Understanding the interface between organic and inorganic materials presents many challenges due to the complex chemistries involved. Modeling and experimental work have elucidated only a few facets of the physical and chemical nature of the adhesion between such surfaces. In this work, we use density functional theory to, understand the adhesion between five different inorganic crystal surfaces (two-dimensional silica, both sides of kaolinite, hydroxylated quartz, hydroxylated albite) with five different organic molecules (benzene, phenol, phthalimide, N-phenylmaleimide, diphenyl ether). In the analysis, we explore the binding motifs that constitute parts of a polyimide monomer and examine their interactions with increasingly complex crystal surfaces. Comparing these systems, we elucidate the key factors (such as electrostatic interactions, hydrogen bond formation, and cation effects) that affect adhesion of organics on inorganic surfaces. It is found that the presence of cations and the availability of the oxygen species, in either the organic or inorganic layers, allows for increased hydrogen bonding. The most significant contribution to adhesion is from the rearrangement of surface electrostatic interactions. These factors can be used to optimize adhesion by decomposing both the organic and inorganic materials into the constituent interactions and help design improved interfacial properties.

Focal adhesions are often observed at the cell's periphery. We provide an explanation for this observation using a system-level mathematical model of a cell interacting with a two-dimensional substrate. The model describes the biological cell as a hypoelastic continuum material whose behavior is coupled to a deformable, linear elastic substrate via focal adhesions that are represented by collections of linear elastic attachments between the cell and the substrate. The evolution of the focal adhesions is coupled to local intracellular stresses which arise from mechanical cell-substrate interactions. Using this model we show that the cell has at least three mechanisms through which it can control its intracellular stresses: focal adhesion position, size, and attachment strength. We also propose that one reason why focal adhesions are typically located on the cell periphery instead of its center is because peripheral focal adhesions allow the cell to be more sensitive to changes in the microenvironment. This increased sensitivity is caused by the fact that peripherally located focal adhesions allow the cells to modulate its intracellular properties over a much larger portion of the cell area.

The effect of nanoscale roughness on the adhesion between glassy silica and polyimides is examined by molecular dynamics simulation. Different silica surfaces, with varying degrees of roughness, were generated by cleaving bulk structures with a predefined surface and a desired average roughness, with different roughness periods and hydroxylation densities in an effort to study the influence of these surface characteristics on adhesion at the silica-polyimide interface. The calculated results reveal that average roughness R-a is the primary controlling factor within the considered conditions. Further, an energy decomposition analysis of the pulling process suggests that hydrogen bonding contributes to the adhesion on all the rough surfaces, while the Coulombic energy contribution becomes significant at higher R-a. From a structural analysis of the vacant volume and surface area, it is shown that the periodicity of roughness provides a rather interesting trend for the adhesion energy. Adhesion can increase with a reduction in period due to the corresponding surface area expansion; however, if vacant volumes exist at the interface, the level of adhesion can decrease. Competition between two opposing tendencies leads to the maximum adhesion, and hence, both R-a and period are key parameters to control the adhesion in nanoscale roughness.

The computer automated radioactive particle tracking (CARPT) and positron emission particle tracking (PEPT) techniques have been developed to characterize opaque multiphase flows. In CARPT and PEPT, the Eulerian flow field is inferred from the knowledge of reconstructed tracer particle trajectories. The present study was undertaken to assess the strengths and limitations of the process of estimating the Eulerian flow field from particle trajectories. A two-dimensional problem, which mimics the characteristics of flow in a stirred tank reactor equipped with a standard Rushton turbine, was considered. The Eulerian flow field was numerically simulated. Care was taken to minimize effects of numerical issues on the computed flow field, which was then used to calculate particle trajectories. Standard CARPT data processing was carried out on the simulated particle trajectories to estimate the Eulerian flow field. This estimated flow field was compared with the original flow field used for trajectory simulations to evaluate possible errors associated with the CARPT data processing and flow follow-ability of the particles. Influence of grid used for data processing, sampling frequency, and particle size and particle density on the estimated flow field was examined. The study highlights several issues pertaining to the estimation of the Eulerian flow field from Lagrangian information. The results provide guidelines for selecting appropriate parameters in processing of CARPT or PEPT data.

Development of a novel polymeric binder material is necessary for improving the electrochemical performance of silicon-based anodes for Li-ion batteries, suffering from irreversible capacity loss due to their huge volume change during the electrochemical cycling. However, relevant mechanisms on how adhesion and mechanical properties of the binder are correlated to the stability of Si anode are still lacking. In this study, we investigate the role of functional groups attached in the polymeric binder on the structural stability of LixSiO2 using molecular dynamics simulations. A pulling test reveals that the binder with a polar group shows better adhesion properties with LixSiO2 than that with a nonpolar group. In addition, cohesive failure dominates the failure mode for the nonpolar group, but an adhesive to cohesive failure transition occurs for the polar group as the amount of lithiation is increased. For mechanical properties, the polar binder exhibits a larger maximum stress, while the nonpolar one can hold a larger strain. Finally, the polar group works more effectively to suppress the volume expansion of LixSiO2 from lithiation. The current study reveals detailed mechanisms on how polar and nonpolar polymeric binders work differently with glasses of varying degrees of lithiation and can guide the design of future generations of Si-based anodes.

Understanding the interaction between polyimide and inorganic surfaces is vital in controlling interfacial adhesion behavior. Here, molecular dynamics simulations are employed to study the adhesion of polyimide on both crystalline and glassy silica surfaces, and the effects of hydroxylation, silica structure, and polyimide chemistry on adhesion are investigated. The results reveal that polyimide monomers have stronger adhesion on hydroxylated surfaces compared to nonhydroxylated surfaces. Also, adhesion of polyimide onto silica glass is stronger compared to the corresponding crystalline surfaces. Finally, we explore the molecular origins of adhesion to understand why some polyimide monomers like Kapton have a stronger adhesion per unit area (adhesion density) than others like BPDAAPB. We find this occurs due to a higher density of oxygen's in the Kapton monomer, which we found to have the highest contribution to, adhesion density.