TY - JOUR A1 - Madkour, Sherif A. A1 - Gawek, Marcel A1 - Penner, P. A1 - Paneff, F. A1 - Zhang, X. A1 - Gölzhäuser, A. A1 - Schönhals, Andreas T1 - Can Polymers be Irreversibly Adsorbed on Carbon Nanomembranes? A Combined XPS, AFM, and Broadband Dielectric Spectroscopy Study N2 - Carbon nanomembranes are synthetic two-dimensional sheets with nanometer thickness, macroscopic lateral dimensions, and high structural homogeneity. They have great application potential in various branches of nanotechnology. Because of their full carbon structure, it is not clear whether macromolecules like poly(methyl methacrylate) (PMMA) can be irreversibly adsorbed on their surface. Here, irreversible adsorption means that the polymer chains cannot be removed by a leaching process, which is assumed in technological transfer processes. However, if polar defects are present on the carbon nanomembranes (CNMs), it may occur that polymers can be irreversibly adsorbed. To address this question, PMMA was spin-coated on top of CNMs, annealed for a specific time at different temperatures, and then tried to be removed by a acetone treatment in a leaching approach. The samples were investigated in detail by atomic force microscopy, X-ray photoelectron spectroscopy, and broadband dielectric spectroscopy, where the latter method has been applied to CNMs for the first time. Unambiguously, it was shown that PMMA can be adsorbed on the surface of CNMs after annealing the sample above the glasstransition temperature of PMMA. The general occurrence of polar defects on the surface of CNMs and the adsorption of polymers open opportunities for advanced innovative hybrid materials combining the properties of the CNM with those of the polymer. KW - Carbon Nanomembranes KW - Irreversible adsorption KW - Broadband dielectric spectroscopy KW - XPS spctroscopy KW - Atomic force microscopy PY - 2022 U6 - https://doi.org/10.1021/acsapm.2c01320 SN - 2637-6105 VL - 4 IS - 11 SP - 8377 EP - 8385 PB - ACS AN - OPUS4-56067 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gawek, Marcel A1 - Madkour, Sherif A1 - Szymoniak, Paulina A1 - Radnik, Jörg A1 - Schönhals, Andreas T1 - Energy Dependent XPS Measurements on Thin Films of a Poly(vinyl methyl ether)/Polystyrene Blend in Dependence on Film Thickness – Concentration Profile on a Nanometer Resolution to Understand the Behavior of Nanofilms N2 - The composition of the surface layer in dependence from the distance of the polymer/air interface in thin films with thicknesses below 100 nm of miscible polymer blends in a spatial region of a few nanometers is not investigated completely. Here, thin films of the blend poly vinyl methyl ether) (PVME)/polystyrene (PS) with a composition of 25/75 wt% are investigated by Energy Resolved X-ray Photoelectron Spectroscopy (ER-XPS) at a synchrotron storage ring using excitation energies lower than 1 keV. By changing the energy of the photons the information depth is varied in the range from ca. 1 nm to 10 nm. Therefore, the PVME concentration could be estimated in dependence from the distance of the polymer/air interface for film thicknesses below 100 nm. Firstly, as expected for increasing information depth the PVME concentration decreases. Secondly, it was found that the PVME concentration at the surface has a complicated dependence on the film thickness. It increases with decreasing film thickness until 30 nm where a maximum is reached. For smaller film thicknesses the PVME concentration decreases. A simplified layer model is used to calculate the effective PVME concentration in the different spatial regions of the surface layer. KW - Energy dependent XPS KW - Soft X-ray KW - Thin films PY - 2021 U6 - https://doi.org/10.1039/d1sm00656h VL - 17 IS - 29 SP - 6985 EP - 6994 PB - The Royal Chemical Society AN - OPUS4-53039 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madkour, Sherif Aly Hassan Aly A1 - Yin, Huajie A1 - Füllbrandt, Marieke A1 - Schönhals, Andreas T1 - Calorimetric evidence for a mobile surface layer in ultrathin polymeric films: poly(2-vinyl pyridine) N2 - Specific heat spectroscopy was used to study the dynamic glass transition of ultrathin poly(2-vinyl pyridine) films (thicknesses: 405–10 nm). The amplitude and the phase angle of the differential voltage were obtained as a measure of the complex heat capacity. In a traditional data analysis, the