Langmuir最新文献

Physical interactions between polypeptide chains and lipid membranes underlie critical cellular processes. Yet, despite fundamental importance, key mechanistic aspects of these interactions remain elusive. Bulk experiments have revealed a linear relationship between free energy and peptide chain length in a model system, but does this linearity extend to the interaction strength and to the kinetics of lipid binding? To address these questions, we utilized a combination of coarse-grained molecular dynamics (CG MD) simulations, analytical modeling, and atomic force microscopy (AFM)-based single molecule force spectroscopy. Following previous bulk experiments, we focused on interactions between short hydrophobic peptides (WL_n, n = 1, ..., 5) with 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) bilayers, a simple system that probes peptide primary structure effects. Potentials of mean force extracted from CG MD recapitulated the linearity of free energy with the chain length. Simulation results were quantitatively connected to bulk biochemical experiments via a single scaling factor of order unity, corroborating the methodology. Additionally, CG MD revealed an increase in the distance to the transition state, a result that weakens the dependence of the dissociation force on the peptide chain length. AFM experiments elucidated rupture force distributions and, through modeling, intrinsic dissociation rates. Taken together, the analysis indicates a rupture force plateau in the WL_n-POPC system, suggesting that the final rupture event involves the last 2 or 3 residues. In contrast, the linear dependence on chain length was preserved in the intrinsic dissociation rate. This study advances the understanding of peptide-lipid interactions and provides potentially useful insights for the design of peptides with tailored membrane-interacting properties.

Surface nanobubbles forming on hydrophobic surfaces in water present an exciting opportunity as potential agents of top-down and bottom-up nanopatterning. The formation and characteristics of surface nanobubbles are strongly influenced by the physical and chemical properties of the substrate. In this study, focused ion beam (FIB) milling is used for the first time to spatially control the nucleation of surface nanobubbles with 75 nm precision. The spontaneous formation of nanobubbles on alternating lines of a self-assembled monolayer (octadecyltrichlorosilane) patterned by FIB is detected by atomic force microscopy. The effect of chemical vs topographical surface heterogeneity on the formation of nanobubbles is investigated by comparing samples with OTS coating applied pre- vs post-FIB patterning. The results confirm that nanoscale FIB-based patterning can effectively control surface nanobubble position by means of chemical heterogeneity. The effect of FIB milling on nanobubble morphology and properties, including contact angle and gas oversaturation, is also reported. Molecular dynamics simulations provide further insight into the effects of FIB amorphization on surface nanobubble formation. Combined experimental and simulation investigations offer insights to guide future nanobubble-based patterning using FIB milling.

The organization of metallic nanoparticles into assembled films is a complex process. The type of nanoparticle stabilizing ligand and the method for creating an organized layer can profoundly affect the optical properties of the resulting nanoparticle assembly. Investigations of the ligand structure and nanoparticle interactions can provide a greater understanding of the design of the assembly process and the quality of the resulting materials. One of the functionalization methods in the preparation of specific gold nanorods is the utilization of thiol-terminated poly(ethylene glycol). This generates gold nanorods capable of forming stable monolayers at the air-water interface upon dispersion in a suitable organic solvent. Herein, we show that depending on the molecular weight of the poly(ethylene glycol), the structures obtained at the air-water and air-solid interfaces differ in the arrangement. The studied structures were characterized by using spectroscopic and microscopic techniques, and the structural type was correlated with the polymer type. Insoluble and stable Langmuir monolayers composed of higher-molecular-weight gold nanorods with poly(ethylene glycol) were formed only in the presence of an additional stabilizer that prevented the formation of gold nanorods in aqueous solutions. At the air-solid interface, conformational changes in poly(ethylene glycol) induced the aggregation of gold nanorods, which became closely packed under the influence of surface pressure. The presented results suggested that the arrangement of two-dimensional layers of gold nanorods could be tailored using poly(ethylene glycol) of various molecular weights.

