Enhanced Water Resistance Research Articles

High-strength and multi-functional gypsum with unidirectionally porous architecture mimicking wood

Porous gypsum materials are of notable significance and demonstrate a broad application in construction and biomedical engineering; nevertheless, it is challenging to simultaneously enhance their mechanical and functional properties. Here by replicating the designs of natural wood, new gypsum materials containing unidirectional micro-pores were fabricated by employing a modified ice-templating technique. The retention of ice-templated architectures was realized based on the hydration-induced self-hardening characteristic of gypsum without using the traditionally long-time freeze drying treatment. The porosities of the wood-like gypsum can be readily adjusted in wide ranges from lower than 60 vol.% to over 80 vol.% by controlling the solid loads in initial slurries. The wood-like gypsum exhibits a notable improvement in compressive strength and energy absorption efficiency along the lamellar direction by more than twofold compared to the unfrozen gypsum materials containing random pores of similar porosity. Additionally, it displays the lowest level of thermal conductivity among gypsum materials along the normal direction of lamellae, which ranges from above 0.21 to ~0.1 W (m K)−1 depending on porosity, thereby demonstrating an outstanding effectiveness for thermal insulation. It can also be easily modified from hydrophilic to hydrophobic towards enhanced water resistance. The high strength and multi-functionalities along with the feasible fabrication approach make the wood-like gypsum appealing for applications, e.g., as construction and biomedical materials. The unidirectionally open pores may also provide new possibilities for regulating the cell behavior in gypsum-based bone implants.

Non-fluorine surface modification of acetylated birch for improved water repellence

Abstract In this work, a non-fluorinated surface treatment, i.e., hydrophobized silicone nanofilaments, was applied on both birch and acetylated birch wood samples via a gas-phase based reaction. A superhydrophobic behavior was observed on both the surface-modified samples as revealed by the static water contact angles (CAs) greater than 160°, also valid for samples prepared with the shortest reaction time of 1 h. The dynamic wettability behavior of the samples was studied by a multicycle Wilhelmy plate method. The surface-modified acetylated birch exhibited a pronounced enhanced water resistance, resulting in very low water uptake of 3 ± 1 wt% after 100 cycles, which was not only about 29 and 5 times lower than that of the non-surface-modified birch and acetylated birch, respectively, but also three times lower than that of the surface-modified birch. Moreover, the aesthetic appearance of the acetylated wood was maintained as the surface modification only resulted in a small color change. This work shows the potential of preparing super water-repellent wood by non-fluorinated surface modification.

Core-shell ammonium polyphosphate@nanoscopic aluminum hydroxide microcapsules: Preparation, characterization, and its flame retardancy performance on wood pulp paper

In the present paper, an environmental fire retardant with core-shell structure ammonium polyphosphate (APP) @ Aluminum hydroxide (ATH) (microencapsulated APP with nanoscale ATH via coprecipitation) was obtained and employed to flame-retard wood pulp paper (WPP). The factors that influence the synthesis of the microcapsule were discussed, and the products with the average diameter of less than 100 nm of the ATH particles formed on APP was obtained at a mutual compound of Al2(SO4)3•18H2O and Al(NO3)3•9H2O with Al molar ratio of 1:9. The optimum reaction conditions including APP kind and amount were studied and 15%APPII@nano-ATH exhibited optimized surface morphology, evenly dispersed state, enhanced water resistance and strong interaction with vapor water. Fundamentally, it imparted WPP excellent flame resistance: for 15 mm * 150 mm WPP, the smoldering rate value of WPP was 100.08 s/150 mm at 1 mg additive amount of the flame retardant, indicating an improvement of 17.7% compared to 85.04 s/150 mm of pure paper; the limiting oxygen index (LOI) of WPP increased from 19.0 to 27.6% at a relatively low 15%APPII@ATH addition of 6 mg. This high-efficient flame retardant performance could be explained by the direct contact and sufficient interaction between APP and ATH which gives full play to their synergy and accelerated the formation of cross-linked P-O-C/Al-O-Al/Al-O-C/Al-O-P/P-O-P structures, leading to a strong and compact char layer with a result of dramatic reduction in heat release rate and smoke production. The specific decomposition and interaction mechanism was conducted associated with the analysis results of thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) etc.

