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High sulfur loading is essential for achieving high energy density lithium-sulfur (Li-S) batteries. However, serious issues such as low sulfur utilization, poor cycling stability, and sluggish rate performance have been exposed when increasing the sulfur loading for freestanding cathodes. To solve these problems, the adsorption/catalytic ability of high-sulfur-loading cathode toward polysulfides must be improved. Herein, based on excellent properties of cationic MOFs, we proposed that Cu-Mo bimetallic nanoparticles embedded in multifunctional freestanding nitrogen-doped porous carbon nanofibers (Cu-Mo@NPCN) with efficient catalytic sites could be prepared by facile MoO

Poly(vinylidenefluoride-trifluoroethylene)-based (P(VDF-TrFE)-based) terpolymers represent a new class of electroactive polymer materials that are relaxor-ferroelectric (RF) polymers and that offer unique and attractive property combinations in comparison with conventional ferroelectric polymers. The RF state is achieved by introducing a fluorine-containing termonomer as a “defect” into the ferroelectric P(VDF-TrFE) copolymer, which reduces the interaction between the VDF/TrFE dipoles. The resulting terpolymer exhibits a low Curie transition temperature and small remanent and coercive fields yielding a slim hysteresis loop that is typical for RF materials. Though the macroscopic behavior is similar to RF ceramics, the mechanisms of relaxor ferroelectricity in semi-crystalline polymers are different and not fully understood yet. Structure-property relationships play an important role in RF terpolymers, as they govern the final RF properties. Hence, a review of important characteristics, previous studies and relevant developments of P(VDF-TrFE)-based terfluoropolymers with either chlorofluoroethylene (CFE) or chlorotrifluoroethylene (CTFE) as the termonomer is deemed useful. The role of the termonomer and of its composition, as well as the effects of the processing conditions on the semi-crystalline structure which in turn affects the final RF properties are discussed in detail. In addition, the presence of noteworthy transition(s) in the mid-temperature range and the influence of preparation conditions on those transitions are reviewed. A better understanding of the fundamental aspects affecting the semi-crystalline structures will help to elucidate the nature of RF activity in VDF-based terpolymers and also help to further improve their applications-relevant electroactive properties. ispartof: FERROELECTRICS vol:586 issue:1 pages:60-81 status: published

ispartof: Physica Status Solidi A-Applications And Materials Science vol:219 issue:23 status: accepted

The behavior of polymers confined in ultrathin films (thickness < 200 nm) can sensitively differ from that observed in macroscopic samples. Based on the simple arguments of finite size and interfacial effects, film thickness, and surface interactions should be sufficient to univocally determine the deviation from bulk behavior. However, recent models suggest that a third key parameter, namely, the interfacial free volume, should also be considered. We describe a novel methodology that quantifies the volume available for structural relaxation at the interface between a thin polymer layer and its supporting substrate. Experiments performed at different annealing conditions verified that the shift in glass transition temperature, measured in thin films upon confinement, is proportional to the degree of adsorption and, thus, to the interfacial free volume.

Confined at the nanoscale level, polymers crystallize much slower than in bulk, and in some cases, the formation of ordered structure is inhibited within extremely long experimental time scales. Here, we report on the thickness dependence of the conversion rate of the amorphous fraction of ultrathin films of poly(ethylene terephthalate) during isothermal cold crystallization. We present a new analytical method assessing the impact of irreversible chain adsorption and permitting to disentangle finite size and interfacial effects. From the μm range down to a few tens of nm, we observed an increase in crystallization time scaling with the inverse of the film thickness, which is a fingerprint of finite size effects. Films thinner than ∼20 nm did not crystallize, even after prolonged annealing in the temperature range where the crystallization rate reaches its maximum value. Noticing that this threshold corresponds to the total thickness of the layer irreversibly adsorbed within our investigation time, we explain these findings considering that chain adsorption increases the entropic barrier required for the formation of crystalline structures.

We introduce a method permitting remote control of the crystallization of thin polymer films, which does not require changes in the film thickness or the interfacial chemistry. The procedure is based on the assembly of hybrid multilayers, where ultrathin films of a crystallizable polymer - poly(ethylene terephthalate), PET, - are embedded in parallel with noncrystalline polymer layers - polystyrene, PS, - into metallic slabs. Variation of the size of the PS film allowed tuning the crystallization rate of PET layers of constant thickness. We demonstrate that this phenomenon is ascribable to an increase in the interfacial dispersive forces that, enhancing physisorption of PET at the polymer/metal interface, causes a shortage of material at the crystal growth front., SCOPUS: ar.j, info:eu-repo/semantics/published

