Effects of an AMPS-Modified Polyacrylic Acid Superplasticizer on the Performance of Cement-based Materials

A self-made AMPS-modified polyacrylic acid superplasticizer and two others of the same type but with different molecular structures, which are commercially available, are used in this study to investigate the effect of a 2-acrylamide-2-methyl propylene sulfonic （AMPS）-modified polyacrylic acid superplasticizer on the properties of cement-based materials. In the experiments, initial fluidity, 1 and 2 h fluidity over time after admixtion, bleeding rate of the net cement mortar, and adsorption capacity and rate of cement particles are determined by adding different dosages of the three superplasticizers into the cement paste to characterize the dispersivity and the dispersion retention capability of each superplasticizer. Water-reducing rates of three kinds of mortars are simultaneously determined to characterize the water-reducing capacity of each superplasticizer, as well as the 3 and 28 d compressive strengths to characterize the compression resistance. Results show that water-reducing effect and fluidity better maintain the capability of the AMPS-modified polyacrylic acid superplasticizer than the two commercially available polyacrylic acid superplasticizers, and the compressive strengths after 3 and 28 d show significant growth. In conclusion, the effects of water reduction and strengthening of the AMPS-modified polyacrylic acid superplasticizer are evidently better than those of the two commercially available polyacrylic acid superplasticizers.

Synthesis of a Macromer, MPEGAA, Used to Prepare an AMPS-modified Polyacrylic Acid Superplasticizer

A macromer, methoxypolyethylene glycol acrylate （MPEGAA）, was synthesized by direct esterification using methoxypolyethylene glycol （MPEG-1200） and acrylic acid （AA） as the main materials. MPEGAA was then used to prepare a polyacrylic acid superplasticizer modified with 2-acrylamido-2- methylpropane sulfonic acid （AMPS）. A single-factor test was performed to investigate the effects of the molar ratio of acid to alcohol （n（AA）/n（MPEG））, inhibitor amount, catalyst amount, temperature, and time of esterification on the synthesis of MPEGAA. The experimental results showed that the optimal esterification conditions were as follows： n（AA）/n（MPEG）, 3.5：1; amount of hydroquinone （as an inhibitor）, 1.2%; amount of para-toluenesulfonic acid （as a catalyst）, 5.5%; reaction temperature, 95 ~C; and reaction time, 6 h. The AMPS- modified polyacrylic acid superplasticizer prepared under the optimal esterification conditions enabled the achievement and maintenance of high cement dispersibility. At an admixture amount of 0.15%, the cement paste fluidity was initially as high as 300 mm, and then decreased to 315 mm after 1 h and to 290 mm after 2 h.

Synthesis and Properties of an AMPS-Modified Polyacrylic Acid Superplasticizer

A 2-acrylamide-2-methyl propylene sodium sulfonic （AMPS）-modified polyacrylic acid superplasticizer was synthesized using aqueous solution polymerization with the major monomers including the self-made active macromers polyethylene glycol mono-methyl ether acrylate acrylic （MPEGAA）, acrylic acid （AA）, AMPS, and sodium methyl allyl sulfonate （SMAS）. The ratios of the monomers were determined using an orthogonal experiment. This research focused on the effects of the dosages of different macromers, the polymerization conditions, and the length of MPEGAA side chains on the properties of the AMPS-modified polyacrylic acid super-plasticizer. The best polymerization conditions of the AMPS-modified polyacrylic acid superplasticizer are when （n（MPEGAA）：n（SMAS）：n（AMPS）：n（AA） equals 0.1：0.1：0.2：0.65, the molecular weight of monomethoxypolyethylene glycol is 1 200, the initiator ammonium persulfate accounts for 5% of the total mass of the polymerized monomers, the polymerization temperature is 80 ~C, and the reaction time is 4 h. The AMPS-modified polyacrylic acid superplasticizer synthesized in the best conditions exhibited excellent dispersivity and dispersion retainability. When the dosage ratio was 0.24%, the initial fluidity was 400 mm and the fluidity had nearly no loss after 1 h.

