Subphase Temperature Research Articles

Temperature-Induced Nanoarchitectonics of Monolayer Self-Assembly of Heterocoronene-Based Discotic Liquid Crystals.

Enhancing molecular self-assembly at the monolayer level offers significant potential for various applications. For monolayers made of π-conjugated discotic liquid crystal (DLC) molecule nanowires, achieving precise separation and alignment of these nanowires has been a long-standing challenge. This research explores an approach using the manipulation of subphase temperature and surface pressure within a Langmuir trough to control molecular nanowire separation. We observe notable temperature-dependent behavior: as the temperature increases from 5 to 30 °C, the monolayer collapse pressure rises steadily. In contrast, temperatures from 35 to 50 °C exhibit an initial small plateau with a nonzero slope that becomes more distinct with rising temperature. Our study of Langmuir-Blodgett (LB) films provides crucial insights into the monolayer's structure. At lower temperatures, the LB films show coalesced molecular nanowires, whereas at higher temperatures, the DLC nanowires separate and form an interconnected network. Remarkably, upon compression, this network transforms into a compact, highly uniform monolayer. To explain these temperature-dependent behaviors, we examine the area relaxation curves, which indicate a two-step molecular loss mechanism involving desorption and monolayer collapse due to the nucleation and growth of critical nuclei. This extensive study offers valuable insights into the dynamic interaction of the temperature, surface pressure, and molecular assembly, enhancing our understanding of the fundamental processes in monolayer self-assembly.

Influence of subphase temperature on Langmuir layers and thin films of A3B-type porphyrine derivative

The influence of aqueous subphase temperature on the formation and stability of floating layers of 5-(4-hydroxyphenyl)-10,15,20-tris(4-hexadecyloxyphenyl)porphyrin (P-OH) was investigated using the Langmuir technology. It was found that the increase in the subphase temperature from 1 to 40 °C leads to a loosening of floating layers (an increase in the area per molecule in the floating layer by ∼15% and a decrease in the surface compression modulus by more than two times). The stability of floating layers (i.e., the ability of a floating layer to maintain its area under the action of a constant compressive force) decreases with increasing subphase temperature. It has been shown that the most stable floating layers are formed at subphase temperatures lower than 30 °C. Monolayer films on solid substrates were obtained using the Langmuir-Schafer technique at subphase temperatures of 1, 10, 20, 30, and 40 °C. The surface relief of these films was studied by atomic force microscopy (AFM). The AFM analysis revealed that the films transferred from the aqueous subphase at a temperature of 20 °C had the highest continuity and the lowest roughness. The absorption spectra of the floating layers were obtained, in which a bathochromic shift of the Soret band and Q-bands were registered (by 19 nm at 20 °C) in comparison with chloroform solution spectrum. This shift is a consequence of the strong intermolecular π–π* interaction, resulting in the formation of J-type aggregates. The Soret band in the spectra of the floating layers shifted from 436 to 441 nm with an increase in subphase temperature from 1 to 40 °C. In the absorption spectra of thin films (8 transfers), the indicated shifts of absorption bands as well as a broadening of the Soret band are preserved. The results of this work can be used in the targeted creation of film samples with specific structure and properties.

Formation of two-dimensional mixed monolayers of integrated-cellulose nanofibers and starch nanoparticles using cellulose acetate and soluble starch

