Transcript MS PowerPoint - Indian Institute of Technology Madras

Chemistry in 21st Century
National Centre for Catalysis Research
INDIAN INSTITUTE OF TECHNOLOGY MADRAS
APRIL 2010
Coverage and Reasons
Title
Periodic properties of elements
Nomenclature and isomerism of coordination compounds
Nuclear reactions and carbon dating
Types of hybridization and geometry of molecules
Chemical equilibrium – Le Chatliers principle
Colloids and applications
Faradays laws and Kohlrausch’s law
Extraction of Metals
Spontaneous and non spontaneous reactions
Corrosion and its prevention
Properties and packing in solids
Wave equation and its significance
Petroleum and Petro chemicals
Bonding in molecules
Conventional concepts of bonding has to undergo change – Why?
Behaviour of molecules and reactivity of molecules – what is so special
selectivity?
Geometry of the molecules, manifestations of molecules – functioning of
molecules.
Architecture in solids – transport restrictions
Electrochemistry turns chemistry to be fully green
Behaviour of electrons – responsible for the science that is usually
generated
Nuclear structure – evolution period and also energy conversion process
20th Century Chemistry
•
•
•
•
It was a silent revolution
Ammonia synthesis provided a means for food
FCC operation brought engineering marvel
Zeolites and solid state materials –
revolutionized electronic industry
• Super conductors – energy concept changed
colours
• Water will it be another wonder molecule this
century
WEAK INTERACTIONS
• Assembly appears to be the order these days – these
assembly can arise out of weak interactions
• Weak interactions may be hydrogen bonding, van der
waals forces and simple over lap of the least amount
of charge cloud.
• Assembly assumes particular geometries, like helical
structure, nano-coils, nano-twisted wires and many
others – these resemble the bio-molecules
What is Green Chemistry?
It is better to prevent waste
than to clear it up afterwards
% Atom economy is the
new % yield
The strive towards the
perfect synthesis
Benign by design
Environmentally friendly
and economically sound?!?
The Twelve Principles of Green Chemistry
• It is better to prevent waste than to treat or clean up waste after it is formed.
• Synthetic methods should be designed to maximize the incorporation of all materials
used in the process into the final product
• Wherever practicable, synthetic methodologies should be designed to use and generate substances
that possess little or no toxicity to human health and the environment
• Chemical products should be designed to preserve the efficacy of function whilst
reducing toxicity
• The use of auxiliary substances (e.g. solvents) should be made unnecessary
wherever possible and innocuous where used
• Energy requirements should be recognized for their environmental and economic impacts and
should be minimized. Synthetic methods should be carried out at ambient temperature and
pressure
• A raw material of feedstock should be renewable rather than depleting wherever technically and
economically possible
• Unnecessary derivatization (e.g. protecting groups) should be avoided wherever possible
• Catalytic reagents (as selective as possible) are superior to stoichiometric reagents
• Chemical products should be designed so that at the end of their function they do not persist in the
environment and breakdown into innocuous degradation products
• Analytical methodologies need to be further developed to allow for real-time inprocess monitoring
and control prior to the formation of hazardous substances
• Substances and the form of substances used in a chemical process should bechosen so as to
minimize the potential for chemical accidents, including releases, explosions and fires
A Series of Reductions
Cost
Risk &
Hazard
Materials
Reducing
Waste
Energy
Nonrenewables
How Efficient is Chemical Manufacturing?
E-factors
Industry
Oil refining
Bulk Chemicals
Fine chemicals
Pharmaceuticals
Product tonnage
106 – 108
104 – 106
102 – 104
10 - 103
Kg by-products /
Kg product
< 0.1
1-5
5 - 50+
25 - 100+
Industrial Ecology Goals for Green Chemistry
• Adopt a life-cycle perspective regarding chemical
products and processes
• Realise that the activities of your suppliers and customers
determine, in part, the greenness of your product
• For non-dissipative products, consider recyclability
• For dissipative products (e.g. pharmaceuticals, crop
protection chemicals) consider the environmental
impact of product delivery
• Perform green process design as well as green product
design
Some Barriers to Adopting Greener Technology
· Lack of global harmonisation on regulation / environmental policy
· Notification processes hinder new product & process development
· Lack of widely accepted measures of product or process “greenness”
· Lack of technically acceptable 'green' substitute products and processes
· Short term view by industry and investors
· Lack of sophisticated accounting practices focussed on individual processes
· Difficult to obtain R&D funding
· Difficult to obtain information on best practice
· Lack of clean, sustainable chemistry examples & topics taught in schools & universities
· Lack of communication / understanding between chemists & engineers
· Culture geared to looking at chemistry not the overall process / life cycle of materials
The Chemical Industry in the 21st Century
Meeting social, environmental and economic responsibilities
• Maintaining a supply of innovative and viable chemical
technology
• Environmentally and socially responsible chemical
manufacturing
• Teaching environmental awareness throughout the education
process
Twilight Can Turn into ““A”” New Dawn
Twilight creates illusion of light getting stronger.
