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INTERFACIAL PHENOMENAin DISPERSED SYSTEMS

LABORATORY OF FORMULATION, INTERFACESRHEOLOGY AND PROCESSESUNIVERSIDAD DE LOS ANDESFACULTAD DE INGENIERIAESCUELA DE INGENIERIA QUIMICAM rida-VenezuelaVersi n # 1 (1994)**Jean-Louis SALAGERTEACHING AID IN SURFACTANT SCIENCE & ENGINEERINGFIRP BOOKLET # E120-NINTERFACIAL PHENOMENAin DISPERSED SYSTEMSFIRP BOOKLET # E120-Nin EnglishFIRP Booklet # 120-N1 INTERFACIAL Phenomena in DISPERSED SystemsINTERFACIAL PHENOMENAin DISPERSED SYSTEMSC ontents1. GENERALITIES on INTERFACIAL INTERFACIAL Phenomena - Where and When? .. Polyphasic Dispersions ..52. PROPERTIES of SURFACTANT INTERFACIAL PHENOMENA at Cohesion and The three kind of DLVO Theory.

FIRP Booklet # 120-N 1 Interfacial Phenomena in Dispersed Systems INTERFACIAL PHENOMENA in DISPERSED SYSTEMS Contents 1. GENERALITIES on INTERFACIAL PHENOMENA .....2

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Transcription of INTERFACIAL PHENOMENAin DISPERSED SYSTEMS

1 LABORATORY OF FORMULATION, INTERFACESRHEOLOGY AND PROCESSESUNIVERSIDAD DE LOS ANDESFACULTAD DE INGENIERIAESCUELA DE INGENIERIA QUIMICAM rida-VenezuelaVersi n # 1 (1994)**Jean-Louis SALAGERTEACHING AID IN SURFACTANT SCIENCE & ENGINEERINGFIRP BOOKLET # E120-NINTERFACIAL PHENOMENAin DISPERSED SYSTEMSFIRP BOOKLET # E120-Nin EnglishFIRP Booklet # 120-N1 INTERFACIAL Phenomena in DISPERSED SystemsINTERFACIAL PHENOMENAin DISPERSED SYSTEMSC ontents1. GENERALITIES on INTERFACIAL INTERFACIAL Phenomena - Where and When? .. Polyphasic Dispersions ..52. PROPERTIES of SURFACTANT INTERFACIAL PHENOMENA at Cohesion and The three kind of DLVO Theory.

2 Wettability and Contact NON-EQUILIBRIUM INTERFACIAL Streaming Electroviscosity Effect - Apparent INTERFACIAL Viscosity .. Motion induced by Wettability Adhesion Dispersion Other Booklet # 120-N2 INTERFACIAL Phenomena in DISPERSED SystemsINTERFACIAL PHENOMENAin DISPERSED GENERALITIES ON INTERFACIAL DEFINITIONSBy definition, INTERFACIAL phenomena are the ones that occur at the limit betweentwo immiscible phases, so-called surface or interface. The most relevant properties insurface science is the surface area, which is very extended in most practical one phase is fragmented into (small) pieces which are DISPERSED in another(continuous) phase, a so-called dispersion or DISPERSED system is produced.

3 There areseveral kinds of DISPERSED SYSTEMS , owing to the nature of both the fragmented and thecontinuous = dispersion of solid particles in a gascloud = dispersion of liquid droplets in a gasfoam = dispersion of gas bubbles in a liquidemulsion = dispersion of liquid drops in another liquidsuspension = dispersion of solid particles in a liquidas well as other SYSTEMS of large area in which the fragments have been consolidated,such as porous media, , sandstones or alumina catalysts, which are many English language Surface Science textbooks, the words surface andinterface are used indifferently with the same basical meaning.

4 Here, a slight shade ofmeaning is introduced, with the word surface for the case of the limit between a gas and acondesed phase, , solid or liquid, whereas interface will be used when dealing withtwo condensed phases, either two liquids or a liquid and a scope of this booklet is aimed at the surfactant science aspects. Sincesurfactants are always found in a liquid solution, the SYSTEMS which are to be consideredhere contain at least one liquid phase. Moreover, this liquid phase must be the continuousphase for the surfactant molecules to be able to move around and attain an equilibriumpattern.

