Polymer Domains Research Articles

Towards biodegradable elastomers: green synthesis of carbohydrate functionalized styrene–butadiene–styrenecopolymer by click chemistry

Random attachment of sugar molecules to synthetic polymers is an important strategy to induce biodegradability in these polymers. The present study successfully employs “click” chemistry to introduce low levels of sugar molecules onto styrene–butadiene–styrene (SBS) copolymer, a widely used commodity polymer which is not biodegradable. Spectral, morphological and thermal studies of the modified polymers were carried out to show the dramatic changes in the properties of these modified polymers. Thermal stability of glucose linked SBS had onset of degradation at 428 °C, down from 478 °C observed for SBS. Morphology studied by WAXRD and SEM showed destructuring of the polymer domains of SBS, which is beneficial for biodegradation of these polymers. Previous studies showed that sugars anchored by hydrolysable ester groups onto polystyrene were biodegradable; current studies show that sugars anchored by unhydrolyzable C–C bonds on the butadiene component of SBS copolymer are also significantly biodegradable.

Predicting the morphology of sickle red blood cells using coarse-grained models of intracellular aligned hemoglobin polymers.

Sickle red blood cells (SS-RBCs) exhibit heterogeneous cell morphologies (sickle, holly leaf, granular, etc.) in the deoxygenated state due to the polymerization of the sickle hemoglobin. Experimental evidence points to a close relationship between SS-RBC morphology and intracellular aligned hemoglobin polymers. Here, we develop a coarse-grained (CG) stochastic model to represent the growth of the intracellular aligned hemoglobin polymer domain. The CG model is calibrated based on the mechanical properties (Young's modulus, bending rigidity) of the sickle hemoglobin fibers reported in experiments. The process of the cell membrane transition is simulated for physiologic aligned hemoglobin polymer configurations and mean corpuscular hemoglobin concentration. Typical SS-RBC morphologies observed in experiments can be obtained from the current model as a result of the intracellular aligned hemoglobin polymer development without introducing any further ad hoc assumptions. It is found that the final shape of SS-RBCs is primarily determined by the angular width of the aligned hemoglobin polymer domain, but it also depends, to a lesser degree, on the polymer growth rate and the cell membrane rigidity. Cell morphologies are quantified by structural shape factors, which agree well with experimental results from medical images.

Enhanced mobility in P3HT-based OTFTs upon blending with a phenylene–thiophene–thiophene–phenylene small molecule

An enhancement in charge transport capacity in a poly(3-hexylthiophene) (P3HT) semicrystalline film, up to field-effect mobilities approaching 0.1 cm(2) V(-1) s(-1), has been achieved by co-deposition with a small molecule, i.e. 5,5'-bis(4-n-hexylphenyl)-2,2'-bithiophene (dH-PTTP), forming highly ordered crystals bridging large polymeric domains.

Exploring Lateral Microphase Separation in Mixed Polymer Brushes by Experiment and Self-Consistent Field Theory Simulations

Similar to block copolymers, mixed polymer brushes are physically constrained and, upon annealing, microphase separate into nanodomains with morphologies largely dependent on the volume fractions of the polymers. A combination of experimental analysis of polystyrene (PS)/poly(methyl methacrylate) (PMMA) brushes and self-consistent field theory (SCFT) simulations is employed to determine the phases of annealed binary brushes. By annealing the brushes under conditions that maximize lateral versus vertical separation, a rich array of phases are observed with general agreement to predictions by SCFT simulations. The incorporation of random perturbations to the grafting density in SCFT simulations accounts for disorder in the arrangement of the polymer domains for the PS/PMMA brushes. Additionally, autocorrelation of the polymer domains yields an experimental domain spacing that is nearly 2 times greater than SCFT predictions, which is hypothesized to result from polydispersity in the PS/PMMA brushes. These fi...

