Dissertations / Theses on the topic 'Temperature-modulated differential scanning calorimetry'

The research described in this thesis focused on the TMDSC technique with respect to both theoretical problems and applications. Theoretically, modelling work has been performed to address the effects of heat transfer in the measuring cell on both dynamic and quasi-isothermal TMDSC experiments. The problems of heat transfer generally influence the measured complex heat capacity and phase angle values, but eventually affect the precise measurements of other frequency dependent quantities such as the in-phase and out-of-phase heat capacities. A procedure has been suggested to correct the measured phase angle obtained by dynamic TMDSC using the scaled complex heat capacity trace (Chapter 3). The modulation frequency dependence of the instrumental phase angle has been fully investigated using more realistic models in terms of various heat transfer interface qualities, sample properties and sensor properties. In these models, it is emphasised that the measured temperatures are the sensor temperatures rather than the sample temperatures, thus, the contributions of the sensor's properties to the heat transfer are, for the first time, separated from the overall effects (Chapter 4 and Chapter 5). The consequent effects of heat transfer on the sample's heat capacity measurements are investigated based on the models suggested (Chapter 6). All the modelling results are compared with the corresponding experimental data obtained by ADSC (Mettler-Toledo Ltd) and they are in good agreement. Ripples and fluctuations which appear on the experimental signals during the glass transition and cold crystallisation transition have been simulated using* a simple model in which the period of the modulation signals changes with the time during the transitions, and then, been shown to be artefacts of the Fourier transformation process used by TMDSC evaluations (Chapter 7). The applications of TMDSC to both research and commercial samples are reported in terms of differing either the experimental conditions or the thermal history of the sample. Separating of time dependent kinetic processes from the time independent dynamic processes has been applied on the studies of the glass transition (for polycarbonate and poly(ethylene terephthalate)), the cold crystallisation (for poly(ethylene terephthalate)), the melting transition (for poly(ethylene terephthalate) and lead/tin alloys), the clearing transition of a liquid crystal polymer, and the vitrification of an epoxy resin under quasi-isothermal conditions. The main conclusion drawn from these studies is that the in-phase heat capacity is greatly influenced by the frequency of the temperature modulations even when the underlying heating (or cooling) rate remains the same. This strongly implies that the sample undergoes different structural change under different modulation conditions for the melting transition and clearing transition, but not for the glass transition and cold crystallisation. However, the interpretations of the in-phase heat capacity and out-of- phase heat capacity still need to be clarified. The detection of the glass transition and clearing point for the liquid crystal polymers, and the determination of wax appearance temperature for crude oils, show the ability of TMDSC for combining the sensitivity of a measurement at high instantaneous heating or cooling rates with the resolution obtained by measuring at a low underlying heating or cooling rates. The work on the isothermal curing of the epoxy resins displays the ability of TMDSC on measuring the heat capacity of the sample and its variation under the quasi-isothermal conditions. The frequency dependent complex heat capacity during the glass transition provides a window to measure the apparent activation energy of the transition, which is different, in some extent, from the window used by conventional DSC. The results are correlated by a shift factor. Some shortcomings of TMDSC, however, have been noticed in both modelling and application work. Firstly, any experiments for the purpose of either understanding or the quantitative measurements of TMDSC output quantities should be performed under carefully selected conditions which can satisfy the linear response assumption. Secondly, some signals in particular those associated with kinetic processes may not be fully sampled by TMDSC due to the limit of the observing window of a modulation. Thirdly, when the sensitivity is improved on TMDSC by separating the kinetics processes and noises from the dynamic processes, the TMDSC evaluation procedure introduces mathematical artefacts into the output signals. As a consequence, it is preferable to include as many temperature modulations as possible within any transition being studied in order to obtain good quality experimental signals by eliminating or minimising these artefacts, which, however, is not an easy task for some very abrupt transitions such as melting of metals.

Slow-scan-rate differential scanning calorimetry of enzymes can detect conformational changes which are under kinetic control and not observable at standard scan rates. This method detected a nondenaturational conformational change of bovine &agr;-chymotrypsin at 286 K. This temperature occurs between bovine physiological temperature of 312 K and x-ray crystallography temperature, typically 277 K. This suggests that there are two conformers of &agr;-chymotrypsin, a low temperature conformation and a physiological temperature conformation. The low-temperature to physiological-temperature conformational change has a high activation energy and thus is temperature dependent. The equilibrium thermodynamic changes suggest a reordering of the enzyme structure to give more favorable inter-residue interactions accompanied by an ordering of the structure but one in which there is no change in associated water molecules. The transition state thermodynamics suggest a very strained transition state but one where, again, no change in water interactions is detectable.

