Development of a coordination chemistry-based approach for functional supramolecular structures

The weak-link approach (WLA) to supramolecular assemblies allows for the design of multimetallic two- and three-dimensional arrays, host-guest architectures, sensors, catalysts, switches, and signal amplification devices. This Account describes the course of our investigations in this area beginning with the development of a chemical tool kit of building blocks consisting of multiple metals and ligands. These building blocks can be rationally mixed and matched to provide structures with a wide range of properties that have been used to develop functional supramolecular architectures, including chemical sensors and allosteric catalysts.     

Kinetics of Mullite Grain Growth in Alumino Silicate Fibers

Grain growth kinetics of mullite in laboratory-produced and commercial (3M-Nextel 720) alumino silicate fibers was analyzed in the temperature range between 1500° and 1700°C. The lab fibers consist of mullite plus traces of α-alumina, while the phase content of the commercial Nextel 720 fibers is about 60 wt% mullite plus 40 wt%α-alumina. The temperature-induced grain coarsening of mullite follows the empirical law D ^{1/ n} − D ₀^{1/ n} = kt . Two different temperature regimes can be distinguished with respect to the grain growth exponents: above 1600°C the growth exponent is ≈1/3, while below 1600°C the growth exponent of ≈1/12 is exceptionally low. Laboratory-produced and commercial fibers show almost identical mullite grain growth kinetics.     

Liquid Phase Sintering of Alumina, II. Penetration of Liquid Phase into Model Microstructures

Alumina preforms containing artificial pores were sintered at 1630°C in air and vacuum. Glass penetration into the alumina preforms was conducted at 1600°C in air. It was found that the trapped gases in alumina preforms sintered in air caused the random and incomplete filling of the smaller and larger artificial pores. In contrast, the pores in the alumina preform sintered in vacuum were completely filled during glass penetration.     

Initial Attempt to Characterize Oxidation Damage in C/Sic Composite Using an Ultrasonic Guided Wave Method

An ultrasonic guided wave scan system was used to non-destructively monitor damage over time and position in a C/enhanced SiC sample that was creep tested to failure at 1200°C in air at a stress of 69 MPa (10 ksi). The use of the guided wave scan system for mapping evolving oxidation profiles (via porosity gradients resulting from oxidation) along the sample length and predicting failure location was explored. The creep-rupture tests were interrupted for ultrasonic evaluation every two hours until failure at ∼17.5 cumulative hours.     

Mineral admixtures in mortars: Quantification of the physical effects of inert materials on short-term hydration

This work is the second part of an overall project, the aim of which is the development of general mix design rules for concrete containing different kinds of mineral admixtures. The first part presented the separation of the different physical effects responsible for changes in cement hydration when chemically inert quartz powders are used in mortars. This second part describes the development of an empirical model, based on semiadiabatic calorimetry measurements, which leads to the quantification of the enhancement of cement hydration due to the heterogeneous nucleation effect at short hydration times. Experimental results show that not all the admixture particles participate in the heterogeneous nucleation process. Consequently, the concept of efficient surface S_eff is introduced in the model. S_eff is the total admixture surface S (m² of mineral admixture/kg of cement) weighted by a function ξ(p). The efficiency function ξ(p) depends only on the replacement rate p and is independent of time, fineness and type of mineral admixture used. It decreases from 1 to 0: Low replacement rates give an efficiency value near 1, which means that all admixture particles enhance the hydration process. An efficiency value near 0 is obtained for high replacement rates, which indicates that, from the hydration point of view, an excess of inert powder does not lead to an increase in the amount of hydrates compared with the reference mortar without mineral admixture. The empirical model, which is mainly related to the specific surface area of the admixtures, quantifies the variation of the degree of hydration induced by the use of inert mineral admixtures. One application of the model, coupled with Powers' law, is the prediction of the short-term compressive strength of mortars.     

A critical assessment of the Jastrzebski interface condition for the capillary flow of pastes, foams and polymers

This paper presents a review of unusual apparent slip effects in capillary flow rheometry. Many cases of paste, foam and polymer capillary flow have been reported where the classic analysis of Mooney has yielded unviable flow curves and apparent slip velocities; often the analysis of Jastrzebski has been used as an alternative and sometimes as the analysis of first choice. It is shown that the recently developed Tikhonov regularization method of Mooney analysis can be used to yield viable results for some of the cases where the classic Mooney analysis could not. All of the problematic foam and polymer results found in the literature were resolved, as well as some of the problematic paste results. It is shown that the use of the Jastrzebski interface condition, relating apparent slip to capillary radius, yields incorrect flow curves and apparent slip velocities. It is proposed that further research is required to understand the capillary flow of paste which does not conform to the classic Mooney analysis. In the absence of any physical grounding for the Jastrzebski interface condition, it is recommended that it should no longer be used.     

神经酰胺脂质体——含角质层脂质膜的脂质体

角质层的渗透屏障大多是由饱和脂质如神经酰胺、胆固醇和游离脂肪酸组成。它是物质交换的有效阻隔并防止皮肤干燥。神经酰胺脂质体(Cerasomes)是一种脂质体,它的膜是由最重要的角质层脂质组成的。神经酰胺脂质体作为类皮肤膜的来源,它能加快受损屏障层的再生、降低皮肤刺激,并且它还提供了将角质层脂质应用于化妆品中简单而有效的途径。     

Enantioselective Platinum‐Catalyzed Silicon‐Boron Addition to 1,3‐Cyclohexadiene

Silaboration of 1,3‐cyclohexadiene in the presence of Pt(acac)₂, DIBALH, and a phosphoramidite prepared from (S)‐1,1′‐bi‐2‐naphthol and diisopropylamine led to (1R,4S)‐1‐(dimethylphenylsilyl)‐4‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐2‐cyclohexene with 70% ee. Chiral catalysts based on Ni gave no or essentially racemic product, whereas complexes containing Pd were inactive.     

Biocompatible polymer blends: Effects of physical processing on the molecular interaction of poly(vinyl alcohol) and poly(vinyl pyrrolidone)

Blending is a very effective method for manufacturing new polymeric materials; however, the process used to combine two polymers can influence the physicochemical properties of the final product. As such, the aim of this study was to investigate how the rapid removal of a solvent from a composite by the spray drying of partially hydrolyzed poly(vinyl alcohol) (PVA)/poly(vinyl pyrrolidone) (PVP) altered the solid‐state properties of the material compared to casting the blend within a film. Although thermal analysis showed that PVP acted as a plasticizer, reducing the melting point of PVA, spray drying the product rather than using a film‐casting procedure improved its solid‐state stability (increasing the glass transition) and resulted in the formation of a second crystalline phase within the material. Spectroscopic studies suggested that the manufacturing‐induced variance in the solid‐state properties of the PVA/PVP blends originated from structural differences in the composite caused by the processing method employed to form the blend. Although blending should still be considered a viable method of generating novel polymeric material, this study illustrated that through careful manipulation of the actual manufacturing process, the solid‐state properties of the product can be altered. This could open a whole range of novel applications for traditionally used polymer composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2290–2299, 2005     

Influence of diesel particulate filter additives on biodiesel quality

The influence of the diesel particulate filter additives (DPA) SATACEN and EOLYS on biodiesel fuel quality has been evaluated. Both additives significantly affected the oxidation stability of neat biodiesel. The influence on acid values and CFPP was found to be only small. Combination of diesel additives with biodiesel additives like oxidation stability and CFPP improvers led to similar results. Results indicated that DPA also lowered the efficiency of the oxidation stability improver Baynox. Furthermore, the CFPP additives Chimec and Infineum were also prone to have a small influence on biodiesel oxidation stability.