dynamic glass transition temperature Tg is estimated from the phase angle. These data showed no thickness dependency on Tg down to 22 nm (error of the measurement of ±3 K). A derivative-based method was established, evidencing a decrease in Tg with decreasing thickness up to 7 K, which can be explained by a surface layer. For ultrathin films, data showed broadening at the lower temperature side of the spectra, supporting the existence of a surface layer. Finally, temperature dependence of the heat capacity in the glassy and liquid states changes with film thickness, which can be considered as a confinement effect. PY - 2015 U6 - https://doi.org/10.1039/c5sm01558h SN - 1744-683X VL - 11 IS - 40 SP - 7942 EP - 7952 PB - RSC Publ. CY - Cambridge AN - OPUS4-34605 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yin, Huajie A1 - Madkour, Sherif Aly Hassan Aly A1 - Schönhals, Andreas T1 - Unambiguous evidence for a highly mobile surface layer in ultrathin polymer films by specific heat spectroscopy on blends N2 - Despite the decade long controversial discussion on the effect of nanometer confinement on the glass transition temperature (Tg) of ultrathin polymer films, there is still no consistent picture. Here, the dynamic calorimetric glass transition of ultrathin films of a blend, which is miscible in the bulk, is directly investigated by specific heat spectroscopy. By a self-assembling process, a nanometer thick surface layer with a higher molecular mobility is formed at the polymer/air interface. By measuring the dynamic calorimetric Tg in dependence on the film thickness, it was shown that the Tg of the whole film was strongly influenced by that nanometer thick surface layer, with a lower Tg. Since the observed thickness dependence of the dynamic Tg is similar to the thickness dependence of the Tg for thin films of homopolymers, it is concluded that also for homopolymer a highly mobile surface layer is relevant for the widely observed Tg depression. PY - 2015 U6 - https://doi.org/10.1021/acs.macromol.5b01259 SN - 0024-9297 SN - 1520-5835 VL - 48 IS - 14 SP - 4936 EP - 4941 PB - American Chemical Society CY - Washington, DC AN - OPUS4-33841 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Said Shabaan Omara, Shereen A1 - Rehim, M.H.A. A1 - Ghoneim, A. A1 - Madkour, Sherif Aly Hassan Aly A1 - Thünemann, Andreas A1 - Turky, G. A1 - Schönhals, Andreas T1 - Structure-property relationships of hyperbranched polymer/kaolinite nanocomposites N2 - Two methods were employed to prepare hyperbranched polyamine ester (HPAE)/kaolinite (Ka) nanocomposites resulting in different morphologies. In the case of the in situ polymerization, diethanolamine is inserted as monomer between the Ka layers and polymerized with methyl acrylate to prepare HPAE/Ka–DEA nanocomposites. For the ex situ method, Ka is modified with dodecylamine and solution-blended with HPAE. The former method leads to an intercalated morphology where the latter approach results in an exfoliated structure, as proofed by SAXS and TEM. A complementary combination of methods like differential scanning calorimetry (DSC), broadband dielectric relaxation (BDS), and specific heat spectroscopy (SHS) was used to investigate both kinds of nanocomposites in detail. Above Tg, the dielectric spectra are dominated by the conductivity contribution while the segmental dynamics is retrieved by SHS. A comparison of the temperature dependencies reveals a decoupling of segmental dynamics and conductivity, which becomes weaker with decreasing fragility. PY - 2015 U6 - https://doi.org/10.1021/acs.macromol.5b01693 SN - 0024-9297 SN - 1520-5835 VL - 48 IS - 18 SP - 6562 EP - 6573 PB - American Chemical Society CY - Washington, DC AN - OPUS4-34424 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madkour, Sherif A1 - Melnichu, I. A1 - Choukourov, A. A1 - Krakovsky, I. A1 - Biedermann, H. A1 - Schönhals, Andreas T1 - In situ nanocalorimetric investigations of plasma assisted deposited poly(ethylene oxide)-like films by specific heat spectroscopy N2 - In the recent years, highly crosslinked plasma polymers have started to unveil their potential in numerous biomedical applications in thin-films form. However, conventional diagnostic methods often fail due to their diverse molecular dynamics conformations. Here, glassy dynamics and the melting transition of thin PEO-like