Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J43: Physics of Copolymers II |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Bradley Olsen, Massachusetts Institute of Technology Room: A306/307 |
Tuesday, March 22, 2011 11:15AM - 11:27AM |
J43.00001: Coil-globule Transitions in Model Bioinspired Polymers Hannah Murnen, Adrianne Rosales, Ronald Zuckermann, Rachel Segalman The monomer sequence of a polypeptide chain has a profound effect on the coil to globule transition of the protein. Both theoretical and experimental efforts to probe the effect of monomer sequence have included the use of chemical modifications post chain collapse in a homopolymer/solvent system followed by further analysis of the chain to understand the resulting sequence. Polypeptoids, or N-substituted glycines, are a far more precise sequence specific model system that can be used to test the effect of monomer sequence on the coil to globule transition. In this study, we synthesized 50mer sequences of a blocky protein-like copolymer using 40 monomers of N-(methyl)glycine and 10 of N-(carboxyethyl)glycine). As predicted in theoretical simulations, the protein like copolymer forms a smaller globule than the periodic control sequence. In addition, decreasing the relative hydrophobicity of the two comonomers results in a looser globule size at room temperature. Future work will focus on using polypeptoids to further probe this transition and to gain insight into the fundamental forces at play in polypeptide folding. [Preview Abstract] |
Tuesday, March 22, 2011 11:27AM - 11:39AM |
J43.00002: Modeling the Heat Capacity of Spider Silk Inspired Di-block Copolymers W. Huang, S. Krishnaji, D. Kaplan, P. Cebe We synthesized and characterized a new family of di-block copolymers based on the amino acid sequences of Nephila clavipes major ampulate dragline spider silk, having the form HABn and HBAn (n=1-6), comprising an alanine-rich hydrophobic block, A, a glycine-rich hydrophilic block, B, and a histidine tag, H. Using temperature modulated differential scanning calorimetry (TMDSC), we captured the effect of bound water acting as a plasticizer for copolymer films which had been cast from water solution and dried. We determined the water content by thermogravimetry and used the weight loss vs. temperature to correct the mass in TMDSC experiments. Our result shows that non-freezing bound water has a strong plasticization effect which lowers the onset of the glass transition by about 10$^{\circ}$C. The reversing heat capacities, Cp(T), for temperatures below and above the glass transition were also characterized by TMDSC. We then calculated the solid state heat capacities of our novel block copolymers below the glass transition (Tg) based on the vibrational motions of the constituent poly(amino acid)s, whose heat capacities are known from the ATHAS Data Bank. Excellent agreement was found between the measured and calculated values of the heat capacity, showing that this model can serve as a standard method to predict the solid state Cp for other biologically inspired block copolymers. [Preview Abstract] |
Tuesday, March 22, 2011 11:39AM - 11:51AM |
J43.00003: Effect of chain shape and monomer sequence on self-assembly of polypeptoid-polystyrene block copolymers Adrianne Rosales, Hannah Murnen, Ronald Zuckermann, Rachel Segalman Polymer chain shape has profound effects on block copolymer self-assembly. In nature, chain shape is controlled by the monomer sequence of biological polymers, but such precise control is difficult with classical synthetic systems. Polypeptoids, a class of sequence-specific bioinspired polymer, are shown to have a chain shape which can be tuned by the introduction of monomers with bulky, chiral side chains. Here, it is shown that introducing chiral monomers into the peptoid chain increases chain stiffness, as reflected by a 20C increase in the glass transition temperature for a chiral polypeptoid compared to its achiral analog. Incorporation into block copolymers enables systematic study of the effect of chain shape while maintaining similar enthalpic interactions. For two otherwise analogous block copolymers, conformational asymmetry is shown to affect both the self-assembled morphology and its order-disorder transition temperature. The ability to tune polymer properties with this biomimetic system will lend insight to the relationship between monomer sequence and self-assembled nanostructures. [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:03PM |
