Stearic Monolayer Research Articles

Mechanically suitable and osteoinductive 3D-printed composite scaffolds with hydroxyapatite nanoparticles having diverse morphologies for bone tissue engineering.

The challenge of integrating hydroxyapatite nanoparticles (nHAp) with polymers is hindered by the conflict between the hydrophilic and hygroscopic properties of nHAp and the hydrophobic properties of polymers. This conflict particularly affects the materials when calcium phosphates, including nHAp, are used as a filler in composites in thermal processing applications such as 3D printing with fused filament fabrication (FFF). To overcome this, we propose a one-step surface modification of nHAp with calcium stearate monolayer. Moreover, to build the scaffold with suitable mechanical strength, we tested the addition of nHAp with diverse morphology-spherical, plate- and rod-like nanoparticles. Our analysis showed that the composite of polycaprolactone (PCL) reinforced with nHAp with rod and plate morphologies modified with calcium stearate monolayer exhibited a significant increase in compressive strength. However, composites with spherical nHAp added to PCL showed a significant reduction in compressive modulus and compressive strength, but both parameters were within the applicability range of hard tissue scaffolds. None of the tested composite scaffolds showed cytotoxicity in L929 murine fibroblasts or MG-63 human osteoblast-like cells, supporting the proliferation of the latter. Additionally, PCL/nHAp scaffolds reinforced with spherical nHAp caused osteoactivation of bone marrow human mesenchymal stem cells, as indicated by alkaline phosphatase activity and COL1, RUNX2, and BGLAP expression. These results suggest that the calcium stearate monolayer on the surface of the nHAp particles allows the production of polymer/nHAp composites suitable for hard tissue engineering and personalized implant production in 3D printing using the FFF technique.

Self-organization of stearic acid salts on the hemispherical surface of the aqueous subphase allows functionalization of matrix-assisted laser desorption/ionization mass spectrometry target plates for on-plate immobilized metal affinity chromatography enrichment

In this work we propose an approach for formation of periodic two-dimensional structures on a solid substrate via self-assembly of stearic acid molecules on an aqueous subphase drop containing metal ions. It was shown that when a saturated solution of stearic acid in n-hexane was applied to the hemispherical surface of an aqueous media containing barium ions, barium stearate monolayer was formed, which spontaneously collapsed during movement from the drop surface to the substrate. By means of infrared and Raman spectroscopy, light and scanning electron microscopy, atomic force microscopy and matrix-assisted laser desorption/ionization mass spectrometry it was proved that a multi-structure of collapsed metal stearate monolayers with a developed surface was formed on the substrate surface. Thin films formed by a single application of stearic acid solution in n-hexane to a drop of aqueous lanthanum nitrate solution were used for selective enrichment of human butyrylcholinesterase adducts with diisopropyl fluorophosphate.

Fabrication of nanoscale multimolecular structures of lanthanum stearate using Langmuir monolayers for laser desorption/ionization mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) from the surface of nanosized multimolecular structures based on lanthanum stearate monolayers (FLa) has been studied. The presence of FLa on the surface of MALDI target was confirmed experimentally by laser desorption of lanthanum-containing organic ions. MALDI target functionalization with FLa is shown to significantly increase the yield of target peptide ions, with the optimum being achieved at a film thickness of about 6 monolayers. An approach is proposed in a "lab-on-a-plate" format, which allows specific extraction of peptides modified with chlorine-containing compounds and includes the following steps: functionalization of the target surface, metal affinity extraction, matrix deposition and MALDI mass spectrometric analysis. Keywords: mass spectrometry, matrix assisted laser desorption/ionization (MALDI), surface, Langmuir monolayers, metal affinity chromatography.

