DEMat - ULisboaweb.ist.utl.pt/ist12456/3D-LIQUIDCRYSTAL.pdf · 2019-04-07 · M. Clara Gonçalves S...
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M. Clara Gonçalves MATERIAIS NANOESTRUTURADOS E NANOTECNOLOGIAS DEMat MATERIAIS NANOESTRUTURADOS E NANOTECNOLOGIAS DEMat Bottom-up approach
Transcript of DEMat - ULisboaweb.ist.utl.pt/ist12456/3D-LIQUIDCRYSTAL.pdf · 2019-04-07 · M. Clara Gonçalves S...
M. Clara Gonçalves
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Bottom-up approach
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Introduction
Lyotropic Liquid Crystals
Case Studies
1. Mayonnaise, Chocolate Mouse
2. Detergent
3. Drug delivery
4. Cell Membrane
5. Origin of Life
Amphiphilic Molecules
DLVO theory
Phase Diagrams
Nanostructures
Further Reading
Summary
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Introduction
What is self-assembly?
Simply put, we’re talking about collections of objects that put themselves
together. Imagine holding a box containing a jigsaw puzzle, giving the box a
shake, and peeking inside to find that the puzzle had assembled itself! While
such behavior would be shocking in a jigsaw puzzle, a little reflection reveals
that it’s not so surprising to find self assembling systems in the natural world.
After all, no one put you together did they?
Biological systems as well as a variety of inorganic physical systems exhibit
self assembling or self ordering behavior. Drawing on these systems for
inspiration, scientists from numerous disciplines, chemistry, physics, biology,
engineering, and mathematics, to name a few, have begun to investigate the
self assembly process in hopes of learning to design and control the behavior
of self assembly systems.
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Introduction
What is self-assembly?
Much of this work is motivated by recent advances in micro- and nanoscale
science. On one hand, fabrication methods in micro- and nanoscience
allow for batch processing. That is, we have the ability to make many copies
of the same device simultaneously. How do we design these devices so that
they spontaneously assemble themselves into a useful working structure?
On the other hand, traditional fabrication methods are limited in resolution.
To make smaller structures, i.e., true nanoscale structures, requires the
development of new methods. Taking their cue from nature, coaxing
nanostructures into self assembling is an avenue many scientists are
exploring. Ultimately, a deeper understanding of self-assembly may shed
light on the nature of life itself.
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Introduction
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Introduction
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Introduction
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Introduction
Water / oil
Mayonnaise
(eggs / cream )
Mayonnaise
(eggs / cream )
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Introduction
White
(white / air)
Chocolate Mousse
(cacao / cacao butter / eggs / sugar)
Chocolate Mousse
(cacao / cacao butter / eggs / sugar)
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Introduction
WATER MOLECULE
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Introduction
WATER MOLECULE
My name is
Bond,
Hydrogen
Bond…
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Introduction
WATER MOLECULE
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Introduction
WATER MOLECULE
LIQUID ORDERED WATER MOLECULES
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Liquid crystals come in two basic classifications:
thermotropic and lyotropic. The phase transitions of
thermotropic liquid crystals depend on temperature, while
those of lyotropic liquid crystals depend on both
temperature and concentration.
This chapter will focus on lyotropic liquid crystals.
Lyotropic Liquid Crystals
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Lyotropic liquid crystals are found in countless everyday
situations. Soaps and detergents form lyotropic liquid
crystals when they combine with water. In the kitchen, cake
batters may harbor the liquid crystals as well. Most
importantly, biological membranes display lyotropic liquid
crystalline behavior.
Lyotropic Liquid Crystals
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Lyotropic Liquid Crystals
AMPHIPHILIC MOLECULES
LIQUID ORDERED AMPHIPHILIC MOLECULES
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The molecules that make up lyotropic liquid crystals are
surfactants consisting of two distinct parts: a polar, often
ionic, head and a nonpolar, often hydrocarbon tail.
Following the rule of ‘like dissolves like’, the head is
attracted to water, or hydrophilic, and the tail is repelled by
water, or hydrophobic.
When dissolved in high enough concentrations, the
molecules arrange themselves so that the polar heads are in
contact with a polar solvent and / or the nonpolar tails are
in contact with a nonpolar solvent.
Lyotropic Liquid Crystals
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AMPHIPHILIC MOLECULES
LIQUID ORDERED AMPHIPHILIC MOLECULES
Lyotropic Liquid Crystals
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1. MAYONNAISE, CHOCOLATE MOUSSE
Mayonnaise
(eggs / cream )
Protein molecules in the interface water / oil
Case Studies
Protein molecules
Mousse Chocolate
(cacao / cacao butter / eggs / sugar)
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Case Studies
Surfactant molecules in the interface water / oil
Water / oil
2. DETERGENT
Detergent molecules
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Case Studies
2. DETERGENT
Soap detergent or shampoo are a part of everybody’s life. What
would we do without them for cleaning our house, washing our
clothes or taking care of our appearance?
