Polyelectrolyte stabilized nanodiamond dispersions

Colloidal stability of negatively charged nanodiamonds (ND) has been realized with the help of double hydrophilic block copolymers poly(ethylene oxide)-block-poly(dimethylaminoethyl methacrylate)-dodecyl (PEO-bPDMAEMA-C12). The polymers were synthesized through RAFT polymerization of DMAEMA with a PEO macromonomer carrying trithiocarbonate and dodecyl end-groups. The NDs and the polymers were complexed by mixing them in different ratios. In addition to the amount of polymers, the effect of the detailed structure of the polymer was of interest and thus, also polymers with different lengths of the PEO-block were synthesized, as well as a block copolymer without the dodecyl end-group. The composition of the polymer, as well as the complexation conditions were varied to find the route to stable nanoparticles. The optimized complexation method gave colloidally stable ND particles with positively charged PDMAEMA coronas. The colloids were stable at room temperature and also in saline solutions up to 0.154 M NaCl.Peer reviewe

Biomimeettiset supramolekulaariset rakenteet

Structurally important biological materials generically show hierarchical structures to allow functional properties. They exploit self-assemblies over the length scales by competing interactions and combining tailored supramolecular interactions. Examples are provided by spider silk, nacre, and bone, which show extraordinary mechanical properties, regardless of the weak individual building blocks. In these materials, the strength and toughness arise from nanoscale toughening mechanisms, where hard and soft domains are connected covalently and by weak interactions. They work in synergy to transfer stress from bulk to the reinforcing parts via sacrificial bonds and hidden lengths through hierarchical design.   In this thesis, an overview of the important aspects in biomimetic material design, such as supramolecular chemistry, self-assembly, hierarchical structures, and sacrificial bonding is first given. In the later chapters, four articles and their important findings towards novel biomimetic materials are highlighted. In the publications I and II, self-assemblies of asymmetric bile acid -based amphiphilic polymers were studied. The results suggest designing complex amphiphilic self-assembling systems to create hierarchical materials from nanoscale to bulk upon "switching-on" supramolecular interactions. In the publication III, a nanocomposite between multi-walled carbon nanotubes and a polymer was synthesized. The adhesion between the polymer and the carbon nanotubes was supramolecularly enhanced to control their relative slipping. Due to supramolecular reinforcements and hierarchical structure, the resulting nanocomposite showed slow crack propagation upon fracturing, reminiscent of natural materials. In the publication IV, well-defined oligomeric oligosaccharide-based molecules with end-groups capable of supramolecular hydrogen bonds were studied. Polarized optical microscopy suggested columnar liquid crystallinity in a specific hydrogen bonding solvent medium and upon complete solvent removal hydrogen bonds between the oligosaccharides were formed allowing supramolecular polymers and fiber spinning. This work paves ways to understand switching-on of hydrogen bonds "on-demand" in the processing, mimicking silk-spinning. In summary, the present work shows ways to incorporate supramolecular interactions of different strengths for functional materials, inspired by biological materials.Biologiset materiaalit tyypillisesti koostuvat funktionaalisuuden mahdollistavista hierarkisista rakenteista, jotka ovat muodostuneet supramolekulaarisesti itsejärjestyneistä molekyyleistä. Esimerkiksi hämähäkinseitti, helmiäinen ja luu koostuvat heikoista lähtöaineista, mutta silti niiden mekaaniset ominaisuudet ovat poikkeuksellisen hyviä. Niiden mekaaniset ominaisuudet selittyvät nanorakenteilla, joissa kovat ja pehmeät alueet ovat sitoutuneet toisiinsa sekä kovalenttisin sidoksin että heikoin vuorovaikutuksin. Vahvojen ja heikkojen sidosten yhdistelmä mahdollistaa, että osa sidoksista aukeaa muodonmuutoksissa ja muodostuu uudelleen muodonmuutoksen päätyttyä. Tämä, yhdistettynä hierarkiseen rakenteeseen mahdollistaa materiaaliin kohdistuvien voimien jakautumisen materiaalia vahvistaviin osiin. Tämän väitöskirjan johdannossa esitellään biomimeettisten materiaalien teoriaa, kuten supramolekulaarista kemiaa, itsejärjestymistä, biologisissa materiaaleissa esiintyviä hierarkisia rakenteita ja venytettäessä deformoituvia "uhrisidoksia". Seuraavissa kappaleissa käydään läpi neljän julkaistun artikkelin oleelliset tulokset. Julkaisut I ja II kuvaavat epäsymmetrisiin amfifiilisiin muokattuihin sappihappoihin liitettyjen supramolekulaaristen ryhmien vaikutusta itsejärjestymiseen. Tulokset voivat auttaa valmistamaan hierarkisia rakenteita itsejärjestymisen kautta molekyylitasolta makroskooppiselle tasolle hallitusti aktivoituvien vuorovaikutusten avulla. Julkaisussa III rakennettiin nanokomposiitti muokatuista hiilinanoputkista ja polymeerimatriisista. Hiilinanoputkien ja matriisin välinen adheesio varmistettiin supramolekulaarisin vuorovaikutuksin. Hierarkisen rakenteen ja supramolekulaaristen vahvistusten ansiosta saavutettiin sitkeä materiaali. Julkaisussa IV tutkittiin molemmista päistä supramolekulaarisilla ryhmillä muokatun, hyvinmääritellyn oligosakkaridin muodostamia rakenteita. Havainnot viittaavat kolumnaarisiin nestekiteisiin vetysidoksen luovuttajana toimivassa liuottimessa. Liuottimen haihtumisen yhteydessä rakenne lukittui supramolekulaarisen dimerisaation myötä, mikä mahdollisti supramolekulaaristen polymeerien kuiduttamisen. Työ avaa mahdollisuuksia silkinkaltaisten materiaalien prosessointiin liuoksesta kuiduksi. Yhteenvetona tämä väitöskirja esittelee mahdollisuuksia supramolekulaaristen vuorovaikutusten hyödyntämiseksi biomimeettisten funktionaalisten materiaalien valmistamiseksi

