Effects of vinyl series polymers on the formation of hematite particles in a forced hydrolysis reaction

The influence of polymers on the formation of hematite particles from forced hydrolysis of acidic FeCl(3) solution was investigated using vinyl series polymers with different functional groups. The disk-like hematite particles were produced from forced hydrolysis of acidic FeCl(3) solution in the presence of polyvinyl alcohol (PVA: 0-1 wt%). On the other hand, spherical particles were produced by addition of very small amounts of polyacrylamide (PAAm: 0-0.004 wt%). The size of spherical particles was slightly decreased with increase in the concentration of PAAm. The ellipsoidal particles were precipitated by addition of a very low concentration of polyacrylic acid (PAAc: 0-0.004 wt%). The effect of polymers on the hematite particle formation was expressed in the order of PVA相似文献   

Effects of Pluronics surfactants on morphology and porosity of hematite particles produced from forced hydrolysis reaction

The shape and porosity of hematite particles, produced from a forced hydrolysis reaction of acidic FeCl₃ solution, were controlled by using Pluronics as nonionic surfactants (0–4 wt.%). Pluronics possess a nominal formula of (PEO) _x –(PPO) _y –(PEO) _x . The effect of Pluronics with low hydrophilicity (PEO contents were less than 50 mol%) was small and provided spherical particles the same as that of the system without Pluronics (control system). However, Pluronics with higher hydrophilicity (PEO contents were over 50 mol%) gave ellipsoidal hematite particles. This effect on the particle morphology was enhanced by an increase in their molecular weight. On the other hand, the Pluronics possessing an opposite nominal formula [(PPO) _x –(PEO) _y –(PPO) _x ] exhibited no effect on the particle shape; it only depressed phase transformation from ?-FeOOH to hematite. Not only the morphology but also the pore size of hematite particles was controlled from nonporous to mesoporous by using Pluronics. The N₂ adsorption experiment and t-plot curve analysis revealed that the hematite particles changed from mesoporous to microporous by an increase in the concentration of Pluronics. On the other hand, in the presence of very low amounts of Pluronics molecules (0.1 wt.%), nonporous hematite particles were produced via strong aggregation of PN particles by their hydrogen bonding between hydroxyl and PEO or PPO groups. The dynamic light scattering measurement for the system with Pluronics clarified the existence of polynuclear (PN) particles with a hydrodynamic particle diameter (D _a) of ca. 40 nm after these were aged for 6 h. The size of PN particles remained constant at ca. 40 nm during aging time of 12 h～3 days, but the scattering intensity was decreased. This decrease in the scattering intensity reveals that the number of PN particles is reduced by aggregation. The transmission electron microscope, inductively coupled plasma atomic emission spectroscopy, and total organic carbon analysis measurements employed on the systems produced for ellipsoidal particles elucidated that the formation of ellipsoidal hematite particles is attributed to the adsorption of Pluronics on the surfaces of PN and growing hematite particles.     

A comparison of the swelling behaviour of copolymer and interpenetrating network microgel particles

 A comparison of the swelling behaviour of two types of hydrogel particles, namely, random poly[(acrylic acid)-co-(acrylamide)] [P(AAc-co-AAm)] particles and PAAc/PAAm interpenetrating network (IPN) particles, has been made using temperature and pH as the triggers. Both types of particles were synthesised by inverse microemulsion polymerisation. The conversion yield of AAc was found to be around 60 wt% due to the partition of this monomer between the aqueous and organic phases. The AAc content was thus lower in the final particles than in the initial composition. Both types of hydrogel particle exhibit an upper critical solution temperature associated with the breakage of the polymer–polymer hydrogen bonds. The maximum swelling ratio occurred in both cases at approximately equimolar AAc and AAm content of the particles. A sharper swelling transition was observed for the PAAc/PAAm IPN particles. This is because of the co-operative nature of the interactions between the PAAc and PAAm chains, the so-called “zipper effect”. A very much higher swelling ratio was obtained using pH as the trigger compared to using temperature. This difference in behaviour is related to the relative strengths of the forces involved in the particle swelling. Electrostatic repulsion forces, associated with the AAc dissociation with increasing pH, are much stronger than the hydrogen bonds. Received: 18 August 1999/Accepted: 28 August 1999     

