5,116 research outputs found
Polymer Adhesion: Seeking New Solutions for an Old Problem
Get PDFPolymer adhesion is ubiquitous in both the natural world and human technology. It is also a complex multiscale phenomenon, such that the solution of adhesion problems requires a convergence of chemistry, physics, and engineering. In this Perspective, we provide an overview of some of the fundamental concepts that have emerged in the field of polymer adhesion, discuss recent work, and identify challenges in three specific areas: (a) theories and simulations, with an emphasis on problems involving chain scission; (b) experimental methods for measuring forces and characterizing interfaces at the molecular scale; and (c) strategies inspired by living organisms to generate underwater adhesion
Tuning Adhesion and Energy Dissipation in Polymer Films between Solid Surfaces via Grafting and Cross-Linking
No full textPolymer adhesion is underpinned by a network of chain molecules forming both adhesive bonds with the surfaces and cohesive bonds among themselves. Understanding how this network propagates mechanical stress and dissipates energy under tension is a challenging but essential task for improving polymer adhesives. To this end, we present a series of coarse-grained molecular dynamics simulations of polymer films joining two parallel flat surfaces. The polymer molecules are modeled as chains of beads that can covalently bind to the surfaces and to each other via a Morse potential, allowing bond breakage and chain scission. The mechanical response of the polymer film is studied under both small oscillatory strains and large deformations, leading to complete breakup. Starting from a melt of ungrafted polymer chains and introducing one feature at a time, we find that polymer cross-linking enhances adhesion more than covalent surface grafting. Cross-linking and grafting may also act in synergy, provided the grafting density is homogeneous. Moreover, surface heterogeneity at the nanometer scale affects the viscoelastic response at small strains. The simple model used in our simulations provides a valuable platform to translate molecular-level features of the polymer network, such as chain connectivity and bond strength, into measurable quantities, such as adhesion forces and energy dissipation
Twist transitions and force generation in cholesteric liquid crystal films
No full textThe response of a cholesteric liquid crystal film to mechanical confinement is theoretically investigated considering planar anchoring conditions on the limiting surfaces and pure twist distortion of the liquid crystal director. We evaluate the total twist angle and normal force acting on the surfaces as a function of the film thickness. Assuming the Rapini-Papoular functional form for the surface anchoring energy, we show that the surface twist angle undergoes discontinuous jumps or continuous transitions as a function of the film thickness and anchoring strength. The transitions take place at well-defined film thicknesses, related to the intrinsic periodicity of the cholesteric liquid crystal, and produce oscillations in the normal force and position of the optical band-gap as the film thickness is varied
Introducing “La fabrique du droit”. A Conversation with Bruno Latour
Get PDFBruno Latour talks with Paolo Landri about his book on the Conseil d'Etat (La Fabrique du droit). The conversation was held in 2006 at the time of the Italian translation of the book and illustrates the research project and the difficulties the author had in the field. At the same time, it clarifies the trajectories of Bruno Latour's work and theoretical framework of his program of study with respect to sociology, anthropology, and philosophy of law. The conversation helps to understand the open-ended character of Bruno Latour's research and reflection including STS as well as sociological, anthropological and philosophical themes
Effect of Ca2+ ions on the adhesion and mechanical properties of adsorbed layers of human Osteopontin
No full textUsing an atomic force microscope and a surface force apparatus, we measured the surface coverage, adhesion, and mechanical properties of layers of osteopontin (OPN), a phosphoprotein of the human bones, adsorbed on mica. OPN is believed to connect mineralized collagen fibrils of the bone in a matrix that dissipates energy, reducing the risk of fractures. Atomic force microscopy normal force measurements showed large adhesion and energy dissipation upon retraction of the tip, which were due to the breaking of the many OPN-OPN and OPN-mica bonds formed during tip-sample contact. The dissipated energy increased in the presence of Ca2+ ions due to the formation of additional OPN-OPN and OPN-mica salt bridges between negative charges. The forces measured by surface force apparatus between two macroscopic mica surfaces were mainly repulsive and became hysteretic only in the presence of Ca2+: adsorbed layers underwent an irreversible compaction during compression due to the formation of long-lived calcium salt bridges. This provides an energy storage mechanism, which is complementary to energy dissipation and may be equally relevant to bone recovery after yield. The prevalence of one mechanism or the other appears to depend on the confinement geometry, adsorption protocol, and loading-unloading rates
Author Correction: Collection of the digital data from the neurological examination.