In this study, mixed monolayers comprising starch and cellulose nanofibers are prepared on the water surface and effectively controlled their surface morphologies. Through the spreading of cellulose acetate on the water surface, we achieve the preparation of integrated films with the spontaneous formation of nanocellulose. It is confirmed that starch, which is insoluble in the spreading solvent, is solubilized through a soluble treatment and spreads into a monolayer on the water surface. Upon mixing the nanocellulose integrated layer and starch particle layer, the morphology changes based on the mixed ratio of these components. In the monolayer film of a 1:1 mixture of cellulose acetate and soluble starch, the morphology predominantly consists of fibers, with particulate aggregates incorporated here and there. Furthermore, when the ratio changes to 1:5, the mixed monolayer transforms into a single particle layer, while the mixed monolayer evolves into a fibrous integrated film at a ratio of 5:1. Meanwhile, from the evaluation of the surface pressure-area isotherms, it is predicted that both components constitute an ideal mesoscopic miscible system. In addition, in the subphase temperature dependence of the cellulose acetate:soluble starch = 1:1 mixed monolayer, fibers are promoted under low-temperature conditions, and substantial domains are formed under high-temperature conditions. Notably, the mixed film remains amorphous at all ratios and exhibits low surface free energy, simultaneously suggesting hydrophobic and oil-repellent properties.

Closely Packed Core-Shell Micelle Structures of Double Hydrophilic Miktoarm Star Copolymers at the Air-Water Interface.

The aggregation behavior of amphiphilic block copolymers at the air-water interface has been extensively studied, but less attention was given to that of star copolymers. In this work, we studied the interfacial aggregation behavior of two double hydrophilic pH- and temperature-responsive miktoarm star copolymers of poly[di(ethylene glycol) methyl ether methacrylate]-poly[2-(dimethylamino)ethyl methacrylate] (PDEGMA3-PDMAEMA3 and PDEGMA4-PDMAEMA7, the subscripts denote arm numbers) with different molecular weights. The effects of subphase pH and temperature on the monolayer isotherms and hysteresis curves of the two star copolymers and the morphologies of their Langmuir-Blodgett (LB) films were studied by the Langmuir film balance technique and atomic force microscopy, respectively. At the air-water interface, the two star copolymers tend to form closely packed micelles. These micelles exhibit a core-shell structure, where the small hydrophobic core consists of cross-linker of ethylene glycol dimethacrylate (EGDMA) and the carbon backbones of PDEGMA and PDMAEMA arms and the short hydrophilic shell is composed of di(ethylene glycol) and tertiary amine side groups. With increasing subphase pH, the surface pressure versus molecular area isotherms shift toward larger mean molecular areas as a result of the enhanced interface adsorption of nonprotonated tertiary amine groups. The isotherm shift of PDEGMA3-PDMAEMA3 monolayers is primarily attributed to high density of tertiary amine groups in the shells, while that of PDEGMA4-PDMAEMA7 is mainly attributed to high density of di(ethylene glycol) groups in the shells. The hysteresis degrees in the monolayers of the two copolymers under alkaline and neutral conditions are greater than those under acidic conditions due to the decreased protonation degree of the tertiary amine groups. At 10 °C, the mobility of the shells is poor and the isotherms are located on the right. Above the lower critical solution temperature, di(ethylene glycol) groups contract, which causes a slight shift of the isotherms toward smaller mean molecular areas.

Dense Monolayer Network Structures of Double Hydrophilic Hyperbranched Copolymers at the Air/Water Interface.

Influences of subphase pH and temperature on the interfacial aggregation behavior of two double hydrophilic hyperbranched copolymers of poly[oligo(ethylene glycol) methacrylate-co-(2-diisopropylamino)ethyl methacrylate] (P(OEGMA-co-DIPAEMA)) at the air/water interface are studied by the Langmuir film balance technique. Morphologies of their Langmuir-Blodgett (LB) films are characterized by atomic force microscopy (AFM). At the interface, P(OEGMA-co-DIPAEMA) copolymers tend to form a dense network structure of circular micelles composed of branching agent-connected carbon backbone cores and mixed shells of OEGMA and DIPAEMA segments (pendant groups). This network structure containing many honeycomb-like holes with diameters of 6-8nm is identified for the first time and clearly observed in the enlarged AFM images of their LB films. Under acidic conditions, surface pressure versus molecular area isotherms of the two copolymers in the low-pressure region show larger mean molecular area than those under neutral and alkaline conditions due to the lack of impediment from DIPAEMA segments. Upon further compression, each isotherm exhibits a wide pseudo-plateau, which corresponds to OEGMA segments being pressed into the subphase. Furthermore, the isotherms under neutral and alkaline conditions exhibit the lower critical solution temperature behavior of OEGMA segments, and the critical temperature is lower when the hyperbranched copolymer contains higher OEGMA content.

