Sequential Adsorption Method Research Articles

Designing Gastric-Stable Adsorption Layers by Whey Protein-Pectin Complexation at the Oil-Water Interface.

This work aims to design gastric-stable emulsions with food-grade biopolymers using a novel multiscale approach. The adsorption layer formation at the oil-water interface was based on opposite charge interactions between whey proteins and pectin (with different esterification levels) at pH 3.0 by a sequential adsorption method. The interfacial assembly and disassembly (interfacial complexation, proteolysis, lipolysis) during in vitro gastric digestion were evaluated using a quartz crystal microbalance with dissipation monitoring, ζ-potential, dynamic interfacial tension, and interfacial dilatational rheology. Besides, the evolution of the particle size and microstructure of bulk emulsions during the digestion was investigated by static light scattering and light microscopy. Compared with whey protein isolate (WPI)-stabilized emulsions, the presence of an additional pectin layer can prevent or at least largely delay gastric destabilization (giving rise to coalescence or/and oiling off). Especially, the esterification degree of the pectin used was found to largely affect the emulsion stability upon gastric digestion.

Co-immobilization of antioxidant enzymes on titania nanosheets for reduction of oxidative stress in colloid systems

Immobilization of single antioxidant enzyme systems was frequently studied in the past, however, there is a lack of reliable reports on the co-immobilization of such enzymes. Here, an antioxidant enzyme cascade involving superoxide dismutase (SOD) and horseradish peroxidase (HRP) was successfully immobilized on titania nanosheets (TNS) by the sequential adsorption method using poly(diallyldimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) polyelectrolyte building blocks. The development of the cascade system was based on a colloid approach, in which the charging and aggregation processes were optimized in each synthetic step. The polyelectrolyte and enzyme multilayers were built up in two different sequences at the particle interface, namely, TNS-PDADMAC-SOD-PSS-HRP and TNS-HRP-PDADMAC-SOD-PSS. The formation of the polyelectrolyte layers led to charge reversal of the carrier and the saturated PDADMAC and PSS layers stabilized the dispersions, in particular, their resistance against salt-induced aggregation was especially excellent. The results of enzymatic assays revealed that the SOD and HRP-like activities of the composites depended on the location of the enzymes in the hybrid material. The obtained compounds showed remarkable antioxidant effect and were able to simultaneously decompose superoxide radical anions and hydrogen peroxide. The cascade systems are of great promise in industrial manufacturing processes during the preparation of high-quality products without any damages by reactive oxygen species.

Adsorption Properties of Soft Hydrophobically Functionalized PSS/MA Polyelectrolytes

We investigated the adsorption properties of the newly synthesized, hydrophobically functionalized polyelectrolyte (HF-PE), poly(4-styrenesulfonic-co-maleic acid) copolymer (PSS/MA). The hydrophobic alkyl side chains (C12 or C16) were incorporated into the polyelectrolyte backbone via the labile amid linker to obtain the soft HF-PE product with the assumed amount of 15% and 40% degree of grafting for every length of the alkyl chain, i.e., PSS/MA-g-C12NH2 (15% or 40%) as well as PSS/MA-g-C16NH2 (15% or 40%). In the present contribution, we determined both the effect of grafting density and the length of alkyl chain on adsorption at water/air and water/decane interfaces, as well as on top of the polyelectrolyte multilayer (PEM) deposited on a solid surface. The dependence of the interfacial tension on copolymer concentration was investigated by the pendant drop method, while the adsorption at solid surface coated by poly(diallyldimethylammonium chloride)/poly(styrene sulphonate) PEM by the quartz crystal microbalance with dissipation (QCM-D), attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) and contact angle analysis. We found that surface activity of the hydrophobized copolymer was practically independent of the grafting ratio for C16 side chains, whereas, for C12, the copolymer with a lower grafting ratio seemed to be more surface active. The results of QCM-D and FTIR-ATR experiments confirmed the adsorption of hydrophobized copolymer at PEM along with the modification of water structure at the interface. Finally, it can be concluded that the hydrophobically modified PSS/MA can be successfully applied either as the efficacious emulsifier for the formation of (nano)emulsions for further active substances encapsulation using the sequential adsorption method or as one of the convenient building blocks for the surface modification materials.

