colloid chemistry - lectures 1 and 2

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

Colloid chemistryRecommended readings: E. Tombcz: Colloid Chemistry for Pharmaceutical Students. Manuscript, Szeged 1988. D. F. Evans, H. Wennerstrm: The Colloidal Domain: Where Physics, 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.

Requirements2 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

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

Examples of colloidal systems from daily life

Detergents

Cosmetics

Colloid science is interdisciplinary1.

2

3

partly physical chemistry - it is not the chemical composition which is important - the state is independent of the composition partly physics - the physical properties are of great importance - basic law of physics can be applied partly biology - biological materials are colloids - the mechanisms of living systems are related to colloid- and interfacial chemistry

The colloidal domainsize range of discontinuity: 1 nm to 500 nm (1000 nm) 1 nm = 10 = 10-7 cm = 10-9 m - small particle size and small pore size imply large interfacial area and the interfacial properties are therefore important !

Colloidal discontinuitiesdensity (x) density (x)

distance x

distance x

colloidal dispersions (incoherent systems)

porous materials; gels (coherent systems)

A. Buzgh: colloids systems with submicroscopic discontinuities (1-500 nm) W. Ostwald: the colloidal state is independent of the chemical composition

Classification of colloids on the basis of structurecolloids incoherent systems colloidal dispersions macromolecular solutions association colloids coherent systems (gels) porodin reticular spongoid

corpuscular fibrillar lamellar liophobic liophilic liophilic

Incoherent systems: (colloidal) dispersionsopt micr cryo TEM198 17% nm SiO2 particles

TEM

3.2 41% m O / W emulsion particles

22 20% nm O / W microemulsion particles

SEM

TEM TEM TEM4 31% nm Pd particles 224 21% nm LDH particles

HRTEM

4 25 % nm cubooctahedral Pd particles

Surface matterslamella fibrilla

corpuscula

Change of surface free energy with particle size

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

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

S/V

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

colloid

Stability of liophilic and liophobic colloidscolloidal dispersions: liophobic colloids - thermodynamically not stable; kinetically may be stable macromolecular solutions: liophilic colloids surfactant solutions: liophilic colloids - both thermodynamically and kinetically stable

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

Non-particulate incoherent systems: macromolecular solutionssome possible comformations of proteins in water structure of a polypeptide molecule in aqueous solution

Non-particulate incoherent systems: association colloids (surfactants)

chemical structure of a single surfactant molecule: sodium dodecyl sulfate

Surfactant micellessurfactant molecule spherical micelle

hydrophobic alkyl chain

self-assembling (association) hydrophilic head group hydrophilic shell hydrophobic core

30-100 molecules d-3-5 nm

cationic surfactant anionic surfactant nonionic surfactantorientation energy minimum Hardy-Harkins principle

Shapes of surfactant aggregates

Surfactants as biocolloids

Surfactants as biocolloids

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

Surfactants as biocolloids

Coherent systems: gelsGel: 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. 1) Floccules of small particles bound by strong van der Waals forces:

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

Formation of liogels

/ / surfactant molecules + liquid

// SOAP GEL

Coherent systems: xerogels (porous MCM-type materials)

Xerogels: porous materials

Coherent systems: liogels (hydrogels and organogels)

coherent system: gelatin (hydrogel)

LiogelsLiogels show a variety of flow (rheological) behaviours:

LiogelsHydrogels may show distinct temperature and pH dependent behaviour:

T= 15 0C

T= 20 0C

T= 25 0C

T= 30 0C

T= 35 0C

T= 400C

T= 450C

Classification of disperse systems by size

Classification of dispersed systemsdispersed systems

amicroscopic true solution 1 nm homogeneous

submicroscopic systems colloids

coarse systems micro heterogeneous 500 nm(1000 nm)

colloids homogenous or heterogeneous?

heterogeneous

Classification of disperse systems by size 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 >1m, do not diffuse, separated by filtration

Solutions Have small particles (ions or molecules) Are transparent Do not separate Cannot be filtered Do not scatter light

Suspensios Have very large particles Settle out Can be filtered Must stir to stay suspended

Have medium size particles

Colloids

Cannot be filtered Separated with semipermeable membranes Scatter light (Tyndall effect)

Classification of disperse systems by sizesystems Colloid systems

fog

micelles

Classification of colloidal dispersions by shape

1. prolate(a>b) 2. oblate (a

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