plasma assisted deposited (ppPEO) films (thickness 100 nm) were In situ studied by a combination of specific heat spectroscopy, utilizing pJ/K sensitive AC-calorimeter chip, and composition analytical techniques. Different crosslinking densities were obtained by different plasma powers during the deposition of the films. Glassy dynamics was observed for all values of the plasma power. It was found that the glassy dynamics slows down with increasing the plasma power. Moreover, the underlying relaxation time spectra broaden indicating that the molecular motions become more heterogeneous with increasing plasma power. In a second set of experiment, the melting behavior of the ppPEO films was studied. The melting temperature of ppPEO was found to be decreasing with increasing plasma power. This was explained by a decrease of the order in the crystals due to formation of chemical defects during the plasma process. KW - Plasma deposited polymers KW - Nanocalorimetry KW - Thin polymer films KW - Glass transition PY - 2016 U6 - https://doi.org/10.1021/acs.jpcb.6b01355 SN - 1520-6106 SN - 1520-5207 VL - 120 IS - 16 SP - 3954 EP - 3962 PB - American Chemical Society CY - Washington, DC, USA AN - OPUS4-35922 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madkour, Sherif A1 - Garwek, Marcel A1 - Hertwig, Andreas A1 - Schönhals, Andreas T1 - Do Interfacial Layers in Thin Films Act as an Independent Layer Within Thin Films? N2 - The thermodynamic behavior of thin PVME films including the irreversible adsorbed layer on the substrate is investigated. In a first step, the growth kinetics of the adsorbed layer was studied combining a leaching technique and atomic force microscopy. Further, it was shown that there is a critical initial film thickness for the formation of a surface-filling adsorbed layer. Additionally, spectroscopic ellipsometry measurements were carried out to investigate the influence of the adsorbed layer on the glass transition temperature of the thin films. For 30 nm films and below, the influence of the adsorbed layer percolates strongly to the bulk-like layer of the film. Finally, the molecular dynamics of the adsorbed layer was studied by broadband dielectric spectroscopy, employing nanostructured-electrode systems. One process was revealed, which was assigned either to molecular fluctuations taking place in a loosely-bounded the part of the adsorbed layer, or to the desorption/adsorption of segments at the substrate. KW - Thin polymer films PY - 2021 U6 - https://doi.org/10.1021/acs.macromol.0c02149 VL - 54 IS - 1 SP - 509 EP - 519 PB - ACS Publications AN - OPUS4-52037 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madkour, Sherif A1 - Szymoniak, Paulina A1 - Schick, Ch. A1 - Schönhals, Andreas T1 - Unexpected behavior of ultra-thin films of blends of polystyrene/poly(vinyl methyl ether) studied by specific heat spectroscopy N2 - Specific heat spectroscopy (SHS) employing AC nanochip calorimetry was used to investigate the glassy dynamics of ultra-thin films (thicknesses: 10 nm–340 nm) of a polymer blend, which is miscible in the bulk. In detail, a Poly(vinyl methyl ether) (PVME)/Polystyrene (PS) blend with the composition of 25/75 wt. % was studied. The film thickness was controlled by ellipsometry while the film topography was checked by atomic force microscopy. The results are discussed in the framework of the balance between an adsorbed and a free surface layer on the glassy dynamics. By a self-assembling process, a layer with a reduced mobility is irreversibly adsorbed at the polymer/substrate interface. This layer is discussed employing two different scenarios. In the first approach, it is assumed that a PS-rich layer is adsorbed at the substrate. Whereas in the second approach, a PVME-rich layer is suggested to be formed at the SiO2 substrate. Further, due to the lower surface tension of PVME, with respect to air, a nanometer thick PVME-rich surface layer, with higher molecular mobility, is formed at the polymer/air interface. By measuring the glassy dynamics of the thin films of PVME/PS in dependence on the film thickness, it was shown that down to 30 nm thicknesses, the dynamic Tg of the whole film was strongly influenced by the adsorbed layer yielding a systematic increase in the dynamic Tg with decreasing the film thickness. However, at a thickness of ca. 30 nm, the influence of the mobile surface layer becomes more pronounced. This results in a systematic decrease in Tg with the further decrease of the film thickness, below 30 nm. These results were discussed with respect to thin films of PVME/PS blend with a composition of 50/50 wt.