3D Micromachined Polyimide Mixing Devices for in Situ X-ray Imaging of Solution-Based Block Copolymer Phase Transitions

Abstract

Advances in modern interface-and material sciences often rely on the understanding of a system's structure−function relationship. Designing reproducible experiments that yield in situ time-resolved structural information at fast time scales is therefore of great interest, e.g., for better understanding the early stages of self-assembly or other phase transitions. However, it can be challenging to accurately control experimental conditions, especially when samples are only available in small amounts, prone to agglomeration, or if X-ray compatibility is required. We address these challenges by presenting a microfluidic chip for triggering dynamics via rapid diffusive mixing for in situ timeresolved X-ray investigations. This polyimide/Kapton-onlybased device can be used to study the structural dynamics and phase transitions of a wide range of colloidal and soft matter samples down to millisecond time scales. The novel multiangle laser ablation three-dimensional (3D) microstructuring approach combines, for the first time, the highly desirable characteristics of Kapton (high X-ray stability with low background, organic solvent compatibility) with a 3D flow-focusing geometry that minimizes mixing dispersion and wall agglomeration. As a model system, to demonstrate the performance of these 3D Kapton microfluidic devices, we selected the non-solvent-induced self-assembly of biocompatible and amphiphilic diblock copolymers. We then followed their structural evolution in situ at millisecond time scales using on-the-chip time-resolved small-angle X-ray scattering under continuous-flow conditions. Combined with complementary results from 3D finite-element method computational fluid dynamics simulations, we find that the nonsolvent mixing is mostly complete within a few tens of milliseconds, which triggers initial spherical micelle formation, while structural transitions into micelle lattices and their deswelling only occur on the hundreds of milliseconds to second time scale. These results could have an important implication for the design and formulation of amphiphilic polymer nanoparticles for industrial applications and their use as drug-delivery systems in medicine.

Millisecond timescale reactions observed via X-ray spectroscopy in a 3D microfabricated fused silica mixer

“…These devices include microfabricated silicon components, UV-curable adhesives, and/or soft lithography components (Brennich et al, 2011;Seibt et al, 2018). As another example, 3D micromachining has been used to create polyimide devices (Vakili et al, 2019). However, it is difficult to create complex 3D geometries (e.g.…”

Time-Resolved Analysis of the Structural Dynamics of Assembling Gold Nanoparticles

“…In order to study how fast the polymer shell collapses and particle agglomerates form, our microfluidic reactor was designed to precisely trigger this process via rapid mixing in a 3Dhydrodynamic flow focusing geometry. 26 First of all, focusing the sample down to a narrow laminar stream allows for fast diffusion-based mixing due to the reduced length scales. 27 Second, the continuous flow enables mapping the reaction time points onto specific positions along the microchannel, which, in combination with microfocused X-ray beam scanning orthogonally to the flow and the lateral focusing directions (see Figure 1B), enables the collection of time-resolved structural data of the centrally focused sample with high spatial and temporal resolution.…”

“…23,24 For this purpose, we produced a completely Kapton®-based microfluidic device that was solventcompatible, X-ray transparent and, therefore, ideally-suited for in situ small-angle X-ray scattering measurements. 26 The device fabrication was based on previously described work combining laser ablation 24,28 and covalent bonding. 26,29,30 and it was equipped with online UV-Vis-NIR spectroscopy (Figures 1a and S1).…”

“…26 The device fabrication was based on previously described work combining laser ablation 24,28 and covalent bonding. 26,29,30 and it was equipped with online UV-Vis-NIR spectroscopy (Figures 1a and S1). The microreactor was connected to three gas-tight syringes:…”

Stable sample delivery in a viscous medium via a polyimide-based single-channel microfluidic chip for serial crystallography

“…Polyimide films are not easily torn or damaged through physical impact, unlike capillaries, and upon X-ray exposure, this material provides data with negligible levels of X-ray background scattering for processing (Thorne et al, 2003). Hence, polyimide can not only be used for data collection by mounting single crystals in traditional crystallography methods (Thorne et al, 2003) but also be applied in X-ray analysis or a sample delivery system for serial crystallography such as a microfluidic device, dynamic virtual nozzle or sample enclosed in a fixed-target sample holder (Barrett et al, 2006;Vakili et al, 2019Vakili et al, , 2020Weinhausen & Kö ster, 2013;Catalano et al, 2014;Ghazal et al, 2016;Monteiro et al, 2020).…”