Mixed Langmuir Monolayers Research Articles

Physical properties of mixed Langmuir monolayers of polystyrene particles with poly(N,N-dimethylaminoethylmethacrylate) hairs and a poly(2-hydroxyethyl methacrylate) polymer at an air/water interface

The effect of adding a poly(2-hydroxyethyl methacrylate) (PHEMA) polymer to a Langmuir monolayer of polystyrene particles carrying poly(N,N-dimethylaminoethylmethacrylate) hair (PDMA-PS particles) at air/water interfaces on the physical properties of the monolayer was studied. The addition of PHEMA to a PDMA-PS particle monolayer at an air/water interface gave a polymer-like monolayer at low surface pressures and a particle-like monolayer at high surface pressures. The PDMA-PS particles formed small aggregates that were dispersed throughout the PHEMA monolayer at low surface pressures, a result suggesting that the particles were trapped in the PHEMA network. Monolayers of closely packed particles were observed at higher surface pressures, suggesting that PHEMA was squeezed-out at higher surface pressures. The stiffness of the mixed monolayer was independent of the surface pressure, but increased as the ratio of PHEMA in the mixed monolayer increased. This increased stiffness was explained by the immobilization of the PDMA-PS particles by PHEMA.

The miscibility of milk sphingomyelin and cholesterol is affected by temperature and surface pressure in mixed Langmuir monolayers.

The miscibility of milk sphingomyelin (milk-SM) and cholesterol was investigated in this study. The effect of different physical states of milk-SM on its interactions with cholesterol was determined by the recording of isotherms of compression of Langmuir films for temperatures above and below the gel to Lα phase transition of milk-SM (Tm∼34°C). For T=15°C<Tm, the liquid expanded (LE) to liquid condensed (LC) phase transition of milk-SM monolayers was observed at surface pressures of 10-15mN/m. For T=43°C>Tm, the milk-SM molecules were in a LE phase regardless of the surface pressure applied. A phase diagram pressure - milk-SM/cholesterol composition was established. This study demonstrated that both temperature and surface pressure affected the miscibility between the milk-SM and cholesterol. The strongest attractive forces (i.e. condensing effect) were identified for 30mol% cholesterol when the milk-SM was in the LE phase state.

Direct observation by using Brewster angle microscopy of the diacetylene polimerization in mixed Langmuir film

Mixed Langmuir monolayers of 10,12-Pentacosadiynoic acid (DA) and amphiphilic hemicyanine (HSP) have been fabricated at the air–water interface. The mixed monolayer has been proved to be completely homogeneous. The DA molecules are arranged in a single monolayer within the mixed Langmuir monolayer, as opposed to the typical trilayer architecture for the pure DA film. Brewster angle microscopy has been used to reveal the mesoscopic structure of the mixed Langmuir monolayer. Flower shape domains with internal anisotropy due the ordered alignment of hemicyanine groups have been observed. Given the absorption features of the hemicyanine groups at the wavelength used in the BAM experiments, the enhancement of reflection provoked by the absorption process leads to the observed anisotropy. The ordering of such groups is promoted by their strong self-aggregation tendency. Under UV irradiation at the air–water interface, polydiacetylene (PDA) has been fabricated. In spite a significant increase in the domains reflectivity has been observed owing to the modification in the mentioned enhanced reflection, the texture of the domains remains equal. The PDA polymer chain therefore grows in the same direction in which the HSP molecules are aligned. This study is expected to enrich the understanding and design of fabrication of PDA at interfaces.

Polymerization of mixed Langmuir monolayers based on 10,12-pentacosadiynoic compounds

This work reports on the preparation and investigation of ultrathin polymer films based on 10,12-pentacosadiynoic acid and 10,12-pentacosadiynamine. Mixed catanionic Langmuir monolayers formed from these compounds at different component ratios have been studied. It has been established that the electrostatic attraction of the head groups of monolayer components facilitates spreading of the diacetylene monomers over the surface of an aqueous subphase and prevents pentacosadiynoic acid from crystallization. Fiber-optic spectrometry has been employed to study the effect of monolayer packing density on the efficiency of polymerization in the system and to investigate the optical properties of two-dimensional copolymers. It has been shown that the interactions between the oppositely charged head groups in a polymerized monolayer facilitate the formation of a film with a low shrinkage and do not hinder the fast relaxation of the strained blue form of the polymer into its red form characterized by a lower bond conjugation. For the first time, optically uniform ultrathin films based on copolymers of diacetylene surfactants have been obtained and their morphology has been investigated with the help of atomic force microscopy.

