Collapse from the top: Brushes of poly(N-isopropylacrylamide) in co-nonsolvent mixtures

Research output: Contribution to journalArticleAcademicpeer-review

32 Citations (Scopus)

Abstract

Using a combination of ellipsometry and friction force microscopy, we study the reversible swelling, collapse and variation in friction properties of covalently bound poly(N-isopropylacrylamide) (PNIPAM) layers on silicon with different grafting densities in response to exposure to good solvents and cononsolvent mixtures. Changes in the thickness and segment density distribution of grafted films are investigated by in situ ellipsometry. Based on quantitative modelling of the ellipsometry spectra, we postulate a structural model, which assumes that collapse takes place in the contacting layer between the brush and the co-nonsolvent and the top-collapsed brushes remain hydrated in the film interior. Using the structural model derived from ellipsometry spectra, we analyse the AFM based friction force microscopy data, which were obtained by silica colloidal probes. Results show a large increase of the friction coefficient of PNIPAM grafts when the grafts swollen by water are brought in contact with cononsolvents. For instance, the value of the friction coefficient for a medium density brush in water is four times lower than the value observed in a water–methanol (50% v/v) mixture. This increase of friction is accompanied by an increase in adherence between the PNIPAM chains and the silica colloidal probes, and is a result of chain collapse in the graft when contacted by a co-nonsolvent mixture in agreement with the model postulated on the basis of ellipsometric characterisation. The kinetic behaviour of the collapse is assessed by measuring the temporal variation of friction in situ as a function of elapsed time following contact with the co-nonsolvent as a function of graft density. In conclusion, the effect of cononsolvency influenced both the thickness of the PNIPAM brushes and the tribological behavior of the brush surfaces.
Original languageEnglish
Pages (from-to)3134-3142
Number of pages9
JournalSoft matter
Volume10
Issue number17
DOIs
Publication statusPublished - 2014

Fingerprint

brushes
Brushes
friction
ellipsometry
Friction
Ellipsometry
Grafts
coefficient of friction
silicon dioxide
Silicon Dioxide
microscopy
Microscopic examination
probes
axioms
swelling
water
density distribution
Water
Silicon
poly-N-isopropylacrylamide

Keywords

  • METIS-303529
  • IR-92622

Cite this

@article{6a266e867f0b424aac72f8687837238c,
title = "Collapse from the top: Brushes of poly(N-isopropylacrylamide) in co-nonsolvent mixtures",
abstract = "Using a combination of ellipsometry and friction force microscopy, we study the reversible swelling, collapse and variation in friction properties of covalently bound poly(N-isopropylacrylamide) (PNIPAM) layers on silicon with different grafting densities in response to exposure to good solvents and cononsolvent mixtures. Changes in the thickness and segment density distribution of grafted films are investigated by in situ ellipsometry. Based on quantitative modelling of the ellipsometry spectra, we postulate a structural model, which assumes that collapse takes place in the contacting layer between the brush and the co-nonsolvent and the top-collapsed brushes remain hydrated in the film interior. Using the structural model derived from ellipsometry spectra, we analyse the AFM based friction force microscopy data, which were obtained by silica colloidal probes. Results show a large increase of the friction coefficient of PNIPAM grafts when the grafts swollen by water are brought in contact with cononsolvents. For instance, the value of the friction coefficient for a medium density brush in water is four times lower than the value observed in a water–methanol (50{\%} v/v) mixture. This increase of friction is accompanied by an increase in adherence between the PNIPAM chains and the silica colloidal probes, and is a result of chain collapse in the graft when contacted by a co-nonsolvent mixture in agreement with the model postulated on the basis of ellipsometric characterisation. The kinetic behaviour of the collapse is assessed by measuring the temporal variation of friction in situ as a function of elapsed time following contact with the co-nonsolvent as a function of graft density. In conclusion, the effect of cononsolvency influenced both the thickness of the PNIPAM brushes and the tribological behavior of the brush surfaces.",
keywords = "METIS-303529, IR-92622",
author = "Qi Chen and Kooij, {Ernst S.} and Xiaofeng Sui and Padberg, {Clemens J.} and Hempenius, {Mark A.} and Sch{\"o}n, {Peter Manfred} and Vancso, {Gyula J.}",
year = "2014",
doi = "10.1039/C4SM00195H",
language = "English",
volume = "10",
pages = "3134--3142",
journal = "Soft matter",
issn = "1744-683X",
publisher = "Royal Society of Chemistry",
number = "17",

}

Collapse from the top: Brushes of poly(N-isopropylacrylamide) in co-nonsolvent mixtures. / Chen, Qi; Kooij, Ernst S.; Sui, Xiaofeng; Padberg, Clemens J.; Hempenius, Mark A.; Schön, Peter Manfred; Vancso, Gyula J.

