La variété de l'offre alimentaire actuelle incite à l'hyperphagie qui est en partie responsable de la prise de poids corporel. Réduire la consommation est ainsi devenu une contrainte pour une certaine partie de la population. Dans ce contexte, les fibres, qui sont des glucides non-digestibles dans l'intestin grêle, permettent de réduire la prise alimentaire, d'atténuer les sensations de faim et/ou d'augmenter les sensations de satiété. Cependant, les mécanismes comportementaux, périphériques et centraux à l'origine de ces effets sont mal-connus. Leur capacité à maintenir cet effet anorexigène en présence d'autres nutriments comme les lipides et les protéines a également été très peu étudiée.L'étude de ces mécanismes est l'objet de cette thèse. Des fibres telles que la gomme de guar (GG) fortement viscosifiante et le fructo-oligosaccharide (FOS) très fermentescible ont été administrées, en début de journée, aux souris sous forme de solution à raison de 700 µL et à une dose de 3%, 5% et 14% via un gavage intra-gastrique. Cette étude a montré que les solutions fortement visqueuses, notamment le GG 5% et le mélange GG-FOS 14% étaient les seules capables d'exercer un effet anorexigène à court terme comparées aux solutions moins visqueuses comme l'eau, le GG 3%, le FOS 14% et les solutions de nutriments comme les protéines (peptides de caséine) et les lipides (huile de colza) qui fournissent 10% de l'ingéré calorique quotidien des animaux (1.2 kcal). Pour le cas du mélange visqueux GG-FOS 14%, la baisse de la prise alimentaire est due au rassasiement (réduction de 50% de la taille et de la durée du repas dans les 30 premières minutes post-ingestion). Cette baisse, non compensée jusqu'à la fin de la journée, n'est pas associée à une aversion gustative conditionnée. Ce rassasiement est dû à l'intégration au niveau du centre de contrôle de la taille du repas (NTS), des signaux vagaux de distension gastrique et de la cholecystokinine (CCK). Quand les fibres visqueuses GG 5% et GG-FOS 14% sont mélangées avec des protéines, elles perdent leur effet anorexigène. L'action de les mélanger avec les lipides a par contre montré que seul le mélange visqueux GG-FOS 14% est capable d'exercer un effet anorexigène. L'effet anorexigène du mélange lipide et GG-FOS 14% est dû au niveau de chaque repas aux signaux mécaniques gastriques et CCK vagaux, et à l'axe PYY- système mélanocortique hypothalamique pour le maintien de l'effet sur la journée.En conclusion, les fibres visqueuses sont des nutriments qui peuvent participer au contrôle de la prise alimentaire en stimulant le rassasiement. Elles sont capables de maintenir cet effet en milieu lipidique. Elles pourraient ainsi être ajoutées aux aliments riches en lipides pour mieux contrôler la prise alimentaire et le poids corporel. / The various types of food currently marketed encourage people to eat more, thus leading to weight gain, and reducing food intake has become challenging. To help deal with this, it was shown that dietary fibers decreased food intake and/or feelings of hunger while increasing those of satiety. However, the behavioral, peripheral and central mechanisms underlying this phenomenon are not well known. This study was undertaken in order to characterize these mechanisms. Dietary fibers such as the highly viscous guar gum (GG) and the highly fermentable fructo-oligosaccharide (FOS), in doses of 3%, 5% and 14%, were given to mice by intra-gastric gavage of 700 µL volume. It appeared that highly viscous fibers such as GG 5% and the mixture GG-FOS 14% were able to decrease food intake compared to less viscous preloads such as water, FOS and nutrient solutions (protein solution with casein peptides, lipid solution with rapeseed oil supplying 1.2 kcal or 10% of daily energy intake in mice). Specifically, the mixture GG-FOS 14% induced satiation by reducing the size and duration of meals during the first 30 min post-treatment. This effect was neither compensated for by the end of the day, nor was it associated with conditioned taste aversion. The GG-FOS 14% -induced satiation was due to gastric distension and vagal CCK signaling which were integrated at the level of the NTS, a nucleus controlling meal size. Moreover, mixing GG 5% and GG-FOS 14% with protein abolished their food intake inhibitory effect. In contrast, when mixed with lipid, GG-FOS 14% maintained its anorexigenic effect. The mixture of lipid and GG-FOS 14% stimulated satiation which involved vagal CCK signaling, gastric distension and the NTS. Additionally, the communication between systemic PYY and melanocortic neurons at the level of the hypothalamus was implicated in the anorexigenic effect of this mixtureIn conclusion, viscous dietary fibers can control food intake by stimulating satiation. They are able to maintain their anorexigenic effect in lipid media such that they can be added to foods containing more fat in order to control food intake and body weight.

