Colorless and transparent polyimide nanocomposites using organically modified montmorillonite and mica.

In this study, we introduce a method for replacing the glass used in existing display electronic materials, lighting, and solar cells by synthesizing a colorless and transparent polyimide (CPI) film with excellent mechanical properties and thermal stability using a combination of new monomers. Poly(amic acid) (PAA) was synthesized using dianhydride 4,4'-biphthalic anhydride (BPA) and diamine 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (AHP). Various contents of organically modified montmorillonite (MMT) and mica were dispersed in PAA solution through solution intercalation, and then CPI hybrid films were prepared through multi-step thermal imidization. The organoclays synthesized to prepare CPI hybrid films were Cloisite 93A (CS-MMT) and hexadimethrine-mica (HM-Mica) based on MMT and mica, respectively. In particular, the diamine monomer AHP containing a -OH group was selected to increase the dispersibility and compatibility between the hydrophilic clays and the CPI matrix. To demonstrate the characteristics of CPI, the overall polymer structure was bent and a strong electron withdrawing -CF3 group was used as a substituent. The thermomechanical properties, morphology of clay dispersion, and optical transparency of the CPI hybrid films were investigated and compared according to the type and content of organoclays. Two types of organoclays, CS-MMT and HM-Mica, were dispersed in a CPI matrix at 1 to 7 wt%, respectively. In electron microscopy, most of the clays were uniformly dispersed in a plate-like shape of less than 20 nm at a certain critical content of the two types of organoclays, but agglomeration of the clays was observed when the content was higher than the critical content. Hybrids using HM-Mica had better thermomechanical properties and hybrids containing CS-MMT had better optical transparency.

Effect of organoclay on the physical properties of colorless and transparent copoly(amide imide) nanocomposites.

Copoly(amic acid) was prepared using the diamine monomer N,N'-[2,2'-bis(trifluoromethyl)-4,4'-biphenylene]bis(4-aminobenzamide) (TFAB) and the anhydride monomers 4,4'-(hexafluoro-isopropylidene)diphthalic anhydride (6FDA) and 4,4'-biphthalic anhydride (BPA). Thereafter, a colorless and transparent copoly(amide imide) (Co-CPAI) film was synthesized through various heat treatments. Co-CPAI hybrid films with a TFAB : 6FDA : BPA molar ratio of 1 : 0.5 : 0.5 were subsequently fabricated using organically modified hectorite (STN) with various contents ranging from 0 to 7 wt% via the solution intercalation method. Finally, the thermomechanical properties, clay dispersion, and optical transmittance of the hybrid films were investigated. The results of wide-angle X-ray diffractometry and transmission electron microscopy demonstrated good dispersion at low clay loadings; however, clay agglomeration was observed above a certain critical STN content. At the critical STN content of 3 wt%, the clay was evenly distributed in the matrix with a nanoscale thickness of approximately 10 nm. Hybrid films containing 3 wt% STN showed excellent thermomechanical properties. Beyond this critical clay content, the physical properties of the films decreased because of the agglomeration of excess clay. Regardless of the clay content, however, the optical properties of the hybrid films remained constant, and their yellow indices, which ranged from 2 to 4, indicated excellent colorless transparency.

Crystal structures, phase transitions, thermodynamics, and molecular dynamics of organic-inorganic hybrid crystal [NH(CH3)3]2ZnCl4.

Understanding the physical properties of organic-inorganic hybrid [NH(CH3)3]2ZnCl4 is necessary for its potential application in batteries and fuel cells due to its environmentally-friendly, and highly stable character. Here, we determine its overall properties in detail, such as its orthorhombic crystal structure, and phase transition temperatures associated with five different phases. Structural geometry was studied by the chemical shifts caused by the local field around 1H. No changes were observed for the environment around 1H for CH3, whereas the 1H chemical shifts around NH in the cation were shown due to the change in the hydrogen bond N‒H···Cl. This is related to the change in Cl around Zn in the anion. In addition, the coordination geometry of 14N and 1H around 13C exhibited increased symmetry at high temperatures. Finally, we were able to understand its molecular dynamics by the significant change with temperature observed from the spin-lattice relaxation time T1ρ values, which represent the energy transfer for the 1H and 13C atoms of the cation. The activation energies obtained from the T1ρ results were 3-4 times large at phase I (> 348 K) than at phase V and IV (< 286 K). The relaxations show that the energy barriers in phases IV and V are related to the reorientation of methyl groups around the triple symmetry axis, while the reorientation of methyl groups of the cation in phase I is related to as a whole.

Effects of various types of organo-mica on the physical properties of polyimide nanocomposites.

Poly(amic acid) (PAA) was synthesized using dianhydride 4,4'-oxydiphthalic anhydride and diamine 3,3'-dihydroxybenzidine, and polyimide (PI) hybrid films were synthesized by dispersing organo-mica in PAA through a solution intercalation method. Hexadimethrine-mica (HM-Mica), 1,2-dimethylhexadecylimidazolium-mica (MI-Mica), and didodecyldiphenylammonium-mica (DP-Mica), which were obtained via the organic modification of pristine mica, were used as the organo-micas for the PI hybrid films. The organo-mica content was varied from 0.5 to 3.0 wt% with respect to the PI matrix. The thermomechanical properties, morphology, and optical transparency of the resultant PI hybrid films were measured and compared. Dispersion of even small amounts of organo-mica effectively improved the physical properties of the PI hybrids, and maximum enhancements in physical properties were observed at a specific critical content. Electron microscopy of the hybrid films revealed that the organo-mica uniformly dispersed throughout the polymer matrix at the nanoscale level when added at low contents but aggregated in the matrix when added at levels above the critical content. Structural changes in the organo-mica closely influenced the changes in the physical properties of the hybrid films. All PI hybrid films with various organo-mica contents showed similar optical properties, but that prepared with MI-Mica demonstrated the best thermomechanical properties. All synthesized PI hybrid films were transparent regardless of the type and content of organo-mica used.

Investigation on the organic-inorganic hybrid crystal [NH2(CH3)2]2CuBr4: structure, phase transition, thermal property, structural geometry, and dynamics.

Understanding the physical properties of the organic-inorganic hybrid [NH2(CH3)2]2CuBr4 is essential to expand its applications. The single [NH2(CH3)2]2CuBr4 crystals were grown and their comprehensive properties were investigated. The crystals had a monoclinic structure with the space group P21/n and lattice constants of a = 8.8651 (5) Å, b = 11.9938 (6) Å, c = 13.3559 (7) Å, and ß = 91.322°. The transition temperature from phase I to phase II was determined to be 388 K. Variations in the 1H nuclear magnetic resonance chemical shifts of NH2 and 14N NMR chemical shifts according to the temperature changes in the cation were attributed to vibrations of NH2 groups at their localization sites. The 1H and 13C spin-lattice relaxation times (T1ρ) in phase II changed significantly with temperature, indicating that these values are governed by molecular motion. The T1ρ values were much longer in phase I than in phase II, which means energy transfer was difficult. Finally, the activation energies for phases I and II were considered. According to the basic mechanism of [NH2(CH3)2]2CuBr4 crystals, organic-inorganic materials may have potential applications in various fields.

Colorless and transparent poly(amide imide) nanocomposites containing organically modified hectorite.

Polyamic acid (PAA) was synthesized using the diamine monomer N,N'-[2,2'-bis(trifluoromethyl)-4,4'-biphenylene]bis(4-aminobenzamide) and dianhydride monomer 4,4'-oxydiphthalic anhydride. Colorless and transparent poly(amide imide) (CPAI) hybrid films were prepared via multi-step thermal imidization of PAA in which various contents of nano-filler were dispersed. The CPAI hybrid films were prepared by dispersing organoclay STN, which was obtained by organically modifying hectorite, in CPAI by solution intercalation with various contents ranging from 1 to 7 wt%. The thermomechanical properties, morphologies, and optical transparencies of the obtained CPAI hybrid films were investigated based on the dispersed STN content, and the results were compared. Some of the clay in the CPAI hybrid film were agglomerated, which was observed using a transmission electron microscope; however, most clays were well-dispersed, with a nano-size of less than 10 nm. The best thermomechanical properties of the CPAI hybrid film were exhibited with an STN content of 3 wt%, but these properties decreased above the critical content. The coefficients of thermal expansion of all the hybrid films were below 20 ppm per °C regardless of the amount of STN, and the yellow index was 1-2 even when the STN content increased to 7 wt%.