Chapter 10
Natural and Biological
Inspired Nanocomposites
Noraiham Mohamad, PhD
Department of Engineering Materials
Faculty of Manufacturing Engineering
Universiti Teknikal Malaysia Melaka
INTRODUCTION
What is Biology?
•
the science of life or living matter in all
its forms and phenomena, especially
with reference to origin, growth,
reproduction, structure, and behavior.
•
is a natural science concerned with the study of life and living
organisms, including their structure, function, growth, origin,
evolution, distribution, and taxonomy.
Biology is a vast subject containing many subdivisions, topics, and
disciplines. Among the most important topics are five unifying
principles that can be said to be the fundamental postulates of
modern biology:
• Cells are the basic unit of life
• New species and inherited traits are the product of evolution
• Genes are the basic unit of heredity
• An organism regulates its internal environment to maintain a
stable and constant condition
• Living organisms consume and transform energy.
•
 Subdisciplines of biology are recognized on the basis of
the scale at which organisms are studied and the
methods used to study them:
 biochemistry examines the rudimentary chemistry of life;
 molecular biology studies the complex interactions of
systems of biological molecules;
 cellular biology examines the basic building block of all life,
the cell;
 physiology examines the physical and chemical functions of
the tissues, organs, and organ systems of an organism; and
 ecology examines how various organisms interact and
associate with their environment.
Biological nanocomposite
materials
 Can be divide into three:
 Entirely inorganic
 Entirely organic
 Mixture of inorganic and organic materials
 What is unique about synthetic process?
 “even final material may be entirely one class of material,
multiple classes of materials may be involved in the
synthetic process, which may or may not remain in the final
structure”.
Example of biological
nanocomposites
The organic material does not remain in the final
product:
 Enamel of the mature human tooth
 95wt% consist of hydroxyapatite
 During tooth formation;
 Enamel consist of proteins (primarily amelogenin and enamelin)
and hydroxyapatite.
 But the proteins removed as the tooth develop.
 Presence of protein and self-assembled structures they form
with other biological macromolecules – help generate the
minerl cross-ply structure of the enamel (plays a major part
in its toughness)
Tooth Enamel
Tooth enamel formation. Coloured scanning electron micrograph (SEM)
of a freeze-fractured section through a tooth, showing the enamelforming cell layer (blue). This epithelium comprises a single layer of
column-like cells called ameloblasts. Enamel (green, top) is a hard
ceramic layer that covers and protects the teeth. The end of the
ameloblasts can be seen originating in the internal tooth tissue (brown,
bottom). Magnification x2700 when printed at 10 centimetres wide.
Tooth enamel. Coloured scanning
electron micrograph (SEM) of a
section through tooth enamel. The
enamel is the outer covering the
crown (visible part) of the tooth. It
is the hardest substance in the
human body. It is composed of
rows of calcium and phosphorous
salts (light brown) embedded in a
protein matrix (grey).
Magnification: x1400 when printed
at 10 centimetres wide.
Example of biological
nanocomposites
Inorganic/organic structural composite for both phases
remain in the final product
 Aragonitic nacreous layer of the abalone shell
 It is exceptionally strong because of its organic/inorganic
layered nanocomposite structure
 Crystalline ceramic layers are separated by highly elastic
organic layers
 Synthetic efforts have been made for more than 10
years- their properties have been inferior
Abalone
 Biological systems are known to selfassemble into organized structures at many
length scales. At the smallest levels, the
resulting structures sometimes act as
templates for the growth of other materials.
The end result is a layered composite with
several levels of structural organization. For
example, the structure of an abalone shell
consists of layered plates of CaCO3 (~200
nm) held together by a much thinner (<10
nm) "mortar" of organic template.
Factors of failure in attempts to
copy biology
 Disconnect between needs of engineering materials and
biological materials:
 Biological materials generally form over a period of days to
years, use a limited set of elements, and are designed to be
used within a limited temperature range.
