Polyvinyl Alcohol Coatings Research Articles

Electrophoretically deposited Asphaltum punjabianum (Shilajit) coatings on polyvinylalcohol/carboxymethylcellulose hydrogels

The present study aims to develop Asphaltum punjabianum (namely Shilajit) coated Polyvinyl alcohol (PVA)/Carboxymethyl cellulose (CMC) hydrogels and examine their structural, morphological, degradation, and biological properties. Hydrogels were produced at two different concentrations: 70:30 PVA/CMC and 90:10 PVA/CMC. Following that, Shilajit was applied to the synthesized hydrogels using electrophoretic deposition for a duration of 3 min at 30 V. The scanning electron microscopy images showed that the hydrogel's surface had a regular distribution of irregular Shilajit particles. Fourier transform infrared spectroscopy (FTIR) analysis demonstrated the presence of hydrogen bonding between PVA and CMC hydrogels and Shilajit, indicating the successful deposition of Shilajit on the hydrogel. The hydrogels coated with Shilajit exhibited strong antimicrobial activity, resulting in an inhibition zone measuring 34 mm against Escherichia coli (E. coli) and 41 mm against Staphylococcus aureus (S. aureus). The hydrogels exhibited a cell viability of 80 % with mesenchymal stem cells (MSCs), and the release of collagen II also increased. Furthermore, the PVA/CMC/Shilajit hydrogel exhibited a lower degradation rate compared to the PVA/CMC hydrogel. The results of the swelling, degradation, and drug release studies indicate that the shilajit coating is appropriate for the long-term process of tissue and cartilage regeneration.

Miniature fiber optic SPR high sensitivity humidity sensor based on coated polyvinyl alcohol film

For the measurement of relative humidity, this study employed Surface Plasmon Resonance (SPR) technology, a sensor with a micro-conical fiber structure (sensing length is only 375 μm) was combined with Polyvinyl Alcohol (PVA) to create a humidity sensor that is highly sensitive, compact, dense, and exhibits good linearity. The humidity sensor is based on a gold film (thickness of about 40 nm) on the surface of the miniature fiber optic structure, and by applying PVA coating, the SPR humidity sensor shows resonance peaks in the transmission spectrum in ambient air, and as the number of layers of PVA coating (thickness) is added, the resonance peaks’ positions are red-shifted. The experimental findings demonstrated that this SPR humidity sensor’s sensitivity was 0.162 nm/%RH at an initial resonance wavelength of about 550 nm (one layer) and about 1.542 nm/%RH at an initial resonance wavelength of 656 nm (five layers) in the range of 46 %RH to 93 %RH. The wavelength and the relative humidity had a good linear connection. Temperature tests revealed the sensor has a −0.152 nm/°C temperature sensitivity between 20 °C and 50 °C and has a high linearity (0.999). Therefore, the sensor has potential applications in humidity measurement.

Polydopamine coated polyvinyl alcohol sponges as floatable co-catalysts for boosting the CaO2/Fe3+ system in dye degradation

Polydopamine (PDA) has shown charming co-catalytic activity in the classical Fenton and Fenton-like reactions. However, the improvement is merely attributed to the Fe2+ regeneration ability of PDA. The co-catalytic role and cycling stability of PDA in the CaO2 based Fenton-like reaction have been rarely explored despite CaO2 is considered safer than the liquid H2O2. In this study, floatable co-catalysts were fabricated by coating PDA on polyvinyl alcohol (PVA) sponges. It is proven that in the composite can accelerate not only the Fe3+ reduction but also the reaction between Fe2+ and H2O2 released by CaO2. Therefore, lower concentrations of Fe2+ and H2O2 in the CaO2/Fe3+ Fenton-like system were detected respectively, along with higher efficiency in Rhodamine B (RhB) removal. In addition, in the reusing test, the RhB degradation still maintained at 81.2% after the fifth cycle. The reasons for the decreased activity were carefully investigated. First, the RhB adsorption is largely disturbed by the Ca2+ and Fe3+/Fe2+ ions adsorbed during the reaction. Secondly, both declined Fe2+ regeneration and H2O2 consumption were observed, due to the reduced content of phenolic hydroxyl groups on the PDA surface.

PVA electrospun fibers coated with PPy nanoparticles for wearable strain sensors.

