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The dynamic surface nature of calcite and its role in determining the adsorptive stability toward hydrophobizing carboxylic fatty acids
KTH Royal Institute of Technology, Sweden.ORCID iD: 0000-0002-6181-1347
2021 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

Calcium carbonate has attracted a lot of interest over the centuries. Nowadays, mainly as mineral pigment and filler, it has a wide use in technological applications ranging from paper, construction, polymers, and environmental solutions to consumer goods. Amongst these uses, the filler pigment is required to display either hydrophilicity (for applications in aqueous colloidal systems, including, for example, in paper and emulsion paints), or, in contrast, oleophilicity (for applications in contact with oil-based systems, such as plastics and volatile solvent-containing sealants).  To achieve oleophilicity, and resulting hydrophobicity, the filler is surface treated, typically using carboxylic fatty acids. In this thesis, effects of humidity and fatty carboxylic acids vapor on CaCO3 surface wettability and nanomechanical properties were studied, with the aim to gain knowledge on layer packing density and order, as well as resistance to water exposure and mechanical wear. A better understanding of the dynamic nature of the calcite surface presented in this work allows the industry to increase sustainable control over materials production and storage. First, a setup combining an atomic force microscope (AFM) with a humidifier was used to map nanomechanical properties of growing surface domains (hydrated form of CaCO3) formed by ion dissolution, diffusion, and redeposition, a process that is not reversible upon drying. Secondly, AFM and contact angle goniometer measurements showed that the stability of the calcite surface improves with increasing carboxylic acid chain length (C2 to C18). Meanwhile, X-ray photoelectron spectroscopy and vibrational sum frequency spectroscopy techniques demonstrated that a coherent layer with maximum packing density of carboxylate and carboxylic acid species was achieved with the use of stearic acid (C18) with high enough vapor pressure and exposure time. The AFM images successfully visualized that a complete C18 monolayer is capable of countering nano-wear of the calcite surface despite the humidity (under the range of loads investigated in this work) and the layer has self-healing properties, while calcite displayed high abrasive wear. Further, when calcite coated by a highly packed monolayer of C18 was covered with a water droplet, a large contact angle hysteresis resulted in a coffee ring effect (CRE). That is leading to formation of hillocks at the contact line consisting of dissolved fatty carboxylic acid and possibly calcium bicarbonate Ca(HCO3)2 molecules transported from the bare calcite region that also is created next to the droplet edge. Interestingly, C18 coated calcite remained considerably more stable in the case where a water droplet saturated with octanoic acid was used instead of water; thus, it was concluded that the CRE can be contained via reduction of the liquid surface tension and contact angle hysteresis.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2021. , p. 100
Series
TRITA-CBH-FOU ; 2021:46
Keywords [en]
calcite, recrystallization, surface modification, fatty acids, wear resistance, water resistance, contact angle hysteresis, AFM, XPS, VSFS, Kalcit, rekristallisation, ytmodifiering, fettsyra, nötningsbeständighet, vattenbeständighet, kontaktvinkelhysteres, Physical Chemistry, Fysikalisk kemi, Natural Sciences, Naturvetenskap, Chemical Sciences, Kemi, Tribology (Interacting Surfaces including Friction, Lubrication and Wear), Tribologi (ytteknik omfattande friktion, nötning och smörjning)
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
URN: urn:nbn:se:ri:diva-57380ISBN: 978-91-8040-066-4 (electronic)OAI: oai:DiVA.org:ri-57380DiVA, id: diva2:1622532
Public defence
2021-12-09, 13:00 (English)
Opponent
Supervisors
Note

Delarbeten1. Iceland spar calcite: Humidity and time effects on surface properties and their reversibility2. Calcite surfaces modified with carboxylic acids (C2 to C18): layer organization, wettability and stability properties3. Nanoscale Wear and Mechanical Properties of Calcite: Effects of Stearic Acid Modification and Water Vapor4. Surface modified and unmodified calcite: Effects of water and saturated aqueous octanoic acid droplets on stability and saturated fatty acid layer organization

Available from: 2021-12-22 Created: 2021-12-22 Last updated: 2023-12-28Bibliographically approved

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Wojas, Natalia

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