Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session P18: Polymer Nanocomposites I |
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Sponsoring Units: DPOLY Chair: Venkat Ganesan, University of Texas at Austin Room: Morial Convention Center 210 |
Wednesday, March 12, 2008 8:00AM - 8:12AM |
P18.00001: Disordered nanoparticle interfaces for defect-tolerance in the self-assembly of block-copolymers Kevin Yager, Alamgir Karim, Eric Amis Directed self-assembly is a promising route to controlling the nanostructure and surface properties of coatings. We describe a general and robust strategy for controlling the self-assembly of thin films by tuning the film-substrate interaction, using an inherently defective nanoparticle layer. These tunable surfaces exhibit hierarchical and controllable roughness via spin-coating conditions (20 nm silica nanoparticle solutions), and tunable surface energy via selective oxidation. Independent manipulation of these parameters enables control of self-assembled order for coatings cast on these tunable substrates. In particular, we demonstrate control of the orientation of lamellae in poly(deuterated-styrene-block-methyl methacrylate), with expression of the vertical lamellae orientation under certain conditions. Moreover we demonstrate that the lamellae orientation depends upon film thickness in a periodic manner in the range from 30 nm to 240 nm, which provides insights into the fundamental driving forces in this self-assembly. The proposed assembly orientations are compared with theory and validated by complementary neutron reflectivity and small-angle neutron scattering measurements. [Preview Abstract] |
Wednesday, March 12, 2008 8:12AM - 8:24AM |
P18.00002: Anisotropic Self-Assembly of Spherical Nanoparticles in Polymer Composites Pinar Akcora, Sanat K. Kumar, Yu Li, Brian Benicewicz, Linda S. Schadler, Devrim Acehan, Jack F. Douglas I will present our recent experimental findings on the organization of isotropic polymer grafted particles forming anisotropic three dimensional structures. Earlier studies have shown that particle shape and anisotropic particle interactions determine the self-assembly process. It has been also shown that isotropic particles can form string like colloidal assemblies within monolayers at two-dimensions but at high particle loadings. Here, I will present the three dimensional sheet structures formed by mixing spherical nanoparticles that are grafted uniformly with long polymers and dispersed in the same homopolymer matrices at relatively low loadings. The molecular origin of this anisotropic organization is the combined short ranged repulsive forces and longer ranged attraction interaction between the particles that is also supported through theory and numerical simulations. The self-assembly of isotropic nanoparticles into anisotropic structures within polymer melts has profound application potentials in improving the electrical and mechanical properties of composite materials. [Preview Abstract] |
Wednesday, March 12, 2008 8:24AM - 8:36AM |
P18.00003: Enthalpic Relaxation of Silica-Polyvinyl Acetate Nanocomposites. Samuel Amanuel, Sanford Sternstein While the effects of nanoparticle size and surface treatment on the glass transition temperature have received well-deserved attention, their effects on other physical parameters associated with the glass transition have received less interest. In order to understand how the incorporation of nanofillers affects the enthalpic relaxations associated with the glass transition, Differential Scanning Calorimeter (DSC) measurements were carried out on silica-polyvinyl acetate nanocomposites with respect to filler content, annealing temperature and annealing period. As expected, longer annealing periods below the glass transition temperature result in an increase of the subsequent enthalpic relaxations. However, the presence of filler substantially reduces the enthalpic relaxation relative to that of the neat polymer. Even after corrections to account for filler weight, the enthalpic relaxations still decrease monotonically with increasing filler content. The underlying enthalpic relaxations and the effects suppressed by the fillers are specific to the annealing temperature. These results suggest a significant alteration of the physical state of the matrix material by the presence of the filler particles. [Preview Abstract] |
