Adsorption of Aldehyde-Functional Diblock Copolymer Spheres onto Surface-Grafted Polymer Brushes via Dynamic Covalent Chemistry Enables Friction Modification

Abstract

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.

Controlling Adsorption of Diblock Copolymer Nanoparticles onto an Aldehyde-Functionalized Hydrophilic Polymer Brush via pH Modulation

“…If nanoparticle adsorption is desired, then an attractive interaction force between the brush and the nanoparticles must be introduced to overcome the repulsive force. Recently, we exploited dynamic covalent chemistry (more specifically, imine bond formation) to adsorb aldehyde-functional nanoparticles onto amine-functional polymer brushes . Herein we examine whether the formation of acetal bonds between cis -diol-functional PGMA 51 –PBzMA y nanoparticles and a hydrophilic aldehyde-functional polymer brush is sufficient to promote adsorption.…”

“…Recently, we exploited dynamic covalent chemistry (more specifically, imine bond formation) to adsorb aldehyde-functional nanoparticles onto amine-functional polymer brushes. 59 Herein we examine whether the formation of acetal bonds between cis -diol-functional PGMA 51 –PBzMA y nanoparticles and a hydrophilic aldehyde-functional polymer brush is sufficient to promote adsorption. It is well-known that acetal bond formation is (i) acid-catalyzed and (ii) more entropically favorable when using a diol rather than two separate alcohols.…”

“…As previously reported, 59 , 62 wafers and/or QCM sensors were immersed in a 3.0 g dm –3 aqueous solution of NaIO 4 for 30 min at 20 °C, washed extensively with ethanol and water, and then dried under a stream of compressed air.…”

“…Very recently, we demonstrated that nanoparticle interactions with a hydrophilic polymer brush can be mediated by dynamic covalent chemistry. 59 More specifically, aldehyde-decorated nanoparticles can adsorb strongly onto a primary amine-functionalized brush via Schiff base chemistry (i.e., the formation of multiple imine bonds). Herein we report that an aqueous PISA formulation can be used to prepare cis -diol-functionalized spherical nanoparticles of tunable size.…”

Strong coupling in molecular systems: a simple predictor employing routine optical measurements

“…These surface layers have been shown to have many desirable properties [ 36 ], including increased antifouling [ 36 ] and lubricity [ 37 ] and can act as a scaffold for various small and large molecules [ 38 ], [ 39 ]. In the example presented here, a hydrophilic aldehyde functional polymer brush (PAGEO5MA) was grown from a glass cover slip [ 40 ], [ 41 ], [ 42 ], with a dry thickness = 40 nm, before decoration with an amino-functionalised Nile Red analogue (2-(2-Aminoethoxy) Nile Red) [ 43 ]. We have shown that PAGEO5MA can be conjugated with reactive amines through reductive amination chemistry to produce highly functionalised coatings ( 80 % of available reactive sites) [ 40 ], [ 41 ], [ 42 ].…”