Photomechanical effects realized in azobenzene-functionalized polyimides have shown large deformation and an exceptional increase in photogenerated force output. Here, we synthesize and characterize the photomechanical output of a series of linear polyimide materials prepared with a bulky substituent, incorporated via the development of a new bis­(azobenzene-diamine) monomer containing a 9,9-diphenylfluorene cardo structure (azoCBODA). All six azoCBODA-containing polyimides are amorphous and exhibit high glass transition temperatures (T g) ranging from 298 to 358 °C, storage moduli ranging from 2.27 to 3.81 GPa (at 30 °C), and good thermal stability. The magnitude of the photoinduced mechanical response of the azobenzene-functionalized polyimide is correlated to the rotational freedom of the polyimide chains (resulting in extensive segmental mobility) and fractional free volume (FFV > 0.1).

onto printed circuit designs, and printing all electronic components onto commercially available textiles. [4][5][6][7][8][9][10][11][12] Sporting goods companies have envisioned a clothing system with integrated touchscreen capabilities that combines functionality with convenience. [13] This clothing would monitor heart rate, record body temperature, and change color. Electrochromic fabrics, which change color upon application of an electric potential, [14] would give the user the ability to create their own designs and upload it directly to their clothing. For the military, a soldier's clothing could be constantly shifting to the most optimal color scheme as their surroundings change.Textile-based electrochromic devices, unlike most conjugated polymer based electrochromic devices, are reflective in nature. They consist of an electrochromic polymer-coated working electrode separated from a counter electrode by a layer of electrolytic gel. Invernale and co-workers reported the fabrication of color changing spandex using poly (3,4-ethylene dioxythiophene):poly (styrene sulfonate) (PEDOT: PSS) coated fabrics as electrodes and poly (BEDOT-T-Sil (Octyl) 2 ) as an electrochromic material. [15] The fabricated electrochromic devices showed a color change from blue to red with a switching speed of ≈15 s. The spandex based electrochromic fabric display (EFD) showed color change even when stretched to 20% of its dimensions though a decrease in color density was observed upon stretching. These devices, while flexible and stretchable, are dual layer devices which would result in a thicker, bulkier garment.The factors determining the expression of color and switching speed of a device are the conductivity of the material, the electrochemical potential window of the electrodes, and the color of the fabric on which the EFD is constructed. [16] In the case of PEDOT:PSS electrodes, the stable window is +/− 2 V. Recent studies on PEDOT:PSS based transmissive devices have shown that having the electrochromic material switch well below the window of the electrode increases the stability of the device. [15,17] For fabric devices, using an electrochromic polymer that switches at low voltages would reduce the expression of PEDOT:PSS in the overall color of the material. Invernale and co-workers investigated color transitions as a function of underlying fabric color and found that bright colors give greater electrochromic contrast than dark colors. [18] Current wearable technology is often bulky and restrictive to fluid movement. This work details a single-layer, hydrophobic, printed electrochromic textile that switches wirelessly from red to blue with a switching speed ≈30 s. Using a hole-through fabrication method, the flexible devices offer aesthetics to the display by concealing all electronic connections on their backsides while maintaining their "fabric" feel. First, an all organic electrochromic planar textile device is fabricated by screen printing commercially available poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) ...

The classical "chair-twist boat−boat" conformational dynamics (CD) of cyclohexane is thermally activated. Here we report on the photoinduced/azobenzene-assisted CD of bilaterally fused cyclohexane moieties contributing to large photomechanical response of cross-linked azobenzene-functionalized polyimides (X-azoPI), based on 1,2,4,5-cyclohexane-tetracarboxylic-dianhydride (CHDA), exhibiting a photobending angle and photogenerated stress, up to ∼90°and 370 kPa, respectively. In contrast, X-azoPI containing planar pyromellitimide (PMDI) or cage-like bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic-diimide (BCDI) show smaller photomechanical responses. The superior photomechanical performance of X-azoPI with constrained cyclohexane-diimide (CHDI) units is attributed to an increased mobility of segments comprising "hinged" p-phenylene rings, azobenzene, and CHDI units in the cross-link sites. Blue light irradiation initiates the motions driven by photoisomerization/reorientation of azobenzenes connected to CHDI units, whose CD is then amplified, leading to longer-range segmental mobility, more local free volume, and culminating in large photoinduced bending. The trapping of redistributed CHDI's stereoisomers in X-azoPI backbone at T room is implicated for the observed photothermal memory.