Gold Nanoparticles Incarcerated in Nanoporous Syndiotactic Polystyrene Matrices as New and Efficient Catalysts for Alcohol Oxidations

The controlled synthesis of gold nanoparticles (AuNPs), incarcerated in a semicrystalline nanoporous polymer matrix that consisted of a syndiotactic polystyrene-co-cis-1,4-polybutadiene multi-block copolymer is described. This catalyst was successfully tested in the oxidation of primary and secondary alcohols, in which we used dioxygen as the oxidant under mild conditions. Accordingly, (±)-1-phenylethanol was oxidised to acetophenone in high yields (96%) in 1 h, at 35 °C, whereas benzyl alcohol was quantitatively oxidised to benzaldehyde with a selectivity of 96% in 6 h. The specific rate constants calculated from the corresponding kinetic plots were among the highest found for polymer-incarcerated AuNPs. Similar values in terms of reactivity and selectivity were found in the oxidation of primary alcohols, such as cinnamyl alcohol and 2-thiophenemethanol, and secondary alcohols, such as indanol and α-tetralol. The remarkable catalytic properties of this system were attributed to the formation, under these reaction conditions, of the nanoporous ε crystalline form of syndiotactic polystyrene, which ensures facile and selective accessibility for the substrates to the gold catalyst incarcerated in the polymer matrix. Moreover, the polymeric crystalline domains produced reversible physical cross-links that resulted in reduced gold leaching and also allowed the recovery and reuse of the catalyst. A comparison of catalytic performance between AuNPs and annealed AuNPs suggested that multiple twinned defective nanoparticles of about 9 nm in diameter constituted the active catalyst in these oxidation reactions.

66 Dehydration at the lens surface: surface energy and surfactant persistence

Purpose: Most published surface wettability data are based on hydrated materials and are dominated by the air-water interface. Water soluble species with hydrophobic domains (such as surfactants) interact directly with the hydrophobic domains in the lens polymer. Characterisation of relative polar and non-polar fractions of the dehydrated material provides an additional approach to surface analysis. Method: Probe liquids (water and diiodomethane) were used to characterise polar and dispersive components of surface energies of dehydrated lenses using the method of Owens and Wendt. A range of conventional and silicone hydrogel soft lenses was studied. The polar fraction (i.e. polar/total) of surface energy was used as a basis for the study of the structural effects that influence surfactant persistence on the lens surface. Results: When plotted against water content of the hydrated lens, polar fraction of surface energy (PFSE) values of the dehydrated lenses fell into two rectilinear bands. One of these bands covered PFSE values ranging from 0.4 to 0.8 and contained only conventional hydrogels, with two notable additions: the plasma coated silicone hydrogels lotrafilcon A and B. The second band covered PFSE values ranging from 0.04 to 0.28 and contained only silicone hydrogels. Significantly, the silicone hydrogel lenses with lowest PFSE values (p<0.15) are found to be prone to lipid deposition duringwear. Additionally, more hydrophobic surfactants were found to be more persistent on lenses with lower PFSE values. Conclusions: Measurement of polar fraction of surface energy provides an importantmechanistic insight into surface interactions of silicone hydrogels.

Electrostatic Contributions in the Increased Compatibility of Polymer Blends

Successful blending of different polymers to make a structural or functional material requires overcoming limitations due to immiscibility and/or incompatibility that arise from large polymer-polymer interfacial tensions. In the case of latex blends, the combination of capillary adhesion during the blended dispersion drying stage with electrostatic adhesion in the final product is an effective strategy to avoid these limitations, which has been extended to a number of polymer blends and composites. This work shows that adhesion of polymer domains in blends made with natural rubber and synthetic latexes is enhanced by electrostatic adhesion that is in turn enhanced by ion migration, according to the results from scanning electric potential microscopy. The additional attractive force between domains improves blend stability and mechanical properties, broadening the possibilities and scope of latex blends, in consonance with the "green chemistry" paradigm. This novel approach based on electrostatic adhesion can be easily extended to multicomponent systems, including nonpolymers.