Влияние температуры на формирование ленгмюровских монослоев с наночастицами Ni-арахиновой кислоты и кластерами Ni-арахидата

The effect of the subphase temperature on the formation of nickel arachinate clusters under a monolayer of arachidic acid was studied. The subphase temperature varied in the range from 10° to 30°C with a step of 4°C. The influence of temperature on the compressibility of the monolayer and the area occupied by one molecule in the Langmuir monolayer of nickel araquinate is demonstrated. The effect of temperature on the morphology of Langmuir-Blodgett films formed on their basis was also studied. It was found that, as the temperature changes, the number of nickel clusters increases and their sizes decrease. This is due to a change in the rate of growth and dissolution of clusters with a change in temperature. The distribution of clusters in the resulting film was random, however, they can be structured using external magnetic fields. Using the magnetic properties of NiArch clusters will make it possible to purposefully change the film structure by an external magnetic field. The results obtained are of great importance for practical applications in the creation of multilayer composite coatings with controlled magnetic properties. These films can be further used as touch coatings for acoustic and electronic sensors.

Interfacial Interactions of a Myoglobin/DOPC Hybrid System at the Air-Water Interface and Its Physicochemical Properties.

In the present study, the intermolecular interactions between a water-insoluble phospholipid (DOPC) and water-soluble protein (myoglobin) and the interaction among themselves were investigated at the air-water interface using the Langmuir and Langmuir-Blodgett techniques. The effects of changes in physicochemical factors, like pH and temperature, on these interactions were also examined. Surface pressure-molecular area (π-A) isotherms of the DOPC monolayer at the air-water interface, with and without myoglobin (Myo) revealed the evolution of various physical properties, such as elastic, thermodynamic, and hysteric properties, in response to changes in subphase pH and temperature. With the increment of subphase pH from 5 to 7 at a fixed temperature (20 °C), the DOPC isotherm expanded, and the in-plane elasticity (CS-1) decreased, but no significant presence of hysteresis was encountered in either of the pH values. On the other hand, a diminution of temperature (from 20 to 5 °C) leads to an expansion of monolayers yielding low elasticity and significant hysteresis. The incorporation of Myo molecules within the DOPC monolayer decreased the CS-1 value of the DOPC monolayer. Such a decrement in CS-1 was also encountered while increasing the pH and decreasing the temperature (T) of the subphase in the absence of Myo. Systematic expansion of DOPC isotherm and increased hysteric area with the increase in Myo proportion were observed and the atomic force microscopy (AFM) observations suggested a strong conjugation between Myo and DOPC in the mixed monolayer. The denaturation effect of Myo molecules was studied using AFM at different temperatures. Furthermore, the Myo molecules were found to be most surface active at pH = 7, which is very close to its isoelectric point. These observations come up with the interaction mechanism between biomolecules under dynamically varied conditions.

Controlling the various phase-separated patterns in mixed monolayers of non-amphiphilic fluorinated derivatives and hydrogenated comb copolymers

Mixed monolayers were prepared on the water surface of non-amphiphilic fluorinated derivatives, as well as hydrocarbon-based comb copolymers, whose intermolecular interactions could be tuned using a copolymerization method. The phase-separated morphologies of the monolayers could also be controlled. Diamino-s-triazine rings, which were critical in morphology formation, were introduced into the hydrophilic groups of the comb copolymers for the phase-separated patterning. The phase-separation pattern was precisely controlled using various parameters, such as the chain length of the fluorinated derivatives, composition of the comb copolymers, mixing ratio, subphase temperature, and surface pressure. The obtained sea-island phase-separated patterns were classified into domain-like, circular, non-circular linear, donut-like, and centrally protruding circular domain morphologies. At 35 °C, a new nucleation phenomenon was observed inside the donut-shaped pattern that had developed through coagulation. During the phase separation of the current system, crystalline regularity was achieved in the fluorinated sea region around the domain, which was generally a continuous phase.

