Spread Monolayers Research Articles

Coadsorption of Human Milk Lactoferrin into the Dipalmitoylglycerolphosphatidylcholine Phospholipid Monolayer Spread at the Air/Water Interface

The coadsorption of human milk lactoferrin into a spread monolayer of dipalmitoylglycerol phosphatidylcholine (DPPC) at the air/water interface has been studied by neutron reflection. The system is a good model of the preocular tear film outer interface, which was the motivation for the study. The association of the protein with the surface was indicated by an increase of the surface pressure exerted by the DPPC monolayer. The extent of lactoferrin coadsorption was found to decrease with increasing surface pressure in the lipid monolayer, a trend consistent with the observation reported for other proteins, such as lysozyme and β-lactoglobulin. The neutron reflectivity measurements were subsequently carried out at the three surface pressures of 8, 15, and 35 mN/m to examine the structure and composition of lactoferrin coadsorbed at the interface. Whereas the DPPC monolayer effectively prevented lactoferrin insertion at the high surface pressure, a measurable amount of lactoferrin was found at the air/water interface at the two lower surface pressures. At 15 mN/m it was difficult to identify the distribution of lactoferrin with respect to the DPPC monolayer, due to its relatively low adsorbed amount and much broader distribution. At the lowest surface pressure of 8 mN/m, the lactoferrin coadsorption was found to increase with time over the first few hours. After 5 h the distribution of the lactoferrin layer became similar to, though quantitatively lower than, that adsorbed in the absence of the DPPC monolayer. It is characterized by a top dense sublayer of 15 Å with a bottom diffuse sublayer of 60 Å, indicating structural unfolding induced by surface adsorption under these conditions.

Temperature Dependence of Poloxamer Insertion Into and Squeeze-Out from Lipid Monolayers

F68, a triblock copolymer of the form poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), is found to effectively seal damaged cell membranes. To better understand the molecular interaction between F68 and cells, we have modeled the outer leaflet of a cell membrane with a dipalmitoylphosphatidylcholine (DPPC) monolayer spread at the air-water interface and introduced poloxamer into the subphase. Subsequent interactions of the polymer with the monolayer either upon expansion or compression were monitored using concurrent Langmuir isotherm and fluorescence microscopy measurements. To alter the activity of the poloxamer, a range of subphase temperatures from 5 to 37 degrees C was used. Lower temperatures increase the solubility of the poloxamer in the subphase and therefore lessen the amount of material at the interface, resulting in a lower equilibrium spreading pressure. Additionally, changes in temperature affect the phase behavior of DPPC. Below the triple point, the monolayer is condensed at pertinent polymer insertion pressures; for temperatures immediately above the triple point, the monolayer is a heterogeneous mix of liquid expanded and condensed phase; for the highest temperature measured, the DPPC monolayer remains completely fluid. At all temperatures, F68 inserts into DPPC monolayers at its equilibrium spreading pressure. Upon compression of the monolayer, polymers are squeezed-out at surface pressures notably higher than those for insertion, with higher temperatures leading to a higher squeeze-out pressure. An increase in temperature decreases the solvent quality of water for the poloxamer, lowering solubility of the polymer in the subphase and thus increasing its propensity to be maintained within the monolayer to higher pressures.

Surface-energy dependent spreading of lipid monolayers and bilayers.

Spontaneous spreading of phospholipids following hydration by water is directly compared on hydrophilic and hydrophobic surfaces using planar, composite substrates exhibiting binary patterns of surface energies. The use of patterned substrates-in conjunction with real-time, quantitative applications of imaging ellipsometry and epifluorescence microscopy-affords a side-by-side comparison of spreading kinetics and equilibrium morphologies following the hydration of a single parent-lipid source. We find that for fluid phospholipids ( > ), substantially contiguous bimolecular and mono-molecular lipid layers spread away from a source on hydrophilic and hydrophobic surfaces, respectively. For bilayers and monolayers, the advancing lipid sheets exhibit square-root-of-time dependent kinetics reflecting a balance between a spreading force and a resistive drag. Furthermore, monolayers advance at only a slightly faster rate (by a factor of 1.7 ± 0.2) than bilayers despite a substantially higher available spreading energy. This apparently counter-intuitive observation can be reconciled in terms of a corresponding rise in the competing drag energy-consistent with the differences in slip-planes associated with mono- and bilayer spreading.