Cell–material interactions are crucial for many biomedical applications, including medical implants, tissue engineering, and biosensors. For implants, while the adhesion of eukaryotic host cells is desirable, bacterial adhesion often leads to infections. Surface free energy (SFE) is an important parameter that controls short- and long-term eukaryotic and prokaryotic cell adhesion. Understanding its effect at a fundamental level is essential for designing materials that minimize bacterial adhesion. Most cell adhesion studies for implants have focused on correlating surface wettability with mammalian cell adhesion and are restricted to short-term time scales. In this work, we used quartz crystal microbalance with dissipation monitoring (QCM-D) and electrical impedance analysis to characterize the adhesion and detachment of S. cerevisiae and E. coli, serving as model eukaryotic and prokaryotic cells within extended time scales. Measurements were performed on surfaces displaying different surface energies (Au, SiO2, and silanized SiO2). Our results demonstrate that tuning the surface free energy of materials is a useful strategy for selectively promoting eukaryotic cell adhesion and preventing bacterial adhesion. Specifically, we show that under flow and steady-state conditions and within time scales up to ∼10 h, a high SFE, especially its polar component, enhances S. cerevisiae adhesion and hinders E. coli adhesion. In the long term, however, both cells tend to detach, but less detachment occurs on surfaces with a high dispersive SFE contribution. The conclusions on S. cerevisiae are also valid for a second eukaryotic cell type, being the human embryonic kidney (HEK) cells on which we performed the same analysis for comparison. Furthermore, each cell adhesion phase is associated with unique cytoskeletal viscoelastic states, which are cell-type-specific and surface free energy-dependent and provide insights into the underlying adhesion mechanisms., info:eu-repo/semantics/published

We are now living in an integrated world full of abrupt political events and socio-political uncertainty. A comprehensive scientometric review in this aspect is useful but lacked in the existing literature. This paper fills the void by using VOSviewer and CiteSpace to systematically analyze the 4200 papers on “political instability”, “political uncertainty” and “political risk” during 1953–2019 from Web of Science Core Collection. We present the annual distribution of papers, the related disciplines, the mainstream journals, hot topics, references with the strongest citation bursts, recent publications with transformative potentials, as well as the collaboration networks of authors, organizations and countries. The hot spots include (1) the causes and impact of political instability, (2) the relationship among political uncertainty, energy price and macroeconomic/financial factors, and (3) the determinants of foreign direct investments. Rangan Gupta from University of Pretoria in South Africa has the most publications in this field, while Witold J Henisz from University of Pennsylvania in the USA has the most citations. As the first endeavor to do comparative study of easily confused terminologies with bibliometric analysis, we find that though literature on “political instability” and “political risk” appeared earlier and have larger volume, research on “political uncertainty” is currently more active and catching up fast. Keywords with on-going citation bursts, two thirds of active co-citation clusters, and potentially transformative papers published recently are all related to political/policy uncertainty. The three strands of literature have obvious overlap and meanwhile their own special foci. Main areas of research on political instability, political uncertainty and political risk

Lithium–sulphur (Li–S) batteries are interesting due to their high theoretical capacity and energy density. However, their commercial implementation is impeded by the lack of suitable sulphur cathodes that have high electrochemical stability and high sulphur loading using a low electrolyte/sulphur ratio. In this work, reduced graphene oxide functionalized with MnO2 nanosheets was demonstrated as a sulphur cathode (MnO2@rGO/S). The high polarity of the MnO2 nanosheets grown on the rGO surface is beneficial for the uniform distribution of sulphur, providing access to Li+ and immobilizing polysulfides in the cathode region. This leads to an improved electrolyte wettability, promoted sulphur utilization and enhanced reaction kinetics. As a result, the obtained cathode enables superior cyclability over 500 cycles with a capacity fading rate of only 0.034% per cycle. Moreover, a sulphur content of 70 wt% with an electrolyte/sulphur ratio of 4 μL mg−1 is achieved, and the volumetric energy density at the cell level is more than 188 W h L−1 at 1.34 mA cm−2 using Li-metal as the anode. It is comparable and even superior to those of recently reported carbon-based sulphur batteries.

Dynamically controlling cell-material interactions has a strong potential for advancing many cell-based technologies, including cell detection and cell sorting systems. To this end, fundamental studies that provide insights into how cells respond biologically to physico-chemical cues are necessary. Studies show that biological responses, such as cytoskeletal reorganization alter the overall viscoelastic properties of cells. Here, we monitored, in real time, and non-invasively, the evolution of the viscoelastic properties of yeast cells as a function of medium ionic strength (IS). Measurements were performed on SiO2-coated sensor surfaces using the quartz crystal microbalance with dissipation monitoring (QCM-D). Our results indicate that, for every adhesion phase, the cell stiffness decreases with increasing IS. This trend was consistent across the various cell concentrations studied. In terms of cell-substrate interactions, we show that a high IS promotes cell adhesion for all cell concentrations, including ultra-low concentrations. Our results also show that while the adhesion signal decreases with cell concentration for each IS, only temporal and close to noise-level adhesion signals were measured in ion-free medium irrespective of the cell concentration. We also show that cell adhesion rates are higher in physiological ionic strengths compared to cells in higher ionic strengths. Finally, from a cell detection perspective, the results reveal that for very low cell concentrations, large signal enhancements can be achieved by measuring the same concentration in a higher ionic strength. This result also applies for measurements on gold surfaces; thus, we suggest ionic tuning as a strategy for promoting trace-level cell detection in biosensors and cell sorting applications. ispartof: Physics in Medicine vol:14 status: Published online

Non-linear dielectric spectroscopy (NLDS) is employed as an effective tool to study relaxation processes and phase transitions of a poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) relaxor-ferroelectric (R-F) terpolymer in detail. Measurements of the non-linear dielectric permittivity$${\varepsilon _{2}^{'}}$$ε2′reveal peaks at 30 and 80$$\,^\circ$$∘C that cannot be identified in conventional dielectric spectroscopy. By combining the results from NLDS experiments with those from other techniques such as thermally stimulated depolarization and dielectric-hysteresis studies, it is possible to explain the processes behind the additional peaks. The former peak, which is associated with the mid-temperature transition, is found in all other vinylidene fluoride-based polymers and may help to understand the non-zero$$\varepsilon _\mathrm {2}^{'}$$ε2′values that are detected on the paraelectric phase of the terpolymer. The latter peak can also be observed during cooling of P(VDF-TrFE) copolymer samples at 100$$\,^\circ$$∘C and is due to conduction and space-charge polarization as a result of the accumulation of real charges at the electrode–sample interface.

Phase-dependent dielectric properties and proton conduction of neopentyl glycol (NPG), which is an organic molecular plastic crystal, were studied via variable-temperature broadband dielectric spectroscopy (BDS). Permittivity and conductivity data show the phase transformations of NPG from the crystalline state to the plastic crystalline state at 315 K and then to the molten state at 402 K across the temperature range of 293-413 K. The Vogel temperatures (T v) fitted from the Vogel-Fulcher-Tammann (VFT) equation agree well with the values extrapolated by the Stickel plot (linearized Vogel plot). Impedance and modulus data display a separation of the -Z'' (the imaginary part of the complex impedance) and M'' (the imaginary part of the complex electric modulus) peaks in the crystalline phase. However, they overlap in both the plastic crystalline phase and the molten phase, indicating long-range proton conduction. In both the molten phase and the plastic crystalline phase, the temperature dependence of direct current conductivity (σ dc) obeys the VFT equation very well. While the vehicle mechanism (translational diffusion) is an intrinsic mechanism for ionic or protonic conduction in the molten phase, it is speculated that the Grotthuss mechanism also works due to the self-dissociation of NPG molecules, which are similar to water molecules. In the plastic crystalline phase, the proton hopping mechanism is most likely the underlying ion-conducting mechanism because of the rotational disorder and intrinsic defects (vacancies) of the NPG molecules. In the ordered crystalline phase, the proton conduction is presumed to follow the proton hopping mechanism as determined from the localized relaxation and the temperature dependence of σ dc (Arrhenius behavior). ispartof: RSC ADVANCES vol:11 issue:38 pages:23228-23234 ispartof: location:England status: published

This work details the acquisition, handling, and measurement of microliters of perilymph, the fluid inside the human hearing organ, using dielectric relaxation spectroscopy and the correlation of the molecular relaxations to the physiological composition. Comparing between ex-vivo fresh, fresh-frozen and fixed sources reveals that dielectric absorption of the pulses is due to alpha- and beta- charge transfer relaxation related to the geometry of white blood cells, lymphocytes, in the perilymph. Interestingly, comparing the presence of molecular relaxations and the amplitude of dielectric absorption, perilymph obtained from fixed temporal bones matches fresh perilymph better than when obtained from fresh frozen source, due to the importance of well-preserved cell geometry. ispartof: Ieee Transactions On Dielectrics And Electrical Insulation vol:28 issue:3 pages:932-937 status: published

The local and cooperative dynamics of atactic PS (a- PS) were studied by broadband dielectric relaxation spectroscopy (BDRS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The a-PS has been subjected to thermal rejuvenation and subsequent quenching, short-term aging (6 weeks), and long-term aging (1 year) at ambient conditions. Where for the rejuvenated sample only an α- and a γ-relaxation is observed, short-term aging results in an additional β*-relaxation that merges with the α-relaxation at longer aging times. The γ-relaxation is increasing in intensity and activation energy during aging. The α-process shows no spectral changes and shift in the relaxation time upon aging. This may be attributed to a possible erasure of history of the material during the temperature-sweep mode measurement. Fourier transform infrared spectroscopy (FTIR) results suggest that the energetically favorable trans-trans (tt) conformers are increased in population with aging. ispartof: JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS vol:57 issue:20 pages:1394-1401 status: published

Understanding microbial adhesion and retention is crucial for controlling many processes, including biofilm formation, antimicrobial therapy as well as cell sorting and cell detection platforms. Cell detachment is inextricably linked to cell adhesion and retention and plays an important part in the mechanisms involved in these processes. Physico-chemical and biological forces play a crucial role in microbial adhesion interactions and altering the medium ionic strength offers a potential means for modulating these interactions. Real-time studies on the effect of ionic strength on microbial adhesion are often limited to short-term bacterial adhesion. Therefore, there is a need, not only for long-term bacterial adhesion studies, but also for similar studies focusing on eukaryotic microbes, such as yeast. Hereby, we monitored, in real-time, S. cerevisiae adhesion on gold and silica as examples of surfaces with different surface charge properties to disclose long-term adhesion, retention and detachment as a function of ionic strength using quartz crystal microbalance with dissipation monitoring. Our results show that short- and long-term cell adhesion levels in terms of mass-loading increase with increasing ionic strength, while cells dispersed in a medium of higher ionic strength experience longer retention and detachment times. The positive correlation between the cell zeta potential and ionic strength suggests that zeta potential plays a role on cell retention and detachment. These trends are similar for measurements on silica and gold, with shorter retention and detachment times for silica due to strong short-range repulsions originating from a high electron-donicity. Furthermore, the results are comparable with measurements in standard yeast culture medium, implying that the overall effect of ionic strength applies for cells in nutrient-rich and nutrient-deficient media., SCOPUS: ar.j, info:eu-repo/semantics/published

A transparent color-tunable device is presented based on an electrothermal response by using interdigitated electrode patterns. The response is generated by applying an in-plane AC electric field that heats up a thermosensitive cholesteric liquid crystal mixture. The induced temperature elevations cause band gap shifting (Δλ > 350 nm) up until a colorless state is reached, corresponding to the isotropic phase. Color shifting can be tuned manually by varying the electric field or autonomously by the surrounding temperature. Broadband dielectric spectroscopy reveals that the electrothermal response originates from resistive heating of the transparent electrode pattern in conjunction with the cell capacitance and is therefore largely dependent on the electrode configuration. Hence, the electrothermal response can be easily modified by changing the electrode pattern, frequency and/or voltage dependent on the user’s 2 requirements. Therefore, the ability of this technique to manipulate the autonomous thermal response by an electric field, using only one conductive substrate, shows promise in the field of optoelectronics, sensors and smart windows. ispartof: Advanced Electronic Materials vol:7 issue:2 status: accepted

The effect of plastic deformation on the molecular dynamics of atactic polystyrene (a-PS) was studied by broadband dielectric relaxation spectroscopy (BDRS), Fourier-transform infrared spectroscopy (FTIR) and polarized-light microscopy. Sheets of a-PS have been subjected to cold rolling, that is, mechanical rejuvenation, followed by a quenching step and fast heating above its glass-transition temperature, resulting in thermal rejuvenation. Cold rolling revealed, in addition to the known α- and γ(I)-relaxations, four hitherto unknown relaxation processes (II, III, IV and V). Using the framework of craze formation and multiplicity of the glass transition (E. Donth, G. H. Michler, Colloid Polym. Sci. 1989, 267, 557–567), supported by an activation-enthalpy/entropy analysis (Starkweather, W. Howard, Macromolecules 1981, 14, 1277–1281), the following physical picture emerges: (a) processes I and II represent local conformation transitions γ referring to chains of two different degrees of stretching (T/G-ratio); and (ii) processes III and IV were identified as helix-inversion processes of T2G2 helices as reported earlier for syndiotactic-rich PS—an assignment supported by FTIR results. Finally, the relaxation V could be attributed to the onset of the fibrillar glass transition (within crazes), leading to stress release by collapse of the fibrils and hence dying out of process V. Polarized-light microscopy confirmed the creation of oriented structures and internal stresses upon cold rolling, and their removal upon thermal rejuvenation.

The protic ionic liquid diethylmethylammonium methanesulfonate ([DEMA][OMs]) was analyzed in depth by differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy and broadband dielectric spectroscopy (BDS) under anhydrous conditions. Karl Fischer titration, NMR and FT-IR spectra confirmed the high purity of [DEMA][OMs]. The melting point (37.7 °C) and the freezing point (14.0 °C) obtained by DSC agree well with the values determined by BDS (40.0 °C and 14.0 °C). The dc conductivity (σdc) above the melting/freezing point obeys Vogel-Fulcher-Tammann (VFT) equation well and thus the proton conduction in [DEMA][OMs] is assumed to be dominated by the vehicle mechanism. In contrast, the σdc below the melting/freezing point can be fitted by the Arrhenius equation separately and therefore the proton conduction is most likely governed by the proton-hopping mechanism. The non-negligible influence of previously reported low water contents on the physicochemical properties of [DEMA][OMs] is found, indicating the importance of reducing water content as much as possible for the study of “intrinsic” properties of protic ionic liquids. ispartof: Journal Of Chemical Physics vol:152 issue:23 ispartof: location:United States status: Published online

In this work, we report on the development of a catheter-based sensor designed for measuring the concentration of histamine in the human duodenum. Certain gut disorders, such as the irritable bowel syndrome (IBS), are associated with elevated levels of intestinal histamine due to chronic immune activation. As it is still impossible to determine histamine concentrations in vivo, a nasointestinal catheter with histamine-sensing capabilities has the potential to become a valuable diagnostic instrument. Regarding the sensing principle, we selected impedance spectroscopy using voltages that are compatible with intra-body applications with molecularly imprinted polymers (MIPs) as recognition elements. MIPs are synthetic receptors that offer the advantages of robustness, high specificity and selectivity for histamine as a target. In this specific case, the MIPs were synthesized from acryclic acid monomers, which guarantees a uniform binding capacity within the pH range of intestinal fluid. We have validated the catheter sensor on human intestinal liquids spiked with histamine in a testing setup that mimics the environment inside the duodenum. The dose-response curves show an analytical range between 5 and 200 nM of histamine, corresponding to physiologically normal conditions while higher concentrations correlate with disease. The key output signal of the sensor is the resistive component of the MIP-functionalized titanium electrodes as derived from the equivalent-circuit modelling of full-range impedance spectra. Future applications could be catheters tailored to cardiovascular, urological, gastrointestinal, and neurovascular applications. This, in combination with the versatility of the MIPs, will make this sensor platform a versatile diagnostic tool.

The translational diffusion of molecules dispersed into polymer matrices slows down tremendously when approaching a nonrepulsive interface. To unravel the origin of this phenomenon, we investigated the diffusion of molecular probes in the direction normal to an adsorbing wall. Using adsorbed polymer layers as matrices, we were able to decouple interfacial and finite size effects and determined the relation between the diffusion time and the area available at the polymer/solid interface. Based on the results of our investigation, we present a physical picture, suggesting that the reduction in diffusion rate is correlated to the degree of chain adsorption onto the substrate, that is, the density of surface obstacles encountered by tracer molecules. ispartof: Acs Macro Letters vol:9 issue:3 pages:318-322 ispartof: location:United States status: Published online

Herein, 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) vesicles are studied using a newly designed setup that combines dielectric and gravimetric (quartz crystal microbalance, QCM) measurements. This setup allows to monitor the molecular dynamics and phase transitions of lipid structures under controlled humidity and temperature conditions. The main relaxation process (R2), related to the intrinsic headgroups' dynamics, is found in all phases and reveals a systematic acceleration with increasing hydration level. In contrast, a faster relaxation mode (R1) is found exclusively in the ?liquid-crystalline,? high-temperature state, favoring water clusters located in the disordered aliphatic phase as origin. A third process (R3), being slower than the R2 mode, is attributed to a decoupled dynamics of hydration water in the hydrophilic part of the lipid bilayers occurring at higher hydration levels. In addition to molecular dynamics, both QCM and dielectric relaxation spectroscopy (DRS) measurements are demonstrated to yield consistent information on the phase behavior of the POPC samples which show a marked sensitivity to the hydration level. Moreover, contact angle measurements and atomic force microscopy confirm irreversible changes from the initial vesicles to a stacked bilayer structure upon repeated hydration-dehydration, which manifests in the hydrophobization of the surface and water reduced absorption kinetics. doi: 10.1002/pssa.201900986 ispartof: Phys. Status Solidi A vol:217 issue:13 status: Published online

Water plays a key role in the functioning of natural and synthetic molecular systems. Despite several hydration studies, different techniques are employed individually for monitoring different physical features such as kinetics, dynamics, and absorption. This study describes a compact hydration cell that enables simultaneous dielectric relaxation spectroscopy (DRS) and mass loss/uptake measurements in thin organic layers under controlled humidity conditions and in a wide temperature range. This approach enabled us to correlate the physical quantities obtained during the same experiment by complementary techniques. To demonstrate the performance of this device, a 200 nm thick poly(methyl methacrylate) (PMMA) layer was measured at various relative humidity levels (0%–75%), temperatures (25–75 °C), and frequencies (DRS: 0.1 Hz–1 MHz) to study how hydration and dehydration processes affect its molecular dynamics. The results show the capability of this setup to study the changes in the PMMA film regarding the kinetics and molecular dynamics upon variation of the water content.Water plays a key role in the functioning of natural and synthetic molecular systems. Despite several hydration studies, different techniques are employed individually for monitoring different physical features such as kinetics, dynamics, and absorption. This study describes a compact hydration cell that enables simultaneous dielectric relaxation spectroscopy (DRS) and mass loss/uptake measurements in thin organic layers under controlled humidity conditions and in a wide temperature range. This approach enabled us to correlate the physical quantities obtained during the same experiment by complementary techniques. To demonstrate the performance of this device, a 200 nm thick poly(methyl methacrylate) (PMMA) layer was measured at various relative humidity levels (0%–75%), temperatures (25–75 °C), and frequencies (DRS: 0.1 Hz–1 MHz) to study how hydration and dehydration processes affect its molecular dynamics. The results show the capability of this setup to study the changes in the PMMA film regarding the...

