Colloid chemistry for pharmacists
The subject of colloid chemistry. Why are so
different the colloids? Classification,
characterization of colloid systems.
Dr Berka Márta,
Bányai István
associate professor
professor
Univ. of Debrecen, Dep. of Colloid- and Environmental
Chemistry
http://dragon.unideb.hu/~kolloid/
1. lecture
1
Reading
• Barnes, GT, Gentle, IR: Interfacial Science A,
– Oxford UP. ISBN 0-19-927882-2, 2005
• Cosgrowe T.: Colloid science
– Blackwell Publishing ISBN:978-14051-2673-1, 2005
• Erbil, H. Y.: Surface Chemistry
– Blackwell, ISBN 1-4051-1968-3, 2006
• Pashley, R. M.: Applied Colloid & Surface
Chemistry
– Wiley&Sons, ISBN 0-470-86883-X, 2004
• McCash, E. M.: Surface Chemistry
– Oxford UP. ISBN 978-0-19-850328-6, 2001 (2007)
• Crowe, J.:Chemistry for the Biosciences
– Oxford UP. ISBN 0-19-928097-5, 2006
2
Exam, requirements
• Written test
– one test in an exam period (2 possibilities)
(50-60% mark 2; 61-75% mark 3; 76-85% mark 4; >85% mark 5.)
• Slides http://dragon.unideb.hu/~kolloid/
3
Place of colloid science
•
•
•
1. partly physical chemistry
– not the chemical composition is important
– the states are independent of the composition
2. partly physics
– the physical properties are important
– basic law of physics are used
3. partly biology
– the biological matters are colloids
– the mechanisms of living systems surface chemistry (enzymes)
perfomation
disappear, stability,
interaction with
external field, force
colloid science
biology
physical chemistry
physics
biochemistry
chemistry
organic
chemistry
The word “colloid” was derived from the Greek,”kolla” for glue (1862), distinguish colloids from crystalloids such as sugar and salt.
Colloids have been studied by scientists since the early 1800's. The early part of the 20th century saw a number of major developments
in both chemistry and physics, some of which had direct influences on the study of colloids. A number of methods for studying
colloidal particles were developed, including diffusion, electrophoresis, and scattering of visible light and X-rays.
4
Homogeneous, heterogeneous ?
•
•
Homogeneous: isotropic. (5% solution)
heterogeneous, Gibbs phases rule
pV = nRT
P+F =C+2
continuum? point like? In case of a colloid system
the properties depend of the sampling scale.
Homogeneous one
isotropic phase
Gold sol Michael
Faraday 1857;
Gustav Mie 1908
It is not distinguishable by appearance. Soup,
jelly, milk, beer, bread, pudding-pie, fog,
smoke, smog, soils, toothpaste, blood,
mayonaise, whip, opal, solution of soap, etc.
Heterogeneous more
phase
Colloids can not be classified as homogeneous or
heterogeneous system
tenzides
Aerogel, “frozen smoke”
liogel
5
Xerogel, modern opal
The colloidal state
1. Definition of colloid state
history:
Solution and suspension theory,
homogeneous-heterogeneous
2. Ultramicroscope, dark field
microscope
R. Zsigmondy Nobel price: 1925
"for his demonstration of the heterogenous nature
of colloid solutions and for the methods he used,
which have since become fundamental in modern
colloid chemistry"
They examined two types of colloids, After cooling one of them jellify, form a
gelatin like matter and other type forms crystals
http://www.wsu.edu/~omoto/papers/darkfield.html
they found that this behavior is in relation with the diffusibility that is with the
size. He saw some illuminating particles and their conclusion was that this
particles had interface so the system must be heterogeneous nature
If he had examined a gelatin solution he would have explained that the colloids
must be homogeneous systems. This experiment was the first evidence for that
the Brown motion is a thermal motion and the Boltzmann-Maxwell kinetic gas
theory
6
Homogeneous, heterogeneous ?
Why are not the colloids heterogeneous? Colloids
don’t obey the rule of Gibbs because the effect of
interface between the phases can not be
neglected.
nano
0.8
F =C−P+2
The phase rule enabled the identification of the number of variables
(or degree of freedom) depending on the system composition and
conditions. It is generally written as F=C-P+2 where F is the
number of possible independent changes of state or degrees of
freedom. C is the number of independent chemical constituents and
P the number of phases present in the system
S/V
surface molecules/ total
R<10 nm nanotechnology
0.6
the effect of surface can
not be ignored
Increasing specific
surface area and
surface energy
10 %
0.4
1%
0.1 %
0.2
0.0
1.0E-7
gold sol
1.0E-6
1.0E-5
1.0E-4
1.0E-3
1.0E-2
1.0E-1
1.0E+0
R ,cm
kolloid
Surface molecules/total molecules
7
Subject of colloid chemistry:
– systems consist of particles in size of 1nm – 500 nm.
