TY - JOUR A1 - Füllbrandt, Marieke A1 - Purohit, Purv A1 - Schönhals, Andreas T1 - Combined FTIR and dielectric investigation of poly(vinyl acetate) adsorbed on silica particles JF - Macromolecules N2 - Samples with different amounts of poly(vinyl acetate) adsorbed on silica particles were prepared in order to study their interfacial interactions and dynamics. The interface of adsorbed polymers to a substrate plays an important role in many applications such as polymer nanocomposites, thin films, and coatings. Characterization of such interfaces is thus of high importance since they were found to differ from bulk properties. Thermogravimetric analysis (TGA) is applied to analyze the amounts of polymer adsorbed on silica particles. Broadband dielectric spectroscopy (BDS) is employed in a broad frequency (10–1–106 Hz) and temperature range (178–423 K) in order to probe the polymer/silica interface. Two relaxation processes can be identified for the composites: one corresponding to the bulklike polymer and a second one related to polymer chains close to the silica surface. For the latter the dynamic glass transition is shifted to higher temperature due to reduced mobility. This effect is investigated in dependence on the polymer content. Further investigations are done to obtain information about bound and free carbonyl fractions of poly(vinyl acetate) using Fourier transform infrared spectroscopy (FTIR) measurements. PY - 2013 DO - https://doi.org/10.1021/ma400461p SN - 0024-9297 SN - 1520-5835 VL - 46 IS - 11 SP - 4626 EP - 4632 PB - American Chemical Society CY - Washington, DC AN - OPUS4-28698 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Füllbrandt, Marieke A1 - von Klitzing, R. A1 - Schönhals, Andreas T1 - The Phase Transition Behaviour of Different Aqueous Poly(N-isopropylacrylamide) Systems monitored by Dielectric Spectroscopy T2 - Spring Meeting DPG 2012 T2 - Spring Meeting DPG 2012 CY - Berlin, Germany DA - 2012-03-26 PY - 2012 AN - OPUS4-25738 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Füllbrandt, Marieke A1 - Schönhals, Andreas T1 - Effect of architecture on thermosensitive response ofo poly(N-isopropylacrylamide) systems monitored by dielectric spectroscopy T2 - ProcessNet T2 - ProcessNet CY - Bad Dürkheim, Germany DA - 2012-03-12 PY - 2012 AN - OPUS4-25728 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Füllbrandt, Marieke A1 - von Klitzing, R. A1 - Schönhals, Andreas T1 - The dielectric signature of poly(N-isopropylacrylamide) microgels at the volume phase transition: dependence on the crosslinking density JF - Soft matter N2 - Temperature sensitive poly(N-isopropylacrylamide) (pNIPAM) microgels are prepared and investigated using dielectric spectroscopy in a frequency range from 10-1 Hz to 106 Hz at temperatures from 15 °C to 50 °C. The microgels were synthesized with different crosslinker molar ratios resulting in microgels with structural differences. From the dielectric response of the pNIPAM microgels the swelling/deswelling behaviour is monitored by both the temperature (T) and the frequency (f) dependence of the conductivity spectra σ*(f, T). The volume phase transition (VPT) at the lower critical solution temperature (LCST) is deduced by a change in the T-dependence of the DC conductivity σ'DC. It can be explained by a decrease in the effective charge mobility and a reduction in the effective charge number contributing to σ'DC at T > LCST. Addressing the f-dependence of the real part of the conductivity σ', a pronounced frequency dependence at temperatures above the LCST can be observed whereas at temperatures below the LCST the conductivity spectra resemble that of the pure solvent (water) which is frequency independent. The f-dependence of σ' at T > LCST is assigned to the collapse of the microgel particles. At the interfaces of the collapsed particles charge carriers are blocked and/or entrapped giving rise to Maxwell–Wagner–Sillars (MWS) polarization effects. The dependence of the MWS effect on the crosslinker amount is studied in detail and conclusions concerning the internal structure of the microgels with respect to their crosslinking density are drawn. Moreover the dielectric data are related to dynamic light scattering data. A correlation between the MWS polarization effect and the swelling/deswelling ratio expressed by the hydrodynamic radius Rh at different temperatures is established for the first time. PY - 2013 DO - https://doi.org/10.1039/c3sm27762c SN - 1744-683X VL - 9 IS - 17 SP - 4464 EP - 4471 PB - RSC Publ. CY - Cambridge AN - OPUS4-28012 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Füllbrandt, Marieke A1 - von Klitzing, R. A1 - Schönhals, Andreas T1 - Probing the internal morphology of different poly(N-isopropylacrylamide) systems by dielectric spectroscopy T2 - BDS 2012 (Broadband Dielectric Spectroscopy and its Applications) T2 - BDS 2012 (Broadband Dielectric Spectroscopy and its Applications) CY - Leipzig, Germany DA - 2012-09-03 PY - 2012 AN - OPUS4-26862 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Füllbrandt, Marieke A1 - von Klitzing, R. A1 - Schönhals, Andreas T1 - Probing the Thermal Collapse of Linear and Crosslinked Poly(N-isopropylacrylamide) by Dielectric Spectroscopy T2 - 19th Ostwald Kolloquium T2 - 19th Ostwald Kolloquium CY - Berlin, Germany DA - 2012-09-20 PY - 2012 AN - OPUS4-26863 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Füllbrandt, Marieke A1 - von Klitzing, R. A1 - Schönhals, Andreas T1 - Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy JF - Soft matter N2 - Aqueous solutions of linear poly(N-isopropylacrylamide) (pNIPAM) with