Inhibitory Effect Of Oxygen Research Articles

The reusage of different wastes by using the multiple's effect technique for sustainable gasoline production.

The unused garbage which is accumulating the landfills, such as raw materials, could be reused for synthetic gasoline production. This study presents the multiple's effect technique, which is based on the reusage of different non, party and sorted municipal solid wastes (MSW), or biogas for syngas, converted into synthetic gasoline. The novelties of this technique include a basic multiple's effect parameter (MUW), which present a level of waste sorting, an effect of oxygen inhibition into different wastes, a simplified mathematical model and simulation with an Aspen Plus® simulator using the retrofitted methanol plan converted into the synthetic gasoline production. This technique includes a circular economy by using a circulated purified flue gas as raw material, co-products of hydrogen and water. This technique was tested on an existing methanol process, replacing natural gas with different alternatives of wastes or biogas for the synthetic gasoline production. The best alternative was the sorted MSW, which could generate an additional profit of 4.8 MEUR/a, including the garbage and CO2 emission reductions of 0.106·106 t/a and of 0.084 ·106 t/a.

Understanding the mechanism of propane dehydrogenation over coordinatively unsaturated Co-O acid-base pairs and the inhibition effect of trace oxygen

High temperature and a reducing atmosphere are characteristic of propane dehydrogenation (PDH) reaction. Under such condition, the real surface structure of catalysts often differs from that in the ambient environment, particularly for CoOx species with multiple valence states and coordination. Here, a combination of in situ/operando Raman spectroscopy, in situ UV–Vis diffuse reflectance spectroscopy (DRS), and density functional theory (DFT) calculations reveal that coordinatively unsaturated Co-O (Cocu-O) acid-base pairs via lattice oxygen consumption are the PDH active sites of CoOx/Al2O3 catalysts. This highly dispersed Cocu-O species exhibit a C3H6 formation rate and C3H6 selectivity as high as 2 mmol‧gcat−1‧min−1 and 95 %, respectively, which is comparable to most state-of-the-art CoOx-based catalysts. However, industrial C3H8 raw gases typically contain 10–1000 ppm oxygen gas, and the complete eliminating oxygen increases costs. PDH catalytic performance of CoOx/Al2O3 catalysts is sensitive to the extremely low concentration of oxygen gas and is significantly inhibited by it. The fundamental reason is that the concentration of Cocu active sites is determined by the competitive reaction between the filling of trace oxygen on oxygen vacancies and lattice oxygen consumption. The reaction rate of the former is significantly higher than that of the latter. The higher reducibility of CoOx species leads to relatively weaken inhibition of trace oxygen for PDH activity. The oxygen content in the propane feed gas is a non-negligible factor in the development of new Co-based PDH catalysts, especially for their industrial applications.

Synthesis, UV-curing behaviors and general properties of acrylate-urethane resins prepared from castor oil-based polyols

Castor oil-based polyols with high OH values are synthesized through the low odor thiol-ene reaction and then are used for preparing UV-curable acrylate-urethane resins (AUCORs). The structure of the AUCORs is confirmed by 1H NMR and IR. The AUCORs based resins containing diluents can rapidly form cured films under UV light irradiation in air, with a very high gel ratio of over 95 %. The UV-curing dynamics shows that polymerization rate and final acrylate conversion under the N2 atmosphere both depend on CC bond content, but they are reduced under air due to oxygen inhibition effect. All the cured films have good heat stability with an initial decomposition temperature over 300 °C. The cured films can display different Tg within the region of 55–85 °C depending on the crosslink density tuned by the acrylate/urethane content. The urethane content/diluter can affect some general properties of the coating films, for instance water absorption ability, wettability, hardness and adhesion force. Interestingly, the cured films have a very good light transmittance in the visible light region, as high as that of glass slides.

