Poly(n-butyl methacrylate) (PBMA) or poly(n-butyl acrylate) (PBA)-grafted brush coatings attached to glass were successfully prepared using atom-transfer radical polymerization "from the surface". The thicknesses and composition of the PBMA and PBA coatings were examined using ellipsometry and time-of-flight secondary ion mass spectrometry (ToF-SIMS), respectively. For PBMA, the glasstransition temperature constitutes a range close to the physiological limit, which is in contrast to PBA, where the glass-transition temperature is around −55 °C. Atomic force microscopy studies at different temperatures suggest a strong morphological transformation for PBMA coatings, in contrast to PBA, where such essential changes in the surface morphology are absent. Besides, for PBMA coatings, protein adsorption depicts a strong temperature dependence. The combination of bovine serum albumin and anti-IgG structure analysis with the principal component analysis of ToF-SIMS spectra revealed a different orientation of proteins adsorbed to PBMA coatings at different temperatures. In addition, the biological activity of anti-IgG molecules adsorbed at different temperatures was evaluated through tracing the specific binding with goat IgG.
By assembling 140 nm-sized fluorescent nanodiamonds (FNDs) in a thin-film on (3-aminopropyl) triethoxysilane functionalized glass surface, we prepare magnetically-sensitive FND-fiber probes for endoscopy. The obtained FND layers show good uniformity over large surfaces and are characterized using confocal, fluorescence, and atomic force microscopes. Further, FNDs are assembled on single large-core multimode optical fibers and imaging fiber bundles end face to detect optically detectable magnetic resonance (ODMR) signals. The ODMR signals are recorded through the fiber’s far end in magnetic fields between 0 to 2.5 mT. A multi-channel sensor is demonstrated with the capability of parallel-in-time mapping and instantaneous readout from individual pixel and enabling magnetic mapping at high spatial resolution. Results of this study are promising for early stage detection in bio-diagnostic applications.
Novel brush coatings
were fabricated with glass surface-grafted
chains copolymerized using surface-initiated atom transfer radical
polymerization (SI-ATRP) from 2-(2-methoxyethoxy)ethyl methacrylate
(OEGMA188) and acrylamide (AAm), taken in different proportions. P(OEGMA188-co-AAm) brushes with AAm mole fraction >44% (determined
with XPS and TOF-SIMS spectroscopy) and nearly constant with the depth
copolymer composition (TOF-SIMS profiling) exhibit unusual temperature-induced
transformations: The contact angle of water droplets on P(OEGMA188-co-AAm) coatings increases by ∼45° with temperature,
compared to 17–18° for POEGMA188 and PAAm. The thickness
of coatings immersed in water and the morphology of coatings imaged
in air show a temperature response for POEGMA188 (using reflectance
spectroscopy and AFM, respectively), but this response is weak for
P(OEGMA188-co-AAm) and absent for PAAm. This suggests
mechanisms more complex than a simple transition between hydrated
loose coils and hydrophobic collapsed chains. For POEGMA188, the hydrogen
bonds between the ether oxygens of poly(ethylene glycol) and water
hydrogens are formed below the transition temperature T
c and disrupted above T
c when
polymer–polymer interactions are favored. Different hydrogen
bond structures of PAAm include free amide groups, cis-trans-multimers, and trans-multimers of amide groups.
Here, hydrogen bonds between free amide groups and water dominate
at T < T
c but structures
favored at T > T
c,
such
as cis-trans-multimers and trans-multimers of amide groups, can still be hydrated. The enhanced temperature-dependent
response of wettability for P(OEGMA188-co-AAm) with
a high mole fraction of AAm suggests the formation at T
c of more hydrophobic structures, realized by hydrogen
bonding between the ether oxygens of OEGMA188 and the amide fragments
of AAm, where water molecules are caged. Furthermore, P(OEGMA188-co-AAm) coatings immersed in pH buffer solutions exhibit
a ‘schizophrenic’ behavior in wettability, with transitions
that mimic LCST and UCST for pH = 3, LCST for pH = 5 and 7, and any
transition blocked for pH = 9.
The surface properties
of poly(3,4-ethylenedioxythiophene):(polystyrene
sulfonate) (PEDOT:PSS) affect the performance of many organic electronic
devices. The work function determines the efficiency of the charge
carrier transfer between PEDOT:PSS electrodes and the active layer
of the device. The surface free energy affects phase separation in
multicomponent blends that are typically used to fabricate active
layers of organic light-emitting diodes and photovoltaic devices.
Here, we present a method to prepare PEDOT:PSS films with a gradient
work function and surface free energy. This modification was achieved
by evaporation of trimethoxy(3,3,3-trifluoropropyl)silane in such
a way that the degree of surface coverage of the molecules varied
in the selected direction. Gradient films were used as electrodes
to fabricate two-terminal PEDOT:PSS/poly(3-hexyl thiophene)/Au devices
to rapidly screen for the influence of the modification on the performance
of the prepared polymer diodes. Gradual changes in the morphology
of the solution-cast model poly(3-butyl thiophene)/poly-bromostyrene
films followed changes in the surface energy of the substrate.
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