Crystal Structure of the Ligand Binding Domain of Netrin G2

Netrin G proteins represent a small family of synaptic cell adhesion molecules related to netrins and to the polymerization domains of laminins. Two netrin G proteins are encoded in vertebrate genomes, netrins G1 and G2, which are known to bind the leucine-rich repeat proteins netrin G ligand (NGL)-1 and NGL-2, respectively. Netrin G proteins share a common multi-domain architecture comprising a laminin N-terminal (LN) domain followed by three laminin epidermal growth factor-like (LE) domains and a C′ region containing a glycosylphosphatidylinositol anchor. Here, we use deletion analysis to show that the LN domain region of netrin Gs contains the binding site for NGLs to which they bind with 1:1 stoichiometry and sub-micromolar affinity. Netrin Gs are alternatively spliced in their LE domain regions, but the binding region, the LN domain, is identical in all splice forms. We determined the crystal structure for a fragment comprising the LN domain and domain LE1 of netrin G2 by sulfur single-wavelength anomalous diffraction phasing and refined it to 1.8 Å resolution. The structure reveals an overall architecture similar to that of laminin α chain LN domains but includes significant differences including a Ca2+ binding site in the LN domain. These results reveal the minimal binding unit for interaction of netrin Gs with NGLs, define structural features specific to netrin Gs, and suggest that netrin G alternative splicing is not involved in NGL recognition.

Imaging nanostructures in organic semiconductor films with scanning transmission X-ray spectro-microscopy

Thin films of organic semiconducting materials are of increasing technological importance in optoelectronic devices such as light emitting diodes (LEDs), lasers, field effect transistors (FETs) and solar cells. However, the morphology of such films is complex, often displaying three dimensional composition structure or molecular alignment effects. The structure of the polymer film incorporated into a device can strongly affect its performance characteristics, e.g. via the connectedness of polymer domains and to the device electrodes, or due to anisotropic material properties due to molecular alignment.Scanning transmission X-ray spectro-microscopy (STXM) has been demonstrated to be an excellent tool for the study of organic materials due to its high spatial resolution (down to about 20nm) and strong contrast based on a variety of spectroscopic mechanisms. In particular, tuning the probing X-ray beam to resonances in the near edge X-ray absorption fine structure (NEXAFS) spectra provides a mechanism for molecular-structure based contrast which is a very powerful tool for studying blends of organic components. A further advantage of STXM is that strategic use of spectroscopic information allows quantitative compositional analysis of imaged areas. Recent work at the PolLux STXM has demonstrated two new developments in the imaging of thin organic films: simultaneous surface and bulk imaging via an additional channeltron electron detector, and molecular orientation mapping via anisotropic near edge resonances.

MORPHOLOGY AND RHEOLOGY OF NONREACTIVE AND REACTIVE EPDM/PP BLENDS IN TRANSIENT SHEAR FLOW: PLASTICIZED VERSUS NONPLASTICIZED BLENDS

Abstract Both nonplasticized and plasticized ethylene-propylene-diene-terpolymer/polypropylene (EPDM/PP) based thermoplastic elastomers (TPEs) were prepared in the presence and absence of a curing system (i.e., reactive vs nonreactive TPEs). The nonlinear viscoelastic behavior and morphology evolution of these blends were investigated through single and multiple start-up transient experiments to find out the effects of composition, plasticizer, and the presence of the curing system in a homogeneous shear flow field. Due to the highly elastic nature of the elastomeric component, the shear rate was set to 0.1 s−1 and in the case of multiple start-up experiments a 10 min rest time was set between consecutive shearing cycles. The specific interfacial area (Q) of the TPEs was analyzed prior and after shearing and subsequently correlated to the corresponding rheological response of these blends. The magnitude and the width of the stress overshoot were correlated to the morphology of the blends, elastomer content, the presence of plasticizer and curing system. The presence of a plasticizer (paraffinic oil) drastically decreased the viscosity and elasticity of both neat polymers and consequently the resulting TPEs; and it further reduced the initial curing rate of the elastomeric component at the early shearing stage of the reactive TPEs. Moreover, the plasticization promoted swelling and coalescence, enlarging the size of the polymeric domains, and decreasing the specific interfacial area. Furthermore, the in situ curing reaction in the reactive TPE blends resulted in less elongated polymeric domains with an irregular and larger interface compared to the nonreactive blends. A phase inverted morphology has also been observed for nonplasticized high elastomer content reactive TPEs sheared for long periods. The obtained experimental morphology data of the nonreactive blends subjected to multiple start-up experiments was fairly well predicted using a phenomenological model proposed by Lee and Park [J. Rheo. 38(5), 1994].

