The mechanical response of disordered solids is governed by nonaffine displacements which are controlled by the microscopic atomic-level structure of the solid.
While the atoms in a liquid move fast and can explore all the available space, atoms in the glass (amorphous solid) are confined to a "cage" made by their nearest neighbours, and one needs to spend a lot more energy to displace them from their "cages". However, the random arrangement has a subtle implication for the rigidity of glass with respect to crystal, and for the way a glass deforms, or moves, when you apply a force on it. Upon applying a force on the crystal, every atom receives the same forces from its neighbours, but these forces cancel to zero because every atom has a mirror-image of itself across the center which is exerting the same force in the opposite direction. These forces then cancel themselves out completely in a crystal, but they cannot in a glass because there is no mirror-image atoms to cancel the force exerted by the neighbours. More details in A. Zaccone & E. Scossa-Romano, Phys. Rev. B 83, 184205 (2011). In this paper we provide the microscopic derivation of the scaling G~(z-2d) found in jammed packings, from the first principles analysis of nonaffine deformations.
Based on the nonaffine
mechanical response, a mathematical theory
of the glass transition in terms of macroscopic behavior can be formulated. The theory predicts the elastic constanst using structural data as input (e.g. the structure factor from scattering experiments).
More details in
A. Zaccone & E.M. Terentjev, Phys. Rev. Lett. 110, 178002 (2013).
We are interested in developing a theoretical framework to link the level of single protein conformation with the level of aggregate morphology and growth.
Several proteins may aggregate in superstructures as they undergo conformational changes (unfolding or partial unfolding). These superstructures are linked with diseases such as Alzheimer's, and they typically occur in fibrillar (right), spherulitic (center), or amorphous (left) form. Our goal is to mathematically predict these different morphologies depending on molecular level (single protein) processes in solution, through a multi-fractal approach first proposed in
V. Fodera', A. Zaccone, M. Lattuada, A. Donald,
Phys. Rev. Lett. 111, 108105 (2013).
We are extending Mott's theory of electron transport in disordered media to account for as much as possible of the morphology of polymer materials on the charge transport kinetics.
Conjugated polymers are relatively novel semiconductor materials which can be used for energy conversion devices. They bring several benefits, including low manufacturing costs. In order to optimize the device performance, it is essential to understand the charge transport physics in polymer materials where crystalline domains coexists with large amorphous regions. Electron transport is very different in the two domains, and the mobility is controlled by structural disorder to a large extent. Our first goal is to predict how the mobility depends on the molecular weight of the polymer which is the most important tunable parameter to optimize electron transport in the device.
Intensification of chemical processes &
We are developing strategies to enable the implementation of industrial chemical reactions in microfluidic reactors. In particular, we focus on understanding instabilities due to uncontrolled aggregation phenomena in liquid-solid microreactors.
Hartman et al.
Org. Process Res. Dev. (2010)
Zaccone et al.
Phys. Rev. Lett. 2011
In the majority of chemical processes carried out in industry, reactions occur in liquid phase in the presence of large or colloidal molecules or other dispersed solid phases, catalysts etc. Moreover, in the reactions relevant to the production of fine chemicals, by-products in solid form (e.g. inorganic salts) are formed. In microreactors under continuous flow, these dispersed solid particles tend to aggregate in an uncontrolled way, leading to a well documented instability: the effective viscosity of the system diverges abruptly. This instability leads to the reactor and plant shut-down with huge costs which makes microreactors still not a viable technology for large scale production. We are working towards a bottom-up approach to predict the occurrence of this instability. The result of our work will contribute towards the industrial implementation of microreactors which are a much more sustainable and environmentally technology compared to standard chemical reactors used at present.
Colloids & radiation scattering techniques
We recently contributed a method, based on statistical mechanics and light scattering, to quantify the attraction energy of bonds between colloidal particles. The method has been succesfully applied to thermosenstive nanoparticles to estimate the hydrophobic attraction energy depending on temperature.