Strain-Assisted Phase Transformation in Two-Dimensional Transition-Metal Dichalcogenides.

Two-dimensional polymorphic transition-metal dichalcogenides have drawn attention for their diverse applications. This work explores the complex interplay between strain-induced phase transformation and crack growth behavior in annealed nanocrystalline MoS2. Employing molecular dynamics (MD) simulations, this research focuses on the effect of grain size, misorientation, and annealing on phase evolution and their effects on the mechanical behavior of MoS2. First, examining phase transformation in monocrystalline MoS2 under various stress states reveals distinct behaviors depending on the initial phase (1T or 2H) and crystallographic orientation with respect to loading directions. Notably, transformation from a layered hexagonal to a body-centered tetragonal structure is more noticeable when strain in a zigzag direction is applied to the 1T sample. As such, single crystalline MoS2 with a 1T phase exhibits a 16% lower fracture stress in the armchair direction compared to that with a 2H phase. On the other hand, the 1T phase shows a 5% higher phonon lifetime compared to the 2H phase with similar phonon group velocities. Next, the influence of thermal energy and mechanical stress on the phase transformation of nanocrystalline MoS2 is investigated through annealing and quenching cycles, uncovering 60 and 44% irreversibility of phase transformation for an average grain size of 3 and 11 nm, respectively. Besides, the evolution of nanocrystalline samples with different initial phases and grain sizes is studied under uniaxial and biaxial stress. This study shows an inverse pseudo-Hall-Petch effect with exponents of 0.11 and 0.09 for 2H and 1T, respectively. The study reveals that phase transformation can occur concurrently with crack initiation and propagation with the 1T phase exhibiting a 19% lower grain size sensitivity of fracture stress compared to the 2H phase.

A Simple Non-Embedded Single Capillary Device for On-Demand Complex Emulsion Formation.

This study includes an examination of the design, fabrication, and experimentation of a rudimentary droplet generator. The device has potential applications in on-demand double and higher-order emulsions as well as tailored emulsions with numerous cores. The phenomenon of a pendant double droplet creation is observed when an inner phase is transported through a capillary, while a middle phase envelops the external surface of the capillary. This leads to the occurrence of a pinching-off process at the tip of the pulled capillary. Following this, the double droplet is introduced into a container that is filled with the outer phase. The present study examines the force equilibrium throughout the droplet break-up process and aims to forecast the final morphology of the droplets within the container by considering the impact of interfacial tension ratios. The shell thickness in a core-shell formation can be calculated based on the inner and middle phase flow rates as well as the middle droplet formation period. The present platform, which enables the simple production of double and higher emulsions, exhibits promising prospects for the controlled manufacturing of complex emulsions. This technology holds potential for various applications, including the experimental exploration of collision behavior or electro-hydrodynamics in emulsions as well as millimeter-size engineered microparticle fabrication.

Mesoporous Starch Cryoaerogel Material as an Emerging Platform for Oral Drug Delivery: Synthesis and In Vitro Evaluation.

In this study, a starch cryoaerogel formulation was developed as a carrier for poorly water-soluble drugs, like atorvastatin. Cryoaerogels were generated through a sol-gel method combined with a freeze-drying technique, and atorvastatin was incorporated into the obtained mesoporous systems during the solvent exchange stage. The formulated drug-loaded polymer structures were characterized in terms of their physicochemical properties, solid-state behavior, and cytotoxicity. They had a pore size of 27.56 nm and a drug loading size of 38.60%. Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) analyses indicated that atorvastatin was successfully incorporated into the cryoaerogel pores. The amorphous nature of the loaded drug was confirmed via X-ray diffraction (XRD). Furthermore, after the atorvastatin incorporation into the cryogel, the volume of nitrogen adsorbed on one gram of cryoaerogel (Vm), as well as the specific surface area (aBET) were reduced. The comparison between the drug release profiles of crystalline atorvastatin and the loaded formulation of atorvastatin showed that by including the drug into the pores of the developed cryoaerogel matrix its solubility was significantly improved-the time for the dissolution of 30% pure atorvastatin (t30%) was approximately 4 h, whereas the determined t30% for the formulated cryoaerogels was only 1 h. Moreover, the data from the MTT assay illustrated that the designed cryoaerogel could be used as a safe oral atorvastatin delivery system. According to obtained results, it could be concluded that the starch cryoaerogel formulation is a promising candidate for oral delivery of poorly water-soluble therapeutic agents.

Defect engineering for thermal transport properties of nanocrystalline molybdenum diselenide.

