Single Particle Layer Research Articles

Formation of two-dimensional mixed monolayers of integrated-cellulose nanofibers and starch nanoparticles using cellulose acetate and soluble starch

In this study, mixed monolayers comprising starch and cellulose nanofibers are prepared on the water surface and effectively controlled their surface morphologies. Through the spreading of cellulose acetate on the water surface, we achieve the preparation of integrated films with the spontaneous formation of nanocellulose. It is confirmed that starch, which is insoluble in the spreading solvent, is solubilized through a soluble treatment and spreads into a monolayer on the water surface. Upon mixing the nanocellulose integrated layer and starch particle layer, the morphology changes based on the mixed ratio of these components. In the monolayer film of a 1:1 mixture of cellulose acetate and soluble starch, the morphology predominantly consists of fibers, with particulate aggregates incorporated here and there. Furthermore, when the ratio changes to 1:5, the mixed monolayer transforms into a single particle layer, while the mixed monolayer evolves into a fibrous integrated film at a ratio of 5:1. Meanwhile, from the evaluation of the surface pressure-area isotherms, it is predicted that both components constitute an ideal mesoscopic miscible system. In addition, in the subphase temperature dependence of the cellulose acetate:soluble starch = 1:1 mixed monolayer, fibers are promoted under low-temperature conditions, and substantial domains are formed under high-temperature conditions. Notably, the mixed film remains amorphous at all ratios and exhibits low surface free energy, simultaneously suggesting hydrophobic and oil-repellent properties.

Occurrence of structural color by assembling single-particle layers of organo-modified nanodiamond

Structural color was realized for the first time by using organo-modified nanodiamonds with a particle size of 5 nm and by the transferring their single particle layers to the substrate as multilayers. The occurrence of various gradations of structural colors was achieved by obtaining step-like multilayers in which the thickness of assembly of the single-particle layer was changed stepwise. It was found that the occurrence of structural color by organo-modified inorganic nanoparticles requires densification of particle packing in the plane by a process of two-dimensional particle integration. As a two-dimensional particle integration process, the method of "repeating compression-expansion" at the air/water interface was effective. In addition, the color tone of each layer was systematically changed by annealing the organo-modified nanodiamond multilayers. Annealing improved the layered regularity, pseudo-lattice distortion, and crystallite size; however, the direct cause of the color phase change was expected to be the uniformity of the mesoscopic particle layer thickness accompanied by defect reduction.

Formation behavior of monolayers on the water surface of water-soluble thermoplastic and insoluble-thermosetting copolymers with hyperbranched units containing s-benzenetricarbamide cores

The formation and structure of Langmuir monolayers and Langmuir-Blodgett films were studied using water-soluble polymers, which have difficulty forming monolayers on the water surface, and polymers that are insoluble in all solvents. The network copolymers consisting of hyperbranched units with an s-benzenetricarbamide core used in this study can be freely controlled by azidation/non-azidation of both ends of the hard segment. The water-soluble copolymer, which exhibits the properties of a thermoplastic resin, can form a monolayer when spread on the water surface at a low temperature at which the solubility decreases. Even when the subphase temperature increased, no significant change in the monolayer behavior of the thermoplastic copolymer was observed. This behavior was attributed to the formation of an insoluble single-particle layer with hydrophilic groups facing inward on the water surface. The insoluble copolymer, which exhibits thermosetting properties, forms a tablet that floats on the water surface for an extended period. The surface pressure-time isotherms showed the formation of a monolayer from the tablet over time, and it was possible to measure the surface pressure-area isotherms by two-dimensional compression after a certain period of time.

Biomolecular Adsorption to Interfacial Single Particle Layer of Organo-Modified Nanodiamond and Its Second-Order Structure.