Twilight then fades into a dark night.
It is always darkest before dawn.
If we solve our energy crisis, the 21st
century will be our greatest dawn.
If we fail, we will have a dark future.
Aggregation is it universal?
• Having seen single molecules and their
behaviour one has to turn the attention to
aggregates.
• Why aggregates, it appears it is the natures
way of preserving and fostering things – trees,
plants, animals, human beings everything live
as aggregates and care for the total aggregated
assemblies and not for the individual species.
Aggregation
• The existence of single molecules can be
understood from the point of view of
minimization of free energy
• Aggregates how do they minimize the energy?
• What is the driving force for this aggregation?
• What is the type of interactions present in
aggregation?
Weak bonding is the cause for aggregation?
• What are weak bonding and how do they cause the
aggregation?
• What are the energies involved in these weak
forces?
• Are there a variety of these weak forces?
• Do they have any constraints in geometry,
functionality, and electronic configuration?
• How these weak forces account for the stabilities
observed
How Universal are aggregates?
• Many bio-molecules are aggregates
• Materials are always aggregates but the
dimensionality ( uni, bi and tri dimensions) impart
unique properties Why?
• Not only dimensions but also size in nanoscale and
bulk scale they are different – shows aggregation
has a role to play even in terms of the number of
species aggregating?
Geometry has this a role in Aggregation
• This is a question one has to ask at this time
• It is known that the helical structure of vital species
like DNA, collagen and other species? Why helical
structure why not strings and wires and ropes?
• Twisted configurations why are they more stable
than strings and wires?
• Nano coils and nano architectures how are they
become more stable?
Some examples of aggregates in molecular systems
• Water when aggregated becomes less dense
than water in liquid state but for all others the
density increases when solidification – to
show that both directions the change can take
place on aggregation.
• Some time back people talked on “poly water”
a concept which has been subsequently
discarded – Why and why poly water cannot
exist – any concept has evolved
Assembly why this is universal?
Directed Assembly addresses the fundamental scientific issues underlying
the design and synthesis of new nanostructured materials, structures,
assemblies, and devices with dramatically improved capabilities for many
industrial and biomedical applications.
It focuses on discovering and developing the means to assemble nanoscale
building blocks with unique properties into functional structures under
well-controlled, intentionally directed conditions.
Directed assembly is
the fundamental gateway to the eventual success of technology. It
is based upon well-integrated research efforts that combine computational design
with experimentation to discover novel pathways to assemble functional multiscale
nanostructures with junctions and interfaces between structurally, dimensionally,
and compositionally different building blocks. These efforts are leading to new
methodologies for assembling novel functional materials and devices from
nanoscale building blocks that will lead to novel applications of nanotechnology to
spur industry into the 21st century.
Control of Polymer Supermolecular Morphology
A collaborative effort between L.S. Schadler, R.W. Siegel, Y. Akpalu (RPI) and ABB focuses on using
nanoparticles to control the supermolecular morphology of semicrystalline polymers and their
properties. The figure shows the effect of 20 nm diameter TiO2 nanoparticles dried or coated with
N-(2-aminoethyl)3-aminopropyl-trimethoxysilane (AEAPS) on low-density polyethylene (LDPE).
There is no change in unit cell dimension, degree of crystallinity, average lamellar thickness, or
average spherulite size. The supermolecular structure, however, is impacted. Neat LDPE and the
dried sample exhibit a well-defined, impinging, banded spherulite structure. The nanoparticles are
embedded between the lamellae. In great contrast, no well-developed banded spherulites are
observed in the AEPS sample, in which nanoparticles segregate to inter-spherulitic regions. This
supermolecular structure is critical in controlling electrical breakdown strength in LDPE.
m
m
m
Figure: AFM tapping mode images of the supermolecular structures of (a) neat LDPE
(b) LDPE filled with more compatible dried TiO2 nanoparticles and (c), LDPE filled with
non-compatible AEAPS coated TiO2 nanoparticles.