Swelling of a cluster phase in Langmuir monolayers containing semi-fluorinated phosphonic acids.

Langmuir monolayers of semi-fluorinated nonadecylphosphonic acid (F8H11PO), hexadecylphosphonic acid (H16PO), and their mixtures were investigated by Brewster angle microscopy (BAM), atomic force microscopy (AFM) and surface-pressure measurements. Nanometre-scale two-dimensional clusters were observed by AFM in a spread monolayer of pure F8H11PO transferred to mica. Two different organized arrangements of clusters were observed. AFM and BAM observations showed that the mixture exhibits a solid phase over a large range of mole fraction and surface pressure, sometimes in coexistence with clusters. With increasing mole fraction of H16PO, the lateral shape of these clusters remains the same while their organization and their height change.

Surface Pressure Analysis of Poly(ethylene oxide)-Modified Fusogenic Liposomes Incorporated into a Phospholipid Monolayer

Fusogenic liposomes have a wide-range of applications as DDS and gene/protein delivery into living cells. A variety of surface modifications of drug carriers, to enable fusion with cells, have been proposed, however, the mechanism of fusion has still not been determined. To further improve the efficiency of drug carriers, a simple and easily examinable model of a living cell surface is needed. In this study, the time-course of a fusion phenomena was made by measuring the surface pressure increase of a phospholipid monolayer spread at the air/water interface due to the fusion of liposomes carrying PEO-lipid (dialkyl-terminated polyethylene oxide) reconstituted on their outer surface. The kinetics of the surface pressure change appeared to be bimodal, indicating the coexistence of different fusion pathways. It was found that the presence of the PEO-lipid on the liposome surface led to a faster lipid transfer compared to non-modified DMPC liposomes. This indicated that the reconstitution of PEO-lipid provided an alternative transfer pathway to that for non-fusogenic liposomes that show only a slow lipid transfer to phospholipid monolayers. The relation between the rate of fusion and the surface pressure of the host membrane is discussed.

Adsorption of water-soluble polymers with surfactant character.: Adsorption kinetics and equilibrium properties

A comparative study between Langmuir and Gibbs monolayers of a hyperbranched polyol, poly(propylene glycol) homopolymers, and poly(propylene glycol)–poly(ethylene glycol) copolymers with different structure and molecular weight, is reported. Dynamic surface tension (DST) and surface pressure measurements have been carried out to characterize these amphiphilic water-soluble polymers. The adsorption kinetics results are consistent with a rapid diffusion stage followed by a slow reorganization at the air–water interface. The characteristic times of these steps, calculated by the Joos model, point out differences among the polymers in the diffusion rate and rearrangement mechanisms for diluted solutions. Short time analysis of DST data leads to diffusion coefficients in qualitative agreement with the diffusion times calculated with Joos' model. Spread monolayers remain stable for long periods of time. The desorption process seems quite inoperative. As a consequence, the surface pressure of the spread monolayers can be studied over a broad surface concentration range. 2D first-order phase transitions have been evidenced from plateaux observed in Langmuir and Gibbs isotherms. It has been found that Gibbs monolayers lead to lower surface tension states than the Langmuir ones.

Template-Directed Self-Assembly of Alkanethiol Monolayers: Selective Growth on Preexisting Monolayer Edges

Self-assembled monolayers were investigated for their suitability as two-dimensional scaffolds for the selective growth of alkanethiol edge structures. Heterostructures with chemical contrast could be grown, whose dimensions were governed by both the initial pattern sizes and the process time. n-Octadecanethiol (ODT) was made to expand from the edges of 16-mercaptohexadecanoic acid (MHDA) monolayer patterns. Likewise, 11-mercaptoundecanol (MUD) was grown on MHDA and on ODT monolayer edges. The results of these experiments are in accordance with the moving boundary model for monolayer spreading. In addition to such surface-bound spreading, a vapor-phase contribution to lateral monolayer growth was identified. MUD was observed to be an excellent ink for creating chemical contrast by means of regioselective deposition from a vapor phase. As a proof of principle, ribbons of 11-mercaptoundecanol with submicrometer widths were grown on pentaerythritol-tetrakis(3-mercaptopropionate) edges, and submicrometer wide gold lines were produced by subsequent wet-chemical etching.

