Surface chemistry studies of (CdSe)ZnS quantum dots at the air-water interface

Trioctylphosphine oxide- (TOPO-) capped (CdSe)ZnS quantum dots (QDs) were prepared through a stepwise synthesis. The surface chemistry behavior of the QDs at the air-water interface was carefully examined by various physical measurements. The surface pressure-area isotherm of the Langmuir film of the QDs gave an average diameter of 4.4 nm, which matched very well with the value determined by transmission electron microscopy (TEM) measurements if the thickness of the TOPO cap was counted. The stability of the Langmuir film of the QDs was tested by two different methods, compression/decompression cycling and kinetic measurements, both of which indicated that TOPO-capped (CdSe)ZnS QDs can form stable Langmuir films at the air-water interface. Epifluorescence microscopy revealed the two-dimensional aggregation of the QDs in Langmuir films during the early stage of the compression process. However, at high surface pressures, the Langmuir film of QDs was more homogeneous and was capable of being deposited on a hydrophobic quartz slide by the Langmuir-Blodgett (LB) film technique. Photoluminescence (PL) spectroscopy was utilized to characterize the LB films. The PL intensity of the LB film of QDs at the first emission maximum was found to increase linearly with increasing number of layers deposited onto the hydrophobic quartz slide, which implied a homogeneous deposition of the Langmuir film of QDs at surface pressures greater than 20 mN.m(-1).     

Pure and mixed films of a nitrostilbene derivative at the air-water interface, Langmuir-Blodgett multilayer fabrication, and optical characterization

This paper reports the preparation and characterization of pure Langmuir and Langmuir-Blodgett (LB) films of a stilbene derivative containing two alkyl chains, namely 4-dioctadecylamino-4'-nitrostilbene. Mixed films incorporating docosanoic acid and the stilbene derivative are also studied. Brewster angle microscopy (BAM) analysis has revealed the existence of randomly oriented three-dimensional (3D) aggregates, spontaneously formed immediately after the spreading process of the stilbene derivative onto the water surface. These 3D aggregates coexist with a Langmuir film that shows the typical gas, liquid, and solid-like phases in the surface pressure and surface potential vs area per molecule isotherms, indicative of an average preferential orientation of the stilbene compound at the air-water interface, and a gradual molecular arrangement into a defined structure upon compression. A blue shift of 55 nm of the reflection spectrum of the Langmuir film with respect to the spectrum of a chloroform solution of the nitrostilbene indicates that two-dimensional (2D) H-aggregates are formed at the air-water interface. The monolayers are transferred undisturbed onto solid substrates with atomic force microscopy (AFM) revealing that the one layer LB films are constituted by a monolayer of the stilbene derivative together with some 3D aggregates. When the nitrostilbene compound is blended with docosanoic acid, the 3D aggregation is avoided in the Langmuir and Langmuir-Blodgett films, but does not limit the formation of 2D H-aggregates, desirable for second-order nonlinear optical response in the blue domain. The AFM images of the mixed LB films show that they are formed by a docosanoic acid monolayer and, on the top of it, a bilayer of the stilbene derivative.     

Structural and topographical characteristics of adsorbed WPI and monoglyceride mixed monolayers at the air-water interface

In this work we have analyzed the structural and topographical characteristics of mixed monolayers formed by an adsorbed whey protein isolate (WPI) and a spread monoglyceride monolayer (monopalmitin or monoolein) on the previously adsorbed protein film. Measurements of the surface pressure (pi)-area (A) isotherm were obtained at 20 degrees C and at pH 7 for protein-adsorbed films from water in a Wilhelmy-type film balance. Since the surface concentration (1/A) is actually unknown for the adsorbed monolayer, the values were derived by assuming that the A values for adsorbed and spread monolayers were equal at the collapse point of the mixed film. The pi-A isotherm deduced for adsorbed WPI monolayer in this work is practically the same as that obtained directly by spreading. For WPI-monoglyceride mixed films, the pi-A isotherms for adsorbed and spread monolayers at pi higher than the equilibrium surface pressure of WPI are practically coincident, a phenomenon which may be attributed to the protein displacement by the monoglyceride from the interface. At lower surface pressures, WPI and monoglyceride coexist at the interface and the adsorbed and spread pi-A isotherms (i.e., the monolayer structure of the mixed films) are different. Monopalmitin has a higher capacity than monoolein for the displacement of protein from the air-water interface. However, some degree of interactions exists between proteins and monoglycerides and these interactions are higher for adsorbed than for spread films. The topography of the monolayer corroborates these conclusions.     

