Electrohydrodynamic Assembly of Multiscale PDMS Microlens Arrays

Abstract

In this paper, we introduce an easy multiscale approach for the fabrication of polymer microlens arrays through a self-assembling process driven by the electrohydrodynamic (EHD) pressure. This method represents a simple alternative to the conventional soft lithography techniques. A thin layer of liquid polymer is deposited on a microengineered ferroelectric crystal and can be self-assembled and cross-linked in a single-step process as a consequence of the pyroelectric effect activated by simply heating the substrate. Although the EHD instability induced by the pyroelectric effect was discovered in principle few years ago, here we demonstrate a systematic investigation for fabrication of microlens arrays in a multiscale range (i.e., between 25 to 200 μm diameter) with high degree of uniformity. By controlling the polymer instability driven by EHD, we report on two different microoptical shapes can be obtained spontaneously, i.e., spherical or toroidal. Here, we show how the geometrical properties and the focal length of the lens array are modulated by controlling two appropriate parameters. Such microlenses can be useful also as polymer patterned arrayed microstructures for optical data interconnections, OLEDs efficient light extraction, concentrating light in energy solar cells, imaging and 3-D display solutions, and other photonics applications.

Twofold Self-Assembling of Nanocrystals Into Nanocomposite Polymer

“…3 the fluorescence microscope pictures clearly reveal the NCs self-collection inside the hexagons of the PPLN substrate. The results show that the presence of NCs does not affect the global behavior of the liquid polymer under the action of the pyro-EHD pressure, so that the physics remains the same as described in the previous papers [35], [38], [39]. The LN is a ferroelectric solid crystal and exhibits a change in electric polarization as a function of temperature because of its pyroelectric properties.…”

“…Increasing the spin speed, the micro-optical elements appear to be distant one from the other with a quite low height while the inter-gap space of two adjacent microstructures increases [35]. In the bottom image of Fig.…”

“…Pyro-EHD and pyro-DEP have been discovered and applied separately as advanced processes for the self-assembling of nanofillers [27]- [29], liquids and polymers, including Polydimethylsiloxane (PDMS) [30]- [34] in a multiscale range (i.e., between 25 to 200 μm diameter) with high degree of uniformity. By controlling the polymer instability driven by EHD, different micro-optical structures can be obtained spontaneously, i.e., spherical or toroidal [35]. Here we show how the thermal stimulus applied to a periodically poled lithium niobate crystal (PPLN) is able to drive in a single step the self-assembling and subsequently the cross-linking of the liquid PDMS matrix in form of a 2-D micro-optical polymer array.…”

“…The thermal stimulus induced simultaneously the formation of PDMS microstructures array, the DEP distribution of the NCs and the curing of the polymer. The fabrication process of multiscale PDMS array based on the EHD self-assembling method, was demonstrated as a straight-forward, fast and simple process suitable to achieve structures with lens/donuts shapes having several size [35]. The geometrical and the optical characteristics of the passive polymer microlenses have been also demonstrated.…”

“…The spin speed allows one to tune the geometry of the microstructures shaping the active polymer layer [35]. We identified the better condition in term of the rounds per minute (RPM) for shaping the micro-elements at 4000 RPM.…”