Effect of PAA-g-MPEO Comb Polymer on TiO2 Suspensions

A comb PAA-g-MPEO was prepared. The PAA-g-MPEO underwent two thermal degradation steps. First, the decarboxylation and the dehydration of the carboxyl in the PAA backbone took place in the range of 204–313°C; the weight loss in the range of 313–450°C was from decomposition of MPEO chains and the survivor of the decomposed PAA backbone. By adding comb PAA-g-MPEO as disperser to TiO₂ suspensions, TiO₂/PAA-g-MPEO suspensions were prepared. The PAA-g-MPEO was adsorbed onto the surfaces of the TiO₂ particles, and the zeta potential of TiO₂/PAA-g-MPEO suspensions was higher than that of TiO₂ suspensions. Compared with that of TiO₂ suspensions, the viscosity of TiO₂/PAA-g-MPEO suspensions decreased, and the viscosity further decreased with increasing PAA-g-MPEO content. After adding PAA-g-MPEO, the size distribution of the TiO₂ particles in the suspensions became narrow and the average diameter of the TiO₂ particles decreased due to electrostatic repulsions and the steric hindrances of the PAA-g-MPEO.     

Cross-Linked Poly(acrylic acid) Microgels from Precipitation Polymerization

Cross-linked poly(acrylic acid) microgels were prepared via thermally initiated free-radical precipitation polymerization in a binary organic solvent. N,N′-Methylenebisacrylamide (MBA) and 2,2′-azobisisobutyronitrile were used as cross-linker and initiator, respectively. The effect of (MAB) concentration on different features of sample (i.e., spectral characteristics, glass transition temperature, equilibrium swelling, gel content and rheological properties) was investigated. The Flory-Rehner equation and rubber elasticity theory were used to discuss the network structure of polymer. Apparent and rotational viscosities were used to determine the optimal cross-linker concentration. The sample maximum with value of viscosity was obtained using 1.6 mmol/L of the cross-linker. In addition the m and n parameter of Ostwald equation were investigated as well.     

Electrokinetic and Rheological Properties of Aqueous TiN Suspensions with Ammonium Salt of Poly(methacrylic acid)

The study illustrates how rheology and electrokinetics can be utilized in the investigation and optimization of the properties of ceramic suspensions. Zeta potential studies show that the isoelectric point of TiN particulates is at pH=4, and for the pH range used, PMAA–NH₄ addition results in a more negative zeta potential value. The rheological behavior of titanium nitride in the presence of PMAA–NH₄ is strongly dependent on pH and three rheological types have been defined.     

Poly(3-Octylthiophene) and Poly(3-Octylthiophene)/TiO2-Coated on Al1050: Electrosynthesis,Characterization and Its Corrosion Protection Ability in NaCl Solution

In this study, 3-octylthiophene (3OT) and its nanocomposites with TiO₂(3OT/TiO₂) were electrochemically synthesized in different initial monomer concentrations (50, 75, 100, and 150 mM) in 0.1 M tetraethylammonium tetrafluoroborate (TEABF₄)/acetonitrile (CH₃CN) on a glassy carbon electrode (GCE). The best modified electrodes, which were taken from the optimum conditions of redox behaviors, were also electropolymerized in 0.5 M oxalic acid/acetonitrile (CH₃CN) solution on Al1050 electrode. The modified Al1050 electrodes were characterized by optical microscope, FTIR-ATR, SEM-EDX, and EIS. The optimum conditions of the electrocoated P(3OT)/Al1050 and P(3OT)/TiO₂ nanocomposites on Al1050 electrode were investigated for corrosion performances against 3.5% NaCl solution. The corrosion tests were performed by EIS and Tafel extrapolation plots together with the equivalent circuit model of R_s(Q_c(R_c(Q_pR_ct))). P(3OT)/TiO₂ nanocomposite films showed higher protection efficiency (PE = 89%) than P(3OT) films (PE = 81%). The P(3OT)/TiO₂ nanocomposite films coated on Al1050 electrodes may be used in industrial applications of corrosion protection against salt water.     

