Ferro- and ferrielectricity and negative piezoelectricity in thioamide-based supramolecular organic discotics.

Amide-based discotic supramolecular organic materials are of interest for fundamental understanding of cooperative self-assembly and collective dipole switching mechanisms as well as for practically relevant ferroelectric and piezoelectric properties. Here, we show how replacing amides (dipole moment of ∼3.5 D) with thioamides (∼5.1 D) as dipolar moieties in the archetypal C3-symmetric discotic molecule BTA leads to ferroelectric materials with a higher remnant polarization and lower coercive field. The thioamide-based materials also demonstrate a rare negative piezoelectricity and a previously predicted, yet never experimentally observed, polarization reversal via asymmetric intermediate states, that is, ferrielectric switching.

Long-term quality of life and posttraumatic stress following elective cardiac surgery: preliminary findings of a 5-year follow-up study.

BACKGROUND: Heart surgery is a major stressful event that can have a significant negative effect on patients' quality of life (QoL) and may cause long-term posttraumatic stress reactions. The aim of this pilot study was to estimate the longitudinal change and predictors of health-related quality of life (HRQOL) dynamics and identify factors associated with PTS at 5-year follow-up (T2) after elective cardiac surgery and associations with pre-surgery (T1) QoL. MATERIALS AND METHODS: Single-centre prospective study was conducted after Regional Bioethics Committee approval. Adult consecutive patients undergoing elective cardiac surgery were included. HRQOL was measured using the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) questionnaire before (T1) and 5-years after (T2) cardiac surgery. Posttraumatic stress was assessed using the International Trauma Questionnaire. RESULTS: The pilot study revealed a significant positive change at 5-year follow-up in several domains of SF-36: physical functioning (PF), energy/fatigue (E/F), and social functioning (SF). Prolonged postoperative hospital stay was associated with change in SF (p < 0.01), E/F (p < 0.05) and emotional well-being (p < 0.05). The percentage of patients that had the posttraumatic stress disorder (PTSD) at T2 was 12.2%. Posttraumatic stress symptoms were associated with longer hospitalization after surgery (p < 0.01). CONCLUSIONS: HRQOL improved from baseline to five years postoperatively. Patients with lower preoperative HRQOL scores tended to have a more significant improvement of HRQOL five years after surgery. A prolonged postoperative hospital stay had a negative impact on postoperative social functioning, energy/fatigue, and emotional well-being. Increased levels of PTSD were found in cardiac surgery patients following five years after the surgery.

Resistive switching in an organic supramolecular semiconducting ferroelectric.

The combination of switchable dipolar side groups and the semiconducting core of the newly synthetized C3-symmetric benzotrithiophene molecule (BTTTA) leads to an ordered columnar material showing continuous tunability from injection- to bulk-limited conductivity modulation.

Suppressing depolarization by tail substitution in an organic supramolecular ferroelectric.

Despite being very well established in the field of electro-optics, ferroelectric liquid crystals so far lacked interest from a ferroelectric device perspective due to a typically high operating temperature, a modest remnant polarization and/or poor polarization retention. Here, we experimentally demonstrate how simple structural modification of a prototypical ferroelectric liquid-crystal benzene-1,3,5-trisamide (BTA) - introduction of branched-tail substituents - results in materials with a wide operating temperature range and a data retention time of more than 10 years in thin-film solution-processed capacitor devices at room temperature. The observed differences between linear- and branched-tail compounds are analyzed using density functional theory (DFT) and molecular dynamics (MD) simulations. We conclude that morphological factors like improved packing quality and reduced disorder, rather than electrostatic interactions or intra/inter-columnar steric hindrance, underlay the superior properties of the branched-tailed BTAs. Synergistic effects upon blending of compounds with branched and linear side-chains can be used to further improve the materials' characteristics.

Kinetic Monte Carlo simulations of organic ferroelectrics.

Ferroelectrics find broad applications, e.g. in non-volatile memories, but the switching kinetics in real, disordered, materials is still incompletely understood. Here, we develop an electrostatic model to study ferroelectric switching using 3D Monte Carlo simulations. We apply this model to the prototypical small molecular ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA) and find good agreement between the Monte Carlo simulations, experiments, and molecular dynamics studies. Since the model lacks any explicit steric effects, we conclude that these are of minor importance. While the material is shown to have a frustrated antiferroelectric ground state, it behaves as a normal ferroelectric under practical conditions due to the large energy barrier for switching that prevents the material from reaching its ground state after poling. We find that field-driven polarization reversal and spontaneous depolarization have orders of magnitude different switching kinetics. For the former, which determines the coercive field and is relevant for data writing, nucleation occurs at the electrodes, whereas for the latter, which governs data retention, nucleation occurs at disorder-induced defects. As a result, by reducing the disorder in the system, the polarization retention time can be increased dramatically while the coercive field remains unchanged.

Physical reality of the Preisach model for organic ferroelectrics.

The Preisach model has been a cornerstone in the fields of ferromagnetism and ferroelectricity since its inception. It describes a real, non-ideal, ferroic material as the sum of a distribution of ideal 'hysterons'. However, the physical reality of the model in ferroelectrics has been hard to establish. Here, we experimentally determine the Preisach (hysteron) distribution for two ferroelectric systems and show how its broadening directly relates to the materials' morphology. We connect the Preisach distribution to measured microscopic switching kinetics that underlay the macroscopic dispersive switching kinetics as commonly observed for practical ferroelectrics. The presented results reveal that the in principle mathematical construct of the Preisach model has a strong physical basis and is a powerful tool to explain polarization switching at all time scales in different types of ferroelectrics. These insights lead to guidelines for further advancement of the ferroelectric materials both for conventional and multi-bit data storage applications.

Impact of pre-operative health-related quality of life on outcomes after heart surgery.

BACKGROUND: Long-term improvement in health-related quality of life (HRQOL) is one of the most important outcomes of cardiac surgery. The aim of this study is to define the impact of perioperative patient and procedural variables on HRQOL dynamics, a year after cardiac surgery. METHODS: Consecutive patients undergoing elective on-pump cardiac surgery were enrolled in this prospective observational cohort study. Patients completed the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) questionnaire a day before surgery and once again a year after surgery. The effect size method was used to determine whether treatment resulted in the improvement of HRQOL. RESULTS: A total of 67.3% of patients achieved long-term improvement in HRQOL. Significant negative association was identified between Physical and Mental Component Summary scores (PCS/MCS) and long-term outcomes. Pre-operative PCS were 40.7 ± 13.7 for improvers and 56.6 ± 14.4 for non-improvers; MCS were 45.8 ± 12.1 and 65.2 ± 13.7, respectively (P < 0.001 for all). There were no statistically significant differences in pre-operative risk factors, demographics, operative factors or post-operative variables between the two groups. CONCLUSION: Among those completing this study, one in three patients did not experience long-term HRQOL improvements following cardiac surgery. Multivariate analysis confirmed that higher pre-operative PCS and MCS are independent predictors of worse HRQOL a year after surgery. Further research should focus on establishing the prevalence of this phenomenon worldwide and develop targeted interventions to improve long-term self-perceived quality of life for patients with relatively good pre-operative health.