Stable Multilayers Research Articles

Electrochemical insights into layered assemblies of silver nanoparticles, poly‐L‐lysine, and bovine serum albumin

AbstractThis study presents a comprehensive exploration of the electrochemical behavior of layer‐by‐layer assemblies comprising silver nanoparticles (AgNPs), poly‐l‐lysine (PLL), and bovine serum albumin (BSA) on gold surfaces. AgNPs were synthesized using the reduction of silver ions with the synergy of ascorbic acid and citrate in the presence of sodium chloride. The obtained silver nanoparticles were characterized using transmission electron microscopy, dynamic light scattering and UV‐Vis spectroscopy. A typical preparation produced AgNPs with a plasmon peak at 402 nm, a diameter of 27.5 nm and zeta potential of −37 mV. Employing a drop‐coating approach, we successfully achieved stable multilayers of AgNPs, PLL, and BSA. Cyclic voltammetry revealed well‐defined, bell‐shaped oxidation and reduction peaks of AgNPs within the multilayers, demonstrating complete conversion to AgCl and back to Ag. Notably, the stripping of AgNPs on a monolayer of PLL prepared at pH 4.00 resulted in the highest current intensity, contrasting with lower intensities observed for PLL monolayers prepared at pH 7.01 and pH 9.01. Despite the absence of a splitting reduction peak in the presence of biopolymer materials, a noteworthy observation emerged: the peak splitting exclusively occurred when PLL/AgNP layers, terminated with PLL, were exposed to BSA in the solution.

Nanomolecularly-induced Effects at Titania/Organo-Diphosphonate Interfaces for Stable Hybrid Multilayers with Emergent Properties.

Nanoscale hybrid inorganic-organic multilayers are attractive for accessing emergent phenomena and properties through superposition of nanomolecularly-induced interface effects for diverse applications. Here, we demonstrate the effects of interfacial molecular nanolayers (MNLs) of organo-diphosphonates on the growth and stability of titania nanolayers during the synthesis of titania/MNL multilayers by sequential atomic layer deposition and single-cycle molecular layer deposition. Interfacial organo-diphosphonate MNLs result in ∼20-40% slower growth of amorphous titania nanolayers and inhibit anatase nanocrystal formation from them when compared to amorphous titania grown without MNLs. Both these effects are more pronounced in multilayers with aliphatic backbone-MNLs and likely related to impurity incorporation and incomplete reduction of the titania precursor indicated by our spectroscopic analyses. In contrast, both MNLs result in two-fold higher titania nanolayer roughness, suggesting that roughening is primarily due to MNL bonding chemistry. Such MNL-induced effects on inorganic nanolayer growth rate, roughening, and stability are germane to realizing high-interface-fraction hybrid nanolaminate multilayers.

Low friction behaviors of self-assembled GO/CMWCNTs composite films on high-speed steel

To reduce the energy loss of high-speed steel (HSS) rolls during the rolling process, coatings with effective friction reduction qualities were studied. In this paper, the magnetic stirring was used to prepare the composites of graphene oxide and carboxylated multi-walled carbon nanotubes (GO/CMWCNTs) with various mass ratios. By using 3-(aminopropyl)triethoxysilane (APTES) as a transition layer on hydroxylated-treated HSS, Si-O and C-N bonds were formed to obtain the assembled GO/CMWCNTs films. The results of the friction tests with Al2O3 ceramic balls indicate that the assembled GO/CMWCNTs-2 (1:2) films have an optimum friction reduction effect with the coefficient of friction of about 0.06 (about 83% lower than bare steel). Analysis of the wear mark surface reveals that the reason for the low friction behaviors is the formation of GO/CMWCNTs lubricating films with more sp2 content at the friction interface. The lubricating mechanism of the self-assembly films is to produce a stable multilayer film stacking system with layers joined by covalent bonds.

On-Demand Transient Paper Substrate for Selective Disposability of Thin-Film Electronic Devices.