The research programme studied the cure reaction of a phenolic novolak resin and the effects of various additives and fillers on the reaction. The programme utilised the recently developed thermal analysis technique of temperature-modulated differential scanning calorimetry (TMDSC) performed in conjunction with other available thermal analysis techniques. TMDSC enables the signal for the heat of reaction to be separated from the underlying specific heat change in the resin. This meant that the reaction could be studied without interference from any physical changes in the resin. The manufacture of composite brake materials required the use of numerous additives and fillers to produce the desired properties. The influence of such additives on the cure rate and final properties of the resin was known to occur but had not previously been measured due to the difficulties presented by the presence of opaque additives. Some additives also underwent thermally induced physical changes in the temperature range of the cure. The final properties and the processing of new brake materials undergoing development often required trial and error adjustments to compensate for changes in cure rate. An understanding of the influence of additives would enable more rapid commercial development of brake materials through an improvement in the ability to predict both the properties of the product and the optimal processing parameters. Processing efficiency could also be improved through detailed knowledge of the kinetics. Moulding cycle times and post-baking times and temperatures were longer than necessary in order to ensure adequate cure at the end of each stage because of the lack of kinetic data. The cure of phenolic resin has been shown to be highly complicated with numerous alternate and competing reactions. For the manufacture of composite materials, knowledge of the kinetic parameters of individual reactions is not considered to be important; rather the overall kinetic parameters are required for prediction. Therefore the kinetic model parameters that best described the observed behaviour were chosen even though the model had no basis in the molecular interaction theory of reaction. Rather it served as a convenient tool for predictions. Characterisation of the resin proved to be difficult due to the presence of overlapping peaks, and volatile reaction products. TMDSC was successfully used to determine the reaction kinetics of the pure resin and the influence of certain additives on the reaction kinetics. The determination of the kinetic parameters using TMDSC agreed well with the traditional Differential Scanning Calorimetry isothermal and non-isothermal techniques. Both the Perkin-Elmer and TA Instruments were utilised for the research and were found to provide reasonably good agreement with each other. The capabilities and limitations of the individual instruments were critically examined, frequently beyond the manufacturers' specifications. TMDSC suffers from a limitation in the heating rate of the sample compared to DSC. However, it was observed that valuable information could still be obtained from TMDSC despite using heating rates that were higher than specified by manufacturers. Hot Stage Microscopy and thermogravimetry were additional experimental techniques used to aid in the characterisation of the resin. Some inhomogeneity of the resin was identified as well as differences in the behaviour of the cure between open (constant pressure) and closed (constant volume) environments were observed. A novel method of determining the orders of the cure reactions and their kinetic parameters was utilised. Reaction models for the overall cure reactions were postulated and tested by fitment to sections of experimental data in temperature regions which appeared to be free of interference from overlapping peaks. Once an individual peak was reasonably well modelled, adjacent overlapping peaks were able to be modelled both individually and in combinations by fitment to experimental data. The Solver function in Microsoft Excel was utilised to find the best fitting model parameters for the experimental data. The model parameters were able to be refined as overlapping peaks were progressively incorporated into the calculations. This method produced results that agreed well with the traditional method of analysing reaction peak temperatures at multiple scanning rates. Model fitment was shown to be of benefit where overlapping reactions occur. Various model scenarios could be tested and optimised to particular sections of experimental data. This enabled the researcher to easily identify areas of possible anomalies and postulate alternative scenarios. The accuracy of the postulated model was able to be determined by its successful fitment to experimental data from experiments run under different conditions.

The structural adhesives widely used in structural strengthening applications are thermoset ambient cure adhesive polymers. At ambient temperatures, these polymers are in a relatively hard and inflexible state. At higher temperatures, the material becomes soft and flexible. The region where the molecular mobility changes dramatically is known as the glass transition temperature Tg and often is presented as a single value. Epoxy polymers exhibit a significant reduction in mechanical properties near glass transition temperature Tg when they are exposed to elevated temperatures. Glass transition temperature Tg is used to characterise the change in epoxy adhesive properties with changing temperature. The mechanical properties of epoxies tend to improve with curing temperature. This is because the crosslink density between the adhesive molecular structures increases during the curing process consequently the Tg improves. The aims of this work are first to demonstrate the importance of curing temperature. Second, to investigate the influence of glass transition temperature !! improvement on the performance of EB-FRP strengthened steel structures in flexure at ambient and elevated temperatures. Third, to compare analytical results with experimental results from the flexure tests results. Finally, to compare the current design guideline recommendations with the flexure tests results. The most commonly used methods to evaluate Tg Dynamic Mechanical Analysis (DMA) and Differential Scanning Calorimetry (DSC) were used to study Tg. Two off-shelf structural adhesives were investigated to understand their property variation with temperature. Epoxy coupons were cured at different elevated temperature and humidity environments up to 28 days. A combination of two extreme relative humidity of 0 and 100% and variable curing temperatures between 15 to 80°C were considered. From a test matrix of 300 DMA and over 250 DSC coupons these conclusions were drawn. First, ambient cured thermosets have a linear relationship between Tg and curing temperature, but Tg is reduced if a certain temperature is reached. Second, a fully cured adhesive requires heating treatment. Without a curing regime, designed Tg may never be achieved. Finally, curing time is crucial at the low curing temperatures while it is less significant at the higher curing temperature. The results of Tg investigation were used to select appropriate curing temperature that the adhesives resistance to temperature can be maximised without damaging the mechanical properties. The study helps designs to understand and assess the behaviour of these two adhesives when they are exposed to extreme temperatures. The study increases the awareness that a fully cured adhesive may never be achieved at ambient or low temperatures. It is important to find the mechanical properties and Tg when the coupons are exposed to the same curing temperature. To investigate the influence of glass transition temperature Tg improvement on the performance of EB-FRP strengthened steel structures in flexure at ambient and elevated temperature, nine three metre length beams were designed to behave as a concrete-steel composite bridge deck. The beams were tested in four-point bending. Lap shear, DMA test, and pull-off adhesion samples were prepared and cured at the same conditions and tested at ambient temperature. Six beams were tested under only mechanically loading at ambient temperature, including the control specimen. Five beams were tested at ambient temperature to show the effects of adhesive curing on FRP strengthened sections. A significant increase of load capacity of the adhesive joints was achieved due to the curing of the joints at elevated temperature. The failure occurred was in the same manner. An increase in the load capacity was observed with increasing curing temperature. An increase of approximately 25% was noticed in the ultimate load capacity of the specimens cured at 50°C compared to the specimens cured at 30°C. The load capacity of lap-shear specimens cured at 50°C was 28% higher than the specimens cured at 30°C. Three specimens were tested under mechanical and thermal loading. A bespoke thermal chamber was designed and fabricated to apply a controlled thermal loading. The beams were loaded mechanically up to 350kN, first. The temperature of the specimens was then increased at a rate of 0.8°C/min. The sustained load 350kN remained constant during the heating phase. Digital Image Correlation (DIC) technique was used to detect the slippage of the tip of the FRP plates. The only specimen cured at 30°C showed relatively poor performance compared to the two specimens cured at 50°C. The plate ends started to slip when the adhesive storage modulus from the DMA runs reduced approximately by 15 and 18% for the beams cured at 30 and 50°C respectively. Pull-off adhesion tests confirmed that adequate surface preparation of over 25 MPa was achieved The flexural model for the composite steel section represented to predicate load-deflection behaviour of the specimens using semi-experimental constitutive material law. The model successfully predicts the load-deflection behaviour of specimens, considering the strain hardening contribution. A bond stress analysis is also presented, which counts for the effect of FRP plate moment effect. The experimental and theoretical FRP plate slippage assuming only adhesive degradation with temperature are compared. The analytical bond models cannot predict the experimental failure because the linear elastic material properties were assumed and the failure was adhesion.