Mixed diacetylene/octadecyl melamine nanowires formed at the air/water interface exhibit unique structural and colorimetric properties.

Polydiacetylene (PDA) assemblies exhibit interesting photophysical properties, specifically, visible colorimetric transformations. A considerable body of work has focused on the formation and characterization of PDA Langmuir monolayer systems, and the overwhelming majority of reports so far have indicated that the adoption of 2D sheetlike structures associated with a hydrogen bond network between the diacetylene headgroups is a prerequisite for polymerization and chromatic properties. Here we report for the first time on the assembly of nanowire networks in mixed Langmuir monolayers comprising diacetylene monomers and octadecyl melamine surfactants. Structural and physical analysis indicates that the nanowires are composed of a helical organization of stacked diacetylene/octadecyl melamine building blocks assembled through hydrogen bonds between the melamine residues and the carboxylic termini of the diacetylenes. Following ultraviolet-induced polymerization, the PDA/octadecyl melamine nanowires exhibited unusual chromatic properties, specifically, an absence of the ubiquitous "blue" phase, rather transforming into a new "purple" PDA phase. This study demonstrates that the incorporation of surfactant constituents within diacetylene frameworks provides a means for modulating the structural and chromatic features of PDA assemblies, giving rise to new morphologies and unique optical properties.

Diacetylene mixed Langmuir monolayers for interfacial polymerization.

Polydiacetylene (PDA) and its derivatives are promising materials for applications in a vast number of fields, from organic electronics to biosensing. PDA is obtained through polymerization of diacetylene (DA) monomers, typically using UV irradiation. DA polymerization is a 1-4 addition reaction with both initiation and growth steps with topochemical control, leading to the "blue" polymer form as primary reaction product in bulk and at interfaces. Herein, the diacetylene monomer 10,12-pentacosadiynoic acid (DA) and the amphiphilic cationic N,N'-dioctadecylthiapentacarbocyanine (OTCC) have been used to build a mixed Langmuir monolayer. The presence of OTCC imposes a monolayer supramolecular structure instead of the typical trilayer of pure DA. Surface pressure, Brewster angle microscopy, and UV-vis reflection spectroscopy measurements, as well as computer simulations, have been used to assess in detail the supramolecular structure of the DA:OTCC Langmuir monolayer. Our experimental results indicate that the DA and OTCC molecules are sequentially arranged, with the two OTCC alkyl chains acting as spacing diacetylene units. Despite this configuration is expected to prevent photopolymerization of DA, the polymerization takes place without phase segregation, thus exclusively leading to the red polydiacetylene form. We propose a simple model for the initial formation of the "blue" or "red" PDA forms as a function of the relative orientation of the DA units. The structural insights and the proposed model concerning the supramolecular structure of the "blue" and "red" forms of the PDA are aimed at the understanding of the relation between the molecular and macroscopical features of PDAs.

Binding of methylene blue onto Langmuir monolayers representing cell membranes may explain its efficiency as photosensitizer in photodynamic therapy.

We provide evidence for the electrostatic interactions between the cationic photosensitizer methylene blue (MB) and cell membrane models represented by neat and mixed Langmuir monolayers of dioleylphosphatidylcholine (DOPC) and 1,1',2,2'-tetraoleoylcardiolipin (CL). From surface pressure measurements, MB was found to adsorb strongly and expand CL-containing monolayers, while it caused an apparent decreasing in molecular area on neat DOPC monolayer. The binding site of MB could be inferred from data with the surface-specific polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) technique, where changes induced by MB were observed in the vibrational modes of the phosphate groups of both CL and DOPC. The incorporation of MB also affected the carbonyl groups and the packing of the alkyl chains, thus indicating that MB binding site favors singlet oxygen generation close to the double bonds in the alkyl chains, an important requirement for photodynamic efficiency. Significantly, the data presented here demonstrate that MB may act in membranes composed by PCs, such as mammalian plasma membranes, and in those containing CL, as in bacterial and inner mitochondrial membranes.

