Brewster Angle Research Articles

Goos-Hänchen shift for an Airyprime beam.

We propose a comprehensive theory to analyze the Goos-Hänchen (GH) shift for an arbitrarily polarized Airyprime beam reflected at the air-dielectric interface. We derive general expressions for the spatial and angular GH shifts and establish a close relationship between the GH shift of the Airyprime beam and the GH shift of the Airy beam. We also predict the novel optical effects of a significantly enhanced spatial GH shift and an almost disappeared angular GH shift when the horizontally polarized Airyprime beam is reflected near Brewster's angle.

Filling the gaps: Introducing plasticizers into π-conjugated OPE-NH2 Langmuir layers for defect-free anisotropic interfaces and membranes towards unidirectional mass, charge, or energy transfer

The construction of ultrathin membranes from linearly aligned π-electron systems is advantageous for targeted energy, charge, or mass transfer. The Langmuir-Blodgett (LB) technique enables the creation of such membranes, especially with amphiphilic π-electron systems. However, these systems often aggregate, forming rigid Langmuir monolayers with defects or holes. In this study we introduce plasticizers to effectively address this issue. To create anisotropic membranes, we used an oligo(phenylene ethynylene) derivative (OPE-NH2) as an linear amphiphile and bisphenol A di-tert-butyl ester (BPAE) as a plasticizer. We analyzed surface pressure (mean molecular area) (Π(mma)) isotherms and characterized Langmuir monolayers with Brewster Angle Microscopy (BAM), to determine the optimal miscibility of OPE-NH2 with BPAE. Detailed analysis of hole areas filled was performed through image binarization. We identified an optimal BPAE concentration of 4 mol-% in the OPE-NH2 Langmuir monolayer. Our BAM image evaluation via binarization determined the difference between the mean molecular areas of close-packed Langmuir domains and those quantified via the Π(mma) isotherm. This study presents an automated method for BAM image analysis and a new approach for fabricating defect-free anisotropic molecular monolayers of π-conjugated amphiphiles.

Interactions of sphingomyelin with biologically crucial side chain-hydroxylated cholesterol derivatives.

Oxysterols are interesting molecules due to their dual nature, reflecting beneficial and harmful effects on the body. An issue that still needs to be solved is how slight modification of their structure owing to the location of the additional polar group in the molecules affects their biological activity. With this in mind, we selected three side chain-hydroxylated oxysterols namely: 20(S)-hydroxycholesterol (20(S)-OH), 24(S)-hydroxycholesterol (24(S)-OH), and 27-hydroxycholesterol (27-OH), and examined their behavior in mixtures with the bioactive sphingolipid - sphingomyelin (SM). Our research was based on the Langmuir monolayer technique supplemented with molecular dynamics (MD) and microscopic observation of the films texture (Brewster angle microscopy, BAM, and atomic force microscopy, AFM). Additionally, since 20(S)-hydroxycholesterol has not been studied so far, we thoroughly characterized this oxysterol in one-component monolayers. Our studies showed differences in the interactions of the studied oxysterols and sphingomyelin. Namely, it was found that 20(S)-OH binds to SM, unlike 24(S)-OH and 27-OH, which both weakly interact with SM. This distinct behavior was interpreted within the molecular dynamics as being due to weak intermolecular interactions between 20(S)-OH molecules, which allowed easy incorporation of SM into the 20(S)-OH monolayer. In contrast, the strong oxysterol-oxysterol interactions occurring in monolayers with 24(S)-OH or 27-OH make this process more difficult. This may be important in the process of bone formation/resorption. Other aspects derived from our study are: (i) the tendency of oxysterols to incorporate into lipid rafts (leading to their modification in structure and function), as well as (ii) the formation of multilayer structures, in which oxysterols are arranged in the characteristic forms of "strings of beads", which may facilitate their transport across the membrane.

