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Internal structure of aqueous foams stabilised by surfactants or microgels

Kühnhammer, Matthias (2022)
Internal structure of aqueous foams stabilised by surfactants or microgels.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00022559
Ph.D. Thesis, Primary publication, Publisher's Version

Abstract

Foams are abundant in everyday life in the form of cleaning agents or personal care products. In addition, they play an important role in certain industrial processes like flotation in the mining industry or textile manufacturing. Many foam properties like stability or rheology are governed by their structure. However, the internal structure of foams is difficult to determine experimentally. Optical methods are only able to probe the first few layers of bubbles, because of the large difference in refractive indices of gas and (mostly aqueous) liquid phase. This thesis aims to extend the experimental accessibility of the foam structure. For this purpose a sample environment enabling small-angle neutron scattering (SANS) experiments with macroscopic foams is designed and constructed. This sample environment allows measuring foams at different drainage stages, controlling the rate of foam formation, temperature and measurement position. In addition, a sample changer for up to three foam cells is included to utilise the full potential of future high brilliance neutron sources like the European Spallation Source (ESS). In order to extract structural information about the foam from the data, a new model for the description of SANS data from foams is presented. This model is based on an incoherent superposition of reflectivity curves, arising from the foam films, and a small-angle scattering (SAS) contribution arising mainly from the Plateau borders. In addition, a correction factor accounting for the spherical geometry of the foam bubble is introduced. The model is capable of describing the complete scattering curves of a foam stabilised by the standard cationic surfactant tetradecyltrimethylammonium bromide (C14TAB) with different water contents, i.e. drainage states, and provides information about the thickness distribution of liquid films inside the foam. The validity of the model is tested further by studying foams stabilised by poly(Nisopropylacrylamide) (PNIPAM) microgels (MGs). The macroscopic foam properties in dependence of the cross-linker concentration of the MGs and temperature are investigated as well as the corresponding structuring in single foam films and macroscopic foams. Furthermore, the deformation of MGs inside the foam films is correlated with their elasticity as predicted by the affine network model.

Item Type: Ph.D. Thesis
Erschienen: 2022
Creators: Kühnhammer, Matthias
Type of entry: Primary publication
Title: Internal structure of aqueous foams stabilised by surfactants or microgels
Language: English
Referees: Klitzing, Prof. Dr. Regine von ; Schneck, Prof. Dr. Emanuel
Date: 2022
Place of Publication: Darmstadt
Collation: xiii, 135 Seiten
Refereed: 19 October 2022
DOI: 10.26083/tuprints-00022559
URL / URN: https://tuprints.ulb.tu-darmstadt.de/22559
Abstract:

Foams are abundant in everyday life in the form of cleaning agents or personal care products. In addition, they play an important role in certain industrial processes like flotation in the mining industry or textile manufacturing. Many foam properties like stability or rheology are governed by their structure. However, the internal structure of foams is difficult to determine experimentally. Optical methods are only able to probe the first few layers of bubbles, because of the large difference in refractive indices of gas and (mostly aqueous) liquid phase. This thesis aims to extend the experimental accessibility of the foam structure. For this purpose a sample environment enabling small-angle neutron scattering (SANS) experiments with macroscopic foams is designed and constructed. This sample environment allows measuring foams at different drainage stages, controlling the rate of foam formation, temperature and measurement position. In addition, a sample changer for up to three foam cells is included to utilise the full potential of future high brilliance neutron sources like the European Spallation Source (ESS). In order to extract structural information about the foam from the data, a new model for the description of SANS data from foams is presented. This model is based on an incoherent superposition of reflectivity curves, arising from the foam films, and a small-angle scattering (SAS) contribution arising mainly from the Plateau borders. In addition, a correction factor accounting for the spherical geometry of the foam bubble is introduced. The model is capable of describing the complete scattering curves of a foam stabilised by the standard cationic surfactant tetradecyltrimethylammonium bromide (C14TAB) with different water contents, i.e. drainage states, and provides information about the thickness distribution of liquid films inside the foam. The validity of the model is tested further by studying foams stabilised by poly(Nisopropylacrylamide) (PNIPAM) microgels (MGs). The macroscopic foam properties in dependence of the cross-linker concentration of the MGs and temperature are investigated as well as the corresponding structuring in single foam films and macroscopic foams. Furthermore, the deformation of MGs inside the foam films is correlated with their elasticity as predicted by the affine network model.