Equilibrium structure and dynamics of (2R, 3R)-(+)-bis(decyloxy)succinic acid at the air-water interface

A twin-tailed, twin-chiral fatty acid, (2R,3R)-(+)-bis(decyloxy)succinic acid was synthesized and its two dimensional behavior at the air-water interface was examined. The pH of the subphase had a profound effect on the monolayer formation. On acidic subphase, stable monolayers with increased area per molecule due to hydrogen bonding and bilayers at collapse pressures were observed. Highly compressible films were formed at 40 degrees C, while stable monolayers with increased area were observed at sub-room temperatures. Langmuir monolayers formed on subphases containing 1 mM ZnCl2 and CaCl2 revealed two dimensional metal complex formation with Zn2+ forming a chelate-type complex, while Ca2+ formed an ionic-type complex. Monolayers transferred from the condensed phase onto hydrophilic Si(100) and quartz substrates revealed the formation of bilayers through transfer-induced monolayer buckling. Compression induced crystallites in 2D from monolayers and vesicle-like supramolecular structures from multilayers were the noted LB film characteristics, adopting optical imaging and electron microscopy. The interfacial monolayer structure studied through molecular dynamics simulation revealed the order and packing at a molecular level; monolayers adsorbed at various simulated specific areas of the molecule corroborated the (pi-A) isotherm and the formation of a hexagonal lattice at the air-water interface.     

A monolayer study on interactions of docetaxel with model lipid membranes

Docetaxel (DCT) is an antineoplastic drug for the treatment of a wide spectrum of cancers. DCT surface properties as well as miscibility studies with l-alpha-dipalmitoyl phosphatidylcholine (DPPC), which constitutes the main component of biological membranes, are comprehensively described in this contribution. Penetration studies have revealed that when DCT is injected under DPPC monolayers compressed to different surface pressures, it penetrates into the lipid monolayer promoting an increase in the surface pressure. DCT is a surface active molecule able to decrease the surface tension of water and to form insoluble films when spread on aqueous subphases. The maximum surface pressure reached after compression of a DCT Langmuir film was 13 mN/m. Miscibility of DPPC and DCT in Langmuir films has been studied by means of thermodynamic properties as well as by Brewster angle microscopy (BAM) analysis of the mixed films at the air-water interface, concluding that DPPC and DCT are miscible and they form non-ideally mixed monolayers at the air-water interface. Helmholtz energies of mixing revealed that no phase separation occurs. In addition, Helmholtz energies of mixing become more negative with decreasing areas per molecule, which suggests that the stability of the mixed monolayers increases as the monolayers become more condensed. Compressibility values together with BAM images indicate that DCT has a fluidizing effect on DPPC monolayers.     

Transition from homogeneous Langmuir-Blodgett monolayers to striped bilayers driven by a wetting instability in octadecylsiloxane monolayers