Multi-angle spectrophotometric reflectance methods for determining refractive indices

The experience of developing and applying methods for measuring the refractive coefficients of crystals of the highest and middle categories based on multi-angle spectrophotometric reflection methods is presented: by the reflection spectrum from one face at an angle of incidence of light close to normal, and by the reflection method when light falls at Brewster angle. The advantages and limitations of the methods and the requirements for the samples are described. It is shown that the reflection method at an angle of incidence close to normal is applicable for optically isotropic media. The Brewster angle method is applicable for crystals of the highest and middle categories. The measurement accuracy of both methods has been determined. The applicability of these methods is shown for samples of crystals of the highest and middle categories Gd3Al2Ga3O12:Ce and La3Ga5.5Ta0.5O14 respectively.

Experimental Analysis of Terahertz Wave Scattering Characteristics of Simulated Lunar Regolith Surface

This study investigates terahertz (THz) wave scattering from a simulated lunar regolith surface, with a focus on the Brewster feature, backscattering, and bistatic scattering within the 325 to 500 GHz range. We employed a generalized power-law spectrum to characterize surface roughness and fabricated Gaussian correlated surfaces from Durable Resin V2 using 3D printing technology. The complex dielectric permittivity of these materials was determined through THz time-domain spectroscopy (THz-TDS). Our experimental setup comprised a vector network analyzer (VNA) equipped with dual waveguide frequency extenders for the WR-2.2 band, transmitter and receiver modules, polarizing components, and a scattering chamber. We systematically analyzed the effects of root-mean-square (RMS) height, correlation length, dielectric constant, frequency, polarization, and observation angle on THz scattering. The findings highlight the significant impact of surface roughness on the Brewster angle shift, backscattering, and bistatic scattering. These insights are crucial for refining theoretical models and developing algorithms to retrieve physical parameters for lunar and other celestial explorations.

Tuning Electrostatics to Promote Ordered Monolayers of Phosphole-Lipids.

Heteroatom-doped π-conjugated systems have been exploited for electronic device applications. Phosphole-containing backbones are particularly intriguing with regard to electron delocalization and ultimately control over the photophysical, redox, and charge transfer characteristics. However, practical application of these materials commonly relies on well-structured, thin film architectures. Self-assembly offers a route to generate ordered 2D structures deposited on solid substrates. The orientation of these deposited films can be manipulated by the introduction of alkyl chains of varying length (to form phosphole-based lipids) and chemical modification of the phosphole-derived headgroup. External controls can also be considered to tune these films' properties, e.g., the electrostatic interactions within the film can be controlled by varying the environment with the addition of simple salt counterions. A series of lipids with phosphole-based π-conjugated headgroups have been designed and exhibit intramolecular conformational changes in response to external conditions. Herein the 2D film structure in Langmuir and Langmuir-Blodgett films is reported in the presence and absence of halide salts. The film morphology obtained from Brewster angle and atomic force microscopy shows the formation of a condensed phase but also 3D aggregates, and grazing incidence X-ray diffraction confirmed the presence of untilted, hexagonally packed chains. The size of the counterion influences its ability to intercalate between the phosphole headgroups, which ultimately provides a means to induce the formation of a well-ordered, single monolayer film without aggregates that can be transferred to the solid substrate.

Optical anisotropy and surface phases of cholesterol derivative monolayer at air–water interface

Cholesterol and its derivatives play crucial roles in regulating processes of biological membranes. Langmuir monolayer can mimic a bio-membrane which can be used to investigate the molecular interaction governing the important physical phenomena. The cholesterol derivative exhibiting mesophases (CHLC molecules) was synthesized and spread at the air–water (A/W) interface to investigate the surface behavior. The monolayer exhibited a variety of surface phases such as gas, liquid expanded (LE), low density liquid like (L1) and liquid condensed (L2) phases. Treating the CHLC molecules to be rod-like, the average tilt of the molecules with respect to the surface normal in these phases are found to be different. The tilt angle decreases systematically from LE to L2 phase. The optical anisotropy of the ultrathin Langmuir-Blodgett (LB) films of CHLC molecules in these phases was measured using the surface plasmon resonance (SPR) spectroscopy. The high tilted molecules in the ultrathin LB film displayed a high value of optical anisotropy. The ultrathin film of CHLC molecules at different interfaces was investigated using Brewster angle microscopy, X-ray reflectivity (XRR), SPR spectroscopy and atomic force microscopy. This study is useful for the systems where the physical phenomena are governed by tilt of the molecules.

