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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”

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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

Die molekularen Grundlagen der anisotropen thermischen Ausdehnung von Paraffinen und Polyäthylen. Eine ramanspektroskopische Untersuchung am Beispiel des N-Tritriacontans
G.R. Strobl. Coll. Polym. Sci. 254, 170-189 (1976)
Packing of Paraffin Chains in 4 Stable Modifications of n-Tritriacontane
W. Piesczek, G.R. Strobl, K. Malzahn. Acta Cryst. B 30, 1278 (1974)
Defect Structure and Molecular-Motion in 4 Modifications of Normal-Tritriacontane. 2. Study of Molecular-Motion Using Infrared Spectroscopy and Wide-Line Nuclear Magnetic-Resonance Measurements
B. Ewen, E.W. Fischer, W. Pieszek, G. Strobl. J. Chem. Phys. 61, 5265-5272 (1974)
Defect Structure and Molecular-Motion in 4 Modifications of Normal-Tritriacontane. 1. Study of Defect Structure in Lamellar Interfaces Using Small-Angle X-Ray-Scattering
G. Strobl, B. Ewen, E.W. Fischer, W. Piesczek. J. Chem. Phys. 61, 5257-5264 (1974)
An exactly solvable model for coherent and incoherent exciton motion
H. Haken and G. Strobl. Zeitschrift für Physik 262, 135-148 (1973)
Small-angle x-ray scattering experiments for investigating the validity of the two-phase model
G.R. Strobl, N. Müller. Journal of Polymer Science B - Polymer Physics 11, 1219-1233 (1973)
Determination of Lamellar Structure of Partially Crystalline Polymers by Direct Analysis of their Small-Angle X-Ray-Scattering Curves
G.R. Strobl. Journal of Applied Crystallography 6, 365-370 (1973)
Synthese und Eigenschaften molekulareinheitlicher n-Paraffine bis zum C140H282
W. Heitz, E.W. Fischer, R. Peters, T. Wirth, G. Strobl. Makromolekulare Chemie 162, 63 (1972)
Analyse von spaltverschmierten Kleinwinkelstreukurven lamellarer Strukturen
G.R. Strobl. Kolloid-Zeitschrift and Zeitschrift für Polymere 250, 1039-1046 (1972)
A New Method for Evaluating Slit-Smeared Small Angle X-Ray Scattering Data
G.R. Strobl. Acta Crystallographica A 26, 367-375 (1970)
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