Master of Science / Department of Physics / Jeremy D. Schmit / Antibodies are large Y-shaped proteins which are used by immune system to identify and neutralize pathogens. Monoclonal antibody therapy is used to treat different patient conditions. There are problems associated with the manufacturability and deliverability of mAb solutions due to the viscous nature of the protein. The viscosity of antibody solutions increases with the increase in concentration and decreases with applied shear. We want to know why these behaviours are seen and to address this problem we have developed a theory describing the rapid viscosity increase with increasing concentration. We use the polymer theory to explain this behaviour. Here antibodies are treated as polymers. The length of the polymer depend on the aggregation. The reptation time increases approximately as the cubic power of size of aggregate (N³ ). We see the shear thinning behaviour is dependent on the Ab-Ab binding energy and find the relationship between the size of the aggregate and the binding energy. We find aggregate size and morphology using several models for Ab-Ab interaction sites. We use the head to head binding (fAb-fAb binding) model to describe aggregation state in our viscosity theory. The size of the aggregate and hence the reptation time is captured by the binding energy. When the binding energy increases the zero shear viscosity increases and the reptation time decreases. Likewise when the binding energy decreases the zero shear viscosity decreases and the reptation time increases. We have yet to find the correct exponents for the shear thinning behaviour of different mAbs which would be our future work.

Fumed silica filler has long been used to structurally reinforce silicone elastomers. Unfortunately, the combination of as little as a few weight percent of untreated fumed silica nanoparticles [uFSN] with a siloxane polymer, such as PDMS, forms a difficult to process waxy solid admixture that even long periods of high shear mixing will not thin. In the course of the current work it was noted that after a period of storage certain solid admixtures would become viscous liquids when subjected to additional high shear mixing. It was further found that the required aging period could be decreased if the admixture storage temperature were increased. The only known interaction of PDMS and uFSN at moderate conditions is the adsorption of polymer on filler, and this interaction is also known to occur more quickly at higher temperature. This study examines the relationship between polymer adsorption and admixture liquefaction. Further, the mechanical properties of cured elastomers containing liquefied admixtures are examined to assess the degree of reinforcement that these materials afford.

No description available.

Doctor of Philosophy / Department of Grain Science and Industry / Xiuzhi Susan Sun / Om Prakash / Rational design of peptide molecules to undergo spontaneous organization as a higher-ordered supramolecular structure is an attractive and fast-growing field for developing new functional biomaterials. Hydrogel, with its high water content and three-dimensional architecture, is formed by a self-assembling peptide and has great potential for broad biomedical applications. The key challenge in controlling the functional properties of final biomaterials can be met by designing the peptide primary structure carefully at the beginning and developing a comprehensive understanding of peptide self-assembly pathways. In this study, we first designed a Ca2+ responsive peptide (eD2) using identified functional native domains from a spider flagelliform silk protein and the Ca2+ binding domain of lipase Lip A from Serratia marcescens. Instead of directly linking the two peptide sequences, we rationally inserted the ion-binding motif into the silk structure sequence and made the new peptide inherit the physical characteristics of both model sequences and assemble into nanofibers when triggered by Ca2+. Next, we introduced the amphiphilic property to the eD2 peptide by conjugating its N-terminus with a strong hydrophobic sequence from a trans-membrane segment of human muscle L-type calcium channel. This self-assembly peptide, called h9e, was responsive to Ca2+, solution pH, and selected proteins for hydrogel formation. Interestingly, the turning segment GSII of h9e was considered to play a critical role in construction of the finial matrix. This hypothesis was further demonstrated by exploiting a series of amphiphilic diblock model peptides with different conformational flexibility. The kinetic rate of peptide assembly was suggested as one of the key influences for peptide supramolecular assembly morphology. To better understand the peptide self-assembly process during hydrogel formation, the conformational, morphological, and mechanical properties of h9e molecules in different dimethylsulfoxide/H2O solutions were monitored by 1D and 2D proton nuclear magnetic resonance (NMR), electron microscopy, and a rheometer. The h9e peptide hydrogel formed with Ca2+ and albumin exhibited superior physiological and specific injectable properties, which provides a more realistic tool for 3D cell culture and drug delivery. This study generates new knowledge and contributes to the field by leading to a better understanding the self-assembly hydrogel formation and designing peptides with unique properties for biomedical applications such as cell culture, drug delivery, and tissue engineering.

