Visualization and Quantification of the Chemical and Physical Properties at a Diffusion-Induced Interface Using AFM Nanomechanical Mapping

Visualization and Quantification of the Chemical and Physical Properties at a Diffusion-Induced Interface Using AFM Nanomechanical Mappin

Atomic Force Microscopy Nanomechanics Visualizes Molecular Diffusion and Microstructure at an Interface

Here we demonstrate a simple, yet powerful method, atomic force microscopy (AFM) nanomechanical mapping, to directly visualize the interdiffusion and microstructure at the interface between two polymers. Nanomechanical measurements on the interface between poly­(vinyl chloride) (PVC) and poly­(caprolactone) (PCL) allow quantification of diffusion kinetics, observation of microstructure, and evaluation of mechanical properties of the interdiffusion regions. These results suggest that nanomechanical mapping of interdiffusion enables the quantification of diffusion with high resolution over large distances without the need of labeling and the assessment of mechanical property changes resulting from the interdiffusion

Nanomechanical Imaging of the Diffusion of Fullerene into Conjugated Polymer

The large Young’s modulus difference between chemically modified fullerene (PCBM) and a conjugated polymer was used to nanomechanically map the diffusion of PCBM into PTB7, a high-efficiency low-band-gap conjugated polymer. The sharp tip in nanomechanical atomic force microscopy ensures a high-resolution nanomechanical characterization of the diffusion front, with the intrinsic benefits of revealing the mechanical properties of the mixtures. Localized structure changes induced by diffusion were investigated by grazing incidence X-ray diffraction methods. We found a most unusual diffusion behavior that shows Case II characteristics, where a front of PTB7 saturated with PCBM moves into the pure PTB7 with a linear time dependence. This diffusion is due mainly to a majority fraction of the disordered PTB7 that has continuous paths for PCBM diffusion without obvious energetic barriers, and as diffusion proceeds, the paths for diffusion gets larger, leading to a step in the concentration profile. The donor/acceptor-dependent diffusion constants may also contribute to the observed Case-II-like diffusion front

Kaplan–Meier analysis of cumulative survival.

<p>Kaplan–Meier analysis of cumulative survival.</p

Risk of ventilator-associated conditions: VAC using Cox proportional hazard model (Stepwise Variable Selection) (n = 303).

<p>Risk of ventilator-associated conditions: VAC using Cox proportional hazard model (Stepwise Variable Selection) (n = 303).</p

Patient disposition chart.

<p>CDC, Centers for Disease Control and Prevention; ECMO, extracorporeal membrane oxygenation; ICU, intensive-care unit; MV, mechanical ventilation; PCPS, percutaneous cardiopulmonary support; NPPV, noninvasive positive pressure ventilation; VAC, ventilator-associated conditions</p

Baseline demographics and outcome.

<p>Baseline demographics and outcome.</p

Ventilator-associated conditions univariate analysis.

<p>Ventilator-associated conditions univariate analysis.</p

Microfluidic Generation of Polydopamine Gradients on Hydrophobic Surfaces

Engineered surface-bound molecular gradients are of great importance for a range of biological applications. In this paper, we fabricated a polydopamine gradient on a hydrophobic surface. A microfluidic device was used to generate a covalently conjugated gradient of polydopamine (PDA), which changed the wettabilty and the surface energy of the substrate. The gradient was subsequently used to enable the spatial deposition of adhesive proteins on the surface. When seeded with human adipose mesenchymal stem cells, the PDA-graded surface induced a gradient of cell adhesion and spreading. The PDA gradient developed in this study is a promising tool for controlling cellular behavior and may be useful in various biological applications

New Insights into Morphology of High Performance BHJ Photovoltaics Revealed by High Resolution AFM

Direct imaging of the bulk heterojunction (BHJ) thin film morphology in polymer-based solar cells is essential to understand device function and optimize efficiency. The morphology of the BHJ active layer consists of bicontinuous domains of the donor and acceptor materials, having characteristic length scales of several tens of nanometers, that reduces charge recombination, enhances charge separation, and enables electron and hole transport to their respective electrodes. Direct imaging of the morphology from the molecular to macroscopic level, though, is lacking. Though transmission electron tomography provides a 3D, real-space image of the morphology, quantifying the structure is not possible. Here we used high-resolution atomic force microscopy (AFM) in the tapping and nanomechanical modes to investigate the BHJ active layer morphology that, when combined with Ar⁺ etching, provided unique insights with unparalleled spatial resolution. PCBM was seen to form a network that interpenetrated into the fibrillar network of the hole-conducting polymer, both being imbedded in a mixture of the two components. The free surface was found to be enriched with polymer crystals having a “face-on” orientation and the morphology at the anode interface was markedly different