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Recent Publications


Measurements of periodically perturbed dewetting force fields and their consequences on the symmetry of the resulting patterns

2021-rei-02.jpgWe studied the origin of breaking the symmetry for moving circular contact lines of dewetting polymer films suspended on a periodic array of pillars. There, dewetting force fields driving polymer flow were perturbed by elastic micro-pillars arranged in a regular square pattern. Elastic restoring forces of deformed pillars locally balance driving capillary forces and broke the circular symmetry of expanding dewetting holes. The observed envelope of the dewetting holes reflected the symmetry of the underlying pattern, even at sizes much larger than the characteristic period of the pillar array, demonstrating that periodic perturbations in a driving force field can establish a well-defined pattern of lower symmetry. For the presented system, we succeeded in squaring the circle. [more...]



Surface-modified elastomeric nanofluidic devices for single nanoparticle trapping

pfohl-02.jpgOur work focuses on the development of simpler and effective production of nanofluidic devices for high-throughput charged single nanoparticle trapping in an aqueous environment. Single nanoparticle confinement using electrostatic trapping has been an effective approach to study the fundamental properties of charged molecules under a controlled aqueous environment. Conventionally, geometry-induced electrostatic trapping devices are fabricated using SiOx-based substrates and comprise nanochannels imbedded with nanoindentations such as nanopockets, nanoslits and nanogrids. These geometry-induced electrostatic trapping devices can only trap negatively charged particles, and therefore, to trap positively charged particles, modification of the device surface is required. [more...]



Changes in Surface Free Energy and Surface Conductivity of Carbon Nanotube/Polyimide Nanocomposite Films Induced by UV Irradiation

am1c02654_0012.gifChanges in surface energy and electrical conductivity of polyimide (PI)-based nanocomposite films filled with carbon nanotubes (CNTs) induced by UV exposure are gaining considerable interest in microelectronic, aeronautical, and aerospace applications. However, the underlying mechanism of PI photochemistry and oxidation reactions induced by UV irradiation upon the surface in the presence of CNTs is still not clear. Here, we probed the interplay between CNTs and PIs under UV exposure in the surface properties of CNT/PI nanocomposite films.   [more...]


  
Continuous Illumination of a Conjugated Polymer Causes Strong Enhancement of Photoluminescence

jp1c01837_0009.jpgWe present measurements of absorbance and photoluminescence (PL) for films of poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT) as a function of temperature (T) and time (t) of illumination. While having no detectable influence on absorbance of this conjugated polymer, our experiments clearly revealed that illumination of PDOPT caused a significant increase in the PL intensity (IPL(T,t)), that is, the emission probability of PDOPT. Without illumination, we always observed a decrease in IPL with time. An increase in IPL was only detectable when the sample was illuminated. [more...]



Self-Seeding Procedure for Obtaining Stacked Block Copolymer Lamellar Crystals in Solution

brahim-polymers.jpgWe examined the formation of self-seeded platelet-like crystals from polystyrene-block-polyethylene oxide (PS-b-PEO) diblock copolymers in toluene as a function of polymer concentration (c), crystallization temperature (TC), and self-seeding temperature (TSS). We showed that the number (N) of platelet-like crystals and their mean lateral size (L) can be controlled through a self-seeding procedure.  [more...]



Formation of Stacked Three-Dimensional Polymer “Single Crystals”

ma1c00081_0006.gif

Stacks of crystalline lamellae all having a uniquely oriented hexagonal shape, referred to as “3D (three-dimensional) single crystals”, were obtained via isothermal crystallization of isotactic polystyrene at a temperature close to the melting point. The height of the stacks of lamellae reached several micrometers corresponding to hundreds of superposed lamellar crystals. We propose that the mechanism of self-induced nucleation allowed propagating the orientation of the basal lamellar crystal to all other lamellae in the stack. [more...]



Concepts of nucleation in polymer crystallization

2021-xujun.jpgNucleation plays a vital role in polymer crystallization, in which chain connectivity and thus the multiple length and time scales make crystal nucleation of polymer chains an interesting but complex subject. Though the topic has been intensively studied in the past decades, there are still many open questions to answer. The final properties of semicrystalline polymer materials are affected by all of the following: the starting melt, paths of nucleation, organization of lamellar crystals and evolution of the final crystalline structures. [more...]



Optimization of Nanofluidic Devices for Geometry‐Induced Electrostatic Trapping

2021-pfo-01c.jpgNanoparticle trapping in a nanofluidic device utilizing geometry-induced electrostatic (GIE) potential trap is an efficient and robust way to perform nano‑object confinement and single particle studies. The GIE‑trapping is a passive method that solely depends on the device geometry and device-particle surface interaction. Therefore, optimization of a nanofluidic device based on experimental requirements, helps to achieve stiffer single-particle trapping. The efficiency of a GIE‑trapping device is defined in terms of residence time and trapping stiffness of the nanoparticle inside a potential trap. The present study reveals all crucial parameters that affect the device efficiency, particle trapping stiffness, and particle residence time. [more...]

 

List of Publications

Self-Seeding Procedure for Obtaining Stacked Block Copolymer Lamellar Crystals in Solution
Brahim Bessif, Thomas Pfohl and Günter Reiter. Polymers 13 (2021) 1676
Concepts of nucleation in polymer crystallization
Jun Xu, Günter Reiter, Rufina G. Alamo. Crystals 11 (2021) 304
Continuous illumination of a conjugated polymer causes strong enhancement of photoluminescence
Yaser AlShetwi, Daniel Schiefer, Michael Sommer. Günter Reiter. J. Phys. Chem. B 125 (2021) 5636–5644
Formation of Stacked Three-Dimensional Polymer “Single Crystals”
Zhixin Guo, Shouke Yan, Günter Reiter. Macromolecules 54 (2021) 4918–4925
Measurements of periodically perturbed dewetting force fields and their consequences on the symmetry of the resulting patterns
Konstantinos Roumpos, Sarah Fontaine, Thomas Pfohl, Oswald Prucker, Jürgen Rühe, and Günter Reiter. Scientific Reports 11 (2021) 13149
Changes in surface free energy and surface conductivity of carbon nanotubes/polyimide nanocomposite films induced by UV irradiation
Baode Zhang, Marialaura Clausi, Barbara Heck, Susanna Laurenzi, Gabriella Santonicola, Janis Kleperis, Andris Antuzevičs, Guenter Reiter, Andrey Aleshin, Anatoly Lobach. ACS Appl. Mater. Interfaces 13 (2021) 24218–24227
Surface-modified elastomeric nanofluidic devices for single nanoparticle trapping
Deepika Sharma, Roderick Y. H. Lim, Thomas Pfohl and Yasin Ekinci. Microsystems & Nanoengineering 7 (2021) 46
Optimization of Nanofluidic Devices for Geometry-Induced Electrostatic Trapping
Deepika Sharma, Roderick Y. H. Lim, Thomas Pfohl, and Yasin Ekinci. Part. Part. Syst. Charact. 2021, 38, 2000275
Tuning topography and patterns of thin polymer films on structured substrates
Konstantinos Roumpos. Inauguraldissertation der Fakultät für Mathematik und Physik 2021. DOI: 10.6094/UNIFR/194127
High-throughput injection molding of transparent fused silica glass
Markus Mader, Oliver Schlatter, Barbara Heck, Andreas Warmbold, Alex Dorn, Hans Zappe, Patrick Risch, Dorothea Helmer, Frederik Kotz, Bastian E. Rapp. Science 372 (2021) 182-186
Formation of large polymer crystals from metastable solutions
Tianyu Wu. Inauguraldissertation der Fakultät für Chemie und Pharmazie 2020, DOI: 10.6094/UNIFR/167415
Exploring pathways to equilibrate Langmuir polymer films
Abhijna Das, Sebastian Noack, Helmut Schlaad, Günter Reiter, Renate Reiter. Langmuir 36 (2020) 8184–8192
Energy transport and light propagation mechanisms in organic single crystals
Bernd Wittmann, Stephan Wiesneth, Sajedeh Motamen, Laurent Simon, Françoise Serein-Spirau, Günter Reiter, and Richard Hildner. Journal of Chemical Physics 153 (2020) 144202
Large quantum efficiency enhancements of pristine conjugated polymer MEH-PPV by interlayer polymer diffusion
Po-Tsun Chen, Ya-Wei Yang, Günter Reiter, Arnold C.-M. Yang. Polymer 204 (2020) 122753
Formation of Needle-like Poly(3-hexylthiophene) Crystals from Metastable Solutions
Tianyu Wu, Thomas Pfohl, Sivasurender Chandran, Michael Sommer and Günter Reiter. Macromolecules 53 (2020) 8303–8312
Rheological Properties of Blends of Isotactic Polystyrene–Isotactic Poly(para-methylstyrene) Films Derived from a Comparative Dewetting Study
Austine Amukayia Mulama, Konstantinos Roumpos, Pradipkanti Lairenjam, Andrew Oduor, Günter Reiter. Macromolecules 53 (2020) 9122–9130
Dewetting-Induced Alignment and Ordering of Cylindrical Mesophases in Thin Block Copolymer Films
Heng Zhang, Binghua Wang, Gang Wang, Changyu Shen, Jingbo Chen, Günter Reiter, Bin Zhang. Macromolecules 53, (2020) 9631–9640
Estimation of the Size of Critical Secondary Nuclei of Melt-Grown Poly(l-lactide) Lamellar Crystals
Shujing Zhang, Baohua Guo, Günter Reiter, Jun Xu. Macromolecules 53 (2020) 3482–3492
Translating molecular relaxations in non-equilibrated polymer melts into lifting macroscopic loads
Farzad Ramezani, Jörg Baschnagel, and Günter Reiter. Phys. Rev. Materials 4 (2020) 082601
A new growth process for crystalline ultra-thin layers of conjugated oligomers used in field-effect transistor applications
Sven Renkert, Sadiara Fall, Sajedeh Motamen, Thibaut Jarrosson, Françoise Serein-Spirau, Thomas Heiser, Laurent Simon, Günter Reiter, Jean-Luc Bubendorff. Applied Surface Science 539 (2021) 148024
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