Liquid Crystalline Polymers for Smart Applications

Polímers cristall-líquids (PCL) posseeixen propietats que són una combinació entre sòlids cristal·lins i fluids. Actualment, PCL que incorporen elements actius en l'estructura (pe, grups de foto-sensibles, dendrons, etc.) condueixen a un material selectivament sensible. S'informa que els polímers es poden aplicar en diversos sistemes pe com materials amb memòria de forma, sensors o pantalles foto-òptiques. Els nostres estudis se centren en dues aplicacions diferents: microcàpsules fotosensibles per a sistemes de lliurament controlat i les membranes autoacoblades conductores de protons per a la fotosíntesi artificial. La versatilitat i les propietats anisotrópicas de PCL, els fan com a candidats ideals per a nombrosos aplicacions intel·ligents. Per obtenir sistemes amb alliberament foto-activa, una família de copolímers, que conté alfa-estilbè i diferents espaiadors s'han dissenyat i sintetitzat. Alfa-estilbè és un mesogéno foto-actiu. Les microcàpsules basades d'alfa-metilestilbeno, amb vainillina en nucli, estaven preparats. Experiment d'alliberament amb i sense fotoirradiación va demostrar l'eficàcia d'aquest sistema. CLP d'estructura adequada per a auto-acoblament en una estructura columnar que podria ser efectiu en el transport de protons selectiu. Alineació homeotrópica de columnes en una membrana polimèrica permet aconseguir conductivitat de protons. Objectiu del nostre treball va ser: aconseguir estructures organitzades utilitzant poliamines modificades amb un mesógeno dendrític en posició lateral; preparació de membranes orientades usant aquests materials polimèrics; avaluar l'eficàcia de les membranes cap al transport de protons. Es van preparar membranes híbrides de ceràmica / poliamina. El material va mostrar alta conductivitat de protons selectiva i transport aigua-independent.Actualmente, PCL que incorporan elementos activos en la estructura (p.e., grupos de foto-sensibles, dendrones, etc.) conducen a un material selectivamente sensible. Se informa de que los polímeros se pueden aplicar en varios sistemas p.e. como materiales con memoria de forma, sensores o pantallas foto-ópticas. Nuestros estudios se centran en dos aplicaciones diferentes: microcápsulas fotosensibles para sistemas de entrega controlada y las membranas autoensambladas conductoras de protones para la fotosíntesis artificial. La versatilidad y las propiedades anisotrópicas de PCL, los hacen como candidatos ideales para numerosos aplicaciones inteligentes. Para obtener sistemas con liberación foto-activa, una familia de copolímeros, que contiene alfa-estilbeno y diferentes espaciadores se han diseñado y sintetizado. Alfa-estilbeno es un mesogéno foto-activo. Las microcápsulas basadas de alfa-metilestilbeno, con vainillina en núcleo, estaban preparados. Experimento de liberación con y sin fotoirradiación demostró la eficacia de este sistema. CLP de estructura adecuada para auto-ensamblaje en una estructura columnar que podría ser efectivo en el transporte de protones selectivo. Alineación homeotrópica de columnas en una membrana polimérica permite conseguir conductividad de protones. Objetivo de nuestro trabajo fue: lograr estructuras organizadas utilizando poliaminas modificadas con un mesógeno dendrítico en posición lateral; preparación de membranas orientadas usando estos materiales poliméricos; evaluar la eficacia de las membranas hacia el transporte de protones. Se prepararon membranas híbridas de cerámica/poliamina. El material mostró alta conductividad de protones selectiva y transporte agua-independiente.Liquid Crystalline Polymers (LCPs) possess properties which are a combination of crystalline solids and fluids. Currently, LCPs which incorporate active elements into the structure (i.e. photo-sensitive groups, dendrons, etc.) lead to selectively sensitive material. It is reported, that those polymers can be applied in a variety of systems i.e. as memory-shape materials, sensors or photo-optical displays. Our studies are focused on two different applications: photosensitive microcapsules for controlled delivery systems and self-assembly proton-conducting membranes for artificial photosynthesis. The extreme versatility and the characteristic anisotropic properties of LCPs, make them the ideal candidates for numerous smart applications. To achieve systems with photo-triggered release, a family of copolymers which contained alpha-methylstilbene and different spacers were designed and synthesized. Alpha-methylstilbene is a well-known photo-active mesogenic group. Microcapsules based on alpha-methylstilbene containing vanillin as a core were prepared. Release experiment in the presence and the absence of photoirradiation proved the effectiveness of this system. LC polymers of proper structure self-assembly into a columnar structure which could be effective in selective proton transport. Homeotropic alignment of columns in a polymeric membrane allows to achieve proton-conductivity. Aim of our work was: achieving organized structures using polyamine modified with a dendritic mesogen in side position; preparing oriented membranes based on this polymeric materials;assessing the effectiveness of the prepared membranes toward proton transport. Hybrid ceramic/polyamine membranes were prepared. The new material showed high selective proton conductivity and water independent transport