Current conductive polymers win wide applications in smart strain/stress sensors, bioinspired actuators, and wearable electronics. This paper investigates a novel strain sensor by using conductive polypyrrole (PPy) nanoparticles coated polyvinyl alcohol (PVA) fibers as matrix. The flexible, water-resistant PVA fibers are initially prepared by combined electrospinning and annealing techniques, and then are coated with PPy nanoparticles through in situ polymerization. The resultant PPy@PVA fibers exhibit stable, favorable electrical conductivities due to the uniform point-to-point connections among PPy nanoparticles, e.g. after three-time' polymerizations, the PPy@PVA3 fiber film presents a sheet resistance of ∼840 Ω/sq and a bulk conductivity of ∼32.1 mS/cm. Cyclic sensing tests reveal that, PPy@PVA sensors show linear relationships between the relative resistance variations and the applied strains, e.g. the linear deviation of PPy@PVA3 is only 0.9 % within 33 % strain. After long-term stretching/releasing cycles, the PPy@PVA sensor exhibits stable, durable, and reversible sensing behaviors, no evident "drift" is observed over 1,000 cycles (5,000 seconds). This article is protected by copyright. All rights reserved.

Preparation and characterization of CO2/O2 selective facilitated transport films by coating polyvinyl alcohol/polyethylene glycol/aminated sodium lignosulfonate on TiO2/ZnO‐modified LDPE

AbstractA novel facilitated transport film was prepared by coating polyvinyl alcohol (PVA)/polyethylene glycol (PEG)/aminated sodium lignosulfonate on TiO2/ZnO‐modified low‐density polyethylene (LDPE). Monoethanolamine (MEA), diethanolamine (DEA), ethylenediamine (EDA), diethylenetriamine (DETA), tetramethylpiperidine amine (TEMP), and acrylamide (AM) were selected to modify sodium lignosulfonate (Ls) for enhancing the selectivity and permeability of CO2/O2. The fabricated Ls were characterized by fourier transform infrared (FTIR), thermogravimetric test (TG), and scanning electron microscopy (SEM). The CO2 permeability and CO2/O2 selectivity were improved with the increase in the amount of amine groups. Compared with the addition of Ls modified by alcohol amine, the composite film has higher selectivity to CO2 after the addition of DETA‐Ls or TEMP‐Ls. The selectivity of the 1:3:3EDA/MEA‐Ls‐g‐AM composite film reached 13.7, and CO2 permeability increased by 5.54 times. The storage test also demonstrated that the composite films have better freshness retention ability. As a result, modified LDPE coated by PVA/PEG/aminated Ls has the potential as an active modified atmosphere packaging material.

EHDA engineering of Piroxicam-PVP components for pharmaceutical dosages

This study aimed to prepare piroxicam loaded polyvinyl pyrollidone (PVP) particulate mat, fabricated mat incorporated tablets and coated polyvinyl alcohol (PVA) films. The mat, engineered by using electrohydrodynamic atomisation (EHDA) technique, was evaluated for morphological features and particle size using scanning electron microscopy. In vitro drug release, ex vivo skin permeation and in vivo anti-inflammatory studies of oral (i.e., tablets) and topical (i.e., films) dosage forms were conducted to assess the efficiency of prepared formulations. The EHDA processed piroxicam-PVP components exhibited spherical shape, uniform surface and particle size of 3.67 ± 0.70 μm. The piroxicam mat incorporated oral and coated topical formulations exhibited release percentage of 73.79 ± 1.9% and 80.11 ± 2.3% respectively over a time period of 180 min. During ex vivo permeation study, treatment of rat skin using 500 μm microneedles led to a higher permeation of piroxicam (from coated films i.e., 75.54 ± 2.2% as compared to unpierced skin i.e., 58.23 ± 2.7% with a gradient of 0.28 and 0.21 respectively within 240 min. During in vivo anti-inflammatory study, a 52.58 ± 3.2% decrease in paw inflammation was observed in mat incorporated tablets administered group within 360 min. In comparison, topical application of coated films led to a 67.28 ± 2.9% decrease in inflammation. Microneedle treatment followed by topical application of coated films resulted in an 81.43 ± 3.1% reduction in paw inflammation over 360 min. Micropiercing of the skin resulted in breaching of uppermost skin barrier layer stratum corneum leading to an increased piroxicam permeation and rapid therapeutic response. It was concluded that EHDA processed mat incorporated tablets and coated topical films can serve as a promising choice for improving the solubility of poorly soluble piroxicam and oral/topical anti-inflammatory therapy.

