Nanotechnology in Mechanical Engineering

Nanotechnology in Mechanical Engineering

Outline of the Presentation Lecture In-class group activities Video Clips Homework

Course Outline Lecture – II Nano-Mechanics Nanoscale Thermal and FlowPhenomena Experimental Techniques Modeling and Simulation Lecture - I Introduction to Nano- Technology in Engineering • Basic concepts • Length and time scales • Nano-structured materials - Nanocomposites - Nanotubes and nanowire • Applications and Examples

Lecture Topics We will address some of the key issues of nano-technology in Mechanical Engineering. Some of the topics that will be addressed are nano-structured materials; nanoparticles and nanofluids, nanodevices and sensors, and applications.

Major Topics in Mechanical Engineering • Design of machines and structures • Dynamics system, sensors and controls • Robotics • Computer-Aided Design (CAD/CAM) • Computational Fluid Dynamics (CFD) and Finite Element Method • Fabrication and • Manufacturing processes • Mechanics: Statics : Deals with forces, Moments, equilibrium of a stationary body Dynamics: Deals with body in motion - velocity, acceleration, torque, momentum, angular momentum. • Structure and properties of material (Including strengths) • Thermodynamics, power generation, alternate energy (power plants, solar, wind, geothermal, engines)

Diesel Engine Simulation Model x = 750mm x = 10 mm x = 1000 mm x = 250 mm x = 500 mm Fuel Cell Design and Development Flow in micro channel No slip condition Slip Conditions

Length Scales in Sciences and Mechanics Quantum Mechanics: Deals with atoms - Molecular Mechanics: Molecular Networks - Nanomechanics: Nano-Materials - Micromechanics: Macro-mechanic: Continuum substance

Quantum and Molecular Mechanics • All substances are composed molecules or atoms in random motion. • For a system consisting of cube of 25-mm on each side and containing gas with atoms. • To specify the position of each molecule, we need to three co-ordinates and three component velocities • So, in order to describe the behavior of this system form atomic view point, we need to deal with at least equations. • This is quite a computational task even with the most powerful (massively parallel multiple processors) computer available today. • There are two approaches to handle this situations: Microscopic or Macroscopic model

Microscopic Vs Macroscopic Approach -1:Microscopic viewpoint based on kinetic theory and statistical mechanics • On the basis of statistical considerations and probability theory, we deal with average values of all atoms or molecules and in connection with a model of the atom. Approach – II Macroscopic view point • Consider gross or average behavior of a number of molecules that can be handled based on the continuum assumption. • We mainly deal with time averaged influence of many molecules. • These macroscopic or average effects can be perceived by our senses and measured by instruments. • This leads to our treatment of substance as an infinitely divisible substance or continuum.

Breakdown of Continuum Model • To show the limit of continuum or macroscopic model, let us consider the concept of density: • Density is defined as the mass per unit volume and expressed as Where is the smallest volume for which substance can be assumed as continuum. • Volume smaller than this will lead to the fact that mass is not uniformly distributed, but rather concentrated in particles as molecules, atoms, electrons etc. • Figure shows such variation in density as volume decreases below the continuum limit.

Macroscopic Properties and Measurement Pressure Pressure is defined as the average normal-component of force per unit area and expressed as Where is the smallest volume for which substance can be assumed as continuum. Pressure Measurement For a pressure gauge, it is the average force (rate of change of momentum) exerted by the randomly moving atoms or molecules over the sensor’s area. Unit: Pascal (Pa) or

Introduction- Nanotechnology • Nanoscale uses “nanometer” as the basic unit of measurement and it represents a billionth of a meter or one billionth of a part. • Nanotechnology deals with nanosized particles and devices • One- nm is about 3 to 5 atoms wide. This is very tiny when compared normal sizes encounter day-to-day. - For example this is 1/1000th the width of human hair.

