Area Isotherms Research Articles

Accurate Simulations of Lipid Monolayers Require a Water Model with Correct Surface Tension.

Lipid monolayers provide our lungs and eyes their functionality and serve as proxy systems in biomembrane research. Therefore, lipid monolayers have been studied intensively including using molecular dynamics simulations, which are able to probe their lateral structure and interactions with, e.g., pharmaceuticals or nanoparticles. However, such simulations have struggled in describing the forces at the air–water interface. Particularly, the surface tension of water and long-range van der Waals interactions have been considered critical, but their importance in monolayer simulations has been evaluated only separately. Here, we combine the recent C36/LJ-PME lipid force field that includes long-range van der Waals forces with water models that reproduce experimental surface tensions to elucidate the importance of these contributions in monolayer simulations. Our results suggest that a water model with correct surface tension is necessary to reproduce experimental surface pressure–area isotherms and monolayer phase behavior. The latter includes the liquid expanded and liquid condensed phases, their coexistence, and the opening of pores at the correct area per lipid upon expansion. Despite these improvements of the C36/LJ-PME with certain water models, the standard cutoff-based CHARMM36 lipid model with the 4-point OPC water model still provides the best agreement with experiments. Our results emphasize the importance of using high-quality water models in applications and parameter development in molecular dynamics simulations of biomolecules.

Examination of Oil Structural Motifs and Temperature in Promoting Reversible Self-Assembly of Gold Nanoparticle Langmuir Films.

The interaction between gold nanoparticles (AuNPs) with other components and phases has important consequences on their use in materials and devices as well as their fate in the environment or at biological interfaces. Previously we determined that long oil chain lengths and lower temperatures optimized the mixing of n-alkanes with alkanethiol-capped AuNPs which improved nanoparticle self-assembly into superlattices at aqueous interfaces. In this study, a variety of liquid phase hydrocarbon oils with structural and functional variations were surveyed for their mixing efficacy and propensity to enable reversible self-assembly of nanoparticle domains. Transmission electron microscopy (TEM) images and pressure vs area isotherms across this series reveal isotherm features that distinguish between the mixing and inclusion of the oil at the interface and that which enables reversible self-assembly. Structural and functional characteristics of the oil for promoting reversible self-assembly are identified which surpass the importance of chain length previously described. Temperatures below the ligand order-disorder transition were found to improve the reversibility of AuNP domains and are understood by application of a reparametrized x-DLVO model.

Surface Chemistry Study of the Interactions of Sesame Oil with Meibomian Films.

A possible approach for the treatment of meibomian gland disease (MGD) can be the supplementation of meibomian gland secretion (MGS) with nonpolar lipids (NPL) rich plant oils. Sesame oil (SO), approximately equal in monounsaturated fat (oleic acid, 40% of total) and polyunsaturated fat (linoleic acid, 42% of total), has shown multiple health benefits due to its anti-inflammatory and antioxidant effects. Thus, the interactions between SO and MGS in surface layers deserve further study. Therefore, pseudobinary films were formed with controlled MGS/SO molar ratios (0%, 10%, 30%, 50%, and 100% SO) at the air/water surface of the Langmuir trough over phosphate buffered saline (pH 7.4) subphase. Surface pressure (π)-area (A) isotherms and Brewster angle microscopy observations showed nonideal interactions where SO aggregates with MGS and complements the NPL stratum of the meibomian layers. The analysis of stress relaxation transients with Kohlrausch–Williams–Watts equation revealed that the supplementation of fixed amount of MGS with excess lipids via SO altered the dilatational elasticity of the films as reflected by the increase of the exponent β. Thus, SO with its unique combination of high oxidative stability and abundance of long polyunsaturated acyl chains might be a useful supplement to MGS layers.

The Influence of Polysaccharides/TiO2 on the Model Membranes of Dipalmitoylphosphatidylglycerol and Bacterial Lipids.

