Confinement Effects on the Crystalline Features of Poly(9,9-dioctylfluorene)

Typical device architectures in polymer-based optoelectronic devices, such as field effect transistors organic light emitting diodes and photovoltaic cells include sub-100 nm semiconducting polymer thin-film active layers, whose microstructure is likely to be subject to finite-size effects. The aim of this study was to investigate effect of the two-dimensional spatial confinement on the internal structure of the semiconducting polymer poly(9,9-dioctylfluorene) (PFO). PFO melts were confined inside the cylindrical nanopores of anodic aluminium oxide (AAO) templates and crystallized via two crystallization strategies, namely, in the presence or in the absence of a surface bulk reservoir located at the template surface. We show that highly textured semiconducting nanowires with tuneable crystal orientation can be thus produced. Moreover, our results indicate that employing the appropriate crystallization conditions extended-chain crystals can be formed in confinement. The results presented here demonstrate the simple fabrication and crystal engineering of ordered arrays of PFO nanowires; a system with potential applications in devices where anisotropic optical properties are required, such as polarized electroluminescence, waveguiding, optical switching, lasing, etc

Dinámica molecular y desarrollo microestructural en vidrios poliméricos : cristalización en timempo real

En este trabajo se ha estudiado la influencia de la microestructura en las propiedades dinámicas de vidrios poliméricos. En particular se ha seguido en tiempo real, la evolución de la relajación "alfa" que aparece en estos materiales a temperaturas por encima de la transición vítrea cuando se desarrolla un proceso de cristalización en los polímeros: poli(hidroxibutirato) (PHB), poli(etileno 2,6-naftaleno dicarboxilato) (PEN) y poli(aril éter éter cetona) (PEEK). Se utilizaron técnicas de espectroscopía dieléctrica y espectroscopía de dispersión de neutrones para el estudio de la dinámica y dispersión de rayos X tanto a ángulos altos como bajos mediante radiación sincrotrón para el estudio de la evolución de la microestructura. Los cambios en los parámetros dieléctricos pueden ser descritos en términos de la ecuación fenomenológica de Havriliak-Negami. El esfuerzo dieléctrico, sigue una forma sigmoidal similar a la de la cristalinidad. Se observa una reducción de la movilidad de las cadenas en la fase amorfa, cuando el tiempo de cristalización avanza. Esta ralentización depende de la cantidad de fase cristalina presente en la muestra. Se ha evaluado también la influencia de la rigidez molecular en las restricciones impuestas por la cristalinidad a las cadenas amorfasDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

Universitāšu ieguldījums Latvijas tautsaimniecībā. Kopsavilkums

Zinātniskā darbība un augstākā izglītība ieņem arvien nozīmīgāku vietu attīstīto valstu ekonomiskās attīstības stratēģijās. Jau vairāk nekā desmitgadi tradicionālajām universitātes funkcijām – studijām un zinātniskajai darbībai – pievienojušās vēl vismaz divas būtiskas funkcijas: inovācijas un citi pakalpojumi sabiedrībai. Mūsdienu teorijās universitātes analizē no dažādiem aspektiem. Apvienojot šīs atziņas, varam teikt, ka universitātes ir kompleksas sistēmas, kurām jārada, jāinterpretē, jāapstrādā, jāizplata un jāuzkrāj zināšanas, kā arī jānodrošina citi pakalpojumi sabiedrībai. Līdz šim tika uzskatīts, ka universitāšu galvenā ietekme uz tautsaimniecību ir izglītotu un augsti kvalificētu speciālistu sagatavošana darba tirgum un jaunu zināšanu komercializācija. Taču šobrīd universitāšu ieguldījums tautsaimniecībā tiek skatīts daudz plašākā nozīmē. Šī pētījuma izklāstam tiks izmantots Kembridžas universitātes piedāvātais modelis. Rakstā minēti tikai daži piemēri, kas ilustrē Latvijas universitāšu ietekmi uz tautsaimniecību. Investīciju izglītībā un zinātnē ienesīguma rādītāju aprēķini un analīze ir ļoti nepieciešami, lai valdība varētu izvērtēt, kur veiksmīgāk investēt valsts līdzekļus un kur sekmēt to ieguldīšanu no privātajiem resursiem. Tāpat šie rezultāti ir ļoti būtiski stratēģijas plānošanā, nosakot politisko dienas kārtību. Ekonomiskais pieaugums ir saistīts ar darbaspēka izmantošanas apjomu, tā efektivitāti un produktivitāti. Speciālistiem ar augstāko izglītību produktivitāte un ieguldījums tautsaimniecības attīstībā ir būtiski lielāks nekā pārējiem speciālistiem. Lai nodrošinātu Latvijas tautsaimniecības turpmāku attīstību, nepieciešams palielināt speciālistu ar augstāko izglītību īpatsvaru nodarbināto sastāvā.Latvijas Universitāte, Rīgas Tehniskā Universitāte, Daugavpils Universitāte, Latvijas Lauksaimniecības Universitāte, Rīgas Stradiņa Universitāte, Liepājas Universitāt

Dispositivo portamuestras para medidas simultáneas utilizando radiación de sincrotrón

