Polyacrylic Acid Solution Research Articles

Effects of Silicon Content in Silicon-Graphite Composite Anode on Capacity Degradation

Silicon, with its theoretical capacity of 4200 mAh g-1,[1] has been exploited as a capacity-booster for mature graphite anodes. However, silicon is prone to fast degradation due to significant volume expansion, which may undermine the intrinsic stability of the graphite, resulting in shorter cycle life. The trade-off between higher capacity and shorter cycle life is therefore worth optimizing. This study investigates the effects of silicon content on the cycling performance of silicon-graphite composite anodes. The composite electrodes were synthesized by mixing both materials at various weight ratios, along with carbon black and polyacrylic acid solution, and coated on a copper foil. A mixture of 1 M of LiPF6 in EC: DMC, 1:1, v/v, and Fluoroethylene carbonate (FEC) was used as the electrolyte. The samples consist of electrodes with silicon content from 8% to 40%. Galvanostatic test was done at various C-rates to determine the specific capacity at each cycle, and the correlation between the voltage and the capacity during the test was used to create differential capacitance curves. Electron microscopy and energy-dispersive X-ray spectroscopy were used to study morphology and to detect agglomeration of silicon particles. The results show that the initial capacity and the capacity retention of each sample indeed depend on the silicon content. As expected, higher silicon contents yield higher initial specific capacities but cause faster degradation. However, the trends do not continue beyond 32% of Si content. This suggests that there is a limit for silicon to enhance the initial specific capacity at a fixed C-rate. Differential capacitance curves show the gradual disappearance of silicon peaks, e.g., a peak at 0.45 V, which indicates that the primary cause of the capacity loss is the degradation of silicon material. Elemental analysis shows the high content of silicon content can promote particle agglomeration. Future tasks will include establishing the relationship between the silicon content and quantifying the amount of silicon agglomeration using X-ray spectroscopy. The results from this study can be used to assess an appropriate amount of silicon in anode material.

Preparation of cellulose-based wipes treated with antimicrobial and antiviral silver nanoparticles as novel effective high-performance coronavirus fighter

Coronaviruses (CoV) are a large family of viruses that cause illness ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS-CoV). We succeeded in preparing disinfectant cellulose-based wipes treated with antimicrobial and antiviral silver nanoparticles to be used for prevention of contamination and transmission of several pathogenic viruses and microbes to human in critical areas such as hospitals and healthcare centers especially coronavirus. In this work, the antimicrobial and antiviral activities of silver nanoparticles (AgNPs) prepared with four different techniques were investigated for the utilization as a disinfectant for cellulose-based wipes. These four methods are namely; 1) trisodium citrate with cotton yarn as a reducing agent, 2) preparing AgNP's using aqueous solution of PVA in the presence of glucose, 3) trisodium citrate with cotton fabric as a reducing agent, and 4) photochemical reaction of polyacrylic acid and silver nitrate solution. Polyester/viscose blended spunlace nonwoven fabrics as cellulose based fabrics were treated with the prepared silver nanoparticles to be used as surfaces disinfection wipes. The properties of the nonwoven fabrics were examined including thickness, tensile strength in dry and wet conditions in both machine direction (MD) and cross-machine direction (CMD), bursting strength, air permeability, water permeability and surface wettability. Characterization of the AgNPs was carried out in terms of UV-VIS spectroscopy, TEM, SEM, and Zeta potential analysis. The assessment of AgNPs active solutions for antimicrobial and antiviral activities was evaluated. The results obtained from the analyses of the AgNPs samples prepared with different techniques showed good uniformity and stability of the particles, as well uniform coating of the AgNPs on the fibers. Additionally, there is a significant effect of the AgNPs preparation method on their disinfectant performance that proved its effectiveness against coronavirus (MERS-CoV), S. aureus and B. subtilis as Gram-positive bacteria, E. coli and P. mirabilis as Gram-negative bacteria, A. niger and C. albicans fungi.