The Synthesis Technique of Polyacrylic Acid Superplasticizer

Using water separation technique,acrylic acid （AA） and polyethylene glycol （PEG） 1000,of which the ratio was 1.5,were esterified and the optimum esterification ratio of 90% could be reached under the condition of 110 ℃×3 h.Using polyoxyethylene acrylate macromonomer （PA） prepared in the esterification,AA and sodium methylacryl sulfonate （MAS） as monomers,a copolymer which could be used as superplasticizer was prepared by free radical coolymerization in n（PA）：n（AA）：n（MAS） of 1：7：3.When the synthesis condition was 80 ℃× 5 h,the optimal dosage of initiator was 3.0%-4.0%,the fluidity of cement paste with the samples could reach 270 mm.By analyzing the effect of the content of residual small molecule sulfonic monomer on the properties of sample,n（MAS）/n（PA） was controlled in a range of 2.5-3.8.

Effect of Molecular Structure on the Performance of Polyacrylic Acid Superplasticizer

The effects of structure parameters, such as molecular structure, segment kinds, molecular weight, and organic functional groups, on the performance of polyacrylic acid superplasticizer were discussed. According to the differences of chain sections, functional groups, eic, polyacrylic acid superplasticizer could be divided into A, B, C three parts. Among them, A chain section included sulfonic acid groups, B chain section carboxyl groups, C chain section polyester. Polyacrylic acid superplasticizers with different matching of A, B, C chain sections, different length of C chain section and different molecular weights were synthesized by acrylic acid, polyethylene glycol, sodium methyl allylsulfonate; the relation between the molecular structure and perfolxnance was also studied. The expetimental results indicate that the water-reduction ratio increases obviously with the increment of the proportion of sodium methyl allylsulfonate chain section in the molecular; the slump retention increases greatly with the increment of the proportion of acrylic acid chain section; the dispersion of cement particles increases with the increment of the chain length of polyethylene glycol; when the molecular weight is in the range of 5000, the dispersion and slump retentibity increase with the increment of the average molecular weight of polymers.

Dynamic Behavior and Mass Transport in Polyacrylic Acid Gel by Dynamic Light Scattering

Dynamic behaviors on polyacrylic acid (PAA) gels and mass (small molecules) transports in the gels have been studied mainly by dynamic light scattering (DLS). The cross-linking degree (fc), monomer concentration (Cm) and temperature of the gels have significant influences on its dynamic behavior and mass transport in the gels. The increase of fc leads to decrease of the mesh sizes of the gels, thus the obstacle of the gels for mass transport is increased. As a result, small molecular diffusion Dk in the gels is decreased. So even if for small molecules, the Dk also is influenced.

IN SITU INTERFEROMETRIC STUDY ON THE GELATION PROCESS OF POLYACRYLIC ACID GELS

In situ interferometry was used to investigate the gelation process of polyacrylic acid (PAA) gels. The basic principle of the in situ interferometry technique is illustrated. It can give sufficient information for non-destructive and successful investigation of the whole gelation process. The effect of initiator concentration on the gelation process was studied. The polymerization rate of AA increases with increasing initiator concentration. The error arising from the thermal effect in the gelation process can be neglected.

Effects of an AMPS-modified Polyacrylic Acid Superplasticizer on the Performance of Concrete Materials