Formation behavior of monolayers on the water surface of water-soluble thermoplastic and insoluble-thermosetting copolymers with hyperbranched units containing s-benzenetricarbamide cores

The formation and structure of Langmuir monolayers and Langmuir-Blodgett films were studied using water-soluble polymers, which have difficulty forming monolayers on the water surface, and polymers that are insoluble in all solvents. The network copolymers consisting of hyperbranched units with an s-benzenetricarbamide core used in this study can be freely controlled by azidation/non-azidation of both ends of the hard segment. The water-soluble copolymer, which exhibits the properties of a thermoplastic resin, can form a monolayer when spread on the water surface at a low temperature at which the solubility decreases. Even when the subphase temperature increased, no significant change in the monolayer behavior of the thermoplastic copolymer was observed. This behavior was attributed to the formation of an insoluble single-particle layer with hydrophilic groups facing inward on the water surface. The insoluble copolymer, which exhibits thermosetting properties, forms a tablet that floats on the water surface for an extended period. The surface pressure-time isotherms showed the formation of a monolayer from the tablet over time, and it was possible to measure the surface pressure-area isotherms by two-dimensional compression after a certain period of time.

Mixing Behavior of the Binary Monolayers of Fatty Acids Based on Their Cohesive Energy Differences.

The morphology involving the height difference and the surface roughness of the binary monolayers of saturated fatty acids were evaluated using atomic force microscopy (AFM) to investigate the mixing behavior of their monolayers. AFM observations revealed that the mixed monolayers of (palmitic acid/arachidic acid) and (arachidic acid/lignoceric acid), which had four methylene group differences between fatty acids, were in a molecularly mixed state. Further, the mixed monolayer of (stearic acid/lignoceric acid), which had six methylene group differences, was in a phase-separated state. From the results of the present and previous studies, it became clear that the difference in the cohesive energy between fatty acids, which corresponds to the enthalpy difference, was an important factor in determining whether the molecular aggregation state of a fatty acid mixed monolayer was in a molecularly mixed or phase-separated state. Moreover, the boundary value of cohesive energy difference was approximately 2.5 kJ mol-1 at a subphase temperature of 293 K.

Aggregation behavior of triblock terpolymer poly[n‐butyl acrylate‐block‐N‐isopropylacrylamide‐block‐2‐(dimethylamino)ethyl acrylate] at the air/water interface

AbstractLangmuir film balance technique was used to study the subphase pH and temperature effects on the aggregation behavior of a dual‐responsive triblock terpolymer poly[n‐butyl acrylate‐block‐N‐isopropylacrylamide‐block‐2‐(dimethylamino)ethyl acrylate] (PnBA‐b‐PNIPAM‐b‐PDMAEA) at the air/water interface. Atomic force microscopy was used to observe the morphologies of its Langmuir–Blodgett (LB) films. At the interface, the terpolymer tends to form isolated circular micelles composed of hydrophobic PnBA cores and hydrophilic PNIPAM‐PDMAEA coronas. The limiting areas in the surface pressure–molecular area isotherms under acidic and alkaline conditions are larger than that under neutral conditions due to the larger interfacial stretching degrees of PNIPAM blocks, which results from the strong electrostatic repulsions of the fully protonated PDMAEA blocks underwater in the acidic case. In our minds, the hysteresis degrees of the compression−expansion cycles under different subphase pH conditions should mainly depend on the initial stretching degrees of the hydrophilic blocks. Under acidic conditions, the isotherms shift toward small areas with the increase of temperature due to the increased solubility of PNIPAM blocks. However, under alkaline conditions, the isotherms significantly exhibit the lower critical solution temperature behavior of PNIPAM blocks, which is a good example to build up the relationship between the interfacial and solution properties of block copolymers.