Master of Science / Food Science / Sajid Alavi / Pulp/paste candy is popular in Mexico and is gaining popularity around the world. Pulp/paste candy is characterized as a soft, semi-fluid candy with particles in a colloidal suspension, typically squeezed out of the package for consumption. It is made by hydrating gums in water and mixing them with corn syrup, acid, powdered/pulverized sugar, and other minor ingredients yielding a product around 80°Brix and pH between 2-3. Over time the sucrose in the candy tends to invert, causing two types of failure: package leakage and solidification in package. Based on the findings of previous work from Molina-Rubio et al. (2010), a modified semi-liquid syrup model system was created with corn syrup, sugar, gums, and water. The model system was used to identify the influence these ingredients had on viscosity and texture since these factors are linked to the typical modes of failure in pulp/paste candy. An oscillatory sweep was used on a controlled force rheometer to identify the linear viscoelastic range. Oneway ANOVA with Tukey HSD was used to compare % total solids levels with complex viscosity at 0.1 rad/sec (there was a significant difference between all levels) and minimum tan (delta) (mid and high level were similar). Using a stepwise method, ANOVA models were generated that showed statistically significant effects on complex viscosity for gum level and sugar level as well as interactions (p < 0.05) between invert syrup-water, gum-water, and sugar type-water. The type of gum and the amount of corn syrup used didn’t significantly impact on the viscosity of the system. Using probe tests helped to analyze samples that were too thick for the rheometer. Analysis showed an inflection point for exponentially increased hardness (85-93%TS) that should be further investigated. The stepwise regression model generated for stickiness showed that the invert syrup-water interaction was significant along with gum type. These results are applicable to the confectionery industry and can help companies test and create a candy that meets the packaging and shelf life constraints that they desire. Targeting invert syrup-water levels and the hydration of the gum will have the most impact on the final product’s viscosity and stickiness, which are important for primary package filling and storage. To create an easy to eat candy, no invert syrup should be used in formulation and gellan gum would be better to use than xanthan. Higher solids (> 85%) should also be avoided since it would create a candy that is harder to squeeze out of the package due to higher viscosity and textural hardness.

The flow behaviour of liquid metals (Sn, Pb and Sn-Pb eutectic) under different shearing conditions is investigated. Experiments were performed with two designs of concentric cylinder viscometers: rotating the inner cylinder (Searle) and rotating the outer cylinder (Couette). The latter technique is uncommon and the equipment was optimised with standard oils. The flow behaviour for the metals differs in the two systems. The curves of 'apparent' viscosity versus shear rate may be divided into two regimes: I. At lower shear rates (<200 s-1): a reduction of 'apparent' viscosity with shear was observed with both viscometers. It is suggested that the high density and high surface tension of the metals and eccentricity between the cylinders at low shear rates, leads to instabilities. Results at low shear rates were therefore discarded and further detailed analysis would be required for a fuller understanding of this behaviour. II. At higher shear rates: a steady, shear-independent behaviour of 'apparent' viscosity with shear rate is observed in the Couette system (upto 600 s-1) whereas in the Searle system the 'apparent' viscosity increases with shear rate (upto 2600 s-1). From hydrodynamic theory about Newtonian fluids, it is suggested that in the Searle type viscometer, the fluid is unstable and Taylor vortices are expected at low shear rates (~80 s-1). This gives rise to an increase in the 'apparent' viscosity with shear rate. Whereas, in the Couette type, the flow is more stable, resulting in a steady 'apparent' viscosity. This interpretation is consistent with liquid metals behaving as Newtonian fluids, but further research is required to confirm this. The author suggests further experiments, with the prime one being the investigation of the fluid with counter and co-rotation of the cylinders in order to observe more complex flows. The results are expected to have implications in the modelling of flow for liquid metal processes, especially the initiation of Taylor vortices under the unstable flow conditions produced by rotating the inner cylinder.

