Super-Helically Twisted Strands of Poly(m-phenylene isophthalamide) (MPDI)

Cathode Electrolyte Interphase Engineering for Prussian Blue Analogues in Lithium-Ion Batteries

The increasing use of low-cost lithium iron phosphate cathodes in low-end electric vehicles has sparked interest in Prussian blue analogues (PBAs) for lithium-ion batteries. A major challenge with iron hexacyanoferrate (FeHCFe), particularly in lithium-ion systems, is its slow kinetics in organic electrolytes and valence state inactivation in aqueous ones. We have addressed these issues by developing a polymeric cathode electrolyte interphase (CEI) layer through a ring-opening reaction of ethylene carbonate triggered by OH- radicals from structural water. This facile approach considerably mitigates the sluggish electrochemical kinetics typically observed in organic electrolytes. As a result, FeHCFe has achieved a specific capacity of 125 mAh g-1 with a stable lifetime over 500 cycles, thanks to the effective activation of Fe low-spin states and the structural integrity of the CEI layers. These advancements shed light on the potential of PBAs to be viable, durable, and efficient cathode materials for commercial use.

Real-Space Crystal Structure Analysis by Low-Dose Focal-Series TEM Imaging of Organic Materials with Near-Atomic Resolution

Structural analysis of beam-sensitive materials by transmission electron microscopy (TEM) represents a significant challenge, as high-resolution TEM (HRTEM) requires high electron doses that limit its applicability to stable inorganic materials. Beam-sensitive materials, e.g., organic crystals, must be imaged under low dose conditions, leading to problematic contrast interpretation and loss of fine structural details. Here, HRTEM imaging of organic crystalline materials with near-atomic resolution of up to 1.6 Å is described, which enables real-space studies of crystal structures, as well as observation of co-existing polymorphs, crystal defects, and atoms. This is made possible by a low-dose focal-series reconstruction methodology, which provides HRTEM images where contrast reflects true object structure and can be performed on contemporary cryo-EM instruments available to many research institutions. Copper phthalocyanine (CuPc), a perchlorinated analogue of CuPc, and indigo crystalline films are imaged. In the case of indigo crystals, co-existing polymorphs and individual atoms (carbonyl oxygen) can be observed. In the case of CuPc, several polymorphs are observed, including a new one, for which the crystal structure is found based on direct in-focus imaging, accomplishing real-space crystal structure elucidation. Such direct analysis can be transformative for structure studies of organic materials.

Flexible, Robust, and Durable Aramid Fiber/CNT Composite Paper as a Multifunctional Sensor for Wearable Applications

Flexible paper-based sensors may be applied in numerous fields, but this requires addressing their limitations related to poor thermal and water resistance, which results in low service life. Herein, we report a paper-based composite sensor composed of carboxylic carbon nanotubes (CCNTs) and poly-m-phenyleneisophthalamide (PMIA), fabricated by a facile papermaking process. The CCNT/PMIA composite sensor exhibits an ability to detect pressures generated by various human movements, attributed to the sensor's conductive network and the characteristic "mud-brick" microstructure. The sensor exhibits the capability to monitor human motions, such as bending of finger joints and elbow joints, speaking, blinking, and smiling, as well as temperature variations in the range of 30-90 °C. Such a capability to sensitively detect pressure can be realized at different applied frequencies, gradient sagittas, and multiple twists with a short response time (104 ms) even after being soaked in water, acid, and alkali solutions. Moreover, the sensor demonstrates excellent mechanical properties and hence can be folded up to 6000 times without failure, can bear 5 kg of load without breaking, and can be cycled 2000 times without energy loss, providing a great possibility for a long sensing life. Additionally, the composite sensor shows exceptional Joule heating performance, which can reach 242 °C in less than 15 s even when powered by a low input voltage (25 V). From the perspective of industrialization, low-cost and large-scale roll-to-roll production of the paper-based sensor can be achieved, with a formed length of thousands of meters, showing great potential for future industrial applications as a wearable smart sensor for detecting pressure and temperature, with the capability of electric heating.

Pushing the limits of high-resolution polymer microscopy using antioxidants

High-resolution transmission electron microscopy (HRTEM) has been transformative to the field of polymer science, enabling the direct imaging of molecular structures. Although some materials have remarkable stability under electron beams, most HRTEM studies are limited by the electron dose the sample can handle. Beam damage of conjugated polymers is not yet fully understood, but it has been suggested that the diffusion of secondary reacting species may play a role. As such, we examine the effect of the addition of antioxidants to a series of solution-processable conjugated polymers as an approach to mitigating beam damage. Characterizing the effects of beam damage by calculating critical dose DC values from the decay of electron diffraction peaks shows that beam damage of conjugated polymers in the TEM can be minimized by using antioxidants at room temperature, even if the antioxidant does not alter or incorporate into polymer crystals. As a consequence, the addition of antioxidants pushes the resolution limit of polymer microscopy, enabling imaging of a 3.6 Å lattice spacing in poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3″'-di(2-octyldodecyl)-2,2';5',2″;5″,2″'-quaterthiophene-5,5″'-diyl)] (PffBT4T-2OD).

