Polydimethylsiloxane (PDMS) is the most widely used silicon-based polymer due to its versatility and its various attractive properties. The fabrication of PDMS involves liquid phase cross-linking to obtain hydrophobic and mechanically flexible material in the final solid form. This allows to add various fillers to affect the properties of the resulting material. PDMS has a relatively low Thermal Conductivity (TC), in the order of 0.2 W/mK, which makes it attractive for thermal insulation applications such as sealing in construction. Although a further decrease in the TC of PDMS can be highly beneficial for such applications, most research on the thermal properties of PDMS composites have focused on fillers that increase the TC rather than decrease it. In the present work, we propose a simple and reliable method for making a PDMS-based composite material with significantly improved thermal insulation properties, by adding hollow glass microspheres (HGMs) to the mixture of the liquid base and the cross-linker (10:1 ratio), followed by degassing and heat-assisted crosslinking. We obtained a 31% reduction of thermal conductivity and a 60% increase in the elastic modulus of samples with HGM content of 17% by weight. At the same time, the sound insulation capacity of the PDMS-HGM composite is slightly decreased in comparison to pure PDMS, as a result of its lower density. Finally, the wettability of the samples had no dependence on HGM content.

In advanced drug delivery, versatile liposomal formulations are commonly employed for safer and more accurate therapies. Here we report a method that allows a straightforward production of synthetic monodisperse (~ 100 μm) giant unilamellar vesicles (GUVs) using a microfluidic system. The stability analysis based on the microscopy imaging showed that at ambient conditions the produced GUVs had a half-life of 61 ± 2 h. However, it was observed that ~ 90% of the calcein dye that was loaded into GUVs was transported into a surrounding medium in 24 h, thus indicating that the GUVs may release these small dye molecules without distinguishable membrane disruption. We further demonstrated the feasibility of our method by loading GUVs with larger and very different cargo objects; small soluble fluorescent proteins and larger magnetic microparticles in a suspension. Compared to previously reported microfluidics-based production techniques, the obtained results indicate that our simplified method could be equally harnessed in creating GUVs with less cost, effort and time, which could further benefit studying closed membrane systems.

We present a credible mechanism of spontaneous field emitter formation in high electric field applications, such as Compact Linear Collider in CERN (The European Organization for Nuclear Research). Discovery of such phenomena opens new pathway to tame the highly destructive and performance limiting vacuum breakdown phenomena. Vacuum breakdowns in particle accelerators and other devices operating at high electric fields is a common problem in the operation of these devices. It has been proposed that the onset of vacuum breakdowns is associated with appearance of surface protrusions while the device is in operation under high electric field. Moreover, the breakdown tolerance of an electrode material was correlated with the type of lattice structure of the material. Although biased diffusion under field has been shown to cause growth of significantly field-enhancing tips starting from initial nm-size protrusions, the mechanisms and the dynamics of the growth of the latter have not been studied yet. In the current paper we conduct molecular dynamics simulations of nanocrystalline copper surfaces and show the possibility of protrusion growth under the stress exerted on the surface by an applied electrostatic field. We show the importance of grain boundaries on the protrusion formation and establish a linear relationship between the necessary electrostatic stress for protrusion formation and the temperature of the system. Finally, we show that the time for protrusion formation decreases with the applied electrostatic stress, we give the Arrhenius extrapolation to the case of lower fields, and we present a general discussion of the protrusion formation mechanisms in the case of polycrystalline copper surfaces.

Microfluidics is a technology that manipulates liquids on the scales ranging from microliters to femtoliters. Such low volumes require precise control over pressures that drive their flow into the microfluidic chips. This article describes a custom-built pressure controller for driving microfluidic chips. The pressure controller features piezoelectrically controlled pressure regulation valves. As an open-source system, it offers high customizability and allows users to modify almost every aspect. The cost is roughly a third of what similar, alternative, commercially available piezoelectrically controlled pressure regulators could be purchased for. The measured output pressure values of the device vary less than 0.7% from the device’s reported pressure values when the requested pressure is between −380 and 380 mbar. Importantly, the output pressure the device creates fluctuates only ±0.2 mbar when the pressure is cycled between 10 and 500 mbar. The pressure reading accuracy and stability validation suggest that the device is highly feasible for many advanced (low-pressure) microfluidic applications. Here, we compare the main features of our device to commercially and non-commercially available alternatives and further demonstrate the device’s performance and accessibility in successful microfluidic hydrodynamic focusing (MHF)-based synthesis of large unilamellar vesicles (LUVs).

Aqueous electrochemical flow capacitors (EFCs) have demonstrated high-power capabilities and safety at low cost, making them promising energy storage devices for grid applications. A primary performance metric of an EFC is the steady-state electrical current density it can accept or deliver. Performance prediction, design improvements, and up-scaling are areas in which modeling can be useful. In this paper, a novel stochastic superparticle (SP) modeling approach was developed and applied to study the charging of carbon electrodes in the EFC system, using computational superparticles representing real carbon particles. The model estimated the exact values of significant operating parameters of an EFC, such as the number of particles in the flow channel and the number of electrolytic ions per carbon particle. Optimized model parameters were applied to three geometrical designs of an EFC to estimate their performance. The modeling approach allowed study of the charge per carbon particle to form the electric double-layer structure. The linear relationship between the concentration of SPs and the ionic charge was observed when optimized at a constant voltage of 0.75 V. The simulation results are in excellent agreement with experimental data, providing a deep insight into the performance of an EFC and identifying limiting parameters for both engineers and material scientists to consider.