Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session B18: Focus Session: Crystallization in Confined Geometry I |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Christopher Li, Drexel University Room: B117 |
Monday, March 15, 2010 11:15AM - 11:27AM |
B18.00001: Polymer Single Crystal Templated by Quasi-One Dimensional Materials Bing Li, Eric Laird, Xi Chen, Wenda Wang, Christopher Li Quasi-one dimensional materials such as nanotubes and nanofibers can induce polymer crystallization and in many cases, the resultant crystals mimic shish kebabs. This hybrid structure is of great interests from both scientific and technological standpoint. We have explored a few quansi-one dimensional structures such as carbon nanotubes and polymer nanofibers. The growth of the crystals is confined by the quasi-one dimensional nucleating sites provided by the tubes/nanofibers. The crystals formed are sensitive to the surface chemistry and diameter of the materials. Using block copolymers allowed us to achieve templated patterning on these one dimensional structures with controlled spacing and the mechanism was attributed to the crystallization driven block copolymer phase separation. Detailed mechanisms will be discussed. [Preview Abstract] |
Monday, March 15, 2010 11:27AM - 11:39AM |
B18.00002: Size-dependent segregation, separation, and ordering in an alkane mixture undergoing slow compression in a confining narrow gap Lina Merchan, Jianping Gao, Uzi Landman With the use of grand-canonical molecular dynamics simulations, we studied the slow compression (0.01m/s) of liquid films made of pure hexane and hexadecane, and of an equimolar mixture of the two alkanes, confined between two opposing crystalline gold surfaces. The organization of the density of the confined films into layered structures, intra-layer ordering in the interfacial layers, orientational order parameters, diffusion coefficients, and force versus gap-size profiles, recorded during slow compressions of the above systems, are analyzed and compared. The longer chain molecule preferentially adsorb to the solid surfaces, resulting in size-induced segregation near the solid-liquid interfaces. As a result, the slow compression (reducing the gap-size, d) causes preferential separation of the hexadecane/hexane mixture, from 50:50 at d = 3.6 nm to 80:20 at d =1.7 nm, with the longer chains of the hexadecane molecules crystallizing into ordered layers between the opposing gold surfaces. [Preview Abstract] |
Monday, March 15, 2010 11:39AM - 11:51AM |
B18.00003: Polymer crystallization in thin films at high cooling rates Christoph Schick, Evgeny Zhuravlev Crystallization kinetics in PCL films was studied in a wide range of scanning rates. Cooling rates equal or above 400 K/s results in amorphous PCL. At even higher cooling rates the influence on nucleation was studied. Heating curves after different thermal histories were recorded to identify differences in nucleation density. The heating after cooling faster than 400 K/s reveals decreasing cold crystallization and melting peaks. That is indication that on previous cooling we not only avoid crystallization, but also create fewer nuclei. Above 10,000 K/s cooling rate the cold crystallization peak reduction saturates. This can be explained by the absence of homogeneously formed nuclei at cooling. The absence of homogeneous nuclei and the possibility to jump fast enough to any temperature, again avoiding nuclei formation, allow us to measure time and temperature dependency of nucleation. Nucleation at 185 K (15 K below Tg) yields a time constant of about 100,000 s. At temperatures above Tg, e.g. 220K, nucleation saturates and eventually superimposes with isothermal crystallization. Comparing the relaxation times of nucleation with previously derived dielectric relaxation data places the nuclei formation process intermediate between $\alpha $- and $\beta $- process, following the temperature dependence of the $\alpha $-process. [Preview Abstract] |
Monday, March 15, 2010 11:51AM - 12:03PM |
B18.00004: Melting and Freezing of Decanol inside Nanoporous Silica Samuel Amanuel It has been demonstrated for decades now that physical restriction leads to the reduction in melting and freezing temperatures. These can be explained, at least qualitatively, through the Gibbs-Thompson equation where the melting/freezing temperatures scale linearly with the inverse of the physical size of the material. One of the assumptions in developing this equation, however, is that the $\Delta $H is supposed to be physical size invariant. Experimental observation, on the other hand, revealed that the apparent $\Delta $H reduces with reduction in physical size. For instance, the apparent $\Delta $H of melting of cyclohexane confined to 50 nm porous silica is only 25{\%} of that of the bulk cyclohexane. Plausible presences of molecules that do not participate in the phase transition seem to reconcile the seeming contradiction. In this talk, extension of the same argument, the presence of non-freezing layers, on a polar and a relatively larger molecule (Decanol) will be presented. [Preview Abstract] |
Monday, March 15, 2010 12:03PM - 12:15PM |
B18.00005: Morphology and Crystal Orientation of Ferroelectric P(VDF-ran-TrFE) in Cylindrical Nanopores Nitin Shingne, Markus Geuss, Martin Steinhart, Thomas Thurn-Albrecht We prepared ferroelectric Poly(vinylidene fluoride -ran- trifluroethylene) nanorods and nanotubes using ordered nanoporous alumina template. The nanostructures were characterized by using DSC, XRD, SEM and TEM. The DSC results show that the melting temperature decreases with increasing confinement while the ferroelectric to paraelectric phase transition temperature does not change. This shows that the size of the ferroelectric domain is independent of the crystal thickness. The x-ray results show that the P(VDF-ran-TrEF) crystallites are preferentially oriented with (110) planes parallel to the template surface with polar b-axis oriented 30\r{ } to the long axis of the pores. While the alignment of the chain perpendicular to the long axis of the pores is a result of crystallization kinetics in the hexagonal phase, the preferred orientation of the b-axis takes place during the paraelectric to ferroelectric phase transition. [Preview Abstract] |
Monday, March 15, 2010 12:15PM - 12:27PM |
B18.00006: Crystallization of Tethered Chain Layers in Crystalline-Crystalline Diblock Copolymers Ryan M. Van Horn, Joseph X. Zheng, Ming-Siao Hsiao, Siwei Leng, Hao-Jan Sun, Stephen Z.D. Cheng Confined-crystallization has been researched in many ways using diblock copolymers. Microphase-separated morphologies provide a controllable environment to tune the confinement parameters. Another method of confined crystallization is through tethering one end to a surface with variable tethering density. Single crystals of crystalline-crystalline diblock copolymers have been made using dilute solution self-seeding. This technique provides a monolayer of chains on the single crystal surface. PEO-b-PCL samples with various molecular weights have been used to crystallize one block into the single crystal, while the other block is sequestered to the basal surfaces. The crystallizability as a function of tethering density as well as the crystal orientation in these single surface layers has been studied. [Preview Abstract] |
Monday, March 15, 2010 12:27PM - 12:39PM |
B18.00007: The Interplay between Chain Diffusion and Crystallization of Polyethylene Oxide in its Monolayers Rui Chen, Jiang Zhao Lateral diffusion of single chain of polyethylene oxide (PEO) in its monolayers on silica surfaces related to the crystallization process is studied by single molecule fluorescence microscopy and single molecule tracking techniques. Diffusion of PEO chains is observed in the super- cooled state before crystallization as well as after crystallization in regions outside crystals, at different temperatures. In the post-crystallization monolayers, the diffusion coefficient of PEO chains in regions outside crystals is an order of magnitude lower than that in the super-cooled state before crystallization. The origin is attributed to the change of polymer surface concentration due to the consumption of polymer molecules in the crystal formation. The results clearly demonstrate a strong mutual effect between the crystallization process and the mass transportation for the polymer crystallization under surface confinement. [Preview Abstract] |
Monday, March 15, 2010 12:39PM - 12:51PM |
B18.00008: Molecular Simulations of Polymer Crystallization under Nano-Confinement Wenbing Hu Crystallization offers polymers under nano-scale-space confinement not only the stability of sizes and properties, but also the anisotropy of electrical conductivity, mechanical strength, and optical dichroism, etc. We make an overview on recent dynamic Monte Carlo simulations of lattice polymers performing crystallization under nano-confinement. The confined geometries include ultrathin films, nano-pores and nano- droplets of homopolymers, as well as lamellar,cylindrical and spherical self-assembled microdomains of diblock copolymers. The effects of nano-confinement on polymer crystallization can be summarized into three categories, i.e. the interface (both on enthalpy and entropy), the anisotropy of geometries and the block junction (both in its restriction and orientation). Such knowledge will facilitate our better understanding on the fabrication of nano-crystals of polymers. [Preview Abstract] |
Monday, March 15, 2010 12:51PM - 1:03PM |
B18.00009: Morphological changes in polyoxymethylene on heating and cooling K. Guruswamy, N. Surve, R. Mathew, N. Bulakh, T. Ajithkumar, P. Rajamohanan, R. Ratnagiri We use modulated DSC, SAXS and solid state NMR to characterize melting, lamellar-level structure and nuclear environments respectively during heating of polyoxymethylene. Two model samples are investigated -- a melt crystallized injection molded sample and a sample obtained by dilute solution crystallization. On heating the molded sample, we observe evidence for pre-melting at temperatures significantly lower than the nominal melting point, and show that this correlates with the melting of thin, imperfect lamellae inserted in-between thicker lamellae. When the temperature is increased from room temperature to around 100$^{\circ}$C, the microstructural changes are essentially reversible on cooling to room temperature. However, on heating to temperatures above 135$^{\circ}$C, melting of the thin lamellae results in irreversible reorganization of the semicrystalline microstructure to form thicker lamellae. In contrast to the behavior of the melt crystallized samples, the solution crystals exhibit no change in the lamellar stacking on heating to 150$^{\circ}$C. With increase in temperature, there is amorphization at the basal surfaces of the lamellae, but the thermal motions of the amorphous chain segments remain highly constrained due to their connectivity to the lamellar surface. [Preview Abstract] |
Monday, March 15, 2010 1:03PM - 1:39PM |
