Aromatic Condensation Research Articles

Accelerated benzene polycarboxylic acid analysis by liquid chromatography–time-of-flight–mass spectrometry for the determination of petrogenic and pyrogenic carbon

Pyrogenic carbon species are of particular interest due to their ubiquitous occurrence in the environment and their high sorption capacities for nonpolar organic compounds. It has recently been shown that the analysis of the molecular markers for complex aromatic carbon structures, benzene polycarboxylic acids (BPCA), has a high potential for aid in the identification of different carbon sources.In this study, the first LC method using mass spectrometry (MS) for reliable and accelerated (<24h) quantification of pyrogenic and petrogenic carbon by BPCA analysis has been developed. The main advantage of LC–MS compared to previous methods is the higher sensitivity, which is important if only small sample amounts are available. Sample pre-treatment could be reduced to a minimum. Deuterated phthalic acid was introduced as internal standard due to its structural similarity to BPCA and its lack of occurrence in the environment. Linear quantification with r2≥0997 was accomplished for all BPCA. Method validation showed an excellent quantification reproducibility (mean CV<5%) which is comparable to LC-DAD methods and more reliable than GC-FID measurements (CV 16–23%). In summary, the presented BPCA method is more economic, efficient and presumably attractive to use.Besides reference materials, various pyrogenic and petrogenic samples were analyzed to test if the sources were indicated by BPCA analysis. In addition to pyrogenic carbon, large amounts of petrogenic carbon species can also be present in urban soils and river sediments, especially in mining regions. They also to a large degree consist of aromatic carbon structures and therefore have an impact on source identification by BPCA analysis. Comparison of petrogenic and pyrogenic carbon samples shows similarities in the BPCA concentrations and patterns, in their aromaticity and degree of aromatic condensation. Thus, a differentiation between petrogenic and pyrogenic carbon only by BPCA analysis of samples with unknown carbon sources is not possible. For reliable source identification of the carbon species, the combination with other methods, such as e. g. analysis of polycyclic aromatic hydrocarbons may be successful.

Chemical and morphological evaluation of chars produced from primary biomass constituents: Cellulose, xylan, and lignin

The effect of pyrolysis temperature on the morphology, bulk and surface chemistry of cellulose, xylan and lignin chars has been examined. Chars were produced between 300 and 700 °C. Raman, X-ray photoelectron, nuclear magnetic resonance spectroscopic techniques, scanning electron microscopy and surface area analysis were used to characterize each sample. Formation of polyaromatic structures were found to be prevalent at 400 °C for both cellulose and lignin chars, and showed development at 300 °C for Xylan. The low A bands identified in the lignin char produced at 400 °C indicate that crosslinking at low temperatures preferentially forms hexagonal or larger rings. Aromatic condensation increased until 500 °C, and remained stable up to 700 °C. The sharp drop in oxygen content as temperature is increased up to 500 °C and the formation of ether (C-O-C) groups indicates that oxygen is a primary reaction component for crosslinking and polycondensation. Despite the considerable increase in ring size for char produced at 700 °C compared to 500 °C, only very mild loss of oxygen is identified, suggesting that C-C bonds are forming with minimal oxygen mediation The increased broadness of the NMR peak and the Raman G band suggest that at these temperatures the increase in ring size occurs largely in a 3 dimensional manner rather than planar with contributions from non-hexagonal rings and out-of-plane distortion. By comparing the NMR dephasing data to the I(D)/I(G) ratio an approximate relation between this Raman data and cluster size has also been derived.

Molecular-Level Structural Insight into Clarified Oil by Nuclear Magnetic Resonance (NMR) Spectroscopy: Estimation of Hydrocarbon Types and Average Structural Parameters

A direct and easy-to-grasp methodology based on the combination of quantitative 1H and 13C nuclear magnetic resonance (NMR) has been developed for the estimation of total aromatics, saturates, and several important structural parameters, such as aromaticity, average number of aromatic rings per molecule, average number of aromatic carbon atoms per molecule, average molecular weight, degree of aromatic substitution, degree of aromatic condensation, nature of condensation, and substitution to aromatic ring, etc. for clarified oil (CLO) from Indian oil refineries. These parameters, along with HPLC analysis data for di- to penta-ring aromatics, provide a molecular-level understanding of this potentially valuable feedstock, which can thus be correlated with process parameters for needle coke production from CLO. The method exploits the concept of group molecular weight (GMWt) and uses three empirical equations governing the nature of aromatic condensation. The various types of CLO that originated from Indian o...

