Isotactic poly(1-butene) is known to have a metastable tetragonal structure upon crystallization from the melt, which transforms to a stable trigonal form over time at room temperature. Using X-ray diffraction we carried out a radial distribution function (RDF) analysis of the stable trigonal structure in a semicrystalline sample of poly(1-butene). We find a prominent characteristic repeat distance of \sim 4 ÅHowever, unlike in the melt, the long range periodicity relating to helix-helix correlations was not distinctively seen in the crystalline material. The local intramolecular structure (bond length, bond angle, and torsion angles) is also examined.
[Q18.002] Helical Single Crystals Grown in Confined Space
Christopher Li, Stephen Cheng, John Zhang, Frank Harris (The Maurice Morton Institute and Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909), Liang-Chy Chien (Liquid Crystal Institute, Kent State University, Kent, Ohio 44010-0001), Bernard Lotz (Institute Charles Sadron, 6 Rue Boussingault, Strasbourg 67083)
We report here the formation and growth process of the
double-twist PET(R*-9) helical single crystals. It has been
observed that the population of helical crystals increases
with increasing the thickness of the thin films. In addition
to the crystallization temperature effect, the pitch lengths
along both the long and short twist axes also change with
thin film thickness, which is attributed to the substrate
confinement effect on the thin film samples. The early stage
of the helical crystals has been studied using solvent
washing experiments. It has been found that the morphology
is a saddle-like shape. Nucleation starts at the center of
the flat-on part, and growth directions include both along
the long and short axes of the crystals. Coexistence of the
flat-elongated and helical forms will also be discussed.
[Q18.003] Spatial Distribution of Metal Cations and Oxygen in Polyethylene Ionomers by Analytical TEM
Karen I Winey, Andreas Taubert (Dept. of Materials Science, University of Pennsylvania, Philadelphia PA 19104)
We have recently shown by means of scanning transmission
electron microscopy (STEM) that zinc neutralized methacrylic
acid groups in poly(ethylene-ran-methacrylic acid) ionomers
form nearly uniform Zn-rich aggregates in a homogeneous
polymer matrix. Here, we present results from an analytical
TEM (ATEM) study on the same materials. The current study
seeks to determine the metal ion and the carboxylate group
(i.e. the oxygen) distribution in the ionic aggregates and
the matrix. We compare results obtained from a series of
zinc neutralized poly(ethylene-ran-methacrylic acid)
copolymers to the non-neutralized ethylene-methacrylic acid
copolymer of the same composition.
[Q18.004] Crystal Morphology Control By Melt Phase Separation in Biodegradable Polymer Blends
Y. A. Akpalu (New York State Center for Polymer Synthesis, Department of Chemistry, Rensselaer Polytechnic Institute), J. C. Meredith (Georgia Institute of Technology), E. J. Amis (Polymers Division, National Institute of Standards and Technology)
The effect of lower critical solution temperature (LCST)
phase separation on the crystallization of
poly(\epsilon-caprolactone) PCL in PCL/poly(D,L-lactide)
(PDLA) blends is studied by simultaneous small-angle x-ray
scattering (SAXS) and wide-angle x-ray scattering (WAXS).
Phase separation is induced by controlled temperature jumps
into the LCST (two-phase) region, which is above the melting
temperature (60 ^oC) of PCL and the glass transition
temperature (50 ^oC) of PDLA. We have followed the
nanoscale structural changes (< 100 nm) during subsequent
crystallization at 45 ^oC of critical (0.36 PCL) and
off-critical (0.50 PCL) blend compositions in both one-phase
and two-phase melts. The spherulite morphology (1-100
\mum) is examined with optical microscopy. When
crystallization follows LCST phase separation, the shape,
size and distribution of the spherulites depends on the
extent of melt phase separation. In our x-ray measurements,
the WAXS crystallinity of PCL is less than 40 % for the
temperature range of interest. We perform a correlation
function and intensity model analysis of our SAXS data to
obtain morphological variables that characterize the
intraspherulitic morphology. These morphological variables
are relatively constant during crystallization and are also
independent of melt phase separation. On the other hand, the
ultimate crystallinity, the crystallization rate and the
intraspherulitic concentration of PDLA depend on the extent
of melt phase separation. In 0.36 PCL the ultimate
crystallinity can be reduced by 50 %. To the best of our
knowledge, this is the first use of simultaneous SAXS/WAXS
to investigate the effect on melt phase separation and
blending on the crystal morphology independently.
