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Arthur Panov
Arthur Panov

Nanoscale Energy Transport And Conversion Pdf 11

This book brings together leading names in the field of nanoscale energy transport to provide a comprehensive and insightful review of this developing topic. The text covers new developments in the scientific basis and the practical relevance of nanoscale energy transport, highlighting the emerging effects at the nanoscale that qualitatively differ from those at the macroscopic scale. Throughout the book, microscopic energy carriers are discussed, including photons, electrons and magnons. State-of-the-art computational and experimental nanoscale energy transport methods are reviewed, and a broad range of materials system topics are considered, from interfaces and molecular junctions to nanostructured bulk materials. Nanoscale Energy Transport is a valuable reference for researchers in physics, materials, mechanical and electrical engineering, and it provides an excellent resource for graduate students.

nanoscale energy transport and conversion pdf 11

Bolin Liao is an assistant professor in the Department of Mechanical Engineering at the University of California, Santa Barbara. Liao obtained his PhD in Mechanical Engineering from MIT in 2016, and his main research interests are nanoscale energy transport and its application to sustainable energy technologies.

Despite the ubiquity of evaporation in the natural environment1 and the wide-ranging adaptations in the biological world that harness evaporation2,3,4,5, the potential of evaporation to power engineered systems is largely neglected. Nanoscale confinement of water in hygroscopic materials provides a means to convert energy from evaporation by generating mechanical force in response to changing relative humidity6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21. However, scaling up this phenomenon to create macroscopic devices faces multiple challenges: unfavourable scaling of hydration kinetics slows down actuation speeds at large dimensions; small strains complicate energy transfer to external systems; and, importantly, the slow rate of change of relative humidity in the environment limits the power output.

While evaporation carries a significant amount of energy22,23, it involves a slow rate of water transfer that limits the relative expansion and contraction of hygroscopic materials. Because the relative volume of the absorbed and released water is small, the pressure change generated during this process has to be large for efficient energy conversion. Water confined to nanoscale cavities within hygroscopic materials (Fig. 1a) can induce large pressures in response to changing relative humidity24,25,26; however, these nanostructures also limit the transport kinetics of water. Simply scaling up the dimensions of hygroscopic materials would not increase power, and may even lead to a decrease, because the time scale of wetting and drying typically depend on the square of the travel distance of water19.

(a) Water confined to nanoscale cavities, conduits and surfaces within hygroscopic materials can induce large pressures in response to changing relative humidity. (b) A scanning electron microscopy image of the cross-section of a B. subtilis spore. Spores exhibit strong mechanical response to changing relative humidity18 by absorbing and releasing moisture. (c) A false-coloured s.e.m. picture of spores (grey) deposited on an 8-micrometre-thick polyimide tape (yellow). (d) The spore-coated films bend and straighten in response to changing relative humidity. (e) Patterning equally spaced spore layers on both sides of the plastic tape creates linearly expanding and contracting structures. (f) Stacking the tapes in e with air gaps between them results in a material that can be scaled in two dimensions without compromising hydration/dehydration kinetics. (g) A shutter mechanism can create oscillations. (h) Photo of a device that exhibit self-starting oscillatory movement when placed above water. (i) Rotary motion can lead to cyclical changes of relative humidity experienced by the spores. The increased curvature on the dry side shifts the centre of mass of the entire structure away from the axis of rotation and creates torque. (j) Photo of a device whose continuous rotation is powered by evaporation from the wet paper within the device.

Addressing the limitations in transport kinetics alone would not be sufficient to increase power, because in typical environmental conditions relative humidity changes on daily and seasonal timescales, which is too slow to generate practically useful levels of power. However, spatial gradients in relative humidity established near evaporating surfaces provide an opportunity. If a small portion of the power generated by the spores could be used to control the evaporation rate or, alternatively, move the spores in and out of the high humidity zone at the surface, the relative humidity experienced by the spores would change rapidly in a cyclical fashion.

In summary, we demonstrate strategies to scale up a nanoscale energy conversion mechanism to create macroscopic devices. Many interesting nanoscale phenomena benefit from increased surface to volume ratios at small-length scales. However, this property also comes at a price due to slow kinetics that begin to dominate as one tries to scale up the sizes of the structures. Our results show that this challenge can be mitigated in the case of hydration-driven systems and our findings may also be applicable to other systems driven by chemical stimuli. In addition, from a technological standpoint, the demonstrations made here with the evaporation-driven car and the powering of LEDs highlight the so-far overlooked capability of water in the environment to supply useful levels of power. Due to the ubiquity of evaporation in nature and the low cost of materials involved (plastic tapes, hygroscopic materials), the engines presented here may find applications as energy sources for a wide range of off-the-grid systems that function in the environment.

How to cite this article: Chen, X. et al. Scaling up nanoscale water-driven energy conversion into evaporation-driven engines and generators. Nat. Commun. 6:7346 doi: 10.1038/ncomms8346 (2015).

Description: This intro lecture gives an overview of the course and the research in the field of nanoscience and technology. It starts with review of the classical laws related to energy transport processes, and introduces microscopic pictures of energy carriers.

Theory and experiment are combined to investigate the nature of low-energy excitons within ordered domains of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-PEN) polycrystalline thin films. First-principles density functional theory and many-body perturbation theory calculations, along with polarization-dependent optical absorption spectro-microscopy on ordered domains, show multiple low-energy absorption peaks that are composed of excitonic states delocalized over several molecules. While the first absorption peak is composed of a single excitonic transition and retains the polarization-dependent behavior of the molecule, higher energy peaks are composed of multiple transitions with optical properties that can not be described by those of the molecule. The predicted structure-dependence of polarization-dependent absorption reveals the exact inter-grain orientation within the TIPS-PEN film. Additionally, the degree of exciton delocalization can be significantly tuned by modest changes in the solid-state structure and the spatial extent of the excitations along a given direction is correlated with the degree of electronic dispersion along the same direction. These findings pave the way for tailoring the singlet fission efficiency of organic crystals by solid-state structure. doi link PDF

Our research focuses on describing details of the energy transport and conversion at the solid surfaces and interfaces in the nanoscale regime. In order to understand their basic mechanism at a single molecule/atom level, we carry out combined study of density functional theory calculation and scanning probe microscopy/spectroscopy on the well-defined solid surfaces under ultra-high vacuum condition. Part of our research is directed toward investigation of single-molecule chemistry on various solid surfaces. Another important part of our research focuses on self-assembled organic thin films aiming at understanding their microscopic structure and controlling their electronic properties. In addition, we also investigate energy conversion between electrons and photons of the nanometer scale materials.

The objective of this subject is to provide the basis for the student to understand the variation of the physical properties (electronic, optical, thermal and transport) of materials on the nanometer scale.


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