Salt-, pH- and temperature-responsive semi-interpenetrating polymer network hydrogel based on poly(aspartic acid) and poly(acrylic acid)

In this study, a novel salt-, pH- and temperature-responsive semi-interpenetrating network (semi-IPN) hydrogel, composed of poly(aspartic acid) (PAsp) and poly(acrylic acid) (PAAc), was prepared. PAsp/PAAc semi-IPN hydrogel being ionic in nature, the swelling behavior was significantly influenced by various swelling medium. The structure of the triply responsive hydrogel was studied by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and the salt-, temperature- and pH-sensitivities were investigated through measuring equilibrium swelling ratios in various environmental solutions. The results indicate that there is a structure of polyelectrolyte complex in the hydrogel, and that the responsive behaviors of this hydrogel to alternating changes in inorganic salt (different physiological bio-fluids), pH and temperature are improved because of the incorporation of PAsp. In addition, during the repeatable swelling and shrinkage period, the semi-IPN hydrogel shows suitable mechanical strength. The salt-, pH- and temperature-responsive hydrogel will have wider applications in biomedical areas.     

Supercritical CO2-assisted synthesis of poly(acrylic acid)/nylon6 and polystyrene/nylon6 blends

Poly(acrylic acid)/nylon6 and polystyrene/nylon6 blends were prepared using supercritical CO₂ as substrate-swelling agent and monomer/initiator carrier. Both supercritical CO₂/nylon6 binary system and SC CO₂/monomer/nylon6 ternary system were studied. Virgin nylon6 and synthesized blends were characterized through differential scanning calorimetry, infrared spectroscopy, and polarizing microscopy. Supercritical CO₂-induced crystallization was found in modified nylon6.     

Mechanism of degradation of nitrilotriacetic acid by heterogeneous photocatalysis over TiO2 and platinized TiO2

TiO₂-heterogeneous photocatalysis of nitrilotriacetic acid (NTA) at pH 2.5 was studied to establish the kinetic regime and the reaction mechanism. Pure Degussa P-25 and Hombikat UV100 commercial samples were compared. A Langmuirian behavior was observed over P-25. Platinization of the Hombikat sample (0.5 wt.%) caused an important increase on the photocatalytic rate with a change in the kinetics from zero order in the pure precursors to first order in the platinized sample. The nature of the intermediates and their evolution with time were compared on all systems. Glycine, iminodiacetic and oxamic acids have been identified in different proportions, together with ammonium and glycolic acid, depending on the catalyst used. The rapid depletion of NTA was not accompanied by a corresponding total organic carbon (TOC) reduction, but 84% of TOC decrease was obtained on P25 after 24 h, a very reasonable result for refractory compounds. A detailed mechanism is proposed for the photocatalytic reaction, suggested to be the same over the three catalysts here tested.     

Electrochemical Polymerization of Thiophene and Poly(3-hexyl)thiophene,Nanocomposites with TiO2, and Corrosion Protection Behaviors

Thiophene, 3-hexylthiophene, and their nanocomposites with TiO₂ were electropolymerized on Al1050 electrode by chronoamperometric technique. Different concentrations of thiophene and 3-hexylthiophene homopolymers and their nanocomposites with TiO₂ (2% in total content) were characterized by attenuated total reflection Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersion X-ray analysis, and electrochemical impedance spectroscopy. The anticorrosion tests for homopolymers and nanocomposite films were examined on Al1050 in 3.5% NaCl solution. Poly(3-hexylthiophene)/TiO₂ nanocomposite films gave the highest protection efficiency of 98% because the amount of defects was much lower than that for the poly(3-hexylthiophene), polythiophene, and polythiophene/TiO₂ films.     