[Q18.005] Molecular Weight Dependence of Crystal Growth Rate and Its Corresponding States
Norimasa Okui (Department of Organic and Polymeric Materials, Tokyo Institute of Technology)
Poly(ethylene succinate) (PESU) was crystallized from the
melt at a wide range of crystallization temperature. The
paper will discuss on molecular weight dependent of
spherulite growth rate. PESU was fractionated by GPC method.
The fractionated molecular weight (Mp) was in the range of
1,000-10,000. PESU was isothermally crystallized on a slide
glass at various temperatures from the melt. Each
fractionated sample showed the maximum growth rate (Gmax).
The Gmax increased with a decrease in molecular weight up to
a certain molecular weight (Mp*=ca. 3,000) and then
decreased with a decrease in molecular weight (below Mp*).
When the growth rates and crystallization temperatures were
normalized with the maximum growth rate and its temperature,
a single master curve was observed. The universal plot
indicates that the ratio of Go/Gmax shows constant. The
molecular weight dependence of growth rate is only
associated with Go and Gmax. In the region of molecular
weight above Mp*, Log(Gmax) showed a linear relation to
Log(Mp) and its slope was about -0.5. On the other hand
below Mp*, the molecular weight dependence showed a positive
slope of 1. The value of Mp* was coincided with a critical
molecular weight of transition from ECC to FCC. The
molecular weight dependence will be discussed on the basis
of molecular adsorption and its diffusion mechanism on the
crystal growing surface.
[Q18.006] The Mechanism of Crystallization in Random Copolymers of Ethylene with Octene
Paul Phillips, Samir Abu Iqyas (University of Tennessee)
Studies have been conducted of the crystallization behavior
of random copolymers of ethylene with small amounts of
octene. Experiments at atmospheric pressure have shown the
presence of as many as three regimes of secondary nucleation
in crystallization experiments, in apparent contradiction of
the in-situ SAXS studies of Strobl, which have been
interpreted as evidence for a new mode of crystallization
incompatible with conventional secondary nucleation theory.
Studies of the crystallization behavior as a function of
elevated pressure show that the phase diagram of
polyethylene is very sensitive to comonomer content. A
copolymer with 4 hexyls per 1000 C atoms shows a triple
point at 1 kbar and one with 11 hexyls per 1000 C atoms has
its triple point below 0.5 kbar, whereas the triple point of
the homopolymer is close 3 kbar. Two distinct melting points
can be easily discerned above the triple point in light
intensity measurements, consistent with studies of Keller et
al on the homopolymer . Hoffman Weeks plots show negative
slopes above the triple point. It is suggested that the SAXS
studies are reflective of this phenomenon and not indicative
of a new form of behavior. It seems likely that the Keller
Yasuniwa model of a hexagonal (or nematic) phase preceding
formation of the orthorhombic phase is an appropriate
description of the crystallization mechanism in
polyethylenes.
[Q18.007] High temperature phase-change in the network phase of PE
Geneviàve Delmas (Universite du Québecà Montréal), H. Phuong-Nguyen, Raphael Marigot, Zohra Ferhat, Dorina Banu (Center for Building Studies, Concordia University, Montréal, H3M 4G8)
This work follows previous investigations of the network phase by slow calorimetry .A third phase was then characterized in a semi-crystalline sample by its melting trace. Short-range order stabilized by annealing was melted in the conditions of reduced strain accompanying the controlled expansion of a slow T-ramp (0.05 K/min ).In the present work,annealing is avoided using a rapid T-ramp. A phase-change in the melt of PE is observed for a range of PE (0.92 < d < 0.97 g/cm3).The signal is exothermic and occurs usually between 220 and 285 oC. When the exotherm is incomplete, the effect is characterized by a \Delta Cp rather than a \Delta H. The amplitude of the phase change depends on the sample history and on the rate of heating. Traces are obtained either in a DSC with a 10K/min T-ramp or in a C80 Setaram calorimeter with a 0.3-0.5 K/min T-ramp The values of \Delta H and of \Delta Cp are larger in the slow ramp and also for samples prepared from solution.This phase change is seen as a tracer of the network phase where tie molecules can stretch and recrystallize and their packing deform during the rapid expansion. .