(more phases system in which the surface plays a significant role)
Homogeneous
Atoms, small
molecules
colloid system
smoke
macromolecules
10−10
10−9
Homogeneous
0.1
Heterogeneous systems
(macroscopic phases)
10−8
fog
10−7
colloid
1
micelles
10
10−5
10−4
2
10
3
10
4
pollen, bacterium
10−3
m
heterogeneous
microscopic
10
virus
10−6
10
5
10
6
nm
8
Submicroscopic discontinuity
blocks:
molecules
sûrûség
property
property
sûrûség
particles
x
Forming a disperse system by
breaking of β phases (any kind
of phases except from 2 gas)
x
length
W. Ostwald: the colloidal state is
independent on the chemical forms
Aladár Buzágh : submicroscopic
discontinuities
A: two homogeneous phase form a heterogeneous system
D: two component form a homogeneous solution, particles are smaller than 1 nm
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Coherent and incoherent systems
•
•
•
Incoherent systems
– Fluid phase characters
– Particles moves individually (the cohesive forces attraction is
weaker than the thermal energy)
Coherent systems
– solid phase characters (crosslinking by covalent or interparticle
forces) (the cohesive forces attraction is stronger than the thermal
energy)
– network structure (the anisometry helps the formation of network )
Intermediate systems (semisolids)
– concentrated emulsions, suspensions, liofil solutions creams,
pastes, gels (thixotropy); sol-gel transformation.
10
Type of colloids
on the basis of structure
colloids
Solid-like consistency
Incoherent (fluid)
Coherent, gel
Macromol. Association Porodin
Colloidal
Dispersions solutions
Colloids
(porous)
sols
Colloidal solutions
lyophobic
gold sol,
micro emulsion
lyofhilic
(IUPAC)
Reticular
Spongoid
lyophilic
Gelatin solution, tenzid, soap, detergent
polyelectrolyte
inorganic catalyzer; fibroids , gel from fibrous molecules: gum, rubber,
viscose, natural synthetic fibers, muscle-fibers; spongoid are formed from
thin lamellas or films
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Type of colloidal dispersions (sols)
categorized by inner/outer phases
•
aerosols
•
liosols
L/G liquid aerosol:
fog, mists, spray,
perfumes, pesticides
G/L gas liosol, gas bubbles in
liquid (sparkling water, foam,
whipped cream)
S/G solid aerosol,
solid in gas: smoke,
colloidal powder
L/L liquid liosol, liquid
droplets in liquid, emulsion
Complex, smog
S/L solid liosol, solid
particles in liquid (gold sol,
toothpaste, paint, ink)
xerosols
G/S bubbles in solid, solid
foam: polystyrene foam
L/S solidified emulsion:
opals, pearls
S/S solidified sols:
pigmented plastics, stained
glass
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Macromolecules
The probably shape and weight of some molecules
Illustration of a polypeptide
macromolecule
Macromolecules are much larger than the solute in a solution, the properties of these
particles depend on their size and shape!
13
Association colloids
Surfactant (soap and detergent)
amphiphilic
spherical
micelle
Micelles are the simplest of all self-assembly structures
14
gels (coherent systems)
Solid-like consistency
Gel for example gelatin, collagen, pectin.
Gelatin may be used for food as a stabilizer,
thickener, or texturizer in foods such as ice
cream, jams, yogurt, cream cheese, margarine;
it is used, as well, in fat-reduced foods to
simulate the mouth feel of fat and to create
volume without adding calories.
Pharmaceutical capsules in order to make their
contents easier to swallow , microcapsule, for
photographic films, hair styling cream.
( sol-gel: blood- coagulated blood, milk -sour
cream)
15
Fundamental forces and energy
•
Gravitational forces
– tending to settle or raise particles depending on their density relative to
the solvent. Colloidal particles are to small to settle out of solution due
to the gravity)
•
Viscous drag force
– Arises as a resistance to motion, since the fluid has to be forced apart
as the particle moves through it
•
Kinetic energy of particles, Brownian motion
– The kinetic random motion will dominate the behavior of small particles
if there is not attractive or repulsive force between them.
•
Van der Waals force,
– a ubiquitous attractive force in nature, electromagnetic in origin
•
Electrostatic repulsion between similarly charged particles
– Most materials when dispersed on water selectively adsorb ions from
solution, and hence become charged.
