Aggregation behaviour of hydrophobically modified poly(allylammonium) chloride

The behaviour of hydrophobically modified poly(allylammonium) chloride having octyl, decyl, dodecyl and hexadecyl side chains has been studied in aqueous solution using fluorescence emission techniques. Micropolarity studies using the I-1/I-3 ratio of the vibronic bands of pyrene show that the formation of hydrophobic microdomains depends on both the length of the side chain and the polymer concentration. The I-1/I-3 ratio of the polymers with low hydrophobe content (less than 5% mel) changes substantially when reaching a certain concentration. These changes are assigned to aggregation originating from interchain interactions. This behaviour is also confirmed by the behaviour of the monomer/excimer emission intensities of pyrene- dodecanoic acid used as a probe. For polymers having dodecyl side chains and hydrophobe contents higher than 10%, aggregates are formed independently of the polymer concentration. Anisotropy measurements show that microdomains resulting from the inter- and/or intramolecular interactions are similar to those observed for cationic surfactants. Viscosity measurements show that the coil dimensions are substantially decreased for the polymers having high hydrophobe contents, indicating intramolecular associations.

Rheological properties of tin oxide suspensions

The rheological properties of tin oxide slurries were studied experimentally and theoretically. The deflocculants used were ammonium polyacrilate (PAA) and the copolymer poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB-PVA-PVAc), in water and ethanol, respectively. The amount of deflocculant was optimized for different solid contents by means of viscosity measurements. In spite of the high stability of PVB-dispersed slurries, a high solid concentration was not obtained. On the other hand, a slurry with a 56.4 vol.% of solids was attained when PAA was used. A theoretical study of the adsorption of PAA in its dissociated (basic solution) and non-dissociated (acidic solution) forms on SnO 2 (110) is presented. This analysis was made by means of the PM3 method using a large cluster Sn 15O 28 for the surface model. The calculated adsorption energy is larger for the ionized PAA than for the non-ionized form, indicating that alkaline slurries favor PAA adsorption on the SnO 2 surface. © 2002 Elsevier Science Ltd. All rights reserved.

Estudo do comportamento reológico de suspensões argilosas da Formação Corumbataí

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Síntese, caracterização e estudo físico-químico das nanopartículas formadas pela interação de amino derivados de quitosana com DNA

Pós-graduação em Química - IBILCE

Aqueous dispersions of DMPG in low salt contain leaky vesicles

Aqueous dispersions of dimyristoyl phosphatidylglycerol (DMPG), at low ionic strength, display uncommon thermal behavior. Models for such behavior need to assign a form to the lipid aggregate. Although most studies accept the presence of lipid vesicles in the lipid gel and fluid phases, this is still controversial. With electron spin resonance (ESR) spectra of spin labels incorporated into DMPG aggregates, quantification of [C-14]sucrose entrapped by the aggregates, and viscosity measurements, we demonstrate the existence of leaky vesicles in dispersions of DMPG at low ionic strength, in both gel and fluid phases of the lipid. As a control system, the ubiquitous lipid dimyristoyl phosphatidylcholine (DMPC) was used. For DMPG in the gel phase, spin labeling only indicated the presence of lipid bilayers, strongly suggesting that DMPG molecules are organized as vesicles and not micelles or bilayer fragments (bicelles), as the latter has a non-bilayer structure at the edges. Quantification of [C-14]sucrose entrapping by DMPG aggregates revealed the presence of highly leaky vesicles. Due to the short hydrocarbon chains (C-14 atoms), DMPC vesicles were also found to be partially permeable to sucrose, but not as much as DMPG vesicles. Viscosity measurements, with the calculation of the intrinsic viscosiiy of the lipid aggregate, showed that DMPG vesicles are rather similar in the gel and fluid phases, and quite different from aggregates observed along the gel-fluid transition. Taken together, our data strongly supports that DMPG forms leaky vesicles at both gel and fluid phases. (C) 2011 Elsevier Ireland Ltd. All rights reserved.

Comparative study and characterization of starches isolated from unconventional tuber sources

Some properties of canna (Canna indica L.) and bore (Alocasia macrorrhiza) starches were evaluated and compared using cassava starch (Manihot esculenta Crantz) as a reference. Proximate analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and viscosity measurements were performed. Canna and bore starches showed a similar degree of purity as that of the cassava starch. Canna starch exhibited higher thermal stability and viscosity of solution values than those of bore and cassava starches. XRD spectra showed that canna starch crystallizes as a B-type structure; however, bore and cassava starches crystallize as an A-type structure. Results proved that canna and bore starches are promising bio(materials), obtained from unconventional sources, to be used for industrial applications, as their physicochemical properties are similar to those of cassava starch, which it is known has potential applications in this area.

