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THERMAL CONDUCTIVITY: A perspective from Nanotechnology. Diego A Gomez- Gualdron Seminar II Nanotechnology CHEN 689-601 Texas A&M University April 13 th 2010. PART I INTRODUCTION & CONTEXTUALIZATION. The thermal conductivity relates to the ability of a material to transfer heat.

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thermal conductivity a perspective from nanotechnology

THERMAL CONDUCTIVITY:A perspective from Nanotechnology

Diego A Gomez-Gualdron

Seminar II

Nanotechnology CHEN 689-601

Texas A&M University

April 13th 2010

slide2

PART I

INTRODUCTION & CONTEXTUALIZATION

relevance

Unsuitable values of thermal conductivity might render a new material useless for an application.

Relevance

POWER DISSIPATION

THERMO

ELECTRICITY

INSULATION

HEAT EXCHANGE FLUIDS

overview power dissipation
Overview: Power Dissipation
  • Decrease in size of electronic devices requires ingenuous ways to dissipate heat and protect the device components structure and performance

THINGS TO LOOK FOR:

  • Good thermal contact between components and heat sink
  • Materials with high thermal conductivity and low coefficient of thermal expansion

www.epotek.com

overview insulation
Overview: Insulation
  • The basic principle is the protection of a system from the harsh (hot or cold) conditions in a neighboring region, while fulfilling additional requirements

A MATTER OF COMPROMISE

  • Space suits require insulating materials, while being light enough to be handled by the astronaut
  • Skylights require insulating characteristics, while allowing light to pass through

www.wikipedia.com

www.mygreenhomeblog.com

overview thermoelectricity
Overview: Thermoelectricity
  • In many technologies a vast quantity of heat is eliminated as waste. Nonetheless, the efficiency of the process would be much higher if some of the heat were transformed into electricity

THE FIGURE OF MERIT

  • Materials with a high Seebeck coefficient (S=∆V/∆T) are needed
  • Also a low thermaland a high electrical conductivity would be ideal

www.iav.com

overview heat exchange fluids
Overview: Heat-Exchange Fluids
  • Conventional heat-transfer fluids have inherently poor thermal conductivity compared to solids. Several industries would benefit from increasing their thermal conductivity to reduce heat exchanger sizes and pumping needs

TO HAVE IN MIND

  • High thermal conductivity
  • Low friction coefficient
  • Clogging of microchannels is undesired
  • Lubricating behavior is a plus

www.engadget.com

preliminary approaches
Preliminary Approaches:

INSULATION

  • Evolution of new materials from ceramics to modern composites

bricks

asbestos

fiber glass

www.wikipedia.com

www.scrapetv.com

www.coolandquiet.com

preliminary approaches10
Preliminary Approaches

POWER DISSIPATION

  • Changes in the electronics technology rather than in cooling methods

CMOS technology

vacuum tube

BJT transistor

www.solarbotics.com

www.digitalcounterproducer.com

www.noveltyradiocom

preliminary approaches11
Preliminary Approaches

THERMOELECTRICS

  • Not much interest until the 90’s, because of conflicting characteristics of materials (figure of merit)

Radioactive heating

Thermoelectric Module

www.thermoelectrics.caltech.edu

www.thermoelectrics.caltech.edu

preliminary approaches13
Preliminary Approaches

HEAT EXCHANGE

  • Playing with the design equation Q=UA (Ti-To) and making heat integration

Microchannel heat exchanger

Helically baffled heat exchanger

www.alltecho.co.uk

www.cerematec.com

contextualization

The intelligent design of the nanostructure of a material can provide all the desired properties, including the thermal conductivity

Contextualization

Nanotechnology-based revolution!!!

REQUIREMENTS

  • Understanding the heat transfer phenomena at the molecular level
  • Modification of the structure of the material accordingly
  • Computational and experimental resources to determine k at the nanolevel

www.salaswildthoughts.blogspot.com

current research nanotechnology
Current Research: Nanotechnology

Nanofluids/Heat Exchange

Aerogels/Insulation

Reduce k

Increase k

www.boingboing.net

www.kostic.niu.edu

current research nanotechnology16
Current Research: Nanotechnology

Thin Film/Thermoelectrics

MEMS/Power Dissipation

Reduce k

Nature Materials (2008) Vol 7, 105

Nature Nanotechnology(2008) Vol 3, 275

emphasis polymer industry
Emphasis: Polymer Industry

www.epotek.com

www.wikipedia.com

www.batchglow.co.uk

motivation polymer industry

One of the most pervasive materials in modern society

Motivation: Polymer Industry

Bayern chemical Plant, Baytown, Texas

  • Ease of processing and versatility
  • Attractive for the development of new materials
  • Integral part of high-tech applications

