D. Daghero, G.A. Ummarino, and R.S. Gonnelli
This article investigates the potential of the point contact Andreev reflection spectroscopy (PCARS) technique for measuring the symmetry of the energy gap and other key parameters of various 0-, 1-, and 2-dimensional superconducting systems. It begins with a brief description of PCARS, explaining what a point contact is and how it can be made and the conditions under which a PC is ballistic, as well as why and to what extent a PC between normal metals is spectroscopic. It then discusses the basics of Andreev reflection and the length scales in mesoscopic systems before considering the limits of applicability of PCARS for spectroscopy of ‘small’ superconductors. Finally, it reviews some examples of PCARS in quasi-0D, quasi-1D and quasi-2D superconductors.
This article considers Josephson junction barriers, focusing on barriers made from insulators, metals, semiconductors, magnets, and nanowires. The main characteristic of Josephson junctions is the local reduction or even suppression of the critical current in the barrier. These barriers affect the static and dynamics properties of Josephson junctions, including coupling strength, ground state, phase damping, and tunability of the critical current. The article first provides an overview of the fundamental physics of Josephson junctions, with particular emphasis on the Josephson effect, before describing the properties of two coupled superconductors. It then discusses tunnel barriers, metallic barriers, semiconducting barriers, and magnetic barriers.
Aidan T. Brown and Pietro Cicuta
This article examines the properties of biological fluid interfaces and membranes, with particular emphasis on monolayers and bilayers. There are several examples of interfaces between biological fluids; the most relevant to human physiology are probably the liquid/air interfaces in the lungs and on the surface of the eyes. Both of these feature films with remarkable properties of compressibility and self-healing. After providing an overview of the constituent molecules of biological interfaces, this article reviews the current knowledge on surface films and membranes, giving context for their role in biology, but paying special attention to the basic physical ideas that underpin fundamental studies of in-vitro model systems. It also considers isolated membranes, characterized by tension, elasticity and viscous damping, as well as closed vesicles and cells where the membrane separates the cytoskeleton from the extracellular matrix.
Lee M. Trask, Nacu Hernandez, and Eric W. Cochran
This article explores the dynamics, thermodynamics, and small-angle scattering of block copolymers. The goal is to determine what drives the applications of block copolymers, i.e. how block copolymers behave and how they are characterized. The article begins with a summary of the experimental data and various theories that comprise our understanding of block copolymer thermodynamics, with particular emphasis on phase behavior and especially the theory of microphase separation. It then considers topics related to block copolymer dynamics, including diffusion, viscoelasticity and rheology, shear-processing, and the kinetics of self-assembly. It also discusses small-angle scattering techniques as applied to block copolymer characterization, including scattering from ordered block copolymer melts.
Matthieu Piel and Raphael Voituriez
This article examines the ‘active’ part of the cell cytoskeleton — which mostly corresponds to actin and tubulin polymers and associated molecular motors — using theoretical tools derived from a soft matter physics coarse-grained approach. It begins with an overview of the cytoskeleton and its components, which include actin filaments and gels, microtubules and specialized microtubule-based organelles, molecular motors, intermediate filaments, the plasma membrane and glycocalix, the cell wall, and the extracellular matrix. It then describes coarse-grained models of the cytoskeleton and gives two examples of models for important cellular functions, namely cell migration and cell polarity. It also proposes a new kind of soft matter model providing a coarse-grained description of cytoskeletal polymers and associated molecular motors.
Wilson C. K. Poon
This article deals with the fundamentals of colloid science, with particular emphasis on the interplay of energy and entropy factors in forming colloidal suspensions. It first considers when a colloidal suspension changes from a liquid at low colloid concentration to various equilibrium, along with metastable (including kinetically arrested) structures at higher concentrations. active driven matter and the selectivity of binding in protein-based colloids. It then discusses a number of key ideas and some recent developments in colloid physics by focusing on the work of Albert Einstein and Jean Perrin. It also explores the physics of entropy, how the liquid state is formed, strategies for tuning colloidal interactions, kinetic arrest and glass transition, and mode coupling theory. Finally, it describes gelation, colloid rheology, concentration effects in colloidal fluids, the rheology of solids, and proteins as ‘a mysterious sort of colloids’.
Ronald G. Larson and Zuowei Wang
This article explores the dynamics of entangled polymers, with particular emphasis on how the unusual and often dramatic mechanical properties of concentrated polymer systems are determined by the physics of entanglements. It begins with an overview of the foundations of entangled polymer dynamics, organized around tubes and slip links used in modeling entanglements, the packing length and concentration effects, the results of computer simulations on entanglements, topological contacts, and the effects of large deformations. The focus is on the nature of ‘entanglement’, both from a bottom-up molecular view, and from a phenomenological one. The discussion then turns to the linear viscoelasticity of entangled polymer solutions and melts, along with nonlinear viscoelasticity. Models of polymer dynamics in the linear regime are also described, including the ‘standard tube model’. The article concludes with suggestions for future work.
James E. Mark and Burak Erman
This article focuses on the rubberlike elasticity of elastomers, with particular emphasis on rubberlike materials that exhibit high deformability and recoverability. It begins with a discussion of the variety of practical ways to form and characterize a rubber-elastic network, including random chemical crosslinking, highly specific chemical end-linking, polymerizations with multi-functional monomers, physical aggregation, and crosslinking in solution and in the deformed state. It then considers the effects of network structure on elastomeric properties, along with the results of elasticity experiments regarding the mechanical properties of elastomeric materials. It also examines the evolution of theories of rubber elasticity describes the specific properties of swollen polymer gels where the possibility of solvent exchange leads to some dramatic transformations in the system. Finally, it evaluates new emerging classes of rubber-elastic materials, such as liquid crystalline elastomers, where the internal microstructure added to the random network leads to some unique mechanical properties.
This article examines fluid transport and solvent dynamics in polymer gels, in equilibrium and under mechanical stress, and the effect of fluids on gel deformation. It also introduces a continuum model that describes the coupled phenomena of electric current, solvent flux, and deformation of gel network. This model is a generalization of the diffusio-mechanical coupling model of non-ionic gels. The discussion begins with an overview of the equilibrium state of non-ionic gels under the action of mechanical forces. This is followed by an analysis of the dynamics of non-ionic gels, especially the relaxation of mechanical responses caused by solvent flow. The article concludes with an assessment of the dynamics of ionic gels as well as the effect of electric field on solvent flow and the gel deformation.
Denis Weaire and Stefan Hutzler
This article focuses on foams, which consist of gas bubbles surrounded by liquid and closely packed together so that they are in contact with each other. As a mixture of two fluids, a foam is paradoxically a solid, at least under a small enough stress — surface tension and gas pressure maintain it in equilibrium when deformed. The corresponding mixture of two liquids is an emulsion, rendered stiff by surface tension under low stress. After explaining what a foam is, this article discusses various applications of foams. It then considers the statics and dynamics of foams, the simple rules that govern local equilibrium, and the structure of foams. It also examines the key properties of foams, such as coarsening due to diffusion, coalescence, drainage, foamability, rheology and rheometry, shear localization, conductivity, and light scattering. Finally, it describes the role of surfactants in foam stability and evaluates analogous systems such as emulsions.