New insights in polydopamine formation via surface adsorption

Polydopamine is a biomimetic self-adherent polymer, which can be easily deposited on a wide variety of materials. Despite the rapidly increasing interest in polydopamine-based coatings, the polymerization mechanism and the key intermediate species formed during the deposition process are still controversial. Herein, we report a systematic investigation of polydopamine formation on halloysite nanotubes; the negative charge and high surface area of halloysite nanotubes favour the capture of intermediates that are involved in polydopamine formation and decelerate the kinetics of the process, to unravel the various polymerization steps. Data from X-ray photoelectron and solid-state nuclear magnetic resonance spectroscopies demonstrate that in the initial stage of polydopamine deposition, oxidative coupling reaction of the dopaminechrome molecules is the main reaction pathway that leads to formation of polycatecholamine oligomers as an intermediate and the post cyclization of the linear oligomers occurs subsequently. Furthermore, TRIS molecules are incorporated into the initially formed oligomers

Synthesis of Polystyrene/MCM–41 Nanocomposites through AGET ATRP and ARGET ATRP

Polystyrene/MCM–41 nanocomposites were synthesized by atom transfer radical polymerization (ATRP) at 110°C. Activators generated by electron transfer (AGET) and activators regenerated by electron transfer (ARGET), as two novel initiation techniques, for ATRP were used. Specific structure, surface area, particles size and their distribution and spongy and porous structure of the synthesized MCM–41 nanoparticles were evaluated using X–ray diffraction, nitrogen adsorption/desorption isotherm analysis, scanning and transmission electron microscopy images, respectively. The final monomer conversion was determined using gas chromatography. Number and weight average molecular weights (Mn and Mw) and polydispersity index (PDI) were also evaluated by gel permeationchromatography. According to the results, addition of 3 wt% MCM–41 nanoparticles into the polymerization media resulted in lowering conversion from 81 to 58% in the AGET ATRP system. Moreover, a reduction in the molecular weight of the products from 17116 to 12798 g/mol was also occurred, although, the polydispersity index increased from 1.24 to 1.58. The similar results were also obtained by ARGET ATRP system; lowering conversion from 69 to 43% and molecular weight from 14892 to 9297 g/mol, and an increase of PDI from 1.14 to 1.41. The improvement in thermal stability of the nanocomposites, as a result of higher MCM–41 nanoparticles loading, was confirmed by thermogravimetric analysis. In addition, according to the analytical results of differential scanning calorimetry, a decrease in glass transition temperature, due to the addition of 3 wt% of MCM–41 nanoparticles (from 100.1 to 91.5°C in AGET ATRP system and from 100.3 to 85.8°C in ARGET ATRP), was achieved

Effect of Pluronic Introduction to Polycaprolactone Substrate on the Blend Hydrophilicity by Molecular Dynamic Simulation

Poly()ε-caprolactone) ()PCL) has been widely investigated for medical applications because of its good physicochemical properties; however hydrophobic nature of PCL has been a colossal obstacle toward achieving scaffolds which offer satisfactory cell attachment and proliferation. To date, different methods have been proposed to lower the hydrophobicity of PCL. Moreover, molecular dynamic simulation (MD) is an excellent method to predict and study the chemical and physical properties of polymeric systems. To this end, MD study was assigned to evaluate the PCL/Pluronic blend. Moreover, some experimental data on PCL/Pluronic blend were collected and compared with the simulated results. Thermodynamic properties of neat and blended PCL were also calculated using MD simulation. The blend of PCL/Pluronic possessed lower density and higher free volume in comparison with neat PCL because of high mobility and low glass transition temperature of Pluronic chains and due to good molecular interactions between polypropylene oxide blocks of Pluronic and PCL. The ratio of the bulk to shear modulus revealed a toughened PCL blended substrate in comparison to its pure form. Moreover, a high interaction energy between the PCL/Pluronic blend and water molecules was observed due to the thermodynamically favored interactions of polyethylene oxide blocks of Pluronic and water molecules. Mean square displacement of water molecules at the bulk and in the surface of water layer placed in the vicinity of neat and blended PCL was calculated. The results revealed a difference between the behavior of the bulk and interfacial water molecules. Water contact angle measurements were carried out in order to evaluate the simulation results and demonstrated a considerable improvement in hydrophilicity of the PCL thin layers when blended with Pluronic

Adsorption kinetics of methylene blue from wastewater using pH-sensitive starch-based hydrogels

Abstract In this work, starch/poly(acylic acid) hydrogels were synthesized through a free radical polymerization technique. The molar ratios of acrylic acid to N,N′-methylenebisacrylamide were 95:5, 94:6, and 93:7. The samples exhibited an amorphous porous structure, indicating that the size of the pores was contingent upon the amount of cross-linking agent. The quantity of acrylic acid in structure rose with a little increase in the amount of the cross-linking agent, which improved the hydrogels’ heat stability. The swelling characteristics of the hydrogels were influenced by both the pH level and the amount of cross-linking agent. The hydrogel with a ratio of 94:6 exhibited the highest degree of swelling (201.90%) at a pH of 7.4. The dominance of the Fickian effect in regulating water absorption in the synthesized hydrogels was demonstrated, and the kinetics of swelling exhibited agreement with Schott's pseudo-second order model. The absorption of methylene blue by the hydrogels that were developed was found to be influenced by various factors, including the concentration of the dye, the quantity of the cross-linking agent, the pH level, and the duration of exposure. The hydrogel 95:5 exhibited the highest adsorption effectiveness (66.7%) for the dye solution with a concentration of 20 mg/L at pH 10.0. The examination of the kinetics and isotherms of adsorption has provided evidence that the process of physisorption takes place on heterogeneous adsorbent surfaces and can be explained by an exothermic nature

