Photoresponsive Superhydrophobic Membrane Crosslinked by Bipedal Pillararenes with Patterned Wettability

Abstract

Electrospraying is a physical process used for the production of nano-to microparticles membranes from polymer liquid atomization using electrical forces. [23][24][25] It has been well documented that relative humidity (RH) has a great impact on the porosity of the obtained particles during the electrospraying process. [26,27] Therefore, it is a smart way to craft a membrane with hierarchical structures by using supramolecules, for instance, polypseudorotaxane (PPR), via integrating electrospraying with breath figure approach (where breath figure method is a facile fabrication process of porous films because of the formation of the water droplet array when water vapor contacts a cold substrate). [12,[28][29][30][31] PPR represents the linear guest molecules encircled by host molecules via hostguest interaction. [32][33][34] Functional or multipedal host molecules have been used to generate guest molecules, such as traditional covalent polymers, with unique physical characteristics or form a distinct class of crosslinked supramolecule as well as supramolecular organic framework (SOF). [34][35][36][37][38][39] Here, we report a crosslinked PPR based on the selective recognition of dimethoxypillar[5]arene (DMP5A) on an azobenzene-containing host molecule, i.e., DMP5A-Azobenzene-DMP5A (P5-Azo-P5) to the PCL block of PCL-b-PEG-b-PCL, which provides a simple strategy to functionalize traditional covalent polymers. Then the PPR was used to fabricate a crosslinked supramolecular membrane by electrospraying under 50% RH and 90% RH (denoted CSM-50 and CSM-90), respectively. CSM-50 and CSM-90 displayed significantly different wettability. The force-distance test measuring the adhesion of membrane revealed that the average value of water adhesion force of CSM-50 was over five times bigger than that of CSM-90, which resulted from the dramatic variation of the external and internal nanostructures. The water droplet could be stuck to the inverted CSM-50 for trace liquid transportation while it could roll randomly on the surface of CSM-90 for self-cleaning purpose. In addition, owing to the reversible trans-cis isomerization of azobenzene, CSM-90 underwent rapid increase of water adhesion force and color conversion in response to UV irradiation. These rules provide us the capability to design the wettability of CSM-90 in the vertical and horizontal directions dissimilarly via re-electrospraying under 50% RH or UV light irradiation with patterned photomask.

Photoinduced Contraction Fibers and Photoswitchable Adhesives Generated by Stretchable Supramolecular Gel

“…The reversible sol-to-gel phase transition was realized via cooling and heating (Figure S3, Supporting Information) and the process of gel-to-sol was achieved by adding competitive guest (1,4-dibromobutane, DBrBu) (Figure S5, Supporting Information), both of which were proved by 1 H NMR spectra (Figure S4, Supporting Information, and previous work). [44] In general, a self-assembled crosslinked supramolecular gel with dual responsiveness has been successfully obtained.…”

“…As seen in Figure 2e,f, the curves show that the main contraction deformation occurs within 50 s of 365 nm light irradiation, followed by a slight increase from 50 to 300 s, which is related to the fast photoisomerization of azo units. [44] The diameters of xerogel fibers with different molar ratios of host to guest were controlled to be nearly 7 µm (d 1.6eq. = 7.12 µm, d 2.4eq.…”

“…The 1D and 2D extension of supramolecular gel represent an unexpected strategy toward the fabrication of smart materials. [43,44] The time required for gelation upon cooling and resting was 6 h and the sol-gel phase transition diagram was tested by the tube-inverting method (Figure S1, Supporting Information). The host-guest interaction causes different parts to cluster into a noncovalently bonded network that retains organic solvent.…”

Photoresponsive Electrospun Nanowire Films Based on N-Isopropylacrylamide and Spiropyran for Regulating Microenvironmental Humidity

“…14,15 The wettability and other special physical properties of photoresponsive materials can be easily adjusted by changing other factors such as the wavelength and intensity of light. 16,17 Stimulus-responsive polymers have been attracting a great deal of interest from the scientific community. In addition to temperature as a physical stimulus, light has attracted equal attention in the field of stimulus-responsive polymers.…”

“…has been studied extensively. In particular, light stimulation has received much attention because it is inexpensive, environmentally friendly, and readily available. , The wettability and other special physical properties of photoresponsive materials can be easily adjusted by changing other factors such as the wavelength and intensity of light. , …”