Soft condensed matter (often abbreviated to soft matter) is basically all forms of condensed matter (i.e. many particles more or less bound together (for e.g., by Intermolecular forces)) that isn't a solid, so that it has features that are easily deformable at low energies (room thermal energies). This includes polymers, Liquid crystals, complex fluids, Granular material, Foams, Emulsions, Colloids, and many kinds of mixtures, that form mesoscopic structures. Also a lot of stuff in life falls under the "soft" category. I like it precisely because of its richness.

Wiki: https://en.wikipedia.org/wiki/Soft_matter

Typial features

• Mesoscopic lengthscales
• Fluctuations (Brownian motion)
• Self-assembly. Block-copolymer self-assembly

Statistical physics is important, in particular interplay of energy and entropy, reflected in the free energy.

For systems of many particles, one uses Statistical field theory. Though one can further simplify by ignoring fluctuations, using a Mean field theory.

Soft materials

• Simple liquids (fully homogeneous/isotropic). See Fluid mechanics. The fluid may be a solution, but that only changes it chemical properties, not its physical ones.
• Several types of complex fluids. Main types:
  • Solid–liquid (Suspensions (particularly Colloids) and Gels)
  • solid–gas (Granular materials, and Fibrous materials)
  • liquid–gas (Foams)
  • liquid–liquid (Emulsions)
• Liquid crystals: nematic, smectic, cholesteric, columnar, etc.
• Several polymeric materials are soft. E.g. some Plastics, Rubbers, Latex
• Surfactants
• Biological matter
• Many kinds of Active matter and Driven matter.
• Pastes, or soft glassy materials

A fruitful way of studying phases, is to study the phase transitions between them.

Universality, coarse-graining, renormalization group. Percolation

Introduction to soft matter physics - 1 by David Pine

Thomas Speck