We show that two dips of an oxidized silicon substrate through a prepolymerized n-octadecylsiloxane monolayer at an air-water interface in a rapid succession produces periodic, linear striped patterns in film morphology extending over macroscopic area of the substrate surface. Langmuir monolayers of n-octadecyltrimethoxysilane were prepared at the surface of an acidic subphase (pH 2) maintained at room temperature (22 +/- 2 degrees C) under relative humidities of 50-70%. The substrate was first withdrawn at a high dipping rate from the quiescent aqueous subphase (upstroke) maintained at several surface pressures corresponding to a condensed monolayer state and lowered soon after at the same rate into the monolayer covered subphase (downstroke). The film structure and morphology were characterized using a combination of optical microscopy, imaging ellipsometry, and Fourier transform infrared spectroscopy. An extended striped pattern, perpendicular to the pushing direction of the second stroke, resulted for all surface pressures when the dipping rate exceeded a threshold value of 40 mm min(-1). Below this threshold value, uniform deposition characterizing formation of a bimolecular film was obtained. Under conditions that favored striped deposition during the downstroke through the monolayer-covered interface, we observed a periodic auto-oscillatory behavior of the meniscus. The stripes appear to be formed by a highly correlated reorganization and/or exchange of the first monolayer, mediated by the Langmuir monolayer at the air-water interface. This mechanism appears distinctly different from nanometer scale stripes observed recently in single transfers of phospholipid monolayers maintained near a phase boundary. The stripes further exhibit wettability patterns useful for spatially selective functionalization, as demonstrated by directed adsorptions of an organic dye (fluorescein) and an oil (hexadecane).     

Structural, topographical, and shear characteristics of milk protein and monoglyceride monolayers spread at the air-water interface

In this contribution we are concerned with the study of structure, topography, and surface rheological characteristics under shear conditions of monoglyceride (monopalmitin and monoolein) and milk protein (beta-casein, kappa-casein, caseinate, and WPI) spread monolayers at the air-water interface. Combined surface chemistry (surface film balance and surface shear rheometry) and microscopy (Brewster angle microscopy: BAM) techniques have been applied in this study to pure emulsifiers (proteins and monoglycerides) spread at the air-water interface. To study the shear characteristics of spread films, a homemade canal viscometer was used. The experiments have demonstrated the sensitivity of the surface shear viscosity (eta(s)) of protein and monoglyceride films at the air-water interface, as a function of surface pressure (or surface density). The surface shear viscosity was higher for proteins than for monoglycerides. In addition, eta(s) was higher for the globular WPI than for disordered beta-casein and caseinate due to the strong forces acting on spread globular proteins. This technique makes it possible to distinguish between beta-casein and caseinate spread films, with the higher eta(s) values for the later due to the presence of kappa-casein. The eta(s) value varies greatly with the surface pressure (or surface density). In general, the greater the surface pressure, the greater the values of eta(s). Finally, the eta(s) value is also sensitive to the monolayer structure, as was observed for monoglycerides with a rich structural polymorphism (i.e., monopalmitin).     

Penetration of beta-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.     

Irreversible Collapse of Poly(vinyl stearate) Monolayers at the Air-Water Interface

The collapse of Langmuir monolayers of poly(vinyl stearate) (PVS) at the air-water interface has been investigated by combined measurements of the surface pressure-area isotherms and Brewster angle microscopy (BAM). Atomic force microscopy (AFM) has been used to gain out-of-plane structural information on collapsed films transferred onto a solid substrate by a modified version of the inverse Langmuir-Schaefer deposition method. At high areas per monomer repeat unit, BAM imaging revealed that the films are heterogeneous, with large solidlike domains (25-200 mum in diameter) coexisting with liquidlike domains. Upon film compression, the domains coalesced to form a homogeneous monolayer before the film collapsed at constant pressure, forming irreversible three-dimensional (3D) structures. BAM images showed that two 3D structures coexisted: buckles of varying width extending across the surface and perpendicular to the direction of the compression and dotted islandlike structures. Upon expansion, the film fractured and both 3D protrusions persisted, explaining the marked hysteresis recorded in the Langmuir isotherms. Experiments with AFM confirmed the 3D nature of both protrusions and revealed that many buckles contain substructures corresponding to narrow buckles whose heights are a multiple of a single bilayer. Additionally, many multilayer islands with diameters spanning from 0.2 mum to over 3.5 mum were characterized by varying heights between 2 nm and up to over 50 nm. The key to the formation of the irreversible 3D structures is the presence of large inhomogeneities in the PVS monolayer, and a generalized phenomenological model is proposed to explain the collapse observed.     

