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DissertationDOI

Interplay Between Long-Range And Short-Range Interactions In Polymer Self-Assembly And Cell Adhesion

01 Jan 2008-
TL;DR: In this paper, reversible gelation of associating polymers and ligand-receptor interactions in membrane adhesion was studied, and the energy barrier of the adhesion as a result of membrane bending deformations and the double-well adhesion potential was calculated.
Abstract: Interplay between long-range and short-range interactions is a common theme in soft and biological matter, which results in complicated self-assembly behaviors. We study two examples of this interplay: reversible gelation of associating polymers and ligand-receptor interactions in membrane adhesion. In associating polymer solutions, the competition between the conformation flexibility of polymer chains and the enthalpic monomer interactions results in phase-separated micro-structures at the mesoscopic scale; both gelation and the microphase order-disorder transition are manifestations of this self-assembly. We further establish that reversible gelation is similar to the glass transition: both are characterized by ergodicity breaking, aperiodic micro-structures, and non-equilibrium relaxations over a finite temperature range. In the study of ligand-receptor interactions between surfaces, we emphasize the interplay between specific ligand-receptor binding, and generic physical interactions. We find that both the finite spatial extension of receptors and their mobilities affect their binding affinity. As a special case of the interplay between receptor binding and generic interactions, we study the dynamics of membrane adhesion that is mediated by receptor binding but fulfilled through membrane deformations. We calculate the energy barrier of the adhesion as a result of membrane bending deformations and the double-well adhesion potential, and analyze the different scenarios according to the shape of the adhesion potential by scaling arguments.

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Citations
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01 Mar 1997
TL;DR: In this paper, a simple model of the doped Mott insulator, where the short-range tendency of the holes to phase separate competes with long-range Coulomb effects, exhibits this "avoided critical" behavior.
Abstract: Long-range frustrating interactions, even if their strength is infinitesimal, can give rise to a dramatic proliferations of ground or near-ground states. As a consequence, the ordering temperature can exhibit a discontinuous drop as a function of the frustration. A simple model of the doped Mott insulator, where the short-range tendency of the holes to phase separate competes with long-range Coulomb effects, exhibits this "avoided critical" behavior. This model may serve as a paradigm for many other systems.

