A reevaluation of forces measured across thin polymer films : nonequillibrium and pinning effects

We have measured forces between molecularly smooth solid surfaces separated by thin films of molten polydimethylsiloxane. We show that a long-range repulsion reported in earlier work is not an equilibrium force, but can be attributed to viscous drag effects. Consistent with previous results, the viscosity of the film can be modeled by assuming that a layer of polymer molecules is immobilized or &lsquo;&lsquo;pinned&rsquo;&rsquo; at each surface for a time longer than the time scale of the measurements. We propose that this pinning is a result of entanglement-like effects in the vicinity of a wall. <br /

Detection and elimination of cellular bottlenecks in protein-producing yeasts

Yeasts are efficient cell factories and are commonly used for the production of recombinant proteins for biopharmaceutical and industrial purposes. For such products high levels of correctly folded proteins are needed, which sometimes requires improvement and engineering of the expression system. The article summarizes major breakthroughs that led to the efficient use of yeasts as production platforms and reviews bottlenecks occurring during protein production. Special focus is given to the metabolic impact of protein production. Furthermore, strategies that were shown to enhance secretion of recombinant proteins in different yeast species are presented

Static and kinetic friction of strongly confined polymer films under shear

In the present work, we investigate the dependence of relaxational processes in strongly confined polymer liquids as a function of the molecular mass and of the confining film thickness, both theoretically and experimentally. A qualitative agreement is observed between the theoretical predictions and experimental findings. On the basis of the proposed theory and experimental data, we estimate the relaxation time of the polymer segments in the first surface layer and far away from the surfaces as well as the maximum stress relaxation time