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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.

The studied object include, e.g. liquids, colloids, polymers, foams, gels, granular materials, and a number of biological materials, e.g. DNA (mechanical and structural response for instance), ATP generated reaction (actin-myosin cycle)...

The studies of soft-matter objects usually consist in the description of some chemical and/or biological properties using the methods of statistical (organisation, ageing, phase transition, linear and non-linear response, ...) as well as elastic (membrane, foam, and gels deformations, ...) or fluid mechanics (low-dimension fluid mechanics among other, ...) physical models.

Soft-matter is one of the most active branch of research at the beginning of the 21-st century, having a lot of possible industrial applications.

51 questions
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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 variational calculus" to derive the following: $$\Delta…
Samuel Reid
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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?
dan
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8
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3 answers

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 heard something about it, but can't remember a thing.
user46147
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7
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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 parameter and $\mathbf{n}$ the director, $i=x, y,…
user65112
6
votes
1 answer

Why do stones in a garden rise to the surface?

Why do stones in a garden rise to the surface? I haven't done my own research on the subject, but experienced gardeners seem to suggest that, even if the garden is cleaned from stones, they reappear after some time. Brief internet search confirms…
Roger V.
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4
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Question about 1D Percolation Theory

I am currently reading "Introduction to Percolation Theory" by Stauffer and Aharony and am doing the problems. Question 2.2 wants me to calculate a closed-form expression for the $k$-th moment $M_k$ of the cluster number $n_k$ in one dimension.…
Brasswyrm
  • 51
4
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2 answers

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.
Rod_Algonquin
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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 the third dimension". However, for a two…
user21090
3
votes
1 answer

Why does dust stick so well to fan blades?

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 effectively remove the dirt. Some scrubbing is still…
Question Overflow
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Why is the energy required to bend a flat bilayer membrane to vesicle independent of its radius?

Imagine that we have a flat bilayer sheet (let it be a disc-shaped bilayer) lipid membrane. When I naively think about this system being bent to form a vesicle (closed bilayer membrane), my intuition says that the larger the radius (surface area) of…
dexterdev
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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 boxes. Is it possible to alter the Ewald summation…
user3107708
  • 153
2
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1 answer

Fourier Transform for sinusoidal number-density to obtain the structure function

I was reading chapter 2 of Chaikin and Lubensky, where I got stuck at this derivation of structure function. While talking about Smectics-A liquid crystal, it was mentioned that the molecules are aligned perpendicular to the layer. The introduction…
Soham Parmar
  • 51
2
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1 answer

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 a variable size $\alpha$ molecules each (where…
Meep
  • 4,167
2
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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 wind). To keep the post as relevant as possible, in…
AlexP
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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.
Caetes
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