Effect Of Copolymer Concentration Research Articles

Prediction of Hydrogel Degradation Time Based on Central Composite Design

Prediction of Hydrogel Degradation Time Based on Central Composite Design

Anti-Fouling and Anti-Bacterial Modification of Poly(vinylidene fluoride) Membrane by Blending with the Capsaicin-Based Copolymer.

Membrane fouling induced by the adsorption of organic matter, and adhesion and propagation of bacteria onto the surfaces, is the major obstacle for the wide application of membrane technology. In this work, the capsaicin-based copolymer (PMMA-PACMO-Capsaicin) was synthesized via radical copolymerization using methyl methacrylate (MMA), N-acrylomorpholine (ACMO) and 8-methyl-N-vanillyl-6-nonenamide (capsaicin) as monomers. Subsequently, the capsaicin-based copolymer was readily blended with PVDF to fabricate PVDF/PMMA-PACMO-Capsaicin flat sheet membrane via immersed phase inversion method. The effects of copolymer concentration on the structure and performance of resultant membranes were evaluated systematically. With increase of PMMA-PACMO-Capsaicin copolymer concentration in the casting solution, the sponge-like layer at the membrane cross-section transfers to macroviod, and the pore size and porosity of membranes increase remarkably. The adsorbed bovine serum albumin protein (BSA) amounts to PVDF/PMMA-PACMO-Capsaicin membranes decrease significantly because of the enhanced surface hydrophilicty. During the cycle filtration of pure water and BSA solution, the prepared PVDF/PMMA-PACMO-Capsaicin membranes have a higher flux recovery ratio (FFR) and lower irreversible membrane fouling ratio (Rir), as compared with pristine PVDF membrane. PVDF/PMMA-PACMO-Capsaicin membrane is found to suppress the growth and propagation of Staphylococcus aureus bacteria, achieving an anti-bacterial efficiency of 88.5%. These results confirm that the anti-fouling and anti-bacterial properties of PVDF membrane are enhanced obviously by blending with the PMMA-PACMO-Capsaicin copolymer.

Bioinert Control of Zwitterionic Poly(ethylene terephtalate) Fibrous Membranes.

Poly(ethylene terephtalate) (PET)-based materials face general biofouling issues that we addressed by grafting a copolymer of glycidyl methacrylate and sulfobetaine methacrylate, poly(GMA- r-SBMA). The grafting procedure involved a dip-coating step followed by UV-exposure and led to successful grafting of the copolymer as evidenced by X-ray photoelectron spectroscopy and zeta potential measurements. It did not modify the pore size nor the porosity of the PET membranes. In addition, their surface hydrophilicity was considerably improved, with a water contact angle falling to 30° in less than 20 s and 0° in less than 1 min. The effect of copolymer concentration in the coating bath (dip-coating procedure) and UV exposure time (UV step) were scrutinized during biofouling studies involving several bacteria such as Escherichia coli and Stenotrophomonas maltophilia, but also whole blood and HT1080 fibroblasts cells. The results indicate that if all conditions led to improved biofouling mitigation, due to the efficiency of the zwitterionic copolymer and grafting procedure, a higher concentration (15 mg/mL) and longer UV exposure time (at least 10 min) enhanced the grafting density which reflected on the biofouling results and permitted a better general biofouling control regardless of the nature of the biofoulant (bacteria, blood cells, fibroblasts).

Effect of copolymer concentration on the structure and permeability of temperature-sensitive poly(vinylidene fluoride) hollow fiber membrane

Temperature-sensitive poly(vinylidene fluoride)-grafted-poly( N-isopropylacrylamide) (PVDF- g-PNIPAAm) copolymer hollow fiber membrane was fabricated by dry–wet spinning technique using N,N-dimethyl formamide as solvent and poly(ethylene glycol) as pore-making agent, respectively. The effect of PVDF- g-PNIPAAm copolymer concentration in the spinning solution on the structure and performance of resultant fiber membranes were investigated by field-emission scanning electronic microscopy, pore size measurements, mechanical tests, and filtration experiments. It was found that the microvoid in the inner cross-section of hollow fiber membrane changed to a finger-like structure with the increase of copolymer concentration from 16 to 20%. The increasing copolymer concentration also led to the increase of the inner diameter, outer diameter, and wall thickness and the decrease of mean pore size and porosity. When the permeation temperature was increased from 20 to 45°C, a remarkable reduction of pure water flux and a drastic increase of the retention of bovine serum albumin were observed around 32°C, indicating an obvious temperature-sensitive permeability.