Alternative Abstract:
Alternative abstract Language

Schäume gibt es im Alltag in Form von Reinigungs- oder Körperpflegeprodukten. Darüber hinaus spielen sie eine wichtige Rolle in industriellen Anwendungen wie der Flotation in der Bergbauindustrie oder in der Textilverarbeitung. Viele Schaumeigenschaften wie ihre Stabilität oder Fließfähigkeit werden von der Schaumstruktur bestimmt. Allerdings ist die innere Struktur von Schäumen ist experimentell schwer zu bestimmen. Aufgrund der stark verschiedenen Brechungsindices der gasförmigen und (meist wässrigen) flüssigen Phase, sind optische Methoden nur dazu geeignet die ersten wenigen Blasenschichten eines makroskopischen Schaumes zu untersuchen. Das Ziel dieser Arbeit ist es die experimentelle Zugänglichkeit zur inneren Struktur von Schäumen zu verbessern. Zu diesem Zweck wird eine Probenumgebung für die Untersuchung von Schäumen mittels Neutronenkleinwinkelstreuung (SANS) entwickelt und konstruiert. Diese Probenumgebung ermöglicht es Schäume in unterschiedlichen Drainagestadien zu untersuchen und erlaubt die Kontrolle der Schaumbildungsrate, Temperatur und Messposition. Um das volle Potential zukünftiger Neutronenquellen mit hoher Brillanz wie der Europäischen Spallationsquelle (ESS) ausschöpfen zu können, wird außerdem ein Probenwechsler für bis zu drei Schaumzellen implementiert. Um strukturelle Informationen aus den Daten zu gewinnen, wird ein neues Modell für die Auswertung von SANS Daten von Schäumen entwickelt und vorgestellt. Das Modell beruht auf der inkohärenten Überlagerung von Reflektivitätskurven einzelner Schaumfilme und einem Kleinwinkelstreuanteil, der hauptsächlich von den Plateau-Kanten herrührt. Um die kugelförmigen Schaumblasen korrekt zu beschreiben, wird ein geometrischer Korrekturterm eingeführt. Das Modell ist in der Lage die kompletten Streukurven eines Schaumes, welcher mit dem kationischen Standardtensid Tetradecyltrimethylammoniumbromid (C14TAB) stabilisiert ist, mit verschiedenenWassergehalten, das heißt Drainagestadien, zu beschreiben und liefert Informationen über die Dickenverteilung der Schaumfilme. Die Validität des Models wird außerdem an Schäumen, welche von poly(N-isopropylacrylamid) (PNIPAM) Mikrogelen (MGs) stabilisiert sind, getestet. Die makroskopischen Schaumeigenschaften in Abhängigkeit des Quervernetzergehalts und der Temperatur werden studiert und die Strukturierung der MGs in einzelnen Schaumfilmen und in makroskopischen Schäumen untersucht. Schließlich wird die Verformbarkeit der MGs in den Schaumfilmen mit dem affinen Netzwerkmodell korreliert.

German
Status: Publisher's Version
URN: urn:nbn:de:tuda-tuprints-225596
Classification DDC: 500 Science and mathematics > 530 Physics
500 Science and mathematics > 540 Chemistry
Divisions: 05 Department of Physics
05 Department of Physics > Institute for Condensed Matter Physics
05 Department of Physics > Institute for Condensed Matter Physics > Soft Matter at Interfaces (SMI)
Date Deposited: 13 Dec 2022 12:39
Last Modified: 14 Dec 2022 11:13
PPN:
Referees: Klitzing, Prof. Dr. Regine von ; Schneck, Prof. Dr. Emanuel
Refereed / Verteidigung / mdl. Prüfung: 19 October 2022
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