Technological Research of Zinc Extraction from Elazığ Simitsonite Ore

Acrodur, aqueous polyacrylic acid solution and dispersion, has been developed as an alternative wood adhesive to phenolic and urea formaldehyde resins. It has many environmental benefits over the conventional thermoset resins that include its non-corrosive nature and non-emission of carcinogenic gases. It has superior tolerance to moisture during composite fabrication and thus drying of the preforms may be minimised or even eliminated contrary to most resins used in natural fibre biocomposites. The aim of this study was to produce optimised hemp fibre reinforced Acrodur resin biocomposites using nonwoven hemp fibre mats by varying Acrodur solution to dispersion ratio, relative humidity, curing time and temperature. The optimised biocomposites gave the best combination of 26.4MPa-cm3/g specific tensile strength and 4.4GPa-cm3/g specific Young’s modulus with 0.94g/cm3density. Thermogravimetric analysis (TGA) and contact angle measurement showed similar thermal stability and increased hydrophobicity of the biocomposites than those of the fibres. From the water immersion test, the path of wicking of water moleculesinto the biocomposites was believed to be rather straight than tortuous and about 43.5% loss of tensile strength and 57.1% loss of Young’s modulus were observed upon 4-week water immersion of the biocomposites.

Oral management with polaprezinc solution reduces adverse events in haematopoietic stem cell transplantation patients

The aim of this study was to analyse the effects of gargling with and then swallowing PPAA (polaprezinc in polyacrylic acid solution), in addition to regular oral management, on patients with a haematopoietic neoplasm scheduled for haematopoietic stem cell transplantation (HSCT). A total of 120 patients scheduled for HSCT during the years 2006–2016 were recruited. Patient background, oral adverse events, the incidence and severity of systemic adverse events (sepsis/septic shock, acute graft-versus-host disease (GVHD) after transplantation), and outcomes (survival/death) were compared between groups treated with and without PPAA. The severities of oral adverse events (oral mucositis, oral pain, and dysgeusia) were significantly lower in patients treated with PPAA. There was no significant difference in the incidence of febrile neutropenia (P=0.622) or sepsis/septic shock (P=0.665) as systemic adverse events. The severity of allograft-induced acute graft-versus-host disease (GVHD) was significantly lower in the PPAA group (P=0.011). There was no significant difference in outcome between the two groups (P=0.285). Within the limitations of the study design, it may be concluded that oral management with PPAA reduces adverse events in HSCT. Oral management with concomitant use of PPAA decreased oral adverse events and reduced the systemic complication of GVHD.

Control of the phase formation process in solutions of anionic polyelectrolyte—cationic surfactant complexes in a microfluidic channel

The process of phase formation in solutions of polyacrylic acid and cetyltrimethylammonium bromide was studied in microfluidic channels with a characteristic size of 100–200 µm. The system of convection—diffusion—reaction equations was solved to develop an association model in polyelectrolyte—surfactant solutions in a microchannel with the laminar flow of the reactants. The phase formation conditions in the microchannel volume were considered. The recommendations for control of the phase behavior in the microchannel were proposed, as well as for the design and operation mode of microfluidic devices used for the synthesis of polymer—surfactant complexes and characterization of association in polyelectrolyte—surfactant solutions.

The role of salt ions and organic molecules in the self-assembled nanolayering

This study investigated effects of polyacrylic acid (PAA) on nanolayering self-assembly, and effects of salt ions on the formation of nanolayering after their chemical interaction with 10-methacryloyloxydecyl dihydrogen phosphate (MDP). ACP–MDP suspension was prepared by dispersing 0.01 g ACP nanoparticles in 4 mL of a 5 wt% MDP solution. Then a PAA solution (100 or 500 μg/mL) was mixed into ACP–MDP suspension. The reaction products were analyzed by transmission electron microscope (TEM). After one of the following metal chlorides (each 0.076 mM of CaCl2, BaCl2, AlCl3, FeCl2, FeCl3, MnCl2, CuCl2, ZnCl2, or MgCl2) was dispersed in a 4 mL MDP solution, they were further analyzed by X-ray diffraction (XRD) and TEM. ACP nanoparticles in the MDP solution could self-assemble into ACP–MDP nanolayering composites. The TEM images show that an amount of ACP nanoparticles were aggregated and fused together after the addition of PAA into ACP–MDP suspensions, while no nanolayering was found. The XRD data and TEM images reveal that nanolayering was self-assembled after the chemical interaction of MDP with some metal chlorides (CaCl2, BaCl2, AlCl3, FeCl2, FeCl3, MnCl2), but not with the others (ZnCl2, CuCl2, MgCl2). PAA could inhibit the self-assembly of nanolayering. Some salt ions play an important role in highly ordered, self-assembled nanostructure after their chemical interaction with MDP. The finding is helpful for functional materials fabrication.