The isothermal crystallization and melting temperatures of poly(ε-caprolactone) were correlated using fast differential scanning calorimetry. The melting kinetics was found to be independent of isothermal crystallization temperature and time. The conventional Hoffman-Weeks method could not be used to determine the equilibrium melting temperature because the observed melting temperatures were greater than the crystallization temperatures by a constant, so the Gibbs-Thomson method was used instead, yielding an equilibrium melting temperature of 103.4 ± 2.3°C. A modification was proposed to the non-linear Hoffman-Weeks equation that included a non-linear undercooling dependence for the kinetic fold surface free energy upon crystallization and permitted accurate modeling of the observed melting behavior. The isothermal crystallization rates of four narrow molecular weight poly(ethylene oxide) fractions were characterized using fast differential scanning calorimetry for crystallization temperatures spanning 100°C range with the lower limit approaching the glass transition. A transition from homogeneous to heterogeneous primary nucleation was observed at −5°C. The kinetic analysis suggested that the crystal growth geometry depends strongly on temperature, where rod-like structures begin to appear near the glass transition temperature, highly branched solid sheaves grow throughout the homogeneous primary nucleation temperature range, and spherulites grow in the heterogenous primary nucleation range. Poly(δ-valerolactone) was synthesized using microwave-assisted techniques. Narrow molecular weight fractions were obtained using successive precipitation fractionation. Preliminary isothermal crystallization studies suggest that conventional thermal analysis methods are not adequate to measure the melting temperatures accurately due to reorganization during heating.
Doctor of Philosophy

In questa tesi si è voluta porre l’attenzione sulla suscettibilità alle alte temperature delle resine che li compongono. Lo studio del comportamento alle alte temperature delle resine utilizzate per l’applicazione dei materiali compositi è risultato un campo di studio ancora non completamente sviluppato, nel quale c’è ancora necessità di ricerche per meglio chiarire alcuni aspetti del comportamento. L’analisi di questi materiali si sviluppa partendo dal contesto storico, e procedendo successivamente ad una accurata classificazione delle varie tipologie di materiali compositi soffermandosi sull’ utilizzo nel campo civile degli FRP (Fiber Reinforced Polymer) e mettendone in risalto le proprietà meccaniche. Considerata l’influenza che il comportamento delle resine riveste nel comportamento alle alte temperature dei materiali compositi si è, per questi elementi, eseguita una classificazione in base alle loro proprietà fisico-chimiche e ne sono state esaminate le principali proprietà meccaniche e termiche quali il modulo elastico, la tensione di rottura, la temperatura di transizione vetrosa e il fenomeno del creep. Sono state successivamente eseguite delle prove sperimentali, effettuate presso il Laboratorio Resistenza Materiali e presso il Laboratorio del Dipartimento di Chimica Applicata e Scienza dei Materiali, su dei provini confezionati con otto differenti resine epossidiche. Per valutarne il comportamento alle alte temperature, le indagini sperimentali hanno valutato dapprima le temperature di transizione vetrosa delle resine in questione e, in seguito, le loro caratteristiche meccaniche. Dalla correlazione dei dati rilevati si sono cercati possibili legami tra le caratteristiche meccaniche e le proprietà termiche delle resine. Si sono infine valutati gli aspetti dell’applicazione degli FRP che possano influire sul comportamento del materiale composito soggetto alle alte temperature valutando delle possibili precauzioni che possano essere considerate in fase progettuale.