A self-made 2-acrylamide-2-methyl propylene sulfonic （AMPS）-modified polyacrylic acid superplasticizer and two other commercially available superplasticizers with different molecular structures are used in this study to investigate the effect of an AMPS-modified polyacrylic acid superplasticizer on the properties of concrete materials. In the experiments, initial and 1.5 h slumps over time after admixtion are determined by adding different dosages of three superplasticizers into the premixed concrete to characterize the slump loss resistance of the premixed concrete. The water-reducing rates of three different types of concrete are determined to characterize the water-reducing capacity of the concrete with each superplasticizer. The 3, 7 and 28 d compressive strength is determined to characterize the mechanical properties of the concrete with each superplasticizer. In the meanwhile, 1, 1.5 and 2.0 h slump loss rates over time after admixtion are determined by adding different dosages of the three superplasticizers into the high-performance concrete （HPC） to characterize the slump loss resistance of HPC. The 7, 28, 60 and 90 d compressive strength is determined to characterize the compressive properties of HPC with each superplasticizer. The dry shrinkage rates of three different types of HPC are determined with each superplasticizer. Electric flux after standard curing for 56 d and chloride ion diffusion coefficient after curing for 28 d of I-IPC are determined to characterize the impermeability of HPC with each superplasticizer. The cross-section was examined using a scanning electron microscopy （SEM） system. Results demonstrate that the AMPS-modified polyacrylic acid superplasticizer has better water-reducing effect and slump than the two commercially available polyacrylie acid superplasticizers. The AMPS-modified polyacrylic acid superplasticizer also shows significant improvement of the compressive strength, especially in comprehensive performance of HPC. In conclusion, the AMPS-modified polyacrylic acid superplastieizer is particularly suitable for the preparation of HPC.

Preparation and Properties of pH-Responsive Intelligent Medical Dressing Based on Bacterial Cellulose/Polyacrylic Acid

Bacterial cellulose/polyacrylic acid (BC/PAA) pH-responsive hydrogels were prepared by free-radical polymerization (in situ) using BC as the raw material and AA as the monomer. The hydrogels were loaded with curcumin (Cur) to prepare pH-responsive intelligent medical dressings. The preparation process of the hydrogels was optimized by a single factor and response surface experiment using their swelling degree as an index. The structures of BC/PAA pH-responsive hydrogels were characterized by scanning electron microscope (SEM), Fourier Transform Infrared spectrometer (FTIR), X-ray diffraction (XRD), and tensile tester, and the swelling properties, mechanical properties, bacteriostatic properties, and drug release behavior were investigated. The results showed that the BC/PAA pH-responsive hydrogel has a three-dimensional network structure with the swelling rate up to 1600 g/g, compressive strength of up to 8 KPa, and good mechanical properties, and the drug release behavior was in line with the logistic dynamics model, and it has good inhibitory effects on common pathogens of wound infection: E. coli, S. aureus, and P. aeruginosa.

Oxygen self-doping pyrolyzed polyacrylic acid as sulfur host with physical/chemical adsorption dual function for lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries with high theoretical capacity and energy density need to solve problems such as the high decomposition energy barrier of Li_(2)S and large volume change of sulfur in the charging process caused by the shuttle effect before practical application.Herein,a green synthesis method is used to prepare polyacrylic acid(PAA)superabsorbent material,and then the pyrolyzed PAA(P/PAA)material is obtained as the positive electrode of Li-S battery.Density functional calculation reveals that the oxygen self-doping pyrolyzed polyacrylic acid(P/PAA)delivered stronger binding energy toward Li2S species in carbonyl C=O than that of graphite powder(GP)which are-1.58 eV and-1.02 eV,respectively.Coupled with the distribution of relaxation time analysis and the in-situ electrochemical impedance approach,it is further demonstrated that the designed P/PAA as sulfur host plays a physical/chemical adsorption dual function in maintaining the stability and rate performance of batteries.With an initial discharge capacity of 1258 mAh/g at 0.1 C and a minimal capacity decline of 0.05%per cycle even after 800 cycles at 0.5 C,the produced cathode demonstrated outstanding electrochemical performance.The average Coulombic efficiency is nearly 100%.The P/PAA electrodes may typically retain 96%of their capacity while declining on average only 0.033%per cycle after 130 cycles at 3 C.This effort provides a new method for the future development of heteroatomic self-doping superabsorbent with promising adsorption properties for polysulfides as cathode materials of Li-S batteries.