Modifying the surface of nanodiamonds, which have antibacterial properties, with organic molecular chains enables biomolecular adsorption on a single particle layer on the water surface. For organo-modification, long-chain fatty acids act on the terminal hydroxyl groups present on the nanodiamond surface, and cytochrome C protein and trypsin enzyme are used as biomolecules. Cytochrome C and trypsin introduced into the subphase were electrostatically adsorbed onto the unmodified hydrophilic surface of the organo-modified nanodiamond monolayers on the water surface. The ampholyte protein is thought to exhibit Coulomb interactions with the positively charged unmodified nanodiamond surface. The protein adsorption was supported by morphological observations and spectroscopic properties; circular dichroism spectra suggested denaturation of the adsorbed proteins. However, the biopolymers could maintain their second-order structure even under a high-temperature environment, after being slightly denatured and adsorbed to the template. The nanodiamonds form excellent templates for structural retention in the atmosphere while yielding minor denaturation corresponding to the chirality of biomolecules upon adsorption.

Annealing-induced rearrangement behavior and heat-resistant regularity of layered assemblies of organo-modified inorganic nanoparticles with different initial orders

The rearrangement effect and maintenance characteristics of heat-resistant order on nanoparticle layered assemblies with different initial orders obtained by two types of film preparation methods were evaluated. The layered structure was prepared by transferring single particle layers on the water surface of an organo-modified magnetite, in which the surface of Fe3O4 nanoparticles having a diameter of 5 nm was modified with a long-chain fatty acid, onto a substrate as multiparticle layers. Two types of multiparticle layers were obtained by the Langmuir–Blodgett (LB) and horizontal lifting/Langmuir–Schafer methods. The initial order of the multiparticle layers was higher in the layered assemblies derived from the LB method. On the other hand, the nanoparticle layered assemblies derived from the horizontal lifting method were remarkably highly ordered by annealing at a mild temperature for a long time. The rearrangement effect at the mild temperature over a long period was considered to originate from the enhancement in the van der Waals interaction between the organo-modified chains on the surface of the inorganic nanoparticles. In other words, it is considered that thermal motion occurs to the layered structure in which a large number of single particle layers are laminated as the pseudo-crystal lattice induces the interaction between the organic molecular chains.

Efficient horizontal lifting and annealing method for creating alternating multilayer structures with hard and soft multi-particle layers

• Alternating multilayer structure was created by the horizontal lifting method. • The regularity of alternating multilayers was improved by annealing. • Rapid compression of the horizontal lifting method resulted in dechaining. • The desorbed chain was able to remove by the solvent. • Slow compression suppressed the occurrence of chain-desorption. An efficient process for manufacturing Nano-mille-feuille/alternating multi-particle layers was developed, in order to elucidate the origin of the physical properties associated with long-period stacking ordered structures. The conventional process employing the upstroke Langmuir-Blodgett method requires approximately five days. Comparatively, the developed process employing the horizontal lifting method, which involved two Langmuir troughs, was shortened to one day. Alternating multi-particle layer was obtained by dividing the horizontal, long trough into two sections, and alternate single-particle layers of polymer and inorganic nanoparticles were transferred to the substrate. However, out-of-plane X-ray diffraction confirmed that there was a significant decrease in the order of the layers. To compensate for any poor order, the samples were annealed at mild temperatures to rearrange the particles. Annealing at 50 °C for 60 h significantly improved the order of the layers (hereinafter layered order) in the alternating multi-particle layers. In addition, increasing the compression rate after horizontal adhesion induced desorption of the organically modified chain of alternating multi-particle layers, which also improved the layered order after annealing. Solvent treatment or low-speed compression can be used to prevent desorption of the components.

Preparation and electrochemical properties of nano-diamond/vertical graphene composite three-dimensional electrodes

Diamond/graphene composite three-dimensional electrode has attracted extensive attention because of its low background current, wide potential window from diamond component, and high electrochemical activity from graphite component. In this work, by using the hot wire chemical vapor deposition method, nano diamonds are embedded in the vertical graphene sheet on the surface of single particle layer of nano diamond by regulating the short-term growth time to form a composite three-dimensional electrode. The results show that the electrode exhibits a wide potential window (3.59 V) and a very low background current (1.27 mA/cm<sup>2</sup>) when nano-diamond crystals grow on the top of the vertical graphene sheet. The composite structure of nano-diamond crystals coated with graphite on the top of the graphene sheet is the key to broadening the potential window and reducing the background current. With the increase of growth time, the vertical graphene sheet grows and nano-diamond grains are embedded into the lamellae, and a novel nano-diamond/graphene composite vertical lamellae structure is constructed. The ordered graphite structure increases the electrochemical active area to 677.19 μC/cm<sup>2</sup> and the specific capacitance to 627.34 μF/cm<sup>2</sup>. The increase of graphite components makes the potential window narrow, and the embedded nano-diamond crystals effectively reduce the background current. This study provides a new method for preparing three-dimensional nanodiamond/graphene composite electrodes by hot wire chemical vapor deposition, and provides a new idea for fully exploiting the synergistic effect of diamond/graphene composite films.