Dielectric, thermal and mechanical properties of l,d-poly(lactic acid) modified by 40-pentyl-4-biphenylcarbonitrile and sngle walled carbon nanotube

We report here the preparation and thermal, electrical and mechanical characterization of binary and ternary films based on l,d-poly(lactic acid) (l,d-PLA) and 4′-pentyl-4-biphenylcarbonitrile (5CB) and Single Walled Carbon Nanotubes (SWCN) with various weight ratio. The transitions for all investigated hybrid compositions detected by differential scanning calorimetry method were shifted to lower temperatures with increasing the concentration of 5CB in the mixture with polymer. Frequency domain dielectric spectroscopy method and thermal imaging together with polarized optical microscope were used to study electric and structural properties of created hybrid compositions. The best electrical conductivity was observed for hybrid composite l,d-PLA:5CB:SWCN with ratio 10:1:0.5 w/w/w - resistance of 41.0 Ω and thermal response up to 160 °C without causing any damages. Films in crystal form are much more inflexible than in amorphous and can be explain by the cold crystallization occurs at heating while the materials changed their physical state. The value of ε′ increases with increasing the 5CB admixture. Moreover, the addition of 5CB to l,d-PLA resulted in increased flexibility of polymeric base films. The best material flexibility and short-term strength were obtained for l,d-PLA sample with 9% 5CB content

Hybrid materials based on L,D-poly(lactic acid) and Single-Walled Carbon Nanotubes as flexible substrate for organic devices

We report on the application of l,d-poly(lactic acid) (l,d-PLA) with dispersed Single-Walled Carbon Nanotubes (SWCN) as a flexible translucent electrode for organic devices. We used commercially available nanotubes in various weight ratios from 0 to 8% dispersed in chloroform polymeric solution by ultrasonication and were drop cast. The created hybrid materials were investigated by differential scanning calorimetry to determine the influence of SWCN content on the thermal behavior, while polarizing optical microscope was used to find the effect of mechanical deformations on the textures. Drop-cast films were studied by optical transmittance, conductivity, dielectric properties and by thermal imaging under applied potential. Thermal imaging provided evidence of visible voltage-activated conduction. Simple mechanical deformation such as bending with stretching at edge to ca. 90 and elongation test were performed. Moreover, interactions between l,d-poly(lactic acid) and SWCN were investigated by FT-IR and NMR spectroscopy. Finally, we can conclude that the thermographic examination of created films permits fast, simple and inexpensive localization of defects on the surface of l,d-PLA:SWCN film, together with the electrical properties of the films

Synthesis and characterization of two new TiO2-containing benzothiazole-based imine composites for organic device applications

