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Muntean, Stela AndreaORCID iD iconorcid.org/0000-0001-9337-2249
Publications (4 of 4) Show all publications
Blazinic, V., Ericsson, L., Muntean, S. A. & Moons, E. (2018). Photo-degradation in air of spin-coated PC60BM and PC70BM films. Synthetic metals, 241, 26-30
Open this publication in new window or tab >>Photo-degradation in air of spin-coated PC60BM and PC70BM films
2018 (English)In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 241, p. 26-30Article in journal (Refereed) Published
Abstract [en]

The fullerene derivatives PC60BM and PC70BM are widely used as electron accepting components in the active layer of polymer solar cells. Here we compare their photochemical stability by exposing thin films of PC60BM and PC70BM to simulated sunlight in ambient air for up to 47 h, and study changes in their UV–vis and FT-IR spectra. We quantify the photo-degradation by tracking the development of oxidation products in the transmission FT-IR spectra. Results indicate that PC60BM photodegrades faster than PC70BM. The rate of photo-oxidation of the thin films is dependent on the rate of oxygen diffusion in to the film and on the photo-oxidation rate of a single molecule. Both factors are dependent on the nature of the fullerene cage. The faster photo-oxidation of PC60BM than of PC70BM is in agreement with its slightly lower density and its higher reactivity. The use of PC70BM in solar cells is advantageous not only because of its absorption spectrum, but also because of its higher stability.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Fullerene derivatives, Photo-oxidation, UV-vis spectroscopy, IR spectroscopy
National Category
Condensed Matter Physics
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-66953 (URN)10.1016/j.synthmet.2018.03.021 (DOI)
Available from: 2018-04-09 Created: 2018-04-09 Last updated: 2018-04-09Bibliographically approved
Muntean, S. A. (2013). Molecular-dynamics simulations of polymeric surfaces for biomolecular applications. (Doctoral dissertation). Technische Universiteit Eindhoven
Open this publication in new window or tab >>Molecular-dynamics simulations of polymeric surfaces for biomolecular applications
2013 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

In-vitro diagnostics plays a very important role in the present healthcare system. It consists of a large variety of medical devices designed to diagnose a medical condition by measuring a target molecule in a sample, such as blood or urine. In vitro is the latin term for in glass and refers here to the fact that the samples are investigated outside the living organism. The range of target molecules is very broad, spanning from salts to small molecules, proteins, nucleic acids and cells. An important segment in this range is the measurement of macromolecules, such as biomarker proteins or nucleic acids, in biological samples. Biosensors are compact systems for rapid detection of biological molecules. The first commercial biosensor was introduced in 1975 for glucose analysis by the Yellow Springs Instrument Company, based on the pioneering work of Clark and Lyons. Since that time, biosensors are becoming more integrated, more sensitive, smaller, faster and cheaper and are becoming available for more and more classes of biomarkers. The immunoassays can be performed nowadays in devices with very different formats, from the high-throughput parallel analysis on well-plates to integrated point-of-care biosensors using lab-on-a-chip technology. The solid phase in these devices is very often a polymeric glass. Polymeric glasses, such as polystyrene, are easy to process and can be produced at low costs, which makes them suitable for disposable cartridges in lab-on-a-chip devices. An important process in the immunoassays is the physisorption of the macromolecules to the polymeric solid phase, such as the non-specific binding of molecules from the biological sample onto the polymeric carrier. This process plays a very important role in the limit of detection, which is given by specific binding (signal) over non-specific binding (background). Therefore, the understanding of the non-specific binding of macromolecules to polymeric surfaces is crucial for the improvement of the sensitivity in these devices. The scope of this thesis is to gain fundamental knowledge on the physisorption of proteins onto polymeric surfaces and to understand how to model this process in atomistic details. The goal of this work is to model the interaction between myoglobin and polystyrene surfaces, within a clean buffer. Computer simulations provide detailed informations about the nature of the non-specific interactions between the biomolecule and the polymeric substrate, at molecular and atomic scales. The high level of detail obtained from simulations on a smaller scale is complementary to the experimental results obtained at a larger scale. The polymeric substrate is in our case modeled by an atactic amorphous polystyrene thin film. We would like to explore the possibility of changing the properties of the polymeric substrate, to prevent non-specific interaction, by chemical modification induced by oxidation. Pure polystyrene is a hydrophobic material. We tune the hydrophilicity of its surface by adding oxygen atoms to the phenyl rings of the polystyrene chain. This addition of oxygen is a way to mimic the oxidation of polystyrene surfaces that is performed in experiments. We represent the buffer solution in simulations by explicit water molecules described at atomistic level, to which we add Na+ and Cl- ions to reproduce the salt concentration in the experimentally used buffer solution. We chose myoglobin as model biomolecule because it is a relatively small globular protein, well studied in the past and represents a good candidate for practical applications. The first question we intend to answer is to which extent the model used to represent the polystyrene chains is important for the macroscopic properties of the polystyrene films and in particular to their interaction with the water molecules. To tackle this issue, we chose two representations of the polystyrene chains: the united atoms representations on one hand, in which only the heavy atoms are modeled explicitly and the hydrogen atoms are collapsed on the carbon atoms to which they are covalently bonded, and the dummy-hydrogens atoms representation on the other hand, in which the hydrogen atoms are modeled as interaction sites with no mass and with a positive partial electrical charge. The results of these simulations are presented in Chapter 3. We begin our systematic study on the interacting species in a biomedical device by characterizing the atactic amorphous polystyrene substrate. In Chapter 4 we present the results of molecular-dynamics simulations of polystyrene surfaces with controlled degree of oxidation. The variations in degree of oxidation at the surface, ranging from 0% to 24%, correspond to different degrees of hydrophilicity of the polystyrene surface, from hydrophobic to hydrophilic. We study the influence of the oxidation on the roughness of the film, both in vacuum and in water environment. We compare our results with experimental results from AFM measurements obtained by our collaborators. We also analyze the ordering of the molecular segments in non-oxidized and oxidized polystyrene at the interface with vacuum and with water. The structure of the water interface near polystyrene surfaces with different hydrophilicity is analyzed as well. Since the interaction between proteins and polymeric surfaces is a water-mediated process, it is very important to know how water behaves near these surfaces. In Chapter 5 we discuss the dynamics of water near non-oxidized (hydrophobic) and oxidized (hydrophilic) polystyrene surfaces, both in united-atoms and dummy-hydrogen atoms representations. We discuss the orientational dynamics of water molecules and its dependence on the distance from the interface. Furthermore, the translational diffusion of water molecules is briefly discussed. In Chapter 6 we study the nature of non-specific adsorption of myoglobin, as model protein, to hydrophobic and hydrophilic polystyrene surfaces. We investigate the importance of the orientation of the protein in the process of adsorption. We also discuss the influence of the hydrophilicity of the surface on the strength of adsorption of the protein. We conclude this thesis by Chapter 7, in which our main results are summarized. In addition, we give there an outlook on further interesting questions.

Place, publisher, year, edition, pages
Technische Universiteit Eindhoven, 2013. p. 124
Keywords
Polystyrenes, Molecular Dynamics, Computer Simulation, Water, Molecules, Atoms, Hydrophilicity, Biosensors, Myoglobin
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-66745 (URN)978-90-386-3345-9 (ISBN)
Public defence
2013-03-14, 16:00 (English)
Supervisors
Available from: 2018-08-13 Created: 2018-03-19 Last updated: 2018-08-13Bibliographically approved
Muntean, S. A., Wedershoven, H. M. J., Gerasimov, R. A. & Lyulin, A. V. (2012). Representation of hydrogen atoms in molecular dynamics simulations: The influence on the computed properties of thin polystyrene films. Macromolecular Theory and Simulations, 21(2), 90-97
Open this publication in new window or tab >>Representation of hydrogen atoms in molecular dynamics simulations: The influence on the computed properties of thin polystyrene films
2012 (English)In: Macromolecular Theory and Simulations, ISSN 1022-1344, E-ISSN 1521-3919, Vol. 21, no 2, p. 90-97Article in journal (Refereed) Published
Abstract [en]

The united atoms (UA) and dummy hydrogen atom (DHA) approaches for molecular dynamics simulations of the interface between oxidized atactic polystyrene (aPS) thin films and water are compared. For both oxidized and non-oxidized aPS films the polymer density profile decays steepest when using the UA model. The surface roughness of the aPS film and the ordering of the phenyl rings near the surface decrease upon changing from vacuum to water for the UA, but not for the DHA model. This also supports the fact that the non-oxidized aPS films modeled in DHA representation become less hydrophobic. The water structure close to the interface also suggests that the aPS films modeled using UA are more hydrophobic compared to the aPS films modeled with DHA in the phenyl rings. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2012
Keywords
Atactic polystyrenes; Hydrogen atoms; Molecular dynamics simulations; Phenyl rings; Polymer densities; Thin polystyrene films; United atoms; Water structure, Amorphous materials; Hydrogen; Hydrophobicity; Molecular dynamics; Polymer films; Polystyrenes; Surface roughness; Thin films, Interfaces (materials)
National Category
Mathematics Polymer Technologies
Research subject
Mathematics
Identifiers
urn:nbn:se:kau:diva-63836 (URN)10.1002/mats.201100056 (DOI)000299824600003 ()2-s2.0-84856703112 (Scopus ID)
Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2018-06-07Bibliographically approved
Muntean, S. A., Kemper, M., Van Ijzendoorn, L. J. & Lyulin, A. V. (2011). Roughness and ordering at the interface of oxidized polystyrene and water. Langmuir, 27(14), 8678-8686
Open this publication in new window or tab >>Roughness and ordering at the interface of oxidized polystyrene and water
2011 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 14, p. 8678-8686Article in journal (Refereed) Published
Abstract [en]

For the first time, atomistically detailed molecular dynamics calculations revealed molecular ordering of the water-oxidized atactic polystyrene (aPS) interface. Both ordering of the water molecules and the phenyl rings occur. In addition, the natural roughness of the surface has been simulated and compared to experimental values. The composition of the simulated aPS films is based on spin-coated aPS films that have been oxidized and characterized experimentally. The aPS surfaces are oxidized with ultraviolet-ozone radiation and have been characterized by XPS, AFM, and water contact angle measurements. XPS measurements show that the oxygen content in the sample increases rapidly with exposure and reaches saturation near 24 at. % of oxygen. The molecular dynamics simulations show smoothening of an hydrophobic aPS surface upon transition from vacuum to water. The smoothening decreases with increasing hydrophilicity. The calculations reveal ordering of oxidized phenyl rings for aPS surfaces in water. The order increases with increasing hydrophilicity. Additionally, we investigated the water structure near the aPS-water interface as a function of the surface hydrophilicity. With increasing hydrophilicity, the density of water at the aPS-water interface increases. The water density profile is steeper in the presence of hydrophobic aPS. The water shows an ordered layer near both the hydrophobic and hydrophilic surfaces; the position of this layer shifts toward the interface with increasing hydrophilicity. © 2011 American Chemical Society.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2011
Keywords
AFM; Atactic polystyrenes; Density of water; Experimental values; Hydrophobic and hydrophilic; Molecular dynamics calculation; Molecular dynamics simulations; Molecular ordering; Ordered layer; Oxygen content; Phenyl rings; Surface hydrophilicity; Ultraviolet-ozone; Water contact angle measurement; Water density; Water molecule; Water structure; XPS measurements, Angle measurement; Contact angle; Hydrophobicity; Molecular dynamics; Ozone; Polystyrenes; X ray photoelectron spectroscopy, Hydrophilicity, polystyrene derivative; water, article; chemical phenomena; chemistry; conformation; molecular dynamics; oxidation reduction reaction; surface property, Hydrophobic and Hydrophilic Interactions; Molecular Conformation; Molecular Dynamics Simulation; Oxidation-Reduction; Polystyrenes; Surface Properties; Water
National Category
Probability Theory and Statistics Mathematics
Research subject
Mathematics
Identifiers
urn:nbn:se:kau:diva-63838 (URN)10.1021/la200203s (DOI)000292617800012 ()2-s2.0-79960281114 (Scopus ID)
Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2018-06-07Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9337-2249

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