Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Q19: Focus Session: Physics of Polymer Nanocomposites II |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Michael Mackay, University of Delaware Room: B118-B119 |
Wednesday, March 17, 2010 11:15AM - 11:27AM |
Q19.00001: Polymer and Nanoparticle Interactions Determining Nanocomposite Physical Properties Katherine Best, Caroline Miesch, James Watkins, Todd Emrick, Alfred Crosby Tailored nanoparticles provide a powerful strategy for tuning the physical properties of polymer matrices, largely due to their high surface area to volume ratio. Although this increase in interfacial area is a dominating parameter, the physical interaction between polymer chains and similarly-sized nanoparticles is not fully understood. This interaction is often mitigated with the presence of tailored polymer ligands that can be physically or chemically attached to the nanoparticle surface. Here, we focus on the effect of nanoparticle core material and associated ligand density on the physical properties of a polymer matrix. Specifically, Au and CdSe nanoparticles are surface modified with low molecular weight polystyrene (PS) and blended with a linear PS matrix. The physical properties of the tailored nanoparticles as well as the elastic moduli and glass transition temperatures of blended nanocomposites are presented. [Preview Abstract] |
Wednesday, March 17, 2010 11:27AM - 11:39AM |
Q19.00002: Fragility of Polymer Nanocomposites with Ideal Nanoparticle Dispersion Beatriz Pazmino, Jack Douglas, Francis Starr We investigate the impact of the addition of nanoparticles (NP) on the fragility of a model glass forming polymer melt by molecular dynamics simulation. We first consider a fixed density path and find that the fragility changes, like the change in the glass transition temperature, follow directly from the attractive or repulsive polymer-NP interactions. We further show how the fragility can be connected with local vibrational changes, quantified by the Debye-Waller factor. We contrast these results with those we obtain along a path of fixed pressure, more experimentally relevant. For the isobaric case, we find changes in packing can have a larger effect on fragility than surface effects due only to NP interactions at fixed system density. [Preview Abstract] |
Wednesday, March 17, 2010 11:39AM - 11:51AM |
Q19.00003: The Percolation Network and The Electrical Conductivity of Carbon Nanotubes in a simple shear Gyemin Kwon, Youngjun Woo, Kwanwoo Shin, Bong June Sung The influence of the shear on the electrical conductivity of carbon nanotubes(CNTs) in CNT/polymer composites is studied using molecular simulations. It has been reported that the shear could decrease the electrical conductivity of CNT/polymer composites by several orders of magnitude. However, it has not been elucidated yet how the electrical conductivity would be decreased. In this work, we perform Monte Carlo simulations using a pseudo-potential to mimic a simple shear flow between impenetrable walls. When the CNT/polymer composite is exposed to the shear, CNTs are forced to align parallel to the shear direction and the local concentration of CNTs is increased near the wall. After a certain period of the shear imposition, however, CNTs become entangled and construct an aggregate. Once the aggregate forms, the percolation network of CNTs breaks down; thus decreasing the electrical conductivity significantly. The non-monotonic behavior and the anisotropy in the conductivity are also discussed. [Preview Abstract] |
Wednesday, March 17, 2010 11:51AM - 12:03PM |
Q19.00004: Nanostructured surface made from polymer/carbon nanotube has higher conductivity than noble metal surface SuPing Lyu, James Coles, Ken Gardenski, Scott Brabec, Chris Hobot We made a nanostructured surface by directly coating carbon nanotubes to a surface that was previously solvent-coated with a polymer/CNT composite. Compared to the surface coated with the same polymer composite where the surface carbon nanotubes were buried in the matrix polymer, the surface directly coated with carbon nanotubes had a significant amount of exposed nanostructures. The surface was immersed in an electrolyte solution. Its AC conductivity was higher than that of a Pt/Ir surface. [Preview Abstract] |
Wednesday, March 17, 2010 12:03PM - 12:15PM |
Q19.00005: Dynamics of Coarse-grained Model of Filled Rubber Composite under Deformation Katsumi Hagita, Shinichi Ueno, Yasumasa Bito, Hiroshi Takano, Masao Doi, Hiroshi Morita We presented a result of coarse-grained Molecular Dynamics simulation of filled polymer melts with Sulfur-crosslink under deformation based on the Kremer-Grest Model. Because all polymer chains are connected to one network gel, the size of simulation box under periodic boundary conditions (PBC) is set to about 33nm. We put 4 fillers, 80 polymer chains of 1024 particles, and many crosslink into the PBC box. One filler consists of 1280 particles of the C$_{1280}$ fullerene structure. A repulsive force from the center of the filler is applied to the particles of C$_{1280}$ in order to make a sphere whose diameter is about 15nm. Some patterns of distribution of the fillers are examined. The stress-strain curves estimated by applying a deformation to the system in simulations qualitatively agree with those in experiments. It is successful to show hysteresis on the S-S curve between elongation / release of the filled rubber. [Preview Abstract] |
