PhD Student
Member of the GRK2516
Group: Dr. Arash Nikoubashman, JGU Physics
Contact: E-mail

Research Project Area C: Supraparticles – Theory
Supraparticles

Drying of colloidal dispersion is an important field of research due to its many practical applications in, e.g., printing, washing and agriculture [1]. A class of engineered materials with increasing scientific interest are supraparticles (SPs), which are formed via the evaporation-induced assembly of smaller nanoparticles (NPs) [2]. SPs can be designed to have specific properties and functions such as enhanced stability, tunable optical properties - by tailoring the chemistry and shape of the constituent NPs and by regulating the drying conditions. However, elucidating the underlying mechanisms analytically is often impossible due to the massive complexity of the systems. Numerical methods such as molecular dynamics (MD) simulations are well suited for studying such complex effects.

Through particle based coarse-grained MD simulations, we systematically investigate structure formation in SPs by varying the (i) constituent nanoparticle sizes and shapes, (ii) controlling particle interactions and (iii) regulating the drying conditions. Through close collaboration with experimentalists, we found:

• Droplets consisting of a bi-disperse colloidal dispersion resulted in SPs exhibiting a core-shell morphology upon fast drying, with smaller particles forming the shell [3].
• In a charge-stabilized suspension, NP-NP interactions can be modulated by addition of salt. Low initial salt concentrations result in SPs with a highly crystalline surface, whereas high initial salt concentrations lead to amorphous SPs [4].
• With rod-shaped NPs, we were able to tune the orientational ordering of the rods in the final SP by changing the drying conditions, with slow drying resulting in long-range ordering. In a rod-sphere mixture we observe a thin shell predominantly occupied by rods followed by a sphere dominant region and finally a homogeneous core.

In addition, we also study the transport properties of colloidal systems with focus on a discrete particle model coupled with multi-particle collision dynamics (MPCD). Comparing with other simulation methods and experimental data available in the literature we found that our method gives a reasonably accurate description of the colloidal suspension dynamics [5].

Fig. 1 Simulation snapshot of SPs made from dispersions with (l) low salt (r) high salt concentration.

Fig. 2 Simulation snapshot of SPs made of rod-sphere mixtures upon (l) fast and (r) slow drying

Fig. 3 Discrete particle model for different shapes of colloidal particles

References:
[1] M. P. Howard, A. Nikoubashman, and A. Z. Panagiotopoulos, Langmuir 2017, 33(15), 3685-3693
[2] Deng, X.; Paven, M.; Papadopoulos, P.; Ye, M.; Wu, S.; Schuster, T.; Klapper, M.; Vollmer, D.; Butt, H. J. Solvent-Free Synthesis of Microparticles on Superamphiphobic Surfaces. Angew. Chem., Int. Ed. 2013, 52, 11286−11289
[3] W. Liu, J. Midya, M. Kappl, H.-J. Butt, A. Nikoubashman; Segregation in Drying Binary Colloidal Droplets, ACS Nano 2019, 13(5), 4972–4979
[4] W. Liu, M. Kappl, W. Steffen, H.-J. Butt; Controlling supraparticle shape and structure by tuning colloidal interactions, J. Colloid Interface Sci. 2002, 607(2), 1661-1670
[5] Y. M. Wani, P. G. Kovakas, A. Nikoubashman, M. P. Howard; Diffusion and sedimentation in colloidal suspensions using multiparticle collision dynamics with a discrete particle model. J. Chem. Phys. 2022, 156 (2), 024901.