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Die Kenntnis des temperaturabhängigen Viskositätsverhaltens η(T) einer Glasschmelze ist für Technik und Wissenschaft aufgrund von Heißumform- und Abkühlprozessen, als auch zur Gewinnung tiefergehender Erkenntnisse über die Schmelzstruktur, z. B. die Fragilität einer Schmelze oder die Rolle der Netzwerkbildner und Netzwerkwandler von großem Interesse. Leider ist es nicht einfach, mit vergleichsweise langsam laufenden viskosimetrischen Methoden die gesamte Viskosität oberhalb der Glasübergangstemperatur Tg bei einigen Glassystemen aufgrund der bei den Messungen auftretenden Kristallisation zu messen. Diese Kristallisation beeinflusst stark die Viskosität der resultierenden heterogenen Systeme. Als Ergebnis wird eine Lücke in den Viskositätsdaten zwischen Tg und der Temperatur der stabilen Flüssigkeit erhalten. Weiterhin wurde in der Literatur gezeigt, dass man die aus kalorimetrischen Experimenten abgeleitete -lg qc vs. 1/Tf-Kurve auf die lg η vs. 1/T-Beziehung überlagern kann, indem man einen sogenannten parallelen Verschiebungsfaktor lg K verwendet. Somit ermöglicht K das Abrufen von η, ohne dass Viskositätsmessungen durchgeführt werden müssen. Dies ist von entscheidender Bedeutung, da die Kristallisationsneigung der hier untersuchten Gläser die Bestimmung der Flüssigkeitsviskosität durch rheologische Methoden in einem weiten Temperaturbereich oberhalb von Tg verhindert. Diese kumulative Doktorarbeit wurde entwickelt, um einen kombinierten experimentellen Ansatz basierend auf Kalorimetrie und Viskosimetrie zu testen und um die Lücke in den Viskositätsdaten für mehrere zerbrechliche Glassysteme zu schließen, die aufgrund schneller Kristallisation auftritt. Ein neues kommerzielles Hochgeschwindigkeitskalorimeter wurde mit konventioneller Kalorimetrie kombiniert, um Abkühl- und Aufheizraten bis zu 40.000 K s−1 (2.400.000 K min−1) abzudecken und durch Anwendung von parallelen Verschiebungsfaktoren Konset, Kpeak und Kend Viskositäten von Tg bis hinunter nach η = 104,9 Pa s zu erhalten. Im Detail handelt es sich bei den in dieser Studie getesteten zerbrechlichen Schmelzen um Silikatgläser (Lithiumdisilikat, Diopsid und Standardglas DGG I), ein Fluorphosphatglas (N-PK52A), Telluritgläser (reines TeO2 und zwei Natriumtelluritgläser) und Zr-basierte metallische Gläser (Vitreloy 105 und AMZ4). Es wurde festgestellt, dass dieser kombinierte experimentelle Ansatz geeignet ist, die η(T)-Lücke für die genannten Schmelzen zu verengen. Neue Daten wurden vom Glasübergangsbereich bis hinunter nach η = 106,3 Pa s für das Fluorphosphatglas, 105,5 Pa s für Silikatgläser, 105,3 Pa s für Telluritgläser und 104,9 Pa s für metallische Gläser erhalten. Eine anschließende stark eingeschränkte Parametrierung der verfügbaren Viskositätsdaten ermöglicht die Beschreibung des gesamten Viskositätsbereichs. Nach dieser experimentellen Vorgehensweise verbleibt eine kleinere Lücke in den Viskositätsdaten aller Gläser. Zusätzlich für reines TeO2, dessen schwache Glasbildungsfähigkeit und starke Kristallisationsneigung zuverlässige Messungen im unterkühlten Zustand verhindern, liefert die Parametrisierung den ersten experimentell ermittelten Viskositätsverlauf. Im Fall der metallischen Gläser deuten die bereits verfügbaren gemessenen Viskositätsdaten aus der Literatur auf die Existenz eines ungewöhnlichen Viskositätsverhaltens hin, den „fragile-to-strong“ (F–S) Übergangs. Die in dieser Dissertation bereitgestellten neuen Daten und Anpassungen grenzten das Auftreten dieses F-S-Übergangs auf eine Region bei höherer Temperatur ein., Knowledge about the temperature-dependent viscosity behaviour η(T) of a glass melt holds strong interest for both, technology and science due to hot-forming and cooling processes as well as to gain deeper knowledge about the melt structure, e.g. the fragility of a melt or the role of the network formers and modifiers. Unfortunately, it is not easy to measure the entire viscosity above the glass transition temperature Tg with comparatively slow running viscometric methods for some glass systems due to crystallisation occurring during the measurements. This crystallisation strongly influences the viscosity of the resulting heterogeneous systems. As a result, a gap in viscosity data is obtained between Tg and the temperature of the stable liquid. Further, it has been demonstrated in the literature that one can superimpose the -lg qc vs 1/Tf curve derived from calorimetry experiments on the lg η vs 1/T relationship by using a so-called parallel shift factor lg K. Thus, K enables retrieving η without the need to conduct viscosity measurements. This holds crucial importance since the proneness to crystallise of the glasses studied here prevents determination of liquid viscosity by rheological methods within a wide temperature range above Tg. This cumulative doctoral thesis was designed to test a combined experimental approach based on calorimetry and viscometry to narrow the gap in viscosity data for several fragile glass systems that appears due to fast crystallisation. A new commercial high-rate calorimeter was combined with conventional calorimetry to cover cooling and heating rates up to 40,000 K s-1 (2,400,000 K min-1) and thereby receive viscosities from Tg down to η = 104.9 Pa s by applying parallel shift factors Konset, Kpeak and Kend. In detail, the fragile melts tested in this study are silicate glasses (lithium disilicate, diopside and standard glass DGG I), a fluorophosphate glass (N-PK52A), tellurite glasses (pure TeO2 and two sodium tellurite glasses) and Zr–based bulk metallic glasses (Vitreloy 105 and AMZ4). It was found that this combined experimental approach is suitable to narrow the η(T) gap for the mentioned melts. New data were obtained from the glass transition region down to η = 106.3 Pa s for the fluorophosphate glass, 105.5 Pa s for silicate glasses, 105.3 Pa s for tellurite glasses and 104.9 Pa s for metallic glasses. A subsequent highly-constrained parameterisation of the available viscosity data makes it possible to describe the entire viscosity range. A smaller gap remains in the viscosity data of all glasses after this experimental procedure. Additionally, for pure TeO2, whose weak glass-forming ability and strong tendency to crystallise prevent reliable measurements in the undercooled state, the parameterisation provides the first experimentally-determined viscosity curve. In case of the metallic glasses, the already-available measured viscosity data from literature suggest the existence of an unusual viscosity behaviour, the fragile-to-strong (F–S) transition. The new data and fits provided in this thesis narrowed down the appearance of this F-S transition to a region at higher temperature.

