Control of polymer wetting of inorganic substrates is critical for many technological applications. We investigate the consequence of nano-particle filler additive (C_60, buckminsterfullerene) on the wettability of low molecular weight model polymers (polystyrene, polybutadiene) on acid-cleaned silicon wafers. Contrary to our original expectations, the filler particles were found to stabilize the films against dewetting. The unfilled films dewet the substrate when annealed above the bulk glass transition temperature, however, the filled films appeared to be stable and smooth over extended annealing times in optical and atomic force microscopy images.
[ZC11.02] Dynamics of Hard Amphiphilic Particles in a Binary Polymeric Mixture
Gongwen Peng, Marco Paniconi, Feng Qiu, Valeriy V. Ginzburg, Anna C. Balazs (Department of Chemical and Petroleum Engineering, University of Pittsburgh), David Jasnow (Department of Physics and Astronomy, University of Pittsburgh)
We simulate the phase separation of a binary fluid mixture in the presence of hard particles. The particles represent Janus beads, which consist of hydrophilic and hydrophobic parts. Surface interactions between the hard particles and the fluids are included in the model. Numerical results for the morphology of the phase separating mixture and the motion of the hard particles are presented.
[ZC11.03] Microrheological Studies Using Brownian Fluctuation Spectroscopy
Jorge Jimenez, Raj Rajagopalan (Department of Chemical Engineering, University of Florida, Gainesville, FL)
The thermal noise of a complex fluid and the resulting
fluctuations of a probe immersed in the fluid can be used as
a source of rheological (and other) information. The present
work focuses on the use of the brownian fluctuations of the
tip of an Atomic Force Microscope (AFM) to obtain
information that complements conventional rheological
measurements. The fluctuations of the probe are modeled by a
Langevin equation and the thermal noise of the probe (the
AFM tip) is recorded and analyzed in Fourier space to obtain
information on the local response of the fluid to the
microscopic perturbations. One of the advantages of this
technique is that it has access to local information and,
therefore, allows for measurement of local rheology close to
an interface. The present work discusses some issues
regarding the modeling of the fluctuations of the probe
(i.e., inertial contribution to the drag force and a
frequency dependent drag coefficient) and presents some
results obtained for both viscous and viscoelastic fluids.
[ZC11.04] Colloidal Interactions between PVA Stabilized Latex Particles
Wentao Li, Shoure Ge, Dilip Gersappe, Mariam Rafailovich, Jonathan Sokolov (Department of Materials Science and Engineering, SUNY , Stony Brook, NY 11794), Glen Ko (MCRIC, cambrigde, MA)
Polymers have been widely used as stabilizers and/or
flocculants of dispersion systems. A basic understanding of
effects of structure on polymer chain interaction will
facilitate the choice of polymers as stabilizers and/or
flocculants. In this study, we investigated the forces
between partially hydrolyzed Polyvinyl Acetate (PVA) as a
function of hydrolysis extent and chain length. Two
complementary techniques, Scanning Force Microscope (SFM)
and LB technique, were compared. PVA chains were adsorbed
onto a SFM tip and a solid substrate. The tip and substrate
interaction was measured with SFM force mode. PVA and PVA
stabilized Polyvinyl Chloride latex particles were spread on
a LB trough and surface pressure -area curves were
determined. Both the SFM and LB results show that the force
between PVA chains is primarily determined by the extent of
hydrolysis. The results are compared with numerical Self
Consistent Field calculations.
[ZC11.05] Equilibrium Interfacial Properties of Polyester Solution in Toluene over Silica Suspension in Water
Sangwook Park, Hyuk Yu (Dept. of Chemistry, University of Wisconsin-Madison)
The interfacial properties of polyester and colloidal silica particles adsorbed at the toluene/water and air/water interfaces were studied using the electrocapillary wave diffraction (ECWD) technique and Wilhelmy plate method by varying concentrations of polymer, silica , and amine at different pHs. We found that smaller silica particles (larger surface area) are more effective in reducing interfacial tension at the same mass concentration at the toluene/water interface. As polymer concentration is increased, the interfacial tension decreases exponentially. The interfacial tensions of pH 9 subphase are much lower than those of pH 4 at the same polymer concentration. This is attributed to stronger interaction between carbonyl groups of polyester and anions on the silica surface at pH 9. The interface excess of polyester at pH 9 is about twice that at pH 4. The interfacial tension is further lowered by adding hydrophobic amines to the subphase. The surface pressure of polyester at pH 9 at the air/water interface is lowered in the presence of silica particles due to polymer - silica interaction.