Facile fabrication of nanocomposites by modified carbon black loading with magnetite nanoparticles for fast removal of cadmium ions

Magnetic nanomaterials have unique advantages in heavy metal ions absorption because of their large specific surface area and easy magnetic manipulation. Carbon nanotube or graphene loaded with magnetite nanoparticles (MNPs) have been utilized to fabricate absorbents with both high absorption capacity and fast magnetic capture. Herein, cheap commercial carbon black was used as a substitute for expensive carbon nanotube or graphene to fabricate nanocomposites (CB-MNP) by modified carbon black loaded with superparamagnetic MNPs. The fabrication process is accomplished by two steps. Carbon blacks (CB) were modified by nitric acid to produce a large number of carboxyl groups on the surface and make stable aqueous dispersion. Subsequently, CB-MNPs with high water stability and fast magnetic response were facilely prepared by iron precursors (the ratio of ferrous to ferric is 1:2) added into the above CB dispersion and tuned pH = 10, finally added polyacrylic acid solution under sonication. Modified CB and CB-MNPs were characterized by transmission electron microscope (TEM), dynamic laser scattering (DLS), thermogravimetric analysis and so on. Water stability and magnetic response can be controlled by changing the proportion of CB and iron precursor. As a proof-of-concept, CB-MNPs were used for absorption removal of cadmium ions. Excellent performance was demonstrated with the removal efficiency of 71.41% and removal capacity of 39.99 mg · g−1 at the initial concentration of Cd2+ as 5 × 10−5 mol · l−1. The effects of initial concentration of Cd2+, pH value and interfering anion ions were also investigated and the results indicate the potential application of CB-MNP in fast removal of heavy metal ions.

High strength, antifreeze, and moisturizing conductive hydrogel for human‐motion detection

Nowadays, high performance conductive hydrogels have become excellent materials for the design of smart devices, medical equipment, and flexible wearable devices. However, conductive hydrogels are often hindered by problems such as the poor mechanical property, difficulty in long-term use, and narrow operating temperature range. Thus, a high strength hydrogel that can be used in various temperature environment is desired. Here, conductive composite hydrogels were delicately designed and prepared via in-situ polymerization of conductive polymer PEDOT in Poly(vinyl alcohol) (PVA) aqueous solution and then soaking in polyacrylic acid (PAA) solution and glycerin in two stages. The resultant composite hydrogels exhibited good conductivity (~0.95 S/m), and high mechanical strength (~3.6 MPa). Especially, the hydrogels exhibited great strain-sensitive electric behavior as biosensors to monitor routine movement signals of the human body. Additionally, such composite hydrogel displayed excellent flexibility and responded well to multiple strain and subtle human motions in a low temperature (−25 °C) or after long periods in the air(168 h). Thus, the hydrogels have potential applications in various fields, such as human-computer interaction, intelligent bionic material, and wearable flexible devices.

Effect of secondary polymer on self‐precipitation of pH‐sensitive polymethylmethacrylate derivatives Eudragit E100 and Eudragit L100

