2962(br), 2880(br), 2604(br), 1946(w), 1829(w), 1730(s), 1662(s), 1557(m,br), 1511(s), 1519(m), 1443(s), 1302(m), 1226(w), 1146(m), 929(w), 837(s), 765(m), 618(w) NC 8 wt% 3780(w), 3573(br), 3264(br), 2922(br), 1946(w), 1886(w), 1782(m), 1732(s), 1557 (m), 1596(m), 1511(m), 1441 (s), 1402(br), 12l9(br), 984(m), 880 (br), 755(w), 721(w), 658(m), 559(m), 525(br) NC 12 wt% 3640(w), 3486(br), 3292(br), 3093(br), 2923(s), 2604(br), 1727(s), 1608(s), 1556(m,sh), 1510(s), 1443 (s), 1348(m,sh), 1302(m), 1239(br), 966(m,sh), 925(br), 872(br), 834(m), 755(m), 66l(m), 526(m) TABLE 2. Roughness parameters for PAA/Ce[O.sub.2], NC 8 wt%. Roughness parameters Values (nm) Roughness average (Ra) 0.98 Root mean square roughness (Rq) 1.23 Maximum height of the roughness (Rt) 8.23 Maximum roughness valley depth (Rv) 4.85 Maximum roughness peak height (Rp) 3.38 Average maximum height of the roughness (Rtm) 5.03 Average maximum roughness valley depth (Rvm) 2.64 Average maximum roughness peak height (Rpm) 2.39 Average third highest peak to third 2.20 lowest valley height (R3z) TABLE 3. Thermal properties of the PAA and PAA/Ce[O.sub.2] NCs. [T.sub.5] [T.sub.10] Char ([degrees]C) ([degrees]C) yield LOI Sample (a) (b) (%) (c) (d) PAA 241 295 48 36.7 PAA/Ce[O.sub.2] NC (4 wt%) 253 332 54 39.1 PAA/Ce[O.sub.2] NC (8 wt%) 267 348 59 41.1 PAA/Ce[O.sub.2] NC (12 wt%) 272 351 62 42.3 (a) Temperature at which 5% weight loss was recorded by TGA at heating rate of 10[degrees]C/min under a nitrogen atmosphere. (b) Temperature at which 10% weight loss was recorded by TGA at heating rate of 10[degrees]C/min under a argon atmosphere. (c) Weight percentage of material left undecomposed after TGA analysis at a temperature of 700[degrees]C under a argon atmosphere. (d) LOI evaluating char yield at 700[degrees]C.
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|Author:||Hatami, Mehdi; Azarkar, Bibi Faezeh; Qandalee, Mohammad; Hasanabadi, Hamed|
|Publication:||Polymer Engineering and Science|
|Date:||Oct 1, 2015|
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