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Association of anionic surfactant and physisorbed branched brush layers probed by neutron and optical reflectometry
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.ORCID iD: 0000-0002-2288-819X
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2015 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 440, 245-252 p.Article in journal (Refereed) Published
Abstract [en]

Pre-adsorbed branched brush layers were formed on silica surfaces by adsorption of a diblock copolymer consisting of a linear cationic block and an uncharged bottle-brush block. The charge of the silica surface was found to affect the adsorption, with lower amounts of the cationic polyelectrolyte depositing on less charged silica. Cleaning under basic conditions rendered surfaces more negatively charged (more negative zeta-potential) than acid cleaning and was therefore used to increase polyelectrolyte adsorption. The structure of adsorbed layers of the diblock copolymer was as determined by neutron reflectometry found to be about 70 nm thick and very water rich (97%). Interactions between the anionic surfactant sodium dodecylsulfate (SDS) and such pre-adsorbed diblock polymer layers were studied by neutron reflectometry and by optical reflectometry. Optical reflectometry was also used for deducing interactions between the individual blocks of the diblock copolymer and SDS at the silica/aqueous interface. We find that SDS is readily incorporated in the diblock copolymer layer at low SDS concentrations, and preferentially co-localized with the cationic block of the polymer next to the silica surface. At higher SDS concentrations some desorption of polyelectrolyte/surfactant complexes takes place.

Place, publisher, year, edition, pages
2015. Vol. 440, 245-252 p.
Keyword [en]
Polymer brush layer, Diblock copolymer, SDS, Adsorption, Polyelectrolyte-surfactant complex, Optical reflectometry, Neutron reflectivity
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-157337DOI: 10.1016/j.jcis.2014.11.002ISI: 000346461100031ScopusID: 2-s2.0-84911423822OAI: diva2:769732
Swedish Research CouncilVINNOVAEU, FP7, Seventh Framework Programme, 290251

QC 20150220. Updated from manuscript to published article.

Available from: 2014-12-09 Created: 2014-12-09 Last updated: 2015-02-20Bibliographically approved
In thesis
1. Surface Force and Friction: effects of adsorbed layers and surface topography
Open this publication in new window or tab >>Surface Force and Friction: effects of adsorbed layers and surface topography
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Interfacial features of polymers are a complex, fascinating topic, and industrially very important. There is clearly a need to understand interactions between polymer layers as they can be used for controlling surface properties, colloidal stability and lubrication. The aim of my Ph.D study was to investigate fundamental phenomena of polymers at interfaces, covering adsorption, interactions between polymer layers and surfactants, surface forces and friction between adsorbed layers.

A branched brush layer with high water content was formed on silica surfaces by a diblock copolymer, (METAC)m-b-(PEO45MEMA)n, via physisorption. The adsorption properties were determined using several complementary methods. Interactions between pre-adsorbed branched brush layers and the anionic surfactant SDS were investigated as well. Surface forces and friction between polymer layers in aqueous media were investigated by employing the Atomic Force Microscopy (AFM) colloidal probe technique. Friction forces between the surfaces coated by (METAC)m-b-(PEO45MEMA)n in water are characterized by a low friction coefficient. Further, the layers remain intact under high load and shear, and no destruction of the layer was noted even under the highest pressure employed, about 50 MPa.

Interactions between polymer layers formed by a temperature responsive diblock copolymer, PIPOZ60-b-PAMPTMA17 (phase transition temperature of 46.1 °C), was investigated in the temperature interval 25-50 °C by using the AFM colloidal probe technique. Friction between the layers increases with increasing temperature (25-45 °C), while at 50 °C friction was found to be slightly lower than that at 45 °C. We suggest that this is due to decreased energy dissipation caused by PIPOZ chains crystallizing in water above the phase transition temperature.

The structure of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers was determined by X-ray reflectometry. Surface forces and friction between DPPC bilayer-coated silica surfaces were measured utilizing the AFM colloidal probe technique. Our study showed that DPPC bilayers are able to provide low friction forces both in the gel (below ≈ 41°C) and in the liquid crystalline state (above ≈ 41°C). However, the load bearing capacity is lower in the gel state. This is attributed to a higher rigidity and lower self-healing capacity of the DPPC bilayer in the gel state.

Friction forces in single asperity contact acting between a micro-patterned silicon surface and an AFM tip was measured in air. We found that both nanoscale surface heterogeneities and the µm-sized depressions affect friction forces, and considerable reproducible variations were found along a particular scan line. Nevertheless, Amontons’ first rule described average friction forces reasonably well. Amontons’ third rule and Euler’s rule were found to be less applicable to our system.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xiv, 78 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:57
Friction, nanotribology, surface forces, diblock copolymer, lipid, QCM-D, AFM, optical reflectometry, neutron reflectivity, X-ray reflectivity, micro-patterned surface
National Category
Chemical Engineering
Research subject
urn:nbn:se:kth:diva-157321 (URN)978-91-7595-362-5 (ISBN)
Public defence
2014-12-18, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)

QC 20141209

Available from: 2014-12-09 Created: 2014-12-08 Last updated: 2015-08-27

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