Characterization of highly sulfonated PEEK based membrane for the fuel cell application

In this study, poly(bisphenol-A-ether ketone) (PBAEK) is synthesized via nucleophilic aromatic substitution poly condensation between bisphenol A and 4,4-difluorobenzophenone, and the synthesized polymers are sulfonated using chlorosulfuric acid and suitable synthesis conditions for the temperature and sulfonating reagent content. The sulfonation degree of polymer is calculated using element analyses. The prepared sulfonated polymers are characterized for potential fuel cell applications through determining their water uptake, proton conductivity, and thermal stability. The significant advantage of the synthesized sulfonated PBAEK (sPBAEK) is its better solubility relative to commercial PEEK in various solvents, because sPBAEK backbones contain bisphenol A. The water uptake of the membrane increases with increases in the sulfonation degree. The sPBAEK membrane exhibits increased proton conductivity compared with the PBAEK membrane at 100% relative humidity conditions. As the sulfonation degree increases, the proton conductivity increases due to the increasing content in the hydrophilic domain. This property allows the prepared membranes to be potential candidates for proton exchange membrane fuel cells.

Sulfonated Block Copolyphenylchinoxalines As Proton Exchange Membranes

The proton exchange membrane fuel cell (PEMFC) is considered to be the most promising power source for portable and automotive applications. Currently, perfluorinated polymers such as Nafion are the state of the art materials because of their good physical and chemical stability along with high proton conductivity under a wide range of relative humidity at moderate operation temperatures. However, high operation temperatures, cause weakening of their properties. In addition, their shortcomings such as high cost and high methanol permeation property, limit their application. To remedy these problems, aromatic hydrocarbon polymers have been extensively studied as alternative materials for proton exchange membranes (PEMs)and many sulfonated aromatic polymers such as poly(phenylene)poly(ether ether ketone)s, poly(ether ether sulfone) poly(arylene ether) and polyimides have been developed as alternate candidates. Generally, membranes based on these polymers can achieve high proton conductivity by increasing their ion exchange capacities (IECs), resulting in huge water uptake and a dramatic loss of mechanical properties. Recently, introduction of block copolymer structures to PEMs has been considered as a strategy to overcome the weak points of a random copolymer system. Block copolymers composed of hydrophilic and hydrophobic segments are expected to form ion transport channels due to hydrophilic/hydrophobic phase separated structures and show improved proton conductivity. Poly(phenlyquinoxalines) are a family of aromatic condensation polymers known their outstanding thermal and chemical stability. Based on this polymer class new sulfonated block copolyphenylchinoxalines with hydrophilic and hydrophobic segments have been developed. The block copolymers were synthesized via polycondensation reactions between 3,3`-4,4`tetraaminodiphenylether and two different tetracetones, followed by sulfonation using a mixture of concentrated sulfuric acid. and oleum (4:1).High molecular-weight polymers over 20 000 in number average molecular weight were easily obtained and gave tough and flexible membranes by solvent casting. The properties of their membranes, such as proton conductivity, water uptake, oxidation and dimensional stability were investigated und presented.

Demetalization of Heavy Oil Based on the Preferential Self-assembly of Heavy Aromatics in Supercritical Water

Demetalization of heavy oil through pyrolysis in the presence of subcritical water or supercritical water (SCW) was experimentally investigated. At a high water-to-oil ratio and high water density, the occurrence of pyrolysis can be transferred to the SCW phase. Driven by the π–π attractive interaction between aromatic sheets and the superb diffusivity in SCW, the coke-like self-assembly of metal-containing heavy aromatics occurs spontaneously and rapidly. The self-assembly behavior of aromatics in SCW depends not only on the thermodynamic state of SCW but also on the average scale of aromatics. With the aid of self-assembly in dense SCW, the condensation of metal-containing heavy aromatics, distributed mainly in a vacuum residue, to coke is significantly accelerated, by which the rate of demetalization is improved simultaneously. Owing to the preferential self-assembly of metal-rich heavy aromatics, an increasing yield of liquid products can also be obtained under an optimized SCW environment.