Effect of hydrocarbon chain and pH on structural and topographical characteristics of phospholipid monolayers

Structural characteristics (structure, elasticity, topography, and film thickness) of dipalmitoyl phosphatidylcholine (DPPC) and dioleoyl phosphatidylcholine (DOPC) monolayers were determined at the air-water interface at 20 degrees C and pH values of 5, 7, and 9 by means of surface pressure (pi)-area (A) isotherms combined with Brewster angle microscopy (BAM) and atomic force microscopy (AFM). From the pi-A isotherms and the monolayer elasticity, we deduced that, during compression, DPPC monolayers present a structural polymorphism at the air-water interface, with the homogeneous liquid-expanded (LE) structure; the liquid-condensed structure (LC) showing film anisotropy and DPPC domains with heterogeneous structures; and, finally, a homogeneous structure when the close-packed film molecules were in the solid (S) structure at higher surface pressures. However, DOPC monolayers had a liquid-expanded (LE) structure under all experimental conditions, a consequence of weak molecular interactions because of the double bond of the hydrocarbon chain. DPPC and DOPC monolayer structures are practically the same at pH values of 5 and 7, but a more expanded structure in the monolayer with a lower elasticity was observed at pH 9. BAM and AFM images corroborate, at the microscopic and nanoscopic levels, respectively, the same structural polymorphism deduced from the pi-A isotherm for DPPC and the homogeneous structure for DOPC monolayers as a function of surface pressure and the aqueous-phase pH. The results also corroborate that the structural characteristics and topography of phospholipids (DPPC and DOPC) are highly dependent on the presence of a double bond in the hydrocarbon chain.     

Mixed monolayers of alkylated azacrown ethers and palmitic acid at the air-water surface

The Langmuir films of two alkylated azacrown ethers at the air-water surface were characterized using surface pressure-area isotherms, ellipsometry, Brewster angle microscopy, and constant-area surface pressure relaxation. The azacrown ether molecules aggregate in the monolayer, which significantly stabilizes the film against dissolution. Mixed azacrown ether-palmitic acid monolayers were also characterized; results suggest that at high compression the two molecules interact repulsively. The influence of Cu(II) ions present in the aqueous subphase on the single components and mixed monolayer characteristics was also studied.     

Monolayer behavior of 1,2-dipalmitoylgalloylglycerol, a synthetic lipid with strong cohesive properties

Monolayers of 1,2-dipalmitoylgalloylglycerol (DPGG) were investigated at the air-water interface. The monolayers exhibit high rigidity which leads to the formation of surface tension gradients in the film. Transfer to solid substrate yields homogeneous Langmuir-Blodgett films with low surface roughness. Large numbers of aggregates were observed by Brewster angle microscopy and imaging ellipsometry at relatively high molecular areas. At all pressures, the DPGG molecules adopt conformations corresponding to low tilt angles. Constant area measurements result in a pressure increase as the film rearranges to maximize the intermolecular interactions. An optimal intermolecular distance required for the formation of a hydrogen-bond network between headgroups is proposed to explain the observed, highly cohesive monolayer behavior.     

Monolayer behavior and Langmuir-Blodgett manipulation of CdS quantum dots

Cadmium sulfide (CdS) quantum dots (QDs) were prepared and surface modified by dodecanthiol or mercaptosuccinic acid (MSA) to render a surface with alkyl chains (C(12)-CdS) or carboxylic acid groups (MSA-CdS), respectively. Due to the hydrophobic property of C(12)-CdS, the nanoparticles disperse well in chloroform and stay stable at the air/water interface. However, 3-dimensional (3D) aggregative domains and particle-free pores were formed in the monolayer due to poor particle-water interaction. For the MSA-CdS nanoparticles, the surface was hydrophobized through physical adsorption of a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The capped MSA on the CdS plays an important role in enhancing the adsorption of CTAB and improving the stability of the QDs at the air/water interface. Due to the reversible adsorption of CTAB on MSA-CdS, a hydrophilic area can be exposed in the water-contacting region of a nanoparticle when it stays at the air/water interface. Thus, the CTAB-MSA-CdS QD behaves as an amphiphilic compound at the air/water interface and has properties superior to those of C(12)-CdS QDs in fabrication of layer-by-layer 2D structure of particulate films. The distinct behaviors of the two QDs at the air/water interface and the related effect on the properties of LB films were studied using a number of methods, including pressure-area (pi-A) isotherm, relaxation and hysteresis experiments, in-situ observation of Brewster angle microscopy (BAM), the postdeposition analysis of atomic force microscopy (AFM), and UV-vis spectroscopy.     