Hierarchical Supramolecular Cross-Linking of Polymers for Biomimetic Fracture Energy Dissipating Sacrificial Bonds and Defect Tolerance under Mechanical Loading

| openaire: EC/FP7/291364/EU//MIMEFUNBiological structural materials offer fascinating models how to synergistically increase the solid-state defect tolerance, toughness, and strength using nanocomposite structures by incorporating different levels of supramolecular sacrificial bonds to dissipate fracture energy. Inspired thereof, we show how to turn a commodity acrylate polymer, characteristically showing a brittle solid state fracture, to become defect tolerant manifesting noncatastrophic crack propagation by incorporation of different levels of fracture energy dissipating supramolecular interactions. Therein, poly(2-hydroxyethyl methacrylate) (pHEMA) is a feasible model polymer showing brittle solid state fracture in spite of a high maximum strain and clear yielding, where the weak hydroxyl group mediated hydrogen bonds do not suffice to dissipate fracture energy. We provide the next level stronger supramolecular interactions toward solid-state networks by postfunctionalizing a minor part of the HEMA repeat units using 2-ureido-4[1H]-pyrimidinone (UPy), capable of forming four strong parallel hydrogen bonds. Interestingly, such a polymer, denoted here as p(HEMA-co-UPyMA), shows toughening by suppressed catastrophic crack propagation, even if the strength and stiffness are synergistically increased. At the still higher hierarchical level, colloidal level cross-linking using oxidized carbon nanotubes with hydrogen bonding surface decorations, including UPy, COOH, and OH groups, leads to further increased stiffness and ultimate strength, still leading to suppressed catastrophic crack propagation. The findings suggest to incorporate a hierarchy of supramolecular groups of different interactions strengths upon pursuing toward biomimetic toughening.Peer reviewe

Remote diagnostics and monitoring using microwave technique:improving healthcare in rural areas and in exceptional situations

Abstract Interests towards wireless portable medical diagnostics and monitoring systems, which could be used outside hospital e.g. during pandemic or catastrophic situations, have increased recently. Additionally, portable monitoring solutions could partially address widely recognized challenges related to healthcare equality in rural areas. Microwave based sensing has recently been recognized as emerging technology for portable medical monitoring and diagnostics devices since they may enable development of safe, reliable, and low-cost solutions for future’s telemedicine. The aim of this paper is to present the basic idea of microwave -based medical monitoring and discuss its possibilities, advantages, and challenges. In particular, we show that microwaves could be exploited in three pre-diagnostics applications: 1) Detection of abnormalities in the brain with a helmet type of monitoring device, 2) Detection of breast cancer with a self-monitoring vest, 3) Detection of blood clots in leg with an antenna band. The technique is based on detecting differences in radio channel responses caused by the abnormalities having different dielectric properties than the surrounding tissues. Our results of realistic simulations and experimental measurements show that even small-sized abnormalities, e.g. tumors, can change channel characteristics in detectable level

High performance carbon-based printed perovskite solar cells with humidity assisted thermal treatment

We report humidity assisted thermal exposure (HTE) as a post-treatment method for carbon based printed perovskite solar cells (CPSCs). The method does not only improve the interfaces of different layers of the printed stack, but also provides a pathway to fabricate high performance CPSCs with low hysteresis along with high stability. The HTE treatment directly influences over the associated components in the stack and remarkably improves each photovoltaic parameter of the CPSCs as seen by several characterization schemes presented in this study. The average initial efficiency (9.0% ± 0.2%) of the CPSCs of a batch was significantly improved to 13.1% ± 0.2% i.e. as high as 45% when subjected to HTE treatment for a period of 200 hours. Furthermore, the highest average efficiency obtained from the same batch from reverse scanning was 13.8% ± 0.4% with a CPSC attaining as high as 14.3% when exposed to the same thermo-humid environment for a period of 115 hours. Above all, the stability of the HTE treated CPSCs wasalso not compromised for over 350 hours under full-sun illumination stress testing at 40 °C. The results presented in this work provide an opportunity to adopt HTE treatment as a complementary step for the fabrication of high-performance carbon-based perovskite solar cells with low hysteresis accompanied by high durability and performance reproducibility.Peer reviewe

Microwave sensing of brain water:a simulation and experimental study using human brain models

Abstract This paper introduces a microwave-based approach that aims to non-invasively measure water, particularly cerebrospinal fluid (CSF) dynamics, in the human brain. The microwave measurement technique is well-known in industrial applications. More recently microwave techniques have awakened interest also in biomedical applications. This is the first time it is suggested to be utilized in measurements of brain water, particularly of CSF. Two different head phantoms were built in order to validate the sensitivity of the technique to sense dynamic variations of CSF and water volume inside a human skull. These were comprised of multilayered head phantom, including a real human skull, mimicking the electromagnetic properties of a human head. In addition, the variation of the CSF is evaluated with electromagnetic simulations using a planar layer model and a hemispherical layer model. Moreover, propagation and power flow inside the head model is evaluated using 2D power flow presentations. Reflection sensor principle was selected due to its simplicity and ability to measure relatively thick samples. Importantly, reflection sensor requires only one-port measurement making it very feasible for in vivo brain monitoring. In addition, the measurement setup does not require attachment of the sensor to the head, thus the measurement can be realized also without touching the head. Our experimental study as well as simulation results demonstrated the possibility to non-invasively sense, by microwaves, small dynamic variations in CSF volume in the brain, in particularly in the subarachnoid space