Update on Women in Physics in Finland

There has not been much change in the status of women in physics in Finland during the last three years. Numbers and problems remain the same. Some interesting events have been held, and excellent websites and initiatives have been started. Finland would benefit from nationwide gathering of statistical data on the numbers and salaries of female students and staff at academic institutions and on women working in STEM fields in industry to better quantify the problems. Lack of coordination and resources make it difficult to have long-term programs and to follow the outcomes of the initiatives started.Peer reviewe

Nanocellulose aerogel membranes for optimal electrolyte filling in dye solar cells

A new method for depositing electrolyte in dye solar cells (DSCs) is introduced: a nanocellulose hydrogel membrane is screen printed on the counter electrode and further freeze-dried to form a highly porous nanocellulose aerogel, which acts as an absorbing sponge for the liquid electrolyte. When the nanoporous dye-sensitized TiO2 photoelectrode film is pressed against the wetted aerogel, it becomes filled with the electrolyte. The electrolyte flows inside the TiO2 film only about ten micrometers (i.e. the TiO2 film thickness) whereas in the conventional filling method, where the electrolyte is pumped through the cell, it flows about 1000-times longer distance, which is known to cause uneven distribution of the electrolyte components due to a molecular filtering effect. Furthermore, with the new method there is no need for electrolyte filling holes which simplifies significantly the sealing of the cells and eliminates one common pathway for leakage. Photovoltaic analysis showed that addition of the nanocellulose aerogel membrane did not have a statistically significant effect on cell efficiency, diffusion in the electrolyte or charge transfer at the counter electrode. There was, however, a clear difference in the short circuit current density and open circuit voltage between the cells filled with the aerogel method and in the reference cells filled with the conventional method, which appeared to be caused by the differences in the electrolyte filling instead of the nanocellulose itself. Moreover, accelerated aging tests at 1 Sun 40 °C for 1000 h showed that the nanocellulose cells were as stable as the conventional DSCs. The nanocellulose aerogel membranes thus appear inert with respect to both performance and stability of the cells, which is an important criterion for any electrolyte solidifying filler material.Peer reviewe

Molecular-level photo-orientation insights into macroscopic photo-induced motion in azobenzene-containing polymer complexes

As part of continuing efforts to deepen the understanding of photo-induced mass transport in azo-containing polymers, we compared the diffraction efficiency (DE) during surface-relief grating (SRG) inscription, photo-induced molecular orientation (), and thermal stability in two sets of supramolecular azopolymer complexes, namely, hydrogen-bonded (H-bonded) and ionically bonded (i-bonded) complexes, both as a function of the polymer degree of polymerization (DP). To that end, poly(4-vinylpyridine) (P4VP) polymers with DPs of 41, 480, and 1900 were H-bonded at an equimolar ratio with 4-hydroxy-4′-dimethylaminoazobenzene (azoOH), and the fully quaternized derivatives of the three P4VPs (P4VPMe) were i-bonded via ion exchange to sodium 4-[(4-dimethylamino)-phenylazo]benzene sulfonate (azoSO3), also known as methyl orange, where the OH functionality of azoOH is replaced by a sulfonate group. The i-bonded complexes show much better DE performances and levels than those of H-bonded complexes, which we relate to the liquid crystal structure of the former complexes. Fitting the curves by a biexponential equation leads to two parameters associated with a fast trans–cis or angular hole burning (AHB) process and a slow angular redistribution (AR) process of the azo, respectively. It is found that AHB is predominant in the H-bonded complexes, whereas the AR contribution is much greater in the i-bonded complexes, assuring their superior SRG efficiency that is enabled by the anisotropic free volume created mainly by the AR process. In each set of complexes, the SRG efficiency is much better for the lowest DP complex, while the AR contribution is constant (and low) for the H-bonded complexes and increases roughly linearly with the decrease in DP for the i-bonded complexes. The latter difference might be related to the presence of entanglements in the complexes with DPs 480 and 1900, which slow down the macroscopic movement during SRG inscription but not the molecular-scale movement in photo-orientation

Photoactive/passive molecular glass blends : an efficient strategy to optimize azomaterials for surface relief grating inscription