Small scale model for predicting transportation-induced particle formation in biotherapeutics

Understanding protein adsorption and aggregation at the air-liquid interfaces of protein solutions is an important open challenge in biopharmaceutical, medical, and biotechnological applications, among others. Proteins, being amphiphilic, adsorb at the surface, partially unfold, and form a viscoelastic film through non-covalent interactions. Mechanical agitation of the surface can break this film up, releasing insoluble protein particles into the solution. These aggregates are usually highly undesirable and even toxic in cases, such as for biopharmaceutical application. Therefore, it is imperative to be able to predict the behavior of such solutions undergoing surface agitation during handling, usually transport or mixing. We apply the findings on the viscoelastic protein film, formed at the air-liquid interface, to the prediction of surface mediated aggregation in selected protein solutions of direct biopharmaceutical relevance. Our broad study of Brewster angle microscopy and aggregation monitoring across multiple size ranges by micro-flow imaging, light scattering, and size exclusion chromatography shows that formation of protein particles is driven by the adsorption rate as compared to the rate of surface turnover and that surface film dynamics in the quiescent phase directly affect aggregation. We demonstrate how these learnings can be directly applied to the design of a novel small scale biopharmaceutical stability study, simulating relevant transport conditions. More generally, we show the impact of adsorption dynamics at the air-liquid interface on the stability of a distinct protein solution, as a general contribution to understanding different colloidal and biological interfacial systems.

A method of multi-bit optical coding by constructing Brewster angles to enhance photonic spin Hall effect

The photonic spin Hall effect, characterized by its polarization-driven spin-related displacement, has played an essential role in coding information processing. In this Letter, using a two-period double-layer dielectric plate, the displacement changes within the angle region are first observed, and a two-bit effective coding is achieved through non-uniform quantization of displacement values and coding. Afterward, by constructing Brewster angles (BAs), effective three-bit coding is achieved at the selected BA by dividing the angle domain. By changing the relative refractive index of the constituent materials (nB), effective coding is achieved at corresponding angles (45°–85°). By connecting two-bit and three-bit coding, a five-bit coding is fulfilled. By setting the last six invalid values, effective correspondence of 26 English letters is obtained. At the same time, the largest displacement peak itself is huge and varies accordingly with different values of nB. This work can provide some reference for designing optical coders.

Interfacial insights: [6]-Gingerol monolayers at the air-water interface and beyond

Ginger is a culinary spice with a millennia-old tradition due to its extensive therapeutic applications, recently validated by scientific studies. In particular [6]-Gingerol, a key active molecule in ginger, exhibits extraordinary capabilities in addressing a wide spectrum of health issues. However, its therapeutic potential is limited by its rather low bioavailability. The incorporation of [6]-Gingerol into membrane systems of liposomes, micelles, or exosomes is a promising strategy to overcome this limitation. In this contribution, we report the hitherto unexplored surface properties of [6]-Gingerol at the air-water interface. Our comprehensive study, which includes a detailed analysis of surface pressure and surface potential vs. area per molecule isotherms, surface compression modulus, and Brewster Angle Microscopy, demonstrates the capability of [6]-Gingerol to form Langmuir films. These films can be transferred onto solid substrates, forming remarkably homogeneous Langmuir-Blodgett films which have been characterized by Quartz Crystal Microbalance and Atomic Force Microscopy. This study may be of interest as it paves the way for future research on introducing [6]-Gingerol into membrane systems and transporting it into living cells.

Hevea brasiliensis rubber particles' fluid interfaces reveal size impact on early coagulation steps

Natural rubber originates from the coagulation of rubber particles (RP) from Hevea brasiliensis latex. The size distribution of Hevea RP is bimodal with the presence of small rubber particles (SRP) and large rubber particles (LRP). This study aims at getting a better understanding of the early coagulation steps of Hevea RP taking into account the particle size. SRP and LRP were obtained by centrifugation of freshly tapped ammonia-free latex from RRIM600 clone. Size and zeta potential measurements showed that both RP fractions were efficiently separated and stable in basic buffer. SRP and LRP dispersions were placed in a Langmuir trough and RP were let to adsorb at the air-liquid interface to form interfacial films. Surface tension and ellipsometry indicate that the formation kinetics and the stabilization of the film at the air-liquid interface are faster for SRP than LRP. Moreover, the arrangement of RP at the interface differs between SRP and LRP, as shown by Brewster angle microscopy, atomic force microscopy and confocal laser scanning microscopy. First, the RP membrane and cis-1,4-polyisoprene core spread at the air-liquid interface before clustering. Then, while the SRP fuse, the LRP keep their structure in individual particles in floating aggregate. The role of the non-isoprene molecules on the different organization of SRP and LRP films is discussed, the one of the two major RP proteins, SRPP1 (Small Rubber Particle Protein) and Rubber Elongation Factor (REF1) in the early coagulation steps.