Anti-Salmonella polyvinyl alcohol coating containing a virulent phage PBSE191 and its application on chicken eggshell

The use of antibiotics in the food industry is avoided due to the increase of antibiotic-resistant bacteria. Therefore, the bacteriophage is emerging as an alternative agent. Here, we characterized the Salmonella Enteritidis phage PBSE191 and applied it to a polyvinyl alcohol (PVA) film. Transmission electron microscopic analysis revealed that it belonged to the Caudoviricetes class, with an icosahedral head and flexible tails. The phage showed rapid and strong lytic activity within 1 h. It was active against a broad range of Salmonella isolates, including six serotypes. In 25 min, 99 % of the initial population was adsorbed to the bacterial cell surface. The phage was also applied to 10 % (w/v) PVA films and coatings, which were then characterized in terms of phage stability and antibacterial performance, both in vitro and in foods. The phage remained stable in the 10 % (w/v) PVA solution containing 20 % (w/w, based on PVA weight) sorbitol (PVAS20), indicating that the phage was stable under dry conditions and strongly released in the polymer. Furthermore, significant bacterial cell reduction (2.0 × 105 CFU/film within 2 h) was observed in the phage-containing PVAS20 films. In addition, the PBSE191-containing PVAS20 coating on the chicken eggshell surface showed significant anti-Salmonella efficiency (about 2 log CFU reduction) within 24 h. Overall, the PBSE191 phage possesses a high potential as a biocontrol agent for use as an additive, or as an active antibacterial packaging to improve food safety against Salmonella contamination.

UV Blocking and Oxygen Barrier Coatings Based on Polyvinyl Alcohol and Zinc Oxide Nanoparticles for Packaging Applications

Photodegradation and oxidation are major causes of the deterioration of food, resulting in darkening, off-flavors, and nutrient deficiency. To reduce this problem, novel functional polymeric materials are being developed to retain food’s light sensitivity. Nanofillers are also used in a polymeric film to produce effective UV blockings and oxygen barrier coatings so that the degradation of the food can be delayed, thereby increasing the shelf life. For this purpose, polyvinyl alcohol coatings were prepared by the incorporation of ZnO nanoparticles. Polyvinyl alcohol is a naturally excellent barrier against oxygen, and the addition of ZnO particles at the nanoscale size has demonstrated effective UV blocking capabilities. In this work, the hydrothermal technique is used to produce ZnO nanoparticles, and these produced particles are then incorporated into the polyvinyl alcohol to produce thin films. These films are characterized in terms of the compositional, macroscopic, microscopic, and optical properties via X-ray diffraction (XRD), FTIR, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), as well as UV–VIS spectroscopy. ZnO nanoparticles at different concentrations were incorporated into the PVA solution, and the films were processed via the blade coating method. With the addition of ZnO, the oxygen transmission rate (OTR) of pure PVA was not altered and remained stable, and the lowest OTR was recorded as 0.65 cm3/m2·day·bar. Furthermore, the addition of ZnO increased the water contact angle (WCA) of PVA, and the highest WCA was recorded to be around more than 70°. Due to this, water permeability decreased. Additionally, PVA/ZnO films were highly flexible and bendable and maintained the OTR even after going through bending cycles of 20K. Furthermore, the addition of ZnO showed a significant UV blocking effect and blocked the rays below a wavelength of 380 nm. Finally, the optimized films were used for packaging applications, and it was observed that the packaged apple remained fresh and unoxidized for a longer period as compared with the piece of apple without packaging. Thus, based on these results, the PVA/ZnO films are ideally suited for packaging purposes and can effectively enhance the shelf life of food.

