Suppressing Evaporative Loss in Slippery Liquid-Infused Porous Surfaces (SLIPS) with Self-Suspended Perfluorinated Nanoparticles.

This article describes an approach to resolving the issue of evaporative loss from slippery liquid-infused porous surfaces (SLIPS). Hydrophobic and oleophobic fluids with significantly reduced evaporative loss rates at temperatures of up to 90 °C were obtained by the one-step mixing of commercially available perfluorinated lubricants with colloidal nanoparticles to form self-suspended nanoparticle fluids (i.e., suspensions nearly devoid of solvent). No evaporative loss was detected at temperatures of as high as 50 °C for over 3 months. Furthermore, the approach allows us to combine the function of the nanoparticles with the slippery characteristic of SLIPS.

On the kinetics of the removal of ligands from films of colloidal nanocrystals by plasmas.

This paper describes the kinetic limitations of etching ligands from colloidal nanocrystal assemblies (CNAs) by plasma processing. We measured the etching kinetics of ligands from a CNA model system (spherical ZrO2 nanocrystals, 2.5-3.5 nm diameter, capped with trioctylphosphine oxide) with inductively coupled plasmas (He and O2 feed gases, powers ranging from 7 to 30 W, at pressures ranging from 100 to 2000 mTorr and exposure times ranging between 6 and 168 h). The etching rate slows down by about one order of magnitude in the first minutes of etching, after which the rate of carbon removal becomes proportional to the third power of the carbon concentration in the CNA. Pressure oscillations in the plasma chamber significantly accelerate the overall rate of etching. These results indicate that the rate of etching is mostly affected by two main factors: (i) the crosslinking of the ligands in the first stage of plasma exposure, and (ii) the formation of a boundary layer at the surface of the CNA. Optimized conditions of plasma processing allow for a 60-fold improvement in etching rates compared to the previous state of the art and make the timeframes of plasma processing comparable to those of calcination.

Plasma-based post-processing of colloidal nanocrystals for applications in heterogeneous catalysis.

This review summarizes the work on the use of plasmas to post-process nanostructures, in particular colloidal nanocrystals, as promising candidates for applications of heterogeneous catalysis. Using plasma to clean or modify the surface of nanostructures is a more precisely controlled method compared to other conventional methods, which is preferable when strict requirements for nanostructure morphology or chemical composition are necessary. The ability of plasma post-processing to create mesoporous materials with high surface areas and controlled microstructure, surfaces, and interfaces has transformational potential in catalysis and other applications that leverage surface/interface processes.

Effectiveness of organic solvents for recovering collapsed PDMS micropillar arrays.

Polydimethylsiloxane (PDMS) micropillar arrays are widely used in research labs and engineering fields as analytical tools for various purposes. When the micropillar length or density surpasses a critical value, micropillars tend to collapse with each other and become unusable. Restoring collapsed PDMS micropillars typically involves the use of low surface tension solvents and ultrasound sonication, but such approach has received little success to date. In this work, we examined the effectiveness of different types of solvents for restoring collapsed PDMS micropillar arrays and show that the swelling ratio of PDMS in selected solvents constitutes an important factor in the effectiveness of restoring collapsed PDMS micropillars. Our results could be a promoter in recycling PDMS micropillar arrays and achieving economic and social benefits.

Direct Observations of Field-Intensity-Dependent Dielectric Breakdown Mechanisms in TiO2 Single Nanocrystals.

One of the main challenges for next-generation electric power systems and electronics is to avoid premature dielectric breakdown in insulators and capacitors and to ensure reliable operations at higher electric fields and higher efficiencies. However, dielectric breakdown is a complex phenomenon and often involves many different processes simultaneously. Here we show distinctly different defect-related and intrinsic breakdown processes by studying individual, single-crystalline TiO2 nanoparticles using in situ transmission electron microscopy (TEM). As the applied electric field intensity rises, rutile-to-anatase phase transition, local amorphization/melting, and ablation are identified as the corresponding breakdown processes, the field intensity thresholds of which are found to be related to the position of the intensified field and the duration of the applied bias relative to the time of charged defects accumulation. Our observations reveal an intensity-dependent dielectric response of crystalline oxides at breakdown and suggest possible routes to suppress the initiation of premature dielectric breakdown. Hence, they will aid the design and development of next-generation robust and efficient solid dielectrics.

In Situ TEM Study of the Amorphous-to-Crystalline Transition during Dielectric Breakdown in TiO2 Film.