The behaviour of viscoplastic drops during formation and detachment from a capillary nozzle, free-fall, impact on a solid substrate and subsequent spreading are investigated experimentally by high-speed imaging. Drop dynamic behaviour is an integral component of many contemporary industrial processes ranging from fuelinjection systems in combustion engines to spray coating, agrochemical and pharmaceutical delivery, fire extinguishment and ink-jet printing. Yield-stress fluids are commonly used nowadays in products ranging from mayonnaise to hair-gel. It is hoped that through understanding the dynamics of viscoplastic fluids, additional spray applications can be developed that will help to advance and optimise industrial processes. Viscoplastic fluids exhibit shear-thinning behaviour when the applied stress exceeds a certain threshold value, called the yield-stress. Below this threshold however, the fluid behaves like an elastic solid. By comparing the behaviour of viscoplastic drops with both Newtonian and shear-thinning fluids, yield-stress is shown to be capable of altering detachment behaviour, drop shape during free-fall, impact morphology and the final sessile shape of drops after spreading. For drops attached to the end of a capillary tube, growth continues until a maximum supportable tensile stress is reached in the drop neck. After this critical point, drops become unstable and detach. The critical break-up behaviour of low yield-stress drops is found to be similar to those of Newtonian and shear-thinning fluids. Above a threshold value however, characterised in terms of the ratio between yield-stress magnitude and capillary pressure, yield-stress forces exceed surface tension forces and the maximum tensile stress achievable in the drop neck at critical stability is governed by the extensional yield-stress, established using the von Mises criterion. This threshold value can also be used to characterise equilibrium drop shapes during free-fall. Whereas Newtonian, shear-thinning and low yield-stress fluids form near spherical equilibrium drop shapes, fluids above a threshold value become increasingly more prolate as the yield-stress increases. Upon impact, viscoplastic drops can exhibit central peaks at the end of inertial spreading. The influence of yield-stress magnitude on impact behaviour is qualitatively established by measuring the size of these peaks. Peaks indicate that deformation during impact is localized and within a threshold radius, shear stresses will not be large enough to overcome the yield-stress, therefore fluid within this region will not deform from the drop shape prior to impact. After impact, spreading will be dependent on the surface energy. Again, the ratio of the yield-stress magnitude to the capillary pressure can be used to characterise the final sessile drop shape. Whilst the equilibrium contact angle of Newtonian, shear-thinning and low yield-stress drops is independent of the yield-stress magnitude, above a threshold value, contact angles vary as a function of yield-stress magnitude. Whilst the research presented in this thesis highlights how fluid yield-stress can influence drop dynamics, some results are only qualitative. To establish more quantitative results, computational fluid dynamics methods should be used to examine viscoplastic drop dynamics. This research should focus primarily on impact behaviour, an aspect that has not received much attention previously. Modelling shear-thinning and viscoplastic fluid behaviour can be achieved by incorporating the relevant rheological models into the flow equations and examining impact morphology using a volume of fluid method. Numerical results can then be directly compared with the experimental results. Useful further experimentation could examine the relaxation behaviour of diamagnetically levitated viscoplastic drops. The results from this work could provide further insight into what rheological model best describes viscoplastic behaviour for shear-stresses below the yield-point.