Ultra-fine polyelectrolyte fibers from electrospinning of poly(acrylic acid)

Ultra-fine polyelectrolyte fibers have been generated from electrospinning of poly(acrylic acid) in aqueous and DMF solutions. The fiber diameters ranged from 80 to 500 nm and increased with increasing solution concentrations and electrospinning voltages. The fibers generated from the aqueous solutions were more homogeneous in sizes, especially when NaCl or NaOH was added. Higher voltages in electrospinning of the aqueous solutions also resulted in fibers with larger heat capacity in the glass transition region, and higher dehydration temperatures. These polyelectrolyte fibers could be rendered water-insoluble by incorporating β-cyclodextrin (at 20 wt% of PAA) in the aqueous solution, then heat-induced crosslinking was performed at 140 °C for 20 min. The resulting hydrogel fibers showed strongly pH-responsive swelling behaviors.     

氧化铁-水悬浮液的流变性研究

应用DV-Ⅲ+型可编程流变仪测定了三氧化二铁-水悬浮液的流变特性。考察因素包括颗粒浓度、pH值以及分散剂用量。结果表明,悬浮液在测定范围内表现出宾汉流体的特征。表观粘度随颗粒浓度的增大显著增加,其模型可用本文提出的三阶多项式模型表示。悬浮液的表观粘度受pH值的影响,pH在等电点处时,溶液的流动性最差;pH低于等电点时的粘度比pH高于等电点时要明显降低。这些现象可用颗粒的空间结构化理论及凝聚原理予以解释。改善悬浮液流动性的分散剂添加量存在最佳点。     

Poly(acrylic acid)-grafted magnetic nanoparticle for conjugation with folic acid

Poly(acrylic acid) (poly(AA))-grafted magnetite nanoparticles (MNPs) prepared via surface-initiated atom transfer radical polymerization (ATRP) of t-butyl acrylate, followed by acid-catalyzed deprotection of t-butyl groups, is herein presented. In addition to serve as both steric and electrostatic stabilizers, poly(AA) grafted on MNP surface also served as a platform for conjugating folic acid, a cancer cell targeting agent. Fourier transform infrared spectroscopy (FTIR) was used to monitor the reaction progress in each step of the syntheses. The particle size was 8 nm in diameter without significant aggregation during the preparation process. Photocorrelation spectroscopy (PCS) indicated that, as increasing pH of the dispersions, their hydrodynamic diameter was decreased and negatively charge surface was obtained. According to thermogravimetric analysis (TGA), up to 14 wt% of folic acid (about 400 molecules of folic acid per particle) was bound to the surface-modified MNPs. This novel nanocomplex is hypothetically viable to efficiently graft other affinity molecules on their surfaces and thus might be suitable for use as an efficient drug delivery vehicle particularly for cancer treatment.     

Swelling and morphological properties of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) hydrogels in solution with high salt concentration

Understanding the swelling properties of hydrogels and how they affect the hydrogel's morphology is of fundamental importance in the development of hydrogel-based artificial muscles, bio-actuators, sensors and other devices. In this paper, the swelling behavior of PVA-PAA hydrogel films in saline water and in buffer solutions of different pH values was investigated. It was observed that the swelling factor of the hydrogel decreases when the ionic strength of the solvent solution increases. Scanning Electron Microscopy (SEM) revealed structures with different pore shapes and sizes depending on the type of solution used for hydration. In saline water, Energy Dispersive X-Ray (EDS) analysis indicated the formation of NaCl crystals within the polymeric network. Finally, the PVA-PAA hydrogel was used as an actuator to strain a fiber Bragg grating sensor, thus providing an indirect measurement of the pH value of the surrounding solution.     