Mapping structure and morphology of amorphous organic thin films by 4D-STEM pair distribution function analysis

Imaging the phase distribution of amorphous or partially crystalline organic materials at the nanoscale and analyzing the local atomic structure of individual phases has been a long-time challenge. We propose a new approach for imaging the phase distribution and for analyzing the local structure of organic materials based on scanning transmission electron diffraction (4D-STEM) pair distribution function analysis (PDF). We show that electron diffraction based PDF analysis can be used to characterize the short- and medium-range order in aperiodically packed organic molecules. Moreover, we show that 4D-STEM-PDF does not only provide local structural information with a resolution of a few nanometers, but can also be used to image the phase distribution of organic composites. The distinct and thickness independent contrast of the phase image is generated by utilizing the structural difference between the different types of molecules and taking advantage of the dose efficiency due to use of the full scattering signal. Therefore, this approach is particularly interesting for imaging unstained organic or polymer composites without distinct valence states for electron energy loss spectroscopy. We explore the possibilities of this new approach using [6,6]-phenyl-C61- butyric acid methyl ester (PC61BM) and poly(3-hexylthiophene-2,5-diyl) (P3HT) as the archetypical and best-investigated semiconductor blend used in organic solar cells, compare our phase distribution with virtual dark-field analysis and validate our approach by electron energy loss spectroscopy.

Effects of isomorphic poly(butylene succinate-co-butylene fumarate) on the nucleation of poly(butylene succinate) and the formation of poly(butylene succinate) ring-banded spherulites

The composition of isomorphic PBSF can dramatically affect the nucleation efficiency, the formation temperature of ring-banded spherulite and the band spacing of the PBS.

In vitro exposure of simulated meat-cooking fumes to assess adverse biological effects

The heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is considered as a human carcinogenic or mutagenic compound that is produced from the co-condensation of creatinine and amino acids as meats cook at high temperatures. The cooking of meats at high temperatures produces fumes, and these fumes can be suspended as aerosols via the vapor-to-particle (or -droplet) process in a temperature gradient field. Size distributions of the aerosols included a significant portion of nano- and submicron-sized particles, and these can be directly deposited in the lungs and on skin by particle transport phenomena near cooking areas. In this study, for the first time, PhIP-incorporated oleic acid (OA, simulating cooking oil) (PhIP@OA) particles, including individual particulate PhIP as simulated fumes from meat cooking, were constantly produced via collison atomization and subsequent drying processes. The aerosol particles were then dispersed in phosphate-buffered saline for cytotoxicity and senescence-associated β-galactosidase assays, which were compared with dissolved PhIP in dimethyl sulfoxide. PhIP and PhIP@OA did not show significant cytotoxic effects on SHSY5Y, MRC5, and human dermal fibroblast cells compared with the dissolved PhIP but clearly induced premature senescence activities that may be caused by a limited release of PhIP molecules from the particulate PhIP.

Formation of banded spherulites and the temperature dependence of the band space in olefin block copolymer

The banded spherulites for olefin block copolymer result from continuous lamellar twisting with an intriguing temperature tendency of the band space.

Manipulating nanoscale interactions in a polymer nanocomposite for chiral control of linear and nonlinear optical functions

The design, synthesis, and supramolecular organization of a nanocomposite in which nanoscale excitonic interactions between quantum dots and the chiral polymer dramatically enhance the optical activity is reported. This material is highly suitable for application in the emerging field of chiral photonics.

Tuning hierarchically aligned structures for high-strength PMIA-MWCNT hybrid nanofibers

Novel hierarchically aligned PMIA-MWCNT hybrid nanofibers with a robust tensile strength of 316.7 MPa were prepared by a facile electrospinning process. The critical roles of humidity and MWCNT contents in tuning hierarchically aligned structures were first proposed, and a two-step break mechanism upon external stress was confirmed.

Characterization of chiral mesoporous materials by transmission electron microscopy

By using transmission electron microscopy (TEM), the chirality of novel mesoporous materials has been studied. In addition, a computer simulation that uses a simple structural model was employed. The existence of chiral channels inside a tubelike material was confirmed by the observation of fringes along the length of the tubes. The chiral pitch of the channels was measured from the intermittent period, the chirality (right- or left-handed) was determined from the tilt direction of a tube compared with the direction of incident electrons and the curvature direction of the curved intermitted fringes as viewed in the TEM images.

Molecular packing and morphology of oligo(m-phenylene ethynylene) foldamers

Understanding and controlling solid-state morphologies and molecular conformations is the key to optimizing the properties of materials. As an example for the influence of small chemical changes on solid-state structures, we studied oligo(m-phenylene ethynylene) foldamers, where the introduction of an endo-methyl group induces a transition from an extended all-transoid to a helical all-cisoid conformation. The resulting structural changes were analyzed by X-ray diffraction (XRD), polarized optical microscopy (POM), and low-dose high-resolution electron microscopy (LD-HREM) over several length scales from the molecular to the mesoscopic level. The strong tendency of the endo-methyl oligomer 1 to form stable compact helices in solution resulted in round droplets with an ordered hexagonal columnar (Col(ho)) liquid crystalline structure, where shrinkage during the crystallization resulted in the formation of a banded texture. On the other hand, the endo-hydrogen oligomer 2 exhibited a very different morphology; its extended linear shape was maintained during crystallization and resulted in an extended lamellar structure, which was determined by a compromise between crystalline packing and minimization of the surface area. Another pronounced difference between both molecular structures was the ability of the extended lamellar "crystals" to bend, whereas the helices form either straight or disordered domains. In addition, both materials exhibit strong surface effects, which extend considerably inside the droplet and induce uniform bending of the supramolecular structures.