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Hamaker constants for talc minerals using spectral ellipsometric data
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Measurements of refractive indices over a large wavelength span for talc minerals using spectral ellipsometry allow more accurate determinations of Hamaker constants than previously reported, or otherwise calculated from literature data. We report that for the birefringent talc minerals different Hamaker constants are obtained for samples cut in different crystallographic orientations. In water, very small differences, from 1.710-20 to 1.910-20 J is obtained for nanocrystalline talc samples cut in different directions, whereas a microcrystalline sample from another source give considerably higher value of the Hamaker constant, 4.210-20J. The difference is explained by a significant difference in the refractive index. Implications for interactions relevant in connection to the use of talc as a pitch control agent, in the action of wetting and dispersing additives used as processing aids, and in combinations of talc with cellulose, calcite and polystyrene are indicated.

Keyword [en]
Talc, Hamaker constant, van der Waals force, spectroscopic ellipsometry, dielectric properties, refractive index
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-24103OAI: oai:DiVA.org:kth-24103DiVA: diva2:343426
Note

QC 20100813

Available from: 2010-08-13 Created: 2010-08-13 Last updated: 2014-09-22Bibliographically approved
In thesis
1. Interactions between non-polar surfaces in water: Fokus on talc, pitch and surface roughness effects
Open this publication in new window or tab >>Interactions between non-polar surfaces in water: Fokus on talc, pitch and surface roughness effects
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis work was to gain understanding of the interactions between talc mineral and surfaces, liquids and chemicals relevant for industrial applications, such as pulp and paper. Talc is used in the pulp and paper industry as a filler pigment, in control of pitch (lipophilic extractives) deposits and as a coating pigment. A deeper understanding of talc interactions will be beneficial in optimizing its use.

Long-range attractive interactions between talc and hydrophobic model probes, as well as pitch probes, have been measured using the atomic force microscope (AFM) colloidal probe method. Two procedures for preparation of pitch colloidal probes were developed to allow these studies. Model hydrophobic, nanorough surfaces with surface energy characteristics similar to talc have also been prepared and their interactions with hydrophobic model probes compared to interactions between hydrophobic model probes and talc. It is demonstrated that talc mineral interacts with model hydrophobic particles, as well as with pitch, by long-range attractive forces, considerably stronger than the expected van der Waals force. The possible origin of the measured interaction forces is discussed, and the conclusion is that the main cause is an attractive capillary force due to formation of a gas/vapor capillary between the surfaces. Force measurements using model hydrophobic, nanorough surfaces show that a large-scale waviness does not significantly influence the range and magnitude of the capillary attraction, but large local variations in these quantities are found. It is demonstrated that a large variation in adhesion force corresponds to a small variation in local contact angle of the capillaries at the surfaces. The nature of the surface topographical features influences the capillary attraction by affecting the local contact angle and by pinning of the three-phase contact line. The effect is clearly dependent on the size of the surface features and whether they exist in the form of crevices or as extending ridges. Entrapment of air also affects the imbibition of water in pressed talc tablets.

The effects of wetting and dispersion agents on the interactions between talc and hydrophobic probes have also been investigated. It is demonstrated that a common dispersing agent used for talc, poly(acrylic acid), does not affect the capillary attraction between talc and non-polar probes. In fact, the results strongly suggest that poly(acrylic acid) does not adsorb on the basal plane of talc. From this finding it is inferred that the stabilizing effect of this additive most likely is due to adsorption to the edges of talc. In contrast, a wetting agent (the non-ionic triblock copolymer Pluronic PE6400) removes the long-range capillary attraction. It is suggested that such an ability to replace air at the talc surface is of great importance for an efficient wetting agent.

The Hamaker constant for talc has also been estimated by using optical data obtained from spectroscopic ellipsometry. It is demonstrated that a nanocrystalline talc mineral, cut in different directions displays very small differences in Hamaker constant between the different crystallographic orientations, whereas a microcrystalline sample displays a significantly higher value. The estimated Hamaker constants are discussed for different material combinations of relevance for the pulp- and paper industry, such as cellulose and calcium carbonate.