Any physical substance or device with structural dimensions below 100 nm is called nanomaterial or nano-device. • Nanotechnology rests on the technology that involves fabrication of material, devices and systems through direct control of matter at nanometer length scale or less than 100 nm.

Nanoparticles can be defined as building blocks of nanomaterials and nanotechnology. • Nanoparticles include nanotubes, nanofibers, fullerenes, dendrimers, nanowires and may be made of ceramics, metal, nonmetal, metal oxide, organic or inorganic. • At this small scale level, the physical, chemical and biological properties of materials differ significantly from the fundamental properties at bulk level. • Many forces or effects such inter-molecular forces, surface tension, electromagnetic, electrostatic, capillary becomes significantly more dominant than gravity. • Nanomaterial can be physically and chemically manipulated to alter the properties, and these properties can be measured using nanoscale sensors and gages.

A structure of the size of an atom represents one of the fundamental limit. • Fabricating or making anything smaller require manipulation in atomic or molecular level and that is like changing one chemical form to other. • Scientist and engineers have just started developing new techniques for making nanostructures. The nanoscience is matured. The age of nanofabrication is here. The age of nanotechnology - that is the practical use of nanostructure has just started.

Nanotechnology in Mechanical Engineering New Basic Concepts Nano-Scale Heat Transfer Nano-Mechanics Nano-fluidics Applications

Applications • Structural materials • Nano devices and sensors • Coolants and heat spreaders • Lubrication • Engine emission reduction • Fuel cell – nanoporous electrode/membranes/nanocatalyst • Hydrogen storage medium • Sustainable energy generation - Photovoltaic cells for power conversion • Biological systems and biomedicine

Basic Concepts Energy Carriers Phonon: Quantized lattice vibration energy with wave nature of propagation - dominant in crystalline material Free Electrons: - dominant in metals Photon: Quantized electromagnetic energy with wave nature of propagation - energy carrier of radiative energy

Length Scales Two regimes: I. Classical microscale size-effect domain – Useful for microscale heat transfer in micron-size environment. Where mean free path length of the substance characteristic device dimension II. Quantum nanoscale size-effect domain – More relevant to nanoscale heat transfer Where characteristic wave length of the electrons or phonons

This length scale will provide the guidelines for analysis method- both theoretical and experimental methods: classical microscale domain or nanoscale size-effect domain.

Flow in Nano-channels The Navier –Stokes (N-S) equation of continuum model fails when the gradients of macroscopic variables become so steep that the length scale is of the order of average distance traveled by the molecules between collision. Knudsen number ( ) is typical parameter used to classify the length scale and flow regimes: Kn < 0.01: Continuum approach with traditional Navier-Stokes and no-slip boundary conditions are valid. 0.01<Kn<0.1: Slip flow regime and N-S with slip boundary conditions are applicable 0.1<Kn<10:Transition regime – Continuum approach completely breaks – Molecular Dynamic Simulation Kn > 10 : Free molecular regime – The collision less Boltzman equation is applicable.

Time Scales Relaxation time for different collision process: Relaxation time for phonon-electron interaction: Relaxation time for electron-electron interaction: Relaxation time for phonon-phonon interaction:

Nanotechnology: Modeling Methods • Quantum Mechanics • Atomistic simulation • Molecular Mechanics/Dynamics Nanomechanics Nanoheat transfer and Nanofluidics

Models for Inter-molecules Force - Inter-molecular Potential Model - Inverse Power Law Model or Point Centre of Repulsion Model - Hard Sphere Model - Maxwell Model - Lennard-Jones Potential Model Inter-molecular Potential Model

Nanotools Nanotools are required for manipulation of matter at nanoscale or atomic level. Certain devices which manipulate matter at atomic or molecular level are Scanning-probe microscopes, atomic force microscopes, atomic layer deposition devices and nanolithography tools. Nanolithography means creation of nanoscale structure by etching or printing. Nanotools comprises of fabrication techniques, analysis and metrology instruments, software for nanotechnology research and development. Softwares are utilized in nanolithography, 3-D printing, nanofluidics and chemical vapor deposition.

