Interparticle interactions
1. Ion-ion interaction (Coulomb interaction)
( z1e)( z2e) 1

4 0
r
Calculation:
Eion1 ion2 
Sign:
repulsion (+), attraction (-)
Range:
50nm
2. Ion-dipole interaction
( z1e)  cos 1
 2
4 0
r
Calculation:
Eion1 dipole2 
Sign:
always attraction (+)
Range:
1.5 nm
E: energy of the interaction (J), z: charge number, e: charge of the electron (C),
ε0: vacuum permittivity (C/m·V), r: distance (m), μ: dipole moment(C·m), θ:angle
3. Dipole-dipole interaction
Low temperature
High temperature
ordered dipoles
freely rotating dipoles
const1 2 1

 3
r
4 0
Edipole1 dipole2
2
1
12 22


3 (4 0 )2 k BT r 6
Calculation:
Edipole1  dipole2
Sign:
repulsion (+), attraction (-)
always attraction (-)
Range:
1.5 nm
1.5 nm
E: energy of the interaction (J),ε0: vacuum permittivity (C/m·V), r: distance (m),
μ: dipole moment(C·m), kB: Boltzmann constant (J/K), T: Temperature (K)
4. Dipole-induced dipole interaction
If polar molecule induces a polarization of nonpolar molecule.
 2 12
1
 4

( 4 0 ) 2 r 6
Calculation:
E dipole1 i .dipole2
Sign:
always attraction (+)
Range:
< 1 nm
The polarizibity depends on the size (molar mass), larger the molecule, larger
is the α value
E: energy of the interaction (J),ε0: vacuum permittivity (C/m·V), r: distance (m),
μ: dipole moment(C·m), α: polarizibility(m3)
5. Instantaneous dipole-induced dipole interaction
(London dispersion, dispersion forces)
Between non-polar molecules
Calculation:
E London  
3 1 2 I1 I 2 1
 6
2 ( I1  I 2 ) r
Sign:
always attraction (+) (temporary)
Range:
< 0.5 nm
The London dispersion interaction depends on the size and the shape of the
molecules. Week, temporary forces.
E: energy of the interaction (J), r: distance (m), α: polarizibility(m3), I: Ionization
energy of the molecule (J)
Total interaction (sum of the attraction and
repulsion)
Etotal  Eattraction  E repulsion
Eattraction ~
const
r6
E repulsion ~
const '
r12
Examples
molecule
dipole moment (D)
molecule
polarizability
HF
1.91
He
0.2
HCl
1.05
Ar
1.63
HBr
0.79
Xe
4
H2O
1.85
H2
0.81
H2S
0.93
Cl2
4.6
methanol
3.09
O2
1.6
ethanol
1.66
CH4
2.6
benzene
0
C2H6
4.5
0
CCl4
molecule dipole moment (D) polarizability orientation%
induction%
dispersion%
CCl4
0
10.5
0
0
10
benzene
0
10.3
0
0
10
water
1.85
1.44
84.8
4.5
10.7
ethanol
1.7
5.49
42.6
9.7
47.7
Special interactions
1. Hydrogene-bond:
Requirements:
- presence of covalently bonded H
- H should bond to an atom with large electronegativity
- The electronegative atom (F, O, N) should have non-bonding
electron pairs
O
O
H
H
H
O
H
CH3
O
H
H3C
H
O
O
H
H
H
CH3
Special interactions
2. Hydrophilic- or hydrophobic interactions:
- Hydrophylic:
Mostly polar, or ionic compounds. Having tendency
toward water molecules. High water solubility.
- Hydrophobic:
Mostly non polar molecules. Doesn’t have preference
for water. Poor solubility in water.
Special interactions
3. Lipophilic- or lipophobic interactions:
- Lipophylic:
Non-polar molecules. Soluble in non-polar solvents.
- lipophobic:
H-bond capable/polar or ionic compounds. Prefer
polar solvents.
Special interactions
3. Lyophilic- or lyophobic interactions:
- Lyophylic:
Highly soluble in the given solvent.
- lyophobic:
Poor solubility in the given solvent.
Examples
Examples
Examples
Examples
Kinetic properties of colloids
Motion of colloidal particles in
liquids .
Motions in liquid media
1. Brownian motion
2. Sedimentation
3. Osmosis
Brownian motion
- Absence of external forces (self diffusion)
- All particles having the same average
translational kinetic energy:
E kinetic
3
 kT
2
- The motion of individual particles has no
specific direction (random, zig-zag path), and
they can collide with each other.
- The average distance (<x>) is taken during „t”
time interval in a given axis:
x  2 Dt
D: diffusion coefficien (m2/s)
Brownian motion
Einstein-Stokes equation for
Diffusion
-
The diffusion coefficient (D) is related to the frictional
coefficient (f):
Df  kT
-
For spherical particles:
f  6r
-
Einstein-Stokes equation
kT
RT
D

6r 6rN A
D: diffusion coefficient (m2/s), k: Boltzmann constant (J/K), r: radius
of the particle (m), η: viscosity (Pas); T: temperature (K), NA: Avogadro
number (1/mol), R: gas constant (J/K·mol)
Sedimentation
-
Tendency for suspension particles to settle.
-
The force of the sedimentation (Fs) : gravity – raising
force
4 3
Fs  mg  mgV l
m  r  s
3
In equilibrium the force of sedimentation equal with the
Friction:
-
F  6rv
-
Therefore:
2 r 2 g (  s  l )
v

9
m: mass of the solid particle (kg), V: volume of the solid particle, r: radius
of the particle (m), η: viscosity (Pas),ρl and ρs density of the liquid and
the solid phase, v: velocity of sedimentation (m/s)
Osmosis
- Definition:
Spontaneous net movement of small molecules or ions (like
solvent) through a semipermeable membrane in order to
reach the equilibrium in concentration.
Applying pressure on the more concentrated side can inhibit,
stop or reverse the transport process. The pressure applied
to stop the movement is called osmotic pressure (Π).
1
  cRT (  B2 c  B3c 2  ...)
M
Donnan membrane equilibrium
http://www.youtube.com/watch?v=9YOiQ7
jnywY
Donnan membrane equilibrium
[K+]=a
[K+]=b
[K+]=a+x
[K+]=b-x
[Pr-]=a
[Cl-]=b
[Pr-]=a
[Cl-]=b-x
[Cl-]=x
INITIAL
FINAL
At equilibrium the rates of diffusion are equal,
and there is an electroneutrality!
( a  x ) x  (b  x ) 2
b2
x
a  2b