[Q18.008] Lamellar morphology of narrow molecular weight PCL fractions
Marcel DOSIERE, Stéphane HOCQUET (Université de Mons-Hainaut)
The molecular weight dependence of the lamellar thickness of
poly(e-caprolactone), a linear biodegradable and
biocompatible polyester, was investigated by time-resolved
small-angle X-ray scattering (SAXS) and wide-angle X-ray
scattering (WAXS), differential scanning calorimetry (DSC)
and Raman LAM measurements. Narrow average molecular weight
fractions of PCL (polydispersity ~1.1) was synthetized by
ring opening polymerization in presence of aluminium
triisopropylate. These fractions cover a range of number
average molecular weights <Mn> of 1300 to 42250 daltons. A
PCL sample obtained from Sigma-Aldrich with a <Mn> = 42500
and a larger degree of polydispersity (1.53) was also
investigated to determine the influence of the degree of
polydispersity on the morphological parameters. Fractions of
PCL were crystallized from the melt at temperatures ranging
between 30 and 55°C during at least 48 hours. The melting of
these fractions was investigated at a rate of 10°C/min by
differential scanning calorimetry. For a given molecular
weight, a slight increase of the lamellar thickness with the
crystallization temperature is observed. The same behavior
seems to be followed by the partial thickness L2 (with
L2>L1) obtained from the correlation fucntion of the SAXS
corrected intensity curve.
[Q18.009] Mosaic structure of alpha phase syndiotactic polystyrene single crystals
Bernard Lotz, Cyrille Mathieu, Annette Thierry (Institut Charles Sadron, 6, Rue Boussingault, F 67000 Strasbourg, France), Edwin L. Thomas (Polymer Physics Lab, DMSE, Room 13-5094, MIT, Cambridge, MA 02139)
Syndioatctic Polystyrene (sPS) single crystals in the alpha
phase have helped establish the frustrated nature of the
so-called alpha” phase, which rests on the packing of three
clusters of three helices (nine chains) in a trigonal
unit-cell. A reexamination of earlier HREM data and new dark
field experiments suggest that the crystals have actually a
composite structure with small domains 10 nm wide of
frustrated alpha” phase coexisting with an alpha’ phase,
itself made of a one triplet cluster in a smaller trigonal
unit-cell. The intermeshing of the two phases and their
orientational and structural relationships suggest that the
single crystals have experienced a martensitic
transformation.
[Q18.010] Nano-Scale Lamellar Orientation in Semi-Crystalline Polymers
G. Skillas, G. Beaucage, A. Bafana, S. Sukumaran (Dept. of Materials Science and Engineering, University of Cincinnati)
Quantification of nano-scale orientation of platelet or
lamellar structures is important to understanding the
physical basis for properties of a variety of materials such
as exfoliated and intercalated clay reinforced polymers and
processed semi-crystalline polymers. Several groups have
presented approaches to the analysis of anisotropic
small-angle x-ray scattering data from such platelet systems
including the recent work of N. S. Murthy et al. (Macro. 33,
1012 (2000)), N. Stribeck et al. (Macro. 32 3368 (1999) and
A. Prasad et al. (Polymer in press). We report on a new
approach using planar projected orientation functions
obtained for several sample planes in small angle x-ray
scattering. These projected orientation functions for the
lamellar normal can be used to determine the average 3-d
orientation of the lamellar normal with respect to the
sample axes. The analysis is used to prepare a Wilchinski
triangle plot of the average lamellar normal orientation in
3-d space for comparison between samples. We have also
applied a variant of this approach to TEM images from
semi-crystalline polymer films using a 2d-Fourier transform
of the micrographs. The TEM and SAXS results agree and can
be used to predict both quantitative physical properties as
well as leading to a qualitative understanding of features
such as haze in blown films.
[Q18.011] A Model Semi-Crystalline Polymer With a Strictly Monodisperse Distribution of Lamellar Thickness.
Alain M. Jonas, Cedric Le Fevere de ten Hove (Department of Materials Science, Universite catholique de Louvain), Jacques Penelle (Department of Polymer Science and Engineering, University of Massachusetts.)
We have succeeded in synthesizing a model polymer which, by
chemical design of the chains, is forced to crystallize into
crystals of identical thickness. This goal was reached with
a polyester of formula (-O(CH_2)_44O(CO)X(CO)-)_m,
where X is a straight trimethylene unit bearing a pendent
propyl group on the central carbon atom. This polymer adopts
the orthorhombic packing of n-alkanes, with rejection of the
pendent propyl groups outside the crystals, and
electron-rich ester functions decorating the surfaces of the
lamellae, which allows an unambiguous determination of
lamellar thickness by small-angle X-ray scattering. For all
crystallization temperatures investigated, the polymer was
found to crystallize in lamellae of strictly 5.8 nm (+/-0.1
nm), in good agreement with the computed extended length of
the long alkane sequence. Although all lamellae are strictly
of identical thickness, they crystallize and melt at
different temperatures (over 10-15^oC), giving rise to
multiple melting and crystallization peaks.