Directionally oriented LB films of an OPE derivative: assembly, characterization, and electrical properties

Langmuir films have been fabricated from 4-[4'-(4'-thioacetyl-phenyleneethynylene)-phenyleneethynylene]-aniline (NOPES) after cleavage of the thioacetyl protecting group. Characterization by surface pressure vs area per molecule isotherms and Brewster angle microscopy reveal the formation of a high quality monolayer at the air-water interface. One layer Langmuir-Blodgett (LB) films were readily fabricated by the transfer of the NOPES Langmuir film onto solid substrates. X-ray photoelectron spectroscopy (XPS), surface polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), and quartz crystal microbalance (QCM) experiments conclusively demonstrate the formation of one layer LB films in which the functional group associated with binding to the substrate can be tailored by the film transfer conditions. Using LB methods this molecule could be transferred to gold samples with either the amine or thiol group attached to the gold surface. The amine group is directly attached to the gold substrate (Au-NH(2)-OPE-SH) when the substrate is initially immersed in the subphase and withdrawn during the transfer process; in contrast, monomolecular films in which the thiolate group is attached to the gold substrate (Au-S-OPE-NH(2)) are obtained when the substrate is initially out of the subphase and immersed during the transfer process. The morphology of these films was analyzed by atomic force microscopy (AFM), showing the formation of homogeneous layers. Film homogeneity was confirmed by cyclic voltammetry, which revealed a large passivation of gold electrodes covered by NOPES monolayers. Electrical properties for both polar orientated junctions have been investigated by scanning tunnelling microscopy (STM), with both orientations featuring a nonrectifying behavior.     

Fabrication of metal nanoparticle monolayers on amphiphilic poly(amido amine) dendrimer Langmuir films

A newly designed 1.5th generation poly(amido amine) dendrimer with an azacrown core, hexylene spacers, and octyl terminals was spread on gold nanoparticle (Au-NP) suspension. The surface pressure-area isothermal curves indicated that the molecular area of dendrimer on Au-NP suspension was significantly smaller than that on water, indicating the formation of dendrimer/Au-NP composites. The dendrimer Langmuir films on the Au-NP suspension were transferred to copper grids at various surface pressures and observed by transmission electron microscopy. The transferred films consisted of a fractal-like network of nanoparticles at low surface pressure and of a defect-rich monolayer of nanoparticles at high surface pressure. From these results, it was suggested that the dendrimers bind Au-NPs, and dendrimer/Au-NP composites formed networks or monolayers at the interface. From the intensity decrease of the Au plasmon band of Au-NP suspension after the formation of composite, it was estimated that some (approximately 14) dendrimer molecules bind to one Au-NP. Furthermore, neutron reflectivity at the air/suspension interface and X-ray reflectivity of the film transferred on a silicon substrate revealed that the dendrimer molecules are localized on the upper-half surface of Au-NP. Metal affinity of azacrown, flexibility of hexylene spacer, and amphiphilicity of dendrimer with octyl terminals played important roles for the formation of dendrimer/Au-NP hybrid films. The present investigation proposed a new method to fabricate the self-assembled functional polymer/nanoparticle hybrid film.     

