Structure Of Droplets Research Articles

Self-assembly and structures of nanoscale double emulsion droplets through coarse-grained molecular dynamics simulations.

Examples of self-assembled multiple emulsion droplets on the nanometre scale are very rare. In this work, we use coarse-grained (CG) molecular dynamics simulations to study the self-assembly of ternary mixtures consisting of water, n-heptane, and nonionic surfactant tetraethylene glycol monododecyl ether (C12E4). The water volume fractions studied are 1%, 3%, and 5%, respectively. Various nanoscale emulsions are obtained in a spontaneous process. When the water/surfactant volume ratio vm/s = 1.0/1.0, the obtained emulsion droplets are identified as oil-in-water-in-oil (O/W/O) double types, consisting of an oil core, an inner surfactant layer, a water layer, and an outer surfactant layer. The water molecules are distributed around the hydrophilic ends of the surfactants, while the hydrophobic ends of the surfactants wrap the oil cores and penetrate into the oil bulk. Hydrogen-bond interactions among water and the hydrophilic ends of the surfactants form cross-links that stabilize the double emulsion droplets. The sizes of all the oil cores inside the droplets are <6 nm in diameter, even with the highest water volume fraction of 5%. Both the concentration of free water molecules on the order of 10-6 mol/cm3 and the favourable energy change during emulsion formation indicate that the emulsion droplets are thermodynamically stable. In contrast, for vm/s = 1.0/5.5, no double emulsion but a simple water-in-oil emulsion was observed, with morphologies evolving from oblate to bicontinuous phases with an increase in the water volume fraction from 1% to 5%. Our coarse-grained molecular dynamics simulations provide valuable insight for the preparation of nanoscale double emulsions and the characterization of their structures.

Shape and interfacial structure of droplets. Exact results and simulations

We consider the fluctuating interface of a droplet pinned on a flat wall. For such a system we compare results obtained within the exact field theory of phase separation in two dimensions and Monte Carlo (MC) simulations for the Ising model. The interface separating coexisting phases splits and hosts drops whose effect is to produce subleading corrections to the order parameter profile and correlation functions. In this paper we establish the first direct measurement of interface structure effects by means of high-performance MC simulations which successfully confirm the field-theoretical results. Simulations are found to corroborate the theoretical predictions for interface structure effects whose analytical expression has recently been obtained. It is thanks to these higher-order corrections that we are able to correctly resettle a longstanding discrepancy between simulations and theory for the order parameter profile. In addition, our results clearly establish the long-ranged decay of interfacial correlations in the direction parallel to the interface and their spatial confinement within the interfacial region also in the presence of a wall from which the interface is entropically repelled.

Spray characterization in a multi-jet airblast injector with swirling air crossflow

Experimental spray characterization in a multi-jet airblast injector with swirling crossflow of air is the goal of the present work. The current injector allows radial injection of six liquid jets from a central hub into swirling and crossflowing air into the annular region around the hub. In the present study, three different aspects related to jet-in-crossflow are concurrently addressed viz. air flow confinement, air swirl and simultaneous atomization of multiple liquid jets. Such key features have been rarely reported in the past in spite of their relevance to practical injectors such as in Lean Premixed Prevaporized (LPP) gas turbine combustors. The spray structure and spatial distribution of droplets are visualized at different cross-sectional planes in the spray by application of the Laser Sheet Imaging (LSI) technique. The Droplet size, three components of droplet velocities and local liquid mass flux are measured at different axial and radial locations using the Phase Doppler Particle Analyzer (PDPA) technique. The injector is operated over a wide range of aerodynamic Weber number (Weg) of the liquid jets (Weg = 57 – 430). The physics behind the spatial evolution of characteristic droplet size is analyzed by estimating the droplet Weber number and the probability of droplet coalescence. The plume-to-plume interaction, subsequent to droplet generation from the primary atomization of adjacent liquid jets, is found to contribute to the variation of droplet size in the current injector. The influence of Weg on the evolution of spray characteristics is investigated in detail.

Oil-in Water Vegetable Emulsions with Oat Bran as Meat Raw Material Replacers: Compositional, Technological and Structural Approach.

