Luis E. Sánchez-Diáz

Scattering functions of yolk–shell particles

The single-particle small-angle scattering properties of the yolk–shell particle, a new type of core–shell particle with a mobile core within the hosting shell, are systematically investigated. The Debye spatial autocorrelation function, pair distance distribution function and intraparticle structure factor (form factor) are calculated and compared with the corresponding scattering functions of reference systems of hard sphere and concentric core–shell particles with identical sizes. On the basis of these theoretical calculations, it is found that the broken centrosymmetry, originating from the mobility of the trapped yolk, results in an imaginary scattering amplitude. As a result, it contributes an additional destructive interference term which smears certain features present in the scattering functions of the reference systems. These theoretical models raise the prospect of jointly using small-angle neutron and X-ray scattering techniques to quantitatively determine the structural characteristics of yolk–shell particles.

A scattering function of star polymers including excluded volume effects

In this work we present a new model for the form factor of a star polymer consisting of self-avoiding branches. This new model incorporates excluded volume effects and is derived from the two point correlation function for a star polymer.. We compare this model to small angle neutron scattering (SANS) measurements from polystyrene (PS) stars immersed in a good solvent, tetrahydrofuran (THF). It is shown that this model provides a good description of the scattering signature originating from the excluded volume effect and it explicitly elucidates the connection between the global conformation of a star polymer and the local stiffness of its constituent branch.

Phase behavior under a noncentrosymmetric interaction: shifted-charge colloids investigated by Monte Carlo simulation.

Using Monte Carlo simulations, we investigate the structural characteristics of an interacting hard-sphere system with shifted charge to elucidate the effect of the noncentrosymmetric interaction on its phase behavior. Two different phase transitions are identified for this model system. With increasing volume fraction, an abrupt liquid-to-crystal transition first occurs at a significantly lower volume fraction than in centrosymmetrically charged systems. This is due to the stronger effective interparticle repulsion caused by the additional charge anisotropy. Moreover, within the crystal state at higher volume fraction, the system further undergoes a continuous disorder-to-order transition with respect to charge orientation. Detailed analyses in this work disclose the nature of these transitions, and orientation fluctuation can cause noncentrosymmetric unit cells. The dependence of crystal formation and orientational ordering on temperature was also examined. These findings indicate that the noncentrosymmetric interaction in this work results in additional freedoms to fine-tune the phase diagram and increase the functionalities of materials. Moreover, these model studies are essential to advance the future understanding regarding the fundamental physiochemical properties of novel Janus colloidal particles and protein crystallization conditions.