Fabrications and Applications of Stimulus-Responsive Polymer Films and Patterns on Surfaces: A Review

Abstract

In the past two decades, we have witnessed significant progress in developing high performance stimuli-responsive polymeric materials. This review focuses on recent developments in the preparation and application of patterned stimuli-responsive polymers, including thermoresponsive layers, pH/ionic-responsive hydrogels, photo-responsive film, magnetically-responsive composites, electroactive composites, and solvent-responsive composites. Many important new applications for stimuli-responsive polymers lie in the field of nano- and micro-fabrication, where stimuli-responsive polymers are being established as important manipulation tools. Some techniques have been developed to selectively position organic molecules and then to obtain well-defined patterned substrates at the micrometer or submicrometer scale. Methods for patterning of stimuli-responsive hydrogels, including photolithography, electron beam lithography, scanning probe writing, and printing techniques (microcontact printing, ink-jet printing) were surveyed. We also surveyed the applications of nanostructured stimuli-responsive hydrogels, such as biotechnology (biological interfaces and purification of biomacromoles), switchable wettability, sensors (optical sensors, biosensors, chemical sensors), and actuators.

Keywords: magnetically-responsive; pH-responsive; photo-responsive; polymer; thermoresponsive.

Figure 1.

(a) Poly(Nisopropylacrylamide) (PNIPAAm); (b) poly(N,N-diethylaminoethyl methacrylate) (PDEAEMA); (c) poly(N,N′-diethylacrylamide) (PDEAAm); (d) poly(2-carboxyisopropylacrylamide) (PCIPAAm); (e) poly[2-(methacryloyloxy)ethyl]-dimethyl(3-sulfopropyl) ammonium hydroxide (PMEDSAH). Reprinted (adapted) with permission from [,–33,35].

Figure 2.

Representation of the supramolecular structure formed from the complexation of PNIPAAm and adenine through a nucleobase-like hydrogen bonding (NLHB) interactions. Reprinted (adapted) with permission from [51].

Figure 3.

(a) Poly(acrylic acid) (PAAc); (b) poly(methacrylic acid) (PMAAc); (c) poly(N,N′-diethyl aminoethyl methacrylate) (PDEAEMA); (d) Poly(4-vinylpyridine) (P4VP); (e) Poly(vinyl imidazole) (PVI); (f) poly[2-(methacryloyloxy)- ethyltrimethylammonium chloride] (PMETAC).

Figure 4.

Schematic illustrations of reversible photoisomerization. (a) photoisomerization of azobenzene groups; (b) isomeric molecular structure of a spiropyran irradiated with light, spiropyran (left), merocyanine (center), and quinoidal canonical form (right); (c) photodimerization of the cinnamic acid group. Reprinted (adapted) with permission from [74,78,82].

Figure 5.

(a) Reconstructed image of a cicada (a familiar insect in Taiwan) standing on the cross section of a branch written in the PANPAC/TDI film; (b) overwritten image of four portraits; (c) dark decay after 1 h; (d) same image as in part a written in the PANTAC/TDI film; (e) chemical structure of the polymer. Reprinted (adapted) with permission from [84]. Copyright (1999) American Chemical Society.

Figure 6.

Schematic illustration for the synthesis of a wire-like assembly of magnetic nanoparticles inside a cylindrical polymer brush. (a) polymer brush with PAA core and PnBA shell; (b) neutralized polymer brush with poly(sodium acrylate) core (Na⁺ ions are not shown); (c) polychelate of the brush with Fe²⁺ or Fe³⁺ ions; and (d) hybrid nanocylinder of the brush and magnetic nanoparticles. Reprinted (adapted) with permission from [10].

Figure 7.

(a) A schematic representation of the controlled dispersed structures of the tubes within the polymer matrix; (b) thermomechanical properties curves (200% elongation at 50 °C); and (c) shape recovery and shape retention (quenching/unloading and subsequently applying an electric voltage of 40 V) for the polyurethane composites prepared by conventional blending, in situ, and cross-linking polymerization. Reproduced from Reference [104] with permission.

Figure 8.