Interpolyelectrolyte complexes or polyplexes can be seen as interesting alternatives in the purpose of active ingredients encapsulation. Working on polymethylmethacrylate derivatives with special focus on controlled oral drug delivery, the influence of charged polyelectrolytes (polyacrylic acid, polyethylenimine, and amino‐dextran) and noncharged ones (polyvinyl alcohol, dextran 40, and Pluronic F68) has been investigated on the precipitation of two pH‐sensitive Eudragit polymers, namely, L100 and E100. Moreover, the possibility of preparing polyplexes involving the two polymethylmethacrylate derivatives with different charged and noncharged secondary polyelectrolytes has been studied. The obtained dispersions have been characterized in terms of mean particle size, size distribution, zeta potential, and morphology. Direct precipitation of Eudragit L100 by medium acidification in a batch process and in the presence of polyethylenimine allowed the production of particles with a narrow size distribution. The mean size was around 200 nm. In this case, the zeta potential was found to be +45 mV at pH = 7 in 1mM aqueous NaCl solution, and the produced suspension was stable in time since no aggregation and sedimentation have been observed. A precipitation pH of 8.16 allows us to suggest the preparation of a polyplex based on Eudragit L100 and polyethylenimine. In contrary, polyvinyl alcohol has shown ability to induce an increase in particle mean size whereas other polyelectrolytes showed no significant effect. Moreover, it was observed that polyethylenimine and polyacrylic acid solutions were able to directly induce Eudragit E100 precipitation whereas amino‐dextran and noncharged polyelectrolytes showed no effect on its precipitation and on particle size distribution.

Polyacrylic acid based plasma fractionation for the production of albumin and IgG: Compatibility with existing commercial downstream processes.

Commercial fractionation of human plasma into immunoglobulin- and albumin-rich fractions is often initiated with sequential cold ethanol-based precipitation methods, which have changed little over the past 70 years. The required low temperature (-4 to -8°C) and high concentrations of ethanol 8-40%) necessitate large-scale fixed processing lines, and major capital investment and operating costs. The resulting fractions are then further purified by ethanol based precipitation or chromatographic procedures to obtain the purified final product. Aqueous polyacrylic acid (PAA) based precipitation, which readily interfaces with existing downstream processing, could offer advantages with respect to cost, safety, environmental impact, and flexibility. Sequential precipitation with 7%, 12%, and 20% (w/v) solutions of PAA 8000 in the presence of a kosmotropic salt (sodium citrate) gave fibrinogen-, immunoglobulin-, and albumin-rich fractions with 80-90% yield and 64%, 55%, and 82% purity, respectively. Further purification of the IgG-rich precipitate by caprylic acid precipitation and anion exchange chromatography, achieved a target purity of >99%. This was also achieved for the downstream processing of the albumin-rich precipitate using a two-step ion exchange chromatographic procedure. This work shows that PAA precipitation can be used in place of cold ethanol precipitation to generate crude IgG and albumin fractions which can be purified to final products of acceptable purity.

Nanocomposite-coated porous templates for engineered bone scaffolds: a parametric study of layer-by-layer assembly conditions

Using the layer-by-layer (LbL) assembly technique to deposit mechanically reinforcing coatings onto porous templates is a route for fabricating engineered bone scaffold materials with a combination of high porosity, strength, and stiffness. LbL assembly involves the sequential deposition of nano- to micro-scale multilayer coatings from aqueous solutions. Here, a design of experiments (DOE) approach was used to evaluate LbL assembly of polyethyleneimine (PEI), polyacrylic acid (PAA), and nanoclay coatings onto open-cell polyurethane foam templates. The thickness of the coatings, and the porosity, elastic modulus and collapse stress of coated foam templates were most strongly affected by the pH of PAA solutions, salt concentration, and interactions between these factors. The mechanical properties of coated foams correlated with the thickness of the coatings, but were also ascribed to changes in the coating properties due to the different assembly conditions. A DOE optimization aimed to balance the trade-off between higher mechanical properties but lower porosity of foam templates with increasing coating thickness. Micromechanical modeling predicted that deposition of 116 QLs would achieve mechanical properties of cancellous bone (>0.05 GPa stiffness and >2 MPa strength) at a suitable porosity of >70%. When capped with a final layer of PAA and cross-linked via thermal treatment, the PEI/PAA/PEI/nanoclay coatings exhibited good indirect cytotoxicity with mesenchymal stem cells. The ability of LbL assembly to deposit a wide range of functional constituents within multilayer-structured coatings makes the general strategy of templated LbL assembly a powerful route for fabricating engineered tissue scaffolds that can be applied onto various porous template materials to achieve a wide range of properties, pore structures, and multifunctionality.

