• Current Research 1: Template-free scalable micro/nano-manufacturing using roll-to-roll systems

This project investigates the spontaneous pattern generation by ribbing on polymer surfaces during roll coating in an ordered manner using a fundamentally new approach to manufacture three-dimensional micro and nano-scale structures on a large-area substrate. One of the applications is hydrodynamic drag reduction. A technology that can reduce the friction or drag on ship hulls would have a substantial economic and environmental impact by improving fuel efficiency. Microstructured superhydrophobic surfaces may retain air pockets that can act as gas lubrication between the water and the ship hull. Although the superhydrophobic surfaces have been studied for nearly two decades, it is only recently that periodic linear-trench structures have been shown to be effective for marine crafts traveling in open water, which represents the sea, oceans, and lakes. The manufacturing of such well-defined micro-trenches has relied on silicon-based microfabrication based on semiconductor manufacturing approaches. These silicon processes are prohibitively expensive and not scalable for large surface areas, such as ship hulls.

The objectives are to establish the scientific foundation to control the microstructures formed during the roll coating and to fabricate and validate the drag reduction efficiency of the surfaces in realistic flow conditions of open water and Reynolds number greater than 1 million. The research team will utilize computational modeling to predict the deformation behavior of the viscoelastic polymer verified by the experimental observations. For the proof-of-concept of drag reduction in realistic flows, a microstructured film and a smooth film will be layered on the bottom of a motorboat specifically outfitted to reliably compare the fluid shear stresses on the two. This new process is researched to develop friction-reduction coatings for ship hulls and study their physical and chemical durability. Hence, outcomes from this research will benefit a wide array of marine applications, including commercial and military ships, which play a significant role in the national and global economies and security applications.

This project will educate the next generation of engineers and scientists through multidisciplinary research involving manufacturing, materials science, computational modeling, and fluid mechanics. The research outcome will be also used to educate K-12, undergraduate, as well as graduate-level students through various formats such as outreach activities and innovative curricular efforts.

  • Current Research 2: Nanomanufacturing and Composites for Plasmonic Metamaterials

A metamaterial is a material engineered to have a property that is not found in nature. They are made from assemblies of multiple elements fashioned from composite materials such as metals or plastics. The materials are usually arranged in repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. Metamaterials derive their properties not from the properties of the base materials, but from their newly designed structures. Their precise shape, geometry, size, orientation, and arrangement give them their smart properties capable of manipulating electromagnetic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials. (Wikipedia)

In our lab, we create metamaterials using scalable nanomanufacturing technologies, such as nanoimprint lithography and nano transfer printing, to apply them in various applications including single bio-molecule detection and infrared polarimetric sensing/imaging.

Composite is defined as a heterogeneous material system consisting of reinforcing materials, which are in form of fibers, whiskers, platelets, and particulates, dispersed in continuous matrix materials. Interactions between the nanoscale inclusions and matrix materials can create extraordinary functionalities, such as electrical conductivity, electromagnetic shielding, magnetoresistance, that the individual constituents could not achieve. ‘Metacomposite’ is a new class of multifunctional composites that can tune electromagnetic properties. We study the multiphysics interactions within the composite material system to take advantage of the un-usual properties to realize novel electromagnetic devices.

  • Current Research 3: Additive Manufacturing for Printed Electronics and Functionally Graded Materials

Additive manufacturing (AM) is a process that creates parts by continuously adding material layer by layer. This technique has been utilized to create complex structures, such as internal hierarchal patterns, which are impossible to create with other conventional manufacturing methods. AM has been used in several fields such as dental, medical, aerospace, electronics, and microfluidics to produce unique devices.

We utilize the printing capability to create electronics on flexible substrates. In high throughput roll-to-roll (R2R) and sheet-to-sheet (S2S) manufacturing environment, direct print technologies (gravure, flexography, and ink-jet) provide lower cost and larger printing area. The use of metallic nano inks, where metal nanoparticles are dispersed in printable carriers, has attracted great interest because of inherently higher electric conductivity and mechanical durability. However, unlike organic-based electronic materials, the metallic nano inks require a sintering process in order to form conductive films. We studied a novel photonic sintering process using a Xe-flash lamp. The advantages of the Xe-flash photonics sintering are: (1) Little impact to polymer substrate – Unlike the conventional furnace whose temperature is detrimental to the substrate, room temperature sintering is achieved through selective heating of nanoparticles over the polymeric substrates; (2) Scalable manufacturing – the photonic process can be applied on much larger areas at once in comparison to laser-based spot sintering technique.

As AM technology matures, the number of printable materials has greatly increased. Research into new materials and the effects of complex structural arrangements has increased tremendously both from industry and academia looking for novel applications to this technology. AM technologies are capable of locally tuning material properties to generate Functionally Graded Materials (FGM). Artificially engineered FGMs have been applied to create aerospace structural materials, lightweight concrete structures, and bone mimicking implants. However, the capability of conducting meaningful computer simulations for FGMs is limited mainly due to the lack of information regarding the material properties and appropriate material models. In our recent study, we developed mechanical models of the printed materials and validated the model-based computational analysis by comparing them with physical tests.

Position Opening

We currently want all levels of research assistants (undergraduate, graduate, and postdoc) in the topics.

  1. Polymer nanocomposites
    1. Synthesis of polymer nanocomposites
    2. Characterization with imaging and analytical experiments (SEM, TEM, LCR, Rheometer, Mechanical tests)
  2. Multiphysics modeling and simulation for device designs. Hands-on experiments.
    1. Simulation coupling thermal, acoustic, mechanical, and optical models (COMSOL Multiphysics).
    2. Hands-on experiments device characterization.
  3. Micro-, nano-scale manufacturing
    1. Developing a manufacturing equipment
    2. Nanomechanics modeling for process parameters and structures generated
    3. Mechanical simulation of the manufacturing process