335 research outputs found
Protein crystallization in vivo
Protein crystallization in vivo provides some fascinating examples of
biological self-assembly. Here, we provide a selective survey to show the
diversity of functions for which protein crystals are used, and the physical
properties of the crystals thatare exploited. Where known, we emphasize how the
nature of the protein-protein interactions leads to control of the
crystallization behaviour.Comment: 17 pages, 1 figur
On polydispersity and the hard-sphere glass transition
We simulate the dynamics of polydisperse hard spheres at high packing
fractions, , with an experimentally-realistic particle size distribution
(PSD) and other commonly-used PSDs such as gaussian or top hat. We find that
the mode of kinetic arrest depends on the PSD's shape and not only on its
variance. For the experimentally-realistic PSD, the largest particles undergo
an ideal glass transition at while the smallest particles
remain mobile. Such species-specific localisation was previously observed only
in asymmetric binary mixtures. Our findings suggest that the recent observation
of ergodic behavior up to in a hard-sphere system is not
evidence for activated dynamics, but an effect of polydispersity
Evaporation of Concentrated Polymer Solutions is Insensitive to Relative Humidity
A recent theory suggests that the evaporation kinetics of macromolecular solutions is insensitive to the ambient relative humidity (RH) due to the formation of a ‘polarisation layer’ of solutes at the air-solution interface. We confirm this insensitivity up to RH ≈ 80% in the evaporation of polyvinylalcohol solutions from open-ended capillaries. To explain the observed drop in evaporation rate at higher RH, we need to invoke compressive stresses due to interfacial polymer gelation. Moreover, RH-insensitive evaporation sets in earlier than theory predicts, suggesting a further role for a gelled ‘skin’. We discuss the relevance of these observations for respiratory virus transmission via aerosols
Celebrating Soft Matter's 10th Anniversary: Simplicity in complexity – towards a soft matter physics of caramel
Turning a yield-stress calcite suspension into a shear-thickening one by tuning inter-particle friction
We show that a suspension of non-Brownian calcite particles in glycerol-water
mixtures can be tuned continuously from being a yield-stress suspension to a
shear-thickening suspension--without a measurable yield stress--by the addition
of various surfactants. We interpret our results within a recent theoretical
framework that models the rheological effects of stress-dependent constraints
on inter-particle motion. Bare calcite particle suspensions are found to have
finite yield stresses. In these suspensions, frictional contacts that constrain
inter-particle sliding form at an infinitesimal applied stress and remain
thereafter, while adhesive bonds that constrain inter-particle rotation are
broken as the applied stress increases. Adding surfactants reduces the yield
stress of such suspensions. We show that, contrary to the case of surfactant
added to colloidal suspensions, this effect in non-Brownian suspensions is
attributable to the emergence of a finite onset stress for the formation of
frictional contacts. Our data suggest that the magnitude of this onset stress
is set by the strength of surfactant adsorption to the particle surfaces, which
therefore constitutes a new design principle for using surfactants to tune the
rheology of formulations consisting of suspensions of adhesive non-Brownian
particulates.Comment: 8 pages, 7 figure
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