Finite element analysis of effect of grain orientation on the thermal conduction of h-BN ceramics

Study of thermal conduction process of ceramics by experimental and theoretical model analysis methods is complicated and non-intuitive. In this work, to analyze the influence mechanism of h-BN grain orientation on the thermal conduction of h-BN ceramics, new mesoscale finite element models considering the anisotropy in the thermal conductivity of h-BN grain were established based on random sequential adsorption method and periodic boundary condition. And the accuracy of the finite element models was verified by theoretical model and experimental results. The heat flux vector and temperature distributions intuitively show that the orientation of h-BN grains will significantly affect the thermal conduction process of the ceramics by affecting the heat flow path. The heat flow will propagate mainly along the “thermal conducting pathways” formed by the h-BN grains when the h-BN layer direction shows small angle with the external temperature difference direction, otherwise, h-BN grains will act as barriers to the heat conduction.

Study of the Effectiveness of the RVEs for Random Short Fiber Reinforced Elastomer Composites

The effectiveness of the representative volume elements (RVEs) established by a modified random sequential adsorption method for random short fiber reinforced elastomer composites (SFECs) was studied. The RVE is considered to be effective when the RVE’s fiber orientation is isotropic. And the effectiveness of the RVEs was verified by evaluating the mechanical properties in different loading directions based on the finite element method. The results show that the fiber number N=4000 can be regarded as a steady threshold for the isotropy of the fiber orientation in RVEs with various fiber aspect ratios and dilute volume fraction.

Numerically-aided 3D printed random isotropic porous materials approaching the Hashin-Shtrikman bounds

The present study introduces a methodology that allows to combine 3D printing, experimental testing, numerical and analytical modeling to create random closed-cell porous materials with statistically controlled and isotropic overall elastic properties that are extremely close to the relevant Hashin-Shtrikman bounds. In this first study, we focus our experimental and 3D printing efforts to isotropic random microstructures consisting of single-sized (i.e. monodisperse) spherical voids embedded in a homogeneous solid matrix. The 3D printed specimens are realized by use of the random sequential adsorption method. A detailed FE numerical study allows to define a cubic representative volume element (RVE) by combined periodic and kinematically uniform (i.e. average strain or affine) boundary conditions. The resulting cubic RVE is subsequently assembled to form a standard dog-bone uniaxial tension specimen, which is 3D printed by use of a photopolymeric resin material. The specimens are then tested at relatively small strains by a proper multi-step relaxation procedure to obtain the effective elastic properties of the porous specimens.

Self-assembled Li3V2(PO4)3/reduced graphene oxide multilayer composite prepared by sequential adsorption

Herein, we report on Li3V2(PO4)3 (LVP)/reduced graphene oxide (rGO) multilayer composites prepared via a sequential adsorption method and subsequent heat treatment, and their use as cathodes for high-rate lithium-ion batteries. The sequential adsorption process includes adsorbing oppositely charged components of anionic inorganic species and cationic head of a surfactant adsorbed to graphite oxide sheets, which is a key step in the fabrication of the LVP/rGO multilayer composites. The multilayer structure has open channels between the highly conductive rGO layers while achieving a relatively high tap density, which could effectively improve the rate capability. Consequently, the LVP/rGO multilayer composites exhibit a high tap density (0.6 g cm−3) and good electrochemical properties. Specifically, in the voltage range of 3.0–4.3 V, the composite exhibits a specific capacity of 131 mAh g−1 at 0.1C, a good rate capabilities (88% capacity retention at 60C), and long cycling performance (97% capacity retention after 500 cycles at 10C). Moreover, in the extended voltage range of 3.0–4.8 V, it exhibits a high specific capacity of 185 mAh g−1 at 0.2C, a good rate capability (66% capacity retention at 30C), and stable cycling performance (96% capacity retention after 500 cycles at 10C).

Elastic and plastic properties of epoxy resin syntactic foams filled with hollow glass microspheres and glass fibers

ABSTRACTRepresentative volume elements of syntactic foams with a random filling of short glass fibers and hollow glass microspheres in epoxy resin were established by a random sequential adsorption method. The fiber volume fraction was set at 4%, and the microsphere volume fraction range was from 5 to 30%. This numerical simulation was studied with ANSYS software. The influence on the elastic and plastic mechanical properties of syntactic foams of the microsphere volume fraction and relative wall thickness were investigated, and the plastic strain evolution process in the composites was analyzed. The results show that the compressive yield limit and Young's modulus values of the syntactic foams decreased with increasing microsphere volume fraction when the microsphere relative wall thickness was 0.02, but these properties were enhanced with increasing microsphere volume fraction when the relative wall thickness exceeded 0.04. The specific strength and tangent modulus values of the composites increased with increasing microsphere volume fraction. In addition, we observed that the yield stress, Young's modulus, and tangent modulus values of the syntactic foams were obviously enhanced by the addition of glass fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44188.

