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Interactions between non-polar surfaces in water: Fokus on talc, pitch and surface roughness effects
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry. (Surface Chemistry)
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 [en]
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.
Keyword [sv]
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: urn:nbn:se:kth:diva-10283ISBN: 978-91-7415-281-4 (print)OAI: oai:DiVA.org:kth-10283DiVA: diva2:214091
Public defence
2009-05-15, F3, Lindstedtsvägen 26, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20100813Available from: 2009-05-12 Created: 2009-05-01 Last updated: 2010-08-13Bibliographically approved
List of papers
1. Interaction forces between talc and hydrophobic particles probed by AFM
Open this publication in new window or tab >>Interaction forces between talc and hydrophobic particles probed by AFM
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2006 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 277, no 03-jan, 183-190 p.Article in journal (Refereed) Published
Abstract [en]

The interaction between cleaved talc surfaces and hydrophobic probe particles, silanized silica and thiolized gold, has been investigated employing the atomic force microscopy (AFM) colloidal probe technique. These model systems have hydrophobicities similar to some of the talc-pitch combinations present during pulp and paper manufacture. The talc surfaces used in this study, in the [0 0 1] plane, show a micro-roughness with sharp peaks of up to 3 nm in height. The force profiles obtained demonstrate the predominance of a long-range attractive force. However, the range and magnitude of the attractive force show large variability. The variability of the attractive force, and the frequent observations of clear steps in the force curve demonstrate that it is caused by gas/vapor cavities bridging the Surfaces once the surfaces are brought sufficiently close together. The results suggest that the same mechanism is of importance in applications where talc is used as a collector for pitch.

Keyword
talc, surface forces, hydrophobic interaction, capillaries, microbubbles, pitch-control, aqueous-solution, surfaces, monolayers, attraction, bubble, gold
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-15576 (URN)10.1016/j.colsurfa.2005.11.101 (DOI)000236499900027 ()2-s2.0-33644527596 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Interaction forces between talc and pitch probed by atomic force microscopy
Open this publication in new window or tab >>Interaction forces between talc and pitch probed by atomic force microscopy
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2007 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 8, 4248-4256 p.Article in journal (Refereed) Published
Abstract [en]

Colloidal wood resin components present in pulp are collectively called pitch. The presence of pitch may cause severe problems due to deposits in and on the paper machine. There is thus a need for controlling pitch aggregation and adsorption. To be able to develop more efficient pitch control systems, one needs to develop the understanding of pitch-pitch interactions and of the interactions between pitch and other materials. With this general goal in mind, we present methods for preparing geometrically well-defined pitch particles attached to atomic force microscopy tips. This has enabled us to investigate the interactions between pitch and talc, an additive commonly used for pitch control. We have used model pitch particles consisting of one component only (abietic acid), a mixture of components (collophonium), and particles prepared from real pitch deposits. We show that the forces acting between pitch and talc are attractive and, once the initial approach is made, exert this attraction out to large distances of separation. We present evidence that the formation of bridging air bubbles or cavities is responsible for this interaction.

Keyword
surfactant-coated surfaces, hydrophobic surfaces, long-range, wood extractives, attraction, water, nanobubbles, bubble, heterogeneity, papermaking
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-16509 (URN)10.1021/la0633435 (DOI)000245370100021 ()2-s2.0-34247401784 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Fluid transport in compacted porous talc blocks
Open this publication in new window or tab >>Fluid transport in compacted porous talc blocks
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2008 (English)In: Fluid Dynamics & Materials Processing, ISSN 1555-256X, E-ISSN 1555-2578, ISSN 1555-256X, Vol. 4, no 2, 85-98 p.Article in journal (Refereed) Published
Abstract [en]

It has been shown that talc powder can be compacted into tablets with a preferred orientation of the platelets. The tablets can be obtained with different controlled porosity depending on pressing methods and applied pressure. The tablets can be obtained with or without additives, which may, in turn, be adsorbed. The orientation of the high aspect ratio platy talc, the surface chemistry imparted by the additives and the transported fluid influence the imbibition and permeation rates. Non-polar hexadecane displays a higher imbibition and permeability than water for all particulate orientations during short timescale absorption, likely due to the oleophilic nature of talc, and thus a more complete filling of the pores for non-polar liquids is to be expected. At longer timescales water is imbibed either at a similar rate to hexadecane or faster depending on the surface chemistry generated by additives leading to hydrophilicity. The swelling of the added polymers used to create wettability leads to break-up of the structure and exposure of hydrophilic surfaces for more rapid imbibition. It is not possible, therefore, to measure reliably the water uptake parameters when talc is fully dispersed with surfactants. Furthermore, dispersing agents tend to contribute to the blocking of pores and throats in the swollen state, and so a limitation in total imbibed volume occurs. The permeability under pressure is also inhibited by additives, which supports the suggestion of partial blockage of the pores and throats. When the individual talc crystal c axes, defining the perpendicular to the [001] planes, are oriented 90° to the primary average liquid flow direction, i.e. are oriented in a planar configuration to the flow, imbibition and permeation of wetting liquid are increased. This is assumed to be due to decreased tortuosity, provided the liquid is wetting in respect to the oriented edge surface. However, non-wetting liquids in respect to all, or geometrically dependent, orientations are subject also to the surface chemistry presented by the orientation, i.e. whether the talc is primarily displaying OH-groups or not, or adsorbed species aiding wetting by the liquid. Measurements where additives are not strongly adsorbed are complicated by the solubility of some wetting and dispersing agents.

