Computational approaches for investigating interfacial adhesion phenomena of polyimide on silica glass

Peel Adhesion Strength between Epoxy Resin and Hydrated Silica Surfaces: A Density Functional Theory Study

Adhesive strength is known to change significantly depending on the direction of the force applied. In this study, the peel and tensile adhesive forces between the hydroxylated silica (001) surface and epoxy resin are estimated based on quantum chemical calculations. Here, density functional theory (DFT) with dispersion correction is used. In the peel process, the epoxy resin is pulled off from the terminal part, while in the tensile process, the entire epoxy resin is pulled off vertically. As a result of these calculations, the maximum adhesive force in the peel process is decreased to be about 40% of that in the tensile process. The adhesion force-displacement curve for the peeling process shows two characteristic peaks corresponding to the process where the adhesive molecule horizontally oriented to the surface shifts to a vertical orientation to the surface and the process where the vertical adhesive molecule is dissociated from the surface. Force decomposition analysis is performed to further understand the peel adhesion force; the contribution of the dispersion force is found to be slightly larger than that of the DFT force. This feature is common to the tensile process as well. Each force in the peel process is about 40% smaller than the corresponding force in the tensile process.

The Impact of the Surface Modification on Tin-Doped Indium Oxide Nanocomposite Properties

This review provides an analysis of the theoretical methods to study the effects of surface modification on structural properties of nanostructured indium tin oxide (ITO), mainly by organic compounds. The computational data are compared with experimental data such as X-ray diffraction (XRD), atomic force microscopy (AFM) and energy-dispersive X-ray spectroscopy (EDS) data with the focus on optoelectronic and electrocatalytic properties of the surface to investigate potential relations of these properties and applications of ITO in fields such as biosensing and electronic device fabrication. Our analysis shows that the change in optoelectronic properties of the surface is mainly due to functionalizing the surface with organic molecules and that the electrocatalytic properties vary as a function of size.

Shear adhesive strength between epoxy resin and copper surfaces: a density functional theory study

Shear adhesive strengths of epoxy resin for copper and copper oxide surfaces are estimated based on quantum chemical calculations. Shear adhesion has periodicity, and its origin is revealed.

Combining ReaxFF Simulations and Experiments to Evaluate the Structure-Property Characteristics of Polymeric Binders in Si-Based Li-Ion Batteries

High energy capacity silicon (Si) anodes in Li-ion batteries incorporate polymeric binders to improve cycle life, which is otherwise limited by large volume and stress fluctuations during charging/discharging cycles. Several properties of the polymeric binder play a role in achieving optimal battery performance, including interfacial adhesion strength, mechanical elasticity, and lithium-ion conduction rate. In this work, we utilize atomistic simulations with the ReaxFF force field and complementary experiments to investigate how these properties dictate the performance of Si/binder anodes. We study three C/N/H-based polymer binders with varying structures (pyrolyzed polyacrylonitrile (PPAN), polyacrylonitrile (PAN), and polyaniline (PANI)) to determine how the structure-property characteristics of the binder affect performance. The Si/binder adhesion analysis reveals some counter-intuitive results: although an individual PANI chain has a stronger affinity to Si compared to PPAN, the PANI bulk binds weaker to the Si surface. Interfacial structural analyses from simulations of the bulk phase show that PANI chains have poor stacking at the interface, while PPAN chains exhibit dense and highly ordered stacking behavior, leading to stronger adhesion. PPAN also has a lower Young's modulus compared to PANI and PAN owing to its ordered and less entangled bulk structure. This added elasticity better accommodates volume changes associated with cycling, making it a more suitable candidate for Si anodes. Finally, both simulations and experimental measurements of Li-ion diffusion rates show higher Li mobility through PPAN than PAN and PANI because the ordered stacking of PPAN chains creates channels that are favorable for Li diffusion to the Si surface. Galvanostatic charge-discharge cycling experiments show that PPAN is indeed a highly promising binder for Si anodes in Li-ion batteries, retaining a capacity of ∼1400 mAh g^-1 for 150 cycles. This work demonstrates that the orientation and structure of the polymer at and near the interface are essential for optimizing binder performance as well as showcases the initial steps for binder evaluation, selection, and application for electrodes in Li-ion batteries.

Wetting characteristics of polymer adhesives with different chain bending stiffness

Polymer adhesives are widely used in daily applications and in industry owing to their flexibility and overall non-toxicity, particularly in interfacial adhesion. The spreading of polymer adhesives on adherend is one of the essential considerations for the interfacial adhesion of polymer adhesives, which is strongly related to their wetting behaviors. While relationships between polymer microstructure and adhesion have been investigated in previous studies, it remains challenging to unveil the effect of polymer microstructure on wettability. To address this issue, here we utilize coarse-grained molecular dynamics (CGMD) simulations to systematically elucidate how the wettability of a polymer adhesive droplet on a surface depends on bending stiffness. The wetting dynamics and the contact angle are studied to show the evolution of morphology of droplets during the wetting process. The results indicate the wettability is weakened by the increase of bending stiffness of polymer chain. Detailed thermodynamic property analysis is further conducted, revealing that the adhesion between the polymer droplet and substrate deteriorates due to the decline of wettability. Interestingly, we observe such deterioration becomes more significant by both increasing the temperature and decreasing the bending stiffness. Our study sheds light on the dependence of chain bending stiffness and temperature on the wetting behavior of polymer adhesive droplets, and offers insights, which, upon experimental validation can then be used for the design of adhesives or hydrogels.

Review on Interfacial Bonding Mechanism of Functional Polymer Coating on Glass in Atomistic Modeling Perspective

Atomistic modeling methods are successfully applied to understand interfacial interaction in nanoscale size and analyze adhesion mechanism in the organic-inorganic interface. In this paper, we review recent representative atomistic simulation works, focusing on the interfacial bonding, adhesion strength, and failure behavior between polymer film and silicate glass. The simulation works are described under two categories, namely non-bonded and bonded interaction. In the works for non-bonded interaction, three main interactions, namely van der Waals interaction, polar interaction, and hydrogen bonds, are investigated, and the contributions to interfacial adhesion energy are analyzed. It is revealed that the most dominant interaction for adhesion is hydrogen bonding, but flexibility of the polymer film and modes of adhesion measurement test do affect adhesion and failure behavior. In the case of bonded interactions, the mechanism of covalent silane bond formation through condensation and hydrolysis process is reviewed, and surface reactivity, molecular density, and adhesion properties are calculated with an example of silane functionalized polymer. Besides interfacial interactions, effects of external conditions, such as surface morphology of the glass substrate and relative humidity on the adhesion and failure behavior, are presented, and modeling techniques developed for building interfacial system and calculating adhesion strengths are briefly introduced.

Wettability of cellulose surfaces under the influence of an external electric field

HYPOTHESIS

Interfacial tensions play an important role in dewatering of hydrophilic materials like nanofibrillated cellulose, and are affected by the molecular organization of water at the interface. Application of an electric field influences the orientation of water molecules along the field direction. Hence, it should be possible to alter the interfacial free energies to tune the wettability of cellulose surface through application of an external electric field thus, aiding the dewatering process.

SIMULATIONS

Molecular dynamics simulations of cellulose surface in contact with water under the influence of an external electric field have been conducted with GLYCAM-06 forcefield. The effect of variation in electric field intensity and directions on the spreading coefficient has been addressed via orientational preference of water molecules and interfacial free energy analyses.

FINDINGS

The application of electric field influences the interfacial free energy difference at the cellulose-water interface. The spreading coefficient increases with the electric field directed parallel to the cellulose-water interface while it decreases in the perpendicular electric field. Variation in interfacial free energies seems to explain the change in contact angle adequately in presence of an electric field. The wettability of cellulose surface can be tuned by the application of an external electric field.

Characterization and Analysis of Metal Adhesion to Parylene Polymer Substrate Using Scotch Tape Test for Peripheral Neural Probe

This paper presents measurement and FEM (Finite Element Method) analysis of metal adhesion force to a parylene substrate for implantable neural probe. A test device composed of 300 nm-thick gold and 30 nm-thick titanium metal electrodes on top of parylene substrate was prepared. The metal electrodes suffer from delamination during wet metal patterning process; thus, CF₄ plasma treatment was applied to the parylene substrate before metal deposition. The two thin film metal layers were deposited by e-beam evaporation process. Metal electrodes had 200 μm in width, 300 μm spacing between the metal lines, and 5 mm length as the neural probe. Adhesion force of the metal lines to parylene substrate was measured with scotch tape test. Angle between the scotch tape and the test device substrate changed from 60° to 90° during characterization. Force exerted the scotch tape was recorded as the function of displacement of the scotch tape. It was found that a peak was created in measured force-displacement curve due to metal delamination. Metal adhesion was estimated 1.3 J/m² by referring to the force peak and metal width at the force-displacement curve. Besides, the scotch tape test was simulated to comprehend delamination behavior of the test through FEM modeling.

