Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session B44: Physics of Copolymers I |
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Sponsoring Units: DPOLY Chair: Darrin Pochan, University of Delaware Room: A309 |
Monday, March 21, 2011 11:15AM - 11:51AM |
B44.00001: Controlling Cellular Endocytosis at the Nanoscale Invited Speaker: One of the most challenging aspects of drug delivery is the intra-cellular delivery of active agents. Several drugs and especially nucleic acids all need to be delivered within the cell interior to exert their therapeutic action. Small hydrophobic molecules can permeate cell membranes with relative ease, but hydrophilic molecules and especially large macromolecules such as proteins and nucleic acids require a vector to assist their transport across the cell membrane. This must be designed so as to ensure intracellular delivery without compromising cell viability. We have recently achieved this by using pH-sensitive poly(2-(methacryloyloxy)ethyl-phosphorylcholine)- co -poly(2-(diisopropylamino)ethyl methacrylate) (PMPC-PDPA) and poly(ethylene oxide)-co- poly(2-(diisopropylamino)ethyl methacrylate) (PEO-PDPA) diblock copolymers that self-assemble to form vesicles in aqueous solution. These vesicles combine a non-fouling PMPC or PEO block with a pH-sensitive PDPA block and have the ability to encapsulate both hydrophobic molecules within the vesicular membrane and hydrophilic molecules within their aqueous cores. The pH sensitive nature of the PDPA blocks make the diblock copolymers forming stable vesicles at physiological pH but that rapid dissociation of these vesicles occurs between pH 5 and pH 6 to form molecularly dissolved copolymer chains (unimers). We used these vesicles to encapsulate small and large macromolecules and these were successfully delivered intracellularly including nucleic acid, drugs, quantum dots, and antibodies. Dynamic light scattering, zeta potential measurements, and transmission electron microscopy were used to study and optimise the encapsulation processes. Confocal laser scanning microscopy, fluorescence flow cytometry and lysates analysis were used to quantify cellular uptake and to study the kinetics of this process in vitro and in vivo. We show the effective cytosolic delivery of nucleic acids, proteins, hydrophobic molecules, amphiphilic molecules, and hydrophilic molecules without affecting the viability of cells or even triggering inflammatory pathways. Finally we show how size, surface chemistry and surface topology of the vesicles affect their interaction with the cell membrane and hence their cellular uptake. \\[4pt] References:\\[0pt] C. Lo Presti, M. Massignani, T. Smart, H. Lomas, and G. Battaglia \textit{J. Mater. Chem}. (2009) 19, 3576-3590 H. Lomas, I. Canton, S. MacNeil, J. Du, S.P. Armes, A.J. Ryan, A.L. Lewis and G. Battaglia \textit{Adv. Mater}. (2007). 19, 4238-4243 \\[0pt] M. Massignani, I. Canton, N. Patikarnmonthon, N. J. Warren, S. P. Armes, A. L. Lewis and G. Battaglia, \textit{Nature Prec.}, 2010, http://hdl.handle.net/10101/npre.2010.4427.1 M. Massignani, C. LoPresti, A. Blanazs, J. Madsen, S. P. Armes, A. L. Lewis and G. Battaglia \textit{Small}, 2009, 5, 2424-2432. \\[0pt] M. Massignani, T. Sun, A. Blanazs, V. Hearnden, I. Canton, P. Desphande, S. Armes, S. MacNeil, A. Lewis and G. Battaglia \textit{PLoS One}, 2010, 5, e10459. [Preview Abstract] |
Monday, March 21, 2011 11:51AM - 12:03PM |
B44.00002: Microphase Separation in Block-Random Copolymers of Styrene and Hydrogenated Isoprene Bryan S. Beckingham, Richard A. Register The capacity to synthesize block-random copolymers, which are block copolymers with one or more random copolymer blocks, allows for continuous tuning of the interblock segregation strength, $\chi $, through the composition of the random copolymer. The ability to tune $\chi $ effectively decouples the block copolymer molecular weight from its order-disorder transition temperature. By lithium-initiated anionic polymerization with added triethylamine, we synthesize near-monodisperse and near-symmetric block-random copolymers of styrene and isoprene: PI-PSrI (50{\%} wt. styrene). In comparison to PS-PI diblock copolymers, the number of unfavorable segmental contacts in the disordered state is decreased and hence the effective interblock $\chi $ is reduced. Isoprene-hydrogenated derivatives of these block-random copolymers exhibit microphase separation into well-ordered lamellae and display sharp thermally-induced order-disorder transitions via small-angle x-ray scattering. The observed reduction in $\chi $, as gauged by the molecular weight required to achieve a desired T$_{ODT}$, matches well with the mean field prediction. [Preview Abstract] |