Regularity maintenance property of multilayered assemblies of organic, inorganic, and their alternating nanoparticle layers under heating

Abstract The regularity maintenance properties of a multi-layered assembly of a polystyrene nanosphere layer, a stearate-modified Fe3O4 nanoparticle layer, and their alternating nanoparticle layers on heating were compared. The purpose is to clarify the heating resistance among the environmental resistance of hard and soft nanoparticle alternating layered structures with excellent mechanical properties. The polystyrene spread at the air/water interface formed a single-particle layer with a uniform height, creating a highly ordered layer structure. Inorganic nanoparticles whose outermost layer surface was modified with organic molecular chains also formed a single-particle layer on the water surface, and the regularity of their layered organization was ensured. Furthermore, the regularity of the alternating multilayers of polystyrene/Fe3O4 nanoparticles with high mechanical resistance that imitate the nacre was not inferior to the regularity of every single component multi-particle layers. When the periodicity of the three types of particle-layered structures was evaluated under high-temperature conditions, it was found that the structures could be maintained up to 80 °C. From paracrystal analysis, it was found that the degree of order reduction was negligible in both the polystyrene nanoparticle layer and the polystyrene/stearate-modified Fe3O4 alternating layers, even at 80 °C. The organo-modified inorganic nanoparticle layers showed outstanding heat resistance, maintaining layered regularity even at 150 °C. This result was predicted to be owing to the effect of two-dimensional crystals formed between the layers of organo-modified chains.

Epifluorescence-based three-dimensional traction force microscopy

We introduce a novel method to compute three-dimensional (3D) displacements and both in-plane and out-of-plane tractions on nominally planar transparent materials using standard epifluorescence microscopy. Despite the importance of out-of-plane components to fully understanding cell behavior, epifluorescence images are generally not used for 3D traction force microscopy (TFM) experiments due to limitations in spatial resolution and measuring out-of-plane motion. To extend an epifluorescence-based technique to 3D, we employ a topology-based single particle tracking algorithm to reconstruct high spatial-frequency 3D motion fields from densely seeded single-particle layer images. Using an open-source finite element (FE) based solver, we then compute the 3D full-field stress and strain and surface traction fields. We demonstrate this technique by measuring tractions generated by both single human neutrophils and multicellular monolayers of Madin–Darby canine kidney cells, highlighting its acuity in reconstructing both individual and collective cellular tractions. In summary, this represents a new, easily accessible method for calculating fully three-dimensional displacement and 3D surface tractions at high spatial frequency from epifluorescence images. We released and support the complete technique as a free and open-source code package.

Analysis of soft and hard nanoparticle alternating multilayers for the development of theory for long-period stacking order structure prepared by Langmuir-Blodgett method

Two types of hard and soft nanoparticles with a size of 5 nm were alternately layered to adjust the multi-particle structure with high regularity, and structural analysis was performed. Specifically, we alternately transferred two kinds of single-particle layers composed of surfactant-modified organo-magnetite and a hydrophobic polymer to a solid substrate using the Langmuir-Blodget (LB) method. The morphology of two-dimensional particle integration in each single particle layer was confirmed by atomic force microscopy observations. The obtained LB multilayers exhibited almost the same periodicity, crystallite size, and lattice distortion, based on X-ray diffraction (XRD) analysis. The alternating multilayers composed of hard and soft particle monolayers were not inferior to single component multilayers in terms of periodicity and regularity. The utilization of this preparation method facilitates effective control of the period of hard and soft layers. It is asserted that the high degree of regularity was attained due to the affinity and miscibility between the organic polymer particle layer and the modified organic chains on the inorganic nanoparticle surface. The most notable result is that in the XRD data, the spacing between inorganic nanoparticles was not enhanced, and the period of the hard-soft particle correlation was confirmed. Therefore, it seems that both layers have the same high degree of regularity.

