Matthew Helgeson is good at shooting neutrons through things — so good, in fact, that he was recently named one of eleven Fellows in the 2026 cohort of the Neutron Scattering Society of America (NSSA). The UC Santa Barbara chemical engineering professor was recognized, according to the NSSA announcement, for his “research and service to the field of neutron scattering, especially dealing with the thermodynamics and dynamics of soft materials,” and for innovations in that area. He will be formally inducted at the American Conference on Neutron Scattering, to be held in Detroit, Michigan, in July. 

“We at The Robert Mehrabian College of Engineering (COE) offer Matthew Helgeson warm congratulations on this important and very well-deserved mid-career honor from the Neutron Scattering Society of America,” said Umesh Mishra, dean of the COE at UCSB. “Through his research and the innovations in equipment developed in his lab, he has significantly expanded how neutron-scattering can be used to determine the structure and character of soft materials in both neutral states and when undergoing some kind of force. It is important work, and we are very proud of Matt's  leadership in the field.” 
 
"Matt Helgeson has made seminal contributions to the fundamental understanding associated with the structure and dynamics of soft materials, including polymers, colloidal systems, and emulsions,” said Frank Bates, a UCSB Distinguished Visiting Professor and a regent at the University of Minnesota. “He has pioneered the use of innovative rheological devices that can be operated in-situ while simultaneously acquiring neutron scattering data, complemented by the development of sophisticated analytical tools."

Helgeson previously received numerous awards that he describes as ‘young-person’ awards, given to graduate students or young faculty members to recognize their potential and encourage them to develop their ideas. “This one hits differently, since it recognizes the ability to execute on those ideas and make a sustained impact,” he said. “It's very rewarding to receive feedback from your peers in the community saying, ‘We value not only your ideas, but the contributions that have resulted from them.’ It’s definitely an honor.” 

There are quite a few reasons to scatter neutrons, especially, in the case of Helgeson’s lab, when working on soft or biological materials made of organic molecules. “In many cases,” he explains, “these materials are mechanically processed in ways that change their microstructure. Polymers stretch and orient, particles change their arrangement relative to each other, droplets deform, and biomolecular assemblies can break or combine in ways that can dramatically alter the properties and function of materials ranging from pharmaceuticals and foods to high-tech polymers for energy efficiency and photovoltaics.”

Scattering, which measures the patterns formed when beams of particles or radiation bounce off atoms and molecules, provides information that can be used to measure those processes – but only if the material remains intact while in the beam. Helgeson explains that whereas X-ray beams produced at synchrotrons [which Helgeson’s group also uses] have high energies and can interact with electrons to cause molecules to undergo chemical reactions that cause decomposition of the material, neutrons are lower-energy and interact only with the nucleus and nothing else, allowing them to interact with the material more passively, without altering its chemistry.

Another advantage of neutrons, Helgeson explains, is that because they interact only with the nucleus, they also penetrate through equipment more easily. “In my research program,” he continues, “we do a lot of work with in situ and in operando measurements, where we place complex processing devices, such as a microfluidic cell or a high-pressure capillary, into the neutron beam [one of the innovations noted in the fellowship announcement]. Because of their non-destructive nature, the neutrons transmit right through metal, plastic, or other materials without reacting with them. That allows us to use the neutron beam to actually see the scattering from materials deep inside a piece of equipment.” In particular, Helgeson and his group develop flow devices that are meant to emulate real manufacturing processing flows, using scattering to track how materials transform in a flow to produce desirable structures and properties.

A third advantage results from a fortuitous quirk of nuclear physics. “When you shoot neutrons or other radiation at an atom, the fraction of particles or radiation that gets scattered is related to something called the scattering length of the atom,” Helgeson says. “In the case of X-rays, the scattering lengths are determined by the electron density. This is unfortunate for soft materials, because most of the atoms that make up organic molecules and solvents (carbon, oxygen, hydrogen, nitrogen, etc.) end up with very similar scattering lengths. “And so there isn’t enough contrast in X-ray scattering between, say, a polymer and its surrounding solvent to distinguish its structure.”

Neutron scattering lengths, especially for soft materials and organic molecules, behave quite differently, and change with the isotope – whether it is, say, carbon-12, carbon-13, or carbon-14. “As it happens, replacing hydrogen (H), which has no neutrons, with deuterium (D) — hydrogen with one neutron — dramatically changes the nuclear properties, so much so that on a line representing the spectrum of scattering lengths, H is on one end and D is on the other, and nearly every other atom is somewhere in between. Because of this, we can use deuteration of organic molecules to artificially enhance or suppress their scattering without altering their chemical interactions,” Helgeson explains. “So, if I have a polymer in solution and change the solvent from H2O to D2O, the scattering is suddenly increased by a factor of hundreds to thousands, making it possible to measure the structure of materials I couldn't if I were using X-rays, light, or electrons.”

In a similar way, he adds, “We can use deuteration to either ‘light up’ or eliminate the scattering from one molecule in a complex mixture of molecules. For example, if we change all of the hydrogen atoms to deuterium atoms in a mixture of polymers and biomolecules but leave one of them with all of its hydrogens, we can collect the scattering only from that molecule and, therefore, see where and how it sits in a particular structure.”

“The measurements, though, are only the beginning,” he added. “It’s really hard to interpret scattering patterns without doing some amount of theoretical modeling to get a picture of the structure you’re trying to measure. Because we’re making measurements on materials in situations [like a processing flow] that people don't usually think about — the scattering images we obtain are very different from those obtained from materials at equilibrium, and so the analysis and interpretation of the data becomes very different as well. It’s as if you speak English, but the scattering pattern is written in Greek.

“When we started doing these experiments, we found that the theory and the analysis to quantitatively interpret scattering images from flowing soft materials just wasn't very well developed, making it difficult to link the measurements to the specific molecular and material properties engineers are interested in. For example, a strong flow will cause a polymer or a protein to stretch. When we started, there was no easy way to decode a scattering image to infer how much stretching occurs. We had to develop new theory, as well as the mathematical tools to be able to decode this kind of information from the experiments.” 
 
Thanks to the tools and techniques developed in his lab, said Helgeson, "We can measure structural transformations that are occurring during flow and that can't be resolved using any other method." This includes, he explains, complex processing flows that occur in real manufacturing equipment, in which a material flowing through a process will experience constantly changing types and speeds of fluid deformation "Being able to resolve structures as they form and change in these flows is allowing us to provide more useful information and guidelines for designing new materials and advanced manufacturing processes."

That kind of pioneering work is what made Helgeson an NSSA Fellow.