(a) Schematic illustrations of reversible poly(methyl methacrylate) (PMMA) brush treated with good and poor solvents; (b) Atomic force microscopy (AFM) images of densely patterned lines polystyrene (PS) brushes (1:1 duty ratio, 160 nm resolution) before and after good (left) and poor (right) solvent treatments, respectively; (c) Schematic of a polymeric sensor based on a surface-grafted polymer layer with AuNPs, adsorbed on a stimuli-responsive polymer line pattern grafted onto a silicon substrate. The AuNPs-surface distance depends on the conformation of the polymer chains and changes in different solvents. The change in height is therefore reported by a variation in the detected diffractive intensity. Reprinted from Reference [108,110,114] with permission.

Figure 9.

(a) Synthetic route toward poly(2-hydroxyethyl methacrylate) (PHEMA) brushes patterned through advanced lithography, and ATRP on Si wafers; (b) 3D, cross-section, and profile AFM image of line patterned PHEMA brushes with 350 nm of resolution. Reprinted from Reference [119,120] with permission.

Figure 10.

Irradiation through a mask, conversion of the terminal nitro group in amine group and diazotization and coupling with malonodinitrile gives a SAM that bears an asymmetric azo-initiator. Reprinted from Reference [128] with permission.

Figure 11.

(a) Schematic representation of the dip-pen nanolithography (DPN) process. A water meniscus forms between the AFM tip which is coated with “ink” molecules and the solid substrate; (b) Preparation of polymer brushes grafted from immobilized precursors on gold nanowires. Reproduced with permission from reference [139]; Reprinted from Reference [135,139] with permission.

Figure 12.

Schematic comparison of photolithography vs. microcontact printing (μCP). The crucial step in both techniques consists of the accurate transfer of the patterned etch-resist layer. Reprinted from Reference [150] with permission.

Figure 13.

Outline procedure for grafting multiple patterned polymer brushes and ATRP passivation. Reprinted from Reference [156] with permission.

Figure 14.

Schematic of the process for capture and release specific DNA by a tethered poly(N-isopropylacrylamide) (PNIPAAm) in the channel surface of a fluid device from a specimen with lysed human blood cells. Reprinted from Reference [181] with permission.

Figure 15.

(a) Schematic representation of the capture and release of specific gDNA from a specimen of lysed human blood cells by tethered Poly[2-(dimethylamino)-ethyl methacrylate] (PDMAEMA) on an Si surface [200]; (b) Optical microscope image of the fluidic system with the straight channels. Reprinted from Reference [178] with permission.

Figure 16.

Schematic representation of the strategy for ferritin capture. (I) The sample surface presenting the patterned PHEMA brushes is immersed for 1 h into a mixture of water and MeOH containing dispersed ferritin; (II) The sample surface is immersed into n-hexane to transform it from a brush-like to a mushroom-like structure, with the OH groups of the PHEMA brushes becoming buried within the PHEMA thin film to form hydrophilic domains; (III) The ferritin species on the PHEMA thin film surface are removed through degradation of the protein sheath under O₂ in an oven at ca. 500 °C to observe the ferrihydrite cores. Reprinted from Reference [204] with permission.

Figure 17.

(a) Schematic representation of the process used to fabricate chemically nanopatterned surfaces of PS-b-PNIPAAm brushes; (b) Reversible Hydrophobic/Hydrophilic adhesive of PS-b-PNIPAAm copolymer brush nanopillar arrays for mimicking the climbing aptitude of geckos. Reprinted from Reference [223] with permission.

Figure 18.

Schematic representation of the PNIPAm-grafted pore-array with different PNIPAm layer thickness, AFM images and thermally responsive wettability induced water droplet profile changes at two different temperatures of (a) ZnO pore-array and PNIPAm-grafted (b) S1; (c) S2; and (d) S3 substrates. Reprinted from Reference [231] with permission.

Figure 19.

(a) Cross section profile of a one-dimensional periodic subwavelength grating; (b) One-dimensional periodic subwavelength gratings; (c) Symmetric two-dimensional subwavelength relief gratings; symmetric two-dimensional subwavelength concave gratings. Reprinted from Reference [232] with permission.

Figure 20.

(a) Geometrical parameters and/or refractive index contrast of a 2DPCG typically change with the temperature resulting color change [238]; (b) neff response and calculated filling factor of 2DPRG of tethered PMMA layer as a function of solvent species for volatile organic compounds (VOC) exposing in the order of chloroform (A); 1,2-dichloroethane (DCE) (B); dioxane (C); toluene (D); tetrahydrofuran (THF) (E); cyclohexane (F); acetone (G); and in dry state (H). Photographic images demonstrate the grating effect of the 2DPRG under VOC exposing of chloroform, dioxane, THF, and acetone, from left to right. Reprinted from Reference [239] with permission.

Figure 21.

(a) Spectroscopic characterization of the porous gel. Photographs and reflection spectra of the porous poly(NIPA-co-AAB) gel in the dark at various temperatures; (b) Multicolor photochromic behavior of the porous gel. Photographs and reflection spectra of the porous poly(NIPA-co-AAB) gel in water at 19, 21, and 24 °C before UV irradiation and after the equilibrium degree of swelling had been reached in response to the UV irradiation (366 nm, 8.0 m·W·cm⁻²). Reprinted from Reference [241] with permission.

Figure 22.

(a) Schematic representation of the process used to fabricate the MAHA-modified NPLA. (A) Silicon oxide film was deposited through plasma-enhanced chemical vapordeposition; the surface was then treated with HMDS in a thermal evaporator; (B) Negative photoresist was spun onto the HMDS-treated surface to pattern the photoresistas a 200-nm-scale NPLA; (C) Only the exposed regions of silicon dioxide were dry-etched by supplying a mixture gas of CHF3and CF4; the remaining photoresist hard maskwas then removed from the surface through the action of solvents; (D) The NPLA of silicon oxide was treated with APTES to assemble an array of amino groups; (E) The NPLApresenting amino groups was treated with a solution of EDC and NHS to immobilize proG on the pillar surfaces; MAHA units were oriented on the proG-modified pillarsurface; the presence of MHHA could be detected through ellipsometry [261]; (b) Values of n_eff, measured using ellipsometry, of (A) bare 2DPRG; (B) proG-2DPRG; (C) MAHA-modified 2DPRG; (D) MAHA-modified 2DPRG after coupling with MHHA; and (E) MAHA-modified 2DPRG after binding BSA (control). Photographic images for (A)–(C) and (D) demonstrate the grating effect of the 2DPRG. Reprinted from Reference [262] with permission.

Figure 22.

(a) Schematic representation of the process used to fabricate the MAHA-modified NPLA. (A) Silicon oxide film was deposited through plasma-enhanced chemical vapordeposition; the surface was then treated with HMDS in a thermal evaporator; (B) Negative photoresist was spun onto the HMDS-treated surface to pattern the photoresistas a 200-nm-scale NPLA; (C) Only the exposed regions of silicon dioxide were dry-etched by supplying a mixture gas of CHF3and CF4; the remaining photoresist hard maskwas then removed from the surface through the action of solvents; (D) The NPLA of silicon oxide was treated with APTES to assemble an array of amino groups; (E) The NPLApresenting amino groups was treated with a solution of EDC and NHS to immobilize proG on the pillar surfaces; MAHA units were oriented on the proG-modified pillarsurface; the presence of MHHA could be detected through ellipsometry [261]; (b) Values of n_eff, measured using ellipsometry, of (A) bare 2DPRG; (B) proG-2DPRG; (C) MAHA-modified 2DPRG; (D) MAHA-modified 2DPRG after coupling with MHHA; and (E) MAHA-modified 2DPRG after binding BSA (control). Photographic images for (A)–(C) and (D) demonstrate the grating effect of the 2DPRG. Reprinted from Reference [262] with permission.

Figure 23.

Confocal images demonstrating the release of rhodamine 6G from the polymer-grafted particles at 50 °C: (A) at t = 0 min; (B) at t = 7 min; (C) Fluorescence intensity line profiles taken from the horizontal midline of the image of the particle as a function of time. Reprinted from Reference [267] with permission.

Figure 24.

Images of the repeated bending and stretching motion of the poly[NIPAAm-co-Ru(bpy)3-co-AMPS] gel strip (R10-A3) in the mixture solution of the BZ substrates. First, the whole gel strip was homogeneous reduced state. Second, the gel strip is in a locally oxidized state when the chemical wave propagates in the gel from one edge to the other edge (1 → 4). Finally, the whole gel strip change reduced state, and was bending (5 → 6). Reprinted from Reference [284] with permission.

Figure 25.

Schematic design of a hydrogel-based microvalve: 1, inlet; 2, outlet; 3, flow channel; 4, actuator chamber filled with hydrogel particles; 5, structure layer; 6, heating meander (located at backside); 7, circuit card; 8, temperature sensor (located at topside); (a) closed state at room temperature; (b) open state (gel actuator is heated above TC). Reprinted from Reference [199] with permission.