All these products have something in common: they are
surfactants. One of their best-known properties is their ability to
make oil and water mix to form an emulsion. They are also
wetting agents; they make it easier for a solution to spread across a
solid. All these properties are due to their amphiphilic character.
Laundry detergents clean clothes by capturing hydrophobic dirt
inside micelles. Dirt is thus solubilised and then removed from the
clothes by water.
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In medical area, a lyotropic liquid crystal can coat a drug to keep
it from being destroyed in the digestive tract. The drug can then be
taken orally, and after it reaches the proper location in the body,
the liquid crystal breaks down and the drug is released.
A lyotropic liquid crystal can dissolve a drug like hydrocortizone.
Hydrocortizone is often taken in topical applications, but its uses
have been limited because the highest concentration possible has
been only 1%. When the drug is blended into a liquid crystal of
lecithin and water, the concentration goes up to 4%.
In time, liquid crystals may become a primary solvent for topical
medications.
3. DRUG DELIVERY
Case Studies
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LIPID
PHOSPHO
PHOSPHO
LIPID
4. CELL MEMBRANE
Case Studies
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Case Studies
Phospholipids contain only two fatty acid tails attached to a
glycerol head. The third alcohol group of the glycerol is
attached to a phosphate molecule. The phosphate group is then
attached to other small molecules such as Cl.
The phosphate group along with the glycerol group make the
head of the phospholipid hydrophilic, whereas the fatty acid tail
is hydrophobic.
Phospholipids are amphipatic: water loving and water hating.
When phospholipids are in aqueous solution they will self-
assemble into micelles or bilayers, structures that exclude water
molecules from the hydrophobic tails while keeping the
hydrophilic head in contact with the aqueous solution.
4. CELL MEMBRANE
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LIPID
PHOSPHO
Case Studies
4. CELL MEMBRANE
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Case Studies
The common feature of all living cells is a distinct, lipid-rich
barrier, the plasma membrane.
This membrane defines the boundary between the outside and the
inside of the cell. The difference between the two is profound.
Outside is mostly water, with few complex molecules. Inside is a
concentrated solution of proteins, nucleic acids and smaller
molecules – the cytoplasm.
This bounded system, or cell, has the properties of life. It can
reproduce itself by using energy taken from beyond the
boundary.
4. CELL MEMBRANE
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Case Studies
4. CELL MEMBRANE
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4. CELL MEMBRANE
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4. CELL MEMBRANE
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Case Studies
Phospholipids serve a major function in the cells of all organisms:
they form the phospholipid membranes that surrounds the cell
and intramolecular structures such as mitochondria.
The cell membrane is a fluid, semi-permeable bilayer that
separates the cell’s contents of from the environment. The
membrane is fluid at physiological temperatures and allows cells
to change shape due to physical constraints or changing cellular
volumes.
The phospholipid membrane allows free diffusion of some
small molecules such as oxygen, carbon dioxide, and small
hydrocarbons, but not water, charged ions, or other larger
molecules such as glucose. This semi-permeable nature of the
membrane allows the cell to maintain the composition of the
cytosol independent of the external environment.
4. CELL MEMBRANE
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4. CELL MEMBRANE
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4. CELL MEMBRANE
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4. CELL MEMBRANE
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4. CELL MEMBRANE
The cell membrane must be a dynamic structure if the cell is to
grow and respond to environmental changes. To keep the
membrane fluid at physiological temperatures the cell alters the
composition of the phospholipids. The right ratio of saturated to
unsaturated fatty acids keeps the membrane fluid at any
temperature conductive to life.
For example, winter wheat responds to decreasing
temperatures by increasing the amount of unsaturated fatty acids
in cell membranes.
In animal cells cholesterol helps to prevent the
packing of fatty acid tails and thus lowers the requirement of
unsaturated fatty acids. This helps maintain the fluid nature of the
cell membrane without it becoming too liquid at body
temperature.
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4. CELL MEMBRANE
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4. CELL MEMBRANE
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4. CELL MEMBRANE
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+ PHOSPHOLIPID
Case Studies
5. ORIGIN OF LIFE
Liposomes are artificial vesicle membranes, which form upon
hydration of membranogenic lipids in an aqueous medium.
They are commonly used as model systems, among others, for
the study of the physical-chemical attributes of early membrane
processes.
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BY SONICATION
Case Studies
5. ORIGIN OF LIFE
There is good evidence that membrane vesicles are the
intermediate between prebiotic cells and the first cells capable of
growth and division.
