Transcript
Page 1: Colloid chemistry - Lectures 1 and 2

Colloid chemistry

Lectures 1 & 2: Colloidal systems.Hystory,classifications and examples.

Page 2: Colloid chemistry - Lectures 1 and 2

Colloid chemistryRecommended readings:

E. Tombácz: Colloid Chemistry for Pharmaceutical Students.Manuscript, Szeged 1988.

D. F. Evans, H. Wennerström: The Colloidal Domain: WherePhysics, Chemistry, Biology and Technology Meet.2nd Ed., Wiley-VCH, New York 1999.

D. H. Everett: Basic Principles of Colloid Science.RSC, London 1988.

R. J. Hunter: Foundations of Colloid Science. Vol. 1.,Clarendon, Oxford 1989.

D. J. Shaw: Introduction to Colloid and Surface Chemistry.4th Ed., Butterworth-Heinemann, Oxford 1992.

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2 written tests per semester: 5 October and 20 November, 20 min each(a few short questions on the fundamentals of colloid chemistry)

bank holidays: 23 and 30 October !

the slides are accessible at: http://koll1.chem.u-szeged.hu/colloids/hallgatoi.htm

Requirements

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Colloid chemistry

Lectures 1 & 2: Colloidal systems.History,classifications and examples.

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Examples of colloidal systems from daily life

CosmeticsCosmetics

DetergentsDetergents

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1. partly physical chemistry- it is not the chemical composition which is important- the state is independent of the composition

2 partly physics- the physical properties are of great importance- basic law of physics can be applied

3 partly biology- biological materials are colloids- the mechanisms of living systems are related to colloid- and interfacial chemistry

Colloid science is interdisciplinary

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size range of discontinuity:

1 nm to 500 nm (1000 nm)

1 nm = 10 Å = 10-7 cm = 10-9 m

- small particle size and small pore size implylarge interfacial area and theinterfacial properties are therefore important !

The colloidal domain

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distance x distance x

dens

ity ρ

(x)

dens

ity ρ

(x)

colloidal dispersions(incoherent systems)

porous materials; gels(coherent systems)

W. Ostwald: the colloidal state is independent of the chemical compositionA. Buzágh: colloids → systems with submicroscopic discontinuities (1-500 nm)

Colloidal discontinuities

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Classification of colloidson the basis of structure

incoherent systems coherent systems (gels)

colloidal macromolecular associationdispersions solutions colloids

liophobic liophilic liophilic

colloids

porodin reticular spongoid

corpuscular fibrillar lamellar

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TEM

HRTEM

4 ± 25 % nm cubooctahedral Pd particles224 ± 21% nmLDH particles

TEM

198 ± 17% nm SiO2 particles

TEM

SEM22 ± 20% nm O / Wmicroemulsion particles

optmicr

cryoTEM

Incoherent systems: (colloidal) dispersions

4 ± 31% nmPd particles

TEM

3.2 ± 41% µm O / Wemulsion particles

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Surface matterslamella

fibrilla

corpuscula

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Change of surface free energywith particle size

when the particle size decreases: the specific surface area increasesthe degree of dispersion increases

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Size-dependent pecific surface area: S/V(surface to volume ratio)

S / V

S / V

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Specific surface area: S/V(surface to volume ratio)

colloid

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Stability of liophilic and liophobic colloids

- liophilic (solvent loving)- liophobic (solvent hating)- hydrophilic- hydrophobic- lipophilic- lipophobic

colloidal dispersions: liophobic colloids - thermodynamically not stable; kinetically may be stable

macromolecular solutions: liophilic colloidssurfactant solutions: liophilic colloids- both thermodynamically and kinetically stable

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structure of a polypeptide molecule in aqueous solution

Non-particulate incoherent systems:macromolecular solutions

some possible comformations ofproteins in water

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Non-particulate incoherent systems:association colloids (surfactants)

chemical structure of a single surfactant molecule: sodium dodecyl sulfate

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Surfactant micellessurfactant molecule

hydrophobicalkyl chain

hydrophilichead group

self-assembling

spherical micelle

hydrophilic shellhydrophobic core

cationic surfactantanionic surfactantnonionic surfactant

orientation → energy minimumHardy-Harkins principle

30-100 moleculesd-3-5 nm(association)

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Shapes of surfactant aggregates

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Surfactants as biocolloids

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plasma membranes are primarily lipid bilayers with associated proteins and glycolipids(cholesterol is also a major component of plasma membranes)

Surfactants as biocolloids

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Surfactants as biocolloids

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Gel: it is a solid or semisolid system of at least two constituents,consisting of a condensed mass and interpenetrated by a fluid (liquid or gas)(liogel; aerogel). Network without distinct boundaries. No sedimentation.