%as well as literature results. KW - Ultra thin polymer films PY - 2017 U6 - https://doi.org/10.1063/1.4978505 SN - 0021-9606 SN - 1089-7690 VL - 146 IS - 20 SP - 203321-1 EP - 203321-9 PB - AIP Publishing AN - OPUS4-39558 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madkour, Sherif A1 - Szymoniak, Paulina A1 - Heídari, M. A1 - von Klitzing, R. A1 - Schönhals, Andreas T1 - Unveiling the dynamics of self-assembled layers of thin films of poly(vinyl methyl ether) (PVME) by nanosized relaxation spectroscopy N2 - A combination of nanosized dielectric relaxation (BDS) and thermal spectroscopy (SHS) was utilized to characterize the dynamics of thin films of Poly(vinyl methyl ether) (PVME) (thicknesses: 7 nm – 160 nm). For the BDS measurements, a recently designed nano-structured electrode system is employed. A thin film is spin-coated on an ultra-flat highly conductive silicon wafer serving as the bottom electrode. As top electrode, a highly conductive wafer with non-conducting nanostructured SiO2 nano-spacers with heights of 35 nm or 70 nm is assembled on the bottom electrode. This procedure results in thin supported films with a free polymer/air interface. The BDS measurements show two relaxation processes, which are analyzed unambiguously for thicknesses smaller than 50 nm. The relaxation rates of both processes have different temperature dependencies. One process coincidences in its position and temperature dependence with the glassy dynamics of bulk PVME and is ascribed to the dynamic glass transition of a bulk-like layer in the middle of the film. The relaxation rates were found to be thickness independent as confirmed by SHS. Unexpectedly, the relaxation rates of the second process obey an Arrhenius-like temperature dependence. This process was not observed by SHS and was related to the constrained fluctuations in a layer, which is irreversibly adsorbed at the substrate with a heterogeneous structure. Its molecular fluctuations undergo a confinement effect resulting in the localization of the segmental dynamics. To our knowledge, this is the first report on the molecular dynamics of an adsorbed layer in thin films. KW - Broadband dielectric spectroscopy KW - AC-nanochip calorimetry KW - Nanostructured capacitors KW - Thin films PY - 2017 UR - http://pubs.acs.org/doi/pdf/10.1021/acsami.6b14404 U6 - https://doi.org/10.1021/acsami.6b14404 SN - 1944-8244 VL - 9 IS - 8 SP - 7535 EP - 7546 PB - ACS Publications CY - Washington DC AN - OPUS4-39291 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madkour, Sherif A1 - Szymoniak, Paulina A1 - Hertwig, Andreas A1 - Heidari, M. A1 - von Klitzing, R. A1 - Napolitano, S. A1 - Sferrazza, M. A1 - Schönhals, Andreas T1 - Decoupling of dynamic and thermal glass transition in thin films of a PVME/PS blend N2 - The discussions on the nanoconfinement effect on the glass transition and glassy dynamics phenomena have yielded many open questions. Here, the thickness dependence of the thermal glass transition temperature of thin films of a PVME/PS blend is investigated by ellipsometry. Its thickness dependence was compared to that of the dynamic glass transition (measured by specific heat spectroscopy), and the deduced Vogel temperature (T0). While and T0 showed a monotonous increase, with decreasing the film thickness, the dynamic glass transition temperature () measured at a finite frequency showed a non-monotonous dependence that peaks at 30 nm. This was discussed by assuming different cooperativity length scales at these temperatures, which have different sensitivities to composition and thickness. This non-monotonous thickness dependence of disappears for frequencies characteristic for T0. Further analysis of the fragility parameter, showed a change in the glassy dynamics from strong to fragile, with decreasing film thickness. KW - Thin polymeric films KW - Ellipsometry KW - Specific heat spectroscopy PY - 2017 U6 - https://doi.org/10.1021/acsmacrolett.7b00625 SN - 2161-1653 VL - 6 IS - 10 SP - 1156 EP - 1161 PB - ACS Publications AN - OPUS4-42266 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -