Questions tagged [soft-matter]
Soft-matter is a vast field of research at the interfaces between physics, chemistry and biology. It consists in the study of the physical properties of composite objects described by a characteristic energy scale of the excitations of a few room temperature thermal energy.
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Intrpretting questions on Fickian diffusion
I am considering the Zimm model for polymer dynamics, and have come across a question
Find an expression for the time it takes for the polymer to diffuse a distance equal to its contour length $L=...
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1answer
36 views
Soft condensed matter: the partition function for cluster formation
I am stuck on understanding the form of the partition function presented in my lectures, for self assembly of clusters from monomeric molecules. If there are $N_T$ molecules that can form clusters of ...
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Overdamped Approximation
I am reading the paper Information transfer and behavioural inertia in starling flocks (Attanasi et al, 2014) in the field of active matter for an undergraduate course I am taking.
The paper describes ...
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Kelvin solid and deformation in transverse direction with Poisson ratio
A Kelvin-Voigt material is a material with such a behavior :
I'm wondering if there is a way to model in a similar way the deformation in the transverse directions $y$. Meaning we have for the ...
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1answer
45 views
Derivation of the upper convected time derivative
I read on wikipedia theat the upper convected time derivatvie is the rate of change of some tensor property of a small parcelof fluid that is written in the coordinate system rotating and stretching ...
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1answer
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Interface between two phases minima of the energy and interface between a minimum and a “vacuum”
Cahn and Hilliard define the energy of an interface:
the difference per unit area of interface between the actual free
energy of the system and that which it would have if the properties of
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Does crosslinking a polymer film increase the stress within the film?
If I crosslink a polymer film, does that increase the internal stress of the film? Intuitively I think it should for entropy reasons; chains with greater links are more restricted and have a smaller ...
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1answer
144 views
Helfrich energy derivation
The Helfrich elastic energy of membranes is given by
$F = \int dS (\kappa H^2 + \kappa_G K)$
where $H$ is the mean curvature and $\kappa_G$ is the Gaussian curvature. The derivation in the original ...
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2answers
153 views
Calculating Elastic Potential Energy of a Stretched Sheet
Essentially, I'm trying to determine the amount of elastic potential energy stored in a thin, elastic sheet that has gone under some type of stretching (ex. A flag of stretchy fabric waving in the ...
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1answer
74 views
Shear strain correlations from displacement Fourier transform
Currently working with molecular dynamics simulations, I would like to compute shear strain correlations in my 2-dimensional system.
How I used to do things
Accumulated shear strain at position $\...
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0answers
54 views
Splitting the mean in the (Backward) Fokker-Planck
A method for deriving the Fokker-Planck equation is outlined below$^1$ (I believe it is a simplified version of the Kramers-Moyal expansion).
Set:
$$P(\vec x, t+\Delta t) =\left<\delta(\vec ...
asked May 7 '18 at 9:42
Quantum spaghettification
1,2427 gold badges31 silver badges91 bronze badges
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Is there any method to calculate surface tension of packing of particles under external potential
I want to calculate surface tension of stacking of particle which the surface is under a repulsive potential. The repulsive potential applying the force to the particles to have a surface (or ...
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31 views
Partition function for a bidisperse packing of soft-core particles
My goal is to study the nematic order in bidisperse packings of soft-core spheroidal particles of identical aspect ratio with harmonic repulsion from a statistical mechanics point of view by adapting ...
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2answers
137 views
Thermostat code for molecular dynamics with angle dependent potential
I'm building molecular dynamics code for the specific purpose of simulating Janus particle because no package supports the custom angle dependent potential to my knowledge.
I'm building thermostat ...
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1answer
51 views
Steps in minimising free-Interfacial thickness
I am trying to obtain the interfacial thickness of a mixture of two fluids in the context of the Cahn-Hilliard equation. In the simplest case and in one dimension the free energy has the form
$$F=\...
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2answers
118 views
Why is it harder to situp on solid floor?
When I situp on solid floor it is harder for me to lift my body upwards versus on a soft/foamy floor which I can do a lot.
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1answer
149 views
Ewald summation without repeating one particle periodically?
I need to perform an Ewald summation for a Brownian Dynamics simulation.
In the normal Ewald summation procedure, all particles in the simulation box are periodically repeated in the neighbouring ...
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1answer
73 views
Deformation in the nematic phase of a liquid crystal survived in solid state
Does anyone know if I cool a liquid crystal with a deformed nematic phase quickly it will preserve the deformation in the crystal lattice? I didn't never see that in classical books on liquid crystals....
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Estimate the persistence length of a rubber band [closed]
Not much more to say here, it's all in the question. The best, most convincing estimate will be chosen as the correct answer.
EDIT: Assume the rubber band is at room temperature, with thickness $t$ ...
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Will the usage of Exo-Skeleton Gear actually weaken the human body over time? [closed]
As we all know, Exo Skeletons as they exist now are just a series of Force multiplying apparatuses working together, also the human body changes to accommodate environment specific factors in order to ...
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1answer
1k views
Equivalent tensor order parameters of nematic liquid crystals?
I found in the literatures two different definitions of the tensor order parameter of nematic liquid crystals.
One is
$$
Q_{ij}=\frac{S}{2}(3n_{i}n_{j}-\delta_{ij}),
$$
where $S$ is the scalar order ...
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1answer
126 views
Is the $2\pi$ disclination topologically stable for a 2d nematic liquid crystal?
For a three dimensional liquid crystal, a $2\pi$ or charge $1$ disclination is topologically unstable. The is generally explained as the disclination can lose its core singularity by "escaping from ...
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271 views
Why is mud muddy?
How to explain properties of mixture of sand with water? Why is it so coherent and slippery at the same time? Is it due to hydrogen bonds? Why is mud of smaller grains more slippery and incoherent ...
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Are there materials that get softer with temperature decrease?
Could be there material that begins melting/softening when it's temperature is lowered?
I would say no, but I've seen enough physics to know that not always life is so easy.
Moreover I think I've ...
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1answer
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Why does dust stick so well to fan blades? [duplicate]
After reading and understanding the reasons why dust stick to rotating fan propeller, I am interested to find out why the dust particles stick so well. Spraying powerful jets of water does not ...
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1answer
109 views
What happens when a bacteria tumble? Is it an active or a passive process? [closed]
I was wondering what actually happens during the tumbling process of a "run and tumble" process. When the bacteria stops to tumble and reorient itself, is that an active process, or is the ...
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What is the physics behind a soap bubble?
A soap bubble is an extremely thin film of soapy water enclosing air that forms a hollow sphere with an iridescent surface.
What fluid dynamical process occurs during the popping of a soap bubble?
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4answers
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Where can I find the full derivation of Helfrich's shape equation for closed membranes?
I have approximately 10 papers that claim that, from the equation for shape energy:
$$ F = \frac{1}{2}k_c \int (c_1+c_2-c_0)^2 dA + \Delta p \int dV + \lambda \int dA$$
one can use "methods of ...
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1answer
475 views
Resource for intermolecular forces in soft condensed matter
I need a book dealing in particular with the intermolecular forces and, if possible, the diffusive processes. Someone knows an appropriate one?
