Soft matter and biology

Neutron beams are particularly well suited for soft matter and biology research. Because they are electrically neutral, neutrons can penetrate deep into materials without damaging sensitive samples. They can be generated with energies and wavelengths ideally matched to probe structures ranging from small molecules (like lipids and peptides) to large macromolecular assemblies (such as viruses).

The expression 'soft matter' (matière molle) was coined in the 1970s by Madeleine Veyssié at Orsay and later popularized by 1991 Nobel laureate Pierre-Gilles de Gennes, who described it as encompassing 'molecular systems giving a strong response to a very weak command signal'. The field spans polymers, colloids, surfactants, liquid crystals, and biological macromolecules—systems that are easily deformed by thermal fluctuations and weak external fields. The relevant energy scale (comparable to room temperature, ~k_BT) and the size of the structures (in the range of nanometers to a few micrometers) make neutron scattering ideal to study these systems.

Please note : K_BT ==> k_BT (k_B is the Boltzmann constant, T the temperature).

Why Use Neutrons for Soft Matter and Biology?

• Sensitivity to Light Elements: Unlike X-rays, neutrons interact quite strongly with light elements, particularly hydrogen. Pinpointing the location and orientation of hydrogen atoms is often critical to understanding biological behavior.
• Isotopic Substitution (Deuteration): Researchers can selectively replace hydrogen with its isotope, deuterium. This process of deuteration significantly improves contrast, allowing specific components within a complex system to be highlighted and detailed.

Capabilities and Environment at the ILL

Research in soft matter and biology accounts for roughly one-third of the ILL’s total beam-time and publication output.

• structural probing: large-scale structure instruments—including small-angle scattering instruments, reflectometers, and small-angle diffractometers - are used to map physical structures.
• dynamic probing: neutron scattering spectroscopy (including inelastic, backscattering, and spin-echo instruments) tracks molecular motions across timescales from femtoseconds (eV) to approximately 100 nanoseconds (neV).

This world-class instrumentation is supported by a vibrant scientific ecosystem on the EPN campus, providing users with specialised facilities through the Biology, Deuteration, Chemistry and Soft Matter Group, Partnership for Soft Condensed Matter and Partnership for structural Biology (PSB).