Direct Nanoscopic Measurement of Laminar Slip Flow
Penetration of Deformable Polymer Brush Surfaces: Synergistic Effect
of Grafting Density and Solvent Quality
Huan Wang
Jeanne E. Pemberton
10.1021/acs.langmuir.9b02357.s001
https://acs.figshare.com/articles/journal_contribution/Direct_Nanoscopic_Measurement_of_Laminar_Slip_Flow_Penetration_of_Deformable_Polymer_Brush_Surfaces_Synergistic_Effect_of_Grafting_Density_and_Solvent_Quality/9963752
A detailed
quantitative nanoscopic description of soft surfaces
under dynamic flow is lacking, despite its importance. To better understand
the role of surface texture in nanoscopic mass transport in complex
media, we used Förster resonance energy transfer in combination
with total internal reflectance fluorescence microscopy (FRET-TIRFM)
to directly measure laminar slip flow penetration depth (slip length)
on poly(<i>N</i>-isopropylacrylamide) (pNIPAM) thin
films (50–110 nm) of different grafting densities (0.60, 0.38,
and 0.27 chain/nm<sup>2</sup>) in solvents of different qualities
created via cononsolvency <i>in situ</i>. Nontrivial synergistic
interplay of grafting density and solvent quality on slip length was
observed. Slip lengths are typically tens of nm (40–100 nm),
increasing and then reaching a plateau with applied linear flow velocity
(192–2,952 μm/s) regardless of experimental system. Slip
length was systematically larger for lower density films, but the
effect of grafting density was more significant in a good solvent
than a poor solvent. Interestingly, however, the stagnant film thickness
(polymer swollen thickness minus the slip length) collapsed to almost
a singular value for a given grafting density regardless of solvent
quality, likely suggesting a large gradient of segmental mobility
at nonequilibrium. Moreover, we found that slip flow penetrates into
soft pNIPAM surfaces more deeply in a good solvent than in a poor
solvent and that this behavior was general and independent of grafting
density. This behavior is counter to the notion that less interaction
between a fluid (probe) and a solid surface promotes slip.
2019-10-10 14:05:17
flow penetration depth
Solvent Quality
reflectance fluorescence microscopy
nanoscopic mass transport
Grafting Density
pNIPAM surfaces
Direct Nanoscopic Measurement
FRET-TIRFM
film thickness
measure laminar
surface texture
density films
Synergistic Effect
Slip lengths
nm
nanoscopic description
Laminar Slip Flow Penetration
Slip length
Deformable Polymer Brush Surfaces