Mica Surface Research Articles

Quantifying chemomechanical weakening in muscovite mica with a simple micromechanical model

In response to gradual nanoindentation, the surface of muscovite mica deforms by sudden stochastic nanometer-scale displacement bursts. Here, the statistics of these displacement events are interpreted using a statistical model previously used to model earthquakes to understand how chemically reactive environments alter the surface properties of this material. We show that the statistics of nanoindentation displacement bursts in muscovite mica are tuned by chemomechanical weakening in a manner similar to how the statistics of model events are tuned by a mechanical weakening parameter that describes how easily system-spanning cracks can be nucleated. Because the predictions of this model are independent of any surface defects or structural details, these results suggest this simple model can be universally used to describe chemomechanical weakening in many systems prone to slip avalanches on a wide range of spatio-temporal scales.

Aggregation Characteristics of Biobased Anionic Surfactant, Hydroxy Alkane Sulfonate in Aqueous CaCl2 Solutions: Vesicle and Supported Bilayer Formation.

Vesicles are known to spontaneously adsorb onto solid-liquid interfaces and to form supported bilayers in aqueous solution. Cationic surfactants have typically been used to generate supported bilayers because solid surfaces in water are often negatively charged. The present study investigated the aggregation behavior of an anionic surfactant, hydroxy alkane sulfonate having a C18 alkyl chain (C18HAS) in aqueous CaCl2 solutions. These assessments were performed by acquiring data related to equilibrium surface tension, the solubilization of an oil-soluble dye, UV-visible transmittance, pyrene fluorescence and dynamic light scattering together with freeze-fracture transmission electron microscopy observations. The results suggest that C18HAS can form vesicles in aqueous CaCl2 solutions under certain surfactant concentrations. Specifically, this aggregation behavior is greatly affected by C18HAS/CaCl2 molar ratio. At the C18HAS/CaCl2 molar ratio is less than an equivalence point (that is, less than 2:1), phase separation occurs with the formation of a vesicle above solubility limit of the C18HAS Ca salt. On the other hand, in the case that the C18HAS/CaCl2 molar ratio is above an equivalence point (that is, above 2:1), the Na salt of C18HAS forms micelles above the critical micelle concentration (cmc), causing solubilization of vesicles. Analyses by high-speed atomic force microscopy demonstrated that the C18HAS vesicles can spontaneously form a supported bilayer on a negatively charged mica surfaces, similar to the behavior of cationic surfactant vesicles, even though C18HAS is an anionic surfactant. These results suggest that C18HAS could serve as a detergent component but also as a surface modifier when the C18HAS/CaCl2 molar ratio is optimized.

Mica Lattice Orientation of Epitaxially Grown Amyloid β25-35 Fibrils.

β-amyloid (Aβ) peptides form self-organizing fibrils in Alzheimer's disease. The biologically active, toxic Aβ25-35 fragment of the full-length Aβ-peptide forms a stable, oriented filament network on the mica surface with an epitaxial mechanism at the timescale of seconds. While many of the structural and dynamic features of the oriented Aβ25-35 fibrils have been investigated before, the β-strand arrangement of the fibrils and their exact orientation with respect to the mica lattice remained unknown. By using high-resolution atomic force microscopy, here, we show that the Aβ25-35 fibrils are oriented along the long diagonal of the oxygen hexagon of mica. To test the structure and stability of the oriented fibrils further, we carried out molecular dynamics simulations on model β-sheets. The models included the mica surface and a single fibril motif built from β-strands. We show that a sheet with parallel β-strands binds to the mica surface with its positively charged groups, but the C-terminals of the strands orient upward. In contrast, the model with antiparallel strands preserves its parallel orientation with the surface in the molecular dynamics simulation, suggesting that this model describes the first β-sheet layer of the mica-bound Aβ25-35 fibrils well. These results pave the way toward nanotechnological construction and applications for the designed amyloid peptides.

Epitaxial Guidance of Adamantyl-Substituted Polythiophenes by Self-Assembled Monolayers.

