This study is an evaluation of epoxy coated reinforcing steel (ECR) and its ability to effectively provide corrosion protection in reinforced concrete highway bridge decks. An analysis was conducted on 10 bridge decks built in the state of Virginia between the years 1981 and 1995. A total of 141 cores containing either ECR or bare steel were evaluated. A chloride solution was applied to the surface on a weekly cycle (for a total duration of 3.06 years) and a nondestructive electrochemical testing was performed on each core on a monthly cycle. Cores were also inspected for surface cracks, the thermal properties of the epoxy coating, and the concrete conditions at bar depth. The concrete was tested for saturation percentages, diffusion coefficients, and chloride contents, while the epoxy was tested for its glass transition temperature, moisture content, and amount of surface cracking. The results indicate that the best predictor for estimating the times to corrosion initiation and cracking is the amount of chlorides present in the concrete encasing the ECR. The presence of chloride ions will have a determining effect on corrosion regardless of the epoxy coating condition. As a result, it is likely that ECR is not the solution to corrosion prevention and it is recommended that closer attention be given to improving concrete conditions that reduce the diffusion of chloride ions. The conclusion that ECR is an unreliable corrosion prevention method is in agreement with the results of previous studies. / Master of Science

Rotational-translational decoupling, a phenomenon commonly observed in supercooled liquids, has been a topic of great interest. Despite its prevalence, the underlying cause of this phenomenon, often attributed to dynamic heterogeneity, has not been conclusively elucidated. This thesis investigates and evaluates how dynamic heterogeneity may lead to this decoupling using simultaneous single-molecule rotational and translational measurements. In the experimental study, single molecule fluorescence imaging experiments are performed on the ideal probe N,N’-dipentyl-3,4,9,10-perylenedicarboximide in high molecular weight polystyrene near its glass transition temperature. A novel trajectory linking method based on hierarchical clustering is developed to facilitate single molecule tracking even in imaging data where specific molecules cannot be observed visually for a substantial number of frames. This linking algorithm then allows molecules to be localized over full movies, such that rotational and translational measurements can be compared over comparable timespans. The investigation of translational dynamics using such long trajectories, which was not previously achieved, reveals that both rotational-translational decoupling and translational enhancement persist on the single molecule level, supporting the hypothesis that temporally heterogeneous dynamics experienced by the probe molecules is a contributing factor in observed rotational-translational breakdown in both ensemble and single molecule studies. A tendency towards dynamical convergence between subgroups with fast and slow dynamics is observed, demonstrating temporal heterogeneity at the single molecule level. In comparison to rotational dynamics, translational dynamics was discovered to have a longer lifetime. Other key observations facilitated by the linked trajectory analysis include that apparent diffusion coefficient of probe molecules decreases with longer observation time, a finding inconsistent with normal diffusive behavior. To investigate the origin of this anomalous slowing in single molecule studies existing alongside the observed overall enhancement in translational motion, temporally heterogeneous models with multiple types of correlation were studied via simulations. The results emphasize the critical role that bias in translational and rotational measurements can play when investigating and observing dynamic heterogeneity, as nearly all models including dynamic heterogeneity show increasing diffusion coefficient with increasing number of dynamic environments explored. Strikingly, translational enhancement is evident in single molecule translational simulations even when slow dynamics are reinforced via positive correlation in the models. A comparison of the diffusion coefficient evolution between simulations and experiments reveals that the sub-diffusive continuous time random walk model is the most plausible candidate to account for the set of observations seen in experiment.