5 As a consequence, the DISPERSED SYSTEMS to be considered here are the foams, theemulsions and the solid suspensions. There will be a gas-liquid surface and two kinds ofinterfaces, , liquid-liquid and discussed elsewhere (see FIRP Booklet # 201), the surfaces or interfaces arevery often covered by a special kind of molecule, so-called surfactant, short for surfaceactive to their main role and to the kind of DISPERSED system they are usedwith, surfactants are labeled: detergent, soap, emulsifier, (de)foamer, dispersant,hydrophobant, wetting agent, corrosion inhibiter and so non exhaustive list evidences the multiple applications of the surfactants, akind of chemical specie which has been called "supermolecule" in a recent paper.

6 Letsfirst take a look at this kind of Booklet # 120-N3 INTERFACIAL Phenomena in DISPERSED are substances whose molecule exhibits both polar and apolar polar group contains hetereoatoms such as O, S, N, P, as part of some functionalgroup such as carboxylate, sulfonate, sulfate, ammonium, phosphate, etc. Nonionic polargroups such as -OH or -O- (ether link) are not very polar, and thus must occur severaltimes to form a proper polar group, , as polyalcohol or nonpolar group is an hydrocarbon radical of the alkyl or alkyl-aryl kind, withtypically 12 to 20 carbon 1 shows the molecular structure of some common surfactants.

7 In generalsurfactants are classified according to their behavior in aqueous solution, as ionic ornonionic which get dissociated into a surfactant negative ion (anion) and a metalliccation, so-called counterion, are labeled anionic surfactants. Soaps, , carboxylic acidsNa or K salts, alkyl benzene sulfonates, , the active substance in powered detergents,dodecyl or lauryl sulfate, , the foaming agent in shampoos, xanthates, , the collectoragent in froth all belong to the anionic surfactant class, which amount tomore that 50 % of the total surfactant C3-O-S-O NaOO+-C H -C-N-CH -CH -OHHO112922C H 1225-S-O NaOO+-HnC H 817 OCH -CH -O22NC H1225Cl-+n-dodecyl pyridinium chloride Dodecyl betaineLauryl monoethanol amideDodecyl benzene sulfonate sodium saltOctyl phenol polyethoxylateDodecyl (ester) sulfate sodium saltOOHOHHOCH OHR-C-O2 OSorbitan Monoester- NH -CH -CH -COOH22C H2512 Fig.

8 1: Some Common SurfactantsThe second class in importance (40 %) gathers the nonionic surfactants, , thosewhich are not dissociated in aqueous solution. In most of these surfactants the polargroup is produced by the polycondensation of ethylene oxide that result in a polyetherchain. The most common surfactants are the ethoxylated alcohols, alkylphenols, acidsand esters (see fig 1). Nonionic surfactants are much less sensitive to electrolytes thananionic surfactants, and they have been replacing the latter in many laundry and bodycare applications, when water hardness can be a Booklet # 120-N4 INTERFACIAL Phenomena in DISPERSED SystemsAnionic and nonionic surfactants production reaches beyond 90 % of the total,and the remaining surfactant, , cationic, amphoteric and polymeric ones.

9 Are only usedfor very special applications when cost is not a sensitive issue such as in cosmetics andbody care INTERFACIAL PHENOMENA -WHERE AND WHEN?There is essentially no human activity, nor commercial, nor industrial, which candismiss the use of cleaners, foams, emulsions or dispersions. Any time a bidimensionallimit is encountered, an INTERFACIAL phenomenon is likely to happen. Since ourtridimensional world is shaped by bidimensional frontiers it is obvious that interfacialphenomena are to be found spite of this evidence there is no Surface Science course in the high school norcolleges curricula all around the World.

10 Only a very few universities offer some graduatecourse on related topics. This is probably due to the fact that the enormous amount ofknowledge accumulated in Surface Science in the past 100 years has been viewed as toodisorganized to earn a full size niche in the overcrowded curricula. This is no longer trueas will be seen in this back to the applications of surfactants in domestic and industrialprocesses, lets consider a few human body synthesized surfactants for use in the lungs alveoli, the liver bile,the tears, the saliva, etc.


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