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We report a combined directing effect of the simultaneously applied graphoepitaxy and electric field on the self-assembly of cylinder forming polystyrene-b-poly(dimethylsiloxane) block copolymer in thin films. A correlation length of up to 20 mu m of uniaxial ordered striped patterns is an order of magnitude greater than that produced by either graphoepitaxy or electric field alignment alone and is achieved at reduced annealing times. The angle between the electric field direction and the topographic guides as well as the dimensions of the trenches affected both the quality of the ordering and the direction of the orientation of cylindrical domains: parallel or perpendicular to the topographic features. We quantified the interplay between the electric field and the geometry of the topographic structures by constructing the phase diagram of microdomain orientation. This combined approach allows the fabrication of highly ordered block copolymer structures using macroscopically prepatterned photolithographic substrates.
It is demonstrated that the orientation of striped patterns can be reversibly switched between two perpendicular in-plane orientations upon exposure to electric fields. The results on thin films of symmetric polystyrene-block-poly(2-vinyl pyridine) polymer in the intermediate segregation regime disclose two types of reorientation mechanisms from perpendicular to parallel relative to the electric field orientation. Domains orient via grain rotation and via formation of defects such as stretched undulations and temporal phase transitions. The contribution of additional fields to the structural evolution is also addressed to elucidate the generality of the observed phenomena. In particular solvent effects are considered. This study reveals the stabilization of the meta-stable in-plane oriented lamella due to sequential swelling and quenching of the film. Further, the reorientation behavior of lamella domains blended with selective nanoparticles is addressed, which affect the interfacial tensions of the blocks and hence introduce another internal field to the studied system. Switching the orientation of aligned block copolymer patterns between two orthogonal directions may open new applications of nanomaterials as switchable electric nanowires or optical gratings.
Electric-Field-Induced Order-Order Transition from Hexagonally Perforated Lamellae to Lamellae
(2015)
Block copolymers form a variety of microphase morphologies due to their ability to phase separate. The hexagonally perforated lamellar (HPL) morphology represents an unusually long-lived, nonequilibrium transient structure between lamellar and cylindrical phases. We present a detailed study of a concentrated, HPL-forming poly(styrene-b-isoprene) diblock copolymer solution in toluene in the presence of an electric field. We will show that this phase is readily aligned by a moderate electric field and provide experimental evidence for an electric-field-induced order order transition toward the lamellar phase under sufficiently strong fields. This process is shown to be fully reversible as lamellar perforations reconnect immediately upon secession of the external stimulus, recovering highly aligned perforated lamellae.
A detailed birefringence analysis of the effect of strong dc electric fields on the order-disorder transition temperature (T-ODT) of lamella forming block copolymers is reported. The setup presented here enabled the measurement of the T-ODT with high temperature resolution while the birefringence measurements were nondestructive and straightforward compared to alternative methods. A downward shift in the transition temperature was found for all samples upon application of the electric field. The data indicate that the dominating parameter that evokes the mixing of block copolymers when exposed to electric fields is the difference in dielectric permittivity Delta epsilon between the block copolymer constituents. The extent to which the T-ODT is shifted is furthermore influenced by the degree of polymerization N. Shifts in the transition temperature of up to 7 degrees C were found upon application of an electric field of 5 kV/mm.
In this work we present the first e-microgel, whose size can be adjusted by application of an electrochemical potential, as seen by dynamic light scattering (3D-DLS in dependence of equilibrium potential) and scanning force microscopy (SFM). Hereby, polyelectrolyte microgels with attracted electroactive counterions provide an effective platform for the manipulation of the microgel size by electrochemical means. The reversible switching of guest molecules, namely, hexacyanoferrates, between oxidized ferricyanide [Fe(CN)(6)](3-) and reduced ferrocyanide [Fe(CN)(6)](4-), influences the cationic host microgel, poly(N-isopropylacrylamide-co-methacrylamidopropyltrimethylammonium chloride) P(NIPAM-co-MAPTAC), and hence the swelling properties of the microgel. The combination of thermo- and redox-responsiveness in one particle leads to a novel type of multistimuli responsive material. In addition, the use of hydrodynamic voltammetry detects directly the preferred uptake of ferricyanide and enables the determination of the nominal charge ratio (ncr) between microgel and entrapped counterions at different states of switching. Further, electrochemical impedance spectroscopy allows a more detailed mechanistic insight into the microgel modulation.