Characteristic Assessment of the Polymeric Films Used for Hair Gel Products in Thailand

The market of hair gel products in Thailand steadily grows with the changing trend of fashion every year. The main component of the hair gel products is the fixative polymer, which plays a role in hair styling properties including stiffness and curl retention. Properties of the hair styling product depending on hair types and climates must be suitably improved for Thai hair. In this study, 10 %w/w gel solutions of polyacrylic acid, polyquaternium-86, polyvinylpyrrolidone (PVP), acrylates copolymer, and vinylpyrrolidone (VP) copolymers were cast as polymeric thin films. The film properties such as mechanical properties, wettability, and crystallinity were characterized afterwards. As a result, the highest puncture strength of 2.2 N/mm2 was found from PVP-K90 film (500-700 μm thick). Whereas, VP/vinyl acetate (VA) copolymer film was the most flexible with 42.5% elongation. For water contact angle analysis, it was noticed that VP copolymers had the angle of ~50o indicating the moderate wettability. The x-ray patterns of raw materials, polymeric films, and humidified films were varied especially for PVP-K30. Morphologies of the Thai hair samples coated with the fixative polymers were visualized through SEM. After storing coated hair samples in the humidified atmosphere (95±2% Relative humidity), acrylates copolymer, VP/Methacrylamide/Vinyl Imidazole copolymer, and VP/VA copolymer appeared the humidity resistance suitable for Thai hair styling gel.

A Facile Approach for Fabricating Microstructured Surface Based on Etched Template by Inkjet Printing Technology.

Microstructures are playing an important role in manufacturing functional devices, due to their unique properties, such as wettability or flexibility. Recently, various microstructured surfaces have been fabricated to realize functional applications. To achieve the applications, photolithography or printing technology is utilized to produce the microstructures. However, these methods require preparing templates or masks, which are usually complex and expensive. Herein, a facile approach for fabricating microstructured surfaces was studied based on etched template by inkjet printing technology. Precured polydimethylsiloxane substrate was etched by inkjet printing water-soluble polyacrylic acid solution. Then, the polydimethylsiloxane substrate was cured and rinsed, which could be directly used as template for fabricating microstructured surfaces. Surfaces with raised dots, lines, and squares, were facilely obtained using the etched templates by inkjet printing technology. Furthermore, controllable anisotropic wettability was exhibited on the raised line microstructured surface. This work provides a flexible and scalable way to fabricate various microstructured surfaces. It would bring about excellent performance, which could find numerous applications in optoelectronic devices, biological chips, microreactors, wearable products, and related fields.

Antibacterial Properties Enhancement of Layer-by-Layer Self-Assembled Nanofiltration Membranes.

Membrane technology is now being widely used in the field of water treatment for its unique advantages. Layer-by-layer (LbL) self-assembly technique is a convenient and versatile method of modified nanofiltration (NF) membranes fabrication, which can be used to control the thickness and the surface properties of membranes by chemical deposition of polyelectrolytes. Herein, a new kind of composite NF membrane with enhanced antibacterial properties was successfully fabricated through LbL self-assembly method, having polyether sulfone (PES) ultrafiltration (UF) membrane as support layer, N-[(2-hydroxy-3-trimethylammonium)propyl] chloride chitosan (HTCC) and polyacrylic acid (PAA) as active layer, and epichlorohydrin (ECH) as crosslinking reagent. Subsequently, nanosilver was finally loaded on the membrane surface by photoreduction technique. Our results revealed that the positively charged four semi-assembled membranes prepared using 5 g/L HTCC aqueous solution, 1 g/L PAA solution (pH = 6-8), and 0.5 g/L NaCl as supporting salt exhibited optimum performance. Atomic force microscopy and contact angle tests showed that the prepared membranes improved the surface roughness and hydrophilicity as compared to those of the polyether sulfone (PES) membranes. The retention test indicated that the (HTCC/PAA)4HTCC membranes exhibited highly-efficient removal of pharmaceuticals and personal care products in the order of Amlodipine > Atenolol > Carbamazepine > Ibuprofen. The X-ray Diffraction results confirmed the presence of nano-silver on the membrane surface. In addition, the prepared membranes exhibited excellent antibacterial activity, especially against gram-negative bacteria.

