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Nonlinear chiral rheology of phospholipid monolayers
Kim, KyuHan,Choi, Siyoung Q.,Zasadzinski, Joseph A.,Squires, Todd M. The Royal Society of Chemistry 2018 SOFT MATTER Vol.14 No.13
<P>Microbutton rheometry reveals that the chiral morphology of dipalmitoylphosphatidylcholine (DPPC) monolayers imparts a chiral nonlinear rheological response. The nonlinear elastic modulus and yield stress of DPPC monolayers are greater when sheared clockwise (C), against the natural winding direction of DPPC domains, than counter-clockwise (CC). Under strong CC shear strains, domains deform plastically; by contrast, domains appear to fracture under strong C shearing. After CC shearing, extended LC domains develop regular patterns of new invaginations as they recoil, which we hypothesize reflect the nucleation and growth of new defect lines across which the tilt direction undergoes a step change in orientation. The regular spacing of these twist-gradient defects is likely set by a competition between the molecular chirality and the correlation length of the DPPC lattice. The macroscopic mechanical consequences of DPPC's underlying molecular chirality are remarkable, given the single-component, non-cross-linked nature of the monolayers they form.</P>
Filtering for Bilinear Systems with a Lipschitz Nonlinearity Using LPV Approach
Benjamin Gerard,Harouna Souley Ali,Michel Zasadzinski,Mohamed Darouach 제어·로봇·시스템학회 2012 International Journal of Control, Automation, and Vol.10 No.6
This paper deals with the H∞ filtering problem for a class of nonlinear systems. This class of nonlinear systems is composed of a bilinear part and of a lipschitzian one. The use of an unbiasedness condition for the bilinear part (called quasi unbiasedness condition) permits to parameterize the filter matrices through a single gain. Two LPV (Linear Parameter Varying) extensions of the bounded real lemma are used to solve the filtering problem. This approach reduces the conservatism inherent to the boundedness of the inputs. Then the filtering solution is expressed in terms of LMI (Linear Matrix Inequality) to be verified at the vertices of a polytope. A numerical example is finally given to illustrate our approach.
Interfacial rheology of coexisting solid and fluid monolayers
Sachan, A. K.,Choi, S. Q.,Kim, K. H.,Tang, Q.,Hwang, L.,Lee, K. Y.,Squires, T. M.,Zasadzinski, J. A. Royal Society of Chemistry 2017 SOFT MATTER Vol.13 No.7
<P>Biologically relevant monolayer and bilayer films often consist of micron-scale high viscosity domains in a continuous low viscosity matrix. Here we show that this morphology can cause the overall monolayer fluidity to vary by orders of magnitude over a limited range of monolayer compositions. Modeling the system as a two-dimensional suspension in analogy with classic three-dimensional suspensions of hard spheres in a liquid solvent explains the rheological data with no adjustable parameters. In monolayers with ordered, highly viscous domains dispersed in a continuous low viscosity matrix, the surface viscosity increases as a power law with the area fraction of viscous domains. Changing the phase of the continuous matrix from a disordered fluid phase to a more ordered, condensed phase dramatically changes the overall monolayer viscosity. Small changes in the domain density and/or continuous matrix composition can alter the monolayer viscosity by orders of magnitude.</P>
Influence of Molecular Coherence on Surface Viscosity
Choi, Siyoung Q.,Kim, Kyuhan,Fellows, Colin M.,Cao, Kathleen D.,Lin, Binhua,Lee, Ka Yee C.,Squires, Todd M.,Zasadzinski, Joseph A. American Chemical Society 2014 Langmuir Vol.30 No.29
<P/><P>Adding small fractions of cholesterol decreases the interfacial viscosity of dipalmitoylphosphatidylcholine (DPPC) monolayers by an order of magnitude per wt %. Grazing incidence X-ray diffraction shows that cholesterol at these small fractions does not mix ideally with DPPC but rather induces nanophase separated structures of an ordered, primarily DPPC phase bordered by a line-active, disordered, mixed DPPC-cholesterol phase. We propose that the free area in the classic Cohen and Turnbull model of viscosity is inversely proportional to the number of molecules in the coherence area, or product of the two coherence lengths. Cholesterol significantly reduces the coherence area of the crystals as well as the interfacial viscosity. Using this free area collapses the surface viscosity data for all surface pressures and cholesterol fractions to a universal logarithmic relation. The extent of molecular coherence appears to be a fundamental factor in determining surface viscosity in ordered monolayers.</P>
Hough, L. E.,Jung, H. T.,Krü,erke, D.,Heberling, M. S.,Nakata, M.,Jones, C. D.,Chen, D.,Link, D. R.,Zasadzinski, J.,Heppke, G.,Rabe, J. P.,Stocker, W.,Kö,rblova, E.,Walba, D. M.,Glaser, M. A. American Association for the Advancement of Scienc 2009 Science Vol.325 No.5939
<P>In the formation of chiral crystals, the tendency for twist in the orientation of neighboring molecules is incompatible with ordering into a lattice: Twist is expelled from planar layers at the expense of local strain. We report the ordered state of a neat material in which a local chiral structure is expressed as twisted layers, a state made possible by spatial limitation of layering to a periodic array of nanoscale filaments. Although made of achiral molecules, the layers in these filaments are twisted and rigorously homochiral--a broken symmetry. The precise structural definition achieved in filament self-assembly enables collective organization into arrays in which an additional broken symmetry--the appearance of macroscopic coherence of the filament twist--produces a liquid crystal phase of helically precessing layers.</P>