Water-Repellent Galvanized Steel Surfaces Obtained by Sintering of Zinc Nanopowder.

Galvanized steel surfaces are widely used in industry as a solution to prevent corrosion of steel tools that operate in outdoor or corrosive and oxidative environments. These objects are coated with a zinc protective layer deposited by hot dip galvanization. Turning the surface of galvanized steel tools into superhydrophobic may lead to very useful functionalities, although it may be a difficult task, because the preservation of the thin zinc layer is a claim. We propose herein the use of a bottom-up approach based on sandblasting, followed by sintering of zinc nanoparticles on the galvanized steel substrate, which allowed us to produce a zinc-made hierarchical structure required for superhydrophobicity. These samples acquired a double-scale structure that led to superhydrophobicity when they were later hydrophobized with a thin fluoropolymer layer. We found that sandblasting might be useful but not mandatory, unlike the sintering process, which was essential to reach superhydrophobicity. We found that, under certain experimental conditions, the surfaces showed outstanding water-repellent properties. We observed that the sandblasting on galvanized steel caused more damage than the sintering process. Sintering of low-melting-point metal nanoparticles was revealed as a promising strategy to fabricate functional metallic surfaces.

A simple strategy to improve the interfacial activity of true Janus gold nanoparticles: a shorter hydrophilic capping ligand.

Janus gold nanoparticles (JPs) of ∼4 nm-diameter half functionalized with 1-hexanethiol as a hydrophobic capping ligand exhibit significantly higher interfacial activity, reproducibility and rheological response when the other half is functionalized with 1,2-mercaptopropanediol (JPs-MPD) than with 2-(2-mercaptoethoxy)ethanol (JPs-MEE), both acting as hydrophilic capping ligands. The interfacial pressure measured by pendant drop tensiometry reaches 50 mN m(-1) and 35 mN m(-1) for the JPs-MPD at the water/air and water/decane interface, respectively. At the same area per particle, the JPs-MEE reveal significantly lower interfacial pressure: 15 mN m(-1) and 5 mN m(-1) at the water/air and water/decane interface, respectively. Interfacial dilatational rheology measurements also show an elastic shell behaviour at higher compression states for JPs-MPD while the JPs-MEE present near-zero elasticity. The enhanced interfacial activity of JPs-MPD is explained in terms of chemical and hydration differences between the MPD and MEE ligands, where MPD has a shorter hydrocarbon chain and twice as many hydroxyl terminal groups as MEE.

Impact of the collective diffusion of charged nanoparticles in the convective/capillary deposition directed by receding contact lines.

The motion of electrically charged particles under crowding conditions and subjected to evaporation-driven capillary flow might be ruled by collective diffusion. The concentration gradient developed inside an evaporating drop of colloidal suspension may reduce by diffusion the number of particles transported toward the contact line by convection. Unlike self-diffusion coefficient, the cooperative diffusion coefficient of interacting particles becomes more pronounced in crowded environments. In this work, we examined experimentally the role of the collective diffusion of charge-stabilized nanoparticles in colloidal patterning. To decouple the sustained evaporation from the contact line motion, we conducted evaporating menisci experiments with driven receding contact lines at low capillary number. This allowed us to explore convective assembly at fixed and low bulk concentration, which enabled to develop high concentration gradients. At fixed velocity of receding contact line, we explored a variety of substrate-particle systems where the particle-particle electrostatic interaction was changed (via p H) as well as the substrate receding contact angle and the relative humidity. We found that the particle deposition directed by receding contact lines may be controlled by the interplay between evaporative convection and collective diffusion, particularly at low particle concentration.

Particle Segregation at Contact Lines of Evaporating Colloidal Drops: Influence of the Substrate Wettability and Particle Charge-Mass Ratio.

Segregation of particles during capillary/convective self-assembly is interesting for self-stratification in colloidal deposits. In evaporating drops containing colloidal particles, the wettability properties of substrate and the sedimentation of particles can affect their accumulation at contact lines. In this work we studied the size segregation and discrimination of charged particles with different densities. We performed in-plane particle counting at evaporating triple lines by using fluorescence confocal microscopy. We studied separately substrates with very different wettability properties and particles with different charge-mass ratios at low ionic strength. We used binary colloidal suspensions to compare simultaneously the deposition of two different particles. The particle deposition rate strongly depends on the receding contact angle of the substrate. We further observed a singular behavior of charged polystyrene particles in binary mixtures under "salt-free" conditions explained by the "colloidal Brazil nut" effect.