Via fast differential scanning calorimetry using an Au-based glass as an example, we show that metallic glasses should be classified into two types of amorphous/monolithic glass. The first type, termed self-doped glass (SDG), forms quenched-in nuclei or nucleation precursors upon cooling, whereas in the so-called chemically homogeneous glass (CHG) no quenched-in structures are found. For the Au-based glass investigated, the critical cooling and heating rates for the SDG are 500 K s−1 and 20,000 K s−1, respectively; for the CHG they are 4000 K s−1 and 6000 K s−1. The similarity in the critical rates for CHG, so far not reported in literature, and CHG’s tendency towards stochastic nucleation underline the novelty of this glass state. Identifying different types of metallic glass, as is possible by advanced chip calorimetry, and comparing them with molecular and polymeric systems may help to elaborate a more generalized glass theory and improve metallic glass processing., Nature Communications, 10 (1), ISSN:2041-1723

Ultra-fast chip calorimetry is a modern thermal analysis technique based on MEMS-type sensors, which allows performing quantitative measurements on samples of only a few nanograms. However, calorimetry alone is sometimes insufficient for in-depth analysis of complex phase transitions occurring during the experiment. Therefore, in-operando structural analysis was found to be helpful in deciphering the nature of the corresponding structural transitions. Here we report on design of accessories for in-operando synchrotron-based X-ray scattering experiments at low temperatures as well as under different atmospheres and humidities. The examples of applications in polymer physics include analysis of the double-melting behavior of poly(trimethylene terephthalate) and structure formation processes in isotactic polypropylene.