Increasing molecular structural complexity and decreasing nitrogen availability depress the mineralization of organic matter in subtropical forest soils

The degradation of soil organic matter (SOM) is determined by its compositional and structural properties, but the properties of the remaining SOM can be modified during the mineralization process. In this study, 12 soils (Ultisols, Alfisols and Inceptisols) from subtropical forests were incubated under laboratory conditions (25 °C, aeration) for 90 days. The mechanisms underlying the changes of these properties were investigated by analyzing pre- and post-incubation soils using UV absorption, fluorescence spectroscopy and acid hydrolysis methods. The turnover rate of SOM decreased with increasing soil depth. The amount of CO2 released ranged from 90 to 620 mg CO2-C kg−1, representing c. 0.9–3.1% of soil organic C (SOC). The proportion of nonhydrolyzable (recalcitrant) N in total N (RN) increased with soil depth, whereas it was not apparent in relation to the proportion of nonhydrolyzable (recalcitrant) C in total C (RC). Furthermore, a negative correlation was observed between SOM mineralization and RN (P < 0.05) rather than RC, implying that the availability of N was a limiting factor in SOM decomposition when compared with C. The decrease in E2-to-E4 ratio and fluorescence intensity (FI) of water-extractable organic C (WEOC) with increasing soil depth suggested that WEOC in the deeper horizons was probably rich in electron-withdrawing groups (COOH) but poor in electron-donating groups (OH, NH2), and it was composed of components with larger molecular size, higher humification degree and structural complexity. These could be responsible for the lower SOM mineralization rates in deeper horizons. After 90 days of incubation, a blue shift of wavelengths in the synchrotron-scan spectra, and an obvious increase of FI values, together with the increase in E2-to-E4 ratio of WEOC implied a reduction in molecular size and the degree of aromatic condensation and humification, resulting in a shift to less complicated structures of WEOC.

Maceral controls on porosity characteristics of lithotypes of Pennsylvanian high volatile bituminous coal: Example from the Illinois Basin

Porosity characteristics of vitrain, clarain, durain, and fusain lithotypes of the Springfield Coal Member of the Petersburg Formation and the Danville and Hymera Coal Members of the Dugger Formation from the Illinois Basin were investigated with a special emphasis on the control of coal macerals on pore-size distribution. These Pennsylvanian coals are of high volatile bituminous rank and have vitrinite reflectance ranging from 0.51 to 0.60%. The lithotypes studied show decreasing values of Brunauer-Emmett-Teller surface area, and micro- and mesopore volumes from vitrain through clarain and durain to fusain. Within the mesopore size range, vitrain and clarain are dominated by pore-size widths of 4 to 10nm, whereas durain and fusain have more volume for pores larger than 20nm. In contrast to mesopores, micropore sizes are very similar for all lithotypes, averaging 1.37 to 1.39nm. In addition to differences among lithotypes, there are significant differences in pore characteristics among the three coals studied, with largest surface areas and pore volumes documented for the Hymera, followed by the Danville and the Springfield. A strong relationship exists between surface area, mesoporosity, and microporosity and maceral composition, with vitrinite having a very strong positive correlation, liptinite having a weak positive correlation, and inertinite having a strong negative correlation. Negative correlations of total porosity with vitrinite and liptinite and positive correlations with inertinite suggest that among the maceral groups, pores in inertinite contribute most to the total porosity. The Fourier transform infrared spectrometry technique demonstrates that fusains from the three coals studied have higher aromaticity and a higher degree of aromatic ring condensation and lower hydrocarbon potential than the other lithotypes, whereas chemical differences between vitrain, clarain, and durain are less distinct. In addition, there is a relationship between aromaticity of the lithotypes and surface area and mesopore and micropore volumes.

