(6fw) Harnessing Flow-Microstructure Interactions Towards Improved Soft Materials Manufacturing and Processing

My interests are in soft matter, transport phenomena, rheology and rheo-optics in a variety of engineering and scientific problems, including emulsions, polymer blends, oil recovery, polyelectrolytes, macromolecules of different kind, gels, foams, biomaterials, printing techniques and flow chemistry at the micro-scale. All of these studies have in common the goal of taming flow-microstructure interactions towards functionalities, or, alternatively said, how to manipulate the microstructure in order to get tailored mechanical and flow properties of materials and fluids.

In recent years I have been using many different experimental techniques (Optical Microscopy, Confocal-Laser-Scanning Microscopy, Bulk Rheology, Interfacial Rheology, Lipid Membranes Electro-formation, Microfluidics, Flow-Visualization) to address how flow affects microstructural properties of complex fluids and materials spanning from suspensions of biocompatible polymeric fibers, vesicles, emulsions, gels, foams, surfactant solutions, crystals, aromatic amines, composites of polymers plus particles, polyelectrolyte solutions etc., to understand how these insights can be transferred towards improved materials/chemicals manufacturing and printing processes.

• Biocompatible Polymeric Gels and Fiber Suspensions

For example, suspensions of flexible fibers are known to be a shear thinning material (resistance to flow decreases by increasing flow strength). However, we demonstrated for the first time that by using ultra-flexible long microfibers, a hydrophilic gel made of a jammed network of fibers can be obtained [1]. This is a noticeable case where the resistance to flow is irreversibly increased by increasing flow strength or applying a constant strain rate for a long enough time. Simply said, one can make a gel by shaking the suspension. We showed these phenomena to be purely topological and to be associated with mechanical entanglements of the fibers, without the requirement of any chemical cross-linking or chemical interactions. The microfibers used in the experiments were hydrophilic, biocompatible and loosely suspended in water, hence the hydrogel can be simply obtained by injection of the microfiber suspension through a syringe needle and is potentially suitable for biomedical applications. This research was awarded the cover page of the “Proceedings of the National Academy of Sciences” in 2017.

• Inkjet and 3D Printing

In another study, we identified the relevant variables for optimal printing within a novel laser-induced printing technique by using polyelectrolyte solutions as a model fluid and dimensionless parameters involving dynamic variables of fluid flow and viscoelasticity of the fluid [2]. Shear and extensional rheometrical measurements were conducted. The use of dimensionless analysis allowed to predict the printing outcome and matched the experimental results. A similar dimensional analysis has been conducted to optimize the printing pattern in 3D-embedded printing, a technique where an ink is deposited in a viscoplastic matrix (a composite made of polymers and particles) to permit manufacturing of morphologically complex 3D objects [3]. Here, the experimental campaign has been conducted coupling rheometrical measurements and particle image velocimetry (PIV).

• Polyelectrolyte Solutions

Another result of my work concerns the effect of salt type on polyelectrolyte solution rheology [4]. Recently, we demonstrated that for a given polyelectrolyte and salt concentration, different salts affect elasticity of the solution depending on the salt counterion ionic radius. This feature can be used to manipulate the solution relaxation time by an order of magnitude, i.e. from tens of seconds to less than a second.

• Emulsions, Immiscible Fluids and Interfaces

Concerning emulsions, we combined rheometry, organic electrochemical transistors, optical microscopy, confocal laser scanning microscopy, cryo-SEM and small angle neutron scattering in flow (Rheo-SANS) to understand the structure of viscoelastic depletion-flocculated emulsion where surfactant self-assembly is relevant and droplet attractive interactions are at play [5,6,7]. We showed for the first time flow-induced structural re-arrangements of the droplets involving droplet coalescence, droplet cluster disruption, droplet breakage and consecutive flow-alignment in strings until the droplets become nanometric in size. The droplet chaining is purely of elastic origin and does not depend on confinement. The typical percolated structure of the emulsion has been also associated with increased conductivity and the peculiar organic electrochemical transistor (OECT) response [8]. We were first to use OECT to “read” emulsion microstructure.

In a separate project, we used the capillary flow of the emulsion to estimate droplet interfacial tension using a simple method that exploit the linear shear rate profile close to channel walls [9]. Interfacial dilational rheology of the surfactant covered droplet has been also performed.

We also focused, in another study, on development of improved emulsion design characterizing the interfacial physical chemistry of the droplets when mixed surfactants are used [10]. Mixed surfactants are key to achieve extremely low interfacial tension values (close to zero) as well as minimize the amount of amphiphile requested to stabilize the emulsion, being the latter one of the most impairing factor regarding the use of emulsion in enhanced oil recovery. We reviewed methods of emulsion, microemulsion and nanoemulsion preparation by phase inversion highlighting avenues for possible improvements [11] and we wrote a book chapter reviewing methods and perspectives within phase inversion emulsification [12]. In another review, we summarized findings on emulsion flow in porous media for enhanced oil recovery and oil-contaminated aquifer remediation and reported several novel perspectives for future work both on the side of emulsion improved design and on the relevance of flow-microstructure interactions to obtain better oil recovery performance [13].