The aim of the study was to determine the bactericidal properties of popular medical, pharmaceutical, and cosmetic ingredients, namely chitosan (Ch), hyaluronic acid (HA), and titanium dioxide (TiO2). The characteristics presented in this paper are based on the Langmuir monolayer studies of the model biological membranes formed on subphases with these compounds or their mixtures. To prepare the Langmuir film, 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DPPG) phospholipid, which is the component of most bacterial membranes, as well as biological material-lipids isolated from bacteria Escherichia coli and Staphylococcus aureus were used. The analysis of the surface pressure-mean molecular area (π-A) isotherms, compression modulus as a function of surface pressure, CS−1 = f(π), relative surface pressure as a function of time, π/π0 = f(t), hysteresis loops, as well as structure visualized using a Brewster angle microscope (BAM) shows clearly that Ch, HA, and TiO2 have antibacterial properties. Ch and TiO2 mostly affect S. aureus monolayer structure during compression. They can enhance the permeability of biological membranes leading to the bacteria cell death. In turn, HA has a greater impact on the thickness of E. coli film.

Influence of Unsaturations on the Organization and Air Reactivity of Triglyceride Monolayers.

The behavior of Langmuir monolayers of saturated and unsaturated C18 triglycerides (TAGs) was studied as two-dimensional (2D) models for paint systems at the air-water interface or transferred onto solid films. The organization of saturated tristearin (C18:0) monolayer was probed thanks to grazing incidence X-ray diffraction: one observes a hexagonal packing of the chains perpendicular to the air-water interface, in contrast to what is described in the literature. Conversely, the mono- and polyunsaturated TAGs (triolein C18:1, trilinolein C18:2, and trilinolenin C18:3) monolayers do not present any organization at the air-water interface but do exhibit peculiar reactivity regarding the air atmosphere. The obtained results derived from the evolution of surface pressure-molecular area isotherms and monolayer compressibility under different atmospheres over time, combined with ultrahigh-vacuum infrared (UHV-FTIR) spectroscopy, showed the adsorption of O2 molecules in the monolayer together with chemical reactions with hydrocarbon chains. The kinetic effect of lead ions, known to be efficient siccative agents in oil paints, was also assessed: the addition of Pb2+ in the subphase induces an increase of the O2 adsorption.

Interaction between Hydrophilic Ionic Liquid and Phospholipid/Cholesterol Mixed Film.

Surface pressure (π)-area (A) isotherms were studied to analyze the interactions between a hydrophilic ionic liquid (IL) (ethyl(2-hydroxyethyl)dimethylammonium methanesulfonate) and a pure dipalmitoylphosphatidylcholine (DPPC) film or a DPPC-cholesterol mixed film. When the hydrophilic IL was added to an underlayer solution, the isotherm shifted toward higher areas. Intriguingly, when the hydrophilic IL was added, the packing of the film materials became loose and the elastic modulus decreased, resulting in increased flexibility. This phenomenon was most evident under a cholesterol mole fraction of 0.2. This composition resembles that of cell membranes, which typically comprise phospholipids and cholesterol, suggesting that this hydrophilic IL may be able to interact significantly with biological membranes.

Aggregation behavior of the strong amphiphilic cationic diblock polyelectrolytes at the air/water interface

AbstractEffects of subphase temperature and pH on the interfacial behavior of two strong amphiphilic cationic diblock polyelectrolytes, quaternized poly(2‐[dimethylamino]ethyl methacrylate)‐block‐poly(lauryl methacrylate) (qPDMAEMA‐b‐PLMA), were studied by the Langmuir film balance technique for the first time. The morphologies of their Langmuir–Blodgett (LB) films were studied by atomic force microscopy. At the air/water interface, surface micelles with hydrophobic PLMA cores and hydrophilic qPDMAEMA coronas form. With the increase of temperature, the condensed surface pressure‐molecular area isotherms move to large area (right shift). The higher the temperature, the more obvious the isotherm shifts to the right. At low temperature, the isotherms of the two copolymers are almost respectively overlapped under different subphase pH conditions. At high temperature, however, the isotherms of the two copolymers show some subphase pH dependence. All initial LB films obtained at different subphase conditions exhibit isolated circular micelles. Under different subphase pH conditions, the diameters of the micelle cores in the two copolymers' LB films obtained at low temperature are close but larger than those at high temperature, which phenomenon is first reported. This is probably due to the relatively lower mobility of polymer individual chains at low temperature, resulting in their higher local surface concentration and larger aggregation.