In situ preparation of cross‐linked polystyrene/poly(methyl methacrylate) blend foams with a bimodal cellular structure

In situ preparation of a cross‐linked poly(methyl methacrylate) (PMMA) and polystyrene (PS) blend and its foaming were investigated for creating a bimodal cellular structure in the foam. Methyl methacrylate (MMA) monomer was dissolved in PS under supercritical CO2 at a temperature of 60 °C and a pressure of 8 MPa, and the polymerization of MMA was conducted at 100 °C and 8 MPa CO2, with a cross‐linking agent in PS. The blend was successively foamed by depressurizing the CO2. CO2 played the roles of plasticizing the PS and enhancing the monomer dispersion in PS during the sorption process and as a physical blowing agent in the foaming process. The cross‐linking agent was used for controlling the elasticity of polymerized PMMA domains and differentiating their elasticity from that of the PS matrix. The difference in elasticity delayed the bubble nucleation in the PMMA domains from that in the PS and made the cell size bimodal distribution, in which the smaller cells ranging from 10 to 30 µm in diameter were located in the wall of large cells of 200–400 µm in diameter. The effects of the initial MMA content, the concentration of cross‐linking agent, and the depressurization rate on the bimodal cell structure and bulk foam density were investigated. Copyright © 2011 John Wiley &amp; Sons, Ltd.

A human sterile alpha motif domain polymerizome

The sterile alpha motif (SAM) domain is one of the most common protein modules found in eukaryotic genomes. Many SAM domains have been shown to form helical polymer structures suggesting that SAM modules can be used to create large protein complexes in the cell. Because many polymeric SAM domains form heterogenous and insoluble aggregates that are experimentally intractable when isolated, it is likely that many polymeric SAM domains have gone uncharacterized. We, therefore, developed a method to maintain polymeric SAM domains in a soluble form that allowed rapid screening for potential SAM polymers. SAM domains were expressed as fusions to a super-negatively charged green fluorescent protein (negGFP). The negGFP imparts three useful properties to the SAM domains: (1) the charge helps to maintain solubility; (2) the charge leads to reliable migration toward the cathode on native gels; and (3) the fluorescence emission allows visualization in crude extracts. Using the negGFP-SAM fusions, we screened a large library of human SAM domains for polymerization using a native gel screen. A selected set of hSAM domains were then purified and examined for true polymer formation by electron microscopy. In this manner, we identified a set of new potential SAM polymers: ANKS3, Atherin, BicaudalC1, Caskin1, Caskin2, Kazrin, L3MBTL3, L3MBTL4, LBP, LiprinB1, LiprinB2, SAMD8, SAMD9, and STIM2. While further characterization will be necessary to verify that the SAM domains identified here truly form polymers, our results provide a much stronger working hypothesis for a large number of proteins that was possible from sequence analysis alone.

Host–Guest Interactions between a Nonmicellized Amphiphilic Invertible Polymer and Insoluble Cyclohexasilane in Acetonitrile

Host-guest interactions between cyclohexasilane (Si(6)H(12)) and amphiphilic invertible macromolecules based on PEG and sebacic acid in acetonitrile (neither a solvent for cyclohexasilane nor a support for the micellization of amphiphilic invertible macromolecules) have been investigated. Despite the extended conformation of the macromolecules and the absence of self-assembled polymeric domains, a macromolecular amphiphilicity itself contributes to localizing Si(6)H(12) by AIP and thus enables Lewis acid-base interactions between Si(6)H(12) and the AIP carbonyl groups. The obtained results demonstrate an interesting phenomenon in that insoluble Si(6)H(12) can be localized by AIP macromolecules in a medium that does not support the formation of polymeric domains.

Alternating Copolymers of Cyclopenta[2,1‐b;3,4‐b′]dithiophene and Thieno[3,4‐c]pyrrole‐4,6‐dione for High‐Performance Polymer Solar Cells

AbstractA series of alternating copolymers of cyclopenta[2,1‐b;3,4‐b′]dithiophene (CPDT) and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) have been prepared and characterized for polymer solar cell (PSC) applications. Different alkyl side chains, including butyl (Bu), hexyl (He), octyl (Oc), and 2‐ethylhexyl (EH), are introduced to the TPD unit in order to adjust the packing of the polymer chain in the solid state, while the hexyl side chain on the CPDT unit remains unchanged to simplify discussion. The polymers in this series have a simple main chain structure and can be synthesized easily, have a narrow band gap and a broad light absorption. The different alkyl chains on the TPD unit not only significantly influence the solubility and chain packing, but also fine tune the energy levels of the polymers. The polymers with Oc or EH group have lower HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels, resulting higher open circuit voltages (Voc) of the PSC devices. Power conversion efficiencies (PCEs) up to 5.5% and 6.4% are obtained from the devices of the Oc substituted polymer (PCPDTTPD‐Oc) with PC61BM and PC71BM, respectively. This side chain effect on the PSC performance is related to the formation of a fine bulk heterojunction structure of polymer and PCBM domains, as observed with atomic force microscopy.

Photoinduced Carrier Generation and Decay Dynamics in Intercalated and Non-intercalated Polymer:Fullerene Bulk Heterojunctions

The dependence of photoinduced carrier generation and decay on donor-acceptor nanomorphology is reported as a function of composition for blends of the polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT-C(14)) with two electron-accepting fullerenes: phenyl-C(71)-butyric acid methyl ester (PC(71)BM) or the bisadduct of phenyl-C(61)-butyric acid methyl ester (bis-PC(61)BM). The formation of partially or fully intercalated bimolecular crystals at weight ratios up to 1:1 for pBTTT-C(14):PC(71)BM blends leads to efficient exciton quenching due to a combination of static and dynamic mechanisms. At higher fullerene loadings, pure PC(71)BM domains are formed that result in an enhanced free carrier lifetime, as a consequence of spatial separation of the electron and hole into different phases, and the dominant contribution to the photoconductance comes from the high-frequency electron mobility in the fullerene clusters. In the pBTTT-C(14):bis-PC(61)BM system, phase separation results in a non-intercalated structure, independent of composition, which is characterized by exciton quenching that is dominated by a dynamic process, an enhanced carrier lifetime and a hole-dominated photoconductance signal. The results indicate that intercalation of fullerene into crystalline polymer domains is not detrimental to the density of long-lived carriers, suggesting that efficient organic photovoltaic devices could be fabricated that incorporate intercalated structures, provided that an additional pure fullerene phase is present for charge extraction.

Polarization Mediated Chemistry on Ferroelectric Polymer Surfaces

We have investigated the chemisorption of two isomers of diiodobenzene on the molecular ferroelectric copolymer poly(vinylidene fluoride) with trifluoroethylene (70:30) as a function of the polymeric ferroelectric domain orientation. We find that the 1,4-p-diiodobenzene adsorption at 150 K strongly favors a positive ferroelectric domain orientation while the 1,2-o-diiodobenzene adsorption at 150 K strongly favors a negative ferroelectric domain orientation. Both polar and nonpolar adsorbates are influenced by the substrate dipole direction. Because a nonpolar isomer is also affected by the surface dipole direction, and hence the surface chemical termination, it is clear that surface chemistry and not simply surface dipoles matter in the chemisorption process.