 Practical engineering must be made rapidly (hours or minutes);
generally, must operate over a wide range of temperature and
other environmental conditions
 Scientists conclude:
 “rather than attempting to directly copy biology, a much better
philosophy is to learn from biology and use the knowledge to
create synthetic materials”
 “this may or may not involve the use of some biological
molecules”
 “But, no attempt is made to ‘copy’ specific biological processes”
1. NATURAL
NANOCOMPOSITE
MATERIALS
Natural composite materials
with structure on the nanoscale
2. BIOMIMETIC
NANOCOMPOSITES
Synthetic nanocomposite materials
formed through processes that mimic
biology as closely as possible
3. BIOLOGICALLY
INSPIRED
NANOCOMPOSITES
• Composite materials with nanoscale order created through processes
that are inspired by a biological process or a biological material
• Without attempting to mimic or directly copy the mechanism of
formation of the biological materials
Natural nanobiocomposite
materials
 Natural composite materials with structure on the
nanoscale
 All the functionality provided by these materials- direct
consequence of the nanoscale dimensions of the
structure.
 Example of nanoscale materials in biology:
 Lipid cellular membranes
 Ion channels
 Proteins
 DNA
 Actin
 Spider silk and etc.
Lipid cellular membranes
Phospholipids, the lipid type that
constitutes the majority of the cell
membrane, are made up from a
phosphate head (circles) that like water
and lipid tail (lines) that hate it. These socalled amphipathic molecules line up so as
to limit the exposure of the hydrophobic
portions to the aqueous phase that is
found on both sides of the membrane.
A: The fluid mosaic model of membrane structure. The membrane consists of a phospholipid double layer with
proteins inserted in it (integral proteins) or bound to the cytoplasmic surface (peripheral proteins). Integral
membrane proteins are firmly embedded in the lipid layers. Some of these proteins completely span the bilayer and
are called transmembrane proteins, whereas others are embedded in either the outer or inner leaflet of the lipid
bilayer. The dotted line in the integral membrane protein is the region where hydrophobic amino acids interact with
the hydrophobic portions of the membrane. Many of the proteins and lipids have externally exposed oligosaccharide
chains. B: Membrane cleavage occurs when a cell is frozen and fractured (cryofracture). Most of the membrane
particles (1) are proteins or aggregates of proteins that remain attached to the half of the membrane adjacent to the
cytoplasm (P, or protoplasmic, face of the membrane). Fewer particles are found attached to the outer half of the
membrane (E, or extracellular, face). For every protein particle that bulges on one surface, a corresponding
depression (2) appears in the opposite surface. Membrane splitting occurs along the line of weakness formed by the
fatty acid tails of membrane phospholipids, since only weak hydrophobic interactions bind the halves of the
membrane along this line. (Modified and reproduced, with permission, from Krstíc RV: Ultrastructure of the
Mammalian Cell. Springer-Verlag, 1979.)
Characteristics of natural
nanocomposites
 Dimension characteristic of the structure- at least in 1D
and often in 3D is on the order of a few nanometers
 Composed of discrete nanoscale building block
 In their active form, when folded:
 proteins are composed of domains with varying hydrophilic
and hydrophilicity
 as well as, domains with structural features as alpha
helixes, beta sheets and turns
 It has complex structures containing nanometer-sized
domains of varying chemical properties
 Because of chemically diverse regions- can exhibit acidic,
basic, hydrogen-bonding, hydrophilic or hydrophobic
behavior
 They can interact in exceedingly diverse ways with
precursors for mineral compounds and the final mineral
product
Completely organic
nanocomposites (Spider silk)
