Mojtaba Rajabi

My research interest is soft matter physics with focus on liquid crystals. Below, I describe my research in more details.

Active matter: We extract useful work from the chaotic motion of micro-swimmers such as bacteria. Liquid crystal environment is used as a mean to enable and direct self-locomotion of micro-swimmers. For instance, aqueous suspension of bacteria dispersed in a nematic environment self-propel unidirectionally, figure 1. The trajectory of the droplet can be predesigned by patterning the molecular orientation of the nematic medium, figure 2 (Left), or be dynamically controlled by realigning the director using electric field or laser beam, figure 2 (Right). The speed of droplets is controlled by electric field and laser as well.


Figure 1. Unidirectional self-locomotion of active droplets in a nematic environment (M. Rajabi, H. Baza, T. Turiv, O. D. Lavrentovich, Nature Physics, (2021)).


Figure 2. Left) Curvilinear trajectory of active droplets in a predesigned path set by photopatterning of the bounding surfaces (M. Rajabi, H. Baza, T. Turiv, O. D. Lavrentovich, Nature Physics, (2021)). Right) Dynamic control of trajectory of an active droplet in a nematic medium using electric field (M. Rajabi, H. Baza, H. Wang, O. D. Lavrentovich, Frontiers in Physics, (2021)).

Plasmonic photopatterning: We design and fabricate plasmonic meta-masks to photopattern orientation of liquid crystal molecules. The mask is made of an aluminum film of thickness 150 nm with an array of rectangular nano-apertures of dimensions 100*210 nm on it. When an unpolarized light passes through an aperture, becomes polarized with the polarization along the short axis of the aperture. The orientation of each nano-aperture is designed individually; thus, the polarization of the transmitted light is spatially patterned. When a surface covered with photosensitive azo-dye is irradiated with the transmitted light from a meta-mask, the azo-dye molecules reorient themselves to become perpendicular to the polarization of light. Therefore, the surface acquires the same pattern as the mask.


Examples of using photopatterned surfacse:

Ferroelectric nematic liquid crystals

Electrokinetics

Liquid crystal elastomers

Liquid crystal characterization

Interactions of active colloids

Characterization of surface properties of photopattetned surfaces

Plasma engineering

Coordinator of 1st STEM Student Symposium, (Feb 2019).

President of the Optical Society (OSA) Student Chapter, (2018-2019).

Vice President of the Optical Society Student Chapter, (2017-2018).

Secretary of Physics graduate student association, (2018-2019).