Stretchable semiconducting polymers have been developed as a key component to enable skin-like wearable electronics, but their electrical performance must be improved to enable more advanced ...functionalities. Here, we report a solution processing approach that can achieve multi-scale ordering and alignment of conjugated polymers in stretchable semiconductors to substantially improve their charge carrier mobility. Using solution shearing with a patterned microtrench coating blade, macroscale alignment of conjugated-polymer nanostructures was achieved along the charge transport direction. In conjunction, the nanoscale spatial confinement aligns chain conformation and promotes short-range π-π ordering, substantially reducing the energetic barrier for charge carrier transport. As a result, the mobilities of stretchable conjugated-polymer films have been enhanced up to threefold and maintained under a strain up to 100%. This method may also serve as the basis for large-area manufacturing of stretchable semiconducting films, as demonstrated by the roll-to-roll coating of metre-scale films.
Recently, confinement of polymers with different geometries has become a research hotspot. Here, we report the dramatic deviation of glass transition behaviors of poly(methyl methacrylate) (PMMA) ...confined in cylindrical nanopores with diameter significantly larger than chain’s radius of gyration (R g ). Fast cooling a PMMA melt in the nanopores results in a glass with one single glass transition temperature (T g). But two distinct T gs are detected after slow cooling the melt. The deviation in T g could be as large as 45 K. This phenomenon is interpreted by a two-layer model. During vitrification under slow cooling two distinct layers are formed: a strongly constrained interfacial layer showing an increased T g as compared to that of the bulk polymer and a core with a decreased T g. By thermal annealing experiments, we find that these two T gs are inherently correlated. In addition, the deviation of T g for PMMA confined in nanopores reveals a dependence on molecular weight.
Soft and conformable wearable electronics require stretchable semiconductors, but existing ones typically sacrifice charge transport mobility to achieve stretchability. We explore a concept based on ...the nanoconfinement of polymers to substantially improve the stretchability of polymer semiconductors, without affecting charge transport mobility. The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon. The fully stretchable transistors exhibit high biaxial stretchability with minimal change in on current even when poked with a sharp object. We demonstrate a skinlike finger-wearable driver for a light-emitting diode.
The understanding of the structure‐mechanical property relationship for semiconducting polymers is essential for the application of flexible organic electronics. Herein pseudo free‐standing tensile ...testing, a technique that measures the mechanical property of thin films floating on the surface of water, is used to obtain the stress–strain behaviors of two semiconducting polymers, poly(3‐hexylthiophene) (P3HT) and poly(2,5‐bis(2‐decyltetradecyl)‐3,6‐di(thiophen‐2‐yl)diketopyrrolo3,4‐cpyrrole‐1,4‐dione‐alt‐thienovinylthiophene (DPP‐TVT) donor–acceptor (D–A) polymer. To our surprise, DPP‐TVT shows similar viscoelastic behavior to P3HT, despite DPP‐TVT possessing a larger conjugated backbone and much higher charge carrier mobility. The viscoelastic behavior of these polymers is due to sub room temperature glass transition temperatures (Tg), as shown by AC chip calorimetry. These results provide a comprehensive understanding of the viscoelastic properties of conjugated D–A polymers by thickness‐dependent, strain rate dependent, hysteresis tests, and stress‐relaxation tests, highlighting the importance of Tg for designing intrinsically stretchable conjugated polymers.
A single stretch test and cyclic hysteresis test are conducted using pseudo‐free standing tensile test and the stress‐strain curves are shown for poly(2,5‐bis(2‐decyltetradecyl)‐3,6‐di(thiophen‐2‐yl)diketopyrrolo3,4‐cpyrrole‐1,4‐dione‐alt‐thienovinylthiophene (DPP‐TVT) donor‐acceptor (D‐A) polymers.
In order to apply polymer semiconductors to stretchable electronics, they need to be easily deformed under strain without being damaged. A small number of conjugated polymers, typically with ...semicrystalline packing structures, have been reported to exhibit mechanical stretchability. Herein, a method is reported to modify polymer semiconductor packing‐structure using a molecular additive, dioctyl phthalate (DOP), which is found to act as a molecular spacer, to be inserted between the amorphous chain networks and disrupt the crystalline packing. As a result, large‐crystal growth is suppressed while short‐range aggregations of conjugated polymers are promoted, which leads to an improved mechanical stretchability without affecting charge‐carrier transport. Due to the reduced conjugated polymer intermolecular interactions, strain‐induced chain alignment and crystallization are observed. By adding DOP to a well‐known conjugated polymer, poly2,5‐bis(4‐decyltetradecyl)pyrrolo3,4‐cpyrrole‐1,4‐(2H,5H)‐dione‐(E)‐1,2‐di(2,2′‐bithiophen‐5‐yl)ethene (DPPTVT), stretchable transistors are obtained with anisotropic charge‐carrier mobilities under strain, and stable current output under strain up to 100%.
Bulky additive molecules residing between amorphous chain networks can disrupt the crystalline ordering of polymer semiconductors. The long‐range crystalline domains are suppressed while short‐range aggregations of conjugated polymers are promoted, leading to an improved thin‐film stretchability without affecting charge transport under an external strain up to 100%.
Mechanical failure of π‐conjugated polymer thin films is unavoidable under cyclic loading conditions, due to intrinsic defects and poor resistance to crack propagation. Here, the first tear‐resistant ...and room‐temperature self‐healable semiconducting composite is presented, consisting of conjugated polymers and butyl rubber elastomers. This new composite displays both a record‐low elastic modulus (<1 MPa) and ultrahigh deformability with fracture strain above 800%. More importantly, failure behavior is not sensitive to precut notches under deformation. Autonomous self‐healing at room temperature, both mechanical and electronic, is demonstrated through the physical contact of two separate films. The composite film also shows device stability in the ambient environment over 5 months due to much‐improved barrier property to both oxygen and water. Butyl rubber is broadly applicable to various p‐type and n‐type semiconducting polymers for fabricating self‐healable electronics to provide new resilient electronics that mimic the tear resistance and healable property of human skin.