Keyword
Absorption, Inhibition, Permeability, Porous media, Surface chemistry, Talc
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-24102 (URN)2-s2.0-44849111501 (Scopus ID)
Note

QC 20100813

Available from: 2010-08-13 Created: 2010-08-13 Last updated: 2017-12-12Bibliographically approved
4. Influence of Wetting and Dispersing Agents on the Interaction between Talc and Hydrophobic Particles
Open this publication in new window or tab >>Influence of Wetting and Dispersing Agents on the Interaction between Talc and Hydrophobic Particles
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2009 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 12, 6909-6915 p.Article in journal (Refereed) Published
Abstract [en]

The interactions between a natural talc surface and a model hydrophobic particle have been investigated in aqueous solutions by employing the atomic force microscopy (AFM) colloidal probe technique. The results demonstrate the presence of long-range attractive forces due to bridging via preadsorbed or induced bubbles/cavities. Due to the natural heterogeneity of talc, and the stochastic nature of the bubble bridging process, the variability in the range and magnitude of the attraction is larger than that for cases when other interactions predominate or than that when only model surfaces are used. Addition of poly(acrylic acid), a common dispersing agent, did not affect the measured forces. Thus, we conclude that poly(acrylic acid) does not adsorb to the basal plane of talc. In sharp contrast, addition of Pluronic PE6400, a nonionic triblock polymer used as wetting agent, resulted in complete removal of the bubble-induced attractive force. Instead, a short-range steric repulsion is the dominating feature. Clearly, Pluronic PE6400 is able to displace air bubbles from the surface and prevent their formation when the particles come into contact. These are suggested to be important features of efficient wetting agents.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-18511 (URN)10.1021/la900192g (DOI)000266929900048 ()2-s2.0-66749176693 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
5. Influence of Surface Topography on Adhesive and Long-Range Capillary Forces between Hydrophobic Surfaces in Water
Open this publication in new window or tab >>Influence of Surface Topography on Adhesive and Long-Range Capillary Forces between Hydrophobic Surfaces in Water
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2009 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 16, 9197-9207 p.Article in journal (Refereed) Published
Abstract [en]

We report oil the interactions between a hydrophobic probe particle and surfaces with nanoscopic surface features, These surfaces have been prepared by spin-coating of nanoparticles and by polishing. The surface topography was characterized by AFM, using the methods of high-resolution imaging, low-resolution imaging using the probe particle, and by the rolling ball method. The spin-coated surfaces can be characterized as nanostructured due to the high density of nanoparticles that oil a short length scale provides a regular pattern of crevices and hills. Oil these surfaces a larger waviness is also distinguished. In contrast, the polished surfaces display sharp nanoscopic peaks and hardly any crevices. I n all cases the dominant force at short separations was found to be a capillary attraction due to the formation of an air/ vapor condensate. Our data show that the large-scale waviness of the surface does not significantly influence the range and magnitude of the capillary attraction, but large local variations in these quantities are found. The large variation in on force corresponds to a small variation in local contact angle of the capillary condensate It the surfaces. The adhesion report discusses how the nature of the surface topographical features influences the capillary attraction by influencing the local contact angle and by pinning of the three-phase contact line. The effect is clearly dependent on whether the surface features exist in the form of crevices or as extending ridges.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-18663 (URN)10.1021/la900759e (DOI)000268719900055 ()2-s2.0-68649128852 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
6. Hamaker constants for talc minerals using spectral ellipsometric data
Open this publication in new window or tab >>Hamaker constants for talc minerals using spectral ellipsometric data
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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
Talc, Hamaker constant, van der Waals force, spectroscopic ellipsometry, dielectric properties, refractive index
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-24103 (URN)
Note

QC 20100813

Available from: 2010-08-13 Created: 2010-08-13 Last updated: 2014-09-22Bibliographically approved

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