Os policarboxilatos são macromoléculas utilizadas como dispersantes de alta eficiência em composições cimentícias reduzindo a viscosidade das suspensões e minimizando a quantidade de água utilizada para o processamento. Estes aditivos são muito eficientes por promover estabilização eletroestérica devido a grupos funcionais que geram cargas e se adsorvem na superfície das partículas e suas cadeias poliméricas laterais apolares (side chains). Por isto, esses aditivos têm sido amplamente empregados em composições de concretos. No entanto, além de alterar as características reológicas dos materiais cimentícios, a utilização de policarboxilatos afeta também o potencial de superfície, as reações de hidratação dos cimentos, e as propriedades viscoelásticas dos materiais. Desta forma, neste trabalho foram avaliados os efeitos da variação do teor de policarboxilato éter - Glenium 51 - em suspensões de cimento Portland (CPIIE) a partir de ensaios de reometria rotacional e oscilatória, calorimetria de condução isotérmica e medidas de potencial zeta por ESA. Os resultados demonstram que para teores de 0.05 a 1.50 % de aditivo ocorre a diminuição da viscosidade e da tensão de escoamento e aumento do tempo de pega dos cimentos. Estes comportamentos foram atribuídos à adsorção do aditivo na superfície das partículas de cimento em que o desempenho varia em função do tempo. Nos primeiros momentos da adsorção o efeito espacial é majoritário e se tornando também eletrostático após 15 h devido à reação do cálcio iônico com as moléculas de policarboxilato. O consumo dos íons cálcio faz com que a velocidade da reação de hidratação seja reduzida retardando o início e o final de pega. Para teores de aditivo superiores a 3,00 % o sistema passa a apresentar um comportamento viscoelástico que não é adequado para o uso em materiais cimentícios. / The polycarboxylates are macromolecules used as high efficiency dispersants in cement compositions reducing the suspensions viscosity and the volume of water used in the processing. These additives are very efficient in promoting electrosteric stabilization due to functional groups that create charges and are absorbed by the particles\' surface and their side chains. That\'s the reason why these additives have been used in concrete compositions. However, besides the change polycarboxylates cause to the rheologic characteristics of cementitious materials, the use of polycarboxylates affects also the surface potential, the cement hydratation reactions, and the materials\' viscoelastic proprieties. In this work, the effects of ester polycarboxylate glenium 51 levels of variation were rated in Portland cement suspension (CP II-E) using rotational rheometry and oscillatory, isothermal conduction calorimetry and zeta potential measurement by ESA. The results show that for 0,05 to 1,50% levels of additives there was a reduction in viscosity and yield stress and an increase in the cement\'s setting time. These behaviors were attributed to the adsorption of the additive by the surface of the cements\' particles whose performance alters because of the time function. In the adsorption\'s first steps the spatial effects are the majority, while after 15 hours they also become electrostatic due to the reaction of the ionic calcium with the polycarboxylate molecules. The calcium ions waste leads to a reduction of the velocity of the hydratation reaction, slowing down the beginning and the end of setting time. For higher than 3,00% additive content, the system shows a viscoelastic behavior that is not fit for the use of cementitious materials.

Neste trabalho, métodos experimentais para estimar as viscosidades elongacional e de cisalhamento mediante um canal de contração abrupta foram desenvolvidos. Os dados reológicos em fluxos de cisalhamento foram comparados com os resultados mediante o reômetro rotacional e o reômetro capilar. Os resultados foram utilizados para avaliar a influência da estrutura molecular nas propriedades reológicas de vários polipropilenos com diferentes massas moleculares, distribuição de massas moleculares e teor de ramificações. Além disso, polipropilenos degradados termomecânicamente foram estudados. A massa molecular e a distribuição de massas moleculares foram obtidas através de Cromatografia de permeação em gel (GPC). Os resultados obtidos mostraram que a matriz elongacional é útil para simular processos de transformação, visto que podem ser alcançadas altas taxas de deformação, que dependem dos valores máximos dos parâmetros de processamento, os quais dependem dos limites máximos do equipamento utilizado. Os resultados em fluxos de cisalhamento avaliados mediante a matriz elongacional mostraram que possuem uma excelente concordância com os resultados obtidos por cisalhamento oscilatório de pequenas amplitudes (COPA) no reômetro rotacional. Os resultados em fluxos elongacionais mostraram que as medidas são muito sensíveis à estrutura molecular, principalmente à presença de ramificações longas, principalmente a baixas taxas de deformação. No caso do polipropileno degradado termomecânicamente, tanto sua massa molecular quanto as suas viscosidades elongacional e de cisalhamento diminuem devido à cisão de cadeias e, as medidas reológicas mostram-se mais sensíveis a essas mudanças do que as medidas de GPC. / In this work, experimental methods to evaluate elongational and shear viscosities using a planar channel with an abrupt contraction (also called Cogwell die) were developed. The shear viscosity measurements were compared to measurements obtained using a rotational rheometer and a capillary rheometer. The elongational die was used to evaluate the influence of the molecular weight, molecular weight distribution and chain structure on the rheological properties of polypropylene. The influence of thermomechanical degradation of PP on its rheological properties was also studied. The molar mass and molar mass distribution were evaluated using GPC. It was found that the planar channel can be used successfully to evaluate the elongational viscosity at rates that correspond to polymer processing conditions. The shear viscosity measurements obtained using the planar die were in good agreement with measurements obtained by small amplitude oscillatory shear (SAOS). The elongational viscosity was sensitive to molecular structure, essentially at low deformations. It was also shown that the molar mass, molar mass distribution and amount of branching affects the shear viscosity and that rheological measurements may be more sensitive to molecular weight changes than GPC.