The anisotropic nature of charge transport through organic materials requires high control over the self-assembly of the organic materials. This is particularly so for conductive polymers, where transport occurs mainly along the polymers' backbone. Herein, we demonstrate the use of self-assembled monolayers (SAMs) to influence the self-assembly of poly(3-adamantylmethylthiophene). We employ two different SAMs, which interact with either the adamantyl- or the thiophene-functionality, respectively, and acquire distinct topologies as compared to the unmodified Au(111) surface. We compare these results with unmodified glass and mica (muscovite) surfaces, which are typically employed in the field of optoelectronics. We prove the usefulness and applicability of epitaxial effects and adamantyl substituents for organic electronics. This presents a viable way toward improved electronic performance for the field as a whole.

Interaction of charged magnetic nanoparticles with surfaces

The behavior of magnetic nanoparticles covering the surface with positive charges (MN), suspended in a continuous medium, was simulated by Brownian dynamics. Then, we studied the behavior of the MN in an aqueous-like suspension and their adsorption on a negatively charged surface, mimicking a mica surface. After several microseconds, particles are deposited onto the charged surface. Experimental results of ordered magnetic nanoparticles in surfaces are compared with the present simulation results of MN in two dimensions. We also demonstrate the effect of charged MN on the hexagonal structure when electrical repulsions dominate against magnetic dipole-dipole and van der Waals attractions. On one hand, the adsorption of MN on the surface depends on the electrostatic attraction force with the surface, while the surface organization of MN results from balancing electrostatic repulsion forces and magnetic attraction forces among particles. In magnetic nanoparticles simulated with a non-charged surface or weakly charged surface, dipole-dipole interactions dominate the particle-particle interactions, and the interactions between particles and a mica-like surface are conducted by van der Waals forces.

Influence of chitosanon on the ability of LPS to interact with cells of the immune system

Complexes of lipopolysaccharide (LPS) from the bacterium Escherichia coli and chitosan (CN) with a molecular weight of 5 kDa were obtained and their supramolecular organization was studied. Using atomic force microscopy, it was shown that during the formation of complexes there is a transition from the micellar structure of the original LPS to linear network structures uniformly distributed over the surface of mica. The stability of LPS-CN complexes of various stoichiometries in biological media in the presence of serum proteins was investigated. It was shown that complexes with an LPS:CN ratio of 1:1 in the presence of serum proteins lost their surface charge and tended to aggregate; while complexes with maximum saturation of CN (1:5) did not aggregate under these conditions and maintained their surface charge. The effect of CNs of different molecular weights on the ability of LPS to interact with neutrophils in human whole blood was studied. It was observed that LPS-CN complexes were capable of binding to neutrophils and entering the cell, and this ability was enhanced in the presence of serum proteins. Chitosan exhibited the ability to suppress the synthesis of the proinflammatory cytokine TNF-α, induced by LPS, not only as part of the complex but also when cells were pretreated with a polycation.

Graphene-assisted remote epitaxy wrinkle-free GaN films on flexible mica

When GaN films were directly deposited onto fluorophlogopite mica substrates, spontaneous wrinkling was frequently observed in GaN films. Because of the non-uniform interface adhesion between GaN and mica, two types of delamination phenomena have been observed by scanning electron microscopy. The maximum thickness of wrinkle-free GaN films on mica substrates was ∼200 nm. Interface pinning effect occurred due to the dangling bonds caused by the damage to mica during the deposition of GaN films. To avoid the formation of dangling bonds, the surface of mica was shielded by a graphene interlayer which was transferred via a wet method. Wrinkles were eradicated after the formation of sliding contact between GaN films and fully graphene-covered mica substrates. Despite the presence of the graphene lattice, the growth of GaN epilayer remained governed by the potential field of mica, indicating that remote epitaxy occurred on a 2D mica support substrate.

