Chitosan for coagulation/flocculation processes - An eco-friendly approach

Chitosan is a partially deacetylated polymer obtained from the alkaline deacetylation of chitin, a biopolymer extracted from shellfish sources. Chitosan exhibits a variety of physico-chemical and biological properties resulting in numerous applications in fields such as cosmetics, biomedical engineering, pharmaceuticals, ophthalmology, biotechnology, agriculture, textiles, oenology, food processing and nutrition. This amino-biopolymer has also received a great deal of attention in the last decades in water treatment processes for the removal of particulate and dissolved contaminants. In particular, the development of chitosan-based materials as useful coagulants and flocculants is an expanding field in the area of water and wastewater treatment. Their coagulation and flocculation properties can be used to remove particulate inorganic or organic suspensions, and also dissolved organic substances. This paper gives an overview of the main results obtained in the treatment of various suspensions and solutions. The effects of the characteristics of the chitosan used and the conditions in solution on the coagulation/flocculation performance are also discussed.     

On the collision efficiency in polymer flocculation of colloidal particles

The applicability of the conventional collision efficiency approach for the case where the collision of colloidal particles is not necessary for the rate-determining step is examined. On the basis of a dynamical treatment, we show that the fundamental assumption made in the conventional analysis may lead to a significant error. Depending upon the ratio of the number of sites on the colloidal surfaces to the number of polymer molecules, and the relative magnitudes of the desorption rate constant and the adsorption rate constant, the collision efficiency calculated by the conventional analysis may be either underestimated or overestimated. The present approach yields the temporal variation of the distribution of the fractional surface coverage. It can be shown that if the number of colloidal particles is large, using the mean fractional surface coverage instead of the exact distribution of the fractional surface coverage is sufficient for the evaluation of the collision efficiency.     

Coalescence coupled with either coagulation or flocculation in dilute emulsions

In current theories [R.G.P. Borwankar, L.A. Lobo, D.T.G. Wasan, Colloids Surf. 69 (1992) 35; K.D. Danov, N.D. Denkov, D.N. Petsev, R. Borwankar, Langmuir 9 (1993) 1731; S.S. Dukhin, J. Sjöblom, J. Dispers. Sci. Technol. 19 (1998) 311], emulsion destabilization is considered as the combined processes of droplet coagulation/flocculation and coalescence. Irreversible aggregation is usually called coagulation, and the term flocculation is used for reversible aggregation. These theories have different conditions of applicability which are not specified. An approximate criterion for discrimination between coalescence coupled with either coagulation or flocculation in dilute emulsions is proposed. Such discrimination is made possible by comparing the characteristic time for coagulation (Smoluchowski time) with that for floc fragmentation (droplet doublet lifetime, τ_d). As droplet dimension and electrolyte concentration decrease, and the Stern potential increases, τ_d is reduced and flocculation takes place. The quantity τ_d enables one to specify the conditions for the two separate cases. The important role of retarded van der Waals forces, screening length and hydration forces in emulsion coalescence is demonstrated.     

The sticking probability of colloidal particles in polymer-induced flocculation

The interaction between colloidal particles in a solution containing polymer molecules is examined theoretically. In particular, the sticking probability of colloidal particles, which plays a significant role in the determination of the collision efficiency of an unstable dispersed system, is analyzed. We found that the sticking probability is extremely sensitive to the variation in the Hamaker constant of a colloidal particle. In the conventional analysis of the collision efficiency in polymer-induced flocculation, it is assumed that the adsorption of polymer is relatively fast than the collision of colloidal particles. Since the adsorption of polymer will significantly affect the properties of the surface of a colloidal particle, this assumption may lead to an appreciable deviation in the prediction of collision efficiency.     

A calcium(II) coordination polymer showing two different bridging 2-carbamoyl-4-nitrobenzoate coordination modes

Aqueous reaction of CaCO₃ with 2-carbamoyl-4-nitrobenzoic acid (2-ca-4nbaH) results in the formation of a 1-D coordination polymer [Ca(H₂O)₂(2-ca-4nba)₂] (1), which crystallizes in the centrosymmetric triclinic space group P 1. The structure consists of a central Ca(II), two coordinated waters, a symmetrical bridging (µ₂-η ¹ : η ¹) 2-ca-4nba, and a tridentate bridging (µ₂-η ² : η ¹) 2-ca-4nba. The calcium in 1 is coordinated by two water molecules and five oxygens of four symmetry-related 2-ca-4nba, resulting in a distorted pentagonal bipyramidal {CaO₇} polyhedron. Pairs of {Ca(H₂O)₂} units are linked into a 1-D coordination polymer extending along the a-axis with the aid of pairs of bridging 2-ca-4nba ligands. In the infinite chain, alternating pairs of Ca(II) ions exhibit Ca ··· Ca separations of 4.124 and 4.855 Å.     

Haloing, flocculation, and bridging in colloid-nanoparticle suspensions

Integral equation theory with a hybrid closure approximation is employed to study the equilibrium structure of highly size asymmetric mixtures of spherical colloids and nanoparticles. Nonequilibrium contact aggregation and bridging gel formation is also qualitatively discussed. The effect of size asymmetry, nanoparticle volume fraction and charge, and the spatial range, strength, and functional form of colloid-nanoparticle and colloid-colloid attractions in determining the potential-of-mean force (PMF) between the large spheres is systematically explored. For hard, neutral particles with weak colloid-nanoparticle attraction qualitatively distinct forms of the PMF are predicted: (i) a contact depletion attraction, (ii) a repulsive form associated with thermodynamically stable "nanoparticle haloing," and (iii) repulsive at contact but with a strong and tight bridging minimum. As the interfacial cohesion strengthens and becomes shorter range the PMF acquires a deep and tight bridging minimum. At sufficiently high nanoparticle volume fractions, a repulsive barrier then emerges which can provide kinetic stabilization. The charging of nanoparticles can greatly reduce the volume fractions where significant changes of the PMF occur. For direct and interfacial van der Waals attractions, the large qualitative consequences of changing the absolute magnitude of nanoparticle and colloid diameters at fixed size asymmetry ratio are also studied. The theoretical results are compared with recent experimental and simulation studies. Calculations of the real and Fourier space mixture structure at nonzero colloid volume fractions reveal complex spatial reorganization of the nanoparticles due to many body correlations.     

Use of Adhesive for the Retention of a Rough-Surfaced Particle on a Solid Support

In a study of the rate of dissolution in water of a single detergent granule, an unexpected experimental artefact was encountered. The granule, attached to a solid support by adhesive, was found on dissolution to leave behind a thin shell or skin. The formation of this residue can be attributed to the capillarity-induced spreading of the uncured adhesive over much of the granule surface due to its irregular surface morphology. No such effect was found with smooth, spherical particles of comparable size. This residue would be likely to modify the observed dissolution process.     

A new two‐dimensional polymeric cadmium(II) complex containing dicyanamide bridging ligands

As part of an exploration of new coordination polymers, a cadmium‐dicyanamide complex, namely poly[benzyltriethylammonium [tri‐μ‐dicyanamido‐κ⁶N ¹:N⁵‐cadmium(II)]], {(C₁₃H₂₂N)[Cd(C₂N₃)₃]}_n , has been synthesized by the reaction of benzyltriethylammonium bromide, cadmium nitrate tetrahydrate and sodium dicyanamide in aqueous solution, and characterized by single‐crystal X‐ray diffraction at room temperature. In the crystal structure, each Cd^II cation is coordinated by six nitrile N atoms from six anionic dicyanamide (dca) ligands to furnish a slightly distorted octahedral geometry. Neighbouring Cd^II cations are linked by dicyanamide bridges to construct a two‐dimensional anionic layer coordination polymer. One amide N atom in the bridging dca ligand is disordered over two sites. The cations lie between the anionic frameworks and there are no hydrogen‐bond interactions between the cations and anions. The organic cations are not involved in the formation of the supramolecular network.     

The importance of force in microbial cell adhesion

Microbes have evolved sophisticated strategies to colonize biotic and abiotic surfaces. Forces play a central role in microbial cell adhesion processes, yet until recently these were not accessible to study at the molecular scale. Unlike traditional assays, atomic force microscopy (AFM) is capable to study forces in single cell surface molecules and appendages, in their biologically relevant conformation and environment. Recent AFM investigations have demonstrated that bacterial pili exhibit a variety of mechanical responses upon contact with surfaces and that cell surface adhesion proteins behave as force-sensitive switches, two phenomena that play critical roles in cell adhesion and biofilm formation. AFM has also enabled to assess the efficiency of sugars, peptides, and antibodies in blocking cell adhesion, opening up new avenues for the development of antiadhesion therapies against pathogens.     

Particle formation and coagulation in the seeded semibatch emulsion polymerization of butyl acrylate

Particle formation and coagulation in the seeded semibatch emulsion polymerization of butyl acrylate were studied under monomer‐starved conditions. To investigate the importance of the kinetics of the water phase in the nucleation process, the monomer feed rate was used as a variable to alter the monomer concentration in the aqueous phase. The emulsifier concentration in the feed was employed to alter the particle stability. Particle formation and coagulation were discussed in terms of critical surface coverage ratios. Particle coagulation occurred if the particle surface coverage dropped below θ_cr1 = 0.25 ± 0.05. The secondary nucleation occurred above a critical surface coverage of θ_cr2 = 0.55 ± 0.05. The number of particles remained approximately constant if the particle surface coverage was within θ_cr1 = 0.25 < θ < θ_cr2 = 0.55. This surface coverage band is equivalent to the surface tension band of 42.50 ± 5.0 dyne/cm that is required to avoid particle formation and coagulation in the course of polymerization. The kinetics of the water phase was shown to play an important role during homogeneous and micellar nucleations. For any fixed emulsifier concentration in the feed and above θ_cr2, the number of secondary particles increased with monomer concentration in the aqueous phase. Moreover, the presence of micelles in the reaction vessel is not the only perquisite for micellar nucleation to occur, a sufficient amount of monomer should be present in the aqueous phase to enhance the radical capture by partially monomer‐swollen micelles. The rate of polymerization increased with the surfactant concentration in the aqueous phase. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3612–3630, 2000     

Enhanced flocculation activity of polyacrylamide‐based flocculant for purification of industrial wastewater

The flocculation activity of commercially available anionic poly (acrylamide‐co‐acrylic acid), p (AAm‐co‐AA) has been significantly improved, without any inorganic coagulant aid. The effect of three types of surfactants, anionic sodium lauryl ether sulfate (SLES) (Palm Epimen), nonionic cocamide DEA, zwitterionic amphoteric Amphotensid B5, and one organic cation, trimethylammonium bromide (TAB) on coagulation/flocculation performance have been investigated. The performance has been analysed in terms of turbidity, total suspended solid (TSS), total iron (TI) content, and BTEX for treating two kinds of industrial wastewater, produced water (PW) and starch water. We have shown that adding a small amount of each of the studied surfactants, and especially cationic TAB, significantly increases the coagulation/flocculation performance without modifying pH levels. A combination of low dosage of flocculant (310 ppb) and TAB (310 ppb), after 5 minutes, presented 88%, 81%, and 62% reduction in turbidity, TSS, and TI content, respectively, whereas by using 5 ppm of flocculant alone (16 times more), only 76%, 75%, and 43% removal was obtained. The results reveal that TAB performs as an efficient coagulant booster. Compared with regular inorganic coagulants, it is more cost‐effective, reduces the consumption of treatment chemicals, and the pH‐dependency of contaminants removal.     

遥爪型聚合物交联反应的耗散粒子动力学模拟

利用耗散粒子动力学(Dissipative particle dynamics, DPD)方法研究了稀溶液中遥爪型聚合物的交联反应过程. 考察了体系中交联度、 链长及浓度等因素对反应达到稳态时所形成的网络结构的影响, 并通过计算聚合物交联结合能(U), 统计达到稳态时特征交联结构的数量来判定各因素对体系的作用. 结果表明, 交联度决定体系的微观结构, 而聚合物链长决定交联结构的连通性. 另外, 特征环形结构数与遥爪型聚合物的浓度及链长均存在线性依赖关系.     

多孔结构聚合物乳胶粒

介绍了多孔结构乳胶粒的制备方法、表征手段以及成孔机理。着重阐述了“碱酸分段处理法”中不饱和酸与交联剂的种类与用量、以及碱酸处理条件等因素对乳胶粒成孔的影响。     

Effects of Various Forces on Particle Distribution and Thermal Features of Suspensions Containing Alumina Nanoparticles

The two-phase Euler-Lagrange method has been used in order to investigate the effects of various forces on particle distribution and thermal characteristics of the water-based Al₂O₃ nanofluid flow inside a pipe under uniform wall heat flux. In the Euler-Lagrange approach, the particles are individually tracked in Lagrangian frame, while the fluid is evaluated in Eulerian frame. Brownian, thermophoretic, drag, lift, and virtual mass forces have been considered. Moreover, experimental data from various researchers were used to analyze the results. Concentration distribution is nonuniform at cross section of the pipe which increasing each parameters of Reynolds number, mean concentration and particles size will intensify its nonuniformity. This nonuniformity will make velocity profile flatter. The Brownian force makes the particle distribution more uniform, whereas the thermophoretic force enhances nonuniformity of the particle distribution. The effects of not considering the Brownian and thermophoretic forces on heat transfer are more significant for finer particles and higher concentrations. Furthermore, at lower Reynolds number, the Brownian force incorporates a more significant role especially in farther distances from entrance.      

The controlled flocculation of submicron emulsion particles. I. A three-step synthetic route to supermicron polymer particles

The basic features of a three-step experimental process to produce supermicron polymer particles are described. First, a submicron emulsifier-free latex is prepared by a well-known technique. Second, the latex is aggregated by destabilizing with cetyl pyridinium chloride under constant stirring conditions, to yield roughly spherical clusters of 6-12 μ diameter. Third, the aggregates are stabilized with poly(vinyl alcohol) and internally coalesced by heating at or above the glass transition temperature. The final product particles have relatively smooth surfaces. Results are qualitatively interpreted in terms of a dynamic equilibrium where the aggregate size is determined by a balance between attractive interparticle potentials and stirring shear forces. Bimodal aggregate size distributions suggest the aggregate break-up mechanism may involve the erosion of individual latex particles and small fragments from the surface of aggregates. © 1996 John Wiley & Sons, Inc.     

Nanoscale interfibrillar adhesion in UHMWPE fibers

The goal of this research is to quantify the fibrillar adhesive energy in ultra‐high molecular weight polyethylene fibers, characteristic of nanoscale fibril interactions. Quantification of these energies is vital to the understanding of fibrillar deformation mechanisms that have been shown to play an important role in fiber performance. This is achieved through the development and implementation of a nanosplitting technique developed through the use of AFM‐enabled nanoindentation. This technique allows the quantification of nanoscale adhesive energies through careful monitoring of load and unload curves as well as examination of the residual split through high‐resolution AFM images. Results indicate that the average nanoscale fibril adhesive energy is over 3 times larger than the energy expected from van der Waals interactions alone. This indicates that a significant degree of physical interactions exist between fibrils, beyond van der Waals interactions, in the form of tie‐molecules, fibrillar network junctions, and bridging lamellar crystals. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 391–401     

Solid state synthesis and characterization of a triple chain calcium(II) coordination polymer showing two different bridging 4-nitrobenzoate coordination modes

The solid state reaction of [Ca(H₂O)₄(η¹-4-nba)(η²-4-nba)] 1 (4-nba = 4-nitrobenzoate) with 2-methylimidazole (L²) at 100 °C results in the formation of a Ca(II) coordination polymer [Ca(H₂O)(L²)(4-nba)₂]_n2. Compound 2 was characterized by elemental analysis, spectral and thermal methods, and its structure determined. The coordination polymer 2 crystallizes in the centrosymmetric monoclinic space group P2₁/n with all atoms situated in general positions and its structure consists of a central Ca(II), a monodentate 2-methylimidazole, a bridging water ligand (μ₂-H₂O), a bidentate bridging (μ₂-η¹:η¹) 4-nba ligand and a monoatomic bridging (μ₂-η²) 4-nba ligand. Each seven-fold coordinated Ca(II) in the title compound is bonded to a nitrogen atom of a terminal 2-methylimidazole (L²) ligand, two symmetry related water molecules and four symmetry related 4-nba ligands, resulting in a distorted pentagonal bipyramidal {CaO₆N} polyhedron. Due to the bridging nature of the aqua and 4-nba ligands [(2-methylimidazole)calcium(II)] units in 2 are linked into a one-dimensional coordination polymer consisting of three chains, all of which propagate along b-axis. In the triple chain coordination polymer a Ca···Ca separation of 3.8432(3) Å is observed between neighbouring Ca(II) ions. The oxygen atoms of the carboxylate and nitro functionalities of the 4-nba ligand and the coordinated water are involved in O–H···O, N–H···O and C–H···O interactions. A comparative study of nine alkaline-earth 4-nitrobenzoate compounds is described.     

淀粉基阳离子絮凝剂的研制及性能测试

用可溶性淀粉为原料,通过接枝改性合成了一种淀粉基阳离子絮凝剂(MSF),其最佳制备工艺条件为:淀粉与丙烯酰胺的质量比为1:2,引发剂用量为0.6 g,反应温度为50 ℃,接枝时间为3.5 h;阳离子化条件为:甲醛和二甲胺摩尔比为1.0:1.4,反应时间2.5 h,反应温度50 ℃.产物结构经FTIR证实.用其处理番茄废水后,废水的透光率提高了78.2%、TOC下降了22.5%、COD下降了37.25%,结果表明该产品对高浓度有机废水的絮凝性能优于聚丙烯酰胺高分子絮凝剂(PAM).     

Influence of the bulk and surface morphology on adhesion of polystyrene-inter-poly-cross-2-ethylhexyl-methacrylate films and particles

The adhesion behavior of semi-interpenetrating polymer networks (semi-IPNs) of linear polystyrene (PS) in crosslinked poly-2-ethylhexylmethacrylate (EHMA) was studied by variation of the bulk and surface morphology, i.e., domain size, continuity, and concentration in the domains. Semi-IPNs were prepared by liquid-liquid demixing upon cooling of a homogeneous solution of PS in methacrylate monomer, followed by gelation of the PS-rich phase and UV polymerization of the methacrylate resin. Welding of films allowed the preparation of larger objects provided that (1) the samples were phase separated to a high degree and contained domains with a high PS concentration (>90%) and (2) polystyrene was present at the interface. For semi-IPN films, a linear dependence of the adhesion strength on the (crack healing time)^1/4 was obtained. Based on these considerations, a process was developed to obtain melt-processable semi-IPN particles, by quenching droplets of the polymer solution into a cold liquid. These particles obtained a PS-rich skin layer and showed good adhesion after blending with a thermoplast. © 1996 John Wiley & Sons, Inc.     

Spectral force analysis using atomic force microscopy reveals the importance of surface heterogeneity in bacterial and colloid adhesion to engineered surfaces

Coatings developed to reduce biofouling of engineered surfaces do not always perform as expected based on their native properties. One reason is that a relatively small number of highly adhesive sites, or the heterogeneity of the coated surface, may control the overall response of the system to initial bacterial deposition. It is shown here using an approach we call spectral force analysis (SFA), based on force volume imaging of the surface with atomic force microscopy, that the behavior of surfaces and coatings can be better understood relative to bacterial adhesion. The application of vapor deposited TiO₂ metal oxide increased bacterial and colloid adhesion, but coating the surface with silica oxide reduced adhesion in a manner consistent with SFA based on analysis of the “stickiest” sites. Application of a TiO₂-based paint to a surface produced a relatively non-fouling surface. Addition of a hydrophilic layer coating to this surface should have decreased fouling. However, it was observed that this coating actually increased fouling. Using SFA it was shown that the reason for the increased adhesion of bacteria and particles to the hydrophilic layer was that the surface produced by this coating was highly heterogeneous, resulting in a small number of sites that created a stickier surface. These results show that while it is important to manufacture surfaces with coatings that are relatively non-adhesive to bacteria, it is also essential that these coatings have a highly uniform surface chemistry.