Flexible films having high dielectric constants with low dielectric loss have promising application in the emerging area of high‐energy‐density materials. Here, for the first time, an organometallic, Sn‐polyester‐containing hybrid free‐standing film in polyimide matrix is reported. Polyimide, pBTDA‐HDA, is used with poly(dimethyltin glutarate) and poly(dimethyltin‐3,3‐dimethyglutarate) (pDMTDMG) for having a processable film with tunable dielectric properties. Hybrid film with 60% pDMTDMG and 40% PI (HB2) is found to have improved dielectric features over previously synthesized organic polyimide and organometallic Sn‐polyester homopolymers. These novel organometallic–organic hybrid systems expanded a new area of dielectrics for next‐generation electronics with superior overall electrical performance.

Dielectric materials are a class of materials that are polarized under an electric field. Typically, highly polarizable, or high dielectric materials are used in energy storage applications such as a capacitor. Materials that have high dielectric constant, low dielectric loss, and high breakdown strength, have high energy density. Other important criteria for choosing a dielectric candidate include good thermal and mechanical stability. For their ease of processability and light weight applications, many polymer dielectrics are currently used commercially. Moreover, research to discover new materials to meet growing demand for lighter and more efficient materials has been ongoing. This article provides information on the basic principles of a capacitor, what makes a good dielectric material for capacitor energy storage applications, common dielectric polymers and their properties, as well as the exploration of next generation dielectric materials. Finally, an examination of current efforts to explore new dielectric materials and how they can be further tuned with the help of theoretical computations and experimental validation, are discussed.

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To discern multiple intertwined effects, a set of azobenzene-functionalized amide–imide block copolymers, azo­(PA-co-PI)-x, where x is amide-block content, viz., [azoPA] = 25, 50, 75 mol %, was synthesized from 2,2-bis­{4-[4-(4-aminophenyldiazenyl)­phenoxy]­phenyl}­propane­(azoBPA), 4,4′-oxydibenzoyl chloride (ODBC), and 4,4′-oxydiphthalic anhydride (OPDA). Including homopolymers (azoPA and azoPI), this series of amorphous azopolymers possesses a high glass-transition temperature (T g > 210 °C) and a modulus (E′ ∼ 1.23–2.50 GPa). Their photobending (ca. 23–90°) and photostress (ca. 250–380 kPa) were assessed in the form of cantilevers with a linearly polarized 445 nm light. Nonlinear composition/[azoPA] dependencies of the thermo- and photomechanical properties are correlated. As [azoPA] increases from 0 mol %; T g, E′, photostress, and photobending angle initially decrease to reach four separate minima for azo­(PA-co-PI)-50; and then all increase with a higher [azoPA]. The trend considerations of film density, dynamic thermomechanical, Fourier transform infrared (FT-IR), and ultraviolet–visible (UV–vis) measurements implicate that (i) intermolecular association and intramolecular segmental mobility collectively influence the photomechanical outcomes and (ii) two types of hydrogen bonding (HB), namely, amide–amide [HB-AA] and amide–imide [HB-AI] coexist in azo­(PA-co-PI)-x copolymers, with [HB-AI] being largely responsible for photomechanical outcomes of azo­(PA-co-PI)-x with [azoPA] <40–50 mol %, and [HB-AA] for [azoPA] >40–50 mol %. We hypothesize that the “U-shaped” photomechanical effect apparently stems from the cooperative “unzipping” of H bonds in the [HB-AA]* excited state with H bonds in [HB-AI]* being stabilized by electrostatic interactions inherent in an excited intermolecular complex.

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