A controversy about chance and the origins of life: thermodynamicist Ilya Prigogine replies to molecular biologist Jacques Monod.

The ancient, interlinked questions about the role of chance in the living world and the origins of life, gained new relevance with the development of molecular biology in the twentieth century. In 1970, French molecular biologist Jacques Monod, joint winner of the 1965 Nobel Prize in Physiology or Medicine, devoted a popular book on modern biology and its philosophical implications to these questions, which was quickly translated into English as Chance and Necessity. Nine years later, Belgian thermodynamicist Ilya Prigogine, 1977 winner of the Nobel Prize in Chemistry, published a popular book on the history and philosophy of natural sciences with Belgian philosopher Isabelle Stengers. Translated into English under the title Order out of Chaos and widely discussed, the whole book can be seen as a response to Monod on these biological and philosophical questions. This study will trace this intellectual controversy between two Nobel Prize winners defending two opposing scientific and philosophical visions of the living world, rooted in two different scientific disciplines.

Ligand-receptor interactions in chains of colloids: when reactions are limited by rotational diffusion.

We discuss the theory of ligand receptor reactions between two freely rotating colloids in close proximity to one other. Such reactions, limited by rotational diffusion, arise in magnetic bead suspensions where the beads are driven into close contact by an applied magnetic field as they align in chainlike structures. By a combination of reaction-diffusion theory, numerical simulations, and heuristic arguments, we compute the time required for a reaction to occur in a number of experimentally relevant situations. We find in all cases that the time required for a reaction to occur is larger than the characteristic rotation time of the diffusion motion tau(rot). When the colloids carry one ligand only and a number n of receptors, we find that the reaction time is, in units of tau(rot), a function simply of n and of the relative surface alpha occupied by one reaction patch alpha = pirC2/(4pir2), where rC is the ligand receptor capture radius and r is the radius of the colloid.

Effective exponents in the long-range critical wetting of alkanes on aqueous substrates.

Alkanes on water show a two-stage wetting transition. Upon raising the temperature, a first-order transition from a molecularly thin to a mesoscopically thick liquid film is followed by a continuous divergence of the film thickness. This second transition is brought about by long-range interactions between adsorbate and substrate and is, therefore, referred to as long-range critical wetting. The divergence of the film thickness is theoretically expected to occur according to the asymptotic power law l approximately (Tw,c-T)betas, with betas=-1. This value has indeed been found for pentane on pure water; however, for hexane on salt solutions of different concentrations, betas=-0.73 was found for a 1.5M solution of NaCl and betas=-0.57 for a 2.5M salt solution. In addition, for hexane on a 2.5M solution of NaCl, an exponent of alphas=0.1 was found from contact-angle measurements, differing greatly from the theoretically expected value of alphas=-1. Using Dzyaloshinskii-Lifshitz-Pitaevskii theory, we calculate effective local exponents in order to explain the experimental findings. Taking into account the uncertainty of the exponents derived from experiments as well as the temperature range in which the measurements were carried out, a reasonable agreement between theory and experiment is found, thereby providing a consistent approach to resolving the apparently anomalous behavior of hexane on brine. The experimentally observed exponents betas=-0.57 and alphas=0.1 are also compatible with a long-range tricritical wetting transition, which is characterized by betas=-1/2 and alphas=0; this alternative explanation of the experimental findings is neither supported nor completely ruled out by our calculations.

Polymer bridging probed by magnetic colloids.

Superparamagnetic particles offer a new way to probe the kinetics of adhesive processes. Two different scenarios of physical adhesion are studied. The thermal activation of van der Waals adhesion is well described by an Arrhenius model. In contrast, it is necessary to go beyond the Arrhenius description to understand the thermal activation of bridging between colloidal particles by a polymer at equilibrium adsorbance. We show that polymer bridging requires some removal of adsorbed polymer and is strongly influenced by the proximity of a glass transition within the adsorbed polymer.

Long-range critical wetting: observation of a critical end point.

Alkanes deposited on aqueous substrates exhibit two different types of wetting behavior: alternatively to the usual first-order wetting transition, a sequential-wetting scenario of a long-range critical wetting transition preceded by a first-order thin-thick transition may be observed. Here, we present the first successful experimental attempt to locate the transition point between the standard first-order wetting and the long-range critical wetting: a critical end point, observed in a mixture of pentane and hexane which is deposited on an aqueous solution of glucose. Furthermore, we present the first direct measurement of the contact angle in the intermediate wetting state (frustrated-complete wetting) in the sequential-wetting scenario of hexane on brine and compare to theoretical predictions.

From shear thickening to shear-induced jamming.

We show that applying shear to a suspension may lead to either thickening or permanent jamming, depending on the volume fraction of the considered suspension. Interpreting measurements of conductivity under shear, we invoke a dynamical structural transition to explain the origin of shear thickening in suspensions of non-Brownian particles. We finally suggest that shear thickening and shear-induced jamming be regarded as two consequences of this dynamical structural transition.