L'objet de cette étude est de mieux formaliser et modéliser de façon générique le processus de structuration d'un produit par le procédé de foisonnement, en reliant les paramètres opératoires aux propriétés des mousses formées et de contribuer ainsi à un meilleur pilotage de l'opération. Une ligne de foisonnement par battage en continu a été instrumentée et l'évolution du diamètre des bulles en fonction des paramètres du produit et du procédé a été suivie pour des milieux modèles newtoniens et rhéofluidifiants. L'analyse dimensionnelle à l'échelle du procédé a permis d'aboutir à un modèle physique de l'opération, et donc d'avoir une compréhension des phénomènes en présence. Elle a aussi permis d'intégrer les paramètres du produit et du procédé et de simplifier la représentation des résultats expérimentaux. Enfin, la cohérence de ce modèle avec d'autres issus de la littérature et une première approche de validation avec un produit réel, semble justifier son caractère générique. / The aim of this study is to better formalize and model in a generic way the structuring of a product by the foaming operation process, by linking the operating parameters to the foams properties and contribute to a better steering of the operation. A continuous whipping line was instrumented and the evolution of bubble diameter depending on both product and process parameters was characterized for Newtonian and shear-thinning model fluids. Dimensional analysis of the process has lead to a physical model of the operation, and therefore makes possible the understanding of the phenomena involved. It also helped to integrate the product and the process parameters and simplify the representation of experimental results. Finally, the consistency of this model with others from the literature and a first validation with a real product seems to justify his relevance.

Many cells exploit the bending or rotation of flagellar filaments in order to self-propel in viscous fluids. Often swimming occurs in complex, nonlinear fluids, e.g. mucus. Futhermore even in simple Newtonian fluids, if swimming appendages are deformable then locomotion is subject to fluid-structure interactions. The fundamental question addressed in this thesis is how exactly locomotion is impacted, in particular if it is faster or slower, with or without these effects. First we study locomotion in shear-thinning and viscoelastic fluids with rigid swimming appendages. Following the introductory Chapter, in Chapter 2 we propose empirical extensions of the classical Newtonian resistive-force theory to model the waving of slender filaments in non-Newtonian fluids, based on experimental measurements for the motion of rigid rods in non-Newtonian fluids and on the Carreau fluid model. We then use our models to address waving locomotion in shear-thinning fluids, and show that the resulting swimming speeds are systematically lowered a result which we are able to capture asymptotically and to interpret physically. In Chapter 3 we consider swimming using small-amplitude periodic waves in a viscoelastic fluid described by the Oldroyd-B constitutive relationship. Using Taylor’s swimming sheet model, we show that if all travelling waves move in the same direction, the locomotion speed of the organism is systematically decreased. However, if we allow waves to travel in two opposite directions, we show that this can lead to enhancement of the swimming speed, which is physically interpreted as due to asymmetric viscoelastic damping of waves with different frequencies. A change of the swimming direction is also possible. Secondly we consider the affect of fluid-structure interactions. In Chapter 4, we use Taylor’s swimming sheet model to describe an active swimmer immersed in an Oldroyd-B fluid. We solve for the shape of an active swimmer as a balance between the external fluid stresses, the internal driving moments, and the passive elastic resistance. We show that this dynamic balance leads to a generic transition from hindered rigid swimming to enhanced flexible locomotion. The results are physically interpreted as due to a viscoelastic suction increasing the swimming amplitude in a non-Newtonian fluid and overcoming viscoelastic damping. In Chapter 5 we consider peritrichously flagellated bacteria, such as Escherichia coli. The rotation of each motor is transmitted to a flexible rod called the hook which in turns transmits it to a helical filament, leading to swimming. The motors are randomly distributed over the body of the organism, and thus one expects the propulsive forces from the filament to almost cancel out leading to negligible swimming. We show that the transition to swimming is an elasto-hydrodynamic instability arising when the flexibility of the hook is below a critical threshold.