Monolayers of Cholesterol and Cholesteryl Stearate at the Water/Vapor Interface: A Physico-Chemical Study of Components of the Meibum Layer

Langmuir monolayers containing different amounts of cholesterol and cholesteryl stearate were studied at two different temperatures (24 °C and 35 °C). The main goal was to contribute towards the understanding of how the variations in the chemical composition may affect the physico-chemical properties of these specific lipid monolayers. The model mixture was chosen considering that cholesteryl esters are present in cell membranes and some other biological systems, including human tear lipids. Therefore, an investigation into the effect of the lipid monolayer composition on their interfacial properties may elucidate some of the fundamental reasons for the deficiencies in cell membranes and tear film functioning in vivo. The experimental results have shown that the molar ratio of the mixture plays a crucial role in the modulation of the Langmuir film properties. The condensing effects of the cholesterol and the interactions between the lipids in the monolayer were the main factors altering the monolayer response to dilatational deformation. The modification of the mixture compositions leads to significant changes in the Langmuir films and the mechanical performance, altering the ability of the monolayer to reduce the surface tension and the viscoelastic properties of the monolayers. This suggests that subtle modifications of the biomembrane composition may significantly alter its physiological function.

Monolayers of Cholesterol and Cholesteryl Stearate at the Water/Vapor Interface: A Physico-Chemical Study of Components of the Meibum Layer

Monolayers of Cholesterol and Cholesteryl Stearate at the Water/Vapor Interface: A Physico-Chemical Study of Components of the Meibum Layer

Molecular dynamics research on geometric effect of nanostructured diamond-like carbon substrates on potassium stearate adsorption

Molecular dynamics (MD) simulations were performed to investigate the geometric effect of nanostructured substrates on adsorptive behavior of potassium stearate monolayers. A typical protective coating, diamond-like carbon (DLC), was employed as adsorptive substrates. For the substrates with square grooves, complete penetration of molecules can only occur under large width and small depth. The occurrence of partial penetration would make monolayer atoms away from substrate surfaces and therefore induce weak substrate-molecules interactions. Compared with the square groove bottoms, monolayers are much more strongly adsorbed to the groove concave corners. For substrates with triangle and semi-circle grooves, complete penetrations are achieved in both cases and thus monolayer atoms can interact with the whole groove surface. The effect of substrate morphology on monolayer adsorption would be sufficiently weakened by the decrease of geometric size, and the surface adsorptivity of semi-circle grooves with large radius is similar to that of the smooth surface. The results indicate that the substrates with triangle grooves have better adsorptivity than other morphologies.

Application of lanthanum stearate monolayers as a metal-affinity sorbent for the selective sorption of soman adducts to human serum albumin

A new metal-affinity sorbent based on lanthanum stearate monolayers has been developed and characterized. The prospect of its application to specific extraction of organophosphorous compound (OP) adducts of blood proteins was demonstrated. For this, the patterns of soman adducts of human serum albumin (HSA) were comprehensively characterized by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS).

Extraction of the insecticide dieldrin from water and biological samples by metal affinity chromatography

A new simple and efficient procedure for the determination of dieldrin in water, milk and blood plasma using metal affinity sorbent based on monolayers of nickel stearate has been proposed.

Bias voltage dependence of molecular orientation of dialkyl ketone and fatty acid alkyl ester at the liquid–graphite interface

Molecular orientations of self-assembled 18-pentatriacontanone (as ketone) and stearyl stearate (as ester) monolayers adsorbed on a graphite surface were studied by scanning tunneling microscopy (STM) at the liquid–solid interface. At a positive sample bias, the central areas of the dialkyl ketone and fatty acid alkyl ester molecules in the STM images appeared as two bright regions on both sides of a dim spot and a bright region on one side of a dim spot, whereas at a negative sample bias, the areas appeared dim. This contrast variation indicates that a perpendicular carbon skeleton-plane orientation with the CO pointing down on the surface is favorable for a substrate with positive charge and vice versa because of the greater electronegativity of the oxygen atom. Upon the bias voltage reversal, the delay time for the STM image contrast change in the region was observed on a time scale of minutes. The difference between the delay time lengths for the direction of bias polarity change indicates that the perpendicular configuration with CO pointing up is more stable than that with CO pointing down. These results indicate that the use of an electric field along a direction vertical to the monolayer on the substrate provides control over the orientations of the molecules between two stable states at the liquid–solid interface.

