The in situ detection of the microconformation of polymers in a shear field from the molecular level not only plays an important role for demonstrating the molecular mechanism of polymer chains'dynamic behavior such as deformation and diffusion,but also serves as a crucial link in developing advanced polymer processing technology.However,due to the conformational change scale of polymer chains falling within the range from 0.1 nm to 10 nm,conventional characterization methods,such as dynamic light scattering and fluorescence microscopy techniques,are difficult to meet the requirements of spatial resolution needed for characterization.To address this problem,the fluorometer was modified by adding a Couette rheofluorescence cell on the detection optical path.Since the Couette fluorescence cell can apply different shear rates to the sample,the modified fluorometer is able to detect in situ fluorescence signals of samples in a shear field.In order to characterize the conformational changes of the polymer chain,fluorescent donor and acceptor groups were labeled to a single polymer chain through covalent bonds Based on the positive correlation between the fluorescence resonance energy transfer(FRET)efficiency and the distance between the fluorescent donor and acceptor groups,a FRET spectroscopy has been used to achieve in situ characterization of the solution shear conformation of polymer chains by analyzing the change of the FRET efficiency between fluorescent donor and acceptor groups labeled on the same polymer chain as a function of the shear rate.For the first time,it was observed in situ at the molecular level that polymer chains under shear showed the conformational change modes of"whole driven by local"in dilute solutions and"local driven by whole"in semi-dilute solutions,respectively.This study provides new methods and ideas for experimentally carrying out in situ studies on the conformational evolution of polymer chains,and has an advancing effect on the development of molecular rheology.

Gallium nitride (GaN) is widely considered as a crucial semiconductor for the nuclear industry and space explorations due to its superior radiation hardness. Despite extensive studies of the electronic and optical properties of irradiated GaN, the effects of particle irradiation on the thermal properties remain largely unexplored. Here, we begin with single-crystalline GaN and employ an accelerator equipped with heavy gold ions (Au2+) as the radiation source in order to imitate extreme environments and maximize lattice damages. Eight different irradiated samples are prepared with the fluence of Au2+ spanning four orders of magnitude from 1011 to 1015 cm−2. The thermal conductivity (κ) of the ion-affected regions is measured using the laser pump–probe technique of frequency-domain thermoreflectance. We find that κ decreased consistently and notably with increasing irradiation fluence and observe a transition from crystal to glass-like thermal transport. Remarkably, the room-temperature κ of the GaN sample with the highest Au2+ fluence of 1 × 1015 cm−2 reaches about 1 Wm−1 K−1, which is two orders of magnitude lower than the κ of pristine GaN and approaches the theoretical minimum. A Callaway-type model captures the phonon–point defect scattering in samples with relatively low ion fluences. At higher fluences, the increased defect types and densities, together with the formation of nitrogen bubbles, further suppress phonon transport. Our findings are instrumental in fundamentally understanding the impact of heavy-ion irradiation on thermal transport and may prove useful for the application of GaN-based devices in radiation-intense environments.

This paper provides a viewpoint of the technology of the fast-scanning calorimetry with the relaxation behavior of disordered side chains of poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C12) around the glass transition temperature of the side chains (Tg,γ). PBTTT is an ideal model of the high-performance copolymer of poly(alkylthiophenes) with side chains. The γ1 relaxation process of the disordered side chains of PBTTT was detected as a small endothermic peak that emerges before the γ2 relaxation process. It shows an increase with increasing temperature as it approaches the glass transition temperature of the disordered side chains of PBTTT. The ductile–brittle transition of PBTTT in low temperatures originating from the thermal relaxation process is probed and illustrated by physical aging experiments. The signature is shown that the relaxation process of the disordered side chain of PBTTT at low temperatures varies from Arrhenius temperature dependence to super Arrhenius temperature dependence at high temperatures. These observations could have significant consequences for the stability of devices based on conjugated polymers, especially those utilized for stretchable or flexible applications, or those demanding mechanical robustness during tensile fabrication or use in a low-temperature environment.

The conformational evolution of a conjugated polymer from amorphous to (poly)crystalline is crucial for achieving charge transport in flexible electronic devices. However, the molecular ordering evolution process between these two states is not yet well understood in poly[2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT). To gain insight into this process, we used a combination of resonance Raman spectroscopy and fast scanning calorimetry (FSC) in real time to investigate morphology-dependent main-chain/side-chain aggregates and thermotropic mesophase formation behavior in PBTTT. Our findings reveal that the conformational transition of the molecular ordering strongly depends on the isothermal temperatures. Specifically, when crystallized at 333 K from an amorphous state, the twist motion of the thienothiophene and thiophene rings caused a decrease in the packed side chains, which was associated with the growth of the thermotropic mesophase. At 353 and 363 K, the competition between the growth of main-chain crystallization and the thermotropic mesophase formation influences the molecular ordering of the sample. Furthermore, during crystallization at 413 K, the increased mobility of the main and side chains causes more perfect crystallization of the main chain without thermotropic mesophase formation, resulting in a more ordered structure. These findings help us better understand the conformational transition in the variations of the molecular ordering of conjugated polymers with the ongoing crystallization and can be employed to fabricate conjugated polymer flexible devices.

