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Biochips & Tissue Chips

Watts, J Biochips Tissue Chips 2015, 5:1

http://dx.doi.org/10.4172/2153-0777.1000111

Opinion Open Access

Continuous Flow Reactor Technology for Nanomaterial Synthesis

Watts P*

InnoVenton: NMMU Institute for Chemical Technology, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa

*Corresponding author: Watts P, InnoVenton: NMMU Institute for Chemical Technology, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa, Tel: +27-41-504-3694; Fax: +27-41-504-9281; E-mail: Paul.Watts@nmmu.ac.za

Rec date: May 23, 2014; Acc date: August 24, 2014;Pub date: January 8, 2015

Copyright: © 2015 Watts P. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use,

distribution, and reproduction in any medium, provided the original author and source are credited.

Introduction

A signi cant number of precisely made nanomaterials have been developed for a wide variety of applications. For example, inorganic nanomaterials, such as quantum dots, are of interest because of their highly de ned optical and electrical properties; where it is well established that their properties can be very nely tuned by carefully controlling their size and shape. Of more interest, nanomaterials have also been developed for diagnostic and therapeutic applications. For example, the speci city and sensitivity of magnetic resonance imaging can be greatly improved by using nanoparticles as contrast agents. As therapeutic agents, they allow targeted delivery and sustained release of drug molecules. Regardless of application, one current problem is to be able to prepare nanomaterials with reproducible properties on a large scale; this article introduces how new chemical technology may o er one solution to this challenge.

Continuous manufacture [1] has been gaining interest in the organic chemistry arena for the last decade. Although the majority of synthetic chemistry in academia and industry is performed using batch techniques that have been in place for decades, a major problem observed with conventional reactor technology is the failure to reproducibly scale-up successful laboratory reactions; this is particularly relevant for exothermic processes. e application of micro reaction technology and continuous ow chemistry is now widely accepted as a way of overcoming this problem, with large volume production demonstrated through the replication of unit processes [2]. A key advantage of ow reactor technology is the ability to very accurately control reaction parameters [1]. For instance, the regulation of temperature and concentration pro le is crucial in maintaining control over a reaction, not only to ensure selective product formation, but also from a safety perspective. Due to the excellent heat and mass transfer, and predictable ow properties exhibited by micro reactor systems a high degree of reaction control is attainable. For example, in traditional large-scale reactor vessels, uctuations in temperature are di cult to correct, as any alterations made take time to have an e ect on the system as a whole; in comparison changes are observed almost immediately within ow reactors. Along with increasing the rate of mixing, decreasing the channel diameter results in an inherently high surface to volume ratio, allowing rapid dissipation of any heat generated over the course of a reaction.

Over the past decade, a wide variety of di erent chemical processes have been performed within such systems [3-5]. Critically it has now been demonstrated that the scale of manufacture can be very easily modi ed by simply increasing the volume of the ow reactor system [6]. Several chemical companies now manufacture at the 100-tonne scale using this approach [7]. In addition to the synthesis of small organic molecules, continuous ow synthesis is emerging as a tool for

J Biochips Tissue Chips

ISSN:2153-0777 JBTC, an open access journal

the preparation of highly de ned materials; a selection of examples being detailed within this article.

Synthesis of Nanomaterials via Polymerization Reactions

When performing polymerizations in batch, the removal of heat from the reaction can be di cult, with the consequence that large molecular weight distributions are o en obtained. Consequently, by performing such reactions in micro uidic continuous ow systems, where the high surface to volume ratio ensures rapid dissipation of heat, polymers with a narrow molecular weight distribution should be attainable.

Yoshida and co-workers [8] reported the controlled polymerization of butyl acrylate in a stainless steel capillary reactor (dimensions = 500 μm (diameter) x 1.0 m (length) consisting of a micro mixer followed by a heated channel (80-100°C) and a cooled (0°C) section. Using pressure-driven ow, the authors introduced a solution of AIBN (azobisisobutyronitrile) (0.03 to 0.05 M) in toluene from one inlet and neat butyl acrylate from the other inlet. Employing a reagent residence time of 3 minutes a orded yields of 87%. Critically the product had a Polydispersity Index (PDI) of 3.14 whereas when performing a comparable reaction in a batch reactor not only was the yield lower (50 %) but the product had a PDI of 212. It was therefore concluded that the reduction in PDI obtained when employing a micro reaction system was simply due to e cient heat removal. With respect to production, the authors importantly demonstrated the ability to operate the reactor, on a laboratory scale, for hours with no sign of fouling or pressure build-up. Other examples of polymer synthesis in such systems are reviewed by Park [9].

Along with the ability to prepare polymers of narrow molecular weight distribution, the preparation of polymeric beads has been demonstrated within micro uidic systems. Zourob and co-workers [10] used a micro reactor consisting of a polymeric reaction channel (dimensions = 200 μm (wide) x 200 μm (deep) x 2.0 cm (length)), for the preparation of molecularly imprinted polymers (MIP). To prepare an MIP, an argon purged solution of (R,S)-propranolol (1.0 mmol), methacrylic acid (10.0 mmol), trimethylolpropane trimethylacrylate (3.0 mmol) and 2,2-dimethoxy-2-phenylacetophenone (1.5 x 10-2 g) in MeCN (3.0 ml) was introduced into a mineral oil carrier stream and polymerization initiated using UV-light (60-80 mW cm-2). e (R,S)- propranolol template was subsequently removed from the polymeric beads by washing with MeOH and MeCN. e aforementioned polymerisation methodology was subsequently repeated using a per uoro-(1,3-dimethylcyclohexane) carrier stream, and the resulting beads washed with chloroform and acetone. Using this approach, near- monodisperse polymeric beads were obtained in all cases, a ording a coe cient of variation (CV) of < 2%, compared to analogous batch

Volume 5 • Issue 1 • 1000111

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