Comparative study on structural properties and combustion kinetics of Chinese Shenhua long flame raw coal and its pyrolytic char

Research on the structural and combustion properties of coal is of great importance for its conversion and applications in view of fundamental studies. In this work, we conducted the first detailed study on the structural properties and combustion kinetics of Chinese Shenhua raw coal (RC) and its pyrolytic char (PC). The combustion kinetics was simulated by using the random pore model (RPM). The results showed that RC and PC were composed of both a plant‐cell‐like structure and a discrete particulate structure. In addition, PC had a larger specific surface area, finer particles, higher aromaticity, and higher degree of aromatic ring condensation than those of RC. Combustion of PC showed higher ignition temperature, lower burnout temperature, and a higher combustion index compared to RC. A high correlation coefficient R2 (0.999) and a low average error θ (0.008) were obtained using the RPM. The combustion apparent activation energy E and the structural parameter ψ of RC were 40.30 kJ mol−1 and 0.53, respectively. For PC, the values of E and ψ were estimated to be 60.01 kJ mol−1 and 0, respectively. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 766–774, 2017

Antifungal Activity of New Eugenol-Benzoxazole Hybrids against Candida spp.

Eugenol is a natural allylphenol responsible for a wide range of biological activities, especially antimicrobial. Benzoxazoles are heterocycles with recognized antimicrobial activities. This paper describes the design, synthesis, and the biological results for benzoxazole type derivatives of eugenol as antifungal agents. The products were obtained in good yields by a four-step synthetic sequence involving aromatic nitration, nitroreduction, amide formation, and cycle condensation. They were evaluated against species of Candida spp. in microdilution assays, and four products (5a, 5b′, 5c, and 5d′) were about five times more active than eugenol against C. albicans and C. glabrata. Two of them (5b′ and 5d′) showed good activity against C. krusei, a species which is naturally resistant to fluconazole. Furthermore, the active products were more selective than eugenol against human blood cells, showing that they are interesting substances for further optimization.

Effect of catalysts on char structural evolution during hydrogasification under high pressure

The catalytic hydrogasification of coal char was investigated in a high-pressure fixed-bed tube reactor using CaO, CaCO3, Na2CO3, and K2CO3 as catalysts. Experimental results showed that the char reactivity could be greatly improved with the addition of catalysts. Analysis of char structural evolution was performed to further explore the catalytic mechanism by employing Raman spectroscopy and scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX). The results revealed that CaO catalyst inhibited the aromatic ring condensation of the char structure during hydrogasification. The catalytic reaction of CaO only occurred on the char surface. Na2CO3 or K2CO3 was reduced to metallic Na or K and diffused into the char under hydrogen atmosphere, enhancing the cracking of large aromatic ring systemsinto small ones, which were the active species for hydrogasification. The catalytic reaction of alkali catalyst occurred simultaneously on the surface of and inside the char. Therefore, the Na2CO3 and K2CO3 displayed higher catalytic activities than CaO in hydrogasification.

Enhanced proton conductivity at low humidity of proton exchange membranes with triazole moieties in the side chains

Highly conductive, novel sulfonated poly(arylene ether) membranes with different amounts of triazole-introduced monomers (SPAE-TM) were prepared via conventional aromatic condensation reactions. The triazole-introduced monomer (TM) was used as a proton transfer moiety to increase the proton conductivities of polymer electrolyte membranes (PEMs). To compare the chemical, mechanical and thermal stabilities of non-crosslinked polymer electrolyte membranes (SPAE-TM10, SPAE-TM20), crosslinked polymer electrolyte membranes were prepared via the thermal crosslinking method (cSPAE-TM10, cSPAE-TM20). The SPAE-TM membranes exhibited excellent thermal stabilities, and the non-crosslinked SPAE-TM membranes showed satisfactory glass transition temperatures (Tg=250°C). The water uptakes and swelling ratios of the SPAE-TM membranes were successfully suppressed in comparison with the SPAE-TM0 membrane. The proton conductivities of all membranes were higher than those of Nafion 212 over a wide range of temperatures (0.211–0.256S/cm at 80°C, 100% R.H.). The SPAE-TM20 presented a proton conductivity that was 2.3 times higher than that of SPAE-TM0 at 80°C and 30% R.H.

