In order to study the effect of surfactants on the adhesive properties, peel measurements were performed with two series of model polymers of ethylhexylmethacrylate (PEHMA), the first prepared by emulsion polymerization with four anionic surfactants, and the second by post-adding the same surfactants to a surfactant-free latex. Cohesive fracture is observed at low peel rates; the peel strength depends on the bulk mechanical properties and is independent of the emulsifier. A transition to another type of separation occurs at higher peel rates, which seems to be an interfacial failure by visual inspection. Surface analytical studies, however, give evidence that this “interfacial” failure is, in fact, a mixed failure, leaving traces of the polymer on the substrate surface. The peel rate at this transition as well as the peel strength at mixed fracture are influenced by the surfactants. Large differences were observed between the four surfactants as well as between both series of polymers, leading to the conclusion that the surfactants have a different mobility within the film. This is also reflected by a different aging behaviour of the films. 相似文献
For better understanding and optimization of multiphase flow in miniaturized devices, micro-computed tomography (μCT) is a promising visualization tool, as it is nondestructive, three-dimensional, and offers a high spatial resolution. Today, computed tomography (CT) is a standard imaging technique. However, using CT in microfluidics is still challenging, since X-ray related artifacts, low phase contrast, and limited spatial resolution complicate the exact localization of interfaces. We apply μCT for the characterization of stationary interfaces in thin capillaries. The entire workflow for imaging stationary interfaces in capillaries, from image acquisition to the analysis of interfaces, is presented. Special emphasis is given to an in-house developed segmentation routine. For demonstration purposes, contact angles of water, liquid polydimethylsiloxane, and air in FEP, glass, and PMMA are determined and the influence of gravity on interface formation is discussed. This work comprises the first steps for a systematic 3D investigation of multiphase flows in capillaries using μCT. 相似文献
Loganin is an iridoid glycoside of interest as both an intermediate in the biosynthesis of indole alkaloids in plants and as a bioactive compound itself. Loganic acid methyltransferase catalyzes the methylation of a monoterpenoid glycoside precursor to produce loganin and demonstrates stereospecificity for the (6S,7R) substrate. We have biochemically characterized this biocatalyst and elucidated the basis for its strict substrate specificity. These studies could help facilitate the design of new classes of monoterpenoid indole alkaloids of pharmaceutical interest. 相似文献
Recent research has demonstrated that biomass density can vary in activated sludge systems, and that this can affect biomass settleability. Other factors related to floc structure are well known to affect settleability, and these can also vary considerably across samples. A new method to isolate density effects on sedimentation was developed and applied based on the addition of commercially available, high and low density microspheres. Density was a linear function of microsphere dose in five full-scale samples, and it was negatively correlated with sludge volume index (SVI) values. Density effects on SVI were similar to previous reports where density varied with biomass polyphosphate content. A new method to calculate water content and floc volume was developed and applied, and water content was inversely correlated with density, polyphosphate, and non-volatile suspended solids. These results suggest microsphere addition may be useful in future studies of biomass sedimentation and other properties. 相似文献
Aqueous dispersions used as binders in low-pigmented solvent-free paint formulations have to cope with the challenge to simultaneously guarantee an excellent film formation and appearance as well as good block resistance and hardness. One strategy to fulfill these contradictory requirements is the employment of multiphase particles.
In this work it is proved that the structure of latex particles, synthesized by a two-stage emulsion polymerization process, can be correlated to the morphology and properties of the dispersion films as well as to the application properties of the corresponding paint films.
Two sets of model dispersions were made. In the first set, the hard/soft ratio was varied, in the second set the amount of the AA. The structure of the particles was determined by TEM, and a morphology map was derived. AFM demonstrated a clear correlation between the particle structure and the morphology of the latex film. Dynamic mechanical analyses verified the presence of two distinct polymers with the hard phase acting as a transparent filler. For the hard/soft series, the properties of the dispersion films such as block resistance, gloss and hardness could be attributed to their structure. A closer look on the block behavior revealed that it can be related to the tack and surface roughness of the dispersion film, but not to its internal strength. Solvent free emulsion gloss paints were formulated, and application tests performed. The properties of the paint films correlated very well with those of the dispersion films. The test results clearly show that dispersions of multiphase particles enable the formulation of solvent free paints with excellent film-forming ability in combination with high block resistance, hardness and gloss. 相似文献
Different procedures for obtaining homology models for P450s are investigated using various sequence alignments sharing various levels of sequence identity with available P450 crystal structures. In this analysis, we have investigated how well homology modeling can reproduce known crystal structures as well as how effectively these homology models can be used to reproduce known ligand-binding modes. Homology models obtained from sequence alignments that discriminate between Class I and Class II P450s are significantly closer to the experimental crystal structures and more closely reproduce known ligand's binding modes, than those obtained using sequence alignments that combine Class I and Class II P450s. The quality of the models is slightly improved by constructing hybrid-structure models that model three of the most variable regions of P450s independently from the rest of the protein: the B region that includes SRS1, the FG region that includes SRS2 and SRS3 and the beta4 region that includes SRS6. 相似文献
Infestation of corn (Zea mays) by corn earworm (Helicoverpa zea) predisposes the plant to infection by Aspergillus fungi and concomitant contamination with the carcinogenic mycotoxin aflatoxin B1 (AFB1). Although effects of ingesting AFB1 are well documented in livestock and humans, the effects on insects that naturally encounter this mycotoxin are not as well defined. Toxicity of AFB1 to different stages of H. zea (first, third, and fifth instars) was evaluated with artificial diets containing varying concentrations. Although not acutely toxic at low concentrations (1−20 ng/g), AFB1 had significant chronic effects, including protracted development, increased mortality, decreased pupation rate, and reduced pupal weight. Sensitivity varied with developmental stage; whereas intermediate concentrations (200 ng/g) caused complete mortality in first instars, this same concentration had no detectable adverse effects on larvae encountering AFB1 in fifth instar. Fifth instars consuming AFB1 at higher concentrations (1 μg/g), however, displayed morphological deformities at pupation. That cytochrome P450 monooxygenases (P450s) are involved in the bioactivation of aflatoxin in this species is evidenced by the effects of piperonyl butoxide (PBO), a known P450 inhibitor, on toxicity; whereas no fourth instars pupated in the presence of 1 μg/g AFB1 in the diet, the presence of 0.1% PBO increased the pupation rate to 71.7%. Pupation rates of both fourth and fifth instars on diets containing 1 μg/g AFB1 also increased significantly in the presence of PBO. Effects of phenobarbital, a P450 inducer, on AFB1 toxicity were less dramatic than those of PBO. Collectively, these findings indicate that, as in many other vertebrates and invertebrates, toxicity of AFB1 to H. zea results from P450-mediated metabolic bioactivation.An erratum to this article can be found at 相似文献