Decrease In Contact Angle Research Articles

Effects of DBD Direct Air Plasma and Gliding Arc Indirect Plasma Activated Mist on Germination, and Physiological Parameters of Rice Seed

AbstractRice seeds (Oryza sativa L.) have been treated with cold atmospheric plasma in air both directly in a dielectric barrier discharge and indirectly by gliding arc discharge with plasma activated mist. Comparisons of impacts of the two methods on rice seeds germination and physiological parameters are presented.Plasma has been found to increase seeds hydrophilization and water uptake through decrease of liquid contact angle and increase of total surface free energy of seed’s coat. Germination of treated seeds and their seedling growth parameters are enhanced by plasma application. After 20 min of seeds direct and indirect exposures respectively, germination potential increases by 36.73 and 50.4%, germination rate by 26.0 and 30.0%, and germination index by 25.92 and 36.53%. Also, total shoot length increases by 42.2 and 48.5%, and total root length by 15.93 and 22.42%. Plasma enhances physiological changes by increasing nonenzymatic antioxidants substances which in turn increase the tolerance against abiotic stresses. After 20 min for direct and indirect exposures respectively, free proline increases by 30.0 and 40.0%, total soluble carbohydrates by 49.7 and 54.6%. Also, cellular reactive oxygen species (ROS) increase by 52.0 and 60.0%, and malondialdehyde (MDA) decreases by 68.0 and 88.0%. Indirect exposure of rice seeds by plasma activated mist shows enhanced effects on germination and physiological parameters compared to direct one and could be more practical when applied to large scale seeds plasma treatment.

Co-Electrospun Poly(ε-Caprolactone)/Zein Articular Cartilage Scaffolds.

Osteoarthritis scaffold-based grafts fail because of poor integration with the surrounding soft tissue and inadequate tribological properties. To circumvent this, we propose electrospun poly(ε-caprolactone)/zein-based scaffolds owing to their biomimetic capabilities. The scaffold surfaces were characterized using Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, static water contact angles, and profilometry. Scaffold biocompatibility properties were assessed by measuring protein adsorption (Bicinchoninic Acid Assay), cell spreading (stained F-actin), and metabolic activity (PrestoBlue™ Cell Viability Reagent) of primary bovine chondrocytes. The data show that zein surface segregation in the membranes not only completely changed the hydrophobic behavior of the materials, but also increased the cell yield and metabolic activity on the scaffolds. The surface segregation is verified by the infrared peak at 1658 cm-1, along with the presence and increase in N1 content in the survey XPS. This observation could explain the decrease in the water contact angles from 125° to approximately 60° in zein-comprised materials and the decrease in the protein adsorption of both bovine serum albumin and synovial fluid by half. Surface nano roughness in the PCL/zein samples additionally benefited the radial spreading of bovine chondrocytes. This study showed that co-electrospun PCL/zein scaffolds have promising surface and biocompatibility properties for use in articular-tissue-engineering applications.

Triggering Degradation of Cellulose Acetate by Embedded Enzymes: Accelerated Enzymatic Degradation and Biodegradation under Simulated Composting Conditions.

A green strategy that significantly accelerates the biodegradation rate of cellulose acetate (CA) by triggering deacetylation was demonstrated. Lipase isolated from Candida rugosa was immobilized on CA particles (immobilized lipase (IL)) by a physical entrapment method and further incorporated in CA films. After 40 days of aging in contact with external enzymes (lipase and cellulase), the number-average molecular weight (Mn) of CA/IL 5% decreased by 88%, while the Mn of CA only exhibited a 48% reduction. Fourier transform infrared and nuclear magnetic resonance spectroscopy of CA/IL 5% indicated significant deacetylation, which was further supported by the decrease of the water contact angle from 59 to 16°. These drastic changes were not observed for CA. Similar differences in the degradation rate were observed during aging under simulated composting conditions. After 180 days of simulated composting, traces of CA/IL 5% were barely observable, while large pieces of CA still remained. This could open the door to modified lignocellulose materials with retained biodegradability, also reducing the requirements for the degradation environment as the process is initiated from inside of the material.