The unique composition and technological properties of some oat bran components (mainly protein and soluble fiber) and olive oil make them a good choice to form oil-in-water vegetable emulsions. The different concentrations of oat bran were studied to form olive oil-in water (O/W) emulsions to apply as a replacement for fat and meat. As a result, four O/W emulsions (OBE) were formulated with 10% (OBE10), 15% (OBE15), 20% (OEB20), and 30% (OBE30) oat bran concentrations and 40% olive oil, with the corresponding amount of water added for each O/W emulsion. Composition, technological properties (thermal stability, pH, texture), and lipid structural characteristics were evaluated. The results showed that low oat bran content (OEB10)-with a lower concentration of oat protein and β-glucans-resulted in an O/W emulsion with an aggregated droplet structure and lower thermal stability and hardness. These connections between composition, technology, and structural properties of olive O/W emulsions elaborated with oat bran could help in making the optimal choice for their potential application in the production of foods such as healthier meat products.

Structure and thermodynamics of droplets with end-grafted polymer-chains of Pickering emulsions from Molecular Dynamics Simulations and Scaling-Theory

We consider a Pickering emulsion (oil-in-water or water-in-oil types) formed by a low-density assembly of droplets (dispersed phase) with end-grafted polymer-chains, which are dispersed in another liquid (continuous phase). The role of the added polymer is to stabilize the emulsion due the excluded volume forces between monomers. Initially, the polymer-chains are anchored onto the droplets surfaces via big amphiphile molecules and then float in the continuous phase (good solvent). As demonstrated very recently, the hairy-droplets interact mutually through an effective pair-potential which is the sum of a steric repulsive part coming from the repulsion between monomers and a van der Waals attractive one. Such a potential depends on the interdistance between adjacent hairy-droplets, their size, the bath temperature, the Hamaker’s constant, the number of grafted-polymer-chains per droplet (or equivalently the grafting-density) and their molecular-weight. The goal of this work is an extensive study of the structural and thermodynamical properties of the dispersion, using Molecular Dynamics Simulations (MDS). We note that for our study, the varied pertinent parameter is the grafting-density keeping fixed the other parameters of the problem. First , we investigate the structure of the dispersed hairy-droplets through the computation of the radial distribution function (RDF), using MDS. Second , we introduce a Scaling-Theory to investigate the hairy-droplets aggregation. The latter approach allows the determination of the fractal dimension of the hairy-droplets aggregates. Third , from the computed RDF, we extract all the thermodynamical quantities which are the virial-pressure, the internal-energy and the isothermal-compressibility. We note that our results from MSD agree well with the theoretical predictions we have deduced from Statistical Mechanics Principles. Finally, a possible link of our simulations to experiment is also discussed. • Systematic study of structure of Pickering emulsions from Molecular Dynamics Simulations. • Investigation of thermal properties of Pickering emulsions from Molecular Dynamics Simulations. • Elaboration of a scaling-theory for aggregation study. • Rigorous results from Statistical Mechanics. • Role of the grafting-density of anchored polymer-chains onto interface between dispersed and continuous phases.

Effects of ginger essential oil on physicochemical and structural properties of agar‑sodium alginate bilayer film and its application to beef refrigeration

To maintain the freshness of meat products, an agar‑sodium alginate (AS) bilayer antibacterial film incorporated with ginger essential oil (GEO) was developed. The effect of GEO at different concentrations (1%, 2%, 3% and 4% v/v) on the physical properties, micro-structure and antibacterial activity closely related to AS film's application to beef refrigeration was extensively studied. In addition, the effects of AS bilayer active film on refrigeration quality and shelf life of beef were systematically evaluated. The porous structure and number of oil droplets became more obvious with the increase of GEO amount in AS film. The incorporation and increase of GEO could delay the lipid oxidation and protein decomposition of beef, reduce the total counts of the tested microorganisms (total viable bacteria, psychrotrophic bacteria, Escherichia coli, Staphylococcus aureus, yeast, and mold) in meat samples. Compared with commercial polyethylene (PE) packaging, the accumulation of basic compounds from the degradation of beef protein as well as the microbial contamination was obviously improved, which could extend the comprehensive shelf life of beef by 4–6 days. Consequently, AS bilayer films incorporated with GEO, especially GEO at 4.0% (v/v) GEO concentration can be developed to be an antibacterial active packaging material for beef refrigeration.