Wednesday, March 12, 2008 8:36AM - 8:48AM |
P18.00004: Particle structuring in stretched soft/hard nanocomposite Yann Le Diagon, Stephanie Mallarino, Christian Fretigny The deformation mechanisms of nanocomposites made of disordered rigid inclusions imbedded in a soft matrix are rather complex as the local geometry and mechanical responses are very intricate. Atomic force microscopy (AFM) is used to analyze the surface of a model elastomer submitted to uniaxial traction. Since the sample contains monodisperse spherical rigid inclusions, images easily yield statistical data on the positions of the fillers. As expected, it is observed that the displacement field is affine at large scales. At short range, important deviations are observed. The 2D-structure factors present the characteristic ``butterfly'' patterns, similar to the neutron scattering patterns obtained on many deformed heterogeneous materials. We show that mechanical confinement of the inter-particular matrix regions must be taken into account in order to explain the results. Finally AFM images reveal higher order correlations: Fillers are observed to be arranged along lines which are roughly perpendicular to the stretching direction. Such a characteristic organization seems to be characteristic of the soft/hard disordered systems. [Preview Abstract] |
Wednesday, March 12, 2008 8:48AM - 9:00AM |
P18.00005: Particle inclusion effect on the rheological properties of polymeric materials Gregory Toepperwein, George Papakonstantopoulos, Juan de Pablo Recently developed algorithms have permitted the extraction of the primitive path and the entanglement length, Ne, from simulations of polymer melts. Experimental studies on the effect of the addition of nanoparticles to a polymer melt have revealed that nanoparticles can alter the plateau modulus and subsequently the entanglement length of the polymer. We use simulations to directly estimate the entanglement length of nanocomposite systems to study the effect of spherical and anisotropic nanoparticles on the entanglement length of a polymer matrix. In this work we present a systematic study of the effects of particle-polymer interactions, particle size, aspect ratio and volume fraction. Advanced Monte Carlo techniques involving chain connectivity algorithms are used to create statistically independent configurations. Attractive, neutral and repulsive polymer particle interactions are considered. Furthermore, we examine the effect of different assumptions on the calculation of Ne. [Preview Abstract] |
Wednesday, March 12, 2008 9:00AM - 9:12AM |
P18.00006: Dimensional Analysis of Percolation Theory: Applications to Polymer Composites Derrick Stevens, Torissa Hoffman, Russell Gorga, Laura Clark Percolation theory is well known to describe functional phenomena in polymer composites such as electrical conductivity, when combining a conducting particle and insulating matrix. Nanostructured composites can, however, present unique morphologies that are not easily described by the typical one, two, or three-dimensional viewpoint. One example is random mats of polymer/carbon nanotube (or silver nanoparticle) composite nanofibers. With this motivation, Monte Carlo simulations were developed to investigate various effects within such a fibrous geometry, including changes to the critical volume fraction due to the dimensionality: particle aspect ratio, relative size of particle and fiber (or film), sample size, continuous vs. porous structure. From these simulations a model was developed to predict the percolation threshold based on the dimensionality of the system. The results of these simulations and the derived model will be presented. [Preview Abstract] |
Wednesday, March 12, 2008 9:12AM - 9:24AM |
P18.00007: A hybrid particle-field (HPF) simulation method for polymer-nanoparticle composites Dominik Duechs, Scott Sides, Glenn Fredrickson A hybrid particle-field (HPF) simulation method for composite systems of polymers and sets of movable particles is presented. The particles are implemented as cavities in an otherwise flat density profile of the polymeric background (corresponding to overall incompressibility), enabling a common treatment of both components in the general framework of well-known self-consistent field theory (SCFT). The particle movements are controlled by force-biased and, where applicable, torque-biased propagation schemes. Particles and polymers interact via local contact interactions originating at the particle surfaces. Simulations with orientationally homogeneous spheres as well as with spheres possessing two distinct sets of interaction parameters on their two hemispheres are compared to experimental results. [Preview Abstract] |