Effect of sodium hypochlorite as a depressant for copper species in Cu-Mo flotation separation

One alternative to replace conventional depressants in Cu-Mo separation is using oxidizing agents to promote the formation of products on chalcopyrite that render its surface hydrophilic and thus favor its depression. This work provides a study to understand how sodium hypochlorite can act as a depressor for chalcopyrite in Cu-Mo flotation separation. The effect of NaClO in flotation tests was evaluated by means of electrochemical techniques, scanning electron microscopy (SEM), Fourier transform infrared analysis and contact angle measurements. The flotation results showed a selective depressant effect at a dosage of 1,020 g/t NaClO, conditioning time of 5 min, and pH 7. The mixed potential showed that the oxidation of chalcopyrite and molybdenite is possible through the addition of NaClO. The SEM observations showed changes in oxidized chalcopyrite morphology, which is supported by the decreasing contact angle change; no morphological changes were observed on molybdenite. FTIR analyses showed the characteristic peaks of the OH group after chalcopyrite was treated with NaClO; when molybdenite was treated with NaClO, the FTIR spectrum did not show changes. A scheme is proposed for the formation of oxidation species.

Binary Mixture Droplet Evaporation on Microstructured Decorated Surfaces and the Mixed Stick-Slip Modes.

The interactions between liquid droplets and solid surfaces during wetting and phase change are important to many applications and are related to the physicochemical properties of the substrate and the fluid. In this work, we investigate experimentally the evaporation of pure water, pure ethanol, and their binary mixture droplets, accessing a wide range of surface tensions, on hydrophobic micro-pillared surfaces varying the spacing between the pillars. Results show that on structured surfaces, droplets evaporate following three classical evaporative behaviors: constant contact radius/pinning, stick-slip, or mixed mode. In addition, we report two further droplet evaporation modes, which are a mixed stick-slip mode where the contact angle increases while the contact radius decreases in a stick-slip fashion and a mixed stick-slip mode where both the contact angle and the contact radius decrease in a stick-slip fashion. We name these evaporation modes not yet reported in the literature as the increasing and decreasing contact angle mixed stick-slip modes, respectively. The former ensues because the fluid surface tension increases as the most volatile fluid evaporates coupled to the presence of structures, whereas the latter is due to the presence of structures for either fluid. The duration of each evaporation mode is dissimilar and depends on the surface tension and on the spacing between structures. Pure water yields longer initial pinning times on all surfaces before stick-slip ensues, whereas for binary mixtures and pure ethanol, initial pinning ensues mainly on short spacing structures due to the different wetting regimes displayed. Meanwhile, mixed stick-slip modes ensue mainly for high ethanol concentrations and/or pure ethanol independent of the solid fraction and for low ethanol concentrations on large spacing. Contact line jumps, changes in contact angle and pinning forces are also presented and discussed. This investigation provides guidelines for tailoring the evaporation of a wide range of surface tension fluids on structured surfaces for inkjet printing, DNA patterning, or microfluidics applications.

Comparative study of the effectiveness of nano-sized iron-containing particles as a foliar top-dressing of peanut in rainy conditions

The high loss of foliar-applied fertilizers in the wet season and other extreme weather conditions reduces fertilizer use efficiency remarkably low. Emerging nano-iron materials, owing to their highly desirable properties such as exceptionally small size, particle surface and interface attributes, strong adhesion and high iron ratio, could overcome the limitations of traditional fertilizers. However, their anti-leaching property, leaching resistance mechanism, iron nutrition enrichment capacity and cost effectiveness remain unclear. In this study, four nano-iron materials (Fe nanoparticles (Fe-NPs), Fe3O4-NPs, α-Fe2O3-NPs and γ-Fe2O3-NPs) were compared with traditional iron fertilizers (FeSO4 and Fe-EDTA). The results showed that the efficiency of traditional iron fertilizers decreased greatly under simulated rainfall conditions due to their poor leaching resistance. In contrast, nano-iron fertilizers performed exceptionally well under simulated rainfall conditions with significant increase in leaf iron concentration, photosynthesis and growth of peanut. This was mainly attributed to their decreased contact angle, increased wetting capacity and increased adhesion on plant surface, which collectively decreased fertilizer leaching remarkably. The adhesion capacity of Fe3O4-NPs (53.5 mN/m), was nearly three times that of traditional iron fertilizer (18.3 mN/m). Therefore, only a small amount of Fe3O4-NPs (4 mg/plant) was needed relative to traditional iron fertilizers (FeSO4, 59 mg/plant) to achieve comparable high leaf Fe concentration (1076.96 μg/g) under rainfall conditions. Cost evaluation suggests that the cost-competitiveness of Fe3O4-NPs will become comparable to that of FeSO4 when its price comes down from the current cost of $139/kg to $36/kg, the cost of FeSO4, which is likely considering the pace of nano-material technology development. Together, these results demonstrate the remarkable potential of nano-iron fertilizers in mitigating the escalating fertilizer cost and improving the environmental outcomes of peanut, as well as potentially other crops grown in wet season.