Get PDFIn this article, the corresponding author was inadvertently designated only to “Bruno Kusznir Vitturi” but it should have been “Bruno Kusznir Vitturi” and “Walter Maetzler”. The original article has been corrected
On Bruno Schulz’s Bookplates
No full textThe Polish version of the article was published in Roczniki Humanistyczne vol. 64, issue 1 (2016).
The article enters into a dialogue with the interpretation of Bruno Schulz’s bookplates made by Władysław Panas in his book Bruno od Mesjasza (Bruno of the Messiah) (Lublin 2001). An attempt to understand them in a different (less holistic) way leads the author of the article to the conclusion that in Schulz’s plates the first veiled variant of the mythical Book may be seen—of the fundamental motif of Bruno Schulz’s later literary work
Jordan "Bruno" Gegenhuber '16 Publishes First-Author Research
No full textJordan "Bruno" Gegenhuber '16 had first-author research, "Gene regulation by gonadal hormone receptors underlies brain sex differences," published in nature magazine on May 4, 2022.Jordan "Bruno" Gegenhuber '16 had first-author research, "Gene regulation by gonadal hormone receptors underlies brain sex differences," published in Nature magazine on May 4, 2022.
Sex hormones play a central role in shaping behavior throughout the animal kingdom, and this study maps where the receptor for estrogen binds to DNA in neurons that regulate rodent social interactions. The findings reveal that estrogen establishes lasting sex differences in gene expression and neuroanatomy during brain development, and identifies hundreds of genes that may mediate estrogen's effects on behavior and disease.
Gegenhuber earned a PhD from the Cold Springs Harbor Laboratory School of Biological Sciences in Long Island, N.Y.. in May 2022. His field of research is in neuroscience, and he has accepted a postdoctoral research position at Harvard Medical Center in Boston, Mass. He also holds the honor of being the Pacific Class of 2016 Valedictorian
Bruno Schulz i polityka
No full textBruno Schulz and politicsThe article discusses Bruno Schulz’s attitude toward politics. It is well known that the author of The Cinnamon Shops was a nonpolitical man. This was the reason for some fi erce attacks against his prose conducted by politically engaged literary critics in the interwar Poland. The author mentions these attacks but he also analyzes Schulz’s less known essays about Piłsudski, Aragon and Brecht, and the way Schulz pictured politics in his prose. It seems that a political dictionary of the author of The Street of Crocodiles comprised terms from different political ideologies; he alluded to Marx, anarchism and Brzozowski. At the end of his article the author discusses the question whether Schulz’s nonpolitical attitude could be compared to the so called conservative revolution in Germany after World War I
Bruno Schulz i polityka
Get PDFBruno Schulz and politicsThe article discusses Bruno Schulz’s attitude toward politics. It is well known that the author of The Cinnamon Shops was a nonpolitical man. This was the reason for some fi erce attacks against his prose conducted by politically engaged literary critics in the interwar Poland. The author mentions these attacks but he also analyzes Schulz’s less known essays about Piłsudski, Aragon and Brecht, and the way Schulz pictured politics in his prose. It seems that a political dictionary of the author of The Street of Crocodiles comprised terms from different political ideologies; he alluded to Marx, anarchism and Brzozowski. At the end of his article the author discusses the question whether Schulz’s nonpolitical attitude could be compared to the so called conservative revolution in Germany after World War I
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