Nature Materials (2008) Vol 7, 261

research status polymer industry

Structural Reinforcement

  • Increase of Electrical Conductivity
  • Increase of Thermal Conductivity
Research Status: Polymer Industry

www.silmore.cn

slide21

PART II

THEORETICAL BACKGROUND

mechanism electron heat transport
Mechanism: Electron Heat Transport
  • Characteristic of metallic compounds

Free Electrons

High Kinetic Energy Electrons

Metal Atoms

Interaction between energetic electron and atom

Strong vibration

HOT REGION

Increased vibration

mechanism electron heat transport23

Very effective heat transport mechanism

  • Characterized by electron mean free path
  • Not so sensitive to lattice defects
  • Typically 20-400 W/m.K
Mechanism: Electron Heat Transport
mechanism phonon heat transport
Mechanism: Phonon Heat Transport
  • Characteristic of most compounds

Vibrational excitation being transmitted

Strong vibration

HOT REGION

A Diamond lattice

mechanism phonon heat transport25
Mechanism: Phonon Heat Transport
  • Heat is transferred through lattice vibrations
mechanism phonon heat transport26
Mechanism: Phonon Heat Transport
  • Phonons are quantized analogous to the vibrations of a guitar string

Phonon velocity (sound speed)

L

k=1/3(CVv l)

Mean free path length

Heat capacity

www.wikipedia.com

mechanism phonon heat transport28

Not as efficient as electron heat transport

  • Characterized by phonon free path and velocity
  • Very sensitive to defects (e.g. amorphous structure of polymers)
  • Typical values range from 0.01-50 W/m.K
Mechanism: Phonon Heat Transport
molecular simulation

The Green-Kubo expression for thermal conductivity is widely used

Molecular Simulation

k= V ∫dt <JQ(t)JQ(0)>

kBT2

  • Force Field defining potential energy
  • Instantaneous velocities related to kinetic energy
  • Sometimes and external field

www.zeolites.nqs.northwetern.edu

thermal conductivity design

Analogy with electric circuits with R ~ 1/k

Thermal Conductivity Design

Aerogel structure

Serial Resistances

www.aip.org

www.boingboing.net

thermal conductivity design32

Altering the value of the resistances…

Thermal Conductivity Design

Improving crystallinity

Adding defects

decrease resistance

Increase resistance

www.chemistryland.com

Nature Materials (2008) Vol 7, 105

slide33

PART III

CASE STUDY:

A Polymer more conductive than metal

alternative work polymer composites

Embedding thermally conductive nanostructures in a polymeric matrix

Alternative work: Polymer Composites

TEM image of a composite

www.physorg.news

Nature (2007), Vol 447, p. 1066

alternative work carbon nanotube conductivity

Molecular simulations reveal a thermal conductivity of ~ 104 W/m.K

Alternative work:Carbon Nanotube Conductivity

Nanotube (10,10)

Green-Kubo relation

Phys. Rev. Let. (2000) Vol 84, p. 4663

alternative work nanotube polymer composites

An effort to conduct through the nanotube network instead of the polymer matrix

Alternative Work: Nanotube-Polymer Composites

TEM side view

Ideal structure model

Adv. Mat. (2005) Vol 17, p. 1562

preliminary work conduction in molecular chains

Experimental work shows ultrafast thermal transport in self-assembled molecules

Preliminary Work: Conduction in Molecular Chains

Set-up schematics

Self-assembly

Summary

  • Sample is heated with a pulsed laser
  • Sum Frequency Generation (SFG) spectroscopy is performed

Science (2007) Vol 317, p. 787

preliminary work thermal conductivity of polymer chains

Polyethylene chains were shown to have k in the order of 103 W/m.K

Preliminary work:Thermal Conductivity of Polymer Chains

Thermal conductivity for different domain sizes

Polyethylene chain

Phys. Rev. Let. (2008) Vol 101, p. 235502

motivation

Modification of thermal properties in polymers composites not as good

Motivation
  • Molecular simulations and experiments suggest high thermal conduction in hydrocarbon chains
  • Thermal conductivity enhancement done on microfibers
featured paper synthesis procedure
Featured Paper:Synthesis Procedure

Fiber Drawing Schematics

a) Polyethylene gel preparation

b) Gel sample heating

c) Tungsten tip contact wit gel

d) Tungsten tip withdrawing

e) Microscope inspection

f) Secondary heating activated

Nature nanotechnology (2010), Vol. 5, p. 251

featured paper nanostructure changes
Featured Paper:Nanostructure Changes
  • Molecular chains are expected to align, thus approaching the ideal case of a thermal transport on a single chain

nanostructure in gel sample

nanostructure in nanofiber

Nature Nanotechnology (2010), Vol. 5, p. 251

featured paper nanostructure changes46
Featured Paper:Nanostructure Changes
  • The structure achieves crystallinity as confirmed by diffraction measurements

TEM image of the fiber

Diffraction pattern of the fiber

Orthorhombic Structure

Nature Nanotechnology (2010), Vol. 5, p. 251

featured paper thermal conductivity measurements
Featured Paper:Thermal Conductivity Measurements

Measurement Setup

a) Cantilever holds the fiber

b) Fiber cut at 300µm from the tip

c) Loose end joined to thermocouple

d) Thermocouple heated up

e) Cantilever is stimulated

f) Laser picks up the signal

general challenges

Improve uncertainty in measurements

  • Understand mechanism in nanostructures
  • Trade-off in design of material properties
General Challenges
particular challenges

Structure uniformity along the nanofiber

  • Adapt process for future scaling up
  • Vanish thermal resistance among fibers
Particular Challenges
follow up research

Dependence of fiber structure from process parameters:

1) Heating rate and strategy

2) Nature of gel preparation

3) Drawing rate

4) Composition

  • Is it possible to make ‘Doped’ nanofibers?
Follow-up Research
follow up research52

Exploration of fillers that reduce thermal contact

Follow-up Research

Nanofiber

Thermal Contact

Nanofiber

  • Design of processesexploiting 1-D heat transport

Q

HEAT SINK

Electrical Component

g4 rebuttal thermal conductivity

G4Rebuttal: Thermal Conductivity

Diego A. Gómez-Gualdrón

slide55

Reviewer G1: “The presenter gave an overview and contextualization of the topic. However, this part of the talk lasted too long and was a little disorganized and there was not direct relation with the papers he talk”

A:/ 1) The thermal conductivity is an important parameter in the design of an overwhelming number of applications and worth of a careful review. The reviewer is assessing part I as it were and introduction to part III. The three sections of the presentations are meant to be independent, and were timed accordingly.

2) I invite the reviewer to check the slides again and he will clearly see the following structure for part I:

a) Definition of thermal conductivity

b) Relevance and fields of application

c) Overview: Power Dissipation → Insulators →

thermoelectricity → Heat Exchange

d) Preliminary Approach: Power Dissipation →

Insulators → thermoelectricity → Heat Exchange

e) Nanotechnology Approach: : Power Dissipation →

Insulators → thermoelectricity → Heat Exchange

Then, It is stated the interest and motivation of manipulating TC in polymers in particular, and the featured paper is announced

slide56

Reviewer G1: “The presenter gave an overview and contextualization of the topic. However, this part of the talk lasted too long and was a little disorganized and there was not direct relation with the papers he talk”

A:/ 3) There was not direct relation, because the three sections are independent. Part I reviews the role of thermal conductivity in several fields, and the role that nanotechnology has started playing in them. Part II visits the theoretical background needed to be able to understand and manipulate thermal transport at the nanoscale. Parts III explores the latest progress in manipulating the thermal conductivity of a material (a polymer in this case) using nanotechnology.

Reviewer G1: “The overall presentation was good, however I think he had the opportunity of exploiting a little more the topic since there are some recent applications of thermal transport to create logical circuits using the rectification capability of designed graphene sheets. This phenomenon opens the possibility to a large variety of applications”

A:/ There has been more than enough examples of nanotechnology applications in electronics during the class. I can understand that due to the academic background of the reviewer he prefers focusing on circuits and whatnot. However, I think that for a class of chemical engineers, an application involving polymers is much more attractive. Besides, the featured application is a beautiful example how nanotechnology can alter commonplace conceptions such as polymers being poor thermal conductors.

slide57

Reviewer G2: “It would have been good mentioning the reason for the difference on the nature of main thermal carriers when comparing metals and polymers”

A:/ During the oral presentation, from slides 22 through 24, this was explained. In slide 22 the graph shows the existence of free electrons in metallic compounds and described a mechanism based on them. In slide 24, the mechanism in all other compounds (this includes polymers) is explained. Diamond was used as a example of a material with no free electrons, hence featuring a phonon-controlled thermal transport

Reviewer G2: “The typical or approximate values of electron and phonon mean free path for metal and polymers were not mentioned”

A:/ I agree. Here are the values : mean free path of electrons varies between 5-50 Å; mean free path of phonons varies from 500 to 700 nm

Reviewer G2: “The Green-Kubo expression for thermal transport was mentioned but not well depicted, neither its relation with Fourier’s law”

A:/ The impact this would have had on the overall presentation is not worth the additional time needed to go into the mathematical details of the equation. The term autocorrelation function was briefly explained, as well what the terms of the equation were, and what you needed to run the simulation. The gist of that slide is that there exists an equation to calculate the thermal conductivity using molecular simulations

slide59

The presenter gave an overview and contextualization of the topic. However, this part of the talk lasted too long and was a little disorganized and there was not direct relation with the papers he talk. He talk in the second part about the difference between electron and phonon heat transport and theoretical background that help to understand the topic.

He showed some attempts to improve the thermal conductivity of polymer using carbon nanotubes. He also showed some Molecular Dynamics simulations and how Polyethylene chains were shown to have k in the order of 103 W/mK. In the actual paper he described the synthesis of the nanofibers. He explained how they were able to measure the thermal conductivity on the nanofibers that was in the range of 110W/mK .

http://images.iop.org/objects/ntw/news/7/3/21/070321-right.jpg

The overall presentation was good, however I think he had the opportunity of exploiting a little more the topic since there are some recent applications of thermal transport to create logical circuits using the rectification capability of designed graphene sheets. This phenomenon opens the possibility to a large variety of applications.

slide61

Thermal conductivity lecture review

It would have been good mentioning the reason for the difference on the

nature of main thermal carriers when comparing metals and polymers.

The typical or approximate values of electron and phonon mean free path

for metal and polymers were not mentioned.

The Green-Kubo expression for thermal transport was mentioned but not well

depicted, neither its relation with Fourier’s law.

It’s noticeable the effort of the presenter on trying to explain the concepts as

far as possible using graphic illustrations.

It was well emphasized the challenges when trying to integrate the polymer

nanofiber in ‘networks’ for potential applications, because it’s desired not

loosing the outstanding 1-D thermal conductivity of a single nanofiber.

Alfredo D. Bobadilla

review
Review
  • Defines Thermal Conductivity and it’s applications
    • New Nanostructure Materials
      • Polymers
        • Structural Reinforcement
        • Increase Electrical Conductivity
        • Increase of Thermal Conductivity
          • Polyethylene Nanofibres
  • Defined
    • Electron Heat Transport
    • Phonon Heat Transport
review64
Review
  • Thermal Conductivity design
    • Can be viewed as an electrical series of resistors or Parallel Resistances
      • Increase defects or Decrease defects to increase or decrease resistance
  • Polymer composites
    • Embedded thermally conductive nanostructure into polymer matrix
  • Nanotube-Polymer Composites
    • Uses a Nanotube matrix instead of a Polymer matrix
review65
Review
  • Conduction through Molecular Chains
    • Polyethylene Chains, k = 103 W/(m*K)
      • Addition of nanofibers might help
  • Polyethylene Nanofibers
    • Synthesis
      • Nanostructure Changes as Nanofiber is pulled
    • Thermal Conductivity Measured
      • K = 110 W/(m*K)
        • Higher than most pure metals
    • Challenges
      • Understand Mechanisms, Scale Up, Uniformity issues
    • Future work was discussed
thermal conductivity by diego gomez gualdron
Thermal Conductivity, by Diego Gomez-Gualdron
  • Diego did an excellent job in his presentation, he has very good skills that he implements well in his oral presentations. Very fluent, well prepared, organized and able to deliver concepts and ideas to the audience.
  • The information presented was highly oriented for undergraduates and Chemical Engineers, I understand his motivation to do that but I believe he underestimated the audience capability to digest more state of the art and deep information.
slide69

The preparation was very well organized.

  • The oral presentation was also very good. It flowed very well and was sequenced nicely to let the audiences to understand the presentation.
  • There were very interesting ideas such as aerogels.
  • The introduction was quite well organized as the topic was a very broad and hard to gather and present ideas.