Mapping the structure-activity relationship of β-sitosteryl fatty acid esters in condensing phospholipid monolayers

The phase behavior of twelve synthesized β-sitosteryl fatty acid esters with acyl moieties with different chain lengths (C2:0–C18:0) and different degrees of unsaturation (C18:1–C18:3) were investigated in pure and mixed Langmuir monolayers with phospholipids. The surface-pressure isotherms showed that short chain β-sitosteryl fatty acid esters gave smaller mean molecular areas and had decreased monolayer stability and the long chain steryl esters did not produce collapsed plateaus. All the steryl esters displayed strong condensing effects, but there was a pronounced structural dependency: medium chain esters (C8 and C10) were less efficient than short and long chain esters. Atomic force microscopy imaging demonstrated that monolayers mixed with dipalmitoyl phosphatidylcholine (DPPC) displayed both DPPC-rich and steryl lipid-rich domains. However, the height and area differences between the two phases and the roughness and morphologic patterns were very dependent on the steryl lipid concentrations as well as the length, the degree of unsaturation and the molecular conformations of the acyl segments. These findings not only provide a better understanding of the interactions between phytosteryl hydrophobic derivatives and biomembranes, but also may be of general use for the design and engineering of phytosterol structural derivations for specific food and pharmaceutical applications. Open image in new window

2D Chiral Structures in Quinoline Mixed Langmuir Monolayers

Chirality at interfaces is a relevant topic in nanoscience, as well as a key point for prebiotic chemistry. Mixed Langmuir monolayers, composed of the anionic phospholipid dimyristoyl phosphatidic acid (DMPA) and the cationic amphiphilic quinoline derivative 2-methyl-1-octadecylquinoline (MQ) have been built at the air–water interface. Both DMPA and MQ molecules are miscible, thus the equimolar mixture yields homogeneous monolayers completely. Chiral domains have been formed by this monolayer and observed in situ by Brewster angle microscopy (BAM). These chiral domains display a large array of shapes and sizes. The chirality of the monolayers has been confirmed by circular dichroism spectroscopy. The ordered aggregation of the quinoline group into large chiral supramolecular structures is proposed as the molecular origin of the observed chirality. Theoretical simulations using molecular mechanics confirm the strong trend of the quinoline group to form chiral aggregates. The great diversity in the size and shape of the chiral domains has been found to be strongly influenced by the competition between two nuclei growth mechanisms. An experimental procedure allowing a minimized growth through one of these mechanism is proposed, achieving a homogeneous distribution of ring-shaped domains. An overshoot in the π–A isotherms of this mixed monolayer appears at an intermediate surface pressure. This overshoot is interpreted as being due to the large difference between the surface pressure which starts the nuclei formation, πcrit, and the superficial pressure in which the nuclei can grow, πe. The rather small πe value compared to πcrit observed for this system must be attributed to the molecular interactions involved in the mixed monolayer, which facilitate the incorporation of molecules in preformed nuclei.

A binary catalytic system based on mixed monolayers of a phospholipid and amphiphilic bis(Zn2+-cyclen)

Herein, we report on the study of the properties of mixed Langmuir monolayers composed of a synthetic amphiphilic receptor, alkylated bis-cyclic zinc complex of 1,4,7,10-tetraazacyclododecane, and a lipid, distearoyl phosphatidylcholine. The kinetics of a hydrolysis of a model substrate, bis(p-nitrophenyl) phosphate in individual and mixed monolayers of the amphiphilic receptor was studied by using fiber-optical absorption/reflection spectroscopy. The hydrolysis of the organic phosphate in these planar systems proceeded by a two-stage mechanism. This mechanism comprises substrate adsorption on the monolayer via a reaction of the zero order with respect to the adsorbate followed by the pseudo-second-order reaction of the hydrolytic decomposition of the substrate. Unlike the reaction in molecular and colloidal solutions, the process in the monolayer results in the complete decomposition of the model substrate into nitrophenol and phosphate anion. The amphiphilic receptor is directly involved in this reaction to yield a stable complex with the phosphate anion as a resulting product of hydrolysis. An increase in the receptor affinity for the phosphate anion is, most likely, due to the effect of the interface on the strength of the coordination bonds in an intermediate product and the receptor-phosphate complex. Immobilization of the receptor within the lipid matrix increases the rate of substrate decomposition in the monolayer by almost an order of magnitude. We suggested an explanation for the observed effect of the lipid matrix on the catalytic properties of the amphiphilic metallocomplex.

Sodium dodecylsulfate bilayer formation under a cationic surfactant Langmuir monolayer at the air-water interface.