 Dragline spider silk which makes up the spokes of a spider
web
 Criteria:
 Strong core that composed of primarily of two protein
components that self assemble into crystalline and amorphous
regions
 Crystalline regions- alternating alanine-rich crystalline forming
block; impart hardness
 Amorphous regions- glycine-rich amorphous blocks; provide
elasticity
 Properties:
 Five times tougher than steel by weight
 Can stretch 30-40% without breaking
 Elastic modulus is significantly less than of steel
 For application in which flexibility and toughness are the
primary need (bullet proof vest)  synthetic route to create
material with properties equivalent to spider silk
Primary structure of spider dragline silk
Fibrous protein composed of Spidroin 1 (MaSp1) and Spidroin 2 (MaSp2)
- Sequences highly conserved
- Repetitive stretches of poly(Ala) and (GlyGlyXaa)n sequences
(Xaa = Tyr, Leu, Gln)
- MW of MaSp1 ~ 275-320 kDa; Sp1+Sp2 ~ 700-750 kDa
Repeating sequence of MaSp1
QGAGAAAAAAGGAGQGGYGGLGGQGAGQGGYGGLGGQGAGQGAGAAAAAAAGGAGQGGYGGLG
GLGGYGGQGAGGAAAAAAGAGQGGRGAGQS
SQGAGRGGLGGQGAGAAAAAAAGGAGQGGYGGLG
GLGGYGGQGAGGAAAAAAGQGGRGAGQN
SQGAGRGGLGGQAGAAAAAAGGAGQGGYGGLGGQGAGQGGYGGLG
GLGGYGGQGAGGAAAASAGAGQGAGQGGLGGQGAGGAAAAAAAGAGQGGLGGRGAGQS
SQGAGRGGEGAGAAAAAAGGAGQGGYGGLGGQGAGQGGYGGLG
GLGGYGGQGAGGAAAAAAGAGQGAGQGGLGGQGAGGAAAAGAGQGGLGGRGAGQS
SQGAGRGGLGGQGAGAVAAAAGGAGQGGYGGLG
GLGGYGRQGAGGAAAAAAGAGQGGRGAGQS
NQGAGRGGLGGQGAGAAAAAAAGGAGQGGYGGLG
GLGGYGGQGAGGAAAAAGQGGRGAGQN
SQGAGRGGQGAGAAAAAAVGAGQEGIRGQGAGQGGYGGLG
GAGGYGGQRVGGAAAAAAGAGQGAGQGGLGGQGAGGAAAAAAGAGQGGLGGRGSGQS
SQGAGRGGQGAGAAAAAAGGAGQGGYGGLGGQGVGRGGLGGQGAGAAAAGGAGQGGYGGVG
SSLRSAAAAASAASAGS
15
Hinman, M.B.; Jones, J. A.; Lewis, R. TIBTECH 2000, 18, 374-379. Vollrath, F.; Knight, D. P. Nature 2001, 410, 541-548.
Simmons, A. H.; Michal, C. A.; Jelinski, L. W. Science 1996, 271, 84-87.
Proposed secondary structure and mode of elasticity
• Poly(Ala) modules form anti-parallel β-sheets (~30-40%)
• Glycine-rich, amorphous regions are thought to be helical
Crystalline region with
-sheet structure
Strain
Disordered
chain region
16
Kubik, S. Angew. Chem. Int. Ed. 2002, 41, 2721-2723.
Van Beek, J. D.; Hess, S.; Vollrath, F. Meier, B. H. Proc. Nat. Acad. Sci. 2002, 99, 10266-10271.
The classic strong synthetic fiber
Kevlar®:
Dupont (1960s)
Uses
- Bulletproof vests and helmets
- Automobile brake pads
- Ropes and cables
- Aerospace components
Material
Dragline Silk
Kevlar
Rubber
Nylon, type 6
Fiber
axis
Strength (GPa
) Elasticity (%)
Energy to break (J/kg
)
1.1
3.6
0.001
0.07
35
5
600
200
4
3
8
6
17
Lewis, R. Chem. Rev. 2006, 106, 3762-3774. Vollrath, F.; Knight, D.P. Nature 2001, 410, 541-548.
Tanner, D.; Fitzgerald, J.A.; Phillips, B.R. Angew. Chem. Int. Ed. Engl. Adv. Mater. 1989, 5, 649-654.
Kubik, S. Angew. Chem. Int. Ed. 2002, 41, 2721-2723.
x
x
x
x
5
10
4
10
4
10
4
10
Spider silks have potential in many applications
Biomedical applications
Surgical sutures
Scaffolds for tissue engineering
Technical and industrial applications
High strength
ropes/cables
Ballistics
18
Parachutes
Fishing line
Naturally production of spider silk
 Inside the spider;
 The silk precursor exists as a lyotropic liquid crystal that is
approximately 50%.
 As the silk excreted, the protein molecules that make up
silk fold and aligned as they approach and then pass
through the spinneret forming a complex insoluble
nanostructured.
 Limitation for sufficient application:
 Spiders cannot be kept in close quarters and harvested;
they eat one another
 The only route: need to be produced synthetically.
Spiders spin 6 different fibers
Flagelliform
Large diameter egg
Case fiber (Tubuliform)
Aggregate Tubuliform
Minor ampullate
Capture Spiral
(Flagelliform)
Pyriform
Major
ampullate
Aciniform
Glue coating
(Aggregate silk) (?)
Wrapping and egg case fiber
(aciniform)
Web reinforcement
(Minor ampullate
1 and 2)
Dragline (major
ampullate 1 and 2)
20
Vollrath, F. J. Biotechnol. 2000, 74, 67-83.