Masking of a malodorous substance on 1,2-dioleoyl-sn-glycero-3-phosphocholine molecular layer

The performance of a trans-2-nonenal (NE)-including 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) molecular layer as a model of epithelial cellular membrane damaged by malodorous substance was investigated to understand the masking effect of odorants (benzaldehyde (BA), cyclohexanecarboxyaldehyde (CA), 4-anisaldehyde (AA), and 4-methoxycyclohexanecarbaldehyde (MA)). The surface pressure of the DOPC monolayer increased upon the addition of NE, and the surface pressure–area isotherm of the DOPC-NE mixture was characteristically responsive to the odorants (BA, CA, AA, and MA). Differential scanning calorimetry, Fourier-transform infrared spectroscopy, and ultraviolet absorption spectrophotometry were conducted to evaluate the interactions among DOPC, NE, and the odorants. The results suggested that odorants with an aromatic ring form a complex with NE and were eliminated from the DOPC membrane. We found that odorants with an aromatic ring play an important role in inducing the masking effect on the DOPC-NE mixed monolayer because of the characteristic interactions between NE and odorant.

Interaction of hectorite clay with a phospholipid monolayer at air-saline interface in presence of a fluorescent dye

The effect of hectorite clay on the monolayer of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at air-saline interface in presence of fluorescent dye acridine orange (AO) is studied. Surface pressure–area isotherm and compressibility studies reveal the phase behavior and rheological properties of DPPC monolayer. Formation of DPPC/clay complex and their aggregation during monolayer compression partially remove DPPC molecules form the interface. UV-vis absorption and fluorescence emission techniques confirm the aggregation of AO in DPPC/clay/AO hybrid Langmuir-Blodgett film. As phospholipids act as lung surfactants, this model study has implication of realizing the detrimental effects of clay on phospholipids during alveolar surface compression while breathing.

What if zeolite LTA4A and zeolite LTA5A used as Nickel catalyst supports for recycling carbon dioxide to green fuel methane

Commercial zeolite LTA4A and zeolite LTA5A were used as nickel metal catalyst supports for CO2 methanation. The catalysts were prepared by incipient wetness impregnation at %weight ranging from 5 % to 20 %. The catalysts were characterized by means of nitrogen physisorption for BET surface area and adsorption-desorption isotherms, thermogravimetric analysis under H2/N2 flowing mixture gases, time resolved X-ray Absorption Near Edge Structure (XANES) reduction, X-Ray Diffraction, H2 chemisorption, CO2 temperature programmed desorption and NH3 temperature programmed desorption. The morphology and particle size distribution were investigated by SEM and TEM. The catalysts exhibited difference in BET surface area, particle size distribution, and surface chemistry leading to the difference in product selectivity of CO2 hydrogenation (CO2/H2 = 1:4). The catalysts can accelerate the reaction initially at 300 °C and it was effective consistently until 500 °C. The nickel-based catalyst supported by zeolite LTA5A favored CO2 hydrogenated to methane, whereas others was mostly active for reverse water gas shift reaction. The catalyst at 5% nickel loaded on zeolite LTA gave the highest total CO2 conversion at 400–500 °C (72 % and 84 %), whereas 20 %Ni/LTA5A possessed the highest CO2 conversion to methane at 400 °C (45 %).

Formation of Surface Wrinkles in Collapsed Langmuir Films of a Polyhedral Oligomeric Silsesquioxane Containing Diblock Copolymer.

Surface pressure versus mean molecular area isotherms of Langmuir films of a hybrid diblock copolymer of poly(ethylene glycol) (PEG) and poly(methacrylo polyhedral oligomeric silsesquioxane) P(MA-POSS) together with Brewster angle microscopy reveal details of the phase transitions. The formation of a periodic wrinkling pattern in collapsed films is observed by epifluorescence microscopy after applying several compression-expansion cycles above the surface pressure of ≈18 mN/m. The wrinkle formation is reversible upon compression and expansion of the Langmuir films. Two distinct orientations of POSS molecules are assumed in Langmuir films upon compression, vertically for chains close to the water surface and horizontally orientated upper layers with significant amounts of PEG in between them. Thus, the wrinkling forms mainly in the top stiffer MA-POSS blocks above a certain compressional stress. The wrinkles disappear during the Langmuir-Blodgett (LB) transfer. Nevertheless, atomic force microscopy and grazing incidence wide-angle X-ray scattering experiments reveal the formation of highly ordered POSS molecules in LB films.

Plasma membrane permeabilization to explain erythrosine B phototoxicity on in vitro breast cancer cell models.

