Colloid chemistry for pharmacy students
The subject of colloid chemistry. Why are
colloids so different?
Classification, characterization of colloid
systems.
Zoltán Nagy,
lecturer
Bányai István
professor
Univ. of Debrecen, Dep. of Colloid- and
Environmental Chemistry
www.kolloid.unideb.hu
1. lecture
1
Motivation 1
•
Everyday experiences
– Silicosis (size), red mud (accident in Hungary), asbestos (shape)
– Smog
– New alloys („micro structure”) (implants)
– Functional polymers (biological macromolecules, drug delivery)
•
Nanotechnology
– Fluorescence is size dependent (diagnostic)
– TiO2 catalytic activity (cosmetics)
– Drug release rate
– Drug imbibition
– Wetting of solids
– Solubilization of drugs
– Polymorhism
Reading
• Barnes, GT, Gentle, IR: Interfacial Science ,
– 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
• Atwood, D., Florence, AT: Phyisical Pharmacy
– Pharmaceutical Press 2008, ISBN 978 0 85369 725 1
• Pashley, R. M.: Applied Colloid & Surface
Chemistry
– Wiley&Sons, ISBN 0-470-86883-X, 2004
3
Exam, requirements
• Written test
– one test in an exam period (2 possibilities )
• Slides: kolloid.unideb.hu
4
Place of colloid science
•
1. partly physical chemistry
•
2. partly physics
•
3. partly biology
– Not (only) the chemical composition is important
– the states are independent of the composition
– the physical properties are important
– basic law of physics are used
– the biological matters are colloids
– the mechanisms of living systems surface chemistry (enzymes)
colloid science
biology
physical chemistry
physics
biochemistry
chemistry
organic
chemistry
5
Lectures
•
•
•
•
•
•
•
•
•
•
•
•
•
1. Colloids. Physical chemistry basics. Colloid systems
2. Molecular, interparticle interactions.
3. Liquid-gas, solid-gas, solid-liquid interfaces
4. Surface chemistry: L-G, S-G, S-L surfaces
5. Adsorption at gas-solid interface
6. Adsorption from solutions. Strong electrolytes
7. Electric double layers
8. Electrokinetic phenomena
9. Colloid stability: lyophobic colloids
10. Foams, emulsions
11. Macromolecules
12. Association colloids
13. Rheology and structure
6
Subject of colloid chemistry:
systems consist of particles in size of 1nm – 500 nm.
systems in which the surface plays a significant role
Homogeneous
Atoms, small molecules
1010
smoke
köd
macromolecules
109
Homogeneous
0.1
Heterogeneous systems
(macroscopic phases)
colloid system
108
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
7
Homogeneous, heterogeneous ?
• Homogeneous: isotropic. (5% solution of NaCl or gelatine?)
• Heterogeneous systems, Gibbs phases rule
interface
PF C2
Homogeneous one
phase
Gold sol
continuum?
dotlike?
It is not distinguishable by
appearance. Soup, jelly, milk, beer,
bread, pudding-pie, fog, smoke,
smog, soils, toothpaste, blood,
mayonnaise, whip, opal, solution of
soap, etc.
degree of dispersion
Heterogeneous more
phase
8
Colloids in everyday life
•
Some times naturally visible, somtimes hidden.
Homogeneous one
phase
Colloids cannot be classified as
homogeneous or heterogeneous system
tenzids
Heterogeneous more
phase
liogel
Aerogel, “frozen smoke”
Xerogel, modern opal
9
The colloidal state
1. Definition of colloid state
history:
Solution (Graham)
and suspension theory,
homogeneousheterogeneous
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"
http://www.wsu.edu/~omoto/papers/darkfield.html
10
Homogeneous, heterogeneous ?
Zsigmondy Nobel price: 1925 : the system must be heterogeneous
nature. If he had examined a gelatin solution he would have explained
that the colloids must be homogeneous systems. (no motion !)
nano
S/V
F CP2
Why are colloids not
heterogeneous?
0.8
Increasing
specific surface
area and
surface energy
surface molecules/ total
R<10 nm nanotechnology
0.6
the effect of surface can
not be ignored
10 %
0.4
1%
0.1 %
0.2
0.0
1.0E-7
1.0E-6
1.0E-5
colloid
1.0E-4
1.0E-3
1.0E-2
1.0E-1
1.0E+0
gold sol
R ,cm
Surface molecules/total molecules %
11
Sub-microscopic discontinuity
blocks:
molecules
d e n s ity
d en sity
particles
x
x
W. Ostwald: the colloidal state is
independent on the chemical forms
Forming a disperse system by
breaking of b phases (any kind
of phases except from 2 gas)
Aladár Buzágh : submicroscopic
discontinuities
A: two homogeneous phases form a
heterogeneous system
D: two components form a homogeneous
solution, particles are smaller than 1 nm
12
Motion in colloid solutions or dispersions
• 1. Gravitational force: tending to settle or rise
particles depending on the density
• 2. Viscous drag force: arises as a resistance to
motion, since the fluid has to be forced apart as the
particle moves thorugh it.
• 3. Natural kinetic energy of particles: Brownian
motion
13
Motion causes separation
Fdrag  6 rV  4r g (  p  liq ) / 3  Fgrav
3
r = radius (m); V = volume (m3); η = viscosity (Pas);
ρp and ρliq densities (kg/m3);
g = gravitation acceleration (m/s2)