Prediction on macroscopic elastic properties of interphase-contained long-fiber-reinforced composites and multiple nonlinear regression analysis

A convenient method to predict the macroscopic elastic performance of composite containing interphase was developed in this paper based on a new modified random sequential adsorption method and multiple nonlinear regression analysis. First, a three-phase micromechanical model with randomly distributed fibers was established with a new modified random sequential adsorption method named the Moving Window Method. Second, the macroscopic elastic behaviors of T300/914C were predicted based on micromechanical parameters of constituent materials using energy method, and the influence of the randomness of fiber distribution on the prediction was analyzed. Third, the effects of interphase thickness, interphase modulus and Poisson’s ratio on the macroscopic elastic properties of the composite were studied by changing these interphase micromechanical parameters gradually within certain ranges. Finally, the multiple nonlinear regression models that describe the relationship between the macroscopic elastic properties of T300/914C and micromechanical characteristic parameters of the interphase were established using a limited number of data from numerical simulation. Results indicate that the relative errors for the longitudinal modulus and the major Poisson's ratio are within ±1% while for the transverse modulus, shear modulus and Poisson’s ratio at cross section, the relative errors are within 5%.

Titanoniobate and niobate nanosheet photocatalysts: superior photoinduced hydrophilicity and enhanced thermal stability of unilamellar Nb3O8nanosheet

Unique photocatalysts based on novel two-dimensional (2D) oxide nanosheets have been synthesized and their photochemical activity has been examined. Monolayer films of titanoniobate and niobate (TiNbO5, Ti2NbO7, Ti5NbO14, and Nb3O8) nanosheets, synthesized by exfoliating layered oxide precursors through a soft-chemical procedure, were fabricated on quartz glass substrate via a sequential adsorption method. All the nanosheet films exhibited good photoinduced hydrophilicity, while their oxidation activity was very low. This behavior can be regarded as inherent features of nanosheet-type photocatalysts having molecularly thin 2D anisotropy. Such ultrathin flexible structures are advantageous for facilitating photo-driven surface wettability change. Especially, the hydrophilic conversion property of Nb3O8 nanosheet was highly efficient, showing activity that was at least one order of magnitude superior to that of the widely used photocatalyst film of polycrystalline anatase TiO2. Moreover, the monolayer film of Nb3O8 nanosheet was found to have enhanced thermal stability and chemical resistance, particularly against diffusion of sodium ions at elevated temperature: Nb3O8 nanosheet film heated on sodium-rich glass (soda-lime glass) substrate maintained excellent hydrophilic conversion activity, whereas Ti0.87O2 nanosheet as well as anatase (TiO2) based photocatalysts was virtually deactivated. These features are a great advantage of Nb3O8 nanosheet photocatalysts for developing the practical super-hydrophilic applications where post-annealing is indispensable.

Hetero-nanostructured Films of Titanium and Manganese Oxide Nanosheets: Photoinduced Charge Transfer and Electrochemical Properties

Multilayer heterostructured films of two different nanosheets, semiconducting Ti0.91O2 nanosheets and redoxable MnO2 nanosheets, were fabricated by the layer-by-layer sequential adsorption method using a polyelectrolyte as a linker. Successful deposition of these two nanosheets in various sequences was confirmed by monitoring UV−visible absorption spectra and X-ray diffraction data on the films. We examined how nanostructures of the heteroassembled films affect the behaviors of photoinduced electron transfer between the two types of nanosheets and electrochemical properties of composite film electrodes. The excitation of Ti0.91O2 nanosheets under light irradiation at 280 nm was found to cause a gradual decrease in intensity of the optical absorption peak at 372 nm, which can be ascribed to the reduction of Mn4+ to Mn3+ of MnO2 nanosheets as confirmed by XANES spectra. This behavior can be understood by a scheme that the excited electrons produced in Ti0.91O2 nanosheets are injected into MnO2 nanosheets. T...