Dynamics of annular solvent droplets under capillary thinning of non-entangled polymer solution

Formation and coalescence of solvent droplets on a thread of polymer solution at the final stage of capillary pinching is studied theoretically. It is considered that macromolecules are already almost completely stretched along the extension axis and their contour length exceeds the diameter of the thread. In this regime, the radius of polymer string decreases slowly with time under the action of capillary forces and the solvent squeezes out to the thread surface forming annular droplets of different sizes. The thinning process stops when the capillary pressure is balanced by the osmotic pressure of the polymer. As a result, a quasistationary two-phase structure of polydisperse solvent droplets on a polymer string is formed. We develop a rigorous theory showing that the polymer core is swollen in the droplet regions but still remains much thinner than the solvent phase. We also demonstrate that such a blistering structure is unstable with respect to droplet coalescence and elucidate two mechanisms of this process due to the solvent flow between the droplets and due to diffusion of solvent droplets along the polymer string. Both mechanisms lead to the same long-time power law (t1/7) for the droplet radius. It is shown that a breakage of the polymer string may occur at time scales exceeding the Rouse time of polymer chains.

Volumetric determination of reverse micelle structural properties and the validity of commonplace approximations

Molecular volumes within reverse micelles are important in determining many aggregate properties. Molecular volumes also depend upon differences in molecular environment and thereby might also be capable of detecting changes in molecular structure and interactions within an aggregate. However, approximations are typically used in their place along with approximations of aggregate radius, aggregation number, surfactant tail length, and reverse micelle shape particularly for Aerosol OT systems. Consequently, volumetric measurements have not been thoroughly tested as a measure of aggregate properties. Volumetric methods do not require the commonly used approximations. Therefore, comparison with previous approaches will demonstrate volumetric measurements’ utility in measuring aggregate structural properties and provide a useful assessment of the applicability of these commonplace approximations. Partial molar volumes of water and surfactant, evaporation rate, and reverse micelle radius are measured over the w0 = 0–40 range for water/Aerosol OT/isooctane solutions. These results are used to calculate how aggregation number, surfactant layer thickness, head group area, and water droplet structure change with aggregate radius. Volumetric measurements reveal a surfactant layer structural transition at w0 = 5, an aggregate shape change at w0 = 25, and reproduced the general trends in structural properties. Important variations from approximated methods are noted. Molecular volume and aggregate radius approximations were found valid in many but not all situations. However, approximations of aggregation number and tail length created important miscalculations of some properties when treating reverse micelles as spherical. It was found that consideration of an ellipsoidal reverse micelle shape for w0 < 10 could account for previously identified changes in surfactant layer thickness and head group area that were based on a spherical geometry.

Controllable droplet self-transport on multi-bioinspired slippery liquid-infused microstructure surface

Inspired by Nepenthes pitcher plant, the surface infused by slippery liquid could significantly reduce the adhesive force and facilitate the movement of droplet. Combined with the gradient structure of cactus spine, the slippery liquid-infused microstructure surfaces (SLIMS) could achieve the droplet self-transport without external energy input. However, combined with experimental findings on the SLIMS with uniformly rough structure, the self-transport distance is still limited by the wedge angle and droplet volume. Although the transport distance can be improved by reducing the wedge angle and increasing the droplet volume, we have demonstrated the control of transport distance by processing different structures on the surface. Benefited from the directional wettability of the V-shaped prism microarray (VPM) surface, the self-transport distance could be controlled in the case of fixed liquid volume and wedge angle. A fraction of the lubricating oil would be squeeze away when the droplet with larger density was dropped on the surface, which can form local contact between droplet and VPM structure. This would result in the imbalance Laplace pressure along the movement direction, which can be further manipulated by the VPM structure. The multi-bioinspired surface provides a new insight for precise liquid manipulation, which could promote liquid directional transport developments in theoretical analysis and further practical applications.

Plastoglobule Lipid Droplet Isolation from Plant Leaf Tissue and Cyanobacteria.