Aggregation-induced emission (AIE) has revolutionized solid-state fluorescence by overcoming the limitations of aggregation-caused quenching. While extensively studied in solutions, AIE's potential on solid surfaces remains largely unexplored, which can be fundamentally interesting and practically useful. In this work, we demonstrate the successful dispersion of tetraphenylethylene (TPE), one of the most classical AIE luminogens, on solid surfaces coated with silicone nanofilaments (SNF). The high surface area of SNF enables the uniform immobilization of TPE luminogens, replicating their dispersal behavior in solutions. Compared to unmodified surfaces, TPE dispersed on SNF-coated surfaces exhibits significantly enhanced fluorescence intensity. Moreover, a fascinating dynamic blue shift in TPE emission on SNF-coated surfaces is observed, with the velocity controllable by the surface group of SNF by up to 4 orders of magnitude, showing that TPE can be applied to the judgment of the nanoscale morphology and surface free energy of the solid surface. Owing to the superhydrophobicity and self-cleaning properties of SNF, the on-surface fluorescence can be sustained underwater and is resistant to dust contamination and rain erosion, with potential applications of information encryption presented. Our approach of uniformly dispersing AIE luminogens on nanomaterials with high surface areas provides a general methodology for creating on-surface fluorescence and saving the usage of expensive AIE luminogens in applications.

In the circulating water system of coastal power plants, various kinds of ions have a great influence on the formation and growth of CaCO₃ scales. This paper focuses on investigating the influence of existing ions on the pulse electrodeposition behaviors of CaCO₃ scales. Different concentrations of ions, such as Fe³⁺, Mg²⁺, PO₄^3- and SiO₃^2-, are introduced to simulate the actual seawater environment, and their influence on the CaCO₃ scale deposition behaviors is assessed by linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy tests. The surface coverage of the CaCO₃ scale layer is evaluated through the residual current density and polarization resistance values, while the crystal structure and surface compactness of the layer are confirmed by the scanning electron microscope and X-ray diffractometer tests. Results indicate that high concentrations of Mg²⁺, Fe³⁺, and PO₄^3- ions have the most significant inhibitory effect on the pulse electrodeposition of CaCO₃ scales, among which the inhibition effect of Mg²⁺ ions is mainly reflected in the change of crystal morphology of CaCO₃, that is, the crystallization growth process is inhibited. The inhibition effect of PO₄^3- ions is mainly reflected in the gradually reduced coverage and density of CaCO₃ crystals on the electrode surface, suggesting that the crystallization nucleation process is inhibited, while Fe³⁺ ions have a certain inhibition effect on both the crystallization nucleation and growth processes. Furthermore, lower concentrations of SiO₃^2- ions also display a significant inhibition effect on the crystallization nucleation and growth process, and the inhibition effect weakens with increased concentration. This study provides a theoretical basis for exploring the removal of ions in the industrial water softening field.

Although simulation results for gaseous adsorption on a surface of infinite extent, modeled with periodic conditions at the boundaries of the simulation box, agree with experimental data at high temperatures, simulated isotherms at temperatures below the triple point temperature show unphysical substeps because of the compromise of interactions within the box and interactions between the box and its mirror image boxes. This has been alleviated with surfaces of finite dimensions (Loi, Q. K.; Colloids Surf., A 2021, 622, 126690 and Castaño Plaza, O.; Langmuir 2023, 39 (21), 7456-7468) to account for free boundaries at the adsorbate patch on the surface, and the critical parameter of this model substrate is the size of the finite surface. If it is too small, the adsorbate patch does not model the physical reality; however, if it is too large, the computation time is excessive, making the simulation impractical. In this study, we used carbon dioxide/graphite as the model system to explore the effects of finite dimensions on the description of experimental data of Terlain, A.; Larher, Y. Surf. Sci. 1983, 125 (1), 304-311, especially for temperatures below the bulk triple point temperature. With the appropriate choice of graphene size, we derived the 2D triple point and 2D critical point temperatures of the monolayer, and most importantly, for temperatures below the 2D critical point temperature, the adsorption mechanism for the formation of the monolayer is due to the interplay between the boundary growth process and the vacancy filling. The extent of this interplay is found to depend on the fractional coverage of the surface.