Improving polymer solar cell performances by manipulating the self-organization of polymer

We have investigated driving force effects on the ordering of polymer, which is a key factor of self-assembly of soft materials. By turning the substrate up-side-down, the downward driving force can form in solution film-growth process and affect the self-organization of polymer chains and domains. We introduce Brown’s capillarity theory [J. Polym. Sci., Polym. Phys. Ed. 22, 423 (1956)] to describe the film formation. Our results show that the better chain and lamellae packing of polymer make hole transport, carrier balance, and power conversion efficiency of annealed and unannealed devices improve even with thick active-layers as compared to conventional devices.

A Route to Nanoscopic Materials via Sequential Infiltration Synthesis on Block Copolymer Templates

Sequential infiltration synthesis (SIS), combining stepwise molecular assembly reactions with self-assembled block copolymer (BCP) substrates, provides a new strategy to pattern nanoscopic materials in a controllable way. The selective reaction of a metal precursor with one of the pristine BCP domains is the key step in the SIS process. Here we present a straightforward strategy to selectively modify self-assembled polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) BCP thin films to enable the SIS of a variety of materials including SiO(2), ZnO, and W. The selective and controlled interaction of trimethyl aluminum with carbonyl groups in the PMMA polymer domains generates Al-CH(3)/Al-OH sites inside the BCP scaffold which can seed the subsequent growth of a diverse range of materials without requiring complex block copolymer design and synthesis.

Immobilization of amphiphilic polycations by catechol functionality for antimicrobial coatings.

A new strategy for preparing antimicrobial surfaces by a simple dip-coating procedure is reported. Amphiphilic polycations with different mole ratios of monomers containing dodecyl quaternary ammonium, methoxyethyl, and catechol groups were synthesized by free-radical polymerization. The polymer coatings were prepared by immersing glass slides into a polymer solution and subsequent drying and heating. The quaternary ammonium side chains endow the coatings with potent antibacterial activity, the methoxyethyl side chains enable tuning the hydrophobic/hydrophilic balance, and the catachol groups promote immobilization of the polymers into films. The polymer-coated surfaces displayed bactericidal activity against Escherichia coli and Staphylococcus aureus in a dynamic contact assay and prevented the accumulation of viable E. coli, S. aureus, and Acinetobacter baumannii for up to 96 h. Atomic force microscopy (AFM) images of coating surfaces indicated that the surfaces exhibit virtually the same smoothness for all polymers except the most hydrophobic. The hydrophobic polymer without methoxyethyl side chains showed clear structuring into polymer domains, causing high surface roughness. Sum-frequency generation (SFG) vibrational spectroscopy characterization of the surface structures demonstrated that the dodecyl chains are predominantly localized at the surface-air interface of the coatings. SFG also showed that the phenyl groups of the catechols are oriented on the substrate surface. These results support our hypothesis that the adhesive or cross-linking functionality of catechol groups discourages polymer leaching, allowing the tuning of the amphiphilic balance by incorporating hydrophilic components into the polymer chains to gain potent biocidal activity.

Charge- and temperature-dependent interactions between anionic poly(N-isopropylacrylamide) polymers in solution and a cationic surfactant at the water/air interface

Due to their expanded coil to collapsed globule transition close to physiological temperatures, N-isopropylacrylamide (NIPAAM) polymers and derivatives thereof represent promising drug delivery vectors. Here, we report on the interaction between anionic PNIPAAM derivatives containing potassium 3-sulfopropylmethacrylate (SPMA) blocks of various sizes and a cationic lipid membrane mimic as a function of temperature, polymer charge density and molecular weight, by injection under a pre-compressed surfactant monolayer. The resulting film properties (including equilibria) were studied using surface pressure–area isotherms, Brewster angle microscopy, and interfacial 2D oscillatory rheology. Whereas mixed films of dioctadecyldimethylammonium bromide (DODAB) and an uncharged PNIPAAM homopolymer resulted in distinct polymer and surfactant domains, the anionic polyelectrolytes were found to ionically cross-link and contract the DODAB film. Film penetration, charge screening and surfactant film contraction were dependent on the molecular weight and size of the SPMA blocks on the polymers.