Enhanced Water Resistance of Recycled Newspaper/High Density Polyethylene Composite Laminates via Hydrophobic Modification of Newspaper Laminas.

A high strength recycled newspaper (NP)/high density polyethylene (HDPE) laminated composite was developed using NP laminas as reinforcement and HDPE film as matrix. Herein, NP fiber was modified with stearic acid (SA) to enhance the water resistance of the NP laminas and NP/HDPE composite. The effects of heat treatment and SA concentration on the water resistance and tensile property of NP and composite samples were investigated. The chemical structure of the NP was characterized with X-ray diffractometer, X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectra techniques. The surface and microstructure of the NP sheets were observed by scanning electron microscopy. An expected high-water resistance of NP sheets was achieved due to a chemical bonding that low surface energy SA were grafted onto the modified NP fibers. Results showed that the hydrophobicity of NP increased with increasing the stearic acid concentration. The water resistance of the composite laminates was depended on the hydrophobicity of the NP sheets. The lowest value of 2 h water absorption rate (3.3% ± 0.3%) and thickness swelling rate (2.2% ± 0.4%) of composite were obtained when the SA concentration was 0.15 M. In addition, the introduction of SA can not only enhance the water resistance of the composite laminates, but also reduce the loss of tensile strength in wet conditions, which shows potential in outdoor applications.

Construction of Superhydrophobic Ru/TiCeOx Catalysts for the Enhanced Water Resistance of o-Dichlorobenzene Catalytic Combustion.

In this paper, a simple method to enhance the H2O resistance of Ru/TiCeOx catalysts for o-DCB catalytic combustion by constructing superhydrophobic coating of phenyltriethoxysilane (PhTES) was proposed. The effect of PhTES content on the pore structure, specific surface area, H2O resistance, contact angle (CA) value, and catalytic activity of the catalyst was studied. When water was added, the pristine Ru/TiCeOx catalytic activity decreased by about 26%, while the Ru/TiCeOx-16Ph activity hardly decreased. According to the analysis results of XRD, FT-IR, SEM, and CA, PhTES was closely coated on the surface of Ru/TiCeOx to produce a more hydrophobic surface. The Ru/TiCeOx-16Ph catalyst had strong hydrophobicity, and the contact angle was 159.8°, which not only significantly enhanced the water resistance and self-cleaning activity but also showed a good elimination temperature (T90 = 341 °C) for the o-DCB. The enhanced water resistance of Ru/TiCeOx-XPh catalysts resulted from the reduction of the active centers consumed (water occupying oxygen vacancy sites). The reaction mechanism of the Ru/TiCeOx-16Ph catalyst based on surface oxygen species and the Deacon reaction was proposed. This method provided new idea for the design of a new water-resistant composite catalyst and promoted the practical application of the composite catalyst in the catalytic oxidation of o-DCB.

Surface Functionalized Ammonium Nitrate Prills with Enhanced Water Resistance Property: Characterizations and its Application as Commercial Explosives

AbstractIncreasing the hydrophobicity of ammonium nitrate is of great significance for its application as commercial explosives. In this article, a surface functionalized ammonium nitrate with enhanced water‐resistance property was demonstrated using a new hydrophobic coating agent. Structural properties and thermal stability of the prepared samples were investigated by powder X‐ray diffraction, scanning electron microscopy and differential scanning calorimetric analysis. Fourier‐transform infrared spectroscopic results show that a uniform hydrophobic layer is successfully coated on the surface of ammonium nitrate prills. Surface coated ammonium nitrate shows excellent stability in aqueous environment with effective detonation property compared to commonly used ammonium nitrate fuel oil (ANFO) explosives. Thus, our surface modified ammonium nitrate could serve as a potential explosive for watery hole blasting operations.