Cell imprinting on polymer layers produces synthetic receptors, so called surface imprinted polymers (SIPs) that are suitable for specific and selective cellular recognition. However, their recognition mechanisms are not yet fully understood. Therefore, various factors that influence cell recognition were explored using different spectroscopic techniques. Specifically, the molecular dynamics of surface-imprinted and non-imprinted polyurethane layers was studied with focus on the dielectric relaxation signatures of proteins and lipids by dielectric relaxation spectroscopy. Furthermore, we have tested an interdigitated comb electrode (IDE) structure placed beneath the cell recognition layer. It was shown that both plane and IDE configurations sense the molecular dynamics of the PU layer correctly, and also reveal specific information about the polymer/cell interface.

Extending the well-established laser intensity modulation method (LIMM) by means of sequential frequency modulation represents a new approach for obtaining polarization depth profiles at both high spatial (nanometer) and temporal (millisecond) resolution. Thin films of the archetypal, organic, ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TrFE) were investigated in this manner to assess local switching kinetics. For subcoercive field conditions of 5 MV/m, the central regions of 2000 nm thick samples show a “bulk”-like, uniform polarization switching behaviour at a time-scale of 250 ms. In contrast, a 100 nm thick region near the metal-polymer interface reveals clear deviations from bulk switching kinetics. This likely reflects local charge generation/injection and trapping effects.

Previous studies have shown that selective synthetic cell receptors can be produced by cell imprinting on polymer layers. However, knowledge on the fundamental detection mechanisms remains limited. In this article, while using yeast cells (Saccharomyces cerevisiae) as model cells, the factors influencing cellular recognition by surface-imprinted polymers (SIPs) are studied by means of spectroscopic and microscopy techniques and a transducer platform based on interfacial thermal transport, the so-called heat-transfer method (HTM). These analyses indicate that cell imprinting creates selective binding sites on the surface of the SIP layer in the form of binding cavities that match the cells in shape and size. Also, we show that phospholipid moieties are incorporated into the SIP cavities during imprinting, while membrane proteins do not seem to be transferred. More importantly, we demonstrate that the incorporated phospholipids significantly enhance cell adhesion to the SIP, and thus play a significant role in the cell-SIP binding mechanism. Furthermore, the hydrophobicity of the SIP layer was found to be considerably higher when compared with a non-imprinted polymer layer (NIP), an effect that could not be attributed to the presence of cavities on the surface of the SIP layer. Therefore, we suggest that the role of phospholipids in the SIP recognition mechanism is mediated by long range hydrophobic forces. ispartof: Sensors and Actuators B, Chemical vol:255 issue:1 pages:907-917 status: published

Since January 2021 I have the honor to serve as the new Editor-in-Chief (EiC) of our Transactions on Dielectrics and Electrical Insulation (TDEI). I have taken over this role from Professor Ed Cherney, whom I thoroughly wish to acknowledge for his training and guidance in the past two months. It was the privilege of the DEIS President Paul Gaberson to credit, in his recent Editorial in the Electrical Insulation Magazine (2021 issue 1), Professor Cherney's specific contributions for his strive to further increase the quality and reputation of our Transactions over the last three years. Since January 2021 I have the honor to serve as the new Editor-in-Chief (EiC) of our Transactions on Dielectrics and Electrical Insulation (TDEI). I have taken over this role from Professor Ed Cherney, whom I thoroughly wish to acknowledge for his training and guidance in the past two months. It was the privilege of the DEIS President Paul Gaberson to credit, in his recent Editorial in the Electrical Insulation Magazine (2021 issue 1), Professor Cherney's specific contributions for his strive to further increase the quality and reputation of our Transactions over the last three years. ispartof: IEEE Transactions on Dielectrics and Electrical Insulation vol:28 issue:1 pages:1-2 status: published

In this work, we present a new technique for the sensitive and facile detection of Saccharomyces strains with a detection limit of 30 cells/mL in both buffer solution and food samples such as beer and yoghurt. This is achieved by combining ultrathin surface-imprinted polymer (SIP) layers as receptors with impedance spectroscopy as the readout principle. Binding of cells to the imprinted polymer surface results in a concentration-dependent increase of the impedance signal. According to the equivalent-circuit modelling of the impedance spectra, this is due to an increase of the resistive component of the solid-liquid interface while capacitive effects are negligible. Regarding selectivity, we prepared imprints with three different template strains and compared the sensor response for using the same three strains as targets. The response is strongest for combinations in which templates and targets belong to the same strain. For other situations, the sensor signal is reduced by a factor of three, indicating a certain level of selectivity, which can be interpreted in terms of size and cell wall differences. In summary, the combination of SIP-type receptors with impedance spectroscopy offers a fast and sensitive technique for on-site analysis of complex food matrices outside a laboratory environment. The results for yeast should be transferable to other microorganisms, including pathogenic ones.

The mechanism governing the electrical properties for phase separating blends containing multiwall carbon nanotubes (MWNTs) is unravelled by tuning the compatibilization efficiency. Thereto, compatibilization by interfacially segregated block and random copolymers (cp) of poly(styrene-random/block-methyl methacrylate)(PS-r/b-PMMA) was achieved in phase separating blends of poly[(α-methyl styrene)-co-acrylonitrile]/poly(methylmethacrylate) (PαMSAN/PMMA) undergoing spinodal decomposition. A systematic study of the effects of copolymer architecture and molecular weight on the percolating network of selectively localized MWNTs is performed. Effective compatibilization is achieved with block cp irrespective of the ability of the blocks to entangle, whereas for random cp only long random cp having the ability to effectively entangle with the homopolymers are as efficient as long block cp. With increasing copolymer concentration, an increase and subsequent saturation of the electrical conductivity is attained. This originates from an increased connectivity and refinement of the MWNT laden PαMSAN phase, as confirmed by optical microscopy and the linear viscoelastic response of the blends. An effective compatibilizer led to an interfacial tension mediated suppression of an interfacial coarsening of the PαMSAN phase during phase separation, subsequently leading to percolation of MWNTs selectively localized in the PαMSAN phase. Furthermore, the copolymer having the ability to promote the development of a percolated network of MWNTs also allowed the network to be formed at a lower copolymer concentration as compared to that of blends with copolymers leading to restricted improvement in the connectivity of MWNTs. Our robust and simple procedure to tune the blend morphology via the efficiency of the compatibilizers can be used to achieve a synergistic increase in conducting properties.

We report on a novel biomimetic sensor that allows sensitive and specific detection of Escherichia coli (E. coli) bacteria in a broad concentration range from 102 up to 106 CFU/mL in both buffer fluids and relevant food samples (i.e. apple juice). The receptors are surface-imprinted polyurethane layers deposited on stainless-steel chips. Regarding the transducer principle, the sensor measures the increase in thermal resistance between the chip and the liquid due to the presence of bacteria captured on the receptor surface. The low noise level that enables the low detection limit originates from a planar meander element that serves as both a heater and a temperature sensor. Furthermore, the experiments show that the presence of bacteria in a liquid enhances the thermal conductivity of the liquid itself. Reference tests with a set of other representative species of Enterobacteriaceae, closely related to E. coli, indicate a very low cross-sensitivity with a sensor response at or below the noise level.

© 2018 American Chemical Society. It is generally accepted in membrane technology that crystalline zones in polymeric membranes do not contribute to transport of liquids or gases. In the current study, poly(3-alkylthiophene)s (P3ATs), i.e., homopolymers and random copolymers, were synthesized to study the influence of the supramolecular organization on membrane gas separations. The monomers were polymerized via KCTCP, and GPC analysis shows that the polymers have a narrow dispersity. DSC analysis of the polymers reveals that the homopolymers, in contrast to the copolymers, crystallized, confirming their higher degree of supramolecular organization. This was supported by UV-vis absorption spectra of the polymer films, where a red-shift and a characteristic shoulder absorption peak around 600 nm were observed for the homopolymers, while absent for the copolymers. More surprisingly, the homopolymers were found to be 2 orders of magnitude more permeable to CO2 than the copolymers and also more selective. ispartof: MACROMOLECULES vol:51 issue:23 pages:9943-9950 status: published

We disclose a supramolecular material that combines semiconducting and dipolar functionalities. The material consists of a discotic semiconducting carbonyl-bridged triarylamine core, which is surrounded by three dipolar amide groups. In thin films, the material self-organizes in a hexagonal columnar fashion through Jr-stacking of the molecular core and hydrogen bonding between the amide groups. Alignment by an electrical field in a simple metal/semiconductor/metal geometry induces a polar order in the interface layers near the metal contacts that can be reversibly switched, while the bulk material remains nonpolarized. On suitably chosen electrodes, the presence of an interfacial polarization field leads to a modulation of the barrier for charge injection into the semiconductor. Consequently, a reversible switching is possible between a high-resistance, injection-limited off-state and a low-resistance, space-charge-limited on-state. The resulting memory diode shows switchable rectification with on/off ratios of up to two orders of magnitude. This demonstrated multifunctionality of a single material is a promising concept toward possible application in lowcost, large-area, nonvolatile organic memories. Funding Agencies|NWO Nano program; Bavarian State Ministry of Science, Research, and the Arts for the Collaborative Research Network Solar Technologies go Hybrid; Deutsche Forschungsgemeinschaft (DFG) [SFB 953]; Vetenskapsradet [2015-03813]