Thesis (PhD)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Impact Polypropylene Copolymers (IPCs) are extremely complex materials, consisting of a mixture of polypropylene homopolymer and copolymers having different comonomer (ethylene) contents and chemical composition distributions. IPC can only be effectively analysed by multidimensional analytical approaches. For this, initially, the individual components have to be separated according to any of their molecular characteristics, either by chemical composition distribution (CCD) or molar mass distribution (MMD), followed by further analysis of these separated fractions with conventional analytical techniques. The combination of preparative temperature rising elution fractionation (TREF) with several other analytical techniques have been reported for the thorough characterization of this material. However, even the combinations of these methods were of limited value due to the complex nature of this polymer. Therefore, novel analytical approaches are needed for a more detailed compositional analysis of IPCs. This work describes a number of multidimensional analytical techniques that are based on the combination of fractionation and hyphenated techniques. Firstly, preparative TREF was combined with high temperature size exclusion chromatography-FTIR (HT SEC-FTIR), HT SEC-HPer DSC (High Performance Differential Scanning Calorimetry) and high temperature two-dimensional liquid chromatography (HT 2D-LC) for the comprehensive analysis of a typical impact polypropylene copolymer and one of its midelution temperature TREF fractions. HT SEC-FTIR analysis provided information regarding the chemical composition and crystallinity as a function of molar mass. Thermal analysis of selected SEC fractions using a novel DSC method - High Speed or High Performance Differential Scanning Calorimetry (HPer DSC) - that allows measuring of minute amounts of material down to micrograms, yielded the melting and crystallization behaviour of these fractions which is related to the chemical heterogeneity of this complex copolymer. High temperature 2D-LC analysis provided the complete separation of this TREF fraction according to the chemical composition of each component along with its molar mass distribution. In a second step, the compositional characterization by advanced thermal analysis (HPer DSC, Flash DSC 1, and solution DSC) of the TREF-SEC fractions was extended to all semi-crystalline and higher temperature TREF fractions. By applying HPer DSC at scan rates of 5−200°C/min and Flash DSC 1 at scan rates of 10−1000°C/s, the metastability of one of the fractions was studied in detail. DSC measurements of TREF-SEC cross-fractions at high scan rates in p-xylene successfully connected reversely to the slow scan rate in TREF elution, if corrected for recrystallization. Finally, the exact chemical structure of all HT HPLC separated components was determined by coupling of HT HPLC with FTIR spectroscopy via an LCTransform interface. This novel approach revealed the capability of this hyphenated technique to determine the exact chemical composition of the individual components in the complex TREF fractions of IPCs. The HT HPLC–FTIR results confirmed the separation mechanism in HPLC using a solvent gradient of 1-decanol/TCB and a graphitic stationary phase at 160°C. FTIR analysis provided information on the ethylene and propylene contents of the fractions as well as on the ethylene and propylene crystallinities.
AFRIKAANSE OPSOMMING: Impak Polipropileen Kopolimere (IPKe) is uiters komplekse materiale, bestaande uit 'n mengsel van polipropileen homopolimeer en kopolimere met verskillende komonomeer (etileen) inhoud en chemiese samestelling verspreiding. IPKe kan slegs doeltreffend ontleed word deur multidimensionele analitiese benaderings te volg. Hiervoor moet die individuele komponente aanvanklik eers geskei word volgens enige van hul molekulêre eienskappe, hetsy deur die chemiese samestelling verspreiding (CSV) of molêre massa verspreiding (MMV), gevolg deur 'n verdere ontleding van hierdie geskeide fraksies met konvensionele analitiese tegnieke. Die kombinasie van voorbereidings temperatuur-verhogings eluasie fraksionering (TVEF) met verskeie ander analitiese tegnieke is gerapporteer vir die deeglike karakterisering van hierdie materiaal. Maar selfs die kombinasies van hierdie metodes was van beperkte waarde as gevolg van die komplekse aard van hierdie polimeer. Daarom word nuwe analitiese benaderings benodig vir 'n meer gedetailleerde komposisionele ontleding van IPKe. Hierdie studie beskryf 'n aantal multidimensionele analitiese tegnieke wat gebaseer is op die kombinasie van fraksionering en gekoppelde tegnieke. Eerstens is voorbereidings TVEF gekombineer met hoë temperatuur grootte-uitsluitingschromatografie-FTIR (HT GUC-FTIR), HT GUC-HPer DSK en hoë temperatuur twee-dimensionele vloeistof chromatografie (HT 2D-VC) vir die omvattende ontleding van 'n tipiese impak polipropileen kopolimeer en een van sy mid-eluasie temperatuur TVEF fraksies. HT GUC-FTIR analiese het inligting verskaf met betrekking tot die chemiese samestelling en kristalliniteit as 'n funksie van molêre massa. Termiese analiese van geselekteerde GUC fraksies deur gebruik te maak van 'n nuwe-DSK metode - Hoë Spoed of Hoë Prestasie Differensïele skandeer kalorimetrie (HPer DSK) - wat die meting van klein hoeveelhede materiaal tot by mikrogram hoeveelhede toelaat, het die smelt en kristallisasie gedrag van hierdie fraksies bepaal wat verwant is aan die chemiese heterogeniteit van hierdie komplekse kopolimeer. Hoë temperatuur 2D-LC analiese het die volledige skeiding van hierdie TVEF fraksie volgens die chemiese samestelling van elke komponent saam met die molêre massa verspreiding moontlik gemaak. In 'n tweede stap, is die komposisionele karakterisering deur gevorderde termiese analiese (HPer DSK, Flash DSK 1 en oplossing DSK) van die TVEF-GUC fraksies uitgebrei na alle semi-kristallyne en hoër temperatuur TVEF fraksies. Deur die gebruik van HPer DSK, teen ’n skandeerspoed van 5-200°C / min, en Flash DSK 1, teen ’n skandeerspoed van 10-1000°C / s, is die meta-stabiliteit van een van die fraksies in detail bestudeer. DSK metings van TVEF-GUC kruis-fraksies by 'n hoë skandeeerspoed in p-xyleen het suksesvol omgekeerd verbind aan die stadige skandeerspoed in TVEF eluasie, wanneer gekorrigeer vir dekristallisatie. Ten slotte is die presiese chemiese struktuur van al die HT HPVC geskeide komponente bepaal deur die koppeling van HT HPVC met FTIR spektroskopie deur middel van 'n LC-transform-koppelvlak. Hierdie nuwe benadering het die vermoë van die gekoppelde tegniek om die presiese chemiese samestelling van die individuele komponente in die komplekse TVEF fraksies of IPKe te bepaal aan die lig gebring. Die HT HPVC-FTIR resultate het die skeidingsmeganisme in HPVC bevestig deur die gebruik van ’n oplosmiddelgradiënt van 1-dekanol/TCB en 'n graphitiese stasionêre fase by 160°C. FTIR analiese verskaf inligting in verband met die etileen en propileen inhoud van die fraksies sowel as die etileen en propileen krystalliniteit.