O comportamento reológico de suspensões concentradas heterogêneas como concretos e argamassas possui influência direta na energia requerida e na produtividade durante o processamento e aplicação destes materiais, além de ser um fator determinante na obtenção de um produto final qualidade. De um modo geral pode-se dizer que a fluidez destas suspensões está diretamente relacionada à facilidade de movimentação das partículas, logo pode-se inferir que a redução dos fenômenos atrito é um fator determinante para o bom desempenho destas suspensões durante o fluxo. Deste modo, este trabalho buscou por meio de modelos ideais de esferas e silicone líquido avaliar a influência do coeficiente de atrito dos agregados e da viscosidade da matriz no comportamento reológico de suspensões concentradas. O coeficiente de atrito de agregados esféricos com diferentes granulometrias foi determinado experimentalmente através do ensaio de cisalhamento direto, também conhecido como shear box, e o comportamento reológico de suspensões compostas por estes agregados e silicones líquidos de diferentes viscosidades foram avaliadas por meio do ensaio de squeeze flow. Os resultados revelam que a distribuição granulométrica possui um influência no coeficiente de atrito dos agregados e que esta propriedades está relacionada a área e ao tipo de contato entre as partículas. Entretanto, para o tipo de fluxo e para as velocidades as suspensões, não houve uma relação direta entre o coeficiente dos agregados e a viscosidade da suspensão. Além disto, apesar de alterar o comportamento reológico das suspensões a viscosidade da matriz não apresentou uma relação direta com viscosidade da suspensão, o que em partes ser explicados pela provável ocorrência de um fluxo não homogêneo das suspensões nas condições aqui estudadas. / The rheological behavior of concentrated suspensions like concrete and mortars plays an important hole during their processing and application, and also has a great influence on the final product quality. The flowability of these suspensions is directly related to the ease of particle motion in the system, therefore reduction of friction phenomena contributes for a good flow behavior. The aim of this work was to determine the influences of aggregates friction coefficient and the liquid viscosity of the fluid matrix on the rheological behavior of concentrated suspensions. The friction coefficient of glass spheres with different particle size distributions were determined by shear box tests, while the rheological behavior of concentrated suspensions composed by these glass spheres and silicone oils was evaluated by squeeze flow tests. Results revealed that the particle size distribution influences the coefficient of friction, and this property is determined by the type and the area of contact between the particles. However, for the kind of flow and the speed used in the experiments, there was no relation between friction coefficient and the suspension viscosity. Additionally, matrix viscosity has an impact on the rheological behavior of the system, but no clear relation was identified, which may be caused by the occurrence of heterogeneous flow under the applied experimental conditions.