Recognition and Blocking of HIV-1 gp41 Pre-transmembrane Sequence by Monoclonal 4E10 Antibody in a Raft-like Membrane Environment

The conserved (664)DKWASLWNWFNITNWLWYIK(683) (preTM) sequence preceding the transmembrane anchor of human immunodeficiency virus (HIV-1) gp41 glycoprotein subunit is accessible to the broadly neutralizing 4E10 antibody and, therefore, constitutes a potential target for vaccine design. Recently reported structural data are compatible with preTM insertion into the viral external membrane monolayer in the gp41 pre-fusion state (Zhu, P., Liu, J., Bess, J., Chertova, E., Lifson, J. D., Grisé, H., Ofek, G. A., Taylor, K. A., and Roux, K. H. (2006) Nature 441, 847-852). Here we demonstrate that the broadly neutralizing 4E10 antibody is able to specifically block the membrane-restructuring activity of a peptide mimic inserted into membranes. Recognition and restructuring blocking occurred in the presence of cholesterol, whereas transmembrane versions as those promoted in 1-palmitoyl-2-oleoylphosphatidylcholine:sphingomyelin mixtures could not be effectively arrested. Spectrofluorimetric assays using rhodamine-labeled peptides revealed that recognition correlated better with pore-formation blocking than with membrane-fusion inhibition. The capacity of the antibody to recognize preTM peptides in a raft-like environment was further corroborated employing planar-supported lipid layers and fluorescence microscopy. These data support that membrane-bound epitope recognition by 4E10 results in clustering reorganization of preTM at the membrane interface. We propose that this process might interfere with the formation of fusion-competent complexes at the low spike densities existing in the HIV-1 membrane. This work comprises the first experimental report on a lipid-modulated antibody capacity to bind a membrane-bound epitope sequence and arrest its restructuring activity.

Penetration of β-Lactoglobulin into Monoglyceride Monolayers. Dynamics, Interactions, and Topography of Mixed Films

In this work we have analyzed the penetration of betalactoglobulin into a monoglyceride monolayer (monopalmitin or monoolein) spread at the air-water interface and its effects on the structural, dilatational, and topographical characteristics of mixed films. Dynamic tensiometry, surface film balance, Brewster angle microscopy (BAM), and surface dilatational rheology have been used, maintaining the temperature constant at 20 degrees C and the pH and ionic strength at 7 and 0.05 M, respectively. The initial surface pressure (mN/m) of the spread monoglyceride monolayer (pii(MONOGLYCERIDE)) at 10, 20, and the collapse point is the variable studied. Beta-lactoglobulin can penetrate into a spread monoglyceride monolayer at every surface pressure. The penetration of beta-lactoglobulin into the monoglyceride monolayer with a more condensed structure, at the collapse point of the monoglyceride, requires monoglyceride molecular loss by collapse and/or desorption. However, the structural, topographical, and dilatational characteristics of monoglyceride penetrated by beta-lactoglobulin mixed monolayers are essentially dominated by the presence of monoglyceride (either monopalmitin or monoolein) in the mixed film. In fact, monoglyceride molecules have the capacity to re-enter the monolayer after expansion and recompression of the mixed monolayer. Thus, monoglyceride molecular loss by collapse and/or desorption is reversible. The topography of the monolayer under dynamic conditions corroborates these conclusions.

Amphiphilic laminin peptides at air/water interface—Effect of single amino acid mutations on surface properties

Amphiphilic derivative of the laminin peptide YIGSR and three other mutated peptides with mutation at Y with V (valine), I (isoleucine), and L (leucine) have been synthesized. The monolayer formation and the stability of these peptide analogues at air/water interface and the interaction with phospholipid monolayers have been studied using surface pressure–molecular area ( π– A) and surface potential–molecular area (Δ V– A) isotherms. The single amino acid mutation in the native sequence leads to appreciable changes in surface activity, orientation and insertion into lipid monolayers with LIGSR showing most hydrophobic character while YIGSR showed most polar nature. The morphology of spread monolayers in the most close packed state was carried out using Brewster angle microscopy (BAM). LB films of these amphiphilic peptide derivatives transferred to hydrophilic quartz surfaces and hydrophobically modified surfaces showed significant changes in the work of adhesion as well as spreading behavior of water with the L substituted sequence showing maximum work of adhesion and the native sequence YIGSR, the least work of adhesion. From theoretical estimates, the long-range effects of the different amino acid residues in position 1 on the alkyl chains have been studied from charge on the carbon and hydrogen atoms of the alkyl tails. The present study demonstrates that amphiphilic derivatives of the laminin peptide YIGSR show enhanced activity compared to the original sequence. This work shows that the amino acid substituents on the head group clearly influence the distal methylene groups of the tail. Thus, any mutation of even single amino acid in a peptide sequence influences and plays an important role in determining macroscopic properties such as surface energy and adhesion both at air/solution and solid/solution interfaces.