Exploring the influence of acetylenic acetogenin unsaturation patterns on lipid interface interactions: Insights from surface chemistry, rheology, and spectroscopy

This study explores how the unsaturation patterns of three acetogenins from Porcelia macrocarpa (2S,3R,4R)-3-hydroxy-4-methyl-2-(eicos-11′-yn-19′-enyl)-butanolide (1), (2S,3R,4R)-3-hydroxy-4-methyl-2-(eicos-11′-ynyl)-butanolide (2), and (2S,3R,4R)-3-hydroxy-4-methyl-2-eicosyl-butanolide (3)—affect their interactions with lipid interfaces, using Langmuir monolayers of dipalmitoyl-phosphoethanolamine (DPPE) as a model for protozoal membranes. The hypothesis posits that unsaturated acetogenins (1 and 2) will exhibit distinct behaviors compared to the saturated acetogenin (3) due to structural differences. Experiments incorporated each acetogenin into DPPE monolayers, employing techniques like tensiometry, dilatational rheology, infrared spectroscopy, and Brewster angle microscopy (BAM) to assess interactions and changes in film properties. Results showed that unsaturated acetogenin 1, active against Leishmania infantum and Trypanosoma cruzi, destabilized the film and induced rapid molecular reorganization, while acetogenin 2, inactive against these parasites, uniquely increased the viscous contribution to viscoelasticity. Saturated acetogenin 3 did not integrate into the film. All acetogenins enhanced fluidity, reducing elasticity and viscosity, with BAM revealing phase separation only in acetogenin 2. Infrared spectroscopy underscored the impact of drug-lipid interactions, leading to the conclusion that unsaturated acetogenins 1 and 2 have a more significant influence on thermodynamic and structural properties than acetogenin 3, offering insights into their potential therapeutic mechanisms.

The influence of blackcurrant extract–based cosmetic antimicrobial agent on skin cells and skin model membranes

The components of blackcurrant extract are known for their antimicrobial properties and the lipid membrane is the important target in terms of the activity of these compounds. In this work, a commercially available product that is PhytoCide Black Currant Powder (BCE), which can be used as a soothing, conditioning and antimicrobial agent in cosmetics, was investigated. The aim of this study was to explore its effect on skin cells and gain insight into the mechanism of its selectivity. The influence of this formulation on keratinocyte and fibroblast cells in in vitro tests was studied and the effect of BCE on model keratinocyte and fibroblast membranes was investigated. As model systems, the lipid monolayers of different compositions were used. The experiments involved the surface pressure/area measurement, penetration studies and Brewster angle microscopy experiments. The BCE formulation was shown to be non-toxic to the skin cells at the concentrations applied. Model membrane experiments confirmed that BCE components do not incorporate into keratinocyte and fibroblast membranes at membrane-related conditions. However, they alter morphology of the studied systems by acting in the region of polar head. Significant differences were found in the affinity of the BCE formulation for bacteria compared to skin lipids, consistent with the proven antibacterial effect of the preservative while lacking toxicity to skin cells. Thus, the membrane of the cell may be critical to the selectivity of the chemicals being tested.

