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Disperse systems. The methods of preparing of colloidal solutions. Their properties. Physical-chemical properties of biopolymer solutions.

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Title: Disperse systems. The methods of preparing of colloidal solutions. Their properties. Physical-chemical properties of biopolymer solutions.


1
Disperse systems. The methods of preparing of
colloidal solutions. Their properties.
Physical-chemical properties of biopolymer
solutions.
ass. Halina Falfushynska
2
Dispersed Systems
A kinetically stable mixture of one phase in
another largely immiscible phase. Usually at
least one length scale is in the colloidal range.
3
Dispersed Systems
Dispersed phase
Continuous phase
Interface
4
Classification of dispersed system in agreement
with particles scale
Molecular dispersions is a true solutions of a
solute phase in a solvent. The dispersed phase
(solute) is in form of separate molecules
homogeneously distributed throughout the
dispersion medium(solvent). The molecule size is
less than 1 nm (410-8 inch). The examples air
(a molecular mixture of Oxygen, Nitrogen and some
other gases), electrolytes (aqueous solutions of
salts). Colloids are micro-heterogeneous
dispersed systems, in which the size of the
dispersed phase particles is within the range 1 -
1000 nm (410-8 - 410-5 inch). The colloids
phases can not be separated under gravity,
centrifugal or other forces. Dispersed phase of
colloids may be separated from the dispersion
medium by micro-filtration. The examples of
colloids milk (emulsion of fat and some other
substances in water), fog (aerosol of water
micro-droplets in air), opal (colloidal silica),
Silica aerogel monolith, Alumina aerogel
monolith. Coarse dispersions (suspensions) are
heterogeneous dispersed systems, in which the
dispersed phase particles are larger than 1000 nm
(410-5). Coarse dispersions are characterized
by relatively fast sedimentation of the dispersed
phase caused by gravity or other forces.
Dispersed phase of coarse dispersions may be
easily separated from the continuous phase by
filtration.
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  • Lyophobic colloids consist of the phases, which
    do not interact between each other. Dispersed
    phase in lyophobic colloids is not solvated by
    the dispersion media.
  • Lyophobic colloids are prepared by mechanical
    agitation, which is required because of high
    interfacial energy of the dispersed particles.
  • Lyophobic colloids are thermodynamically
    unstable. Their dispersed particles have a
    tendency to aggregation or coalescence. Thermodyna
    mic stability of lyophobic colloids may be
    increased by an addition of relatively small
    amount of surface active substances (surfacants)
    lowering the interfacial energy of the
    system. Some of lyophobic colloids possess
    lyophilic properties (eg. hydrosols of silica and
    alumina).

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http//www.youtube.com/watch?v-jZyqqN4uqcfeature
related
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Classification of Colloids Based on Type of
Particles of the Dispersed Phase
  • Multimolecular colloids In this type of colloids
    the colloidal particles are aggregates of atoms
    or small molecules with molecular size less than
    one nanometer (1 nm). For e.g., gold sol consists
    of particles of various sizes which are clusters
    of several gold atoms. The molecules in the
    aggregates are held together by Van der Waal
    forces.
  • Macromolecular colloids Macromolecular colloidal
    particles are formed when on dissolution in a
    suitable solvent, the macromolecules have sizes
    which are in the colloidal range. Naturally
    occurring macromolecules are starch, proteins and
    cellulose. Man made macromolecules are polymers
    such as polyethylene, nylon and polystyrene.
  • Associated colloids (Micelles) Certain substances
    behave as strong electrolytes at low
    concentration but at higher concentrations these
    substances exhibit colloidal characteristics due
    to the formation of aggregated particles. These
    aggregated particles are called micelles. The
    formation of micelles takes place only above a
    particular temperature called Kraft Temperature
    (Tk) and above particular concentration called
    the Critical micelle concentration (CMC). On
    dilution, these colloids revert back to
    individual ions.

