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Colloid chemistry for pharmacy students

The subject of colloid chemistry. Why are colloids so different?

Classification, characterization of colloid systems.

www.kolloid.unideb.hu

1. lecture

Zoltán Nagy, Bányai István lecturer professor

Univ. of Debrecen, Dep. of Colloid- and

Environmental Chemistry

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

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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

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Exam, requirements

• Written test – one test in an exam period (2 possibilities )

• Slides: kolloid.unideb.hu

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Place of colloid science

• 1. partly physical chemistry – Not (only) 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)

biology

chemistry

physics

organic

chemistry

physical chemistrybio-

chemistry

colloid science

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

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Subject of colloid chemistry: systems consist of particles in size of 1nm – 500 nm.

systems in which the surface plays a significant role

m

nm

1010 810 610910 710 510 410 310

0.1 1 10 210 310 410 510 610

Atoms, small molecules

macromolecules

smoke

köd

colloid

micelles virus pollen, bacterium

microscopic heterogeneous

Homogeneous Heterogeneous systems

(macroscopic phases) colloid system

Homogeneous

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Homogeneous, heterogeneous ?

• Homogeneous: isotropic. (5% solution of NaCl or gelatine?) • Heterogeneous systems, Gibbs phases rule

interface

Homogeneous one

phase

Heterogeneous more

phase

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.

Gold sol

continuum? dotlike?

2 CFP

degree of dispersion

Colloids in everyday life

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Colloids cannot be classified as homogeneous or heterogeneous system

Aerogel, “frozen smoke”

liogel tenzids

• Some times naturally visible, somtimes hidden.

Xerogel, modern opal

Homogeneous one

phase

Heterogeneous more

phase

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The colloidal state 1. Definition of colloid state

history:

Solution (Graham) 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"

http://www.wsu.edu/~omoto/papers/darkfield.html

0.0

0.2

0.4

0.6

0.8

1.0E-7 1.0E-6 1.0E-5 1.0E-4 1.0E-3 1.0E-2 1.0E-1 1.0E+0

R ,cm

surf

ace m

ole

cule

s/ to

tal

0.1 % 1 %

the effect of surface can

not be ignored

10 %

R<10 nm nanotechnology

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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 !)

Surface molecules/total molecules %

Increasing specific surface area and surface energy

Why are colloids not

heterogeneous?

gold sol

colloid

nano S/V

Homogeneous, heterogeneous ?

2F C P

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Sub-microscopic discontinuity

d e n s ity d en sity

x x

Forming a disperse system by

breaking of b phases (any kind

of phases except from 2 gas)

blocks:

molecules

particles

W. Ostwald: the colloidal state is independent on the chemical forms

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

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

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Motion causes separation

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36 4 ( ) / 3drag p liq gravF rV r g F

r = radius (m); V = volume (m3); η = viscosity (Pas);

ρp and ρliq densities (kg/m3);

g = gravitation acceleration (m/s2)

Δρ = 1g cm-3

Brownian motion

• Each particle has a kinetic energy: appr. 1 kT

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2 2114 10 J

2kinE mv kT

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.

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)

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Classifications

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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)

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Type of colloids on the basis of structure (appearance)

Porodin

colloids

Incoherent (fluid-like) Coherent (solid-like) gel

Colloidal Dispersions sols

Macromol. solutions

Association Colloids

Colloidal solutions

(porous) Reticular Spongoid

corpuscular fibrillar lamellar diszpersion macromolecular association

liofób liofil liofil

(IUPAC proposal)

categorized by inner / outer phases

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Type of sols (incoherent)

• aerosols • liosols xerosols, xerogels

L/G liquid in air: fog, mists, spray

S/G solid aerosol, solid in gas: smoke, colloidal powder

Complex, smog

G/L gas phase in liquid (sparkling water, foam, whipped cream)

L/L emulsion, liquid in liquid, milk

S/L colloid suspension (gold sol, toothpaste, paint, ink)

G/S solid foam: polystyrene foam

L/S solid emulsion: opals, pearls

S/S solid suspensions: pigmented plastics

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Macromolecules (incoherent) The probable shape and weight of some proteins

Colloidal particles are much larger than the solvent molecules in a solution, the properties of these particles depend on their size and shape

Illustration of a polypeptide macromolecule

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Association colloids (incoherent)

Surfactant (soap and detergent)

spherical micelle (targeted medicine) amphiphilic

Micelles are the simplest of all self-assembly structures

Coherent systems

examples

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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

Clays: similar chemical composition

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4.7 m

Trovey, 1971 ( from Mitchell, 1993)

Attapulgit

illite

7 micrometer

Opal

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Simply hydrated silica (SiO2) particles

Precious opal consists of spheres of silicon dioxide

molecules arranged in regular, closely packed planes.

(Idealized picture)

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)

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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.

Characterization of colloids

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Stability of (colloid) systems

Thermodynamic stability – Stable (true solutions): lyophilic colloids

Gsolution < Ginitial , (G=H-TS)

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

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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)

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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?)