Oxygen tolerance and detoxification mechanisms of highly enriched planktonic anaerobic ammonium-oxidizing (anammox) bacteria

Oxygen is a key regulatory factor of anaerobic ammonium oxidation (anammox). Although the inhibitory effect of oxygen is evident, a wide range of oxygen sensitivities of anammox bacteria have been reported so far, which makes it difficult to model the marine nitrogen loss and design anammox-based technologies. Here, oxygen tolerance and detoxification mechanisms of four genera of anammox bacteria; one marine species (“Ca. Scalindua sp.”) and four freshwater anammox species (“Ca. Brocadia sinica”, “Ca. Brocadia sapporoensis”, “Ca. Jettenia caeni”, and “Ca. Kuenenia stuttgartiensis”) were determined and then related to the activities of anti-oxidative enzymes. Highly enriched planktonic anammox cells were exposed to various levels of oxygen, and oxygen inhibition kinetics (50% inhibitory concentration (IC50) and upper O2 limits (DOmax) of anammox activity) were quantitatively determined. A marine anammox species, “Ca. Scalindua sp.”, exhibited much higher oxygen tolerance capability (IC50 = 18.0 µM and DOmax = 51.6 µM) than freshwater species (IC50 = 2.7–4.2 µM and DOmax = 10.9–26.6 µM). The upper DO limit of “Ca. Scalindua sp.” was much higher than the values reported so far (~20 µM). Furthermore, the oxygen inhibition was reversible even after exposed to ambient air for 12–24 h. The comparative genome analysis confirmed that all anammox species commonly possess the genes considered to function for reduction of O2, superoxide anion (O2•-), and H2O2. However, the superoxide reductase (Sor)-peroxidase dependent detoxification system alone may not be sufficient for cell survival under microaerobic conditions. Despite the fact that anaerobes normally possess no or little superoxide dismutase (Sod) or catalase (Cat), only Scalindua exhibited high Sod activity of 22.6 ± 1.9 U/mg-protein with moderate Cat activity of 1.6 ± 0.7 U/mg-protein, which was consistent with the genome sequence analysis. This Sod-Cat dependent detoxification system could be responsible for the higher O2 tolerance of Scalindua than other freshwater anammox species lacking the Sod activity.

Synthesis, metal–insulator transition, and photoresponse characteristics of VO2 nanobeams via an oxygen inhibitor-assisted vapor transport method

We demonstrate a straightforward and useful technique to control morphology and surface density of the resultant VO2 crystal by changing the O2 flow during the reduction of V2O5 powder, and a growth model related to the inhibition effect of oxygen is also proposed.

Evaluation of the color stability of 3D printed resin according to the oxygen inhibition effect and temperature difference in the post-polymerization process

The aim of this study was to determine the color stability of 3D printed resin according to the post-curing conditions (polymerization conditions and temperature). Specimens were post-polymerized under different conditions of oxygen inhibition, such as on glycerin immersion (GLY), medium-low vacuum environment (VA), and oxygen contact (CON, the control group), and temperature (35 °C, 60 °C, and 80 °C). The degree of conversion (DC), water sorption (Wsp) and solubility (Wsl), surface roughness (Ra) were measured. Additionally, surface free energy (SFE), pH values of colorants were measured. Grape juice (grape), coffee, and curry were used as the colorants, and distilled water (DW) was used as a control. And the color value was measured before and after immersion using a spectrophotometer. Then, Calculated the color change. For statistical methods, The Shapiro-Wilk test performed to check for normality revealed that the data presented a normal distribution (p>0.05). ΔE values were analyzed using three-way ANOVA. DC, Wsp, Wsl, SFE, and Ra were analyzed using two-way ANOVA. To confirm the linear correlation, Pearson's correlation coefficient was determined. The threshold for significance (p) was set at 0.05 (95% confidence interval) for all tests. DC was the highest at 80 °C in the GLY group (95.08 ± 4.88%). And Wsl decreased with increasing temperature, and was lowest at 80 °C in the GLY group (0.46 ± 0.30 um/mm3). After the colorants were immersed for 30 days, as the temperature increased, ΔE decreased in the GLY group but not in the VA and CON groups, and was the lowest at 80 °C in the GLY group: (DW, 0.95 ± 0.45 [mean± SD]; grape, 6.45± 0.69; coffee, 4.50± 0.56; curry, 9.37± 1.40). There was also a significant inverse relation between DC and ΔE. A significant inverse relation was found between Wsl and DC, and a significant positive correlation was found between Wsl and ΔE. Wsp, SFE, and Ra did not affect color stability. In the post-polymerization process, increasing the temperature and GLY were effective in reducing ΔE, which was lowest at 80 °C in the GLY group. It was also observed that a complex mechanism between the DC, Wsl of 3D printed resin affects ΔE of the resin.