Bioinspired structure-robust cellulose nanocrystal films with enhanced water resistance, photothermal conversion ability, and fluorescence

Assembling 1D cellulose nanocrystal into robust functional 3D macro-materials can be conducive to the broad application of nanocomposites, but it remains a huge challenge. Inspired by mussel-like adhesion and nacre structures, functionalized sodium alginate was in-situ synthesized with dopamine as a reinforcement agent and an interface jointer for the cellulose nanocrystal (CNC) nanocomposites with excellent mechanical properties. A rhodamine derivative was developed as a structural modifier to extend bulk strength as well as generate outstanding fluorescence. Through facile vacuum-assisted assembly, the resulting nanocomposites showed 210% and 220% increase in strength and Young’s modulus respectively, without losing ductility. Such experiment results were much higher than those of the reported. The thermal stability and water resistance were also improved remarkably, with favorable fluorescent and photothermal conversion functionalities. This study explored a promising approach to prepare biomimetic CNC nanocomposites with favorable properties and extra functionality, showing great potentials for various applications in fluorescent probe field.

Enhancing properties and water resistance of PEO-based electrospun nanofibrous membranes by photo-crosslinking

In this study, modified fibrous mats of poly(ethylene oxide) (PEO) were fabricated through the versatile technique of electrospinning. Acrylic monomers were added to PEO with different composition ratios, and the mats were irradiated. The kinetics of photo-cross-linking reaction in the presence of the acrylic cross-linkers, as well as the structural, thermal and mechanical properties of the nanofibers, were studied. The morphology of the fibrous membranes before and after water treatment was monitored, and the insoluble fraction of the fibers was measured. As a result, by tuning the photo-cross-linking reaction, the control over fibers properties was feasible. The photo-cured PEO-based nanofibrous mats showed the solubility resistance needed to use them as membranes and to apply them in aqueous environments, as in water treatment processes and biomedical applications.Graphical

Preparation and characterization of modified castor oil via photo‐click chemistry forUV‐curable waterborne polyurethane with enhanced water resistance and low conductive percolation threshold

AbstractA castor oil (CO) was modified via thiol‐ene click chemistry reaction between CO and 3‐mercaptopropyl trimethoxysilane, with the conversion of CC bonds of CO over 99% based on1HNMR spectra. The obtained modified castor oil (MCO) was used as a biobased polyol to prepare waterborne polyurethane (WPU) dispersions. The modification of CO exhibited a great effect on the properties of WPU dispersions and coatings, and an obvious change is the improvement of the water resistance of WPU coatings. WPU dispersions with MCO had good storage stability. A WPU coating with 7% MCO had high surface hydrophobicity, and its water absorption was as low as 3.2%. Conductive carbon black filled WPU coatings with MCO were cured by efficient UV radiation, and their conductive percolation threshold could decrease to 0.76%, which could be attributed to the well filler dispersion and strong filler‐polymer interaction. The WPU dispersions are ecofriendly, and can be used to produce biobased WPU coatings with a great application potential in antistatic coating fields.

Marine sponge spicules-inspired magnesium oxychloride cement with both enhanced water resistance and compressive strength via incorporating acid-activated palygorskite

The high energy consumption, large CO2 emission and mass pollutant release during the preparation process of Ordinary Portland cement (OPC) promote the development of sustainable magnesium oxychloride cement (MOC), which can increase the potash industrial waste utilization and alleviate ecological problems. However, MOC is limited by the poor water resistance, and integrating high water resistance with compressive strength for the MOC still remains a challenge. Herein, inspired by marine sponge spicules, acid-activated palygorskite (APal) was introduced into MOC to construct the inorganic fiber reinforced structure, thus both the water resistance (enhanced from 0.37 to 0.71 in water resistance coefficient) and compressive strength (37.1% increase) were improved. This improvement can be due to the physical filling, surface complexation, electrostatic adsorption interaction and fiber reinforcement of APal, as well as the transformation to gel-like phase 5. Especially, this strategy offers a new and effective approach to enhance the water resistance of MOC that although phase 5 content exhibit a reduction trend in soaked MOC-APal, the composite still present enhanced water resistance. This may be attributed to the sponge spicules-inspired fibrous structure serving as an effective supporting skeleton to provide a certain mechanical strength for soaked MOC-APal.

Nanofluid to Nanocomposite Film: Chitosan and Cellulose-Based Edible Packaging.

Chitosan (CH)-based materials are compatible to form biocomposite film for food packaging applications. In order to enhance water resistance and mechanical properties, cellulose can be introduced to the chitosan-based film. In this work, we evaluate the morphology and water resistance of films prepared from chitosan and cellulose in their nanoscale form and study the phenomena underlying the film formation. Nanofluid properties are shown to be dependent on the particle form and drive the morphology of the prepared film. Film thickness and water resistance (in vapor or liquid phase) are clearly enhanced by the adjunction of nanocrystalline cellulose.

