Dispersions Of Polyethylene Glycol Research Articles

A novel method for the synthesis of solvent‐free and high‐solid‐content waterborne polyurethanes by introducing a small amount of polyethylene glycol

AbstractIn the study, the synthesis process involved the reaction of dimethylolbutyric acid and polytetramethylene ether glycol 1000 (PTMG1000) with hexamethylene diisocyanate (H12MDI), taking advantage of their mutual dissolution at high temperatures. The chain‐extension reaction with 1,4‐butanediol (BDO) was successfully conducted without the use of organic solvents. The emulsification reaction was carried out using the polyurethane prepolymer at 60% solids content, along with aqueous dispersions of polyethylene glycol (PEG) with varying molecular weights and amounts as interfacially active agents. Fourier transform infrared spectroscopy analysis suggested potential hydrogen bonding interactions between the PEG molecular chain and the polyurethane chain. Rheometer analysis demonstrated a significant reduction in viscosity with the addition of 1–5 wt.% PEG, accompanied by an increase in average particle size. This phenomenon was attributed to the formation of a hydrophilic lubrication layer of PEG around the water‐based polyurethane (WPU) microcells. Among them, WPU films containing 4 wt.% PEG4000 not only exhibited soft properties with a mechanical elongation rate exceeding 2000% but also showed excellent storage stability. The addition of long‐chain PEG facilitated the formation of a lubrication layer between the microcells, contributing to spatial stabilization and reducing particle aggregation at high solids content. It is noteworthy that this solvent‐free process, without any organic solvents, together with the adjusted PEG content, successfully synthesized waterborne polyurethanes with low viscosity and high solids content. This provides a new sustainable and environmentally friendly method for the future production of waterborne polyurethanes.

Thermophysical, rheological and dielectric behaviour of stable carbon black dispersions in PEG200

Phase change materials can store or release large amounts of energy during phase change. An increasing number of authors are studying the influence of the dispersion of nanometric particles on these materials. This article presents the design and experimental characterization of temporal stability, thermal conductivity, isobaric heat capacity, phase change transitions, rheological behaviour, and dielectric properties of nano-enhanced phase change materials based on carbon black (CB) dispersions in polyethylene glycol (PEG200) by using polyvinylpyrrolidone (PVP) as surfactant. We studied the temporal stability of carbon black nanoparticles dispersed in PEG200 using dynamic light scattering and spectrophotometry techniques. All the samples showed good temporal stability, since the measurements of the hydrodynamic size of the nanoparticles are practically constant over time and the wavelength observed by UV–vis shows a small variation of around 4% for static conditions. We observed small changes in thermal conductivity and isobaric heat capacity. Nevertheless, the thermograms evidence how the latent heat clearly increases with the load of carbon black nanoparticles up to four times that of the PEG200. The viscosity studies do not show variation with shear rate, indicating a Newtonian behaviour, excluding the 2.0 wt% CB/PVP + PEG200 nanofluid. Additionally, we noticed frequency dependent and independent regions for permittivity.

Multi-stimuli temperature, reusable, recyclable, and healable shape-memory epoxy–PEG multifunctional films by regulating polyethylene glycol

This study developed a multi-stimuli temperature shape-memory epoxy–polyethylene glycol (PEG) film with skin-responsive and self-healing properties. The epoxy–PEG films can be regulated between rigid and flexible by the dispersion of PEG with different contents. All have excellent shape-memory properties at the respective stimuli temperatures with recovery rates between 92.6 % and 99.0 %. The epoxy–PEG films can perform shape-memory response and healing at room and human body temperatures based on the PEG regulation. The completely cut films with a PEG content of 30 wt% can maintain an average tensile strength of 63.1 % after healing at room temperature. Films with a PEG content of 40 wt% after healing at room and human body temperatures can maintain average tensile strengths of 70.0 % and 93.3 %, respectively. The films healed at human body temperature still maintained an average recovery rate of 85.0 % in the shape-memory cycling test. The environmentally developed shape-memory epoxy–PEG film with controllable thermal and mechanical properties can meet the needs of various stimuli temperatures and execution modes, switching between multiple shapes, self-healing, reuse, reprocessing, and recycling, significantly expanding the application potential for thermoplastic epoxy, especially in the fields of flexible smart materials.