Structural Rearrangement of C70 Monolayers Induced by Octanethiol Adsorption

Mixed monolayers of C70 and octanethiol are prepared on Au(111) by a sequential adsorption method. A partial C70 monolayer is first formed and characterized, followed by the vapor deposition of octanethiol. This results in a well-ordered alkanethiol film where single C70 molecules and small molecular clusters are located at domain boundaries and in disordered regions. Substrate step defects have a large influence on the spatial distribution of C70; adjacent to a substrate defect, C70 binds preferentially on the upper terrace and is depleted on the lower terrace. We explain these observations as resulting from the kinetics of alkanethiol monolayer formation, and we present a simple model for the evolution of surface structure in the C70/octanethiol system.

Nanoparticle Ferrite Multilayers Prepared by New Self-Assembling Sequential Adsorption Method

The nanoparticle magnetite of which diameter was about 3 nm was synthesized in a homogeneous aqueous solution without a template. The synthesized magnetite nanoparticle was easily oxidized to maghemite in an ambient condition. The magnetic properties of the ferrite nanoparticle show superparamagnetism at room temperature and its blocking temperature is around 93 K. Modifying the sequential adsorption method of metal bisphosphonate, we have prepared a multilayer thin film of the ferrite nanoparticle on planar substrates such as glass, quartz and Si wafer. In this multilayer the ferrite nanoparticle layer and an alkylbisphosphonate layer are alternately placed on the substrates by simple immersion in the solutions of the ferrite nanoparticle and 1, 10-decanediylbis (phosphonic acid) (DBPA), alternately. This is the first example, as far as we know, of nanoparticle/alkyl-bisphosphonate multilayer which is an analogy of metal bisphosphonate multilayer. UV-visible absorption and infrared reflection-absorption studies show that the growth of each layer is very systematic and the film is considerably optically transparent to visible light of 400-700 nm. Atomic force microscopic images of the film show that the surface morphology of the film follows that of the substrate in μm-scale image and the nanoparticle-terminated surface is differentiated from the DBPA-terminated one in nm-scale image. The magnetic properties of this ferrite/DBPA thin film are almost the same as those of the ferrite nanoparticle powder only.

Automatic film formation system for ultra-thin organic/inorganic hetero-structure by mass-controlled layer-by-layer sequential adsorption method with ‘nm’ scale accuracy

A mass-controlled layer-by-layer sequential adsorption process was newly developed for the fabrication of ultra-thin organic films formed by various polymers, monomers, and inorganic materials. This technique can be applied to both water solutions and volatile solvents. In this process, a quartz crystal microbalance (QCM) was attached to the arm of a robot and the frequency shifts during the adsorption of the materials were monitored. By feeding back the data acquired by the QCM from the deposition to the dipping time, a high quality self-assembly film was produced. As a result, the layer thickness of the films can be controlled with nm-order accuracy. The cross-sectional transmission electron microscopy (TEM) observation of the films formed by the conventional time controlled dipping method and the newly established mass-controlled dipping method reveals that the interface of the hetero structure of the latter was much smoother than the former. The remarkable advantage of the mass-controlled dipping method was also proved by in-situ observation of the adsorption process of the polyelectrolytes in solution using an atomic force microscopy.

Ultra-Thin Organic/Inorganic Hetero-Structures for Photonic Crystal by Mass-Controlled Layer-by-Layer Sequential Adsorption Method

By the combination of surface sol-gel process of metal alkoxides (TiO2) and the mass-controlled layer-by-layer sequential adsorption process of polyelectrolytes, highly ordered organic / inorganic interface was successfully fabricated. The one dimensional photonic crystal such as photorefractive device can be produced by using this method owing to the large differences of the refractive index between the layers.

The fabrication of organic/inorganic multilayer by wet process and sequential adsorption method

Sequential adsorption process of polyelectrolyte and surface sol–gel process was used to deposit on the substrate as the fabrication of ultra-thin films for the wet process method. The film thickness was precisely controlled using the automatic dipping machine that we developed. Self-assembled film of polyelectrolytes and titanium oxide/polymer composite gel film was sequentially deposited on the polystyrene substrate. The cross-sectional organic/inorganic heterostructure was observed by TEM. It was found that the inorganic layer was homogeneous and flat by the effect of the affinity between the deposited layer and solutions. It was also found that the organic layer was homogeneous and flat when using strong polyelectrolyte.