Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Water Structure Next to Ordered and Disordered Hydrophobic Silane Monolayers: A Vibrational Sum Frequency Spectroscopy Study
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.ORCID iD: 0000-0003-2734-2847
2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 4, 1780-1790 p.Article in journal (Refereed) Published
Abstract [en]

Vibrational sum frequency spectroscopy (VSFS) has been used to study the structure of water incontact to fused silica surfaces, hydrophobically modified with series of alkyl trichlorosilanemonolayers of varying degrees of order. The interfacial molecular structural information wascomplemented using total internal reflection (TIR) Raman spectroscopy. The silane moleculesconsisted of octadecyltrichlorosilane (OTS) and its shorter chain analogue with eight carbonatoms. The VSFS spectra show a direct correlation between monolayer order and the intensity ofthe free OH mode, characteristic of straddling water molecules vibrating in direct contact to thehydrophobic layer, with a concurrent reduction of the bands associated with hydrogen bondedwater molecules. The results imply that the structure of water in the most ordered monolayers isnot much affected beyond the first layer of water molecules, with bulk isotropic propertiesbecoming apparent already at sub-nanometer distances from the surface. Contact anglemeasurements with both water and hexadecane were also performed in an effort to relatemacroscopically measureable parameters to the molecular surface structure provided by VSFSand TIR Raman. Only the receding contact angles, and in particular those with hexadecane, werefound to correlate with the monolayer order. Finally, to obtain an additional insight into the waterstructure in direct contact to an ordered hydrophobic surface, isotopic dilution experiments withD2O were also performed. They indicate that the vibrational coupling mechanism of watermolecules at the hydrophobized solid/water interface is different from what has been observed atthe liquid/vapor interface.

Place, publisher, year, edition, pages
2013. Vol. 117, no 4, 1780-1790 p.
Keyword [en]
TIR Raman, silica interface, contact angles, surface molecular structure, octadecyltrichlorosilane
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-101080DOI: 10.1021/jp310732fISI: 000314492400030Scopus ID: 2-s2.0-84874413657OAI: oai:DiVA.org:kth-101080DiVA: diva2:546304
Funder
Swedish Research Council
Note

Uppdaterad från Manuskript till Artikel (20130308) QC 20130308

Available from: 2012-08-23 Created: 2012-08-23 Last updated: 2017-12-07Bibliographically approved
In thesis
1. A Spectroscopic Study of Interfacial Films: Internal Structuring, Stability, and Hydration
Open this publication in new window or tab >>A Spectroscopic Study of Interfacial Films: Internal Structuring, Stability, and Hydration
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Monolayers of molecules are capable of completely changing the nature of surfaces and their interactions with the surroundings despite their almost negligible thickness. In the research presented in this doctoral thesis the surface specific technique Vibrational Sum Frequency Spectroscopy (VSFS) was combined with the Langmuir trough to investigate various manifestations of monolayers, such as biomimetic membranes, mono methyl branched long chain fatty acids in contact with air, and hydrophobic silane monolayers in contact with water.

VSFS was applied to in situ studies of the oxidative degradation of Langmuir monolayers of 1,2-diacylphosphocholines with identical C-18 chains featuring various degrees of unsaturation. The monolayer area and vinyl CH signal intensity were probed at constant surface pressure to monitor the degradation. The rapid degradation of the unsaturated lipids in contact with the ambient air is attributed to oxidation of the C=C bonds mediated by reactive species in the air and can be inhibited by purging the compartment surrounding the monolayer with nitrogen.

The molecular structure and order of Langmuir monolayers of 1,2-distearoyl-phosphocholine (18:0 PC) and their hydrating water were investigated at different surface pressures using VSFS. The monolayers are conformationally well ordered at all surface pressures and the signal intensity increases due to larger molecular number density at increasing surface pressures. Also, water signals with different vibrational frequencies are observed in different polarization combinations.

Additionally, a selection of common phospholipids (18:0 PC, 18:0 PC-D83 and 18:0 PS) were Langmuir-Blodgett (LB) deposited on CaF2 substrates and the CH- and OH-stretching regions as well as lower wavenumber regions were probed using VSFS. The orientation of the conformationally well ordered aliphatic chains was determined to be approximately perpendicular to the sample surface.

Monolayers of eicosanoic acid, its iso (19-MEA), and anteiso (18-MEA) analogues were investigated with VSFS, AFM imaging, and the Langmuir trough. The EA forms smooth, featureless monolayers when deposited on silica, while 19-MEA and 18-MEA form 10 -50 nm large domains with homogeneous size distribution. It was not possible to discriminate between the monolayers of racemic and chiral 18-MEA using any of the techniques employed

The influence of the experimental geometry on the SF spectral shape and en-hancement at and near total internal reflection conditions (TIR) were systematically investigated by comparing simulations with recorded data from a hydrophobized silica / water interface. The data agree qualitatively, but not quantitatively, with the simulations, and the reasons were critically discussed.

