Synthesis,characterization and properties of magnetic colloids supported on chitosan

This work proposes the synthesis, characterization and investigation of the stabilization capabilities of chitosan doped with magnetic nanoparticles. Nanoparticles of Fe, Co, Co(II,III) oxide, Ni and Ni/Ag mixture in 2-propanol were synthesized by chemical liquid deposition and the incorporation on the polymeric matrix was performed by solvated metal atom dispersion. Colloids and nanoparticles supported on chitosan were characterized by ultraviolet, Fourier-transform infrared, thermogravimetric analysis, electron diffraction X-ray and magnetic behaviour; transmission and field electronic scanning electron microscopy. The particle size distribution of colloids ranges from 6 to 50 nm with low particle stability due to flocculation after 120 days. The nanoparticles supported on chitosan had a particle size distribution of approximately between 10 and 80 nm, with low particle distribution; however, these particles do not flocculate because the matrix increases the stabilization of nanoparticles. All compounds present superparamagnetic behaviour at low temperature.     

Transport of Water and Ions Through a Clay Membrane

Colloidal platinum nanoparticles were prepared by ethanol reduction of PtCl(6)(2-) in the presence of poly(N-vinylformamide) (PNVF), poly(N-vinylacetamide) (PNVA), or poly(N-vinylisobuty-ramide) (PNVIBA). The effects of molecular weight and molar ratio of monomeric unit/Pt on the particle sizes and size distributions were characterized by transmission electron microscopy and UV-visible spectroscopy. The flocculation behavior of the polymer-stabilized colloidal Pt nanoparticles was studied with respect to the effects of temperature, addition of inorganic salts, and composition of the mixed solvents. The dispersion stability of the platinum colloids stabilized by poly(N-isopropylacrylamide) (PNIPAAm) and poly(vinylpyrrolidone) (PVP) was also examined. The sequence of polymer-stabilized platinum colloids in increasing order of dispersion stability was found to be PNIPAAm-Pt相似文献   

Flocculation of Bacillus amyloliquefaciens H Disintegrates with Cationized Starch and Aminated Hydroxyethylcellulose

The ability of cationized hydroxyethylated starch (CHES) and aminated hydroxyethylcellulose (DEAE-HEC) to flocculate cell disintegrate of Bacillus amyloliquefaciens H (BamHI) was investigated. The efficiency of flocculation was compared to that of synthetic polymer polyethyleneimine (PEI) and natural polysaccharide chitosan. The influence of salt concentration and biomass concentration on flocculation efficiency was investigated. It was found that the efficiency of flocculation with CHES and DEAE-HEC was similar to that of PEI but better compared to chitosan. Recovery of total soluble proteins at higher than 0.3% concentration of flocculant decreased by more than 18.8% and 42.3% compared to PEI and chitosan, respectively. The yield of BamHI restriction endonuclease activity with all flocculants was similar except for chitosan where 13.1% lower yield was obtained. Meanwhile, efficiency of flocculation with CHES and DEAE-HEC depends drastically on the salt concentration, that is, flocculation diminishes if NaCl concentrations higher than 0.2 M (for CHES) or 0.1 M (for DEAE-HEC) are used. The results have shown that CHES and DEAE-HEC are promising flocculants of cell disintegrates if higher yield of protein is of great concern.     

Removal of Tannic Acid by Chitosan and N-Hydroxypropyl Trimethyl Ammonium Chloride Chitosan: Flocculation Mechanism and Performance

The cationic organic flocculant chitosan and its derivative, N-hydroxypropyl trimethyl ammonium chloride chitosan (HTCC), were used in the flocculation of tannic acid, the impurity widespread in Chinese medicine water extractions. This study aimed at investigating the flocculation performance and mechanism of chitosan and HTCC on the tannic acid colloidal particles. The results showed that chitosan and HTCC effectively flocculated the tannic acid solution and the mechanism was mainly for the adsorption bridging and charge neutralization by hydrogen bonding, electrostatic interaction, and hydrophobic interaction. Meanwhile, the charge neutralization of HTCC was stronger than that of chitosan. The optimal flocculation conditions of chitosan and HTCC on tannic acid were achieved.     

