High throughput kinetic analysis of photopolymer conversion using composition and exposure time gradients

In this work, monomer composition and exposure time gradients were produced, allowing for rapid, parallel measurements of conversion as a function of composition and exposure time using Fourier transform infrared (FT-IR) spectroscopy. A more comprehensive understanding of how composition affects photopolymerization kinetics is needed due to the complexity of current industrial formulations. In nearly all cases, these applications use multiple monomers, fillers, initiators, and other components to achieve the required properties. The developed technique allows for photopolymerization kinetics to be analyzed rapidly over a large range of compositions, giving a unique insight into the role composition contributes to polymerization kinetics and ultimate conversion within complex formulations. This work analyzed three varied two-component systems, each showing different effects from composition on polymerization kinetics due to formulation changes in functionality, viscosity, and reactivity.     

Low-angle laser light scattering from polystyrene solutions: intensity measurements and photon correlation spectroscopy

Light scattering measurements have been made on polystyrenes with a range of molecular weights in toluene and for one polystyrene with a range of molecular weights in toluene and for one polystyrene in a range of solvents including a theta solvent. Intensity data were used to calculate second virial coefficients and molecular weights, whilst photon correlation spectroscopy was used to calculate diffusion coefficients. All measurements were made at 30°C and at a scattering angle of ca.4°. The data were used to examine current theories of polymer diffusion and the relation between hydrodynamic radius (R_H) and radius of gyrations ($\text{〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$). The results support accepted theories of polymer diffusion, but suggest that the relation between R_H and $\text{〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ requires further analysis.     

Gel time prediction of multifunctional acrylates using a kinetics model

A kinetics model for prediction of double-bond conversion and gel time in the photopolymerization of multifunctional acrylates is presented. The system consisting of a trifunctional acrylate, trimethylolpropane triacrylate (TMPTA), and a photoinitiator, 2,2-dimethoxy-1,2-diphenylethan-1-one (DMPA), was studied using Fourier-transform infrared spectroscopy (FTIR) measurements to monitor double-bond conversion and microrheology techniques to quantify the gel time for this system. Rate constants for the kinetics model were first estimated by fitting the model only to the FTIR double-bond conversion data, and later to both the FTIR and microrheology data. The measured gel time correlated with both the calculated initial rate of radical generation and a constant value of the predicted double-bond conversion, over a broad range of conditions. The model allows for materials formulation and exposure source intensity variables to be included in stereolithography inverse problem solutions, and could be applied to other cross-linking based photopolymerization systems.     

Investigating polymer crystallization by time-dependent light scattering: a direct approach in the data analysis applied for s-polypropylene

We developed a procedure for a direct evaluation of light scattering patterns registered during an isothermal crystallization of s-polypropylene. Analysis is based on the determination of three parameters of the scattering curve for both, polarized and depolarized measuring conditions: (i) the forward scattering intensity I(q→0) (ii) the width Δq of the intensity distribution (iii) the integral intensity in the registration plane, Q₂. We derive equations for these parameters and relate them to the size and the inner structure of the hedrites which develop in s-polypropylene during a crystallization.     

Photopolymerization kinetics of poly(acrylate)-clay composites using polymerizable surfactants

Photopolymerization kinetics of polymer-clay nanocomposite systems utilizing polymerizable quaternary ammonium surfactants as dispersants were systematically investigated to determine the effects of surfactant type and clay morphology on polymerization behavior. For these studies, either polymerizable surfactants were mixed into a clay-monomer system or the surfactants were ionically anchored to clay surfaces and added to the monomer for in situ photopolymerization. Higher photopolymerization rates are observed with increasing polymerizable surfactant concentration, while no significant change or decreases in polymerization rate occur with incorporation of non-polymerizable surfactants. The higher rates observed for polymerizable surfactant systems are due to lower apparent termination rate parameters stemming from immobilization of the surfactants. For clay that is modified with ionically bonded quaternary ammonium surfactants, polymerization rates decrease in both polymerizable and non-polymerizable organoclay systems with increasing concentration, but this decrease is much smaller when polymerizable organoclays are utilized. For the same organoclay concentration, higher polymerization rates and double bond conversions result with increasing polymerizable surfactant concentration via cation exchange. Significant increases in polymerization rate also occur with increasing degree of clay exfoliation.     

