Flocculation Structure Research Articles

The effect of sonication and high pressure homogenisation on the properties of pure cream

The homogenisation of milk and cream has been widely studied but the effect of sonication on the structural and functional properties of cream is not well known. In this study, raw milk, ultrafiltration retentate and cream samples were sonicated at 20 kHz and the rennet and acid gelation properties of these sonicated samples investigated. High pressure homogenisation at 80 bar was also performed for comparison. Sonication of raw milk and retentate samples led to a decrease in the fat globule size. Conversely, the fat globules in cream samples sonicated at < 10 °C flocculated to form grapelike structures whereas the cream samples sonicated at 50 °C did not form such aggregates. High pressure homogenisation at 50 °C led to similar flocculated structures, but these were not observed at low temperatures. This suggests a potential benefit of sonication technology in allowing low temperatures to be utilised for cream homogenisation, reducing energy demand. However, a gel made using cheese-milk with sonicated cream resulted in separation of a fat layer rather than the incorporation of the fat globules into the gel matrix. Rennet gelation properties of both the sonicated or homogenised samples were significantly superior to a native control sample where the resultant gels had shorter coagulation times and decreased syneresis.

Preparation of Associative Polyurethane Thickener and Its Thickening Mechanism Research

Associative polyurethane (PU) thickener has been synthesized by preparing the prepolymer with the reaction of polyethylene glycol (PEG) and isophorone diisocyanate (IPDI), which then end‐capping with long‐chain alkanol. The synthesis process, as well as hydrophilic chain length, theoretical molecular weight, solvent ratio, and thickener percentages, has been researched. The results shows that it reaches the upmost thickening effect when the theoretical molecular weight is under 20000, soft‐segment length is under 4000, solvent ratio is 1 : 1, and thickener percentages are controlled at 10%. Furthermore, thickening mechanism of PU thickener has been analyzed detailedly through the measurement of the critical micelle concentration (CMC) of PU thickener and analysis of the influence of PU thickener on the particle size and morphology of PU dispersions. It has been observed from the scanning electron microscopy (SEM) that the PU aqueous dispersions produce a certain degree of flocculation when the PU thickener was added, and this flocculation structure has been proved to be a thixotropic structure through the characterization of the change of particle size before and after the thickener is introduced into the PU aqueous dispersions. The CMC measurement results present that the thickening effect will be apparent when the concentration is controlled in a low range.

Rheological responses of Pickering emulsions prepared using colloidal hydrophilic silica particles in the presence of NaCl

We investigated the effects of flocculated structures of silica nanoparticles on the interfacial and rheological properties of Pickering emulsions. Pickering emulsions were prepared using diisopropyl adipate and aqueous colloidal silica nanoparticles flocculated in the presence of different NaCl concentrations. Averaged silica particle sizes were measured by dynamic laser scattering measurements; and we obtained a critical flocculation concentration (cfc) determined as a NaCl concentration at which size of silica particles was steeply increased. The resulting emulsions were classified as oil-dispersed-in-water type, and characterized by measuring droplet diameters, oil volume fraction, the amount of adsorbed silica nanoparticles on droplet surfaces, and the stress–strain (S–S) sweep curves. The Pickering emulsions increased droplet size over time due to partial coalescence, except at the cfc of NaCl for silica nanoparticles. The droplet size at two weeks after preparation decreased as NaCl concentration increased, while droplet size increased for NaCl concentrations above the cfc. The resulting yield stress and critical shear strain determined from the S–S sweep curves increased with increasing NaCl concentration at or above the cfc. This can be attributed to the formation of a three-dimensional network of silica particles between the droplets.

The formation of a structural framework in gelled Wyoming bentonite: Direct observation in aqueous solutions

HypothesisParticle space arrangement is a very important factor that determines the physico-mechanical properties of soil. Formations of three-dimensional (3D) structured networks within gelled or flocculated suspension may prevent clay particles and aggregates from settling under gravity force and by encapsulate water within such a network, lead to poor sludge dewatering. To better understand this phenomenon, a microstructural investigation of a smectite clay (SWy2) suspension was conducted. ExperimentsSWy-2 was diluted in water and a moderately salty aqueous solution and was studied with the aid of a synchrotron-powered transmission X-ray microscope (TXM) and cryogenic transmission electron microscope (Cryo-TEM). Observations of mutual particle arrangement in 3D spaces were conducted within a natural water environment after vitrification without drying. FindingsA new type of micro-architecture in particle space arrangement was observed. Smectite flakes were mostly in edge-to-edge (EE) contact and formed a 3D network, confirming a “net of flakes” structural model. Clay particles form a complex and multi-hierarchic flocculated structure with characteristic cellular chained networking. Chained aggregates build cellular elements, encapsulating water inside closed voids. Increasing ionic strength results in the development of multi-hierarchic voids categories, with most water retained within nano-pores.

Different effects of process conditions on PA6/nanoclay composites at nanoclay contents above and below percolation threshold: Rheological, thermo‐dynamical, and thermal properties

The effects of several factors (i.e., nanoclay content (NC), melt temperature, screw speed, and feeding rate), on morphology, rheology, thermodynamics, and thermal stability of PA6/NC samples produced in a co‐rotating twin‐screw extruder were studied. We discuss how changes in the level of these factors can vary diffusion or imposed shear, how these variations in diffusion and/or shear can affect NC dispersion, and how the changes in the state of NC dispersion can influence several properties of the samples. Samples with low NC content, below percolation threshold, showed exfoliated/intercalated structure with negligible sensitivity to changes in the level of the factors; whereas, samples with high NC content, above percolation threshold, showed intercalated with sporadic flocculated structures and noticeable sensitivity to the changes in the level of the factors. Moreover, NC dispersion was found to be mostly diffusion‐controlled: changes that resulted in higher diffusion or residence time (i.e., high melt temperature or low screw speed) also eventuated in better NC dispersion. What is more, percolation threshold was seen to move to lower NC contents as diffusion rate was increased. Moreover, as NC content increased, opposite thermal stability behaviors were observed at above and below the percolation threshold. J. VINYL ADDIT. TECHNOL., 22:259–266, 2016. © 2014 Society of Plastics Engineers

Multi-level flocculation structures of fresh cement paste by confocal laser scanning microscope

Under saturation dosage of all kinds of SP, the free water amount was examined by centrifuge. The distribution of solution and flocculation microstructures in fresh cement paste was observed in three-dimensional space by confocal laser scanning microscope(CLSM). Results indicate that SP can increase the free water amount by destroying the flocculated cement particle structure and different free water amount is released by different kinds of SP. The changes of the size of flocculation structures and the dispersion of solution were obviously detected with confocal laser scanning microscope: the size of flocculation structures was smaller and more dispersed in fresh cement paste with polycarboxylate superplasticizer, but the size of flocculation structures was bigger and cannot be dispersed uniformly in fresh cement paste with others SP. The multi-level flocculation structures theoretical model of fresh cement paste was then set up. The theory indicates that different kinds of SP with different dispersion strength will open the flocculation structures at different levels, which in turn present different water reducing rate.

Aggregation and breakage kinetics of fresh cement paste

The influence of shear-induced forces on the microstructure of fresh cement pastes was studied. Aggregation and breakage kinetics of the paste matrix are highly influenced by the shear history. It was found that the kinetics of re-aggregation is relatively slow, and time scale for recovery is longer than the time needed for breakdown. When the aggregation kinetics dominates, network interactions among particles develop and the average floc size increases. When the breakage kinetics dominates, network interactions among particles are broken and are accompanied by a decrease in the average floc size. The results suggest that there is a limiting size to floc growth. Minor additions of clays can significantly impact the structural network development and result in a more flocculated structure. The flocs produced by the clays were highly stable flocs with strong interparticle bonds that were able to oppose floc breakage and floc erosion.

Colloidal Clay Gelation: Relevance to Current Oil Sands Operations

Ultrafines are predominantly delaminated colloidal clays with dimensions <0.3 μm that exist naturally in oil sands and are released during conditioning of surface-mined ores. Critical concentrations of these ultrafines and the cations present in process water are capable of forming flocculated structures with a very high water holding capacity. During primary separation of bitumen these ultrafines are detrimental to recovery as a result of increased slurry viscosity as well as through slime coating of released bitumen. Disposition into tailings ponds eventually produces mature fine tailings (MFT) as a result of thixotropic gel formation that entraps coarser solids. The ultrafines concentration of ~3 wt% observed in MFT coincides with the critical gelation concentration determined for suspensions of ultrafines in salt solutions with cationic concentrations representative of that in pond water. This observation accounts for 100% of the water holding capacity of MFT and also explains why virtually no water is released once an MFT gel state has been formed. Here, we review earlier research in this area and identify the harmful effects of ultrafines in some current problematic ores.

Using Light Scattering to Screen Polyelectrolytes (PEL) Performance in Flocculation

Flocculation of precipitated calcium carbonate (PCC) was monitored using light diffraction spectroscopy (LDS). Four cationic polyacrylamides of high molar mass and with different degrees of branching, all copolymers of acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (Q9), were tested. LDS supplied information about the kinetic curves for flocs growth and also for the flocs structure evolution. Flocculation kinetics, flocs size and structure, flocs resistance and reflocculation capacity could be correlated with the degree of branching of the polyelectrolytes (PEL). Furthermore, PEL with different degrees of branching corresponded to different values for the intrinsic viscosity, indicating differences in the polymer conformation, which explained well the performance differences in flocculation.

Compressibility and permeability of Bangkok clay compared with kaolinite and bentonite

The physical and engineering properties of remolded clays are intrinsic and can be used as a frame of reference for the behavior of clay. Compressibility and permeability of remolded Bangkok clay at different ion concentrations and valences were compared with kaolin and bentonite as representatives of non- and high swelling clays. Bangkok clay, a low-swelling clay, exhibited physical and engineering properties similar to those of kaolin. The texture of coagulated Bangkok clay became a more flocculated structure with increasing ion concentration and valence, resulting in higher water holding capacity and liquid limit. Even though the physical properties of all tested clays varied significantly with pore water chemistry, the ( PI, LL) points lied above the A-line in the plasticity chart (where PI is the plasticity index and LL is the liquid limit) and could be represented by a unique relationship. The change of the intrinsic compressibility and permeability with the concentration and valence of the ions was interpreted by a generalized stress state e/ e L . The lower e/ e L value was associated with higher shear strength (resistance to vertical consolidation pressure in K 0-consolidation) and lower permeability. As the ion concentration and valence were increased for both kaolin and Bangkok clay, the resistance to consolidation pressure increased and permeability decreased for the same void ratio due to the decrease in e/ e L . The liquid limit for bentonite decreased with increasing ion concentration and valence due to the compression of the diffuse double layer. Hence, for the same void ratio, the resistance to consolidation pressure decreased and permeability increased due to the increase of e/ e L . Finally, relationships of the modified void index, I′ v and consolidation pressure, σ′ v , and generalized stress state e/ e L and permeability k were proposed. These relationships are useful and practical tools for assessing the intrinsic compressibility and permeability of non- to high-swelling clays in terms of liquid limit, which is easily obtained from conventional laboratory tests.

Smectite flocculation structure modified by Al 13 macro-molecules – As revealed by the transmission X-ray microscopy (TXM)

The aggregate structure which occurs in aqueous smectitic suspensions is responsible for poor water clarification, difficulties in sludge dewatering and the unusual rheological behaviour of smectite rich soils. These macroscopic properties are dictated by the 3D structural arrangement of smectite finest fraction within flocculated aggregates. Here, we report results from a relatively new technique, transmission X-ray microscopy (TXM), which makes it possible to investigate the internal structure and 3D tomographic reconstruction of the smectite clay aggregates modified by Al 13 Keggin macro-molecule [Al 13(O) 4(OH) 24(H 2O) 12] 7+. Three different treatment methods were shown resulted in three different micro-structural environments of the resulting flocculation. In case of smectite sample prepared in Methods 1 and 3 particles fall into the primary minimum where Van der Waals forces act between FF oriented smectite flakes and aggregates become approach irreversible flocculation. In case of sample prepared using Method 2, particles contacting by edges (EE) and edge to face (EF) orientation fell into secondary minimum and weak flocculation resulted in severe gelation and formation of the micelle-like texture in fringe superstructure, which was first time observed in smectite based gel.

Yield Behavior of Moderately Filled Epoxy/Ni Suspensions

Epoxy/nickel (Ni) adhesives can be used as integrated circuit (IC) packaging materials due to their lower cost than epoxy/silver (Ag) adhesives with acceptable electrical conductivity. In this work, yield behavior was studied for moderately filled bisphenol-A based epoxy/Ni suspensions (10–60 wt% of Ni). Effects of the preshear history, resin viscosity, temperature, particle size, solid loading, as well as different yield stress determination methods were investigated. The preshear effect manifests itself in successive shear rate sweeps with the same sample. Consequently, an initial shear rate sweep was employed to serve as preshear conditioning and obtain reproducible results on all samples. Shear thinning generally occurs for epoxy/Ni suspensions. The fractal dimension (D f) may be employed to describe these flocculated structures, and a higher D f value was observed for Epon815C/Ni system as compared to Epon830/Ni system. The Arrhenius equation describes the temperature dependence of suspension viscositys adequately. Incorporation of Ni nanopowder significantly reduces flow and the activation energy for yielding. The stronger van der Waals attractions created within the nanoparticles lead to larger yield stress. Also, different yield stress values are calculated using different determination methods.

Influence of molecular character of chitosan on the adsorption of chitosan to oil droplet interfaces in an in vitro digestion model

The relationship between the adsorption of chitosan to oil droplet interfaces (surface adsorption) and the molecular characteristics of the chitosan (molecular weight and charge density) was examined using an in vitro digestion model. This model involved adding different concentrations (3–10 wt%) of oil droplets to a 0.1 wt% chitosan solution at pH 3 to simulate consumption of an oil-containing meal after ingestion of chitosan. The pH was then incrementally raised to investigate pH variations that occur when a food material passes through the human digestive tract at an oil concentration of 3%. The amount of chitosan adsorbed to the oil droplet interface decreased with decreasing molecular weight (MW) and with increasing degree of deacetylation (DDA): ≈132, 85, and 78 g of oil per g of chitosan for MWs of 200, 500 and 750 kDa (all 90% DDA), respectively; and, 47, 65, and 78 g of oil per g of chitosan for DDAs of 40%, 70% and 90% (all 750 kDa), respectively at pH 3. In addition, the extent of droplet aggregation and the nature of the aggregates formed (strong versus weak; large versus small) also depended on chitosan characteristics. The pH dependence of the interaction between anionic oil droplets and cationic chitosan molecules depended on both MW and DDA. Microscope images showed formation of large flocculated structures at pH > 7 except for low DDA chitosan which remained soluble at all pH levels. Our results may have important consequences for understanding the bioactivity of chitosan, and for designing functional food ingredients to reduce lipid digestion and absorption.

Investigation of multi‐walled carbon nanotube‐reinforced high‐density polyethylene/carbon black nanocomposites using electrical, DSC and positron lifetime spectroscopy techniques

AbstractBACKGROUND: The positive temperature coefficient (PTC) effect on material properties has attracted much attention in recent years due to the prospects of many applications like temperature sensors, thermistors, self‐regulating heaters, etc. It has been suggested that incorporation of multi‐walled carbon nanotubes (MWNTs) into carbon black (CB)‐filled polymers could improve the electrical properties of composites due to high conductivity and network structure and significantly reduce the required CB loading.RESULTS: We observed no change in melting temperature and crystalline transition temperature on addition of MWNTs. However, the heat of fusion decreases as the amount of conducting carboxylated MWNT (c‐MWNT) filler increases and the resistivity of the composite decreases. The free volume shows an increase up to 1.5 wt% of c‐MWNT content and then decreases.CONCLUSION: Well‐developed crystals could not be formed due to restricted chain mobility as filler content increases. This results in minimum intermolecular interactions, and thus a decreased heat of fusion. A composite with c‐MWNT content of 0.5 wt% showed the highest PTC and higher resistivity at 150 °C possibly due to the formation of flocculated structures at elevated temperature. For filler content greater than 1.5 wt%, the decrease in free volume may be due to restricted chain mobility. Copyright © 2009 Society of Chemical Industry

Rheological Properties of Fresh Cement Paste and its Relation to Adsorption Behavior of Superplasticizer

This paper studied rheological properties of fresh cement pastes and adsorption behavior of superplasticizers which are FDN-5R, a type of naphthalene sulfonic acid based condensate, 3350, a type of polycarboxylate superplasticizer, by R/S-SST rheometer and UV Visible Spectrometer. Results show that superplasticizers can reduce the flocculation structure of fresh cement paste obviously and reduce the yield stress and apparent viscosity. The turn of thixotropic property is: blank sample &gt; FDN-5R &gt; 3350, especially the sample with 3350’s curve of upward and downward almost match together and the thixotropic property drives to zero. Shearing stress, apparent viscosity and thixotropic property are decreased, adsorption capacity is higher by the superplasticizer adding. The bigger effectual adsorption, the better dispersive action of flocculation and rheological properties of fresh cement pastes. Therefore, we can understand the effect mechanism and properties of superplasticizer much better by combining the molecular structure, adsorption capacity, dispersive action and rheological properties.

The Effects of the pH‐influenced Structure on the Dielectric Properties of Kaolinite–Water Mixtures

The properties of clay–water mixtures are reflected in their wide‐frequency dielectric responses that result from different polarization mechanisms. This feature is useful in various soil science applications but has not been systematically investigated. The objective of this study was to characterize the broadband dielectric spectrum of kaolinite sediments with different charge properties and structures using a slim‐form open‐ended coaxial probe. The sediment structure in this study was manipulated by changing the pore‐fluid pH. When the pH was below the isoelectrical point of the edge surface, IEPedge, the edge‐to‐face flocculation structure was formed in voluminous sediments with an average porosity of 0.87 (Group A samples). A higher dielectric constant due to bulk water polarization (an average of 65.47) was measured because of the higher water content. As the pH was increased to greater than the IEPedge, a dense sediment with face‐to‐face aggregation was produced in the Group B samples, and a lower dielectric constant (an average of 60.11) was obtained. In bound water polarization, a higher relaxation strength (∼2.7 times higher on average) and a longer relaxation time (∼1.5 times longer on average) were observed in the Group B samples compared with those of the Group A samples. Similar trends can also be found in the results of spatial polarization. These findings can be attributed to more negatively charged surfaces and denser packing. Fluid conductivity dominated the global conductivity of the sediment in the Group A samples so that the β value, i.e., the ratio between the conductivity of the sediment and the fluid, was &lt;1. The β value was &gt;1 in the Group B samples owing to an overcompensation of surface conduction.

Preparation and rheological behavior of lead-free graphite conducting paste

A lead-free graphite conducting paste was prepared by using graphite powder, lead-free barium boron low-melting glass and ethyl cellulose solution. By analyzing the sheet resistance, Vickers hardness as well as the adhesion strength of the fired film prepared by the pastes formulated with different composition, the composition of the paste with preferable properties was evaluated in weight percent: organic vehicle 60, graphite powder 15–20, and low-melting glass 20–25. The films, prepared by the pastes using the lead-free glass with a glass transition temperature of 476°C, were perfectly flat and compact after fired at a peak temperature within the range of 540 to 590°C. The sheet resistance of the fired film with glass content of 25 wt% was 135 Ω/mm2 at the film thickness of 25 ± 3 μm, while the Vickers hardness was 12.3 N/mm2 and the adhesion strength to soda lime silicate glass substrate was 45.6 N/mm2. In addition, the rheological, thixotropic, and viscoelasticity behaviors of the typical paste were characterized and the effects on the screen-printing ability were analyzed in detail. It is found that a slight flocculated network structure is formed in the paste at rest, but the flocculated structure is very slight due to the steric effect of the ethyl cellulose macromolecules and good dispersing. The rheological, thixotropic, and viscoelasticity behaviors of the typical paste were similar to those of the screen-printing pastes with a high solid content of filler.

Degree of flocculation and viscoelastic behaviour of kaolinite-sodium chloride dispersions

Abstract The effect of electrolyte concentration and pH on the degree of flocculation of kaolinite dispersions has been investigated. The viscoelastic behaviour is discussed and quantitatively linked to the degree of flocculation. This degree of flocculation dispersions changes significantly with both ionic strength and pH. At low pH, regardless of electrolyte concentration, kaolinite dispersions are highly flocculated (i.e. strong edge–face interactions at pH G ′, is greater in the acid pH range. These results together with those obtained from creep experiments suggest the existence of a strong elastic, flocculated structure up to pH 7, at low ionic strength, further increase in pH causes breakdown in flocs structure and when the ionic strength is increased weak randomly structured flocs are produced.

Simultaneous measurement of rheological and conductive properties of carbon black filled ethylene–tetrafluorothylene copolymer

Composites composed of carbon black (CB) filled polymers have been widely applied in many areas such as electromagnetic/radio-frequency interference shielding, electrostatic discharge, conductive adhesives for die attachment in electronic packaging applications, and electroactive polymeric sensors in hand prostheses [1, 2]. It is well known that the morphology and properties of filled polymer composites are greatly influenced by the state of filler dispersion [3]. Due to the small size and high specific surface, the filler particles are favorable to form a three-dimensional flocculation structure [4]. Even though scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations can give us a lot of information on structure and morphology involving fillers, they only reflect the dispersion localized within a two-dimensional microscopic site and thereby are easily misinterpreted with respect on the correlation of the information to the real dispersion space and its contribution to the target properties [5, 6]. It is accepted that dynamic rheological measurements are effective for dealing with the structure and morphology of filled polymers as well as the filler dispersion because the structure of samples tested is indestructible under small strain (c) amplitudes [7]. The rheological properties of highly filled polymer composites may provide essential information about the flocculation structure of the filler that contributes to the physical properties such as mechanical strength, electrical resistivity, and heat conductivity [8]. Much work has been performed on the rheological behavior of various filled polymers. Krishnamoorti and Giannelis [9] observed nonterminal low-frequency rheological behavior in nanocomposites containing layered silicates. Zhang and Archer [10] reported a transition to solid-like response at low oscillation frequencies due to the presence of a filler network in poly(ethyl oxide)/silica nanocomposites. Simultaneous measurement of rheological and conductive behaviors under c has been made on CB-filled natural rubbers [11] or vulcanizates [12] to study the carbon black structure inside these materials. It was found that shear moduli and electrical conductivity vary in an approximately similar way as the amplitude of dynamic oscillation increases. In the aforementioned literatures, small strain oscillation was achieved by using spring while the large one is controlled using machine driving or hand wheel. Recently, Pan and Mckinley [13] studied viscoelasticity and conduction behaviors of an electrorheological fluid suspension using simultaneous measurement technique. To our knowledge, few work has been reported to study filled semicrystalline polymers at temperatures above melting point (Tm) using simultaneous measurement of rheological and conductive behaviors. In a previous paper [14], we examined the conductive behavior of ethylene–tetrafluorothylene (ETFE) copolymer/CB composites and found that the switching characteristic show a reproducible stability at the upper limit of the percolation transition. Here we present some unique results from simultaneous measurements of the dynamic storage modulus (G0) and electrical resistance (R) for ETFE/CB melt. It is noted that the modified rheometer allows us to obtain the data of measuring G0 and R for ETFE/CB composites in a relative wide strain range in one mode. The composites were prepared by mixing ETFE (ETFE750 from DuPont, density 0.942 g cm , melting point Z. Liu Y. Song J. Zhou Q. Zheng (&) Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, 310027, P.R. China e-mail: zhengqiang@cmsce.zju.edu.cn

Rheology and UV-protecting properties of complex suspensions of titanium dioxides and zinc oxides

Ultra-fine particles of titanium dioxide (TiO 2) and zinc oxides (ZnO) are very attractive as UV-protecting ingredients in cosmetic products. The UV-scattering behavior of complex suspensions in a silicone oil is studied in relation to rheological properties. To control the dispersion stability of suspensions, three polyoxyethylene (POE)-modified silicones of branch-type, (AB) n -type, and ABA-type are used as dispersants. Irrespective of molecular structure, the dispersants can stabilize the TiO 2 and ZnO particles and the flow of both single suspensions is Newtonian with low viscosity. However, the Newtonian flow profiles and high dispersion states are maintained only for complex suspensions prepared with ABA-type dispersant. Since the POE groups which are incorporated between terminal silicones groups attach to the particle surfaces, the steric stabilization is responsible for low viscosity and high dispersions. Because the UV scattering of suspensions is determined by the sizes of flocculated structures, the high transmittance in the visible ranges and low transmittance in the UVA and UVB ranges can be achieved in the presence of ABA-type dispersant.