6 citations

DissertationDOI
06 Aug 2012
TL;DR: In this article, the authors used a hybrid molecular dynamics/Monte Carlo simulation to study the structural changes of the Telechelic network under constant shear and different shear rates.
Abstract: of the Dissertation Simulated Associating Polymer Networks by Joris Billen San Diego State University and Claremont Graduate University Telechelic associating polymer networks consist of polymer chains terminated by endgroups that have a different chemical composition than the polymer backbone. When dissolved in a solution, the endgroups cluster together to form aggregates. Their lifetime depends on temperature. At the micelle transition the temperature is sufficiently low for these aggregates to be substantial in size. At low temperature, a strongly connected reversible network is formed and the system behaves like a gel. Telechelic networks are of interest since they are representative of biopolymer networks and are widely used in medical applications and consumer products. The material properties of these polymer networks pose complex and current problems in polymer physics. Many of the most basic questions concerning these networks, such as how they deform under stress, remain unanswered. Experiments under constant shear reveal a rich variety of non-Newtonian responses, including shear thinning and shear thickening. Within the shear thinning regime, shear banding is observed: when a constant shear is applied, the system forms two coexisting bands with different shear rates. The goal of this work is to study such systems using computer simulations. A hybrid molecular dynamics/Monte Carlo simulation is used for this purpose. First we investigate how the network topology of an ensemble of telechelic polymers changes with temperature using graph theory. The aggregates are considered as nodes and the polymer chains as links between them. Our analysis shows that the degree distribution of the system is bimodal and consists of two Poissonian distributions with different average degrees. The number of nodes in each of them as well as the distribution of links depend on temperature. By comparing the eigenvalue spectra of the simulated gel networks with those of reconstructed networks, the most likely topology at each temperature is determined. Below the micelle transition the topology can be described by a robust bimodal network in which superpeer nodes are linked among themselves and all peer nodes are linked only to superpeers. At even lower temperatures the peers completely disappear leaving a structure of interconnected superpeers. Many real life networks exhibit a spatial dependence, i.e. the probability to form a link between two nodes in the network depends on the distance between them. The study of the eigenvalue spectra of the simulated gel revealed that spatial dependent networks show universal spectral properties. This led to an in-depth study of such spectra. When increasing spatial dependence in Erdos-Renyi, scale-free and smallworld networks, it is found that the spectrum changes. Due to the spatial dependence, the degree of clustering and the number of triangles increase. This results in a higher asymmetry (skewness). Our results show that the spectrum can be used to detect and quantify clustering and spatial dependence in a network. Next, we study the rheological response of the polymer network under constant shear. The transient stress response shows an overshoot, followed by fluctuations around a lower, average value. When different shear rates are applied, there is a region in which the average stress does not increase significantly. Within this plateau, shear banding occurs. Experiments suggest possible differences between both bands in several properties. The simulation allows for a study of these differences on the microscopical scale. The average aggregate size is lower in the high shear rate band, due to an increase in aggregates consisting of a single endgroup. There is an increase in dynamics and this is highest in the high shear band. These changes are gradual as a function of the distance between the moving walls, and we did not find a sharp increase at the interface. Next, we focus on structural changes of the sheared system as a whole, compared to the unsheared system. The aggregate size distribution becomes bimodal and preferential aggregate size formation decreases under shear. There is a decrease in links and a rearrangement of the structure under shear. This leads to larger aggregates that are connected by “stronger” links of high weight, consisting of multiple bridging chains. Such rearrangement is of importance in the observed decrease in stress in the transient stress response. The loop/bridge ratio increases, but only for high strain rates. Finally we investigate the relation between percolation and gelation. Since the junctions between the endgroups in our system are temporary, geometric percolation does not occur at the gelation temperature. To explain the rheological changes that occur around this transition, only the network made up of endgroups that have junctions that survive over longer times is important. The percolation threshold, the time where the system shows 50% probability to percolate, increases with decreasing temperature. Vogel-Fulcher-Tamman (VFT) theory predicts that this time will diverge at T = 0.29. This is in agreement with the gelation temperature obtained from earlier measurements of relaxation times. A master curve can be constructed for percolation probability and survival rate by empirically shifting them up to T = 0.6. The scaling factors follow the Williams-Landel-Ferry (WLF) equations and the T0 from WLF corresponds to the one from VFT. This is in support of recent ideas that gelation phenomena and glass transition show similarities.

2 citations


Cites background from "Interplay Between Long-Range And Sh..."

  • ...Recently it has been pointed out that there are natural parallels between reversible gelation and glass transition [63] and there is considerable interest in unifying these two classes of disordered materials [64]....

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References
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Book
01 Jan 1985
TL;DR: The forces between atoms and molecules are discussed in detail in this article, including the van der Waals forces between surfaces, and the forces between particles and surfaces, as well as their interactions with other forces.
Abstract: The Forces between Atoms and Molecules. Principles and Concepts. Historical Perspective. Some Thermodynamic Aspects of Intermolecular Forces. Strong Intermolecular Forces: Covalent and Coulomb Interactions. Interactions Involving Polar Molecules. Interactions Involving the Polarization of Molecules. van der Waals Forces. Repulsive Forces, Total Intermolecular Pair Potentials, and Liquid Structure. Special Interactions. Hydrogen-Bonding, Hydrophobic, and Hydrophilic Interactions. The Forces between Particles and Surfaces. Some Unifying Concepts in Intermolecular and Interparticle Forces. Contrasts between Intermolecular, Interparticle, and Intersurface Forces. van der Waals Forces between Surfaces. Electrostatic Forces between Surfaces in Liquids. Solvation, Structural and Hydration Forces. Steric and Fluctuation Forces. Adhesion. Fluid-Like Structures and Self-Assembling Systems. Micelles, Bilayers, and Biological Membranes. Thermodynamic Principles of Self-Assembly. Aggregation of Amphiphilic Molecules into Micelles, Bilayers, Vesicles, and Biological Membranes. The Interactions between Lipid Bilayers and Biological Membranes. References. Index.

