Stresses associated with diffusion in polyimide and polyacrylics films

When a constrained polymeric thin film is immersed in a liquid medium, its state of stress changes because the diffusion of the liquid into the film causes it to swell. Polyimide and polyacrylics films are used in the laminated structures of inkjet printheads. Swelling behavior of the films in various ink component solutions are of great interest because they are closely related to the delamination problem. Swelling stress at constant strain was measured using an environmental tensile tester at both ambient and elevated temperatures. Two kinds of information were extracted. One is the extent of stress relaxation, which is the amount of stress decay between initial stress and equilibrium stress. The difference in the extent of stress relaxation could result in delamination if two different materials with different swelling characteristics are bonded together and exposed to a swelling agent. The other piece of information was the diffusion coefficients of the liquid agents into the polymer films. The magnitude of the diffusion coefficient indicates the rate of proceeding by the penetrant, i.e., the rate of swelling of the films. The results show that the extent of stress relaxation and diffusivity are different for two films. In addition, the diffusion in polyimide film is Fickian and the diffusion in polyacrylics film is pseudo‐Fickian. The changes in mechanical properties after swelling also differ. Among all the ink solutions tested, one component was identified as the most influential and detrimental agent. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Preparation and characterization of magnetic polyimide hybrid thin films

Magnetic polyimide hybrid thin films were synthesized from pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and Fe₃O₄ magnetic nanoparticles via thermal imidiazation in nitrogen environments. The magnetic polyimide hybrid thin films were analyzed and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The magnetic properties of magnetic nanoparticles and polymer hybrid thin films were assessed using a vibrating sample magnetometer (VSM), and the physical properties of hybrid thin films were tested. Results revealed that the magnetic polyimide hybrid thin films had superparamagnetic behavior and excellent mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Water sorption behaviors of the BPDA‐based polyimide films depending upon the structural isomers of diamine

For the biphenyltetracarboxylic dianhydride (BPDA)‐based polyimide thin films, the water sorption behaviors were gravimetrically investigated by using a thin film diffusion analyzer. The water sorption behaviors of the polyimide thin films are quite different and strongly dependent upon the sort of polyimide. The diffusion coefficients of the polyimide thin films vary in the range of 1.6 × 10⁻¹⁰ to 12.4 × 10⁻¹⁰cm²/s and the water uptakes vary from 1.52 to 5.25 wt %. Both the diffusion coefficient and water uptake of the polyimide thin films are in the increasing order: BPDA‐pPDA < BPDA‐p,p′ODA < BPDA‐p,m′ODA < BPDA‐mPDA ∼ BPDA‐p,p′DDS < BPDA‐m,m′DDS. Specifically, the polyimide films with para‐oriented linkages in backbone structure showed relatively lower diffusion coefficient and water uptake than the corresponding polyimide films with meta‐oriented linkages because of the well‐developed crystalline structure and good intermolecular chain ordering. In addition, the polyimide thin films having higher chain order showed relatively lower diffusion coefficient and water uptake. The crystallinity and intermolecular chain ordering in the morphological structure are critical parameters in controlling the water sorption behaviors of the polyimide thin films. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2121–2127, 2001     

Effect of hydrophobic hexafluoroisopropylidene group on the water sorption behaviors of rigid poly(p‐phenylene pyromellitimide) polyimide thin films

We prepared poly(p‐phenylene pyromellitimide) (PMDA–PDA), poly(p‐phenylene 4,4′‐hexafluoroisopropylidene diphthalimide), and their copolyimides with various compositions to explore the relationship between the water sorption and structure. The water sorption behaviors were gravimetrically investigated as a function of composition and temperature and interpreted with a Fickian diffusion model in films. Overall, the water sorption behaviors were strongly dependent on the changes in morphological structure, which originated from the variations in composition. When the content of the bulky hexafluoroisopropylidene group (6FDA) was increased, the water uptake decreased from 5.80 to 3.18 wt %, whereas the diffusion coefficient increased from 3.6 × 10^?10 to 11.3 × 10^?10 cm²/s. The relatively high water uptake in the PMDA–PDA polyimide film was successfully healed by the incorporation of 6FDA, which may have resulted from the increases in the intermolecular packing order and hydrophobicity. The degree of orientation and crystallinity, which are in‐plane characteristics, were directly correlated to the diffusion coefficient and activation energy in the polyimide film. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3442–3446, 2003     

Tuning the aggregation of polyimide thin films by modification of their molecular interactions

Thin films of an organo‐soluble polyimide based on 1,4‐(3,4‐dicarboxyphenoxy)benzene dianhydride (HQDPA) and 2,2′‐dimethyl‐4,4′‐methylene dianiline (DMMDA) have been studied. A prism coupler was used to measure the refractive indices. The average refractive indices of thin films prepared by annealing at different temperatures and times were chosen to characterize the condensation states of thin films. Thin films annealed at 200 °C show irreversible changes in physical properties, eg solubility. FTIR spectroscopy showed that the chain structures of the above thin films remained unchanged. It is proposed that specific molecular interactions induce the irreversible changes revealed by fluorescence spectroscopy. © 2000 Society of Chemical Industry     

