Surface-Grafted, Covalently Cross-Linked Hydrogel Brushes with Tunable Interfacial and Bulk Properties

Abstract

Tethering macromolecules to surfaces represents a versatile approach for functionalizing, protecting, and structuring both organic and inorganic materials. In this study, thin films of poly(acrylamide) (PAAm) brushes and covalently cross-linked hydrogel brushes were grown from iniferter-functionalized silicon substrates by UVLED-initiated photopolymerization and their properties subsequently studied by means of a variety of analytical methods. The employed photografting method allowed the controlled fabrication of very thick films (up to 1 μm) in an aqueous environment, over a period of less than 1 h of polymerization and in the absence of side reactions. PAAm covalently cross-linked hydrogel brushes were prepared by feeding trace amounts of the cross-linker bis(acrylamide) (up to 1.0 wt % of monomer solution) into the reaction vessel. Both bulk and interfacial properties of these polymer films were found to be strongly influenced by lateral cross-linking of the grafted polymer chains. In agreement with theoretical expectations, the decrease of polymer-brush conformational freedom with increasing cross-link density resulted in a substantial increase of film wettability with water. The swelling ratio of the hydrogel brushes, as measured by ellipsometry and atomic force microscopy (AFM), also confirmed the formation of grafted networks and was found to be directly related to the amount of cross-linker in the monomer feed. In addition, the Young’s moduli and tribological properties of PAAm brushes and hydrogel brushes were tuned by adjusting the cross-linker concentration. Because of the additional constraint given by the surface tethering of each chain end, intermolecular cross-linking generated very high mechanical stresses within the brush structure. Covalently cross-linked hydrogel brushes thus displayed higher Young’s moduli and coefficients of friction, when compared to the grafted polymer-brush analogues. These hydrogel brushes present an opportunity for readily tailoring physical properties, especially as they allow tuning of the physical characteristics of surfaces while maintaining the interfacial chemical composition nearly constant.

Probing biomechanical properties with a centrifugal force quartz crystal microbalance

“…As per Fig. 5 these are as follows: cells 38 , agarose microparticles 39,40 and protein microcrystals 41 . Each is treated in the finite element simulation as a discrete sphere, with complex shear modulus…”

Lubrication with Oil-Compatible Polymer Brushes

“…The use of surface-grafted polymers to enhance lubricity has been reported extensively in the presence of aqueous [12,[19][20][21] lubricants, but sparsely [5,22] for non-aqueous (e.g., oil) systems. The combination of a polymer brush with an oil has the potential to combine the excellent boundary-lubrication properties of brushes with the rheological and high-temperature advantages of oil.…”

Effect of silver nanoparticle on the properties of poly(methyl methacrylate) nanocomposite network made by in situ photoiniferter-mediated photopolymerization

“…[22][23][24][25][26] Moreover, in another work brush and crosslinked hydrogel brushes were from polyacrylamide using SBDC as photoiniferter. 27 Although PMMA/Ag nanocomposites have been synthesized and investigated by several researchers via free radical thermal polymerization 28 and photopolymerization, 5 to the best of our knowledge, no empirical research exists addressing the investigation of AgNP effect on PMMA network properties prepared via living radical photopolymerization, i.e., PMP.…”