2 H-NMR und Viskositätsuntersuchungen zum Studium der molekularen Dynamik unterkühlter Flüssigkeiten unter Hochdruck

In der vorliegenden Arbeit wurde die Druckabhängigkeit der molekularen Dynamik mittels 2H-NMR und Viskositätsmessungen untersucht. Für die Messungen wurde der niedermolekulare organische Glasbildner ortho-Terphenyl (OTP) ausgewählt, da dieser aufgrund einer Vielzahl vorliegender Arbeiten als Modellsubstanz angesehen werden kann. Daneben wurden auch Messungen an Salol durchgeführt.Die Untersuchungen erstreckten sich über einen weiten Druck- und Temperaturbereich ausgehend von der Schmelze bis weit in die unterkühlte Flüssigkeit. Dieser Bereich wurde aufgrund experimenteller Voraussetzungen immer durch eine Druckerhöhung erreicht.Beide Substanzen zeigten druckabhängig ein Verhalten, das dem der Temperaturvariation bei Normaldruck sehr ähnelt. Auf einer Zeitskala der molekularen Dynamik von 10E-9 s bis zu 10E+2 s wurde daher am Beispiel von OTP ein Druck-Temperatur-Zeit-Superpositionsprinzip diskutiert. Zudem konnte eine Temperatur-Dichte-Skalierung mit rho T-1/4 erfolgreich durchgeführt werden. Dies entspricht einem rein repulsiven Potentialverlauf mit rho -12±3 .Zur Entscheidung, ob die Verteilungsbreiten der mittleren Rotationskorrelationszeiten durch Druckvariation beeinflußt werden, wurden auch Ergebnisse anderer experimenteller Methoden herangezogen. Unter Hinzuziehung aller Meßergebnisse kann sowohl eine Temperatur- als auch Druckabhängigkeit der Verteilungsbreite bestätigt werden. Zur Auswertung von Viskositätsdaten wurde ein Verfahren vorgestellt, das eine quantitative Aussage über den Fragilitätsindex von unterkühlten Flüssigkeiten auch dann zuläßt, wenn die Messungen nicht bis zur Glasübergangstemperatur Tg durchgeführt werden. Die Auswertung der druckabhängigen Viskositätsdaten von OTP und Salol zeigt einen sehr differenzierten druckabhängigen Verlauf des Fragilitätsindexes für beide Glasbildner. OTP zeigt zunächst eine leichte Abnahme und danach wieder eine Zunahme des Fragilitätsindexes, dieses Ergebnis wird auch von Simulationsdaten, die der Literatur entnommen wurden, unterstützt. Salol hingegen zeigt zunächst eine deutliche Zunahme und danach eine Abnahme des Fragilitätsindexes. Das unterschiedliche Verhalten der beiden Glasbildner mit ähnlichem Fragilitätsindex bei Normaldruck wird auf die Wasserstoffbrückenbindungen innerhalb von Salol zurückgeführt.

Klassische und ab initio Molekulardynamik-Untersuchungen zu Germaniumdioxidschmelzen

