Rheological Properties Of Aqueous Suspensions Research Articles

Stabilisation, rheology and application of aqueous suspensions of oxidised vs. non-oxidised SiC powder

The study aimed at evaluating the stabilisation and rheological properties of aqueous suspensions (30 vol%) of pristine (non-oxidised) and oxidised fine SiC powders which were stabilised either with NaOH or TMAH (tetramethylammonium hydroxide). The extensive oxidation of the SiC powder surface was confirmed by the results of XPS and FT-IR analyses. The optimal amount of a given dispersant depended, according to the results of zeta potential measurements, on a pH range guaranteeing formation of a stable suspension. This effect allowed the authors to propose a mechanism of stabilisation of the SiC suspensions. Herein, the maximum amount of silanol groups is formed on the SiC particles surface in the pH range of 9.5–11 which then adsorb Na+ or TMA+ cations, thus creating a favourable system of electrostatic interactions. In turn, it increases the electrostatic repulsion between SiC particles and improves the stabilisation of the suspensions and their rheological characteristics. An increase in the surface oxidation of the SiC particles leads to reducing the repulsive forces between the powder particles. Apparent viscosity of the suspensions made of SiC UF10 powder, regardless of the type and amount of the fluidizer, is very low (5–10 mPa s) and shows a slight increase as the shear rate increases. The oxidation of the SiC powder changes the rheological characteristics of the suspensions, which may be caused by their rapid sedimentation. Stability of the prepared SiC suspensions was also assessed by casting them into a plaster mould and then by sintering and characterisation of the resulting samples.

Shear and extensional rheological properties of whole grain rye and oat aqueous suspensions

Whole grain flours contain polysaccharides with techno-functional and nutritional properties which make them good candidates as natural texturisers in foods and beverages, thus reducing the use of highly refined ingredients. However, the use of plant components to develop complex fluids and soft materials, requires an enhanced understanding of the relationship between their physicochemical and rheological properties. Here, we systematically investigated the shear and extensional rheological properties of aqueous suspensions of whole grain rye and oat flours. Our results indicated that both types of suspensions (3.5 wt %) showed similar shear thinning behaviour (n = 0.4) however, oat suspensions presented higher viscosity and gel-like behaviour (G'>G'') compared to rye. Additionally, the oat suspensions exhibited an apparent extensional viscosity, which was not present in rye suspensions. The rheological properties of the continuous and disperse phases, separated by centrifugation, were investigated before and after starch hydrolysis and protein removal. Our results indicate that the distinct behaviour of oat suspensions is mainly due to the molecular structure of starch in the liquid phase of i.e oat starch had a higher amylose/amylopectin ratio than rye. Whilst the presence of protein and cell wall polysaccharides in the solid phase contribute to the overall rheology of the suspensions. Furthermore, our results show that the systems do not follow the Cox-Merz rule, indicating that they behaved as suspensions of soft particles rather than macromolecules in solution. Aqueous suspensions of whole grain rye and oat flours showed rheological properties that could be of interest to design low-medium viscosity food and beverage products.

ZTA Pipes with a Gradient Structure-Effect of the Rheological the Behavior of Ceramic Suspensions on the Gradient Structure and Characterized of the Obtained Products.

This paper focuses on the verifying the possibility of producing Al2O3-ZrO2 composite pipes with a gradient structure using centrifugal slip casting method. The aim of the research is to define the correlation between the rheological properties of aqueous suspensions of ceramic powders with different solid loading and obtaining the ZrO2 phase gradient in the Al2O3 matrix. Such products, due to their unique properties, can be utilized in the transport of aggressive substances, even in extreme temperature or corrosive conditions. The suspensions and the sintered samples were characterized by: broad rheological analysis, scanning electron microscopy, X-ray diffraction, stereological analysis and Vickers hardness tests. The study reports on a series of samples produced of ceramic suspensions (70 vol.% Al2O3–30 vol.% ZrO2) differing in the total solid loading in the range of 30–55 vol.%. The results clearly indicate that obtaining the gradient structure of ceramic-ceramic composite pipes is closely related to the rheological properties of the suspensions from which the samples are cast. The phase gradient is obtainable from suspensions 30–40 vol.%, in which the possibility of moving ZrO2 particles relative to the Al2O3 is quite high—these suspensions are characterized by low viscosity and the dominance of viscous over elastic properties (G′ > G″).

Composition and rheological properties of microalgae suspensions: Impact of ultrasound processing

In this study the rheological properties of aqueous suspensions of three microalgae species, Nannochloropsis gaditana, Scenedesmus almeriensis and Spirulina platensis, were investigated as a function of solids content, and related to their composition and microstructure. In addition, the impact of ultrasound processing on their structuring ability was also studied. The less rigid character of the Spirulina platensis cell walls (with very low carbohydrate contents) and the presence of extracellular components promoted cell-cell interactions, yielding suspensions which showed a shear thinning behaviour at lower concentrations than Nannochloropsis gaditana and Scenedesmus almeriensis. It is noteworthy that the three species showed different viscoelastic properties at 25 wt.% total solids. Spirulina platensis suspensions showed a more elastic behaviour and lower frequency dependence, characteristic of weak gels, whilst Nannochloropsis gaditana and Scenedesmus almeriensis behaved more like viscous liquids. The ultrasound treatment did not affect the cell wall integrity, but it promoted the release of intracellular components (some of which could have been partially degraded) and disrupted physical interparticle interactions in Nannochloropsis gaditana and Scenedesmus almeriensis. This has an impact on the rheological properties, increasing the viscosity of Nannochloropsis gaditana suspensions, whilst the viscosity of Scenedesmus almeriensis suspensions was reduced. The outcomes of this work give insights into the exploitation of these microalgae species in soft materials for food, pharma and other technological applications.

Rheological Behavior of Nanocellulose Aqueous Suspensions

The rheological properties of aqueous suspensions of spherical and needle-shaped nanocellulose particles in the range of 25–70°C are compared. Nanocellulose samples are obtained by the acid hydrolysis of cotton cellulose fibers in H2SO4 (61–65%) at 25–45°C. The shape of nanocellulose particles affects the yield strength and non-Newtonian character of the suspension flow. In the shear stress region above 100 Pa, a decrease in effective viscosity occurs, depending on the shape of the particles and the temperature of the suspension. In the region of the shear rate close to the yield strength, the activation energy of the viscous flow of suspensions of spherical particles is 12 kJ/mol; needle-shaped particles, 18 kJ/mol. Features of the rheological behavior are due to the fact that spherical particles are involved mainly in rotational-translational motion, while the needle-like particles are oriented in the direction of flow.

Influence of TMAH and NaOH on the stability of SiC aqueous suspensions

The study aimed at evaluation of the rheological properties of aqueous suspensions of SiC stabilized with either TMAH (tetramethyloammonium hydroxide) or NaOH in the amount of a given dispersant in the range of 0–1.0 wt% as calculated on the dry mass of SiC powder. The optimal amount of the dispersants was finally evaluated at 0.4–0.6 wt %, based on the results of rheological studies (flow curves and viscosity curves) and the sedimentation rate, which corresponded to the pH of the suspension within the range of 9.5–10.5. The amount of the dispersant here did not depend on the solid volume fraction in the suspension, but rather, according to the zeta potential measurement results, the pH range guaranteed the formation of a stable suspension. This effect allowed to propose a dispersant mechanism for stabilizing the suspension. The maximum amount of silicate anions formed, accordingly, in the pH range of 9.5–10.5 on the surface of SiC particles, which in turn could be able to adsorb Na+ or TMA+ cations and thus increase the thickness of the Stern layer, increasing electrostatic repulsion between the SiC particles and improving the stabilization of suspensions and their rheological properties. However, the increase in suspension pH deteriorated their stabilization – most likely due to the occurrence of polymerization of amorphous silica and the presence of additional cations in water increasing its ionic strength. These suggestions were confirmed by the results of XPS analysis of the chemical state of SiC particle surfaces.

Особенности реологических свойств теста из ржаной муки и смесей на ее основе

Реологические свойства теста предопределяют качество готовой продукции, в связи с этим целью настоящей работы явилось комплексное изучение реологических характеристик теста и водных суспензий на основе образцов муки ржаной обдирной; образцов муки, полученной из сортов белозерной ржи Памяти Бамбышева и Солнышко, и композитных смесей с морковным порошком на их основе. Исследования проводились в учебной лаборатории по хлебопекарному, кондитерскому производству кафедры «Технологии продуктов питания» Саратовского ГАУ им. Н.И. Вавилова и в лаборатории качества зерна ФГБНУ «НИИСХ Юго-Востока». Полученные результаты исследования указывают на то, что в смесях с овощным (морковным) порошком, по сравнению с чистым компонентом, увеличивается влажность и «число падения» в среднем на 15%! Тесто становится менее расплывчатым и липким по сравнению с контролем (ржаной мукой), то есть структура оптимальна для получения конечного продукта. Пробная выпечка показала, что наилучшей для получения хлеба является смесь состава: мука из белозерной ржи сорта Солнышко + порошок из моркови. Изучение реологических свойств водных суспензий на основе ржаной муки и композитных систем на ее основе в режиме ротации показало, что дозировка овощного порошка повышает максимальную вязкость системы во всех вариантах эксперимента в среднем на 290 единиц вискографа, что составляет примерно 35% (!). При изучении реологии теста установили следующие показатели у систем соответственно: мука ржаная обдирная и мука ржаная обдирная + морковный порошок - водопоглотительная способность 72,9 и 70,1%; время образования теста 1,35 и 1,70 минуты, стабильность теста 1,53 и 2,67 минуты; мука из белозерного сорта озимой ржи Памяти Бамбышева и мука из белозерного сорта озимой ржи Памяти Бамбышева + морковный порошок - водопоглотительная способность 64,5 и 63,7%; время образования теста 0,95 и 1,27 минут, стабильность теста 1,35 и 1,90 минуты; мука из белозерной ржи сорта Солнышко и Солнышко +морковный порошок - водопоглотительная способность 60,9 и 60,4%; время образования теста 0,72 и 1,08 минуты, стабильность теста 0,67 и 1,70 минуты.

Features of the rheological properties of aqueous suspensions based on whole-grain oil flax

The rheological curves of aqueous suspensions based on whole-milled flax were obtained in the experimental protocols of a Brabender viscograph in several temperature modes and features of swelling of the components were revealed. The quantitative intensity of some indicators of the rheograms was studied. The experimental technique at 200C had the highest distinguishing ability at the varietal level. The suspension based on whole-milled flax seeds of the ITIL variety had the highest viscosity.

Ultrasonication of spray- and freeze-dried cellulose nanocrystals in water

The structural and rheological properties of aqueous suspensions of spray-dried cellulose nanocrystals (CNCs) were investigated and compared to those of freeze-dried. The cellulose nanocrystals were obtained from sulfuric acid hydrolysis of wood pulp. Ultrasonication was used to disperse cellulose nanocrystals in Milli-Q water and the power applied during ultrasonication was shown to be the controlling parameter for their dispersion, more than total energy. Dynamic light scattering measurements showed a decrease of the average hydrodynamic diameter down to the same limiting value, i.e. ∼75 nm, for both spray and freeze-dried cellulose nanocrystals. Since the same maximum dispersion state was reached for both CNC types, it indicated that the spray drying process did not limit dispersion, provided that sufficient ultrasonication was provided. Moreover, no desulfation occurred during ultrasonication at ambient temperature. Strong ultrasonication also caused a decrease of intrinsic viscosity, along with an increase in maximum packing concentration. These properties were correlated to agglomerates break-up, which released both ions and water in suspension. The ionic strength increase may lead to a thinner electrostatic double layer surrounding the cellulose nanocrystals, reducing their apparent concentration.

Mechanism and method for controlling low-temperature rheology of water-based drilling fluids in deepwater drilling

In deepwater oil and gas drilling, water-based drilling fluids (WBDFs) apparently thicken at a low temperature (usually 4°C), causing lost circulation, high flow resistance, and leakage of drilling fluid from the shaking screen. In this study, the rheological properties of aqueous suspensions containing different components were tested from 4 to 75°C. Furthermore, the influencing mechanism of a low temperature on the rheology of WBDFs was comprehensively analyzed, and a basic method for controlling low-temperature rheology was proposed. The results showed that all the aqueous suspensions exhibited thickening at a low temperature. The thickening of WBDF at a low temperature could be attributed to the intrinsic feature of water, edge-to-edge and edge-to-face attraction bond structures formed by clay particles, and remarkable polymer molecular entanglement. The development of a rheology modifier that increases the rheology at a high temperature while does not work at a low temperature, optimization of the solid components including bentonites and weight materials, rational design of the molecular structure of polymers, and selection of the additives that do not cause remarkable thickening can help to control the low-temperature rheology of WBDF. Based on this method, a thermosensitive copolymer rheological modifier and a low-molecular-weight coating agent were developed, and two high performance WBDFs were optimized. Their rheological properties were found to be more stable than those of the three typical WBDFs over a wide temperature range from 4 to 75°C. Therefore, the rheology control method proposed in this study can help to design a WBDF with good low-temperature rheology.

Rheological properties of nanocellulose suspensions: effects of fibril/particle dimensions and surface characteristics

The rheological properties of aqueous suspensions based on three different nanocelluloses were compared. One system was obtained via acid hydrolysis (thus yielding crystalline nanocellulose, CNC) and the other two from mechanical shearing, but from different origins and subjected to different pretreatments. Of the latter two, one was considered to be a rather typical cellulose nanofibril (CNF) suspension whereas the other was a kind of intermediate between CNF and CNC. All three nanocellulose elements differed in dimensions as evident from transmission electron microscopy and atomic force microscopy. With regard to the length of the fibrils/particles, the three nanocelluloses formed three distinct groups with lengths between 200 and slightly more than 800 nm. The three cellulosic elements were also subjected to a TEMPO-mediated oxidation yielding a similar carboxylate content in the three systems. Furthermore, the TEMPO-oxidized elements were grafted with poly(ethylene glycol) (PEG). The amount of grafted PEG was about 35 wt%. The shear viscosity, the storage modulus and the loss modulus of suspensions of the unmodified, the TEMPO-oxidized and the grafted nanocelluloses were determined at room temperature and the solids content of the suspensions was varied between 0.7 and 2.0 wt%. It was concluded that the rheological properties varied significantly between the suspensions depending on the dimensions of the cellulosic elements and their surface characteristics. In this context, the length (or the aspect ratio) of the particles played a very important role.

Rheological properties of TiO2 suspensions varied by shifting the electrostatic inter-particle interactions with an organic co-solvent

The rheology of mineral suspensions is a key factor in many application fields. In particular, adjusting either the solid amount or the solvent composition appears as a possibility to control the rheological properties. These modifications should lead to variations of the electrostatic inter-particle interactions influencing thus the suspensions viscoelastic behavior. TiO2 suspensions were firstly formulated in water by adjusting the pH close to the isoelectric point of the TiO2 nanoparticles. The influence of the solid amount as well as the pH was study and coupled to the rheological properties of aqueous suspensions. In a second time, a part of water was substituted by an organic solvent (i.e. ethanol). Rheological measurements were performed and coupled to the zeta potentials of the TiO2 into different solvents. The rheological properties of TiO2 suspensions were adjusted by varying the electrostatic inter-particle interactions. The pH has to be close enough to the TiO2 isoelectric point and the particle concentration high enough to create a percolating network. With adding ethanol, transient shear thickening is suppressed and, even far from the isoelectric point, the resulting flocculated suspensions show high yield stresses over a large pH range.

Experimental study for rheological property of exhaustively deionized aqueous suspension of very small colloidal spheres (diameter < ca. 60 nm)

The rheological properties of aqueous suspensions of small silica spheres (18–56nm in diameter), in an exhaustively deionized state and the presence of a salt, have been investigated. In a deionized state, the suspensions of larger spheres, 29nm and 56nm in diameter, were Newtonian fluids at sphere volume fraction ϕ=0.10, although the suspension of the smallest spheres, 18nm, showed shear thinning at ϕ=0.087. Debye screening lengths were calculated based on electrical conductivity. The effective volume fractions, including the electrical double layers, of suspensions in the above condition were 0.37, 0.23, and 0.21 for spheres of 18nm, 29nm, and 56nm in diameter, respectively. Experiments provide strong evidence that all of the small spheres form steady electrical double layers in water and that the suspension of 18-nm spheres was in a glassy state.

Stability and Flow-Induced Flocculation of Fumed Silica Suspensions in Mixture of Water-Glycerol

A systematic investigation has been performed to relate the effect of glycerol composition to the rheological properties of aqueous suspensions of hydrophilic fumed silica at pH far from the isoelectric point. Steady state/dynamic rheology and electrophoresis measurements are compared to correlate the stability of the suspension with particle-particle and particle-solvent interactions. Although the extent of electrostatic stability is reduced by addition of glycerol, the rheological properties show a transition from a highly flocculated gel to stable dispersions containing no microstructures. This is attributed to a high degree of hydrogen-bonding between glycerol and the Aerosil surface silanol groups. Small dissociation of NaCl and particles reduce the effect of ion exchange and particle bridging mechanisms when the suspensions destabilise in the presence of glycerol. The high viscosity of glycerol is important with respect to the formation of a thick solvation layer around the particles. These parameters give rise to short-range, non-DLVO repulsive solvation forces, which stabilise the dispersion. At intermediate concentrations of glycerol (30–60 wt%) the apparent viscosity increase abruptly and irreversibly as both the extent and time of shearing are increased. The shear rate for the onset of the shear thickening is found to be retarded by decreasing the particle and salt concentration as well as by increasing the glycerol concentration. It is postulated that at intermediate glycerol concentration, where the height of the energy barrier is small, mechanical forces can activate the particles to overcome the energy barrier to enter the region where attractive forces dominate. Here, domination of the hydrodynamic forces to the colloidal forces under the shear results in formation of irreversible gels which does not relax to its initial condition.

Self-Assembled Bolaamphiphile Fibers Have Intermediate Properties between Crystalline Nanofibers and Wormlike Micelles: Formation of Viscoelastic Hydrogels Switchable by Changes in pH and Salinity

The aggregation behavior and rheological properties of aqueous suspensions of the bolaamphiphile dotriacontane-1,32-diyl-bis[2-(dimethylammonio)ethylphosphate] (Me(2)PE-C32-Me(2)PE) were investigated depending on the pH value and the salinity by means of differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and oscillatory rheology. This bolaamphiphile self-assembles into helical fibers of approximately 5 nm thickness with an all-trans conformation of the alkyl chains. These nanofibers can gel water very effectively by forming a three-dimensional network. The headgroups' protonation depends on the pH value of the solution and influences the ability of the molecules to aggregate into fibers. At low pH values the headgroups are zwitterionic and stable hydrogels are formed, whereas at high pH values the headgroups are negatively charged and the length of the fiber aggregates diminishes as does the stability of the gel structure. We can show that by the addition of cations it is possible to shield the repulsive interaction between the molecules at high pH values so that the formation of the fiber aggregates and the gelation of the system occur. By addition of salt at high pH values the viscous flow behavior of Me(2)PE-C32-Me(2)PE suspensions could be transformed into the viscoelastic behavior of a gel. The gels show characteristics that are common in systems of wormlike micelles. However, there are also significant differences that arise from the unique bolaamphiphile fiber structure with highly ordered alkyl chains that render the properties similar to crystalline nanofibers.

Thixotropy of Aqueous Suspensions Containing Mg-Al Hydrotalcite-like Compound and Low-substituted Cationic Starch: Comparison between Oscillatory Shear and Thixotropic Loop Measurements

The rheological properties of aqueous suspensions consisting of positively charged aluminum magnesium hydrotalcite-like compound (HTlc) and low-substituted cationic starch (LCS) were investigated. Special emphasis was placed on the thixotropic phenomenon. Thixotropic behavior was investigated by two thixotropic methods: thixotropic loop and oscillatory shear measurements. LCS molecules could be adsorbed onto HTlc particles due to the hydrogen bonding between ether groups or hydroxyl groups of LCS and hydroxyl groups of HTlc. The elastic dynamic response of the HTlc/LCS suspension increased with increasing mass ratio (R) of HTlc and a three-dimensional network structure could be formed in the suspension with higher R value. The thixotropic type of the HTlc/LCS suspension transformed from negative to positive and then to complex thixotropy when R changed from 0 to 0.5. By comparing between the thixotropic results obtained by thixotropic loop and oscillatory shear measurements, it was validated that the thixotropic loop for the suspension showing complex thixotropy had a crossover point.

Rheological behavior of aqueous suspensions containing cationic starch and aluminum magnesium hydrotalcite-like compound in the presence of different electrolytes

The rheological properties of aqueous suspensions consisting of cationic starch (CS) and positively charged aluminum magnesium hydrotalcite-like compound (HTlc) in the presence of different electrolytes (NaCl, CaCl 2 and AlCl 3) were investigated. It is found that the network-like structure of pure CS solution is formed by the interaction between CS molecules. Both the equilibrium viscosities and the elastic response of CS solution decrease with the addition of NaCl, CaCl 2 and AlCl 3. Small amplitude sinusoidal oscillation tests show that a three-dimensional network of the HTlc/CS suspension can be formed through the bridge effect between CS molecules and HTlc particles due to the hydrogen bonding between the ether groups or hydroxyl groups of CS and the hydroxyl groups of HTlc. Both the equilibrium viscosity and dynamic property of the HTlc/CS suspensions indicate that the network-like structural strength of the suspensions increases firstly and then decreases with increasing HTlc content. The equilibrium viscosity and the elastic response of the HTlc/CS suspensions decrease gradually with the addition of NaCl or CaCl 2, but decrease firstly then increase and then decrease with increasing AlCl 3 concentration, i.e., the structural strength of the HTlc/CS suspensions can be strengthened by the addition of appropriate amount of AlCl 3 content.

Influence of pH, high salinity and particle concentration on stability and rheological properties of aqueous suspensions of fumed silica

Multiphase light scattering and transient-dynamic rheometry were used in combination in order to control the stability, rheology and gelation of aqueous Aerosil 200 suspensions with regard to the influence of pH, particle and electrolyte concentrations. Effects of these parameters were studied by obtaining the critical concentration of particles for transition from Newtonian to shear thinning flow in each system. This was attributed to microstructural changes due to the interparticle forces. Further confirmation of results was obtained by measuring apparent viscosities, yield stresses, time dependent transient rheometry and light scattering from the samples. All results were described by extended-DLVO theory. Suspensions with acidic pH or at the isoelectric point had high stability even in presence of high concentration of NaCl due to the short-range repulsive hydration forces. On the other hand, suspensions with the highest salt concentration and basic pH showed time dependant rheology, largest yield values and viscosities, smallest critical particle concentration for flow regime transition and high capability of gel formation. Verification of gelation kinetics and the gel strength with regard to particle and salt concentration were implemented by three typical tests: time sweep, strain amplitude and frequency amplitude sweep in the dynamic oscillation mode at pH 8.5. Strength of the gelled networks was found to be greater at either higher salt concentration or higher concentration of particles. Strong-link regime of gel was found to govern the system regarding to increase either in particle volume fraction or in electrolyte. The scaling theory was tested for the system at 0.6 M NaCl and power-law exponent of the volume fraction dependence of storage modulus was found to be 3.8. In addition, applying the fractal model for strong gels calculated fractal dimension of flocs d f around 1.85. Based on the exponent value of 3.78 for G′ and the fractal flocs dimension of 1.85, it was proposed that cluster-diffusion-limited cluster aggregation (DLCA) was mainly governing the gel formation mechanism.

Planejamento experimental aplicado à otimização de massas cerâmicas contendo matérias-primas naturais

A otimização da composição é uma etapa de fundamental importância no processamento cerâmico. Neste trabalho, planejamento experimental foi aplicado a fim de se avaliar a relação entre propriedade e a composição de um sistema obtido a partir de matérias-primas naturais extraídas no Pegmatito do Seridó, na região fronteiriça RN-PB. Para o estudo do sistema ternário foram combinadas variáveis de processo (temperatura: 1100 e 1200 ºC; patamar de calcinação: 0 e 2 h), com a utilização de planejamento de misturas, de acordo com o planejamento simplex centróide. Os percentuais mínimos de cada componente na mistura foram de 10% v/v. Foram avaliadas as propriedades reológicas de suspensões aquosas das misturas com 50% v/v, otimizadas com PAA-Na. Determinou-se a porosidade aparente e massa específica aparente, além da retração de queima. A composição mineralógica das peças cerâmicas obtidas a 1200 ºC foi basicamente mulita e quartzo. O estudo permitiu especificar a região de composição que leva à maior densidade após sinterização, com um número relativamente pequeno de amostras.

Thixotropic properties of aqueous suspensions containing cationic starch and aluminum magnesium hydrotalcite-like compound

The rheological properties of aqueous suspensions consisting of cationic starch (CS) and positively charged aluminum magnesium hydrotalcite-like compound (HTlc) were investigated. Special emphasis was placed on the thixotropic phenomena. With the increase of mass ratio ( R) of HTlc to CS, the equilibrium viscosity ( η eq ) and the consistency coefficient ( m) values of the suspensions increase in the range of neutral and alkaline pH (higher than 6.5) while decrease in the range of acid pH (lower than 6.5). With the increase of pH value, the η eq and m values of the suspensions in the R range of 0–0.08 studied increase initially and then decrease, appearing a maximum value at about pH 7.41 ± 0.25 . The CS/HTlc suspensions display viscid character and the yield point of the suspensions was not observed except the suspension with R = 0.08 in the pH range of 7.66–9.70, which showed a yield point and viscoelasticity. The CS/HTlc suspensions may display different thixotropic types: negative, complex or positive thixotropy, depending on pH and R value. The thixotropic type of the CS/HTlc suspension may be transformed from negative (pure CS solution), through complex ( R = 0.02 ), into positive thixotropy ( R = 0.05 and 0.08) with the increase of R in the studied R range of 0–0.08, and the thixotropic strength of the suspensions increases initially and then decreases with pH value in the pH range studied. The mechanism of the thixotropic phenomenon is discussed.