Investigation of the effect of diethylene triamine pentaacetic acid chelating agent as an enhanced oil recovery fluid on wettability alteration of sandstone rocks

This study used the diethylene triamine pentaacetic acid (DTPA)-seawater (SW) system to modify the sandstone rock wettability and enhance oil recovery. The investigation involved conducting wettability measurement, Zeta potential measurement, and spontaneous imbibition experiment. The introduction of 5% DTPA-SW solution resulted in a significant decrease in the rock-oil contact angle from 143° to 23°, along with a reduction in the Zeta potential from −2.29 mV to −13.06 mV, thereby altering the rock surface charge and shifting its wettability from an oil-wet state to a strongly water-wet state. The presence or absence of potential determining ions (Ca2+, Mg2+, SO42−) in the solution did not impact the effectiveness of DTPA in changing the rock wettability. However, by tripling the concentration of these ions in the solution, the performance of 5% DTPA-SW solution in changing wettability was impaired. Additionally, spontaneous imbibition tests demonstrated that the 5% DTPA-SW solution led to an increase in oil recovery up to 39.6%. Thus, the optimum mass fraction of DTPA for changing sandstone wettability was determined to be 5%.

The effect of ion shape and concentration on tunable wetting of water droplets on graphite surfaces

We study the wetting behaviors of aqueous NaCl and NaNO3 electrolyte nano-droplets on graphite surfaces by molecular dynamics simulations. Despite the same ion charge and similar Stokes radii, while the contact angle increases with NaCl concentration up to 3 M, the contact angle decreases with NaNO3 concentration up to 3 M. We show that while the liquid/vapor surface tension increases with both NaCl and NaNO3 concentrations, the solid/liquid interfacial tension varies with NaCl and NaNO3 concentrations oppositely. The Cl− ions are depleted from the first dense water layer at the graphite/water interface, leading to an increasing interfacial tension and an increasing contact angle with ion concentration. Beyond 3 M NaCl, the ionic double layer at the interface counteracts the depletion of ions at the immediate graphite/water interface. Therefore, the contact angle saturates beyond around 3 M NaCl. By contrast, the planar NO3− ions are adsorbed in the dense water layer at the immediate graphite/water interfaces, conform to the interface, and form excessive hydrogen bonds with water at the interface. Consequently, the interfacial tension is decreased with increasing NaNO3 concentrations, leading to a decreasing contact angle up to around 3 M NaNO3. At NaNO3 concentrations beyond 3 M, the interfacial tension no longer decreases, likely due to the saturation of NO3− in the dense region; therefore, the contact angle slightly increases with NaNO3 concentration due to the increasing liquid/vapor surface tension. Our research sheds light on the mechanisms of the effect of ion shape and concentration on droplet wetting on solids.