Creation of Highly Ordered "Nano-Mille-Feuille" Hard/Soft Nanoparticle Multilayers with Interparticle Cross-Linking by Diacetylene-Containing Chains.

In this study, we attempted to create a precise nanostructure in which hard and soft layers were alternately stacked with a period of 5 nm. Such a periodically stacked structure can be used as a model material to elucidate the origin of the innovative mechanical property improvement proposed for Mg alloy systems. The soft layer was a single layer of nanoparticles made of a ternary copolymer containing a carbazole ring and both hydrocarbon and fluorocarbon chains. The hard layer was a single-particle layer made of magnetite nanoparticles; the surface of these particles was modified with long-chain diynoic acid. The multilayers of each single-particle layer were 54% crystalline and ordered with a D001 crystallite size of approximately 20 nm. The nano-mille-feuille structure, in which the hard and soft layers are repeated in a single-digit nanoperiod, was 56% crystalline and ordered with a D001 crystallite size of approximately 15 nm. Infrared absorption spectroscopy and X-ray photoelectron spectroscopy did not show any loss of both hard and soft layers. Even when the thickness/number of layers was changed variously, no remarkable decrease was observed in the order. Cross-linking between particles by ultraviolet irradiation polymerization was performed for the direct evaluation of the mechanical properties of this structure in the future. Even after topochemical polymerization between the modified chains, the order of the particle stacking structure was maintained.

Formation of organized films with fluorocarbon-modified inorganic nanoparticles and their nanodispersion behavior in solvent

Nanodispersion behavior in organic solvents of nanodiamonds with surfaces modified by amphiphiles containing fluorocarbon chains of different lengths was investigated for future lubricant applications. Fluorocarbon-modified nanodiamonds exhibit excellent dispersion behavior, specifically in nonpolar solvents. This is a phenomenon that is not seen in hydrocarbon-modified nanoparticles. The reduction in the aggregated particle size in organic solvents is more dependent on the modified chain length than on the modification rate. In addition, the behaviors of these organo-modified nanodiamonds on a water surface were systematically compared. These single-particle layers on the water surface were confirmed to depend on the compression rate. The slower the compression speed, the more homogeneous the single-particle layer formed is. Further, proper lattice spacing and high regularity in this system were achieved by low-speed compression. Good dispersibility in organic solvents was related to a long relaxation time to achieve a stable conformation on the water surface. In other words, it was suggested that nanoparticles with better dispersibility in organic solvent require a longer relaxation time for rearrangement in the air/water interface field.

Modeling dust dispersion and suspension pattern under turbulence

Controlling dust generation and minimizing volumetric dust concentration, within confined space, are key to the prevention of dust explosion. Dust dispersion pattern under pressure, such as primary explosion or dust leakage from equipment, can be simulated using unsteady state computational fluid dynamics – discrete phase models (CFD-DPMs). Although they offer computational efficiency, DPM simulations do not incorporate particle-wall or particle-particle interactions. In this paper, we therefore adapt the model to include particle-wall interaction based on energy conservation. In a confined volume, to experimentally observe the dust dispersion pattern, a theoretical concentration of 0.05 and 0.10 kg/m3 was generated and the turbulence was created with airflow of 2 and 10 m/s using an air compressor. Similar conditions were used to model the dust dispersion pattern. Our findings show that the dust concentration inside the confined chamber is not evenly distributed throughout its entirety and that explosive dust cloud concentration only takes up to 37.8% of a chamber's volume for a 0.10 kg/m³ injected dust concentration at 10 m/s air velocity. With a decrease in the dust injection rate and air velocity, the dust cloud volume decreased due to lesser amount of particles and low kinetic energy. This study presents an efficient dust dispersion modeling method, and the result shows the dust cloud volume is highly dependent on the dispersion velocity. The predicted dust concentration and the experimental results indicate that this boundary corrected CFD-DPM modeling approach is suitable for dilute particle dispersion flow, where the volume fraction of particles is lower and the adhered particles only form a single particle layer on the wall boundary.