This diploma thesis is focused on issues concerning the stability of selected vegetable oils which are used in cosmetic industry. The stability of eight oils without additives were determined by a differential scanning calorimeter. In the first phase, the temperatures of oil degradation were determined for different rates of heating, i.e. nonisothermal stabilities. They were consequetly used to calculate isothermal stabilities alias induction periods. The calculation of induction periods was completed by using integral isoconversional methods, which applied four different temperature functions. One of the temperature functions corresponded to Arrhenius equation while the others to non-Arrhenius functions. The confrontation of induction periods under standart conditions showed that an optimal temperature function to calculate oil stabilities is one of the non-Arrhenius functions in exponential form. We can state that all oils are degraded by similar, if not the same, mechanism. The specified stabilities, in periods of months, have proved the importance of using stabilizers and other additives in the commercial and technological use of vegetable oils.

La mise en place, l'étalonnage et l'utilisation d'un nouveau banc expérimental basses températures basé sur une technique photothermique appelée photo pyroélectricité (PPE) sont décrits dans ce manuscrit. Les échantillons que nous avons étudiés en utilisant ce nouvel instrument sont le glycérol, le 1,2 propanediol et leurs mélanges binaires avec l'eau. Ce sont des cryoprotecteurs bien connus (CPAs) utilisés dans la cryoconservation, qui est une technique de préservation des cellules et tissus vivants en les refroidissant à des très basses températures. Le but ultime de la cryoconservation est d'éviter ou de maîtriser la formation de glace et d'atteindre un état vitreux ou amorphe. La vitesse de refroidissement, de chauffage et la concentration des CPAs utilisés sont les paramètres clés qui déterminent la formation de la glace. Par conséquent, l'étude des propriétés thermiques, en particulier près de la transition vitreuse (Tg) des solutions binaires des CPAs avec de l'eau est très importante pour comprendre leur comportement lors du refroidissement. La PPE a été utilisée pour étudier l'effusivité et le temps de relaxation ∝ caractéristique de la transition vitreuse. Le Tg et la fragilité (m) ont été déterminés à partir des données de la PPE en utilisant le modèle d'Havriliak Negami. L'état vitreux présente une très grande viscosité, de l'ordre de 10¹² Pa.s au voisinage du Tg. Le Tg et m peuvent être calculés à partir de l'évolution de la viscosité en fonction de la température ou par calorimétrie différentielle à balayage (DSC). Ainsi, des études à l'aide de ces deux techniques ont été menées et les résultats ont été comparés avec les données de la PPE
The construction, calibration and application of a new low temperature instrument based on a photothermal technique called photo pyroelectricity (PPE) is described in this manuscript. The samples we studied using the new PPE instrument were glycerol, 1,2 propanediol and their binary mixtures with water. These liquids are well known cryoprotectants (CPAs) used in cryopreservation, which is a technique to preserve the living cells and tissues from biological degradation by cooling to sub zero temperatures. The ultimate goal in cryopreservation is to avoid or control the ice formation and attain a glassy or amorphous state.The rate of cooling and heating and the concentration of the CPAs used are the key parameters that determine the ice formation. Therefore, studying the temperature dependent thermal properties especially near their glass transition temperature (Tg) of the binary solutions of CPAs with water at different concentrations are highly important to understand their behavior while cooling. The PPE technique was used to study the effusity and the ∝ relaxation time near the glass transition phenomenon. The Tg and fragility (m) were determined from the PPE data using the Havriliak Negami model. The glassy state has a characteristic property of very high viscosity, of the order of 10¹² Pa.s at Tg. The Tg and m can be calculated from the temperature evolution of viscosity or from Differential Scanning Calorimetry (DSC) measurements. Therefore, viscosity and DSC studies were conducted on the samples and were compared with PPE data

Additives, incorporated in film coating formulations, and their process parameters are generally selected using a trial-and-error approach. However, coating problems and defects, especially those associated with aqueous coating systems, indicate the necessity of embracing a quality-by-design approach to identify the optimum coating parameters. In this study, the feasibility of using thermal and rheological measurements to help evaluate and design novel coating formulations has been investigated. Hydroxypropyl methylcellulose acetate succinate (HPMCAS), an enteric coating polymer, was used as the film forming polymer. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and Parallel Plate Shear Rheometery (PPSR) were used to evaluate the effect of different plasticisers on the performance of HPMCAS. The results illustrate that, for identical formulations, the DSC and DMA methods yielded up to 40% differences in glass transition temperature (Tg) values. Moreover, Tg measured using loss modulus signals were always 20-30 oC less than those measured using tan delta results in DMA testing. Absolute and relative Tg values can significantly vary depending on the geometry of the samples, clamp size, temperature ramping rate and the frequency of the oscillations. Complex viscosity data for different formulations demonstrated a variable shear thinning behaviour and a Tg independent ranking. It is, therefore, insufficient to rely purely on Tg values to determine the relative performance of additives. In addition, complex viscosity results, obtained using both the DMA and PPSR techniques at similar temperatures, are shown to be comparable. The results from both techniques were therefore used to produce continuous master curves for the HPMCAS formulations. Additionally, step strain tests showed that HPMCAS chains do not fully III disentangle after 105 seconds as predicted by the Maxwell model. Finally, in situ aqueous-based coating experiments proved that mixtures of triethyl acetyl citrate and acetylated monoglyceride (TEAC/AMG), even without cooling of the suspension, do not cause blocking of the spray nozzle whereas triethyl citrate (TEC) based formulae did. TEAC (alone or in a combination with AMG) exhibits superior wettability to HPMCAS than TEC/AMG formulations and can be used to enhance the efficiency and film quality of the dry coating process.

Biomolecular interactions are fundamentally important for a wide variety of biological processes. Understanding the temperature dependence of biomolecular interactions is hence critical for applications in fundamental sciences and drug discovery. Micro-Electro-Mechanical Systems (MEMS) technology holds great potential in facilitating temperature-dependent characterization of biomolecular interactions by providing on-chip microfluidic handling with drastically reduced sample consumption, and well controlled micro- or nanoscale environments in which biomolecules are effectively and efficiently manipulated and analyzed. This dissertation is focused on a high-through and miniaturized differential scanning calorimeter for thermodynamic study of bio-molecules using MEMS techniques. The dissertation firstly introduces the overall design and operation principles. This miniaturized DSC was fabricated based on a polyimide (PI) thin film. Highly temperature sensitive vanadium oxide was used as the thermistor material. A PDMS (Polydimethylsiloxane) microfluidic chamber was separately fabricated and then bonded firmly with the PI substrate by a stamp-and-stick method. Meanwhile, the micro heater design was optimized to reach better uniformity. A heating stage was constructed for fast and reliable scanning. In this study, we used syringes to deliver the 0.63 μL liquid sample into both the sample and reference chambers. All the testing processes were functionalized using the LabVIEW programs. The sensing material was also characterized. To seek a higher temperature coefficient of resistance (TCR) and less resistive behavior, explorations about various PVD (physical vapor deposition) parameters and annealing conditions were conducted for optimization. In this research, we found vanadium oxide deposited under certain conditions leads to the highest TCR value (a maximum of 2.51%/oC). To better understand the material’s property, we also did the XRD (X-ray Diffraction), SEM (Scanning electron microscope). The micro calorimeter was calibrated using a step thermal response. The time constant was around 3s, the thermal conductance was 0.6mW/K, and the sensitivity was 6.1V/W. The static power resolution of the device at equilibrium is 100 nW, corresponding to 250 nJ/K. These performances confirmed the design and material to be appropriate for both good thermal isolation and power sensitivity. We demonstrated the miniaturized DSC’s performance on several different kinds of protein samples: lysozyme, and mAb (monoclonal antibody) and a DVD IgG (double variable domain immunoglobulin G). The results were found to be reasonable by comparing it with the commercial DSC’s tests. Finally, this instrument may be ideal for incorporation into high throughput screening workflows for the relative comparison of thermal properties between large numbers of proteins when only small quantities are available. The micro-DSC has the potential to characterize the thermal stability of the protein sample with significantly higher throughput and less sample consumption, which could potentially reduce the time and cost for the drug formulation in the pharmaceutical industry.
Ph. D.
Virtually all biological phenomena depend on molecular interactions, which is either intra-molecular as protein folding/unfolding or intermolecular as in ligand binding. A basic biology problem is to understand the folding and denaturation processes of a protein: the kinetics, thermodynamics and how a protein unfolds and folds back into its native state. Both folding/unfolding and denaturation processes are associated with enthalpy changes. The thermodynamics of binding compounds helps a great deal to understand the nature and potency of such molecules and is essential in drug discovery. As a label-free and immobilization-free method, calorimetry can evaluate the Gibbs free energy, enthalpy, entropy, specific heat, and stoichiometry, and thus provides a fundamental understanding of the molecular interactions. Calorimetric systems including isothermal titration calorimeters (ITC) and differential scanning calorimeters (DSC) are the gold standard for characterizing molecular interactions. In this research, a micro DSC is developed for direct thermodynamic study of bio-molecules. Compared with the current commercial DSC, it is on a much smaller scale. It consumes much less sample and time in each DSC measurement. It can enable comprehensive high-content thermodynamics study in the early stage of drug discovery and formulation. It also enables direct, precise, and rapid evaluation of the folding and unfolding of the large biomolecules like proteins, DNAs, and enzymes without labeling or immobilization. It can also be used as a powerful tool to study the membrane proteins, which is often impractical or impossible before.