[Q18.012] The Role of Fluid Instabilities in Electrospinning of Polymer Nanofibers
Y.M. Shin (MIT), M.M. Hohman (University of Chicago), M.P. Brenner, G.C. Rutledge (MIT)
Polymeric nanofibers can be produced by accelerating a fluid
jet in an electric field, in a process known as
electrostatic spinning, or "electrospinning." Crucial to
this process is the mechanism by which a ca. 100 micrometer
diameter fluid stream is reduced by 3 to 4 orders of
magnitude to produce ca. 100 nanometer diameter solid fiber.
Experimental observations and theoretical analysis suggest
that the essential element of the process is a fluid
instability, the rapidly whipping jet. The phenomena
responsible for the onset of whipping are revealed by a
linear instability analysis that describes the jet behavior
in terms of known fluid properties and operating conditions.
As a result, direct correspondence can be demonstrated
between theory and experimental observations, and the
important roles played by viscosity, conductivity and charge
density identified. Stability of the electrospinning process
is summarized through the use of diagrams delineating
regimes of operation, which are in good agreement with
experimental observations.
[Q18.013] SANS STUDIES OF LIQUID-LIQUID PHASE SEPARATION IN HETEROGENEOUS AND METALLOCENE-BASED LINEAR LOW-DENSITY POLYETHYLENES
George D. Wignall (Solid State Division, Oak Ridge National Laboratory, Oak Ridge TN37931-6393), Rufina G. Alamo (Chemical Engineering Department, Florida Aamp;M University and Florida State University College of Engineering, Tallahassee FL), Leo Mandelkern (Department of Chemistry, Florida State University, Tallahassee, FL), Dietmar Schwahn (Institute für Festkörperforschung, Forschungszentrum Jülich D-52425 Germany)
The issue of multiple equilibrium phases in compositionally heterogeneous random copolymers has been addressed by small-angle neutron scattering (SANS) experiments. An ethylene-hexene copolymer, representative of many linear low-density polyethylenes (LLDPE) has been shown to contain a dispersed minority phase (volume fraction 0.01) consisting of highly branched, amorphous material. SANS contrast was provided by adding a fraction of deuterated (linear) high density polyethylene (d-HDPE) and the dispersed phase was manifested by departures from a Q^-2 variation of the cross section at low Q-values. After xylene extraction, which removes the low molecular weight and highly branched material, the dispersed phase is removed to a good approximation. Similarly, metallocene-based LLDPEs, which have a more homogenous distribution of branch contents do not not exhibit an upturn in the cross section in the limit of low-Q, indicating that the LLDPE and d-HDPE molecules are mixed homogenously within a single phase. These findings support previous conclusions [Macromolecules, 29, 5332 (1996)] concerning liquid-liquid phase separation for compositionally polydisperse LLDPEs, whereby the highly branched molecules in the distribution may phase segregate, even if the overall branch content is low.
ORNL is managed by UT-Battelle, LLC under contract
DE-AC05-00OR22725 with the US -DOE
[Q18.014] Numerical Study of Amorphous Layers in Semicrystalline Polymers
Hiroya Kodama, Takashi Honda (Japan Chemical Innovation Institute, Nagoya University), Toshihiro Kawakatsu, Masao Doi (Nagoya University)
A self-consistent mean-field theory for amorphous layers in
semicrystalline polymers is proposed and solved numerically.
Chains are assumed to be sufficiently long so that the
presence of free terminals can be neglected. Populations of
loops and bridges with various contour length as well as
spatial distributions of their constituent segments are
evaluated to characterize the intercrystalline amorphous
layers. The distirubion of chain contour length of each
population exhibits deviation from the exponential
distribution predicted by a simple Gaussian chain model.
[Q18.015] Structure Development in the Early Stages of Crystallization during Melt Spinning
Joshua M. Samon (Ethicon, Inc.), Jerold M. Schultz (University of Delaware), Benjamin S. Hsiao (SUNY - Stony Brook)
The earliest stage of crystallization during melt-spinning was examined for four polymers: HDPE, PVDF, nylon 6 and poly(oxymethylene). The four polymers have very similar melt viscosities. Of particular interest is the dependence of the time for the onset of detectable crystallization on the take-up speed. The results for all four polymers lie on the same curve, indicating that this condition depends chiefly upon chain orientation and not appreciably on chain chemistry or specific undercooling. The result is consistent with a condition of critical strain level. A similar, but less stringent, result is found for further crystallization in the spinline.