• Micro-scale Reactive Flows, Crystals and Fouling

We were the first to realize the synthesis of an important pharmaceutical intermediate compound in a continuous flow stainless steel micro/millireactor [14]. This simple small-sized reactor can be easily scaled-up by running several reactors in parallel, and was used to characterize the reaction kinetics. Building on these results, an industrial pilot plant has been built through a collaboration of many academic groups and a pharmaceutical company [15]. The chemical reaction is based on the most popular catalytic reaction used in pharmaceuticals, known as Buchwald-Hartwig cross-coupling, i.e. an organometallic synthesis to produce aromatic amines, and using an ad-hoc developed Pd-based catalyst. Clogging issues of the reactor where then characterized [16] and the manipulation of fluid flow has been used to tailor microfluidic crystals production [16].

• Future Research Directions

Flow can be used as a microstructural designer to provide soft materials and chemicals with specific functionalities. Likewise, these materials are often harnessed in continuous operations/processing and the effect of flow on their microstructure and functionality is a key-step towards materials development. As a faculty, I aim to exploit various flow conditions and physico-chemical interactions to design new materials with tailored properties and understand how to control these parameters to achieve a unique realization in many applications such as flow in porous media and materials for biomedical applications.

Teaching Interests:

I am interested in teaching courses broadly focused on fluid mechanics, non-Newtonian fluid mechanics, rheology, transport phenomena, thermodynamics, polymer physics, physical chemistry (with a focus on colloids and interfaces), soft materials mechanics (both biomaterials and non) and chemical reaction engineering at both the undergraduate and graduate levels.

_{[1] Perazzo, A., Nunes, J. K., Guido, S., & Stone, H. A. (2017). Flow-induced gelation of microfiber suspensions. Proceedings of the National Academy of Sciences, 114(41), E8557-E8564.}

_{[2] Turkoz, E., Perazzo, A., Kim, H., Stone, H. A., & Arnold, C. B. (2018). Impulsively Induced Jets from Viscoelastic Films for High-Resolution Printing. Physical review letters, 120(7), 074501.}

_{[3] Grosskopf, A., Truby, R., Kim, H., Perazzo, A., Lewis, J. A., & Stone, H. A. (2018). Viscoplastic Matrix Materials for Embedded 3D Printing. ACS applied materials & interfaces. DOI: 10.1021/acsami.7b19818}

_{[4] Turkoz, E., Perazzo, A.*, Arnold, C. B., Stone, H. A., (2018). Salt Type and Concentration affect the Viscoelasticity of Polyelectrolyte Solutions, Applied Physics Letters, 112, 203701, *co-first author}

_{[5] Preziosi, V., Perazzo, A.*, Tomaiuolo, G., Pipich, V., Danino, D., Paduano, L., & Guido, S. (2017). Flow-induced nanostructuring of gelled emulsions. Soft matter, 13(34), 5696-5703. *co-first author}

_{[6] Preziosi, V., Perazzo, A., Tomaiuolo, G., & Guido, S. (2018). Flow-switchable morphology of concentrated emulsions. Chemical Engineering and Processing-Process Intensification, 125, 275-279.}

_{[7] Preziosi, V., Perazzo, A., Tomaiuolo, G., & Guido, S. (2018). The effect of flow on viscoelastic emulsion microstructure. The European Physical Journal E, 41(3), 45.}

_{[8] Preziosi, V., Barra, M., Perazzo, A., Tarabella, G., Romeo, A., Marasso, S. L., ... & Guido, S. (2017). Monitoring emulsion microstructure by using organic electrochemical transistors. Journal of Materials Chemistry C, 5(8), 2056-2065.}

_{[9] D'Apolito, R., Perazzo, A., Preziosi, V., D'Antuono, M., Tomaiuolo, G., Miller, R. and Guido, S., (2018). Measuring interfacial tension of emulsions in situ by microfluidics. Langmuir, 34 (17), 4991-4997}

_{[10] Posocco, P., Perazzo, A.*, Preziosi, V., Laurini, E., Pricl, S., & Guido, S. (2016). Interfacial tension of oil/water emulsions with mixed non-ionic surfactants: comparison between experiments and molecular simulations. RSC Advances, 6(6), 4723-4729.*corresponding author}

_{[11] Perazzo, A., Preziosi, V., & Guido, S. (2015). Phase inversion emulsification: Current understanding and applications. Advances in colloid and interface science, 222, 581-599.}

_{[12] Perazzo, A., & Preziosi, V. (2018). Catastrophic Phase Inversion Techniques for Nanoemulsification. In Nanoemulsions (pp. 53-76), Elsevier-Academic Press.}

_{[13] Perazzo, A., Tomaiuolo, G., Preziosi, V., & Guido, S. (2018). Emulsions in porous media: From single droplet behavior to applications for oil recovery. Advances in colloid and interface science, 256, 326-339}

_{[14] Perazzo, A., Tomaiuolo, G., Sicignano, L., Toscano, G., Meadows, R. E., Nolan, S. P., & Guido, S. (2015). A microfluidic approach for flexible and efficient operation of a cross-coupling reactive flow. RSC Advances, 5(78), 63786-63792.}

_{[15] Falß, S., Tomaiuolo, G., Perazzo, A., Hodgson, P., Yaseneva, P., Zakrzewski, J., ... & Meadows, R. E. (2016). A continuous process for Buchwald–Hartwig amination at micro-, lab-, and mesoscale using a novel reactor concept. Organic Process Research & Development, 20(2), 558-567.}

_{[16] Sicignano, L., Tomaiuolo, G., Perazzo, A., Nolan, S. P., Maffettone, P. L., & Guido, S. (2018). The effect of shear flow on microreactor clogging. Chemical Engineering Journal, 341, 639-647.}