The heterogeneous dynamics exhibited by supercooled liquids near the glass transition temperature (𝑇_𝑔) has been a topic of much research over the past several decades. In particular, the advent of single molecule (𝖲𝖬) methods has permitted great insight into the extent of both spatial and temporal heterogeneities in these systems, information which is either difficult or impossible to access via ensemble approaches. Despite this, the related phenomenon of rotational-translation decoupling, whereby the translational motion observed in supercooled systems is enhanced relative to Debye-Stokes-Einstein predictions, is difficult to study with 𝖲𝖬 approaches. This is due to the very low localization uncertainty required to accurately report the extremely slow translational motion in supercooled systems near 𝑇_𝑔. In this thesis, a new approach for quantifying rotational dynamics in supercooled liquids is introduced which leverages fluorescence intensity fluctuations due to out-of-plane fluorophore rotations. Unlike linear dichroism (LD) measurements, the most common experiment used to access rotational dynamics, this technique does not require a polarizing optical element, thus improving localization precision in the acquired images. This intensity fluctuation-based approach is shown to report comparable rotational correlation timescales (𝝉_𝘤) and information on dynamic heterogeneity to that typically extracted via LD measurements. On a probe-by-probe basis, rotational correlation times obtained from simultaneous measurement of LD (𝝉_𝘤,𝘓𝘋) and intensity fluctuations (𝝉_𝘤,𝘐 ) are found to be only moderately well-correlated. We postulate that this is a consequence of dynamic heterogeneity due to temporal dynamic exchange, the process in which a probe (and its surroundings) undergoes sudden changes in dynamics. This hypothesis is explored through simulations, which reveal that the Pearson R correlation coefficients associated comparing log 𝝉_𝘤,𝘐 and log 𝝉_𝘤,𝘓𝘋 increases as the time between dynamic exchange increases. The information obtained from such simulations is then used to estimate the exchange timescales from experimental data. When examined in concert with experimentally measured degrees of relaxation non-exponentiality - generally considered a metric of heterogeneity in an interrogated supercooled liquid – this permits access to previously inaccessible information regarding the breadth of the distribution of underlying timescales experienced by these supercooled systems. In addition to this work focused on rotational dynamics, we also aim to further clarify information contained in 𝖲𝖬 experiments characterizing translational dynamics, towards the goal of full understanding of rotational-translational decoupling. Here, two widefield fluorescence imaging setups are optimized to minimize localization uncertainty, and differences in how localization uncertainties manifest in perceived translational motion near 𝑇_𝑔 are examined. The setup with greater localization uncertainty reports faster translational dynamics compared to the other optical setup, suggesting significant influence of the localization noise floor on perceived dynamics and highlighting the importance of maximizing the signal to noise ratio of 𝖲𝖬 experiments aiming to study the underlying cause of rotational-translational decoupling.

Broadband Dielectric Spectroscopy (BDS) in combination with a nanostructured electrode arrangement – which circumvents the conventional need to evaporate metal electrodes onto soft matter – is used to study the molecular dynamics of several glass forming materials confined in nanometric (> 5 nm) layers. Other complementary experimental tools employed in this work include spectroscopic vis-Ellipsometry (SE), AC-chip calorimetry (ACC), X-ray reflectrometry (XRR), Differential Scanning Calorimetry (DSC) and Atomic Force Microscopy (AFM). The latter is used to characterize the topography of the samples and to determine their thicknesses. Under the conditions of annealing samples (Tg + 50K) in high oil-free vacuum (10E-6 mbars) for at least 12 h and carrying out measurements in inert (dry nitrogen or argon) atmosphere, it is found for all studied thin layers that the structural relaxation, and hence the dynamic glass transition – in its mean relaxation times – remains within a margin ±3 K from the respective bulk behaviour. It is revealed, inter alia, that the one-dimensional confinement of thin films introduces restrictions on other (slower) molecular relaxation processes which manifest, depending on the specific system under investigation, as (i) an interruption of the end-to-end (normal mode) fluctuation of the chains, or (ii) a slowing down of the delta-relaxation when the system is cooled towards glass-formation. Furthermore, (iii) evidence is provided to show that the dimensionality of confinement plays a significant role in determining the resulting dynamics. A molecular understanding of these findings is given, and the discussion presented with respect to the on-going international debate about dynamics in confinement.

The aim of the work reported here was to determine the influence of an amine curing agent, and postcure cycle on the mechanical and thermal properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The results of this initial study were then used as the basis for selecting material to obtain optimum toughness in epoxy/glass fibre systems. These basic materials were further used to make comparisons with the properties of modified resin systems which contained commercial elastomers. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA), Fourier Transform Infrared Spectroscopy (FTIR), flexural and interlaminar shear tests, Instrumented Falling Weight Impact (IFWI), visual observation, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) were all used to investigate various properties and the structures which gave rise to them. The properties of cured products were found to be affected by the amounts of curing agent, curing times and temperatures, and the structure of the elastomers. Not surprisingly the maximum thermal and mechanical properties tended to be found in the stoichiometric (standard) mix systems. However, postcuring at higher than room temperature, which was used as the basic curing temperature, led to more conversion. This effect improved the thermal and mechanical properties of both the unmodified and modified resin systems. The maximum flexural strength of 104 MPa of the unreinforced resins was found in the stoichiometric mix ratio after postcure at 150°C for 4 hr. However, the maximum flexural modulus and glass transition temperature (Tg) were found after postcuring at the same temperature for 48 hr. This was believed to be due to increased crosslinking, but unfortunately the longer curing time led to degradation of the resins. In the systems modified with -20 phr of polyetheramine elastomers, the one modified with the lowest molecular weight (2000) was found to have the highest flexural strength (85.8 MPa) and modulus (2.5 GPa). The impact properties of all the composites with modified resin matrices were found to be higher than the unmodified resin matrix composites. The best impact properties were, however, obtained with the elastomer modifier with a molecular weight of 4000. The impact energy at maximum force increased from 11.9 to 16.4 J, and energy at failure increased from 18.7 to 21.6 J. This increase in impact properties was due to the increase in areas of phase separated elastomer particles over similar systems with lower molecular weight modifier.

