Muhammad Tariq on \u201cInterface Controlled Thermodynamics of First-Order Prefreezing\u201d
\nand
\nAnika Wurl on \u201cPolymer crystallization under anisotropic confinement in liquid crystals\u201d<\/p>\n
<\/p>\n
Location: UL, Linn\u00e9str. 5, SR 532\r\nTime: 3.30pm-5.00pm\r\n\r\nLink to OpenStreetMap<\/a><\/pre>\nAbstracts<\/h3>\n
\n\n\nInterface Controlled Thermodynamics of First-Order Prefreezing<\/h5>\n<\/div>\n<\/div>\n<\/div>\n
Muhammad Tariq<\/p>\n
Heterogeneous nucleation and prefreezing are two possible mechanism by which a solid surface can induce crystallization of liquids. In contrast to heterogeneous nucleation, first-order prefreezing is an equilibrium phenomenon that refers to the reversible and abrupt formation of a crystalline layer of thickness ????<\/sub> at an interface to a solid surface at the temperature ?max<\/sub> well above the bulk melting temperature \u00a0?m<\/sub> [1, 2]. Thickness of the prefrozen layer ?eq<\/sub>(?) diverges upon further cooling to bulk ?m<\/sub> [1]. Most recently developed phenomenological theory of prefreezing [3] predicts ?max<\/sub> to be a function of the difference of interfacial free energies \u2206? =\u00a0????,????<\/sub> \u2212 (????,???<\/sub> + ????,????<\/sub>) and ????,????<\/sub>, whereas ???<\/sub> and ????<\/sub> are determined by ????,????<\/sub> and \u2206?\/ ????,????<\/sub> respectively.<\/p>\n
Here, I will be presenting an experimental test of the theory by extending our investigations of prefreezing of poly(\u03b5-caprolactone) (PCL) on graphite to a MoS2<\/sub> substrate. Using in-situ atomic force microscopy AFM measurements at elevated temperatures, we determine equilibrium properties of the prefrozen PCL layer on MoS2<\/sub>. These properties include the temperature range of prefreezing ????<\/sub>, prefrozen layer thickness ?eq<\/sub> (?) above the bulk ?m<\/sub>, and discontinuous jump in thickness lmin\u00a0<\/sub>at Tmax<\/sub>.\u00a0In comparison with PCL-HOPG, we find a clear decrease in leq<\/sub>(T) and lmin<\/sub> but Tmax<\/sub> remains nearly unaffected. We analyze our experimental results with the phenomenological theory [3] and estimate the material parameters at the solid interface. A comparison of the material parameters for prefrozen PCL on MoS2<\/sub> and HOPG shows that above mentioned experimental observations are in good agreement with the predictions of the phenomenological theory.<\/p>\n
References:
\n[1] A.-K. Flieger, M. Schulz, T. Thurn-Albrecht, Macromolecules, 51, 189 (2018).
\n[2] A.-K. L\u00f6hmann, T. Henze, T. Thurn-Albrecht, PNAS, 111, 17368 (2014).
\n[3] O. Dolynchuk, M. Tariq, T. Thurn-Albrecht, J. Phys. Chem. Lett. 10, 1942 (2019).<\/p>\n\n\n\nPolymer crystallization under anisotropic confinement in liquid crystals<\/h5>\n<\/div>\n<\/div>\n<\/div>\n
Anika Wurl<\/p>\n
With increasing amounts of polymer nanoparticles in earth’s oceans and rivers, the study of interactions between lipid membranes and synthetic polymers is receiving a growing interest. In this project, we investigate if hydrophobic polymer chains, e.g. poly(\u03b5-caprolactone) (PCL), can crystallize in anisotropically confined environments such as lipid bilayers or synthetic liquid-crystalline systems. In a system of PCL, dipalmitoylphosphatidylcholine (DOPC) and water, 13<\/sup>C INEPT NMR and differential scanning calorimetry (DSC) results showed that the system seperated into a phase of pure PCL as well as a mixed phase of DOPC and PCL, where crystallization of PCL possible. We now extend our research to liquid-crystal phases of block-copolymers of type (EO)n<\/sub>-(PO)m<\/sub>-(EO)n<\/sub>. In this way, we aim to study the effects of different confinement variables on crystallization properties such as nucleation, growth and crystal morphology using a combination of 1<\/sup>H, 2<\/sup>H and 13<\/sup>C NMR, polarized optical microscopy and molecular dynamics simulations.<\/p>\n
<\/p>\n","protected":false},"excerpt":{"rendered":"