[ZC11.06] Clay-Block Copolymer Nanoncomposites
Jan Groenewold, Glenn H. Fredrickson (Department of Chemical Engineering, UC Santa Barbara)
In combining clay with block-copolymers, lamellar structures are very likely to emerge as both components have this tendency. To successfully disperse the clay particles a favorable clay-polymer surface interaction has to overcome the elastic penalty due to deformation of the block copolymer lamellae.
As an application, these dispersions can be used to facilitate blending with appropriate homopolymers.
[ZC11.07] Scanning Force Microscopy and Neutron Reflectivity Studies on Carbon Black-Filled Elastomers
Yimin Zhang, S. Ge, B. Tang, M. Rafailovich, J. Sokolov (Dept. of Material Sci. & Eng., SUNY at Stony Brook, NY11794), D. G. Peiffer (Exxon Res. & Eng., Annadale, NJ08801), J. A. Dias, K. O. McElrath (Exxon Chem. Co., Baytown, TX77520), M. Lin, S. Satija (NIST, Gaithersburg, MD20899)
The reinforcement of elastomers by carbon black particles
is fundamental to the rubber industry. We have studied the
effect of carbon black filler particles on the interface
formation between BIMS ( Brominated
poly(isobutylene-co-4-methylstyrene) ) and dPB (d6-1,
4-polybutadiene) layers by NR (neutron reflectivity). The
results show a dramatic decrease in interfacial width when
as little as 0.5% carbon black material is mixed in either
of the two polymers. With the addition of 5% carbon black,
the interfacial width decreases to about 3 nm, as compared
to about 30 nm in the absence of filler at the same
annealing time and temperature. Lateral force microscopy
studies on carbon black reinforced dPB films show a large
decrease in surface viscosity with increasing carbon
concentration. In the absence of fillers, the thickness of
dPB thin films also affects the viscosity as well as the
diffusion rate in the BIMS/dPB bilayer systems. The results
are interpreted in terms of long range interaction due to
adsorption of polymer to the carbon black particle surface.
[ZC11.08] Phase Diagram of a Polymer-Clay Nanocomposite Determined by Density Functional Theory
Anna C. Balazs, Valeriy V. Ginzburg, Chandralekha L. Singh (Department of Chemical and Petroleum Engineering, University of Pittsburgh)
We use a density functional theory to calculate the phase diagram of a polymer-clay nanocomposite. By explicitly incorporating the self-consistent field (SCF) interaction potentials between the clay sheets, we establish a direct relationship between the structure of grafted polymers and the equilibrium morphology of the final nanocomposite. For attracting clay particles, we find a broad two-phase isotropic-crystal region, while for a repulsive interaction between particles, we observe an isotropic-nematic-crystal sequence with increasing clay volume fraction. These results can provide additional guidance for future studies of composite morphology.
[ZC11.09] Relaxation Behavior of Polymethyl Methacrylate Nanocomposites
Alex J. Hsieh (Army Research Laboratory, AMSRL-WM-MA, Aberdeen Proving Ground, MD 21005-5069), Emmanuel P. Giannelis (Cornell University, Dept. of Science and Engineering, Ithaca, NY 14853)
Effect of layered silicates on the molecular relaxation of polymer nanocomposites has been investigated using dynamic mechanical analysis (DMA). Polymethyl methacrylate (PMMA) nanocomposites with 5% of Na+-montmorillonite (MMT) were prepared via either in-situ emulsion polymerization or melt extrusion. In the latter, MMT functionalized with an octadecyl ammonium salt (C18) was used to enhance miscibility between the organoclay and PMMA. DMA data showed an increase in storage modulus for nanocomposites prepared in either approach compared to that of the corresponding pristine PMMA. Glass transition temperature (Tg) was increased with an addition of MMT in the in-situ polymerized nanocomposites; however, a decrease in Tg was observed in the extruded nanocomposites as compared to the PMMA control. The apparent activation energy values were unchanged when the extruded PMMA was added with C18-modified MMT. Further analysis to verify the extent of variation in dynamic properties is included. In addition, studies of the effect of MMT on the chain mobility of the host polymer will be carried out on polyethyl methacrylate (PEMA) for comparison.
