Barbara Heck

 中文

Institute of Physics, Faculty of Mathematics and Physics
Albert-Ludwig-University of Freiburg
Hermann-Herder-Str. 3, 79104 Freiburg, Germany
Tel.: +49 761 203 5856
Email: heckbarb[at]uni-freiburg.de

 Fields of Activity

• Structure analysis with X-ray scattering (SAXS, SWAXS, WAXS)
• X-ray reflexion
• polymers, cellulose

 Google Scholar

 Selected Publications

• Transparent, thermoplastic, aliphatic polyesters through crystallization under molecular confinement. Maziar Matloubi, Melika Sarema, Barbara Heck, Günter Reiter and V. Prasad Shastri. Matter 6 (2023) 3057-3074
• Unraveling the complex polymorphic crystallization behavior of the alternating copolymer DMDS-alt-DVE. Valentina Pirela, Justine Elgoyhen, Radmila Tomovska, Jaime Martin Perez, Cuong Minh Quoc Le, Abraham Chemtob, Brahim Bessif, Barbara Heck, Günter Reiter, and Alejandro Müller. ACS Appl. Polym. Mater. 5 (2023) 5260–5269
• Nucleation Assisted through the Memory of a Polymer Melt: A Different Polymorph Emerging from the Melt of another One. Brahim Bessif, Barbara Heck, Thomas Pfohl, Cuong Minh Quoc Le, Abraham Chemtob, Valentina Pirela, Justine Elgoyhen, Radmila Tomovska, Alejandro Müller, Günter Reiter. Macromolecules 56 (2023) 1461–1470
• In situ dissolution and swelling of confined lamellar polymer crystals through exposure to humid air. Brahim Bessif, Thomas Pfohl, Barbara Heck, Yaser Alshetwi, Emna Khechine, Jun Xu, and Günter Reiter. Macromolecules 55 (2022) 6015–6022
• Semi-crystalline poly(thioether) prepared by visible-light-induced organocatalyzed thiol-ene polymerization in emulsion. Cuong Minh Quoc Le, Gautier Schrodj, Ibrahima Ndao, Brahim Bessif, Barbara Heck, Thomas Pfohl, Günter Reiter, Justine Elgoyen, Radmila Tomovaska and Abraham Chemtob. Macromol. Rapid Commun.  43 (2022) 2100740
• 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
• 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
• Following isothermal and non-isothermal crystallization of poly(3- hexylthiophene) thin films by UV-vis spectroscopy. Mina Alizadehaghdam, Barbara Heck, Silvia Siegenführ, Yaser AlShetwi, Fanuel M. Keheze, Sebastian Stäter, Farhang Abbasia, Günter Reiter. Polymer 2020, 122959 Abstract
  
  

  We investigated non-isothermal and isothermal crystallization of spin-coated poly(3-hexylthiophene) thin films prepared from the melt by in-situ ultraviolet-visible absorption spectroscopy. Analyzing the absorption spectra according to the Franck-Condon principle allowed for a quantitative assessment of the degree of crystallinity as well as the quality of order within crystalline regions of the films. Measured at room temperature, we observed a similar crystallinity for all differently crystallized films. The highest quality of order, however, was found for the P3HT film cooled slowly from the melt. These results were in full agreement with the results obtained by X-ray diffraction and calorimetry measurements. Consistently, in spite of similar crystallinities, atomic force microscopy images did not show a well-defined structure of ordered domains of preferentially aligned lamellae for the films rapidly cooled from the melt. In addition, heating the P3HT films in a specific range of temperature showed no change in crystallinity in spite of a continuous loss of order quality. Our results revealed that crystallinity and crystalline quality could behave differently while processing a semicrystalline polymer.

• Fully Isotactic Poly(p-methylstyrene): Precise Synthesis via Catalytic Polymerization and Crystallization Studies. Tianyu Wu, Luis Valencia, Thomas Pfohl, Barbara Heck, Günter Reiter, Pierre J. Lutz, Rolf Mülhaupt. Macromolecules 52 (2019) 4839-4846 Abstract
  
  

