Structural Dynamics in UV Curable Resins Resolved by In Situ 3D Printing X-ray Photon Correlation Spectroscopy

Abstract

Additive manufacturing (AM) is a promising technique to rapidly produce polymeric materials into complex 3-dimensional (3D) geometries. While AM is widespread and relevant for a range of applications, implementation in industry has outpaced our fundamental understanding of polymer dynamics and structure development during the printing process. Characterization and quantification of such dynamics is necessary to optimize final material properties and design future materials and processes for 3D printing. Here, we utilize X-ray photon correlation spectroscopy (XPCS) to measure spatial and time-resolved, out-of-equilibrium dynamics during direct ink write (DIW) 3D printing. Specifically, we investigate the progression of structural dynamics in a dual cure (UV/thermal) nanocomposite during and directly after printing. As the filament is printed and cured in situ, the relaxation processes of the cross-linking network are measured through the dynamics of inorganic filler particles. The characteristic relaxation time of the dynamics is calculated through the intensity–intensity autocorrelation function g 2 and directly correlated to the printing process parameters, such as printhead velocity and UV light intensity. The time-resolved evolution of nanoscale dynamics follows a power-law dependence as the filament is cured. Bulk rheological characterizations reveal the macroscopic solidification of the resin, providing correlation of material properties across a wide range of length and time scales. The measurement of multiscale, out-of-equilibrium dynamics provides insight into the development of structure in polymer nanocomposite filaments during 3D printing and is used to further understand the influence of such parameters on the AM process.

Heterogeneous dynamics in the curing process of epoxy resins

“…Thus, it will be interesting to analyze the size dependence of probe particles. These results will be particularly useful for improving the quality of thermosetting epoxy resins as well as various materials, such as 3D printing products 54 , 55 .…”

Operando Characterization of Organic Mixed Ionic/Electronic Conducting Materials

“…The thickness of the studied sample in a recent report was only 140 μm, which is only a factor of 20× thicker than drop-cast OMIEC films . The experimental approach has now been reported for studying soft materials, including the growth and the diffusion of nanoparticles, , the cross-linking of polymers under heating, , and UV curing processes, as well as the stress relaxation of polymer electrolytes. , …”

“…The thickness of the studied sample in a recent report was only 140 μm, which is only a factor of 20× thicker than drop-cast OMIEC films. 352 The experimental approach has now been reported for studying soft materials, including the growth and the diffusion of nanoparticles, 353,354 the crosslinking of polymers 355 under heating, 347,356 and UV curing processes, 357 as well as the stress relaxation of polymer electrolytes. 350,358 The statistical interpretation of the XPCS pattern requires the calculation of the time correlation function (eq 6), and the complex morphology and rheology of material at short time scales can be studied:…”

Surface-Functionalized Cellulose Nanocrystals as Nanofillers for Crosslinking Processes: Implications for Thermosetting Resins

“…68 As stated above, eq 1 assumes that the dynamics are in equilibrium, meaning the dynamic timescales are independent of the measurement time t. If different regions relax on different timescales in the sample, then the out-of-equilibrium dynamics must be considered and accounted for in the calculation of g 2 . Many systems display such nonequilibrium dynamics, 33,36,51,69 and time-resolved experiments can monitor their behavior. In XPCS, this behavior is measured using the two-time autocorrelation function, where the correlation analysis must be performed explicitly as a function of time.…”