Master of Science / Department of Chemical Engineering / Jennifer L. Anthony / A polymer has drastically different physical properties above versus below some characteristic temperature. For this reason, the precise identification of this glass transition temperature, T[subscript]g, is critical in evaluating product feasibility for a given application. The objective of this report is to review the behavior of polymers near their T[subscript]g and assess the capability of predicting T[subscript]g using theoretical and empirical models. It was determined that all polymers begin to undergo structural relaxation at various temperatures both nearly above and below T[subscript]g, and that practical assessment of a single consistent T[subscript]g is successfully performed through consideration of only immediate thermal history and thermodynamic properties. It was found that the best quantitative structure-property relationship (QSPR) models accurately predict T[subscript]g of polymers of theoretically infinite chain length with an average error of less than 20 K or about 6%, while T[subscript]g prediction for shorter polymers must be done by supplementing these T[subscript]g (∞) values with configurational entropy or molecular weight relational models. These latter models were found to be reliable only for polymers of molecular weight greater than about 2,000 g/mol and possessing a T[subscript]g (∞) of less than about 400 K.

Novel surgical strategies for spinal disc repair are currently being developed that require materials that (1) possess the appropriate mechanical properties to mimic the tissue the material is replacing or repairing and (2) maintain their mechanical function for long durations without negatively affecting the tissue response of adjacent tissue (i.e. bone). Polymers formed through photopolymerization have emerged as candidate biomaterials for many biomedical applications, but these materials possess limited toughness in vivo due to the presence of water inherent in most tissues. Therefore, the overall objective of this research was to develop photopolymerizable (meth)acrylate networks that are both mechanically and biologically compatible under physiological conditions to be implemented in spinal repair procedures. The fundamental approach was to determine structure-property relationships between toughness and network structure in the presence of phosphate buffered saline (PBS) using several model copolymer networks in order to facilitate the design of photopolymerizable networks that are tough in physiological solution. It was demonstrated that networks toughness could be optimized in PBS by tailoring the Tg of the copolymer network close to body temperature and incorporating the appropriate "tough" chemical structures. The ability to maintain toughness up to 9 months in PBS was dependent upon the viscoelastic state and overall hydrophobicity of the network. In tandem, the effect of network chemistry and stiffness on the response of MG63 pre-osteoblast cells was assessed in vitro. The ability of MG63 cells to differentiate on (meth)acrylate network surfaces was found to be primarily dependent on surface chemistry with PEG-based materials promoting a more mature osteoblast phenotype than 2HEMA surfaces. Amongst each copolymer group, copolymer stiffness was found to regulate osteoblast differentiation in a manner dependent upon the surface chemistry. In general, photopolymerizable (meth)acrylate networks that were deemed "tough" were able to promote osteoblast differentiation in a manner comparable if not exceeding that on tissue culture polystyrene (TCPS). This research will impact the field of biomaterials by elucidating the interrelationships between materials science, mechanics, and biology.

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Orientador: Celso Costa Lopes / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-09T15:17:24Z (GMT). No. of bitstreams: 1 Hofsetz_Kelly_D.pdf: 10880310 bytes, checksum: a6cd1fb5002b3963054fc23a04552ed4 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho estudou-se a secagem de banana utilizando um pulso inicial a alta temperatura e curto tempo, combinado com uma etapa de secagem convencional a ar quente a 70°C. Numa primeira etapa, foram analisadas as mudanças de encolhimento, porosidade e estrutura ao longo da secagem com bananas de origem portuguesa e brasileira. Esses resultados foram comparados com os de uma secagem convencional feita somente a 70°C. Na segunda etapa, estudaram-se as isotermas de sorção e as transições de fase nas amostras das duas origens (Portugal e Brasil) através de Calorimetria Diferencial de Varredura. Os resultados da primeira parte mostraram que o grau de encolhimento da banana foi maior para a secagem convencional a 70°C, na qual o volume apresentou um decréscimo linear com o conteúdo de umidade, chegando a 30%, enquanto que a porosidade aumentou progressivamente até 32%. A secagem combinada resultou na formação de um produto com uma estrutura altamente porosa (45,5% a 57,5%) e menor grau de encolhimento (42% a 68,5%), quando comparada com a secagem convencional a 70°C. As observações estruturais nas amostras de banana ajudaram a explicar as mudanças na porosidade e encolhimento. Os resultados das isotermas de sorção tiveram um bom ajuste para o modelo de BET e de GAB para as amostras frescas de origem portuguesa e, para as amostras secas das duas origens, o modelo de GAB foi o mais adequado. A ocorrência da temperatura de transição vítrea foi verificada em todas as amostras estudadas e decresceu com o aumento do conteúdo de umidade, comprovando o efeito plasticizante da água. O modelo de Gordon-Taylor permitiu uma boa predição da dependência da temperatura de transição vítrea com o conteúdo de água para as amostras de origem portuguesa. No caso das amostras de origem brasileira, foi encontrada uma relação de dependência linear do parâmetro kGT do modelo de Gordon-Taylor com a temperatura de transição vítrea experimental / Abstract: This study was conducted to evaluate the drying of bananas by a high temperature and short time drying pulse combined with hot air-drying process stage at 70°C. Firstly, Portuguese and Brazilian bananas samples were dried and the changes of shrinkage, porosity and structure during drying were analyzed. This results were compared with those obtained in a conventional air-drying process at 70°C. After that, sorption isotherms of samples from Portugal and Brazil, as well the phase transitions of the Brazilian banana, were studied. The results of the first part showed that shrinkage changes during drying was more intense to the conventional air-drying process at 70°C, and a line ar decrease in volume with the decrease in moisture ratio was observed reaching 30%, while the porosity increased uniformly reaching values of about 32%. The high temperature and short time drying pulse combined with hot air- drying process stage at 70°C resulted in the formation of a highly porous structure (45,5% to 57,5%) and reduced shrinkage (42% to 68,5%) when compared with the conventional air-drying process. Structural observations of the banana samples during the processes studied were able to explain the volume and porosity changes. The BET and GAB equations gave the best fit to the experimental sorption data for Portuguese fresh bananas and the GAB model was found to be the best-fitted equation for all dried bananas (Portuguese and Brazilian samples) and both models gave information about the shelf-stability for the samples. The glass transition temperature occurred for all samples studied and decreased as water content increased, confirming the water plasticization effect. The Gordon-Taylor equation was able to predict the dependence of the glass transition temperature on moisture content for the Portuguese fresh samples. A linear dependence of the kGT (Gordon-Taylor equation¿s constant) and the experimental glass transition temperature was found for the Brazilian samples / Doutorado / Doutor em Engenharia de Alimentos

Orientadores: Rafael Augustus de Oliveira, Kil Jin Park / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-25T10:54:18Z (GMT). No. of bitstreams: 1 SanchezSaenz_CarolinaMaria_D.pdf: 5939209 bytes, checksum: 43efccade58fb536d9e9c45782a43cc3 (MD5) Previous issue date: 2014 / Resumo: As pesquisas atuais em secagem de alimentos levam em consideração a qualidade do produto e a eficiência energética do processo, já que este processo consome cerca de 20-25% da energia utilizada pelo processamento na indústria de alimentos. Isto faz com que sejam exploradas novas técnicas e combinações de métodos de secagem e avaliação da intermitência do processo. Assim, realizou-se mais um estudo com o secador agitador/misturador (patente PI 0506639-5), iniciando pela adequação das pás do eixo misturador e adaptação do sistema de controle de velocidade e aquecimento do ar. O tempo de residência foi determinado considerando a rotação do eixo das pás e a rotação do eixo de alimentação do secador. Foi avaliada a influência dos parâmetros de secagem sobre o processo, de modo que foi possível determinar as melhores condições de pré-secagem HTST (High Temperature and Short Time) combinada com a secagem convectiva contínua com aplicação de radiação infravermelha, para obtenção de um produto de qualidade e com baixa demanda de energia elétrica no processo. Foi feito também o estudo da influência desses processos nas propriedades físicas e mecânicas de raízes de chicória. A redução da demanda de energia elétrica foi obtida considerando a intermitência da aplicação de radiação infravermelha. Os testes e análises realizados nestas condições resultaram em uma série de dados que garantem que a combinação de métodos de secagem e de técnicas de intermitência são eficientes energeticamente e resultam em um produto de boa qualidade / Abstract: In recent research works, food drying takes into account product quality and energy efficiency of process, since drying process consumes about 20-25 % of the energy used by the food processing industry. This fact indicates that new techniques combining drying methods and intermittency of the process must be evaluated. Thus, a study with the agitator / mixer dryer (patent PI 0506639-5) was performed, beginning with the mixer blades adequacy and velocity control and air heating systems adaptation. Residence time distribution determination has been conducted, considering rotation of blades and feed rotation of dryer. The influence of dying parameters on the process was evaluated, so that it was possible to determine the best conditions of HTST (High Temperature and Short Time) drying combined with the continuous drying with pulse of infrared radiation application, to obtain a good quality dried product and electric energy efficiency of the process. Study the influence of these processes was also done on the physical and mechanical properties of chicory roots. Finally, the electric energy efficiency was obtained considering the intermittency of pulse infrared radiation application. The experimental runs and analyses under these conditions have generated data which ensure that the combination of drying methods and intermittency techniques are energy efficient and result in a good quality product / Doutorado / Tecnologia Pós-Colheita / Doutora em Engenharia