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Matthew G Moffitt - One of the best experts on this subject based on the ideXlab platform.

  • structural hierarchy in blends of amphiphilic block copolymers self assembled at the air water Interface
    Journal of Colloid and Interface Science, 2019
    Co-Authors: Janet Hood, Kyle Van Gordon, Patricia Thomson, Brian R Coleman, Fraser P Burns, Matthew G Moffitt
    Abstract:

    We present a concurrent self-assembly strategy for patterning hierarchical polymeric surface features by depositing variable-composition blends of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polybutadiene-block-poly(ethylene oxide) (PB-b-PEO) block copolymers at the Air-Water Interface. Hierarchical strand networks of hydrophobic PS/PB blocks anchored via PEO blocks to the water surface, with an internal phase-separation structure consisting of periodic domains of PS blocks surrounded and connected by a matrix of PB blocks, are generated by the interplay of interfacial amphiphilic block copolymer aggregation and polymer/polymer phase separation. In contrast to the cylinder-in-strand structures previously formed by our group in which interfacial microphase separation between PS and PB blocks was constrained by chemical connectivity between the blocks, in the current system phase separation between PS and PB is not constrained by chemical connectivity and yet is confined laterally within surface features at the Air-Water Interface. Investigations of multi-component polymer systems with different connectivities constraining repulsive and attractive interactions provides routes to new hierarchical surface patterns for a variety of applications, including photolithography masks, display technology, surface-guided cell growth and tissue engineering.

  • block copolymer strands with internal microphase separation structure via self assembly at the air water Interface
    Langmuir, 2009
    Co-Authors: Eric W Price, Yunyong Guo, Canchen Wang, Matthew G Moffitt
    Abstract:

    Block copolymer microphase separation in the bulk is coupled to amphiphilic block copolymer self-assembly at the air−water Interface to yield hierarchical Langmuir−Blodgett (LB) structures combining organization at the meso- and nanoscales. A blend of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) (Mn = 141K, 11.4 wt % PEO) and polystyrene-b-poly(butadiene) (PS-b-PB) (Mn = 31.9K, 28.5 wt % PB) containing a PS-b-PB weight fraction of f = 0.75 was deposited at the air−water Interface, resulting in the spontaneous generation of aggregates with multiscale organization, including nanoscale cylinders in mesoscale strands, via evaporation of the spreading solvent. The resulting features were characterized in LB films via AFM and TEM and at the air−water Interface via Langmuir compression isotherms. Blends containing lower PS-b-PB contents formed mesoscale aggregate morphologies of continents and strands (f = 0.50) or mesoscale continents with holes (f = 0.25), but without the internal nanoscale organization found...

  • self assembly of polystyrene block poly ethylene oxide copolymers at the air water Interface is dewetting the genesis of surface aggregate formation
    Langmuir, 2006
    Co-Authors: Robert B Cheyne, Matthew G Moffitt
    Abstract:

    Block copolymer self-assembly at the air−water Interface is commonly regarded as a two-dimensional counterpart of equilibrium block copolymer self-assembly in solution and in the bulk; however, the present analysis of atomic force microscopy (AFM) and isotherm data at different spreading concentrations suggests a nonequilibrium mechanism for the formation of various polystyrene-b-poly(ethylene oxide) (PS-b-PEO) aggregates (spaghetti, dots, rings, and chainlike aggregates) at the air−water Interface starting with an initial dewetting of the copolymer spreading solution from the water surface. We show that different spreading concentrations provide kinetic snapshots of various stages of self-assembly at the air−water Interface as a result of different degrees of PS chain entanglements in the spreading solution. Two block copolymers are investigated:  MW = 141k (11.4 wt % PEO) and MW = 185k (18.9 wt % PEO). Langmuir compression isotherms for the 185k sample deposited from a range of spreading concentrations ...

Markus Linder - One of the best experts on this subject based on the ideXlab platform.