Fast scanning chip calorimetry was used to perform an elaborate isothermal study of poly(3‐hexyl thiophene)/[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT/PC61BM) submicron layers. The used scanning rates of 30 000 K s−1 allow for a ‘true’ isothermal study, where non‐isothermal effects are avoided. Results were obtained over a wide temperature range for the 1:1 composition, used in organic solar cells, and for selected temperatures for the 3:7 composition. The results can be clearly interpreted according to the eutectic behaviour expected for this system, with the 1:1 composition being enriched in P3HT and the 3:7 composition being enriched in PC61BM. In both cases, the start of the melting trajectory corresponding to the eutectic transition coincided with the Tg of PC61BM. This is in agreement with earlier studies that report a vitrification effect caused by PC61BM. A bell‐shaped curve of isothermal crystallization rates could be constructed for the 1:1 composition, where the Tg of the mixed amorphous phase as well as of the separate components can be seen to play a role. For the 3:7 composition, clear indications are observed that a vitrified PC61BM phase can be formed in which isothermal crystallization takes place.

A novel infrared (IR) thermo-spectroscopic imaging technique is applied to the simultaneous measurements of IR transmittance spectroscopic images and thermal emission images of heat and mass transfers of styrene monomer polymerization in microfluidics. The heat released is observed in the mixing layer between two laminar flows of styrene monomer and toluene containing an initiator for polymerization. The concentration of chemical species and the independently measured temperature distribution within the mixing layer are determined at the microscale. This is the first report, of such a non-invasive method, to determine both the chemical composition and temperature distribution in microfluidic chemical reactions.

A combination of fast scanning chip calorimetry and X-ray ptychography is explored to study the effects of thermal annealing on the active layer of bulk heterojunction organic photovoltaics. The well-known P3HT/PC 61 BM 1:1 system is investigated as a test case. By using a custom chip calorimetry setup, it is possible to give a thermal treatment at 127 °C (400 K) to P3HT/PC 61 BM 1:1 thin layers, using a heating and cooling rate of 30000 K s −1 , after which the resulting morphology is investigated with X-ray ptychography. Applying only heating and cooling, without isothermal annealing, yields a featureless morphology. This corresponds well with thermal data which indicate a mixed amorphous phase only. For increasing isothermal annealing times, a well-defined morphology appears with increasing domain size, corresponding to the formation of an endothermal melting trajectory. This melting trajectory is expected to consist of both eutectic melting and melting of coarsened crystals. In contrast to chip calorimetry results, large domain sizes are obtained for heating and cooling without isothermal annealing at a conventional rate of 20 K min −1 . This initial morphology then develops further with increased isothermal annealing. The combination of chip calorimetry and ptychography allows separating the effects of each single thermal step on morphology development.

Aging of glassy poly(l-lactic acid) (PLLA) allows formation of crystal nuclei which enhances/accelerates subsequent crystallization at temperatures above the glass transition. The effects of the time and temperature of aging on nuclei formation have quantitatively been probed by analysis of isothermal crystallization at 393 K, using fast scanning chip calorimetry and polarizing optical microscopy. Crystal nuclei begin to form on aging the glass of PLLA at 343 K after about 101 s. The time of nuclei formation increases exponentially with decreasing temperature, so that aging at 323 K requires a minimum time of 104 s, and the extrapolated time for generation of nuclei at 295 K is about 108 s. The aging-controlled increase of the nuclei density in glassy PLLA leads to a distinct decrease of the half-time of crystallization. The half-time of crystallization of nonaged PLLA at 393 K is about 600 s and decreases to less than half of this value due to aging at 343 K for a period of only 103 s. Nuclei formation on aging the glass of PLLA is connected with a tremendous decrease of the size of spherulites which develop upon subsequent cold-crystallization. The detection of formation of crystal nuclei in glassy PLLA is discussed in the framework of prior analyses of the effect of the crystallization pathway on structure and properties of crystallizable polymers.