Molybdenum diselenide (MoSe2) is attracting great attention as a transition metal dichalcogenide (TMDC) due to its unique applications in micro-electronics and beyond. In this study, the role of defects in the thermal transport properties of single-layer MoSe2 is investigated using non-equilibrium molecular dynamics (NEMD) simulations. Specifically, this work quantifies how different microstructural defects such as vacancies and grain boundaries (GBs) and their concentration (N) alter the thermal conductivity (TC) of single crystal and nanocrystalline MoSe2. These results show a significant drop in thermal conductivity as the concentration of defects increases. Specifically, point defects lower the TC of MoSe2 in the form of N-ß where ß is 0.5, 0.48 and 0.36 for VMo, VMo-Se and VSe vacancies, respectively. This study also examines the impact of grain boundaries on the thermal conductivity of nanocrystalline MoSe2. These results suggest that GB migration and stress-assisted twinning along with localized phase transformation (2H to 1T) are the primary factors affecting the thermal conductivity of nanocrystalline MoSe2. Based on MD simulations, TC of polycrystalline MoSe2 increases with the average grain size (d̄) in the form of d̄4.5. For example, the TC of nanocrystalline MoSe2 with d̄ = 11 nm is around 40% lower than the TC of the pristine monocrystalline sample with the same dimensions. Finally, the influence of sample size and temperature is studied to determine the sensitivity of quantitative thermal properties to the length scale and phonon scattering, respectively. The results of this work could provide valuable insights into the role of defects in engineering the thermal properties of next generation semiconductor-based devices.

Immunomagnetic Isolation of HER2-Positive Breast Cancer Cells Using a Microfluidic Device.

Analysis of circulating tumor cells (CTCs) as a tool for monitoring metastatic cancers, early diagnosis, and evaluation of disease prognosis paves the way toward personalized cancer treatment. Developing an effective, feasible, and low-cost method to facilitate CTC isolation is, therefore, vital. In the present study, we integrated magnetic nanoparticles (MNPs) with microfluidics and used them for the isolation of HER2-positive breast cancer cells. Iron oxide MNPs were synthesized and functionalized with the anti-HER2 antibody. The chemical conjugation was verified by Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and dynamic light scattering/zeta potential analysis. The specificity of the functionalized NPs for the separation of HER2-positive from HER2-negative cells was demonstrated in an off-chip test setting. The off-chip isolation efficiency was 59.38%. The efficiency of SK-BR-3 cell isolation using a microfluidic chip with a S-shaped microchannel was considerably enhanced to 96% (a flow rate of 0.5 mL/h) without chip clogging. Besides, the analysis time for the on-chip cell separation was 50% faster. The clear advantages of the present microfluidic system offer a competitive solution in clinical applications.

Geometrically-controlled evaporation-driven deposition of conductive carbon nanotube patterns on inclined surfaces.

Controllable accumulation of carbon nanotubes in self-assembly techniques is of critical importance in smart patterning and printed electronics. This study investigates how inclining the substrate and inhibiting the droplet spreading by sharp solid edges can affect the droplet contact angle and pinning time to improve the electrical conductivity and uniformity of the deposited patterns. Rectangular and circular pedestals were employed to investigate the effect of geometry on the deposition characteristics and to incorporate the gravitational effect by varying the substrate inclination angle. The results indicate that confining the droplet contact line to remain pinned to the pedestal edge can significantly alter the width, uniformity, and precision of the deposited patterns. These improvements correspond to the enhancement of the droplet pinning time (due to the edge effect) and to the further increase of the local evaporation rate near the contact line (due to the droplet elevation). By conducting experiments on different rectangular pedestals with varying solid-liquid interfacial areas and comparing their deposition characteristics, a rectangular pedestal with specific dimensions is selected in terms of pattern consistency and material usage efficiency. It is also shown that higher inclination angles further increase the deposited line accumulation density. Combining confinement and inclination techniques yields promising deposited patterns with high consistency and low resistivity, ranging from 8.75 kΩ mm-1 to a minimum of 0.63 kΩ mm-1 for a 3 × 6 mm2 rectangular pedestal.

Effect of surfactant concentration on the evaporation-driven deposition of carbon nanotubes: from coffee-ring effect to strain sensing.