PH-dependent self-assembly of an acid derivative of cholesterol at interfaces

Understanding and control over the self-assembly of molecules is desirable in many physico-chemical processes. Functional groups responsive to a pH change offer immense scope in driving selective molecular self-assembly. pH-dependent self-assembly of an aromatic acid derivative of cholesterol, 4-(6-(cholest-5-ene-3-yloxy)-5-(oxopentyloxy)) benzoic acid, ChBA, is investigated at the air-aqueous interface and characterized using different interface-sensitive techniques. Evidence for the presence of unstable films of ChBA at the air-water interface or for pH < 10 emerges from the surface pressure – area per molecule isotherm, surface pressure relaxation, and Brewster angle microscopy studies. In contrast, for pH > 10.6, ChBA forms a relatively stable film with a higher magnitude of the collapse pressure (45 mN/m). The compressional moduli and the textures obtained using Brewster angle microscopy reveal the presence of two phases (L1 and L2), which are also highly stable with temperature. The surface topography of ChBA films transferred from the air-water interface reveals the presence of multilayers of different thicknesses, for film transferred at pH 11 reveals primarily a uniform and homogenous monolayer. Based on the dependence of the collapse pressure with pH, the surface pKa of ChBA is estimated to be about 10.6. Our studies show that the undissociated ChBA spontaneously forms multilayers, whereas partially or fully dissociated ChBA forms distinct and ordered monolayer phases, highlighting the role of electrostatic interactions.

Square versus hexagonal lattices effects on the optical and dielectric properties of plasmonic Ag–LiNbO[formula omitted] composite

We investigate the effect on the optical and transport properties of square and hexagonal lattice arrangements of silver nanoparticles (NPs) in uniaxial LiNbO3 as optically active layer within a multilayer configuration. This multilayer is constituted by Indium Tin Oxide (ITO), the polymer PMMA and a substrate of SiO2. The effective dielectric function of the ensemble of Ag NPs and uniaxial LiNbO3 crystal are treated through the Bruggeman approximation. The multilayer absorbance for s- and p-polarization at normal and oblique incidences are determined by means of the Transfer Matrix Method. Changes in the ratio between the diameter of the nanoparticles, D, and the distance between particles or pitch, P, are analyzed. A change in the D/P ratio implies a different filling factor. For small D/P ratio, the calculated absorbance for square- and hexagonal-lattices are equivalent; however, for greater D/P factor, the hexagonal lattice clearly shows higher absorbance values. Moreover, the Brewster angle seems to be sensitive to the Ag NPs size as well as the type of arrangement (square or hexagonal). The ac-electrical conductivity of the effective medium layer of the two arrangements in the perpendicular and parallel directions of the Ag NPs plane were analyzed. Our results demonstrate that the ac-conductivity is higher for hexagonal lattice than for square case, which means a higher density of Ag NPs. In addition, for the perpendicular direction, in the hexagonal-lattice (D/P = 0.5), we have found the negative epsilon (NE) condition, characteristic of metamaterials.

High-power diode laser spectrally narrowed with prism-etalon feedback.

A simple method for reducing the linewidth of a diode laser while maintaining high output power is described. It is based on a dispersive prism and a thin etalon for retroreflective feedback. The etalon creates two weak external cavities that provide spectral selectivity that is periodic with a period equal to the etalon's free spectral range. The method was applied to a multimode blue laser diode, which in the absence of feedback features a linewidth of several nanometers. The spectral properties of the laser were investigated for different etalon thicknesses and operating currents and tested in the presence of temperature fluctuations. With a SF11 equilateral uncoated prism near Brewster's angle and a 0.3 mm-thick uncoated fused silica etalon, the linewidth was reduced 20-fold to 70pm (3.6 cm-1) with an output power of 3W at a current of 2.15A. The largest diode current probed was 2.75A, which resulted in a linewidth of 100pm (5.1 cm-1) and an output power of 4W. In contrast to the use of, for example, a volume Bragg grating, a high degree of flexibility is afforded as the same prism-etalon pair can be used across the visible and near infrared.

Optical directional differential operation enabled visual chirality detection.

Directional differential operation can extract the changes of directional information from complex signals, and plays an important role in target recognition and texture image processing. Here, we propose an optical directional differential operation based on large cross-polarization rotation, and realize the visual detection of chiral enantiomers. By using cross-polarization rotation in a specified direction, we design a corresponding directional spatial spectral transfer function whose transmission efficiency increases as the incident angle approaches the Brewster angle. The differential direction can be adjusted by changing the initial polarization state, and can be used to detect the concentration of chiral solutions. Finally, we apply the directional differential operation to achieve the visual detection of chiral enantiomers.