Superhydrophobic sponge with nanoneedle-like surface for efficiently separating immiscible and emulsified oil-water mixtures

To increase the collision probability between emulsified droplets and sponge surface for more efficient separation of emulsions, a durable superhydrophobic melamine sponge (MS) with nanoneedle-like surface was prepared through a simple and inexpensive route in this work. The fabrication processes included the formation of ZnO nanoneedles on MS surface via a hydrothermal method, followed by coating with polybenzoxazine based bisphenol A and dodecylamine (PB-D). As excepted, the resulting superhydrophobic sponge (PB-D/ZnO/MS) could effectively separate various surfactant-stabilized water-in-oil and oil-in-water emulsions, with a high permeation flux of up to 14,050 L m−2 h−1 and separation efficiency above 98.5 %, driven solely by gravity due to its nanoneedle-like surface. Moreover, PB-D/ZnO/MS also displayed outstanding absorption capacities for various oils and organic solvents (57.4–123.0 g/g) as well as prominent reusability, enduring 30 cycles of repeated absorption-squeezing without any evident decrease in water contact angle and absorption capacity (maintaining 90.9–96.6 % of initial value). In addition, the superhydrophobicity of PB-D/ZnO/MS remained almost unchanged after being immersed in strong acidic, alkaline and salty solutions for 48 h. Furthermore, PB-D/ZnO/MS not only showed outstanding flame retardancy but also remained rapid oil absorption rate under combustion conditions. Thus, the obtained superhydrophobic MS is a promising candidate for practical oil/water separation.

A strategy to alleviate membrane fouling by optimizing the structure of the cake layer formed by flocs deposited directly on the membrane in the ultrafiltration process through coagulation and nanoscale Fe3O4/Fe3O4@SiO2 load

Membrane fouling has always been a problem hindering the practicability of ultrafiltration. Direct regulation of the structure of the cake layer formed by rapid deposition of flocs as a “secondary barrier” in the in-line coagulation ultrafiltration (C-UF) process has acquired importance as a research topic in comparison to membrane modification and standard coagulation ultrafiltration. In this study, membrane fouling was controlled in the C-UF process via coagulation/nano-scale Fe3O4 load (C/FL-UF) and coagulation/nano-scale Fe3O4@SiO2 load (C/FSL-UF). The promotion effects of these two processes (C/FL-UF and C/FSL-UF) on the reduction of membrane fouling and improvement of water quality were systematically studied employing simulated surface water. Floc characteristics, XDLVO theory, and the Hermia model, etc were employed to explain the optimization of cake layer. For coagulation/Fe3O4 load, the floc size was large and loose, whereas, for coagulation/Fe3O4@SiO2 load with high recoverability., the floc size was slightly loose. The newly constructed cake layer had improved porosity, structural stability and capacity of water transport. Meanwhile, decrease of unit adhesion free energy and secondary minimum depth along with the substantial increase of energy barrier between the reconstructed cake layers and membranes or colloids explained the mechanism of reduced membrane fouling from the surface energetics. The gradual decrease of water contact angle and the optical images proved that the affinity of the cake layer was significantly reduced. Hermia model further validated the accuracy of this study in controlling membrane fouling by regulating the formation of the cake layer. Finally, the study concluded by analyzing the practicability and efficacy of the procedure to further elucidate the applicability of this research.

ZnO/PDA/Mesoporous Cellular Foam Functionalized Thin-Film Nanocomposite Membrane towards Enhanced Nanofiltration Performance.

Thin-film nanocomposite (TFN) membranes are the third-generation membranes being explored for nanofiltration applications. Incorporating nanofillers in the dense selective polyamide (PA) layer improves the permeability-selectivity trade-off. The mesoporous cellular foam composite Zn-PDA-MCF-5 was used as a hydrophilic filler in this study to prepare TFN membranes. Incorporating the nanomaterial onto the TFN-2 membrane resulted in a decrease in the water contact angle and suppression of the membrane surface roughness. The pure water permeability of 6.40 LMH bar-1 at the optimal loading ratio of 0.25 wt.% obtained was higher than the TFN-0 (4.20 LMH bar-1). The optimal TFN-2 demonstrated a high rejection of small-sized organics (>95% rejection for 2,4-dichlorophenol over five cycles) and salts-Na2SO4 (≈95%) > MgCl2 (≈88%) > NaCl (86%) through size sieving and Donnan exclusion mechanisms. Furthermore, the flux recovery ratio for TFN-2 increased from 78.9 to 94.2% when challenged with a model protein foulant (bovine serum albumin), indicating improved anti-fouling abilities. Overall, these findings provided a concrete step forward in fabricating TFN membranes that are highly suitable for wastewater treatment and desalination applications.