Computer Simulations on the Anticancer Drug Delivery System of Docetaxel and PLGA-PEG Copolymer

Molecular dynamics (MD) and dissipative particle dynamics (DPD) simulations were integrated to study the morphologies of the drug delivery system self-assembled by amphiphilic block copolymer poly(lactic-co-glycolic acid)-b-poly(ethylene glycol) (PLGA-PEG) and anticancer drug docetaxel. In this work, the solubility parameters used in DPD simulations were calculated by MD simulations. In DPD simulations, the effects of copolymer concentration, copoly- mer composition and drug content on self-assembled morphologies were investigated. Simulation results show that the mor- phologies self-assembled by PLGA-PEG and docetaxel (Dtx) undergo the transition from spherical to cylindrical and finally to lamellar micelles when increasing the copolymer concentration from 10% to 50% while maintaining the mass ratio of co- polymer to drug as 5∶1. In all cases, core-shell structures were obtained with the hydrophobic PLGA as the core and the hydrophilic PEG as the shell. It is found that PLGA-PEG copolymer with the composition of PEG block ranging from 10% to 90% (the total number of the blocks of PLGA-PEG is kept as 100) self-assembles into spherical core-shell structures in aqueous solutions without drug when the copolymer concentration is 10%. When the mole fraction of PEG in PLGA-PEG copolymer is less than 20%, PEG is unable to pack PLGA completely. With the increase of mole fraction of PEG, the PEG shell becomes thicker and the size of the core becomes smaller. In order to moderate the micelle's drug loading efficiency (a small PLGA core will load small amount of hydrophobic anticancer drug Dtx) and stability (a thin PEG shell may make the core-shell micelle unstable), PLGA-PEG copolymer with the molar ratio of PEG to PLGA as 40∶60 is considered to be the best drug carrier candidate. Besides, the simulation results show that the content of drugs also affects the self-assembled structure. When the drug content is under a certain value, spherical core-shell structures are gained and the size of them grows up with the increase of the drug content. When the drug content is above that value, the spherical structures will con- nect each other to form cylindrical structures. Considering the advantage of spherical core-shell structures in drug delivery, the optimal mass ratio of docetaxel, PLGA40-PEG60 copolymer and water is 5∶10∶90. This work is expected to provide some guidance for the design and development of drug delivery systems. Keywords drug delivery system; computer simulation; self-assembly; block copolymer; core-shell structure

Induced micellization and micellar transitions in aqueous solutions of non-linear block copolymer Tetronic® T904

Tetronics® (Poloxamines) are the least studied block copolymers with an X-shaped molecular geometry formed by four poly (propylene oxide, PPO) and poly (ethylene oxide, PEO) block chains, bonded to a central ethylenediamine group. Compared to their linear counterparts, the Pluronics, Tetronics® are novel, in that they possess superior physicochemical properties, and are relatively less studied. A complete understanding of their solution behavior under different solution conditions can make them competitive candidates for novel drug delivery systems. The micellization behavior and aqueous solution properties of Tetronic® T904 [(EO(15)PO(17)) (2)NCH(2)CH(2)N (PO(17)EO(15))(2)] have been determined by cloud point, viscosity, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and nuclear magnetic resonance (NMR) measurements. The copolymer formed spherical micelles at 30°C with a core radius (R(c)) of about 2.5 nm, a hard sphere radius (R(hs)) of 5.2 nm and an aggregation number (N(agg)) of 10. The effect of copolymer concentration, temperature, pH and salt on the micellar and phase behavior is examined. The copolymer has been found to exist in aggregated form only at higher pH values of >8. An increase in micelle size and aggregation has been observed for an increase in temperature and salt concentration, mainly due to the dehydration of the hydrated PEO shell. The added salts (NaCl, Na(2)SO(4) and Na(3)PO(4)) induce micellization and favor the micellar transition at lower temperatures due to the "salting out effect"; the effect of anions follows the Hofmeister series (PO(4)(3-)>SO(4)(2-)>Cl(-)).

Effects of copolymer concentration and chain length on the pH-responsive behavior of diblock copolymer micellar films

The pH-responsive behavior of adsorbed diblock copolymer films of PDMA–PDEA (poly(2-(dimethylamino)ethyl methacrylate)– block–poly(2-(diethylamino)ethyl methacrylate)) on silica has been characterized using a quartz crystal microbalance with dissipation monitoring (QCM-D), an optical reflectometer (OR) and an atomic force microscope (AFM). The copolymer was adsorbed at pH 9 from various copolymer concentrations; QCM-D measurements indicate that the level of desorption when rinsed at pH 9 depends on the initial copolymer concentration. The adsorbed films produced at pH 9 generally have low charge densities; adjusting the solution pH to 4 results in a significant protonation of the constituent copolymers and a related interfacial structural change for the copolymer film. OR studies show no significant change during pH cycling, while QCM-D measurements indicate that the adsorbed mass and dissipation alter dramatically in response to the solution pH. The difference between the QCM-D adsorbed masses and dissipation values at pH 4 and 9 were found to be dependent on the initial copolymer concentration. This is due to differences in the initial conformations within the adsorbed copolymer layers at pH 9. The effect of the PDMA chain length on the pH-responsive behavior has also been studied; both the QCM-D adsorbed mass and dissipation of PDMA 54–PDEA 24 (shorter PDMA block) at pH 4 and 9 were observed to be greater than those of PDMA 9X–PDEA 2Y (longer PDMA block). This suggests that the normal extension of the adsorbed PDMA 54–PDEA 24 copolymer films is more significant than that of the PDMA 9X–PDEA 2Y films on silica.