Monday, March 21, 2011 12:03PM - 12:15PM |
B44.00003: Micellization kinetics of diblock copolymers in a homopolymer matrix: A self-consistent field study Raghuram Thiagarajan, David Morse Self-consistent field theory is used to calculate free energy barriers and reaction rates for the spontaneous association and dissociation of micelles formed of block copolymers in a homopolymer matrix. The barriers are prohibitively large for copolymers of typical molecular weights when the unimer (free surfactant) concentration is near the equilibrium critical micelle concentration. As a result, polymeric micelles normally cannot reach true thermodynamic equilibrium. The rates of association and dissociation are, however, sensitive to unimer concentration, making it possible to form or destroy micelles at observable rates in sufficiently highly supersaturated or subsaturated solutions, respectively, even when both reactions are suppressed near the equilibrium CMC. The barrier to disassociation is particularly sensitive to unimer concentration, and vanishes when the unimer concentration is only slightly (e.g., tens of percent) below the equilibrium CMC. [Preview Abstract] |
Monday, March 21, 2011 12:15PM - 12:27PM |
B44.00004: Manipulating the structural conformation of block copolymer micelles using co-solvent mixtures Elizabeth G. Kelley, Thomas P. Smart, Millicent O. Sullivan, Thomas H. Epps, III The internal structure of poly(butadiene-$b$-ethylene oxide) (PB-PEO) block copolymer micelles was manipulated through the use of co-solvent mixtures. In aqueous solutions, the PB-PEO block copolymers self-assembled into monodisperse, spherical micelles with well-defined PB cores surrounded by PEO coronas. The addition of tetrahydrofuran (THF) to the micelle solution improved the solvent quality for the PB block and resulted in the swelling of the micelle cores. The average micelle size decreased with increasing THF content as shown by dynamic light scattering, small angle X-ray scattering, and cryogenic transmission electron microscopy. The distribution of PB in the micelles was studied using nuclear magnetic resonance spectroscopy and small angle neutron scattering. Finally, the spherical micelles disassembled in co-solvent mixtures containing greater than 72 vol{\%} THF. This result was consistent with phase behavior studies of PB homopolymer, which indicated that PB is soluble in water-THF mixtures up to a similar THF solution composition. [Preview Abstract] |
Monday, March 21, 2011 12:27PM - 12:39PM |
B44.00005: Molecular Exchange in Ordered Diblock Copolymer Micelles Soo-Hyung Choi, Timothy Lodge, Frank Bates Previously, molecular exchange between spherical micelles in dilute solution (1 vol{\%} polymer) was investigated using time-resolved small-angle neutron scattering (TR-SANS). As the concentration of spherical micelles formed by the diblock copolymers increases, the micelles begin to overlap and eventually pack onto body-centered cubic (BCC) lattice. In this study, concentrated, ordered micelles (15 vol{\%} polymers) prepared by dispersing isotopically labeled poly(styrene-$b$-ethylene-\textit{alt}-propylene) in an isotopic squalane mixture was investigated to understand the micellar concentration dependence of the molecular exchange. Perfectly random mixing of isotopically labeled micelles on the BCC lattice was confirmed by SANS patterns where the interparticle contribution vanishes, resulting in an intensity that directly relates to the exchange kinetics. The measured molecular exchange process for the concentrated, ordered system is qualitatively consistent with the previous observations, but the rate is more than an order of magnitude slower than that for the dilute, disordered system. [Preview Abstract] |
Monday, March 21, 2011 12:39PM - 12:51PM |