Microscopic and physicochemical studies of polymer-modified kaolinite suspensions

Sedimentation tests on kaolinite in biopolymers (xanthan gum, chitosan, polyacrylic acid and polyacrylamide) solutions were conducted and recorded with time-lapsed technique up to 35 days. Microscopic particle size, zeta potential, final volume and solid content were measured along the elevation of the graduated cylinder at the end of tests, and settling velocity and intensity calculated. Test results suggested that positive charged edges of kaolinite particles attached to negatively-charged xanthan gum (0.001 and 0.5 g/l) long chain via electrostatic force, exhibiting edge-to-edge (EE) fabric structure, and that charge neutralization was the primary interaction mechanism between kaolinite and either chitosan (0.05 and 5 g/l) or PAA(0.05 and 1 g/l),and that steric stabilization dominates the interaction between kaolinite and PAM molecules at 0.1 and 0.5 g/l PAM solutions.

Self-assembled MXene-based nanocomposites via layer-by-layer strategy for elevated adsorption capacities

The chemical modification and organized self-assembly of MXene-based nanocomposites demonstrate critical importance to a wide range of material applications. Herein, we have investigated the preparation of new hierarchical core-shell type MXene-based composite materials for high-efficient dye removal in wastewater treatment via layer-by-layer (LbL) strategy. From the carboxyl functionalization of the MXene material, the negative functional groups were obtained on the surface of the shell composite layer. Carboxyl functionalized MXene materials are immersed in polyimide and polyacrylic acid solution respectively, which leads to formation of shell structure on the surface of MXene layer. Alternating self-assembly processes in the solutions of the polyimide and polyacrylic acid polymers are investigated until the desired number of shell layers is fabricated around MXene layer structures. Finally, the core-shell nanocomposites were characterized by morphological and spectral techniques, demonstrating that the core-shell nanocomposites have more reaction sites and mesoporous structures. The as-obtained core-shell nanocomposites were evaluated with well adsorption capacities via three kinds of dyes. Thus the study of MXene based composites assembled by LbL provides a new choice for the application of MXene composite nanomaterials in wastewater treatment.

Influence of the PAA concentration on PAA/NH3 emulsion template method for synthesizing hollow silica nanoparticles

This paper describes the synthesis mechanism of the hollow silica nanoparticles (HSNPs) with various concentrated poly acrylic acid (PAA) solutions, and the effect of the PAA concentration on the morphology of the HSNPs was investigated. The PAA interacting with ammonium hydroxide (NH3 aq.) acts as the template for the silica coating in ethanol, and the template is easily removed by water to obtain the HSNPs. When a low PAA solution (<1 mM) was used as the template, the silica shell was hardly formed on the PAA aggregates because of high molecular motion of the PAA aggregate’s surface. When a highly concentrated PAA solution (>15 mM) was used as the template, the dense silica nanoparticles coexisted with the HSNPs because of the high solubility of the PAA aggregates in the ethanol. As a result, the stable PAA aggregates could be prepared at PAA concentrations from 3 mM to 15 mM. In this range, the HSNPs became smaller and more monodispersed with the decreasing PAA concentration. As a result, the interaction between PAA and NH3 was the most important factor for controlling the HSNP’s morphologies.

Nanoscale Mobility of Aqueous Polyacrylic Acid in Dental Restorative Cements.

Hydrogen dynamics in a time range from hundreds of femtoseconds to nanoseconds can be directly analyzed using neutron spectroscopy, where information on the inelastic and quasi-elastic scattering, hereafter INS and QENS, can be obtained. In this study, we applied these techniques to understand how the nanoscale mobility of the aqueous solution of polyacrylic acid (PAA) used in conventional glass ionomer cements (GICs) changes under confinement. Combining the spectroscopic analysis with calorimetric results, we were able to separate distinct motions within both the liquid and the GICs. The QENS analysis revealed that the self-diffusion translational motion identified in the liquid is also visible in the GIC. However, as a result of the formation of the cement matrix and its setting, both translational diffusion and residence time differed from the PAA solution. When comparing the local diffusion obtained for the selected GIC, the only noticeable difference was observed for the slow dynamics associated with the polymer chain. Additionally, over short-term aging, progressive water binding to the polymer chain occurred in one of the investigated GICs. Finally, a considerable change in the density of the GIC without progressive water binding indicates an increased polymer cross-linking. Taken together, our results suggest that accurate and deep understanding of polymer-water binding, polymer cross-linking, as well as material density changes occurring during the maturation process of GIC are necessary for the development of advanced dental restorative materials.