Preparation and characterization of pseudocubic hematite particles by utilizing polyethylene amine nonionic surfactants in forced hydrolysis reaction

The shape and porosity of hematite particles, produced from a forced hydrolysis reaction of acidic FeCl₃ solution, were controlled by using polyethylene amine nonionic surfactants (Surfonamine®; 0～10 wt.%). Surfonamine® possesses a nominal formula of CH₃-(PEO) _x -(PPO) _y -NH₂. Surfonamine with the highest total amine content (PEO contents were over 76 mol%, L-100) gave spherical particles, but those with lower total amine contents (L-200, L-207 and L-300) produced pseudocubic hematite particles. The pH value of the system with 10 wt.% of L-100 rose up to 8.49. With this pH rise, the diameter of the spherical particles was dramatically decreased. This fast particle formation was explained by the aggregation of very fine 6-line ferrihydrite particles produced at their high pH conditions. The uniformity of pseudocubic hematite particles produced with L-200, L-207 and L-300 were improved by increasing their concentrations. Since the pH values of these systems before aging were controlled between 2.03 and 2.35, it was presumed that the Surfonamine molecules acts as a buffer agent and attained pseudocubic particles. From the calculation of crystallite size, all the pseudocubic hematite particles were regarded as a polycrystal as well as the large spherical hematite particles produced without Surfonamine (control system). This polycrystallinity of the particles provided evidence that the particles are grown by aggregation of polynuclear (PN) primary particles. Not only the morphology but also the pore size of hematite particles was controlled from nonporous to microporous by using Surfonamines. The N₂ adsorption experiment and t-plot curve analysis revealed that the pseudocubic hematite particles have uniform micropores. The XRD, transmission electron microscope, inductively coupled plasma atomic emission spectroscopy and total organic carbon analysis measurements employed on the systems produced for pseudocubic particles elucidated that the pseudocubic crystal habit was formed by the specific adsorption of chloride ions and/or chloroferric complexes to the {012} faces, restraining the growth process through stacking of ultrafine PN particles in the direction of normal to the {012} faces but strictly restricting the growth and mutual fusion of PN ones. The uniform micropores could be produced between the PN particles. The uniform pseudocubic particles were found to be an effective photocatalytic material than the spherical particles due to their large size with uniform flat crystal faces.     

Study on the hydrothermal reaction of FeCl<Subscript>3</Subscript> solution in the presence of poly(vinyl alcohol)

A 0.5 dm³ aqueous solution of 0.1 M FeCl₃ dissolving 1 wt% poly(vinyl alcohol) (PVA) was treated hydrothermally in a stainless steel autoclave at various temperatures (T _h=110–200 °C). Highly ordered red corpuscle-like hematite particles around 2 m in diameter were produced after aging the solution at T _h=110 °C for 7 days, though large numbers of spherical PVA microgels around 2–4 m in diameter were produced together with the red corpuscle-like particles at T _h120 °C. The number of red corpuscle-like hematite particles decreased but that of spherical PVA microgels increased with increasing T _h, leading to the proposal that the method carried out in the present study will become a new synthetic method of polymer microgels. The ferric ions acted as a cross-linking agent to make PVA insoluble in water. The red corpuscle-like hematite particles produced at T _h=110 °C had high specific surface areas and showed high mesoporosity. The mesoporosity appeared to be more pronounced after evacuating the particles above 300 °C. The diameter of the mesopores after evacuation above 300 °C ranged from 2 to 20 nm, with a maximum at around 5–6 nm. The H₂O and N₂ adsorption experiments revealed that there are no ultramicropores in the particles. The H₂O and CCl₄ adsorption experiments further disclosed that the surface hydrophobicity of the particles is low even though PVA molecules remain after evacuation of the particles at 100–400 °C. Furthermore, the micropores produced after evacuation of the particles at 400 °C exhibited a high size restriction effect, i.e., the micropores produced were accessible to H₂O (diameter 0.253 nm) and N₂ (diameter 0.318 nm) molecules but not to CCl₄ (diameter 0.514 nm).     

