Citation: Stella, G.; Barcellona, M.;
Saitta, L.; Tosto, C.; Cicala, G.; Gulino,
A.; Bucolo, M.; Fragalà, M.E. 3D
Printing Manufacturing of
Polydimethyl-Siloxane/Zinc Oxide
Micro-Optofluidic Device for
Two-Phase Flows Control. Polymers
2022, 14, 2113. https://doi.org/
10.3390/polym14102113
Academic Editor: Andrea Ehrmann
Received: 12 April 2022
Accepted: 18 May 2022
Published: 22 May 2022
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Article
3D Printing Manufacturing of Polydimethyl-Siloxane/Zinc
Oxide Micro-Optofluidic Device for Two-Phase Flows Control
Giovanna Stella
1
, Matteo Barcellona
2
, Lorena Saitta
3
, Claudio Tosto
3
, Gianluca Cicala
3
,
Antonino Gulino
2
, Maide Bucolo
1
and Maria Elena Fragalà
2,
*
1
Dipartimento di Ingegneria Elettrica, Elettronica ed Informatica dell’Università degli Studi di Catania,
Viale Andrea Doria, 6, 95125 Catania, Italy; giovanna.stella@phd.unict.it (G.S.); maide.bucolo@unict.it (M.B.)
2
Dipartimento di Scienze Chimiche, Università degli Studi di Catania and INSTM Udr Catania,
Viale Andrea Doria, 6, 95125 Catania, Italy; matteo.barcellona@phd.unict.it (M.B.); agulino@unict.it (A.G.)
3
Dipartimento di Ingegneria Civile ed Architettura, Università di Catania ed INSTM Udr Catania,
Viale Andrea Doria, 6, 95125 Catania, Italy; lorena.saitta@phd.unict.it (L.S.); claudio.tosto@unict.it (C.T.);
gcicala@unict.it (G.C.)
* Correspondence: me.fragala@unict.it; Tel.: + 39-095-738-5149
Abstract:
Tailored ZnO surface functionalization was performed inside a polydimethyl-siloxane
(PDMS) microchannel of a micro-optofluidic device (mofd) to modulate its surface hydrophobicity to
develop a method for fine tuning the fluid dynamics inside a microchannel. The wetting behavior of
the surface is of particular importance if two different phases are used for system operations. There-
fore, the fluid dynamic behavior of two immiscible fluids, (i) air–water and (ii) air–glycerol/water
in PDMS mofds and ZnO-PDMS mofds was investigated by using different experimental conditions.
The results showed that air–glycerol/water fluid was always faster than air–water flow, despite the
microchannel treatment: however, in the presence of ZnO microstructures, the velocity of the air–
glycerol/water fluid decreased compared with that observed for the air–water fluid. This behavior
was associated with the strong ability of glycerol to create an H-bond network with the exposed
surface of the zinc oxide microparticles. The results presented in this paper allow an understanding
of the role of ZnO functionalization, which allows control of the microfluidic two-phase flow using
different liquids that undergo different chemical interactions with the surface chemical terminations
of the microchannel. This chemical approach is proposed as a control strategy that is easily adaptable
for any embedded micro-device.
Keywords:
polydimethyl-siloxane (PDMS); ZnO; microfluidic; 3D printing; surface functionalization
1. Introduction
Currently, the hydrodynamic of two-phase flows in a microchannel plays an impor-
tant role in micro–nano technology, enabling the design of point-of-care devices in the
biomedical field and micro-electrical–mechanical systems in chemical processes [1–3].
An open issue in this context is the design of control systems easily adaptable to differ-
ent operative conditions and able to guarantee process reproducibility and reliability [
4
,
5
].
The studies presented in the literature are strictly related to specific experimental conditions,
far from being a well-established framework that can drive flow control. Recently, some
case studies have been presented in the literature using a system-on-a-chip (SoC) approach
that embeds model predictive control strategies [
6
]. The SoC offers a high level of control
and modularity, but its functionalities are strongly dependent on both integrated control
logic and knowledge of the process model [7].
In this work, a chemical approach based on the treatment of the microchannel surface
is presented as a control strategy that is easily adaptable for embedded micro-devices.
The interaction between fluids and the microchannel surface was studied to investigate
the possibility of slowing-down or accelerating the two-phase flows, generated by the
Polymers 2022, 14, 2113. https://doi.org/10.3390/polym14102113 https://www.mdpi.com/journal/polymers