Plastoglobule lipid droplets are a dynamic sub-compartment of plant chloroplasts and cyanobacteria. Found ubiquitously among photosynthetic species, they are believed to serve a central role in the adaptation and remodeling of the thylakoid membrane under rapidly changing environmental conditions. The capacity to isolate plastoglobules of high purity has greatly facilitated their study through proteomic, lipidomic, and other methodologies. With plastoglobules of high purity and yield, it is possible to investigate their lipid and protein composition, enzymatic activity, and protein topology, among other possible molecular characteristics. This article presents a rapid and effective protocol for the isolation of plastoglobules from chloroplasts of plant leaf tissue and presents methodological variations for the isolation of plastoglobules and related lipid droplet structures from maize leaves, the desiccated leaf tissue of the resurrection plant, Eragrostis nindensis, and the cyanobacterium, Synechocystis sp. PCC 6803. Isolation relies on the low density of these lipid-rich particles, which facilitates their purification by sucrose density flotation. This methodology will prove valuable in the study of plastoglobules from diverse species.

Plastoglobule Lipid Droplet Isolation from Plant Leaf Tissue and Cyanobacteria

Plastoglobule lipid droplets are a dynamic sub-compartment of plant chloroplasts and cyanobacteria. Found ubiquitously among photosynthetic species, they are believed to serve a central role in the adaptation and remodeling of the thylakoid membrane under rapidly changing environmental conditions. The capacity to isolate plastoglobules of high purity has greatly facilitated their study through proteomic, lipidomic, and other methodologies. With plastoglobules of high purity and yield, it is possible to investigate their lipid and protein composition, enzymatic activity, and protein topology, among other possible molecular characteristics. This article presents a rapid and effective protocol for the isolation of plastoglobules from chloroplasts of plant leaf tissue and presents methodological variations for the isolation of plastoglobules and related lipid droplet structures from maize leaves, the desiccated leaf tissue of the resurrection plant, Eragrostis nindensis, and the cyanobacterium, Synechocystis sp. PCC 6803. Isolation relies on the low density of these lipid-rich particles, which facilitates their purification by sucrose density flotation. This methodology will prove valuable in the study of plastoglobules from diverse species.

PREPARATION AND CHARACTERIZATION OF COMBINED SALICYLIC ACID AND POVIDONE-IODINE CONTAINING NANOEMULGELS: A PRELIMINARY STUDY

Objective: The aim of this preliminary study is to prepare and characterize combined salicylic acid and povidone-iodine-containing nanoemulgels for use in disease models such as wounds and burns in the future. Material and Method: Within the scope of the study, first of all, analytical method validation of salicylic acid was performed. Then, oil solubility studies were carried out and nanoemulsions and nanoemulgels were prepared. Morphology, zetasizer analysis, type and pH determination, FTIR analysis, spreadability, and in vitro release studies were performed to determine the characterization of the formulations. Result and Discussion: Nanoemulsions and nanoemulgels have been prepared successfully. Nanoemulsions with spherical droplet structure and outer phase water were obtained, and their morphology and zeta sizer results were compatible. In the 1-month stability study, only the F1 formulation did not decompose. There was not much change in pH after holding. At the end of the FTIR analysis, it was seen that there was no interaction between the items. In the release study performed with pH 5.5 phosphate buffer, approximately 40% of the release occurred after 8 hours. This study is a preliminary study, and formulations with long-term stability and release rate can be developed by conducting more detailed studies in the future. Salicylic acid and povidone-iodine were used in combination for the first time. This combination can be translated into formulations that may be beneficial for skin diseases in the future.

Cepharanthine action in preventing obesity and hyperlipidemia in rats on a high-fat high sucrose diet

BackgroundIt was demonstrated that cepharanthine (CEP), derived from Stephania cepharantha hayata, is a potent inhibitor of the ABCC10 transmembrane protein. It is approved to be a natural product or remedy. The present study focuses on investigating whether cepharanthine effectively reduces hyperlipidemia and obesity in an experimental hyperlipidemic rat model. MethodFour groups of Wistar rats were assigned randomly to the following groups: a high-fat high sucrose diet (HFHS), normal-fat diet (NFD), HFHS plus cepraranthine (10 mg/kg) (HFHS-C), and a HFHS diet with atorvastatin (HFHS-A). The responses of rats were observed on the basis of serum and hepatic biochemical parameters, food intake, and body weight after CEP treatment, and assessing the histopathological modifications by the optical microscope in the liver and its cells. ResultsSignificant improvement in the serum total cholesterol (TC), serum triglycerides (TG), and serum low-density lipoprotein (LDL) levels were observed following CEP treatment. We have also observed significant improvement in the structure of liver tissue and reduced-fat droplets in the cytoplasm. Moreover, CEP had a significant effect in preventing the gain in body weight of animals, and food intake was not significantly affected. ConclusionOur research results revealed that CEP significantly improved dyslipidemia and prevented the accumulation of fatty deposits in the rats' liver tissue fed an HFHS diet. In addition, CEP exerted an anti-obesity effect.