Wednesday, March 12, 2008 9:24AM - 9:36AM |
P18.00008: Responsive Assemblies: Gold Nanoparticles with Mixed Ligands in Microphase Separated Block Copolymers Jinbo He, Elizabeth Glogowski, Qifang Li, Todd Emrick, Thomas Russell, Xuefa Li, Jin Wang A simple method for controlling the spatial distribution of gold nanoparticles in a polystryrene-\textit{block}-poly (2-vinylpyridine) (PS-$b$-P2VP) diblock copolymer is shown. By varying the ligand functionality of the gold nanoparticles, as well as the processing and annealing conditions, the distribution of gold nanoparticles in the microdomains of the diblock copolymer was controlled and altered. In addition, the presence of nanoparticles was also found to affect the diblock copolymer morphologies. Subsequent thermal annealing causes a coarsening of the nanoparticles, and a sequestration of the nanoparticles to the P2VP microdomain. Further heating leads to an expulsion of the particles from the microdomains, a modification of the interfacial interactions, and a reorientation of the copolymer morphology. [Preview Abstract] |
Wednesday, March 12, 2008 9:36AM - 9:48AM |
P18.00009: Dynamics of polystyrene/polystyrene-capped gold nanoparticle mixtures Peter Green, Hyunjoon Oh Studies of the chain dynamics and of the glass transition, T$_{g}$, of low molecular weight, unentangled, bulk mixtures of polystyrene (PS) with polystyrene-capped gold (AuPS$_{10})$ nanoparticles were performed using dielectric spectroscopy, capacitive scanning dilatometry and differential scanning calorimetry. Mixtures containing up to 5 weight percent of nanoparticles were examined; the nanoparticles were well distributed throughout all samples. A significant reduction of T$_{g}$ was observed with the addition of the AuPS$_{10}$ nanoparticles. The dielectric spectroscopy measurements reveal significantly decreases in $\alpha $ relaxation times in these nanocomposites compared to pure PS. [Preview Abstract] |
Wednesday, March 12, 2008 9:48AM - 10:00AM |
P18.00010: Magnetic Nanoparticle Dispersion in HOMO and Block Copolymer Films Russell Composto, Kohji Ohno, Vincent Ladmiral, Grant Smith, Dmitry Bedrov, Chen Xu Self-assembly in polymer films containing nanoparticles (NPs) can result in novel structures with attractive properties that depend on NP functionality. Here, magnetic iron oxide NPs (5nm) are dispersed in both poly(methyl methacrylate) (PMMA) and lamella forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) films. The NPs are grafted with PMMA brushes ranging from 3k to 37k Da. Increasing brush length improves dispersion in PMMA in agreement with trends observed for potential of mean force between two nanoparticles as obtained from coarse-grained molecular dynamics simulations of equivalent systems. For the 3k brush, NPs disperse uniformly in PS-b-PMMA only at low loadings (1wt{\%}), locate in the PMMA domains, and slow down the perpendicular to parallel morphology transition. At 10 wt{\%}, the NPs form uniform sized aggregates ($\sim $22nm) and perturb the lamellar morphology. Increasing brush length leads to aggregation in the solution state and as a result large aggregates in the spin cast films. A correlation between the magnetic properties and aggregate size is observed. [Preview Abstract] |
Wednesday, March 12, 2008 10:00AM - 10:12AM |
P18.00011: ABSTRACT WITHDRAWN |
Wednesday, March 12, 2008 10:12AM - 10:24AM |
P18.00012: Novel Non-toxic Antifouling/Fouling Release Nanocomposite Materials Jason Fang Biofouling is a significant environmental problem. Traditional solutions to this problem have involved incorporation of toxic organometallic species into the paint. This approach while effective, is harmful to the environment. The resultant ban on the use of many of these coatings has created a need for alternative systems to control marine fouling. Silicones represent the only class of polymers currently used commercially, due to their inherently low surface energy, glass transition temperature, and modulus, combined with good chemical stability and ease of application. In this talk I will present our efforts to develop a new generation of practical, non-toxic coatings that combine antifouling/fouling release characteristics with good mechanical properties, ease of application and low cost. Specifically we have been focusing on a series of fouling release coatings based on PDMS-polyurea segmented copolymers and nanocomposites. The PDMS copolymers are much stronger than pure PDMS yet they exhibit fouling release performance comparable and, in some cases, better than pure PDMS. [Preview Abstract] |