Fabrication of cellulose nanofibers by the method of interfacial molecular films and the creation of organized soluble starch molecular films

This study investigated a new method for producing cellulose nanofibers (CNFs) at the air/water interface employing the monolayer on the water surface approach. The formation of hydrogen bonding networks in the two-dimensional plane facilitated the formation of the fibrous nanocellulose monolayer. The layered assembly of the interfacial cellulose monolayer exhibited periodic regularity, and its morphology changed with the subphase temperature. Further, insoluble starch was solubilized to create a spreading solvent for the monomolecular film on the water surface. The monolayer of the obtained soluble starch was particulate rather than sheetlike or fibrous. The hydrogen bonds might have been developed inside the particles. The subphase temperature dependency of the starch monolayer was also confirmed, revealing that these β- or α-glucose-derived natural polymer monolayers were affected by the molecular motion due to heating and the changes in their morphologies. Additionally, the introduction of the two natural polymers into the air/water interface, as well as the application of the repeated compression/expansion method ensured the formation of high-density NF/nanoparticle (NP) integrated monolayers.

Formation and phase behavior of porphyrin/arachidic acid mixed systems and morphology study of Langmuir-Schaefer thin films

ABSTRACT The paper is focused on the study of the dynamic surface properties of mixed monolayers of porphyrin and arachidic acid with various mole fractions at the air–water interface. The choice of porphyrin solid thin film as an object of study is explained by its high potential application in the area of photovoltaics and medicine. The Langmuir monolayers of porphyrin and arachidic acid were formed under different conditions using the Langmuir-Blodgett technique. The increase of subphase temperature led to a decrease in the rigidity of the porphyrin monolayer and leads to accelerating the relaxation process of the monolayer. The chosen surface pressure (4, 5, 15 and 35 mN/m) affected the stability of the floating monolayer. The higher miscibility of the monolayers was obtained at the mole fraction of porphyrin = 0.333. The change in the phase of monolayers surface was reported on the basis of surface potential data. The morphology properties of the mixed systems transferred on silicon substrates by Schaeffer method are studied.

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.

Ordering of ZnS Nanorods at the Air–Liquid Interface: An In Situ X-ray Scattering Study

Self-assembly of anisotropic nanomaterials into ordered multidimensional (2D and 3D) arrays facilitate versatile collective properties. Monitoring of this self-assembly processes is essential to control the emerging properties of these nanostructured materials. We report here results of in situ X-ray reflectivity (XRR) and grazing incidence small-angle X-ray scattering (GISAXS) studies carried out at the air–liquid interface to understand the self-assembly process of ZnS nanorods (NRs) in real-time. Our study shows that at high surface pressure, ZnS NRs self-assemble into a bilayer 2D square superlattice, coupled by their organic surface ligands along the out-of-plane direction with NRs lying side by side flat in the in-plane direction at the liquid surface. Upon increasing subphase temperature, we observed a transformation of the 2D superlattice into a 3D multilayer structure of the nanorods. On the basis of the extracted parameters (film thickness, electron density of each layer, and in-plane lattice parameters), we propose a packing model of the hierarchical self-assembly of anisotropic NRs on the water surface.

Dielectric properties of the system: 4-n-pentyloxybenzoic acid– N-(4-n-butyloxybenzylidene)-4᾽-methylaniline