B44.00006: Kinetics of Pressure Jump for Block Copolymer Phase Transition in Selective Solvent Yongsheng Liu, Rama Bansil, Milos Steinhart Synchrotron based time-resolved small angle x-ray scattering (SAXS) was used to study the kinetics of the order-disorder transition (ODT) in a 30{\%} (w/v) solution of a diblock copolymer of poly(styrene -- isoprene) (SI 18-12) in diethyl phthalate, a selective solvent for the PS block using pressure jump methods. Time resolved pressure jump SAXS experiments were done to study the kinetics of disorder to BCC phase transition and the reverse transition. The results show that the ODT temperature increases at about 20C/kbar with pressure. Analysis of Percus-Yevik model following pressure jumps and pressure ramps will be presented. The analysis shows that core radius of micelles are independent of pressure, but hard sphere radius increases with pressure. [Preview Abstract] |
Monday, March 21, 2011 12:51PM - 1:03PM |
B44.00007: Transition Behavior of Hydrogen Bonding mediated Block Copolymer complex Sudhakar Naidu, Hyungju Ahn, Hoyeon Lee, Du Yeol Ryu We have investigated transition behavior for block copolymer (BCP) complexes composed of a lamella-forming polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) and phenyl acetamide derivatives. Influence of small molecules on transition temperatures such as order-to-disorder transitions (ODT) were analyzed by by in-situ small angle x-ray scattering (SAXS) and depolarized light scattering (DPLS). The importance of the availability for H-bonding mediation to control over transition behavior for BCP mixtures with the functional molecules was shown by changing the annealing temperatures. Non-covalent interactions between the nitrogen units of P2VP block and small molecules enhances nonfavorable segmental interactions between two block components, leading to a significant increase in d-spacing for BCP mixtures. [Preview Abstract] |
Monday, March 21, 2011 1:03PM - 1:15PM |
B44.00008: Phase Behavior of Binary Mixtures of Block Copolymers having Hydrogen Bonding Sung Hyun Han, Jin Kon Kim The phase behavior of binary mixtures of high molecular weight polystyrene-\textit{block}-poly(2-vinyl pyridine) (PS-$b$-P2VP) and low molecular weight polystyrene-\textit{block}-poly(4-hydroxystyrene) (PS-$b$-PHS) copolymers was investigated by using small angle X-ray scattering and transmission electron microscopy. Both block copolymers exhibited lamellar microdomains. When the weight fraction of PS-$b$-PHS in the blend was less than 0.1, lamellar microdomains are maintained. However, with increasing amount of PS-$b$-PHS, the microdomains are transformed to hexagonally-packed cylindrical microdomains, and body-centered cubic spherical microdomains. This is attributed to the hydrogen bonding between P2VP and PHS blocks. [Preview Abstract] |
Monday, March 21, 2011 1:15PM - 1:27PM |
B44.00009: Highly Localized Optically Induced Melting Transitions in Block Copolymers Azar Alizadeh, Eugene Boden, Xialei Shi, Victor Ostroverkhov, Daniel Brunnelle, Vicki Watkins, Charles Kerbage, Matthew Misner, Brian Lawrence Semi-crystalline block copolymers are well known to exhibit confined crystallization and/or melting phase transitions in sub-50 nm domains. Confined crystallization within these nano-domains is favored under the following conditions: 1) the crystallizable block forms discrete spherical or cylindrical domains; 2) the glass transition temperature of the matrix block is above the crystallization and melting temperatures of the crystallizable minority block; and 3) the block constituents form a strongly segregating system, such that the phase separation dominates the crystallization process. Here we report on optically induced highly localized crystalline-to-amorphous phase transitions in a composite medium comprised of a semi-crystalline block copolymer and a heat generating dye. We use an optical probe-pump and a Bragg reflective grating to both induce and detect the optically induced phase transitions in these block copolymers. We show that extremely fast and localized melting in these block copolymers can be achieved by exposing the samples to very short (5-20 ns) pulses of light. This study provides a new insight on the timescale of melting transitions in polymeric materials. [Preview Abstract] |
Monday, March 21, 2011 1:27PM - 1:39PM |
