TY - CONF A1 - Omar, Hassan T1 - Invesitgation of Thin Film Interactions with Inorganic Surfaces N2 - Thin polymer films are of vital importance due to their low production costs and wide range of applications in sensors, electronics, and coatings. Their geometry is ideal for the study of confinement effects, specifically one-dimensional confinement, on the thermodynamic properties and segmental dynamics of polymers. For this investigation, films of PC are prepared on both glass and silica substrates to measure the dielectric and calorimetric behavior as a function of film thickness. The methodology consists of broadband dielectric spectroscopy (BDS), ellipsometry, and atomic force microscopy (AFM). Using ellipsometry, the glass transition shows an increase with decreasing film thickness. Compared to a previous investigation of PC where dilatometry was used, an increase in PC was seen, but now only at thicknesses below 20 nm. Therefore, the critical thickness of PC, where the bulk-like layer no longer percolates through the film, is dependent on the method probing the glass transition. The dielectric behavior shows a deviation from bulk behavior with decreasing film thickness, although still showing a Vogel-Fulcher-Tammann (VFT) temperature dependence for all films. The influence of the adsorbed layer on the molecular mobility was also addressed. T2 - Deutschen Physikalische Gesellschaft (DPG) Tagung CY - Regensburg, Germany DA - 04.09.2022 KW - Thin films KW - Adsorbed Layer KW - Broadband dielectric spectroscopy PY - 2022 AN - OPUS4-55706 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Omar, Hassan T1 - Growth Kinetics and Molecular Mobility of the adsorbed Layer of Poly(bisphenol-A Carbonate) (PBAC), Polysulfone (PSU), and Poly (2-Vinyl Pyridine) (P2VP) N2 - Interactions between a polymer and a substrate interface play a vital role in understanding the improvement in thin film material properties as well as serving as a model for nanocomposites. For any non-repulsive polymer-substrate interactions, polymer segments form an irreversibly adsorbed layer and show a slowdown in the glassy dynamics and thus an increase in the thermal glass transition temperature compared to the bulk-like values. The growth kinetics of the adsorbed layer obey a two-step mechanism: formation of immobilized layer with flat segmental conformations and a loosely bound layer with stretched chains pinned to the surface. Here the adsorbed layer was studied for: poly (bisphenol-A carbonate) (PBAC) and polysulfone (PSU), two bulky polymers containing a functional group (phenyl ring) in the backbone and compared to poly (2-vinyl pyridine) (P2VP), where the backbone is a vinyl-derivative and the functional group (pyridine) is in the side chain. The growth kinetics for PBAC and PSU were found to deviate from the well-known mechanism, observed for polymers such as P2VP. Atomic force microscopy and ellipsometry were used for this investigation and was additionally supported by broadband dielectric spectroscopy. T2 - Deutschen Physikalische Gesellschaft (DPG) Tagung CY - Dresden, Germany DA - 26.03.2023 KW - Thin films KW - Adsorbed Layer KW - Broadband dielectric spectroscopy KW - Atomic force microscopy KW - Growth Kinetics PY - 2023 AN - OPUS4-57282 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Omar, Hassan T1 - Probing Nanoscale Relaxation Behavior in Thin Polymer Films N2 - The investigations into the complicated effects of film thickness on bulk properties of thin polymer films has yielded conflicting results. The reduction in molecular mobility, and with it an increase in the glass transition temperature, for thin films of poly (bisphenol A carbonate) (PBAC) was assigned to the formation of an adsorbed layer. The adsorbed layer was obtained by washing away the loosely bounded chains using a good solvent. Next, using atomic force microscopy (AFM), the thickness of each sample was measured after annealing for various times at three different annealing temperatures. The growth of this adsorbed layer was shown to deviate from the previously reported 2-step mechanism seen for other polymers. For PBAC, after very long annealing times at high temperatures the thin films were dewetted, where segments of the adsorbed layer were removed from the substrate. T2 - Royal Society of Chemistry (RSC) Poster CY - Online meeting DA - 28.02.2023 KW - Thin films KW - Adsorbed Layer KW - Broadband dielectric spectroscopy KW - Atomic force microscopy KW - Growth Kinetics PY - 2023 AN - OPUS4-57196 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Omar, Hassan A1 - Smales, Glen Jacob A1 - Henning, S. A1 - Li, Z. A1 - Wang, D.-Y. A1 - Schönhals, Andreas A1 - Szymoniak, Paulina T1 - Calorimetric and Dielectric Investigations of Epoxy-Based Nanocomposites with Halloysite Nanotubes as Nanofillers N2 - Epoxy nanocomposites are promising materials for industrial applications (i.e., aerospace, marine and automotive industry) due to their extraordinary mechanical and thermal properties. Here, the effect of hollow halloysite nanotubes (HNT) on an epoxy matrix (Ep) was the focus of the study. The structure and molecular mobility of the nanocomposites were investigated using a combination of X-ray scattering, calorimetry (differential (DSC) and fast scanning calorimetry (FSC)) and dielectric spectroscopy. Additionally, the effect of surface modification of HNT (polydopamine (PDA) and Fe(OH)3 nanodots) was considered. For Ep/HNT, the glass transition temperature (Tg) is was de-creased due to a nanoparticle-related decrease of the crosslinking density. For the modified system, Ep/m-HNT, the surface modification resulted in enhanced filler–matrix interactions leading to higher Tg values than the pure epoxy in some cases. For Ep/m-HNT, the amount of interface formed between the nanoparticles and the matrix ranged from 5% to 15%. Through BDS measurements, localized fluctuations were detected as a β- and γ-relaxation, related to rotational fluctuations of phenyl rings and local reorientations of unreacted components. A combination of calorimetry and BDS dielectric spectroscopy revealed a dynamic and structural heterogeneity of the matrix, as confirmed by two glassy dynamics in both systems, related to regions with different crosslinking densities. KW - Rigid amorphous fraction KW - Epoxy nanocomposites KW - Halloysite nanotubes KW - X-ray scattering KW - Differential scanning calorimetry KW - Broadband dielectric spectroscopy KW - Flash DSC PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-526668 DO - https://doi.org/10.3390/polym13101634 VL - 13 IS - 10 SP - 1634 PB - MDPI AN - OPUS4-52666 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Waniek, Tassilo A1 - Omar, Hassan A1 - Szymoniak, Paulina A1 - Silbernagl, Dorothee A1 - Sturm, Heinz T1 - The influence of water released from particles in epoxy‐based nanocomposites N2 - AbstractRecent studies have hypothesized that the reinforcing effects of boehmite nanoparticles (BNPs) in polymer nanocomposites (PNCs) are partly related to the particles themselves and partly to the water released from the BNP during curing. In this work, PNCs made from dried BNP (dBNP) with concentrations up to 15 wt% are investigated to differentiate particle and water related effects. The observed trend of the storage modulus in dynamic mechanical thermal analysis measurements was found to be independent of the drying procedure. Stiffness maps from intermodulation atomic force microscopy showed that dBNP leads to a stiffening of the interphase surrounding the particles compared with the unaffected epoxy matrix, while a softer interphase was reported for PNCs with as received BNP. A slight decrease in the glass transition temperature was observed by broadband dielectric spectroscopy related to a lowered crosslink density due to the particles. A significantly higher decrease was reported for PNCs with BNP, attributed to water influencing the curing process. In conclusion, the stiffening of PNC with BNP is related to the particles themselves, while the release of water causes the formation of a soft interphase in the vicinity of the particles and a significant decrease in crosslink density. KW - AFM stiffness of interface KW - Aluminium oxide hydroxide KW - Boehmit nanoparticle KW - Glass transition temperature KW - Broadband dielectric spectroscopy KW - Crosslink density control KW - Structure–property relationship KW - Nanocomposites KW - Thermoset PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-606772 DO - https://doi.org/10.1002/app.55937 SN - 0021-8995 SP - 1 EP - 16 PB - Wiley AN - OPUS4-60677 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -