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Correlation between the onset of beadless character of nanofibrous webs and rheological characteristics of electrospun polymer solutions
Zelenková, Jana ; Peer, Petra ; Filip, Petr
An overwhelming majority of applications of nanofibrous webs requires sufficiently smooth character of nanofibres surface. This character is apart other parameters strongly influenced by a concentration of chosen polymeric material in the solvents. Qualitative attributes roughly depend on the prepared concentration, specifically whether it belongs to one of the four basic regions: dilute, semidilute unentangled, semidilute entangled and concentrated. A concentration separating the latter two regions is often taken as a zero-th approximation indicating an onset of beadless nanofibrous webs. The present contribution uses as a more precise indicator behaviour of so-called phase angle relating viscous and elastic moduli, in other words mutual participation of viscous and elastic components. To this aim three frequently used polymers were used: copolymer of poly(vinylidene fluoride) and hexafluoropropylene (PVDF-co-HFP), poly(ethylene oxide) (PEO) and poly(vinyl butyral) (PVB). For materials exhibiting first a constant behaviour or moderate decrease in a phase angle for lower concentrations, an approximation of the starting concentration is given by a concentration value where a phase angle curve starts to decrease, apparently reflecting a more progressive viscoelastic nature. As shown, such approximation provides relatively very good approximation enabling to eliminate a traditional trial-and-error method.
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Viskoelastické vlastnosti ferrokapaliny - Studium normálových napětí
Šustková, Hana ; Krakovský, Ivan (advisor) ; Filip, Petr (referee)
Viscoelastic properties of ferrofluid - Study of normal stresses differences Master Thesis Hana Šustková Abstract: Since 1960, a liquid becoming strongly magnetized in the presence of a mag- netic field, called ferrofluid, is known. This colloidal liquid made of ferro- or ferrimagnetic nanoparticles, with diameter in range 10-20 nm, suspended in a carrier fluid. This work focuses on the study of the viscoelastic properties of a selected ferrofluid - the steady-state and dynamic properties of the fluid with comparison to a standard fluid (basis fluid, etc.) and a MR fluid. Rheological measurements are carried out using a commercial rheometer. A magnetic cell for this rheometer is designed and built. In this magnetic cell the experiments are realized, the whole system is calibrated and the experiments performed. The ferrofluid APG513a, MR-fluid and reference fluid were used. Study of normal stresses differences (N1,N2) in liquids is carried out. Ac- cording to derived theoretical model, the course of N1 and N2 should be strongly dependent on the field - this was studied directly by measuring of the normal forces or indirectly applying the Laun's rule. A good accordance of theory and experiment was found and an anisotropic behaviour of ferrofluid was studied. The shear-thinning ability of the ferrofluid in normal direction...
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Antibacterial electrospun membrane prepared from poly(vinylidene fluoride)-co-hexafluoropropylene with lauric acid monoacylglycerol
Zelenková, Jana ; Peer, Petra ; Pleva, P. ; Janalíková, M. ; Sedlaříková, J. ; Filip, Petr
The aim of this study was to prepare an antibacterial nanofibrous membrane using electrospinning technique. The nanofibrous membranes were spun from polymer solution of poly(vinylidne fluoride)-co-hexafluoropropylene (PVDF-co-HFP) dissolved in N,N´-dimethylformamide. Monoacylglycerol of lauric acid (MAG C12) was used as an antimicrobial agent at the concentrations ranging from 1 to 3 wt%. The impact of MAG C12 incorporation on the rheological, structural and antibacterial properties was investigated. The rheological tests of polymer solutions, as steady shear and oscillatory shear, proved that addition of MAG C12 changed marginally rheological quantities such as viscosity, elastic (storage) and viscous (loss) moduli. Measurement of mean nanofibres diameter indicated a slight decrease with increasing MAG C12 concentration. Antimicrobial activity of PVDF-co-HFP nanofibre membranes with incorporated MAG C12 against Gram-positive bacteria Staphylococcus aureus and Gram-negative Escherichia coli was studied. An antibacterial activity was revealed for the samples containing MAG C12 at all concentrations against Gram-positive bacteria Staphylococcus aureus by the disk diffusion method.
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Dependence of morphology of electrospun PVB nanofibres containing fumed silica on elasticity of the processed solutions
Peer, Petra ; Polášková, M. ; Filip, Petr
Application of various types of fumed silica gives a possibility to tailor a degree of hydrophilicity or hydrophobicity of the resulting electrospun nanofibrous mats where as a basic polymeric material is taken poly(vinyl butyral) (PVB) solved in methanol. Presence of fumed silica substantially changes viscoelastic attributes in comparison with the neat PVB solution.\nThe aim of this contribution is to compare morphological structures of the resulting electrospun mats generated from the solutions with presence and absence of various types of fumed silica differing in surface morphology, size and the specific surface area. This comparison is based on the rheological characteristics with the emphasis to elasticity of the pre-processed solutions. The differences in elasticity among fumed silica based solutions are indeed remarkable. The obtained results show that elasticity does not play a crucial role in creation and morphological aspects of the corresponding nanofibrous mats including fibres diameter.
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Modelling of non-monotonous course of shear viscosity
Filip, Petr
A number of parameters appearing in the 'classical' empirical constitutive equations usually oscillate between two and five. With the onset of new rheologically more complex materials exhibiting non-monotonous behaviour of flow curves this range (2-5) is no longer tenable and more additional parameters are required for a proper description of the flow curves. An 8-parameter model is presented and testified.
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The role of solvents in the preparation of hydrophobic nanofibrous membrane containing fumed silica
Peer, Petra ; Polášková, M. ; Musilová, I. ; Filip, Petr
It is well-known that a type of used fumed silica nanoparticles plays a dominant role in wettability of the corresponding nanofibrous mats. As a result, the desired contact angle can be approximately achieved by a choice of adequate fumed silica nanoparticles. However, less attention has been hitherto paid to an active role of solvents in connection with the tailoring this contact angle. For analysis we used poly(vinyl butyral) representing electrospun-friendly material, various types of fumed silica nanoparticles and two solvents - methanol and ethanol. It is demonstrated that a choice of polymer solvents plays a significant role in contact angle changes. Hence, in combination of the type of fumed silica nanoparticles and the type of solvent it is possible to achieve a finer partition of the required contact angles.
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Social network monitoring as a service to monitor business environment
Filip, Petr ; Jelínek, Ivan (advisor) ; Novotný, Ota (referee)
This project is focused on gathering information about environs of the company presented on the social networks and choosing the right tools to analyze the perception of the firm and its products between the users of the social network. In the first part, the benefits of analization on social network based on the rating metrics gained from the datas of social networks are explained. In the second part the right social network is chosen to analyze and then the proccess of accessing the datas is revealed. The last part of the project is about different political situations in addition of monitoring the traditional medias and complete informational value of the analysation is shown. The result of this whole project is to compare the differences between informational value from the classic medias and the informational valuenof the social networks and eventually whole application for the company.
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Viskoelastické vlastnosti ferrokapaliny - Studium normálových napětí
Šustková, Hana ; Krakovský, Ivan (advisor) ; Filip, Petr (referee)
Viscoelastic properties of ferrofluid - Study of normal stresses differences Master Thesis Hana Šustková Abstract: Since 1960, a liquid becoming strongly magnetized in the presence of a mag- netic field, called ferrofluid, is known. This colloidal liquid made of ferro- or ferrimagnetic nanoparticles, with diameter in range 10-20 nm, suspended in a carrier fluid. This work focuses on the study of the viscoelastic properties of a selected ferrofluid - the steady-state and dynamic properties of the fluid with comparison to a standard fluid (basis fluid, etc.) and a MR fluid. Rheological measurements are carried out using a commercial rheometer. A magnetic cell for this rheometer is designed and built. In this magnetic cell the experiments are realized, the whole system is calibrated and the experiments performed. The ferrofluid APG513a, MR-fluid and reference fluid were used. Study of normal stresses differences (N1,N2) in liquids is carried out. Ac- cording to derived theoretical model, the course of N1 and N2 should be strongly dependent on the field - this was studied directly by measuring of the normal forces or indirectly applying the Laun's rule. A good accordance of theory and experiment was found and an anisotropic behaviour of ferrofluid was studied. The shear-thinning ability of the ferrofluid in normal direction...
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The role of sonication of polyethyleneoxide solutions containing magnetic nanoparticles on morphology of nanofibrous mats
Peer, Petra ; Stěnička, M. ; Filip, Petr ; Pizúrová, Naděžda ; Babayan, V.
Properties of the resulting polymer nanofibers are often tailored by sonication technique applied prior or past an electrospinning process. The aim of this contribution is to evaluate morphology of nanofibrous mats formed by poly(ethylene oxide) with distributed magnetic nanoparticles (MNP) (about 20 nm in diameter) in dependence on time of sonication of the used polymer solutions. The solutions were exposed to sonication (intensity 200W, frequency 24 kHz) for 10, 30, and 60 minutes. It was shown that rheological characteristics (viscosity, storage and loss moduli) strongly depend on time of sonication (particularly phase angle) in contrast to electric conductivity and surface tension. For analysis of homogeneous distribution of MNP in polymer solution, the rheological measurements were carried out also in presence of external magnetic field. Magnetorheological efficiency (a relation of corresponding viscosities) was determined for 80, 170, and 255 mT. Consequently, changed rheological characteristics participate significantly in the process of electrospinning and resulting quality of the obtained nanofibrous mats. Qualitative changes were described by\nmeans of scanning electron microscopy (variance of mean diameter of nanofibers), transmission electron microscopy (distribution of MNP within nanofibrous mats). Static magnetic properties were determined by a vibration sample magnetometer. It was shown that even distribution of MNP in the mats can be achieved by mere sonication process without application of external magnetic field during an electrospinning process. However, time of sonication generates a degree of embedding of MNP into individual nanofibers.
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