Referencia OEPM: P200001388.-- Fecha de solicitud: 31/05/2000.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Dispositivo portamuestras para medidas simultáneas utilizando radiación de sincrotrón (ver figura en archivo de texto adjunto). La presente invención describe el desarrollo de un nuevo prototipo de portamuestras para utilización simultánea en una línea de difracción de rayos-X utilizando la para detección simultánea de dispersión en ángulos altos y bajos y espectroscopia dieléctrica. El prototipo consiste en: (i) dos bloques metálicos con cuatro resistencias calefactoras empotradas que permiten calentar los bloques metálicos y la muestra hasta 350ºC. Uno de los bloques esta atravesado por un tubo en forma de U por el cual circula aire de refrigeración y que al mismo tiempo conecta el bloque principal del portamuestras con la tapa; (ii) dos discos metálicos con orificios efectuados en el centro (electrodos); (iii) dos discos finos de aluminio; (iv) una placa superior (tapa), para cerrar el horno donde se introduce el portamuestras, con las correspondientes conexiones para el cableado.Peer reviewe

Evidence of early stage precursors of polymer crystals by dielectric spectroscopy

Dielectric spectra of the polyester poly(propylene succinate) were measured upon crystallization. For this model aliphatic polyester the α and β relaxations appear simultaneously and are well resolved in the experimental frequency window. During isothermal crystallization, this fact allows one to use the β relaxation to characterize the crystalline structural development while the α relaxation provides information about the evolution of the amorphous phase dynamics. In this way structure development and dynamics evolution can be characterized by a single experiment during the crystallization process. The unambiguous analysis of the dielectric loss clearly supports the existence of precursors of crystallization in the induction period. © 2007 The American Physical Society.Finnancial support from the MCYT (Grant No. MAT2005-01768), Spain.Peer Reviewe

Cooperativity of the β-relaxations in aromatic polymers

The measurement of the dielectric loss spectra of a series of copolyesters of poly(ethylene terephthalate) and poly(ethylene isophthalate) as a function of temperature in a broad frequency range was presented. The complex temperature behavior of the β relaxation in aromatic copolyesters was also studied. It was observed that the β processes exhibit a complex temperature dependence, showing a clear Arrhenius dependence at temperatures well below the glass transition temperature. The results show that the onset of the glass transition affects markedly to the β relaxation. It was observed that the strength of β relaxation remains nearly constant for all the samples for temperatures below their calorimetric Tg.©2004 The American Physical SocietyMCYT (Grant No. FPA2001-2139), Spain. Ramón y Cajal program of the Spanish MCYT.Peer Reviewe

Preparation, Physical Properties, and Applications of Water-Based Functional Polymer Inks

In this study, water-based functional polymer inks are prepared using different solvent displacement methods, in particular, polymer functional inks based on semiconducting polymer poly(3-hexylthiophene) and the ferroelectric polymer poly(vinylidene fluoride) and its copolymers with trifluoroethylene. The nanoparticles that are included in the inks are prepared by miniemulsion, as well as flash and dialysis nanoprecipitation techniques and we discuss the properties of the inks obtained by each technique. Finally, an example of the functionality of a semiconducting/ferroelectric polymer coating prepared from water-based inks is presented.This research was funded by the Ministry of Science, grant number PID2019-107514GB-I00 and the National Natural Science Foundation of China (no. 51903224)

Simultaneous crystalline-amorphous phase evolution during crystallization of polymer systems

Despite the fact that polymer crystallization has been the object of intense research, this process is far from being fully understood. Traditional polymer crystallization studies using X-ray scattering techniques mainly provide information about the ordered regions. To obtain a more complete information about the time evolution of both the crystalline and the amorphous phase during polymer crystallization, we have developed a technique which allows one to obtain information about both the crystalline and the amorphous phase simultaneously. We report here simultaneous information about three key aspects of the isothermal polymer crystallization process: i) polymer chain ordering, through Wide-Angle X-ray Scattering; ii) lamellar crystals arrangement, through Small-Angle X-ray Scattering; iii) amorphous phase evolution through dielectric spectroscopy. Our results probe that during primary crystallization the average mobility of the amorphous phase is not notably affected. Upon passing through the crossover time, marking the transition from primary to secondary crystallization, the restriction to the mobility of the amorphous phase mainly occurs in the regions between the lamellar stacks regions and not in the amorphous regions within the lamellar stacks. We hypothesize that molecular mobility in the amorphous regions located between consecutive crystals become strongly arrested as soon as the lamellar stack is formed. © EDP SciencesMCYT (grants FPA2001-2139, BMF2000-1474), Spain. MEC “Científicos y Tecnólogos Extranjeros” program. IHP-Contract HPRI-CT-1999-00040 of the European Commission (EC(ERBFMGEDT 950059) and II-00-015 EC).Peer Reviewe

Controlling morphology using low molar mass nucleators

This chapter focuses on the use of low molar mass compounds which self-assemble in to fibrillar structures within a polymer melt. Application of modest shear rate to the system will result in a common alignment of these fibrils which can serve as row nuclei for the subsequent crystallisation of the polymer matrix. Thus the combination of small quantities of a low molar mass compound and modest shear flow leads to a semi-crystalline morphology with a well defined anisotropy and morphology