In the first part of this talk I will give a very brief overview on what questions on glasses can be addressed by means of computer simulations. As a result I will argue why the response to the above question is "No". In the second part of the talk I will discuss a method, called "parallel tempering", that allows to overcome one of the big issues encountered in the simulation of glasses, the equilibration at low fictive temperatures.

We use large scale computer simulations of a glass-forming liquid in which a fraction c of the particles has been permanently pinned. We find that the relaxation dynamics shows an exponential dependence on c. This result can be rationalized by assuming that the configurational entropy of the pinned liquid decreases linearly upon increasing of c. This behavior is discussed in the context of thermodynamic theories for the glass transition, notably the Adam-Gibbs picture and the random first order transition theory. For intermediate and low temperatures we find that the slowing down of the dynamics due to the pinning saturates and that the cooperativity decreases with increasing c, results which indicate that in glass-forming liquids there is a dynamic crossover at which the shape of the relaxing entities changes.

Single-walled carbon nanotubes are one-dimensional nanostructures where the Coulomb interactions between charge carriers are strongly enhanced compared to systems of higher dimensionality. This results in an electron-hole bound state -the so-called exciton- with a binding energy of the order of one third of the bandgap, which controls the SWNTs optical properties. I will review the importance of the exciton-exciton interactions in SWNTs in the light of the exciton recombination dynamics, the excitonic collision broadening, and the biexciton.

Single-walled carbon nanotubes are one-dimensional nanostructures where the Coulomb interactions between charge carriers are strongly enhanced compared to systems of higher dimensionality. This results in an electron-hole bound state -the so-called exciton- with a binding energy of the order of one third of the bandgap, which controls the SWNTs optical properties. I will review the importance of the exciton-exciton interactions in SWNTs in the light of the exciton recombination dynamics, the excitonic collision broadening, and the biexciton.

We demonstrate the instability of the free surface of a soft elastic solid facing downwards. Experiments are carried out using a gel of constant density rho, shear modulus mu, put in a rigid cylindrical dish of depth h. When turned upside down, the free surface of the gel undergoes a normal outgoing acceleration g. It remains perfectly flat for rhogh/mu

The talk is divided into two parts. First, I will show some experimental results obtained in my group on the Brownian dynamics of micrometric spherical silica colloids trapped at a planar air-water interface. The particle contact angle is finely tuned in the range 30°-140° by surface treatments and measured in situ at 0.5° resolution by a homemade Vertical Scanning Interferometer. Translational diffusion coefficients of colloids trapped at the water interface are obtained by particle tracking video-microscopy. Counter-intuitively, the diffusion coefficient decreases when the contact angle increases (i.e. when particles are less immersed in water and more in air). To explain the slowing down of the diffusion, I will discuss the effects of the hydrodynamic friction together with an extra friction term originating from the contact line fluctuations. The second part of the talk deals with the active motion of Janus colloids. Here, we have investigated the motion of self-propelled colloids at the air-water interface, where particles have been confined. The interplay of colloid’s self-propulsion, given by an asymmetric catalytic reaction occurring on the colloid, and interfacial frictions controls the direction and the speed of the movement. Two dimensional motion of micron-sized Silica-Platinum Janus colloids have been experimentally measured by particle tracking video-microscopy under increasing concentration of the catalytic fuel, i.e. H2O2,. Compared to previous bulk investigations, we observe a dramatic enhancement both of the length of trajectories travelled by particles and the speed. The slowing down of the rotational diffusion at the interface, also measured experimentally, plays a pivotal role in the control and enhancement of active motion.