Some examples of aggregation
In the next few slides ( mostly reproduced from
literature and none of them are our own) we
demonstrate how aggregated systems are relevant,
perform and exhibit unusual properties.
These are chosen randomly and no specific
significance to be attached to the choice.
What is the aggregation that we talk about?
water molecule
Molecule of DNA
Protein molecule
Carbon nanotube
Water molecules – 3 atoms
Protein molecules – thousands of atoms
DNA molecules – millions of atoms
Nanowires, carbon nanotubes – millions of
atoms
What are Nanostructures?
At least one dimension is between 1 - 100 nm
2-D structures (1-D confinement):
• Thin films
• Planar quantum wells
• Superlattices
1-D structures (2-D confinement):
• Nanowires
• Quantum wires
• Nanorods
• Nanotubes
0-D structures (3-D confinement): Multi-wall carbon
• Nanoparticles
nanotube
• Quantum dots
Dimensionality, confinement depends on
structure:
• Bulk nanocrystalline films
• Nanocomposites
http://www.aip.org/mgr/png/2003/186.htm
2 m
Si Nanowire Array
Si0.76Ge0.24 / Si0.84Ge0.16 superlattice
Thin Films
Nanoscale Thin Film
• Single “two dimensional” film, thickness < ~100 nm
• Electrons can be confined in one dimension;
affects wavefunction, density of states
• Phonons can confined in one dimension; affects thermal
transport
• Boundaries, interfaces affect transport
a
Thin film
Bulk
crystal
Substrate
Free
standing
thin film
d
http://scsx01.sc.ehu.es/waporcoj/charl
as/cursodoctorado/12
Nanowires
• Solid, “one dimensional”
• Can be conducting, semiconducting, insulating
• Can be crystalline, low defects
• Can exhibit quantum confinement effects
(electron, phonon)
• Narrowing wire diameter results in increase in
band gap
• Narrowing wire diameter can result in
decrease in thermal conductivity
• New forms include core-shell and
superlattice nanowires
Nanotube defined – a long cylinder with
inner and outer nm-sized diameters
Nanowire defined – a long, solid wire
with nm diameter
Abramson et al, JMEMS (2003)
Wu et al, Nanoletters, Vol. 2, 83 – 86 (2002)
2 m
Si Nanowire Array
Si/SiGe Nanowires
Carbon Nanotubes
Carbon nanotube properties:
• One dimensional sheets of hexagonal
network of carbon rolled to form tubes
• Approximately 1 nm in diameter
• Can be microns long
• Essentially free of defects
• Ends can be “capped” with half a buckyball
• Varieties include single-wall and multi- wall
nanotubes,ropes, bundles, arrays
• Structure (chirality, diameter)
influences properties:
– Semiconducting vs. metallic
– Thermal, electrical conductance
– Mechanical strength, elasticity
Multi-wall carbon
nanotube
Armchair
Zigzag
http://physicsweb.org/article/world/11/1/9/1
http://www.aip.org/mgr/png/2003/186.htm
Chiral
Other Nanotubes…
Boron nitride nanotubes
Boron nitride
nanotubes
• Resistance to oxidation,
adopt various
suited for high temperatures
shapes
• Young’s modulus of 1.22 TPa
(red=boron,
blue=nitrogen):
• Semiconducting
• Predictable electronic
properties independent of
diameter and # of layers
SiC nanotubes:
• Resistance to oxidation
SiC nanotubes
• Suitable for harsh
grown at NASA
Glenn:
environments
• Can functionalize surface Si
atoms
http://www.grc.nasa.gov/WWW/RT2002/5000/5510lienhard.html
http://pubs.acs.org/cen/topstory/7912/7912notw1.html
Energy Applications: Conversion, Generation
and Storage
Cold
Metal organic
framework for
hydrogen storage
Hot
2 m
I
Dresselhaus group, MIT
Replace conventional
material with nanocomposite
to enhance performance
Abramson et al, JMEMS, in review.
Rosi et al, Science, Vol. 300, pp. 1127
-1129 (2003).
Energy Applications: Catalysis
Oil refinement: zeolites are
nanoporous (pores 3 – 10 Å)
crystalline solids with well-defined
structures (“molecular sieves”) used
in oil refinement – increases
gasoline yield from each barrel of
crude oil by 50%
http://www.iaee.org/docum
ents/p03eagan.pdf
http://www.bza.org/zeolit
es.html
2 atomic layer thick Au
nanoclusters on TiO2
Porous zeolite structure
Energy Applications: LEDs
Change the nanostructure
of Si (a very cheap
material) to become
nanoporous and visible
light is emitted!