Objectives. Our aim was to study the dielectric properties of the 4-n-pentyloxybenzoic acid– N-(4-n-butyloxybenzylidene)-4’-methylaniline system and reveal how different concentrations of N-(4-n-butyloxybenzylidene)-4’-methylaniline additives affect the dielectric properties of 4-n-pentyloxybenzoic acid.Methods. System properties were investigated using polarization thermomicroscopy and dielcometry.Results. We found that dielectric anisotropy changes its sign from positive to negative at the transition temperature of the high-temperature nematic subphase to the low-temperature one. The anisotropy of the dielectric constant of N-4-n-butoxybenzylidene-4’-methylaniline has a positive value and increases as to the system approaches the crystalline phase. The crystal structure of the 4-n-pentyloxybenzoic acid contains dimers formed by two independent molecules due to a pair of hydrogen bonds. The crystal structure of N-(4-n-butoxybenzylidene)-4’-methylaniline contains associates formed by orientational interactions of two independent molecules. 4-n-Pentyloxybenzoic acid dimers (270 nm) and associates of N-4-n-butoxybenzylidene-4’- methylaniline (250 nm) proved to have approximately the identical length. Considering the close length values of the structural units of both compounds and the dielectric anisotropy sign, we assume that the N-4-n-butoxybenzylidene-4’-methylaniline associates are incorporated into the supramolecular structure of the 4-n-pentyloxybenzoic acid. The specific electrical conductivity of the compounds under study lies between 10−7 and 10−12 S∙cm−1. The relationship between the specific electrical conductivity anisotropy and the system composition in the nematic phase at the identical reduced temperature, obtained between 100 and 1000 Hz is symbatic. However, the electrical conductivity anisotropy values of the system obtained at 1000 Hz are lower compared to those obtained at 100 Hz. At N-(4-n-butoxybenzylidene)-4’-methylaniline concentrations between 30 and 60 mol %, the electrical conductivity anisotropy values are higher than those of the individual component.Conclusions. A change in the sign of the dielectric constant anisotropy of the 4-n-pentyloxybenzoic acid during nematic subphase transitions was established. We showed that the system has the highest dielectric constant anisotropy value when components have an equal number of moles. Highest electrical conductivity anisotropy values are observed when the concentration of the N-4-n-butoxybenzylidene-4᾽-methylaniline system lies between 30 and 60 mol %.

Influences of subphase pH and temperature on the interfacial aggregation behavior of poly(lauryl methacrylate)-block-poly(methacrylic acid)

We previously reported that poly(acrylic acid) (PAA) blocks at the air/water interface spontaneously immersed into water at high pH before monolayer compression. To investigate the influence of the hydrophobic methyl groups in poly(methacrylic acid) (PMAA) blocks, in this work, subphase pH and temperature effects on the aggregation behaviors of two pH-responsive amphiphilic diblock copolymers poly(lauryl methacrylate)-block-poly(methacrylic acid) (PLMA-b-PMAA) (PLMA49%-PMAA and PLMA61%-PMAA, composition in weight percent) at the air/water interface were studied. The surface pressure–molecular area isotherms of the two copolymers move to small mean molecular area (mma) as subphase pH increases and a quasi-plateau exists under various subphase conditions, which is quite different from its absence in our previous PAA-containing block copolymer system. The quasi-plateau is attributed to the pancake-to-brush transition as non-ionized PMAA chains submerge into subphase upon monolayer compression. Under acidic condition, PMAA chains of the two copolymers are almost non-ionized, the compression and expansion isotherms show large hysteresis phenomena. Under neutral and alkaline conditions, the isotherms show small hysteresis, which is because more ionized PMAA chains immerse in subphase before compression. The isotherms shift toward small mma with increasing temperature under neutral and alkaline conditions, whereas a slight shift back to large mma is observed under acidic conditions. The plateau surface pressures of the two PLMA-b-PMAA copolymers decrease with increasing temperature under different pH conditions, which is because the micelles move more freely and easier to rearrange at high temperature. The plateau surface pressures of PLMA49%-PMAA are higher than those of PLMA61%-PMAA under the corresponding conditions due to the higher PMAA content in the former. The initial Langmuir–Blodgett (LB) films of the two copolymers transferred under different pH conditions at various temperatures exhibit isolated circular micelles because of the steric hindrance and/or repulsive interactions among the long PMAA chains. Furthermore, temperature has almost no effect on the micelle core diameters of the initial LB films.