A research program was designed to investigate the characteristics of three-dimensional laminar wall jet flow of both Newtonian and two shear-thinning non-Newtonian fluids. The non-Newtonian fluids were prepared from xanthan gum solutions of various concentrations. Both experimental and numerical methodologies were employed in this study. The wall jet was created using a circular pipe of diameter 7 mm and flows into an open fluid tank. The initial Reynolds numbers based on the pipe diameter and jet exit velocity ranged from 250 to 800. The velocity measurements were conducted using a particle image velocimetry technique. The measurements were conducted at several streamwise locations to cover both the developing and self-similar regions. For the numerical study, the complete nonlinear Navier-Stokes equation was solved using an in-house colocated finite volume based CFD code. A Carreau model was employed for the non-Newtonian fluids. The viscosity in the governing equations was obtained explicitly. From the PIV measurements and CFD results, velocity profiles and jet half-widths were extracted at selected downstream locations to study the effects of Reynolds number and specific fluid type on the jet characteristics. It was observed that the numerical results are in reasonable agreement with the experimental data. The decay of maximum velocity, jet spread rates, skin friction coefficient, streamwise velocity profiles, and secondary flows depend strongly on the initial Reynolds number irrespective of the fluid. The results also show that the jet spreads more in the spanwise direction than in the transverse direction in the early flow development whereas the reverse is true in the downstream region. Important differences were observed when the results for the non-Newtonian fluids were compared with those for Newtonian fluid.

A research program was designed to investigate the characteristics of three-dimensional laminar wall jet flow of both Newtonian and two shear-thinning non-Newtonian fluids. The non-Newtonian fluids were prepared from xanthan gum solutions of various concentrations. Both experimental and numerical methodologies were employed in this study. The wall jet was created using a circular pipe of diameter 7 mm and flows into an open fluid tank. The initial Reynolds numbers based on the pipe diameter and jet exit velocity ranged from 250 to 800. The velocity measurements were conducted using a particle image velocimetry technique. The measurements were conducted at several streamwise locations to cover both the developing and self-similar regions. For the numerical study, the complete nonlinear Navier-Stokes equation was solved using an in-house colocated finite volume based CFD code. A Carreau model was employed for the non-Newtonian fluids. The viscosity in the governing equations was obtained explicitly. From the PIV measurements and CFD results, velocity profiles and jet half-widths were extracted at selected downstream locations to study the effects of Reynolds number and specific fluid type on the jet characteristics. It was observed that the numerical results are in reasonable agreement with the experimental data. The decay of maximum velocity, jet spread rates, skin friction coefficient, streamwise velocity profiles, and secondary flows depend strongly on the initial Reynolds number irrespective of the fluid. The results also show that the jet spreads more in the spanwise direction than in the transverse direction in the early flow development whereas the reverse is true in the downstream region. Important differences were observed when the results for the non-Newtonian fluids were compared with those for Newtonian fluid.

An investigation has been carried out into the rheology of chocolate in relation to its flow and mixing features in a real industrial environment. The chocolate manufacturing plant of Rowntree at York provided a base for this study. The project aims were: a) to measure the viscous and time dependent properties of chocolate. b) to explain the observed flow properties in relation to the constituents of chocolate. c) to determine the shear rate which, for a given recipe, yields a minimum stable viscosity (of particular commercial value). d) to assess the type of mixer able to provide this duty. The experimental work involved rheological studies with concentric cylinder and tubular viscometers, operated to measure viscosity as a function of shear rate and shearing time. The chocolate samples studied were taken from various points in the manufacture process at Rowntree, York. Model chocolate systems were made from cocoa liquor, and sugar with cocoa butter, which were studied to underpin the basic mechanisms of the flow properties of the total chocolate. Shear thinning in milk chocolate has been shown to be accounted for by surface coating and fat release from the cocoa cellular material. Analysis of the sugar and cocoa butter system gave large hysteresis loops which may be explained as due to agglomeration of the sugar particles. The level of hysteresis was found to be related to the polarity of the liquid phase, such that a more polar fluid results in less hysteresis. Laboratory experiments have revealed that the level of work input to give permanent viscosity reduction for milk chocolate is dependent on the measuring shear rate. The level of optimum shear input for the measuring range 10 to 130 sec 1 is 645 sec for 30 minutes. The apparent viscosity measured at lower shear rates requires much longer ([approx]100 minutes).