Dielectric breakdown of oxides is a main limiting factor for improvement of the performance of electronic devices. Present understanding suggests that defects produced by intense voltage accumulate in the oxide to form a percolation path connecting the two electrodes and trigger the dielectric breakdown. However, reports on directly visualizing the process at nanoscale are very limited. Here, we apply in situ transmission electron microscopy to characterize the structural and compositional changes of amorphous TiO2 under extreme electric field (∼100 kV/mm) in a Si/TiO2/W system. Upon applying voltage pulses, the amorphous TiO2 gradually transformed into crystalline substoichiometric rutile TiO2-x and the Magnéli phase Ti3O5. The transitions started from the anode/oxide interface under both field polarities. Preferred growth orientation of rutile TiO2-x with respect to the Si substrate was observed when Si was the anode, while oxidation and melting of the W probe occurred when W was the anode. We associate the TiO2 crystallization process with the electrochemical reduction of TiO2, polarity-dependent oxygen migration, and Joule heating. The experimental results are supported by our phase-field modeling. These findings provide direct details of the defect formation process during dielectric breakdown in amorphous oxides and will help the design of electronic devices with higher efficiency and reliability.

Self-Limiting Processes in the Flame-Based Fabrication of Superhydrophobic Surfaces from Silicones.

Outdoor applications of superhydrophobic coatings require synthetic approaches that allow their simple, fast, scalable, and environmentally benign deployment on large, heterogeneous surfaces and their rapid regeneration in situ. We recently showed that the thermal degradation of silicones by flames fulfills these characteristics by spontaneously structuring silicone surfaces into a hierarchical, textured structure that provides wear-resistant, healable superhydrophobicity. This paper elucidates how flame processing-a simple, rapid, and out-of-equilibrium process-can be so counterintuitively reliable and robust in producing such a complex structure. A comprehensive study of the effect of the processing speed and flame temperature on the chemical and physical properties of the coatings yielded three surprising results. (i) Three thermal degradation mechanisms drive the surface texturing: depolymerization (in the O2-rich conditions of the surface), decomposition (in the O2-poor conditions found a few micrometers from the surface), and pyrolysis at excessive temperatures. (ii) The operational condition is delimited by the onset of the depolymerization at low temperatures and the onset of pyrolysis at high temperatures. (iii) The remarkably wide operational conditions and robustness of this approach result from self-limiting growth and oxidation of the silicone particles that are responsible for the surface texturing and in the extent of their deposition. As a result of this analysis we show that superhydrophobic surfaces can be produced or regenerated with this approach at a speed of 15 cm s-1 (i.e., the length of an airport runway in ∼4.5 h).

Stress response to CO2 deprivation by Arabidopsis thaliana in plant cultures.

After being the standard plant propagation protocol for decades, cultures of Arabidopsis thaliana sealed with Parafilm remain common today out of practicality, habit, or necessity (as in co-cultures with microorganisms). Regardless of concerns over the aeration of these cultures, no investigation has explored the CO2 transport inside these cultures and its effect on the plants. Thereby, it was impossible to assess whether Parafilm-seals used today or in thousands of older papers in the literature constitute a treatment, and whether this treatment could potentially affect the study of other treatments.For the first time we report the CO2 concentrations in Parafilm-sealed cultures of A. thaliana with a 1 minute temporal resolution, and the transcriptome comparison with aerated cultures. The data show significant CO2 deprivation to the plants, a drastic suppression of photosynthesis, respiration, starch accumulation, chlorophyll biosynthesis, and an increased accumulation of reactive oxygen species. Most importantly, CO2 deprivation occurs as soon as the cotyledons emerge. Gene expression analysis indicates a significant alteration of 35% of the pathways when compared to aerated cultures, especially in stress response and secondary metabolism processes. On the other hand, the observed increase in the production of glucosinolates and flavonoids suggests intriguing possibilities for CO2 deprivation as an organic biofortification treatment in high-value crops.

Ovarian Primary and Metastatic Tumors Suppressed by Survivin Knockout or a Novel Survivin Inhibitor.

Survivin, a member of the inhibitor of apoptosis family, is upregulated in multiple cancers including ovarian cancer, but is rarely detectable in normal tissues. We previously reported that survivin promoted epithelial-to-mesenchymal transition (EMT) in ovarian cancer cells, suggesting that survivin may contribute to ovarian tumor metastasis and chemoresistance. In this study, we tested whether knockout or pharmacologic inhibition of survivin overcomes chemoresistance and suppresses tumor metastasis. The genetic loss of survivin suppressed tumor metastasis in an orthotopic ovarian cancer mouse model. To pharmacologically test the role of survivin on ovarian tumor metastasis, we treated chemo-resistant ovarian cancer cells with a selective survivin inhibitor, MX106, and found that MX106 effectively overcame chemoresistance in vitro MX106 inhibited cell migration and invasion by attenuating the TGFß pathway and inhibiting EMT in ovarian cancer cells. To evaluate the efficacy of MX106 in inhibiting ovarian tumor metastasis, we treated an orthotopic ovarian cancer mouse model with MX106, and found that MX106 efficiently inhibited primary tumor growth in ovaries and metastasis in multiple peritoneal organs as compared with vehicle-treated control mice. Our data demonstrate that inhibition of survivin using either genetic knockout or a novel inhibitor MX106 suppresses primary ovarian tumor growth and metastasis, supporting that targeting survivin could be an effective therapeutic approach in ovarian cancer.

From Petri Dishes to Model Ecosystems.

Model ecosystems could provide significant insight into the evolution and behavior of real ecosystems. We discuss the advantages and limitations of common approaches like mesocosms. In this context, we highlight recent breakthroughs that allow for the creation of networks of organisms with independently controlled environments and rates of chemical exchange.

Large-Scale Synthesis of Colloidal Si Nanocrystals and Their Helium Plasma Processing into Spin-On, Carbon-Free Nanocrystalline Si Films.

This paper describes a simple approach to the large-scale synthesis of colloidal Si nanocrystals and their processing into spin-on carbon-free nanocrystalline Si films. The synthesized silicon nanoparticles are capped with decene, dispersed in hexane, and deposited on silicon substrates. The deposited films are exposed to nonoxidizing room-temperature He plasma to remove the organic ligands without adversely affecting the silicon nanoparticles to form crack-free thin films. We further show that the reactive ion etching rate in these films is 1.87 times faster than that for single-crystalline Si, consistent with a simple geometric argument that accounts for the nanoscale roughness caused by the nanoparticle shape.

HOMEs for plants and microbes - a phenotyping approach with quantitative control of signaling between organisms and their individual environments.

We describe a simple, scalable, modular, and frugal approach to create model ecosystems as millifluidic networks of interconnected habitats (hosting microbes or plants), which offers (i) quantitative and dynamic control over the exchange of chemicals between habitats, and (ii) independent control over their environment. Oscillatory laminar flows produce regions of vortex mixing around obstacles. When these overlap, rapid mass transport by dispersion occurs, which is quantitatively describable as diffusion, but is directional and tunable in rate over 3 orders of magnitude. This acceleration in the rate of diffusion is equivalent to reducing the distance between the habitats, and therefore, the organisms, down to the length scales characteristic of signaling in soil (<2 mm).

Simplicity as a Route to Impact in Materials Research.

Materials scientists and engineers desire to have an impact. In this Progress Report we postulate a close correlation between impact - whether academic, technological, or scientific - and simple solutions, here defined as solutions that are inexpensive, reliable, predictable, highly performing, "stackable" (i.e., they can be combined and compounded with little increase in complexity), and "hackable" (i.e., they can be easily modified and optimized). In light of examples and our own experience, we propose how impact can be pursued systematically in materials research through a simplicity-driven approach to discovery-driven or problem-driven research.

Calcination does not remove all carbon from colloidal nanocrystal assemblies.

Removing organics from hybrid nanostructures is a crucial step in many bottom-up materials fabrication approaches. It is usually assumed that calcination is an effective solution to this problem, especially for thin films. This assumption has led to its application in thousands of papers. We here show that this general assumption is incorrect by using a relevant and highly controlled model system consisting of thin films of ligand-capped ZrO2 nanocrystals. After calcination at 800 °C for 12 h, while Raman spectroscopy fails to detect the ligands after calcination, elastic backscattering spectrometry characterization demonstrates that ~18% of the original carbon atoms are still present in the film. By comparison plasma processing successfully removes the ligands. Our growth kinetic analysis shows that the calcined materials have significantly different interfacial properties than the plasma-processed counterparts. Calcination is not a reliable strategy for the production of single-phase all-inorganic materials from colloidal nanoparticles.

Thermal Processing of Silicones for Green, Scalable, and Healable Superhydrophobic Coatings.

The thermal degradation of silicones is exploited and engineered to make super-hydrophobic coatings that are scalable, healable, and ecofriendly for various outdoor applications. The coatings can be generated and regenerated at the rate of 1 m(2) min(-1) using premixed flames, adhere to a variety of substrates, and tolerate foot traffic (>1000 steps) after moderate wear and healing.

Building Materials from Colloidal Nanocrystal Arrays: Preventing Crack Formation during Ligand Removal by Controlling Structure and Solvation.

Crack-free, ligand-free, phase-pure nanostructured solids, using colloidal nanocrystals as precursors, are fabricated by a scalable and facile approach. Films produced by this approach have conductivities comparable to those of bulk crystals over more than 1 cm (1.370 S cm-1 for PbS films).

Photonic structure arrays generated using butterfly wing scales as biological units.

We report an effective process to transfer the scales of Morpho butterflies onto various substrates. Based on the difference in binding strength between molecular interactions and chemical bonds, this method provides photonic structure arrays with biological units, which are difficult to obtain otherwise.