Maintenance Properties of Enzyme Molecule Stereostructure at High Temperature by Adsorption on Organo-Modified Magnetic Nanoparticle Layer Template

Abstract The transition behavior of Gibbs monolayers of biomolecules at the air/water interface, and the sustainability of their three-dimensional structure during heating by adsorption/immobilization on inorganic particle nanosheets were investigated. Lysozyme (enzyme), cytochrome C (protein), trypsin (digestive enzyme), and luciferase (luminescent enzyme) were the biomolecules used in this study. The surface pressure-time isotherms of these biomolecules showed that the crystal transition of the Gibbs monolayer corresponding to denaturation and deactivation was systematically different. The Gibbs monolayers of these biomolecules were observed to become increasingly unstable with an increase in the number of apparent hydrophobic units, and were susceptible to denaturation by crystal transition. These biomolecules were adsorbed/immobilized on a nanosheet of organo-modified magnetic fine particles. After forming a monolayer on the water surface of the organo-magnetic nanoparticles, these biomolecules were introduced into the subphase and electrostatic interaction between the nanoparticle hydrophilic surface and the biomolecules was induced. When the bio-adsorbed single particle layer was transferred onto the solid substrate, an infra-red (IR) band derived from the adsorbed species was confirmed in this multi-particle layer. In addition, shapeless adsorbed matter was observed by atomic force microscopy images. From the IR measurement under heating, it was found that the secondary structure of the adsorbed lysozyme enzyme was maintained up to about 100 °C by substrate adsorption. This is probably because the three-dimensional structure of biomolecules is less likely to be denatured by using inorganic nanosheets with high density and low defects as the templates.

Correlation between nanodispersion of organo-modified nanodiamond in solvent and condensed behavior of their organized particle films

Organo-nanodiamond (ND) by surface modification using several surfactants has achieved nanodispersion in organic solvent as if these nanoparticles were dissolved. High surface coverage has reduced the aggregated particle size of organo-ND particles in the solvent, and their modification by fluorocarbon chain has achieved nanodispersion in a nonpolar solvent. By using a spreading solvent for single particle layers on the water surface of various organo-NDs of resulting dispersion medium, a close relation was found between the dispersion characteristics of organo-nanoparticles in the solvent and the condensation behavior in their two-dimensional single particle layer. Organo-ND with high dispersion ability in solvent has inferior two-dimensional condensability as a single particle layer. Sufficient retention time is necessary to form a homogeneous single particle layer on the water surface. The reason behind this property was found to be the secondary aggregation of organo-modified nanoparticles at the air/water interface. Since lipophilicized ND is not necessarily stable on the water surface, increasing aggregated particle size and three-dimensionality were confirmed in the case where the particle compression rate during two-dimensional integration was relatively fast.

Division of roles of modified chains in organo-magnetic nanoparticles using Organo-modified agents having hydrophilic reactive polar groups at both ends: Formation of high-density single-particle layers and bioconjugation.

The behavior of an organo-modified chain that changes its role depending on the environment has been investigated. Long-chain carboxylic acids having a hydrophilic reactive polar group at both ends were allowed to act on magnetic nanoparticles to produce organo-modified particles. These amphiphilic organo-magnetic nanoparticles are synthesized by the reaction of a hydroxyl terminal group on the outermost surface of the magnetic particle and a carboxylic acid. With spreading at the air/water interface, an extremely condensed single-particle layer on the water surface was formed. It is evident that a long-chain carboxylic acid having a hydrophilic group at the terminal acts as a hydrophobic chain. Furthermore, when a Lysozyme enzyme as an ampholyte was allowed to act from the subphase, we observed that it adsorbed at the end of the modified chain. This implies that a hydrophilic group facing the subphase side exists. This phenomenon also occurred when the terminal comprised amino or carboxyl groups. Therefore, we observed that the surface-modified chain having the same chemical structure changed its role depending on the environment, and it can function as both a hydrophilic and a hydrophobic group.

Crystallization process of a three-dimensional complex plasma.

