Coffee stain morphologies obtained by drying suspension droplets of gold nanorods of different aspect ratios

Sk Jasim, A.W. Zaibudeen, Ranjini Bandyopadhyay*

Rheology and dynamic light scattering lab, Raman Research Institute, Bengaluru-

560080, India.

The evaporation of colloidal suspension droplet results in the deposition of the solute phase in coffee stain patterns. The dried deposits are interesting to study from the viewpoint of applications in biomedicine, nanotechnology, printing, coating, etc. We have synthesized aqueous colloidal suspensions of surfactant (CTAB) stabilized gold nanorods using a seed mediated growth method. The obtained gold nanorod aspect ratio has been tailored by varying the silver nitrate (AgNO3) concentration for small aspect ratios and surfactant ratio (BDAC/CTAB) for high aspect ratios. The formation of gold nanorod of different aspect ratios was confirmed using UV-Visible spectroscopy measurement and the nanorod size and morphology were studied using scanning electron microscopy (SEM). We are studying the evaporation kinematics at room temperature using a contact angle meter and the final coffee stain patterns that are left behind after solvent evaporation using SEM. We find that the evaporation of a sessile suspension droplet of gold colloidal nanorods results in coffee stain with formation of various distinct regions. Our preliminary results show an enhancement in ordering of the self-assembled structures with increasing nanorod aspect ratio. Also, there are distinct depinning behaviour is noted for suspensions of different aspect ratio gold nanorods.

References

1. Colloids and Surfaces A: Physicochemical and Engineering Aspects 646 (2022) 128982

2. J. Phys. Chem. B 2001, 105, 4065-4067