16
Stability
Thermodynamic
– Stable (true solutions): lyophilic colloids
Gsolution < Ginitial , (ΔG=ΔH-TΔS)
Macromolecular solution, association colloids give true solution in
thermodynamic sense with the medium which surround them.This is
entropic and enthalpic stabilization
–
Not stable: Lyophobic colloids
Gsol > Ginitial
Sols , of large specific surface area (ratio of surface to volume)
Kinetic
- Stable (unchanged within the examination )
- Unstable
17
Characterization of colloids
Buzágh:
gh colloidal state parameters
1. Dispersity (or size distribution)
Monodispersed, isometric (spheres with the same radius)
Heterodispersed, anisometric (rod, plate)
2. Morphology: shape as spheres, cubes, plates, rods etc., inner
structure as crystal or amorphous.
3. Spatial distribution
4. Interparticle interaction
18
Dispersity (or size distribution)
Heterodispersed systems
•The average diameters
Number, surface and volume weighted diameters
• Polydispersity.
Colloidal systems are polydisperse with regard to
their size or/and shapes, to a greater or lesser
extent.
19
Average diameters
The mean and the standard deviation are used to
represent for polydispersed systems
The arithmetic mean is relevant any time several quantities add together to
produce a total. The arithmetic mean answers the question, "if all the quantities
had the same value, what would that value have to be in order to achieve the
same total?"
Arithmetic mean
dφ
∑
d=
∑φ
i
i
Φ the weighting factor
i
d
i index the class or fraction
The mean diameter
Φ the multiplier may be number, surface, volume, intensity, credit etc.. hence number
weighted, surface weighted, mass weighted , etc.
20
Number average
Φ is the factor by which the contribution of the constituent is proportional in the
measured property . In case of number average the weighting factor is the number in
class. Number average is often referred to as simply the average or mean.
Φ=N the weighting factor is number in class
Example: colligative properties yield number averages
…. stb.
φi = N i
dN
diameters: 1, 2, 3, 4, 5, 6, 7, 8, 9,10
Number of class, Ni=1
∑N
i
L
∑
=
∑N
= 10
i
i
=
55
= 5.5
10
The total number
of particles
The length of the string 55 is the same from the original spheres and from spheres of average
21size
Calculation of the number average
Properties, di, diameter, Ni the weighting factor, number
Sample:
L
N1=2, d1=1; N2=1, d2=10
L
N=3, dN=4
L
dN = =
N
∑L = ∑d N
∑N ∑N
i
i
i
i
i
=
1× 2 + 10 ×1 12
= =4
2 +1
3
The average diameter: 4. meaning: 3 pieces with
length of dN=4 together give the same length (L) than
the original string
The number is known and remain valid for the
average spheres
22
Other weighted averages
The measurement of colligative properties
results number average
The numbers or diameter are not known or there is not any tool for
their determination. It is known the correlation between the volume
and surface, V/S (the constants are neglected!):
Si = d i2 N i
hence
L
Vi = d i3 N i
V / S = d? (= 9,8)
N1=2, d1=1; N2=1, d2=10
We can measure the total volume and total surface and calculate the diameter.
What kind of diameter is V/S ?
23
Surface weighted averages
When the numbers are not known,
For example the number of drops in a mug of milk.
d? (= 9,8) >> d N (= 4)
d? (= 9,8) ∼ d 2 (= 10)
Comparing the definition of arithmetic mean it can be seen, that the weighting factor is the surface
xφ
∑
x=
∑φ
i
S weighting factor
V
dS ~ =
S
∑Vi
∑ d i Si
i
i
3
d
∑ i Ni
113 × 2 + 1032 ×1
=
=
= 2
= 9.8
2
2
∑ Si ∑ Si ∑ di Ni 11 × 2 + 102 ×1
S/ds2= 1.06 pieces
if di and Ni known
V/ds3= 1.06 pieces
1.06 pieces of d~9.8 spheres have the same total volume and surface as the origin
ones.
The number changed !
dN < dS
24
Mass weighted averages
When the numbers are not known,
for example particles in a sack of powder.
Sample: We got a sack from the previous
spheres. We select them by sieve, measure
their weights and calculate an effective
diameter.
N1=?, d1=1;
N2=?, d2=10
W
But what kind of ???
d1W1 + d 2W2
=
d? =
W1 + W2
∑ diWi
x=
∑W
∑x φ
∑φ
i
i
i
i
This is a volume or mass weighted average
http://en.wikipedia.org/wiki/Center_of_mass
25
Mass weighted averages
When the numbers are not known.
From the original system
dw(= 9,98) d2 (=10)
W
dW =
∑ diWi
∑W
i
=
4
d
∑ i Ni
∑d
3
i
Ni
= 9.98
W/dw3= 1.007 ps
if di and Ni known
In this average the larger particles dominate.