Hu, X. et al. Cell. Mol. Life Sci. 2006, 63, 1986-1999.
Pyriform silk (?)
Forced silking to obtain silk fibers
Spiders are anesthetized with CO2
and secured ventral side up
Silk is pulled from the spinneret,
attached to a reel, and drawn at a
specified speed
21
Work, R. W.; Emerson, P. D. J. Arachnol. 1982, 10, 1-10.
Elices, M.; Perez-Rigueiro, J.; Plaza, G. R.; Guinea, G. V. JOM 2005, 57.
Spiders are highly developed fiber “spinners”
Lumen
Duct
Spidroin
secretion
Spinneret
Fiber
alignment
Tail
Funnel
22
Lewis, R. Chem. Rev. 2006, 106, 3762-3774.
Dicko, C.; Vollrath, F.; Kenney, J.M. Biomacromolecules 2004, 5, 704-710.
Duct
1 mm
Antiparallel and parallel -sheet structure
N
C
N-terminus
C-terminus
N-terminus
C-terminus
C
N
N
C
C-terminus
N-terminus
Poly(alanine) segment
N-terminus
C-terminus
N
C
23
Rotondi, K. S.; Gierasch, L. M. Biopolymers 2005, 84, 13-22.
Simmons, A.; Ray, E.; Jelinski, L. W. Macromolecules 1994, 27, 5235-5237.
Solid state 13C-NMR and FT-IR spectroscopy
13C-NMR
chemical shifts (ppm)
Infrared
wavelengths (cm-1)
-sheet
α-helix
Ala C
48.7
52.5
Anti-parallel β-sheet
1630, 1685
Ala C
20.1
15.1
Parallel β-sheet
1630, 1645
Ala CC=O
171.9
176.5
α-helix
1650, 1560
-carbon
13C-labeled
Alanine
1691
Absorbance
1666
0.4050
1612
-carbon
1637
Infrared spectrum of silk from
Nephila clavipes
0.2800
Amide I
(antiparallel
-sheet)
0.1550
24
Marcotte, I.; van Beek, J. D.; Meier, B. H. Macromolecules 2007, 40, 1995-2001.
Simmons, A.; Ray, E.; Jelinski, L.W. Macromolecules 1994, 27, 5235-5237.
Dong, Z.; Lewis, R.; Middaugh, C. R. Arch. Biochem. Biophys. 1991, 1, 53-57.
1700
1600
Wavenumber (cm-1)
1500
Synthetically production of spider
silk
 First, synthesis of silk precursor
 Created by expressing two of the dragline silk genes in
mammalian cells
 Cannot be created by conventional organic synthesis due to
high complexity
 Second, silk precursor (soluble recombinant dragline silk
proteins) is wet spun into fibers of diameters ranging
from 10-40 m
 Third, a postspinning draw produced fibers with
mechanical properties approaching those of natural silk
Synthetic approaches to spider dragline silk
Protein sequences
Biosynthesis
Chemical Synthesis

BioSteel is a trademark name for a high-strength based fiber material made of
the recombinant spider silk-like protein extracted from the milk of transgenic
goats, made by Nexia Biotechnologies. [1]

The company has created lines of goats that produce recombinant versions of
either the MaSpI[expand acronym] or MaSpII[expand acronym] dragline silk proteins in their
milk.[2][3] When the female goats lactate, the milk, containing the recombinant
silk, is harvested and subjected to chromatographic techniques to purify the
recombinant silk proteins.

The purified silk proteins are then dried, dissolved using solvents (DOPE
formation) and transformed into microfibers using wet-spinning fiber production
methodologies. The spun fibers so far have tenacities in the range of 2 - 3
grams/denier and elongation range of 25-45%. The "Biosteel biopolymer" has
been transformed into nanofibers and nanomeshes using the electrospinning
technique.[4]

Biosteel and other biopolymers are being researched to provide lightweight,
strong, and versatile materials for a variety of medical and industrial
applications.[5] Nexia Biotechnologies plans to use the spider silk from the milk of
transgenic goats for bulletproof vests and anti-ballistic missile systems.

No one has been able to produce the silk in commercial quantities. Nexia is the
only company which has successfully produced fibres from recombinant spider
silk and is currently in the process of developing commercial quantities of
BioSteel using its transgenic goat technology.[6] The Company was founded in
1993 by Dr. Jeffrey Turner and Mr. Paul Ballard, and was sold in 2005 to
PharmAthene.