[ZC11.10] Morphology and Structure of Polystyrene/Clay Nanocomposite by Interfacial Polymerization
J.Y. Wu (National Chung Hsing University), K.C. Liu
High purity clay was employed in this study to render its surface hydrophobic through surface adsorption, solubilization and polymerization steps. The clay was adsorbed with cetyl pyridinium chloride, by an ion exchange and adsorption mechanism. The clay surface was adsorbed by a first surfactant layer with its hydrophobic tail extending away from the clay surface together with the adsorption of second surfactant layer to constitute the organized bilayer structure. The styrene monomer was added and solubilized into the surfactant bilayer with subsequent addition of water soluble persulfite initiator to induce the interfacial polymerization of styrene in the adsorbed bilayer. Results show that the polymerization rate is fast and the clay surface was coated with ultrathin polystyrene film that exhibits a nonwetting property against water. A hydrophobic clay surface coated with an ultrathin polystyrene film can be prepared by this scheme. FTIR confirmed the formation of polystyrene on clay surface. DSC and TGA were also employed to measure the glass transition temperature and the amount of polystyrene formed. X-ray diffraction study reveals the d-spacing of clay increased from 1.17 nm for pristine clay to 2.22 nm for polystyrene coated on clay with different styrene ratios.
[ZC11.11] Phase Behavior of Binary Fluids with Solid Particles under Flow Fields
Feng Qiu, Valeriy V. Ginzburg, Gongwen Peng, Marco Paniconi, Anna C. Balazs (Department of Chemical and Petroleum Engineering, University of Pittsburgh), David Jasnow (Department of Physics and Astronomy, University of Pittsburgh)
We simulate the phase separation dynamics of a binary AB-mixture with solid impurity particles under a flow field. By combining cell dynamical equations with Langevin dynamics, we analyze the dependence of the morphology and the coarsening dynamics on the temperature and the shear rate. The domain growth under shear flow is anisotropic at low temperatures. With increasing temperature, the anisotropy is destroyed due to the particle diffusion. We propose a scaling theory to describe this effect and compare our results with earlier experimental and numerical data.
[ZC11.12] Dynamics of polyethylene oxide-fluorohectorite intercalates studied by inelastic neutron techniqes
Robert Ivkov, Peter M. Gehring, Nicholas C. Maliszewskyj, Peter Papanek (NIST), Krishnamoorti Ramanan (University of Houston)
Polymer-clay nanocomposites have proven useful as materials with both enhanced properties, and as systems that model polymer structure and dynamicss in severely confined geometries. We present results from neutron time-of-flight and filter-analyzer measurements of polyethylene oxide (PEO) intercalated into fluorohectorite (FH) clay. We compare the
spectra obtained from two samples of intercalated materials, with PEO mass fractions of 0.18 and 0.30, with those obtained from bulk PEO and pure FH clay. X-ray diffraction of the two intercalated samples, mass fractions 0.18 and 0.30 reveals that the PEO chains are confined to spaces with a height of 1.4 nm and 1.7 nm, respectively. We find that the intercalated polymers exhibit features that are significantly different from those of the bulk polymer.
[ZC11.13] Rheological Characterization of A Diblock Copolymer Based Nanocomposite
Jiaxiang Ren, Ramanan Krishnamoorti (University of Houston)
Intercalated nanocomposites based on an organically modified
layered silicate and a polystyrene-polyisoprene (PS-PI)
symmetrical diblock copolymer were examined by melt-rheology
and using in-situ shear SANS measurements. The layered
silicate forms intercalated nanocomposites with pure PS and
in contrast phase demixed composites with pure PI. It is
thus expected that the PS part of the chain would
intercalate the silicate layers with the PI segments
excluded from the layered structure. This hypothesis has
been confirmed based on SANS measurements and the structure
is shown to resemble that of hairy discs. The structure
leads to dramatic changes in the rheological properties of
these nanocomposites -- such as diminished frequency
dependence of the storage and loss moduli in oscillatory
shear experiments, significant non-newtonian behavior in
steady shear, and prolonged solid like characteristics in
stress relaxation experiments.
[ZC11.14] The Ductile to Brittle Transition in Particulate Polymer Composites
Donald Wiegand (Picatinny Arsenal)
The ductile to brittle transition is being investigated in composites containing 85 to 99 percent organic polycrystalline particulate and a polymer binder with and without a plastizer. While the ductile to brittle transition is identified primarily by the change in the work which can be done on the sample as a function of temperature, it is also identified by a significant change in the compressive stress-strain curve, and/or by a change in the condition of the sample after deformation, both also as functions of temperature. For a given particulate the transition temperature is dependent on the binder, the percentage of binder and the strain rate. The transition temperature increases with increasing strain rate as expected. One of the primary purposes of the polymer (with or without a plastizer) is to improve the mechanical properties over those of the particulate alone and it has been possible to significantly reduce the ductile to brittle transition temperature by the addition of small percentages of polymer. The results will be related to the glass transition temperatures in those cases where the latter are known.