Evolution of 2D Nanostructures on Charged Surfaces through the Precipitation of Hydrolyzable Ions

The significance of surface charge at solid-liquid interfaces extends to crucial roles in diverse chemical processes, including crystallization, self-assembly, fuel cell reactions, and heterogeneous catalysis. Building upon the classical mean field description derived from the Gouy–Chapman model, the electrostatic attraction between a charged interface and counterions in solutions prompts oppositely charged ions from the solution to accumulate at the interface, forming an electric double layer (EDL), with distinct properties from those observed in bulk solutions. While the model accounts for the distribution of ions based on their spatial average perpendicular to the surface, the discussion regarding the lateral structure at the interface, particularly the local molecular-level details, is relatively limited.In this study, we explored the interfacial structure of mica, a mineral with an atomically flat surface and intrinsic negative charge, in electrolytes containing different multi-valent cations, utilizing in-situ liquid phase atomic force microscopy (LP-AFM). We find that, as the solution pH is gradually raised, cations precipitate and form a monolayer hydroxide film on mica surface. Divalent ions such as Mg2+, Ni2+, and Co2+, form large continuous monolayers in a manner that aligns with expectations based on classical nucleation theory. For trivalent ions like Al3+, Fe3+, and Cr3+, hydrolyzed species adsorb in increasing amounts as pH is increased. Instead of exhibiting a random distribution, these ions reveal intricate lateral ordering and eventually evolve into an ordered ion network. Upon further pH increase, the ion network undergoes a transition to a discontinuous film with a persistent network of gaps. The links between the surface nanostructure and local surface charge were investigated using three-dimensional fast force mapping (3D FFM) and complementary streaming potential apparatus (SPA) measurements. As films form, an inversion from negative to positive zeta potential on mica is observed through SPA and is accompanied by the appearance of a long-range tip-sample forces through 3D FFM. These findings suggest that electrostatic interactions between positively charged ions/films and a negatively charged substrate stabilize the surface nanostructure. Furthermore, films created by trivalent ions are more strongly charged compared to those formed by divalent ions.The lateral structure at mica-electrolyte interfaces was simulated using a charge-frustrated lattice gas model, where the ions experience competing interactions between short-range chemical bonding and long-range electrostatic forces. For weak charge effects, the film undergoes a first-order transition from sparse adsorbates to large continuous sheets, aligning with the behavior observed with divalent ions. When the charge effect is sufficiently strong, the surface forms various states, including ordered patterns of ions, ion clusters, and microphase-separated partial films, corresponding to the behavior observed with trivalent ions. This study provides molecular-level understanding of how electric fields control the spontaneous formation of interfacial nanostructures, and offers valuable insights into using electric fields to control crystallization processes for the development of functional materials.

Real-time single-molecule observation of incipient collagen fibrillogenesis and remodeling

The hierarchic assembly of fibrillar collagen into an extensive and ordered supramolecular protein fibril is critical for extracellular matrix function and tissue mechanics. Despite decades of study, we still know very little about the complex process of fibrillogenesis, particularly at the earliest stages where observation of rapidly forming, nanoscale intermediates challenges the spatial and temporal resolution of most existing microscopy methods. Using video rate scanning atomic force microscopy (VRS-AFM), we can observe details of the first few minutes of collagen fibril formation and growth on a mica surface in solution. A defining feature of fibrillar collagens is a 67-nm periodic banding along the fibril driven by the organized assembly of individual monomers over multiple length scales. VRS-AFM videos show the concurrent growth and maturation of small fibrils from an initial uniform height to structures that display the canonical banding within seconds. Fibrils grow in a primarily unidirectional manner, with frayed ends of the growing tip latching onto adjacent fibrils. We find that, even at extremely early time points, remodeling of growing fibrils proceeds through bird-caging intermediates and propose that these dynamics may provide a pathway to mature hierarchic assembly. VRS-AFM provides a unique glimpse into the early emergence of banding and pathways for remodeling of the supramolecular assembly of collagen during the inception of fibrillogenesis.