The anchor effect in nanomolding technology (NMT) refers to the effect that polymer nanorods in nanopores on metal surfaces act as anchors to firmly bond the outside polymer components onto the metal surface. In this work, the influences of thermal treatments on the anchor effect are studied at microscopic level from the perspective of interfacial interaction by a model system (poly(n-butyl methacrylate) (PBMA) and alumina nanopore composite). The differential scanning calorimeter and fluorescence results indicate that the formation of a dense polymer layer in close contact with the pore walls after proper thermal treatments is the key for a strong interfacial interaction. Such polymer layers were formed in NMT products composed of PBMA and aluminum after slow cooling or annealing, with an up to eighteen-fold improvement of the interfacial bonding strength. The polymer chains near the nanopore walls eliminate the thermal stress induced by the mismatch of thermal expansion coefficients through relaxation over time and remain in close proximity with the pore walls during the cooling process of nanomolding. The above dynamic behaviors of the polymer chains ensure the formation of stable interfacial interaction, and then lead to the formation of the anchor effect.

A novel TPE-o-carborane-based star-shaped molecule with a triphenylamine core has been synthesized. This star-shaped molecule consists of three TPE-o-carborane moieties as dendrons and triphenylamine as the core. In the solid state, the absolute luminescent quantum yield can be improved to 62%.

Due to its unique advantages, capacitive electronic skin (E-skin) has shown excellent application potential in robotics, human-computer interaction, and biomedical equipment in recent years. However, the low sensitivity and nonlinear response caused by the classic working mechanism of compressing the microstructured elastic dielectric layer and the low dielectric constant of the elastomer limit practical applications of E-skin. To make the device respond linearly to pressure over a wide range, a new strategy of controlling the contact area between the elastic electrode and the dielectric layer is adopted. This design also reduces signal distortion, which originates from the viscoelasticity of the polymer. Furthermore, by using ferroelectric polymers and ionic gels with high capacitance in the dielectric layer, the sensitivity of the device can be adjusted in the range of 0.644-26.6 kPa(-1), and the lower limit of pressure detection is as low as 2.88 Pa. The performance of the device remains stable even after 8000 cycles of compression. On this basis, the successful application of the linear-response E-skin obtained in this work in physiological signal monitoring and the collection of basic object information, such as shape and hardness, proves the rationality of the design and provides the possibility for capacitive electronic skin to move towards real life applications.

A novel kind of expanded tetraphenylethylene (TPE)-carborane-TPE pentad has been synthesized by using two adjacent carborane moieties as central bridges and three TPE units in lateral positions. Its solid-state fluorescence quantum yield was substantially increased to 68.2% by expanding the number of bridges between carborane and TPE. Subsequently, the emission color shifted from blue to orange-yellow (126 nm). Mechanical insights into the electronic structure of the extended TPE-carborane-TPE pentads were obtained from density functional theory (DFT) calculations.

Two Z/E isomers, namely, Z-TPE-2Car and E-TPE-2Car, with clear configuration were synthesized using an effective route and have high solid-state fluorescence quantum yields, reaching 99% and 90%, respectively.

An effective cellulose-based antiscalant, namely, carboxymethyl cellulose-graft-poly(acrylic acid) (CMC-g-PAA) was synthesized via the graft copolymerization of carboxymethyl cellulose (CMC) and acrylic acid. The addition of CMC-g-PAAs can evidently delay the formation of the CaSO4 scale, effectively mitigate reverse osmosis (RO) membrane scaling and flux decline, and increase the induction time of crystallization due to the grafted carboxyl groups efficiently interacting with scale-forming substances. The inhibition performance of CMC-g-PAA in the static test was mostly consistent with that in the RO test. Combining the results of the RO and static tests and the relevant characterizations by scanning electron microscopy, optical microscope, x-ray diffraction, and conductivity measurements, the scale-inhibition mechanisms of CMC-g-PAA are mainly ascribed to enhanced chelation, dispersion, and threshold effects. Moreover, the two structural factors of CMC-g-PAAs, grafting ratio and grafted-chain distribution, play important roles in their inhibition effects. Appropriate grafting ratio was necessary to obtain high-performance CMC-g-PAA. With a similar grafting ratio, a higher average number of PAA grafted chains can lead to better inhibition performance because of more active inhibition sites contained. However, the grafting ratio has more contributions than grafted-chain distribution. This study provides a better understanding of the structure–activity relationship of the grafting-modified polymeric inhibitor and fundamental guidance for the exploitation and design of novel and efficient scale inhibitors.