Superior chemical–mechanical polishing performance of silica slurries made of surface-active siloxane/acrylic polymers

Two new anionic polymers have been synthesized by opening the epoxide ring attached with polysiloxane (SHS) and polyacrylic (CHS) backbones with a comparable weight-average molecular weight range. The colloidal stability of the experimental silica slurries made of these polymers has been investigated and their performance in the chemical–mechanical polishing (CMP) has been studied. A nonionic polysiloxane copolymer (SHE) was also used as a cosurfactant. It was observed from surface tension and fluorescence studies that all these polymers transfer to the air–water interface before forming any aggregates and the ease of forming the aggregates is in the order CHS–SHE (1:1 blend) ≈ SHS–SHE (1:1 blend)>SHE>SHS>CHS. The apparent viscosity data and the scanning electron microscopy micrographs of the silica slurries indicate that all the polymers provide good colloidal stability over a wide range of concentrations. The superior CMP performance over commercial slurry is reported and the order of performance due to the presence of these polymers was also determined and is correlated with the dynamic contact-angle values. The results were interpreted in view of the hydrophilicity of the copolymers and their surface wetting ability. Received: 12 December 2000 Accepted: 5 July 2001     

Kinetics study on the dissolution of UO<Subscript>2</Subscript> particles by microwave and conventional heating in 4 mol/L nitric acid

The dissolution of UO₂ particles in 4 mol·L⁻¹ nitric acid medium at temperatures of 90–110°C by microwave heating and conventional heating has been investigated, respectively. It is found that the dissolution ratios of UO₂ particles by microwave heating were 10%–40% higher than that by conventional heating. Kinetics research shows that the dissolution of UO₂ particles in 4 mol·L⁻¹ nitric acid is controlled by the diffusion control model for microwave heating and by the surface reaction control model for conventional heating. The diffusion control model for the dissolution of UO₂ particles by microwave heating could be explained by the diffuseness on the surface of UO₂ particles.     

Size effect of silica nanoparticles on thermal decomposition of PMMA

The size effect of silica nanoparticles (SiO₂) on thermal decomposition of poly(methylmethacrylate) (PMMA) was investigated by the controlled rate thermogravimetry. Thermal degradation temperature of PMMA–SiO₂ composites depended on both fraction and size of SiO₂, the thermal degradation temperature of 23 nm (diameter) SiO₂–PMMA (6.1 wt%) was 13.5 °C higher than that of PMMA. The thermal stabilities of 17 nm SiO₂–PMMA (3.2 wt%) and 13 nm SiO₂–PMMA (4.8 wt%) were 21 and 23 °C, respectively, higher than that of PMMA without SiO₂. The degree of degradation improvement was increased linearly with the surface area of SiO₂. The number of surface hydroxyl group in unit volume of SiO₂ particle increased with increasing the specific surface area of SiO₂, and the interaction between hydroxide group of SiO₂ and carbonyl group of PMMA had an important role to improve the thermal stability of PMMA.     

Cobalt nanoparticles in block copolymer micelles: Preparation and properties

 The preparation and properties of Co nanoparticles in polystyrene(PS)-poly-4-vinyl-py-ridine(PVP) micelles were studied. Elementary Co was generated by two methods: (i) by reduction of micelles loaded with CoCl₂, and (ii) by thermal decomposition of Co₂(CO)₈ in micel-lar solutions of such block copolymers. Co particles formed by both processes are effectively stabilized by the block copolymer matrix and do not aggregate. For CoCl₂ as a Co-source, the formed particles have a size less than 1 nm. Thermal treatment of such dried polymers at 200 ^°C for 2 h leads to spherical particles of 3–5 nm in size. The polymeric hybrid materials prepared in this way display remarkably high values of magnetization at rather low Co contents in the polymer, i.e., we obtain a tenfold increase of the specific magnetization density. Co₂(CO)₈ as a Co source, results in a more complex behavior. Co₂(CO)₈ dissolves in the solvent as well as in the micelle core where it is converted to an cationic–anionic complex involving the 4-VP units. The shape and size of the Co nanoparticles formed by thermolysis can be controlled by the balance of 4-VP/Co and can be varied from spherical particles in the limit of lower Co loads being mainly attached to the micelle core to a star-like and cubic morphology in case of excess of Co₂(CO)₈. Both superparamagnetic and ferromagnetic materials can be prepared. For ferromagnetic samples coercive force varies from 250 to 475 Oe depending on Co content and polymer sample. Received : 27 September 1996 Accepted: 22 November 1996     