  The synthesis of stereoregular styrenic polymers on single-site catalysts has received great attention for the last decades, however, little is known with respect to tailoring fully isotactic poly(p-methylstyrene) (PpMS). Here, we demonstrate that isospecific coordination polymerization of p-methylstyrene can be achieved in the presence of the catalyst dichloro[1,4-dithiabutanediyl-2,20-bis(4,6-ditert-butyl-phenoxy)]titanium activated by methylaluminoxane (MAO). Moreover, iPpMS has been assumed to be non-crystallizable for decades, as X-ray diffraction (XRD) and differential scanning calorimeter (DSC) measurements of powder samples failed to reveal a well-defined crystal structure. However, we successfully generated dendritic crystals of iPpMS from dilute solutions by carefully controlling the evaporation rate of the solvent. The crystal morphology was studied by optical microscopy and atomic force microscopy (AFM). In-situ heating experiments of dendritic crystals allowed us to measure the melting temperature of iPpMS crystals. Moreover, a vapor annealing process was carried out to prepare multilamellar crystals for small angle X-ray scattering (SAXS) measurements, in order to characterize the spacing and orientation of the formed crystalline lamellae.

• Thermodynamic Features of Perfectly Crystalline Poly(3-hexylthiophene) Revealed Through Studies of Imperfect Crystals. Mina Alizadehaghdam, Barbara Heck, Silvia Siegenführ, Farhang Abbasi, and Günter Reiter. Macromolecules 52, 2487–2494 (2019) Abstract
  
  

  Reliable value for the enthalpy of fusion of a perfect Poly(3-hexylthiophene) (P3HT) crystal (ΔH°m) is still in doubt. In the published works, ΔH°m ranging from 33 to 50 J/g, obtained from measuring the dependence of the heat of fusion on crystallinity and crystal thickness, is in clear contradiction to ΔH°m = 99 J/g, resulted from measuring melting point depression of P3HT crystals in the polymer-diluent mixtures. In this work, we satisfied a requisite of the Flory relation, ignored in the literature, by presenting a new conception as the “dry melting temperature”. We confirmed that the correct value for the melting temperature of the undiluted polymer to use in the Flory relation is the “dry melting temperature” of the P3HT crystals prepared in presence of the diluent and not the melting temperature of those prepared in absence of the diluent. We also employed UV-vis spectroscopy along with a Frank-Condon analysis to determine crystallinity of the P3HT samples and revealed that the two mentioned methods support each other and lead to a common value of ΔH°m = 75 ± 5 J/g.

• A structural fibrillation parameter from small angle X-ray scattering to quantify pulp refining. Jia Mao, Barbara Heck, Hatem Abushammala, Günter Reiter, Marie-Pierre Laborie. Cellulose 26, 4265–4277 (2019) Abstract
  
  

  Pulp fibrillation results from refining and is of prime importance for papermaking. Yet a structural parameter reflecting the extent of fibrillation remains elusive. In this work, we demonstrate that in refined pulps, the interfibrillar distance at water saturated state (Ls), as derived from the interference factor from small angle X-ray scattering (SAXS), structurally reflects fibrillation degree. Interestingly, the minimal L obtained at low water content is close to the crystal thickness derived from wide angle X-ray scattering (WAXS). For a series of refined pulp samples, significant regressions are established between Ls and equilibrium moisture content (EMC), transmittance (T%), surface energy components, and the normalized crystallinity index (CrIn). These regressions establish Ls as a unique structural parameter for quantifying the fibrillation degree and derived properties of refined pulps without the need of a multi-parameter and time-consuming analyses.

• Semicrystalline Non-Isocyanate Polyhydroxyurethanes as Thermoplastics and Thermoplastic Elastomers and Their Use in 3D Printing by Fused Filament Fabrication. Vitalij Schimpf, Johannes B. Max, Benjamin Stolz, Barbara Heck, and Rolf Mülhaupt. Macromolecules 52, 320-331 (2019) Abstract
  
  