Δρ = 1g cm-3
14
Brownian motion
• Each particle has a kinetic energy: appr. 1 kT
Ekin 
1 2
mv
2
kT
4 1021 J
This leads us to colloid science because small particles
moves fast (no sedimentation) but a lot of collision: may
cause aggregation because of the van der Waals
interactions.
15
Messages
• 1. In colloid state the heterogeneity and homogeneity have no
meaning, or have different meaning.
• 2. All materials can be in colloid state
• 3. The colloid state is not defined in sharp terminology.
• Colloids are the systems:
– in which particles are between 1-500 nm in size (microscope).
– where the surface particles strongly affect the behaviour.
– in solution the Brownian motion is typical (energy is larger
than that of the sedimentation)
16
Classifications
17
Coherent and incoherent systems
• Incoherent systems
– Fluid phase characters
– Particles moves individually
(the cohesive forces
(attraction) are weaker than the thermal energy)
• Coherent systems
– solid phase characters (cross-linking 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)
– creams, pastes, gels (rheology: tixotropy)
18
Type of colloids
on the basis of structure (appearance)
colloids
Coherent (solid-like) gel
Incoherent (fluid-like)
Macromol.
Colloidal
Association Porodin
Dispersions solutions
Colloids
(porous)
sols
Colloidal solutions
corpuscular
diszpersion
macromolecular
liofób
liofil
(IUPAC proposal)
Reticular
fibrillar
Spongoid
lamellar
association
liofil
19
Type of sols (incoherent)
categorized by inner / outer phases
• aerosols
L/G liquid in air:
fog, mists, spray
S/G solid aerosol,
solid in gas:
smoke, colloidal
powder
Complex, smog
• liosols
xerosols, xerogels
G/L gas phase in liquid
(sparkling water, foam,
whipped cream)
G/S solid foam:
polystyrene foam
L/L emulsion, liquid in liquid,
milk
L/S solid emulsion: opals,
pearls
S/L colloid suspension (gold
sol, toothpaste, paint, ink)
S/S solid suspensions:
pigmented plastics
20
Macromolecules (incoherent)
The probable shape and weight of some proteins
Illustration of a polypeptide
macromolecule
Colloidal particles are much larger than the solvent molecules in a solution,
the properties of these particles depend on their size and shape
21
Association colloids (incoherent)
Surfactant (soap and
detergent)
spherical
micelle
(targeted
medicine)
amphiphilic
Micelles are the simplest of all self-assembly
structures
22
Coherent systems
examples
23
Gels (most interesting in coherent systems)
Solid-like consistency
Examples: gelatins, collagens (proteins), pectins (polysacharide)
may be used for food as a stabilizer, thickener, or texturizer for 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
to create volume without adding calories.
Pharmaceutical capsules in order to make their contents easier to swallow,
microcapsule
for photografic films , hair styling cream
Blood, coagulated blood, milk sour
cream
24
Clays: similar chemical composition
4.7 m
Trovey, 1971 ( from Mitchell, 1993)
Attapulgit
7 micrometer
illite
25
Opal
Simply hydrated silica (SiO2) particles
Precious opal consists of spheres of silicon dioxide
molecules arranged in regular, closely packed planes.
(Idealized picture)
26
Messages
• Colloids are classified
– Coherent (solid-like) eg. gels
• Porodin
• reticular
• Spongoid
– Incoherent (liquid like)
• Sols (liophobic, not-stable thermodynamically)
– L/G, SG
– G/L, L/L, S/L
– G/S, L/S, S/S (coherent)
• Macromelucules (liophilic, stable)
• Association colloids (liophilic, stable)
27
Messages 2
Fundamental forces and energy in physical chemistry
• Gravitational forces (special for colloids)
– 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.
28
Characterization of colloids
29
Stability of (colloid) systems
Thermodynamic stability
– Stable (true solutions): lyophilic colloids
Gsolution < Ginitial , (G=H-TS)
Macromolecular solutions, association colloids
–
Not stable: lyophobic colloids
Gsol > Ginitial
Sols , of large specific surface area (ratio of surface to
volume)
Kinetic stability
- Stable (unchanged within the examination )
- Unstable
kinetically
30
Characterization of colloids
Colloidal state parameters, beyond the usual
physical parameters (p,v,T)
1.
Dispersity (or size distribution)
monodispersed,
heterodispersed
2. Morphology
shape, inner structure,
isometric vs anisometric,
crystalline vs amorphous
3. Spatial distribution
4. Interparticle interaction (analogous to molecular
interactions)
31
Dispersity (or size)
(Characterization of colloids)
Ideal:
Monodispersed, (isometric: eg. spheres with
the same radius)
Real:
Heterodispersed (anisometric: distorted
spheres, rod, plate in different sizes (what
is size?)
32
Heterodispersed systems
•The average diameters
•Number, surface and volume
weighted average diameters
• Polydispersity
33
Average diameters (isometric)
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
d