Dispersion of Polyethylene Glycol in Perfluorodecalin for Liquid Phase Fluorination

This work aims to obtain the dispersions based on polyethylene glycols (PEGs) of various molecular masses (MM) and perfluorodecalin (PFD) for subsequent direct fluorination. The solubility of the components was estimated using laser interferometry and differential scanning calorimetry, and it was shown that PEGs with different MM are not highly compatible with PFD. The dispersions were prepared during sonication. Gel permeation chromatography (GPC) analysis indicated that MMs almost did not change in this process. While the sonication of PEG-PFD, there is a formation of dispersion with the particle sizes distribution in a range of 0.4‒2 μm depending on the MM of PEG. The dispersion is metastable for several hours, even though its stability was significantly affected by additional bubbling with the gas flow. Moreover, the dispersions with a solid PEG phase (MM > 600 Da) were subjected to a smaller change compared to a liquid one (MM < 600 Da). The results of this research shed light on the applicability of the ultrasonic preparation of PEGs in PFD for liquid-phase fluorination with obtaining perfluorinated polyether of target MM.

Preparation and Tribological Behaviors of Modified Rice Husk Carbon/MoS2 Composite Particles as a Functional Additive in Polyethylene Glycol

Rice husk carbon/molybdenum disulfide (RHC/MoS2) nanoparticles were prepared by a chemical precipitation method in order to comprehensively utilize the rice husk. 3-Aminopropyl trimethoxysilane (ATS) was used as a surface modifier to promote the dispersion capability of RHC/MoS2 particles in polyethylene glycol. The tribological behavior of polyethylene glycol (PEG) with different amount of modified particles was investigated using a ball-disk tribometer at the different velocities and loads. A three-dimensional (3D) laser scanning microscope (LSM) and x-ray photoelectron spectroscopy (XPS) were used to clarify the friction and wear mechanisms of modified composite particles in PEG. Results show that the modified RHC/MoS2 has good friction characteristics and dispersion in PEG. Modified RHC/MoS2 particles can effectively improve the wear resistance and friction reduction properties of PEG. The optimal additions of two kinds of particles are both 0.5 wt%. Friction and wear mechanism of composite particles were ascribed to the tribofilm that came from the components of composite particles.

Multifunctional Doxorubicin@Hollow-Cu9S8 nanoplatforms for Photothermally-Augmented Chemodynamic-Chemo therapy

Multimodal therapy has attracted increasing interests in tumor treatment due to its high anti-cancer efficacy, and the key is to develop multifunctional nanoagents. The classic multifunctional nanoagents are made up of expensive and complex components, leading to limited practical applications. To solve these problems, we have developed the polyethylene glycol (PEG) coated hollow Cu9S8 nanoparticles (H-Cu9S8/PEG NPs), whose H-Cu9S8 component exhibits the photothermal effect for near-infrared (NIR) photothermal therapy (PTT), the Fenton-like catalytic activity for chemodynamic therapy (CDT), and the drug-loading capacity for chemotherapy. The H-Cu9S8/PEG NPs with a diameter of ∼ 100 nm have been synthesized by sulfurizing cuprous oxide (Cu2O) nanoparticles through “Kirkendall effect”, and they exhibit high photothermal conversion efficiency of 40.9%. Meanwhile, the H-Cu9S8/PEG NPs are capable of a Fenton-like reaction, which can be augmented by 2 times under the NIR irradiation. The hollow structure gives the H-Cu9S8/PEG high doxorubicin (DOX) loading capacity (21.1%), and then the DOX release can be further improved by pH and photothermal effect. When the DOX@H-Cu9S8/PEG dispersions are injected into the tumor-bearing mice, the tumor growth can be efficiently inhibited due to the synergistic effect of photothermally-augmented CDT-chemo therapy. Therefore, the DOX@H-Cu9S8/PEG can serve as a multifunctional nanoplatform for photothermally-augmented CDT-chemo treatment of malignant tumors.