different polymer concentrations are investigated using dielectric spectroscopy in a frequency range of 10-1 Hz to 106 Hz at temperatures from 15 °C to 50 °C. The phase transition of pNIPAM is monitored by both the temperature (T) and the frequency (ƒ) dependence of the conductivity spectra σ*(ƒ, T). First, the T-dependence of the DC conductivity σ'DC is investigated and the phase transition ('coil-to-globule' transition) at the lower critical solution temperature (LCST) of pNIPAM is deduced by a change in the T-dependence of σ'DC. The observed hysteresis between heating and cooling runs is discussed in detail in dependence on both the polymer concentration and the rate. Second, for the first time a pronounced ƒ-dependence of the real part of conductivity σ' is observed at temperatures above the LCST whereas at temperatures below the LCST the conductivity spectra are more or less similar to that of water (frequency independent). This ƒ-dependence of σ' is assigned to the formation of a kind of soft particle ('globular structure') at the LCST which is more or less impermeable to water and ions therefore giving rise to Maxwell–Wagner–Sillars (MWS) polarization effects (blocking of charges at the soft particle). The dependence on the concentration is studied in detail. PY - 2012 DO - https://doi.org/10.1039/c2sm26826d SN - 1744-683X VL - 8 IS - 48 SP - 12116 EP - 12123 PB - RSC Publ. CY - Cambridge AN - OPUS4-27320 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Füllbrandt, Marieke A1 - Turner, Sarah T. A1 - von Klitzing, R. A1 - Schönhals, Andreas T1 - Poly(N-isopropylacrylamide) chains adsorbed on silica nanoparticles: A dielectric study of the phase transition of interfacial pNIPAM T2 - DPG Frühjahrstagung 2013 T2 - DPG Frühjahrstagung 2013 CY - Regensburg, Germany DA - 2013-03-10 PY - 2013 AN - OPUS4-29193 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Füllbrandt, Marieke A1 - Ermilova, E. A1 - Asadujjaman, Asad A1 - Hölzel, R. A1 - Bier, F.F. A1 - Von Klitzing, R. A1 - Schönhals, Andreas T1 - Dynamics of linear poly(N-isopropylacrylamide) in water around the phase transition investigated by dielectric relaxation spectroscopy JF - The journal of physical chemistry / B N2 - The molecular dynamics of linear poly(N-isopropylacrylamide) (pNIPAM) in aqueous media at temperatures below and above the lower critical solution temperature (LCST) are investigated using broadband dielectric relaxation spectroscopy in a frequency range from 10–1 to 1011 Hz. Below the LCST, two relaxation processes are observed in the megahertz and gigahertz region assigned to the reorientation of dipoles of the solvated polymer segments (p-process) and water molecules (w-process), respectively. Both relaxation processes are analyzed using the Havriliak–Negami (HN) function, taking special attention to the w-process. Above the LCST, the dielectric spectra of the pNIPAM solutions resemble that of pure water, showing only the high frequency relaxation process of the water molecules with a more or less Debye-type behavior. The non-Debye behavior of the w-process below the LCST is mainly induced by the interactions between water and pNIPAM chains via hydrogen bonding. The relaxation time and strength of the w-process is studied with dependence on the concentration, temperature, and the polymer chain length (molecular weight). The information obtained is useful for a deeper understanding of the dehydration behavior at the phase transition. The suggestion of dehydration of the pNIPAM chains at the LCST is confirmed by calculating a dehydration number. PY - 2014 DO - https://doi.org/10.1021/jp501325x SN - 1520-6106 SN - 1520-5207 SN - 1089-5647 VL - 118 IS - 13 SP - 3750 EP - 3759 PB - Soc. CY - Washington, DC AN - OPUS4-30578 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Füllbrandt, Marieke A1 - Ermilova, E. A1 - Asadujjaman, Asad A1 - Hölzel, R. A1 - Bier, Frank A1 - von Klitzing, R. A1 - Schönhals, Andreas T1 - Interactions between Water and Linear Poly(N-isopropylacrylamide) Chains Around the Phase Transition Investigated by Dielectric Relaxation Spectroscopy T2 - DPG-Frühjahrstagung T2 - DPG-Frühjahrstagung CY - Dresden, Germany DA - 2014-03-30 PY - 2014 AN - OPUS4-30658 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Füllbrandt, Marieke A1 - Purohit, Purv A1 - Schönhals, Andreas T1 - Dielectric and Thermal Investigation of Poly(vinyl acetate) adsorbed on Silica particles T2 - Deutsche Physikalische Gesellschaft (DPG) Spring Meeting 2011 T2 - Deutsche Physikalische Gesellschaft (DPG) Spring Meeting 2011 CY - Dresden, Germany DA - 2011-03-13 PY - 2011 AN - OPUS4-23744 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Füllbrandt, Marieke A1 - Schönhals, Andreas A1 - von Klitzing, R. T1 - Polymer/metal hybrids: Adhesion behaviour and polymer dynamics before and after corrosion treatment T2 - Frühjahrstagung DPG Berlin 2015 T2 - Frühjahrstagung DPG Berlin 2015 CY - Berlin, Germany DA - 2015-03-15 PY - 2015 AN - OPUS4-32894 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Füllbrandt, Marieke A1 - Schönhals, Andreas A1 - von Klitzing, R. T1 - The influence of a thermal and corrosive treatment on the interface properties of polymer/metal hybrids: Adhesion behaviour and polymer dynamics T2 - 20. International Conference on Composite Materials T2 - 20. International Conference on Composite Materials CY - Copenhagen/Denmark DA - 2015-07-19 PY - 2015 AN - OPUS4-34316 LA - deu 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) JF - Soft matter 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 DO - 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 -