Development of Disulfide Bond Crosslinked Gelatin/ε-Polylysine Active Edible Film with Antibacterial and Antioxidant Activities

It is of great significance to use safe raw materials, and spontaneously form covalent crosslinking during the fabrication process to obtain active edible films with excellent performance. Herein, l-cysteine as the source of thiol group was firstly conjugated onto gelatin backbone via 1-ethyl-3-(30-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) chemistry. Afterwards, the thiol groups in gelatin-l-cysteine (G-Cys) conjugates were oxidized in air to form disulfide bonds, meanwhile the antibacterial polypeptide e-polylysine (e-PL) was incorporated into gelatin matrix to fabricate gelatin/e-polylysine active edible films. The results show that the amount of conjugated l-Cys in G-Cys conjugates ranges from 43.5 to 159.4 mg/g. The disulfide bond crosslinking generated by the oxidation of thiol groups resulted in compact and dense microstructure, which in turn could decrease the moisture content, total soluble matter, water vapor permeability and swelling behavior of gelatin-based edible films, means enhanced water resistance. Moreover, the fabricated gelatin-based edible films showed good mechanical properties, excellent UV light barrier property and effective antioxidant activity. In addition, the incorporated antibacterial polypeptide e-PL endowed gelatin-based edible films with robust antibacterial activity. Overall, the disulfide bond crosslinked gelatin-based edible films incorporated with e-PL could find potential application in the food and drug packaging fields.

Synthesis of Lignin-Based Polyacid Catalyst and Its Utilization to Improve Water Resistance of Urea-formaldehyde Resins.

In this study, a lignin-based polyacid catalyst was synthesized via two steps to enhance water resistance of urea–formaldehyde (UF) resins. The first steps involved a hydroxymethylation reaction to increase the hydroxyl content in lignin. Then, hydroxymethylated lignins were reacted with maleic anhydride to form maleated lignin-based polyacids. The acid groups were expected to function as acid catalysts to catalyze the curing process of UF resin. In order to elucidate the structural variation, 3-methoxy-4-hydroxyphenylpropane as a typical guaiacol lignin structural unit was used as a model compound to observe the hydroxymethylation and the reaction with maleic anhydride analyzed by 1H and 13C NMR. After the structural analysis of synthesized lignin-based polyacid by FTIR and 13C NMR, it was used to produce UF resin as an adhesive in plywood and medium density fiberboard (MDF) production, respectively. The results showed that when the addition of lignin-based polyacid was 5% in plywood, it could effectively improve the water resistance of UF resins as compared to commercial additive NH4Cl. It also exhibited a lower formaldehyde emission. Like plywood, lignin-based catalysts used in medium density fiberboard production could not only maintain the mechanical properties, but also inhibit the water adsorption of fiberboards.

Enhancing the Water Resistance of Mn-MOF-74 by Modification in Low Temperature NH3-SCR

In this study, Mn-MOF-74 was successfully synthesized and further modified via two paths for enhanced water resistance. The structure and morphology of the modified samples were investigated by a series of characterization methods. The results of selective catalytic reduction (SCR) performance tests showed that polyethylene oxide-polypropylene-polyethylene oxide (P123)-modified Mn-MOF-74 exhibited outstanding NO conversion of up to 92.1% in the presence of 5 vol.% water at 250 °C, compared to 52% for Mn-MOF-74 under the same conditions. It was concluded that the water resistance of Mn-MOF-74 was significantly promoted after the introduction of P123 and that the unmodified P123-Mn-MOF-74 was proven to be a potential low-temperature SCR catalyst.

Electrospun Core-Shell Nanofibrous Membranes with Nanocellulose-Stabilized Carbon Nanotubes for Use as High-Performance Flexible Supercapacitor Electrodes with Enhanced Water Resistance, Thermal Stability, and Mechanical Toughness.