Photoacoustic spectroscopy applied in the monitoring of photocuring process in epoxy diacrylate resins: Positive effect

AbstractThe main goal of this study is to show that photoacoustic spectroscopy (PAS) can be applied in the monitoring of photocuring processes in epoxy diacrylate resins. The resin used was EBECRYL 3720‐TP25 with the photoinitiator Omnirad 808. Comparison between the conventional transmission and absorption photoacoustic spectra of the resin is presented. Amplitude and phase of the photoacoustic signal were used to monitor the photocuring. The wavelength of the modulated photocuring light and the concentration of the photoinitiator were the parameters varied in the monitoring. The novelty was found when the resin was irradiated by a continuous light, centered at the absorption peak of the photoinitiator and simultaneously with the modulated light. In the time window when this continuous light was on (off) the amplitude of the photoacoustic signal increased (decreased). This is called “positive effect,” as it has been observed when PAS was applied to study photosynthesis in leaves. A mechanism is proposed to correlate the positive effect with the oxygen inhibition effect during the photocuring of the epoxy diacrylate resin. The results suggest that the amplitude of the photoacoustic signal and the positive effect can be used as monitoring parameters in the studies of photocuring process in epoxy diacrylate resins.

Light Intensity-Selective Photopolymerization and Photoisomerization for Creating Colorful Polymer-Stabilized Cholesteric Liquid Crystal Patterns.

Polymer-stabilized cholesteric liquid crystal (PSCLC) films have been widely studied for their application as sensors, polarizers, and reflective windows. However, the preparation of programmable and colorful patterns based on the structural color is still challenging. Herein, the photochromic CLC mixtures were prepared by adding a photoisomerizable chiral additive (CA) and a photoinitiator in the nematic liquid crystal LC242. Under UV irradiation with weak intensity, photoisomerization of the CA was carried out and photopolymerization was suppressed by oxygen inhibition. With extending the irradiation time, the helical pitch of the CLC film increased and the selective Bragg reflection band tended to redshift. Under strong UV irradiation, oxygen inhibition was overcome and photopolymerization dominates the reaction. Therefore, the colorful-patterned PSCLC films were able to be prepared using masks. The results shown here not only give us a better understanding of the effect of oxygen inhibition but also lay the foundations for practical applications such as decoration and optical devices.

Effects of operational variations of micro-oxygenation and pH shock on the competition between methane production and sulfate reduction in a UASB reactor

To investigate the effect of oxygen, pH shock, and H2S inhibition on the competition between sulfate-reducing bacteria (SRB) and methane-producing archaea (MPA), a UASB reactor treating wastewater containing sulfate, ethanol and acetate was operated for 360 days. With micro-oxygenation performed at a flow rate of 100 mL/min in the upper part of the up-flow anaerobic sludge blanket (UASB) reactor, the sulfate removal and total sulfide concentration increased to 68.6% and 500 mg S/L, while the methane production rate slightly reduced from 2.5 to 2.1 L/L/d. However, methane production was still the main reaction in the reactor. The pH shock and high H2S concentration finally changed the competition results between SRB and MPA. Sulfate reduction was not affected while methane production was completely inhibited at H2S concentration more than 200 mg/L. Complete sulfate reduction (99.0%) was maintained over the long term with a stable organic COD removal (70.4%). The experimental results proved that in the complete sulfate-reducing stage, ethanol was mainly utilized by incomplete-oxidizing SRB for sulfate reduction.