Surface modification studies of Kapton® HN polyimide films

Surface imide hydrolysis of Kapton HN polyimide films in a 1 M KOH aqueous solution was studied using dynamic contact angle measurements, X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). The surface energy of Kapton HN increased quickly upon KOH treatment due to the formation of polar polyamate. Prolonged treatment led to a jump in surface energy that we ascribe to the onset of etching causing increased surface roughness. Potassium depth profiles of treated Kapton HN samples measured by XPS and TOF‐SIMS demonstrated that during the first 10 minutes of 1 M KOH treatment the modification depth increased rapidly. Thereafter the thickness of the modified layer no longer increased. For Kapton H films, however, the development of etching was much slower and a steady increase in modification depth was observed even after long treatment times. The different behaviours between Kapton HN and Kapton H films in alkali solutions are analysed and discussed. Copyright © 2003 Society of Chemical Industry     

Atomic force microscopy study of rubbed polyimide films

The surface of rubbed polyimide films was studied as a function of the film thickness and applied load using atomic force microscopy (AFM). Three dominant consequences of rubbing on the film topography were observed: scratches confined to the near surface of the film, tears that extended to the substrate, and strings of islands or droplets aligned parallel to the rubbing direction. Tears, found only in films less than 50 nm thick, varied in areal density and shape due to variations in the film thickness, rubbing load, and adhesion to the substrate. Strings of droplets aligned in the rubbing direction were seen on most samples without discernible dependence on the thickness or rubbing load. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1470–1477, 2001     

Studies on the diffusion characteristics of some aromatic solvents into polypropylene film

The sorption properties of the solvents benzene, toluene, and xylene into polypropylene films at 40, 60, and 80°C have been investigated. The diffusivity and permeability of the solvents into polypropylene films were found to increase in the order of solvent, benzene, toluene, and xylene at the different temperatures studied. The properties were also found to be temperature dependent. The zsolubility of the solvents into polypropylene films was found to be highest in toluene, followed by xylene, and least in benzene. However, a general increase in solubility with temperature was observed for all the solvents studied. The calculated values of activation energy of diffusion did not show any relationship with solvent properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1985–1989, 2006     

Moisture diffusion properties of HFPE‐II‐52 polyimide

Moisture diffusion properties of the polyimide HFPE‐II‐52 were determined using weight gain, weight loss, and swelling experiments over a temperature range of 25–200°C. Below 100°C, diffusivity was measured using standard weight loss and weight gain methods. Above 100°C, diffusivity is found by weight loss experiments performed by placing moisture saturated samples in an oven and recording weight loss dynamically. The diffusivity of the polyimide was found to obey the Arrhenius relation over the entire range of temperature. Weight gain experiments were performed to determine the equilibrium level of moisture absorbed by the polyimide as a function of relative humidity. Swelling experiments were performed to measure swelling strain as a function of moisture absorption. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3471‐3479, 2006     

Residual stress and mechanical properties of polyimide thin films

Four different structure polyimide thin films based on 1,4‐phenylene diamine (PDA) and 4,4′‐oxydianiline (ODA) were synthesized by using two different dianhydrides, pyromellitic dianhydride (PMDA) and 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), and their residual stress behavior and mechanical properties were investigated by using a thin film stress analyzer and nanoindentation method. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films. The morphological structure of polyimide thin films was characterized by X‐ray diffraction patterns and refractive indices. The residual stress was in the range of ?5 to 38 MPa and increased in the following order: PMDA‐PDA < BPDA‐PDA < PMDA‐ODA < BPDA‐ODA. The hardness of the polyimide films increased in the following order: PMDA‐ODA < BPDA‐ODA < PMDA‐PDA < BPDA‐PDA. The PDA‐based polyimide films showed relatively lower residual stress and higher hardness than the corresponding ODA‐based polyimide films. The in‐plane orientation and molecularly ordered phase were enhanced with the increasing order as follows: PMDA‐ODA < BPDA‐ODA < BPDA‐PDA ～ PMDA‐PDA. The PDA‐based polyimides, having a rigid structure, showed relatively better‐developed morphological structure than the corresponding ODA‐based polyimides. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Growth of ODPA-APB polyimide films using molecular beam deposition, and their characterization

We report the first growth of polyimide ODPA—APB films by the molecular beam deposition (MBD) technique and characterize these films using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. MBD is a dry, ultra-high vacuum technique based on the co-deposition of monomers from two different sources, followed by a thermally induced polycondensation reaction to form polyimide. This technique is an alternative to standard wet processing techniques involving the use of solvents. Asdeposited films consist largely of low-molecular-weight species. Heat-treated films are chemically indistinguishable from thermally cured, spin-coated films. Different heat treatment conditions are compared.     