Interfacial Activity and Contact Angle of Homogeneous, Functionalized, and Janus Nanoparticles at the Water/Decane Interface.

Surface heterogeneity affects the behavior of nanoparticles at liquid interfaces. To gain a deeper understanding on the details of these phenomena, we have measured the interfacial activity and contact angle at water/decane interfaces for three different types of nanoparticles: homogeneous poly(methyl methacrylate) (PMMA), silica functionalized with a capping ligand containing a methacrylate terminal group, and Ag-based Janus colloids with two capping ligands of different hydrophobicity. The interfacial activity was analyzed by pendant drop tensiometry, and the contact angle was measured directly by freeze-fracture shadow-casting cryo-scanning electron microscopy. The silver Janus nanoparticles presented the highest interfacial activity, compared to the silica nanoparticles and the homogeneous PMMA nanoparticles. Additionally, increasing the bulk concentration of the PMMA and silica nanoparticles up to 100-fold compared to the Janus nanoparticles led to silica particles forming fractal-like structures at the interface, contrary to the PMMA particles that did not show any spontaneous adsorption.

In-plane particle counting at contact lines of evaporating colloidal drops: effect of the particle electric charge.

Complete understanding of colloidal assembly is still a goal to be reached. In convective assembly deposition, the concentration gradients developed in evaporating drops or reservoirs are usually significant. However, collective diffusion of charge-stabilized particles has been barely explored. The balance between convective and diffusive flows may dictate the particle dynamics inside evaporating colloidal drops. In this work we performed in situ counting of fluorescent particles in the vicinity of the triple line of evaporating sessile drops by using confocal laser scanning microscopy. We used particles of different sizes, with different charge response over the pH scale and we focused on charged and nearly uncharged particles. Two substrates with different receding contact angles were used. Binary colloidal mixtures were used to illustrate simultaneously the accumulation of particles with two different charge states at the triple line. The deposition rate close to the triple line was different depending on the electric state of the particle, regardless of the substrate used.

Transition from stripe-like patterns to a particulate film using driven evaporating menisci.

Better control of colloidal assembly by convective deposition is particularly helpful in particle templating. However, knowledge of the different factors that can alter colloidal patterning mechanisms is still insufficient. Deposit morphology is strongly ruled by contact line dynamics, but the wettability properties of the substrate can alter it drastically. In this work, we experimentally examined the roles of substrate contact angle hysteresis and receding contact angle using driven evaporating menisci similar to the dip-coating technique but at a low capillary number. We used smooth substrates with very different wettability properties and nanoparticles of different sizes. For fixed withdrawal velocity, evaporation conditions, and nanoparticle concentration, we analyzed the morphology of the deposits formed on each substrate. A gradual transition from stripe-like patterns to a film was observed as the contact angle hysteresis and receding contact angle were lowered.

Comparison of the interfacial activity between homogeneous and Janus gold nanoparticles by pendant drop tensiometry.

The interfacial activity of 3.5 nm homogeneous (HPs) and amphiphilic Janus gold nanoparticles (JPs) was characterized by pendant drop tensiometry for water/air and water/decane interfaces. This technique requires a smaller quantity of nanoparticles than the traditional Langmuir balance technique. The direct deposition at the interface of the nanoparticles dispersed in a spreading solvent also requires smaller quantities of sample than does adsorption from the bulk. From the growing and shrinking of the pendant drops, the interfacial activity of the nanoparticles can be evaluated and compared within a wide range of area per particle. In this work, the JPs exhibited a higher interfacial activity than did the HPs in all cases. A hard disk model fits the piecewise compression isotherm of the HPs, yet this model underestimates the interactions between the JPs adsorbed at the interface.

Improved digestibility of ß-lactoglobulin by pulsed light processing: a dilatational and shear study.