Point-of-care detection of Japanese encephalitis virus biomarker in clinical samples using a portable smartphone-enabled electrochemical "Sensit" device.

Japanese encephalitis (JE), a neglected tropical zoonotic disease prevalent in south-east Asian and western pacific countries, caused by the flavivirus JE virus (JEV), has a dearth of electrochemical point-of-care (PoC) diagnostic tools available to manage endemic breakouts. To overcome this, we have developed a screen-printed carbon electrode (SPCE) immunosensor for rapid PoC detection of JEV nonstructural 1 (NS1) antigen (Ag), found circulating in serum of infected individuals using a smartphone based portable "Sensit" device. The modification of SPCE surface with JEV NS1 antibody (Ab) was confirmed via observation of globular protein structures via scanning electron microscopy (SEM), increase in electrode surface hydrophilicity via contact angle measurement and decrease in current via differential pulse voltammetry (DPV). The fabrication and testing parameters were optimized based on highest current output obtained using DPV. The SPCE was tested for detection limit of target JEV NS1 Ag ranging from 1fM to 1μM, which was determined as 0.45 fM in spiked serum. The disposable immunosensor was also found to be highly specific in detecting JEV NS1 Ag over other flaviviral NS1 Ag. Finally, the modified SPCE was clinically validated by testing 62 clinical JEV samples using both a portable miniaturized electrochemical "Sensit" device coupled with a smartphone and a laboratory-based potentiostat. The results were corroborated with gold-standard RT-PCR and showed 96.77% accuracy, 96.15% sensitivity, and 97.22% specificity. Hence, this technique may further be developed into a one-step rapid diagnostic tool for JEV, especially in rural areas.

Hydrophobic-oleophilic surfaces based on chemical modification of nanoporous alumina

Hydrophobic/oleophilic nanoporous anodic alumina substrates were fabricated by two-step anodization method following of chemical modification with 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (FOTS). Surface morphology was characterized using a scanning electron microscopy. The influence of the topography and the pore size of the surface in the contact angle measurements with different solvents have been studied. The water repellence capacity of the nanoporous anodic alumina structure as fabricated depends on pore diameter but, there is a critical value of pore size beyond which the water contact angle decrease. After chemical modification of the surface, this effect is not observed. The porous topography of the material is not an advantage for the oleophibicity. The CA values for the non-porous surface using different solvents are lower than the structured surface.The results obtained in this study can be used to desire wettability properties. Modified NAA exhibit hydrophobicity and at the same time permeability for solvents with low surface tension.

Effect of Gamma Radiation on the Properties of Poly(Methyl Methacrylate)/Titanium Dioxide Nanocomposite Films

In this study, poly(methyl methacrylate)/titanium dioxide (PMMA/TiO2) nanocomposite films (NFs) were prepared by a solution casting method and afterward irradiated with gamma (γ)-rays at different doses. The structural and optical properties of the PMMA/TiO2NFs before and afterγ-irradiation at different doses were analyzed by X-ray diffraction (XRD) and ultraviolet-visible (UV-vis) spectroscopy, respectively. In addition, the impact ofγ-dose on the wetting properties of PMMA/TiO2was determined by measuring the water contact angle. The XRD patterns illustrated new sharp peaks after the incorporation of TiO2nanoparticles (NPs) into the PMMA matrix, which could be due to the interaction of TiO2with PMMA owing to the change in the crystallographic organization. Moreover, the degree of the disorder increases with increasingγ-dose. Optical property studies revealed that the optical gap-band energy of the PMMA/TiO2dropped to 3.92 eV at the highestγ-dose compared with pure PMMA, which was estimated to be 4.5 eV. A remarkable increase in the number of carbon atoms per cluster was observed with increasingγ-dose. The water contact angle was decreased with increasingγ-dose. The decrease in water contact angle is due to the formation of an oxidized layer and/or carbonaceous clusters on the surface of theγ-irradiated nanocomposite films. Therefore, it can be concluded that PMMA/TiO2NFs with controlled optical gap-band energy and controlled water contact angle can be prepared by theγ-irradiation technique to be used for the fabrication of optoelectronic products.

