Colloid chemistry - Lectures 1 and 2

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<p>Colloid chemistryLectures 1 &amp; 2: Colloidal systems. Hystory,classifications and examples.</p> <p>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.</p> <p>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:</p> <p>Colloid chemistryLectures 1 &amp; 2: Colloidal systems. History,classifications and examples.</p> <p>Examples of colloidal systems from daily life</p> <p>Detergents</p> <p>Cosmetics</p> <p>Colloid science is interdisciplinary1.</p> <p>2</p> <p>3</p> <p>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</p> <p>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 !</p> <p>Colloidal discontinuitiesdensity (x) density (x)</p> <p>distance x</p> <p>distance x</p> <p>colloidal dispersions (incoherent systems)</p> <p>porous materials; gels (coherent systems)</p> <p>A. Buzgh: colloids systems with submicroscopic discontinuities (1-500 nm) W. Ostwald: the colloidal state is independent of the chemical composition</p> <p>Classification of colloids on the basis of structurecolloids incoherent systems colloidal dispersions macromolecular solutions association colloids coherent systems (gels) porodin reticular spongoid</p> <p>corpuscular fibrillar lamellar liophobic liophilic liophilic</p> <p>Incoherent systems: (colloidal) dispersionsopt micr cryo TEM198 17% nm SiO2 particles</p> <p>TEM</p> <p>3.2 41% m O / W emulsion particles</p> <p>22 20% nm O / W microemulsion particles</p> <p>SEM</p> <p>TEM TEM TEM4 31% nm Pd particles 224 21% nm LDH particles</p> <p>HRTEM</p> <p>4 25 % nm cubooctahedral Pd particles</p> <p>Surface matterslamella fibrilla</p> <p>corpuscula</p> <p>Change of surface free energy with particle size</p> <p>when the particle size decreases: the specific surface area increases the degree of dispersion increases</p> <p>Size-dependent pecific surface area: S/V (surface to volume ratio)</p> <p>S/V</p> <p>Specific surface area: S/V (surface to volume ratio)</p> <p>colloid</p> <p>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</p> <p>- liophilic (solvent loving) - liophobic (solvent hating) - hydrophilic - hydrophobic - lipophilic - lipophobic</p> <p>Non-particulate incoherent systems: macromolecular solutionssome possible comformations of proteins in water structure of a polypeptide molecule in aqueous solution</p> <p>Non-particulate incoherent systems: association colloids (surfactants)</p> <p>chemical structure of a single surfactant molecule: sodium dodecyl sulfate</p> <p>Surfactant micellessurfactant molecule spherical micelle</p> <p>hydrophobic alkyl chain</p> <p>self-assembling (association) hydrophilic head group hydrophilic shell hydrophobic core</p> <p>30-100 molecules d-3-5 nm</p> <p>cationic surfactant anionic surfactant nonionic surfactantorientation energy minimum Hardy-Harkins principle</p> <p>Shapes of surfactant aggregates</p> <p>Surfactants as biocolloids</p> <p>Surfactants as biocolloids</p> <p>plasma membranes are primarily lipid bilayers with associated proteins andglycolipids (cholesterol is also a major component of plasma membranes)</p> <p>Surfactants as biocolloids</p> <p>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:</p> <p>2) Macromolecules bound by strong van der Waals forces or cross-linked by chemical bonds:</p> <p>Formation of liogels</p> <p>/ / surfactant molecules + liquid</p> <p>// SOAP GEL</p> <p>Coherent systems: xerogels (porous MCM-type materials)</p> <p>Xerogels: porous materials</p> <p>Coherent systems: liogels (hydrogels and organogels)</p> <p>coherent system: gelatin (hydrogel)</p> <p>LiogelsLiogels show a variety of flow (rheological) behaviours:</p> <p>LiogelsHydrogels may show distinct temperature and pH dependent behaviour:</p> <p>T= 15 0C</p> <p>T= 20 0C</p> <p>T= 25 0C</p> <p>T= 30 0C</p> <p>T= 35 0C</p> <p>T= 400C</p> <p>T= 450C</p> <p>Classification of disperse systems by size</p> <p>Classification of dispersed systemsdispersed systems</p> <p>amicroscopic true solution 1 nm homogeneous</p> <p>submicroscopic systems colloids</p> <p>coarse systems micro heterogeneous 500 nm(1000 nm)</p> <p>colloids homogenous or heterogeneous?</p> <p>heterogeneous</p> <p>Classification of disperse systems by size true solutions (molecular dispersions) (molecules, ions) in gas, liquid (solutions) &lt; 1 nm, diffuse easily, pass through paper filters</p> <p> fine dispersions (colloidal dispersions ) sols (lyophobic colloidal solutions); microemulsions, micelles, polymers (lyophilic colloidal solutions); smoke, films &amp; foams 1 to 1000 nm, diffuse slowly, separated by ultrafiltration</p> <p> coarse dispersions most pharmaceutical suspensions and emulsions, dust, powder, cells, sands &gt;1m, do not diffuse, separated by filtration</p> <p>Solutions Have small particles (ions or molecules) Are transparent Do not separate Cannot be filtered Do not scatter light</p> <p>Suspensios Have very large particles Settle out Can be filtered Must stir to stay suspended</p> <p> Have medium size particles</p> <p>Colloids</p> <p> Cannot be filtered Separated with semipermeable membranes Scatter light (Tyndall effect)</p> <p>Classification of disperse systems by sizesystems Colloid systems</p> <p>fog</p> <p>micelles</p> <p>Classification of colloidal dispersions by shape</p> <p>1. prolate(a&gt;b) 2. oblate (a</p>


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