Magnesium-based biodegradable metal bone implants exhibit superior mechanical properties compared to biodegradable polymers for orthopedic and cardiovascular stents. In this study, MgZZC-x (x = 1, 1.2) alloys were screened by in vitro biocompatibility tests in three simulated body fluids under nontoxic conditions. The MgZZC-1 alloys with better biocompatibility were selected to predict the days required for complete degradation. The evolution of degradation products was analyzed, and the mechanism of formation of the product film was inferred. A degradation kinetic model was established to investigate the effect of MEM components on the degradation of the alloys. The results demonstrate that the proteins in MEM can greatly retard the degradation progress by attaching to the surface of MgZZC-1 alloys, which are predicted to degrade completely within 341 days. The carbonate and phosphate buffers were adjusted to pH in MEM solution, delaying the degradation of magnesium alloys. This process in MEM more accurately reflects the actual degradation in the body and is superior to that in Hanks and SBF solutions. This study will promote the application of biodegradable materials in clinical medicine.

The antifouling properties of conductive polymers have received extensive attention for biosensor and bioelectronic applications. Polyethylene glycol (PEG) is a well-known antifouling material, but the controlled regulation of the surface topography of PEG without a template remains a challenge. Here, we show a columnar structure antifouling conductive polymer brush with enhanced antifouling properties and considerable conductivity. The method involves synthesizing the 3,4-ethylenedioxythiophene monomer modified with azide (EDOT-N₃), the electropolymerization of PEDOT-N₃, and the in situ growth of PEG polymer brushes on PEDOT through double-click reactions. The resultant columnar structure polymer brush exhibits high electrical conductivity (3.5 Ω·cm²), ultrahigh antifouling property, electrochemical stability (capacitance retention was 93.8% after 2000 cycles of CV scans in serum), and biocompatibility.

Shale reservoirs are characterized by an abundance of nanoscale porosities and microfractures. The states of fluid occurrence and flow behaviors within nanoconfined spaces necessitate novel research approaches, as traditional percolation mathematical models are inadequate for accurately depicting these phenomena. This study takes the Gulong shale reservoir in China as the subject of its research. Initially, the unique mixed wetting characteristics of the Gulong shale reservoir are examined and characterized using actual micropore images. Subsequently, the occurrence and flow behavior of oil within the nanoscale bedding fractures under various wettability scenarios are described through a combination of microscopic pore image and molecular dynamics simulations. Ultimately, a mathematical model is established that depicts the velocity distribution of oil and its apparent permeability. This study findings indicate that when the scale of the shale bedding fractures is less than 100 nm, the impact of the nanoconfinement effect is significant and cannot be overlooked. In this scenario, the state of oil occurrence and its flow behavior are influenced by the initial oil-wet surface area on the mixed wetting walls. The study quantifies the velocity and density distribution of oil in mixed wetting nanoscale shale bedding fractures through a mathematical model, providing a crucial theoretical basis for upscaling from the nanoscale to the macroscale.

In this study, a water-soluble quaternary ammonium salt (QAS)-functionalized montmorillonite (MMT) was fabricated using a mechanochemical method as a high-performance water lubrication additive. The intercalation of QAS into the MMT layer expands the layer spacing of MMT, but does not affect the hydrophilicity of MMT. The ultrathin layer QAS-functionalized montmorillonite (QAS-MMT) demonstrated excellent water-stable dispersion and can be used as a water-based lubrication additive. Only 0.1% addition can reduce the friction coefficient by more than 71.4% and the wear volume by about 58.8% when compared to water, demonstrating its excellent friction reduction and antiwear performance. The frictional mechanism indicates that the physical adsorption film, together with the chemical reaction film, endows the QAS-MMT additives with outstanding tribological performance, provides excellent lubrication for the contact of steel/steel pairs, and prevents the steel surface from being further worn.