Fabrication of poly(lactic acid) films with resveratrol and the diffusion of resveratrol into ethanol

Poly(94% L ‐lactic acid) (PLA) films containing 0, 1, and 3 wt % resveratrol (PR0, PR1, and PR3) were extruded in a pilot‐plant scale blown‐extrusion machine. Yellow‐colored PLA films with reduced crystallinity were obtained, and the films absorbed UV‐visible light at 350–200 nm. The diffusion kinetics of resveratrol into ethanol at 9, 23, 33, and 43°C displayed Fick's behavior, and diffusion coefficients between 10⁻¹³ and 10⁻¹⁰ cm²/s were obtained. According to the Arrhenius equation, the energy of activation for the diffusion of resveratrol from PR1 and PR3 films was 175 and 177 kJ/mol, respectively. The temperature of diffusion had a stronger effect on the reduction of the weight average molecular weight of PLA than the processing conditions and the contact time with ethanol. However, diffusion of resveratrol was not affected by the degradation of PLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of polyimide/silica/silver composite films

Polyimide/silica/silver hybrid films were prepared by the sol-gel method combined with in situ single-stage self-metallization technique. The structure of polyimide films in the thermal curing process and the influence of silica content on the migration and aggregation of silver particles to the surface of hybrid films were investigated. The hybrid films were characterized by transmission electron microscopy, dynamic mechanical thermal analysis, Fourier transform infrared spectroscopy, ultraviolet visible spectroscopy and mechanical measurements. The results indicated that there was no degradation of the polyimide matrix after the formation of silica and silver particles. Silica acted as the nucleus for the silver particles. With increasing silica content, more and more silver particles were kept in the hybrid films instead of being migrated onto the surface of the hybrid films and the reflections of hybrid films decreased gradually. __________ Translated from Acta Polymerica Sinica, 2007, (11): 1047–1051 [译自: 高分子学报     

Relationship between thermal properties and diffusion coefficients of gases for polyimide films

The relationships between the chemical structure, packing density (1/V_F), and cohesive energy density (CED) and the thermal properties of polyimides were investigated. Particularly, the correlation of tan δ measured by stress–strain/thermal mechanical analysis with 1/V_F and CED was found for eight polyimides. We measured the relationship between the apparent diffusion coefficient (D_a) and 1/V_F and CED, respectively, as described in previous articles. From these experiments, we found that the thermal properties, especially tan δ, were correlated with the apparent diffusion coefficient of gas. These results are well explained by use of micro-Brownian motion. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 389–397, 1997     

Uptake of aromatic solvents by polyethylene films

The sorption properties of the solvents benzene, toluene, and xylene in polyethylene films at 40, 60, and 80°C were investigated. The diffusion coefficient increased with an increase in the sorption temperature for the solvents and was highest for xylene and least for benzene. The inability of xylene to show a definite order of the diffusion coefficients at the investigated temperatures was attributed to the presence of two methyl side groups in the molecule. The solubilities of the solvents in polyethylene increased with an increase in the sorption temperature, and the following order of the solubilities could be observed: xylene > toluene > benzene. The permeabilities of the solvents in polyethylene depended on the sorption temperature, and the following order of the permeabilities was observed: xylene > toluene > benzene. The calculated activation energies of sorption in polyethylene films were all positive; benzene had the highest energy of sorption, and xylene had the lowest. The calculated enthalpies of sorption (ΔH_S) were also positive for the three solvents and were in the following order: xylene > toluene > benzene. The calculated entropies of sorption (ΔS) were negative for the solvents and showed trends similar to the variation of ΔH_S among the solvents. The change in the Gibbs free energies of sorption (ΔG_S), evaluated with the expression ΔG_S = ΔH_S ? TΔS (where T is the Kelvin temperature), were all positive, and this was an indication of the nonspontaneity of the solubility of polyethylene in the aromatic solvents at 313 K. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3849–3854, 2007     

Water vapor sorption and transport in dense polyimide membranes

The sorption and transport of water vapor in five dense polyimide membranes were studied by thermogravimetry. The sorption isotherms of water vapor in the polyimides could be successfully interpreted by both the dual‐mode sorption model and the Guggenheim–Anderson–de Boer equation. The water vapor diffusion behavior was found to be nearly Fickian at higher water vapor activities, whereas non‐Fickian diffusion was observed at lower water activities. The phenomena could be well described by the mechanism of combined Fickian and time‐dependent diffusion. The diffusion coefficient and water vapor uptake in the polyimides were strongly dependent on the polymer molecular structure. Except for the polyimide prepared from 3,3′,4,4′‐diphenylsulfone tetracarboxylic dianhydride and 1,3‐bis(4‐aminophenoxy) benzene, the permeability of water vapor in the dense polyimide membranes predicted from the sorption measurement at 30°C corresponded well with the water vapor permeability measured at 85°C. Among the polyimides studied, pyromellitic dianhydride–4,4′‐diaminophenylsulfone (50 mol%)/4,4′‐oxydianiline (50 mol%) showed both high water sorption and diffusion and, therefore, high water vapor permeability, which for vapor permeation membranes is necessary for the separation of water vapor from gas streams. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2306–2317, 2003     