A mechanically durable and electronically stable semiconducting composite is engineered by introducing a blend of donor–acceptor polymer and butyl rubber elastomer. The composite exhibits ultralow modulus, ultrahigh deformability, tear resistance, and self‐healing performance, as well as ambient stable device stability. This method is widely applicable to different semiconducting polymers.
Diketopyrrolopyrrole (DPP)-based donor–acceptor conjugated polymers, with increasing amount of weak H-bonding units, namely 2,6-pyridinedicarboxamide (PDCA), inserted as end groups in alkyl side ...chains were prepared and investigated. In contrast to previously reported DPP polymers containing PDCA units as conjugation breakers along the polymer backbone, PDCA in the alkyl side chains readily produced almost quantitative formation of intermolecular H-bonding even at low PDCA unit content (<10 mol %) as shown by Fourier transform infrared spectroscopy (FTIR). The efficient intermolecular H-bonding was further supported by the appearance of a pronounced vibronic shoulder in the UV–vis spectra and a reduction of interlamellar spacing (from 24.02 to 22.87 Å) compared to the neat DPP polymer. Increasing mol % of PDCA units in side chains of DPP conjugated polymers also has a clear effect on the thermal and mechanical properties of the films as investigated by dynamic mechanical analysis (DMA). Polymers with a high loading of PDCA showed a linear increase in both tan delta intensity and temperature at which softening of film cross-linking occurs. In particular, at a comparable mol %, polymers with PDCA units along the conjugated backbone showed a lower transition intensity and on average a 10–20 °C higher temperature required for H-bonding breaking. FTIR coupled with crack onset measurements showed that H-bonding breaking during tensile deformation happens only at strains close to crack onset. All these observations suggest that molecular engineering of conjugated polymers bearing H-bonding units has a strong influence on microstructure, thermal and mechanical properties of solution processed films, and final energy dissipation mechanisms in stretchable electronics applications.
This study aims to investigate the crystallization behavior and molecular dynamics of amorphous griseofulvin (GSF) in the presence of low-concentration poly(ethylene oxide) (PEO). We observe that ...the addition of 3% w/w PEO remarkably increases the crystal growth rate of GSF by two orders of magnitude in both the supercooled liquid and glassy states. The liquid dynamics of amorphous GSF in the presence and absence of PEO are characterized by dielectric spectroscopy. With an increase of the PEO content, the α-relaxation times of the systems decrease, indicating the increase of global molecular mobility. The couplings between molecular mobility and crystallization kinetics of GSF systems show strong time-dependences below T g. The overlapping of α-relaxation times of GSF in presence and absence of PEO as a function of T g/T suggest the “plasticization” effect of PEO additives. However, the crystallization kinetics of amorphous GSF containing low-concentration PEO do not overlap with those of pure GSF on a T g/T scale. The remarkable accelerating effect of crystal growth of amorphous GSF by low-concentration PEO can be partially attributed to the increase of global mobility. The high segmental mobility of PEO is expected to strongly affect the crystal growth rates of GSF. These findings are relevant for understanding and predicting the physical stability of amorphous pharmaceutical solid dispersions.
Understanding the interfacial molecular structures of antifouling polymers in solutions is extremely important in research and applications related to chemistry, biology, and medicine. However, it is ...generally challenging to probe such buried solid/liquid interfaces in situ. We herein report a molecular-level study on detecting the interfacial molecular structures of an antifouling hydrogel material, poly(2-hydroxyethyl methacrylate) (PHEMA), in contact with water and bovine serum albumin (BSA) solution in situ using sum frequency generation (SFG) vibrational spectroscopy. To compare to and validate our in situ experiments, molecular-level structures of the substrate/PHEMA interface before and after water exposure were also detected. The detected strong O–H vibrational signals from water and hydroxyethyl and carbonyl vibrational signals from PHEMA prove that the PHEMA surface hydration was attributed to the interaction between water and PHEMA side hydrophilic groups. SFG experimental results verify that the adsorbed BSA molecules at the PHEMA/solution interface were disorderly arranged, supported by data from the laser scanning confocal microscopic (LSCM) experiment. This indicates the weak interaction between the BSA molecules and PHEMA surface. This direct detection of the surface hydrated structures of PHEMA sheds light on understanding the interfacial properties of antifouling materials in aqueous environments. The capability reported here to probe the PHEMA/solution interface and the hidden substrate/PHEMA interface after water exposure can be applied to investigate a broad range of interfaces of antifouling materials.
The kinetics of the isothermal reduction of iron ore–coke, iron ore–charcoal, and iron ore–biomass (straw) composite pellets were studied at 900–1200 °C. Compared with the other two composite ...pellets, the composite pellet using biomass as a reducing agent showed a more rapid reduction rate at a relatively low temperature. With an increase in the temperature, the reduction rates of the three different composite pellets tended to be equal. The reducing reactions of the three different composite pellets were all mainly controlled by gasification diffusion. The reduction rates can be described by the interface reaction kinetic model (1−(1−m)1/32=kt). The apparent activation energies of the gasification diffusion of coke, charcoal, and biomass composite pellets at 900–1200 °C were calculated using the Arrhenius equation, and they were 95.81, 71.67, and 58.69 kJ/mol, respectively. The biomass composite pellets exhibited a lower apparent activation energy than the composite pellets with other reduction agents.
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