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Life emerged through a complex chain of evolutionary events,
dictated by the physical-chemical environment on the early Earth.
The reducing atmosphere, provided energetic surroundings for
the formation of relatively complex polymers from organic
monomers which were already present on the primitive Earth.
Over time, simple molecules developed into larger, more
complex biological molecules and eventually to cells. Following
further diversification, some cells developed that became
metabolically capable of photosynthesis.
Assembly of the first cellular life on the prebiotic Earth required
the presence of three essential substances: water, a source of free
energy and a source of organic compounds.
Case Studies
5. ORIGIN OF LIFE
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+ PHOSPHOLIPID
Case Studies
5. ORIGIN OF LIFE
The self-aggregation of amphiphilic molecules would have
constituted local high concentrations within the dilute solution of
organic compounds.
Held together primarily by weak non-covalent interactions
driven by hydrophobic forces, the early amphiphilics assemblies
would have been extremely stable over time.
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The earliest forms of life required membranes. Phospholipids
are the primary components of modern cell membranes, but it is
improbable that such complex molecules were part of the prebiotic
soup. Instead, simpler membranogenic amphiphilic molecules
probably served as precursors, which then evolved chemically to
the varied and complex phospholipid form.
It is speculated that although modern phospholipids were absent,
these amphiphilic molecules were abundant in the prebiotic
environment. This components are capable of spontaneously
forming stable membrane vesicles with defined compositions
and organization.
Case Studies
5. ORIGIN OF LIFE
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Case Studies
5. ORIGIN OF LIFE
Once formed, cell membranes also have the potential to
maintain a concentration gradient, providing a source of free
energy that can drive transport processes across the membrane
boundary.
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When amphiphilic molecules self-assemble into membranes, their
vesicular organization creates an effective permeability between
interior and the exterior aqueous compartments. The selective entry of
the early membranes that formed the boundary of primitive cells
permitted the permeation of essential nutrients.
However, less sophisticated than their modern counterparts, the early
membranes would have been impermeable to larger, polymeric
molecules, such as the precursors of nucleic acid and protein polymers.
As the composition of the interior compartments became more specific,
a population of these bounded molecular systems advanced and
increase in metabolic complexity.
The amphiphilic molecules on the primitive earth have undeniably
undergone considerable evolution as the first forms of life emerged and
acquired new catalytic capacities.
Case Studies
5. ORIGIN OF LIFE
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Electrostatic Stabilization
DLVO theory
Lyotropic Liquid Crystals: DLVO theory
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DEMat ii) REPULSIVE INTERACTIONSi) ATRACTIVE INTERACTIONS +
COLOIDAL STABILITY: DLVO theory
Lyotropic Liquid Crystals: DLVO theory
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AMPHIPHILIC MOLECULE: PHASE DIAGRAMS
vesicle
lamellar
micelleshexagonal
random
Lyotropic Liquid Crystals: Phase Diagrams
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AMPHIPHILIC MOLECULE: PHASE DIAGRAMSAMPHIPHILIC MOLECULE: PHASE DIAGRAMS
In dilute solution, the surfactants do not form any particular structure. As the
concentration is increased, however, the amphiphiles condense into well defined structures.
The most readily formed structure is micelles, where the surfactants hide the hydrophobic
tails inside a sphere, leaving only the water-soluble ionic heads exposed to solution.
At higher concentrations, surfactants can also form elongated columns that pack into
hexagonal arrays. The columns have hydrophobic cores and hydrophilic surfaces. The
columns are separated from one another by water.
At extremely high concentration (neat soap), surfactants crystallize into a lamellar
structure, with elongated sheets separated by thin water layers. The structure is very
reminiscent of the lipid bilayers seen in biological systems.
Phospholipids spontaneously form vesicles in water, encapsulating a small water droplet in
a spherical shell of phospholipid molecules. Both the inner and the outer wall of the shell
are composed of hydrophilic heads, whereas the inside of the vesicle shell is the alkane
tails.
vesicle
lamellar
micelles
hexagonal
random
Lyotropic Liquid Crystals: Phase Diagrams
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AMPHIPHILIC MOLECULE: PHASE DIAGRAMS
cubic
lamellar
micelles
hexagonal
micelles cubic
Lyotropic Liquid Crystals: Phase Diagrams
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AMPHIPHILIC MOLECULE: PHASE DIAGRAMS
Transfer of structure from Brij56
surfactant aggregates to
a-SiO2 inorganic films.