Atom Transfer Radical Polymerization of Styrene in Presence of Mesoporous Silica Nanoparticles: Application of Reverse, Simultaneous Reverse and Normal Initiation Techniques

Atom transfer radical polymerization (ATRP) of styrene in presence of mesoporous silica nanoparticles was carried out at 110 °C. Reverse atom transfer radical polymerization (RATRP) and simultaneous reverse and normal initiation for atom transfer radical polymerization (SR&NI ATRP) techniques were used as two appropriate introduced techniques for circumventing oxidation problems. Usage of metal catalyst in its higher oxidation state was the main feature of these initiation techniques in which deficiencies of normal ATRP were circumvented. Structure, surface area and pore diameter of synthesized mesoporous silica nanoparticles were evaluated using X–ray diffraction and nitrogen adsorption/desorption isotherm analysis. Average particle size was estimated around 600 nm by electron microscopy images. In addition, according to these images, nanoparticles revealed an appropriate size distribution. Particles size and their distribution were examined using scanning. Final monomer conversion was determined by using gas chromatography. The number and weight average molecular weights (Mn and Mw) and polydispersity indexes (PDI) were also evaluated by gel permeation chromatography. According to the results obtained, addition of mesoporous silica nanoparticles in both RATRP and SR&NI ATRP systems revealed similar effects: decrement of conversion and Mn and also increment of PDI values observed by increasing of mesoporous silica nanoparticles content. Improvement in thermal stability of the nanocomposites in comparison with neat polystyrene was demonstrated by thermogravimetric analysis (TGA). Moreover, in case of nanocomposites, thermal stability was obtained by higher loading of nanoparticles. A decrease in glass transition temperature by higher content of mesoporous silica nanoparticles has been demonstrated by differential scanning calorimetry analysis

Nanofiber-based polyelectrolytes as novel membranes for fuel cell applications

Partially sulfonated poly(ether sulfone) (SPES) was prepared and electrospun to bead-free nanofibers. The obtained data from solution conductivity measurements and scanning electron microscopy illustrated that sulfonation leads to a drastic increase in polymer solution conductivity and a considerable decrease in nanofiber diameter and a narrower diameter distribution. The new types of membranes were fabricated using Nafion-filled electrospun mats. The porous SPES nanofibrous membranes were impregnated with appropriate amount of Nafion solution. After a good pore-filling, an excess amount of Nafion solution was used to form a uniform top layer (SPES-N-N). Another bilayer polyelectrolyte membrane was prepared by direct electrospinning of SPES nanofibers on Nafion112 membrane's surface and followed by impregnation of Nafion solution into the pores of electrospun SPES (SPES-N-N112). The membranes were characterized by methanol permeability, proton conductivity, oxidative/hydrolytic stability as well as single cell direct methanol fuel cell (DMFC) performance tests. The proton to methanol selectivity of the SPES nanofiber-based bilayer membranes is about 53,680 and 45,500S s cm(-3) for SPES-N-N and SPES-N-N112 in comparison with 28,300 and 40,500S s cm(-3) for Nafion112 and Nafion117, respectively. The single cell DMFC performance results revealed that the SPES nanofiber-based-bilayer membranes have higher electrochemical performance than Nafion112 and Nafion117 membranes especially in elevated methanol concentration. The results showed that the fabricated bilayer membranes can be used as a promising polyelectrolyte membrane for fuel cell applications (C) 2010 Elsevier B.V. All rights reserved

Poly(styrene-co-butyl acrylate)/Clay Nanocomposite Latexes Synthesized via In Situ Atom Transfer Radical Polymerization in Miniemulsion: Activators Generated by Electron Transfer Approach

W       ater born poly(styrene-butyl acrylate)/clay nanocomposite latexes were synthesized by a novel initiating system of activators generated by   electron transfer (AGET) in a system of atom transfer radical polymerization   (ATRP). Initially, the clay was swelled in a mixture of styrene, butyl acrylate,   and hexadecane. The mixture was then sonicated to obtain a stable miniemulsion. To   synthesize poly(styrene-butyl acrylate)/clay nanocomposite latexes, the reducing   agent (ascorbic acid) was added dropwise to the reactor (to reduce termination reactions).   Particle size and particle size distribution of resulting nanocomposite latexes   were determined by dynamic light scattering (DLS). These latex particles were produced   with diameters in the size range of 138-171 nm. In addition, the increase in   clay content led to increased particles size. Number and weight-average molecular   weights of the resultant copolymer nanocomposites and their molecular weight distributions   were determined by gel permeation chromatography. The narrow molecular   weight distribution of the nanocomposites is an indication of a successful ATRP   which was accomplished in miniemulsion formation. Using         1   H NMR, copolymers were characterized and the mol ratios of monomers in copolymer composition were   calculated. X-Ray diffraction and transmission electron microscopy results showed   the mixed intercalated and exfoliated morphologies of nanocomposites in which   homogeneous distributions of clay layers in the polymer matrix have been achieved