Functionalized graphene oxide dispersed polyvinyl alcohol-epoxidized linseed oil composite: An eco-friendly and promising anticorrosion coating material

Polyvinyl alcohol (PVA) is an extensively used biodegradable polymer including corrosion inhibition, but it fails to withstand long time protection due to water solubility. The present work emphasized an efficient way to transform PVA to hydrophobic nature and further modification for corrosion protection of mild steel (MS). In this backdrop, PVA was blended with varying amounts of the synthesized amine-functionalized graphene oxide (AGO) and then assimilated with the epoxidized linseed oil (ELO). The fabricated composite material was coated on MS surface by the doctor's blade technique, and their adhesion character, roughness, wettability, and sustainability in saline media were confirmed by atomic force microscopy (AFM), contact angle, and electrochemical techniques. The chemical bonding as well as structural interactions of the prepared AGO were ascertained by Fourier-transform infrared (FT-IR), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) methods. Electrochemical impedance spectroscopy (EIS) measurements of the PVA coatings showed improved Nyquist semicircle diameter by increasing the AGO content, and the potentiometric polarization (PP) data supports the EIS results. The different weight percentages of AGO dispersed PVA/ELO composite coatings revealed enormous changes in their Nyquist, Bode, and phase angle plots. The highest impedance and charge transfer resistance of PVA/ELO-AGO (0.25 wt%) coating are found to be 108.6 Ω cm2 and 4.541 × 108 Ω cm2, respectively. Further, the composite coating was sustained for 20 days in 3.5 wt% NaCl solution showing its enhanced barrier property. This can be ascribed due to the strong cross-linkages in PVA/ELO-AGO that makes it a durable and promising anti-corrosion coating material.

SYNTHESIS AND CHARACTERIZATION OF MAGNETIC NANOPARTICLES EMBEDDED ON IONIC POLYMER BY CHEMICAL REDUCTION METHOD

Magnetite nanoparticles (Fe3O4 NPs) are prepared using chemical reduction method. This is a simple, economical, nontoxic, facile, clean, and environment friendly process. Preparation of composite polymeric membrane of polyvinyl alcohol (PVA)/Fe3O4 has been performed using dry phase inversion technique for different medical/filtration applications. PVA coatings using magnetite NPs are focused to passivate the surface and decrease agglomeration and also reduce module biomedical absorption and most of the times increase dispersion stability. Therefore, research on PVA coatings on magnetite NPs are in trend now a days, as they are of high charge density that makes them stable in dispersion by electrostatic repulsion. The prepared samples (Fe3O4 NPs) and PVA/Fe3O4 composite membrane have been analyzed for their different properties by using X-ray direction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis) and thermogravimetric Analysis (TGA).

Design of water-based polyvinyl alcohol coatings using a drying modifier to minimize the residual solvent and coating defects

Design of water-based polyvinyl alcohol coatings using a drying modifier to minimize the residual solvent and coating defects

Polyvinyl Alcohol Coating Induced Preferred Crystallographic Orientation in Aqueous Zinc Battery Anodes

Polyvinyl Alcohol Coating Induced Preferred Crystallographic Orientation in Aqueous Zinc Battery Anodes

Poly-o-toluidine coated polyvinyl alcohol film: Reaction driven sensing capabilities

Conducting polymers have the ability to self-sense the surrounding working ambient through their unique electrochemical reactions based on the ionic and aqueous exchanges with the electrolyte. The reaction-driven sensing characteristics of poly-o-toluidine/polyvinyl alcohol hybrid film fabricated through in situ chemical polymerization of o-toluidine on polyvinyl alcohol film are presented. The resulted hybrid film comprised of mixed coral and agglomerated granular morphology of poly-o-toluidine grown on the surface of the film with sufficient porosity and surface area. Cyclic voltammograms revealed two pairs of redox peaks and verified that the electroactivity of the hybrid film is imparted by poly-o-toluidine. The coulovoltammetric response of the hybrid film is closed in an acidic aqueous solution, suggesting that only reversible POT redox reactions take place in the studied potential interval. The sensing abilities of the hybrid film with regard to applied current and electrolyte concentration monitored by square current waves (under galvanostatic conditions) at a constant charge (to achieve the same reaction extension) shows that the consumed electrical energy has a linear relation with the applied current (working electrical condition) and a semi-logarithmic relation with the concentration of electrolyte (working chemical condition). Thus any reactive device based on the redox reactions of POT/PVA hybrid film can respond to, adapt to and sense the surrounding working conditions.