The water structure next to ordered and disordered hydrophobic silane monolayers on silica was investigated using VSFS. The results indicate that the structure of water next to a well ordered hydrophobic monolayer, with the exception of the first layer of water molecules, is not much different from that in the isotropic bulk. This is in contrast to the previous notion where such monolayers were assumed to induce a more ordered interfacial water structure.

Abstract [sv]

Trots sin begränsade tjocklek har monolager förmågan att totalt kunna förändra en ytas egenskaper och dess växelverkan med omgivningen. I forskningen som beskrivs i denna doktorsavhandling har den ytspecifika tekniken vibrationssumfrekvensspektroskopi (VSFS) kombinerats med Langmuir-tråget för att undersöka olika varianter av monolager, såsom biomimetiska membran, monometylgrenade långkedjiga fettsyror och hydrofoba silanmonolager i kontakt med vatten.

VSFS användes för att genomföra in situ undersökningar av den oxidativa nedbrytningen av Langmuir-monolager av 1,2-diacylfosfokoliner med identiska 18 kolatomer långa kedjor med varierande grader av omättnad. Monolagerarean och vinylCH-signalens intensitet mättes vid konstant yttryck för att övervaka nedbrytningen. Den snabba nedbrytningen av de omättade lipiderna i kontakt med den omgivande luften tillskrivs oxidation orsakad av reaktiva ämnen i luften och kan inhiberas fullständigt genom att genomblåsa utrymmet som omger monolagret med kvävgas.

Den molekylära strukturen och ordningen hos Langmuir-monolager av 1,2-distearoylfosfokolin (18:0 PC) och deras hydratiseringsvatten undersöktes vid olika yttryck med VSFS. Monolagerna har en välordnad konformation vid alla yttryck och signalintensiteten ökar vid ökande yttryck på grund av den större numerära molekyltätheten. Dessutom observeras vattensignaler med olika vibrationsfrekvenser i olika polarisationskombinationer.

Vidare LB-deponerades ett urval av vanligt förekommande fosfolipider (18:0 PC, 18:0 PC-D83 och 18:0 PS) på ett substrat av CaF2 varefter CH- och vattenregionen såväl som lågvågtalsområdet undersöktes med hjälp av VSFS. Orienteringen hos kolvätekedjorna, som hade en välordnad konformation, befanns vara ungefär vinkelrät mot provytan.

Monolager av eicosansyra, samt dess iso (19-MEA), och anteiso (18-MEA) analoger undersöktes med VSFS, AFM avbildning och Langmuirtråget. Eicosanssyran bildar jämna, strukturlösa monolager då den deponeras på kiseldioxid medan 19-MEA och 18-MEA formar 10 – 50 nm stora domäner med homogen storleksfördelning. Ingen av de använda teknikerna kunde särskilja racemisk och kiral 18-MEA.

Inverkan av försöksuppställningens geometri på SF-spektrumets form och förstärkning vid och i närheten av total internreflektion (TIR) undersöktes systematiskt genom att jämföra simuleringar med mätdata från en gränsyta mellan hydro-foberad kiseldioxid och vatten. Mätdata överensstämmer kvalitativt, men inte kvantitativt, med simuleringarna och orsakerna till detta diskuterades kritiskt.

Vattenstrukturen intill ordnade och oordnade hydrofoba silanmonolager undersöktes med VSFS. Resultaten visar att vattenstrukturen nära ett välordnat hydrofobt monolager, med undantag av det första lagret av vattenmolekyler, inte är särskilt olik den isotropa bulkfasens. Detta är i motsats till den tidigare uppfattningen att sådana monolager ansågs orsaka en mera välordnad vattenstruktur.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. viii, 80 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:35
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-101081 (URN)978-91-7501-436-4 (ISBN)
Public defence
2012-09-21, KTH, Hörsal F3, Lindstedtsvägen 26, KTH, Stockholm, 13:30 (English)
Opponent
Supervisors
Note

QC 20120824

Available from: 2012-08-24 Created: 2012-08-23 Last updated: 2012-08-24Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Authority records BETA

Liljeblad, Jonathan F. D.

Search in DiVA

By author/editor
Tyrode, EricLiljeblad, Jonathan F. D.
By organisation
Surface and Corrosion Science
In the same journal
The Journal of Physical Chemistry C
Physical Chemistry

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 153 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf