Light-Responsive Polymer Surfaces via Postpolymerization Modification of Grafted Polymer-Brush Structures

Abstract

Light-induced, spatially well-defined, reversible switching of surface properties enables the creation of remote-controlled smart surfaces. We have taken advantage of the unique high-resolution structuring capabilities of extreme ultraviolet (EUV) interference lithography to produce nanostructured photoresponsive polymer brushes. Patterns of poly(glycidyl methacrylate) (PGMA) and poly(methacrylic acid) (PMAA) were grafted from two different 100 μm thick fluoropolymer substrates by means of a radiation-initiated, grafting-from approach based on free-radical polymerization (FRP). Photochromic properties were introduced via novel one- or two-step postpolymerization modifications with spiropyran (SP) derivatives, which allowed us to control the number of photochromic groups on the polymer brushes. Depending on the degree of functionalization and the local chemical environment, the SP moieties can open upon UV-light exposure to form zwitterionic, deeply colored, and fluorescent merocyanines (MCs) and reclose to the colorless SP configuration via thermal or visible light-induced relaxation. Switching kinetics were studied by means of time-resolved fluorescence microscopy and compared with kinetic measurements of the SP moiety in solution. The results indicated the importance, for the intensity of the switching, of the local chemical environment provided by both the polymer brush and added solvents, and showed the predominant influence on the ring-closing kinetics of polar solvents, which stabilize the MC form. To allow further characterization of the polymer-brush arrangements on a macroscopic scale, similar, but unstructured brush systems were grafted from fluoropolymers after large-area activation using EUV radiation or argon plasma. All steps of the postpolymerization modification were characterized in detail using attenuated total reflection infrared (ATR-IR) spectroscopy. Furthermore, a light-induced reversible static-contact-angle switch with a range of up to 15° for PGMA-SP brushes and up to 30° for PMA-SP brushes was demonstrated upon alternating UV- and visible-light irradiation.

Fabrication of Thiol–Ene “Clickable” Copolymer-Brush Nanostructures on Polymeric Substrates via Extreme Ultraviolet Interference Lithography

“…This has been described in detail in a previous publication. 56 In brief, ETFE samples were exposed to EUV light with a central wavelength of 13.5 nm under vacuum. Patterns of radicals were created on the polymeric surfaces by irradiation through silicon nitride masks with chromium gratings of different periods in a dedicated interference lithography setup at the Swiss Light Source.…”

“…The measurement strategy using a Hyperion 3000 IR microscope (Bruker, Fallanden, Switzerland) equipped with an ATR objective with a circular contact area with 100 um diameter has been described in detail in previous work. 56 2.7. Water Contact Angle Determination.…”

“…The color switch could also be detected in the appearance of a strong absorbance band in the transmission spectra around 570 nm, which is in the typical range for spiropyrans (Figure 6b). 56 The heterocyclic spiropyrans carry a chromene moiety, which is orthogonally linked through a spiro-carbon atom. UV-light causes the reversible heterolytic cleavage of the sp 3 carbon−oxygen bond, forming the planar zwitterionic open form of the deeply colored merocyanine.…”

ON/OFF switching of silicon wafer electrochemistry by pH-responsive polymer brushes

“…[11][12][13][14] They enable the development of functional interfaces with switchable properties controlled by external physical (e.g. heat, 15 light, 16 electricity, 17 and magnetism 18 ) or chemical (e.g. the presence or absence of chemicals, variation of their concentrations) inputs and have therefore received considerable attention in the last two decades.…”

Functional Polymer-on-Polymer Structures

“…Recently, we explored strategies for binding spiropyran moieties to structured brushes grafted from ETFE and Teflon (PTFE) surfaces in order to obtain light-sensitive structured polymer surfaces [18]. We focused on post-polymerization modification of grafted brush structures because this strategy increases the flexibility with respect to the optimization of the concentration of spiropyran moieties in the brushes.…”