Flocculation of kaolin particles by two typical polyelectrolytes: A comparative study on the kinetics and floc structures

The flocculation kinetics of kaolin particles induced by two polyelectrolytes is studied by using small-angle laser light scattering (SALLS). Two different methods, image analysis and SALLS, are used to calculated the fractal dimensions of flocs formed under different flocculation mechanisms. For a high charge density of polydiallyldimethylammonium chloride (PDADMAC), the initially flocculation rates are slow due to the quite low molecular weight. Smaller and more compact flocs are in the particle–particle connections, and restructuring of the flocs occurs in the flocculation process. With cationic polyacrylamide C498 of very high molecular weight and low charge density, however, the initially flocculation rates are much higher due to its rapid adsorption on kaolin particles, but it will take the adsorbed polymer a much longer time to reach equilibrium due to re-conformation. High potentialities of adsorption prevent the particles from entering the interior of the floc structure or rearrangement, which results in a more open floc structure. Different underlying flocculation mechanisms are evident for these two kinds of polyelectrolytes, in which charge neutralization is mainly involved for the low molecular weight and high charge density polymer of PDADMAC while polymer bridging is suggested to be the dominant mechanism for the high molecular weight polyelectrolyte of C498.     

Synthesis, characterization and flocculation performance of zwitterionic copolymer of acrylamide and 4-vinylpyridine propylsulfobetaine

A novel zwitterionic polyacrylamide AMVPPS copolymer containing sulfobetaine groups was synthesized by copolymerizing acrylamide (AM) and 4-vinylpyridine propylsulfobetaine (4-VPPS) in 0.5 mol/L NaCl solution with potassium persulfate (K₂S₂O₈) and sodium bisulfite (NaHSO₃) as initiator. The structure and composition of AMVPPS copolymer were characterized by FT-IR spectroscopy, ¹H NMR and elemental analyses. Thermal stability and solution properties of AMVPPS copolymer were studied by thermogravimetry analysis (TGA) and viscometry. Anti-polyelectrolyte behavior was observed and was found to be enhanced with increasing 4-VPPS content in copolymer. The flocculation performance for 2.5 g/L kaolin suspension and 2.5 g/L hematite suspension was evaluated by transmittance measurement and phase contrast microscopy. The effects of 4-VPPS content in the copolymer, intrinsic viscosity and the added salt on the flocculation performance were investigated. It was found that AMVPPS copolymer was a good flocculant for both anionic kaolin and cationic hematite suspensions and the flocculation performance of copolymer was much better than that of pure polyacrylamide (PAM). A very wide range of the optimum flocculation concentration, named as “flocculation window”, was found for both suspensions. These flocculation characteristics were mainly dependent on the charge neutralization, the intragroup conformation transition from water to NaCl solution and then the interchain bridging of the zwitterionic AMVPPS copolymer.     

Synthesis of cationic polyacrylamide via inverse emulsion polymerization method for the application in water treatment

In order to improve the flocculent efficiency of wastewater treatment, a cationic flocculant poly (acrylamide-[2-(methacryloyloxy) ethyl] trimethyl ammonium chloride) (P (AM-DMC)) (CPAM) has been synthesized successfully via an inverse emulsion polymerization. Acrylamide (AM) and [2-(methacryloyloxy) ethyl] trimethyl ammonium chloride (DMC) were served as monomers. The molecular structure of CPAM was characterized by Fourier transform infrared spectra (FT-IR) and ¹H nuclear magnetic resonance spectrum (¹H-NMR). The morphology of CPAM particles has been investigated by transmission electron microscope (TEM). Results showed that CPAM was the copolymer of AM and DMC and the particles of CPAM were uniform spheres (the size was about 200?nm). The synthetic conditions of CPAM have been studied and optimized by single-factor experiments. An optimized product was obtained at an intrinsic viscosity of 560?mL/g with a total monomer concentration of 25% and initiator concentration V50 of 0.2% (based on the total monomer mass). The amount of emulsion was 6% and the HLB (Hydrophile-Lipophile-Balance) of emulsion was 7.3. In addition, the flocculation property of CPAM was evaluated with kaolin suspension using jar test, and the result demonstrated that the flocculation property of CPAM performed better than kaolin flocculation.     