Influence of pyrolysis temperature on properties and environmental safety of heavy metals in biochars derived from municipal sewage sludge

Dried raw sludge was pyrolyzed at temperatures ranging from 400 to 600°C at the increase of 50°C intervals to investigate the influence of pyrolysis temperature on properties and environmental safety of heavy metals in biochar derived from municipal sewage sludge. The sludge biochar yield decreased significantly with increasing pyrolysis temperature but the pH, ash content and specific surface area increased. Conversion of sludge to biochar markedly decreased the H/C and N/C ratios. FT-IR analysis confirmed a dramatic depletion of H and N and a higher degree of aromatic condensation in process of biochar formation at higher temperatures. The total concentrations of Cu, Zn, Pb, Cr, Mn, and Ni increased with conversion of sludge to biochar and increasing pyrolysis temperature. However, using BCR sequential extraction and analysis, it was found that most of the heavy metals existed in the oxizable and residual forms after pyrolysis, especially at 600°C, resulting in a significant reduction in their bioavailability, leading to a very low environmental risk of the biochar. The present study indicates pyrolysis is a promising sludge treatment method for heavy metals immobilization in biochar, and highlights the potential to minimize the harmful effects of biochar by controlling pyrolysis temperature.

Quantification of pyrogenic carbon in the environment: An integration of analytical approaches

Pyrogenic carbon (PyC), the product of incomplete combustion of biomass during fire, is now recognized as a significant component of the global carbon cycle. However, quantitative determination of PyC is challenging, in particular at a large scale. We conducted a comparison of three methods for PyC analysis: benzene polycarboxylic acid (BPCA) method, hydrogen pyrolysis (hypy) and mid infrared spectroscopy (MIR) to identify a suitable approach for the determination of PyC at large geographical scales and across different environmental matrices. We analyzed samples (n=165) derived from a variety of matrices (i.e. forest floor, soils, sediments and char), most of which were collected in the natural environment after fire. BPCA and hypy PyC estimates correlated linearly (R2 between 0.74 and 0.92), thus suggesting that they can be merged in larger scale PyC syntheses. However, the slope of the regression varied among different matrices, ranging between 0.1 and 0.44, likely due to differences in the degree of aromatic condensation. MIR coupled with partial least-squares regression (MIR-PLSR) was demonstrated to be a powerful tool for estimating PyC across a variety of environmental matrices, with high throughput and low analytical cost in comparison with the other two PyC analytical methods. Furthermore, we obtained accurate calibrations for MIR-PLSR from the hypy and the BPCA method, the latter in particular for soil samples. We thus conclude that PyC estimates at large geographical scales and across different environmental matrices can be obtained from MIR-PLSR, previous calibration with hypy or BPCA, for matrices for which the PyC yields are known.

Synthesis and Characterization of Bio-based Epoxy Resins Derived from Vanillyl Alcohol

Vanillyl alcohol, a lignin derived aromatic diol, is a potential platform chemical for the production of renewable epoxy thermosets. A bio-based bisphenolic analogue, bisguaiacol (BG), was synthesized via electrophilic aromatic condensation of vanillyl alcohol and guaiacol, from which diglycidyl ether of BG (DGEBG) was prepared. In addition, three single aromatic diglycidyl ethers were synthesized from vanillyl alcohol (DGEVA), gastrodigenin (DGEGD), and hydroquinone (DGEHQ). All epoxies were characterized via 1H NMR, 13C NMR, FTIR, MS, and GPC. Dynamic mechanical analyses of the epoxies by themselves or blended with a commercial epoxy resin and cured with a diamine were conducted to determine the effect of the methoxy and methylene moieties on polymer properties. The thermomechanical results indicate that the methoxy lowers the glass transition temperature (Tg) yet increases the glassy storage modulus at 25 °C, while the methylene spacer between the aromatic ring and the epoxide further lowers the Tg in ...

Composition to Interfacial Activity Relationship Approach of Petroleum Sulfonates by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

In the present work, petroleum sulfonates were obtained from three atmospheric residues (ARs) and characterized by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry [(−) ESI FT-ICR MS], looking for an approach to establish a relationship between molecular composition and interfacial activity for chemical enhanced oil recovery (CEOR) formulations. From the correlation of the (−) ESI FT-ICR MS data and the interfacial tension measurements, it was possible to infer that the composition and some characteristics, such as aromatic and/or naphthenic condensation, must be taken into account to understand the performance of petroleum sulfonates. Obtained sulfonates contained mainly O3S, NO3S, O3S2, and O4S compounds, but the relative abundance of each class depended directly upon the chemical composition of the raw AR. Both carbon number (CN) and double bound equivalent (DBE) distributions of the main classes provided a way to explain the lipophilicity and interfacial...