The effect of titania content on the physical properties of polyimide/titania nanohybrid films

In this study, a series of PI/TiO₂ nanohybrid materials were prepared from polyamic acid of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride/3,3′-diaminodiphenyl sulfone, and titania precursor by the sol-gel method. The titania content in the hybrid system was varied from 0 to 5 wt %. The physical and mechanical properties of the hybrids such as refractive index, optical transmission, and tensile strength were investigated. It was determined that incorporation of titania precursor into the PI matrix improved the refractive indices and tensile modulus of the hybrid films. It was observed that the optical transmittance and tensile strength of the nanohybrids were slightly decreased with the increasing titania content. It was determined that the hybrid films might have enhanced the UV shielding properties compare to the PI films. Furhermore, the hybrid materials showed better thermal stability than the PI. SEM studies demonstrated that titania particles (1 and 3 wt %) were distributed homogeneously through the PI matrix. The effect of the titania content in the PI on DC conductivity and dielectric constant were also analyzed. For the PI film containing 5 wt % titania, activation energy value increased to 1.0 eV from the value of 0.65 eV. DC conductivity value of the films depending on titania content varied between 3.0 × 10⁻¹¹ and 1.4 × 10⁻¹⁰ S/cm at room temperature. Relative dielectric constants of the films were calculated from capacitance measurements depending on frequency (40–100 kHz) at different temperatures (303–360 K). The values increased with the increasing titania content. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Water vapour permeability,diffusion and solubility in latex films

Water vapour diffusion D, solubility S and permeability P coefficients have been determined for films obtained from carboxylated styrene-butadiene (SB) copolymer latexes. The experimental method is water vapour sorption performed in the range 30–60d?C. Using the small angle neutron scattering (SANS) method and a selective labelling with D₂O vapour, it has been shown that water molecules mainly diffuse in the films through the particle-particle interfaces, which consist of a polar carboxyl-rich copolymer. It has been shown that the degree of cross-linking of the particles does not significantly affect the values of D and S. Moreover, the effect of neutralization conditions, regarding both the pH value of the initial latex and the nature of the neutralizing agent, has also been investigated. It has been found that D does not depend on these parameters, whereas S appears to be very sensitive to them. The results have been interpreted on the basis of the structural modifications of the films induced by neutralization. Finally, the hydrophilicity (or hydrophobicity) of the neutralizing agent has been identified as one of the key features for controlling the affinity of the latex film for water vapour and hence its permeability properties.     

Reduced copper diffusion in layered silicate/fluorinated polyimide (6FDA‐ODA) nanocomposites

The copper diffusion barrier properties of layered silicate/fluorinated polyimide nanocomposites were analyzed by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). It was found that the particles of copper are effectively retarded from penetrating into the polyimide matrix by layered silicates. The diffusion coefficients of layered silicate/polyimide nanocomposites are lower than that of the pure polyimide. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1422–1425, 2004     

Changes in the adhesion strength between copper thin films and polyimide substrates after heat treatment

The adhesion strength between a copper (Cu) thin film and a polyimide [pyromellitic dianhydride-oxydianiline (PMDA-ODA)] substrate is reduced by heat treatment at 150°C in air. In this work, we determined the changes in adhesion strength between Cu films and polyimide substrates using Auger electron spectroscopy (AES), attenuated total reflection Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The analysis showed that the weak boundary layer (WBL) shifted towards the Cu interface as the heat treatment time was increased. To confirm this shift, we looked at two other polyimide substrates: biphenyl dianhydride-p-phenylene diamine (BPDA-PDA) and biphenyl dianhydride-oxydianiline (BPDA-ODA). Comparing the adhesion strength for the Cu thin film, the adhesion strength was high for the Cu/PMDA-ODA and Cu/BPDA-ODA laminates, but very low for the Cu/BPDA-PDA laminate. One of the possible reasons for this behavior could be that the ether moiety between the two benzene rings in ODA is related to the adhesion between a Cu film and an 0₂-plasma-treated polyimide (PI) substrate. The relationship between the adhesion strength and chemical bonding states is also discussed. We conclude that a Cu thin film sputtered onto a PI substrate is apt to peel at the oxidized interface, due to the heat treatment.