Lipid oxidation is ubiquitous in cell life under oxygen and essential for photodynamic therapy (PDT) of carcinomas. However, the mechanisms underlying lipid oxidation in rather complex systems such as plasma membranes remain elusive. Herein, Langmuir monolayers were assembled with the lipid extract of glandular breast cancer (MCF7) cells and used to probe the molecular interactions allowing adsorption of the photosensitizer (PS) erythrosine B and subsequent photooxidation outcomes. Surface pressure (π) versus area (cm2/mL) isotherms of MCF7 lipid extract shifted to larger areas upon erythrosine incorporation, driven by secondary interactions that affected the orientation of the carbonyl groups and lipid chain organization. Light-irradiation increased the surface area of the MCF7 lipid extract monolayer containing erythrosine owing to the lipid hydroperoxidation, which may further undergo decomposition, resulting in the chain cleavage of phospholipids and membrane permeabilization. Incorporation of erythrosine by MCF7 cells induced slight toxic effects on in vitro assays, differently of the severe phototoxicity caused by light-irradiation, which significantly decreased cell viability by more than 75% at 2.5×10-6 mol/L of erythrosine incubated for 3 and 24h, reaching nearly 90% at 48h of incubation. The origin of the phototoxic effects is in the rupture of the plasma membrane shown by the frontal (FSC) and side (SSC) light scattering of flow cytometry. Consistent with hydroperoxide decomposition, membrane permeabilization was also confirmed by cleaved lipids detected in mass spectrometry and subsidizes the necrotic pathway of cell death.

Composition, functionality and structural correlates of mixed lipid monolayers at air-water interface

Physicochemical properties of lipid monolayer depend on its composition where a blend of lipids exhibit superior behaviour than the individual component. Surface pressure ( π ) – area ( A ) isotherms of mixed monolayer (PC mix ) formed by dipalmitoylphosphatidylcholine (DPPC), palmitoleylphosphatidylcholine (POPC), soyphosphatidylcholine (SPC) and hydrogenated soy phosphatidylcholine (HSPC) in combination with 30 mole % cholesterol (Chol) were obtained by using Langmuir trough. Effects of dipalmitoylphosphatidyethanolamine (DPPE) on its mutual miscibility at the air-water interface with DPPC ​+ ​Chol, POPC ​+ ​Chol, HSPC ​+ ​Chol and SPC ​+ ​Chol were also investigated separately, followed by studying the effects of DPPE and dipalmitoylphosphatidylglycerol (DPPG) to PC mix ​+ ​Chol and PC mix ​+ ​DPPE ​+ ​Chol respectively. Lift-off area, minimum molecular area, excess molecular area, collapse pressure, Gibbs free energy of interfacial mixing, compressibility modulii values were evaluated by analyzing the isotherms. Deviations from the ideal mixing behaviours were dependent on the composition of the lipid blends. Surface dilatational rheology studies could assess monolayer elasticity, whereas the film morphologies were analysed by Brewster angle microscopic (BAM) studies. DPPC induced formation of condensed monolayer, whereas film rigidity was increased with the incorporation of DPPE and DPPG into mixed systems. Interactions among the lipid components of the investigated mixed systems were thoroughly discussed from the point of view of polar head and acyl chain saturation and obtained results follow the sequence: PC mix ​+ ​DPPE ​+ ​DPPG ​+ ​Chol ​> ​PC mix ​+ ​DPPE ​+ ​Chol ​> ​individual PC ​+ ​DPPE ​+ ​Chol which could be translated into the bilayer studies. Such investigation of mixed lipid is important for class of its own composition and combined results are expected to contribute in better understanding the interaction of selected lipid in proposed blend.

Influence of amphotericin B on the DPPC/DOPC/sterols mixed monolayer in the presence of calcium ions