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Interaction between colloid particles
  • The following forces play an important role in
    the interaction of colloid particles
  • Electrostatic interaction Colloidal particles
    often carry an electrical charge and therefore
    attract or repel each other. The charge of both
    the continuous and the dispersed phase, as well
    as the mobility of the phases are factors
    affecting this interaction.
  • van der Waals forces This is due to interaction
    between two dipoles that are either permanent or
    induced. Even if the particles do not have a
    permanent dipole, fluctuations of the electron
    density gives rise to a temporary dipole in a
    particle. This temporary dipole induces a dipole
    in particles nearby. The temporary dipole and the
    induced dipoles are then attracted to each other.
    This is known as van der Waals force, and is
    always present (unless the refractive indexes of
    the dispersed and continuous phases are matched),
    is short-range, and is attractive.

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Interaction between colloid particles
  • Entropic forces According to the second law of
    thermodynamics, a system progresses to a state in
    which entropy is maximized. This can result in
    effective forces even between hard spheres.
  • Steric forces between polymer-covered surfaces or
    in solutions containing non-adsorbing polymer can
    modulate interparticle forces, producing an
    additional steric repulsive force (which is
    predominantly entropic in origin) or an
    attractive depletion force between them.

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http//www.youtube.com/watch?vk5HMVIb4J7ANR1
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Nobel Prize for Chemistry for his work on the
heterogeneous nature of colloidal solutions.
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The Faraday-Tindall effect
30º
The distilled solution of absent, solve by water
in different ratio
Crab nebulosity
Opal
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Tooth opalescence
Light for the dental technician is essential,
especially when it comes to aesthetics. In a
healthy tooth light effects manifest themselves
from inside. Separate layers of tissues react for
the light at different angles. Interestingly, the
structure of dentin and enamel differently behave
to the light. Especially noticeable light blue
opalescent glow enamel
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Preparation of Lyophilic Sols
  • Since lyophilic sols are quite stable, they can
    be easily prepared by shaking the lyophilic
    substance with the dispersion medium.
  • Examples are Colloidal sols of gum, starch,
    gelatine and egg albumin.

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Preparation of Lyophobic Sols
  • Lyophobic sols are prepared by two methods. They
    are
  • 1) Condensation methods - In condensation methods
    particles of atomic or molecular size are induced
    to combine to form aggregates of colloidal
    dimensions. To achieve this, chemical as well as
    physical methods are employed.
  • 2) Dispersion methods. - In dispersion methods,
    colloidal particles are obtained by breaking
    large particles of a substance in the presence of
    a dispersion medium. Since the sols formed are
    unstable, they are stabilized by adding
    stabilizing agents.

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Condensation methods
  • a) Chemical methods
  • Colloidal sols can be prepared by chemical
    reactions, which involve double decomposition,
    oxidation, reduction and hydrolysis. Examples of
    sols made by these methods are given below
  • i) Double decomposition
  • ii) Oxidation
  • iii) Reduction
  • iv) Hydrolysis

b) Physical methods
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Dispersion methods
  • a) Mechanical dispersion - In mechanical
    dispersion, the coarse suspension of the
    substance is ground in a colloid mill, a ball
    mill or an ultrasonic disintegrator. The colloid
    mill consists of two metal discs, close together
    and rotating at high speed (7000 revolutions per
    minute) in opposite directions. By the process of
    such grinding, the suspension particles are torn
    off to the colloidal sizes.

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b) Electrical disintegration or Bredig's Arc
Method
  • In this method, an electric arc is struck between
    electrodes of the metal immersed in the
    dispersion medium.

The intense heat produced by the arc vaporizes
the metal, which then condenses to form particles
of colloidal size. By this method, sols of metals
such as gold, silver and platinum can be
prepared.
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Toothpaste
Toothpaste is a colloid, because it's part solid
and part liquid.
  • A tooth paste composition comprising, in
    combination with a detergent base, a mixture of
    micronized colloidal silica gel and activated
    charcoal.
  • The present invention discloses a nano colloidal
    silver toothpaste, firstly, the silver is used as
    electrode, and the colloidal silver particles are
    prepared by means of electric spark bombardment,
    then are directly added into the toothpaste.

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Toothpaste ingredients typically consist of
  • Thickening agents or binders to stabilize the
    toothpaste formula. They include mineral
    colloids, natural gums, seaweed colloids or
    synthetic cellulose.     Detergents to create
    foaming action. They include sodium lauryl
    sulfate, sodium N-Lauryl sarcosinate.

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  • Hydrocolloids and silicate cements are examples
    of dental colloids. A colloidal model for the
    nanostructure of hydrated cement paste was
    proposed by Jennings in 2000 and has been
    referred to as CM-I.

