Ionic shape memory polymer gels as multifunctional sensors.

Novel ionic shape memory polymer (SMP) gels were fabricated using SMPs and ionic liquids (ILs) of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) at different weight ratios (WIL). The shape memory effect and sensor performance of the ionic SMP gels were investigated by means of thermomechanical and mechanoelectrical analyses. It was found that the ionic SMP gel at WIL = 25 wt% showed a shape memory effect with the shape fixing ratio (Rf) and shape recovery ratio (Rr) of 72.7% and 72.9%, respectively. Upon bending, the ionic SMP gel sensors with PEDOT:PSS electrodes generated an open circuit voltage of 3.3 mV and a charge of 1.6 nC which linearly increased with increasing bending displacement and velocity, respectively. Furthermore, the wearable shape memory multifunctional sensor array was demonstrated as a self-powered motion sensor for IoT applications.

Fully soluble self-doped poly(3,4-ethylenedioxythiophene) with an electrical conductivity greater than 1000 S cm-1.

Wet-processable and highly conductive polymers are promising candidates for key materials in organic electronics. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is commercially available as a water dispersion of colloidal particles but has some technical issues with PSS. Here, we developed a novel fully soluble self-doped PEDOT (S-PEDOT) with an electrical conductivity as high as 1089 S cm-1 without additives (solvent effect). Our results indicate that the molecular weight of S-PEDOT is the critical parameter for increasing the number of nanocrystals, corresponding to the S-PEDOT crystallites evaluated by x-ray diffraction and conductive atomic force microscopic analyses as having high electrical conductivity, which reduced both the average distance between adjacent nanocrystals and the activation energy for the hopping of charge carriers, leading to the highest bulk conductivity.

Thermo-responsive nanofiber mats fabricated by electrospinning of poly(N-isopropylacrylamide-co-stearyl acrylate).

Copolymers of N-isopropylacrylamide and stearyl acrylate (PNIPA-SAX) with various SA feed ratios (X = 1-10 mol%) were synthesized and electrospun into nanofiber mats. It was found that average diameter of nanofibers electrospun at concentration of 25% and voltage of 30 kV linearly increased from 165 nm (PNIPA) to 497 nm (PNIPA-SA10) with increasing the SA content. The PNIPA-SAX (X = 3-10 mol%) nanofiber mats were insoluble in water at 25 degrees C, in which inter-polymer and interfiber physical cross-links were formed through hydrophobic interaction of stearyl side-chains. With increasing the temperature from 25 to 40 degrees C the PNIPA-SA3 nanofiber mat exhibited significant volume contraction of 66%, while that of a single nanofiber estimated by AFM measurements was found to be 37%. The results allowed us to conclude that not only swelling-deswelling but also dissociation-association of the nanofibers via hydrophobic interactions were crucially important for the macroscopic volume changes of the nanofiber mats.

Electromechanical properties of poly(3,4-ethylenedioxythiophene)/poly(4-styrene sulfonate) films.

Free-standing films made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrene sulfonate) (PEDOT/PSS) were prepared by casting water dispersion of its colloidal particles. Morphology, water vapor sorption, and electro-active polymer actuating behavior of the resulting films were investigated by means of atomic force microscopy, sorption isotherm, thermal mechanical analysis, and electromechanical analysis. It was found that the PEDOT/PSS film sorbed 60% of moisture at relative water vapor pressure of 0.95. Upon application of 10 V, the film underwent contraction of 2.4% in air at 50% relative humidity (RH) which significantly increased to 4.5% at 90% RH. The principle lay in desorption of water vapor sorbed in the film due to Joule heating, where electric field was capable of controlling the equilibrium of water vapor sorption. The film generated contractile stress as high as 17 MPa under isometric conditions and work capacity attained 174 kJ m(-3), where Young's modulus of the film increased from 1.8 to 2.6 GPa by application of 6 V at 50% RH.