Wednesday, March 12, 2008 10:24AM - 10:36AM |
P18.00013: Physical Characterization of Hierarchically Structured Nanocomposites Ross Behling, Eric Cochran In this contribution we present various aspects of the thermodynamics of self assembly in block copolymer / layered silicate nanocomposites (BCPLSs). Hierarchically structured BCPLSs were prepared using an \textit{in situ} atom transfer radical polymerization (ATRP) approach. The three part synthesis of the materials included an ion exchange functionalization of the clays, sonication during styrene (St) polymerization, and a block copolymer \textit{tert}-butyl acrylate (tBA) synthesis. Highly organized lamellar structures were formed with a periodicity of $\sim $200 nm, much larger than the $\sim $35 nm periods of bulk block copolymers of comparable molecular weights. The final material had two distinct glass transitions (Tg) 69\r{ }C for the tBA and 103\r{ }C for the St. This is a significant Tg enhancement for atactic tBA (Tg = 42\r{ }C) and is attributed to the chain extension which occurs in the confined geometry of the silicate sheets. [Preview Abstract] |
Wednesday, March 12, 2008 10:36AM - 10:48AM |
P18.00014: Conducting polymer nanofibers for high sensitivity detection of chemical analytes. Abhishek Kumar, Ignaty Leshchiner, Subhalakshmi Nagarajan, Ramaswamy Nagarajan, Jayant Kumar Possessing large surface area materials is vital for high sensitivity detection of analyte. We report a novel, inexpensive and simple technique to make high surface area sensing interfaces using electrospinning. Conducting polymers (CP) nanotubes were made by electrospinning a solution of a catalyst (ferric tosylate) along with poly (lactic acid), which is an environment friendly biodegradable polymer. Further vapor deposition polymerization of the monomer ethylenedioxy thiophene (EDOT) on the nanofiber surface yielded poly (EDOT) covered fibers. X-ray photo electron spectroscopy (XPS) study reveals the presence of PEDOT predominantly on the surface of nanofibers. Conducting nanotubes had been received by dissolving the polymer in the fiber core. By a similar technique we had covalently incorporated fluorescent dyes on the nanofiber surface. The materials obtained show promise as efficient sensing elements. UV-Vis characterization confirms the formation of PEDOT nanotubes and incorporation of chromophores on the fiber surface. The morphological characterization was carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). [Preview Abstract] |
Wednesday, March 12, 2008 10:48AM - 11:00AM |
P18.00015: Relaxation Dynamics of Nano Particles Embedded in a Soft Glassy Matrix Jaydeep Basu, Sunita Srivastava, Ajoy Kandar, Mrinmay Mukhopadhyay, Laurence Lurio, Sunil Sinha Using x-ray photon correlation spectroscopy, we have studied slow, wave vector and temperature dependent microrheology of nano particles embedded in glassy matrix with unique viscoelastic properties. The measurements were done for a polymer matrix (PMMA) using gold nanoparticles as probe. The intensity auto-correlation function exhibits a cross-over from compressed to stretched relaxation behavior on cooling from above the glass transition temperature (T$_{g})$ of PMMA. Although stretched exponential relaxation is expected in the glassy state one would expect simple exponential relaxation above the T$_{g}$. We also find that the relaxation time ($\tau)$, follows $\tau \sim $ q$^{-1}$ dependence indicating super-diffusive motion of nanoparticles. Interestingly, we have also observed subtle effects like length scale dependence of the stretching exponent. This points to the importance of the nanoparticles in modifying the viscoelastic property of the polymer matrix and highlights the strength of this technique in extracting their micro-rheological properties. [Preview Abstract] |
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