Amphotericin B, an acquainted antifungal drug, has reattracted the attention of most scholars due to its one important advantage of making the fungus less resistant. Amphotericin B's antifungal properties are derived from its ability to interact with ergosterols on the fungal cells' membrane to form pores. However, the cholesterol in the human cell membranes is similar in structure to ergosterol, which cause the drug to produce certain toxicity and make the clinical use of amphotericin B limited. The study of the interaction between amphotericin B and lipid monolayer in the presence of cholesterol or ergosterol is crucial to understanding the mechanism of effect of the drug on cell membranes. Langmuir monolayer as a model for half of cell membranes can precisely control the proportion of components and the solution environment, which has been used to do a lot of research about the interaction of amphotericin B with lipids. It is noteworthy that some ions associated with life activities play an important role in it, such as calcium ions. In this work, the surface pressure-mean molecular area isotherms, elastic modulus and the surface pressure-time curves of DPPC/DOPC/sterol mixed monolayer with or without amphotericin B were studied in the different concentration of calcium ions. The morphology of the Langmuir-Blodgett films transferred on the mica were observed by atomic force microscopy. The results shown that AmB changed the elastic modulus and surface morphology of DPPC/DOPC/sterol mxied monolayer, which was significantly different with different types of sterols. Calcium ions can regulate the effect of this drug, which was clearly different due to different types of sterols. This work provides useful information to further understand the influence mechanism of calcium ions on the interaction between AmB and phospholipid/sterol monolayer, which is helpful to find out the effect mechanism of calcium ion on the interaction between AmB and phospholipid monolayer containing ergosterol or cholesterol and to understand the mechanism of AmB influencing on the membrane of fungal or human cells.

Development and characterization of magnetic iron oxide nanoparticles using microwave for the combustion reaction ignition, as possible candidates for biomedical applications

Magnetic iron oxide nanoparticles were prepared by solution combustion synthesis, using iron nitrate as oxidizer and citric acid as fuel. The influence of the combustion reaction ignition procedure, conventional heating and microwave heating, on nanoparticles characteristics was investigated. The synthesized nanoparticles were characterized by scanning and transmission electron microscopy, X-ray powder diffraction, thermogravimetric and differential scanning calorimetry, magnetic measurements, specific surface area and adsorption-desorption isotherms. The magnetic nanoparticles prepared by microwave heating exhibit larger specific surface area (70.7 m2/g), lower particle medium size (10.7 ± 3.09 nm) and lower saturation magnetization (41.8 emu/g) as compared to the sample prepared by conventional heating. Magnetic nanoparticles prepared by microwave heating were coated with oleic acid and Tween 80, and dispersed in phosphate buffered saline and distilled water. The colloidal suspensions demonstrated good stability, small polydispersity and small values of the hydrodynamic diameter, characteristics which recommend them to be tested for biomedical applications.

Immobilization of lipase in Langmuir − Blogett film of cubic silsesquioxane on the surface of zirconium dioxide

In this work, we report on the formation of interfacial films by amphiphilic, incompletely condensed silsesquioxane and enzyme, lipase. Besides, we deposited the mixed film on the surface of zirconium dioxide to be used as an efficient biocatalyst. The films were characterized at the air/liquid interface using the surface pressure−area isotherms, relaxation curves and dilatational rheology. For the characterization of the films deposited on a solid substrate we used atomic force microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and low−temperature N2 sorption analysis. The results are discussed in terms of formation, stability, and enzymatic activity of silsesquioxane−lipase interfacial film depending on enzyme concentration, properties of zirconia, and storage time.Lipase immobilized into the ultrathin film of trisilanolcyclohexyl POSS (TCyPOSS) exhibited high activity and could be recycled three times while retaining relatively high activity (ca. 70% for TCyPOSS+LP/ZrO2 and 60% TCyPOSS+LP/ZrO2-NHx). The effect of storage time on the activity of immobilized lipase was studied as well. Lipase immobilized in Langmuir−Blodgett film built by TCyPOSS on ZrO2 and ZrO2-NHx surface retained 98% activity after 7 days. We showed that the coating of zirconia by TCyPOSS film with the incorporated enzyme is a promising strategy for the immobilization of lipase with the controlled architecture at a molecular level.

Laponite elementary sheets assisted fluorescence resonance energy transfer: A demonstration by Langmuir-Blodgett technique

The fluorescence resonance energy transfer (FRET) between donor-acceptor molecules of fluorescein (FL) and rhodamine B (RhB) was enhanced by clay sheets of laponite. This enhancement was implemented by the Langmuir-Blodgett (LB) technique. Hybrid films were prepared by incorporating elementary clay sheets into dye molecules (FL and RhB for different molar ratios) at the air/water interface. The spectroscopic measurements (UV–Vis absorption and photoluminescence) of these mixture systems (FL, RhB and clay mineral) were analyzed both in colloidal dispersion and LB films. A high efficiency (92%) of FRET from FL to RhB was achieved with presence of laponite. Characterizations such as surface pressure versus area (π-A) isotherms, atomic force microscopy (AFM) and contact angle measurements were used to confirm the successful incorporation of clay sheets in hybrid films with loaded dye molecules. The clay incorporation were indicated to shorten the distance between donor and acceptor chromophores (Förster radius), which was realized by the tightly bounded dye molecules on clay sheets and self-assembly of dye molecule pairs.

