ABSTRACT
Stimuli-responsive membranes play an important role in the fields of biomedicine, food and chemical industries, and environmental applications, including separation of water-oil emulsions. In this study, we present a method to fabricate pH-sensitive membranes using UV-initiated RAFT graft copolymerization of styrene (ST) and acrylic acid (AA) on poly(ethylene terephthalate) (PET) track-etched membranes (TeMs). The optimization of polymerization conditions led to successful grafting of polystyrene (PS) and poly(acrylic acid) (PAA) onto PET TeMs, resulting in membranes with stable hydrophobicity and pH change responsiveness. The membranes show a contact angle of 65° in basic environments (pH 9) and 97° in acidic environments (pH 2). The membranes were characterized by atomic force microscopy (AFM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), thermogravimetric analyses (TGA), Fourier transform infrared spectroscopy (FTIR), contact angle (CA) methods. The PET TeMs-g-PS-g-PAA exhibited good performance in separating water-oil emulsions with a high efficiency of more than 90% and flux for direct chloroform-water 2500 L m-2 h-1 and reverse emulsions of benzene-water 1700 L m-2 h-1. This method of preparing stimuli-responsive membranes with controlled wettability and responsiveness to environmental pH provides versatility in their use in separating two types of emulsions: direct and reverse.
ABSTRACT
In this work, the nanoindentations on bilayer composite nanofilms composed of metal Ag and polymer PMMA were simulated using molecular dynamics. The effects of the thickness of Ag and PMMA on the elastic moduli of the composite films were analyzed from Hertz contact theory, dislocation evolution and atomic migration. The results show that the maximum penetration depth that the Hertz model could well describe is about 6 Å, and this limiting value is almost independent on the film thickness. The deformation mode of the Ag films gradually changes from bending mode to indentation mode with an increase in Ag thickness, which improves the elastic modulus of the composite films. The rule of mixtures could give a theoretical prediction about the elastic modulus of the composite film close to the nanoindentation, and Hertz theory could also be used as long as the thickness of Ag films exceeded a certain value. The introduction of a PMMA layer impedes the development of dislocation in the Ag layer and improves the elastic limit of the composite films. This work provides an important basis for experimentally measuring the overall elastic modulus of metal/polymer composite film based on nanoindentation or extracting the elastic modulus of metal film from the overall indentation response of the composite film.
ABSTRACT
In this work, we have developed a method for the preparation of pH-responsive track-etched membranes (TeMs) based on poly(ethylene terephthalate) (PET) with pore diameters of 2.0 ± 0.1 µm of cylindrical shape by RAFT block copolymerization of styrene (ST) and 4-vinylpyridine (4-VP) to be used in the separation of water-oil emulsions. The influence of the monomer concentration (1-4 vol%), the molar ratio of RAFT agent: initiator (1:2-1:100) and the grafting time (30-120 min) on the contact angle (CA) was studied. The optimal conditions for ST and 4-VP grafting were found. The obtained membranes showed pH-responsive properties: at pH 7-9, the membrane was hydrophobic with a CA of 95°; at pH 2, the CA decreased to 52°, which was due to the protonated grafted layer of poly-4-vinylpyridine (P4VP), which had an isoelectric point of pI = 3.2. The obtained membranes with controlled hydrophobic-hydrophilic properties were tested by separating the direct and reverse "oil-water" emulsions. The stability of the hydrophobic membrane was studied for 8 cycles. The degree of purification was in the range of 95-100%.
ABSTRACT
The paper describes the separation of an oil-water emulsion by filtration using poly(ethylene terephthalate) track-etched membranes (PET TeMs) with regular pore geometry and narrow pore size distribution. PET TeMs were modified with trichloro(octyl)silane to increase their hydrophobic properties. Conditions for the modification of PET TeMs with trichloro(octyl)silane were investigated. The results of changes in the pore diameters and the contact angle depend on the concentration of trichloro(octyl)silane and the soaking time are presented. The obtained samples were characterized by FTIR, AFM, SEM-EDX and gas-permeability test. Chloroform-water and cetane-water emulsions have been used as a test liquid for oil-water separation.
ABSTRACT
Molecular dynamics simulations have been performed to study the influence of five different heating rates on the sintering of aluminum nanoparticles with a diameter of 4-10 nm, mainly by exploring the atomic migration, radial distribution function (RDF), atomic average displacement, mean square displacement (MSD), radius ratio (i.e., the ratio of the neck radius to the particle radius), shrinkage rate, radius of gyration, sintering temperature and melting point. It is found that the displacement of surface atoms is always larger than the displacement of the internal atoms at the same heating rate during the sintering process. Radius ratio and shrinkage go through three stages as the temperature increases: (1) an abrupt increase after reaching the sintering temperature; (2) an almost plateau region within a wide temperature range; (3) finally a drastic increase again after reaching the melting point. Although the radius of gyration also goes through three stages, nonetheless the trend is opposite to radius ratio and shrinkage. For aluminum nanoparticles with the same diameter, at a lower heating rate, the atomic displacement, mean square displacement, radius ratio, shrinkage, and radius of gyration change more remarkably with increasing temperature. The lower heating rate and smaller nanoparticle diameter correspond to a lower sintering temperature and melting point.