Nanoparticles and Nanomaterials Nanoparticles: • Nanoparticles are significantly larger than individual atoms and molecules. • Nanoparticles are not completely governed by either quantum chemistry or by laws of classical physics. • Nanoparticles have high surface area per unit volume. • When material size is reduced the number of atoms on the surface increases than number of atoms in the material itself. This surface structure dominates the properties related to it. • Nanoparticles are made from chemically stable metals, metal oxides and carbon in different forms.

Carbon -Nanotubes • Carbon nanotubes are hollow cylinders made up of carbon atoms. • The diameter of carbon nanotube is few nanometers and they can be several millimeters in length. • Carbon nanotubes looks like rolled tubes of graphite and their walls are like hexagonal carbon rings and are formed in large bundles. • Have high surface area per unit volume • Carbon nanotubes are 100 times stronger than steel at one-sixth of the weight. • Carbon nanotubes have the ability to sustain high temperature ~ 2000 C.

There are four types of carbon nanotube: Single Walled Carbon Nanotube (SWNT),Multi Walled Xarbon nanotube (MWNT), Fullerene and Torus. SWNTs are made up of single cylindrical grapheme layer MWNTs is made up of multiple Grapheme layers. SWNT possess important electric properties which MWNT does not. SWNT are excellent conductors, so finds its application in miniaturizing electronics components.

Nanocomposites • Formed by combining two or more nanomaterials to achieve better properties. • Gives the best properties of each individual nanomaterial. • Show increase in strength, modulus of elasticity and strain in failure. • Interfacial characteristics, shape, structure and properties of individual nanomaterials decide the properties. • Find use in high performance, lightweight, energy savings and environmental protection applications - buildings and structures, automobiles and aircrafts.

Examples of nanocomposites include nanowires and metal matrix composites. • Classified into multilayered structures and inorganic or organic composites. • Multilayered structures are formed from self-assembly of • monolayers. • Nanocomposites may provide heterostructures formed from various inorganic or organic layers, leading to multifunctional materials. • Nanowires are made up of various materials and find its • application in microelectronics for semiconductor devices.

Nanostructured Materials • All the properties of nanostructured are controlled by changes in atomic structure, in length scales, in sizes and in alloying components. • Nanostructured materials are formed by controlling grain sizes and creating increased surface area per unit volume. • Decrease in grain size causes increase in volumetric fraction of grain boundaries, which leads to changes in fundamental properties of materials. Different behavior of atoms at surface has been observed than atom at interior. Structural and compositional differences between bulk material and nanomaterial cause change in properties.

The size affected properties are color, thermal conductivity, mechanical, electrical, magnetic etc. • Nanophase metals show increase in hardness and modulus of elasticity than bulk metals. • Nanostructured materials are produced in the form of powders, thin films and in coatings. • Synthesis of nanostructured materials take place by Top – Down or Bottom- Up method. • - In Top-Down method the bulk solid is decomposed into • nanostructure. • - In Bottom-Up method atoms or molecules are • assembled into bulk solid. • The future of nanostructured materials deal with controlling characteristics, processing into and from bulk material and in new manufacturing technologies.

Nanofluids Nanofluidsare engineered colloid formed with stable suspemsions of solid nano-particles in traditional base liquids. Base fluids: Water, organic fluids, Glycol, oil, lubricants and other fluids Nanoparticle materials: - Metal Oxides: - Stable metals: Au, cu - Carbon: carbon nanotubes (SWNTs, MWNTs), diamond, graphite, fullerene, Amorphous Carbon - Polymers : Teflon Nanoparticle size: 1-100 nm

Nanofluid Heat Transfer Enhancement • Thermal conductivity enhancement - Reported breakthrough in substantially increase ( 20-30%) in thermal conductivity of fluid by adding very small amounts (3-4%) of suspended metallic or metallic oxides or nanotubes. • Increased convective heat transfer characteristic for heat transfer fluids as coolant or heating fluid. -