PVC mixtures’ mechanical properties with the addition of modified calcite as filler

In this study mechanical properties of PVC mixtures (PVC, stabilizer, lubricant, filler) such as tensile strength, tensile elongation, breaking strength, and breaking elongation were investigated. Unmodified calcite, as well as calcite modified by stearic acid, were used as fillers in wet and dry processes. The PVC mixtures containing the calcite modified by wet procedure have better mechanical properties compared to those with the calcite modified by the dry process. Tensile and breaking strength of the PVC mixture containing the calcite modified with 1.5% stearic acid using wet process, are higher for 2.8% and 5.2%, respectively, compared to the PVC mixture containing the calcite modified with the same amount of acid used in the dry process. The tensile strength difference between the mixtures increases with the increase of the concentration of used stearic acid up to 3%. The strength of PVC mixture with the calcite modified by wet process is 3.1% higher compared to the mixture containing calcite modified by dry process. The results showed that the bonding strength between calcite and the adsorbed organic component affected tensile strength, tensile elongation and breaking strength of the PVC mixtures. The best filler was obtained by wet modification using 1.5% stearic acid solution that provided the formation of a stearate monolayer chemisorbed on calcite. The PVC mixtures containing the calcite modified by wet process using 1.5% stearic acid solution exhibited the best mechanical properties. This calcite was completely hydrophobic with dominant chemically adsorbed surfactant, which means that stearate chemisorbed on calcite provided stronger interaction in the calcite-stearic acid-PVC system.

Langmuir-Blodgett deposition selects carboxylate headgroup coordination

Infrared reflection-absorption spectroscopy results on stearic acid Langmuir monolayers containing Mn, Co, and Cd ions show that on the water surface, the ions induce unidentate and bidentate (both chelate and bridged) coordination in the carboxylate headgroup with some trace of undissociated acid. Moreover, with Cd and Mn ions in subphase, the preferred coordination is found to be unidentate, whereas for Co, bidentate chelate is most preferred. After transfer onto amorphous substrate, not all coordinations are found to exist in the same ratio for the deposited metal stearate monolayers. More specifically, after transfer, Mn is found to coordinate with the carboxylate group as bidentate chelate, Cd as unidentate and bidentate bridged (with unidentate as the preferred coordination), and Co as preferably bidentate bridged (although all coordinations are present). Results suggest a specific interaction in each case, as the metal-carboxylate pair at the water surface is transferred to the substrate surface during Langmuir-Blodgett deposition.

Dilatational Yielding of Solid Langmuir Monolayers

In a previous work, Muruganathan and Fischer observed laser-induced local collapse of a methyl stearate monolayer. These experiments opened the possibility of studying the collapse mechanism in a highly controlled manner, since the laser intensity can be easily varied and collapse happens in a definite place (the laser focus). In this paper we extended the work presented by Muruganathan et al., describing the local yielding as an alternative pathway toward monolayer collapse competing with the global collapse of the monolayer. We first corroborated that the laser-induced collapse is a thermocapillary effect and afterward determined the threshold laser power necessary for the local pathway to win over the global collapse. We show that the laser threshold is determined more by the gradients in temperature and pressure than by the global pressure and temperature. We propose that the flow of material into the focus of the laser is observed after the yield stress of the monolayer is overcome. The higher the yield stress, the higher the temperature gradient that is necessary for the monolayer to yield. The local pathway opens only when the derivative of surface pressure with temperature is negative such that stress gradients point toward the laser focus and a sink of material is generated. In such a case we are able to give estimates of the dilatational yield pressure of the solid monolayer.

Fabrication of a superhydrophobic surface on a wood substrate

A layer of lamellar superhydrophobic coating was fabricated on a wood surface through a wet chemical process. The superhydrophobic property of the wood surface was measured by contact angle (CA) measurements. The microstructure and chemical composition of the superhydrophobic coating were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). An analytical characterization revealed that the microscale roughness of the lamellar particles was uniformly distributed on the wood surface and that a zinc stearate monolayer (with the hydrophobic groups oriented outward) formed on the ZnO surface as the result of the reaction between stearic acid and ZnO. This process transformed the wood surface from hydrophilic to superhydrophobic: the water contact angle of the surface was 151°, and the sliding angle was less than 5°.