Two biosynthetic routes to spidroin proteins
Nephila clavipes
Spider silk protein
sequences/mRNA
Eukaryotic host
(insect cells)
Reverse
transcription
Spider
cDNA
Protein fibers
Gene design
Synthetic
DNA
28
Vendrely, C.; Scheibel, T. Macromol. Biosci. 2007, 7, 401-409.
Altman, G.H. et al. Biomaterials 2003, 24, 401-416.
Flexibility with
host
Expression of spider silk cDNA in mammalian cells
protein
synthesis
Transformation
of vector in
mammalian cells
Dragline silk
gene sequence
from A. diadematus
Protein purification,
and characterization
Gene sequence
inserted into
expression vector
Protein: MW ~ 60-140 kDa
Fiber diameter ~ 40 μm
Yield ~ 37 mg/L
Mechanical Properties:
Protein sample
Actin depolymerizing factor 3 (ADF-3)
A. diadematus dragline
29
Lazaris, A. et al. Science 2002, 295, 472-476.
Toughness
(MJ/m3)
Modulus
(GPa)
Elasticity
(%)
Strength
(GPa)
85
13
43.4
0.26
130
10
30
1.1
Recombinant expression of synthetic silk genes
Ligate 8 or 16
DNA fragments
Spidroin 1 analog: DP-1B
[ AGQGGYGGLGSQG-------------------------------------------AGQGGYGGLGSQGAGRGGLGGQGAGAAAAAAAGG
AGQG-------GLGSQGA---------- GQGAGAAAAAA----GG
AGQGGYGGLGSQGAGRG-----GQGAGAAAAAA---GG] n=8-16
Protein fibers
300 mg/L
Protein fibers
1 g/L
DNA fragment
Hybridize
complementary
strands
Transform in
Escherichia coli
Insert gene into
plasmid vector
DNA duplex
Or transform in
yeast
170 nm diameter fibers
Premature termination with
expression in E. coli
High MW polymers from yeast
Fahnestock,
30 S. R.; Irwin, S. L. Appl. Microbiol. Biotechnol. 1997, 47, 23-32.
Stephens, S.J. et al. Mat. Res. Soc. Symp. Proc. 2003, 774, 2.3.1-2.3.10.
Fahnestock, S. R.; Bedzyk, L. A. Appl. Microbiol.Biotechnol. 1997, 47, 33-39.
O’Brien, J. P.; Fahnestock, S. R.; Termonia, Y.; Gardner, K. H. Adv. Mater. 1998, 10, 1185-1195.
Summary of biosynthetic pathways
Biosynthetic Method
Spider Silk cDNA
Synthetic DNA
Advantages
Produce proteins most
like native silk
Difficulty with protein
purification (aggregation)
High MW polymers
are readily attainable
Eukaryotic hosts are
expensive
Polymer structure can
be tuned based on
DNA sequence used
Flexibility with
expression host
31
Disadvantages
Truncated syntheses in
many hosts
Natural organic/inorganic
Nanocomposites
 Also formed through self-assembly
 Two extremes of the formation mechanism:
 1st route- The organic matrix form first followed by
mineralization (biologically directed nucleation and growth
of a mineral phase); organic matrix restructures and
reorganizes continuously as the mineral deposits
 2nd route- Organic and inorganic materials coassemble into
nanostructured composite
 No evidence in which inorganic structure forms first
followed by organic structure formation.
Natural organic/inorganic
Nanocomposites
3 types according to level of complexity:
 Simplest example- those in which mineral phase is simply deposited onto
or within an organic structure (1st route). Eg:
 Grasses – many species precipitate SiO2 within their cellular structures
 Bacteria- magnetic bacteria has internal chain of magnetite (Fe3O4)
nanocrystals running down their long axis.
 Medium level- in which the structure of mineral phase is clearly
determined by the organic matrix (1st route).
 Bacteria S-layer- serves as protein template for the formation of thin film
of mesostructured gypsum
 Highest level- in which the structure of mineral is intimately associated
with the organic phase to create a structure with properties superior to
those of either the mineral or organic phases (2nd route)
 Sea urchin spine- single crystal essentially composed of calcite,
containing only about 0.02% glycoproteins trapped within the crystal
lattice of the spine
 Nacreous (mother-of-pearl) layer of the abalone shell- alternating layers
of 500 nm thick aragonite platelets and ~30 nm thick sheets of an organic
matrix
 Bone- Complex structure and function
Schematic drawing of the isolation of S-layer proteins from bacterial cells and their
reassembly into crystalline arrays in suspension (a), at solid supports (b), at the airwater interface (c), on lipid films (d) and on liposomes (e). The orientation of the
recrystallized lattice is determined by the physicochemical properties of the
surfaces.
