Definition of colloid systems, classification and characterization. Interparticle interactions.

Place of colloid science Biology

Colloid chemistry

Physical chemistry Biochemistry Organic Chemistry

Physics

•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)

What kind of systems are colloid systems? Many definitions exist: • Those systems in which the surface plays significant role in their behaviour. • Colloids are those (disperse) systems which consist particles in size of 1nm-500nm (1nm = 10-9 m) The colloid state is independent on the chemical nature, every condensed phase can be turned into colloidal system.

Are the colloid systems are homogeneous or heterogeneous? • •

Homogeneous: the same physical properties (density, structure, refractive index…) all over the phase (isotropic). Heterogeneous: Different physical state depending on the location. – Gibbs phase rule: P+F = C+2

– Does the surface have an influence?

P: number of phases F: degree of freedom C: number of components

colloids

Are the colloid systems are homogeneous or heterogeneous? homogeneous Atoms, small molecules

1010

homogeneous

0.1

smoke

macromolecules

109

108

fog

107

colloid

1 micelles

Heterogeneous (macroscopic multiphase)

Colloid systems

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

Classification of colloids Colloid systems INCOHERENT „fluid like” (individual particles) The attraction (coherent forces) is weaker than thermal energy

Colloidal dispersions (sols)

Solution of macromolecules

Association colloids

proteins DNA, RNA polymers

Association of small molecules

COHERENT „solid” like (network structure) The attraction is stronger than the thermal energy (because of cross-links)

Porodin (porous materials)

Reticular (cross-linked fibrils)

Spongoid „sponge”-like systems

Classification of colloids Colloidal dispersions (sols) Aerosols (the medium is gas)

Xerosols (the medium is solid)

- L/G: fog, mists, spray - S/G: smoke, colloidal powder - S/L/G: smog

- G/S: solid foam (bread) - L/S: solid emulsion (opals, pearls) - S/S: solid suspensions (pigmented plastics)

Liosols (the medium is liquid) - G/L: foam (whipped cream) - L/L: emulsion (milk) - S/L: suspension (toothpaste, mud)

Classification of colloids Association colloids

Macromolecular colloids

Characterization by stability Thermodynamic Stable (lyophilic colloids) Gcolloid < Ginitial

Unstable (lyophobic colloids) Gcolloid > Ginitial

Association and macromolecular colloids

Colloidal dispersions

Kinetic Stable

Unstable

NO change during the examination

Significant change can be observed Within the examination

Characterization by colloidal state parameters (Aladár Buzágh) 1. Dispersity in size 2. Morphology (shape, inner structure) 3. Spatial distribution 4. Interparticle interactions

Characterization by colloidal state parameters (Aladár Buzágh) 1. Dispersity in size

Monodisperse: isometric (same size) Heterodisperse: mixture of particles having different size (molecular weight) Size (molecular weight) can be determined by various methods, and an average size will be obtained. Size distribution can be given by the mean value and the standard deviation. In most cases normal distribution is used.

Determination of size and it’s distribution Depending on the method we can get different types of average. What type of average values can be obtained? Number weighted average: (Arithmetic mean) Colligative properties always give number weighted mean

x

 xi N i N



 xi N i  Ni

Mass weighted average: (if the exact numbers are not known)

xM  x i

M

i

xM   M i

i

i

Determination of size and it’s distribution Polydispersity (PD): Can be calculated as the ratio of the mass and number weighted avereges.

MN

MN   i

N

i

MN   N i

i

i

2 N M Mw   i i  M

Mw PD  1 Mn If the ratio is 1, than the system is monodisperse!

2 N M  i i  Mi

Determination of size and it’s distribution Example Let’s have a system with two components (A and B) MA=1000g/mol, MB=100000g/mol a, 1pc A, 100pcs B

b, 50pcs A, 50pcs B

c, 100pcs A, 1pc B

1  1000 2  100  100000 2 Mw   99990 1  1000  100  100000

50  1000 2  50  100000 2 Mw   99020 50  1000  50  100000

Mw 

100  1000 2  1  100000 2  50500 100  1000  1  100000

1  1000  100  100000 MN   99020 1  100

50  1000  50  100000 MN   50500 50  50

MN 

100  1000  1  100000  1980 100  1

PD=1.01

PD=1.96

PD=25.51

Size determination methods Sieve 25 m-125 mm Wet sieve 10 m-100 m Microscope 200 nm-150 m Ultramicroscope 10 nm -1 m Elektronmicroscope, (TEM, SEM surface) 1 nm- 1 m • Sedimentation above 1 m (from suspension) • Centrifuge 5 m and below • Light scattering 1 nm- few m

• • • • •

Morphology

1. Prolate 2. Oblate 3. Rod 4. plate 5. coil

a. lamellar b. fibrillar c. corpuscular

Spatial distribution, partially ordered structures •Homogeneous •Diffuse (exponential) •Heterogeneous •Ordered

Special behaviour. Depends on the interparticle interactions.

nematic

smectic

tactoid

Interactions between the particles • The interactions between the particles can be originated from intermolecular interactions. These have a significant effect on the size, shape, solubility and the stability of the colloid systems. – – – – – – – –

Ion - ion Ion – permanent dipol Permanent dipol – permanent dipol Permanent dipol – induced dipol Instantaneous dipol - Induced dipol (London dispersion) Hidrogen bond Stacking interaction Repulsion

• Hydrophilic and hydrophobic interactions