Langmuir-Blodgett film of hydrophobin protein from Pleurotus ostreatus at the air-water interface

We present results concerning the formation of Langmuir-Blodgett (LB) films of a class I hydrophobin from Pleurotus ostreatus at the air-water interface, and their structure as Langmuir-Blodgett (LB) films when deposited on silicon substrates. LB films of the hydrophobin were investigated by atomic force microscopy (AFM). We observed that the compressed film at the air-water interface exhibits a molecular depletion even at low surface pressure. In order to estimate the surface molecular concentration, we fit the experimental isotherm with Volmer's equation describing the equation of state for molecular monolayers. We found that about (1)/ 10 of the molecules contribute to the surface film formation. When transferred on silicon substrates, compact and uniform monomolecular layers about 2.5 nm thick, comparable to a typical molecular size, were observed. The monolayers coexist with protein aggregates, under the typical rodlet form with a uniform thickness of about 5.0 nm. The observed rodlets appear to be a hydrophilic bilayer and can then be responsible for the surface molecular depletion.     

Unexpected bilayer formation in Langmuir films of nucleolipids

Langmuir monolayers have been extensively investigated by various experimental techniques. These studies allowed an in-depth understanding of the molecular conformation in the layer, phase transitions, and the structure of the multilayer. As the monolayer is compressed and the surface pressure is increased beyond a critical value, usually occurring in the minimal closely packed molecular area, the monolayer fractures and/or folds, forming multilayers in a process referred to as collapse. Various mechanisms for monolayer collapse and the resulting reorganization of the film have been proposed, and only a few studies have demonstrated the formation of a bilayer after collapse and with the use of a Ca(2+) solution. In this work, Langmuir isotherms coupled with imaging ellipsometry and polarization modulation infrared reflection absorption spectroscopy were recorded to investigate the air-water interface properties of Langmuir films of anionic nucleolipids. We report for these new molecules the formation of a quasi-hexagonal packing of bilayer domains at a low compression rate, a singular behavior for lipids at the air-water interface that has not yet been documented.     

Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers

In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)(2)(tmphen)]PF(6), (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air-water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as pi-A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer at pi approximately equal to 37 mNm(-1). Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir-Blodgett) technique.     

聚苯乙烯-聚(4-乙烯基吡啶)嵌段共聚物LB膜结构形态的研究

采用氯仿作为铺展溶剂,将嵌段共聚物聚苯乙烯-聚(4-乙烯基吡啶)(PS-b-P4VP)稀溶液铺展于空气与水界面上,利用Langmuir-Blodgett(LB)膜技术转移至固体基底.研究了不同的嵌段比、表面压和小分子1-芘丁酸(PBA)的加入对嵌段共聚物气液界面聚集组装的影响.研究发现随着亲水段(P4VP)的增加,聚集组装结构由纳米片状、带状转变成纳米条状、纳米点状结构.表面压对纯PS-b-P4VP聚集组装产生影响,表面压增大,组装体排列紧密;随着表面压的继续增大,单层聚集结构遭到破坏,发生堆叠.加入PBA小分子后,PBA与PS-b-P4VP形成氢键,形态发生明显变化,原来的片状结构转变为条状或点状结构.     

Time-dependent complexation of glucose-reduced gold nanoparticles with octadecylamine Langmuir monolayers

We report on the reduction of aqueous chloroaurate ions by glucose to form gold nanoparticles of uniform size. We further demonstrate the complexation of these particles with octadecylamine (ODA) monolayers at the air-water interface. Pressure-area (pi-A) isotherms as a function of time of complexation revealed a significant expansion of the monolayer. Surface pressure variation with time for constant areas after spreading of the monolayer was carried out to observe the kinetics of complexation of the colloidal particles at the interface. The kinetics of complexation of the particles at the interface was also monitored by Brewster angle microscopy (BAM) measurements. Langmuir-Blodgett films of the particles complexed with ODA were formed at a subphase pH of 9 onto different substrates. Quartz crystal microgravimetry (QCM) was used to quantify the amount of particles deposited per immersion cycle of the quartz crystal. The LB films were further characterized by UV-vis and transmission electron microscopy (TEM) measurements. TEM measurements indicate a close packed and equidistant arrangement of colloidal particles in the LB film, probably due to hydrogen-bonding interactions.