Smart organic-inorganic nanohybrid stars based on star-shaped poly(acrylic acid) and functional silsesquioxane nanoparticles

pH- and salinity-responsive organic-inorganic nanohybrid stars based on poly(acrylic acid) (PAA) stars and N,N-di(2,3-dihydroxypropyl)3-aminopropylfunctional silsesquioxane nanoparticles are readily formed by mixing of aqueous solutions of the components. The interaction between stars of two different arm lengths, (PAA₁₀₀)₂₁, (PAA₂₀₀)₂₄, with water-soluble silsesquioxane nanoparticles is studied according to changes in pH and salt concentration. The original size of the stars is conserved during complexation according to dynamic light scattering (DLS) measurements and light scattering (LS) titration experiments, which exclude star-star aggregation or crosslinking during the interaction. The proposed interaction mechanism is based on hydrogen-bonding and Coulomb interactions. Cryogenic transmission electron microscopy measurements demonstrate the formation of nanohybrid stars. Small-angle neutron scattering experiments enable a quantitative determination of the fraction of bound nanoparticles and indicate an equilibrium between free and bound nanoparticles.     

Synthesis and stimuli-responsive properties of chitosan/poly(acrylic acid) hollow nanospheres

We report here a synthetic study on the formation process of hollow polymeric nanospheres based on a simple, core-template-free route, and the effects of polymerization concentration, shell cross-linking, pH, salt concentration and temperature on the size and stability of hollow polymeric nanospheres. The hollow structure of polymeric nanospheres is spontaneously formed by polymerization of acrylic acid monomers inside the chitosan–acrylic acid assemblies. It is found that (i) the hollow structure of nanospheres is stabilized by both physical cross-linking in the inner shell and chemical cross-linking in the outmost shell; (ii) the size of the hollow spheres can be adjusted over the range of 77–500 nm by controlling the concentration of chitosan–acrylic acid assemblies in the reaction system; (iii) the synthesized nanospheres are stimuli-responsive. The size of the hollow nanospheres can be manipulated by changing pH, salt concentration and temperature. Furthermore, with heating and cooling the variation in size of hollow nanospheres is completely reversible and reproducible; (iv) the surface of the hollow nanospheres obtained is chemically active, which provides the functional sites with chemical groups for subsequent chemical reactions at the surface.     

Photocatalytic decomposition of acetic acid on TiO2

During room‐temperature transient experiments, acetic acid decomposes photocatalytically on TiO₂ in an inert atmosphere by two parallel pathways. One pathway forms CO₂ and C₂H₆ in a 2:1 ratio, and H₂O forms with lattice oxygen that was extracted from the surface. The other pathway forms CO₂ and CH₄ in a 1:1 ratio. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Inorganic Filler on the Crystallization,Mechanical Properties and Rheological Behavior of Poly(trimethylene terephthalate)

Poly(trimethylene terephthalate) filled with nano-CaCO₃ and ultra-fine talc was prepared by melt blending using a co-rotating twin screw extruder. The effect of these two inorganic filler on the crystallization and melting behavior, mechanical properties and rheological behavior of PTT were characterized. The DSC results indicated that both nano-CaCO₃ and ultra-fine talc exhibited heterogeneous nucleation effect on the crystallization of PTT, and more significant nucleation effect were observed in PTT/nano-CaCO₃ composite due to the smaller size and better dispersion of nano-CaCO₃ in PTT matrix. Mechanical properties study suggested that the incorporation of nano-CaCO₃ and ultra-fine talc greatly improved the tensile and flexural properties of PTT. Ultra-fine talc tends to lower the impact properties, while nano-CaCO₃ tend to increase the impact strength of the PTT/nano-CaCO₃ composite. When 2 wt.% of nano-CaCO₃ was added, the impact strength increased by one time. Rheological behavior study indicated nano-CaCO₃ exhibited plasticization effect on PTT melt and decreased the viscosity of PTT, while ultra-fine talc increased the viscosity of PTT due to the hindrance of the layer structure of talc.     

