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Adhesion of fluorinated ethylene propylene polymer (FEP) to poly(co-ethylene-vinyl acetate) (EVA) is discussed in the context of photovoltaic modules, where FEP film has the potential to improve photovoltaic efficiency when used as a sun-facing weathering layer. While virgin FEP has practically no adhesion to EVA, it is demonstrated that cementable FEP, which has a surface chemically enriched in nitrogen and oxygen, has much improved as-laminated adhesion to EVA. However, when subjected to accelerated weathering tests involving exposure to 85°C, 85% relative humidity environment, or temperature cycling to -40°C from this state, the improvement in adhesion is not well maintained. To overcome such limited durability, the benefit is shown of adding an aluminum oxide coating to cementable FEP such that when laminated, the alumina layer is sandwiched between the FEP and EVA surfaces. This structure not only has excellent as-laminated adhesion to EVA, but adhesion performance is maintained for extended accelerated weathering. [ABSTRACT FROM AUTHOR]

In this work, we study the collapse of nanotubes using an inextensible elastica model. Through phase plane analysis, we show that there exist collapsed configurations of different orders, each involving a different number of collapsed layers. Solutions corresponding to each order only exist if the equilibrium separation in the contact zone (a material property) is smaller than a certain value. Below the critical separation, there are two solutions for each order corresponding to each separation, a high energy solution and a low energy one. Some of the collapsed configurations are not physically accessible due to material interpenetration. This work puts a limitation on the applicability of the inextensible elastica model for the collapse of nanotubes. [ABSTRACT FROM AUTHOR]

We present a synthetic adaptation of the fibrillar adhesion surfaces found in nature. The structure consists of protruding fibrils topped by a thin plate and shows an experimentally measured enhancement in adhesion energy of up to a factor of 9 over a flat control. Additionally, this structure solves the robustness problems of previous mimic structures and has preferred contact properties (i.e., a large surface area and a highly compliant structure). We show that this geometry enhances adhesion because of its ability to trap interfacial cracks in highly compliant contact regimes between successive fibril detachments. This results in the requirement that the externally supplied energy release rate for interfacial separation be greater than the intrinsic work of adhesion, in a manner analogous to lattice trapping of cracks in crystalline solids. [ABSTRACT FROM AUTHOR]

For a continuous healthcare or environmental monitoring system, it is essential to reliably sense the analyte concentration reported by electrochemical sensors. However, environmental perturbation, sensor drift, and power-constraint make reliable sensing with wearable and implantable sensors difficult. While most studies focus on improving sensor stability and precision by increasing the system's complexity and cost, we aim to address this challenge using low-cost sensors. To obtain the desired accuracy from low-cost sensors, we borrow two fundamental concepts from communication theory and computer science. First, inspired by reliable data transmission over a noisy communication channel by incorporating redundancy, we propose to measure the same quantity (i.e., analyte concentration) with multiple sensors. Second, we estimate the true signal by aggregating the output of the sensors based on their credibility, a technique originally developed for "truth discovery" in social sensing applications. We use the Maximum Likelihood Estimation to estimate the true signal and the credibility index of the sensors over time. Using the estimated signal, we develop an on-the-fly drift-correction method to make unreliable sensors reliable by correcting any systematic drifts during operation. Our approach can determine solution pH within 0.09 pH for more than three months by detecting and correcting the gradual drift of pH sensors as a function of gamma-ray irradiation. In the field study, we validate our method by measuring nitrate levels in an agricultural field onsite over 22 days within 0.06 mM of a high-precision laboratory-based sensor. We theoretically demonstrate and numerically validate that our approach can estimate the true signal even when the majority (~ 80%) of the sensors are unreliable. Moreover, by restricting wireless transmission to high-credible sensors, we achieve near-perfect information transfer at a fraction of the energy cost. The high-precision sensing with low-cost sensors at reduced transmission cost will pave the way for pervasive in-field sensing with electrochemical sensors. The approach is general and can improve the accuracy of any field-deployed sensors undergoing drift and degradation during operation. [ABSTRACT FROM AUTHOR]

Traditional Potentiometric Ion-selective Electrodes (ISE) are widely used in industrial and clinical settings. The simplicity and small footprint of ISE have encouraged their recent adoption as wearable/implantable sensors for personalized healthcare and precision agriculture, creating a new set of unique challenges absent in traditional ISE. In this paper, we develop a fundamental physics-based model to describe both steady-state and transient responses of ISE relevant for wearable/implantable sensors. The model is encapsulated in a “generalized Nernst formula” that explicitly accounts for the analyte density, time-dynamics of signal transduction, ion-selective membrane thickness, and other sensor parameters. The formula is validated numerically by self-consistent modeling of multispecies ion-transport and experimentally by interpreting the time dynamics and thickness dependence of thin-film solid-contact and graphene-based ISE sensors for measuring soil nitrate concentration. These fundamental results will support the accelerated development of ISE for wearable/implantable applications. [ABSTRACT FROM AUTHOR]

Phosphate is one of the main nutrients playing many key roles in the human body and plant growth. Because of this essential demand, phosphate is often used as a micronutrient additive in both fertilizers and dietary supplements. However, its excessive amount could result in severe health issues in the human body and the ecosystem of aquatic life. Therefore, there is a need for an inexpensive rapid measurement approach that could assess the optimum level of phosphate by using simple low-cost sensors. Here, for the first time, we demonstrate the use of a nickel oxide modified screen printed carbon (PrC) electrode as a low-cost electrochemical potentiometric phosphate detection sensor. The nickel oxide/oxyhydroxide (NiO/NiOOH)-PrC electrode has been prepared by a facile anodic electrodeposition process onto a screen printed carbon electrode. The characterization performed by field emission scanning electron microscopy (FE-SEM) and energy diffractive X-ray spectroscopy (EDS) techniques confirmed the formation of NiO/NiOOH by significant changes in surface morphology and elemental composition of PrC after electrodeposition. The results exhibited a porous deposited layer containing nickel and an increased oxygen value of the modified electrode as compared to pristine PrC. Potentiometric phosphate detection on the NiO/NiOOH-PrC electrode showed a linear response in the concentration range of 10−6–10−1 M, yielding a slope of −78.48 mV per decade with a fast response time. The electrode demonstrated a stable response with less than 0.8% variability of the recorded potential over 2000 seconds. High durability and reusability of the electrode were confirmed by repeated potentiometric phosphate determination tests over a course of 21 days. Interference tests with chloride, nitrate, sulfate, bromide, acetate, and carbonate solutions revealed very low selectivity coefficients within the range of 10−11–10−2, which indicated a high phosphate-selectivity of the developed sensor. This novel technology provides great potential for future scalable production and applications in portable real-time monitoring of phosphate ions in different precision agricultural and point-of-care diagnostic applications. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotubes with a circular cross section can collapse into ribbons under the influence ot' self-van der Waals interactions. We present closed-form results for the energetics of this self-collapse using continuum analysis verified by molecular simulations. Two critical tube radii are predicted by the continuum analysis: Rmin, below which there is no collapse; and Rmax above which the collapsed configuration is energetically favored. We present simpleandaccurate analytical results for Rmin and Rmax as functions of two length scales, d0 and &radicD/Wflat;, where d0 is the equilibrium distance between two flat parallel graphite sheets, Wflat is the work per unit area needed to separate the two sheets, and D is the effective bending stillness of the tube. [ABSTRACT FROM AUTHOR]

Geckos can adhere upside down on a horizontal surface and yet can climb rapidly on most vertical walls. This feat is accomplished using a hierarchical fibrillar interface. This paper reviews design principles of synthetic fibrillar interfaces that mimic surface structures in lizards and insects designed for enhanced contact and adhesion. In addition, we will address the role that statistics plays in quantifying fibrillar adhesion. [ABSTRACT FROM AUTHOR]