J43.00004: Self-Assembly of Globular Protein-Polymer Diblock Copolymers C.S. Thomas, B.D. Olsen The self-assembly of globular protein-polymer diblock copolymers into nanostructured phases is demonstrated as an elegant and simple method for structural control in biocatalysis or bioelectronics. In order to fundamentally investigate self-assembly in these complex block copolymer systems, a red fluorescent protein was expressed in \emph{E. coli} and site-specifically conjugated to a low polydispersity poly(N-isopropyl acrylamide) (PNIPAM) block using thiol-maleimide coupling to form a well-defined model globular protein-polymer diblock. Functional protein materials are obtained by solvent evaporation and solvent annealing above and below the lower critical solution temperature of PNIPAM in order to access different pathways toward self-assembly. Small angle x-ray scattering and microscopy are used to show that the diblock forms lamellar nanostructures and to explore dependence of nanostructure formation on processing conditions. Circular dichroism and UV-vis show that a large fraction of the protein remains in its folded state after conjugation, and wide angle x-ray scattering demonstrates that diblock copolymer self-assembly changes the protein packing symmetry. [Preview Abstract] |
Tuesday, March 22, 2011 12:03PM - 12:15PM |
J43.00005: Phase Behavior and Significantly Enhanced Toughness in Polylactide Graft Copolymers Megan Robertson, Grayce Theryo, Feng Jing, Marc Hillmyer Polylactide (PLA), a biodegradable polyester derived from plant sugars, is commercially available and used in a variety of applications ranging from serviceware to resorbable sutures. One limitation to diversifying the applications of the material is its inherent brittleness. Graft copolymers containing PLA arms and a rubbery aliphatic polymer backbone were synthesized by a combination of ring-opening metathesis and ring-opening transesterification polymerizations. The high degree of incompatibility between the arms and backbone resulted in microphase separation of the graft copolymer at increasingly low fractions of the backbone polymer, as evidenced by small-angle x-ray scattering. In graft copolymers with a rubbery content of only 5 wt percent, the tensile strain at break was observed to be as high as twenty times that of neat PLA. Studies are underway to provide insight into the critical polymer molecular parameters for enhanced toughness and the deformation mechanisms. [Preview Abstract] |
Tuesday, March 22, 2011 12:15PM - 12:27PM |
J43.00006: Thermoresponsive Polymers and Block Copolymers in Ionic Liquids Hau-Nan Lee, Zhifeng Bai, Nakisha Newell, Timothy Lodge We recently discovered that poly(ethylene oxide) (PEO) and poly(n-butyl methacrylate) (PnBMA) exhibit two completely different types of lower critical solution temperature (LCST) phase behavior in certain ionic liquids (ILs). While typical LCST type phase diagrams were shown in PnBMA/IL systems, we observed unusual temperature-composition phase diagrams in the PEO/IL systems, in which the cloud point curves are strongly asymmetric, with the critical composition located at 80 wt {\%} of PEO. In addition, an important feature of these thermosensitive polymer/IL systems is that the LCST can be easily tuned over a wide range by blending different ILs, without changing the chemical structure of the polymers. On the basis of the LCST of PEO and the upper critical solution temperature (UCST) of poly(N-isopropylacrylamide) (PNIPAm) in ILs, we designed a PEO-PNIPAm block copolymer that exhibits interesting doubly thermosensitive self-assembly. The block copolymer forms PNIPAm-core micelles at low temperatures and transforms into PEO-core micelles at high temperatures. The critical micellization temperatures (CMT) of both blocks can be manipulated by adjusting the mixing ratio of ILs. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 12:39PM |
J43.00007: Effect of homopolymer additives on texture evolution in block copolymer composites Hyung Ju Ryu, Jane Sun, Michael Bockstaller This contribution presents a systematic study of the effect of homopolymer (hP) addition on the texture evolution in block copolymer (BCP) blends. The microstructures of poly(styrene-b-isoprene) based symmetric di-BCP blended with homopolystyrene additives at various filling fraction were analyzed after different thermal annealing time. For the analysis we utilized serial electron imaging in conjunction with image reconstruction {\&} stereological analysis. Particular emphasis was on the elucidation of the evolution of type and frequency of grain boundary (GB) formation as well as average grain size and orientation. Relative GB energies were determined from triple junction analysis. The results demonstrate that the presence of even small amount of hP impurities significantly reduce grain growth and annealing of high energy GB surfaces. This is interpreted as a consequence of selective segregation of the fillers within high energy GB regions and the associated stabilization of the GB surfaces. These results have important implication on the use of BCPs in areas ranging from plastic electronics to tunable photonic crystals. [Preview Abstract] |