B44.00010: Self-Assembly of Lamellar Microphases in Linear Gradient Copolymer Melts Nicholas B. Tito, Scott T. Milner, Jane E. G. Lipson The ability to create `designer copolymers' with tunable properties by tailoring their monomer composition has garnered recent interest in their molecular self-assembly. Here we investigate lamellar microphases in linear gradient binary copolymer melts using a variety of techniques, including solutions of self-consistent field equations, scaling theory, and analysis of the strong-segregation limit. The Flory scaling theory predicts the scaling of the equilibrium lamellar width $L_{eq}$ as a function of comonomer incompatibility as characterized by \textit{$\chi $}. From the strongly segregated limit there are conformational fluctuations, and it is the tradeoff between the entropic effect of these relative to repulsive comonomer interactions that determines $L_{eq}$. We discover that $L_{eq}$ /$R_{g} \quad \sim $ (\textit{$\chi $N})$^{1/6}$; remarkably, this is the same result as for symmetric diblock copolymers, although for quite different physical reasons. [Preview Abstract] |
Monday, March 21, 2011 1:39PM - 1:51PM |
B44.00011: Kinetics and Dynamics of HEX to Gyroid Transition of a Diblock Copolymer in Selective Solvent Julian Spring, Yongsheng Liu, Rama Bansil Synchrotron based time-resolved small angle x-ray scattering (SAXS) was used to study the kinetics of the formation of a gyroid phase in solutions of a poly (styrene -isoprene) diblock copolymer in dimethyl phthalate, a selective solvent for the polystyrene block. From temperature ramp measurements on an 80{\%} (w/v) sample, a hexagonally-packed cylinders (HEX) phase was identifed below 95 C,while a gyroid formed above 95C. The kinetics of the transitions from HEX to gyroid was examined using temperature jump and ramp experiments over the temperature range of 50-150C. In addition, x-ray photon correlation spectroscopy was used to study the dynamics of the HEX and Gyroid phases, as well as the transition regime. Analysis of the time evolution of the Bragg peaks to follow the kinetics of the transition between these phases will be presented, in addition to analysis of the dynamics of this sample throughout the phase space under investigation. The formation of the Gyroid structure was also modeled using Molecular Dynamics (MD) simulations, and the results of these simulations will also be presented. [Preview Abstract] |
Monday, March 21, 2011 1:51PM - 2:03PM |
B44.00012: Dynamics of Cloud Point Transitions in Dilute Solutions of Gradient Copolymers with Prescribed Gradient Strengths Keith Gallow, Yueh-Lin Loo We have investigated dilute solutions of gradient copolymers comprising hydroxyethyl methacrylate and dimethylaminoethyl methacrylate with different gradient strengths undergoing their cloud point transitions. The gradient strength defines the maximum difference in instantaneous compositions along the polymer backbone. Isothermal dynamic light scattering tracks the fractions of unimers and aggregates with which the half times characterizing this transition can be quantified. We find the temperature dependence of this transition to depend on gradient strength, ranging from -2.22 decades/$^{\circ}$C for a random copolymer to -0.75 decades/$^{\circ}$C for a gradient copolymer of comparable molecular weight and overall composition but a gradient strength of 0.52. The progressively shallower temperature dependence of this transition with increasing gradient strength suggests of a nucleation and growth mechanism of aggregate formation. [Preview Abstract] |
Monday, March 21, 2011 2:03PM - 2:15PM |
B44.00013: Effect of Macromolecular Architecture on the Morphology of Polystyrene/Polyisoprene Block Copolymers Caleb Dyer, Paraskevi Driva, Scott Sides, Bobby Sumpter, Jimmy Mays, Mark Dadmun, Feng Zuo, Frank Bates The molecular architecture of branched block copolymers has been shown to dramatically effect morphological behavior. A study of four polystyrene/polyisoprene block copolymers with varying architecture (branched PSPI$_{2}$, PS$_{2}$PI, PS$_{2}$PI$_{2}$, and linear PSPI), and constant composition and molecular weight is presented. The morphologies of each sample were determined using SCFT simulations and, experimentally using SAXS and TEM. The PS$_{2}$PI$_{2 }$miktoarm star exhibits the same morphology as the linear$_{ }$diblock but with a reduction in the domain size. The PS$_{2}$PI and PSPI$_{2}$ copolymers demonstrated different morphologies from the diblock copolymer, a result of the architectural asymmetry. The results were then compared to Milner's theoretical predictions and found to be in good agreement. These results, therefore, provide detailed insight into the effect of copolymer architecture on the morphological behavior of block copolymers. [Preview Abstract] |
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