Collapse of preformed cobalt stearate film on water surface

Preformed cobalt stearate (CoSt) molecules form a film on the water surface, which with barrier compression shows multilayers of different heights that are evidenced from the structures of the films deposited on hydrophilic silicon (0 0 1) substrates by using a horizontal deposition technique at different positions of the surface pressure ( π)–specific molecular area ( A) isotherm. In-plane morphology and out-of-plane structures are obtained from the atomic force microscopy (AFM) and X-ray reflectivity studies. Electron density profiles (EDPs), extracted from the reflectivity data, show that the monolayer coverage is maximum when π is far before the collapse point ( π c) but with barrier compression domains of multilayers start to form even before π c. After π c, two different bilayer repeat distances have been observed from the two different series of the Bragg peaks implying the formation of domains by both the tilted and untilted CoSt molecules. Far after π c, reflectivity decreases rapidly and morphology of the deposited films changes totally. Structures before and after π c of the CoSt film have also been obtained by changing the pH of the subphase water. From all the structural information it is clear that the preformed CoSt film collapses in a different way in comparison with the collapse of the standard cobalt stearate monolayer where cobalt stearate molecules were formed at the air–water interface. Reasons for obtaining different structures on the water surface with barrier compression have been proposed.

Chain orientation and headgroup structure in Langmuir monolayers of stearic acid and metal stearate (Ag, Co, Zn, and Pb) studied by infrared reflection-absorption spectroscopy

The monolayers of stearic acid at the air-water interface on pure water and ion-containing subphases have been studied using infrared reflection-absorption spectroscopy. In the presence of Co(2+), Zn(2+), and Pb(2+), ordered hydrocarbon chains and hexagonal subcell structure remain almost unchanged in comparison with those for the monolayer on pure water at the surface pressure of 20 m/Nm. In the cases of Co(2+) and Zn(2+), the H-bonded monodentate and unsymmetric bidentate chelating structure within the headgroups were formed, and in the case of Pb(2+), three types of structures, bidentate chelating, unsymmetric chelating, and bidentate bridging coordinations, were formed. The hydrocarbon chains in the monolayers are uniaxially oriented at a tilt angle of approximately 0 degrees with respect to the surface normal in contrast to a tilt angle of approximately 20 degrees on pure water surface at 20 m/Nm by the computer simulation of theoretical calculation to experimental data. In the presence of Ag(+), multilayers were developed with the highly ordered hydrocarbon chains in a triclinic subcell structure and a bidentate bridging structure within the headgroups. The multilayers were composed of three monolayers and the hydrocarbon chains in each monolayer were oriented at an angle of approximately 30 degrees away from the surface normal with their C-C-C planes almost perpendicular to the water surface.

A Novel Non-destructive Interfacing Technique for Molecular Scale Switching Junctions

ABSTRACTCharacterization of molecular scale electronic devices generally involves deposition of a metal top electrode onto an organic film. During the evaporation process, high energetic granules of metals may lead to unwanted reactions between the organic molecules and deposited top electrodes. This can cause, as commonly reported, lasting damage which leaves most junctions either short or open. To overcome this important issue of physical damage to the molecules, we developed a novel technique of interfacing molecules by laying prefabricated metallic electrodes on top of a monolayer of molecules. For the bottom electrode a monolayer of cadmium stearate ((C17H35COO)2Cd) was deposited, using the Langmuir-Blodgett technique, onto platinum (Pt) electrodes which further rested on 200nm of oxide used for isolation. A separate set of Aluminum (Al) electrodes were fabricated on a different oxide free, highly doped substrate and was gently placed on the cadmium stearate monolayer in room ambient. Conduction to the top electrode was accomplished by probing the backside of the highly doped wafer whereas the bottom electrodes were individually addressed. Pressure was applied to ensure firm contact between the molecules and the top electrodes. Preliminary results showed an observed switching voltage of 3.5V. Most of the devices with Al as the top electrodes exhibited a gradual progression from switching on the positive side, closing, and then switching towards the negative side.