Wednesday, March 17, 2010 12:15PM - 12:27PM |
Q19.00006: Mechanical Reinforcement Induced by Polymer-Decorated Nanoparticles in Polymer Thin Films Damien Maillard, Sanat Kumar, Benjamin Fragneaud, Jeffrey Kysar PS-grafted nanoparticles mixed in a PS matrix and annealed at a temperature above the Tg of the polymer can self assemble to form large complex structures. The morphology of these structures is ruled by the grafting density of the particles and the grafted/matrix chains molecular weight ratio, and can vary from spherical aggregates to sheets or strings. In the case of thin films, in addition to those particles-particles aggregation, a surface segregation leads to 2D structure formation. The mechanical reinforcement provided by those particles and their structures to 100 nm thick films has been studied with a homemade bulge test system. The inter-particle interaction, the structure form factor and the lateral chains alignment seem to be able to modify the Young modulus, the Yield and the fracture of the samples at the same time. [Preview Abstract] |
Wednesday, March 17, 2010 12:27PM - 12:39PM |
Q19.00007: Unique Plastic and Recovery Behaviour of Nano-Filled Elastomers and Thermoplastic Elastomers Didier Long, Samy Merabia, Paul Sotta We have proposed recently that the mechanical properties of nano-filled elastomers are governed by the kinetics of rupture and re-birth of glassy bridges which link neighboring nanoparticles. We show that this death and re-birth process allows for predicting unusual plastic behaviour for these systems. We study the behaviour after large deformation amplitude cycles. At some point we put the systems at rest under large applied deformation, and let the stress relax in this new deformed state. During this relaxation process the life-time of glassy bridges increases progressively. The systems thus acquire a new reference state very different from the initial one, which corresponds to a plastic deformation. The stretching energy of the polymer strands of the rubbery matrix is larger than in the initial undeformed state, but this effect is compensated by a new configuration of glassy bridges. For deformation amplitudes (as compared to the initial state) of less than about $10\%$, the new system acquires mechanical properties around this new reference state which are very close to those of the initial system, regarding the elastic and dissipative moduli and the non-linear behaviour (e.g. same amplitude for Payne effect). This recovery takes place in a relatively short period of rest time (e.g. from a few hundred to a few thousand seconds). [Preview Abstract] |
Wednesday, March 17, 2010 12:39PM - 12:51PM |
Q19.00008: Investigation of crazing and cavitation in polymer nanocomposites via simulation Gregory Toepperwein, Juan de Pablo Crazing is a unique mode of failure by which polymer strands are stretched into a periodic array of columns. It has been shown that these crazes follow cavitation under deformation. Molecular simulation studies of crazing in nanocomposites have been limited. To explore the connection between nanocomposite structure and some of the local dynamic mechanical effects that are difficult to probe experimentally, we have performed extensive Molecular Dynamics and Monte Carlo simulations of highly entangled polymer nanocomposites with nanoparticles whose size, shape, and concentration have been varied systematically. We investigate the nucleation and growth of voids that precede craze formation to elucidate the role those inclusions play in failure. Calculation of local densities, local stresses and local elastic moduli are used to explain the molecular origins of void formation. The main outcome of our study is a better understanding of how inclusions alter local mechanical properties and how those properties influence failure. [Preview Abstract] |
Wednesday, March 17, 2010 12:51PM - 1:03PM |
Q19.00009: Anisotropic Magnetic and Mechanical Properties of Epoxy Reinforced with Magnetic Nanofillers Olga Malkina, Korey D. Sorge, Hassan Mahfuz Polymer nanocomposites have attracted much attention due to the unique properties introduced by nanofillers. Nanocomposites with different physical attributes and organized appropriately are shown to enhance the physical characteristics of the polymer matrix. Numerous studied have been performed on polymers with non-magnetic nanofillers that were subjected to high uniform magnetic fields during the curing stages---leading to enhancements in various properties. Reinforcing an SC-15 epoxy matrix with magnetically active nanoparticles may then show similar enhancement in some behavior with significantly lower applied fields. In this investigation, a combination of Fe$_{2}$O$_{3}$ nanoparticles and chemically functionalized carbon nanotubes are used. The applied field drives the Fe$_{2}$O$_{3}$ particles to align in chain-like structures along the field direction and orient the nanotubes. The anisotropy in the system that is introduced in the curing process will allow for analysis of the anisotropy of magnetic, structural and physical properties in the resultant nanocomposites. [Preview Abstract] |
Wednesday, March 17, 2010 1:03PM - 1:15PM |