A high-performance flexible supercapacitor electrode with a core-shell structure is successfully developed from cellulose nanocrystal (CNC)-stabilized carbon nanotubes (CNTs). By incorporating poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA), a cross-linked nanofibrous membrane (CNT-CNC/PVA-PAA) is prepared as the core material via directional electrospinning, followed by a thermal treatment. The flexible supercapacitor electrodes are eventually fabricated via the in situ polymerization of polyaniline (PANI), which was used as the coating shell material, on the aligned electrospun nanofibers. By taking advantage of the thermally induced esterification cross-linking that occurs among PVA, PAA, and the CNT-CNC nanohybrids, the membranes present with enhanced water resistance, mechanical strength, and thermal stability. After the surface coating of the PANI shell, the optimized PANI@CNT-CNC/PVA-PAA nanofibrous membranes exhibit a large porosity, an enhanced specific surface area, a superior tensile strength of ∼54.8 MPa, and a favorable electroconductivity of ∼0.44 S m-1. As expected, the nanofibrous electrodes with a specific capacitance of 164.6 F g-1 can maintain 91% of the original capacitance after 2000 cycles. The symmetrical solid-state supercapacitor assembled by the nanofibrous electrodes shows an excellent capacitance of 155.5 F g-1 and a remarkable capacitance retention of 92, 90, and 89% after 2000 cycles under flat, bending, and twisting deformations, respectively.

Hydrophobic modification of pentaerythritol and its application in fire-retardant coatings for steel structures

Pentaerythritol (PER) is generally used as carbon source in intumescent fire- retardant coating. In order to enhance water resistance of the coating, PER reacted with C9 maleic anhydride copolymer microsphere (C9-MAH) by esterification. The composition of the product PER-C9-MAH was analyzed by FTIR; TGA results show the thermostability of PER-C9-MAH is better than PER; and SEM observation clearly showed the obvious enlargement in particle size from PER to PER-C9-MAH. The contact angle of PER is 26.5° and it raised to 87.2° for PER-C9-MAH. The fire resistance changes of the coating before and after water/salt water soaking are compared. After soaking in distilled water and 5 g/L salt water for 48 h respectively, phenomena such as blistering and falling off will be found in the coating containing PER accompanied with 1.9 ± 0.01% (in water) and 2.4 ± 0.01% (in salt water) weight losses; however the coating containing PER-C9-MAH looked smooth with little defects, and the weight losses are just 0.3 ± 0.01% (in water) and 0.3 ± 0.01% (in salt water) respectively. After burning 30 min, the back temperature of coating containing PER raises 76.2 °C (soaked in water) and 157.0 °C (soaked in salt water) respectively; However, it is just 19.7 °C and 33.7 °C rise for coating containing PER-C9-MAH. TGA, SEM and Raman spectroscopy results document the char of the coating containing PER-C9-MAH shows higher quantity, density and degree of graphitization, so it exhibits enhanced strength.

Experimental research on magnesium phosphate cements modified by red mud

The main concern of this article is to understand the influences of red mud on the properties of magnesium phosphate cement (MPC), which were determined in terms of the fluidity, setting characteristic, temperature evolution during the hardening stage, mechanical properties, water resistance, hydration products, pore structure and microstructure. The results showed that the fluidity can increase to a value of 272.5 mm at a level of 20% red mud, and red mud was found to decrease the exothermic reaction intensity of the fresh mortar and to prolong the setting time to 25 min during the hardening stage. The mortar prepared with suitable addition of red mud presented with improved mechanical properties and enhanced water resistance during the whole ageing period, and the group containing 20% red mud yielded the highest compressive strength of 90.2 MPa at 28 days. Then, the pore structure was measured by low-field nuclear magnetic resonance (LF-NMR), which was found that adding red mud can reduce the total porosity and form more small pores. Moreover, the microstructure and the hydration products of the samples were tested by X-ray diffraction (XRD), scanning electron microscopy (SEM) along with energy dispersive spectrometer (EDS). The obtained results illustrated that red mud can fill in the microcracks, making the structure denser, and also formed with some new hydrates. The present work aimed at the utilization of red mud and the results illustrated that MPC can be modified by red mud significantly.