Bulk-heterojunction (BHJ) organic photovoltaics are based on an active layer consisting of a donor polymer and an acceptor material blend. For an optimal BHJ, this active layer has to form a phase separated co-continuous nanoscale morphology. In practise, thermal treatments (annealing) are often used to obtain the desired morphology. Using advanced fast-scanning thermal analysis techniques has made it possible to avoid the thermal effects that occur during heating or cooling (e.g. nucleation) and only study the effect of an annealing treatment. A drawback of most thermal analysis techniques however, is that they work with bulk materials. The active layers used in organic photovoltaics on the other hand, have thicknesses in the order of 100 nm. In this study, the thermal transitions and isothermal crystallization kinetics of the P3HT:PCBM (poly[3-hexyl thiophene] : [6,6]-phenyl C61 butyric acid methyl ester) system, a benchmark BHJ system, was studied by Rapid Heating Cooling Calorimetry (RHC) [1,2] and Fast Scanning Differential Chip Calorimetry (FSDCC) [3]. This allows for thermal characterization of the blend in bulk and, for the first time, in thin layers as used in actual organic photovoltaic devices. Due to the very high scanning rates reached in FSDCC, it is now also possible to perform a similar study of pure P3HT, which is impossible using more conventional techniques due to its very fast crystallization kinetics. [1] R.L. Danley, P.A. Caulfield, S.R. Aubuchon, American Laboratory 40 (2008) 9. [2] F. Demir, N. Van den Brande, B. Van Mele, S. Bertho, D. Vanderzande, J. Manca, G. Van Assche, J. Therm. Anal. Calorim., 105 (2011) 845. [3] A.A. Minakov, A.W. van Herwaarden, W. Wien, A. Wurm, C. Schick, Thermochim. Acta, 461 (2007) 96.

Organic photovoltaics of the bulk-heterojunction type rely on an active layer consisting of a co-continuous morphology of donor and acceptor phases in order to reach their optimum efficiency. In these active layers, the donor is a conjugated polymer, and the acceptor is most often a fullerene derivative. In order to fine-tune the morphology and crystallinity and thus increasing the efficiency a post-production isothermal annealing is performed on these systems before operation [1-2]. An optimal annealing treatment can only be carried out when the thermal transition and annealing kinetics are known for the used active layer. Using advanced fast-scanning thermal analysis techniques, the thermal effects that occur during heating or cooling (e.g. nucleation) can be avoided, making it possible to study only the effects of isothermal annealing. In this study, the thermal transitions and isothermal crystallization kinetics of the P3HT:PCBM (poly(3-hexyl thiophene: [6,6] - phenyl C61 - butyric acid methyl ester) system, a model system for organic photovoltaics, was studied by Rapid Heating Cooling Calorimetry (RHC) [3] and Fast Scanning Differential Chip Calorimetry (FSDCC) [4]. For a thorough simulation of thermal annealing, both isothermal crystallization directly from the molten state and by first cooling to the glassy state were studied. A double bell shaped peak is found for the crystallization rates, obtained by applying the Avrami model on RHC results. However, a clear rate difference between the melt and glass pathways is visible [5]. The higher rates for the glass pathway can be attributed to the effect of nucleation, which was not sufficiently avoided by the scanning rates of RHC. This rate difference is clearly reduced when using the much increased scanning rates allowed by FSDCC, resulting in an effective simulation of isothermal annealing.

Bulk-heterojunction organic solar cells rely on an active layer consisting of a co-continuous morphology of donor and acceptor phases in order to reach their optimum efficiency. A conjugated, light-excitable polymer is most often used as an electron donor, and fullerene derivatives are the most widespread type of electron acceptor. Post-production isothermal annealing plays an important role for these systems, both for fine-tuning the morphology and crystallinity and thus increasing the efficiency, but also for retaining the desired morphology during long-term operation. Optimal thermal annealing can only be carried out when the thermal transitions and annealing kinetics for the used systems are known. Using advanced fastscanning thermal analysis techniques, the thermal effects that occur during heating or cooling (e.g. nucleation) can be avoided, making it possible to study only the effects of isothermal annealing. In this study, the thermal transitions and isothermal crystallization kinetics of the P3HT:PCBM (poly(3-hexyl thiophene: [6,6] - phenyl C61 - butyric acid methyl ester) system as used in organic photovoltaics was studied by Rapid Heating Cooling Calorimetry (RHC) and Fast Scanning Differential Chip Calorimetry (FSDCC). In order to simulate thermal annealing in a complete way, both annealing directly from the molten state and by first cooling to the glassy state were studied. From RHC results a double bell shaped peak is found for the crystallization rates, but a clear rate difference between the melt and glass pathways is visible. The consistently higher rates for the glass pathway can be attributed to the effect of nucleation, which was not sufficiently avoided by using RHC. This rate difference is clearly reduces when using the much increased rates allowed by FSDCC, resulting in an effective simulation of isothermal annealing.