Characteristic timescales and length scales for phase transitions of real materials are in ranges where a direct visualization is unfeasible. Therefore, model systems can be useful. Here, the crystallization process of a three-dimensional complex plasma under gravity conditions is considered where the system ranges up to a large extent into the bulk plasma. Time-resolved measurements exhibit the process down to a single-particle level. Primary clusters, consisting of particles in the solid state, grow vertically and, secondarily, horizontally. The box-counting method shows a fractal dimension of d_{f}≈2.72 for the clusters. This value gives a hint that the formation process is a combination of local epitaxial and diffusion-limited growth. The particle density and the interparticle distance to the nearest neighbor remain constant within the clusters during crystallization. All results are in good agreement with former observations of a single-particle layer.

Controlling the phase-separated morphology of a two-dimensional integrated layer of magnetic nanoparticles by surface modifications using immiscible amphiphiles

Surface modification with immiscible surfactants was utilized to induce phase separation at the nanometer scale in a two-dimensional particle layer of magnetic nanoparticles. Cobalt ferrite (CoFe2O4) particles (diameter=30nm) and magnetite (Fe3O4) particles (diameters=5 and 30nm) were typically subjected to surface modification with a hydrogenated and fluorinated long-chain carboxylic acid. A mixed monolayer of hydrogenated and fluorinated organo-magnetic nanoparticles was spread at the air/water interface. This system was used to assess the phase separation because the collapsed surface pressures of both components were individually observed in the isotherms that were measured by systematically changing the composition ratio. A nano-sized phase separation morphology was observed on the surface of the mixed single-particle layers by atomic force microscopy. A “sea-island” structure was observed in which the expanded phase formed by the fluorinated organo-magnetic nanoparticles surrounded the condensed nano-domains of the hydrogenated organo-magnetic nanoparticles. The separate (particulate) nano-phase morphology showed a temperature dependence, and in this case, the fluorinated “sea” phase transformed into a network morphology. The nano-domain of the hydrogenated organo-modified magnetic nanoparticles was a crystalline phase in which the modified chain was packed with two-dimensional hexagonal or orthorhombic systems. The nanophase separation on the surface of the magnetic single-nanoparticle layers likely formed because of repulsive interactions between the immiscible surface modifiers.

High-Density Packing of Amorphous Polymer with Bulky Aromatic Rings in Interfacial Molecular Films

High-density packing of the main chains of amorphous high-refractive-index polyguanamine derivatives and aromatic polyamide block copolymers has been investigated in 2D molecular films. Polymer main chains with multiple and bulky aromatic rings are difficult to pack owing to steric hindrance. However, the intermolecular affinity can be enhanced by chain rearrangement. The polymer chain arrangement in 2D films has been controlled at the air/water interface. Furthermore, rearrangement of the main chains at the water/substrate interface during transfer to the solid substrate is also important. The highly hydrophobic polyguanamine derivatives form single-particle layers at the air/water interface, with their bulky functional groups packed densely in nanospheres owing to π–π interactions. The hydrophobic aromatic polyamide copolymers form an expanded monolayer including unpacked chains at the air/water interface. As these copolymers are rearranged during transfer to the solid substrate, densely packed molecular arrangements with end-on configurations are attained in the films.

Versatile Antireflection Coating for Plastics: Partial Embedding of Mesoporous Silica Nanoparticles onto Substrate Surface.

Antireflection (AR) coating for transparent plastic substrates is constructed by partially embedding mesoporous silica nanoparticles (MSNs) onto the surface of the substrates. Simulation of optical properties of polymer substrates coated with a single-particle MSN layer indicates that the surface has a low and graded refractive index in the direction of the thickness and effectively decreases the reflectance of visible light. The MSN-coated surfaces can be prepared by exposure of the MSN-painted substrates to a solvent vapor, irrespective of the shape of the polymer substrates. The plastic substrates with a single-particle layer of MSNs with diameters of 145-165 nm exhibit high transparency and good AR behavior as simulated. The mesoporous structures of MSNs play important roles not only in decreasing the refractive index but also in strengthening the adhesion between MSNs and substrate surfaces. Moreover, fixation of MSNs onto a thermosetting epoxy resin is successfully achieved by transfer of a single layer of MSNs from flexible films for which MSNs are weakly bonded. The present simple AR coating is applicable to a wide range of substrates with various materials and shapes, and useful for various applications such as optical devices, displays, and solar cells.