Insights into interphase thickness characterization for graphene/epoxy nanocomposites: a molecular dynamics simulation

This work presents a molecular dynamics simulation study on the interfacial characterization of graphene/epoxy nanocomposites. In polymeric nanocomposites, the thermo-mechanical properties of a system strongly depend on the characteristics of the interphase region between the matrix and the inclusions. The first step in the characterization of this interphase is to distinguish its border limit (i.e., the interphase thickness). Here, we present a methodology to systematically quantify the interphase thickness based on analyzing the variation of the local mass density profile. To this end, three functions (average accumulated mass density, accumulated standard deviation (ASD) and its first derivative) are successively applied on the local mass density profile. Using this procedure, the interphase limit can be easily detected regardless of the oscillatory nature of the local mass density. The effect of the epoxy crosslinking density and number of graphene layers on the interphase thickness is then investigated, and the results are analyzed by studying the interaction energies, polymer dynamics and distribution quality of reacted and unreacted components, as well as conformational changes of the polymer chains in the interphase region. The results reveal that the crosslinking density is the most influential parameter on the interphase thickness: the higher the crosslinking degree, the thicker the interphase region. To a lower extent, the interaction energy has also an effect on the interphase thickness since there is an inverse relationship between the interaction energy and the crosslinking density in our case study. Overall, the reported findings highlight useful insights into the detection and properties of the interphase region in thermoset composites.

Preparation and Thermal Evaluation of Novel Polyimide Protective Coatings for Quartz Capillary Chromatographic Columns Operated over 320 °C for High-Temperature Gas Chromatography Analysis

Protection of intrinsically brittle quartz chromatographic columns (CCs) from breakage or property deterioration in gas chromatography (GC) analysis has become an important research topic regarding high-temperature GC techniques. Polyimide (PI) has proved to be the most suitable protective coating for quartz CCs. In the current research, a series of novel high-temperature-resistant PI coatings for quartz CCs operated over 320 °C have been successfully prepared. For this purpose, the aromatic diamine with a rigid skeleton structure 2-(4-aminophenyl)-5-aminobenzimidazole (APBI) was copolymerized with two aromatic dianhydrides—3,3’,4,4’-benzophenotetracarboxylic acid dianhydride (BTDA) and 4,4’-oxydiphthalic anhydride (ODPA)—and an aromatic diamine with flexible ether linkages—4,4’-oxydianiline (ODA)—by a two-step polymerization procedure via soluble poly(amic acid) (PAA) precursors, followed by thermal imidization at elevated temperatures. The developed PI coatings exhibited good comprehensive properties, including glass transition temperatures (T_g) as high as 346.9 °C, measured by dynamic mechanical analysis (DMA), and coefficients of linear thermal expansion (CTEs) as low as 24.6 × 10⁻⁶/K in the range of 50–300 °C. In addition, the PI coatings exhibited good adhesion to the fused quartz capillary columns. No cracking, delamination, warpage, or other failures occurred during the 100-cycle thermal shock test in the range of 25–320 °C.

Characterization of Mechanical Degradation in Perfluoropolyether Film for Its Application to Antifingerprint Coatings

Enhancing the mechanical durability of antifingerprint films is critical for its industrial application on touch-screen devices to withstand friction damage from repeated rubbing in daily usage. Using reactive molecular dynamics simulations, we herein implement adhesion, mechanical, and deposition tests to investigate two durability-determining factors: intrachain and interchain strength, which affect the structural stability of the antifingerprint film (perfluoropolyether) on silica. From the intrachain perspective, it is found that the Si-C bond in the polymer chain is the weakest, and therefore prone to dissociation and potentially forming a C-O bond. This behavior is demonstrated consistently, regardless of the cross-linking density between polymer chains. For the interchain interaction, increasing the chain length enhances the mechanical properties of the film. Furthermore, the chain deposition test, mimicking the experimental coating process, demonstrates that placing shorter chains first to the surface of silica and then depositing longer chains is an ideal way to improve the interchain interaction in the film structure. The current study reveals a clear pathway to optimize the configuration of the polymer chain as well as its film structure to prolong the product life of the coated antifingerprint film.