Fig.8 Transmission electron
micrograph of palladium (Pd)
nanoparticles precipitated on a
S-layer with square lattice
symmetry. Bar, 20nm
Transmission electron micrograph of palladium (Pd)
nanoparticles precipitated on a S-layer with square lattice
symmetry. Bar, 20nm
Biologically Inspired
Nanocomposites
 Inspired by properties of biocomposites & synthetic
pathways for their formation
 Rationale:
 Not always necessary or even desirable to use biologically
derived materials for many applications
 May be possible to simply use biology as an inspiration for
totally synthetic nanocomposites system
 Many lessons can be learned from biology (how to form
complicated nanostructures & potential properties of
synthetic nanostructured materials)
Learn from biological system
 To develop synthetic approach to form complex inorganic
structures
 Example of routes to nanostructure formation;
 Producing nanoparticles
 Producing thin film
Production of II-IV semiconductor
nanoparticles
 Example: formation of metal sulfide and selenide
 Semiconducting nanoparticles can be synthesized
through:
 1st method: Grinding of large chunks rarely done for nanoparticle,
 grinding process is poor regulated,
 generally generating very polydisperse population of
particles
 Introduces too many contaminates
 2nd method: Gas phase synthesis – is a vaporation and
condensation process
 Crucible containing the desired semiconductor (@ other
materials) is heated until it is start to sublime
 Then, inert gas is flowed over the material
 Carrier gas heads to cool region where the gaseous
semiconductor atoms or molecules condense into
nanoparticles  collated
 Advantages: It is versatile
 Disadvantages: operates under conditions of high
temperature; generally produces solid spherical particles
 3rd method: Solution based synthetic routes for
nanoparticles- range from simple precipitation reactions
to much more complex self-assembly based routes.
 Simple precipitation:
 Results in agglomerates of nanoparticles
 Size distribution varies widely
 To prevent aggregation and to narrow down size
distribution-to use self-assembly-based techniques
 Self-assembly based routes: resemble nanostructure
development in biological systems (biomineralization, cell
membrane development, other biological structure
formation)
 Solution-phase synthesis of semiconductor
 Often preferred over other techniques
 Generally mild (even being carried out at room T and P)
 Can be used to create reasonable volumes of materials
 Has been widely used to grow semiconductor quantum dots
(Cd3P2)
 Solution-based chemical synthesis are very attractive- allow
for direct control over actual concentrations of the chemical
precursors
 Even possible to cap the surface with organic molecules –
allows for further solution-based processing

More conventional route to creating
nanostructured materials- through topdown lithographic methods:
 Extreme UV lithography
 Electron beam writing
 Focused ion-beam lithography
 Formation through selfassembly based routes:
 Not limited to feature
generation on flat surface
 It can be massively parallel
 X-ray lithography
 Disadvantages;
 Scanning probe lithography and
 It is not possible to highly
regulate the exact spatial
position of the nanostructure
 Micro-contact printing

Can form nanostructures on scale of 10
to 100 nm

Disadvantages;

Generally on flat surface/substrate

Can be quite slow

Often very expensive
 We are still many years away
from creating highly functional
self-assembled electronic
circuits
Another example of selfassembly based route to produce
nanoparticle- Micellar routes
 Micelles are self-assembled from surfactant molecules +
solvent (that contains at least one of the precursors for
the inorganic nanoparticles in solution)
 Solution- that contains vast numbers of discrete
nanoreactors (individually contain only a finite number
of precursor species for the inorganic phase)
 Reduction/oxidation
 Ions are converted to mineral  one nanoparticle per
micelle
 If possible to create a suspension of monodisperse
micelles; it will a straightforward process to create
nanoparticle with a very narrow distribution
Micellar routes
 A lesson from biology: the process might be possible
through the use of complex macromolecules that
organize into particles of only a specific size.