Polysilazane-derived SiCN ceramics-based layerless printing

In the process of light curing printing, layer steps are formed in the stacking direction. As these steps, i.e., by-products, affect the accuracy and quality of the printed surface significantly, avoiding their formation during printing is a prominent research topic. In this study, we propose a layerless printing method.Layerless printing uses the inhibition effect of oxygen on the polymerization reaction of ceramic precursor photosensitive resins, construct the oxygen inhibition layer during the printing process. We control the oxygen inhibition layer to weaken/eliminate the steps. In layerless printing, the high viscosity ceramic precursor photosensitive resin reduces the viscosity by heating up to make the fluidity of the material meet the printing conditions.The ceramic material can be realized straight-walled layerless in the z direction with a traditional layer thickness (100 µm). Furthermore, after pyrolysis of the printed ceramic precursor structure,the ceramic structure continued to retain zero layer steps.The result is that layerless printing reduced the surface roughness of the ceramic by 86.4%, the hardness and modulus of the ceramic were increased by approximately 10%, and the ceramic lattice of layerless printing was more uniformly stressed when subjected to compression stress. • Layer steps are eliminated by layerless printing. • The use of layerless printing can obtain a ceramic structure with a more uniform force. • Layerless printing can improve the accuracy of the print structure.

Bis(trimethylsilyl)amino modified Type Ⅱ photoinitiators can alleviate oxygen inhibition of near-UV LED photopolymerization due to moisture induced decomposition of initiators

Near UV-LED photopolymerization of acrylates can find many crucial applications in industrial fields, such as coatings, adhesives and 3D printing of hydrogels. However, developing the photoinitiators (PIs) well matching with the commercial LED light sources and reducing oxygen inhibition effect remain challenges. Herein, we have synthesized three kinds of type Ⅱ PIs containing bis(trimethylsilyl)amino groups; Molar extinction coefficients of these PIs are all at the 103 ∼ 104 (L·mol−1·cm−1) order of magnitude at the 365 ∼ 395 nm, comparable to the commercial PIs including Michler’s ketone (MK) and 2-isopropylthioxanthone (ITX); However, their photoinitiation capacity is much better than the MK and the ITX. In addition, these PIs have better resistance to the oxygen inhibition effect than the MK. Some researchers think the PIs containing rich Si/F elements can self-migrate towards upper layers of curing systems to reduce the oxygen inhibition effect, however, these obtained PIs with high Si fraction did not have such effect. Based on the obtained experimental results, we have proposed a new mechanism explaining their good ability to reduce the oxygen inhibition: The moisture induced decomposition of the initiators can play a key role in alleviating the oxygen inhibition; The generated Si-containing fragments after PIs’ hydrolysis can self-float towards the top surfaces to hinder the oxygen penetration, not the self-floating effect of the PIs by themselves.

KINETICS OF FORMATION AND PROPERTIES OF PHOTOCURED SIMULTANEOUS EPOXY-ACRYLATE IPNS WITH THE PREVAILING CONTENT OF AN EPOXY COMPONENT

The distinct features of UV induced polymerization of epoxy-acrylate blends leading to the formation of simultaneous interpenetrating polymer networks (IPNs) have been studied. Different ratios of components within a prevailing content of an epoxy one have been used for the synthesis. Such a content of epoxy monomer is required to create a barrier preventing oxygen diffusion into a curing sample. It allows retardation of the well-known oxygen-inhibition effect, which acrylate monomers are susceptible to. Hence, the conduction of their polymerization in open-air conditions is possible. The proceeding of the polymerization reactions of acrylate (TEGDM) via free radical mechanism and of epoxy (UP-650D) via cationic one have been monitored by FTIR-spectroscopy. Namely, the conversion degrees have been calculated for double bonds of TEGDM and for epoxy groups of UP-650D respectively. A mixture of triphenylsulfonium hexafluorophosphate salts, which is capable of generating both free radical and cationic reactive species, have been used as a single photoinitiator for the formulations being investigated. Almost complete conversion of acrylate double bonds was reached after 60 min of UV irradiation irrespective of epoxy content. On the contrary, conversion of epoxy groups of aliphatic epoxy, which is known to be rather unreactive towards cationic photopolymerization, when mixed may be either higher or lower compared to the neat epoxy network. Such results are attributed to dual influence of acrylate network on the formation of epoxy one. Firstly, cationic polymerization of epoxy component is sensitized by acrylate macroradicals in terms of free radical promoted cationic polymerization. On the other hand, the mobility of epoxy macrocations is restricted by the rapid build-up of acrylate network. At the weight ratio of UP-650D and TEGDM 70/30 the sensitizing effect of acrylate is revealed to be dominant, so the given composition may be considered as optimal. Regardless of low conversion of epoxy groups, the content of the estimated gel fraction is high, and the epoxy component is found not to be leached in the process of extraction in acetone. Furthermore, physicomechanical properties of obtained UV-cured IPNs have been investigated. The results of the measurements, namely, impact resistance by the Gardner test, crosshatch adhesion test to different substrates (including silicon), and accelerated weathering test in a climatic chamber, show that all the samples exhibit good operational properties essential for effective protecting coatings of outdoor exposure.