The effect of the presence of titanium dioxide in two new imines, (E,E)-(butane-1,4-diyl)bis(oxybutane-4,1-diyl) bis(4- {[(benzo[d][1,3]thiazol-2-yl)methylidene]amino}benzoate) (SP1) and (E)-N-[(benzo[d][1,3]thiazol-2-yl)methylidene]-4-dodecylaniline (SP2), on the properties and stability of imine:TiO2 composites for organic device applications were examined. The investigated titanium dioxide (in anatase form, obtained via the sol–gel method) exhibited a surface area of 59.5 m2 /g according to Brunauer–Emmett–Teller theory, and its structure is a combination of both meso- and microporous. The average pore diameter calculated by the Barrett–Joyner–Halenda method was 6.2 nm and the cumulative volume of pores was 0.117 m3 /g. The imine SP1 exhibited columnar organization (Col), while SP2 revealed a hexagonal columnar crystalline phase (Colhk). The imine:TiO2 mixtures in various weight ratio (3:0, 3:1, 3:2, 3:3) showed a lower energy gap and HOMO–LUMO energy levels compared to pure TiO2 . This implies that TiO2 provides not only a larger surface area for sensitizer adsorption and good electron collection, but also causes a shift of the imine energy levels resulting from intermolecular interaction. Also the temperature of the phase transition was slightly affected with the increase of TiO2 concentration in imine-based composites. The changes observed in the Fourier transform middle-infrared absorption (FT-MIR) spectra confirmed the significant influence of TiO2 on structural properties of both investigated imines. Similar interactions of oxygen vacancies existing on the TiO2 surface with SP1 and SP2 were observed. The imine:TiO2 mixtures showed good air stability and reusability, which demonstrates its potential for organic device applications

Molecular Mobility in Oriented and Unoriented Membranes Based on Poly[2-(Aziridin-1-yl)ethanol]

Unoriented and oriented membranes based on dendronized polymers and copolymers obtained by chemical modification of poly[2-(aziridin-1-yl) ethanol] (PAZE) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate were considered. DSC, XRD, CP-MAS NMR and DETA, contribute to characterize the tendency to crystallize, the molecular mobility of the benzyloxy substituent, the dendritic liquid crystalline group and the clearing transition. The orientation of the mesogenic chain somewhat hindered this molecular motion, especially in the full substituted PAZE. The fragility, free volume and thermal expansion coefficients of these membranes near the glass transition are related to the orientation and the addition of the dendritic groups. PAZE-based membranes combine both order and mobility on a supramolecular and macroscopic level, controlled by the dendritic group and the thermal orientation, and open the possibility of preparing membranes with proper channel mobility that promotes selective ionic transport

Synthesis and characterization of two new TiO2-containing benzothiazole-based imine composites for organic device applications

The effect of the presence of titanium dioxide in two new imines, (E,E)-(butane-1,4-diyl)bis(oxybutane-4,1-diyl) bis(4- {[(benzo[d][1,3]thiazol-2-yl)methylidene]amino}benzoate) (SP1) and (E)-N-[(benzo[d][1,3]thiazol-2-yl)methylidene]-4-dodecylaniline (SP2), on the properties and stability of imine:TiO2 composites for organic device applications were examined. The investigated titanium dioxide (in anatase form, obtained via the sol–gel method) exhibited a surface area of 59.5 m2/g according to Brunauer–Emmett–Teller theory, and its structure is a combination of both meso- and microporous. The average pore diameter calculated by the Barrett–Joyner–Halenda method was 6.2 nm and the cumulative volume of pores was 0.117 m3/g. The imine SP1 exhibited columnar organization (Col), while SP2 revealed a hexagonal columnar crystalline phase (Colhk). The imine:TiO2 mixtures in various weight ratio (3:0, 3:1, 3:2, 3:3) showed a lower energy gap and HOMO–LUMO energy levels compared to pure TiO2. This implies that TiO2 provides not only a larger surface area for sensitizer adsorption and good electron collection, but also causes a shift of the imine energy levels resulting from intermolecular interaction. Also the temperature of the phase transition was slightly affected with the increase of TiO2 concentration in imine-based composites. The changes observed in the Fourier transform middle-infrared absorption (FT-MIR) spectra confirmed the significant influence of TiO2 on structural properties of both investigated imines. Similar interactions of oxygen vacancies existing on the TiO2 surface with SP1 and SP2 were observed. The imine:TiO2 mixtures showed good air stability and reusability, which demonstrates its potential for organic device applications