Modifying the protein conformation appears to improve the digestibility of proteins in the battle against allergies. However, it is important not to lose the protein functionality in the process. Light pulse technology has been recently tested as an efficient non-thermal process which alters the conformation of proteins while improving their functionality as stabilizers. Also, in order to rationally design emulsion based food products with specific digestion profiles, we need to understand how interfacial composition influences the digestion of coated interfaces. This study has been designed to investigate the effects of pulsed light (PL) treatment on the gastrointestinal digestion of protein covered interfaces. We have used a combination of dilatational and shear rheology which highlights inter and intra-molecular interactions providing new molecular details on protein digestibility. The in vitro digestion model analyses sequentially pepsinolysis, trypsinolysis and lipolysis of ß-lactoglobulin (BLG) and pulsed light treated ß-lactoglobulin (PL-BLG). The results show that the PL-treatment seems to facilitate digestibility of the protein network, especially regarding trypsinolysis. Firstly, PL treatment just barely enhances the enzymatic degradation of BLG by pepsin, which dilutes and weakens the interfacial layer, due to increased hydrophobicity of the protein owing to PL-treatment. Secondly, PL treatment importantly modifies the susceptibility of BLG to trypsin hydrolysis. While it dilutes the interfacial layer in all cases, it strengthens the BLG and weakens the PL-BLG interfacial layer. Finally, this weakening appears to slightly facilitate lipolysis as evidenced by the results obtained upon addition of lipase and bile salts (BS). This research allows identification of the interfacial mechanisms affecting enzymatic hydrolysis of proteins and lipolysis, which demonstrates an improved digestibility of PL-BLG. The fact that PL treatment did not affect the functionality of the protein makes it a valuable alternative for tailoring novel food matrices with improved functional properties such as decreased digestibility, controlled energy intake and low allergenicity.

Using AFM to probe the complexation of DNA with anionic lipids mediated by Ca(2+): the role of surface pressure.

Complexation of DNA with lipids is currently being developed as an alternative to classical vectors based on viruses. Most of the research to date focuses on cationic lipids owing to their spontaneous complexation with DNA. Nonetheless, recent investigations have revealed that cationic lipids induce a large number of adverse effects on DNA delivery. Precisely, the lower cytotoxicity of anionic lipids accounts for their use as a promising alternative. However, the complexation of DNA with anionic lipids (mediated by cations) is still in early stages and is not yet well understood. In order to explore the molecular mechanisms underlying the complexation of anionic lipids and DNA we proposed a combined methodology based on the surface pressure-area isotherms, Gibbs elasticity and Atomic Force Microscopy (AFM). These techniques allow elucidation of the role of the surface pressure in the complexation and visualization of the interfacial aggregates for the first time. We demonstrate that the DNA complexes with negatively charged model monolayers (DPPC/DPPS 4 : 1) only in the presence of Ca(2+), but is expelled at very high surface pressures. Also, according to the Gibbs elasticity plot, the complexation of lipids and DNA implies a whole fluidisation of the monolayer and a completely different phase transition map in the presence of DNA and Ca(2+). AFM imaging allows identification for the first time of specific morphologies associated with different packing densities. At low surface coverage, a branched net like structure is observed whereas at high surface pressure fibers formed of interfacial aggregates appear. In summary, Ca(2+) mediates the interaction between DNA and negatively charged lipids and also the conformation of the ternary system depends on the surface pressure. Such observations are important new generic features of the interaction between DNA and anionic lipids.

Understanding the petal effect: Wetting properties and surface structure of natural rose petals and rose petal-derived surfaces.

The petal effect is identified as a non-wetting state with high drop adhesion. The wetting behavior of petal surfaces is attributed to the papillose structure of their epidermis, which leads to a Cassie-Baxter regime combined with strong pinning sites. Under this scenario, sessile drops are pearl shaped and, unlike lotus-like surfaces, firmly attached to the surface. Petal surfaces are used as inspiration for the fabrication of functional parahydrophobic surfaces such as antibacterial or water-harvesting surfaces. In this work, two types of rose petals were replicated by using a templating technique based in Polydimethylsiloxane (PDMS) nanocasting. The topographic structure, the condensation mechanism under saturated environments and the wetting properties of the natural rose petal and their negative and positive replicas were analyzed. Finally, we performed prospective ice adhesion studies to elucidate whether petal-like surfaces may be used as deicing solutions.

Effect of hygroscopic expansion of resin filling on interfacial gap and sealing: a confocal microscopy study.

PURPOSE: To measure dimensional changes due to hygroscopic expansion and their effect on interface gaps and sealing in four light-cured restorative materials using an original confocal microscopic methodology. MATERIALS AND METHODS: The materials tested were an ormocer (Admira [Voco]), a compomer (Dyract AP [Dentsply]), a hybrid composite (Spectrum [Dentsply]), and a nanohybrid composite (Esthet·X [Dentsply]). Water sorption was evaluated by weighing material disks after immersion. Hygroscopic expansion was measured from volumetric variations of material fillings in cylindrical cavities in dentin slices; the interfacial gap size was obtained from the same cavities using a novel confocal microscopic method. Microleakage was evaluated in cavities prepared in extracted third molars. Measurements followed water immersion for 24 h, 1 week, 4 weeks, and 8 weeks. A factorial ANOVA, the Student Newman Keuls test for post-hoc comparisons, the Student's t-test, and the Pearson test were used for the statistical analysis (p < 0.05). RESULTS: Positive correlations were found among water sorption, hygroscopic expansion, and sealing. Hygroscopic expansion reduced post-polymerization interfacial gaps and improved cavity sealing. Dyract AP and Admira showed the highest water sorption, hygroscopic expansion, and gap size reduction. CONCLUSIONS: 1. The proposed methodology is valid to measure hygroscopic expansion and interfacial gap. 2. Water sorption and hygroscopic expansion are positively correlated, and hygroscopic expansion, gap size, and sealing are also positively correlated. 3. The adhesive influences the interfacial gap size and its variation after hygroscopic expansion. 4. Hygroscopic expansion reduces the interfacial gaps generated by polymerization shrinkage and improves cavity sealing.

Determining efficacy of monitoring devices on ceramic bond to resin composite.

OBJECTIVES: This paper aims to assess the effectiveness of 3D nanoroughness and 2D microroughness evaluations, by their correlation with contact angle measurements and shear bond strength test, in order to evaluate the effect of two different acids conditioning on the bonding efficacy of a leucite-based glass-ceramic to a composite resin. STUDY DESIGN: Ceramic (IPS Empress) blocks were treated as follows: 1) no treatment, 2) 37% phosphoric acid (H3PO4), 15 s, 3) 9% hydrofluoric acid (HF), 5 min. Micro- and nano-roughness were assessed with a profilometer and by means of an atomic force microscopy (AFM). Water contact angle (CA) measurements were determined to assess wettability of the ceramic surfaces with the asixymetric drop shape analysis contact diameter technique. Shear bond strength (SBS) was tested to a resin composite (Z100) with three different adhesive systems (Scotchbond Multipurpose Plus, Clearfil New Bond, ProBOND). Scanning electron microscopy (SEM) images were performed. RESULTS: nanoroughness values assesed in 50x50 µm areas showed differences between groups did not found by profilometer. HF treatment created the nano- roughest surfaces and the smallest CA (p<0.05), producing the highest SBS to the composite resin with all tested adhesive systems (p<0.05). No differences existed between the SBS produced by the adhesive systems evaluated with any of the surface treatments tested. CONCLUSIONS: Nano-roughness obtained in a 50x50 µm scan size areas was the most reliable data to evaluate the topographical changes produced by the different acid treatments on ceramic surfaces.

In vitro Digestion of Emulsions in a Single Droplet via Multi Subphase Exchange of Simulated Gastrointestinal Fluids.

Emulsions are currently being used to encapsulate and deliver nutrients and drugs to tackle different gastrointestinal conditions such as obesity, nutrient fortification, food allergies, and digestive diseases. The ability of an emulsion to provide the desired functionality, namely, reaching a specific site within the gastrointestinal tract, inhibiting/retarding lipolysis, or facilitating digestibility, ultimately depends on its susceptibility to enzymatic degradation in the gastrointestinal tract. In oil-in-water emulsions, lipid droplets are surrounded by interfacial layers, where the emulsifiers stabilize the emulsion and protect the encapsulated compound. Achieving a tailored digestibility of emulsions depends on their initial composition but also requires monitoring the evolution of those interfacial layers as they are subjected to different phases of gastrointestinal digestion. A pendant drop surface film balance implemented with a multi-subphase exchange allows for simulating the in vitro digestion of emulsions in a single aqueous droplet immersed in oil by applying a customized static digestion model. The transit through the gastrointestinal tract is mimicked by the subphase exchange of the original droplet bulk solution with artificial media, mimicking the physiological conditions of each compartment/step of the gastrointestinal tract. The dynamic evolution of the interfacial tension is recorded in situ throughout the whole simulated gastrointestinal digestion. The mechanical properties of digested interfaces, such as interfacial dilatational elasticity and viscosity, are measured after each digestion phase (oral, gastric, small intestine). The composition of each digestive media can be tuned to account for the particularities of the digestive conditions, including gastrointestinal pathologies and infant digestive media. The specific interfacial mechanisms affecting proteolysis and lipolysis are identified, providing tools to modulate digestion by the interfacial engineering of emulsions. The obtained results can be manipulated for designing novel food matrices with tailored functionalities such as low allergenicity, controlled energy intake, and decreased digestibility.

Mechanical Durability of Low Ice Adhesion Polydimethylsiloxane Surfaces.

Elastomeric surfaces and oil-infused elastic surfaces reveal low ice adhesion, in part because of their deformability. However, these soft surfaces might jeopardize their mechanical durability. In this work, we analyzed the mechanical durability of elastic polydimethylsiloxane (PDMS) surfaces with different balances between elasticity and deicing performances. The durability was studied in terms of shear/tensile ice adhesion strength before and after different wear tests. These tests consisted of abrasion/erosion cycles using standard procedures aimed to reproduce different environmental wearing agents. The main objective is to evaluate if our PDMS surfaces can become long-lasting solutions for ice removal in real conditions. We found that our elastic surfaces show excellent durability. After the wear tests, the ice adhesion strength values remained low or even unaltered. Although the oil-infused PDMS surface was the softest one, it presented considerable durability and excellent low ice adhesion, being a promising solution.

Ice adhesion of PDMS surfaces with balanced elastic and water-repellent properties.

HYPOTHESIS: Ice adhesion to rigid materials is reduced with low energy surfaces of high receding contact angles. However, their adhesion strength values are above the threshold value to be considered as icephobic materials. Surface deformability is a promising route to further reduce ice adhesion. EXPERIMENTS: In this work, we prepared elastomer surfaces with a wide range of elastic moduli and hydrophobicity degree and we measured their ice adhesion strength. Moreover, we also explored the deicing performance of oil-infused elastomeric surfaces. The ice adhesion was characterized by two detachment modes: tensile and shear. FINDINGS: The variety of elastomeric surfaces allowed us to simultaneously analyze the ice adhesion dependence with deformability and contact angle hysteresis. We found that the impact of these properties depends on the detachment mode, being deformability more important in shear mode and hydrophobicity more relevant in tensile mode. In addition, oil infusion further reduces ice adhesion due to the interfacial slippage. From an optimal balance between deformability and hydrophobicity, we were able to identify surfaces with super-low ice adhesion.

Contact line relaxation of sessile drops on PDMS surfaces: A methodological perspective.

HYPOTHESIS: Characterization of contact angle hysteresis on soft surfaces is sensitive to the measurement protocol and might present adventitious time-dependencies. Contact line dynamics on solid surfaces is altered by the surface chemistry, surface roughness and/or surface elasticity. We observed a "slow" spontaneous relaxation of static water sessile drops placed on elastic surfaces. This unexpected drop motion reveals unresolved equilibrium configurations that may affect the observed values of contact angle hysteresis. Drop relaxation on deformable surfaces is partially governed by a viscoelastic dissipation located at the contact line. EXPERIMENTS: In this work, we studied the natural relaxation of water drops formed on several smooth PDMS surfaces with different elastic moduli. We monitored in time the contact angle and contact radius of each drop. For varying the initial contact angle, we used the growing-shrinking drop method. FINDINGS: We postulate that the so-called "braking effect", produced by the surface deformability, affects the contact line velocity and in consequence, the contact angle measurements. We conclude that the wetting properties of elastic surfaces should be properly examined with reliable values of contact angle measured after drop relaxation.