A robust polyacrylic acid/chitosan cryogel for rapid hemostasis

Currently,it is a challenge to develop hemostatic materials with high water absorption capacity and anti-fatigue properties for quickly preventing massive hemorrhage from arteries and visceral organs.A series of polyacrylic acid/chitosan(PAA/CS)cryogels were prepared by a cryostructurization technique to improve mechanical performance and hemostatic efficiency of chitosan(CS).In this system,the chemically cross-linked PAA network was used as a framework to improve water absorption behaviors and mechanical strength.The CS network was co-blended by hydrogen bonding and electrostatic interactions,both of which synergistically promoted hemostasis.These cryogels had high porosity(>94%),rapid water absorption rate(<3 s),high blood absorption capacity(>2000%),outstanding mechanical strength,and fatigue resistance.Moreover,the results of cytotoxicity and hemolysis demonstrated that the cryogels had good biocompatibility.Notably,the PAA/CS cryogels exhibited superior whole blood coagulation ability and red blood cell and platelet adhesion ability compared to those of commercial hemostatic dressing(gauze,gelatin sponges,and CS sponges).Based on these results,mouse femoral artery hemorrhage models and liver hemorrhage models were prepared to investigate the hemostatic ability of the prepared PAA/CS cryogels.Results suggested that the hemostatic ability of PAA5/CS cryogels was superior to that of commercial hemostatic materials.Therefore,the PAA/CS cryogels showed potential application in preventing massive hemorrhage from arteries and visceral organs.

Investigation on the Inverse Emulsion Polymerization of Acrylic Acid

Polyacrylic acid particles in nano-scale were synthesized using an inverse (W/O) emulsion polymerization method. The particle size and size change of inverse micelles which solubilize a part of monomer solution was monitored by PCS (photon correlation spectroscopy) and the particles of polyacrylic acid were viewed in scanning electron microscope for the first time. It was concluded that the inverse micelles were primarily the polymerization reaction sites.

Ni^(2+)-PAA Adsorbent for Purifying 6His-OmpTS Recombinant Protein

Functional Ni2+-polyacrylic acid (Ni2+-PAA) adsorbent has been prepared for metal chelate affinity chromatography. DNA elements coding for adjacent histidines were fused to the Aeromonas hydrophila ompTS gene. Subsequent expression in E. coli resulted in the production of hybrid protein 6His-OmpTS that could be purified by Ni2+-PAA affinity chromatography.

The In-situ Reinforcement of Calcium Phosphate Cement and Its Micro-structural Analysis

Carbon nanotubes （ CNTs ） and polyacrylic acid were employed to modify the setting process and hydration products of β-TCP/TTCP calcium phosphate cement. The micro-structure of hydration product and the fashion of how additives and hydration particles interconnected were investigated. With the modification effect of CNTs , the setting particles and CNTs got winded and interconnected and thus made the composite more compact and denser.

Mechanical Behaviour of Composite Bioactive Bone Cements Consisting of Two Different Types of Surface Treated Hydroxyapatite as Filler

Bioactive bone cements based on a paste-paste system for orthopaedic applications were developed consisting of hydroxyapatite （ HA ） filler panicles in a methacrylate matrix comprising urethane dimethacrylate （ UDMA ） and triethylene glycol dimethacrylate （ TEGDMA ）. To improve the interface between inorganic filler and organic matrix the HA panicles were subjected to two different surface treatment methods, using polyacrylic acid （PAA） and γ-methacryloxy propyl trimethoxy silane （γMPS）. The aim of the present study was to determine the influence of surface treatment and the inclusion of multifunctional methacrylates on the mechanical properties, namely 3-point flexural strength （FS） and fracture toughness of the cements and the effect of ageing in simulated body fluid. Comparing the mechanical properties of the two cements, the γMPS- HA cement showed that the fracture toughness of the experimental bone cements were significantly greater （ p 〈 0.001） compared to that of the PMMA cement, whereas PAA-HA containing cement had strength vollues around 20% lower. Interestingly, PAA was found to be more effective in improving the interface as the PAA treated HA cement （ UTHAPPA ） maintained its strength on immersion in SBF, suggesting that PAA provided a coupling, which was less sensitive to moisture, a similar trend was also observed with the inclusion of the carboxyl containing multifunctional methacrylates.