Coherent systems: gels

2) Macromolecules bound by strong van der Waals forces or cross-linkedby chemical bonds:

1) Floccules of small particles bound by strong van der Waals forces:

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/ / surfactant molecules + liquidsurfactant molecules + liquid

/ ”SOAP” GEL/ ”SOAP” GEL

Formation of liogels

/

/

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Coherent systems: xerogels(porous MCM-type materials)

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Xerogels: porous materials

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coherent system: gelatin (hydrogel)

Coherent systems: liogels(hydrogels and organogels)

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LiogelsLiogels show a variety of flow (rheological) behaviours:

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T= 15 0C T= 20 0C T= 25 0C T= 30 0C T= 35 0C T= 400C T= 450C

Liogels

Hydrogels may show distinct temperature and pH dependent behaviour:

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Classification of disperse systems by size

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Classification of dispersed systems

dispersed systems

amicroscopic

“true” solution

submicroscopic systems

colloids

coarse systems

micro heterogeneous

1 nm 500 nm(1000 nm)

homogeneous colloids

homogenous or heterogeneous?

heterogeneous

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• true solutions (“molecular dispersions”)• (molecules, ions) in gas, liquid (solutions) • < 1 nm, diffuse easily, pass through paper filters

• fine dispersions (colloidal dispersions )• sols (”lyophobic colloidal solutions”); • microemulsions, micelles, polymers

(”lyophilic colloidal solutions”); • smoke, films & foams• 1 to 1000 nm, diffuse slowly, separated by ultrafiltration

• coarse dispersions• most pharmaceutical suspensions and emulsions, dust,

powder, cells, sands• >1µm, do not diffuse, separated by filtration

Classification of disperse systemsby size

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Solutions

♦ Have small particles

(ions or molecules)

♦ Are transparent

♦ Do not separate

♦ Cannot be filtered

♦ Do not scatter light

Colloids♦ Have medium size particles

♦ Cannot be filtered

♦ Separated with semipermeable membranes

♦ Scatter light (Tyndall effect)

Suspensios

♦ Have very large particles

♦ Settle out

♦ Can be filtered

♦ Must stir to stay suspended

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Classification of disperse systemsby size

systemssystems

micellesmicelles

Colloid systems

fog

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Classification of colloidal dispersionsby shape

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

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Classification of colloidal dispersionsin terms of the physical states of the

internal and external phases

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L/G: fog, mist, spray(liquid aerosols)

S/G: smoke, loose soot (powders)(solid aerosols)

G/L: sparkling water, foam,whipped cream

(liquid gas dispersions)

L/L: milk; mayonnaize; crude oil((micro)emulsions)

S/L: paint, ink, toothpaste(sols/suspensions)

G/S: polysterene foam,silica gel

(aerogels, xerogels)

L/S: opal, pearl(solid emulsions)

S/S: pigmented plastics(solid suspensions)

Classification of colloidal dispersionsin terms of the physical states of the

internal and external phases

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Some tidbits from thehistory of colloids

motion.

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Brownian motion

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Dynamics of colloidal particles

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Brownian motion

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The Faraday-Tyndall effect.Dark-field microscopy: the ultramicroscope.

Zsigmondy, 1903

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Ultramicroscopic images

blood red cells

Ag nanoparticles

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The Faraday-Tyndall effect

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The Faraday-Tyndall effect

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Dialysis

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Kidney and dialysis

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Artificial kidney

Water and small solute particles

pass through a semipermeable

membrane, large particles are

Retained inside.

Hemodialysis is used medically

(artificial kidney) to remove

waste particles such as

urea from blood.

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A dialysis unit

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Principle ofdialysis

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Osmotic pressure of the blood

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Osmotic Pressure of the Blood♦ Cell walls are semipermeable membranes

♦ The osmotic pressure of blood cells cannot change or damage occurs

♦ The flow of water between a red blood cell and its surrounding environment must be equal

isotonic solutions♦ Exert the same osmotic pressure as red blood cells. ♦ Medically 5% glucose and 0.9% NaCl are used their solute concentrations

provide an osmotic pressure equal to that of red blood cells

H2O

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hypotonicsolutions

♦ Lower osmotic pressure than red blood cells

♦ Lower concentration of particles than RBCs

♦ In a hypotonic solution, water flows into the RBC

♦ The RBC undergoes hemolysis;

it swells and may burst

H2O

hypertonicsolutions

♦ Has higher osmotic pressure than RBC♦ Has a higher particle concentration ♦ In hypertonic solutions, water flows out of the RBC♦ The RBC shrinks in size (crenation)

H2O

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Stability of colloidal dispersions


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