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Heterodispersed systems

•The average diameters

•Number, surface and volume weighted average diameters

• Polydispersity

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Average diameters (isometric)

The mean and the standard deviation are used to represent for polydispersed systems

the mean diameter d

the weighting factor i i

i

dd

i index the class or fraction

Arithmetic mean

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?"

the multiplier may be number, surface, volume, intensity, etc.. hence number weighted, surface weighted, mass weighted etc average.

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Number weighted average (mean)

diameters: 1, 2, 3, 4, 5, 6, 7, 8, 9,10

Number of class, Ni=1

=N the weighting factor is number in class

…. etc.

i iN

10iN The total number of particles

is the factor by which the contribution of the constituent is proportional in the measured property

Number averages

Example: colligative properties (osmosis) yield number weighted averages

1 1 2 1 3 1 ... 10 1 555.5

1 1 1 ... 1 10

i i

N

i

d NLd

N N

The length of the string 55 is the same

from the original and 10 spheres of average size

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Calculation of the number average Properties, di, diameter, Ni the weighting factor, number

N1=2, d1=1; N2=1, d2=10

1 2 10 1 124

2 1 3

i i i

N

i i

L d NLd

N N N

The number is known and still valid for the average spheres

The average diameter: 4. meaning: 3 pieces with length of dN=4 together give the same length (L) than the original string

L

L

Sample:

N=3, dN=4

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Other averages

The measurement of colligative properties results number average (osmosis)

2

i i iS d N 3

i i iV d N

?/ ( 9,8)V S dhence

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:

We can measure the total volume and surface and calculate the diameter.

But what kind of ???

L

N1=2, d1=1; N2=1, d2=10

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Surface weighted averages

3 3 3

1 2

2 2 2

1 2

1 2 10 1~ 9.8

1 2 10 1

i i i i i

S

i i i i

V d S d NVd

S S S d N

N Sd d

S/ds2= 1.06

pieces

The same total surface, S: 1.06 pcs d~9,8

When the numbers are not known,

For example the number of drops in a mug of milk.

S weighting factor

?( 9,8) ( 4)Nd d ? 2( 9,8) ( 10)d d

i i

i

xx

if di and Ni known

The number changed !

Comparison!!!!

L

N1=2, d1=1;

N2=1, d2=10

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Sample: We got a sack from the previous spheres. We select them by sieve, measure their weigths and calculate an effective diameter.

http://en.wikipedia.org/wiki/Center_of_mass

N1=?, d1=1;

N2=?, d2=10

1 1 2 2?

1 2

i i

i

d Wd W d Wd

W W W

This is a volume or mass weighted average

But what kind of ???

W

i i

i

xx

When the numbers are not known,

for example particles in a sack of powder.

Mass weighted averages

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Mass weighted averages When the numbers are not known.

4

39.98

i i i i

W

i i i

d W d Nd

W d N

In this average the larger particles dominate. (for example the center of mass.)

W/dw3= 1.007

pieces

N S Wd d d

From the original system

W

http://en.wikipedia.org/wiki/Center_of_mass

2( 9,98) ( 10)wd d

The number changed !

if di and Ni known

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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.

polydispersity PD: / 2.5w NPD d d

4Nd

9,8Sd

9,98Wd

Φ=N

Φ=S

Φ=W

N1=2, d1=1; N2=1, d2=10

The average does not say anything from the details

i i

i

xx

(more dozens average exist)

http://en.wikipedia.org/wiki/Average

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Polydispersity

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

/ 2W NM M

/ 25W NM M 1)

2) i i

n

i

n MM

n

2( )i i i i i i i

w

i i i i i

w M n M M n MM

w n M n M

1w

N

d

d

3) / 1W NM M

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N S wx x x

1w

N

xPD

x

Polydispersity

Sample: A M= 1, B M= 100

100 pcs A + 1pc B 1 pc A + 100 pcs B

/ 2W NM M / 25W NM M

1 1 100 100 100 150,5

1 100 100 1WM

1 100 100 11,98

100 1NM

1 1 100 100 100 10099,0

1 100 100 100WM

1 100 100 10050,5

100 100NM

1 1 1 100 100 10099.99

1 1 100 100WM

100 pcs A + 100 pcs B

1 1 100 10099.02

1 100NM

/ 1,01W NM M

pc~ piece; pcs pieces

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Normal distribution, cumulative function

50

100

0 50 100 150 200

x

%

mean +

mean -

84

16

mean ± ~ 68 %

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Normal distribution, frequency function

2

2

1 ( )( ) exp

22

x xf x

2

2x x d

68%x

http://en.wikipedia.org/wiki/Average

50

100

0 50 100 150 200

x

%

mean +

mean -

84

16

mean ± ~ 68 %

Variance= (deviation)2: ̄x is the mean or expectation (median) a is the standard deviation

Mean + is 68.26 % Mean + 2 is 95.5 %

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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

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2. Morphology (shape, inner structure)

1. Prolate (a>b), 2. oblate (a<b), 3. rod, 4. plate, 5. coil

Irregular particle, equivalent radius

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3. Spatial distribution, ordered structure

•Homogeneous

•Diffuse

•Heterogeneous

•Ordered

nematic smectic tactoid

Special behavior