Water resistance and corrosion protection properties of waterborne polyurethane coating enhanced by montmorillonite modified with Ce3+

In this study, waterborne coatings containing modified montmorillonites were investigated to enhance water resistance and corrosion protection on steel substrates. It is considered to use Ce3+ for substituting Na+ because directly adding Na-montmorillonite (Na-Mt) into coating would cause weak water resistance of coating due to its water absorption and swelling properties. Further, in order to increase the loading capacity of montmorillonite to Ce3+, it was pretreated by chitosan (CS) and was modified by Ce3+. Subsequently, Na-Mt and two modified montmorillonites (Ce-Mt, Ce-CS-Mt) were added to the waterborne polyurethane (WPU) matrix. The modification results of montmorillonite samples were examined by XRD and SEM/EDS. The results showed that Ce3+ was successfully loaded to the montmorillonite. Chitosan pretreatment increased Ce content in montmorillonite particles and improved their dispersion stability in the WPU matrix according to the Zeta potential results. In comparison, coating containing the Ce-CS-Mt particles exhibited the lowest water absorption, which indicated that adding Ce-CS-Mt particles had a significant improvement for the water resistance of WPU coating. Results of salt spray test revealed that no obvious corrosion products were found on the composite WPU coating after 768 h of exposure to salt spray, and it showed the highest |Z|f=10mHz in EIS measurement. These results indicated that the Ce-CS-Mt particles also enhanced the corrosion protection property of WPU coating.

Enhancing Water Resistance of a Mn-Based Catalyst for Low Temperature Selective Catalytic Reduction Reaction by Modifying Super Hydrophobic Layers.

OMS-2 catalysts exhibit excellent selective catalytic reduction (SCR) activity at low temperature but weak H2O resistance restricts its industrial application. To remarkably improve the water resistance of Mn-based catalysts is a key technical problem. In this work, the H2O endurance and self-cleaning properties of OMS-2 catalysts are remarkably improved by the facile process, construction of hydrophobic coating. The performance of the hydrophobic layer on the bulk OMS-2 catalyst surface could be effectively controlled by adjusting the polydimethylsiloxane (PDMS) vapor deposition temperature. It is discovered that the 200 °C catalyst obtained super hydrophobic properties and formed with a contact angle of 160.3°, which not only exhibited satisfactory NH3-SCR activity at low temperatures (140-300 °C) but also dramatically improved H2O endurance and self-cleaning performance. Moreover, the mechanism of improving H2O resistance and stability of the 200 °C catalyst was investigated in detail through a series of characterizations. Although the SCR activity of the 200 °C catalyst decreased slightly because of the combination of some active species (Oα and Mn3+) with PDMS, the H2O passivation of the active species was eliminated. The advantage of self-cleaning was confirmed by the analysis of surface species and simulation experiments, which could avoid the accumulation of intermediates on the surface and promote the stability of the OMS-2 catalyst for NH3-SCR at low temperature. This method of constructing special coating might be a huge step to remarkably improve the H2O endurance properties of the catalyst and provided a new concept for future industrial application.

Reversible Photochromic Nanofiber Membrane Containing Comb‐Like Poly(octadecyl acrylate) Nanoparticles Used for Ultraviolet Intensity Indicator

AbstractA novel reversible photo‐responsive polyvinyl alcohol (PVA)/polyethylenimine (PEI) electrospinning nanofiber membrane (NFM), assembled with photochromic nanoparticles containing spiropyran, is herein presented and the water resistance, mechanical properties as well as photochromic properties are investigated systematically. Here, glutaraldehyde, which can undergo a cross‐linking reaction with PVA/PEI, is selected as a cross‐linker to enhance water resistance and mechanical behavior of the NFM. Photochromic polymer nanoparticles are prepared using octadecyl acrylate as polymer matrix monomer through miniemulsion polymerization. Effect factors of the whole preparation process such as the PVA/PEI mass ratio, the amount of emulsifier, and the amount of photochromic nanoparticles added are regulated to obtain the optimal experimental parameters. The surface morphology and microstructure, water resistance, and mechanical properties of NFMs are studied by thermal field emission scanning electron microscopy, static water contact angle tester, and tensile universal testing machine, respectively. Furthermore, UV–vis spectrophotometer is employed to investigate the photochromic performance and fatigue resistance of NFMs. Overall, analyses reveal that the reversible photo‐responsive electrospinning NFM exhibit excellent photoresponsivity, photoreversibility, and fatigue resistance upon UV irradiation, thus showing promising application in the field of ultraviolet intensity indicator.