In: Soft matter, Vol. 10, No. 17, 2014, p. 3134-3142.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Collapse from the top: Brushes of poly(N-isopropylacrylamide) in co-nonsolvent mixtures

AU - Chen, Qi

AU - Kooij, Ernst S.

AU - Sui, Xiaofeng

AU - Padberg, Clemens J.

AU - Hempenius, Mark A.

AU - Schön, Peter Manfred

AU - Vancso, Gyula J.

PY - 2014

Y1 - 2014

N2 - Using a combination of ellipsometry and friction force microscopy, we study the reversible swelling, collapse and variation in friction properties of covalently bound poly(N-isopropylacrylamide) (PNIPAM) layers on silicon with different grafting densities in response to exposure to good solvents and cononsolvent mixtures. Changes in the thickness and segment density distribution of grafted films are investigated by in situ ellipsometry. Based on quantitative modelling of the ellipsometry spectra, we postulate a structural model, which assumes that collapse takes place in the contacting layer between the brush and the co-nonsolvent and the top-collapsed brushes remain hydrated in the film interior. Using the structural model derived from ellipsometry spectra, we analyse the AFM based friction force microscopy data, which were obtained by silica colloidal probes. Results show a large increase of the friction coefficient of PNIPAM grafts when the grafts swollen by water are brought in contact with cononsolvents. For instance, the value of the friction coefficient for a medium density brush in water is four times lower than the value observed in a water–methanol (50% v/v) mixture. This increase of friction is accompanied by an increase in adherence between the PNIPAM chains and the silica colloidal probes, and is a result of chain collapse in the graft when contacted by a co-nonsolvent mixture in agreement with the model postulated on the basis of ellipsometric characterisation. The kinetic behaviour of the collapse is assessed by measuring the temporal variation of friction in situ as a function of elapsed time following contact with the co-nonsolvent as a function of graft density. In conclusion, the effect of cononsolvency influenced both the thickness of the PNIPAM brushes and the tribological behavior of the brush surfaces.

AB - Using a combination of ellipsometry and friction force microscopy, we study the reversible swelling, collapse and variation in friction properties of covalently bound poly(N-isopropylacrylamide) (PNIPAM) layers on silicon with different grafting densities in response to exposure to good solvents and cononsolvent mixtures. Changes in the thickness and segment density distribution of grafted films are investigated by in situ ellipsometry. Based on quantitative modelling of the ellipsometry spectra, we postulate a structural model, which assumes that collapse takes place in the contacting layer between the brush and the co-nonsolvent and the top-collapsed brushes remain hydrated in the film interior. Using the structural model derived from ellipsometry spectra, we analyse the AFM based friction force microscopy data, which were obtained by silica colloidal probes. Results show a large increase of the friction coefficient of PNIPAM grafts when the grafts swollen by water are brought in contact with cononsolvents. For instance, the value of the friction coefficient for a medium density brush in water is four times lower than the value observed in a water–methanol (50% v/v) mixture. This increase of friction is accompanied by an increase in adherence between the PNIPAM chains and the silica colloidal probes, and is a result of chain collapse in the graft when contacted by a co-nonsolvent mixture in agreement with the model postulated on the basis of ellipsometric characterisation. The kinetic behaviour of the collapse is assessed by measuring the temporal variation of friction in situ as a function of elapsed time following contact with the co-nonsolvent as a function of graft density. In conclusion, the effect of cononsolvency influenced both the thickness of the PNIPAM brushes and the tribological behavior of the brush surfaces.

KW - METIS-303529

KW - IR-92622

U2 - 10.1039/C4SM00195H

DO - 10.1039/C4SM00195H

M3 - Article

VL - 10

SP - 3134

EP - 3142

JO - Soft matter

JF - Soft matter

SN - 1744-683X

IS - 17

ER -