Germaniumdioxid (GeO2) ist ein Glasbildner, der wie das homologe SiO2 ein ungeordnetes tetraedrisches Netzwerk ausbildet. In dieser Arbeit werden mit Hilfe von Molekulardynamik-Computersimulationen die Struktur und Dynamik von GeO2 in Abhängigkeit von der Temperatur untersucht. Dazu werden sowohl Simulationen mit einem klassischen Paarpotentialmodell von Oeffner und Elliott als auch ab initio-Simulationen gemäß der Car-Parrinello-Molekulardynamik (CPMD), bei der elektronische Freiheitsgrade mittels Dichtefunktionaltheorie beschrieben werden, durchgeführt. In der klassischen Simulation werden dazu ein Temperaturen zwischen 6100 K und 2530 K betrachtet. Darüberhinaus ermöglichen Abkühlläufe auf T=300 K das Studium der Struktur des Glases. Zum Vergleich werden CPMD-Simulationen für kleinere Systeme mit 60 bzw. 120 Teilchen bei den Temperaturen 3760 K und 3000 K durchgeführt. In den klassischen Simulationen kann die im Experiment bis 1700 K nachgewiesene, im Vergleich zu SiO2 starke, Temperaturabhängigkeit der Dichte auch bei höheren Temperaturen beobachtet werden. Gute Übereinstimmungen der Simulationen mit experimentellen Daten zeigen sich bei der Untersuchung verschiedener struktureller Größen, wie z.B. Paarkorrelationsfunktionen, Winkelverteilungen, Koordinationszahlen und Strukturfaktoren. Es können leichte strukturelle Abweichungen der CPMD-Simulationen von den klassischen Simulationen aufgezeigt werden: 1. Die Paarabstände in CPMD sind durchweg etwas kleiner. 2. Es zeigt sich, daß die Bindungen in den ab initio-Simulationen weicher sind, was sich auch in einer etwas stärkeren Temperaturabhängigkeit der strukturellen Größen im Vergleich zu den klassischen Simulationen niederschlägt. 3. Für CPMD kann ein vermehrtes Auftreten von Dreierringstrukturen gezeigt werden. 4. In der CPMD werden temperaturabhängige Defektstrukturen in Form von Sauerstoffpaaren beobachtet, die vor allem bei 3760 K, kaum jedoch bei 3000 K auftreten. Alle strukturellen Unterschiede zwischen klassischer und CPMD-Simulation sind eindeutig nicht auf Finite-Size-Effekte aufgrund der kleinen Systemgrößen in den CPMD-Simulationen zurückzuführen, d.h. sie sind tatsächlich methodisch bedingt. Bei der Dynamik von GeO2 wird in den klassischen Simulationen ebenfalls eine gute Übereinstimmung mit experimentellen Daten beobachtet, was ein Vergleich der Diffusionskonstanten mit Viskositätsmessungen bei hohen Temperaturen belegt. Die Diffusionskonstanten zeigen teilweise ein verschiedenes Verhalten zum homologen SiO2. Sie folgen in GeO2 bei Temperaturen unter 3000 K einem Arrheniusgesetz mit einer deutlich niedrigeren Aktivierungsenergie. Darüberhinaus werden die Möglichkeiten der Parametrisierung eines neuen klassischen Paarpotentials mittels der Kräfte entlang der CPMD-Trajektorien untersucht. Es zeigt sich, daß derartige Parametrisierungen sehr stark von den gewählten Startparametern abhängen. Ferner führen sämtliche an die Schmelze parametrisierten Potentiale zu zu hohen Dichten im Vergleich zum Experiment. Zum einen liegt dies sehr wahrscheinlich daran,daß für das System GeO2 Kraftdaten allein nicht ausreichen, um grundlegende strukturelle Größen, wie z.B. Paarkorrelationen und Winkelverteilungen, der CPMD-Simulationen gut reproduzieren zu können. Zum anderen ist wohl die Beschreibung mittels Paarpotentialen nicht ausreichend und es ist erforderlich, Merkörperwechselwirkungen in Betracht zu ziehen.

Le reologia dei leganti bituminosi stradali: studio delle proprietà meccaniche a seguito di processi di “aging” in laboratorio

Lo studio effettuato pone le sue basi sulla ricerca di materiali stradali che combinino ad elevati standard prestazionali, la riduzione dell’impatto ambientale in fase realizzativa e manutentiva. In particolare il seguente lavoro si occupa dello studio di 7 leganti modificati con polimeri ed additivati con cere. I primi infatti conferiscono alla miscela maggiore elastoplasticità, incrementandone la durabilità e la resistenza a fatica. Nei secondi la presenza del materiale paraffinico contribuisce a ridurre la viscosità del bitume, consentendo un notevole abbassamento della temperatura di produzione e stesa della miscela. Numerosi studi hanno dimostrato che le caratteristiche meccaniche della pavimentazione sono fortemente influenzate dal grado di ossidazione delle componenti organiche del bitume, ovvero dal fenomeno dell’invecchiamento o aging. Pertanto allo studio reologico del bitume, si sono affiancate prove di simulazione dell’ invecchiamento nel breve e lungo termine. In fase di ricerca sperimentale si sono analizzati i leganti modificati ed additivati secondo la teoria della viscoelasticità, simulando le reali condizioni di carico ed invecchiamento alle quali il bitume è sottoposto. Tutte le prove di caratterizzazione reologica avanzata sono state effettuate mediante l’utilizzo del DSR (Dynamic Shear Rheometer - UNI EN 14770 ) in varie configurazioni di prova e l’invecchiamento a breve termine è stato simulato mediante RTFOT (Rolling thin film oven test -UNI EN 12607-1). Si è proposto inoltre una nuova procedura di aging invecchiando il bitume alla temperatura di Twork, ovvero a quel valore della temperatura tale per cui, in fase di messa in opera, si avrà una distribuzione molecolare omogenea del modificante all’interno del bitume.