Oxidation of lipid membrane cholesterol by cholesterol oxidase and its effects on raft model membrane structure

The effects of a peripheral protein – cholesterol oxidase (3β-hydroxysteroid oxidase, ChOx) on the characteristics of model lipid membranes composed of cholesterol, cholesterol:sphingomyelin (1:1), and the raft model composed of DOPC:Chol:SM (1:1:1) were investigated using two membrane model systems: the flat monolayer prepared by the Langmuir technique and the curved model consisting of liposome of the same lipids. The planar monolayers and liposomes were employed to follow membrane cholesterol oxidation to cholestenone catalyzed by ChOx and changes in the lipid membrane structure accompanying this reaction. Changes in the structure of liposomes in the presence of the enzyme were reflected in the changes of hydrodynamic diameter and fluorescence microscopy images, while changes of surface properties of planar membranes were evaluated by grazing incidence X-ray diffraction (GIXD) and Brewster angle microscopy. UV-Vis absorbance measurements confirmed the activity of the enzyme in the tested systems. A better understanding of the interactions between the enzyme and the cell membrane may help in finding alternative ways to decrease excessive cholesterol levels than the common approach of treating hypercholesterolemia with statins, which are not free from undesirable side effects, repeatedly reported in the literature and observed by the patients.

Facile preparation and study of supramolecular architecture of an efficient nanocomposite LB film AHSM/SA based on azo-functionalized hockey stick-shaped mesogen at air-water and air-solid interface

Hockey stick-shaped mesogens are fascinating thermotropic liquid crystal systems owing to their exceptional supramolecular assembly properties and shape anisotropy compared to conventional rod-and bent-shaped mesogens. In this article, we present an investigation of the supramolecular organization of a new azo-functionalized hockey stick-shaped mesogen with stearic acid at the air-water interface and air-solid interfaces by applying the Langmuir-Blodgett film deposition method. The incorporation of stearic acid can change the molecular organization of azo-functionalized hockey stick-shaped mesogen at an aqueous interface through hydrophobic-hydrophobic interactions and form a supramolecular nanostructure at the solid interface. The interfacial nature of the Langmuir monolayer was studied by recording the isotherm (surface pressure area, π–A), which was further analyzed by using Brewster angle microscopy. The significant reduction in molecular area, increased surface pressure, and lower isotherm slope of the AHSM/SA composite mixture indicate the hybrid AHSM/SA monolayer's greater stability compared to pure AHSM. BAM images of the AHSM/SA composite signify nanostructure aggregates formed by the interaction of AHSM and SA molecules at the air-water interface. Field emission scanning electron microscopic analysis of composite films revealed the formation of supramolecular domains. The impact of changing the surface pressure and the number of depositions on the morphology of the composite film surface was monitored using field emission scanning electron microscopy. The supramolecular H-type aggregation of azo-functionalized hockey stick-shaped mesogen and stearic acid molecules in the composite LB film was characterized using UV–visible absorption and steady-state fluorescence spectroscopy. The adsorption of stearic acid onto azo-functionalized hockey stick-shaped mesogen via hydrophobic interactions was confirmed by Fourier transform infrared spectroscopy of the composite Langmuir Blodgett film. Further, Raman spectroscopy of the LB films of the AHSM/SA composites is distinct from the pristine film components due to the merging of signals at similar wave numbers for both SA and AHSM with a lack of typical packing pattern further supported by PXRD studies of the films.

Spatial mode conversion of a reflected polarized beam from an isotropic medium at brewster angle

Abstract In this study, the spatial mode evolution of a chiral polarized beam during reflection on an isotropic medium surface at Brewster angle is both theoretically and experimentally investigated. In this process, the topological charge of the reflection field’s horizontal component increases (decreases) by one, relative to the specific left (right) elliptical polarization incident beam. While incident l i -order vortex beam is in a certain polarization state, the intensity distribution of the reflection field’s horizontal component appears as the interference pattern of the l i ± 1 -order output vortex beams. The conversion occurs between the spin and orbital angular momentum and does not violate the conservation of the total angular momentum. We explain the physical mechanism of this phenomenon using phase shift theorem, and analyze the effect of ellipticity and polarization angle on this physical phenomenon.