Tuesday, March 22, 2011 12:39PM - 12:51PM |
J43.00008: Influence of Chemical Heterogeneity on the Viscoelastic Properties of Polystyrene-b-Poly(alkyl methacrylate) Baroplastics Asem Abdulahad, Chang Y. Ryu The development of purification and fractionation techniques of block copolymers is important for overcoming the synthetic difficulty of preparing well-defined block copolymers using various living polymerization techniques. A large scale separation technique would lead us to obtaining sufficient amounts of homopolymer-free block copolymers for subsequent physical characterization. This can potentially aid in the elucidation of the role of chemical heterogeneity on the thermodynamic transitions and viscoelastic properties of block copolymer materials. Atom transfer radical polymerization by the activators regenerated by electron transfer method (ARGET-ATRP) was used to prepare a series of polystyrene-b-poly(alkyl methacrylate) copolymers that would inherently consist of homopolymers and a high polydispersity. Leveraging the understanding of polymer adsorption/desorption in solution onto silica and C18-modified silica surfaces during HPLC, we demonstrate how a large scale purification and fraction is achievable using flash chromatography. Finally, the viscoelastic properties of the purified, homopolymer-free block copolymers will be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 12:51PM - 1:03PM |
J43.00009: Effects of B Segment Polydispersity on ABA Triblock Copolymer Phase Behavior Mahesh Mahanthappa, Joan Schroeder, Andrew Schmitt, Adam Schmitt, Kyuhyun Im Advanced polymerization techniques enable the synthesis of a variety of polymeric materials with well-defined chain architectures, compositions, and tunable molecular weights and molecular weight distributions. The inherent chain length polydispersity of polymers derived from these syntheses affects their ultimate materials properties and applications. Relying on tandem ring-opening metathesis polymerization with chain transfer (ROMP-CT) and atom transfer radical polymerization (ATRP), we have synthesized a series of poly(styrene-b-1,4-butadiene-b-styrene) triblock copolymers in which the polybutadiene blocks are polydisperse (Mw/Mn = 1.7-2.0) and the polystyrene end blocks are monodisperse (Mw/Mn = 1.05-1.30). We systematically explore the role of block polydispersity, a molecular chain length heterogeneity, on the melt-phase self-assembly behavior of these block copolymers. Using a combination of temperature-dependent X-ray scattering and transmission electron microscopy, we demonstrate that monodispersity is not a necessary condition for molecular self-assembly into well-defined supramolecular morphologies. The origins of these effects are discussed and a preliminary experimental phase portrait for this system is presented. [Preview Abstract] |
Tuesday, March 22, 2011 1:03PM - 1:15PM |
J43.00010: Elucidation of an Unusual Pull Out Mechanism for the Additive-Driven Assembly of Poly(ethylene oxide)-Poly(propylene oxide)-Poly(ethylene oxide)Tri-block Copolymers Vikram Daga, Hua-Gen Peng, Ying Lin, Wen-Li Wu, Christopher Soles, James Watkins The addition of poly(acrylic acid) (PAA) to disordered poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) tri-block copolymers induces microphase segregation to yield well ordered blends with sub-10 nm domain sizes. Unexpectedly, even with large changes in the chain length (up to 10 times that of tri-block copolymer) and loading of PAA ($>$40{\%}), the domain spacing of the ordered blend remains nearly invariant although order-to-order transitions are still observed. Here we use neutron scattering and selective deuteration of the tri-block copolymer to probe phase segregation and structure in these systems. One interesting observation is the emergence of a pullout mechanism during ordering in which PEO chain segments are drawn across the interface of a mixed PEO-PPO phase to stabilize the addition for PAA and to create a mixed PAA-PEO phase. [Preview Abstract] |
Tuesday, March 22, 2011 1:15PM - 1:27PM |