In-line monitoring of the conversion in photopolymerized acrylate coatings on polymer foils using NIR spectroscopy

Near-infrared (NIR) reflection spectroscopy was used to monitor the conversion of double bonds in acrylate coatings after irradiation with UV light or electron beams. Quantitative analysis of the spectroscopic data was performed either with a chemometric method on the basis of the PLS algorithm or according to the Beer-Lambert law. FTIR spectroscopy was used for calibration. In-line monitoring of the conversion in pilot-scale was carried out on clear and pigmented coatings, which were applied to polymer foils or paper by roll coating. Useful data were obtained from layers with a thickness from 4 g/m² upwards and at line speeds of at least up to 120 m/min. It was shown that any change of the irradiation dose or other parameters such as inertization leads to an immediate response in the conversion record. Similar investigations were also performed on layers of UV-curable adhesives on the basis of acrylic hot-melts.     

Study of special cases where the enhanced photocatalytic activities of Pt/TiO2 vanish under low light intensity

Surface platinized TiO₂ (Pt/TiO₂) has been widely used and investigated but their properties are yet to be understood fully. Although it is known that the Pt effects depend on many experimental parameters and the kind of substrates, this study newly finds that the Pt effects could be also influenced by the light intensity. As for the photocatalytic degradation of trichloroethylene (TCE), the Pt effect was positive at high light intensity but was negative at low light intensity. A similar behavior was also observed in the photocurrent collection in the Pt/TiO₂ suspension with polyoxometalate (POM: PW₁₂O₄₀³⁻) used as an electron shuttle. The photocurrent collection in the Pt/TiO₂ suspension was less efficient than in TiO₂ suspension when the light intensity was low. Such abnormal light intensity-dependent behaviors were not observed in the photocatalytic degradation of dichloroacetate on Pt/TiO₂ and the Fe³⁺-mediated photocurrent collection in the Pt/TiO₂ suspension. It is proposed that the photochemical interactions between the Pt surface and reactive intermediates (TCE radical anions and reduced POM anions) induce a null reaction favorably at low light intensity condition.     

Visible light induced photopolymerization: speeding up the rate of polymerization by using co-initiators in dye/amine photoinitiating systems

The activity of six newly designed three-component systems (containing a dye, an amine and a triazine derivative) for the initiation of the photopolymerization of multifunctional acrylates under visible light has been evaluated. The selection of the dyes was based on thermodynamic considerations. A discussion of the photochemical reactivity of these systems reveals the role played by thermodynamics and outlines different aspects concerned with kinetics.     

Time dependent light attenuation measurements used in studies of the kinetics of polymer crystallization

Results obtained for different samples of s-polypropylene and poly (ethylene-co-octene) demonstrated the usefulness of light attenuation measurements in investigations of polymer crystallization. The earlier stages with separated growing spherulites fall in the range of Rayleigh-Debye-Gans scattering. Known relationships describing the dependence of the linear attenuation coefficient on the radius and the index of refraction of the spherulite can be applied in evaluations. The sensitivity of attenuation measurements is higher than that of conventional tools.     

Synthesis, formulation, and characterization of siloxane–polyurethane coatings for underwater marine applications using combinatorial high-throughput experimentation

Crosslinked siloxane–polyurethane coatings were designed, synthesized, formulated, applied, and characterized using combinatorial high-throughput experimentation and eight coatings were selected as candidates for further characterization. First, 72 novel hydroxyalkyl carbamate and dihydroxyalkyl carbamate-terminated poly(dimethylsiloxane) (PDMS) oligomers and their carbamate-linked block copolymers with poly(ε-caprolactone) (PCL) were synthesized using a high-throughput synthesis system. These PDMS oligomers and block copolymers were characterized for their molecular weight using high-throughput Gel Permeation Chromatography (Rapid-GPC). The 72 oligomers were then incorporated into siloxane–polyurethane formulations at four different levels resulting in 288 coatings. After initial screening of these 288 coatings, eight coatings were selected for further characterization. Differential scanning calorimetry, dynamic mechanical analysis, X-ray photoelectron spectroscopy and surface energy analysis demonstrate the presence of PDMS on the surface with a polyurethane underlayer. Pseudo-barnacle adhesion and the attachment strength of reattached live barnacles (Balanus amphitrite) were in good agreement. Out of the eight coatings that were down-selected, two coatings performed well in algal (Ulva), bacterial (Cytophaga lytica, Halomonas pacifica), and barnacle (Balanus amphitrite) laboratory screening assays and are potential candidates for ocean testing. This paper was awarded Second Place in the 2006 Roon Awards competition, held as part of the FutureCoat! conference, sponsored by the Federation of Societies for Coatings Technology, in New Orleans, LA, on November 1-3, 2006.     