 A nanoreactor with tight size distribution is –virus
particles
 Load the interior of the virus particles with precursors
for nanoparticles
Type of nanoparticles produced
by self-assembly based routes
 Cadmium Sulphide (CdS):
 Dendritic structure were generated
 Others: resulted in rod-like and even complex nanoparticles
 Cadmium Selenide (CdSe)
 Nanorods with aspect ratio of 30:1 (arrow-, teardrop- and
branched tetrapod-shaped nanocrystals)
Production of nanostructure thin
film
 Next level complexity in nanostructure formation- creation
nanostructures with complex, predefined morphologies
 In biology- common to have complex predefined structures
on nanometer scale
 But, exceedingly difficult to syntheticly produced
 Possible: power of assembly + materials synthesis
strategies known today:
 Liquid crystal templating
 Colloidal particle templating
 Block copolymer templating
 Surfactant inorganic self-assembly (most famous in producing
mesoporous silica)
What are Liquid Crystals?
 A liquid crystal is a substance that flows like a liquid but
maintains some of the ordered structure characteristic of crystals.
 Under certain circumstances, phases, liquid crystals have a liquidlike behaviour and during others they have the opposite
behaviour.
 Liquid crystals are partly ordered materials, somewhere between
their solid and liquid phases. Their molecules are often shaped
like rods or plates or some other forms that encourage them to
align collectively along a certain direction. The order of liquid
crystals can be manipulated with mechanical, magnetic or electric
forces.
Solidify
Melt
Liquid
Heat
Cool
Heat
Intermediate
Phase
Cool
Crystal
Liquid Crystals (LCs)
What is so special about liquid crystals?
LCs are orientationally ordered fluids with anisotropic properties
A variety of physical phenomena makes them one of the most
interesting subjects of modern fundamental science.
Their unique properties of optical anisotropy and sensitivity to
external electric fields allow numerous practical application.
Finally, liquid crystals are temperature sensitive since they
turn
into solid if it is too cold, and into liquid if it is too hot.
Types of Liquid Crystals
Liquid crystals
Lyotropic
Calamitic
Thermotropic
Polycatenar
Nematic (N)
Smectic (S)
Discotic
Banana-shaped
Nematic Discotic(ND)
Columnar (Col)
Lyotropic Liquid-Crystal
Templating
 Nanostrcture & nanocomposites formation that utilizes
the self-assembled structure of a iquid crystal to
regulate the structure of growing inorganic material
 When processed correctly, structure of inorganic phase
directly replicates the structure of the liquid crystal
 Liquid crystal is “template’ for the inorganic
 Lyotropic liquid crystal composed of at least two
covalently linked components:
 One is usually amphiphile (molecule that has two or more
physically distinct components)
 Other one- solvent
Lyotropic LCs
Lyotropic LCs are two-component systems where an amphiphile is dissolved
in a solvent. Thus, lyotropic mesophases are concentration and solvent
dependent.
The amphiphilic compounds are characterised by two distinct components, a
hydrophilic polar“ head” and a hydrophobic “tail”.
Examples of these kinds of molecules are soaps (Figure-a) and various
phospholipids like those present in cell membranes (Figure-b).
[a]
[b]
General concept of liquid-crystal
templating
 First, form a liquid crystal that contains at least one of
the precursors of the mineral phase
 Then, induce a mineral phase to precipitate in ONLY one
chemical region of the liquid crystals – by applying
perturbation.
 Formation of nanostructures
 Type of nanostructures according to the type of liquid
crystal:
 Hexagonal
 Lamellar
 Cubic phases
 Bicontinouous phase
Advantages of liquid crystal
templating vs lithographic
 Dimensions of the synthesized materials smaller than
obtainable by lithographic
 Often attainable through bulk synthesis, which obviously
not possible via lithography
 Generates semiconductor/organic superlattice containing
both the symmetry and the long-range order of the
precursor liquid crystal
 Large number of amphiphilic liquid crystals with lattice
constant from a few nanometers to tens of nanometers
 Many of the amphiphilic system can be mineralizedproduce materials with an array of novel structures and
properties.
Example of the process
 Grown of body-centred phase CdS
 Using a triblock copolymer of poly(oxyethylene)poly(oxypropylene)-poly(oxyethylene) as the amphiphile
 Mix with water, PO segment is only weakly solveted, but
EO is highly solvated.
 The molecule is hydrated to form micelles which closely
pack, forming cubic phase
 Precipitation in the cubic phase formation of hollow
nanospheres of CdS