High Conductivity and Excitation-Power Sensitivity of Upconversion Emission in Silica Decoration of Regular Hexagonal Yb and Er Codoped ZnO Core–Shell Particles

The structure of upconversion materials has an important influence on their photoelectric properties. Herein, we show that the quadrilateral-like structure of Yb/Er/ZnO micronanoparticles grew to regular hexagonal-like structure by increasing the reaction time from 6 to 24 h. Yb/Er/ZnO samples were prepared via a hydrothermal method with polyethylene glycol (PEG) as the dispersant. The structural evolution originated from the addition of PEG dispersant. The Yb/Er/ZnO particles with hexagonal-like structure had increased carrier concentration, carrier mobility rate, Hall coefficient, and resistivity. In addition, a silica shell coating on Yb/Er/ZnO micronanoparticles with hexagonal-like structure (Yb/Er/ZnO@SiO2) was achieved by the Stöber method and improved the electrical conductivity. The migration rate of Yb/Er/ZnO@SiO2 increased to 163.6 cm V s–1. The core–shell interactions decreased the band gap of Yb/Er/ZnO and the energy of defect transition in ZnO host, which significantly improved host sensitization. With increasing power density from 2.04 to 9.04 W/cm2, the intensity of the red upconversion emission was clearly enhanced. Power-dependent multicolor emission excitation was achieved, and the color changed from red to yellow and to green. Moreover, color-correlated temperature (CCT) values changed between the cool region and the warm CCT region, indicating that tricolor emission was controlled via adjusting the excitation power. The regular hexagonal-like structure of Yb/Er/ZnO@SiO2 can be potentially extended to optoelectronic device applications.

Halloysite Nanotubes Loaded with Calcium Hydroxide: Alkaline Fillers for the Deacidification of Waterlogged Archeological Woods.

A novel green protocol for the deacidifying consolidation of waterlogged archaeological woods through aqueous dispersions of polyethylene glycol (PEG) 1500 and halloysite nanotubes containing calcium hydroxide has been designed. First, we prepared functionalized halloysite nanotubes filled with Ca(OH)2 in their lumen. The controlled and sustained release of Ca(OH)2 from the halloysite lumen extended its neutralization action over time, allowing the development of a long-term deacidification of the wood samples. A preliminary thermomechanical characterization of clay/polymer nanocomposites allows us to determine the experimental conditions to maximize the consolidation efficiency of the wood samples. The penetration of the halloysite-Ca(OH)2/PEG composite within the wooden pores conferred the robustness of the archaeological woods based on the clay/polymer composition of the consolidant mixture. Compared to the archeological woods treated with pure PEG 1500, the addition of modified nanotubes in the consolidant induced a remarkable improvement in the mechanical performance in terms of flexural strength and rigidity. The pH measurements of the treated woods showed that the halloysite-Ca(OH)2 are effective alkaline fillers. Accordingly, the modified nanotubes provided a long-term protection for lignin present in the woods that are exposed to artificial aging under acidic atmosphere. The attained knowledge shows that an easy and green protocol for the long-term preservation of wooden artworks can be achieved by the combination of PEG polymers and alkaline tubular nanostructures obtained through the confinement of Ca(OH)2 within the halloysite cavity.

Recovery of magnetite from waste ferrous sulfate using polyethylene glycol (PEG) as a dispersant

Abstract The effect of PEG dispersant on the magnetic separation of magnetite (Fe3O4) synthesized from ferrous sulfate solution via co-precipitation method with calcium hydroxide as the precipitant was investigated. The results indicated that a PEG dispersant could significantly affect Fe3O4 recovery. Adding PEG during the preparation of Fe3O4 was unfavorable for Fe3O4 recovery. When the PEG-6000 concentration was increased from 0 to 8 g/L, the iron grade and median particle size of the Fe3O4 product decreased from 65.58% and 2.35 μm to 57.79% and 1.35 μm, respectively. However, adding PEG during the wet milling of the mixed product promoted the subsequent recovery of Fe3O4. When the amount of PEG-200 increased from 0% to 4% of the powder mass, the grade of iron in the Fe3O4 product increased from 65.58% to 68.32%. While the relative molecular mass of PEG at an amount of 4% of the powder mass increased from 200 to 20000, the grade of iron was reduced from 68.32% to 66.70%.

Microstructure of Pharmaceutical Semicrystalline Dispersions: The Significance of Polymer Conformation.