Langmuir monolayer approaches to protein recognition through molecular imprinting

Surface plasmon resonance (SPR) spectroscopy and atomic force microscopy (AFM) have been employed to investigate ferritin adsorption to binary surfactant monolayers of cationic dioctadecyldimethylammonium bromide (DOMA) and non-ionic methyl stearate (SME). Surfactant molar ratios, miscibility, and lateral mobility were controlled to define the number, size, and distribution of "binding sites" for ferritin, which under the low ionic strength conditions investigated, adsorbed to the monolayers predominantly through electrostatic interactions. Successive adsorption/desorption cycles revealed that fluid monolayers, capable of laterally restructuring during the initial protein adsorption event, bound up to 60% more ferritin (dependent on SME:DOMA ratios) as compared to monolayers that were immobilized on a hydrophobic support during this first adsorption step. The enhanced binding of ferritin to fluid monolayers was accentuated in films having non-ionic SME as the principal component. These findings support the premise that the surfactants reorganize to form favorable interactions with an adsorbing protein, leading to protein specific charge patterns, or templates, in the films. Template assessment, however, was complicated by the presence of an irreversibly bound protein fraction, which AFM revealed to be locally ordered protein clusters.

XAFS Study of the Adsorbed Ions onto the Monolayers at Air/Solution Interface

Solution surface can be studied by using X-ray Absorption Fine Structure (XAFS) method. To obtain surface sensitivity, the X-rays are introduced onto the solution surface at a very small grazing incidence angle to meet the total-reflection condition. This new spectroscopic method was successfully applied to the surfaces of aqueous solutions covered with monolayers of alkylammonium bromide, zinc stearate, and also zinc porphyrine complex. The spectra from these surfaces indicated quite interesting but not yet known facts such as, dehydration of anions adsorbed onto the alkylammonium monolayer and coordination change of zinc ions from the octahedral to tetrahedral when the metal ions come to the stearate monolayer from the bulk solution. The XAFS experiments were also performed with linearly polarized X-rays to elucidate the selective orientation of the planar Zn porphyrine complex on the solution surface.

An investigation of the structure of stearate monolayers on Au@ZrO2and Ag@ZrO2core–shell nanoparticles

Monolayer protected nanoparticles, Au@ZrO2@stearate and Ag@ZrO2@stearate, in which the core–shell nanoparticles, Au@ZrO2 and Ag@ZrO2 (ZrO2 coated Au and Ag nanoparticles) are functionalized with stearic acid, have been synthesized and characterized. The air-dried powders, freely dispersible in several organic solvents (both polar and non-polar), are stable for extended periods. The materials were characterized by spectroscopic, microscopic, diffraction and thermal analysis techniques. The monolayer cover is stable up to 200 °C. Monolayers do not exhibit strong inter-chain interactions, unlike in the case of those on metal nanoparticles, suggesting that their surface anchoring sites are widely spaced. As a result, temperature-dependent infrared spectra of the monolayers are featureless. The oxide surface is accessible for small molecules in solution even after stearic acid coverage. Freely dispersible nanoparticles with oxide shells may offer new possibilities in catalysis, photophysics and materials science.

Sodium stearate adsorption onto titania pigment

The interaction of sodium stearate with titania pigment particles from aqueous suspension has been investigated using thermal analysis and infrared spectroscopy combined with electrochemical studies. Thermogravimetric analysis (TGA) was used both to determine the adsorption isotherm and to investigate the interaction behavior. Monolayer coverage is determined to be 0.95 mg/m 2; however, unlike the case with organic solvents, multilayer adsorption occurs. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, combined with TGA, revealed that the surface monolayer is chemically bound. DRIFT spectroscopic data also indicated that the stearate bridged across two aluminum atoms. Subsequent stearate layers were physisorbed to the stearate monolayer and were readily removed with acetone washing.