Structural Characteristics of Dipalmitoylphosphatidylcholine and Hydrolysates from Sunflower Protein Isolate Mixed Monolayers Spread at the Air−Water Interface

In this work, surface film balance and Brewster angle microscopy techniques have been used to analyze the structural characteristics (structure, topography, reflectivity, thickness, miscibility, and interactions) of hydrolysates from sunflower protein isolate (SPI) and dipalmitoylphosphatidylcholine (DPPC) mixed monolayers spread on the air-water interface. The degree of hydrolysis (DH) of SPI, low (5.62%), medium (23.5%), and high (46.3%), and the protein/DPPC mass fraction were analyzed as variables. The structural characteristics of the mixed monolayers deduced from the surface pressure (pi)-area (A) isotherms depend on the interfacial composition and degree of hydrolysis. At surface pressures lower than the equilibrium surface pressure of SPI hydrolysate (pi(e)(SPI hydrolysate)), both DPPC and protein are present in the mixed monolayer. At higher surface pressures (at pi > pi(e)(SPI hydrolysate)), collapsed protein residues may be displaced from the interface by DPPC molecules. The differences observed between pure SPI hydrolysates and DPPC in reflectivity (I) and monolayer thickness during monolayer compression have been used to analyze the topographical characteristics of SPI hydrolysates and DPPC mixed monolayers at the air-water interface. The topography, reflectivity, and thickness of mixed monolayers confirm at microscopic and nanoscopic levels the structural characteristics deduced from the pi-A isotherms.

Formation of a Highly Ordered Dot Array of Surface Micelles of a Block Copolymer via Liquid Crystal-Hybridized Self-Assembly

A highly ordered dot array pattern of surface micelles on water is formed by a spread monolayer of an amphiphilic block copolymer, polystyrene-block-poly(4-vinylpyridine) (PS-4VP), via hybridization with a liquid crystal molecule, 4'-pentyl-4-cyanobiphenyl (5CB), on water. Simple co-spreading of PS-4VP with 5CB provides a flat homogeneous monolayer of PS-4VP on water without the aggregation of PS blocks. With increasing surface pressure, well-defined dots of the PS blocks start to grow and are arrayed in a highly ordered hexagonal structure. The exact coincidence of the surface pressure-area curves for the hybrid monolayer in the compression and expansion processes confirms that the flat spread monolayer and the dot array are formed on water in the equilibrium state by a self-assembly process.

The Effect of Polysaccharide Adsorption on Surface Potential of Phospholipid Monolayers Spread at Water–Air Interface

The Effect of Polysaccharide Adsorption on Surface Potential of Phospholipid Monolayers Spread at Water–Air Interface

Effects of albumin and erythrocyte membranes on spread monolayers of lung surfactant lipids

Dipalmitoyl phosphatidylcholine (DPPC), one of the main constituents of lung surfactant is mainly responsible for reduction of surface tension to near 0 mN/m during expiration, resisting alveolar collapse. Other unsaturated phospholipids like palmitoyloleoyl phosphatidylglycerol (PG), palmitoyloleoyl phosphatidylcholine (POPC) and neutral lipids help in adsorption of lung surfactant to the air–aqueous interface. Lung surfactant lipids may interact with plasma proteins and hematological agents flooding the alveoli in diseased states. In this study, we evaluated the effects of albumin and erythrocyte membranes on spread films of DPPC alone and mixtures of DPPC with each of PG, POPC, palmitoyloleoyl phosphatidylethanolamine (PE), cholesterol (CHOL) and palmitic acid (PA) in 9:1 molar ratios. Surface tension–area isotherms were recorded using a Langmuir–Blodgett (LB) trough at 37 °C with 0.9% saline as the sub-phase. In the presence of erythrocyte membranes, DPPC and DPPC + PA monolayers reached minimum surface tensions of 7.3 ± 0.9 and 9.6 ± 1.4 mN/m, respectively. Other lipid combinations reached significantly higher minimum surface tensions >18 mN/m in presence of membranes (Newman Keul's test, p < 0.05). The relative susceptibility to membrane inhibition was [(DPPC + PG, 7:3) = (DPPC + PG, 9:1) = (DPPC + POPC) = (DPPC + PE) = (DPPC + CHOL)] > [(DPPC + PA) = (DPPC)]. The differential response was more pronounced in case of albumin with DPPC and DPPC + PA monolayers reaching minimum surface tensions less than 2.4 mN/m in presence of albumin, whereas DPPC + PG and DPPC + POPC reached minimum surface tensions of around 20 mN/m in presence of albumin. Descending order of susceptibility of the spread monolayers of lipid mixtures to albumin destabilization was as follows: [(DPPC + PG, 7:3) = (DPPC + PG, 9:1) = (DPPC + POPC)] > [(DPPC + PE) = (DPPC + CHOL)] > [(DPPC + PA) = (DPPC)] The increase in minimum surface tension in presence of albumin and erythrocyte membranes was accompanied by sudden increases in compressibility at surface tensions of 15–30 mN/m. This suggests a monolayer destabilization and could be indicative of phase transitions in the mixed lipid films due to the presence of the hydrophobic constituents of erythrocyte membranes.