An aqueous solution of sodium dodecylsulfate (SDS) was injected into a Langmuir monolayer of dioctadecyldimethylammonium chloride (DODAC) at the air-water interface. Infrared external spectra, atomic force microscopy (AFM), and quartz crystal microbalance (QCM) measurements revealed that the resulting surface monolayer was a multilayer structure consisting of a DODAC monolayer as the upper layer and an SDS bilayer as the underlayer. Furthermore, the SDS alkyl chain was in the all-trans conformation, and the molecular packing of the DODAC alkyl chains was hexagonal with the trans-zigzag plane of the methylene chain oriented randomly around the chain axis. We also discuss the structure of the multilayer obtained by injecting SDS into a mixed Langmuir monolayer of DODAC + SDS.

Nanoparticle Self-Assembly Assisted by Polymers: The Role of Shear Stress in the Nanoparticle Arrangement of Langmuir and Langmuir–Blodgett Films

We propose to use the self-assembly ability of a block copolymer combined with compression-expansion cycles to obtain CdSe quantum dots (QDs) structures of different morphology. The methodology proposed consists in transferring onto mica mixed Langmuir monolayers of QDs and the polymer poly(styrene-co-maleic anhydride) partial 2-butoxyethyl ester cumene terminated, PS-MA-BEE, previously sheared by 50 compression-expansion cycles. Results indicate that the shear stress takes out nanoparticles at the air-water interface from metastable states and promotes a new equilibrium state of the Langmuir monolayer. This new state was transferred onto mica by the Langmuir-Blodgett (LB) methodology, and the morphology of the LB films was analyzed by atomic force microscopy and transmission electron microscopy measurements. Our results show that when the amplitude strain increases, the QDs domain size decreases and the QDs LB film arrangement becomes more ordered. The dynamics of the monolayer relaxation after cycling involves at least three time scales which are related to the damping of surface fluctuation, raft rearrangement, and component movements inside each raft. Brewster angle microscopy allowed visualizing in situ the raft rearrangement at the air-water interface.

Adsorption of Dimethyl Silicone onto Hair-surface Models Prepared with Micro-phase Separated Monolayers

The adsorption of dimethylsilicone (DMS) from its emulsion onto hair-surface models was investigated. The model surfaces were prepared on silicon wafers by utilizing a micro-phase separation in mixed Langmuir monolayers with a chemically adsorptive organosilane, n-octadecyltriethoxysilane (ODTES), as one component. The resulting surfaces consisted of hydrophobic micro-domains of polymerized ODTES and a surrounding hydrophilic surface silanol (SiOH) region of the silicon wafer, corresponding to the healthy and damaged regions of the hair surface, respectively, in terms of surface wettability. DMS preferentially adsorbed onto the high surface energy hydrophilic region of the model surface when the hydrophobic micro-domains were composed of fully condensed alkyl chains. The surface energy of the micro-domains could be controlled by using palmitic acid (PA) as the second component to form the micro-domains in the phase-separated Langmuir monolayers. The increase in the surface energy of the micro-domains induced the adsorption of DMS onto the intrinsically hydrophobic domain surface.

Effect of selective solvent on the aggregate behavior of the mixed Langmuir monolayers of PS-b-PEO and PS-b-PMMA

An interesting way to control morphology evolution in the mixed LB films was performed by mainly using a selective spreading solvent. Furthermore, a peculiar hysteresis phenomenon in the polymeric Langmuir monolayers is reported.

Studies of Lateral Interactions Between C18 Unsaturated Fatty Acid with Polyethoxylated Phospholipid Mixed Langmuir Monolayer at Air-Aqueous Interface for Liposome Formulation

Studies of Lateral Interactions Between C18 Unsaturated Fatty Acid with Polyethoxylated Phospholipid Mixed Langmuir Monolayer at Air-Aqueous Interface for Liposome Formulation

Characterization of the binary mixed monolayers of α-tocopherol with phospholipids at the air-water interface

The mixed Langmuir monolayers composed of model constituents of biological membranes, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC), and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), were investigated to provide information on the intermolecular interactions between these membrane components and the physiologically active vitamin E–α-tocopherol (TF), as well as on the phase behavior of these mixed systems. Additionally, topography of these monolayers transferred onto the mica support was investigated by the inverted metallurgical microscope. Morphological characteristics were directly observed by Brewster angle microscopy (BAM). From the surface pressure–area isotherms and the analysis of physicochemical parameters (compressibility and mean molecular area at the maximum compressibility) it was found that depending on the acyl chains saturation degree, TF has different effect on the phospholipids. In the case of DPPC, the addition of TF to the phospholipid film causes destabilization of the ordered hydrocarbon chains, while in the POPC/DOPC–TF systems, the attractive interactions are responsible for the monolayer increased stability. Thus, the results of these studies confirm the hypothesis that α-tocopherol may play a role in the stabilization of biological membranes.