In this paper, the bitstream of 28 nm field-programmable-gate-array was resolved. The relationship between the frame address and the resource was obtained. The fault injection platform was designed based on the information of the bitstream which obtained by partial reconfiguration. With this fault injection platform, the equivalence of the global fault and random fault injections was verified. Also, the sensitivities of different circuits were tested by random fault injection. The reinforcement effect of the triple module redundancy for sensitive resources in 28 nm FPGA was also be tested.

Proton experiments were performed on Kintex-7 XC7K70T field programmable gate array by using a self-developed test system at EN tandem accelerator in Peking University. The single-event upset and multiple-bit upsets induced by low-energy proton were presented, and a cross section peak under the low-energy protons was tested. Also, the experiments under high-energy protons were performed on the proton cyclotron accelerator in the China Institute of Atomic Energy, cross sections of some blocks in FPGA were obtained. Data of low-energy and high-energy experiments showed that the LET threshold of some resources were different. Results suggest that the low-energy proton-induced single event effect must be considered.

The conformations of polymers in solutions are of great importance, and scattering techniques prevail in detecting these conformations. However, most studies only focus on polymer species with high molecular weights or those well above their entanglement molecular weights, and studies on polymer solutions with low molecular weights, e.g., lower than 10,000 Da, are lacking. Here, the conformation of low molecular weight polymers in solutions with different concentrations was investigated via fluorescence resonance energy transfer (FRET). Based on a site-specific chromophore-labeling protocol, the conformational information of the polymer was inferred from the end-to-end FRET response. In principle, the FRET efficiency increases with increasing polymer concentration since the size of the polymer coil decreases. For low molecular weight polymers, the trend of the FRET efficiency shows the opposite effect as the polymer concentration increases, which is rationalized by the counterbalance of the intrinsic size contraction (static item) of and terminal diffusion (dynamic item) from the polymer coil. The universality of this law is verified by similar results from the polymethyl methacrylate (PMMA) system. This work provides new efforts for the conformational study of polymer solutions and demonstrates that the diffusion effect should be taken into account for low molecular weight polymers but is negligible for polymers with high molecular weights.

In this paper, the low-energy proton-induced single event effect sensitivity of multiple feature size NAND flash memories has been investigated. Under 0.41 MeV proton, the single event effect cross-section peak appeared in 25 nm and 16 nm flash devices. SRIM simulation revealed the primary reason of this phenomenon. Single event upsets caused by direct ionization of low-energy proton could be several orders of magnitude higher than those caused by high-energy proton nuclear reactions. Moreover, the influence of cumulative dose on the single event effect sensitivity of flash device was investigated. As the cumulative dose increased, the single event upset cross-section was increased considerably. This phenomenon appears due to the threshold voltage shift induced by the combination of the proton and the cumulative dose.

The proton-induced single-event effect sensitivity of multiple feature size NAND flash memories has been studied. The single-event upset cross section of memories was obtained as a function of feature size, and the cross section of device increases significantly with increasing integration. Monitoring of the proton-irradiated devices for up to 2 months indicates that the retention errors of devices due to reduced insulating properties of the tunnel oxide layer are more critical than error annealing due to the annealing of the trapped charge. During the dynamic test, a large number of semipermanent and regular data "stuck bit" errors were captured, which disappeared after a few days of annealing. Micro-dose effect, which occurred in the external control circuit of NAND flash by proton-produced secondary particles, is considered responsible to the "stuck bit" errors.

The static and dynamic behaviors of linear and ring polymers under shear flow over a wide range of shear rates are studied using a hybrid simulation method that couples multiple-particle collision dynamics with molecular dynamics. The results reveal that the polymer size increases monotonically with increasing shear rate when hydrodynamic interactions are ignored, in agreement with classic theoretical predictions. However, for the cases with hydrodynamic interactions, due to the transition from a linear to a nonlinear velocity profile, the size of both linear and ring chains exhibits a nonmonotonic dependence on the shear rate, and this counterintuitive behavior could be divided into three main regimes. At specific shear rates, linear polymers exhibit a relatively stable stretched state and a rapidly rotating collapsed state, which correspond to the maximum and minimum sizes, respectively. Although the rings behave similarly to the linear polymers, there exist two different relatively stable stretched states: one with an oval-shaped conformation and the other with an S-shaped conformation. For the oval-shaped state, the tumbling motion almost disappears but the tank-treading motion persists, whereas for the S-shaped state, both tumbling and tank-treading motions are greatly suppressed. Moreover, contrary to previous theoretical predictions, a noticeable bulge is observed for the polymer size in the gradient direction and the alignment angle deviates considerably from theoretical prediction, indicating the existence of relatively stable collapsed conformations at large shear rates for both linear and ring polymers. However, in ideal linear shear flow introduced by using the "fix deform" command to Dissipative Particle Dynamics system in LAMMPS package, both linear and ring polymers exhibit a monotonic dependence of size on shear rate. These results shed new light on the understanding of the dynamic response of linear and ring polymers in ultrahigh shear flows.

The critical overlap concentration C* is an important concept in polymer solutions and is defined as the boundary between dilute and semidilute regimes. In this study, the chain conformational changes of polystyrene (PS) with both high (Mn = 200,000 Da) and low (Mn = 13,000 Da) molecular weights in cis-decalin were compared by intrachain fluorescence resonance energy transfer (FRET). The random labeling of donor and acceptor chromophores strategy was employed for long PS chains, whereas chain-end labeling was used for short PS chains. By monitoring the spectroscopic intensity ratio between acceptor and donor, the concentration dependence on chain conformation from dilute to semidilute solutions was determined. Both long and short chains exhibit a conformational transition concentration, above which the polymer chains begin to collapse with concentration significantly. Interestingly, for randomly labeled polymer long chains, such concentration is consistent with C* determined from the viscosity result, below which only slight conformational change of polymer chain takes place. However, for the chain-end labeled short chain, the conformational transition concentration takes place earlier than C*, below which no significant polymer conformation change is observed.

The variable C-C bond of o-carborane cage was treated as a vibrational factor. A temptation to synthesize AIE-active o-carborane luminophores were carried out via coupling o-carborane with conventional luminophores who suffered from ACQ (aggregation-caused quenching) effect. Meanwhile, the photophysical properties were investigated by UV-Vis spectra, DFT calculations, PL spectra and crystal structure analysis. The results indicate that different substituents (H, ethyl and phenyl) in o-carboranes could remarkably affect its vibration performance. Ultimately, photophysical properties can be tuned from ACQ to ATE. CCDC: 1834185, o-me-an; 1834186, ph-o-an; 1838538, o-et-an.

Water-soluble polymers are generally required in the process of nonsolvent-induced phase separation (NIPS) as additives or modifiers to enhance the hydrophilicity and permeability of ultrafiltration membranes. In this work, we demonstrate that amphiphilic block copolymers, polysulfone-block-poly (ethyleneglycol) (PSf-b-PEG), dissolved alone in solvents without any additives lead to highly permeable, fouling-resistant membranes via the NIPS process. PEG blocks deliver dual functions in the membranes. Selective enrichment of PEG blocks on the membrane surface as a result of surface segregation enhances the hydrophilicity and consequently fouling resistance of the membranes. Moreover, microscale phase separation of the block copolymers drives the formation of interconnected PEG microdomains distributed throughout the bulk membrane as confirmed by the transmission electron microscopy analysis on stained membrane slices. PEG microdomains serve as water channels facilitating water transport through the membrane. As a result, thus produced membranes exhibit excellent permeability a few times higher than other PSf-based ultrafiltration membranes with similar retentions. For instance, a membrane having the molecular weight cut-off of 70 kDa gives a water permeability as high as 450 m−2 h−1 bar−1. Furthermore, the retentions of the PSf-b-PEG membranes can be tuned in a relatively wide range simply by adjusting the copolymer concentration in the casting solutions. Using amphiphilic block copolymers alone as the base materials for the preparation of ultrafiltration membranes by NIPS not only simplifies membrane manufacturing process but also opens a new avenue to prepare advanced membranes with upgraded permeability and fouling resistance.

Understanding and controlling the glass transition temperature (Tg) and dynamics of polymers in confined geometries are of significance in both academia and industry. Here, we investigate how the thermal stress induced by a mismatch in the coefficient of thermal expansion affects the Tg behavior of polystyrene (PS) nanorods located inside cylindrical alumina nanopores. The size effects and molecular weight dependence of the Tg are also studied. A multi-step relaxation process was employed to study the relationship between thermal stress and cooling rate. At fast cooling rates, the imparted thermal stress would overcome the yield stress of PS and peel chains off the pore walls, while at slow cooling rates, chains are kept in contact with the pore walls due to timely dissipation of the produced thermal stress during vitrification. In smaller nanopores, more PS chains closely contact with pore walls, then stronger internal thermal stress would be generated between core and shell of PS nanorod, which results in a larger deviation between two Tgs. The core part of PS shows lower Tg than bulk value, which can induce faster dynamics in the center region. A complex and important role stress plays is supposed in complex confinement condition, e.g., in nanopores, during vitrification.