Abstracts
Nanobubbles
Phil Attard
The history of nanobubbles is reviewed, primarily focussing on the author's role in their discovery and
characterization. The experimental evidence for them,
and the theoretical arguments against them, are discussed in detail. Possible
explanations that reconcile the two are canvassed. Some consequences and
applications of nanobubbles are mentioned. The long
ranged hydrophobic attraction is also discussed in the context of nanobubbles and other possible explanations.
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The Second Entropy: How Fast Time Flies
Phil Attard
The second entropy is introduced, which is a new type of entropy that is
suitable for time-dependent systems [1]. A new law of thermodynamics is given
that invokes the second entropy and that provides a basis for determining the
rate of change of systems. In the case of statistical mechanics, the
probability distribution for an arbitrary non-equilibrium system is given.
Quantitative evidence is provided that proves the validity of the theory. In
particular, the non-equilibrium probability distribution is used to create the first
ever non-equilibrium Monte Carlo algorithm.
This is applied to the case of a Lennard-Jones fluid
subject to an imposed thermal gradient, and the thermal conductivity is
obtained and shown to be in agreement with known results. A Brownian particle
subject to a time-varying external field is also analysed,
and a stochastic molecular dynamics algorithm is given and shown to agree
quantitatively with other approaches. The new theory is contrasted with the
Principle of Maximum (or Minimum) Dissipation used by
Prigogine and by others. The theory has interesting implications for
evolution of life and for the rate of environmental change.
[1] P. Attard, Phys. Chem.
Chem. Phys. 8, 3585 (2006).
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The role of micromenisci
at superhydrophobic surfaces
Frieder
Mugele
The stability
of the superhydrophobic state is determined by the
properties of the liquid micromenisci spanning the
gaps between adjacent peaks of the surface profile of the underlying solid.
Ideally, the menisci have a constant mean curvature determined by the pressure
in the liquid phase and three-phase contact lines are pinned to the ridges of
the surface profile, in the present experiments the top edges posts arranged in
a regular lattice. If the pressure in the liquid exceeds a certain threshold,
the micromenisci become unstable and the superhydrophobic state collapses.
I will discuss
a number of experiments in which we used a non-invasive optical diffraction and
interference technique to determine the shape and the deflection amplitude of
the liquid micromenisci as a function of a) the
hydrostatic pressure in the liquid phase, b) acoustic fields impinging on the
surface, and c) electrostatic fields in an electrowetting
configuration.
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Driven soft matter in nano-confinement
Roland Netz
A few exampes illustrate how soft matter under confinement reacts
to external driving fields.
i)
Surface-anchored polymers that are beating back and forth can be used to pump
liquids over surfaces, which is a concept realized by biological ciliae but also attractive for synthetic designs. ii)
Polymers in shear flows are repelled from surfaces, useful for desorption of DNA in gene-chip applications.
iii)
Structured surfaces consisting of obstacles can be used for efficient
length-dependent sieving
iv)
The dynamic
charging of nano capacitors filled with liquid
electrolyte
shows strong departure from the mean-field
type Poisson-Nernst-Planck equation, which is traced back to various types of
dynamic structure formation.
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Wetting Failure and contact line
dynamics in a Couette Flow
M. Sbragaglia
Liquid-liquid wetting failure is here investigated for the case of contact line motion in a two-dimensional Couette
system with two immiscible fluids
of arbitrary viscosity. The problem is solved exactly using a sharp interface treatment of hydrodynamics
(lubrication theory) as a function of the capillary number, viscous ratio, and
separation of scale, i.e. slip length versus macroscopic scale of
the system. The existence of critical velocities, above which no
stationary solutions are found, will be analyzed in detail in terms of the
relevant parameters of the system. Comparisons with existing analysis for other
geometries are also carried out. Finally,
another computational method of analysis is
presented, based on diffuse interface models obtained from multiphase
extensions of the Lattice Boltzmann equation (LBE). Sharp interface and diffuse
interface models will be quantitatively compared face to face indicating the
correct limit of applicability of the diffuse interface models.
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