A tool for rapid quenching of elongated polymer melts

In this article, we present a device for rapid quenching of elongated polymer melts. The tool is an accessory to the uniaxial elongational rheometer RME of Meissner and Hostettler. It is intended to be used for microscopic and other investigations of stretched polymers. The device allows us to solidify a polymer melt by pouring liquid nitrogen on it and to cut it at the nearly same instant of time. Then the sample can be easily removed from the stretching apparatus. Solving the heat diffusion equation for a polymer melt, which is cooled by liquid nitrogen, we theoretically estimate the quenching time of this method. To demonstrate that this quenching procedure indeed rapidly cools a polymer melt, the stress birefringence of elongated and subsequently quenched polystyrene melts is measured and the stress-optical coefficient C is determined. The experimental value of the stress-optical coefficient is |C|= 4.65×10⁻⁹ Pa⁻¹, which agrees well with the data in literature. Using this tool for elongation experiments with the RME, polymer melts can be solidified in between approximately 0.2 and 2.0 s, depending on the thickness of the sample.     

Fifteenth International Symposium on Biological and Environmental Reference Materials (BERM-15)

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Some Aspects of Time-Reversal in Chemical Kinetics

Chemical kinetics govern the dynamics of chemical systems leading towards chemical equilibrium. There are several general properties of the dynamics of chemical reactions such as the existence of disparate time scales and the fact that most time scales are dissipative. This causes a transient relaxation to lower dimensional attracting manifolds in composition space. In this work, we discuss this behavior and investigate how a time reversal effects this behavior. For this, both macroscopic chemical systems as well as microscopic chemical systems (elementary reactions) are considered.     

Triggering the Directional Selectivity of a Ring‐Closure Reaction Leads to Pyridoazacarbazoles with Anticancer Properties

We herein describe a facile and versatile synthetic route to the tetracyclic system of 6‐substituted 5,6‐dihydro‐11H‐pyrido[3,2‐i]‐1‐azacarbazoles with promising anticancer properties. These derivatives are built up by an elegant one‐step base‐catalyzed synthetic procedure from commercially available building blocks. One additional step provides the corresponding skeleton hitherto unknown in the literature. The possibility to synthesize a large library of compounds with various substitution patterns utilizing this method underlines the importance of this synthetic procedure.     

Optimum operating conditions for manufacturing ibuprofen tablets coated with polyethylene glycol by melt crystallization process

Journal of Thermal Analysis and Calorimetry - The aim of this work is to apply the melt crystallization technology to manufacture ibuprofen tablets coated with polyethylene glycol in a single step....