d

i
i
 the weighting factor
i
i index the class or
d
the mean diameter
fraction
 the multiplier may be number, surface, volume, intensity,
etc.. hence number weighted, surface weighted, mass weighted
etc average.
34
Number weighted average (mean)
 is the factor by which the contribution of the constituent is
proportional in the measured property
Number averages
 =N the weighting factor is
number in class
Example: colligative properties (osmosis) yield number
weighted averages
…. etc.
L
dN  
N
d N
N
i
i
diameters: 1, 2, 3, 4, 5, 6, 7, 8, 9,10
Number of class, Ni=1
i  Ni
i
11  2 1  3 1  ...  10 1 55


 5.5
1  1  1  ...  1
10
N
i
 10
The total number
of particles
The length of the string 55 is the same
from the original and 10 spheres of average size
35
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  Li  di Ni 1 2  10 1 12
dN  


 4
N  Ni
2 1
3
 Ni
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 still valid for the
average spheres
36
Other averages
The measurement of colligative properties
results number average (osmosis)
The numbers or diameters are not known or there is no
any tool for their determination. It is known the
correlation between the volume and surface:
Si
hence
di2 Ni
V /S
Vi
L
di3 Ni
d? ( 9,8)
N1=2, d1=1; N2=1, d2=10
We can measure the total volume and surface and calculate
the diameter.
But what kind of ???
37
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)
L
d2 ( 10)
Comparison!!!!
N1=2, d1=1;
N2=1, d2=10
x

x

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
if di and Ni known
S/ds2= 1.06
pieces
The same total surface, S: 1.06 pcs d~9,8
The number changed !
d N  dS
38
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 weigths and
calculate an effective diameter.
N1=?, d1=1;
N2=?, d2=10
W
But what kind of ???
d1W1  d 2W2  diWi
d? 

W1  W2
Wi
x
x 

i
i
i
This is a volume or mass weighted average
http://en.wikipedia.org/wiki/Center_of_mass
39
Mass weighted averages
When the numbers are not known.
From the original system
dw ( 9,98) d2 ( 10)
W
dW 
 diWi
Wi

4
d
 i Ni
 d Ni
3
i
 9.98
In this average the larger particles dominate.
(for example the center of mass.)
The number changed !
W/dw3= 1.007
pieces
if di and Ni known
d N  d S  dW
http://en.wikipedia.org/wiki/Center_of_mass
40
Why do we need the different averages?
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
x

x

Φ=N
i
i
i
Φ=S
Φ=W
(more dozens average exist)
http://en.wikipedia.org/wiki/Average
The average does not say anything from the details
polydispersity PD:
PD  d w / d N
2.5
41
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)
MW / M N  25
MW / M N  2
Mn
i
i
i
MW / M N  1
Mw 
nM


n
 wi M i
w
i

 (ni M i )M i
n M
i
i

2
n
M
i i
n M
i
i
42
Polydispersity
xN  xS  xw
xw
PD 
1
xN
Sample: A M= 1, B M= 100
100 pcs A + 1pc B
MW 
100 pcs A + 100 pcs B
11100  100 100 1
 50,5
1100  100 1
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
MN 
MW / M N  25
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
MW / M N  1,01
43
pc~ piece; pcs pieces
Normal distribution,
cumulative function
100
mean + 
%
84
  
mean ±  ~ 68 %
50
mean - 
16
0
50
100
150
200
x
44
Normal distribution,
frequency function
100
mean + 
%
84
  
mean ±  ~ 68 %
50
1
( x  x ) 2
f ( x) 
exp
2 2
2
mean - 
16
0
50
100
150
200
x
̄x is the mean or
expectation (median)
a  is the standard
deviation
Variance=
(deviation)2:  2
Mean +  is 68.26 %
Mean + 2 is 95.5 %

 x  x 
2
d

x    68%
http://en.wikipedia.org/wiki/Average
45
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 too small to
settle out of solution due to the gravity)
• Centrifuge d<5 micron
• Light scattering 1 nm- some microns
46
2. Morphology (shape, inner structure)
1. Prolate (a>b), 2. oblate (a<b), 3. rod, 4. plate, 5. coil
Irregular particle, equivalent radius
47
3. Spatial distribution, ordered structure
•Homogeneous
•Diffuse
•Heterogeneous
•Ordered
Special
behavior
nematic
smectic
tactoid
48

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