Viologen based electroactive polymers and composites for durable electrochromic systems

Electrochromism, the phenomenon of reversible color change induced by a small electric charge, forms the basis for operation of several devices including mirrors, displays and smart windows. Although, the history of electrochromism dates back to the 19th century, only the last quarter of the 20th century has its considerable scientific and technological impact. The commercial applications of electrochromics (ECs) are rather limited, besides top selling EC anti-glare mirrors by Gentex Corporation and airplane windows by Boeing, which made a huge commercial success and exposed the potential of EC materials for future glass industry. It is evident from their patents that viologens (salts of 4,4ʹ-bipyridilium) were the major active EC component for most of these marketed devices, signifying the motivation of this thesis focusing on EC viologens. Among the family of electrochromes, viologens have been utilized in electrochromic devices (ECDs) for a while, due to its intensely colored radical cation formation induced by applying a small cathodic potential. Viologens can be synthesized as oligomer or in the polymeric form or as functionality to conjugated polymers. In this thesis, polyviologens (PVs) were synthesized starting from cyanopyridinium (CNP) based monomer precursors. Reductive coupling of cross-connected cyano groups yields viologen and polyviologen under successive electropolymerization using for example the cyclic voltammetry (CV) technique. For further development, a polyviologen-graphene composite system was fabricated, focusing at the stability of the PV electrochrome without sacrificing its excellent EC properties. High electrical conductivity, high surface area offered by graphene sheets together with its non-covalent interactions and synergism with PV significantly improved the electrochrome durability in the composite matrix. The work thereby continued in developing a CNP functionalized thiophene derivative and its copolymer for possible utilization of viologen in the copolymer blend. Furthermore, the viologen functionalized thiophene derivative was synthesized and electropolymerized in order to explore enhancement in the EC contrast and overall EC performance. The findings suggest that such electroactive viologen/polyviologen systems and their nanostructured composite films as well as viologen functionalized conjugated polymers, can be potentially applied as an active EC material in future ECDs aiming at durable device performances.Elektrokromismi on ilmiö, jossa pienellä sähköisellä varauksella saadaan aikaan palautuva värinmuutos. Monien laitteiden, kuten peilien, näyttöjen tai älykkäiden ikkunoiden, toiminta perustuu tähän ilmiöön. Historiallisesti elektrokromismi on tunnettu 19. vuosisadalta asti, mutta vasta 20. vuosisadan viimeinen neljännes on osoittanut ilmiön huomattavan tieteellisen ja teknologisen merkityksen. Näiden elektrokromismiin perustuvien tekniikoiden kaupallinen hyödyntäminen on vielä melko vähäistä. Tähän asti myydyimpiä tuotteita ovat olleet häikäisysuojatut peilit (Gentex Corporation) ja lentokoneen ikkunat (Boeing), jotka olivat valtavia kaupallisia menestyksiä osoittaen tekniikan mahdollisuudet tulevaisuuden lasiteollisuudessa. Patenteista selviää, että viologeenit (4,4ʹ-bipyridiniumin suolat) ovat yleisimpiä aktiivisia komponentteja useimmissa markkinoilla olevissa sovelluksissa, minkä perusteella tässä väitöskirjassa keskitytään viologeeneihin. Erilaisista sähköväriaineista viologeenejä on käytetty elektrokromisissa laitteissa jo jonkin aikaa johtuen niiden voimakkaan värisestä radikaalikationista, joka saadaan syntymään pienellä katodisella jännitteellä.Viologeenejä voidaan syntetisoida oligomeerinä tai polymeerinä, sekä toiminnallisena ryhmänä osana konjugoitua polymeeriä. Tässä väitöskirjassa polyviologeenit syntetisoitiin käyttämällä lähtöaineena syanopyridinium-pohjaista monomeeriä. Ristiinkytkettyjen syanoryhmien pelkistävä kytkeytyminen tuottaa viologeeniä ja polyviologeeniä peräkkäisissä sähköpolymerisaatioreaktioissa, mikä voidaan toteuttaa käyttämällä menetelmänä esimerkiksi syklistä voltammetriaa. Systeemiä kehitettiin edelleen siten, että polyviologeenistä ja rafeenista valmistettiin komposiitti, jossa parannettiin polyviologeenin stabiilisuutta, menettämättä sen erinomaisia elektrokromisia ominaisuuksia. Grafeenilevyjen hyvä sähköinen johtavuus ja suuri pinta-ala yhdistettynä ei-kovalenttisiin vuorovaikutuksiin ja synergiaetuihin PV:n kanssa paransi huomattavasti komposiittimatriisin elektrokromista kestävyyttä. Työtä jatkettiin kehittämällä CNP:llä funktionalisoitu tiofeenijohdos ja vastaava polymeeri, mikä mahdollisti viologeenin hyödyntämisen kopolymeeriseoksessa. Lisäksi syntetisoitiin ja sähköpolymeroitiin viologeenillä funktionalisoitu tiofeenijohdos, jonka avulla tutkittiin elektrokromisen kontrastin ja kokonaissuorituskyvyn parantumista. Havainnot osoittavat, että sähköisesti aktiivisia viologeeni/polyviologeenisysteemejä ja niistä valmistettuja nanorakenteisia komposiittikalvoja, sekä myös viologeenillä funktionalisoituja konjugoituja polymeerejä on mahdollista hyödyntää aktiivisena elektrokromisena materiaalina tulevissa suorituskyvyltään kestävissä elektrokromisissa laitteissa.Siirretty Doriast

Assessing geographical and economic inequalities in caesarean section rates between the districts of Bihar, India: a secondary analysis of the National Family Health Survey