Poly(ethylene oxide)s hydrophobically modified. Adsorption and spreading at the air–water interface

A comparative study of spread and adsorbed monolayer of poly(ethylene oxide)s of different molecular weight hydrophobically modified with alkyl isocyanates of different length chain is reported. The modification of the polymer was carried out according to reported procedures. The polymers obtained were studied at the air–water interface by Langmuir isotherms for spread monolayers and by Gibbs isotherms for the adsorption process. Isotherms obtained are interpreted in terms of the hydrophobic and hydrophilic balance of the polymers. Limiting area per repeating unit ( A 0 ) and collapse pressure ( π c ) from spread monolayers were obtained. Spread monolayers of the hydrophobically modified polymers show larger collapse pressure values than unmodified polymer monolayers. In the adsorption process the excess surface concentration Γ ∞ , area per repeat unit σ, and efficiency of the adsorption were determined. The values of the area occupied per repeat unit in adsorbed monolayer ( σ) were larger than those of the spread monolayer. The efficiency of the adsorption of poly(ethylene oxide)s increases with the hydrophobic modification and with the alkyl chain length.

Deformation and breakup of a stretching liquid bridge covered with an insoluble surfactant monolayer

The breakup of surfactant-laden drops and jets is of technological interest and fundamental scientific importance. Surfactants are routinely used to control the breakup of drops and jets in applications ranging from inkjet printing to crop spraying. Accurate computation of breakup of surfactant-laden drops and jets is often the key to the development of new applications and to providing a rational fundamental understanding of both existing and emerging applications. While highly accurate algorithms for studying the breakup of surfactant-free drops and jets are well documented and much is now known about the dynamics in such situations, little is known by contrast about the closely related problem of interface rupture when surfactant effects cannot be neglected. The deformation and breakup of a stretching liquid bridge of an incompressible Newtonian fluid whose surface is covered with an insoluble surfactant monolayer are analyzed here experimentally and computationally. In the experiments, high-speed visualization is used to capture the transient deformation of a bridge. The dynamic shapes of bridges (captive between two rods of 3.15 mm diameter) are captured and analyzed with a time resolution of 1 ms. The bridge lengths are 3.15 mm initially and about 4–7 mm at breakup, which occurs after stretching for about 0.1–0.2 s, depending on the volume and viscosity of the liquid and the surface density of spread monolayers. The dynamics of a surfactant-covered bridge is governed by the Navier-Stokes and convection-diffusion equations. First, these equations are solved with a three-dimensional, but axisymmetric, or two-dimensional (2D), finite element algorithm using elliptic mesh generation. Second, the governing set of 2D equations is reduced to a set of one-dimensional (1D) equations by means of the slender-jet approximation and the resulting set of 1D equations is solved with a 1D finite element algorithm. The presence of surfactant results not only in the lowering of surface tension and the capillary pressure, but also in surface tension gradients and Marangoni stresses, both of which affect the transient dynamics leading to breakup. In particular, the role of Marangoni stresses in delaying bridge breakup and on formation of satellite droplets is investigated as a function of the initial surface density and surface activity of the surfactant, and surface Peclet number that measures the importance of convection relative to diffusion. The predictions of the 2D algorithm are confirmed to be faithful to the physics by demonstrating that the computed results accord well with the experiments and existing scaling theories. In the pinch-off region, the surfactant is swept out of a thinning neck by strong convection. The calculations thus reveal that the scaling behavior in the presence of surfactant parallels that observed in the absence of surfactant, in accordance with recent reports by others. The 2D computations and the experiments are used in tandem to identify regions in the space of governing parameters where the 1D equations can be used with confidence.