[EN] The present work examines the influence of the chemical structure of polymers on thermal, mechanical and dielectric behavior. The experimental techniques used for the purpose are differential scanning calorimetry, dynamo-mechanical analysis and dielectric spectroscopy. Additionally, in order to confirm the results obtained using the above methods, other techniques such as ray diffraction have also been employed. Chapters 1 and 2 contain the introduction and the objectives, respectively. Chapter 3 briefly describes the experimental techniques used. Chapter 4 contains the findings of the comparative analysis of the response to electrical noise fields for three poly(benzyl methacrylates) with different structures. The analysis was carried out under a wide range of frequencies and temperatures on three poly(benzyl methacrylates) containing two dimethoxy groups in positions 2,5-, 2,3- and 3,4-. The results show that the position of the dimethoxy groups on the aromatic ring has a significant effect on the molecular dynamics of poly(benzyl methacrylate). The spectra obtained were of high complexity and therefore, in order to perform a better analysis, numerical methods for time-frequency transformation including the use of parametric regularization techniques were used. We studied the effect of this structural change on the secondary relaxation processes and relaxation process , relating to the glass transition. We also analyzed the effect of the dimethoxy group position on the formation of nanodomains, in which the side chains are predominant, and on the conduction processes of the materials tested. In Chapter 5, the conductivity of rubbery liquids was studied by analyzing poly(2,3-dimethoxybenzyl methacrylate), which exhibits its own particular behavior. The chapter analyzes the principle of time-temperature superposition, employing different interrelated variables. Chapter 6 focuses on how the presence of crosslinking affects the molecular mobility of polymethacrylates containing aliphatic alcohol ether residues. In this case, the effect of crosslinking on the secondary and primary relaxation processes was analyzed. The creation of nanodomains in the side chains as a result of the presence of crosslinking was also studied.
[ES] En este trabajo se presenta un estudio de la influencia de la estructura química de los polímeros en su comportamiento térmico, mecánico y dieléctrico. Las técnicas experimentales empleadas para ello han sido la calorimetría diferencial de barrido, el análisis dinamo-mecánico y la espectroscopia dieléctrica. Adicionalmente, se han empleado otras técnicas como la difracción de rayos, con objeto de corroborar los resultados obtenidos por las primeras. En los Capítulos 1 y 2 se recoge la introducción y los objetivos, respectivamente. El Capítulo 3 presenta una breve descripción de las técnicas experimentales empleadas. En el Capítulo 4 se recogen los resultados obtenidos en el análisis comparativo de la respuesta a campos de perturbación eléctrica en un amplio rango de frecuencias y temperaturas para tres polimetacrilatos de bencilo con dos grupos dimetoxi en posiciones 2,5-, 2,3- y 3,4-. Los resultados obtenidos señalan el importante efecto de la posición de los grupos dimetoxi en el anillo aromático, sobre la dinámica molecular del polimetacrilato de bencilo. Los espectros obtenidos fueron muy complejos, por ello en orden a llevar a cabo un mejor análisis se emplearon métodos numéricos para la transformación tiempo-frecuencia que incluyeron el uso de técnicas de regularización paramétrica. Se ha estudiado el efecto que dicho cambio estructural ejerce tanto sobre los procesos de relajación secundaria como sobre el proceso de relajación α, relacionado con la transición vítrea. Así mismo, se ha analizado el efecto de la posición de los grupos dimetoxi en la formación de iii nanodominios en los que predominan las cadenas laterales, y su efecto en los procesos de conducción de los materiales analizados. En el Capítulo 5 se recoge el estudio de la conductividad de líquidos gomosos tomando como modelo el poli (metacrilato de 2,3-dimetoxibencilo), por su peculiar comportamiento. En este capítulo se ha realizado un análisis del principio de superposición tiempo-temperatura, empleando para ello diferentes variables relacionadas entre sí. En el Capítulo 6 se recoge el efecto de la presencia de entrecruzante en la movilidad molecular de polimetacrilatos que contienen residuos de éteres de alcoholes alifáticos. En este caso, se ha analizado el efecto de la presencia de entrecruzante tanto en los procesos de relajación secundarios, como en el proceso de relajación principal. También se llevó a cabo un análisis del efecto que la presencia de entrecruzante tiene sobre la creación de nanodominios gobernados por las cadenas laterales.
[CAT] En aquest treball es presenta un estudi de la influència de l'estructura química dels polímers en el seu comportament tèrmic, mecànic i dielèctric. Les tècniques experimentals utilitzades han sigut la calorimetria diferencial de rastreig, l'anàlisi dinamo-mecànic i l'espectroscòpia dielèctrica. Addicionalment, s'han empleat altres tècniques com la difracció de rajos X a fi de corroborar els resultats obtinguts per les primeres. En els Capítols 1 i 2 s'arreplega la introducció i els objectius, respectivament. Al Capítol 3 es presenta una breu descripció de les tècniques experimentals emprades. En el Capítol 4 es recull els resultats obtinguts en l'anàlisi comparativa de la resposta a camps de pertorbació elèctrica en un ampli rang de freqüències i temperatures de tres polimetacrilats de benzil amb dos grups metoxi en posicions 2,5-, 2,3- i 3,4-. Els resultats obtinguts assenyalen l'important efecte de la posició dels grups metoxi en l'anell aromàtic, sobre la dinàmica molecular del polimetacrilat de benzil. Els espectres obtinguts van ser molt complexos, per aquesta raó per a dur a terme un millor anàlisi es van emprar mètodes numèrics per a la transformació temps-freqüència que van incloure l'ús de tècniques de regularització paramètrica. S'ha estudiat l'efecte que el dit canvi estructural exerceix tant sobre els processos de relaxació secundària com sobre el procés de relaxació , relacionat amb la transició vítria. Així mateix, s'ha analitzat l'efecte de la posició dels grups metoxi en la formació de nanodominis en els que predominen les cadenes laterals, i el seu efecte en els processos de conducció dels materials analitzats. En el Capítol 5 s'arreplega l'estudi de la conductivitat de líquids gomosos prenent com a model el poli-(metacrilat de 2,3-dimetoxibencilo), pel seu peculiar comportament. En aquest capítol s'ha realitzat un anàlisi del principi de superposició temps-temperatura, emprant per a això diferents variables relacionades entre sí. En el Capítol 6 s'arreplega l'efecte de la presència d'entrecreuat en la mobilitat molecular de polimetacrilats que contenen residus d'èters d'alcohols alifàtics. En aquest cas, s'ha analitzat l'efecte de la presència d'entrecreuat tant en els processos de relaxació secundaris, com en el procés de relaxació principal. També es va dur a terme un anàlisi de l'efecte que la presència d'entrecreuat químic té sobre la creació de nanodominis governats per les cadenes laterals.
Carsí Rosique, M. (2015). Molecular mobility. Structure-property relationship of polymeric materials [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/59460
TESIS
Premiado