Highly Reversible Zn Plating/Stripping Enabled by Polyvinyl Alcohol Coating Layers for Stable Aqueous Rechargeable Zinc Batteries

Given their intrinsic safety, low cost, and high energy density, aqueous zinc (Zn) batteries hold substantial promise in large-scale energy storage applications. However, Zn dendrite formation and serious side reactions in metallic Zn anodes significantly compromise the reversibility of electrochemical Zn plating/stripping, restricting their lifespan and practical applications. Herein, we demonstrate that the polyvinyl alcohol (PVA) coated Zn anode can alleviate those issues. The PVA molecules at the Zn anode/electrolyte interface enable homogeneous Zn plating/stripping behavior by regulating the nucleation and ion diffusion barriers and effectively suppress the corrosion and hydrogen evolution reaction in mildly acidic electrolytes. As a result, a highly reversible and dendrite-free Zn anode can be obtained. The content of PVA plays a critical role in governing the cycling lifetime and stability. With the optimized content of PVA, stable Zn plating/stripping with a cycling capacity of 1 mAh cm-2 over 1500 hours has been achieved at 1 mA cm-2. In contrast, the bare Zn anode showed an unstable plating/stripping behavior with obvious polarization and limited cycling lifetime. Even at a high current density of 5 mA cm-2, the PVA-coated Zn anode remained stable for 1000 cycles. The present work provides a promising strategy to stabilize Zn anodes towards long-lifespan, cost-effective, and scalable aqueous rechargeable zinc-based batteries.

Comparative study on use of pervaporation membrane reactor for lauric acid – Methanol esterification

In this study, an esterification reaction between lauric acid and methanol was performed in an inert and catalytic pervaporation membrane reactor (PVMR) and the conversion results were compared. Reactions were also performed in a batch reactor, demonstrating the advantage of membrane reactors over conventional reactors. Phosphotungstic acid (PTA), a strongly heteropolyacid, was used as a catalyst. An inert and PTA coated polyvinyl alcohol membranes were synthesized for use in the inert and catalytic membrane reactor, respectively. Effects of catalyst concentration (from 1 wt% to 2 wt%), methanol/lauric acid molar ratio (from 2 to 6), and temperature (from 50 °C to 65 °C) on lauric acid conversion and membrane separation performance were studied. Throughout the study, the effect of membrane separation performance on acid conversion was clearly demonstrated. Under all operating conditions, the acid conversion results obtained in inert and catalytic PVMR were higher than in batch reactors. When the methanol/lauric acid molar ratio was 6, the temperature was 65 °C, and the catalyst ratio was 2 wt%, a conversion of 80.7% was obtained in the batch reactor, while 98.9% and 97.5% of conversions were obtained in the inert and catalytic membrane reactor, respectively. Based on these results, it has been relatively demonstrated that inert and catalytic PVMR systems are efficient in producing fatty acid methyl ester.

A transparent hydrophilic anti-biofouling coating for intraocular lens materials prepared by "bridging" of the intermediate adhesive layer.

The attachment of bio-foulants, including unwanted cells, proteins, and bacteria, to a medical device such as an intraocular lens can lead to implantation failure. Hydrophilic polymers are often used as surface modifiers in the fabrication of anti-biofouling coatings, but a hydrophilic coating can easily become swollen and peel off the substrate. In this study, we chose polymethyl methacrylate (PMMA) as the representative material of intraocular lenses because PMMA has better biocompatibility, a higher refractive index, better optical clarity, lighter weight, more stable performance, and lower cost than other intraocular lens materials. We fabricated polyvinyl alcohol (PVA) coatings with or without a "bridge", that is, an intermediate adhesive layer (AL), to increase the adhesion bonding effect between the anti-biofouling coating and the substrate. The results indicated that the prepared coatings were transparent and noncytotoxic. Moreover, the anti-adhesion properties of the cells and the resistance properties to nonspecific protein adsorption of PMMA modified by both AL and PVA coatings were better and more durable compared with the sample only modified with a physically dipped PVA coating. The coating prepared by AL "bridging" provides a new strategy for the preparation of a transparent hydrophilic anti-biofouling coating suitable for PMMA intraocular lens materials.

Anti-Platelet Effect Induced by Iron Oxide Nanoparticles: Correlation with Conformational Change in Fibrinogen.