Use quantum dots
(quantum confinement) for
light emission
Cross-hairs of p-type and
n-type nanowires (to get a
p-n junction)
Network of nanowires
http://www.trnmag.com/Stories/011701/Crossed_nano
wires_make_Lilliputian_LEDs_011701.html
Quantum dot layers
http://www.trnmag.com/Stories/2002/103002/Nanoscale_LED_debuts_103002.html
Energy Applications: LEDs
Quantum dots/
nanocrystals are smaller
than the wavelength of
light, so they do not
scatter light; scattering
can reduce optical
efficiency by up to 50%!
Energy Applications: Batteries
Change electrode materials by nanostructuring (texturing) to
improved electrical performance; nanoscale particles boost
energy storage and power delivery by reducing the distance
Li ions travel during diffusion
Nanobattery: Fill a nanoscale membrane with an electrolyte,
cap with electrodes; contact with a probe tip
Energy Applications: Solar
Solar cells integrated into roof
shingles
Nanoscale crystals of semiconductor
coated with light-absorbing dye emit
electrons
Nanostructured diamond solar thermal
cells capture light, which heats the
lattice, which emits electrons; small tip
gives high energy electrons
Tetrapods (the light absorbing
materials) double the efficiency of
plastic solar cells because they always
point in the right direction
http://www.spacer.com/news/solarcell-01b.html
Nanostructured diamond
solar thermal cells
Branched tetrapod
Dendritic Macromolecules as Unimolecular Micelles for
Organic Solutes
(Stribaet al. 2002, Angwate. Chemie. Int.
Ed., 41 (8), pp 1329-1324)
MD Simulations of the Meijer
Dendrimer Box Mikliset al. 1997,
JACS, 131, 7458
Catalytic DendriticMacromolecules
(AstrucD. and Chardac, F. Chem. Rev. 2001, 101, 2991-3023)
Dendrimer-Encapsulated Zero Valent Metal Clusters
(Scott et al. J. Phys. Chem. B. 2005, 109, 692-704)
Bioactive Dendritic Macromolecules
(Chen et al. 2000, Biomacromolecules,1 (3): 473-480)
Fate, Transport and Toxicity of Dendritic aggregates
• Numerous dendrimers their toxicity and bio-distribution
studies have carried out during the last 5 years
• –The effects of dendrimer core and terminal group
chemistry, size, shape, hydrophobicity on dendrimer
interactions with cell membranes and toxicity are
becoming known and understood.
• •Only a limited number of studies have been published on
the fate and tranport of dendrimers in the environment
• –Sorption of dendrimers onto mineral surfaces
Basic Research Needs to Assure
a Secure Energy Future - Role of aggregates
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
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Materials Research to Transcend Energy Barriers
Energy Biosciences
Research Towards the Hydrogen Economy
Energy Storage
Novel Membrane Assemblies an example
aggregates
Heterogeneous Catalysis- aggregate site density
Energy ConversionEnergy Utilization Efficiency
Nuclear Fuel Cycles and Actinide Chemistry
Geosciences
of
Some concepts already in vogue
• The concept of “ensemble effect” in catalysis is well known – this is a
form of the aggregates that we call.
• The concept of “active site” is known in catalysis but these are not
single atom site but some sites in particular locations with definite
neighbours this is another version of aggregated sites.
• The concept of metal support interaction or as a matter of fact SMW
interactions always imply an aggregated site – therefore the concept of
aggregation and they behaving differently is known. SMSI and other
interactions do not involve specific bonds and should be involving
weak interactions.
• Weak interactions and its manifestations are therefore already known
but has not been specifically indicated or identified.
Drivers for the Hydrogen Economy:
% of U.S.