  • dynamic assembly of class ii hydrophobins from t reesei at the air water Interface
    Langmuir, 2019
    Co-Authors: Hendrik Hahl, Markus Linder, Alessandra Griffo, Neda Safaridehkohneh, Jonas Heppe, Sebastian Backes, Michael Lienemann, Ludger Santen, Paivi Laaksonen
    Abstract:

    Class II hydrophobins are amphiphilic proteins produced by filamentous fungi. One of their typical features is the tendency to accumulate at the Interface between an aqueous phase and a hydrophobic phase, such as the Air-Water Interface. The kinetics of the interfacial self-assembly of wild-type hydrophobins HFBI and HFBII and some of their engineered variants at the Air-Water Interface were measured by monitoring the accumulated mass at the Interface via nondestructive ellipsometry measurements. The resulting mass vs time curves revealed unusual kinetics for a monolayer formation that did not follow a typical Langmuir-type of behavior but had a rather coverage-independent rate instead. Typically, the full surface coverage was obtained at masses corresponding to a monolayer. The formation of multilayers was not observed. Atomic force microscopy revealed formation and growth of non-fusing protein clusters at the Interface. The mechanism of the adsorption was studied by varying the structure or charges of the protein or the ionic strength of the subphase, revealing that the lateral interactions between the hydrophobins play a role in their interfacial assembly. Additionally, a theoretical model was introduced to identify the underlying mechanism of the unconventional adsorption kinetics.

  • self assembled hydrophobin protein films at the air water Interface structural analysis and molecular engineering
    Biochemistry, 2007
    Co-Authors: Géza R. Szilvay, Arja Paananen, Elina Vuorimaa, Helge Lemmetyinen, Katri Laurikainen, Jouko Peltonen, Markus Linder
    Abstract:

    Hydrophobins are amphiphilic proteins produced by filamentous fungi. They function in a variety of roles that involve interfacial interactions, as in growth through the air−water Interface, adhesion to surfaces, and formation of coatings on various fungal structures. In this work, we have studied the formation of films of the class II hydrophobin HFBI from Trichoderma reesei at the air−water Interface. Analysis of hydrophobin aqueous solution drops showed that a protein film is formed at the air−water Interface. This elastic film was clearly visible, and it appeared to cause the drops to take unusual shapes. Because adhesion and formation of coatings are important biological functions for hydrophobins, a closer structural analysis of the film was made. The method involved picking up the surface film onto a solid substrate and imaging the surface by atomic force microscopy. High-resolution images were obtained showing both the hydrophilic and hydrophobic sides of the film at nanometer resolution. It was fo...

  • self assembled hydrophobin protein films at the air water Interface structural analysis and molecular engineering
    Biochemistry, 2007
    Co-Authors: Géza R. Szilvay, Arja Paananen, Elina Vuorimaa, Helge Lemmetyinen, Katri Laurikainen, Jouko Peltonen, Markus Linder
    Abstract:

    Hydrophobins are amphiphilic proteins produced by filamentous fungi. They function in a variety of roles that involve interfacial interactions, as in growth through the Air-Water Interface, adhesion to surfaces, and formation of coatings on various fungal structures. In this work, we have studied the formation of films of the class II hydrophobin HFBI from Trichoderma reesei at the Air-Water Interface. Analysis of hydrophobin aqueous solution drops showed that a protein film is formed at the Air-Water Interface. This elastic film was clearly visible, and it appeared to cause the drops to take unusual shapes. Because adhesion and formation of coatings are important biological functions for hydrophobins, a closer structural analysis of the film was made. The method involved picking up the surface film onto a solid substrate and imaging the surface by atomic force microscopy. High-resolution images were obtained showing both the hydrophilic and hydrophobic sides of the film at nanometer resolution. It was found that the hydrophobin film had a highly ordered structure. To study the orientation of molecules and to obtain further insight in film formation, we made variants of HFBI that could be site specifically conjugated. We then used the avidin-biotin interaction as a probe. On the basis of this work, we suggest that the unusual interfacial properties of this type of hydrophobins are due to specific molecular interactions which lead to an ordered network of proteins in the surface films that have a thickness of only one molecule. The interactions between the proteins in the network are likely to be responsible for the unusual surface elasticity of the hydrophobin film.

Paul M. Bummer - One of the best experts on this subject based on the ideXlab platform.

  • mixing of partially fluorinated carboxylic acids with their hydrocarbon analogs at the air water Interface
    Joint International Conference on Information Sciences, 2002
    Co-Authors: Hans-joachim Lehmler, Paul M. Bummer
    Abstract:

    Abstract The mixing behavior of 1-(perfluorobutyl)undecanoic acid–pentadecanoic acid (C15), 1-(perfluorohexyl)undecanoic acid–heptadecanoic acid (C17), and 1-(perfluorooctyl) undecanoic acid–nonadecanoic acid (C19) mixtures was investigated at the air–water Interface. The compression isotherms of the fluorocarbon acid–hydrocarbon acid mixtures were recorded at various compositions on hydrochloric acid (pH 1.9, 37±2°C) as a subphase. The phase transition, limiting molecular area, area at collapse pressure, and collapse pressure were determined for all π–A isotherms. The mixing behavior was assessed by analyzing the concentration dependence of the average molecular area at constant film pressure (area/mole fraction or A–X diagram) and the concentration dependence of the phase transition, where possible. All three acid mixtures show a negative deviation from ideal behavior at surface pressures between 5 and 20 mN/m, which is indicative of an attractive interaction of both compounds in the mixed monolayer at the air–water Interface. The miscibility apparently decreases with increasing chain length of the carboxylic acids (C15>C17>C19).

  • mixing of partially fluorinated carboxylic acids and their hydrocarbon analogues with dipalmitoylphosphatidylcholine at the air water Interface
    Langmuir, 2000
    Co-Authors: Hans-joachim Lehmler, Paul M. Bummer
    Abstract:

    The interaction of partially fluorinated carboxylic acids with a biologically relevant surfactant, dipalmitoylphosphatidylcholine (DPPC), was investigated at the air−water Interface. The compression isotherms of mixtures of three partially fluorinated carboxylic acids (1−3) and their hydrocarbon analogues (4−6) with DPPC were recorded at various compositions on hydrochloric acid (pH = 1.9, 32 ± 2 °C) as a subphase. The mixing behavior was assessed by analyzing the concentration dependence of the average molecular area at constant film pressure (area/mole fraction or A−X diagram). All six carboxylic acids (1−6) show a negative deviation from ideal behavior at surface pressures between 3 and 25 mN/m, which is indicative of an attractive interaction with DPPC in the mixed monolayer at the air−water Interface. With the exception of nonafluorpentadecanoic acid (1), all carboxylic acids investigated show a concentration dependence of the breakpoint of the phase transition from the liquid-expanded to the liquid-...

Francoise Nau - One of the best experts on this subject based on the ideXlab platform.

  • evidence for synergy in the denaturation at the air water Interface of ovalbumin ovotransferrin and lysozyme in ternary mixture
    Food Chemistry, 2005
    Co-Authors: Valerie Lechevalier, Thomas Croguennec, Stephane Pezennec, Catherine Guerindubiard, M Pasco, Francoise Nau
    Abstract:

    The conformational changes of egg-white proteins, in a ternary-protein system, at the air–water Interface have been studied. Three of the major egg-white proteins, ovalbumin, ovotransferrin and lysozyme, were studied with concentration ratios reflecting those in egg-white. Results were compared to those obtained in a previous work on protein denaturation at the air–water Interface in single-protein systems (Lechevalier, V., Croguennec, T., Pezennec, S., Guerin-Dubiard, C., Pasco, M., & Nau, F. (2003). Ovalbumin, ovotransferrin, lysozyme: Three model proteins for structural modifications at the air–water Interface. Journal of Agricultural and Food Chemistry 51, 6354–6361). Foaming altered the protein structure more profoundly in the mixture than in single-protein systems. Strong electrostatic interactions were observed between the three proteins. Their existence at the air–water Interface could ease intermolecular sulfhydryl–disulfide exchange reactions between ovalbumin and both ovotransferrin and lysozyme. This study highlighted the fact that results obtained on single-protein systems were not easily extrapolable to complex systems, such as egg-white.

  • ovalbumin ovotransferrin lysozyme three model proteins for structural modifications at the air water Interface
    Journal of Agricultural and Food Chemistry, 2003
    Co-Authors: Valerie Lechevalier, Thomas Croguennec, Stephane Pezennec, Catherine Guerindubiard, M Pasco, Francoise Nau
    Abstract:

    Structural modifications of ovalbumin, ovotransferrin, and lysozyme at the air−water Interface have been investigated using SDS-PAGE, both intrinsic and ANS fluorometry, and circular dichroism experiments. Ovalbumin contact with an Interface induced an exposure of aromatic residues, a slight decrease in α-helix structures (−1.7%), and an increase in both β-sheet (+3.4%) and β-turn (+7.9%) structures. Moreover, these conformational changes led to the formation of insoluble polymers of ovalbumin through intermolecular disulfide bonds. Ovotransferrin contact with an Interface led to an increase in its surface hydrophobicity (+30%) and modifications of its secondary structure (−33% of α-helices, +96.4% of β-sheets, +13.2% of β-turns, and +21.2% of random coils), characteristic of major conformational changes. On the other hand, lysozyme did not undergo any structural modification. These results clearly underscore that at the air−water Interface proteins are susceptible to denaturation. Keywords: Ovalbumin; ov...

Christopher J Mundy - One of the best experts on this subject based on the ideXlab platform.

  • the electrochemical surface potential due to classical point charge models drives anion adsorption to the air water Interface
    arXiv: Soft Condensed Matter, 2013
    Co-Authors: Marcel D Baer, Douglas J Tobias, Abraham C Stern, Yan Levin, Christopher J Mundy
    Abstract:

    We demonstrate that the driving forces for ion adsorption to the Air-Water Interface for point charge models results from both cavitation and a term that is of the form of a negative electrochemical surface potential. We carefully characterize the role of the free energy due to the electrochemical surface potential computed from simple empirical models and its role in ionic adsorption within the context of dielectric continuum theory. Our research suggests that the electrochemical surface potential due to point charge models provides anions with a significant driving force to the Air-Water Interface. This is contrary to the results of ab initio simulations that indicate that the average electrostatic surface potential should favor the desorption of anions at the Air-Water Interface. The results have profound implications for the studies of ionic distributions in the vicinity of hydrophobic surfaces and proteins.

  • electrochemical surface potential due to classical point charge models drives anion adsorption to the air water Interface
    Journal of Physical Chemistry Letters, 2012
    Co-Authors: Marcel D Baer, Douglas J Tobias, Abraham C Stern, Yan Levin, Christopher J Mundy
    Abstract:

    We demonstrate that the driving forces for ion adsorption to the Air-Water Interface for point charge models result from both cavitation and a term that is of the form of a negative electrochemical surface potential. We carefully characterize the role of the free energy due to the electrochemical surface potential computed from simple empirical models and its role in ionic adsorption within the context of dielectric continuum theory. Our research suggests that the electrochemical surface potential due to point charge models provides anions with a significant driving force for adsoprtion to the Air-Water Interface. This is contrary to the results of ab initio simulations that indicate that the average electrostatic surface potential should favor the desorption of anions at the Air-Water Interface. The results have profound implications for the studies of ionic distributions in the vicinity of hydrophobic surfaces and proteins.