Strain to shine: stretching-induced three-dimensional colloidal lattice transformations and optical transitions

Combining three-dimensional colloidal lattices with soft polymer matrices imbues these materials with strain resilience and responsive properties1–4, holding promise for various applications5,6. Understanding how they deform under strain is crucial, yet current knowledge is confined to one- or two-dimensional simplifications7–9. Here we provide three-dimensional analytical models and experimental results for colloidal-assembled polymeric opals with close-packed lattices subjected to uniaxial stretching. By extending the investigation to strains of up to 200%, we elucidate distinct deformation principles and pathways for three-dimensional elastic colloidal lattices, contrasting with those of atomic lattices. We detail the evolution of lattice transformations and optical transitions that occur during material stretching in distinct directions, presenting an unprecedented narrative from a three-dimensional perspective. The stretched lattices display unusual optical properties exclusive to three-dimensional structures. Notably, stretching beyond a critical 40% strain threshold in particular directions reveals previously hidden Bragg reflections inside the opals, resulting in retro-reflective colours that are far brighter than surface diffraction, surpassing their original bandgap limit. We stretch green opals to show red and redshift colours when tilted. Our findings revolutionize the transformative mechanics in elastic colloidal lattices, showcasing a new route to achieve exceptional performance and novel structures with controlled lattice transformations10,11.