The C-S-H is modeled as a network of
prismatic-shaped aggregates or particles referred
to as globules for consistency with the
original model (CM-I). A schematic of the model
is illustrated in Fig. The particles have a least
dimension of about 5 nm and the other dimensions
vary from 30-60nm.The particles are depicted as
having outer surface and internal porosity as
well as interlayer space.
33
Micelle
A micelle is an aggregate of surfactant molecules
dispersed in a liquid colloid. A typical micelle
in aqueous solution forms an aggregate with the
hydrophilic "head" regions in contact with
surrounding solvent, sequestering the hydrophobic
single tail regions in the micelle centre.
  • Inverse micelles have the head-groups at the
    centre with the tails extending out (water-in-oil
    micelle).

A normal phase micelle (oil-in-water micelle)
34
  • Micelles are approximately spherical in shape.
    Other phases, including shapes such as
    ellipsoids, cylinders, and bilayers are also
    possible. The shape and size of a micelle is a
    function of the molecular geometry of its
    surfactant molecules and solution conditions such
    as surfactant concentration, temperature, pH, and
    ionic strength.

The process of forming micellae is known as
micellization
35
In medicine, dialysis (from Greek "dialusis",
meaning dissolution, "dia", meaning through, and
"lysis", meaning loosening) is a process for
removing waste and excess water from the blood.
Dialysis works on the principles of the diffusion
of solutes and ultrafiltration of fluid across a
semi-permeable membrane.
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Types of Emulsion
A fine dispersion of one liquid in a second,
largely immiscible liquid. In foods the liquids
are inevitably oil and an aqueous solution.
mm
Water
Oil
Emulsions are an example of colloids composed of
tiny particles suspended in another immiscible
(unmixable) material.
Oil-in-water emulsion
Water-in-oil emulsion
39
Biopolymers
Biopolymers are polymers produced by living
organisms. Since they are polymers, Biopolymers
contain monomeric units that are covalently
bonded to form larger structures. There are three
main classes of biopolymers based on the
differing monomeric units used and the structure
of the biopolymer formed. Polynucleotides long
polymers which are composed of 13 or more
nucleotide monomers, Polypeptides short polymers
of amino acids, and Polysaccharides which are
often linear bonded polymeric carbohydrate
structures.
Cellulose is the most common organic compound and
biopolymer on Earth. About 33 percent of all
plant matter is cellulose. The cellulose content
of cotton is 90 percent and that of wood is 50
percent.
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Characteristics of biopolymer
Polymer samples usually are irregular in shape,
making it difficult to measure their volume
directly. The useful properties of polymer is
density. The density can be used to calculate the
percent of a polymer that is crystalline.
The tensile strength of a material quantifies how
much stress the material will endure before
suffering permanent deformation This is very
important in applications that rely upon a
polymer's physical strength or durability Young's
modulus of elasticity. Young's Modulus quantifies
the elasticity of the polymer. It is defined, for
small strains, as the ratio of rate of change of
stress to strain. Like tensile strength, this is
highly relevant in polymer applications involving
the physical properties of polymers, such as
rubber bands. The modulus is strongly dependent
on temperature.
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Transport properties such as diffusivity relate
to how rapidly molecules move through the polymer
matrix. These are very important in many
applications of polymers for films and
membranes. Phase behavior a) Melting
point The term melting point, when applied to
polymers, suggests not a solid-liquid phase
transition but a transition from a crystalline or
semi-crystalline phase to a solid amorphous
phase. b) Glass transition temperature A
parameter of particular interest in synthetic
polymer manufacturing is the glass transition
temperature (Tg), which describes the temperature
at which amorphous polymers undergo a transition
from a rubbery, viscous amorphous liquid, to a
brittle, glassy amorphous solid. The glass
transition temperature may be engineered by
altering the degree of branching or crosslinking
in the polymer or by the addition of plasticizer.
44
Chemical properties
The attractive forces between polymer chains play
a large part in determining a polymer's
properties. Because polymer chains are so long,
these interchain forces are amplified far beyond
the attractions between conventional molecules.
Different side groups on the polymer can lend the
polymer to ionic bonding or hydrogen bonding
between its own chains. These stronger forces
typically result in higher tensile strength and
higher crystalline melting points.
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