: Irradiation of azomaterials causes various photophysical and photomechanical effects that can be exploited for the preparation of functional materials such as surface relief gratings (SRGs). Herein, we develop and apply an efficient strategy to optimize the SRG inscription process by decoupling, for the first time, the important effects of the azo content and glass transition temperature (Tg). We prepare blends of a photoactive molecular glass functionalized with the azo Dis‐ perse Red 1 (gDR1) with a series of analogous photopassive molecular glasses. Blends with 10 and 40 mol% of gDR1 are completely miscible, present very similar optical properties, and cover a wide range of Tg from below to well above ambient temperature. SRG inscription experiments show that the diffraction efficiency (DE), residual DE and initial inscription rate reach a maximum when Tg is 25 to 40 °C above ambient temperature for low to high azo content, respectively. Indeed, for a fixed 40 mol% azo content, choosing the optimal Tg enables doubling the SRG inscription rate and increasing DE sixfold. Moreover, a higher azo content enables higher DE for a similar Tg. Spectroscopy measurements indicate that the photo‐ orientation of DR1 and its thermal stability are maximal with Tg around 70 °C, independent of the azo content. We conclude that the SRG potential of azomaterials depends on their capability to photo‐orient but that the matrix rigidity eventually limits the inscription kinetics, leading to an optimal Tg that depends on the azo content. This study exposes clear material design guidelines to optimize the SRG inscription process and the photoactivity of azomaterials

Biomimetic zinc chlorin-poly(4-vinylpyridine) assemblies : doping level dependent emission-absorption regimes

Peer reviewe

Plant-Based Structures as an Opportunity to Engineer Optical Functions in Next-Generation Light Management

This review addresses the reconstruction of structural plant components (cellulose, lignin, and hemicelluloses) into materials displaying advanced optical properties. The strategies to isolate the main building blocks are discussed, and the effects of fibrillation, fibril alignment, densification, self-assembly, surface-patterning, and compositing are presented considering their role in engineering optical performance. Then, key elements that enable lignocellulosic to be translated into materials that present optical functionality, such as transparency, haze, reflectance, UV-blocking, luminescence, and structural colors, are described. Mapping the optical landscape that is accessible from lignocellulosics is shown as an essential step toward their utilization in smart devices. Advanced materials built from sustainable resources, including those obtained from industrial or agricultural side streams, demonstrate enormous promise in optoelectronics due to their potentially lower cost, while meeting or even exceeding current demands in performance. The requirements are summarized for the production and application of plant-based optically functional materials in different smart material applications and the review is concluded with a perspective about this active field of knowledge