Fabrication of c-axis oriented hydroxyapatite ceramics in a rotating high magnetic field using photopolymerization

C-axis oriented hydroxyapatite (HAp) was prepared by colloidal processing using a photopolymerization reaction in a rotating magnetic field with a UV-curable binder as the solvent. This technique achieved a short processing time of 150 s in a magnetic field as a result of rapid solidification induced by the photopolymerization. The slight difference in refractive index between the HAp material and UV curable resin allowed the fabrication of 1.6 mm thick green compacts. The oriented structure in the compact was maintained from the surface down to a depth of 700 μm, but was randomized at depths of 700 μm and beyond. The orientation degree was retained after sintering at 1250 °C, and the relative density of the compact was approximately 97 %. This technique can be effectively utilized for the manufacture of high-performance biomaterials.     

One-step conversion of syngas to light olefins over bifunctional metal-zeolite catalyst

Light olefins(C_2–C_4) are fundamental building blocks for the manufacture of polymers, chemical intermediates,and solvents. In this work, we realized a composite catalyst, comprising Mn_xZr _yoxides and SAPO-34 zeolite,which can convert syngas(CO + H_2) into light olefins. Mn_xZr_yoxide catalysts with different Mn/Zr molar ratios were facilely prepared using the coprecipitation method prior to physical mixing with SAPO-34 zeolite. The redox properties, surface morphology, electronic state, crystal structure, and chemical elemental composition of the catalysts were examined using H_2-TPR, SEM, XPS, XRD, and EDS techniques, respectively. Tandem reactions involved activation of CO and subsequent hydrogenation over the metal oxide catalyst, producing methanol and dimethyl ether as the main reaction intermediates, which then migrated onto SAPO-34 zeolite for light olefins synthesis. Effects of temperature, pressure and reactant gas flow rate on CO conversion and light olefins selectivity were investigated in detail. The Mn_1Zr_2/SAPO-34 catalyst(Mn/Zr ratio of 1:2) attained a CO conversion of 10.8% and light olefins selectivity of 60.7%, at an optimized temperature, pressure and GHSV of 380 °C, 3MPa and 3000 h~(-1) respectively. These findings open avenues to exploit other metal oxides with CO activation capabilities for a more efficient syngas conversion and product selectivity.     

Effect of photoinitiator segregation on polymerization kinetics in lyotropic liquid crystals

Through photopolymerization lyotropic liquid crystalline (LLC) phases may be templated onto organic polymers to yield highly complex nanostructures. In order to understand the unique polymerization behavior controlling structural development in LLC media, the polymerization kinetics in these systems have been studied using several commercially available photoinitiators. Although monomer segregation and diffusional restrictions largely govern the kinetics in these systems, the initiation may also be influenced by changing LLC order and composition. Nonpolar monomers, which partition to the oil soluble domains of the LLC phase typically display the fastest rate of polymerization in micellar aggregates. The rate decreases in phases with larger nonpolar domains due to decreasing localized double bond concentration. Polar monomers exhibit the opposite behavior. However, the segregation of photoinitiator may contribute to significantly different trends in polymerization behavior. Relatively mobile initiators, displaying favorable interaction with water, yield a trend in polymerization that is governed primarily by monomer and diffusional effects. When bulkier, hydrophobic initiators are used, the polymerization appears much less dependent on these effects. Rather than the decreasing rate usually observed at higher surfactant concentrations, polymerization of oil soluble monomers with the less mobile initiators shows the opposite trend of increasing rate at higher surfactant concentration. This behavior likely results from increasing initiator efficiency of the bulky, hydrophobic initiator in the surfactant rich environment.     

Adaptation of high-throughput screening in drug discovery-toxicological screening tests

High-throughput screening (HTS) is one of the newest techniques used in drug design and may be applied in biological and chemical sciences. This method, due to utilization of robots, detectors and software that regulate the whole process, enables a series of analyses of chemical compounds to be conducted in a short time and the affinity of biological structures which is often related to toxicity to be defined. Since 2008 we have implemented the automation of this technique and as a consequence, the possibility to examine 100,000 compounds per day. The HTS method is more frequently utilized in conjunction with analytical techniques such as NMR or coupled methods e.g., LC-MS/MS. Series of studies enable the establishment of the rate of affinity for targets or the level of toxicity. Moreover, researches are conducted concerning conjugation of nanoparticles with drugs and the determination of the toxicity of such structures. For these purposes there are frequently used cell lines. Due to the miniaturization of all systems, it is possible to examine the compound's toxicity having only 1-3 mg of this compound. Determination of cytotoxicity in this way leads to a significant decrease in the expenditure and to a reduction in the length of the study.     

Reaction kinetics of rye straw for thermnochemical conversion

Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were conducted on two common types of rye straws (Danko and Kustro) at a heating rate of 20°C/min in an oxidizing atmosphere (15% oxygen and 85% nitrogen, by volume) between ambient temperature and 700°C. The two step nature of the TGA curves and the dual peak characteristics of the DTA curves showed that rye straw had two distinct reaction zones. The initial degradation temperatures, the residual mass at 700°C, the thermal degradation rates in the first and second reaction zones and the kinetic parameters of each reaction zone (order of reaction, activation energy and pre-exponential factor) were determined. Higher thermal degradation rates were observed in the first reaction zone as compared to those in the second reaction zone.     