Abstract [sv]

Målet med detta avhandlingsarbete var att öka förståelsen för interaktioner mellan talkmineral och ytor, vätskor och kemikalier relevanta för industriella applikationer, såsom papper och massa. Talk används i pappers- och massaindustrin som fyllmedel, för kontroll av hartsrika (lipofila extraktivämnen) avsättningar och som bestrykningspigment. En djupare förståelse för talkinteraktioner kommer att vara användbart för att optimera dess användning.

Långväga attraktiva interaktioner mellan talk och hydrofoba modellpartiklar, såväl som mellan talk och hartspartiklar, har uppmätts med hjälp av atomkraftsmikroskopi (AFM) genom att fästa kolloidala partiklar på kraftsensorn. Två metoder för att framställa partiklar gjorda av harts har utvecklats för att möjliggöra dessa studier. Hydrofoba, nanostrukturerade modellytor med ytenergier liknande de för talk har också tillverkats och deras växelverkan med hydrofoba modellpartiklar har jämförts med dem mellan talk och hydrofoba modellpartiklar. Studierna visar att talkmineral växelverkar med hydrofoba modellpartiklar, såväl som med harts, genom långväga attraktiva krafter som är betydligt starkare än den förväntade van der Waals kraften. Möjliga orsaker till de uppmätta växelverkanskrafterna diskuteras och slutsatsen blir att huvudorsaken är en attraktiv kapillärkraft som uppkommer genom att en gas-/ångkapillär bildas mellan ytorna. Kraftmätningar gjorda med hydrofoba nanostrukturerade modellytor visar att en storskalig vågighet inte nämnvärt påverkar storleken av kapillärattraktionen, men stora lokala variationer existerar. Det demonstreras att en stor variation i adhesionskraft motsvaras av en liten variation i lokal kontaktvinkel för kapillärerna på ytorna. Ytornas topografi påverkar kapillärattraktionen genom att påverka den lokala kontaktvinkeln samt genom att trefaskontaktlinjen inte kan röra sig fritt över ytan. Effekten är tydligt beroende av huruvida ytojämnheterna existerar i form av nedsänkningar eller upphöjningar. Instängd luft påverkar också pressade talktabletters uppsugningsförmåga av vatten.

Vätnings- och dispergeringsmedels inverkan på växelverkan mellan talk och hydrofoba partiklar har undersökts. Resultaten visar att ett vanligt dispergeringsmedel för talk, polyakrylsyra, inte påverkar kapillärattraktionen. I själva verket tyder data på att polyakrylsyra inte adsorberas på talks basalplan. Utifrån dessa resultat dras slutsatsen att polyakrylsyra stabiliserar talkdispersioner genom att adsorbera på talkkanterna. Ett vanligt vätmedel (nonjonisk triblock sampolymer Pluronic PE6400) tar å andra sidan bort långväga kapillärattraktion. Detta antyder att egenskapen att ersätta luft på talkytan är av stor betydelse för effektiva vätmedel.

Hamakerkonstanten för talk har uppskattats genom att utnyttja optiska data från ellipsometrimätningar. Det demonstreras att ett nanokristallint talkmineral kapat i olika riktningar uppvisar mycket små skillnader i Hamakerkonstant mellan de olika kristallografiska orienteringarna, medan ett mikrokristallint prov uppvisar ett betydligt högre värde. De beräknade Hamakerkonstanterna diskuteras för olika materialkombinationer relevanta för pappersindustrin, såsom cellulosa och kalciumkarbonat.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. ix, 52 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:14
Keyword
Talc, surface forces, capillary attraction, hydrophobic interaction, pitch control, wetting agent, dispersing agent, adsorption, imbibition, absorption, permeation, atomic force microscopy, colloidal probe, Hamaker constant, surface roughness, nanostructure., Talk, kapillärattraktion, ytkrafter, hydrofob växelverkan, hartskontroll, vätningsmedel, dispergeringsmedel, adsorption, uppsugning, absorption, permeabilitet, atomkraftsmikroskopi, kolloidal partikel, Hamakerkonstant, ytråhet, nanostrukturerad yta.
National Category
Physical Chemistry Physical Chemistry Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-10283 (URN)978-91-7415-281-4 (ISBN)
Public defence
2009-05-15, F3, Lindstedtsvägen 26, KTH, Stockholm, 13:00 (English)
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Supervisors
Note
QC 20100813Available from: 2009-05-12 Created: 2009-05-01 Last updated: 2010-08-13Bibliographically approved

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