Microfluidic emulsification techniques for controllable emulsion production and functional microparticle synthesis

Emulsions play important roles in template synthesis of functional microparticles for myriad fields. The size, shape, composition and structure of emulsion droplets generally determine those features of the resultant microparticles and their functions. Precise control over these features of emulsions is vital to template synthesis of controllable application-oriented microparticles with advanced functions. This review summarizes recent progress on microfluidic emulsification techniques for controllable emulsion production and functional microparticle synthesis. First, versatile microfluidic emulsification techniques for controllable generation of emulsions from simple single emulsions to complex multiple emulsions are introduced. The flexible structural changes of emulsions induced by regulating the mesoscale structures of packed surfactant molecules at the interfaces are discussed. Then, rational synthesis of microparticles with controllable sizes, shapes, compositions, structures and functions from emulsion templates are introduced. The rational design of emulsion templates and interplay between the shape, structure and composition of microparticles to achieve desired functions for applications such as controlled release, water remediation, and catalysis are highlighted. Particularly, interplay between the mesoscale structures of functional components in the emulsion templates and the fine structures and advanced functions of certain microparticles, is discussed. Finally, future development of microfluidics in controllable emulsion production and microparticle synthesis is discussed.

Application of Gurma Melon (Citrullus lantus var. colocynthoides) Pulp-Based Gel Fat Replacer in Mayonnaise.

Gurma melon pulp-based gel (GMPG) was examined as a fat replacement in mayonnaise. GMPG was used to partially replace fat in quantities of 25, 50, and 70%, abbreviated as GMPG-25, GMPG-50, and GMPG-70, respectively. Mayonnaise’s physicochemical and sensory properties were studied. The data demonstrated that all low-fat mayonnaises had much lower energy value but significantly higher water content than their full-fat equivalents and that these differences developed as GMPG replacement levels increased. A microstructure analysis revealed compact the packing structures of big droplets in the whole fat sample and a baggy structure network of aggregated tiny droplets in the GMPG-25, GMPG-50, and GMPG-70 samples. There were no significant differences in pH or water activity after one day of storage between the full-fat and low-fat mayonnaises. Mayonnaises with GMPG-50 and GMPG-70 exhibited the same hardness as full-fat, whereas mayonnaises with GMPG-25 were harder than the other samples. Increased mayonnaise whiteness (L* increase and a* and b* reduction) was seen with reductions in fat. All samples had good sensory approval, with the 50% oil mayonnaise appearing to be the most appealing. It has been demonstrated that GMPG is an effective fat replacement agent.

Electric field induced buckling of inversion walls in lens-shape liquid crystal droplets

Lens-shaped liquid crystal samples have the potential for their use in tunable multifocal optical lenses. In previous observations (Phys. Rev. Research, 2, 023261 (2020) and J. Mol. Liq., 334, 116085 (2021)) plano-convex spherical lens-shaped liquid crystal sessile droplets were studied either in magnetic or AC electric fields, and the formation of an inversion wall (a one-dimensional soliton) moving toward the periphery was observed and explained.Here we present experimental observations of the structure of plano-convex lens-shaped nematic liquid crystal droplets subjected to simultaneous competing magnetic and electric fields. It is found that above a threshold electric field the initially straight defect wall buckles to form a zig-zag shape. This phenomenon is compared to those observed in sandwich cells with uniform thickness and the differences in their theoretical description are discussed.

Virus Dynamics and Decay in Evaporating Human Saliva Droplets on Fomites.