This study demonstrates a novel approach to creating a thin-film electronic device that offers selective or complete disposability only in on-demand conditions while maintaining stable operation reliability during everyday use. The approach involves a transient paper substrate, combined with phase change encapsulation and highly bendable planarization materials, achieved through a simple solution process. The substrate used in this study offers a smooth surface morphology that enables the creation of stable multilayers for thin-film electronic devices. It also exhibits superior waterproof properties, which allows the proof-of-concept organic light-emitting device to function even when submerged in water. Additionally, the substrate provides controlled surface roughness under repeated bending, demonstrating reliable folding stability for 1000 cycles at 10 mm of curvature. Furthermore, a specific component of the electronic device can be selectively made to malfunction through predetermined voltage input, and the entire device can be fully disposed of via Joule-heating-induced combustion.

Progress towards Stable and High-Performance Polyelectrolyte Multilayer Nanofiltration Membranes for Future Wastewater Treatment Applications

The increasing demand for nanofiltration processes in drinking water treatment, industrial separation and wastewater treatment processes has highlighted several shortcomings of current state-of-the-art thin film composite (TFC NF) membranes, including limitations in chemical resistance, fouling resistance and selectivity. Polyelectrolyte multilayer (PEM) membranes provide a viable, industrially applicable alternative, providing significant improvements in these limitations. Laboratory experiments using artificial feedwaters have demonstrated selectivity an order of magnitude higher than polyamide NF, significantly higher fouling resistance and excellent chemical resistance (e.g., 200,000 ppmh chlorine resistance and stability over the 0-14 pH range). This review provides a brief overview of the various parameters that can be modified during the layer-by-layer procedure to determine and fine-tune the properties of the resulting NF membrane. The different parameters that can be adjusted during the layer-by-layer process are presented, which are used to optimize the properties of the resulting nanofiltration membrane. Substantial progress in PEM membrane development is presented, particularly selectivity improvements, of which the most promising route seems to be asymmetric PEM NF membranes, offering a breakthrough in active layer thickness and organic/salt selectivity: an average of 98% micropollutant rejection coupled with a NaCl rejection below 15%. Advantages for wastewater treatment are highlighted, including high selectivity, fouling resistance, chemical stability and a wide range of cleaning methods. Additionally, disadvantages of the current PEM NF membranes are also outlined; while these may impede their use in some industrial wastewater applications, they are largely not restrictive. The effect of realistic feeds (wastewaters and challenging surface waters) on PEM NF membrane performance is also presented: pilot studies conducted for up to 12 months show stable rejection values and no significant irreversible fouling. We close our review by identifying research areas where further studies are needed to facilitate the adoption of this notable technology.

Engineering of Stable Cross-Linked Multilayers Based on Thermo-Responsive PNIPAM-Grafted-Chitosan/Heparin to Tailor Their Physiochemical Properties and Biocompatibility.

The thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) is ubiquitously applied in controlled drug release and tissue engineering. However, the lack of bioactivity of PNIPAM restricts its use in cell-containing systems being a thermo-responsive adhesive substratum with no regulating effect on cell growth and differentiation. In this study, integrating PNIPAM with chitosan into PNIPAM-grafted-chitosan (PNIPAM-Chi) allows a layer-by-layer assembly with bioactive heparin to fabricate PNIPAM-modified polyelectrolyte multilayers (PNIPAM-PEMs). Grafting PNIPAM chains of either 2 (LMW) or 10 kDa (HMW) on the chitosan backbone influences the cloud point (CP) temperature in the range from 31 to 33 °C. PNIPAM-Chi with either a higher molecular weight or a higher degree of substitution of PNIPAM chains exhibiting a significant increase in diameter above CP as ensured by dynamic light scattering is selected to fabricate PEM with heparin as a polyanion at pH 4. Little difference of layer growth is detected between the chosen PNIPAM-Chi used as polycations by surface plasmon resonance, while multilayers formed with HMW-0.02 are more hydrated and show striking swelling-and-shrinking abilities when studied with quartz crystal microbalance with dissipation monitoring. Subsequently, the multilayers are covalently cross-linked using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide to strengthen the stability of the systems under physiological conditions. Ellipsometry results confirm the layer integrity after exposure to the physiological buffer at pH 7.4 compared to those without cross-linking. Moreover, significantly higher adhesion and more spreading of C3H10T1/2 multipotent embryonic mouse fibroblasts on cross-linked PEMs, particularly with heparin terminal layers, are observed owing to the bioactivity of heparin. The slightly more hydrophobic surfaces of cross-linked PNIPAM-PEMs at 37 °C also increase cell attachment and growth. Thus, layer-by-layer constructed PNIPAM-PEM with cross-linking represents an interesting cell culture system that can be potentially employed for thermally uploading and controlled release of growth factors that further promotes tissue regeneration.