Calculation of Average Molecular Parameters, Functional Groups, and a Surrogate Molecule for Heavy Fuel Oils Using 1H and 13C Nuclear Magnetic Resonance Spectroscopy

Heavy fuel oil (HFO) is primarily used as fuel in marine engines and boilers to generate electricity. Nuclear magnetic resonance (NMR) is a powerful analytical tool for structure elucidation, and in this study, 1H and 13C NMR spectroscopy were used for the structural characterization of two HFO samples. The NMR data were combined with elemental analysis and average molecular weight to quantify average molecular parameters (AMPs), such as the number of paraffinic carbon, naphthenic carbon, aromatic hydrogen, olefinic hydrogen, etc., in the HFO samples. Recent formulas published in the literature were used for calculating various derived AMPs, such as aromaticity factor (fa), C/H ratio, average paraffinic chain length (n), naphthenic ring number (RN), aromatic ring number (RA), total ring number (RT), aromatic condensation index (φ), and aromatic condensation degree (Ω). These derived AMPs help in understanding the overall structure of the fuel. A total of 19 functional groups were defined to represent the...

Effect of nitrogen/phosphorus concentration on algal organic matter generation of the diatom Nitzschia palea: Total indicators and spectroscopic characterization

Critical algal blooms in great lakes increase the level of algal organic matters (AOMs), significantly altering the composition of natural organic matters (NOMs) in freshwater of lake. This study examined the AOM's characteristics of Nitzschia palea (N. palea), one kind of the predominant diatom and an important biomarker of water quality in the great lakes of China, to investigate the effect of AOMs on the variation of NOMs in lakes and the process of algal energy. Excitation–emission matrix fluorescence (EEM) spectroscopy, synchronous fluorescence (SF) spectroscopy and deconvolution UV–vis (D-UV) spectroscopy were utilized to characterize AOMs to study the effects of nutrient loading on the composition change of AOMs. From results, it was revealed that the phosphorus is the limiting factor for N. palea's growth and the generation of both total organic carbon and amino acids but the nitrogen is more important for the generation of carbohydrates and proteins. EEM spectra revealed differences in the composition of extracellular organic matter and intracellular organic matter. Regardless of the nitrogen and phosphorus concentrations, aromatic proteins and soluble microbial products were the main components, but the nitrogen concentration had a significant impact on their composition. The SF spectra were used to study the AOMs for the first time and identified that the protein-like substances were the major component of AOMs, creating as a result of aromatic group condensation. The D-UV spectra showed carboxylic acid and esters were the main functional groups in the EOMs, with –OCH3, –SO2NH2, –CN, –NH2, –O– and –COCH3 functional groups substituting into benzene rings.

Physico-chemical characterization of products from vacuum oil under delayed coking process by infrared spectroscopy and chemometrics methods

Eight vacuum residues and their delayed coking liquids products from Colombian crude were study by infrared spectroscopy with attenuated total reflectance (FTIR-ATR) and principal component analysis (PCA). For the samples the structural parameters of aromaticity factor (fa), alifaticity (A2500-3100cm-1), aromatic condensation degree (GCA), length of aliphatic chains (LCA) and aliphatic chain length associated with aromatic (LACAR) were determined through the development of a methodology, which includes the previous processing of spectroscopy data, identifying the regions in the IR spectra of greatest variance using PCA and molecules patterns. The parameters were compared with the results obtained from proton magnetic resonance (1H-NMR) and 13C-NMR. The results showed the influence and correlation of structural parameters with some physicochemical properties such as API gravity, weight percent sulphur (% S) and Conradson carbon content (% CCR)

Well-ordered Nanostructure Formation of Wholly Aromatic Poly(amic acid)s in Spin-casted Thin Films

We successfully obtained well-ordered spherical nanostructures in spin-casted films prepared by combining wholly aromatic condensation polymers and olefin type BCPs. No other structures were obtained despite increasing the ratio of PAA to BCP. These results indicate that the micelle structures formed in solution were deposited onto the substrates to form the spherical nanostructures selectively. By increasing the concentrations of the solution used and adding methanesulfonic acid to catalyze the cross-linking reaction of the resol, it is possible to decrease the areal density of defects, such as terracing, and the surface roughness on the thin film. However, as the spherical structure had partially collapsed during imidization on the thin film as the temperature increased, further studies are required to obtain the optimal experimental conditions to obtain a stiff and well-ordered porous polyimide thin film.