Tutkimuksia vetysitoutuneiden polymeeriväriainekompleksien kahtaistaittavuudesta

Photoresponsive polymers containing azobenzene chromophores have attracted much attention because polarized light can induce significant anisotropy into such materials. This concept is of pontential interest for holographic data storage and waveguiding, to mention a few examples. The goal of this work was to study the effect of the hydrogen bonding between an azobenzene dye and polymeric matrix on the photo-orientation behaviour by using the complex of 4-nitro-4'-hydroxyazobenzene (NHA) and poly(4-vinylpyridine) (P4VP). The properties of these NHA-P4VP complexes were compared to two conventional guest-host systems lacking the specific interactions between the dye and the polymer. For all of the three studied systems, series of seven different compositions was prepared. The interaction between the chromophores and polymers was studied by Fourier-Transformed Infrared Spectroscopy (FTIR). Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) were used to test the thermal properties of the complexes. The optical characterization consisted of Ultraviolet-Visible Spectroscopy (UV-Vis) and photoinduced birefringence measurements on spin-coated thin films. In order to calculate the birefringence, the thicknesses of the films were measured with a profilometer. The optical results obtained from the reference systems behaved as expected based on the literature: After a certain threshold concentration the aggregation of the dye molecules was seen in the UV-Vis spectra and in the degradation of the film quality. Beyond this onset of aggregation, photo-orientation was suppressed. In contrast, the hydrogen-bonded NHAP4VP complex behaved differently. The hydrogen bonding allowed to prepare high-quality thin films even for the nominally equimolar complex. Furthermore, the competing dye-polymer and dye-dye interactions were observed to enhance the values of saturated birefringence as well as its stability. With the sample of equimolar composition, the maximum value of saturated birefringence was 0.14 and 94% of it was preserved after blocking the inducing illumination. By exploiting the spontaneus hydrogen bonding between a dye and a polymer, it is possible to produce photoorientable materials having the same performance than corresponding functionalized polymers. Based on the results of this thesis, an article has been published in Chemistry of Materials (Hydrogen-Bonded Polymer-Azobenzene Complexes: Enhanced Photoinduced Birefringence with High Temporal Stability through Interplay of Intermolecular Interactions, Arri Priimagi, Jaana Vapaavuori, Francisco J. Rodriguez, Charl F. J. Faul, Markku T. Heino, Olli Ikkala, Martti Kauranen and Matti Kaivola, Chem. Mater. 2008, 20,Polymeeriväriainekompleksit ovat erittäin mielenkiintoista, sillä niitä voidaan hyodyntää optisessa tiedontallennuksessa, aaltojohteissa ja taajuudenkahdennuksessa, muutamia esimerkkejä mainitakseni. Tässä työssä tutkittiin atsobentseenijohdannaisen 4-nitro-4'-hydroksiatsobentseenin (NHA) ja poly(4-vinyylipyridiinin) (P4VP) vetysitoutumista ja syntyneiden kompleksien orientoimista lineaarisesti polaroidun valon avulla. Vetysitoutuneen NHA-P4VP-kompleksin ominaisuuksia verrattiin kahteen vetysitoutumattomaan polymeeriväriainesysteemiin. Työssä valmistettiin kaikista kolmesta tutkittavasta polymeeriväriainesysteemistä seitsemän moolisuhteen näytesarjat. Polymeerien ja väriainemolekyylien välisiä sidoksia tutkittiin Fourier-muunnetulla infrapunaspektroskopialla (FTIR). Vetysidotun materiaalin termistä stabiilisuutta tutkittiin termogravimetrialla (TGA) ja differentiaalisella pyyhkäisykalorimetrialla (DSC). Optista karakterisointia varten näyteliuoksista spinnattiin ohutkalvoja kvartsilasisubstraateille. Optisina karakterisointimenetelminä käytettiin näkyvän ja ultraviolettivalon spketroskopiaa (UV-Vis) sekä valoherätteisen kahtaistaittavuuden mittausta. Vertailunäytesarjat käyttäytyivät odotetusti: Väriainemolekyylien ja polymeeriketjujen välillä ei havaittu oleellisia fysikaalisia vuorovaikutuksia ja kun tietty kynnyskonsentraatio ylitettiin, alkoivat väriainemolekyylit aggregoitua keskenään. Aggregoituminen havaittiin sekä muutoksina molekyylien UV-Vis-spektrissä että kvalitatiivisesti ohutkalvojen laadun huononemisena. Aggregoituminen myös häiritsi molekyylien orientoitumista pienentäen saturoitunutta kahtaistaittavuutta. Vetysitoutunut NHA-P4VP-kompleksi puolestaan käyttäytyi päinvastaisesti: Väriainemolekyylien välinen vuorovaikutus nähtiin UV-Vis-spektreissä, mutta sen kanssa kilpaileva vetysitoutuminen mahdollisti molekyylien orientoimisen aina stoikiometriseen kompleksiin asti. Saturoituneen kahtaistaittavuuden suuruus moolisuhteella 1.0 olikin 0.14, ja 94% arvosta säilyi vielä orientoinnin lopettamisen jälkeen. Hyödyntäen spontaanisti tapahtuvaa vetysitoutumista voidaan siis valmistaa foto-orientoituvia materiaaleja, joiden suorituskyky on oleellisesti yhtä hyvä kuin perinteisten funktionaalisten polymeerien, jossa väriaineet on sidottu kovalenttisesti polymeeriketjuun. Tämän työn tulokset on julkaistu myös Chemistry of Materials -lehdessä (Hydrogen-Bonded Polymer-Azobenzene Complexes: Enhanced Photoinduced Birefringence with High Temporal Stability through Interplay of Intermolecular Interactions, Arri Priimagi, Jaana Vapaavuori, Francisco J. Rodriguez, Charl F. J. Faul, Markku T. Heino, Olli Ikkala, Martti Kauranen and Matti Kaivola, Chem. Mater. 2008, 20, 6358)