Photopolymerizable chitosan hydrogels with improved strength and 3D printability

Chitosan hydrogel have presented great potential in biomedical applications due to its biocompatibility, biodegradability and characteristic similarity to native extracellular matrix. However, 3D printing of chitosan hydrogel often suffers from weak formability and poor mechanical property, limiting its further utilization. In this study, a novel chiotsan hydrogel is prepared from maleic chitosan (MCS) with high acrylate group substitution (i.e. 1.67) and thiol-terminated poly (ethylene glycol) (TPEG) via step-chain growth photopolymerization approach, which can overcome significantly the oxygen inhibition effect. Rheological property, microstructure, mechanical properties and in vitro degradation can be regulated by changing the thiol/acrylate molar ratio. There is strong intermolecular action between MCS and TPEG. Notably, photopolymerized MCS/TPEG hydrogel exhibited ~2-fold and ~ 10-fold increase in gelling rate and compressive strength, respectively, compared to pure chitosan hydrogel. Based on these results, 3D printing of chitosan hydrogel fabricated by simultaneous extrusion deposition and thiol-acrylate photopolymerization, demonstrates printing accuracy and improved scaffold stability. This 3D printing of chitosan hydrogel shows no cytotoxicity and can support adherence of L929 cells, suggesting its potential in biomedical applications such as tissue engineering and drug delivery.

Thiol‐Ene Photopolymerization under Blue, Green and Red LED Irradiation

AbstractPhotopolymerization allows fast production of materials with special properties; however, a short wavelength of light is required for most commercial photoinitiating systems and the oxygen inhibition effect for the free radical polymerization has limited possible applications. Herein, we investigate thiol‐ene photopolymerization with various types of “ene” derivatives and thiols using our previously reported photoinitiator 2‐(4‐methoxystyryl)‐4,6‐bis(trichloromethyl)‐1,3,5‐triazine (triazine) alone or in combination with rubrene or 1,4‐bis(isopropylamino)anthraquinone (SB36) as the photoinitiating systems to trigger polymerization under irradiation with blue, green, and red LEDs. An analysis of photopolymerization kinetics and the effects of different light irradiation conditions, chemical structures, composites of “ene” and thiol monomers, and air on the thiol‐ene photopolymerization reaction are presented. Specifically, rates of photopolymerization of all thiol‐ene formulations decrease as the wavelength of irradiation increases and show no significant difference when polymerization occurs under air or in laminate. Mechanical properties and homogeneity of the photocured samples are analyzed and demonstrated that all thiol‐ene formulations appear to have a homogeneous network. Regarding mechanical properties, with a lower amount of thiol incorporated in the network, the storage modulus and the glass transition temperature (Tg) of the photocured product increased. Storage stability of thiol‐ene formulations is also studied and 5‐hydroxy‐1,4‐naphthoquinone (5HNQ), a naturally derived dye derivative, is found to be successful in inhibiting premature gelation in thiol‐ene systems without significantly affecting the photopolymerization performance.

Oxygen Inhibition of Surface Composites and Its Correlation with Degree of Conversion and Color Stability.