Block copolymer assisted self-assembly of nanoparticles into Langmuir–Blodgett films: Effect of polymer concentration

We propose to use the self-assembly ability of a block copolymer to obtain CdSe quantum dots (QDs) structures of different morphology. The methodology proposed consist in transferring mixed Langmuir monolayers of QDs and the polymer poly (styrene-co-maleic anhydride) partial 2 buthoxy ethyl ester cumene terminated, PS-MA-BEE onto mica by the Langmuir–Blodgett (LB) methodology. The morphology of the LB films was analyzed by AFM and TEM measurements. Our results show that it is possible to modulate the self-assembly process by modifying the composition of the mixed Langmuir monolayer precursor of the LB film. The different morphologies are interpreted according to two different dewetting mechanisms, growth of holes and spinodal-like dewetting. The growth of holes dewetting process is driven by gravitatory effects and was observed for LB films obtained by transferring Langmuir monolayer of the smallest elasticity values in which the polymer is in brush conformation. The spinodal dewetting mechanism prevailed when the Langmuir monolayer presents the highest elasticity values.

2D “Soap”-Assembly of Nanoparticles via Colloid-Induced Condensation of Mixed Langmuir Monolayers of Fatty Surfactants

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correction2D “Soap”-Assembly of Nanoparticles via Colloid-Induced Condensation of Mixed Langmuir Monolayers of Fatty SurfactantsDenis I. Babenko, Alexander A. Ezhov, Dmitry S. Turygin, Vladimir K. Ivanov, Vladimir V. Arslanov, and Maria A. Kalinina*Cite this: Langmuir 2012, 28, 23, 8822Publication Date (Web):June 1, 2012Publication History Published online1 June 2012Published inissue 12 June 2012https://doi.org/10.1021/la301421eCopyright © 2012 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views364Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (99 KB) Get e-Alerts Get e-Alerts

Towards the understanding of the behavior of single-chained ether phospholipids in model biomembranes: Interactions with phosphatidylethanolamines in Langmuir monolayers

Three single-chained ether lipids of comparable chemical structure but different biological activities (namely natural platelet activating factor – PAF, its deacetylated precursor – lyso-PAF and synthetic compound – edelfosine – ED) have been investigated in mixed Langmuir monolayers with phosphatidylethanolamines, PEs (DSPE, SOPE and DOPE), serving as model of inner shell of cellular membrane. The aim of undertaken studies was to verify the correlation between minor differences in chemical structures of the investigated ether lipids and their behavior in membrane-mimicking environment. To reach this goal the interactions between particular ether lipids and PEs have been analyzed with ΔGExc values derived from the surface pressure–area isotherms. To get insight into miscibility between film components, Brewster angle microscopy, enabling direct visualization of monolayers structure, has been applied. The obtained results prove significant differences in both mixing properties and the interactions in the investigated systems. On one hand, they are related to the structure of polar head-groups of the studied ether lipids, which determine their capability of hydrogen bond(s) formation with head-groups of PEs. Edelfosine, lacking this property, interacts with PEs the most unfavorably among all the investigated compounds. Another important parameter in this context is the structure of PEs monolayers – the most closely packed DSPE film was found to be most unfavorable for incorporation of ether lipid molecules. Our results prove that the analysis of the interaction between ether lipids and components of biomembrane in Langmuir monolayers is a potent method to explain differences in biological activity of the investigated ether lipids.

An Investigation of the Behavior of Binary Mixed Langmuir Monolayer of 2,2′-p-Phenylenebis (5-phenyloxazol) and Arachidic Acid

A systematic study is reported on the monolayer characteristics of 2,2′-p-phenylenebis (5-phenyloxazol) (POPOP) mixed with arachidic acid (AA) at the air-water interface, using surface pressure versus area per molecule (π-A) isotherms complemented with absorption spectroscopy as well as scanning electron microscopy. The (π-A) isotherms of POPOP mixed with AA at different mole fractions show a plateau like region at very low surface pressure, which suggests a phase transition corresponding to a reorientation of the POPOP molecules at the air-water interface. The mixing behavior was obtained from surface pressure-area isotherms by using the surface phase rule and excess area criterion. Results show that POPOP is immiscible in AA, leading to the formation of aggregates. These observations are confirmed by ultraviolet-visible absorption spectroscopy and scanning electron microscopy. Absorption spectra of the mixed LB films reveal that I-type of aggregates play their prominent role in the mixed LB films.