Background In Bihar, one of the most populous and poorest states in India, caesarean sections have increased over the last decade. However, an aggregated caesarean section rate at the state level may conceal inequities at the district level. Objectives The primary aim of this study was to analyse the inequalities in the geographical and socioeconomic distribution of caesarean sections between the districts of Bihar. The secondary aim was to compare the contribution of free-for-service government-funded public facilities and fee-for-service private facilities to the caesarean section rate. Setting Bihar, with a population in the 2011 census of approximately 104 million people, has a low GDP per capita (US$610), compared with other Indian states. The state has the highest crude birth rate (26.1 per 1000 population) in India, with one baby born every two seconds. Bihar is divided into 38 administrative districts, 101 subdivisions and 534 blocks. Each district has a district (Sadar) hospital, and six districts also have one or more medical college hospitals. Methods This retrospective secondary data analysis was based on open-source national datasets from the 2015 and 2019 National Family Health Surveys, with respective sample sizes of 45 812 and 42 843 women aged 15–49 years. Participants Secondary data analysis of pregnant women delivering in public and private institutions. Results The caesarean section rate increased from 6.2% in 2015 to 9.7% in 2019 in Bihar. Districts with a lower proportion of poor population had higher caesarean section rates (R2=0.45) among all institutional births, with 10.3% in private and 2.9% in public facilities. Access to private caesarean sections decreased (R2=0.46) for districts with poorer populations. Conclusion Marked inequalities exist in access to caesarean sections. The public sector needs to be strengthened to improve access to obstetric services for those who need it most.publishedVersio

Exploring amide linkage in a polyviologen derivative towards simultaneous voltammetric determination of Pb(II), Cu(II) and Hg(II) ions

In this study, we report reductive electrosynthesis of a polyviologen derivative bearing amide linkage in its side chain, derived from a cyanopyridinium based monomer with amide functionality. The as grown film was characterized by cyclic voltammetry which displays a well-defined and reversible two step redox response characteristic of viologen. FTIR analysis show evidence of amide linkage and successful reduction of cyanopyridinium moieties to polyviologen. In situ multi ESR/UV-Vis-NIR spectroelectrochemistry show a single line in ESR signal, thereby suggesting polarons as the only charge carrier involved during charging/discharging process. Furthermore, a characteristic UV&ndash;Vis absorption spectra confirms viologen formation. Finally, the polyviologen film is subjected to simultaneous voltammetric determination of heavy metal ions, Pb(II), Cu(II) and Hg(II). The amide linkage in the polyviologen derivative is supposedly complexing these divalent metal ions, enabling their sensitive and simultaneous determination with low detection limits.</div

Are LMICs Achieving the Lancet Commission Global Benchmark for Surgical Volumes? A Systematic Review

Abstract Introduction The Lancet Commission on Global Surgery (LCoGS) set the benchmark of 5000 procedures per 100,000 population annually to meet surgical needs adequately. This systematic review provides an overview of the last ten years of surgical volumes in Low and Middle-Income-Countries (LMICs). Methodology We searched PubMed, Web of Science, Scopus, Cochrane, and EMBASE databases for studies from LMICs addressing surgical volume. The number of surgeries performed per 100,000 population was estimated. We used cesarean sections, hernia, and laparotomies as index cases for the surgical capacities of the country. Their proportions to total surgical volumes were estimated. The association of country-specific surgical volumes and the proportion of index cases with its Gross Domestic Product (GDP) per capita was analyzed. Results A total of 26 articles were included in this review. In LMICs, on average, 877 surgeries were performed per 100,000 population. The proportion of cesarean sections was found to be high in all LMICs, with an average of 30.1% of the total surgeries, followed by hernia (16.4%) and laparotomy (5.1%). The overall surgical volumes increased as the GDP per capita increased. The proportions of cesarean section and hernia to total surgical volumes decreased with increased GDP per capita. Significant heterogeneity was found in the methodologies to assess surgical volumes, and inconsistent reporting hindered comparison between countries. Conclusion Most LMICs have surgical volumes below the LCoGS benchmark of 5000 procedures per 100,000 population, with an average of 877 surgeries. The surgical volume increased while the proportions of hernia and cesarean sections reduced with increased GDP per capita. In the future, it's essential to apply uniform and reproducible data collection methods for obtaining multinational data that can be more accurately compared.Are LMICs Achieving the Lancet Commission Global Benchmark for Surgical Volumes? A Systematic ReviewpublishedVersio

An Electrostatically Strong Polyviologen-Reduced Graphene Composite Film for Highly Stable Electrochromic Systems

Polyviologen (PV)-reduced graphene oxide (rGO) nanocomposite films were fabricated by simple, one step reductive electropolymerization of cyanopyridinium based precursor monomer in an aqueous dispersion of graphene oxide (GO). Since the polymer formation and reduction of GO occurs at the same potential window, electrocodeposition technique was chosen for obtaining nanostructured PV-rGO film. The cyclic voltammetry experiments of PV-rGO displayed two well resolved, highly stable one-electron redox processes typical of viologen. Being a redox polymer, incorporation of rGO further enhances the electroactivity of the PV in the composite films. FTIR, Raman, XRD and XPS analysis revealed structural changes occurred after composite formation.  The PV-rGO nanostructured film exhibits a conspicuous electrochromism with low driving voltage and striking color changes. It was found that the PV-rGO film exhibit high coloration efficiency, fast response times and better cycling stability compared to pristine PV thin film. This performance can be attributed to the high stability of the electrochrome in the composite assembly induced by electrostatically driven non-covalent interactions between redox PV and rGO, high electrical conductivity and enlarged surface area through reinforced nanostructured graphene sheets for tethering PV molecules. Figure 1 <jats:p /