Understanding the generation and maintenance of supersaturation during the dissolution of amorphous solid dispersions using modulated DSC and 1H NMR

In this study, the dissolution behaviour of dipyridamole (DPM) and cinnarizine (CNZ) spray-dried amorphous solid dispersions (ASDs) using polyvinyl pyrrolidone (PVP) and polyacrylic acid (PAA) as a carrier matrix were evaluated and compared. The drug concentrations achieved from the dissolution of PVP and PAA solid dispersions were significantly greater than the equilibrium solubility of crystalline DPM and CNZ in phosphate buffer pH 6.8 (PBS 6.8). The maximum drug concentration achieved by dissolution of PVP and PAA solid dispersions did not exceed the theoretically calculated apparent solubility of amorphous DPM and CNZ. However, the degree of supersaturation of DPM and CNZ increased considerably as the polymer weight fraction within the solid dispersion increased. In addition, the supersaturation profile of DPM and CNZ were studied in the presence and absence of the polymers. PAA was found to maintain a higher level of supersaturation compared to PVP. The enhanced drug solution concentration following dissolution of ASDs can be attributed to the reduced crystal growth rates of DPM and CNZ at an equivalent supersaturation. We have also shown that, for drugs having high crystallization tendency and weak drug-polymer interaction, the feasible way to increase dissolution might be increase the polymer weight fraction in the ASD. Solution 1H NMR spectra were used to understand dissolution mechanism and to identify drug-polymer interaction. The change in electron densities of proton attached to different groups in DPM and CNZ suggested drug-polymer interaction in solution. The relative intensities of peak shift and nature of interaction between drug and polymer in different systems are different. These different effects suggest that DPM and CNZ interacts in a different way with PVP and PAA in solution which goes some way towards explaining the different polymeric effect, particularly in terms of inhibition of drug recrystallization and dissolution of DPM and CNZ ASDs. These results established that the different drug/polymer interactions in the solid state and in solution give rise to the variation in dissolution profile observed for different systems.

Effect of anti-corrosive performance, roughness and chemical composition of pre-treatment layer on the overall performance of the paint system on cold-rolled steel

Many fundamental researches about the effect of some basic properties of a pre-treatment layer, such as anti-corrosive performance, surface roughness and chemical composition on the overall performance of paint systems were investigated. Three kinds of pre-treatment layers: bare polyacrylic acid (PAA) layer, Mo based layer and Mo doped PAA layer were deposited on cold-rolled steel surfaces through immersing the steel samples in the corresponding solution. The electrochemical measurements results indicated that after been treated in PAA solution, the steels became vulnerable to corrosion and the Mo based layer and Mo doped PAA layer could improve the corrosion resistance of steel to a certain degree. The values of root-mean-square roughness of the bare steel, bare PAA layer, Mo based layer and Mo doped PAA layer were 15.0nm, 11.3nm, 13.0nm and 59.1nm, respectively. The corresponding values of arithmetic average roughness of the samples were 16.9nm, 10.5nm, 9.1nm and 41.0nm, respectively. The spectroscopy results indicated that the surface of the bare PAA and Mo doped PAA layer covered steels contained abundant COOH groups and the composition of Mo based layer covered steel surface was mainly oxides. According to the impact test and neutral salt spray test results, the corrosion mitigation performance, microstructure and chemical composition of the pre-treatment layer could all affect the overall performance of the paint system. All the results indicated that the anti-corrosive performance was not the only index, the microstructure and chemical composition also needed to be considered in the development of a new generation pre-treatment layer.