3 research outputs found
Arginine-Functional Methacrylic Block Copolymer Nanoparticles: Synthesis, Characterization, and Adsorption onto a Model Planar Substrate
Recently, we reported
the synthesis of a hydrophilic
aldehyde-functional
methacrylic polymer (Angew. Chem., 2021, 60, 12032–12037). Herein we demonstrate
that such polymers can be reacted with arginine in aqueous solution
to produce arginine-functional methacrylic polymers without recourse
to protecting group chemistry. Careful control of the solution pH
is essential to ensure regioselective imine bond formation; subsequent
reductive amination leads to a hydrolytically stable amide linkage.
This new protocol was used to prepare a series of arginine-functionalized
diblock copolymer nanoparticles of varying size via polymerization-induced
self-assembly in aqueous media. Adsorption of these cationic nanoparticles
onto silica was monitored using a quartz crystal microbalance. Strong
electrostatic adsorption occurred at pH 7 (Γ = 14.7 mg m–2), whereas much weaker adsorption occurred at pH 3
(Γ = 1.9 mg m–2). These findings were corroborated
by electron microscopy, which indicated a surface coverage of 42%
at pH 7 but only 5% at pH 3
Adsorption of Aldehyde-Functional Diblock Copolymer Spheres onto Surface-Grafted Polymer Brushes via Dynamic Covalent Chemistry Enables Friction Modification
Dynamic covalent chemistry has been exploited to prepare
numerous
examples of adaptable polymeric materials that exhibit unique properties.
Herein, the chemical adsorption of aldehyde-functional diblock copolymer
spherical nanoparticles onto amine-functionalized surface-grafted
polymer brushes via dynamic Schiff base chemistry is demonstrated.
Initially, a series of cis-diol-functional sterically-stabilized
spheres of 30–250 nm diameter were prepared via reversible
addition–fragmentation chain transfer (RAFT) aqueous dispersion
polymerization. The pendent cis-diol groups within
the steric stabilizer chains of these precursor nanoparticles were
then oxidized using sodium periodate to produce the corresponding
aldehyde-functional spheres. Similarly, hydrophilic cis-diol-functionalized methacrylic brushes grafted from a planar silicon
surface using activators regenerated by electron transfer atom transfer
radical polymerization (ARGET ATRP) were selectively oxidized to generate
the corresponding aldehyde-functional brushes. Ellipsometry and X-ray
photoelectron spectroscopy were used to confirm brush oxidation, while
scanning electron microscopy studies demonstrated that the nanoparticles
did not adsorb onto a cis-diol-functional precursor
brush. Subsequently, the aldehyde-functional brushes were treated
with excess small-molecule diamine, and the resulting imine linkages
were converted into secondary amine bonds via reductive amination.
The resulting primary amine-functionalized brushes formed multiple
dynamic imine bonds with the aldehyde-functional diblock copolymer
spheres, leading to a mean surface coverage of approximately 0.33
on the upper brush layer surface, regardless of the nanoparticle size.
Friction force microscopy studies of the resulting nanoparticle-decorated
brushes enabled calculation of friction coefficients, which were compared
to that measured for the bare aldehyde-functional brush. Friction
coefficients were reasonably consistent across all surfaces except
when particle size was comparable to the size of the probe tip. In
this case, differences were ascribed to an increase in contact area
between the tip and the brush-nanoparticle layer. This new model system
enhances our understanding of nanoparticle adsorption onto hydrophilic
brush layers
Strong coupling in molecular systems: a simple predictor employing routine optical measurements
We provide a simple method that enables readily acquired experimental data to be used to predict whether or not a candidate molecular material may exhibit strong coupling. Specifically, we explore the relationship between the hybrid molecular/photonic (polaritonic) states and the bulk optical response of the molecular material. For a given material this approach enables a prediction of the maximum extent of strong coupling (vacuum Rabi splitting), irrespective of the nature of the confined light field. We provide formulae for the upper limit of the splitting in terms of the molar absorption coefficient, the attenuation coefficient, the extinction coefficient (imaginary part of the refractive index) and the absorbance. To illustrate this approach we provide a number of examples, we also discuss some of the limitations of our approach