Carbon nanotubes (CNTs) as electrically conductive materials are of great importance in the fabrication of flexible electronic devices and wearable sensors. In this regard, the evaporation-driven self-assembly of CNTs has attracted increasing attention. CNT-based applications are mostly concerned with the alignment of CNTs and the density of CNT films. In the present work, we focus on the latter by trying to achieve an optimal evaporation-driven deposition with the densest CNT ring. Although surfactants are used for effective dispersion and colloidal stabilization of CNTs in the aqueous phase, their excessive usage induces Marangoni eddies in the evaporating sessile droplets, leading to poor ring depositions. Thus, there is an optimum surfactant concentration that contributes to CNTs deagglomeration and results in the densest ring-like deposition with relatively high thickness. We report that this optimum concentration for sodium dodecyl sulfate (SDS) as a surfactant can be approximately considered as much as the concentration of multi-walled carbon nanotubes (MWCNTs) as the colloidal nanoparticles. Optimal depositions show the lowest electrical resistances for each CNT concentration, making them suitable for electronic applications. We also propose the multiple depositions method in which a new droplet is printed after the complete evaporation of the previous droplet. This method can lead to denser rings with a higher conductivity using lower concentrations of CNTs. Lastly, we fabricate strain sensors based on the optimal evaporation-driven deposition of CNTs which show higher gauge factors than the commercial strain gauges, corroborating the applicability of our method.

Effect of Particle Concentration on Surfactant-Induced Alteration of the Contact Line Deposition in Evaporating Sessile Droplets.

Controlling and suppressing the so-called "coffee-ring effect" (CRE) is an issue of cardinal importance and intense interest in many industries and scientific fields. Here, the combined effect of the particle and surfactant concentration on the CRE is investigated by gradually adding Triton X-100 surfactant to colloidal suspensions of SiO2 nanoparticles in ethanol for various particle concentrations. First, the effect of particle concentration on the contact line dynamics during the evaporation of a sessile droplet is investigated. It is shown that increasing the particle concentration leads to an increase in pinning time and ring width, whereas the droplet's initial and dynamic contact angle remains unchanged. Afterward, the effect of different concentrations of surfactant is studied for different particle concentrations. It is concluded that the surfactant concentration at which the CRE is suppressed is dependent on the initial particle concentration of the colloid, and it increases as the particle concentration increases. Furthermore, as adding surfactant with a concentration lower than this critical concentration results in an unsuppressed CRE, it is shown that surpassing this concentration will result in a depletion of particles in the contact line. Moreover, it is demonstrated that this critical surfactant concentration has no significant effect on the droplet's geometry and the total evaporation time.

Effect of substrate conductivity on the evaporation of small sessile droplets.

Here we show the effect of the thermal conductivity of the substrate on the evaporation process of small droplets. We deposited small droplets on the order of 100-500 µm in diameter on four different substrates with different thermal conductivities and surface properties, and we measured the evaporation time. Also, a numerical model that describes this process was developed to include thermal effects inside the droplet and heat transfer from the substrate. Our model considers the entire time of evaporation including the pinned and depinned stages. This model uses a new approach for the contact line behavior. It uses experimental results to define the movement of the contact line as a function of the contact angle.

Flow manipulation and cell immobilization for biochemical applications using thermally responsive fluids.

A flow redirection and single cell immobilization method in a microfluidic chip is presented. Microheaters generated localized heating and induced poly(N-isopropylacrylamide) phase transition, creating a hydrogel that blocked a channel or immobilized a single cell. The heaters were activated in sets to redirect flow and exchange the fluid in which an immobilized cell was immersed. A yeast cell was immobilized in hydrogel and a 4',6-diamidino-2-phenylindole (DAPI) fluorescent stain was introduced using flow redirection. DAPI diffused through the hydrogel and fluorescently labelled the yeast DNA, demonstrating in situ single cell biochemistry by means of immobilization and fluid exchange.

The effect of adhesion promoter on the adhesion of PDMS to different substrate materials.

The effect of the adhesion promoter GE SS4120 on the adhesion strength of PDMS to different substrates was tested. The adhesion to silicon, glass and aluminium was significantly increased, while adhesion of PDMS to Teflon remained poor, and the adhesion strength of PDMS to PDMS decreased.

Moving temporary wall in microfluidic devices.

This paper describes the formation of a temporary wall between two fluid streams in a microfluidic channel. Diffusion of ions from one fluid stream into a costreaming thermally responsive polymer solution is used to lower the local gelation temperature of the polymer, leading to formation of a gel wall in the center of the flow channel. The mechanisms driving either the generation or removal of the wall on its both sides are described and discussed. This wall allows well-controlled transport of particles from one stream into the other.