Nonwettable Thin Films from Hybrid Polymer Brushes Can Be Hydrophilic

Abstract

Hybrid brushes composed of two liquid polymers, poly(dimethylsiloxane) (PDMS) and a highly branched ethoxylated polyethylenimine (EPEI), were synthesized on Si wafers by the "grafting to" method and by applying a combinatorial approach (fabrication of gradient brushes). The combinatorial approach revealed a strong effect of "layer assisted tethering", which allowed us to synthesize hybrid brushes twice as thick as the reference homopolymer brushes. The hybrid brushes are stable thin films that can rapidly and reversibly switch between hydrophilic and hydrophobic states in water and air, respectively. The switching in water affects a rapid release of amino functional groups which can be used to regulate adhesion and reactivity of the material. The switching in air rapidly returns the brush to a hydrophobic state. The hybrid brush is hydrophilic because of two mechanisms: (1) exposure of EPEI chains to the brush-water interface under water, and (2) retention of some fraction of water via swollen EPEI chains (the EPEI chains swell by 2-3 times), which are conserved by a PDMS cap in air. The hybrid brush is wettable under water, and at the same time, the brush is nonwettable in air because water droplets are trapped in a metastable state when the water contact angle is above 90°.

In-situ characterization of the temperature-sensitive swelling behavior of poly(N-isopropylacrylamide) brushes by infrared and visible ellipsometry

“…Temperature, pH, or solvent, when acting as typical external stimulus, can induce changes in brush structure and chemistry, leading to attractive surface functionalizations and promising applications like miniaturized sensors [1], tunable surface wetting [2], controlled adsorption of biomolecules [3][4][5], and drug delivery systems [6,7]. One of the most extensively studied and important representatives for temperature-sensitive polymers is poly(N-isopropylacrylamide) [PNIPAAm].…”

Polymer Brushes by the “Grafting to” Method

“…The second approach is based on gradual controlled immersion of the sample into a reactor with liquid reactive polymer or a solution of the polymer, to regulate the time of contact of the substrate with the reagent and, consequently, time of the grafting reaction. [37] The patterned layers were prepared using lithographic techniques. [17,38,39] The chemistry underlying the coupling reaction between the polymer functional groups and the complementary reactive surface groups defines the nature of the surfaces that can be modified, the grafting density of the layers, and their long term and chemical stability (Figure 1).…”

“…This approach brings a tremendous degree of flexibility to the choice of various functional groups suitable for the grafting procedures. Examples reported in the scientific literature include the utilization of reactions between epoxy and carboxy groups, [71,76,77,80,83,84,88,92,95,96] epoxy and amino groups, [37,67,73,74,88,95,97] and carboxy and amino groups. [62,98] Less frequent combinations of functional groups used for the ''grafting to'' procedure on oxide and/or gold surfaces are ''click'' chemistry, [99] reaction of epoxy group with maleic anhydride, [81,82] interaction between epoxy and thiol groups, [67] and alkylation of a pyridine ring in a polymer with a halogen atom attached to the surface via silane chemistry.…”

Superparamagnetic Iron Oxide Nanoparticles: Promises for Diagnosis and Treatment of Multiple Sclerosis

“…In this case, the use of stimuli-responsive polymers on the surface of SPIONs would be vital. "Smart" SPIONs could be formed using stimuli-responsive polymers (e.g., poly-(N-isopropylacrylamide) (202), triblock poly(styrene-block-2-vinylpyridine-block-ethylene oxide) (203), polystyrenepoly(methylmethacrylate) (204), polystyrene-poly-(methylmethacrylate) (205), and poly(vinylmethylsiloxane) (206)) as coating on their surfaces. The conformation of these polymers can be changed with variations of surrounding environments (e.g., different dispersion solvents), regulation of the transport of ions and molecules, changing wettability and adhesion of different species on external stimuli, or conversion of chemical and biochemical signals into optical, electrical, thermal, and mechanical signals (207).…”