Effect of the Anchoring Layer and Transport Type on the Adsorption Kinetics of Lambda Carrageenan.

The kinetics of lambda carrageenan (λ-car) adsorption/desorption on/from anchoring layers under diffusion- and convection-controlled transport conditions were investigated. The eighth generation of poly(amidoamine) dendrimers and branched polyethyleneimine possessing different shapes and polydispersity indexes were used for anchoring layer formation. Dynamic light scattering, electrophoresis, streaming potential measurements, optical waveguide lightmode spectroscopy, and quartz crystal microbalance were applied to characterize the formation of mono- and bilayers. The unique combination of the employed techniques enabled detailed insights into the mechanism of the λ-car adsorption mainly controlled by electrostatic interactions. The results show that the macroion adsorption efficiency is strictly correlated with the value of the final zeta potentials of the anchoring layers, the transport type, and the initial bulk concentration of the macroions. The type of the macroion forming the anchoring layer had a minor impact on the kinetics of λ-car adsorption. Besides significance to basic science, the results presented in this paper can be used for the development of biocompatible and stable macroion multilayers of well-defined electrokinetic properties and structure.

15564 Going with the Flow: Engineering Vascularized Urothelial Flaps for Female-to-Male Phalloplasty in Transgender Patients

ABSTRACT IMPACT: This project uses rapid prototyping, 3D printing, and cell seeding to solve the most common post-operative complications that arise from the current methods of urethral elongation during phalloplasty. OBJECTIVES/GOALS: Post-op fistula and stricture formation occur in up to 50% of phalloplasty patients. These complications arise from the mismatch between skin and uroepithelium, or from scarring secondary to ischemia. Here we describe the fabrication of a novel vascularized urothelial flap for phalloplasty that contains discrete urothelial and vascular channels. METHODS/STUDY POPULATION: A custom designed 3D negative mold, with a urethral channel and a vascular inlet and outlet channel was prototyped in Adobe Fusion 360 and printed on a Prusa i3 MK3S printer in PLA. A 2mm diameter pluronic sacrificial macrofiber was used to connect the channels to form a vascular loop, and 1% type-I collagen was extruded over the mold. After solidifying, the scaffold was demolded and seeded with grade I urothelial carcinoma (SW780 cells, at 5-10 x 106 cells/mL) in the urethral channel, and adenovirus-infected E4 endothelial cells (at 3x106 cells/mL) in the vascular channel. The scaffolds were cultured up to 14 days and then fixed for histologic analysis. RESULTS/ANTICIPATED RESULTS: Collagen scaffolds were fabricated reliably using the custom 3D negative molds. After both seven and fourteen days of culture, the urothelial channel contained a robust, stable urothelial monolayer lining throughout the channel. By 14 days urothelial multilayer formation was seen, providing definitive evidence of a more mature urothelial layer. Grooves within the collagen allowed for nests of urothelial cells to develop, leading to increased multilayer formation. In addition, the vascular channels supported a healthy endothelial lining at both seven and fourteen days. There were no significant histological differences between constructs seeded with 5x106 urothelial cells/mL and 107 cells/mL. We anticipate that multilayer formation will increase with time, and that constructs will survive beyond 28 days. DISCUSSION/SIGNIFICANCE OF FINDINGS: We have developed a novel strategy to engineer vascularized urethral tissue. These constructs can be kept for at least 14 days and form stable monolayers and multilayers consistent with native urothelial architecture. Using 3D printing and autologous cell seeding promises to create patient-specific vascularized urethral flaps for phalloplasty.