Phase diagram of n-tetradecyl phosphate in Gibbs monolayers

A phase diagram for Gibbs monolayers of n-tetradecyl phosphate ( n-TDP) has been constructed from the surface pressure–time isotherms and the direct observation of the monolayer morphology using Brewster angle microscopy (BAM). Three different phases, which are gas (G), liquid expanded (LE) and liquid condensed (LC) are observed during the formation of the monolayers under different conditions. All of these phases coexist at the triple point of 6.5 °C of n-TDP monolayers. Below this triple point, a first-order G-LC phase transition has been found to occur. Above the triple point, a first-order G-LE phase transition is followed by another first-order LE-LC phase transition. BAM images confirmed the order of phase transitions and the nature of phases. The critical temperature for the LC phase formation has been found to be 36.5 °C. All the findings are in line with the present understanding of the spread monolayers.

Kinetic Appearance of First-Order Gas−Liquid Expanded and Liquid Expanded−Liquid Condensed Phase Transitions below the Triple Point

Phase diagram of Gibbs monolayers of mixtures containing n-hexadecyl phosphate (n-HDP) and L-arginine (L-arg) at a molar ratio of 1:2 has been constructed by measuring surface-pressure-time (pi-t) isotherms with film balance and by observing monolayer morphology with Brewster angle microscopy (BAM). This phase diagram shows a triple point for gas (G), liquid expanded (LE), and liquid condensed (LC) phases at around 6.7 degrees C. Above this triple point, a first-order G-LE phase transition occurring at 0 surface pressure is followed by another first-order LE-LC phase transition taking place at a certain higher surface pressure that depends upon temperature. The BAM observation supports these results. Below the triple point, the pi-t measurements show only one first-order phase transition that should be G-LC. All of these findings are in agreement with the general phase diagram of the spread monolayers. However, the BAM observation at a temperature below the triple point shows that the thermodynamically allowed G-LC phase transition is, in fact, a combination of the G-LE and LE-LC phase transitions. The latter two-phase transitions are separated by time and not by the surface pressure, indicating that the G-LC phase transition is kinetically separated into these two-phase transitions. The position of the LE phase below the triple point in the phase diagram is along the phase boundary between the G and LC phases.

Cyclic peptides as scaffold for oriented functional groups on surface

Surface modification with Disperse Red-1 (DR-1), which is a chromophore for optical second harmonic generation (SHG), was carried out by using cyclic peptides as a scaffold for DR-1. Cyclic dipeptide and cyclic octapeptide having DR-1 at the side chain were synthesized. The surfaces of quartz or glass substrates were covered with the cyclic peptides by transfer of the monolayer spread on water subphase (Langmuir–Blodgett film) or by cast of thin film. The planar cyclic skeleton lay down on the surface with face-to-face orientation. The orientation of the DR-1 unit in the side chain of the cyclic peptides was evaluated by polarization modulation Fourier transform infrared reflection–absorption spectroscopy and SHG measurement. The results indicate that the DR-1 unit was fixed on the surface with anisotropic orientation due to the scaffold ability of the cyclic peptides.

Diffusive spreading and mixing of fluid monolayers

The use of ultra-thin, i.e. monolayer, films plays an important role in the emerging field ofnano-fluidics. Since the dynamics of such films is governed by the interplay betweensubstrate–fluid and fluid–fluid interactions, the transport of matter in nanoscale devicesmay eventually be efficiently controlled by substrate engineering. For such films, thedynamics is expected to be captured by two-dimensional lattice-gas models with interactingparticles. Using a lattice-gas model and the non-linear diffusion equation derived from themicroscopic dynamics in the continuum limit, we study two problems of relevance in thecontext of nano-fluidics. The first one is the case in which along the spreading direction of amonolayer a mesoscopic-sized obstacle is present, with a particular focus on the relaxationof the fluid density profile upon encountering and passing the obstacle. The second one isthe mixing of two monolayers of different particle species which spread side by sidefollowing the merger of two chemical lanes, here defined as domains of high affinityfor fluid adsorption surrounded by domains of low affinity for fluid adsorption.