Octadecyltriethoxysilane (OTE) monolayers on mica are imaged using force modulation microscopy (FMM) and dynamic force modulation (DFM). Nanoscopic areas of mica are produced within OTE layers and serve as an internal standard for contact stiffness measurements. The contact stiffness is systematically studied as a function of imaging medium and force modulation amplitude and frequency. Measurements taken in liquid media are found to reflect more accurately the viscoelastic properties of the sample, while imaging in air is perturbed by the capillary neck at contact. Increasing modulation amplitude increases the overall signal in FMM. However, extremely large amplitudes diminish the contrast difference between OTE and mica because the sensing depth is much higher than the monolayer. The measured contact stiffness is found to depend sensitively upon the modulation frequency because of the presence of several resonances within 10−50 kHz, which cause the image contrast to vary or to flip. Collective motion of the molecules under contact is most likely responsible for these resonances. The observed amplitude and frequency dependence also allows active control of FMM image contrast.

In recent years, traditional printing methods have been integrated to print flexible electronic devices and circuits. Since process requirements for electronics differ from those for graphic printing, the fundamentals require rediscovery mainly to optimize manufacturing techniques and to find cost reduction methods without compromising functional performance. In addition, alternative inks need to be formulated to increase the variety of functional inks and to pioneer new product developments. In this report, we investigate a thermoplastic-based nickel ink prototype to print electrodes using a screen-printing process. Process fundamentals are explored, and cost reduction methods are addressed by studying the effect of substrate roughness, print direction, and number of ink layers on the electrical performance of printed nickel. Multilayered electrodes are printed on paper and heat stabilized engineered film. A novel fundamental mechanism is found that explains the effect of substrate roughness on ink film roughness in screen printing, including the roughness measurement of the screen mesh wire that is reported for the first time. Results demonstrated that (i) surface roughness of substrates does not have significant effect on printed ink film roughness in screen printing; (ii) ink film thickness is higher on nonabsorbent materials, while line gain is higher on absorbent materials; (iii) the effect of electrode orientation on electrical performance is insignificant; and (iv) the effect of substrate roughness on the electrical performance for the first print layer can be eliminated by printing multiple layers. The results significantly affect substrate choice and number of ink layers, which are considered the major cost factors in the manufacturing of printed electronics.

Understanding the physical properties associated with the gelation and fusion of a PVC plastisol will help to improve process efficiency. Plastisol gelation and fusion were characterized by using both scanning electron microscopy (SEM) and atomic force microscopy (AFM) and were compared with the tensile properties developed at various temperatures. Both SEM and AFM showed good agreement during the early stages of gelation. However, AFM continued to show particle boundaries during the latter stages of gelation and fusion that provided a more nearly accurate comparison with the resulting tensile properties.

Poly(styrene-butadiene-styrene), or SBS, is commonly added to asphalt mixtures to improve their thermal stability and mechanical performance under working conditions in pavements and roads. However, the resulting SBSmodified blend suffers from separation between the SBS polymer and asphalt molecular components, thereby decreasing the expected mechanical performance of the material in the long term. Here, we present how adding methylene diphenyl diisocyanate (MDI)-based additives may improve the phase stability of SBSmodified asphalt as measured by AFM and separation testing. We then discuss the fundamental mechanisms that involve SBS, MDI, and asphalt molecules to achieve such an improvement. To this end, we utilize molecular modeling methods of semiempirical tight binding, density functional theory, and reaction rate calculations to simulate and characterize the intermolecular interactions of SBS and MDI with asphaltene molecules, a key component of asphalt bitumen. We find that, while noncovalent π−π stacking does not significantly explain the macroscopic properties of asphalt blends, reactions between asphaltene and MDI likely occur. As such, we propose that MDI acts as a compatibilizing agent between asphaltenes and SBS, which enhances the phase stability of MDI−SBS-modified asphalt. We also demonstrate that MDI additives with asphalt have lower chemical softness and polarizability, indicating a lower tendency toward degradation by oxidative agents.

The extraction and characterization of secondary microplastics, those formed through subjection to the environment, must continuously improve in accuracy and applicability in order to generate robust microplastics exposure and risk assessments. Currently, there is a dearth of reliable extraction and quantitation methods for solid microplastic particles in sediment with chemical specificity. Herein we present advances in methodologies to extract and quantify microplastic particles from sediment, utilizing an outdoor mesocosm to model a freshwater coastal environment. Model secondary microplastics of crosslinked polyurethane (PU) were studied in comparison to model secondary polypropylene (PP) microplastics. Techniques to characterize particles in sediment included pyrolysis gas chromatography mass spectrometry (py GC/MS), stereoscope microscopy, and scanning electron microscopy. To complement particle analysis, plastic-associated leachable molecules were extracted from sediment and analyzed semi-quantitatively by high performance liquid chromatography with high-resolution mass spectrometry (HPLC/HR-MS). After developing and optimizing extraction and analytical methods we quantitated PU microparticles by count and weight and discovered that model PU particles fell from the water column into the sediment over the course of a year, while no PP particles were located in sediment samples. In addition, target small molecules associated with the crosslinked PU were identified in sediment by HPLC/HR-MS but leachable molecules associated with polypropylene could not be identified in sediment samples. We share the new py GC/MS method to quantify highly crosslinked PUs in complex environmental matrices containing both inorganic and organic components. In the process of generating robust extraction methods for microplastics in sediment, we discovered important considerations for the quantitation of microplastics by py GC/MS and the impacts of sample matrix on the quantitation of PU and PP specifically. We provide guidance for the preparation of microplastics from complex environmental matrices (e.g., sediment and soil) for analysis by py GC/MS. Graphical Abstract