(for example the center of mass.)
The number changed !
d N < d S < dW
http://en.wikipedia.org/wiki/Center_of_mass
26
Why we need the different average?
The different experimental method perceive the polydispersity systems
with different way. They are sensitive for different properties of the
fractions so they result different averages.
dN = 4
d S = 9,8
dW = 9,98
N1=2, d1=1; N2=1, d2=10
xφ
∑
x=
∑φ
i
Φ=N
i
i
Φ=S
Φ=W
(more dozens average exist)
The average does not say anything from the details
Beside the average we have to give the average deviation or the
polydispersity, PD for characterize the distribution.
PD = d w / d N ∼ 2.5
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Polydispersity
dw
≥1
dN
Example:
1, MA= 1, NA= 100, MB=100, NB=1
2, MA= 1, NA= 100, MB=100, NB=100
3, MA= 1, NA= 1, MB=100, NB=100
1)
2)
3)
M W / M N = 25
MW / M N = 2
Mn
i
i
i
M W / M N = 1.01
Mw =
N M
∑
=
∑N
∑Wi M i
∑W
i
=
∑ ( Ni M i ) M i
∑N M
i
i
=
2
N
M
∑ i i
∑N M
i
i
M molar mass, W weight, N number
28
Polydispersity
x N < xS < xw
xw
PD =
≥1
xN
Mw =
∑N M
i
Sample: A M= 1,
100 pcs A + 1pc B
MW =
2
N
M
∑ i i
i
100 pcs A + 100 pcs B
MW =
1× 1× 100 + 100 × 100 × 100
= 99, 0
1× 100 + 100 × 100
1× 100 + 100 × 1
= 1,98
100 + 1
MN =
1× 100 + 100 × 100
= 50,5
100 + 100
M W / M N = 25
∑N M
∑N
i
i
i
B M= 100
1× 1× 100 + 100 × 100 × 1
= 50,5
1× 100 + 100 × 1
MN =
Mn =
MW / M N = 2
1 pc A + 100 pcs B
MW =
1× 1× 1 + 100 × 100 × 100
= 99.99
1× 1 + 100 × 100
MN =
1× 1 + 100 × 100
= 99.02
1 + 100
M W / M N = 1, 01
29
Number or pc~ piece; pcs pieces
Polydispersity
Sample A: M= 100, B: M= 10000
100 pcs A + 1pc B
100 pcs A + 100 pcs B
M W / M N = 5050 /198 = 25
1 pc A + 100 pcs B
M W / M N = 9999 / 9902 = 1, 01
M W / M N = 9902 / 5050 = 2
M molar mass, W weight, N number
Only the ratio of the molar masses is important, not their absolute values
30
pc~ piece; pcs pieces
Normal distribution,
cumulative function
100
mean + σ
%
84
The Φ cumulative distribution
function describes probabilities for a
random variable to fall in the intervals
of the form (0, x) or (-∞, x).
σ = 15
mean ± σ ~ 68 %
50
mean - σ
16
0
50
100
150
200
x
f(x) probability density function is "bell"shaped, and is known as the Gaussian function,
it describes the relative likelihood for this
random variable to occur at a given point
31
dφ
f ( x) =
( x)
dx
Normal distribution,
frequency function
1
−( x − x ) 2
f ( x) =
exp
2σ 2
2πσ
σ
2
(x − x)
∑
=
2
dϕ
ϕ
x ± σ → 68%
where parameter is the mean (location of the peak) and σ2
is the variance (the measure of the width of the
distribution). The distribution with and is called the
standard normal.
32
Determination of sizes
•
•
•
•
•
•
Sieve 25 micron-125 mm
Wet sieve 10mikron-100 mikron
Microscope 200 nm-150 mikron
Ultramicroscope 10 nm -1 mikron
Electron microscope 1 nm- 1 mikron
Sedimentation d>1 micron (colloidal particles are to small to
settle out of solution due to the gravity)
• Centrifuge d<5 micron
• Light scattering 1 nm- some microns
33
2. Morphology (shape, inner structure)
1. Prolate (a>b), 2. oblate (a<b), 3. rod, 4. plate, 5. coil
Irregular particle, equivalent radius
34
3. Spatial distribution, ordered structure
•Homogeneous
•Diffuse (or exponential)
•Heterogeneous
•Ordered
Special
behavior
nematic
smectic
tactoid
The diffuse distribution or Boltzmann distribution law says that if the energy associated with some state or condition of a system is ε
then the frequency with which that state or condition occurs, or the probability of its occurrence, is proportional to exp (−ε/kT) ,
where T is the system’s absolute temperature and where k is the Boltzmann constant,
35