RESUMO
In this paper we systematically investigated effect of separator morphology on the performance of Li-S batteries. We tested two kinds of commercially available non-woven fibrous separators made of polypropylene in conjunction with trilayer PP/PE/PP porous separator. Among the non-woven separators, the fibers of the separator of first kind are rough and more acidic than the fibers of the separator of second art, which are smooth. It was found that batteries with smooth separator demonstrate higher Coulombic efficiency, higher charging/discharging capacity and better cycling stability. We attribute better performance of batteries with smooth fibers of separators to lower acidity than that of rough fibers. We believe that negatively charged polysulfides are unable to adsorb on more acidic rough fibers and diffuse readily to lithium electrode. In contrast, polysulfides are able to adsorb on the surface of less acidic smooth fibers that reduces their polysulfides shuttle and rapid decay of battery capacity. Strategic deployment of non-woven Freudenberg and Celgard separator in combination leads to high active mass utilization, superior wettability, reduced short circuit tendency caused by dendritic growth and slower capacity decay.
RESUMO
In this paper, we investigated the aggregation and assembly behavior of hairy core-shell particles with different architectures consisting of a hard silica core and soft polymer brush shells. We varied the nature of the polymers which form the shell: we used different hydrophilic positively (poly(2-(dimethylamino)ethyl methacrylate), PDMAEMA) and negatively (poly(acrylic acid), PAA) charged polymers, uncharged hydrophilic (polyethylene glycol, PEG) polymers, and hydrophobic (poly(lauryl methacrylate), PLMA; polystyrene, PS) polymers. We synthesized particles covered by polymer of one sort (homogeneously coated particles) as well as Janus particles (two polymers are grafted to the opposite sides of the core) and investigated/compared the aggregation behavior of different fully covered particles, their mixtures, and Janus particles.
RESUMO
We investigated the adaptive adhesion properties of comb-like random copolymer brushes made of poly(ethylene glycol) (PEG)-poly(dimethylsiloxane) (PDMS) grafted on flat and rough substrates. The properties of the brush layers were investigated using ARXPS, contact angle, electrokinetics, null ellipsometry, and adhesion measurements. It was found that hydrophobic PDMS segments segregate at the brush topmost layer in the dry state. However, hydrophilic PEG chains segregate at the brush topmost layer in the wet state. The adhesion properties of fabricated materials were tested using the AFM colloid probe technique and probe tack tester. It was found that the adhesive properties depend strongly on the mechanical properties (stiff/soft) and chemical functionality (hydrophobicity/hydrophilicity) of the applied adhesion tester as well as on the chemical composition, surface roughness, and thickness of the brush. In particular, hydrophobic PDMS and hydrophilic PEG adhere more strongly to hydrophobically modified and hydrophilic native colloid probes, respectively. Thick brushes are more adhesive than thin ones, and brushes grafted to flat substrates are stickier than those grafted to rough substrates when measured with a hard AFM probe. Unlike the results of adhesion measurements performed using hard AFM probes, the PDMS surface probed by soft pressure-sensitive adhesives (PSA) is almost nonadhesive. However, PEG is strongly adhesive, and the adhesion increases with the PEG fraction in the brush when probed by both hydrophilic and hydrophobic soft adhesives. The surfaces roughness also has a considerable effect on adhesion. Contrary to the adhesion measurements performed by hard AFM colloid probes, the adhesion of rough surfaces measured with a soft PAA or SIS tack tester is greater than that on the corresponding flat one.