This study investigated the effects of oxygen inhibition and finishing/polishing procedures on the composite resin properties. One bulk-fill and two conventional composite resins (nanoparticle and microhybrid) were evaluated. Specimens were prepared using 4 surface treatments: control, no treatment; Gly, oxygen inhibition with glycerin; FP, finishing and polishing; Gly + FP, glycerin followed by finishing and polishing. The degree of conversion (DC) was measured using Fourier Transformed Infrared Spectroscopy (FTIR) immediately and after 15 days (n=5). Color stability (ΔEab, and ΔE00) and opacity were evaluated using a spectrophotometer after 15 days of immersion in coffee, using the CIELAB system (n=5). Data were analyzed by two-way ANOVA and Tukey tests (α=0.05) and opacity by two-way repeated-measures ANOVA. Glycerin usage increased significantly the DC however had no influence on the ΔEab, ΔE00 and, opacity values. Finishing and polishing reduced ΔEab and ΔE00 values, regardless of composite resins. Microhybrid showed higher opacity, followed by the nanoparticle and bulk fill, regardless of surface treatment. Post-polymerization polishing procedures resulted in lower conversion than using an oxygen inhibitor agent (Gly condition), but similar staining caused by coffee.

Oxygen inhibition induced hydrophilic-hydrophobic surface for self-assembled droplet microarrays

Hydrophilic-hydrophobic surface is vital for the study of the wettability behavior of microdroplets. In this paper, a method for preparation of hydrophilic-hydrophobic patterned surface is proposed based on the oxygen inhibition effect. Oxygen inhibition is very common in photo-cured process, and usually should be avoided for its adverse effect on curing quality. However, it also results in numerous nanostructures naturally formed on the cured layer surface, and the density and sizes of the nanostructures can be modulated conveniently by adjusting the exposure time. Based on this phenomenon, the cured layer surface having hydrophobicity can be processed. The contact angle system is used to measure the contact angle of the cured layer surface, and the morphology of the cured layer surface is measured in detail by atomic force microscopy and scanning electron microscope.The hydrophobic layer is only 1.5 $$\upmu $$ m thick. By combining maskless lithography, patterned surface with nanostructures can be easily formed in just one step without any special treatment. This helps us to generate highly controllable hydrophilic-hydrophobic surface effectively in a very simple and low-cost way. With this method self-assembled droplet microarrays are successfully achieved. The results offer a new idea for the control of surface wettability and may find wide potential applications in microfluidics.

Influence of micro-feature parameters of a constrained substrate on mass transfer of photopolymerization inhibition gas in continuous liquid interface production

<p indent=0mm>The continuous liquid interface production (CLIP) process has dramatically improved the fabrication speed of 3D printing technology, which makes it possible for Stereolithography to be used for direct manufacturing of functional parts. The effect of the CLIP process is significant owing to the skillful application of the photopolymerization inhibition effect of oxygen; therefore, the mass transfer behavior of the oxygen across the substrate is the key factor affecting the thickness and stability of the inhibition zone. In this paper, a low-cost scheme for a constrained substrate with good oxygen permeability that is made of PDMS membrane has been proposed, and the paper focuses on the effect of PDMS membrane and microscopic pore characteristics on the oxygen mass transfer behavior in the substrate. Based on the calculation result of the oxygen-diffusion coefficient in the PDMS membrane through molecular dynamics simulation, the influencing factors and laws of oxygen permeability of substrate are numerically studied using COMSOL software. The substrates with oxygen permeability that was measured based on the constructed experiment device were fabricated. The results show that the PDMS membrane possesses good oxygen content and the diffusion coefficient of the content in the PDMS film is 4.018 ×10⁻⁵ cm²/s. The thickness of the PDMS film and the area ratio and diameter of the micro-pores in the supporting glass substrate affect the oxygen permeability. Reducing the thickness of the PDMS film, increasing the pore-area ratio, and reducing the micro-pore diameter facilitate the oxygen permeability improvement under the premise of meeting the strength requirements. The research results can provide process improvement direction and theoretical basis for the preparation of constrained substrates.