Organic photovoltaics (OPVs) can still only achieve efficiencies below those of conventional silicon photovoltaics. To date the highest OPV efficiencies have been found for so-called bulk-heterojunction (BHJ) solar cells, where the active layer is a bi-continuous composite of donor (a conjugated polymer) and acceptor (a small molecule) phases. As in conventional polymer blend systems, the morphology formed will strongly influence the material characteristics, and post-production annealing has been shown to increase device efficiencies. In this study, the active layer of BHJ devices is analysed using fast-scanning calorimetry techniques in order to investigate the transitions that play a role in stability and morphology development. In particular, Rapid Heat-Cool Calorimetry (RHC) [1], and fast scanning differential chip calorimetry (FSDCC) were used. FSDCC especially shows great potential for these systems due to the very high scanning rates and the ability to study thin layer samples, like in actual BHJ devices.

In this study, the isothermal crystallization rates of a poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend of 50 wt% PCBM (1:1) were investigated by means of Rapid Heat Cool Calorimetry (RHC) and Fast-Scanning Differential Chip Calorimetry (FSDCC) . Since attaining the best performance requires finely dispersed phase morphology, with crystalline P3HT and PCBM structures of 10-nm dimensions, [1-3] optimizing the annealing conditions is vitally important for increasing the efficiency of the solar cell. In order to investigate the nucleation and growth of the crystals formed during the isothermal crystallization, the crystallization during heating or cooling should be avoided [4]. Preventing fast crystallization processes can only succeed using fast-scanning techniques such as RHC and FSDCC. RHC is a fast-scanning DSC technique developed by TA Instruments [4, 5], having a 10 times smaller furnace heated by infrared light and a sample size of about 50 to 500 µg. The RHC permits to heat at rates of up to 2000 K.min-1 and cool at 750 K.min-1 and 500 K.min-1 down to 60 °C and 0 °C. FSDCC allows temperature control of the sample and determination of its heat capacity by employing cooling and heating rates from up to 1x106 Ks-1 [6]. Since it is also possible to control the cooling rate, studying the kinetics of extremely fast crystallization and reorganization processes in thin films of semi-crystalline polymers on heating becomes possible. The rate of crystallization during thermal annealing of 250 µg samples (by RHC) and less than 100 ng samples (by FSDCC) will be investigated and compared. REFERENCES: 1. Erb T., Advanced Functional Materials; 15(7):1193-1196, (2005). 2. Ma W. L., Advanced Materials;19(10):1387-1390, (2007). 3. Thompson BC, Angewandte Chemie-International Edition; 47(1):58-77, (2008). 4. Demir F., Journal of Thermal Analysis and Calorimetry; 105(3):845-849, (2011). 5. Danley R. L, American Laboratory, 40(1), 9-11, (2008). 6. Minakov A. A., Review of Scientific Instruments; 78(7), (2007).

Phase separation and remixing are important transformations in the processing and application of polymer blends and polymer solutions. Modulated temperature DSC (MTDSC) proves to be very valuable for studying phase separation and remixing, for determining whether the systems are homogeneous or heterogeneous (from the glass transition(s)), to get an idea of the phase compositions, and for building phase or state diagrams and determining demixing or remixing kinetics. The origin of the contribution of the demixing-remixing phenomena to the MTDSC heat capacity signal will be discussed. For studying the thermoresponsive behavior of 100-nm thin films of polymer blends, AC chip calorimetry was successfully explored. It permits studying the influence of the substrate surface chemistry and the film thickness on the state diagram and the process kinetics. Combining these modern thermal analysis techniques, giving information on bulk and thin film thermal behavior, with hot-stage atomic force microscopy and nano-thermal analysis, provides a detailed insight in the material behavior. The paper will give some highlights of our recent work in these fields.

