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Semifluorinated thiols in Langmuir monolayers - A study by nonlinear and linear vibrational spectroscopies

Volpati, Diogo LU ; Chachaj-Brekiesz, Anna ; Souza, Adriano L. ; Rimoli, Caio Vaz ; Miranda, Paulo B. ; Oliveira, Osvaldo N. and Dynarowicz-Łatka, Patrycja (2015) In Journal of Colloid and Interface Science 460. p.290-302
Abstract

A series of semifluorinated thiols of the general formula CmF2
m
+1CnH2
nSH (abbr. FmHnSH) have been synthesized and characterized in Langmuir monolayers with surface pressure-area isotherms, complemented with polarization-modulated reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation (SFG) techniques. A comparative analysis was performed for compounds having the same length of fluorinated segment (F10) and variable length of the hydrogenated part (H6, H10, H12), and having... (More)

A series of semifluorinated thiols of the general formula CmF2
m
+1CnH2
nSH (abbr. FmHnSH) have been synthesized and characterized in Langmuir monolayers with surface pressure-area isotherms, complemented with polarization-modulated reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation (SFG) techniques. A comparative analysis was performed for compounds having the same length of fluorinated segment (F10) and variable length of the hydrogenated part (H6, H10, H12), and having identical hydrogenated segment (H12) connected to a fluorinated moiety of different lengths (F6, F8, F10). For the sake of comparison, an alkanethiol (H18SH) was also examined, and F10H10COOH and F10H10OH molecules were used for helping the assignment of SFG spectra of CH stretches. SFG was applied to investigate the hydrocarbon chain and the terminal CF3 group, while PM-IRRAS was used to probe CF2 groups. The number of gauche defects in the hydrocarbon chain increased with the increasing length of the molecule, either by elongation of the hydrogenated or perfluorinated part. SFG measurements recorded at three polarization combinations (ppp, ssp, sps) enabled us to estimate the tilt angle of the terminal CF3 group in semifluorinated thiol molecules as ranging from 35° to 45°, which is consistent with nearly vertical fluorinated segments. Upon increasing the surface pressure, the fluorinated segment gets slightly more upright, but the hydrocarbon chain tilt increases while keeping the same average number of gauche defects. The extent of disorder in the hydrogenated segment may be controlled by varying the size of the fluorinated segment, and this could be exploited for designing functionalized surfaces with insertion of other molecules in the defect region.

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author
; ; ; ; ; and
publishing date
type
Contribution to journal
publication status
published
keywords
Air/water interface, Alkanethiols, Langmuir monolayers, Nonlinear spectroscopy, Polarization-modulated reflection absorption spectroscopy, Semifluorinated alkanes, Sum-frequency generation spectroscopy, Vibrational spectroscopy
in
Journal of Colloid and Interface Science
volume
460
pages
13 pages
publisher
Elsevier
external identifiers
  • scopus:84941281003
ISSN
0021-9797
DOI
10.1016/j.jcis.2015.08.069
language
English
LU publication?
no
id
974ee844-15ac-45b7-894c-127f1f0c3b20
date added to LUP
2019-05-17 14:30:55
date last changed
2022-11-14 06:09:40
@article{974ee844-15ac-45b7-894c-127f1f0c3b20,
  abstract     = {{<p>A series of semifluorinated thiols of the general formula C<sub>m</sub>F<sub>2</sub><br>
                            <sub>m</sub><br>
                            <sub>+1</sub>C<sub>n</sub>H<sub>2</sub><br>
                            <sub>n</sub>SH (abbr. F<sub>m</sub>H<sub>n</sub>SH) have been synthesized and characterized in Langmuir monolayers with surface pressure-area isotherms, complemented with polarization-modulated reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation (SFG) techniques. A comparative analysis was performed for compounds having the same length of fluorinated segment (F<sub>10</sub>) and variable length of the hydrogenated part (H<sub>6</sub>, H<sub>10</sub>, H<sub>12</sub>), and having identical hydrogenated segment (H<sub>12</sub>) connected to a fluorinated moiety of different lengths (F<sub>6</sub>, F<sub>8</sub>, F<sub>10</sub>). For the sake of comparison, an alkanethiol (H<sub>18</sub>SH) was also examined, and F<sub>10</sub>H<sub>10</sub>COOH and F<sub>10</sub>H<sub>10</sub>OH molecules were used for helping the assignment of SFG spectra of CH stretches. SFG was applied to investigate the hydrocarbon chain and the terminal CF<sub>3</sub> group, while PM-IRRAS was used to probe CF<sub>2</sub> groups. The number of gauche defects in the hydrocarbon chain increased with the increasing length of the molecule, either by elongation of the hydrogenated or perfluorinated part. SFG measurements recorded at three polarization combinations (ppp, ssp, sps) enabled us to estimate the tilt angle of the terminal CF<sub>3</sub> group in semifluorinated thiol molecules as ranging from 35° to 45°, which is consistent with nearly vertical fluorinated segments. Upon increasing the surface pressure, the fluorinated segment gets slightly more upright, but the hydrocarbon chain tilt increases while keeping the same average number of gauche defects. The extent of disorder in the hydrogenated segment may be controlled by varying the size of the fluorinated segment, and this could be exploited for designing functionalized surfaces with insertion of other molecules in the defect region.</p>}},
  author       = {{Volpati, Diogo and Chachaj-Brekiesz, Anna and Souza, Adriano L. and Rimoli, Caio Vaz and Miranda, Paulo B. and Oliveira, Osvaldo N. and Dynarowicz-Łatka, Patrycja}},
  issn         = {{0021-9797}},
  keywords     = {{Air/water interface; Alkanethiols; Langmuir monolayers; Nonlinear spectroscopy; Polarization-modulated reflection absorption spectroscopy; Semifluorinated alkanes; Sum-frequency generation spectroscopy; Vibrational spectroscopy}},
  language     = {{eng}},
  month        = {{12}},
  pages        = {{290--302}},
  publisher    = {{Elsevier}},
  series       = {{Journal of Colloid and Interface Science}},
  title        = {{Semifluorinated thiols in Langmuir monolayers - A study by nonlinear and linear vibrational spectroscopies}},
  url          = {{http://dx.doi.org/10.1016/j.jcis.2015.08.069}},
  doi          = {{10.1016/j.jcis.2015.08.069}},
  volume       = {{460}},
  year         = {{2015}},
}