Thermal stability of immiscible Cu-Ag/Fe triphase multilayers with triple junctions

Nanostructured metallic multilayers have attracted significant attention due to their high mechanical strength. However, they often have limited thermal stability at elevated temperatures. Multilayers with immiscible constituents also suffer from high temperature microstructure instability due to thermal grooving and subsequent layer pinch-off. Here we report the enhanced thermal stability of immiscible triphase Cu-Ag/Fe multilayer with triple junctions comparing to Cu/Fe multilayers. The immiscible Cu/Fe multilayers experienced drastic thermal grooving and rapid grain growth at 500°C, followed by the complete breakdown of layer structure and spheroidization at 600°C. In comparison, the layer structures of Cu-Ag/Fe triphase multilayers remain stable up to 600°C with insignificant grain coarsening. The grooving kinetics as well as the underlying mechanisms that lead to the excellent thermal stability of the triphase multilayers are discussed. This study provides a fresh perspective on designing thermally stable nanostructured multilayers for high temperature applications.

Hydrogel membranes made from crosslinked microgel multilayers with tunable density

Membranes with precisely adjustable properties are needed to master the separation challenges in modern biochemical processes. Composite membranes are composed of a conventional membrane and an adaptive coating. Adaptive polymers like polymer brushes or hydrogels have proven to be excellent candidates for this challenge. In the present work we envision the utilization of temperature responsive microgels as colloidal building blocks, forming an adaptive separation layer on top of a porous support. Until now, microgels are mainly used as a functional gating element, influencing the retention or permeability of conventional membranes. In the present study microgel assemblies should be used as the only selective layer. To overcome the repulsive forces between the microgel particles, we utilize the interparticle crosslinking within a microgel filter cake. We could show that the crosslinking leads to stable and responsive microgel multilayers with a temperature responsive retention performance based on charge repulsion and size exclusion. The developed methodology enables the control of the filter cake compression, which can be adjusted and preserved via crosslinking enabling full control over the thickness and density of the selective layer. While the resistance of the crosslinked microgel multilayer shows the classical temperature responsiveness and collapse into a low resistance state, the retention increases simultaneously, indicating that the crosslinked microgels behave like a macroscopic hydrogel.

On the long-term pH stability of polyelectrolyte multilayer nanofiltration membranes

Long-term pH stability is critical for nanofiltration membranes in many applications, e.g. dairy and mining industry. We present a systematic study on the long-term pH stability of four different polyelectrolyte multilayer (PEM) nanofiltration membranes. The stability was assessed by comparing their performance before and after exposure to up to 1 M HNO3 (~pH 0) and 1 M NaOH (~pH 14), in terms of pure water permeance (PWP), salt retention, and molecular weight cut-off (MWCO).Poly(diallyldimethylammonium chloride) (PDADMAC)/poly(styrenesulfonate) (PSS) nanofiltration membranes show excellent stability under extreme acidic and basic conditions for more than 2 months (10.7 L m−2h−1bar−1 PWP, 95.5% MgSO4 retention, 279 g mol−1 MWCO), attributed to the use of strong polyelectrolytes, of which the charge is unaffected by pH. Poly(allylamine hydrochloride) (PAH)/PSS membranes show stable performance when exposed to extreme acidic conditions (9.7 L m−2h−1bar−1 PWP, 97.5% MgSO4 retention, 249 g mol−1 MWCO). Under these conditions, PAH remains charged and therefore a stable multilayer is maintained. PDADMAC/poly(acrylic acid) (PAA) and PAH/PAA membranes are not stable at extreme pH conditions.These results highlight that PEM nanofiltration membranes, especially PDADMAC/PSS membranes, have tremendous potential for use at extreme pH conditions. Compared to most commercially available membranes they have superior long-term stability and very relevant performance.

A continuum study of ionic layer analysis for single species ion transport in coaxial carbon nanotubes

In this letter, we employ the Poisson-Nernst-Planck equation and the continuum molecular model to investigate the ionic layers formation in coaxial carbon nanotubes, which are crucial for understanding the ion transport in nanomaterials, as well as modern solar cells and batteries. Owing to the curvature of nanotubes and the strong ion-nanotubes interactions, our simulations show that stable ionic multi-layers can always be formed inside nanotubes under a wide range of external electric fields and operating temperatures. Approximate solutions have also been deduced to support our numerical results. Most importantly, our hybrid model enjoys rapid and efficient computational times and hence fluid flow, conductivity and VI curve can be extracted almost instantaneously, which opens up a new research direction for the ion transport in nanomaterials.

A monolithic artificial iconic memory based on highly stable perovskite-metal multilayers

Artificial iconic memories, also called photomemories, are new types of nonvolatile memory that can simultaneously detect and store light information in a monolithic device. Several approaches have been proposed to construct artificial iconic memories, such as three-terminal field effect transistors, which can achieve an effective control of the gate voltage and external light terminals. The drawbacks in constructing these memories involve complicated fabrication processes, and the resulting performance of, for example, perovskite transistor-type photomemories is limited by the low carrier mobilities and poor ambient stabilities, whereas architectures based on floating gate modulations entail strict interface engineering and poor device reliability. In this paper, we propose a novel monolithic artificial iconic memory with a multilayer architecture of indium tin oxide/perovskite/gold/perovskite/silver, which combines the memory and photodetector functionalities of perovskites in an integrated device. The bottom perovskite layer plays the role of a photodetector, modulating the voltage bias on the top perovskite layer that serves as a resistive switching memory. This multilayer perovskite device can store photo-sensing data in its resistive states, with a memory retention of 5 × 103 s and ambient stability longer than sixty days. As a prototype demonstration, a 7 × 7 artificial iconic memory array is constructed to detect and store data on light intensity distribution, enabling a nonvolatile imaging functionality. Our work provides a new platform for designing perovskite-based architectures with simultaneous light detection and data storage capabilities.

Functionalization of Polymeric Nanofilter Biointerface for Small Biomarker Sensing

Small biomolecules contained in body fluids are often recognized as indicators of diseases and health conditions. Therefore, the development of biosensors capable of recognizing significant biomarkers from body fluids such as blood, sweat, tears, and saliva, leads to early diagnosis and contribute to the realization of next-generation medical care. In this regard, we have recently developed the potentiometric biosensor based on the extended-gate field-effect transistor (EG-FET) for small-biomolecule recognition. The catalytically active extended-Au electrodes have the capability to detect various small biomolecules with high sensitivity on the basis of the surface electrochemical reaction. However, since the Au electrode may react with various electrochemically active biomolecules, it is necessary to limit the interfering biomolecules from approaching the Au surface in order to enhance target selectivity. Therefore, a suitable polymeric nanofilter was developed on the Au electrode where interfering biomolecules are prevented from penetrating through the nanofilter, and only the target biomolecules can access the Au sensing surface to generate an electrical signal.1,2 The polymeric nanofilter biointerface is composed of two layers. The first layer is an anchor layer directly grafted on the Au surface, which controls the density of the polymeric nanofilter to make enough space for only small biomolecules to penetrate through and prevent large-biomolecule interferences from approaching the Au sensing surface. Then, a polymeric filter layer as the second layer is precisely grafted from the surface of the anchor layer by atom transfer radical polymerization (ATRP). The filter layer selectively captures the small-biomolecule interferences outside the Debye’s length; therefore, the interfering small-biomolecules will not cause the change in Au surface potential. In our previous study, we designed and developed the polymeric nanofilter by using aryldiazonium reduction chemistry and boronate affinity. Aryldiazonium reduction chemistry enabled the grafting of chemically stable multilayer film on the Au surface, having an adequate density in order to suppress the penetration of large biomolecules. Phenylboronic acid was included in the polymeric filter layer to capture the model interfering small biomolecule, L-DOPA, via a reversible PBA/diol boronate affinity binding. Resultantly, the polymeric nanofilter-coated EG-FET biosensor specifically detected the model target biomolecule, L-cysteine. In this study, we designed and developed the second polymeric layer on the polymeric nanofilter to give an additional function. Although the space-controlled nanofilter suppresses the penetration of the large biomolecules, the non-specific adsorption can cause severe fouling of the nanofilter surface. Therefore, in order to improve the anti-fouling function of the nanofilter interface, poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC) was chosen as the second polymeric layer. PMPC is a bio-inspired polymer that has been widely used as a biocompatible, anti-fouling coating material. In order to investigate the anti-fouling function of pMPC coating, we firstly grafted the pMPC layer directly from the anchor layer surface via surface-initiated ATRP. Then, the response of pMPC-nanofilter coated EG-FET biosensor to human-serum albumin (HSA) was compared with the response of the control (unmodified) sensor. Resultantly, the pMPC-coated sensor suppressed the non-specific response up to 60% compared with the control sensor. Therefore, we verified the successful enhancement of the anti-fouling property on the nanofilter surface.Reference(1) Nishitani, S.; Sakata, T. ACS Appl. Mater. Interfaces 2019, 11 (5), 5561–5569.(2) Himori, S.; Nishitani, S.; Sakata, T. Langmuir 2019, 35 (10), 3701–3709.

Stable polymer/inorganic composite multilayers using covalent cross-linking assisted by a magnetic field

In this study, stable composite multilayers incorporating magnetic montmorillonite (MMT) and weak polyelectrolyte were prepared under the assistance of a magnetic field. We reported a facile method for fabrication of covalently cross-linked Layer-by-Layer (LbL) multilayers using a photosensitive cross-linking agent 4,4′-diazostilbene-2,2′-disulfonic acid disodium salt that carried double azido groups. The multilayers after cross-linking presented improved stability against extreme solution conditions (basic solution pH = 14), and over 78.15% of magnetic MMT remained on the substrate, in clear contrast with the non-cross-linked multilayers, for which less than 8% of the magnetic MMT remained. The results of UV–Vis spectroscopy and scanning electron microscopy (SEM) measurements supported the improvement in the stability of the multilayers. Moreover, the assistance of the external magnetic field improved the LbL assembly efficiency and the cross-linking step achieved the molecular retarded release. When gauze was used as the substrate, the mass loading under the magnetic field was approximately 0.976 mg/cm2, which was 4.2 times the amount deposited on gauze without an external magnetic field. After interfacial modification of gauze using LbL multilayers, the static contact angle transformed from hydrophobic (111.25°) to perfect hydrophilic. When we employed aspirin as the target drug, it took 23 h for the cross-linked multilayers to achieve saturated release, as opposed to 9 h for the non-cross-linked multilayers.

Versatile Layer-By-Layer Highly Stable Multilayer Films: Study of the Loading and Release of FITC-Labeled Short Peptide in the Drug Delivery Field.

A viable short FITC-peptide immobilization is the most essential step in the fabrication of multilayer films based on FITC-peptide. These functional multilayer films have potential applications in drug delivery, medical therapy, and so forth. These FITC-peptides films needed to be handled with a lot of care and precision due to their sensitive nature. In this study, a general immobilization method is reported for the purpose of stabilizing various kinds of peptides at the interfacial regions. Utilizing Mesoporous silica nanoparticles can help in the preservation of these FITC-peptides by embedding themselves into these covalently cross-linked multilayers. This basic outlook of the multilayer films is potent enough and could be reused as a positive substrate. The spatio-temporal retention property of peptides can be modulated by varying the number of capping layers. The release speed of guest molecules such as tyrosine within FITC-peptide or/and adamantane (Ad)-in short peptides could also be fine-tuned by the specific arrangements of the multilayers of mesoporous silica nanoparticles (MSNs) and hyaluronic acid- cyclodextrin (HA-CD) multilayer films.