Estudio del espectro de relajaciones dieléctricas y la conductividad en cristales líquidos poliméricos columnares

Las actuales membranas en el mercado para pilas de combustible alimentadas por bioalcoholes presentan el fenómeno del crossover o flujo cruzado, responsable de la pérdida de eficiencia de la pila. Los polímeros obtenidos como una modificación química de la poliepiclorhidrina (PECH) y de la poli(1-(2-hidroxietil)aziridina) (PAZE) suponen un importante avance, puesto que se utiliza la capacidad coordinativa del oxígeno y del nitrógeno frente a los cationes para transportar los protones. En este trabajo se ha sintetizado y caracterizado el comportamiento dieléctrico de diferentes cristales líquidos columnares poliméricos obtenidos por modificación de estos polímeros [1-2]. Estos polímeros modificados contienen grupos con una estructura cónico-plana que se ensamblan formando una columna de canal iónico, cuyo centro está formado por una cadena continua hidrofílica de poliéter o poliamina, que actúa como transportador de protones. Para obtener el espectro de relajaciones dieléctricas y la conductividad iónica se realizaron medidas en el rango de frecuencias f = 10-2/107 Hz y desde -150ºC hasta la temperatura de isotropización, que depende de la estructura química del polímero. El espectro de relajaciones de los polímeros se representan en términos de la permitividad dieléctrica compleja, ε’ y ε’’, la tangente de pérdidas, tan(δ), y el módulo eléctrico, M* y se observan las relajaciones correspondientes a fenómenos de movilidad local en este tipo de cristales líquidos [3]. Estos polímeros exhiben una conductividad protónica que alcanza valores similares a los que muestran las membranas comerciales de Nafión. Los resultados obtenidos indican que se puede conseguir un alto grado de selectividad de los protones frente a otras moléculas como el agua y el metanol, eliminando en gran medida el fenómeno del crossover. Por tanto es posible diseñar nuevas estrategias para preparar electrolitos anisótropos aplicables a pilas de combustible alimentadas por bioalcoholes, donde los mecanismos de conductividad se controlan a través de la formación de mesofases columnares.Los autores quieren agradecer al Ministerio de Economía y Competitividad por su apoyo a través de los proyectos de investigación ENE2011-28735-C02-01 (DOMEPOL) y CTQC2013-46825-R y la Generalitat Valenciana a través de los programas GRISOLIAP/2012/056 y APOSTD/2014/041

Review on thermoelectrical properties of selected imines in neat and multicomponent layers towards organic opto-electronics and photovoltaics

The present review is mainly focused on the extended analysis of the results obtained from coupled measurement techniques of a thermal imaging camera and chronoamperometry for imines in undoped and doped states. This coupled technique allows to identify the current-voltage characteristics of thin films based on imine, as well as to assess layer defects in thermal images. Additional analysis of results provides further information regarding sample parameters, such as resistance, conductivity, thermal resistance, and Joule power heat correlated with increasing temperature. As can be concluded from this review, it is possible not only to study material properties at the supramolecular level, but also to tune macroscopic properties of -conjugated systems. A detailed study of the structure-thermoelectrical properties in a series of eight unsymmetrical and symmetrical imines for the field of optoelectronics and photovoltaics has been undertaken. Apart from this molecular engineering, the imines properties were also tuned by supramolecular engineering via protonation with camphorsulfonic acid and by creation of bulk-heterojunction compositions based on poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl) and/or [6,6]-phenyl-C71-butyric acid methyl ester, poly(3,4-ethylenedioxythiophene) towards the analysed donor or acceptor ability of imines in the active layer. The use of coupled measurement techniques of a thermal imaging camera and chronoamperometry allows obtaining comprehensive data on thermoelectric properties and defects indicating possible molecule rearrangement within the layer