Post on 26-Oct-2014
Colloid chemistry
Lectures 1 & 2: Colloidal systems.Hystory,classifications and examples.
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.
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
Colloid chemistry
Lectures 1 & 2: Colloidal systems.History,classifications and examples.
Examples of colloidal systems from daily life
CosmeticsCosmetics
DetergentsDetergents
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
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
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
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
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
Surface matterslamella
fibrilla
corpuscula
Change of surface free energywith particle size
when the particle size decreases: the specific surface area increasesthe degree of dispersion increases
Size-dependent pecific surface area: S/V(surface to volume ratio)
S / V
S / V
Specific surface area: S/V(surface to volume ratio)
colloid
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
structure of a polypeptide molecule in aqueous solution
Non-particulate incoherent systems:macromolecular solutions
some possible comformations ofproteins in water
Non-particulate incoherent systems:association colloids (surfactants)
chemical structure of a single surfactant molecule: sodium dodecyl sulfate
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)
Shapes of surfactant aggregates
Surfactants as biocolloids
plasma membranes are primarily lipid bilayers with associated proteins and glycolipids(cholesterol is also a major component of plasma membranes)
Surfactants as biocolloids
Surfactants as biocolloids
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:
/ / surfactant molecules + liquidsurfactant molecules + liquid
/ ”SOAP” GEL/ ”SOAP” GEL
Formation of liogels
/
/
Coherent systems: xerogels(porous MCM-type materials)
Xerogels: porous materials
coherent system: gelatin (hydrogel)
Coherent systems: liogels(hydrogels and organogels)
LiogelsLiogels show a variety of flow (rheological) behaviours:
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:
Classification of disperse systems by size
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
• 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
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
Classification of disperse systemsby size
systemssystems
micellesmicelles
Colloid systems
fog
Classification of colloidal dispersionsby shape
1. prolate(a>b) 2. oblate (a<b) 3 rod 4. plate 5. coil
Classification of colloidal dispersionsin terms of the physical states of the
internal and external phases
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
Some tidbits from thehistory of colloids
motion.
Brownian motion
Dynamics of colloidal particles
Brownian motion
The Faraday-Tyndall effect.Dark-field microscopy: the ultramicroscope.
Zsigmondy, 1903
Ultramicroscopic images
blood red cells
Ag nanoparticles
The Faraday-Tyndall effect
The Faraday-Tyndall effect
Dialysis
Kidney and dialysis
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.
A dialysis unit
Principle ofdialysis
Osmotic pressure of the blood
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
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
Stability of colloidal dispersions