Control of polymer colloidal crystal structure and orientation on patterned substrates by electrophoresis

Abstract

The method of electrophoretic deposition of charged polymer (polystyrene) microspheres on topologically patterned substrates is discussed. Surface patterning with different symmetries and structure periodicity in the sub-micrometer range over large surface areas was realized by laser interference lithography. Growth of colloidal crystals on patterned and bare electrode surfaces was compared. Surface patterning predetermined the colloidal crystal structure and orientation. Fcc colloidal crystals with (111), (100) and (110) crystal plane orientations parallel to the electrode surfaces were successfully grown on patterned electrodes with the corresponding pattern symmetry. The growth of colloidal crystals with (111) and (100) crystal plane orientations parallel to the electrode surface was easily controlled by patterned surfaces, while only two layers of colloidal crystals having the (110) plane orientation parallel to the electrode surface were grown in a controlled way. The growth of thick colloidal crystals in the non-close-packed [110] direction generated a mixture of small domains of different orientations, where domains with (111) and (100) orientations dominated. The thickness of the colloidal crystals was controlled by varying the deposition parameters. Thickness increased with increasing the applied voltage, deposition time, concentration of colloidal particles and with decreasing the withdrawal speed of the electrodes from the colloidal suspension. A threshold voltage of 3.36 V was determined, beyond which a significant increase in the thickness of the colloidal crystals with applied voltage was observed. A gradient in the thickness of the colloidal crystals was obtained across the electrode surface at low withdrawal speed (0.04 mm/s). Colloidal crystals with a homogeneous thickness over the electrode area were formed at withdrawal speeds of 0.07 - 0.1 mm/s.