DIFFERENT TYPES OF MICROFIBRILLATED CELLULOSE AS FILLER MATERIALS IN POLYSODIUM ACRYLATE SUPERABSORBENTS

Three types of microfibrillated cellulose （MFC） with differences in structure and surface charge were used at low concentration as filler materials in polysodium acrylate superabsorbents （SAPs）. The swelling of the composite hydrogels was determined in 0.9% NaCl solution as well as in deionized water. The shear modulus of the samples was determined through uniaxial compression analysis after synthesis and after swelling in 0.9% NaC1 solution. Furthermore, the ability to retain filler effects after washing was investigated. The results showed that all of the investigated MFCs had a strong reinforcing effect on the shear modulus after synthesis. The filler effect on swelling and on the associated shear modulus of swollen samples showed a more complicated dependence on structure and surface charge. Finally, it was found that the filler effects were reasonably retained after washing and subsequent drying. The results confirm that MFC holds great potential as a filler material in superabsorbent applications. Furthermore, the results provide some insight on how the structural properties and surface charge of MFC will affect gel properties depending on swelling conditions. This information should be useful in evaluating the use of different types of MFC in future applications.

A multifunctional upconversion nanoparticles probe for Cu^(2+)sensing and pattern recognition of biothiols

Lanthanide-doped upconversion nanoparticles(Ln-UCNPs)are a new type of nanomaterials with excellent fluorescence properties,which are well applied in fluorescent biosensing.Herein we developed a multifunctional probe based on the surface engineering of core-shell structure UCNPs with polyacrylic acid(PAA).The developed PAA/UCNPs probe could be highly selective to detect and respond to Cu^(2+) at different pH.Cu^(2+) could easily combine with the carboxylate anion of PAA to quench the fluorescence of UCNPs.Therefore,we creatively proposed a fluorescent array sensor(PAA/UCNPs-Cu^(2+)),in which the same material acted as the sensing element by coupled with pH regulation for pattern recognition of 5 thiols.It could also easily identify the chiral enantiomer of cystine(L-Cys-and D-Cys),and distinguish their mixed samples with different concentrations,and more importantly,it could be combined with urine samples to detect actual level of homocysteine(Hcys)to provide a new solution for judging whether the human body suffers from homocystinuria.

A pH-responsive mesoporous silica nanoparticles-based drug delivery system with controlled release of andrographolide for OA treatment

Andrographolide(AG)has favorable anti-inflammatory and antioxidative capacity.However,it has low bioavailability due to high lipophilicity and can be easily cleared by the synovial fluid after intra-articular injection,leading to low therapeutic efficiency in osteoarthritis(OA).Herein,we designed a nano-sized pH-responsive drug delivery system(DDS)for OA treatment by using modified mesoporous silica nanoparticles(MSNs)with pH-responsive polyacrylic acid(PAA)for loading of AG to form AG@MSNs-PAA nanoplatform.The nanoparticles have uniform size(120 nm),high drug loading efficiency(22.3860.71%)and pH-responsive properties,beneficial to sustained release in OA environment.Compared with AG,AG@MSNs-PAA showed enhanced antiarthritic efficacy and chondro-protective capacity based on IL-1b-stimulated chondrocytes and anterior cruciate ligament transection-induced rat OA model,as demonstrated by lower expression of inflammatory factors and better prevention of proteoglycan loss.Therefore,the AG@MSNs-PAA nanoplatform may be developed as a promising OA-specific and on-demand DDS.

Self-assembly of Carboxyl Functionalized Polystyrene Nano-spheres into Close-packed Monolayers via Chemical Adsorption

The polyacrylic acid functionalized polystyrene nanospheres were synthesized and self-assembled into irregular, densely packed monolayers in non-aqueous media. The polymer nanoparticles were chemically adhered to sub-strates. The morphologies of the resulting films were investigated. The impact of the volume fraction of alcohol in the mixed solvents on the particle adsorption and fabrication of nanosphere assembled films was examined.