Probing the interfacial behaviors of interfacially active and non-active asphaltenes and their impact on emulsion stability

HypothesisAsphaltenes subfractions with distinct interfacial behaviors may play different roles in stabilizing oil–water emulsions. ExperimentsIn this work, whole asphaltenes were separated into interfacially active asphaltenes (IAA) and interfacially non-active asphaltenes (INAA). Employing advanced nanomechanical techniques, we have explored the compositions, morphologies, sizes, adsorption, and interfacial behaviors of IAA and INAA. FindingsIAA exhibits a high and unevenly distributed oxygen content, distinguishing it from INAA. In toluene, the diameters of IAA and INAA are about 60 nm and 6 nm, respectively. When adsorbed irreversibly on mica surfaces, the thickness of the IAA and INAA film was measured at ∼5.5 nm or 1 nm, respectively; while in a toluene solution, the film thickness reached ∼46 nm and 3.1 nm for IAA and INAA, respectively. IAA demonstrates superior interfacial activity, and elastic/viscous moduli compared to INAA at the water-toluene interface. Quantified surface force measurements reveal that IAA stabilizes water droplets in toluene at a concentration of only 10 mg/L, while INAA requires a higher concentration of 100 mg/L. This work provides the first comprehensive investigation into the adsorption and interfacial behaviors of asphaltene subfractions and provides useful insights into the asphaltenes-stabilization mechanism of emulsions.

The Influence of Ionic Environment on Nucleosome-Mica Interactions Revealed via Molecular Dynamics Simulations.

Mica serves as a crucial substrate in Atomic Force Microscopy (AFM) studies for visualizing and characterizing nucleosomes. Nucleosomes interact with the negatively charged mica surface via adsorbed cations. However, the specific influences of monovalent and divalent cations on nucleosome adsorption to the mica surface remain unclear. In this study, we investigated the binding of nucleosomes to the mica surface in the presence of monovalent potassium ions and divalent magnesium ions using molecular dynamics simulations. We also explored the impact of pre-treated mica surfaces on nucleosome binding and structure. Our findings reveal that nucleosome-mica interactions vary depending on the cations present, resulting in distinct effects on nucleosome structure. Notably, nucleosomes bind effectively to a mica surface in the presence of potassium ions with minimal structural perturbations.

An ab-initio deep neural network potential for accurate large-scale simulations of the muscovite mica-water interface

Mineral-water interfaces play a critical role in several geochemical processes relevant to the habitability of our planet. These processes are often underpinned by the hydration of the ions covering the mineral surface and the resultant ion exchange with the aqueous environment. Muscovite mica, whose surface is nominally covered by K + ions, has long been considered an ideal system for probing some of these processes. However, despite several decades of both experimental and computational work, there still remains a lack of consensus on ion hydration and exchange at the mica-water interface. To obtain a detailed microscopic picture of these processes, we have developed an ab-initio based deep neural network potential (DP) describing the potential energy surface (PES) of the mica(001)-water interface. Our training dataset consisted of bulk mica, bulk liquid water, the mica(001) surface in vacuum and the explicit mica(001)-water interface, both with different surface K + arrangements. The trained model is able to reproduce the energies and forces derived from Density functional theory (DFT) based on the SCAN exchange correlation functional with good accuracy. For the surface in vacuum, K + ions located in the ditrigonal cavities composed of 2 Al atoms are predicted to be energetically more favourable, while the specific surface arrangement of K + ions does not affect the water density profile at the mica-water interface. The developed model sets the stage for estimating the energetics of the ion-exchange process at affordable computational cost without compromising the accuracy of first-principles methods.

Silk Fibroin Self-Assembly at the Air–Water Interface

Amphiphilic silk fibroin (SF) forms stable adsorption layers at the air–water interface. The range of the investigated protein concentrations can be divided into two parts according to the peculiarities of the surface layer properties. At protein concentrations from 0.0005 to 0.01 mg/mL, the dynamic surface elasticity monotonically increases with the concentration and surface age and reaches values of up to 220 mN/m. In this range, the adsorption layer compression leads to a fast increase of the surface pressure. In the second part (>0.01 mg/mL), the surface elasticity decreases again and the kinetic dependences of the film thickness and adsorbed amount change only a little. In this case, the layer compression leads only to a slight increase of the surface pressure. These two types of behavior can be attributed to the distinctions in the protein aggregation in the surface layer. Atomic force microscopy (AFM) investigations of the layers transferred from the liquid surface onto a mica surface by the Langmuir–Schaefer method show some peculiarities of the layer morphology in the intermediate concentration range (~0.02 mg/mL).

Superconducting Two-Dimensional FeSe Grown on the Fe-Enriched Interface.