探索利用无机结合肽PT2(DRTSTWR)制备纳米铂晶体

实验中首先利用固定化于PET(聚对苯二甲酸己二醇酯)膜上无机结合肽PT2 (DRTSTWR)制备出铂微晶体. 然后用游离的PT2与PtCl₄在室温和pH中性环境中反应24 h, 所得产物用TEM观察, 其多数为1～2 nm呈方形和球形晶体, 经EDX分析显示晶体的元素组成中Pt远大于Cl的含量, 显然晶体不可能是PtCl₄或PtCl₂; 样品的XPS谱图中出现了结合能值为71.0 eV峰(Pt_4f标准值71.1 eV), 确认晶体为铂纳晶, 由此推断无机结合肽PT2在无细胞状态下能够作为模板仿生合成铂晶体. 继而在反应体系中加入不同浓度的壳聚糖和聚丙烯酸钠, 观察到纳米粒子的粒径和形貌随表面活性剂的加入发生了改变. 加入5倍的壳聚糖制备的铂晶体的直径在12～15.5 nm之间, 晶体排布似乎有成线状的趋势. 加入5倍的聚丙烯酸钠制备的铂晶体, 形貌更加规整, 以球形颗粒为主, 粒子直径在6～8 nm之间.     

Weak flocculation of aqueous kaolin suspensions initiating by NaCMC with different molecular weights

The present work is an investigation of the effect of NaCMC with different viscosities (molecular weights) on the stability of aqueous kaolin suspensions at pH 5-6. The stabilizing effect of polymers was characterized by measuring the sedimentation volumes (for 2.5% kaolin suspensions) and some important rheological parameters (for 40% and 50% kaolin suspensions). In certain cases the stability of suspensions was also studied in the presence of 0.5-1.0% NaCl. The additives were incorporated into the suspensions separately and simultaneously, as well. In certain cases the effect of mixing order of NaCMCs was also studied. The lower viscosity NaCMC was found to be a better stabilizing agent than its medium viscosity counterpart at the studied polymer concentrations (0.005-1.0%). This was manifested in smaller sedimentation volumes and lower rheological parameters (viscosity, yield stress, degree of thixotropy and elasticity). The lower and the medium viscosity polymer were simultaneously and consecutively added in a mass ratio of 50:1 and 10:1. The resulted observation of low viscosity and yield stress, and more importantly thixotropy and elasticity, can be interpreted in terms of a “site-blocking” type flocculation.     

壳聚糖纳米粒子荧光探针的制备和表征

通过低分子量的壳聚糖(LCS)聚阳离子与三聚磷酸钠(TPP)的静电作用制备纳米级壳聚糖微球,并利用壳聚糖链上丰富的氨基与荧光素异硫氰酸酯(FITC)反应从而制备纳米壳聚糖微球荧光探针(NFCS)。结果表明,当壳聚糖分子量为60000,LCS与TPP的质量比为6∶1时,可得到粒度均一的球形纳米粒子,平均粒径为40±3 nm。荧光倒置显微镜观察证实FITC结合到壳聚糖微球上。荧光光谱分析显示NFCS的最大激发波长、最大发射波长与游离态FITC无显著差异。光漂白实验证实NFCS的稳定性比游离态FITC有显著提高。     

The flocculation of kaolin suspensions with cationic polyacrylamides of varying molar mass but the same cationic character

Cationic polyacrylamides of varying molar masses but of similar charge density were tested as flocculants for kaolin suspensions. Flocculant performance was assessed by determining the extent of polymer adsorption, the subsidence rates of the flocculated suspensions and the residual turbidities of the resulting supernatants. The sol concentration was kept constant at 20 g kaolin dm⁻³ in 10⁻³ mol dm⁻³ NaCl solution; pH was varied from 3 to 10. It was found that the subsidence rates did not reflect the trends of polymer adsorption. Polymer adsorption decreased while subsidence rates increased as the molar mass of the polymers increased. Increased adsorption of polymer with pH did not result in higher rates of subsidence. The principal effect of the quaternary cationic charge is to produce a partially extended polymer molecule at all values of the pH. The positive polymeric charge is of secondary importance to the length of the molecule in determining the efficacy of flocculation by polymer bridging and does not counteract the increasing self-repulsion of the clay particles with increasing pH which produced poor floc formation.     

Elaboration of chitosan-coated nanoparticles loaded with curcumin for mucoadhesive applications

Polycaprolactone (PCL) nanoparticles decorated with a mucoadhesive polysaccharide chitosan (CS) containing curcumin were developed aiming the buccal delivery of this drug. These nanoparticles were prepared by the nanoprecipitation method using different molar masses and concentrations of chitosan and concentrations of triblock surfactant poloxamer (PEO-PPO-PEO), in order to optimize the preparation conditions. Chitosan-coated nanoparticles showed positive surface charge and a mean particle radius ranging between 114 and 125 nm, confirming the decoration of the nanoparticles with the mucoadhesive polymer, through hydrogen bonds between ether and amino groups from PEO and CS, respectively. Dynamic Light Scattering (DLS) studies at different scattering angles and concentrations have shown that the nanoparticles are monodisperse (polydispersity indices were lower than 0.3). The nanoparticle systems were also examined with Nanoparticle Tracking Analysis (NTA), and the results were in good agreement with those obtained by DLS. Colloidal systems showed mean drug content about 460 μg/mL and encapsulation efficiency higher than 99%. Finally, when coated with chitosan, these nanoparticles show a great ability to interact with mucin indicating also their suitability for mucoadhesive applications.     

壳聚糖-海藻酸盐纳米粒子的制备及其对BSA的载药与释放特性

带相反电荷的聚电解质在水溶液中能通过静电相互作用自组装形成壳聚糖-海藻酸盐纳米粒。利用动态光散射纳米粒度分析仪考察了钙离子及壳聚糖对粒子粒径的影响。结果表明：钙离子的存在可使粒子粒径从268．5nm降为203．4nm,但随着钙离子含量的继续升高,粒径迅速增大,当钙离子浓度大于0．45g／L时形成凝胶。壳聚糖含量的增加和蛋白的包裹均会使粒径增大。所制备的纳米粒对BSA具有较高的包栽能力,并有一定的缓释作用。当壳聚糖投料量增加时,可使BSA在pH=7．4的PBS中的释放减慢。     

Coagulation and flocculation measurements by photon correlation spectroscopy — colloidal SiO2 bare and covered by polyethylene oxide

With photon correlation spectrometry (PCS) the diffusion coefficients, average diameters and polydispersities of colloidal particles can be determined in dilute aqueous suspensions. In this study PCS is used to follow the coagulation and flocculation of silica particles. Electrolyte solution added to suspensions of bare particles and of particles covered with adsorbed polyethylene oxide layers induces aggregation. The rate constants of aggregation are evaluated by the second-order Smoluchowski theory with the assumptions of spherical aggregated particles and volume proportional light-scattering amplitude. Adsorbed PEO layers of molar mass lower thanM _w=160000 decrease the critical flocculation concentration and the flocculation states and rate constants for bare and covered particles are the same at high electrolyte concentrations. Polymer layers of high molar mass (M _w=325000, 900000) reducved at full coverage the rate constants and stabilize the suspensions even at high electrolyte concentrations. At low coverage adsorption of high molar mass polymers results in the same values as of low molar mass PEO. The correlation between rate constants and hydrodynamic PEO layer thicknesses demonstrates the steric influence of the tails of the adsorbed macromolecules on stability and flocculation.Dedicated to Prof. Dr. Joachim Klein on the occasion of his 60th birthday     