Tutkimuksia supramolekylääristen atsobentseenimateriaalien valovasteesta

Azobenzene molecules are known to change their geometry upon photon absorption. The photoisomerization process, taking place at the nanometer scale, can give rise to remarkable photoinduced macroscopic motions into the material system. The most pronounced examples of such effects are photoinduced bending of free-standing films and the formation of micron-scale surface patterns due to photoinduced mass transport. Due to their anisotropic shape, azobenzenes also contain directional information and are polarization sensitive. The phenomena arising from the photoisomerization reaction have applications not only in optics and photonics, but also in the interfaces between light and surface science, information storage, imaging, biology, energy storage and actuation. Despite the extensive research, many fundamental questions concerning the coupling between the molecular-scale reactions and the photoresponse of the material at larger scales still remain a conundrum. This thesis seeks for guidelines for designing efficient photoresponsive materials through exploiting the toolkit of supramolecular chemistry. Supramolecular functionalization  provides a powerful tool for precisely controlling the composition of the material system, which is imperative when exploring the structure–performance relationships that govern the material's light-responsive behavior. By  selecting the constituent compounds in a systematic and controlled manner, we study the effect of the structural and physical parameters of the azobenzene units on their packing density, which again profoundly influences their optical performance. More specifically, the role of  (i) chromophore-chromophore intermolecular interactions, (ii) flexible spacer groups, (iii) the polarity of the azobenzene units, and (iv) the architecture of the host material on photoalignment and photoinduced surface patterning are discussed. In addition to contributing to fundamental understanding of light-matter interactions in azobenzene-containing materials, our findings highlight more generally the potential of supramolecular material design in optics and photonics, and we believe that this interface will bring about applications far beyond the scope now seen.Atsobentseenipohjaiset molekyylit voivat muuttaa muotoaan fotonin absorboitumisen seurauksena. Nämä nanomittakaavassa tapahtuvat valoisomerisaatioreaktiot voivat johtaa makroskooppisiin valoherätteisiin ilmiöihin, esimerkiksi kokonaisen polymeerikalvon taipumiseen tai mikrometriskaalan pintakuvioiden muodostumiseen valon vaikutuksesta. Sauvamaisen muotonsa ansiosta atsobentseenimolekyylejä voidaan myös suunnata hyödyntäen valon polarisaatiota. Näille ilmiöille on jo löytynyt käyttökohteita niin optiikan, pintatieteiden kuin biologiankin alalta. Erityisen mielenkiintoista on mahdollisuus tuottaa valovoimalla liikkuvia koneita, sillä atsobentseenimolekyylit pystyvät muuttamaan absorboimansa valoenergian suoraan liikkeeksi: mikrotasolla atsobentseenimolekyylejä voidaan käyttää muun muassa optisina kytkiminä, kun taas makrotasolla voidaan rakentaa valolla liikkuvia keinolihaksia ja moottoreita. Huolimatta laajasta tutkimustiedosta, monet valon aikaansaamat materiaalin liikkeeseen liittyvät peruskysymykset ovat vielä vastaamatta. Tässä työssä tutkitaan, miten pienillä ja hallituilla materiaalisysteemin ominaisuuksien muutoksilla voidaan ohjata materiaalin käyttäytymistä ja valovastetta haluttuun suuntaan. Työ hyödyntää supramolekylääristä kemiaa atsobentseenimateriaalien valmistuksessa ja korostaa entisestään tämän lähestymistavan etuja. Väitöskirja antaa uutta tietoa siitä, miten yksittäisten atsobentseenimolekyylien fysikaaliset ja kemialliset ominaisuudet vaikuttavat supramolekylääristen kompleksien valovasteeseen. Työssä pureudutaan muun muassa atsobentseenien välisiin vuorovaikutuksiin, pehmentävien hiilivetyketjujen merkitykseen, atsobentseeniyksikköjen polaarisuuteen ja atsobentseenit vastaanottavan isäntämolekyylin arkkitehtuurin vaikutukseen. Työ lisää ymmärrystä valoherätteisistä atsobentseenimateriaaleista ja edesauttaa uusien valoliikkeeseen perustuvien sovellusten suunnittelua.

Taming macromolecules with light : lessons learned from vibrational spectroscopy

Exciting new applications, from large-area nanopatterning and templating to soft light-powered robotics, are emerging from the fundamental research on light-triggered changes in macromolecular systems upon photoisomeriza-tion of azobenzene-based molecular photoswitches. The understanding of how the initial molecular-scale photoisomerization of azobenzene, a complex photochemical event in itself, is translated into the response of macromol-ecules and even into macroscopic-scale motion of illuminated azomaterials is an enormous task. The focus here is on how this knowledge has advanced by applying different vibrational spectroscopy techniques that provide rich molecular insight into the photoresponse of chemically specific molecular moieties. In particular, infrared and Raman spectroscopy studies are high-lighted, in the context of phototriggered perturbation of self-assembled structures and photoinduced linear and circular anisotropy, as well as photo-induced surface patterning, with the objective of offering a perspective on how vibrational spectroscopy can help in answering an array of essential yet unsettled questions