Desulfurization in a plate-type gas-lift photobioreactor using light emitting diodes

Hydrogen sulfide gas was removed in a 2-dimensional gas-lift reactor by the photosynthetic microorganismChlorobium thiosulfatophilum using light emitting diodes (LEDs) as a light source. LEDs saved light energy by 99% compared with the incandescent light source. The plate-type gas-lift reactor removed hydrogen sulfide five times better per unit mg of protein, and performed two times better in the maximum performance per unit luminous flux, compared with cylindrical fermentors.     

Photocurable ceramic slurry using solid camphor as novel diluent for conventional digital light processing (DLP) process

This study presents the utility of solid camphor as a novel type of diluent for the preparation of photocurable ceramic slurries with sufficiently low viscosity at high solid loading (48 vol%), which can be applicable for the conventional digital light processing (DLP) process. The camphor addition remarkably decreased the viscosity of calcium phosphate (CaP) ceramic slurries without affecting their photopolymerization behavior. This approach could effectively mitigate the clogging of pores with residual slurries, and thus the porous structure of porous CaP scaffolds with 3D channels could be tightly controlled. Furthermore, the high densification of CaP frameworks after sintering at 1250 °C for 3 h could be achieved owing to the use of the high solid loading in the CaP slurry. The porous CaP scaffolds produced displayed high compressive strength (˜ 23.8 MPa) and modulus (˜ 276 MPa) at a high porosity of ˜ 50.6 vol%.     

Using a new approach to analyze a depth profile of double bond conversion in model formulations

A new approach of analyzing the depth profile of double bond conversion as a function of film depth has been studied. By using a combination of statistical calculation and traditional FTIR, a new approach to analyze the depth profile of conversion “layer by layer” in the characterization of photopolymerization was explored. Utilizing a formula (X₁ + X₂ +  + X_n)/n = average conversion, n = 1, 2, 3, n is a number of layers (μm), an average conversion of any 5 μm depth could be calculated from the prior 5 μm conversion and the total average conversion. More detailed information of photopolymerization, such as the depth profile of conversion and a difference in conversion between the top 5 μm and the bottom 5 μm in a 25 μm film as a function of film depth, was obtained. This investigation was accomplished using a variation of film depth, non-photo bleaching photo initiator [PhI] as well as the concentration of PhIs in the presence of air and in the absence of air. Results of analyzing double bond conversion between traditional FTIR and the new approach (statistical calculation/FTIR) were compared.     

扁管换热器内纵向涡强度与换热强度对应关系

纵向涡强化传热技术在管翅式换热器中得到了广泛的应用。但是一直以来对纵向涡强化传热的研究主要停留在涡产生器结构参数及布置方式对换热的影响方面,文献对纵向涡强度与换热强度之间定量关系的研究鲜有报道。建立了采用纵向涡强化传热的扁管管翅换热器数值模型,采用二次流强度参数Se分析了翅片及涡产生器结构参数变化时,通道内纵向涡强度与换热强度之间的定量关系;并定量分析了通道中涡产生器引起的纵向涡强度增量与传热强化量之间的定量关系。结果表明:翅片及涡产生器结构参数变化时,Nu、Se与Re之间,以及阻力系数f与Re及Se之间均不存在定量对应关系,但Se与Nu以及ΔSe与ΔNu之间存在对应关系。这表明,在布置有纵向涡产生器的扁管管翅换热器翅侧通道内,纵向涡强度决定了通道内的换热强度。     

Photopolymerization kinetics of bis-aromatic based urethane acrylate macromonomers in the presence of reactive diluent

The present work deals with the photopolymerization of bis-aromatic based urethane acrylate macromonomers in the presence of excess end capping agent as reactive diluent and estimation of their kinetic parameters. Formulations were made by independently homogenizing the macromonomers with photoinitiators of three different classes. Three different compositions of photoinitiators were used to study the effect of concentration of photoinitiator on cure kinetics. These compositions obtained were tested for photo curing performance using photo DSC under polychromatic radiation. The heat flows against time were recorded for all formulations under isothermal condition and the rates of polymerization, peak maximum times as well as the percentage conversions were estimated. It was observed that due to a longer timescale for reaction diffusion, formulations with macromonomer containing propoxylated backbone showed higher conversions than the corresponding ethoxylated analogue. The photopolymerization and kinetic estimations of the formulations including evaluation of kinetic model are discussed.