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Natural and Biological Inspired Nanocomposites
Noraiham Mohamad, PhD
Department of Engineering Materials
Faculty of Manufacturing Engineering
Universiti Teknikal Malaysia Melaka
Chapter 10
INTRODUCTIONWhat 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 nanocompositesThe 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 enamel-forming 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 self-assemble 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
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.)
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 so-called 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.
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
15
Primary structure of spider dragline silk
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.
QGAGAAAAAAGGAGQGGYGGLGGQGAGQGGYGGLGGQGAGQGAGAAAAAAAGGAGQGGYGGLGGLGGYGGQGAGGAAAAAAGAGQGGRGAGQS
SQGAGRGGLGGQGAGAAAAAAAGGAGQGGYGGLGGLGGYGGQGAGGAAAAAAGQGGRGAGQNSQGAGRGGLGGQAGAAAAAAGGAGQGGYGGLGGQGAGQGGYGGLG
GLGGYGGQGAGGAAAASAGAGQGAGQGGLGGQGAGGAAAAAAAGAGQGGLGGRGAGQSSQGAGRGGEGAGAAAAAAGGAGQGGYGGLGGQGAGQGGYGGLG
GLGGYGGQGAGGAAAAAAGAGQGAGQGGLGGQGAGGAAAAGAGQGGLGGRGAGQSSQGAGRGGLGGQGAGAVAAAAGGAGQGGYGGLG
GLGGYGRQGAGGAAAAAAGAGQGGRGAGQSNQGAGRGGLGGQGAGAAAAAAAGGAGQGGYGGLG
GLGGYGGQGAGGAAAAAGQGGRGAGQNSQGAGRGGQGAGAAAAAAVGAGQEGIRGQGAGQGGYGGLG
GAGGYGGQRVGGAAAAAAGAGQGAGQGGLGGQGAGGAAAAAAGAGQGGLGGRGSGQSSQGAGRGGQGAGAAAAAAGGAGQGGYGGLGGQGVGRGGLGGQGAGAAAAGGAGQGGYGGVG
SSLRSAAAAASAASAGS
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
16
Proposed secondary structure and mode of elasticity
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.
• Poly(Ala) modules form anti-parallel β-sheets (~30-40%)• Glycine-rich, amorphous regions are thought to be helical
Disordered chain region
Strain
Crystalline region with-sheet structure
17
The classic strong synthetic fiber
Material Strength (GPa)Elasticity (%)Energy to break (J/kg)
Dragline Silk 1.1 35 4 x 105
Kevlar 3.6 5 3 x 104
Rubber 0.001 600 8 x 104
Nylon, type 6 0.07 200 6 x 104
Fiber axis
Kevlar®: Dupont (1960s) Uses
- Bulletproof vests and helmets- Automobile brake pads- Ropes and cables- Aerospace components
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.
18
Spider silks have potential in many applications
Surgical sutures Scaffolds for tissue engineering
Biomedical applications
Parachutes
High strength ropes/cables
Fishing line
Technical and industrial applications
Ballistics
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.
20
Vollrath, F. J. Biotechnol. 2000, 74, 67-83.Hu, X. et al. Cell. Mol. Life Sci. 2006, 63, 1986-1999.
Spiders spin 6 different fibers
Web reinforcement (Minor ampullate 1 and 2) Dragline (major
ampullate 1 and 2)
Wrapping and egg case fiber (aciniform)
Pyriform silk (?)
Acini-form
Capture Spiral(Flagelliform)
Glue coating(Aggregate silk) (?)
Large diameter eggCase fiber (Tubuliform)
Aggregate TubuliformFlagelliform
Pyriform
Minor ampullate
Major ampullate
21
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
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.
22
Spiders are highly developed fiber “spinners”
Lewis, R. Chem. Rev. 2006, 106, 3762-3774.Dicko, C.; Vollrath, F.; Kenney, J.M. Biomacromolecules 2004, 5, 704-710.
Spidroin secretion
Lumen
Spinneret
Duct
Fiber alignment
Duct
Tail
Funnel
1 mm
23
Antiparallel and parallel -sheet structure
Poly(alanine) segment
Rotondi, K. S.; Gierasch, L. M. Biopolymers 2005, 84, 13-22. Simmons, A.; Ray, E.; Jelinski, L. W. Macromolecules 1994, 27, 5235-5237.