Morphology and size-controlled synthesis of silver nanoparticles in aqueous surfactant polymer solutions

We have employed a number of reducing and capping agents to obtain Ag(0) metallic nanoparticles of various sizes and morphologies. The size and morphology were tuned by selecting reducing and capping agents. Spherical particles of 15 and 43 nm diameter were obtained when 1 wt% aqueous starch solution of AgNO₃ precursor salt was reduced by d(+)-glucose and NaOH, respectively, on heating at 70 °C for 30 min. Smaller size particles obtained in the case of d(+)-glucose reduction has been attributed to the slow reduction rate by mild reducing agent d(+)-glucose compared to strong NaOH. Conducting the reduction at ambient temperature of silver salt in liquid crystalline pluronic P123 and L64 also gave spherical particles of 8 and 24 nm, respectively, without the addition of any separate reducing agent. NaOH reduction of salt in ethylene glycol (11 g)/polyvinyl pyrolidone (PVP; 0.053 g) mixture produced large self-assembled cubes of 520 nm when smaller (26–53 nm) star-shaped sharp-edged structures formed initially aggregated on heating the preparation at 190 °C for 1 h. Increasing the amount of PVP (0.5 g) in ethylene glycol (11 g) and heating at 70 °C for 30 min yielded a mixture of spherical and non-spherical (cubes, hexagons, pentagons, and triangle) particles without the addition of an extra reducing agent. Addition of 5 wt% PVP to 1 wt% aqueous starched solution resulted in the formation of a mixture of spherical and anisotropic structures when solution heated at 70 °C for 1 h. Homogeneous smaller sized (29 nm) cubes were synthesized by NaOH reduction of AgNO₃ in 12.5 wt% of water-soluble polymer poly(methyl vinyl ether) at ambient temperature in 30 min reaction time.     

Control on the porosity of disk-like hematite particles prepared from a forced hydrolysis reaction using polyvinyl alcohol

The effects of polyvinyl alcohol (PVA) molecules on the porosity of disk-like hematite particles produced from the forced hydrolysis reaction using two kinds of PVA molecules with a well-defined molecular weight and a high degree of saponification (PVA-105 and PVA-124) were investigated. It is evident from TEM and field-emission scanning electron microscope (FE-SEM) measurements that a fraction of particles lost their spherical habit and acquired a disk-like shape by the addition of small amounts of both PVA molecules, though no difference in the particle size between the two PVA systems was observed. FE-SEM images of the particles revealed that the disk-like hematite particles are made up of small cluster particles with a diameter of approx. 5–10 nm. The disk-like particles produced a rather lower concentration for PVA-124 with a higher molecular weight than that for PVA-105 with a lower molecular weight. This fact was due to the large number of hydroxy groups in PVA-124 molecules than in PVA-105; hydroxy groups act as adsorption sites onto polynuclear (PN) primary particles and cause pronounced effects on the formation and structure of particles during the aggregation of PN particles. It was clarified from N₂ adsorption measurements at 77 K that the porosity of the hematite particles can be controlled from microporous to mesoporous by changing the concentrations of PVA-105 and PVA-124, as was classified into three groups, i.e., groups 1, 2, and 3. The control particles produced without PVA molecules, classified into group 1, showed type IV adsorption isotherms, and only the voids produced between spherical particles were detected as mesopores. On the other hand, the particles produced with small amounts of PVA produced micropores as classified in group 2. In this group, the particles produced uniform micropores after being outgassed at 100–200 °C. The hematite particles produced with high concentrations of PVAs were classified into group 3. In this group, the particles after being outgassed at lower temperature produced micropores with diameters between 0.6 and 2.0 nm, though the micropores in the particles changed to mesopores after outgassing at 300 °C. This mesopore formation was attributed to the elimination of the PVA-adsorbed layer by evacuation at 300 °C, i.e., the large voids residing in the disk-like hematite particles make the particles mesoporous. This mesopore formation was further confirmed by adsorption experiments of C₆H₆(benzene) and CCl₄ molecules at 298 K.     