AC chip calorimetry is used to study the phase separation behavior of 100 nm thin poly(vinyl methyl ether)/poly(styrene) (PVME/PS) blend films. Using the on-chip heaters, very short (10 ms–10 s) temperature jumps into the temperature window of phase separation are applied, simulating laser heating induced patterning. These temperature pulses produce a measurable shift in the glass transition temperature, evidencing phase separation. The effect of pulse length and height on phase separation can be studied. The thus phase separated PVME/PS thin films remix rapidly, in contrast with measurements in bulk. AC chip calorimetry seems to be a more sensitive technique than atomic force microscopy to detect the early stages of phase separation in polymer blend thin films.

Polymer blend thin films are interesting both for their technological applications (e.g. coatings, adhesion, surface friction,...), as from an academic point of view. By confining a polymer blend in a thin film, the influence of both the air-polymer as the substrate-polymer interface can (significantly) influence its physical properties in comparison to those observed in bulk; increasing and decreasing cloud point temperatures or changes in the phase separation mechanism have been reported. One of the possible applications of phase separation in polymer blend thin films, are the so called 'smart surfaces', whose properties change due to thermal or chemical stimuli, e.g. the patterning of polymer blend films by local heating. The idea is to use a polymer blend film, which is stable at the storage/working temperature, but can be annealed in the two phase region upon heating. This local heating could, for instance, be obtained using an infra red laser. However, several questions arise; firstly, can there be phase separation at these typically very short irradiation times (µs to ms), secondly, can this morphology be fixated and thirdly, can the difference between degradation and phase separation be demonstrated? Modulated temperature differential calorimetry (MTDSC) has proved to be a valuable technique for studying bulk phase separation in polymer blends. On the other hand, chip based nano calorimetry could allow the calorimetric study of phase separation in thin films. We would like to demonstrate that AC calorimetry can be used to study phase separation in thin polymer blend films, using the methodology developed for bulk samples in MTDSC and compare the behavior in bulk to the one in 100 nm thick films. The poly(vinyl methyl ether) / poly(styrene) (PVME/PS) blend system is chosen as a model system. PVME/PS blend thin films have been studied in detail in literature [1-12] and show a lower critical solution temperature (LCST) behavior, which means that, starting from a homogeneous system, they will phase separate above a certain temperature. Furthermore, the on chip heater can be used to apply temperature jumps above the cloud point temperature for very short times from 5 ms to several seconds, allowing us to study the influence of very short jumps into the heterogeneous region of the state diagram and thus simulating laser heating. References 1. Reich S and Cohen Y. Journal of Polymer Science: Polymer Physics Edition 1981;19(8):1255-1267. 2. Tanaka K, Yoon J-S, Takahara A, and Kajiyama T. Macromolecules 1995;28(4):934-938. 3. Karim A, Slawecki TM, Kumar SK, Douglas JF, Satija SK, Han CC, Russell TP, Liu Y, Overney R, Sokolov J, and Rafailovich MH. Macromolecules 1998;31(3):857-862. 4. Kawaguchi D, Tanaka K, Kajiyama T, Takahara A, and Tasaki S. Macromolecules 2003;36(18):6824-6830. 5. Li X, Wang Z, Cui L, Xing R, Han Y, and An L. Surface Science - Including Surface Science Letters 2004;571(13):12-20. 6. El-Mabrouk K, Belaiche M, and Bousmina M. Journal of Colloid and Interface Science 2007;306(2):354-367. 7. Ogawa H, Kanaya T, Nishida K, and Matsuba G. Polymer 2008;49(1):254-262. 8. Pan DHK and Prest WM. Journal of Applied Physics 58 1985;58(8):2861-2870. 9. Bhatia Q.S. PDH, Koberstein J.T. Macromolecules 1988;21:2166-2175. 10. Dee GT and Sauer BB. Macromolecules 1993;26(11):2771-2778. 11. Lee S and Sung CSP. Macromolecules 2001;34(3):599-604. 12. Pavawongsak S. HJS, Clarke N. McLeish T.C.B. Peiffer D.G. Polymer 2000;41:757-763.