N-terminus
N-terminus
C-terminus
C-terminus
N-terminus
N-terminus
C-terminus
C-terminus
N C
NC
N C
N C
24
Solid state 13C-NMR and FT-IR spectroscopy
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.
13C-NMR chemical shifts (ppm)
13C-labeledAlanine
Wavenumber (cm-1)
1700 1600 15000.1550
0.2800
0.4050
Ab
sorb
an
ce
1691
1666
1637
1612
Infrared spectrum of silk from Nephila clavipes
Amide I (antiparallel-sheet)
-carbon
-carbon
Anti-parallel β-sheet
Parallel β-sheet
α-helixAla C
α-helix
Ala C
Ala CC=O
-sheet
20.1 15.1
48.7 52.5
171.9 176.5
Infrared wavelengths (cm-1)
1630, 1685
1630, 1645
1650, 1560
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
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.
28
Two biosynthetic routes to spidroin proteins
Vendrely, C.; Scheibel, T. Macromol. Biosci. 2007, 7, 401-409.Altman, G.H. et al. Biomaterials 2003, 24, 401-416.
Synthetic DNA
Spider cDNA
Flexibility withhost
Protein fibers
Reverse transcription
Eukaryotic host (insect cells)
Spider silk protein sequences/mRNA
Gene design
Nephila clavipes
29
Expression of spider silk cDNA in mammalian cells
Lazaris, A. et al. Science 2002, 295, 472-476.
Dragline silk gene sequencefrom A. diadematus
Gene sequence inserted intoexpression vector
Transformation of vector in mammalian cells
protein synthesis
Protein purification, and characterization
Protein: MW ~ 60-140 kDa Fiber diameter ~ 40 μm Yield ~ 37 mg/L
Mechanical Properties:
Protein sample Toughness(MJ/m3)
Modulus(GPa)
Elasticity(%)
Strength(GPa)
Actin depolymerizing factor 3 (ADF-3)
A. diadematus dragline
85 13 43.4 0.26
130 10 30 1.1
30
Recombinant expression of synthetic silk genes
DNA fragment
Fahnestock, 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.
AGQGGYGGLGSQG--------------------------------------------AGQGGYGGLGSQGAGRGGLGGQGAGAAAAAAAGGAGQG-------GLGSQGA---------- GQGAGAAAAAA----GGAGQGGYGGLGSQGAGRG-----GQGAGAAAAAA---GG
Spidroin 1 analog: DP-1B[
]n=8-16
Ligate 8 or 16DNA fragments
DNA duplex
Hybridize complementary
strands
Premature termination with expression in E. coli
High MW polymers from yeast
Transform inEscherichia coli
Insert gene into plasmid vector
Or transform inyeast
Protein fibers1 g/L
Protein fibers300 mg/L
170 nm diameter fibers
31
Summary of biosynthetic pathways
Biosynthetic Method Advantages Disadvantages
Spider Silk cDNA Difficulty with protein
purification (aggregation)Produce proteins most
like native silk
High MW polymers
are readily attainable
Eukaryotic hosts are expensive
Synthetic DNA Polymer structure can
be tuned based on
DNA sequence used
Flexibility with
expression host
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 Nanocomposites3 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 air-water 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 top-down lithographic methods:
Extreme UV lithography
Electron beam writing
Focused ion-beam lithography
X-ray lithography
Scanning probe lithography and
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
Formation through self-assembly based routes: Not limited to feature
generation on flat surface
It can be massively parallel
Disadvantages;
It is not possible to highly regulate the exact spatial position of the nanostructure
We are still many years away from creating highly functional self-assembled electronic circuits
Another example of self-assembly 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)
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 liquid-like 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.
Liquid Crystal
Melt
Solidify
Intermediate Phase
Heat
Cool
Heat
Cool
What are Liquid Crystals?
Liquid Crystals (LCs)
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.
What is so special about liquid crystals?
Types of Liquid Crystals
Liquid crystals
Lyotropic Thermotropic
Calamitic Polycatenar Discotic Banana-shaped
Nematic (N)
Smectic (S)
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 LCsLyotropic 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 mineralized- produce 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