Iron oxide nanoparticles are developed for various biomedical applications, however, there is limited understanding regarding their effects and toxicity on blood components. The particles traveling in circulation inevitably interact with blood cells and plasma proteins and may interfere with hemostasis. Specifically, this study focuses on the influence of superparamagnetic iron oxide nanoparticles (SPIONs) coated with a biocompatible polymer, polyvinyl alcohol (PVA), on platelet function. Here, engineered SPIONs that are functionalized with various PVA coatings to provide these particles with different surface charges and polymer packing are described. These formulations are assessed for any interference with human platelet functions and coagulation, ex vivo. Positively charged SPIONs induce a significant change in platelet GPIIb-IIIa conformation, indicative of platelet activation at the dose of 500µg mL-1 . Remarkably, engineered PVA(polyvinyl alcohol)-SPIONs all display a robust dose-dependent anti-platelet effect on platelet aggregation, regardless of the PVA charge and molecular weight. After assessing hypotheses involving SPION-induced steric hindrance in platelet-platelet bridging, as well as protein corona involvement in the antiplatelet effect, the study concludes that the presence of PVA-SPIONs induces fibrinogen conformational change, which correlates with the observed dose-dependent anti-platelet effect.

Highly Sensitive Humidity Sensor With Low-Temperature Cross-Sensitivity Based on a Polyvinyl Alcohol Coating Tapered Fiber

A highly sensitive humidity sensor with low-temperature sensitivity is proposed and demonstrated using a polyvinyl alcohol (PVA) coating tapered fiber. The taper fiber is highly sensitive to the environmental medium due to its microscale diameter. Thus, a humidity sensor can be prepared by plating a PVA moisture-sensitive film in a tapered region. The experimental results show that the sensor has a high humidity sensitivity of 0.1194 nm/%RH but with a relatively low-temperature sensitivity of 0.029 nm/°C. Thus, the sensor can eliminate temperature interference and achieve accurate measurement of environmental humidity. At the same time, the sensor has excellent reversibility, stability, and advantages common to optical fiber sensors, such as small size, antielectromagnetic interference, and remote measurement.

Antifungal Polyvinyl Alcohol Coatings Incorporating Carvacrol for the Postharvest Preservation of Golden Delicious Apple

Different polyvinyl alcohol (PVA) coating formulations incorporating starch (S) and carvacrol (C) as the active agent were applied to Golden Delicious apples to evaluate their effectiveness at controlling weight loss, respiration rate, fruit firmness, and fungal decay against B. cinerea and P. expansum throughout storage time. Moreover, the impact of these coatings on the sensory attributes of the fruit was also analyzed. The application of the coatings did not notably affect the weight loss, firmness changes, or respiration pathway of apples, probably due to the low solid surface density of the coatings. Nevertheless, they exhibited a highly efficient disease control against both black and green mold growths, as a function of the carvacrol content and distribution in the films. The sensory analysis revealed the great persistence of the carvacrol aroma and flavor in the coated samples, which negatively impact the acceptability of the coated products.

Film thickness limits of a buckling-based method to determine mechanical properties of polymer coatings

Characterizing the mechanical properties of polymer coatings typically requires access to specialty equipment, the analysis through which can be tedious despite instrumental precision. An alternative method reported in the literature,strain-induced elastic buckling instability for mechanical measurements (SIEBIMM), is a high throughput, facile yet accurate method, used to characterize the Young’s modulus of supported films and coatings. SIEBIMM can easily be implemented in both academic and industrial settings.Hypothesis: We hypothesize that the SIEBIMM method has an upper coating thickness limit beyond which the assumptions and practicality of the method are no longer valid.Experiments: The Young’s moduli of model polyvinyl alcohol coatings (on polydimethylsiloxanesubstrates) with thicknesses ranging from 67 nm to 40 µm were determined using the SIEBIMM method and the data were subjected to a rigorous statistical analysis.Findings: SIEBIMM could accurately characterize coatings up to 35 µm thick. The Young’s modulus of all coatings ≤ 35 µm was 1.6 ± 0.1 GPa at 50% RH, which agreed with free-standing polyvinyl alcohol films measured by traditional tensile testing. For the method to be used on thicker coatings, it is essential to consistently measure coating thickness and buckling wavelength at the same location to minimize potential error.