Selective Adsorption of Functionalized Nanoparticles to Patterned Polymer Brush Surfaces and Its Probing with an Optical Trap

Abstract

The site-specific attachment of nanoparticles is of interest for biomaterials or biosensor applications. Polymer brushes can be used to regulate this adsorption, so the conditions for selective adsorption of phosphonate-functionalized nanoparticles onto micropatterned polymer brushes with different functional groups are optimized. By choosing the strong polyelectrolytes poly(3-sulfopropyl methacrylate), poly(sulfobetaine methacrylate), and poly[2-(methacryloyloxy)ethyl trimethylammonium chloride], it is possible to direct the adsorption of nanoparticles to specific regions of the patterned substrates. A pH-dependent adsorption can be achieved by using the polycarboxylate brush poly(methacrylic acid) (PMAA) as substrate coating. On PMAA brushes, the nanoparticles switch from attachment to the brush regions to attachment to the grooves of a patterned substrate on changing the pH from 3 to 7. In this manner, patterned substrates are realized that assemble nanoparticles in pattern grooves, in polymer brush areas, or substrates that resist the deposition of the nanoparticles. The nanoparticle deposition can be directed in a pH-dependent manner on a weak polyelectrolyte, or is solely charge-dependent on strong polyelectrolytes. These results are correlated with surface potential measurements and show that an optical trap is a versatile method to directly probe interactions between nanoparticles and polymer brushes. A model for these interactions is proposed based on the optical trap measurements.

Ordering nanoparticles with polymer brushes

“…We model the solvent as a Lennard-Jones (LJ) liquid and the polymer as linear chains of 100 beads connected by permanent bonds. All solvent and polymer beads have a mass m and interact through a standard LJ 12-6 pairwise potential, U LJ (r) = 4ǫ[(σ/r) 12 − (σ/r) 6 − (σ/r c ) 12 + (σ/r c ) 6 ], where r is the distance between the centers of two beads, ǫ the strength of interaction, and σ the size of beads. The cut off distance is r c = 3.0σ for all nonbonded pairs and r c = 2 1/6 σ for bonded pairs of neighboring polymer beads on a chain.…”

“…These considerations have motivated many experimental studies on controlling the NP distribution and organization in a polymer brush so that certain functions can be realized. [4] The hybrid structure is determined collectively by the strength of enthalpic NP-polymer interaction, [7] the brush characteristics including grafting density, [8] thickness, [9] pattern, [10][11][12] composition, [13] and possible gradients of these properties, [14][15][16] and the solvent being used. [17] Various theoretical and computational techniques have been employed to study the interactions between NPs and a polymer brush, including the self-consistent field theory (SCFT), [18][19][20][21][22][23][24][25][26][27][28][29] Monte Carlo simulations, [30][31][32] molecular dynamics (MD) simulations, [33][34][35] dissipative particle dynamics (DPD), [36] and Brownian dynamics simulations.…”

Adhesion of nanoparticles to polymer brushes studied with the ghost tweezers method

“…30 In the optical tweezers experiments, NP location is controlled by a laser beam. Displacement of NP from the beam focus indicates the effective force due to NP-PB interaction.…”

“…Displacement of NP from the beam focus indicates the effective force due to NP-PB interaction. Very recently, Steinbach et al 30 applied the optical tweezers to study interactions between charged NPs and a solid substrate functionalized with strong and weak polyelectrolyte chains. Depending on the pH, the authors observed NP binding to or repulsion from the brush and concluded that optical tweezers is a versatile method to directly probe NP-PB interactions.…”

Simultaneous fluorescence and surface charge measurements on organic semiconductor-coated silica microspheres in (non)polar liquids

“…Processes occurring at solid-liquid interfaces are of critical importance for a variety of applications spanning diverse fields including geochemistry, environmental science, catalysis, solar energy, corrosion protection, and many others [1]. Examples of such processes include interactions involving (dis)charging of colloids [2][3][4][5][6][7][8], physisorption and chemisorption [9][10][11][12], (electro)chemical reactions, and photocharging [13], all of which involve evolution of the effective surface charge. In order to understand these processes, it is important to develop tools that enable systematic studies of these interactions, depending on the nature of the interface.…”