壳聚糖/聚丙烯酸共聚物微球的制备及性能

以环己烷为油相,壳聚糖溶液为水相,运用反相乳液聚合法制得了具有pH敏感性的壳聚糖/聚丙烯酸共聚物微球。讨论了微球在pH=1～10缓冲溶液中的溶胀率变化,研究表明,微球在强酸性(pH≈1)和碱性(pH>7)条件下,溶胀率均在10倍以上;而在pH=2～6时溶胀较差,当pH=4时出现最低值,溶胀率低于1倍。光学显微镜所观察到的微球粒径均在40μm以内,且大小均匀。采用傅里叶红外光谱仪分析了不同配比样品特征峰的峰值和峰面积的变化。用722光栅分光光度计研究了共聚物微球包埋考马斯亮蓝的溶胀释放过程。     

Effects of Ammonium Chloride on the Rheological Properties and Sedimentation Behavior of Aqueous Silica Suspensions

The influence of ammonium chloride (NH₄Cl) on the rheological properties and sedimentation behavior of aqueous silica (SiO₂) suspensions of varying solids volume fraction (φ_s) was studied. SiO₂ suspensions with low NH₄Cl concentration (≤0.05 M , pH 5.2) exhibited Newtonian behavior and a constant settling velocity ( U ). The volume fraction dependence was well described by the Richardson–Zaki form, U = U ₀(1 −φ_s) ⁿ , where n = 4.63 and U ₀= 1.0419 × 10⁻⁵ cm/s. At higher NH₄Cl concentrations (0.07–2.0 M , pH 5.2), suspensions exhibited shear thinning and more complicated sedimentation behavior due to their aggregated nature. For all suspensions studied, however, the apparent suspension viscosity, characteristic cluster size, and initial settling velocity were greatest at ∼0.5 M NH₄Cl and exhibited a similar dependence on salt concentration. Above 0.5 M NH₄Cl, considerable restabilization was observed. This behavior cannot be explained by traditional DLVO theory.     

Rheology control by modulating hydrophobic and inclusion associations in modified poly(acrylic acid) solutions

The rheology of modified poly(acrylic acid) (PAA) solutions can be tuned by controlling the inclusion interactions between α-cyclodextrins and alkyl hydrophobes. We demonstrate three modes of control: (1) using free cyclodextrins (CD) to displace hydrophobe-hydrophobe association in hydrophobically modified poly(acrylic acid) (HMPAA) polymers—which reduces fluid viscosity, (2) using competitive inclusion interactions where stronger SDS:CD binding can be used to ‘unmask’ CD:hydropobe inclusion interactions—which increases viscosity, and (3) employing HMPAA inclusion interactions with CD groups grafted to PAA chains (CDPAA)—which produces higher viscosities than purely hydrophobic association systems at the same concentration. The inclusion association between alkyl side-group in HMPAA and CD, either free or grafted onto PAA, obeys a 1-to-1 stoichiometry at low polymer concentrations (<1 wt%). In contrast to purely hydrophobically associating polymers, the CD:hydrophobe interaction is only binary, and, therefore, these associated networks should be ideal model systems to test theoretical predictions for associative fluids.     

Temperature- and pH-sensitive membrane formed from blends of poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide) and poly(acrylic acid) microgels

Temperature- and pH-responsive membranes prepared from blends of poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide)(PVDF-g-PNIPAM) copolymer and poly(acrylic acid) (PAA) microgels in N,N-dimethylformamide (DMF) solution by phase inversion method. PAA microgels help PNIPAM chains largely enrich onto membrane surface. Furthermore, adding PAA microgels increases the porous size, porosity and hydrophilic property of the blend membrane. The membranes show temperature-sensitivity between 30 and 35 °C, and pH-sensitivity between pH 3 and 5 on permeating aqueous solutions. Meanwhile, the blend membranes keep good antifouling property even if one of the hydrophilic components becoming hydrophobic in response to temperature or pH stimuli, which is superior to single-sensitive PVDF membrane.