Q19.00010: Electron microscopy of polystyrene grafted silica nanoparticles in a homopolymer matrix subjected to steady shear Joseph Moll, Sanat Kumar, Ralph Colby, Yu Li, Brian Benicewicz Silica nanoparticles grafted with polymers, dispersed in a polymer matrix, and annealed over time adopt a broad range of dispersion states which depend on grafting density, annealing time, weight percent silica, and the molecular weights of the polymers.~ We are able to tune these variables to give desired dispersion states, from uniformly dispersed particles to agglomerated clusters.~ Steady shear rheological tests were used to critically determine how the dispersion state is affected by strain and by shear rate.~ As a function of strain, nanoparticles agglomerate as well as align themselves with the direction of flow in the matrix. Numerous image analysis tools were used to quantify the differences in the dispersion state as a function of strain. Initial dispersion states ranged from small clusters of particles to fractal-like networks to well dispersed particles. [Preview Abstract] |
Wednesday, March 17, 2010 1:15PM - 1:27PM |
Q19.00011: A New Aspect to Nano-Composite Rheology -- the Localized Memory Effect Xiaorong Wang, Christopher Robertson We discovered that particle-reinforced elastomers after being sheared (or aged) in oscillation at a frequency $f_{a}$ at a small strain \textit{$\gamma $}$_{a}$ (e.g., $\sim $1{\%} strain) for time $t_{a}$ can often produce a spectrum hole or drop in their dissipation spectra. The location of the hole depends on the aging strain amplitude \textit{$\gamma $}$_{a}$. The depth of this hole is influenced by both the oscillatory aging frequency $f_{a}$ and the aging duration$ t_{a}$, and follows a simple power relationship of the product of $f_{a}$ and$ t_{a}$. Sequential shear at two strains reveals that when $\gamma _{a1}>$ $\gamma _{a2}$ the resulting dynamic spectra appear to be a combination of that aged at $\gamma _{a1}$and $\gamma _{a2}$; whereas for $\gamma _{a1}< \quad \gamma _{a2}$, the resulting dynamic spectra only reflect the characteristic hole burning of the second strain after holding at $\gamma _{a2}$. This new memory effect occurs at very small strains and involves material stiffening during the strain aging, and both of those features are quite different from the Mullins effect in filled elastomers.$_{ }$Also, this new memory is found to last for more than 10 days without noticeable sign of disappearing. [Preview Abstract] |
Wednesday, March 17, 2010 1:27PM - 1:39PM |
Q19.00012: Percolation behavior for high performance polyimide nanocomposites processed by melt mixing Michelle Schlea, Eric Mintz, Meisha Shofner In this work, high shear melt mixing was utilized to disperse carbon nanotubes in PETI-330, a phenylethynyl-terminated imide oligomer with a glass transition temperature of 330$^{\circ}$C. Achieving full particle dispersion with carbon nanotubes is a common problem due to particle dimensions and interaction between the nanotubes and polymer; however, by controlling the processing conditions during melt-mixing, a range of morphologies could be obtained by using up to 3 wt{\%} multiwall carbon nanotubes in PETI-330. Rheological and electrical properties were used to characterize percolation behavior and quantitatively analyze particle morphology. The effects of particle size on these properties were examined by comparing composites containing multiwall carbon nanotubes with those containing carbon nanofibers. Results indicate processing conditions required for desired morphologies, differences in behavior between the particle systems, and implications on subsequent processing methods such as resin transfer molding. [Preview Abstract] |
Wednesday, March 17, 2010 1:39PM - 2:15PM |
Q19.00013: New Mechanism Responsible for the Tg-broadening and Nonlinear Response of Nanoparticle-Reinforced Elastomers Invited Speaker: Particle-filled elastomers are employed extensively in modern industry, because they are high-elasticity and relatively low- cost materials that can potentially have their physical characteristics matched to a given design specification. Despite their technological importance, particle-filled elastomers are extremely complicated with pronounced mechanical nonlinearity and temperature dependence and Tg-broadening. In this presentation, we report the fundamentals accounting for this nonlinear effect and Tg-broadening using hairy polymeric nanoparticles of well-defined core-shell structure that are dispersed in polymer matrices of identical chains. By adjusting the filler interaction potential, we are able to show that much of this rheological phenomenon comes from the phase behavior of particles in the polymer matrices and there is a strong connection between the rheological dynamics of particle-filled system and the thermodynamics of phase behavior of particles. The phenomenon of Tg-broadening in one-phase regime appears to differ significantly from that in two-phase regime despite the fact that the polymer around the particles is the same. The strain-induced nonlinearity in particle-filled system is found to display features of singularity near the phase transition point. Although there were attempts in the past to interpret this phenomenon as arising from formation of polymer glassy shells around particles, the present study clearly demonstrates that a glassy shell model is not capable to describe the behavior of particle-filled systems in a unified way. Our finding also suggests new mechanism responsible for the Tg- broadening and nonlinear response of nanoparticle-reinforced elastomers. [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