Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - microCrysFact (Microfluidic Crystal Factories (μ-CrysFact): a breakthrough approach for crystal engineering)

Teaser

The self-organization of molecules into periodically ordered structures, such as crystalline matter, is of crucial importance in many fields ranging from biology to nanotechnology. An optimal control over crystallization processes in biological systems is a key step in the...

Summary

The self-organization of molecules into periodically ordered structures, such as crystalline matter, is of crucial importance in many fields ranging from biology to nanotechnology. An optimal control over crystallization processes in biological systems is a key step in the emergence of diverse survival functions (for example, skeletal tissues formation), or it can be of great use to suppress certain diseases (e.g., cholesterol gallstone disease). In nanotechnology, nano- and micro-sized crystalline matter with functions determined at the molecular level, require an effective and well-defined pattern to assemble and organise in order to potentially improve their performance. Today, however, the mechanisms and processes occurring during crystallisation processes remain largely unknown and unresolved, which hampers advancements in these key societal and technological challenges.
Despite the impressive progress made in molecular engineering during the last few decades, the quest for a general tool-box technology to study, control and monitor crystallisation processes as well as to isolate metastable states is still incomplete. That is because crystalline assemblies are frequently investigated in their equilibrium form (thermodynamic products), driving the system to its minimum energy state. This methodology limits the emergence of new chemicals and crystals with advanced functionalities, and thus hampers advances in the field of materials engineering.
µ-CrysFact will develop tool-box technologies where diffusion-limited and kinetically controlled environments will be achieved during crystallisation and where the isolation of non-equilibrium species will be facilitated by pushing crystallisation processes out of equilibrium. In addition, µ-CrysFact’s technologies will be used to localise, integrate and chemically treat crystals with the aim of honing their functionality. This unprecedented approach has the potential to lead to the discovery of new materials with advanced functions and unique properties, thus opening new horizons in materials engineering research.

Work performed

The main results achieved so far can be divided in three different blocks which correspond to the three work packages (WP) of the proposal:

1) WP1. Design and fabrication of microfluidic platforms

We have concentrated our efforts in the design of the first generation and second generation of dynamic single-layer microfluidic devices. While the first generation has been employed to perform self-assembly studies of various metal-organic compounds under controlled dynamic conditions (see next section WP2, two papers submitted), we have recently published the fabrication of the second generation devices using glass as an alternative material to polydimethylsiloxane (PDMS), Nature Communications, 2019, 10, Article number: 1439. This achievement is crucial for the proper development of µ-CrysFact project because as proposed in the Description of the action (Task 1.2.ii), even though the materials considered in µ-CrysFact are PDMS-compatible, we foresaw a contingency plan that included the fabrication of microfluidic devices made of glass. This devices made of glass will now meet the chemical/solvent resistant requirements to study other molecular-based systems that are not PDMS-compatible (if required). Additionally to these microfluidic devices, we have recently patented a nanoreactor approach that enables the preparation of unique porous crystalline nanoparticles. The patent is entitled “‘Nanoreactors for the synthesis of porous crystalline materials”. The patent is still confidential but we are preparing a manuscript that we will submit this year (2019).
On the other hand, we have also prepared a microfluidic device that allows a high-throughput combinatorial sample preparation to optimize the performance of organic solar cells (manuscript under preparation). The devices fabricated enable the formation of organic solar cells where their thickness and composition gradients are controlled in unprecedented manner and over large areas (several cm2). The results obtained indicate that a single sample prepared with our method can rapidly denote which conditions are necessary to yield the optimum device performance.

2) WP2. Self-assembly studies under controlled dynamic conditions

We have tested dynamic single-layer microfluidic devices (first generation devices) as advanced tools to control the crystallization process of different metal-organic materials. We have reported that these devices allow diffusion-limited and kinetically controlled environments which could be crucial to unveil the pathway followed by a molecular-based system during its formation (Crystals, 2019, 12; doi:10.3390/cryst9010012), or additionally could be key to achieve out-of-equilibrium assemblies which may display different functions than their thermodynamic counterparts (Chem. Soc. Rev., 2018, 47, 3788-3803).
In WP2, we have already studied different metal-organic based compounds. Initially, we have worked with [Fe(btzbp)3](BF4)2 (where btzbp stands for 4,4′-bis((1Htetrazol-1-yl)methyl)-1,1′-biphenyl). We have demonstrated that the devices produced in WP1 uncover different crystallization pathways undertaken by this system towards its thermodynamic product. Specifically, microfluidic mixing (providing kinetic control) enables two peculiar nucleation-growth pathways characterized by well-defined metastable intermediates, which have never been observed in bulk environments (under thermodynamic control). These results are unprecedented and provide a sound basis for understanding coordination polymer growth, and open up new avenues for the engineering of advanced functional materials. This paper is currently under review.
A second system that we have investigated is the well-known spin-crossover (SCO) complex (i.e. [Fe(Htrz)2(trz)]n(BF4)n, where Htrz stands for 1,2,4−triazole and trz for 1,2,4−triazolato). Herein, we show that while the bulk synthesis of complex [Fe(Htrz)2(trz)]n(BF4)n uniformly yields a crystalline thermodynamic product, ex

Final results

The expected results until the end of the project are listed below. They all represent a major challenge in chemistry and the materials science field:

- To control pathway complexity in crystallization processes
- To push crystallization processes out of equilibrium to isolate kinetically trapped states
- To control the growth and localization of multiple functional materials in a single surface