Zinc–Carboxylate Binding in Mixed Octadecanoic Acid and Octadecanol Monolayers on Proxy Seawater Solution Surfaces

Organic coatings on sea spray aerosol are largely comprised of fatty acids in addition to a vast array of other organic molecules including fatty alcohols. The seawater from which sea spray aerosol originates contains metal ions that interact with the organic coating at the air–seawater interface, resulting in transport of these metals into the atmosphere. Metal binding within single-substance monolayers on aqueous solutions has been previously studied. However, such binding events within mixed monolayers, especially those of ocean-relevant ratios, are not well-explored. Here, we examine four monolayer ratios of octadecanoic acid (stearic acid) to octadecanol (stearyl alcohol) on aqueous solutions with varying ZnCl2 concentrations and a seawater-relevant NaCl concentration of 0.465 M. Surface pressure–area (Π-A) isotherms and infrared reflection–absorption spectroscopy (IRRAS) are used to quantify the Zn2+–carboxylate surface binding affinities for each monolayer composition. We find that Zn2+–carboxylate binding is enhanced by ∼300 times at the surface when compared to the bulk solution. Addition of 10% octadecanol reduces the apparent surface binding affinity by over 50% from 3.6 × 103 to 1.4 × 103 M–1; this is significantly more than predicted from the slight reduction in viable 1:1 binding sites. Furthermore, 1:2 Zn2+–carboxylate binding is shown to only be viable for the 100 and 95% fatty acid film, whereas 1:1 binding is observed for all film ratios investigated.

Effects of Carboxyl or Amino Group Modified InP/ZnS Nanoparticles Toward Simulated Lung Surfactant Membrane.

Quantum dots (QDs) as a promising optical probe have been widely used for in vivo biomedical imaging; especially enormous efforts recently have focused on the potential toxicity of QDs to the human body. The toxicological effects of the representative InP/ZnS QDs as a cadmium-free emitter are still in the early stage and have not been fully unveiled. In this study, the DPPC/DPPG mixed monolayer was used to simulate the lung surfactant monolayer. The InP/ZnS-COOH QDs and InP/ZnS-NH2 QDs were introduced to simulate the lung surfactant membrane’s environment in the presence of InP/ZnS QDs. The effects of InP/ZnS QDs on the surface behavior, elastic modulus, and stability of DPPC/DPPG mixed monolayer were explored by the surface pressure-mean molecular area isotherms and surface pressure-time curves. The images observed by Brewster angle microscope and atomic force microscope showed that the InP/ZnS QDs affected the morphology of the monolayer. The results further demonstrated that the InP/ZnS QDs coated with different surface groups can obviously adjust the mean molecular area, elastic modulus, stability, and microstructure of DPPC/DPPG mixed monolayer. Overall, this work provided useful information for in-depth understanding of the effects of the −COOH or −NH2 group coated InP/ZnS QDs on the surface of lung surfactant membrane, which will help scientists to further study the physiological toxicity of InP/ZnS QDs to lung health.

Interactions between silica particles and model phospholipid monolayers

The rapid increase in the air pollution level observed in recent years is considered to be one of the main social and economic problems due to the strong direct influence on living organisms. From the point of view of proper prophylaxis, explanation of the mechanism of the impact of suspended dust particles (PMs ≤ 10 µm) on model biological membranes at the molecular level is becoming increasingly important. In this work, we present the effects of the quantity and distribution of solid silica particles on the properties of Langmuir monolayers formed by the main phospholipids of biological membranes, i.e. 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-ethanolamine (POPE). Dispersions of silica particles (0.1%, 1.0% and 2.5%) have been added to the DPPC or POPE to form a mixed monolayer and investigated using a combination of Langmuir trough technique and Brewster Angle Microscopy (BAM). This study shows that the presence of silica particles (PMs) affects the run of the surface pressure–area (π–A) isotherm, leading to a different phase behaviour of the monolayer and it also has an impact on the lipid membrane morphology. Moreover, relaxation experiments of the phospholipid-PMs monolayer were performed to determine the influence of both concentration and distribution of silica particles on the stability of phospholipid membrane.