Showing papers by "Tingrui Pan published in 2010"

Photopatternable Superhydrophobic Nanocomposites for Microfabrication

Abstract: In this paper, we first report on direct-photolithography-based microfabrication of transparent super-hydrophobic micropatterns using novel photodefinable nanocomposites, combining the nanomorphology and hydrophobicity of polytetrafluoroethylene (PTFE) nanoparticles and the photopatternability and transparency of an SU-8 photoresist using both direct-mixing and coating-immobilization methods. The direct mixture of PTFE-SU-8 nanocomposite can be reliably spin-coated and photopatterned onto transparent substrates (e.g., glass or polymers) with a minimal feature resolution of 50 ?m. The resulting nanocomposite film possesses a contact angle of water at 150°, although its optical transparency is less than 30%. Furthermore, a modified coating-immobilization approach, employing spray coating and thermal immobilization of PTFE nanoparticles onto an SU-8 polymer matrix, significantly enhances superhydrophobicity, lithography resolution, as well as optical transparency. The highest optical transparency of 80% and a minimal feature resolution of 10 ?m have been achieved using the standard photolithography approach, while the contact angle of water above 165° enables extraordinary superhydrophobicity with low hysteresis. The novel PTFE-SU-8 nanocomposites provide a unique combination of superhydrophobicity, optical transparency, and photopatternability, along with excellent adaptability and simple processability, which offer great extension to rapidly evolving micro-nanoengineering applications.

Three-dimensional surface microfluidics enabled by spatiotemporal control of elastic fluidic interface

Abstract: As an emerging alternative to the conventional counterpart, surface microfluidics incorporates both intrinsic resistive solid-liquid and elastic frictionless gas-liquid interfaces, leading to unique flow-pressure characteristics. Furthermore, the open-surface microfluidic platforms can be fabricated on a monolithic substrate with high wettability contrast by the previously reported one-step lithographic process of a photosensitive superhydrophobic nanocomposite material, which permits flexible fluidic operations and direct surface modifications. In the paper, we first present three-dimensional microfluidic manipulations utilizing the unconventional gas-liquid interfaces of surface microfluidics, outlined by the micropatterned wetting boundaries (also known as the triple lines). In contrast to the primary linear (resistive) nature of the conventional closed-channel microfluidics, the distinct elastic interface of surface microfluidics enables remarkable three-dimensional (deformable) and time-dependent (capacitive) operations of the flow. Specifically, spatiotemporal dependence of microflow patterns on the planar fluidic surfaces has been theoretically analyzed and experimentally characterized. Utilizing the unconventional interface-enabled flow-pressure relationship, novel surface fluidic operations, including microflow regulation and flow-controlled switching, have been demonstrated and fully investigated. Furthermore, three-dimensional surface microfluidic networks together with analog-to-digital stereo-flow activations have been established, in which miniature capillary bridges form fluidic connections between two independent surface microfluidic circuits.

CNT-based photopatternable nanocomposites with high electrical conductivity and optical transparency

Abstract: In this paper, a nanocomposite approach is introduced to provide both electrically conductive and optically transparent micropatterns on any flexible substrate employing photolithography-based microfabrication. The nanocomposite materials combine the highly directional nanoscopic networks and electrical conductivity of single-wall carbon nanotubes (SWNTs) with the photopatternability and optical transparency of SU-8 photoresist. The photopatternable nanocomposites have yielded high optical transparency of 90% and high electrical conductivity of 27.5 S m−1 with the minimal feature resolution of 10 µm. Additionally, an interesting nano-bridge phenomenon has been discovered during fabrication of the microscale features. Moreover, the photopatternable transparent conductive nanocomposite has demonstrated its application to biomedical sensing for exceptional adaptability and flexibility.

Surface microfluidics fabricated by superhydrophobic nanocomposite photoresist

Abstract: Surface microfluidics can be of potential use in a variety of emerging applications, including biological and chemical analysis, cellular detection and manipulation, and high-throughput pharmaceutical screening. In comparison with the conventional closed-channel microfluidic system, surface microfluidics shows the distinct advantages of simple construction, direct fluidic connection, no cavitation or interphase obstruction, no optical barrier, and reusability. In this paper, we present the first surface microfluidic networks microfabricated by a single-step photolithographic process using a novel superhydrophobic photosensitive nanocomposite. The superhydrophobic photoresist incorporates PTFE nanoparticles into a photosensitive SU-8 matrix, in which superhydrophobicity (contact angle of 160°) is primarily contributed by the extremely low chemical energy and nanotopology of PTFE nanoparticles, while the SU-8 matrix offers photopatternability (lithographic resolution of 10µm) and substrate adhesion. Furthermore, surface microfluidic pumps self-propelled by surface tension force have been fabricated and characterized to demonstrate the applicability of the novel nanocomposite material.