Stable Multilayer Reflective Coatings for λ(HeI) = 58.4 nm for the KORTES Solar Telescope

Multilayer aluminum-based structures reflecting at λ(HeI) = 58.4 nm were studied. Spectral and angular dependences of the reflection coefficient of these coatings were determined using a laboratory reflectometer and at the ELETTRA and BESSY II synchrotrons. The optical characteristics of multilayer Ru/Al and Mo/Al mirrors with a protective MoSi2 layer were found to be stable: the absolute change in the reflection coefficient within 18 months of storage in air was no larger than 1.5%. The peak near-normal reflection coefficient for Mo/Al mirrors at 58.4 nm was R = 26.1% with FWHM Δλ0.5 = 10 nm of the reflection curve.

Modeling of fouling in cross‐flow microfiltration of suspensions

Cross‐flow filtration of fine suspensions through microsieves occurs in microprocessing. The interaction of particles with surfaces in microenvironments has been extensively studied, but predominantly in monolayers and not with an eye to microfiltration. Here, we introduce a microfiltration model that pertains to particles that might be seen as fine in a macroscopic environment, but are large enough to intrude significantly into the shear layer of a microchannel. Thus, particle accumulation upon the sieve couples the steady‐state filtrate flux and the suspension flow through the microchannel that feeds the sieve. We envision and create a stable, stationary multilayer of particles whose thickness is shear‐limited and we identify and verify the structure and parameters that limit steady filtration in this environment. At first, a packed bed of particles forms, growing into and regulated by the micro channel's shear flow. A critical shear stress is shown to determine the thickness of the bed, seen as a stationary and stable multilayer of particles through which filtration may occur. As the bed thickens, at the expense of channel area for suspension flow, surface shear stress increases until no further particle adherence is possible. We built a simple example using hard noninteracting polymer microspheres and conducted cross‐flow filtration experiments over Aquamarijn™ microsieves (uniform pore size of 0.8 μm). We observed a steady cake‐layer thickness and because of the simple geometry afforded by uniform spheres, we could approximate the force balance, cake resistance, and filtration rate from first principles. The good fit of our data to the proposed mechanism lays a firm basis for the semiquantitative analysis of the behavior of more complex suspensions. © 2018 American Institute of Chemical Engineers AIChE J, 65: 207–213, 2019

Thickness-dependent structural characteristics for a sputtering-deposited chromium monolayer and Cr/C and Cr/Sc multilayers.

The interior structure, morphology and ligand surrounding of a sputtering-deposited chromium monolayer and Cr/C and Cr/Sc multilayers are determined by various hard X-ray techniques in order to reveal the growth characteristics of Cr-based thin films. A Cr monolayer presents a three-stage growth mode with sudden changes occurring at a layer thickness of ∼2 nm and beyond 6 nm. Cr-based multilayers are proven to have denser structures due to interfacial diffusion and layer growth mode. Cr/C and Cr/Sc multilayers have different interfacial widths resulting from asymmetry, degree of crystallinity and thermal stability. Cr/Sc multilayers present similar ligand surroundings to Cr foil, whereas Cr/C multilayers are similar to Cr monolayers. The aim of this study is to help understand the structural evolution regulation versus layer thickness and to improve the deposition technology of Cr-based thin films, in particular for obtaining stable Cr-based multilayers with ultra-short periods.

Combined Experimental and Theoretical Study of Methyl Acetoacetate Adsorption on Ni{100}

The enantioselective hydrogenation of methyl acetoacetate (MAA) over modified Ni-based catalysts is a key reaction in the understanding of enantioselective heterogeneous catalysis as it represents the only example of this class of reactions catalyzed by base metals. Yet, there is very little molecular-level information available about the adsorption complex formed by the reactants on Ni surfaces. Here, we report a combined experimental and theoretical study of the adsorption of MAA on the Ni{100} surface. X-ray photoelectron spectroscopy shows that MAA forms stable multilayers at low temperatures, which desorb between 200 and 220 K. At higher temperatures a single chemisorbed layer is formed, which decomposes between 300 and 350 K. Density functional theory modeling predicts an enolate species with bidentate coordination as the most stable chemisorbed species. Comparison of photoelectron spectroscopy and X-ray absorption data with simulations using this adsorption model show good qualitative and quantitat...