  Chemical fixation of the greenhouse gas carbon dioxide with diepoxides followed by melt-phase polyaddition of the resulting difunctional cyclic carbonates with 1,12-diaminododecane (DDA) yields semicrystalline polyhydroxurethane (PHU) thermoplastics. Also, 100% biobased semicrystalline PHU thermoplastics are feasible. Opposite to conventional polyurethane syntheses, neither isocyanates nor phosgene are required as intermediates. Preferably, melt-phase polyaddition is performed in a twin-screw compounder in the absence of catalysts, which also catalyze side-reactions. Calorimetric measurements and small-angle X-ray scattering reveal the fundamental structure–property relationships governing PHU crystallization. The PHU melting temperatures vary between 40 and 115 °C, and PHU Young’s moduli range from 220 to 1430 MPa. Moreover, non-isocyanate PHU thermoplastic elastomers (TPHE) are readily tailored via melt-phase polyaddition of diamine-terminated flexible PHU prepolymers serving as soft segments combined with semicrystalline PHU as hard segments. As verified by means of thermal analysis (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (SAXS), and microscopy (AFM), the careful balance between soft and semicrystalline hard-segment incorporation accounts for nanophase-separation, which in the past has failed as a result of phase intermixing resulting from strong hydrogen bonding between soft and hard segments. For the first time, tailored PHU thermoplastics are employed in extrusion-based additive manufacturing by means of fused deposition modeling (FDM) or fused filament fabrication (FFF). Clearly, the presence of hydroxyl groups and their hydrogen bonding improves filament fusion and adhesion essential for achieving mechanical properties similar to PHU melt extrusion without encountering warpage.

• Triple-Shape Memory Materials via Thermoresponsive Behavior of Nanocrystalline Non-Isocyanate Polyhydroxyurethanes. Vitalij Schimpf, Barbara Heck, Günter Reiter, Rolf Mülhaupt. Macromolecules 50, 3598–3606 (2017) Abstract
  
  

  Crystallization of long n-alkyl side chains within the confined environment of nonisocyanate polyhydroxyurethane (PHU) networks renders PHUs thermoresponsive, enabling thermomechanical programming of temperature-induced shape changes. Key intermediates of shape memory PHUs are highly branched, semicrystalline polyamidoamine curing agents tailored by amidation of a polyamine-terminated hyperbranched polyethylenimine with semicrystalline long chain behenic acid. Both cure temperature and content of n-alkyl side chains, varied independently, govern crystallization behavior, phase separation and mechanical properties of semicrystalline PHU networks obtained by curing pentaerythritol-based polyfunctional cyclic carbonates with hyperbranched, semicrystalline polyamidoamines. As compared to conventional PHUs, the incorporation of hydrophobic, crystalline n-alkyl side chains significantly lowers hydrophilicity. Typically, the n-alkyl side chains of behenic amides in PHU networks melt at temperatures varying between 40 and 75 °C. According to analyses by means of atomic force microscopy (AFM) and differential scanning calorimetry (DSC) crystallization of the behenic amide side chains accounts for nanophase separation producing nanocrystalline PHUs with programmable shapes. Hence, controlled PHU crystallization and PHU nanostructure formation afford thermomechanical programming of PHU triple-shape memory materials memorizing two different shapes in addition to the original shape within a single shape memory cycle. Opposite to conventional polyurethanes, triple-shape memory PHUs require neither the use of isocyanates nor phosgene.

• Stabilization of nuclei of lamellar polymer crystals: Insights from a comparison of the Hoffman-Weeks line with the crystallization line. Jun Xu, Barbara Heck, Hai-Mu Ye, Jing Jiang, Yi-Ren Tang, Jin Liu, Bao-Hua Guo, Renate Reiter, Dongshan Zhou, Günter Reiter. Macromolecules 49,  2206–2215 (2016)
• Cellulose nanocrystals’ production in near theoretical yields by 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO4) – mediated hydrolysis. Jia Mao, Barbara Heck, Günter Reiter, Marie-Pierre Laborie. Carbohydrate Polymers, 117, 443–451 (2015) Abstract
  
  

  We report on near theoretical yield production of cellulose I nanocrystals (CNCs) using a two-step hydrolysis with the mildly acidic ionic liquid (IL) 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO4) in aqueous solution from common cellulosic sources. Two successive Taguchi experimental plans were performed to evaluate the impact of selected reaction parameters (T, t, H2O:IL ratio) and their interactions on the CNCs’ yield from bleached softwood kraft pulp (SWP), bleached hardwood kraft pulp (HWP) and microcrystalline cellulose (MCC). With these experimental plans, the molar yield for extraction of nanocrystals was optimized to near theoretical levels, reaching 57.7 ± 3.0%, 57.0 ± 2.0%, and 75.6 ± 3.0%, for SWP, HWP and MCC, respectively. The reaction yields corresponded to a relative crystalline region recovery of 84.1 ± 5.3%, 71.7 ± 1.3%, 76.0 ± 2.0% from SWP, HWP and MCC, respectively. The collected nanocrystals exhibited high aspect ratios (36–43), negligible sulfur content (0.02–0.21%) and high solvent dispersibility in comparison to those obtained with the traditional sulfuric acid method. Additionally these near theoretical yields were achieved for mild reaction conditions with the combined severity factor of 2 and 3 for MCC and pulp, respectively. Overall this two-stage IL-mediated preparation of nanocrystals combines the advantages of achieving high product quality, high reaction yields and mild conditions.