Effects of amino acids on the formation of hematite particles in a forced hydrolysis reaction

The influence of amino acids on the formation of hematite particles from a forced hydrolysis reaction of acidic FeCl3 solution was examined. The spherical particles were produced on the systems with L-phenylalanine (L-Phe), L-serine (L-Ser) and L-alanine (L-Ala), though L-glutamine (L-Gln) and L-glutamic acid (L-Glu) gave ellipsoidal hematite particles. This morphological change in hematite particles is consistent with the order of stability constant of amino acids against to Fe3+ ions (K). The hematite particles produced with L-Glu, L-Gln and L-Ser were highly porous because they are formed by aggregation of cluster particles. These particles exhibited microporous behavior by outgassing the particles below 200 degrees C while they changed to mesoporous after treating above 300 degrees C by elimination of amino acids molecules remained between the cluster particles within the hematite particles. The hematite particles strongly depended on the nature of amino acids such as alternation of solution pH and adsorption affinity to beta-FeOOH and/or polynuclear primary (PN) particles. The systems on L-Ala and L-Phe, showing very rapid phase transformation from beta-FeOOH to hematite, exhibited the Ostwald ripening. A rotational particle preparation procedure suggested that the morphology of hematite particle is governed by the mode and strength of amino acid adsorption onto beta-FeOOH and/or PN particles.     

Influence of Amines on Formation and Texture of Uniform Hematite Particles

The structure and properties of hematite particles obtained by hydrolysis of ferric chloride solution doped with various kinds of amines were examined by TEM, XRD, TG-DTA, N₂and H₂O adsorption, and zeta potential measurements. The shape of precipitates was concentration dependent; they changed from large spheres (diameter: ca. 820 nm) to cubes (edge length: ca. 400 nm) via double-spheres (long axis length: ca. 600 nm) with increasing monoamine concentrations. This effect was enhanced by increasing their pK_avalues. Much pronounced effects of di- and triamines on the particle formation were observed; cubic and double-spherical particles were obtained at a much lower concentration of di- and triamines and small spherical (diameter: ca. 100 nm) and diamond-like (long axis length: ca. 100 nm) particles were further produced at higher concentration. It was suggested that the acceleration of the rate of phase transformation from β-FeOOH to hematite induced by amines plays an important role for producing fairly uniform hematite particles with different shape and size. The hematite particles produced with amines contained small amounts of OH⁻ions in the lattice but were confirmed to be nearly single crystal.     

Effect of humic acid on the sorption of technetium on hematite colloids using <Superscript>95m</Superscript>Tc and <Superscript>96</Superscript>Tc as tracers

Sorption of technetium on hematite colloids, at varying pH (3–10), has been studied in absence and presence of humic acid using ^95mTc-⁹⁶Tc radiotracers. Technetium was found to be weakly sorbed on hematite at lower pH (<5) values, while no sorption was observed at higher pH values. Humic acid was found to have no effect on the sorption of technetium on hematite under aerobic conditions, while at lower pH values small reduction was observed which was attributed to the reduced zeta potential of the hematite colloids owing to the strong sorption of humic acid.     

Effect of tetraethoxysilane pretreatment on synthesis of colloidal particles of amorphous silicon dioxide

The effect of the time passed after tetraethoxysilane treatment with ammonia on the diameter of particles produced by tetraethoxysilane hydrolysis in alcohol-water-ammonia media is studied. The regulation the time passed after of tetraethoxysilane treatment results in the synthesis of submicron monodisperse spherical silica particles with diameters differing by a factor of two. The difference is explained by the formation of SiO₂ particles with sizes of 10–100 nm in tetraethoxysilane during 10–30 h after treatment with ammonia. These particles enhance the concentration of nucleation centers in a reaction mixture, thus decreasing the final size of monodisperse silica spheres. Opal films with a high structural perfection and pronounced photonic crystal properties are grown based on the obtained monodisperse SiO₂ particles.     