B18.00010: Crystallization of Unbranched Polyethylene Confined within Block Copolymer Mesophases Invited Speaker: Confinement of polymer crystallites between or within block copolymer microdomains provides an exceptional opportunity for their manipulation and study. Much work over the past three decades has employed hydrogenated low-vinyl polybutadiene (hPBd) as the crystallizable block, whose limited crystal thickness and moderate crystallinity limit the extent of confinement which the microdomains can impose on the crystals. This talk will report the morphology and orientation of the crystals which form within the microdomain structures of diblock copolymers of linear polyethylene and glassy poly(vinylcyclohexane), LPE/PVCH, across the spherical, cylindrical, and lamellar morphologies. Synthesized by ring-opening methathesis polymerization followed by catalytic hydrogenation, LPE is entirely unbranched, and thus capable of producing thick crystals and achieving a high degree of crystallinity. Compared with short-branched polyethylene (such as hPBd), confinement of LPE within spheres, within cylinders, or between PVCH cylinders directly limits the crystal thickness and thereby the crystal melting point. Conversely, crystals formed within LPE lamellae are stacked orthogonally to the LPE/PVCH microdomain layering, so there is no direct limitation imposed on crystal thickness by confinement. As with LPE homopolymer, LPE crystals within lamellae thicken when annealed below the melting point, ultimately forming crystals whose thickness is significantly larger than their lateral extent, set by the bounding PVCH layers. The ribbon-like crystals which form within LPE cylinders or lamellae have a strong orientational coupling to the microdomains; prealignment of the cylindrical or lamellar mesophase by extensional flow yields macroscopic specimens with pronounced $b$-axial and $a$-axial orientations, respectively, after subsequent quiescent crystallization, complementing the usual $c$-axial texture produced by fiber spinning. [Preview Abstract] |
Monday, March 15, 2010 1:39PM - 1:51PM |
B18.00011: Early Stages in Polymer Crystal Growth for Isotactic Poly-1-Butene: From Nucleation to Network Percolation Deepak Arora, Horst Winter Isothermal crystallization experiments on isotactic poly-1-butene at early stages of spherulite growth provide quantitative information about nucleation density, volume fraction of spherulites and their crystallinity, and the mechanism of connecting into a sample spanning structure. An attempt is made to connect the crystal fraction inside spherulites with the average crystallinity of the entire sample. The crystal fraction inside spherulites is very small initially but increases with time and catches up with the sample crystallinity later on. Experiments include optical microscopy, DSC, SALS, and rheology. Optical microscopy near the fluid-to-solid transition suggests that the transition, as determined by rheology, is not caused by packing/jamming of spherulites but by the formation of a percolating structure. Impingement of pairs of spherulites occurs already much before percolation. This makes it difficult to predict crystal growth and define spherulitic impingement for the whole sample. At percolation, the absolute crystallinity is about 7-8 vol{\%}. This shows that spherulites are mostly amorphous before impingement. [Preview Abstract] |
Monday, March 15, 2010 1:51PM - 2:03PM |
B18.00012: Effect of Matrix Molecular Mass on the Crystallization of $\beta $-Form Isotactic Polypropylene Around an Oriented Polypropylene Fiber Jerold Schultz, Xiaioli Sun, Huihui Li, Xinqin Zhang, Dujin Wang, Shouke Yan The role of molecular mass in an existing method for inducing the $\beta $-phase of isotactic polypropylene (iPP) has been investigated. The method consists of introducing oriented $\langle $-phase fibers into a molten iPP matrix, followed by crystallization of $\alpha $- or $\beta $-form iPP in the matrix around the fiber at a lower temperature. Comparing the effects of iPPs of two different molecular masses, it is found that the lower molecular mass polymer is more efficient in inducing the $\beta $ form. This result, coupled with results on the effects of fiber introduction temperature and crystallization temperature, leads to the hypothesis that the matrix chains are involved in the $\beta $-nucleation event and that partial relaxation of the surface of the oriented fiber is essential to the penetration of matrix chains into the oriented material prior to nucleation. [Preview Abstract] |
Monday, March 15, 2010 2:03PM - 2:15PM |
B18.00013: Nucleation from Supercooled Liquid Crystal and Crystallization Reveled by the Fast Scanning Calorimeter Dongshan Zhou, Wei Jiang, Cao Teng, Xiaoliang Wang, Gi Xue, Christoph Schick Homogenous nuclei free liquid crystal glass of 4-cyano-4'-octyloxy biphenyl-carbonitrile (8OCB) was obtained by fast cooling with a rate of 20000 K/s. The glass was then heated rapidly (20000 K/s) from far below the $T_{g}$ to a temperature near its $T_{g}$ and hold for varied time $t_{a}$. After that, the sample was once again quenched below its $T_{g}$. Finally, the sample was heated again to isotropic melt. We use evolution of the cold crystallization peak $h_{cc}$ with the holding time during the last heating scan to investigate the nucleation and crystallization processes occurring in the holding process. The $h_{cc}$ was found to increase at short $t_{a}$, indicating the increased number of nuclei; and decrease in the longer $t_{a}$, indicating the superposition of crystallization over the nucleation. Such technique shows potential for the study of nucleation kinetics in the condensed supercooled liquids. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700