• Anisotropic Photophysical Properties of Highly Aligned Crystalline Structures of a Bulky Substituted Poly(thiophene). Yingying Wang, Barbara Heck, Daniel Schiefer, John O. Agumba, Michael Sommer, Tao Wen, and Günter Reiter. ACS Macro Letters, 3, 881-885 (2014) Abstract
  
  

  The photophysical properties of a phenyl substituted poly(thiophene), poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT), were studied as a function of polarization and degree of orientation of the crystalline structure. Under well-chosen controlled conditions, large-sized spherulitic crystals of PDOPT were successfully prepared from the melt. From polarized optical microscopy and X-ray diffraction, the molecular orientation of PDOPT within the spherulite was determined, indicating that the fastest growth direction of spherulite was the a-axis. This implied that crystallization of PDOPT was directed by the packing of the side chains rather than the backbones, which are significantly separated. As the crystalline lamellae were all radially oriented, the local absorbance strongly depended on the polarization of the incoming light. Compared to randomly oriented crystals in a quenched and thus rapidly crystallized sample, PDOPT spherulites displayed red-shifted absorption and emission spectra, combined with a reduced photoluminescence quantum yield. Even for these markedly separated polymer backbones (1.47 nm), the reduced photoluminescence suggests an enhancement of interchain interactions of highly ordered bulky substituted polythiophene induced by crystallization.

• Crystallization of Poly(γ-benzyl L-glutamate) in Thin Film Solutions: Structure and Pattern Formation. Kaiwan Jahanshahi, Ioan Botiz, Renate Reiter, Ralf Thomann, Barbara Heck, Roozbeh Shokri, Werner Stille and Günter Reiter. Macromolecules, 46, 1470-1476 (2013) Abstract
  
  

  We have investigated the formation of poly(γ-benzyl L-glutamate) (PBLG) crystals from semi-dilute thin film solutions. Crystallization was initiated by adding methanol, a non-solvent. After drying, each PBLG crystal possessed an internal domain structure exhibiting a zig-zag pattern consisting of parallel stripes of alternating orientations between domains. X-ray scattering and electron diffraction revealed within these crystals a pseudo-hexagonal packing of the PBLG α-helices with their axis oriented parallel to the plane of the substrate. Based on optical anisotropy studies, it could be shown that the orientation of the helix axis was parallel to the stripes. While forming in solution, the objects are assumed to consist of a hexagonal columnar liquid crystalline phase. Upon drying, lateral packing density of the helices increased and resulted in a net dilative strain perpendicular to the columns, which is supposed to cause the formation of zig-zag patterns.

• Effect of Shear Stress on Crystallization of Isotactic Polypropylene from a Structured Melt, Bin Zhang, Jingbo Chen, Jing Cui, Fangfang Ji, Guoqiang Zhen, Hui Zhang, Barbara Heck, Günter Reiter, Changyu Shen. Macromolecules, 45, 8933–8937 (2012)
• Two Competing Crystallization Modes in a Smectogenic Polyester, Barbara Heck, Ernesto Perez and Gert Strobl, Macromolecules, 43, 4172-4183 (2010)
• Gradient Interfaces in SBS and SBS/PS Blends and Their Influence on Morphology Development and Material Properties, Yi Thomann, Ralf Thomann, Alfred Hasenhindl, Rolf Mülhaupt, Barbara Heck, Konrad Knoll, Helmut Steininger, Kay Saalwächter. Macromolecules, 42, 5684-5699 (2009)
• Stabilization, reformation and melting of poly(L-lactide) crystallites, Tai-Yon Cho, Barbara Heck, Gert Strobl, Chin. J. Polym. Science, 25, 83-94 (2007)
• A law controlling polymer recrystallization showing up in experiments on s-polypropylene, Barbara Heck, Silvia Siegenführ, Gert Strobl, Ralf Thomann, Polymer, 48, 1352-1359 (2007)
• Time dependent light attenuation measurements used in studies of the kinetics of polymer crystallization, Barbara Heck, Takahiko Kawai, Gert Strobl, Polymer, 47, 5538-5543 (2006)
• Crystallization of a poly(ethylene-co-octene): I - A precursor structure and two competing mechanisms, Andreas Häfele, Barbara Heck, Takahiko Kawai, Peter Kohn, Gert Strobl, Eur. Phys. J. E, 16, 207-216 (2005)
• Crystallization of poly(ethylene-co-octene): II - Melt memory effects on first order kinetics, Andreas Häfele, Barbara Heck, Thomas Hippler, Takahiko Kawai, Peter Kohn, Gert Strobl, Eur. Phys. J. E, 16, 217-224 (2005)
• Equations describing lamellar structure parameters and melting points of polyethylene-co-(butene/octene)s, Tai-Yon Cho, Barbara Heck, Gert Strobl, Coll. Polym. Science, 282, 825-832 (2004)
• Interplay between domain microstructure and nematic order in liquid crystalline/isotropic block copolymers, R. Ivanova, R. Staneva, S. Geppert, B. Heck, B. Walter, W. Gronski, B. Stühn. Coll. Polym. Science 282, 810-824 (2004)
• Crystallization of s-polypropylene: a qualitative change in the kinetics induced by the temperature of the melt, Barbara Heck, Gert Strobl, Coll. Polym. Science, 282, 511-513 (2004)
• Characteristic variations in the effect of diluents on polymer crystallization and melting observed for a sample of poly (ethylene-co-octene), Barbara Heck, Gert Strobl, Michael Grasruck, Eur. Phys. J. E, 11, 117-130 (2003)
• A temperature- and molar mass-dependent change in the crystallization mechanism of poly(1-butene): Transition from chain-folded to chain-extended crystallization? Qiang Fu, Barbara Heck, Gert Strobl, Yi Thomann, Macromolecules, 34, 2502-2511 (2001)
• Steps in the formation of the partially crystalline state, Barbara Heck, Thorsten Hugel, Masanori Iijima, Gert Strobl, Polymer, 41, 8839-8848 (2000)
• Steps in the transition of an entangled polymer melt to the partially crystalline state, Barbara Heck, Thorsten Hugel, Masanori Iijima, Emmanuel Sadiku, Gert Strobl, New Journal of Physics 1, 17 (1999) Abstract, PDF
  
  

  For s-polypropylene, three different s-poly(propene-co-octene)s, two poly(ethylene-co-octene)s and poly(epsilon-caprolactone) we determined the relationships between the crystallization temperature Tc, the crystal thickness dc and the melting peak temperature Tf by carrying out time- and temperature-dependent small-angle x-ray scattering experiments. As a general law, dc is found to be inversely proportional to the supercooling below a characteristic temperature, Tc∞, which is always located above the equilibrium melting point following from an application of the Gibbs-Thomson equation. Tc∞ is not (for the polypropylene-based copolymers) or only weakly (for the polyethylene-based copolymers) dependent on the co-unit content. The 'crystallization line' Tc versus dc-1 and the Gibbs-Thomson melting line Tf versus dc-1 limit the range of the accessible partially crystalline states. The occurrence of two well defined independent boundary lines may be understood as indicating that the transformation from the melt into the partially crystalline state is generally, for homopolymers and copolymerized derivatives likewise, a two-step process, beginning with the building up of an initial form of lower order at the crystallization line which then becomes stabilized to end up in the state with layer-like morphology melting at Tf. Stabilization is achieved without a change in dc. AFM and TEM observations suggest that the initial structure could be composed of crystal blocks in planar assemblies. The stabilization then would result from their merging into a continuous lamella. It is proposed that the size of the blocks represents the minimum necessary to retain intrinsic stability. As a further result it was found that crystallinities reached at the end of isothermal crystallization processes remain invariant over larger ranges of Tc, in contrast to the changing length scales of the structure.

• Structural transition in a nematic LC block copolymer induced by the transition to the LC phase, J. Sänger, W. Gronski, S. Maas, B. Stühn, B. Heck, Macromolecules, 30, 6783-6787 (1997)
• SAXS and TEM studies on poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) in bulk and at various interfaces, B. Heck, P. Arends, M. Ganter, J. Kressler, B. Stühn, Macromolecules, 30, 4559-4566 (1997)