% of Total
Electricity U.S. Energy
Energy Source
Supply
Supply
Oil
3
39
Natural Gas
15
23
Coal
51
22
Nuclear
20
8
Hydroelectric
8
4
Biomass
1
3
Other Renewables
1
1
• Reduce Reliance on Fossil
Fuels
• Reduce Accumulation of
Greenhouse Gases
20
Actual Projected
18
16
14
Domestic
Production
12
Marine
10
8
6
Off-road
Light Trucks
Rail
4
Passenger
Vehicles
Millions of Barrels per Day
22
Cars
2
0
1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025
Year
The Hydrogen Economy
solar
wind
hydro
H2O
nuclear/solar
thermochemical
cycles
Bio- and
bioinspired
automotive
fuel cells
H2
gas or
hydride
storage
H2
stationary
electricity/heat
generation
fossil fuel
reforming
production
storage
9M tons/yr
4.4 MJ/L (Gas, 10,000 psi)
8.4 MJ/L (LH2)
150 M tons/yr
(light cars and trucks in 2040)
consumer
electronics
9.70 MJ/L
(2015 FreedomCAR Target)
use
in fuel cells
$3000/kW
$30/kW
(Internal Combustion Engine)
Fundamental Issues
The hydrogen economy is a compelling vision:
- It potentially provides an abundant, clean, secure and flexible
energy carrier
- Its elements have been demonstrated in the laboratory or
in prototypes
However . . .
- It does not operate as an integrated network
- It is not yet competitive with the fossil fuel economy in
cost, performance, or reliability
- The most optimistic estimates put the hydrogen economy
decades away
Thus . . .
- An aggressive basic research program is needed,
especially in gaining a fundamental understanding of the
interaction between hydrogen and materials at the nanoscale
Hydrogen Production versus other fuel sources
Current status:
• Steam-reforming of oil and natural gas produces 9M tons H2/yr
• We will need 150M tons/yr for transportation
• Requires CO2 sequestration.
Alternative sources and technologies:
Coal:
• Cheap, lower H2 yield/C, more contaminants
• Research and Development needed for process development,
gas separations, catalysis, impurity removal.
Solar:
• Widely distributed carbon-neutral; low energy density.
• Photovoltaic/electrolysis current standard – 15% efficient
• Requires 0.3% of land area to serve transportation.
Nuclear: Abundant; carbon-neutral; long development cycle.
Priority Research Areas in Hydrogen Production
Fossil Fuel Reforming Intermediate Term
Molecular level understanding of catalytic mechanisms,
nanoscale catalyst design, high temperature gas
separation
Solar Photoelectrochemistry/Photocatalysis
Light harvesting, charge transport, chemical assemblies,
bandgap engineering, interfacial chemistry, catalysis
and photocatalysis, organic semiconductors, theory and
modeling, and stability
Ni surface-alloyed with Au to reduce
carbon poisoning
Bio- and Bio-inspired H2 Production
Microbes & component redox enzymes, nanostructured
2D & 3D hydrogen/oxygen catalysis, sensing, and energy
transduction, engineer robust biological and biomimetic
Dye-Sensitized Solar Cells
H2 production systems
Synthetic Catalysts
for H2 Production
Nuclear and Solar Thermal Hydrogen
Thermodynamic data and modeling for thermochemical
cycle (TC), high temperature materials: membranes, TC
heat exchanger materials, gas separation, improved
catalysts
Thermochemical Water Splitting
Hydrogen Storage Panel
Current Technology for automotive applications
• Tanks for gaseous or liquid hydrogen storage.
• Progress demonstrated in solid state storage materials.
System Requirements
• Compact, light-weight, affordable storage.
• System requirements set for FreedomCAR: 4.5 wt% hydrogen for 2005,
9 wt% hydrogen in the near future.
• No current storage system or material meets all targets.
30
Volumetric Energy Density
MJ / L system
Energy Density of Fuels
gasoline
liquid H2
20
compressed
gas H2
10
proposed DOE goal
chemical
hydrides
0
0
complex
hydrides
10
20
30
Gravimetric Energy Density
MJ/kg system
40
Ideal Solid State Storage Material
• High gravimetric and volumetric density (9 wt %)
• Fast kinetics
• Favorable thermodynamics
• Reversible and recyclable
• Safe, material integrity
• Cost effective
• Minimal lattice expansion
• Absence of embrittlement
Fuel Cells and Novel Fuel Cell Materials Panel
What are Fuel Cells?
2H2+ O2 2H2O + electricalpower + heat
2H2 + O2  2H2O + electrical power + heat
Current status:
Limits to performance are materials, which
have not changed much in 15 years.
Challenges:
Membranes
Operation in lower humidity, more strength,
membrane conducts protons from anode to cath
Membrane
conducts protons from anode to cathode
ProtonExchangeMembrane (PEM)
durability and higher ionic conductivity. www.hpower.com
cathodeproton
proton exchange membrane (PEM)
(PEM)
Cathodes
Materials with lower overpotential and resistance to impurities.
Low temperature operation needs cheaper (non- Pt) materials.
Tolerance to impurities: S, hydrocarbons, Cl.