Batchelor's theory extended to elongated cylindrical or ellipsoidal particles

Extensions to Batchelor's theory have been derived to take into account different shaped particles while relating extensional viscosity enhancement to three parameters - shape, volume fraction and particle aspect ratio. The extended theory now allows calculation of the extensional viscosity enhancement, at a given volume fraction of particles, for either ellipsoidal or cylindrical particles. The formula improves the predictive capability of Batchelor's theory when compared with measurements found in the literature for different rod-like polymer solutions. (c) 2005 Elsevier B.V. All rights reserved.

The behaviour of polymer quenchants

The internationally accepted Wolfson Heat Treatment Centre Engineering Group test was used to evaluate the cooling characteristics of the most popular commercial polymer quenchants: polyalkylene glycols, polyvinylpyrrolidones and polyacrylates. Prototype solutions containing poly(ethyloxazoline) were also examined. Each class of polymer was capable of providing a wide range of cooling rates depending on the product formulation, concentration, temperature, agitation, ageing and contamination. Cooling rates for synthetic quenchants were generally intermediate between those of water and oil. Control techniques, drag-out losses and response to quenching in terms of hardness and residual stress for a plain carbon steel, were also considered. A laboratory scale method for providing a controllable level of forced convection was developed. Test reproducibility was improved by positioning the preheated Wolfson probe 25mm above the geometric centre of a 25mm diameter orifice through which the quenchant was pumped at a velocity of 0.5m/s. On examination, all polymer quenchants were found to operate by the same fundamental mechanism associated with their viscosity and ability to form an insulating polymer-rich-film. The nature of this film, which formed at the vapour/liquid interface during boiling, was dependent on the polymer's solubility characteristics. High molecular weight polymers and high concentration solutions produced thicker, more stable insulating films. Agitation produced thinner more uniform films. Higher molecular weight polymers were more susceptible to degradation, and increased cooling rates, with usage. Polyvinylpyrrolidones can be cross-linked resulting in erratic performance, whilst the anionic character of polyacrylates can lead to control problems. Volatile contaminants tend to decrease the rate of cooling and salts to increase it. Drag-out increases upon raising the molecular weight of the polymer and its solution viscosity. Kinematic viscosity measurements are more effective than refractometer readings for concentration control, although a quench test is the most satisfactory process control method.

Small volume laboratory on a chip measurements incorporating the quartz crystal microbalance to measure the viscosity-density product of room temperature ionic liquids

A microfluidic glass chip system incorporating a quartz crystal microbalance (QCM) to measure the square root of the viscosity-density product of room temperature ionic liquids (RTILs) is presented. The QCM covers a central recess on a glass chip, with a seal formed by tightly clamping from above outside the sensing region. The change in resonant frequency of the QCM allows for the determination of the square root viscosity-density product of RTILs to a limit of similar to 10 kg m(-2) s(-0.5). This method has reduced the sample size needed for characterization from 1.5 ml to only 30 mu l and allows the measurement to be made in an enclosed system.

Transport Properties Investigation of Aqueous Protic Ionic Liquid Solutions through Conductivity, Viscosity, and NMR Self-Diffusion Measurements

We present a study on the transport properties through conductivity (s), viscosity (?), and self-diffusion coefficient (D) measurements of two pure protic ionic liquids—pyrrolidinium hydrogen sulfate, [Pyrr][HSO4], and pyrrolidinium trifluoroacetate, [Pyrr][CF3COO]—and their mixtures with water over the whole composition range at 298.15 K and atmospheric pressure. Based on these experimental results, transport mobilities of ions have been then investigated in each case through the Stokes–Einstein equation. From this, the proton conduction in these PILs follows a combination of Grotthuss and vehicle-type mechanisms, which depends also on the water composition in solution. In each case, the displacement of the NMR peak attributed to the labile proton on the pyrrolidinium cation with the PILs concentration in aqueous solution indicates that this proton is located between the cation and the anion for a water weight fraction lower than 8%. In other words, for such compositions, it appears that this labile proton is not solvated by water molecules. However, for higher water content, the labile protons are in solution as H3O+. This water weight fraction appears to be the solvation limit of the H+ ions by water molecules in these two PILs solutions. However, [Pyrr][HSO4] and [Pyrr][CF3COO] PILs present opposed comportment in aqueous solution. In the case of [Pyrr][CF3COO], ?, s, D, and the attractive potential, Epot, between ions indicate clearly that the diffusion of each ion is similar. In other words, these ions are tightly bound together as ion pairs, reflecting in fact the importance of the hydrophobicity of the trifluoroacetate anion, whereas, in the case of the [Pyrr][HSO4], the strong H-bond between the HSO4– anion and water promotes a drastic change in the viscosity of the aqueous solution, as well as on the conductivity which is up to 187 mS·cm–1 for water weight fraction close to 60% at 298 K.

Comparative study on transport properties for LiFAP and LiPF6 in alkyl-carbonates as electrolytes through conductivity, viscosity and NMR self-diffusion measurements

We present in this work a comparative study on density and transport properties, such as the conductivity (sigma), viscosity (eta) and self-diffusion coefficients (D), for electrolytes based on the lithium hexafluorophosphate, LiPF6; or on the lithium tris(pentafluoroethane)-trifluorophosphate, LiFAP dissolved in a binary mixture of ethylene carbonate (EC) and dimethylcarbonate (DMC) (50:50 wt%). For each electrolyte, the temperature dependence on transport properties over a temperature range from 10 to 80 degrees C and 20 to 70 degrees C for viscosity and conductivity, respectively, exhibits a non-Arrhenius behavior. However, this dependence is correctly correlated by using the Vogel-Tamman-Fulcher (VTF) type fitting equation. In each case, the best-fit parameters, such as the pseudo activation energy and ideal glass transition temperature were then extracted. The self-diffusion coefficients (D) of the Li+ cation and PF6- or FAP(-) anions species, in each studied electrolyte, were then independently determined by observing Li-3, F-19 and P-31 nuclei with the pulsed-gradient spin-echo (PGSE) NMR technique over the same temperature range from 20 to 80 degrees C. Results show that even if the diffusion of the lithium cation is quite similar in both electrolytes, the anions diffusion differs notably. In the case of the LiPF6-based electrolyte, for example at T approximate to 75 degrees C (high temperature), the self-diffusion coefficients of Li+ cations in solution (D (Li+)approximate to 5 x 10(-19) m(2) s(-1)) is 1.6 times smaller than that of PF6- anions (D (PF6-) = 8.5 x 10(-19) m(2) s(-1)), whereas in the case of the LiFAP-based electrolyte, FAP(-) anions diffuse at same rate as the Li+ cations (D (FAP(-)) = 5 x 10(-1) m(2) s(-1)). Based on these experimental results, the transport mobility of ions were then investigated through Stokes-Einstein and Nernst-Einstein equations to determine the transport number of lithium t(Li)(+), effective radius of solvated Li+ and of PF6- and FAP(-) anions, and the degree of dissociation of these lithium salts in the selected EC/DMC (50:50 wt%) mixture over a the temperature range from 20 to 80 degrees C. This study demonstrates the conflicting nature of the requirements and the advantage of the well-balanced properties as ionic mobility and dissociation constant of the selected electrolytes. (C) 2013 Elsevier Ltd. All rights reserved.

Clinical investigations of polymethylmethacrylate cement viscosity during vertebroplasty and related in vitro measurements

Percutaneous vertebroplasty, comprising an injection of polymethylmethacrylate (PMMA) into vertebral bodies, is a practical procedure for the stabilization of osteoporotic compression fractures as well as other weakening lesions. Cement leakage is considered to be one of the major and most severe complications during percutaneous vertebroplasty. The viscosity of the material plays a key role in this context. In order to enhance the safety for the patient, a rheometer system was developed to measure the cement viscosity intraoperatively. For this development, it is of great importance to know the proper viscosity to start the procedure determined by experienced surgeons and the relation between the time period when different injection devices are used and the cement viscosity. The purpose of the study was to investigate the viscosity ranges for different injection systems during conventional vertebroplasty. Clinically observed viscosity values and related time periods showed high scattering. In order to get a better understanding of the clinical observations, cement viscosity during hardening at different ambient temperatures and by simulation of the body temperature was investigated in vitro. It could be concluded, that the direct viscosity assessment with a rheometer during vertebroplasty can help clinicians to define a lower threshold viscosity and thereby decrease the risk of leakage and make adjustments to their injection technique in real time. Secondly, the acceleration in hardening of PMMA-based cements at body temperature can be useful in minimizing leakages by addressing them with a short injection break.