The transmission of most respiratory pathogens, including SARS-CoV-2, occurs via virus-containing respiratory droplets, and thus, factors that affect virus viability in droplet residues on surfaces are of critical medical and public health importance. Relative humidity (RH) is known to play a role in virus survival, with a U-shaped relationship between RH and virus viability. The mechanisms affecting virus viability in droplet residues, however, are unclear. This study examines the structure and evaporation dynamics of virus-containing saliva droplets on fomites and their impact on virus viability using four model viruses: vesicular stomatitis virus, herpes simplex virus 1, Newcastle disease virus, and coronavirus HCoV-OC43. The results support the hypothesis that the direct contact of antiviral proteins and virions within the "coffee ring" region of the droplet residue gives rise to the observed U-shaped relationship between virus viability and RH. Viruses survive much better at low and high RH, and their viability is substantially reduced at intermediate RH. A phenomenological theory explaining this phenomenon and a quantitative model analyzing and correlating the experimentally measured virus survivability are developed on the basis of the observations. The mechanisms by which RH affects virus viability are explored. At intermediate RH, antiviral proteins have optimal influence on virions because of their largest contact time and overlap area, which leads to the lowest level of virus activity.

Design and experimental research of a novel droplet flow field in proton exchange membrane fuel cell

The flow field plays a vital role in the performance and cost of the proton exchange membrane fuel cell (PEMFC). However, the traditional flow field structure cannot meet the high-power density requirements of PEMFC commercialization due to poor mass transport capacity. In addition, new flow field designs have some problems, such as complicated structure, high pressure drop and high manufacturing cost, which make them unsuitable for large-scale applications. In this paper, a novel droplet flow field (DFF) structure is proposed to further improve cell performance and reduce manufacturing cost. In particular, in-situ electrochemical measurement and printed circuit board segmented fuel cell technology are used to investigate the performance of cells with different DFFs. Based on the experimental results, the mass transport mechanism of DFF and its influence on the cell performance and current density distribution are deeply analyzed. The results indicate that DFFs have excellent oxygen transport and water management capabilities, thus improving the cell performance, especially at high current density. By optimizing the droplet placement direction in DFF, we found that the structure with the gas flow direction in contact with the droplet tail (DFF(a)) has the highest cell performance. Compared with the conventional parallel flow field, the maximum power density of the DFF(a) can be increased by 23.7%. Also, the introduction of droplet structure improves the current density distribution uniformity. Furthermore, DFFs have a lower pressure drop, which reduces the pump parasitic power and increases the PEMFC system net output power. Considering the cell performance, current density distribution uniformity and pressure drop, we think that the DFFs (especially the optimized DFF(a)) are more suitable for the practical application of PEMFC.

Emulsified Ni paste for damage-free coating on BaTiO3/polymer dielectric composite layer in MLCCs

ABSTRACT The interaction between the dielectric BaTiO3/poly(vinyl butyral) composite layer (BT@PVB sheet) and the metallic Ni/ethyl cellulose composite layer (Ni@EC sheet) in developing MLCC has been considered an inevitable factor. In this paper, we devised Ni/polymer composite solution (Ni@EC paste) with new concept, which does not damage the dielectric composite layer underneath due to its lack of interaction with the BT@PVB sheet, and introduced emulsified-state suspension as a systematic template. Emulsified Ni@EC paste consists largely of hydrophobic phases, water phases, and PVB surfactants. The components that make up the hydrophobic phase were Ni nanoparticles, EC binders, and organic solvents. Within the emulsified paste (Ni@EC/water), the hydrophobic phase formed the structure of droplets surrounded by surrounding water, resulting in only the water phase being exposed to the outside. During the coating process, the water phase in Ni@EC/water emulsion paste came into contact with the as-prepared BT@PVB sheet, and the hydrophobic phase could not affect the sheet due to the blocking effect of the surrounding water phase. Afterwards, organic solvents as well as water were co-evaporated through the drying process, and most of the organic solvents were removed and solidified before molecular diffusion into BT@PVB sheet occurred.

Laser processing of microdroplet structure of liquid crystal in 3D

Processing of mesoscale structures of soft matter and liquid is of great importance in both science and engineering. In this work, we introduce the concept of laser-assisted micromachining to this field and inject a certain number of microdroplets into a preselected location on the surface of a liquid crystal drop through laser irradiation. The impact of laser energy on the triggered injection is discussed. The sequentially injected microdroplets are spontaneously captured by the defect ring in the host drop and transported along this defect track as micro-cargos. By precisely manipulating the laser beam, the tailored injection of droplets is achieved, and the injected droplets self-assemble into one necklace ring within the host drop. The result provides a bottom-up approach for the in-situ and three-dimensional microfabrication of droplet structure of soft matter using a laser beam, which may be applicable in the development of optical and photonic devices.