Anodes
Tolerance to impurities: CO, S, Cl.
Cheaper (non or low Pt) catalysts.
Reformers
Need low temperature and inexpensive reformer catalysts.
Fuel Cell Model
THE ISSUE: better, cheaper, more durable, impurity tolerant
materials. Most must/will be structured on the nanoscale.
NOT TO SCALE
Fuel:
H2, CH4, CH3OH
External Load
Oxygen (O2)
e-’s
Chemical Reduction:
Chemical Oxidation:
Consumes e-
Liberates eIon
Transp.
Reaction
Products
Anode
(Oxidation)
Frank DiSalvo (Cornell)
Reaction
Products
Ionic Conductor
(Membrane)
Cathode
(Reduction)
Electrode/Membrane Design
Very challenging. Electrodes need to support three
percolation networks: electronic, ionic,
fuel/oxidizer/product access/egress.
2 –5 nm
20 -50
m
Alloys vs. Ordered Intermetallics
Alloy; e.g. Pt/Ru (1:1)
(A)
Ordered Intermetallic
e.g. BiPt
(B)
“Electrocatalytic Oxidation of Formic Acid at an Ordered Intermetallic PtBi Surface”, E.
Casado-Rivera, Z. Gál, A.C.D. Angelo, C. Lind, F.J. DiSalvo, and H.D. Abruña, Chem.
Phys. Chem. 4, 193-199 (2003)
Enhanced Catalytic Activity for Formic Acid Oxidation
 Cyclic Voltammetry in 0.1 M H2SO4 + 0.125 M formic acid
solution at a sweep rate of 10 mV/s
Pt
PtBi
0.063 mA/cm2
-0.2
0.0
0.2
2.4 mA/cm2
0.4
0.6
0.8
-0.2
0.0
0.2
E(V) vs. Ag/AgCl
0.4
0.6
0.8
1.0
Basic Research Needs for the Hydrogen Economy
Cross-Cutting Research
Directions
 Nanoscale Materials and Nanostructured Assemblies
 Catalysis
- hydrocarbon reforming
- hydrogen storage kinetics
- fuel cell and electrolysis electrochemistry
 Membranes and Separation
 Characterization and Measurement Techniques
 Theory, Modeling and Simulations
 Safety and Environment
Hydrogen Studies
universal finding:
the hydrogen economy requires
breakthrough basic research to find new materials and processes
 define a new state of the art
Directed Assembly addresses the fundamental scientific issues underlying
the design and synthesis of new nanostructured materials, structures,
assemblies, and devices with dramatically improved capabilities for many
industrial and biomedical applications.
It focuses on discovering and developing the means to assemble nanoscale
building blocks with unique properties into functional structures under wellcontrolled, intentionally directed conditions.
Directed assembly is the fundamental gateway to the eventual success of
nanotechnology. It is based upon well-integrated research efforts that
combine computational design with experimentation to discover novel
pathways to assemble functional multiscale nanostructures with junctions
and interfaces between structurally, dimensionally, and compositionally
different building blocks. These efforts are leading to new methodologies for
assembling novel functional materials and devices from nanoscale building
blocks that will lead to novel applications of nanotechnology to spur industry
into the 21st century.
Nanoparticle Control of Polymer Supermolecular
Morphology
A collaborative effort between L.S. Schadler, R.W. Siegel, Y. Akpalu (RPI) and ABB focuses on using
nanoparticles to control the supermolecular morphology of semicrystalline polymers and their
properties. The figure shows the effect of 20 nm diameter TiO2 nanoparticles dried or coated with
N-(2-aminoethyl)3-aminopropyl-trimethoxysilane (AEAPS) on low-density polyethylene (LDPE).
There is no change in unit cell dimension, degree of crystallinity, average lamellar thickness, or
average spherulite size. The supermolecular structure, however, is impacted. Neat LDPE and the
dried sample exhibit a well-defined, impinging, banded spherulite structure. The nanoparticles are
embedded between the lamellae. In great contrast, no well-developed banded spherulites are
observed in the AEPS sample, in which nanoparticles segregate to inter-spherulitic regions. This
supermolecular structure is critical in controlling electrical breakdown strength in LDPE.
m
m
m
Figure: AFM tapping mode images of the supermolecular structures of (a) neat LDPE
(b) LDPE filled with more compatible dried TiO2 nanoparticles and (c), LDPE filled with
non-compatible AEAPS coated TiO2 nanoparticles.
Thank you all for your patience