Two-dimensional (2D) tetragonal FeSe has sparked extensive research interest owing to its tunable superconductivity, providing valuable insights into the design of high-temperature superconductors. Currently, the intricate Fe-Se phase diagram poses a challenge to the controlled synthesis of superconducting 2D FeSe in a pure tetragonal phase. Here, we exploit the ion-exchange property of fluorophlogopite mica to devise a straightforward approach for the phase-controlled synthesis of tetragonal FeSe on an Fe-enriched mica surface within a molten salt environment. This method successfully produces highly crystalline FeSe in a pure tetragonal phase with adjustable thickness. We investigated the surface composition of the postgrowth mica substrate using various microscopic and spectroscopic characterizations to highlight the importance of the Fe-enriched growth interface in the phase-selective synthesis of 2D tetragonal FeSe. The obtained 2D FeSe exhibited 2D superconductivity, comparable to that of FeSe mechanically exfoliated from bulk crystals, confirming the high quality of our samples. Beyond tetragonal FeSe, 2D antiferromagnetic FeTe and superconducting FeSxSeyTe1-x-y have been phase-selectively synthesized via this approach. Our study elucidates the significance of the growth interface on the phase-selective synthesis of 2D materials and presents potential opportunities for the phase-controlled synthesis of 2D multiphase materials via the rational design of the growth interface.

Preparation and release of antibacterial Na-mica-4/chlorhexidine nanocomposites

High charge swelling micas are layered silicates used in adsorption of several inorganic and organic species. In this study, we evaluated the adsorption of chlorhexidine digluconate on highly charge mica Na-mica-4. Drug release and antibacterial action against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) using the direct contact test for mica/chlorhexidine hybrids were evaluated. The hybrids were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential measurements, CHN elemental analysis, and scanning electron microscopy. Chlorhexidine interacts successfully with the mica surface. The maximum amount of chlorhexidine incorporated was 583 mg g−1, and the characterizations indicated that electrostatic attraction between the protonated amino group of the drug and the negative surface of clay was predominant in the formation of hybrids. Release kinetics study indicated that 80% of the drug release occurred in the first 12 h. The antibacterial test proved to be dependent on the time of chlorhexidine release, reaching 100% inhibition against S. aureus and E. coli after 0.5 h and 6 h, respectively.

Toward Modeling the Structure of Electrolytes at Charged Mineral Interfaces Using Classical Density Functional Theory.

The organization of water molecules and ions between charged mineral surfaces determines the stability of colloidal suspensions and the strength of phase-separated particulate gels. In this article, we assemble a density functional that measures the free energy due to the interaction of water molecules and ions in electric double layers. The model accounts for the finite size of the particles using fundamental measure theory, hydrogen-bonding between water molecules using Wertheim's statistical association theory, long-range dispersion interactions using Barker and Henderson's high-temperature expansion, electrostatic correlations using a functionalized mean-spherical approximation, and Coulomb forces through the Poisson equation. These contributions are shown to produce highly correlated structures, aptly rendering the layering of counterions and co-ions at highly charged surfaces and permitting the solvation of ions and surfaces to be measured by a combination of short-range associations and long-ranged attractions. The model is tested in a planar geometry near soft, charged surfaces to reproduce the structure of water near graphene and mica. For mica surfaces, explicitly representing the density of the outer oxygen layer of the exposed silica tetrahedra allows water molecules to hydrogen-bond to the solid. When electrostatic interactions are included, water molecules assume a hybrid character, being accounted for implicitly in the dielectric constant but explicitly otherwise. The disjoining pressure between approaching like-charged surfaces is calculated, demonstrating the model's ability to probe pressure oscillations that arise during the expulsion of ions and water layers from the interfacial gap and predict strong interattractive stresses that form at narrow interfacial spacing when the surface charge is overscreened. This interattractive stress arises not due to in-plane correlations under strong electrostatic coupling but due to the out-of-plane structuring of associating ions and water molecules.