Nanofluids and Nanofludics Nanofluids have been investigated - to identify the specific transport mechanism - to identify critical parameters - to characterize flow characteristics in macro, micro and nano-channels - to quantify heat exchange performance, - to develop specific production, management and safety issues, and measurement and simulation techniques

Nano-fluid Applications • Energy conversion and energy storage system • Electronics cooling techniques • Thermal management of fuel cell energy systems • Nuclear reactor coolants • Combustion engine coolants • Super conducting magnets • Biological systems and biomedicine

Nano-Biotechnology When the tools and processes of nanotechnology are applied towards biosystems, it is called nanobiotechnology. Due to characteristic length scale and unique properties, nanomaterials can find its application in biosystems. Nanocomposite materials can play great role in development of materials for biocompatible implant. Nano sensors and nanofluidcs have started playing an important role in diagnostic tests and drug delivering system for decease control. The long term aim of nano-biotechnology is to build tiny devices with biological tools incorporated into it diagonistic and treatment..

National Nanotechnology Initiative in Medicine Improved imaging (See: www.3DImaging.com) Treatment of Disease Superior Implant Drug delivery system and treatment using Denrimers, Nanoshells, Micro- and Nanofluidics and Plasmonics

- In order to improve the durability and bio-compatibility, the implant surfaces are modified with nano-thin film coating (Carbon nano-particles). - An artificial knee joint or hip coated with nanoparticles bonds to the adjacent bones more tightly. • Nano-particles delivers treatment to targeted area or targeted tumors • - Release drugs or release radiation to heat up and destroy tumors or cancer cells

Self Powered Nanodevices and Nanogenerators Nanosize devices or machined need nano-size power generator call nanogenerators without the need of a battery. Power requirements of nanodevices or nanosystems are generally very small – in the range of nanowatts to microwatts. Example: Power source for a biosensor - Such devices may allow us to develop implantable biosensors that can continuously monitor human’s blood sugar level

Waste energy in the form of vibrations or even the human pulse could power tiny devices. Arrays of piezoelectric could capture and transmit that waste energy to nanodevices There are many power sources in a human body: - Mechanical energy, Heat energy, Vibration energy, Chemical energy A small fraction of this energy can be converted into electricity to power nano-bio devices. Nanogenerators can also be used for other applications - Autonomous strain sensors for structures such as bridges - Environmental sensors for detecting toxins - Energy sensors for nano-robotics - Microelectromecanical systems (MEMS) or nanoelectromechanical system (NEMS) - A pacemaker’s battery could be charged without requiring any replacement

Nano-sensor and Nano-generator

Example: Piezoelectric Nanogenerator Piezoelectric Effect Some crystalline materials generates electrical voltage when mechanically stressed A Typical Vibration-based Piezoelectric Transducer - Uses a two-layered beam with one end fixed and other end mounted with a mass - Under the action of the gravity the beam is bent with upper-layer subjected to tension and lower-layer subjected to tension.

Conversion of Mechanical Energy to Electricityin a Nanosystem Gravity do not play any role for motion in nanoscale. Nanowire is flexed by moving a ridged from side to side. Array of nanowires (Zinc Oxide) with piezoelectric and semiconductor properties Rectangular electrode with ridged underside. Moves side to side in response to external motion of the structure

Example: Thermo Electric Nano-generator Thermoelectric generator relies on the Seebeck Effectwhere an electric potential exists at the junction of two dissimilar metals that are at different temperatures. The potential difference or the voltage produced is proportional to the temperature difference. - Already used in Seiko Thermic Wrist Watch

Bio-Nano Generators Questions: 1. How much and what different kind of energy does body produce? 2. How this energy source can be utilized to produce power. 3. What are the technological challenges?

Nanotechnology in Mechanical Engineering