The microstructure of pharmaceutical semicrystalline solid dispersions has attracted extensive attention due to its complexity that might result in the diversity in physical stability, dissolution behavior, and pharmaceutical performance of the systems. Numerous factors have been reported that dictate the microstructure of semicrystalline dispersions. Nevertheless, the importance of the complicated conformation of the polymer has never been elucidated. In this study, we investigate the microstructure of dispersions of polyethylene glycol and active pharmaceutical ingredients by small-angle X-ray scattering and high performance differential scanning calorimetry. Polyethylene glycol with molecular weight of 2000 g/mol (PEG2000) and 6000 g/mol (PEG6000) exhibited remarkable discrepancy in the lamellar periodicity in dispersions with APIs which was attributed to the differences in their folding behavior. The long period of PEG2000 always decreased upon aging-induced exclusion of APIs from the interlamellar region of extended chain crystals whereas the periodicity of PEG6000 may decrease or increase during storage as a consequence of the competition between the drug segregation and the lamellar thickening from nonintegral-folded into integral-folded chain crystals. These processes were in turn significantly influenced by the crystallization tendency of the pharmaceutical compounds, drug-polymer interactions, as well as the dispersion composition and crystallization temperature. This study highlights the significance of the polymer conformation on the microstructure of semicrystalline systems that is critical for the preparation of solid dispersions with consistent and reproducible quality.

Process Optimization and Characterization of YSZ Thin Film Electrolyte on Anode Substrate Prepared by Electrophoretic Deposition Technique

Thin film electrolyte made of 8-mol% yttria stabilized zirconia (8YSZ) was fabricated on porous NiO-8YSZ anode substrates using electrophoretic deposition (EPD). The porous NiO-8YSZ anode substrates were prepared by powder injection molding technique. The electrolyte suspensions containing 8YSZ nanoparticles and polyethylene glycol (PEG) as a dispersant (1-19 wt%) were formed in ethanol. The maximum zeta potential value was obtained from the 8YSZ suspension with 5 wt% PEG considered as an optimal content of PEG dispersant. The electrophoretic deposition of 8YSZ film was performed on the porous anode substrate using a constant voltage of 30 V for 150 sec prior to co-sintering at different temperatures in order to obtain dense 8YSZ electrolyte film on the porous anode substrate. Co-sintering at 1250°C for 1 h resulted in a formation of a dense 8YSZ thin-film electrolyte with a thickness of 6.35 mm. An open circuit voltage at 800°C of a single cell having 8YSZ thin-film electrolyte on porous NiO-8YSZ anode substrate was 1.09 V, indicating a gas-tightness of 8YSZ thin-film electrolyte fabricated by using EPD.

EFFECT OF SELECTED POLYMERS ON DISSOLUTION AND STABILIZATION OF AMORPHOUS FORM OF MELOXICAM

Objective: Meloxicam is classified as class II corresponding to its high permeability and low solubility (12μg/ml). This study aims to compare the effect of selected polymers on stabilization of amorphous form, and dissolution of meloxicam by preparation of different solid dispersions using selected polymers (chitosan oligomers, polyvinylpyrrolidone K30, and polyethylene glycols).Methods: These solid dispersions were prepared using two different methods; solvent evaporation method for the two molecular weights chitosan carriers (16 and 11KDa) and polyvinylpyrrolidone-K30 and melting method for the two different molecular weights polyethylene glycol (4000 and 6000). The physicochemical properties of solid dispersions were analyzed using differential scanning calorimetry, Fourier transform infra-red analysis, Powder X-ray diffraction, and scanning electron microscopy. Selected dispersions were then compared to two selected marketed drugs (Mobic® and Moven®).Results: Best dissolution rates were obtained for both polyvinylpyrrolidone-K30 and polyethylene glycol 6000, followed by chitosan 16 kDa, chitosan 11 kDa, and polyethylene glycol 4000. Increasing polymeric ratio increased dissolution rate except for chitosan. Precipitation of the drug as amorphous form occurred in chitosan and polyvinylpyrrolidone-K30 dispersions, while no change in crystallinity obtained for polyethylene glycol dispersions. Failure of polyvinylpyrrolidone-K30 in the maintenance of stability during storage time was observed while re-crystallization occurred in chitosan-based dispersions, which ends with preferences to polyethylene glycol dispersions. After comparing the release of selected dispersions with the two selected polymers; all dispersions got a higher release than that of the two marketed drugs release.Conclusion: The dissolution profile of meloxicam has been increased successfully in a reproducible manner.