Epoxy resin is an important engineering material in many industries such as electronics, automotive, aerospace, etc not only because it is an excellent adhesive but also because the materials based on it provide outstanding mechanical, thermal, and electrical properties. Epoxy resin has been proved to be an excellent matrix material for the nanocomposites when including another phase such as inorganic nanofillers. The properties of a nanocomposite material, in general, are a hybrid between the properties of matrix material and the nanofillers. In this sense, the thermal, mechanical, and electrical properties of a nanocomposite may be affected by the corresponding properties of matrix material. When the sonication is used to disperse the nanofillers in the polymer matrix, with the dispersal of the nanofillers, there comes some modification in the matrix as well and it finally affects the properties of nanocomposites. In this regard, we attempted to study the thermal, mechanical, and dynamic properties of EPON 862 epoxy resin where ultrasonic processing was taken as the effect causing variable. Uncured epoxy was subjected to thermal behavior studies before and after ultrasonic treatment and the cured epoxies with amine hardener EPICURE 3223 (diethylenetriamine) after sonications were tested for mechanical and dynamic properties. We monitored the ultrasonic processing effect in fictive temperature, enthalpy, and specific heat capacity using differential scanning calorimetry. Fictive temperature decreased whereas enthalpy and specific heat capacity were found to increase with the increased ultrasonic processing time. Cured epoxy rectangular solid strips were used to study the mechanical and dynamic properties. Flexural strength at 3% strain value measured with Dillon universal testing machine under 3-point bending method was found to degrade with the ultrasonic processing. The storage modulus and damping properties were studied for the two samples sonicated for 60 minutes and 120 minutes. Our study showed that the 60 minutes sonicated sample has higher damping or loss modulus than 120 minutes sonicated sample.

No
PURPOSE: To explore hot melt extrusion (HME) as a scalable, solvent-free, continuous technology to design cocrystals in agglomerated form. METHODS: Cocrystal agglomerates of ibuprofen and nicotinamide in 1:1 ratio were produced using HME at different barrel temperature profiles, screw speeds, and screw configurations. Product was characterized for crystallinity by XRPD and DSC, while the morphology was determined by SEM. Dissolution rate and tabletting properties were compared with ibuprofen. RESULTS: Process parameters significantly affected the extent of cocrystallization which improved with temperature, applied shear and residence time. Processing above eutectic point was required for cocrystallization to occur, and it improved with mixing intensity by changing screw configuration. Product was in the form of spherical agglomerates, which showed directly compressible nature with enhanced dissolution rate compared to ibuprofen. This marks an important advantage over the conventional techniques, as it negates the need for further size modification steps. CONCLUSIONS: A single-step, scalable, solvent-free, continuous cocrystallization and agglomeration technology was developed using HME, offering flexibility for tailoring the cocrystal purity. HME being an established technology readily addresses the regulatory demand of quality by design (QbD) and process analytical technology (PAT), offering high potential for pharmaceuticals.

Self-emulsifying systems are mixtures of oils and surfactants, ideally isotropic, sometimes including cosolvents, which emulsify under conditions of gentle agitation, similar to those which would be encountered in the gastrointestinal tract. The process of self-emulsification has remained the center of attraction for most researchers. Controlled hydration of self-emulsifying systems shows formation of an intermediate gel phase which upon rupture forms an emulsion. Current work was undertaken to understand and explore the microstructural properties of intermediate gel phase which are believed to influence the performance (droplet size) of the final formulation. The effect of additives on microstructural properties of intermediate gel phase has also been investigated. Microstructural elucidation of hydrated samples of intermediate regimes was done by using techniques such as small angle X-ray scattering, differential scanning calorimetry and rheology. Samples from intermediate regimes showed formation of local lamellar structure which swelled with hydration. In the present work, the effect of addition of salt form of naproxen (sodium and potassium) and naproxen (base) on microstructural properties of intermediate regimes was investigated. Systems containing naproxen salts formed larger droplets whereas naproxen base formed smaller ones. Microstructural properties of intermediate lamellar structures were well correlated with performance of the final formulation. The current studies indicate that by controlling the properties of intermediate regimes optimized formulations with desired performance can be tailor-made.

Indiana University-Purdue University Indianapolis (IUPUI)
Background: Elucidating the lithium disilicate system like the popular IPS e.max® CAD (LS2), made specifically for Computer-Aided Design and Computer-Aided Manufacturing (CAD-CAM), as a function of temperature unravels new ways to enhance material properties and performance. Objective: To study the effect of various thermal processing on the crystallization kinetics, crystallite microstructure, and strength of LS2. Methods: The control group of the LS2 samples was heated using the standard manufacturer heating-schedule. Two experimental groups were tested: (1) an extended temperature range (750-840 °C vs. 820-840 °C) at the segment of 30 °C/min heating rate, and (2) a protracted holding time (14 min vs. 7 min) at the isothermal temperature of 840 °C. Five other groups of different heating schedules with lower-targeted temperatures were evaluated to investigate the microstructural changes. For each group, the crystalline phases and morphologies were measured by X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Differential scanning calorimeter (DSC) was used to determine the activation energy of LS2 under non-isothermal conditions. A MTS universal testing machine was used to measure 3-point flexural strength and fracture toughness, and elastic modulus and hardness were measured by the MTS Nanoindenter® XP. A one-way ANOVA/Tukey was performed per property (alpha = 0.05). Results: DSC, XRD, and SEM revealed three distinct microstructures during LS2 crystallization. Significant differences were found between the control group, the two aforementioned experimental groups, and the five lower-targeted-temperature groups per property (p<0.05). The activation energy for lithium disilicate growth was 667.45 (± 28.97) KJ/mole. Conclusions: Groups with the extended temperature range (750-840 °C) and protracted holding time (820-840 °C H14) produced significantly higher elastic-modulus and hardness properties than the control group but showed similar significant flexural-strength and fracture-toughness properties with the control group. In general, explosive growth of lithium disilicates occurred only when maximum formation of lithium metasilicates had ended.