The dynamics of supramolecular networks made up of partially hydrolyzed poly(n-butyl acrylate) [PnBA] is investigated. These linear entangled random copolymers [PnBA-AA] self-assemble via hydrogen bonding interactions between carboxylic acid groups. Two types of supramolecular assemblies are revealed, i.e., binary assembly of carboxylic acid dimers and collective assembly of dimers into distinct poly(acrylic acid) [PAA] domains. The latter is proved by emergence of new relaxation processes in broadband dielectric spectroscopy while the former is evident by an increase of the glass transition temperature as well as retardation of segmental mobility observed by rheology. Therefore, a “sea–island” morphology containing geometrically confined PAA nanodomains embedded in a PnBA-rich matrix is suggested for the supramolecular network. Thermodynamic theories are employed to rationalize the existence of an interlayer with restricted mobility between the two phases. A fraction of PnBA-AA segments that are trapped ...

We describe an approach to tailor the dielectric interfacial properties of polymer blends by the interplay of compatibilizer effects on blend morphology and on blocking of charge carriers. A systematic study of the effect of the concentration of the compatibilizer, a random copolymer of poly(styrene-random-methyl methacrylate) (PS-r-PMMA), on the interfacial properties of stacked polymer films and a phase separating blend of poly[(α-methylstyrene)-co-acrylonitrile]/poly(methyl methacrylate) (PαMSAN/PMMA) was performed. From dielectric spectroscopy, "conductivity free" dielectric loss spectra revealed interfacial blocking of charge carriers at low frequencies owing to the conductivity contrast of the blend components, resulting in a dielectric interfacial peak. From the dielectric response of stacked polymer films, the interfacial polarization was significantly suppressed when the thickness of the more conducting film approached the Debye length (LD), on the basis of which LD could be calculated using the Trukhan model. With increasing concentration of interfacially localized copolymer, an increase of the relaxation strength of the interfacial polarization occurred due to a pronounced decrease of LD. The characteristics of the former were further investigated in biphasic polymer blends and were governed by the intrinsic length scale of the system, i.e., the ratio of structure dimension (Dv) to Debye length (LD). Upon compatibilization, the interfacially segregated copolymer not only results in refinement of the PαMSAN phase but also provides an augmented conductivity difference leading to a slower dynamics of PαMSAN charges at the interface. This resulted in a substantial increase of the peak intensity of the interfacial polarization, which was attributed to a pronounced attenuation of LD. The latter parameter was estimated using either the impedance formalism or the interfacial relaxation time. Similar to the stacked polymer films, upon compatibilization, an increase of the relaxation strength of the interfacial polarization occurred in biphasic polymer blends, which corroborated a pronounced decrease of LD. Our results provide a methodology to characterize and tune the morphology and blocking of charge carriers with the aim of tailoring the dielectric interfacial properties of biphasic morphologies.

Two dipolar biphenyls show significant 180° orientational disorder resulting in bipolar as-grown crystals. An added symmetrical biphenyl interferes with polarity formation and inverts the initial bipolar state., 180° orientational disorder of molecular building blocks can lead to a peculiar spatial distribution of polar properties in molecular crystals. Here we present two examples [4-bromo-4′-nitrobiphenyl (BNBP) and 4-bromo-4′-cyanobiphenyl (BCNBP)] which develop into a bipolar final growth state. This means orientational disorder taking place at the crystal/nutrient interface produces domains of opposite average polarity for as-grown crystals. The spatial inhomogeneous distribution of polarity was investigated by scanning pyroelectric microscopy (SPEM), phase-sensitive second harmonic microscopy (PS-SHM) and selected volume X-ray diffraction (SVXD). As a result, the acceptor groups (NO2 or CN) are predominantly present at crystal surfaces. However, the stochastic process of polarity formation can be influenced by adding a symmetrical biphenyl to a growing system. For this case, Monte Carlo simulations predict an inverted net polarity compared with the growth of pure BNBP and BCNBP. SPEM results clearly demonstrate that 4,4′-dibromobiphenyl (DBBP) can invert the polarity for both crystals. Phenomena reported in this paper belong to the most striking processes seen for molecular crystals, demonstrated by a stochastic process giving rise to symmetry breaking. We encounter here further examples supporting the general thesis that monodomain polar molecular crystals for fundamental reasons cannot exist.

Scanning Pyroelectric Microscopy (SPEM) at micrometer resolutions has been employed to study permanent polarity and its spatial organization in various insect wings containing chitin, one of the most abundant biopolymers. Both measurements on wings of houseflies and wasps revealed a well defined pyroelectric response, showing a multidomain polarization pattern at several length scales, from millimeter sized domains in the wing veins, to 20 micrometer sized domains in the membranes. The size of the smaller domains correlates well with the average chitin fiber length of 18 micrometers.