Polyelectrolyte multilayers have received broad interests in the fields of functional coatings due to their easy deposition procedure, environmentally friendly nature and wide sensitivities to manifold external stimuli. Stimuli-triggered generation of nanoscopic structures on polyelectrolyte multilayers can be reversible generally when their structural size is less than dozens of nanometers. Transforming larger structures reversibly would represent a breakthrough of these materials for novel applications. Herein, we report that surface structures up to hundreds of nanometers can be developed on exponentially growing polyelectrolyte multilayers reversibly, which feature the diffusion of polyelectrolytes throughout the whole assemblies. These multilayers are prepared utilizing pH-amplified layer-by-layer assembly of branched polyethylenimine and photo-reactive poly(acrylic acid) azido derivative. Other than applying a single stimulus on the mobility of polymeric chains, the surface structures were developed by inducing electrostatic repulsion between chains in aqueous phases while subsequently erased by shielding supramolecular electrostatic interactions in gaseous phases. These processes are completely reversible and one potential application of this dynamic platform is to be a “smart” material for reversible visualization of various high-definition patterns with fine brightness contrast, which can be especially significant in some cutting-edge fields like the Internet of Things, information encryption/decryption and anti-counterfeiting. Beyond that, such dynamic platform can be very useful in many other research fields, such as surface wettability and smart homes.
Intelligent or smart polymer materials are those which are either “active” or responsive to a variety of environmental stimuli, such as changes in pH, temperature, ionic strength or electric field, or the presence of a specific chemical substrate. A thermally sensitive polymer, poly(N-isopropylacrylamide) (PNIPAAm), has been of great interest because aqueous solutions of PNIPAAm undergo fast, reversible switching of hydrophilicity/hydrophobicity around 32 °C at their lower critical solution temperature (LCST) of about 29–38 °C (different with variations in their structure). PNIPAAm chains show an expanded conformation in water below the LCST because of strong hydration and change to the compact forms above the LCST by sudden dehydration; this is the reversible switching effect of hydrophilic to hydrophobic. These switchable materials may have wide applications in functional textiles, controllable drug release and special fibers. Electrospinning is a simple, convenient, and versatile technique for generating fibers with diameters that range from several micrometers to tens of nanometers. Herein, we report an electrospinning method to prepare nano PNIPAAm fiber and their thermal response was characterized. Based on the results, the diameters of the PNIPAAm nanofibers within the respective system were around 200 nm and beads-less; they were successfully prepared by an electrospinning method in all cases and the reversible switching with LCST (32 °C) feature was observed clearly in the fibers.
危险品化学品经营许可证（带存储）