Multifunctional surfaces produced by femtosecond laser pulses

Abstract

In this work, viscoelastic, isothermal extrusion film casting modeling utilizing 1D membrane model and modified Leonov model was performed in order to understand the role of viscoelastic stress state at the die exit on the polymer melt film stretching in the post die area. Experimental data for LDPE and theoretical predictions based on the eXtended Pom-Pom (XPP) model taken from the open literature were used for the validation purposes. It was found that predicting capabilities of 1D membrane model utilizing XPP and modified Leonov model are comparable for the given processing conditions and material. Consequent theoretical parametric study revealed that increase in the viscoelastic stress state at the die exit, characterized as the ratio of second and first normal stress differences, -N 2 /N 1 , leads to increase in neck-in phenomenon. This suggests that specific attention should be paid to optimization of the extrusion die design in order to stabilize polymer melt film stretching in the post die area. respectively, for the long chain branched (LDPE, PP) and the linear (HDPE, PP) polymers. Even if many useful findings and conclusions regarding to neck-in phenomenon can be found in the open literature [29][30][31][32][33], the effect of polymer melt flow history, generated inside the extrusion die, on the neck-in phenomenon occurring in post die area still remains unclear. In order to extend the knowledge in this field, the 1D membrane model proposed by Silagy et al. [14] together with viscoelastic modified Leonov model [34] was utilized in this work for the EFC modeling. MODELING Modified Leonov ModelThis constitutive equation is based on heuristic thermodynamic arguments resulting from the theory of rubber elasticity [35][36][37]. Mathematically it is relating the stress and elastic strain stored in the material as:

Recent Progress in Self-Cleaning Materials with Different Suitable Applications

“…There is a research that shows that by covering with active concrete 15% of ceilings in city of Milan, the pollution would be decreased up to 50% (Miljkovic et al, 2013;Zhang et al, 2015b). Another company named Heidelberg Cement has produced TioCemTM, which is another air pollution reducer in case of self-cleaning cement (Hancock et al, 2012;Vorobyev and Guo, 2015;Long et al, 2015). Also, in Japan the tiles made of self-cleaning material for using in windows and roof from company Ecofriendly are used widely.…”

Induced hydrophobicity in micro‐ and nanostructured nickel thin films obtained by ultraviolet pulsed laser treatment

“…Micro-and nanopatterning can also be achieved with lasers, however their use as a procedure to induce direct hydrophobicity and superhydrophobicity in metallic surfaces is only emerging. Recent studies have used picosecond to nanosecond pulsed lasers with infrarred to ultraviolet wavelengths to successfully induce superhydrophobicity in platinum [17], brass [17][18][19], iron and stainless steels [20][21][22][23][24][25], titanium and Ti6Al4V [17,[20][21][22], silicon [26], copper [18,22], cobalt [22], aluminium [22,27] or carbon nanotubes [28]. No such surface patterning has been reported on nickel to date.…”

Micro- and nanostructuring of metal surfaces with polarized femtosecond laser pulses

“…Modification of surface topology under the influence of laser irradiation leads to changes in physical properties of matter, including the mechanical and optical ones, and therefore surface structuring becomes widely used, for example for creation of "black" and "color" films [5], superhydrophobic surfaces [6,7], etc. Good biostability and biocompatibility of some refractory metals make them promising for biomedical applications.…”