Effect of laponite clay particles on thermal and rheological properties of Pluronic triblock copolymer

The high concentration 17 wt% triblock copolymer poly(ethylene oxide)₁₀₀–poly(propylene oxide)₆₅–poly(ethylene oxide)₁₀₀ Pluronic F127 aqueous solutions with the addition of laponite is investigated as a novel temperature-sensitive hydrogel system. The critical micelle temperature (cmt) and the sol-to-gel transition were characterized by rheological experiments and differential scanning calorimetry. Experimental results showed that laponite particles have no significant influence on the cmt. On the other hand, viscoelastic measurements have highlighted an increase of the sol-to-gel transition temperature for mixtures with 2 and 3 wt% of laponite particles. This additive can be used to adjust the gelation temperature close to physiological temperature in medical applications.     

Structure and spectral-optical characteristics of Se,Se/CdS,and Se/Cd<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>S nanoparticles,stabilized in polymer-containing media

A method was proposed for the production of colloidal nanoparticles of selenium stabilized by polymers and surfactants, and their structural and optical characteristics were studied. It was shown that during the deposition of CdS and Cd_0.5Zn_0.5S on the surface of the Se nanoparticles followed by dissolution of the selenium with sodium sulfite it is possible to obtain network “nanoframeworks” with size 30–50 nm, formed by CdS or Cd_0.5Zn_0.5S particles measuring 3–5 nm. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 24–29, January–February, 2007.     

In vitro drug release from silicone rubber–polyacrylamide composite

Composite materials containing drugs were prepared from silicone rubber and hydrogel. Cross linked polyacrylamide (PAAm) hydrogel particles were incorporated into a silicone rubber to enhance the hydrophilicity and drug release capacity of silicone rubber as a matrix. Progesterone and Thymol Blue were used as a hydrophobic and hydrophilic drug model, respectively. Different amounts of polyacrylamide (PAAm) were mixed with the drugs and uncured silicone rubber at room temperature. The composite matrices were formed using a compression molding press and cured by thermal and γ-irradiation curing methods. In vitro drug release behavior of composites and their physical and mechanical properties were investigated. The results indicated that the hydrophilic character of silicone rubber was more pronounced with increasing the amount of PAAm. Also, a significant effect on the drug release profiles was observed. The γ-irradiation curing method improved mechanical properties of composites and affected the drug release profiles. It was found that the amounts of released progesterone from γ-irradiated samples increased in comparison with the thermally cross linked composite since released Thymol Blue was reduced.     

Estimation of polydispersity in polymers and colloids by field-flow fractionaion

Various methodologies of sedimentation, thermal, and steric field-flow fractionation for the estimation of the polydispersity in polymers and colloids are presented. These are based either on retention and/or on zone-spreading data. The reference materials used are nearly monodisperse and polydisperse submicron polystyrene and PVC latex beads, nearly monodisperse spherical particles of hematite, and polydisperse irregular particles of strengite (FePO₄·2H₂O) and PS polymers of various molecular weights. The results found are compared with those determined by other techniques or given by the manufacturers.     

Photodegradation of humic acid using spherical activated carbon contained Zn in a fluidized bed system

In this study, a strong acid ion-exchange resin, as the starting material of spherical activated carbon contained Zn (Zn-SPAC), was treated by 0.1 N zinc solution. Ion-exchange treatment was performed from one to three times for controlling the zinc content. The ion-exchanged resins were activated under N₂/H₂O vapor atmosphere at 900°C for 0.5 h, followed by carbonization treatment at 700°C under N₂ atmosphere. The Zn-SPAC samples were measured for their physicochemical characteristics, such as X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) images, electron probe micro analyzer (EPMA) images, energy dispersive X-ray spectroscopy (EDXS), Brunauer–Emmett–Teller (BET) specific surface area, strength, and zinc content. Also, the samples were used in order to measure photochemical activities, such as the removal efficiency of humic acid (HA) in a fluidized batch reactor. The XRD patterns appeared as the ZnS type. The Zn-SPAC had a large BET specific surface area and their shape was spherical, with a diameter of about 350–400 μm. When the Zn-SPAC was dosed in a fluidized bed reactor with UV light, the HA removal efficiency increased by up to 60%. On the other hand, the HA removal efficiency by only UV-C (λ _max = 254 nm) irradiation was very low, about 15%. Therefore, we infer that Zn-SPAC has good photochemical activity and presented the possibility of being a useful photocatalyst for water purification.