Effect of different polymeric dispersions on In-vitro dissolution rate and stability of celecoxib class II drug

Solid dispersions can play a significant role in the enhancement of drug dissolution and stability. Still, the polymeric effect can vary according to the possibility of intermolecular forces with the drug. The objective of this study was to evaluate the effect of several polymers on enhancement in-vitro dissolution behavior of celecoxib; in addition to comparing prepared dispersions with selected commercial products. Solid dispersions of celecoxib were prepared with different ratios between the drug and selected polymer (Soluplus®, polyvinyl pyrrolidine, Chitosan, polyethylene glycol). Physicochemical characterizations were performed using Powder X-ray diffraction, Differential Scanning Calorimetry, Fourier Transform Infra-Red analysis and Scanning Electron Microscopy. Dispersions were subjected to in-vitro drug release studies. Results revealed enhancement in dissolution rate for all dispersions prepared except for Chitosan-based dispersions that showed clear retardation in the drug release. Prepared dispersions from other polymers succeeded to match with release profile of two commercially marketed products (Celebrex® and Flamex®). Further Characterization of Chitosan dispersions revealed presence celecoxib in its crystalline form entrapped inside Chitosan carrier with the presence of two hydrogen bonding between Chitosan and celecoxib. Although both Polyvinylpyrrolidone, and polyethylene glycol dispersions showed a great enhancement in drug release; both failed to maintain stability. Sticky paste formation occurred to dispersions, and recrystallization took place in polyethylene glycol dispersions.

A study of the formation of magnetically active solid dispersions of phenacetin using atomic and magnetic force microscopy.

A lot of pharmaceutical substances have a poor solubility that limits their absorption and distribution to the targeted sites to elicit the desired action without causing untoward effects on healthy cells or tissues. For such drugs, new modes of delivery have to be developed for efficient and effective delivery of the drug to the target site. Formation of magnetically active solid dispersion of such drugs could be a useful approach to addressing this problem because they combine targeted delivery and good solubility. In this work, the distribution of superparamagnetic nanoparticles in the solid dispersion of polyethylene glycol with average molecular weight 950–1050 g/mol and phenacetin was studied using atomic force and magnetic force microscopy. The distribution of nanoparticles was found to be uniform in studied composites. Magnetically active solid dispersions may find application in the production of the capsulated drug delivery systems with enhanced solubility parameters.

Determination of riboflavin based on fluorescence quenching by graphene dispersions in polyethylene glycol

A quenching phenomenon of riboflavin fluorescence was found in graphene dispersions in PEG ascribed to π–π stacking and H-bonding interactions.

High-Performance Simultaneous Two-Photon Absorption Upconverted Stimulated Single-Component Sr2V2O7 Phosphor for White LEDs

Notwithstanding the wide use of white light-emitting diodes (w-LEDs), conventionally consisting of multiple emitting components, some inevitable issues still exist nowadays, such as the intrinsic color balance, device complexity, and high cost associated with such multiple emitting components. We have synthesized simultaneous two-photon absorption upconverted stimulated single-component Sr2V2O7 phosphor for use in w-LEDs. Due to the photon avalanche upconversion, the as-grown phosphor exhibits an enhanced photoluminescence spectrum in the range of 400 nm to 650 nm for white light when excited by red light at 693 nm. Moreover, when evenly dispersed in polyethylene glycol dispersant, the as-grown phosphor simultaneously produced strong visible white light when using an excitation wavelength λex of 693 nm, suggesting a possible route to produce w-LEDs by using red chips as an excellent substitute for traditional w-LEDs with multiple emitting components based on rare-earth metals. Finally, density functional calculations were performed using the generalized gradient approximation to study the electronic structure of Sr2V2O7 crystal. A reasonable model is proposed to explain the two-photon absorption luminescence mechanism.

Leaching of lead slag component by sodium chloride and diluted nitric acid and synthesis of ultrafine lead oxide powders

The compounds in lead slag are transformed into [PbCl4]2− in a mixed solution of HNO3 and NaCl, which is converted into PbC2O4 by the addition of sodium oxalate and polyethylene glycol dispersant. Novel lead oxides are prepared via a combustion-calcination process from lead oxalate precursor. Key properties of the new oxides, such as crystalline phases and morphology, have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that lead oxides synthesized at different calcination temperatures comprise mainly α-PbO and β-PbO phases. In battery testing, the results reveal that the α-PbO phase exhibits higher initial capacity as positive active material, discharging about 150 mAh g−1 at 20 mA g−1. While β-PbO yields a relatively improved cycle life, in 50 cycles, its capacity loss is 5%. Further work is being carried out with the aim to optimize the battery manufacturing process or to find out the optimum ratio of α-PbO to β-PbO in order to sustain high discharge capacity and acceptable cycle life.