Visualizing ribonuclease digestion of RNA-like polymers produced by hot wet-dry cycles

Polymerization of nucleotides under prebiotic conditions simulating the early Earth has been extensively studied. Several independent methods have been used to verify that RNA-like polymers can be produced by hot wet-dry cycling of nucleotides. However, it has not been shown that these RNA-like polymers are similar to biological RNA with 3′-5′ phosphodiester bonds. In the results described here, RNA-like polymers were generated from 5′-monophosphate nucleosides AMP and UMP. To confirm that the polymers resemble biological RNA, ribonuclease A should catalyze hydrolysis of the 3′-5′ phosphodiester bonds between pyrimidine nucleotides to each other or to purine nucleotides, but not purine-purine nucleotide bonds. Here we show AFM images of specific polymers produced by hot wet-dry cycling of AMP, UMP and AMP/UMP (1:1) solutions on mica surfaces, before and after exposure to ribonuclease A. AMP polymers were unaffected by ribonuclease A but UMP polymers disappeared. This indicates that a major fraction of the bonds in the UMP polymers is indeed 3′-5′ phosphodiester bonds. Some of the polymers generated from the AMP/UMP mixture also showed clear signs of cleavage. Because ribonuclease A recognizes the ester bonds in the polymers, we show for the first time that these prebiotically produced polymers are in fact similar to biological RNA but are likely to be linked by a mixture of 3′-5′ and 2′-5′ phosphodiester bonds.

Alginate-based water-soluble adhesives: effect of incorporated phenolic hydroxy groups on adhesiveness

Abstract Alginic acid (Alg) was modified with tyramine (TA), homoveratrylamine (HVTA), and 2-phenylethylamine (PA) to obtain Alg-based adhesives, AlgTA, AlgHVTA, and AlgPA. The adhesiveness of the modified Algs were evaluated and compared with previously reported catechol-modified alginate, AlgDA. AlgTA showed adhesion tendency differently from AlgDA, depending on the incorporation ratios of TA. AlgHVTA with protected phenolic hydroxy groups showed lower adhesiveness than AlgDA for mica surfaces, but higher for polymethyl methacrylate surfaces. AlgPA without a phenolic hydroxy group also exhibited moderate adhesiveness for mica.

Self-Competitive Growth of CsPbBr3 Planar Nanowire Array.

Semiconductor planar nanowire arrays (PNAs) are essential for achieving large-scale device integration. Direct heteroepitaxy of PNAs on a flat substrate is constrained by the mismatch in crystalline symmetry and lattice parameters between the substrate and epitaxial nanowires. This study presents a novel approach termed "self-competitive growth" for heteroepitaxy of CsPbBr3 PNAs on mica. The key to inducing the self-competitive growth of CsPbBr3 PNAs on mica involves restricting the nucleation of CsPbBr3 nanowires in a high-adsorption region, which is accomplished by overlaying graphite sheets on the mica surface. Theoretical calculations and experimental results demonstrate that CsPbBr3 nanowires oriented perpendicular to the boundary of the high-adsorption area exhibit greater competitiveness in intercepting the growth of nanowires in the other two directions, resulting in PNAs with a consistent orientation. Moreover, these PNAs exhibit low-threshold and stable amplified spontaneous emission under one-, two-, and three-photon excitation, indicating their potential for an integrated laser array.

VO2 nano-rod coated mica composite pearlescent pigment for temperature control packaging

A temperature control mica/VO2 functional pearlescent pigment was designed for the packaging industry. Firstly, a layer of VO2 nanorod film was coated on the surface of flake mica powder by hydrothermal method. Then, the surface of pure mica was modified by silane coupling agent KH-570 and sandwiched between inorganic powders to strengthen the combination. Secondly, the mica/VO2 composite pearlescent powder with gray-green pearlescent effect were successfully obtained by thermal annealing. The crystal structure of the VO2 coating and the chemical valence state of vanadium were verified by X-ray diffraction and X-ray photoelectron spectroscopy. Finally, powders were mixed with polyurethane resin to obtain a functional film. The infrared transmittance of film at 28 °C and 70 °C showed that the composite film with mica content of 3 g had greater temperature control properties, and the difference between high and low temperature transmittance was about 16%. Most importantly, the shiny decorative effect of pearlescent pigment can be still be maintained after being endowed with temperature control property. This work proposes the preparation of functional mica/VO2 composite with pearlescent effect and temperature control property.