Designing polymer-based piezoresistive strain sensors

Piezoresistive strain sensors have generated considerable interest due to their extensive applications [1]. Tremendous efforts have been devoted to develop highly sensitive strain sensors through a delicate assembly of conductive fillers or unique dedicated microstructure design [2]. The approaches toward conductive polymer composites (CPCs) lack although manufacturing scalability and extensibility. Efforts are still needed to carefully tailor the properties of CPCs based strain sensors so that they can demonstrate competitive advantages over those special structural designed competitors. Another challenge is to achieve optimum functionality with less filler materials In this contribution, extrusion processed carbon black (CB)-filled CPCs, including polymer blends comprising of thermoplastic polyurethane (TPU) and olefin block copolymer (OBC), are explored as industrially relevant strain sensors. The influence of filler content, kinetic (compounding sequence) and thermodynamic (post thermal annealing treatment) factors on the conductivity and electro-mechanical sensing performances is investigated. For the more conventional binary CPCs, a general trend is demonstrated, showing a three-regime variation of fractional resistance change, ΔR/R0 versus strain, namely, initiation (I), reversible (II), and re-coverable damage (III) [3]. By exploiting the ternary blend system and controlling kinetic and thermodynamic factors as well as the amount of CB in each polymer phase, it is possible to design the phase morphology and tune the strain sensing performance. Compared with the binary system, comparable initial conductivity and especially monotonic variation relationship and higher gauge factor (sensitivity) can be realized with a lower filler content. With the developed sensor type a wide range of applications is possible, including the biomedical field. [1] M. Amjadi, K-U. Kyung, I. Park, M. Sitti, Adv. Funct. Mater., 2016, 26, 1678-1698. [2] X.-D. Wu, Y.-Y. Han, X.-X. Zhang, and C.-H. Lu, ACS Appl. Mater. Interfaces, 2016, 8, 9936-9945. [3] L. Flandin, A. Hiltner, E, Baer, Polymer, 2001, 42, 827-83

Designing controlled radical polymerization: A selection of a terminal or penultimate model for the intrinsic reactivities

In the past decades many efforts have been devoted to understand and design controlled radical polymerization (CRP) techniques such as atom transfer radical polymerization (ATRP) and nitroxide mediated polymerization (NMP). A crucial aspect is the use of detailed reaction schemes and the appropriate correction for diffusional limitations. Limited focus has however paid to the impact of penultimate monomer unit (PMU) effects, which can be explained by the complexity of the associated kinetic models with multiple reaction channels and the lack of data on reactivity ratios, in particular for NMP specific reactions. In the present contribution, it is demonstrated that depending on the comonomer pairs and the reaction conditions either a terminal [2] or penultimate model [3] is more suited. For copolymerizations with equimolar conditions for the comonomer amounts the PMU can be very pronounced even if based on the reactivity ratios as such this is not expected (Figure 1). Please click Additional Files below to see the full abstract

A detailed characterization and design of copolymerization

Many industrial polymerizations are copolymerizations in which two or more comonomers are copolymerized together to obtain a final product with a wide variety of properties originating from the related homopolymers. Crucial is the identification of the correct comonomer types and the reaction conditions so that the suited connectivity of monomer units is ensured in the copolymer chains. In view of this challenge a detailed characterization tool is indispensable. A sole focus on experimental tools is insufficient as they only allow the assessment of copolymer properties through relative properties and/or are limited to average properties [1-4]. The latter implies the lack of validation of intermolecular homogeneities, inhibiting process control on the polymer property level. To solve this issue and thanks to the advance in recent computer technologies, simulation tools have been developed which allow a characterization of copolymerization processes at the molecular level (see Figure 1; [3]). Monomer sequences of individual chains can be visualized allowing an unambiguous product qualification. In this contribution, the potential of these simulation tools is highlighted through several case studies. Focus in on both bulk/solution radical and cationic polymerizations and the interplay of chemistry and diffusional limitations [5-7]. Please click Additional Files below to see the full abstrac

Model-based design of MADIX under bulk and solution conditions

Macromolecular design by interchange of xanthates (MADIX) is a less studied controlled radical polymerization technique from a mechanistic and modeling point of view. In this contribution, MADIX of styrene and chain extension toward the synthesis of block copolymers is investigated, with azobisisobutyronitrile as conventional radical initiator and O-ethylxanthyl ethyl propionate as initial RAFT agent (R0X). Degenerative transfer coefficients for both the exchange with R0X and macro-RAFT agent are reported and their difference is highlighted to be relevant for the kinetic description. The model validity is supported by measurement of end-group functionality (EGF) data considering elemental analysis. Novel mechanistic insights are that in contrast to typical reversible addition fragmentation chain transfer (RAFT) polymerizations the macroradical CLD follows a Schulz-Flory distribution and that both during the homopolymerization and the chain extensions an exchange, so with monomer incorporation, only takes place once [1]. [1] D.J.G. Devlaminck, P.H.M. Van Steenberge, M.-F. Reyniers, D.R. D’hooge, Polym Chem. 2017, 8, 694

Deficiency of the miR-29a/b-1 cluster leads to ataxic features and cerebellar alterations in mice

miR-29 is expressed strongly in the brain and alterations in expression have been linked to several neurological disorders. To further explore the function of this miRNA in the brain, we generated miR-29a/b-1 knockout animals. Knockout mice develop a progressive disorder characterized by locomotor impairment and ataxia. The different members of the miR-29 family are strongly expressed in neurons of the olfactory bulb, the hippocampus and in the Purkinje cells of the cerebellum. Morphological analysis showed that Purkinje cells are smaller and display less dendritic arborisation compared to their wildtype littermates. In addition, a decreased number of parallel fibers form synapses on the Purkinje cells. We identified several mRNAs significantly up-regulated in the absence of the miR-29a/b-1 cluster. At the protein level, however, the voltage-gated potassium channel Kcnc3 (Kv3.3) was significantly up-regulated in the cerebella of the miR-29a/b knockout mice. Dysregulation of KCNC3 expression may contribute to the ataxic phenotype

Black aspergilli: A remaining challenge in fungal taxonomy?

&lt;p&gt;Aspergillus section Nigri is a taxonomically difficult but medically and economically important group. In this study, an update of the taxonomy of A. section Nigri strains within the BCCM/IHEM collection has been conducted. The identification accuracy of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was tested and the antifungal susceptibilities of clinical isolates were evaluated. A total of 175 strains were molecularly analyzed. Three regions were amplified (ITS, benA, and caM) and a multi-locus phylogeny of the combined loci was created by using maximum likelihood analysis. The in-house MALDI-TOF MS reference database was extended and an identification data set of 135 strains was run against a reference data set. Antifungal susceptibility was tested for voriconazole, itraconazole, and amphotericin B, using the EUCAST method. Phylogenetic analysis revealed 18 species in our data set. MALDI-TOF MS was able to distinguish between A. brasiliensis, A. brunneoviolaceus, A. neoniger, A. niger, A. tubingensis, and A. welwitschiae of A. sect. Nigri. In the routine clinical lab, isolates of A. sect. Nigri are often identified as A. niger. However, in the clinical isolates of our data set, A. tubingensis (n = 35) and A. welwitschiae (n = 34) are more common than A. niger (n = 9). Decreased antifungal susceptibility to azoles was observed in clinical isolates of the /tubingensis clade. This emphasizes the importance of identification up to species level or at least up to clade level in the clinical lab. Our results indicate that MALDI-TOF MS can be a powerful tool to replace classical morphology.&lt;/p&gt;</p