Rheological characterization of polyethylene glycol based TiO2 nanofluids

Rheological characterization of TiO2 nanoparticle dispersions in polyethylene glycol (PEG 200) is presented over 1–10 wt% particle mass fraction range in terms of shear viscosity, thixotropy and linear viscoelasticity. A stress controlled rheometer fitted by a cone-and-plate system was employed for the rheological measurements between −10°C and 40°C. The non-linear viscoelastic experiments revealed that TiO2-PEG 200 nanofluid exhibits a shear thinning behavior when particle mass fraction exceeds 1%. No appreciable change in the shear viscosity versus shear rate behavior was detected over the course of four days of dispersion storage. At high particle concentrations the dispersions had a yield stress that was determined by fitting the results through Herschel-Bukley model. Within the studied range of particle concentration, no evidence of thixotropic behavior was observed. In addition, relative viscosity measured at high shear region was found to be independent of the temperature. On the other hand, strong temperature dependency was observed at low shear region particularly at high temperatures. Storage and loss moduli of the TiO2-PEG 200 nanofluid were determined by frequency sweep measurements with applied stresses in the linear viscoelastic region. It was found that when the applied stress is lower than the corresponding yield stress TiO2-PEG 200 nanofluid showed a gel structure especially at high particle mass concentration.

Two-step debinding and co-extrusion of ceramic-filled PEBA and EVA blends

The objective of this study is to investigate the choice of thermoplastic binders in a two-step debinding process involving solvent extraction (SE) and thermal debinding (TD) of samples produced using polymer (co-)extrusion. Two-step debinding uses a binder system combining soluble binders and thermoplastic binders, which are removed by SE and TD, respectively. In prior work, it was demonstrated that the two-step protocol eliminates debinding defects that are commonly observed in TD (Sharmin and Schoegl, 2014 [1]). The primary goal of this follow-up study is to establish that two-step debinding eliminates debinding defects irrespective of the choice of thermoplastic binders; a secondary goal is to investigate how the binder choice affects the co-extrusion process. In total, five batches using alumina powder and a binder system with a 1:1 ratio of thermoplastic binder and polyethylene glycol (PEG) as water soluble binder were tested. Three grades of polyethylene butyl acrylate (PEBA) and two grades of polyethylene vinyl acetate (EVA) with different melt flow indices were investigated. In all cases, extraction tests resulted in 80wt% removal of the original PEG content. However, PEBA samples showed a significantly faster PEG removal compared to EVA samples, which is attributed to a better dispersion of PEG within EVA. Tests with 4h extracted PEBA and 6h extracted EVA samples resulted in 60wt% removal of PEG and a defect-free specimen after TD and sintering. Also, microstructures of sintered PEBA and EVA samples are comparable, which confirms that the choice of thermoplastic binders has no effect on the two-step debinding process. Co-extrusion tests were performed for selected EVA and PEBA blends, where results showed better performance for co-extrusion of EVA blends.

Synthesis and near-infrared fluorescence of K5NdLi2F10 nanocrystals and their dispersion with high doping concentration and long lifetime.

K5NdLi2F10 nanocrystals were synthesized by a novel synthetic route in the liquid phase, which could improve the morphology and reduce the size effectively, for the first time. The luminescence intensities of the K5NdLi2F10 nanocrystals and their dispersion in polyethylene glycol 400 (PEG-400) approximate to that of neodymium doped phosphate glass (3 mol%), while the lifetimes of the nanocrystals alone and when dispersed with Nd(3+) ions (1 × 10(20) cm(-3)) are 303.4 μs and 174.6 μs respectively. Based on the Judd-Ofelt analysis, the emission quantum yield of the dispersion reaches 39.57%. In all, the K5NdLi2F10 nanocrystals and their dispersion have promising applications as liquid laser materials and biological fluorescent markers.