J43.00011: Influence of thermal fluctuations on nucleation in a diblock copolymer melt Russell Spencer, Robert Wickham We study the effect of thermal fluctuations on the kinetics of nucleation of lamellar droplets from a metastable cylinder phase in a diblock copolymer melt by simulating the time-dependent Landau-Brazovskii model in three dimensions. We investigate the shift in the location of phase coexistence, due to fluctuations, as well as changes in nucleus shape, critical size and interfacial velocity. We also examine the kinetics of the transition in the spinodal regime. [Preview Abstract] |
Tuesday, March 22, 2011 1:27PM - 1:39PM |
J43.00012: Disorder-to-Order Transition Induced by Alkyne/Azide Click Chemistry in Diblock Copolymer Thin Films Xinyu Wei, Wei Chen, Joseph Strzalka, Thomas Russell The thin film morphology of binary blends of poly(ethylene oxide)-\textit{block}-poly(n-butyl methacrylate-\textit{random}-propargyl methacrylate) (PEO-$b$-P(nBMA-$r$-PgMA)) diblock copolymer and Rhodamine B azide was investigated. During thermal annealing, the click reaction between the alkyne-bearing diblock copolymer and the azide lead to a significant increase in non-favorable segmental interaction and thus microphase separation of the block copolymer. Different morphologies were realized by controlling block copolymer composition and the mole ratio between the alkyne and azide groups. The effects of film thickness and annealing temperature on microdomain orientation and lateral ordering were also revealed. Our studies suggest a promising approach to fabricate nanostructured materials with long-range lateral ordering. [Preview Abstract] |
Tuesday, March 22, 2011 1:39PM - 1:51PM |
J43.00013: Correlation in SANS $\chi$ upon heating and pressurization for a diblock copolymer Junhan Cho, Jumi Lee, Du Yeol Ryu The response of phase behavior to pressure for an A-$b$-B diblock copolymer in the disordered state has been studied by small-angle neutron scattering (SANS). Deuterated polystyrene-$b$-poly(n-propyl methacrylate) (dPS-$b$-PPrMA) copolymer, which possesses ordering transition upon heating and baroplasticity (suppressed demixing by pressurization), was taken as our model system. It was shown that effective Flory-Huggins parameter $\chi _F$ from scattering intensity profiles upon heating and pressurization forms a characteristic curve that is a function of pressure increment $\Delta P$ ($\equiv P-P_0$) divided by temperature dependent bulk modulus $B_0 $ at a reference pressure $P_0$. Each isotherm of $\chi _F$ is superposed into the curve by a scale factor $\tau$ determined by $B_0 $. The scattering intensity maxima $I_{max}$, which is governed by $\chi _F$, were also shown to reveal a similar superposition. [Preview Abstract] |
Tuesday, March 22, 2011 1:51PM - 2:03PM |
J43.00014: Rouse and Entangled Dynamics in Coarse Grain Polymeric Systems Abelardo Ramirez-Hernandez, Darin Pike, Francois Detcheverry, Juan de Pablo The understanding of the kinetics of microphase ordering of block copolymers is important for controlling the morphology of these polymeric materials. Much of our current understanding of the equilibrium morphologies of block copolymers has emerged from studies using Self-Consistent Field Theory (SCFT), in which the effect of non-crossability of chains is not taken into account. In this work, we use a particle-based coarse grain model of block copolymers, and introduced elastic slip-links to model the effect of entanglements on the dynamics of the melts. These effects can be important when the self-assembly occurs in non-equilibrium conditions. We show that our model is able to reproduce both Rouse and Entangled dynamical behavior for a homopolymeric melt. We apply our computational approach to block copolymer systems under equilibrium and non equilibrium (shear flow) conditions. [Preview Abstract] |
Tuesday, March 22, 2011 2:03PM - 2:15PM |
J43.00015: Facile Synthesis and Characterization of Well-Defined Rod-Coil Block Copolymers Composed of Regioregular Poly(3-hexyl thiophene) Hong Chul Moon, Jin Kon Kim We synthesized rod-coil block copolymers composed of regioregular poly(3-hexyl thiopene) (P3HT) block via anionic coupling reaction. Three different coil blocks (poly(2-vinyl pyridine) (P2VP) and polyisoprene (PI)) and poly(methyl methacrylate) (PMMA)) were selected. For the synthesis of P2VP-$b$-P3HT-$b$-P2VP and P2VP-$b$-P3HT-$b$-P2VP, the chain ends of the P3HT were capped by the aldehyde group. On the other hand, phenyl acrylate (PA)-capped P3HT was prepared for coupling reaction with living PMMA anions. When the excess amount of the used living anions was removed by column chromatography, all of the neat block copolymers showed lower PDI without leaving any homopolymers. We also investigated the optical property and thin film morphology of synthesized various block copolymers. [Preview Abstract] |
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