Microfluidic Devices for Neutron Scattering Applications

FASCISZEWSKI, A.; FOSSA OLANDINI, CECILIA; MAGALÍ MERCURI; MORETTI, GIANNI

Córdoba

Congreso; II Brazil-Argentine Microfluidics Congress. V Congreso de Microfluídica Argentina; 2019

Facultad de Matemática, Astronomía, Física y Computación, Universidad Nacional de Córdoba

Small Angle Neutron Scattering (SANS) is one of many characterization techniques by means of neutron beam experiments. It is a non invasive probe for the structure and dynamics of soft matter. Developments during the last years in neutron flux and improved beam guides now enable microfluidic experiments with these techniques for a wide range of applications. For this, it is necessary, among other things, that the materials used in the microfabrication process have a high neutron transmission coefficient.The objective of the project consists on optimizing a technique for the fabrication of microfluidic devices in PDMS/Glass compatible with neutron beam experiments. This will require that the thickness of the polymer ranges from 0.1 mm to 1 mm, because in this range neutron transmission for PDMS varies from 0.96 to 0.60 respectively[3]. Some of the advantages of PDMS microfluidic devices are its low cost and the good resolution of the PDMS at micrometer scale. This material is also bio-compatible, which increases the range of applications.As a proof of concept and with the aim of learning microfabrication tools using PDMS, a pattern of microchannels with a T-Junction was chosen. For this purpose the standard process of design and fabrication[4] was carried out for the assembling of devices with a thickness in the order of 5 mm. First, the masters were fabricated using photolithography.Then the patterns were transferred to PDMS by pouring the polymer into the master. Finally the covalent union between PDMS and glass was obtained by oxidation with a microwave plasma. The injection of liquids was also performed to check the quality and integrity of the devices.On the other hand, the study of an alternative technique to achieve thin films of PDMS was carried out. In this case the spin-coating technique was used for the depositiOn of PDMS thin films. In preliminary assays a glass substrate without a master was used to characterize the thickness of PDMS as a function of spin speed. Films with a thickness in the range of 40 μm to 360 μm were obtained with speeds of 1500 rpm and 700 rpm respectively, which will supposedly allow for a high neutron transmission.Currently, the covalent union between micrometer-thin films of PDMS and glass using microwave plasma is being tested. For the next months, the spin-coating technique will be used in the soft-lithography process with the already made masters. In the long term it is expected that these devices will be tested to verify the high neutron transmission, which will open new routes toward novel researches on technological microdevices compatible with neutron beam applications.