Concentration, temperature, and salt-induced micellization of a triblock copolymer Pluronic L64 in aqueous media

The effect of copolymer concentration, temperature, and sodium halides (NaI, NaBr, NaCl, and NaF) on micellization and micellar properties of a poly(ethylene oxide)- block-poly(propylene oxide)- block-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic copolymer (Pluronic L64: EO 13PO 30EO 13), was examined by different methods such as dye spectral change, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), small angle neutron scattering (SANS), dynamic light scattering (DLS), viscosity, and cloud point (CP). Temperature/polymer concentration/salt dependent aggregation behavior of L64 was observed. The data on critical micelle concentration (CMC), critical micelle temperature (CMT), (CP), micelle size, and shape are reported. The Fourier transform infrared (FTIR) showed temperature dependent changes in C–O–C stretching variation band towards higher wave numbers and broadening of band width during the micellization process; this was attributed to increase in proportion of the anhydrous methyl groups, while the proportion of the hydrated methyl groups was decreased. Differential scanning calorimetry (DSC) provides CMTs and CPs from the same experiment. CMC values derived from dye spectral change, decrease significantly with the addition of salt. The increases in salt/copolymer concentration lower the onset temperature of micellization (CMT). Halide anions influence both CMT and CP in the order of F − > Cl − > Br − > I − when total salt and copolymer concentration kept constant. SANS results show the increase of inter-micellar interaction due to the increase in temperature/salt concentration; this is supported by viscosity data.

A study of the versatile micropatterns of diblock copolymer micelles: the effect of copolymer concentration, substrate, film thickness and micelles morphology

We report the novel use of polystyrene- block-poly(acrylic acid) (PS- b-PAA) diblock copolymer micelles as the nano-building blocks in fabricating orderly aligned three-dimensional micropatterns with high regularity through a one-step evaporation-induced cracking process. Crack patterns of square, rectangular, stripe-like and mesh-like structures in micron scale were obtained. The effect of the concentration of diblock copolymer, the properties of the substrates, the thickness of the drying layer, and the morphology of the micelles on the regularity of the crack patterns was studied. By regulating the above factors, we achieved micropatterns of various structures. We further developed a cheap, fast, and simple method for fabricating micromolded structures using the crack patterns as templates.

Solubility of Poly(ethylene-co-acrylic acid) in Low Molecular Weight Hydrocarbons and Dimethyl Ether. Effect of Copolymer Concentration, Solvent Quality, and Copolymer Molecular Weight

Cloud-point data to 260 o C and 2600 bar are presented for four different solvents, propane, butane, butene, and dimethyl ether (DME), with polyethylene (PE) and four poly(ethylene-co-acrylic acid) copolymers (2.4, 3.9, 6.9, and 9.2 mol % acrylic acid). The pressure-concentration isotherms measured for PE-DME and poly(ethylene-co-3.9 mol % acrylic acid)-butene mixtures have broad maximums that range between 5 and 10 wt %. The cloud-point curves for the acid copolymers in the olefinic and paraffinic hydrocarbons dramatically increase in pressure to as high as 2600 bar with decreasing temperature, especially below ∼180 o C where intra- and interpolymer acid dimerization occurs

Interfacial activity of polycarbonate/PMMA graft copolymers in polycarbonate/PMMA blends: effect of copolymer concentration

This paper discusses the effectiveness of polycarbonate/poly(methyl methacrylate) graft copolymers as emulsifiers in solvent-cast dispersions of poly(methyl methacrylate)/polycarbonate blends. The molecular weight of the copolymer block corresponding to the minor (polycarbonate) phase was distinctly higher than that of the corresponding homopolymer. The results indicate that small amounts (<5% w/w) of copolymer can act as an effective surfactant, producing fine dispersions and creating significant amounts of interfacial area. Further addition of copolymer into the blend had no effect on the size of dispersed regions or on interfacial area. Dynamic mechanical spectra, microscopy and phase diagrams of the systems provide evidence that additional copolymer causes compositional rearrangement. Although some increased miscibility of the polymer components has been effected by the addition of copolymer in the blend, there is no evidence that the copolymers act primarily as miscibilizers for the blend.

Model for micelle formation in copolymer/homopolymer blends

Polydisperse micelle formation in dilute solutions of A–B diblock copolymer in A homopolymer is studied. The standard free energy of micellization, the critical micelle concentration (c.m.c.), the average micelle sizes, and the micelle size distribution are determined. The effects of copolymer concentration, B block length nB, and temperature (in terms of the Flory’s interaction parameter χ) on micellar behavior are examined. The width of the micelle size distribution is shown to be inversely proportional to the square root of the curvature of the standard free energy of micellization. The polydispersity of the micelles decreases with increasing copolymer concentration, being high for concentration below and around the c.m.c. The polydispersity also depends on nBχ, with high polydispersity corresponding to small nBχ values. The average micelle size exhibits sudden growth at the c.m.c. and increases slightly beyond the c.m.c.