Autoradiolysis of Radiopharmaceutical 2-[18F]Fluorodeoxyglucose with Activity Concentrations of 4–5.5 GBq/mL

The kinetics of the autoradiolytic decomposition of the radiopharmaceutical 2-[18F]fluorodeoxyglucose ([18F]FDG) with initial activity concentrations of 4.02–5.45 GBq/mL in physiological saline solution has been studied. It has been shown that an increase in the initial activity concentration or a decrease in the concentration of ethanol (chemical impurity) leads to a greater buildup of radiolytic [18F]fluoride and a decline in the radiochemical purity of the drug. During storage of the radiopharmaceutical, a decrease in the concentration of ethanol and the formation of acetaldehyde, a product of its radiation-induced transformations, have been detected, the aldehyde concentration correlating with the relative activity of [18F]fluoride. It has been found that after storage of [18F]FDG with the same initial activity concentration in sealed 15-mL vials for 8 hours, the relative activity of [18F]fluoride is significantly higher in 8-mL than in 1.5-mL solutions. This difference may be due to both an increase in the dose absorbed by the drug and the inhibitory effect of oxygen on the autoradiolytic dehalogenation process. An [18F]fluoride removal procedure for purifying [18F]FDG is described, which ensures the preservation of aseptic and pyrogen-free injectable drugs under the conditions of an operating positron emission tomography center.

Modeling the Kinetics, Curing Depth, and Efficacy of Radical-Mediated Photopolymerization: The Role of Oxygen Inhibition, Viscosity, and Dynamic Light Intensity.

Kinetic equations for a modeling system with type-I radical-mediated and type-II oxygen-mediated pathways are derived and numerically solved for the photopolymerization efficacy and curing depth, under the quasi-steady state assumption, and bimolecular termination. We show that photopolymerization efficacy is an increasing function of photosensitizer (PS) concentration (C0) and the light dose at transient state, but it is a decreasing function of the light intensity, scaled by [C0/I0]0.5 at steady state. The curing (or cross-link) depth is an increasing function of C0 and light dose (time × intensity), but it is a decreasing function of the oxygen concentration, viscosity effect, and oxygen external supply rate. Higher intensity results in a faster depletion of PS and oxygen. For optically thick polymers (>100 um), light intensity is an increasing function of time due to PS depletion, which cannot be neglected. With oxygen inhibition effect, the efficacy temporal profile has an induction time defined by the oxygen depletion rate. Efficacy is also an increasing function of the effective rate constant, K = k′/, defined by the radical producing rate (k′) and the bimolecular termination rate (kT). In conclusion, the curing depth has a non-linear dependence on the PS concentration, light intensity, and dose and a decreasing function of the oxygen inhibition effect. Efficacy is scaled by [C0/I0]0.5 at steady state. Analytic formulas for the efficacy and curing depth are derived, for the first time, and utilized to analyze the measured pillar height in microfabrication. Finally, various strategies for improved efficacy and curing depth are discussed.

Creating an Interface: Rendering a Double-Network Hydrogel Lubricious via Spontaneous Delamination.

Hydrogels engineered with specific surface chemistries and architectures have foundmyriadapplications in electronics, biofouling, biolubrication, and biomedical devices. Free-radical polymerization is frequently employed to construct covalently bonded networks in hydrogels, and any inhibition of the radical reactions by oxygen at the surface of the reaction mixture is generally undesirable. The internal stress caused by the resulting gradient in the cross-linking density during polymerization can give rise to a physical deformation of the surface, resulting in wrinkles, creases, or cracks. However, this oxygen-inhibition effect can be positively utilized to create finely controlled surface structures. We describe a two-step cross-linking strategy for the fabrication of a P(AAm-AMPS)/alginate double-network hydrogel in the presence of air, which enables greater independent control over surface chemistry and functionality than homogeneously processed conventional double-network hydrogels. An alginate-rich "skin" layer is spontaneously delaminated due to the mechanical instability and osmotic mismatch between the swollen double-network hydrogel matrix and the rigid "skin" layer. Removal of the "skin" layer results in a lubricious surface with coefficients of friction as low as 0.02 against glass in aqueous solutions. The proposed strategy can be generalized to develop soft functional materials with unique structures and properties and precise control over the surface chemistry.