18,048 citations


"Interplay Between Long-Range And Sh..." refers background in this paper

  • ..., 2006; Moore and Kuhl, 2006; Moreira and Marques, 2004; Sain and Wortis, 2004), and suggests a new route to controlling the interactions between surfaces typically achieved by generic physical interactions (Israelachvili, 1992; Hiddessen et al., 2000; Carignano and Szleifer, 2003; Nap and Szleifer, 2005)....

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  • ...The interplay between specific and other generic physical interactions, such as electrostatic, hydrophobic and steric interactions (Israelachvili, 1992), is crucial to the adhesion and signalling between cells and the extracellular matrix, and has been extensively studied by researchers in physiology, biochemistry, biophysics, and bioengineering (Alberts et al....

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Book
01 Jan 1953

16,827 citations


"Interplay Between Long-Range And Sh..." refers background or methods in this paper

  • ...Near the mean-field spinodal γ2(q,−q) can be approximated as γ2(q,−q) = c2 4 ( q2Nb2 − q2mNb2 )2 + 2 (χN)S − 2χN, where χN is the Flory-Huggins interaction parameter between A and B blocks, (χN)S is its value at the spinodal, and c is a parameter independent of N ....

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  • ...It was Flory (1953) who first calculated the amount of crosslinkers that are necessary to generate a macroscopic network (Flory-Stockmayer model) and studied the elasticity of this network (“rubber elasticity” theory)....

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  • ...In the classical model by Flory and Stockmayer (see Flory, 1953), the crosslinked network (e.g., vulcanized rubber) is assumed to be an infinitely large branched tree (without cycles), which is the mean-field limit of the percolation model (i.e., percolation on a Cayley tree)....

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  • ...The polymer solution is treated following the mean-field theory of Flory and Huggins (Flory, 1953) and the reversible gelation is treated as a micellation....

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Book
15 Dec 1979

10,942 citations


"Interplay Between Long-Range And Sh..." refers background in this paper

  • ...Such polyfunctional units are interconnected 1An exception is the network generated by topological entanglements, such as in melts of very long polymer chains, or a series of interconnected rings (de Gennes, 1979)....

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  • ...Furthermore, as each crosslinker (multi-functional unit) is surrounded by many monomers, cycle structures are rare, therefore the Flory-Stockmayer model is accurate even near the critical threshold (de Gennes, 1979)....

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Book
01 Jan 1986
TL;DR: In this article, the viscoelasticity of polymeric liquids was studied in the context of rigid rod-like polymers and concentrated solutions of rigid rods like polymers.
Abstract: Introduction Static properties of polymers Brownian motion Dynamics of flexible polymers in dilute solution Many chain systems Dynamics of a polymer in a fixed network Molecular theory for the viscoelasticity of polymeric liquids Dilute solutions of rigid rodlike polymers Semidilute solutions of rigid rodlike polymers Concentrated solutions of rigid rodlike polymers Index.

10,225 citations


"Interplay Between Long-Range And Sh..." refers background in this paper

  • ...Second, we construct the mean-field phase diagram through a quadratic expansion of the free energy (effective potential) from the Edwards Hamiltonian....

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  • ...A continuum Gaussian chain with length N in an external field V (r) is described by the Edwards Hamiltonian (Doi and Edwards, 1986) h0[R(t)] = 3kBT 2Nb2 ∫ 1 0 [( ∂R(t) ∂t )2 + V (R(t)) ] dt (2.1) where R(t) maps the configuration of the polymer (0 ≤ t ≤ 1 is a parametrization of the polymer chain), and Nb2 is mean square end-to-end distance....

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  • ...A continuum Gaussian chain with length N in an external field V (r) is described by the Edwards Hamiltonian (Doi and Edwards, 1986) h0[R(t)] = 3kBT 2Nb2 ∫ 1 0 [( ∂R(t) ∂t )2 + V (R(t)) ] dt (2.1) where R(t) maps the configuration of the polymer (0 ≤ t ≤ 1 is a parametrization of the polymer chain),…...

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  • ...Using the Green’s function for Gaussian chains (Doi and Edwards, 1986) we can express the partition function qp as qp = ∫ G(r, r′;N), where G(r, r′;N) satisfies [ ∂ ∂N − b 2 6 ∇2r +W (r) ] G(r, r′;N) = δ(r− r′)....

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