Applications of serum albumins in delivery systems: Differences in interfacial behaviour and interacting abilities with polysaccharides.

One of the major applications of Serum Albumins is their use as delivery systems for lipophilic compounds in biomedicine. Their biomedical application is based on the similarity with Human Serum Albumin (HSA), as a fully biocompatible protein. In general, Bovine Serum Albumin (BSA) is treated as comparable to its human homologue and used as a model protein for fundamental studies since it is available in high amounts and well understood. This protein can act as a carrier for lipophilic compounds or as protective shell in an emulsion-based vehicle. Polysaccharides are generally included in these formulations in order to increase the stability and/or applicability of the carrier. In this review, the main biomedical applications of Albumins as drug delivery systems are first presented. Secondly, the differences between BSA and HSA are highlighted, exploring the similarities and differences between these proteins and their interaction with polysaccharides, both in solution and adsorbed at interfaces. Finally, the use of Albumins as emulsifiers for emulsion-based delivery systems, concretely as Liquid Lipid Nanocapsules (LLNs), is revised and discussed in terms of the differences encountered in the molecular structure and in the interfacial properties. The specific case of Hyaluronic Acid is considered as a promising additive with important applications in biomedicine. The literature works are thoroughly discussed highlighting similarities and differences between BSA and HSA and their interaction with polysaccharides encountered at different structural levels, hence providing routes to control the optimal design of delivery systems.

Effect of Hyaluronic Acid and Pluronic-F68 on the Surface Properties of Foam as a Delivery System for Polidocanol in Sclerotherapy.

The use of foams to deliver bioactive agents and drugs is increasing in pharmaceutics. One example is the use of foam as a delivery system for polidocanol (POL) in sclerotherapy, with the addition of bioactive compounds to improve the delivery system being a current subject of study. This work shows the influence of two bioactive additives on the structure and stability of POL foam: hyaluronic acid (HA) and Pluronic-F68 (F68). HA is a natural non-surface-active biopolymer present in the extracellular matrix while F68 is a surface-active poloxamer that is biocompatible with plasma-derived fluids. Both additives increase the bulk viscosity of the sample, improving foam stability. However, HA doubled and F68 quadruplicated the foam half lifetime of POL. HA reduced the size and polydispersity of the bubble size distribution and increased the surface elasticity with respect to POL. Both facts have a positive impact in terms of foam stability. F68 also altered bubble structure and increased surface elasticity, again contributing to the enhancement of foam stability. The surface characterization of these systems is important, as in foam sclerotherapy it is crucial to assure the presence of POL at the surface of the bubbles in order to deliver the sclerosant agent in the target vein.

Wetting transitions on rough surfaces revealed with captive bubble experiments. The role of surface energy.

HYPOTHESIS: Wettability of solid surfaces is mostly probed with sessile drops rather than bubbles because this method is readily followed out. This recurrent use may lead to a misleading connection of certain phenomena to the hydrophobicity/hydrophilicity of materials. For instance, the Cassie-Baxter regime and the wicking effect are generally associated only to hydrophobic and hydrophilic surfaces, respectively. However, the same phenomenology should be observed when air bubbles (underwater conditions) in contact with solid surfaces are used instead. In particular, one might expect that rough-hydrophilic surfaces become superaerophobic due to the appearance of a hybrid dewetting regime, like the Cassie-Baxter regime described for rough-hydrophobic surfaces. Otherwise, rough-hydrophobic surfaces might become superaerophilic due to air-wicking. EXPERIMENTS: To elucidate this issue, in this work, we analyzed the wettability of surfaces with very different intrinsic contact angle and roughness degree. The analysis was performed with both Sessile Drop and Captive Bubble methods. FINDINGS: Our results with captive bubbles for rough-hydrophilic surfaces revealed phenomena only explained by the occurrence of a transition from the Wenzel regime to an "inverse" Cassie-Baxter regime. In addition, our results with captive bubbles for rough-hydrophobic surfaces showed evidences of air percolation through the interconnected asperities. This effect reminds the wicking effect reproduced on rough-hydrophilic surfaces, responsible for superhydrophilicity.