Effect of the Addition of Polyacrylic Acid of Different Molecular Weights to Coagulation Bath on the Structure and Performance of Polysulfone Ultrafiltration Membranes

Membrane fouling is a serious issue in membrane technology which cannot be completely avoided but can be diminished. The perspective technique of membrane modification is the introduction of hydrophilic polymers or polyelectrolytes into the coagulation bath during membrane preparation via non-solvent-induced phase separation. The influence of polyacrylic acid (PAA) molecular weight (100,000, 250,000 and 450,000 g·mol-1) added to the aqueous coagulation bath (0.4-2.0 wt.%) on the polysulfone membrane structure, surface roughness, water contact angle and zeta potential of the selective layer, as well as the separation and antifouling performance, was systematically studied. It was found that membranes obtained via the addition of PAA with higher molecular weight feature smaller pore size and porosity, extremely high hydrophilicity and higher values of negative charge of membrane surface. It was shown that the increase in PAA concentration from 0.4 wt.% to 2.0 wt.% for all studied PAA molecular weights yielded a substantial decrease in water contact angle compared with the reference membrane (65 ± 2°) (from 27 ± 2° to 17 ± 2° for PAA with Mn = 100,000 g·mol-1; from 25 ± 2° to 16 ± 2° for PAA with Mn = 250,000 g·mol-1; and from 19 ± 2° to 10 ± 2° for PAA with Mn = 450,000 g·mol-1). An increase in PAA molecular weight from 100,000 to 450,000 g·mol-1 led to a decrease in membrane permeability, an increase in rejection and tailoring excellent antifouling performance in the ultrafiltration of humic acid solutions. The fouling recovery ratio increased from 73% for the reference membrane up to 91%, 100% and 136% for membranes modified with the addition to the coagulation bath of 1.5 wt.% of PAA with molecular weights of 100,000 g·mol-1, 250,000 g·mol-1 and 450,000 g·mol-1, respectively. Overall, the addition of PAA of different molecular weights to the coagulation bath is an efficient tool to adjust membrane separation and antifouling properties for different separation tasks.

Minimal Impacts of Microplastics on Soil Physical Properties under Environmentally Relevant Concentrations.

Agricultural soils are a major reservoir of microplastics, and concerns have arisen about the impacts of microplastics on soil properties and functioning. Here, we measured the physical properties of a silt loam in response to the incorporation of polyester fibers and polypropylene granules over a wide range of concentrations. We further elucidated the underlying mechanisms by determining the role of microplastic shape and the baseline effects from the amendment of soil particles. The incorporation of microplastics into soil tended to increase contact angle and saturated hydraulic conductivity and decrease bulk density and water holding capacity, but not affect aggregate stability. Polyester fibers affected soil physical properties more profoundly than polypropylene granules, due to the vastly different shape of fibers from that of soil particles. However, changes in soil properties were gradual, and significant changes did not occur until a high concentration of microplastics was reached (i.e., 0.5% w/w for polyester fibers and 2% w/w for polypropylene granules). Currently, microplastic concentrations in soils not heavily polluted with plastics are far below these concentrations, and results from this study suggest that microplastics at environmentally relevant concentrations have no significant effects on soil physical properties.

Complex evaporation kinetics of a volatile droplet of methanol

An experimental study is carried out to investigate the different stages of the evaporation phenomenon of a methanol drop that exhibits a complex behavior because of its high volatility. An optical technique is employed with top and side view cameras; it allows to follow the drop shape evolution and determine the geometric parameters: contact angle and base diameter from which the volume of the droplet is computed. The outcomes of this study show three distinct stages. First, the evaporation kinetics is very fast (33% of the droplet lifetime) where 85% of the volume evaporates with a nearly pinned contact line. It is followed by a short stage (12% of lifetime) where 8% of the volume evaporates. In this stage, the drop forms a thin liquid film followed by a motion of the contact line in which the drop retracts. The wetting surface deforms and loses its quasi-circular shape. Then, the wetting area shrinks drastically to form a smaller droplet with a higher contact angle. In the third stage (55% of lifetime), the 7% remaining drop volume evaporates with a low evaporation rate accompanied by a strong decrease of contact angle and a slight decline of wetting area until total evaporation.