Electrostatic attraction between charged nano particles and oppositely charged nanopatterned polymeric films enables tailored structuring of functional nanoscopic surfaces. The bottom-up fabrication of organic/inorganic composites for example bears promising potential toward cheap fabrication of catalysts, optical sensors, and the manufacture of miniaturized electric circuitry. However, only little is known about the time-dependent adsorption behavior and the electronic or ionic charge transfer in the film bulk and at interfaces during nanoparticle assembly via electrostatic interactions. In situ electrochemical impedance spectroscopy (EIS) in combination with a microfluidic system for fast and reproducible liquid delivery was thus applied to monitor the selective deposition of negatively charged gold nanoparticles on top of positively charged poly(2-vinylpyridinium) (qP2VP) domains of phase separated lamellar poly(styrene)-block-poly(2-vinylpyridinium) (PS-b-qP2VP) diblock copolymer thin films. The acquired impedance data delivered information with respect to interfacial charge alteration, ionic diffusion, and the charge dependent nanoparticle adsorption kinetics, considering this yet unexplored system. We demonstrate that the selective adsorption of negatively charged gold nanoparticles (AuNPs) on positively charged qP2VP domains of lamellar PS-b-qP2VP thin films can indeed be tracked by EIS. Moreover, we show that the nanoparticle adsorption kinetics and the nanoparticle packing density are functions of the charge density in the qP2VP domains.
Tailoring cell–surface interactions is important for the of design medical implants as well as regenerative medicine and tissue engineering materials. Here the single parameter system is transcended via translating hard nanotopology into soft polymeric hydrogel structures via hydrogel imprinting lithography. The response of these cells to the nanotopology of the same dimensions but with different mechanical properties displays unexpected behavior between “hard” tissue cells and “soft” tissue cells.
We report an experimental method to measure the translational and rotational dynamics of colloidal spheres in three dimensions with confocal microscopy and show that the experimental values reasonably agree with the theoretical values. This method can be extended to study rotational dynamics in concentrated colloidal systems and complex bio-systems.
The research on protein-polymer conjugates by grafting from the surface of proteins has gained significant interest in the last decade. While there are many studies with globular proteins, membrane proteins have remained untouched to the best of our knowledge. In this study, we established the conjugate formation with a class of transmembrane proteins and grow polymer chains from the ferric hydroxamate uptake protein component A (FhuA; a beta-barrel transmembrane protein of Escherichia coli). As the lysine residues of naturally occurring FhuA are distributed over the whole protein, FhuA was reengineered to have up to 11 lysines, distributed symmetrically in a rim on the membrane exposed side (outside) of the protein channel and exclusively above the hydrophobic region. Reengineering of FhuA ensures a polymer growth only on the outside of the beta-barrel and prevents blockage of the channel as a result of the polymerization. A water-soluble initiator for controlled radical polymerization (CRP) was consecutively linked to the lysine residues of FhuA and N-isopropylacrylamide (NIPAAm) polymerized under copper mediated CRP conditions. The conjugate formation was analyzed by using MALDI-ToF mass spectrometry, SDS-PAGE, circular dichroism spectroscopy, analytical ultracentrifugation, dynamic light scattering, transmission electron microscopy and size exclusion chromatography. Such conjugates combine the specific functions of the transmembrane proteins, like maintaining membrane potential gradients or translocation of substrates with the unique properties of synthetic polymers such as temperature and pH stimuli handles. FhuA-PNIPAAm conjugates will serve as functional nanosized building blocks for applications in targeted drug delivery, self-assembly systems, functional membranes and transmembrane protein gated nanoreactors. (C) 2016 Elsevier Ltd. All rights reserved.
Electric field manipulated nanopatterns in thin films of metalorganic 3-miktoarm star terpolymers
(2016)
We report the effect of electric field on the morphological transitions and ordering behavior of polyferrocenylethylmethylsilane block (PFEMS)-containing copolymers. By analyzing structures in solvent-annealed films of metalorganic sphere-and cylinder-forming diblock copolymers, as well as of 3-miktoarm polyisoprene-arm-polystyrene-arm-PFEMS (3 mu-ISF) terpolymers, we decouple two types of responses to the electric field: morphological transformations as a result of an increase in the volume fraction of the PFEMS block by oxidation of the ferrocenyl groups, and the orientation of the dielectric interfaces of microdomains parallel to the electric field vector. In the case of 3m-ISF, the former effect dominates at high electric field strengths which results in an unexpected cylinder-to-sphere transition, leading to a well-ordered hexagonal dot pattern. Our results demonstrate multiple tunability of ordered microdomain morphologies, suggesting future applications in nanofabrication and surface patterning.