Adsorption of polyelectrolytes on colloidal latex particles, electrostatic interactions and stability behaviour

The stabilization and flocculation behaviour of colloidal latex particles covered with cationic polyelectrolytes (PE) is studied with photon correlation spectroscopy and zetapotential measurements. Diffusion coefficients, flocculation rate constants and zetapotentials have been determined as a function of adsorbed amount of cationic poly-(diallyl-dimethyl-ammoniumchloride) (PDADMAC) of different molar masses and of statistic copolymers of DADMAC and N-methyl-N-vinyl-acetamide (NMVA) of various compositions in water and at high ionic strength. Flocculation by van der Waals attraction can be observed if the zetapotential is low. This occurs, if the surface charge is screened by the oppositely charged cations. Furthermore, in the case of adsorption of high molecular polycations mosaic flocculation occurs if the adsorbed amount is low. At high ionic strength, flocculation takes place if the adsorbed amount is below the adsorption plateau. If the adsorption plateau is reached the suspensions become stabilized. In water the charge reversal at full coverage leads to electrosteric stabilization both with low and high molar mass polycations. At high ionic strength only polycations with high molar mass are able to stabilize the suspension. If a certain molar mass of the polycation is exceeded, steric stabilization of the suspension occurs due to the formation of long adsorbed PE tails and their osmotic repulsion. The layer thicknesses are determined as a function of the molar mass. Received: 4 July 2000/Accepted: 18 August 2000     

A novel flocculant of Al(OH)3-polyacrylamide ionic hybrid

A novel flocculant based on hybrid Al(OH)(3)-polyacrylamide (HAPAM) has been synthesized using a redox initiation system ((NH(4))(2)S(2)O(8)-NaHSO(3)) at 40 degrees C in aqueous medium. The HAPAM was characterized by viscometry, IR spectroscopy, TEM, conductivity, and TGA. The flocculation behavior for 0.25 wt% kaolin suspension was evaluated by spectrophotometry and phase contrast microscopy. It was found that an ionic bond exists between Al(OH)(3) colloid and polyacrylamide (PAM) chains in the HAPAM and the flocculation efficiency of HAPAM is much better than that of commercial polyacrylamide (PAM) and PAM/AlCl(3) blend.     

Preparation and flocculating properties of highly substituted cationic starches of different vegetable origins

Kinetic regularities of flocculation of model kaolin suspensions by highly substituted cationic flocculants synthesized from different starches (corn, waxy corn, potato, and tapioca starches) have been studied as depending on the doses and vegetable origins of the flocculants. The rate of kaolin suspension flocculation has been found to increase with the dose of the cationic starches of all types. It has been shown that, irrespective of the dose, the highest rate of kaolin sedimentation in the model systems is observed in the presence of cationic potato starch. It has been demonstrated that cationic potato starch flocculates kaolin suspensions with concentrations of 0.1, 0.5, and 1.0% with the same efficiency. In this case, the suspensions are almost completely clarified within 2–5 min. Moreover, the dependence of the flocculating efficiency for a 0.1% model suspension on the dose of cationic starch has been found to pass through a maximum at a starch content of 1.0–5.0 mg/g of kaolin depending on the type of starch.     

N,N,N-trimethylchitosan iodide complexes with a weak or a strong polyacid and nanoparticles thereof

Polyelectrolyte complexes (PECs) were prepared from N,N,N-trimethylchitosan iodide (TMCh) of different molar mass and a weak polyacid-poly(acrylic acid) (PAA) or a strong polyacid-poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS). The quaternization of the amino groups of chitosan enabled the formation of water-insoluble PECs in a broad pH range—from 3 to 12 and from 1 to 12 for TMCh/PAA and TMCh/PAMPS, respectively. Whereas the stoichiometry of the TMCh/PAA complex was pH dependant, the stoichiometry of the TMCh/PAMPS complex did not depend on pH. The stoichiometry and the yield of the complexes were influenced by the molar mass of TMCh. PEC nanoparticles were produced by mixing dilute solutions of the oppositely charged polyelectrolytes as revealed by dynamic light scattering analyses. The size of the particles was in the range of 135–924 nm and depended on the polyelectrolyte molar mass, the initial polyelectrolyte concentration, and the molar fraction of the TMCh units. Microbiological screening against Staphylococcus aureus and Escherichia coli revealed that PECs between TMCh and PAA or PAMPS have a good antibacterial effect, which is more slowly pronounced than that of the starting TMCh of different molar mass.     

Size control of self-assembled nanoparticles by an emulsion/solvent evaporation method

A novel and simple method for size control of self-assembled nanoparticles is suggested in this paper. Polymeric nanoparticles were prepared from amphiphilic chitosan derivatives fluorescein isothiocyanate (FITC)-conjugated glycol chitosans (FGCs). The attachment of hydrophobic FITC onto hydrophilic glycol chitosan induced the amphiphilic conjugate to form self-assembled nanoparticles in aqueous media, depending on degree of substitution. The size of self-assembled nanoparticles was controlled by a novel emulsion/solvent evaporation method. Adding a small amount of an immiscible solvent with water (chloroform) to FGC nanoparticle suspensions in aqueous media followed by ultrasonification and solvent evaporation led to partial dissociation and subsequent reformation of nanoparticles. The evaporation of chloroform facilitated the hydrophobic association, which resulted in more dense and hardened hydrophobic cores. The size of nanoparticles was closely related with the FGC concentration in the emulsion. The mean diameters of self-assembled nanoparticles were 150–500 nm at the FGC concentrations of 0.3–2.5 mg/ml. Higher FGC concentration resulted in larger particles. The polydispersity factors (μ ₂/Γ ²) of the reformed nanoparticles were fairly low (0.001–0.094), indicating narrow size distribution. The FGC nanoparticles were stable in phosphate-buffered saline at 37°C up to 20 days. Lactose was a good excipient for maintaining the structural integrity of nanoparticles during freeze-drying. Without lactose, the freeze-dried nanoparticles were not homogeneously redispersed in aqueous media. However, the freeze-dried nanoparticles with lactose were spontaneously redispersed in aqueous milieu with their own sizes.     

Size control of nanostructured silica using chitosan template and fractal geometry: effect of chitosan/silica ratio and aging temperature

The uses of low cost, renewable, environmentally friendly chitosan biopolymer as the structural template to control the size of silica particles in the range of nanometer scales are attractive for their practical industrial applications. In this paper, the nanostructured silica was synthesized using sodium silicate as the silica source and chitosan as the template under mild conditions. Effects of chitosan/silica ratio and aging temperature on the formation and the control of nanostructured silica was investigated by using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), N₂-sorption measurement, and transmission electron microscopy (TEM). It was found that the silica products were composed of the aggregates of primary silica nanoparticles and nanostructured silica units. At low aging temperature, the size of nanostructured silica was decreased when increasing the chitosan/silica ratio from 0.1 to 0.4. In contrast, the reverse trend was observed at the chitosan/silica ratio of higher than 0.4. The increase of aging temperature led to the formation of larger primary silica nanoparticles and nanostructured silica, and also promoted the formation of silica/chitosan composites. The fractal dimension calculated using modified FHH method found the linear correlation at two different regimes which might reflect the aggregates of silica products at different length scales.