Optical Electronics & Smart Windows
Materials with switchable transparency have found numerous applications, especially in dynamic tintable or smart windows. These materials have found utility in applications in agriculture , automobile sunroofs, personal privacy, photovoltaics, and energy-efficient buildings. Switchable transparency is achievable following various techniques, all of which utilize external stimuli or triggers. The most common are chromic materials, liquid crystals,
and suspended-particle devices. The chromic materials are most commonly photochromic, in which case the external stimulus is light, e.g. photochromic lenses. However, other types of stimuli for chromic materials have been developed, namely, electricity (electrochromic), gases (gasochromic), and heat (thermochromic). Liquid crystal devices while they share the same stimulus with electrochromic, are fundamentally different since they rely on changes in the orientation of the liquid crystal molecules rather than through ion insertion/extraction. Suspended-particle devices that exist today also rely on electrical stimuli to create an electronic field to align light-absorbing particles suspended in a fluid or gel between two transparent and conductive surfaces. The alignment of the particles yields a rapid increase in transmittance that was reported to reach as high as 79% .
Reference: Kamran Moradi, Bilal El-Zahab, “Controllable optical transparency using an acoustic standing-wave device”, Optic Materials, 2015, 47, 582-585.
Wearable & Flexible Electronics
Transparent conducting oxides such as indium tin oxide (ITO) and fluorine tin oxide (FTO) have been standard optoelectronic electrode materials due to their electrical conductivity and optical transparency. However, with the emergence of new transparent electronic materials these materials’ shortcomings became apparent. Some of these shortcomings are the limited worldwide resources of indium, acid/base instability, and limited transparency in the near-IR region. Therefore, highly stable, transparent, and flexible electrically conductive materials are in high demand. Advances in flexible organic electronics enabled great developments in research areas such as light emitting diodes (LED), transistors, solar cells, and wearable devices. These organic electronics distinguish themselves from their inorganic counterparts by possessing superior physical properties such as flexibility,
low gravimetric density, corrosion resistance while being generally low-cost. Several research studies reported on thin layers with optical transparencies exceeding 70% and in one case reaching 86% using carbon nanotubes and with sheet resistance of 471 Ω/square. Optoelectronic devices require conductive electrodes which are flexible, cheap and compatible with large-scale manufacturing methods. In this research the aim is to develop a thin, transparent, flexible, and at the same time highly anisotropically conductive film templated using acoustic focusing. Since freestanding and flexible films were favored in different industries such as medical device, wearable electronics, wearable sensors, the conductive particles were suspended in a liquid monomer or acetonic solution of the monomer during the focusing studies.
Reference: Kamran Moradi, Bilal El-Zahab, “Transparent and anisotropic conductive film templated using acoustic focusing”, Electronic Materials Letters, 2016, 12(1), 121-126
Microfluidics and Medical Research
A microfluidic lab-on-chip device can perform a sequence of analyses on less than a microliter of a fluid that may include filtration, mixing, concentrating, heating, reacting, and detection with similar accuracy compared to a full-size laboratory. The science that deals with the flow of fluids and suspensions in channels with less than millimeter-
sized cross-sections under influence of external forces is called microfluidics [2-7]. In microfluidics, viscosity dominates over inertia and ensures the presence of laminar flow. Having laminar flow and combining it with external forces results in particle controlling methods which are useful in analytical sciences, based on different physical
mechanisms including, inertia, electrokinetics, dielectrophoretics, magneto-phoretics, as well as mechanical contact forces.Acoustic focusing is a science which utilizes the ultra sound external forces to handle microparticles in microchannels. Advantages like gentle and label free separations based on purely mechanical properties: size, shape, density and compressibility have garnered a lot of excitement and attention to this science. Interesting applications can be conducted by microfluidic platforms such as:
-Sorting of Microparticles and Cells
-Separation of Microparticles and Cells
-Chemical Analysis
-Physical analysis
-Electronic cooling and heating
-Mixing process
References:
Kamran Moradi, Bilal El-Zahab, “Blood lipid profiling using a lab-on-chip device powered by acoustic sounds waves”, 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), August 2014
Kamran Moradi, Bilal El-Zahab, “Silicon Based Lab-On-Chip Device for Acoustic Focusing Applications”, The 12th International Conference on Nanochannels, Microchannels and Minichannels, ASME, August 2014