Complex displacement behavior during foaming gas drainage in 2D microfluidic networks

Foam injection, which can significantly reduce gas mobility and improve sweep efficiency, has been used as an enhanced oil recovery (EOR) technique for decades. In this work, a mechanistic pore network model is proposed to simulate foam propagation in porous media. The model includes wettability through critical pressures for pore filling events and tracks the motion of gas–water interface during foam propagation process. It also allows a quantitative assessment of the thermodynamic and flow properties of foam, such as mobilization pressure gradient, invasion morphology, and foam texture evolution.Our results show that the inclusion of wettability impacts the evolution of the capillary pressure signal, and the mobilization pressure gradient. Both increasing foam texture and reducing contact angle provide a similar effect on the invasion morphology: a transition from the regime of capillary fingering to compact displacement as indicated by fractal dimension and finger width. The effect of disorder depends on its coupling with wettability and foam texture: increasing disorder decreases the pattern compactness; decreasing contact angle or increasing foam texture smooths the gas–water interface, hence increasing compactness, leading to small sensitivity of the emergent pattern to disorder. The comparison between simulations and experiments shows that the proposed model is able to capture the relevant pore-level events that characterize the foaming gas drainage process in a microfluidic device filled with vertical posts and is reliable to be used for providing information needed for parameters in mechanistic foam simulators that are not accessible in conventional laboratory experiments.

Characterization of the Temperature Profile near Contact Lines of an Evaporating Sessile Drop

Evaporation of a sessile drop is ubiquitous in nature and has many industrial applications. Despite extensive studies over recent decades, a critical issue, i.e., how temperature varies near contact lines, remains elusive. In this work, we report to date the first direct experimental measurement showing the microscopic temperature distribution near contact lines of an evaporating pinned sessile drop. Using a fluorescence-based thermometry, we find that the temperature at the free interface near contact lines varies drastically along the radial direction, engendering a concentric fringe pattern that evolves over the evaporation lifespan. The formation of such fringe patterns is attributed to a combined mechanism of locally enhanced evaporative cooling at the drop edge and the development of interfacial convective vortices due to Bénard-Marangoni instability. We also study the evaporation dynamics at different initial contact angles and find that the characteristics of this fringe pattern vary as the initial contact angle decreases. Our experimental investigation and theoretical analysis in this work reveal insights to the understanding of droplet evaporation dynamics in various heat transfer systems.

Branched Amphiphilic Polylactides as a Polymer Matrix Component for Biodegradable Implants.

The combination of biocompatibility, biodegradability, and high mechanical strength has provided a steady growth in interest in the synthesis and application of lactic acid-based polyesters for the creation of implants. On the other hand, the hydrophobicity of polylactide limits the possibilities of its use in biomedical fields. The ring-opening polymerization of L-lactide, catalyzed by tin (II) 2-ethylhexanoate in the presence of 2,2-bis(hydroxymethyl)propionic acid, and an ester of polyethylene glycol monomethyl ester and 2,2-bis(hydroxymethyl)propionic acid accompanied by the introduction of a pool of hydrophilic groups, that reduce the contact angle, were considered. The structures of the synthesized amphiphilic branched pegylated copolylactides were characterized by 1H NMR spectroscopy and gel permeation chromatography. The resulting amphiphilic copolylactides, with a narrow MWD (1.14-1.22) and molecular weight of 5000-13,000, were used to prepare interpolymer mixtures with PLLA. Already, with the introduction of 10 wt% branched pegylated copolylactides, PLLA-based films had reduced brittleness, hydrophilicity, with a water contact angle of 71.9-88.5°, and increased water absorption. An additional decrease in the water contact angle, of 66.1°, was achieved by filling the mixed polylactide films with 20 wt% hydroxyapatite, which also led to a moderate decrease in strength and ultimate tensile elongation. At the same time, the PLLA modification did not have a significant effect on the melting point and the glass transition temperature; however, the filling with hydroxyapatite increased the thermal stability.