Electrowetting on Langmuir-Blodgett films from epicuticular wax

Langmuir and Langmuir-Blodgett (LB) films were fabricated from epicuticular wax, that had been extracted from Vitis vinifera. For Langmuir films, the influence of subphase temperature on their structure was examined, whereas for LB films, the surface morphology at various temperatures and the effect of the layer number on electrowetting were investigated. Isotherms of surface pressure revealed no well-defined phase transition or collapse on Langmuir films at 22 °C, whereas Brewster angle microscopy showed that even before starting the compression procedure, there are platelets of epicuticular wax floating on the subphase. Those platelets give rise to the Langmuir films of epicuticular wax during compression. In contrast, for higher temperatures (40 °C and 50 °C), a well-defined phase transition was found – without epicuticular wax platelets, with a behavior close to those found in typical fatty acids. For LB films, atomic force microscopy images indicated a decreasing of roughness as a function of the subphase temperature as a result of greater organization of the epicuticular wax film. A significant modulation of about 20 ° (under applied voltage range of 0 to 100 V) was demonstrated of the electrowetting on LB films, which did not depend on the LB layer number. Our results suggest that epicuticular wax LB films have the potential for being applied in electrowetting-based devices. Furthermore, the Langmuir-Blodgett technique is feasible to fabricate films with various compositions focusing on the electrowetting.

Structure and Elastic Properties of an Unsymmetrical Bi-Heterocyclic Azo Compound in the Langmuir Monolayer and Langmuir-Blodgett Film.

We study the structure and elastic properties of the bi-heterocyclic azo compound at the air–water interface through surface pressure (π)–area (A) isotherm recording followed by transferring them on hydrophilic and hydrophobic Si surfaces by the Langmuir–Blodgett (LB) deposition method. A substantial change in the area/molecule is observed as a function of subphase pH and temperature. Such parameters strongly influence intramolecular interactions within azo molecules and the interactions between azo molecules and water that manifested in higher surface activity at low temperature and high pH, which in turn modifies the elasticity of azo assembly at the air–water interface. A large pH-dependent hysteresis with negative change in entropy, indicating molecular rearrangements, is observed. Molecular assembly formed at the air–water interface is then transferred onto hydrophilic and hydrophobic Si surfaces at two different surface pressures (5 and 30 mN/m) by the LB technique. The structural analysis performed by X-ray reflectivity and atomic force microscopy techniques suggests that the LB films exhibit an abrupt layered structure on hydrophilic Si, whereas an overall rough film is formed on hydrophobic Si. The coverage and compactness of individual layers are found to increase with the deposition pressure (5 to 30 mN/m).

Formation of Gibbs and Langmuir floating layers based on copper nanoparticles: temperature and concentration effects

This paper is devoted to study of the formation of Gibbs floating layers from aqueous solutions of copper nanoparticles (Cu NPs) stabilized by the sodium dodecyl sulfate surfactant. Langmuir floating layers of arachidic acid formed on the surface of a water subphase containing Cu NPs were also studied. Adsorption of copper nanoparticles on a monolayer of arachidic acid at different conditions has been investigated. In the experiments the amount of copper nanoparticles in the subphase and the temperature of the subphase were changed. The performed analysis showed that the increase of subphase temperature from 29 to 42 °C leads to the increase of the area occupied by Langmuir floating layers in a liquid-condensed state by 30 and 32 %, respectively. After a single transfer of the floating layer onto the highly oriented pyrolytic graphite substrates, their surface microrelief was investigated by atomic force microscopy (AFM). The AFM scans showed that the obtained copper nanoparticles films contained separate areas with copper particles and their aggregates. With an increase of surface pressure from 10 to 40 mN/m, an increase of the height difference of the surface microrelief from 4 to 7 nm and an increase of the large aggregates number with lateral dimensions about 100 nm were observed.