cubic
lamellar
micelles
hexagonal
micelles cubic
Lyotropic Liquid Crystals: Phase Diagrams
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AMPHIPHILIC MOLECULE: PHASE DIAGRAMS
100
90
80
70
60
50
40
30
20
10
100
90
80
70
60
50
40
30
20
10
100 90 80 70 60 50 40 30 20 10
Brij56 (wt%)
TMOS (wt%) 0.5 M HCl (wt%)
£
£
u
«
«
«
r
r
x
x
x
£
u
u
u
«
1d (1wt%) - I1 (very ord.)r
1e (5wt%) - I1 r
1f(10wt%) - I1+HI(very ord.)x
1g (20wt%) - I1 + HIx
1h (30wt%) - I1 + HI x
1i (40wt%) - HI (very ord.) £
1j (50wt%) -HI+La u
1k (60wt%) -HI+La (very ord.)u
1l (70wt%)- HI + Lau
1m (80wt%)- La«
3a (1.00:1) - HI£
3b (1.40:1) - HI£
3c (2.20:1) -HI+ Lau
3d (2.60:1) - La«
3e (3.00:1)- La«
3f (4.00:1) - La«
Nanostructure of
the as
synthesised
films.
Lyotropic Liquid Crystals: Phase Diagrams
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AMPHIPHILIC MOLECULE: PHASE DIAGRAMS
Nanostructure of
the calcined
films.
100
90
80
70
60
50
40
30
20
10
100
90
80
70
60
50
40
30
20
10
100 90 80 70 60 50 40 30 20 10
Brij56 (wt%)
TMOS (wt%) 0.5 M HCl (wt%)
u
r
r
x
x
x
u
u
u
1d (1wt%) - I1 (very ord.)r
1e (5wt%) - I1 r
1f(10wt%) - I1+HI(very ord.)x
1g (20wt%) - I1 + HIx
1h (30wt%) - I1 + HI x
1i (40wt%) - HI (very ord.)
1j (50wt%) -HI+La u
1k (60wt%) -HI+La (very ord.)u
1l (70wt%)- HI + Lau
1m (80wt%)- La
3a (1.00:1) -without order
3b (1.40:1) - without order
3c (2.20:1) -HI+ Lau
3d (2.60:1) - La
3e (3.00:1)- La
3f (4.00:1) - La
Lyotropic Liquid Crystals: Phase Diagrams
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AMPHIPHILIC MOLECULE: PHASE DIAGRAMS
1f 1j
Wt% Surfactant (Brij56)
0 20 40 60 80 100
II HI LaII +HI HI+La
1e 1i1g 1m1k1d 1h 1l
0 20 40 60 80 100
II HI LaL2
II +HI LaL2
Wt% Surfactant (Brij56)
Series 1
bulks
films
Lyotropic Liquid Crystals: Phase Diagrams
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AMPHIPHILIC MOLECULE: PHASE DIAGRAMS
3a 3e 3f
TMOS/ Brij56 (mass ratio)
0 1 2 3 4 5
without
orderLa
La +HI
3b 3c 3d1j
0 1 2 3 4 5
HI
TMOS/ Brij56 (mass ratio)
very
disordered
without
order
Series 3
bulks
films
Lyotropic Liquid Crystals: Phase Diagrams
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AMPHIPHILIC MOLECULE: PHASE DIAGRAMS
Lyotropic Liquid Crystals: Phase Diagrams
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AMPHIPHILIC MOLECULE: MICROSTRUCTURES
1i - 40 wt% BRIJ56 1j - 50 wt% BRIJ56 1k - 60 wt% BRIJ56 1l - 70 wt% BRIJ56
1e - 5.0 wt% BRIJ56 1f - 10 wt% BRIJ56 1g - 20 wt% BRIJ56 1h - 30 wt% BRIJ56
Lyotropic Liquid Crystals: Nanostructures
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DEMatSeries 1 and 3 (1 d, 1 e)
Cubic domain
TEM
1e - 5.0 wt% BRIJ56
AMPHIPHILIC MOLECULE: MICROSTRUCTURES
Lyotropic Liquid Crystals: Nanostructures
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AMPHIPHILIC MOLECULE: MICROSTRUCTURES
Series 1 and 3 (1m, 3c, 3d, 3e, 3f)
Lamellar domain
La
3d - 2.60:1 3e - 3.30:1 3f - 4.00:13c - 2.20:11m - 80 wt% BRIJ56
Lyotropic Liquid Crystals: Nanostructures
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Applications
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Further Reading
Nanostructures and Nanomaterials. Synthesis, Properties & Applications, G.
Cao, ICP Imperial College Press, 2007 (ISBN 1-86094-480-9).
The Colloidal Domain. Where Physics, Chemistry, Biology, and Technology
Meet, D. Fennell Evans and H. Wennerström, Wiley-VCH, 1999, ISBN 0-471-
24247-0