Leung, Chung Yin = 聚合物濃度對湍流減阻的影響 / 梁頌賢. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 106-108). / Abstracts in English and Chinese. / Leung, Chung Yin = Ju he wu nong du dui tuan liu jian zu de ying xiang / Liang Songxian. / Abstract --- p.i / 概要 --- p.iii / Acknowledgements --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The phenomenon of polymer drag reduction --- p.1 / Chapter 1.2 --- The Phenomenology of drag reduction --- p.9 / Chapter 1.3 --- A recent theory --- p.19 / Chapter 2 --- Review of a recent theory of drag reduction --- p.21 / Chapter 2.1 --- The balance equations --- p.21 / Chapter 2.2 --- Estimating the average terms --- p.26 / Chapter 2.2.1 --- Average terms for flexible polymers --- p.27 / Chapter 2.2.2 --- Average terms for rodlike polymers --- p.32 / Chapter 2.3 --- Solving the balance equations --- p.34 / Chapter 3 --- Behavior near the maximum drag reduction asymptote --- p.42 / Chapter 4 --- Reduction of drag at small concentrations --- p.57 / Chapter 5 --- Velocity profiles and friction factor relations --- p.61 / Chapter 5.1 --- Newtonian flow without polymer --- p.61 / Chapter 5.2 --- Flow at high polymer concentration --- p.63 / Chapter 5.3 --- Flow at intermediate concentration --- p.68 / Chapter 6 --- The Reynolds stress profile --- p.88 / Chapter 7 --- Percentage drag reduction --- p.95 / Chapter 8 --- Conclusion and future work --- p.104 / Bibliography --- p.106

Han, Zuoyan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 43-46). / Abstracts in English and Chinese. / Abstract (Chinese) --- p.i / Abstract (English) --- p.ii / Acknowledgements --- p.iv / Glossary --- p.vi / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Physics parameter viscosity --- p.1 / Chapter 1.2 --- PDMS microfluidics device --- p.4 / Chapter Chapter 2 --- PDMS viscometer for microliter Newtonian fluid / Chapter 2.1 --- Introduction --- p.5 / Chapter 2.2 --- Configuration of the PDMS Viscometer --- p.8 / Chapter 2.3 --- Mechanism of passive pumping --- p.10 / Chapter 2.4 --- Theory of the PDMS viscometer --- p.11 / Chapter 2.5 --- Viscosity Measurement in PDMS Viscometer --- p.15 / Chapter 2.5.1 --- Preparation of Blood Plasma --- p.16 / Chapter 2.5.2 --- Measurements of Glycerol Solutions --- p.16 / Chapter 2.5.3 --- Measurements of Protein Solution and Blood Plasma --- p.19 / Chapter 2.5.4 --- Measurements of Organic Solvents --- p.19 / Chapter 2.6 --- Data Analysis --- p.21 / Chapter 2.7 --- Dynamic Contact Angle --- p.22 / Chapter 2.8 --- Conclusions --- p.23 / Chapter Chapter 3 --- PDMS viscometer for microliter Non-Newtonian fluid / Chapter 3.1 --- Introduction --- p.25 / Chapter 3.2 --- Configuration of the PDMS viscometer --- p.29 / Chapter 3.3 --- Theory for non-Newtonian fluid --- p.31 / Chapter 3.4 --- Viscosity Measurement of non-Newtonian fluids --- p.35 / Chapter 3.4.1 --- Preparation of Blood Plasma --- p.36 / Chapter 3.4.2 --- Measurement of starch solutions --- p.36 / Chapter 3.5 --- Data analysis --- p.37 / Chapter 3.6 --- Conclusion --- p.41 / References --- p.43

Neste trabalho foram obtidos nanocompósitos de polipropileno (PP) e argilas. Três tipos de PP com índices de fluidez de 1,5; 2,2 e 37,9 g/10min (230ºC/216kg) foram utilizados. O PP com maior índice de fluidez é um produto modificado com peróxido. Essas amostras de PP foram misturadas ao masterbatch da Nanocor nanoMax®-PP. Concentrações de masterbatch variando de 3 a 12% em peso foram utilizadas. Os compósitos foram obtidos em uma extrusora dupla rosca e em um misturador. O Masterbatch foi caracterizado por fluorescência de raios X, difração de raios X (DRX) e por espectroscopia no infravermelho (FTIR). Os compósitos foram caracterizados por DRX, microscopia ótica (MO) e de transmissão (MET), e reologicamente. A caracterização reológica foi realizada conduzindo ensaios de varredura de tempo e ensaios de Cisalhamento Oscilatório de Pequena Amplitude (COPA) no regime de viscoelasticidade linear. Ensaios utilizando uma matriz cônica que permite a avaliação da viscosidade elongacional foram também conduzidos. Com essa matriz foi também possível a avaliação da viscosidade de cisalhamento dos compósitos para taxas de cisalhamento que correspondem a regime de viscoelasticidade linear. Os resultados da caracterização do Masterbatch mostraram que este consiste de uma mistura de polipropileno enxertado com anidrido maleico e uma argila do tipo esmectita, predominantemente montmorilonita (MMT). O espaçamento basal das argilas nos compósitos obtidos foi maior do que aquele da argila no masterbatch para todos os compósitos, diminuindo com o aumento da concentração de masterbatch no compósito. A viscosidade dos compostos obtidos aumentou com o tempo durante os ensaios de varredura de tempo devido a variações morfológicas. Essas variações foram mais importantes quando a freqüência utilizada no ensaio era menor. Essas variações foram correlacionadas com a evolução da morfologia dos compostos em função do tempo. O módulo de armazenamento obtido nos ensaios de COPA a baixas frequências para os compósitos foi maior do que o módulo dos polímeros puros para concentrações de argila acima de 6%. Esse aumento do módulo foi muito mais intenso para o PP de maior índice de fluidez. Os ensaios de caracterização reológica utilizando a matriz cônica mostraram que os nanocompósitos não seguem a Regra de Cox-Merz e que para o PP de maior índice de fluidez a viscosidade elongacional aumenta com o aumento da concentração de masterbatch. / In this work nanocomposites of polypropylene (PP) were obtained. Three types of PP with melt flow rates of 1,5; 2,2 e 37,9 g/10min (230ºC/216kg) were used. The PP with the largest melt flow rate is a product modified with peroxide. These samples were mixed with PP masterbatch Nanocor nanoMax ®-PP. Masterbatch in different concentrations ranging from 3 to 12 wt%. The composites were obtained using a twin screw extruder and internal mixer. The masterbatch was characterized by X-ray fluorescence, X-ray diffraction (XRD) and infrared spectroscopy (FTIR). The composites were characterized by XRD, optical microscopy (OM) and transmission (TEM) and rheologically. The rheological characterization was made carrying out time sweep, small amplitude oscillatory shear (SAOS) tests in order to study the rheological behavior on the linear viscoelastic regime. Tests using a conical diewith which it is possible to measure elongational viscosity were also conducted. The shear viscosity at high shear rates was evaluated using a slit die The characterization results showed that the masterbatch is a mixture of polypropylene grafted with maleic anhydride and a smectite type clay, predominantly montmorillonite (MMT). The basal spacing of clay in the composites was greater than that of the clay within the masterbatch for every composites. It was shown to decrease with increasing concentration of masterbatch in the composite. The viscosity of composites increased during the time sweep experiments. This evolution of viscosity was attributed to changes of morphology of the composites. These variations were more important when the frequency used in the test was lower. The storage modulus obtained during COPA at low frequencies for composites was higher than the modulus of the pure polymers when the clay content was above 6%. This increase in modulus was greater for the lower melt flow index PP The rheological tests performed using the slit die showed that Cox-Merz rule was not valid for the composites. The elongational viscosity was shown to increase with increasing concentration of masterbatch.

As a comparison to the suction feeding mechanics in aquatic environments, I investigated buccal pumping in an ontogenetic series of suspension feeding Xenopus laevis tadpoles (4-18 mm snout-vent length) by examining the morphology, kinematics, fluid flow, pressure generated in the buccal cavity, and effects of viscosity manipulation. Investigation of the dimensions of the feeding apparatus of Xenopus revealed that the feeding muscles exhibited strong negative allometry, indicating that larger tadpoles had relatively smaller muscles, while the mechanical advantage of those muscles did not change across the size range examined. Buccal volume and head width also exhibited negative allometry: smaller tadpoles had relatively wider heads and larger volumes. Tadpoles were imaged during buccal pumping to obtain kinematics of jaw and hyoid movements as well as fluid velocity. Scaling patterns were inconsistent with models of geometric growth, which predict that durations of movements are proportional to body length. Only scaling of maximum hyoid distance, duration of mouth closing, and duration of hyoid elevation could not be distinguished from isometry. The only negatively allometric variable was maximum gape distance. No effect of size was found for duration of mouth opening, duration of hyoid depression, and velocity of hyoid elevation. Velocity of mouth opening, velocity of mouth closing, and velocity of hyoid depression decreased with increasing size. Fluid velocity increased with size, and is best predicted by a piston model that includes head width and hyoid depression velocity. Reynolds number increased with size and spanned two flow regimes (laminar and intermediate) ranging from 2 to over 100. Pressure was found to be greatest in the smallest tadpoles and decreased as size increased, ranging from 2 kPa to 80 kPa. The viscosity of the water was altered to explore changes in body size, independent of development (higher viscosity mimicked smaller tadpole size). Viscosity manipulations had a significant effect on the kinematics. Xenopus initially increased velocity and distance of movements as viscosity increased, but these values declined as viscosity increased further. These results suggest that abiotic factors such as fluid viscosity may set a lower size limit on suspension feeding.