This application note on how to utilize high precision microfluidic for single walled carbon nanotube alignment was written by Christian Rust, Han Li, Georgy Gordeev, Manuel Spari, Markus Guttmann, Qihao Jin, Stephanie Reich & Benjamin S. Flavel.
Single-wall carbon nanotubes (SWCNTs) are considered as quasi 1-dimensional (1D) carbon nanostructures, which are known for their outstanding anisotropic electronic, mechanical, thermal and optical properties. They can be understood as a rolled-up sheet of graphene, where the diameter of the nanotube is determined by the chiral vectors (n,m) of the hexagonal arrangement of carbon atoms [1]. Depending on the diameter, nanotubes can exhibit metallic or semiconducting properties and are consequently found in energy [2], photonics [3] and electronics [4].
Despite continuous research, difficulties to control large-scale thin film architectures are limiting their application range. Recently, alignment of SWCNTs with a vacuum filtration method has shown to facilitate high degrees of alignment over an area of A= 1 cm², but remains challenging to reproduce, due to a lack of control of the process parameters [5]. Hence, we developed a filtration setup, which is capable of producing large areas (A= 3.81 cm²) of aligned carbon nanotubes benefitting from the precision of microfluidic components.
How this experimental protocol could be used?
Due to its precision, this setup can be used to study the fouling of membranes with nanoparticles and the alignment of other nanotubes or other one-dimensional nanomaterials.
In our custom-made filtration cell shown in Animation 1, the membrane is placed on a 300 µm fine stainless-steel mesh laser-welded to a thin metal ring. The inner diameter and thus the effective filtration diameter is 22 mm, while the remaining membrane area is used to pinch the membrane in, using Teflon cylinders from either side. The intermediate flange fixes the membrane in place and allows for the addition of feed solution through the top, whilst the second makes a gas tight seal for filtration. The inlet and outlet of the stainless-steel sleeve can be connected via 1/4”-28 UNF standard threads and we use 1/8” and 1/16” polytetrafluoroethylene (PTFE) tubing with an inner diameter of 2 mm and 1 mm to connect nitrogen gas and fluid, respectively. Positive pressure is provided through the inlet by electronic pressure regulator rated to 0 bar – 2 bar operation. The outlet of the filtration cell is met by an arrangement of two 3/2 solenoid valves, which can be actuated to pass the permeate either through a MPS 2, MPS 1 pressure piezoelectric sensor or stop the flow completely. After the pressure sensors, the permeate passes into a bubble trap and the BFS 1+ Coriolis flow sensor followed by a UV-diode array. .The gravity flow of the system without a membrane in place and with the solenoid valve open was adjusted to a constant value of 100 µL min-1 by raising or lowering the position of the waste container relative to the height of the filter holder. In this way, the fluid flow driven by gravity in the setup was hindered by the backpressure of the water in the waste bottle with respect to its relative height to the filtration cell. The complete system shown in Figure 1 (A) and (B) can be operated in constant inlet pressure or constant volume rate, while the latter is realized with a PI controller using an automated first order plus dead time (FOPDT)- model, which evaluates the controller parameters of the response of an inlet pressure step.
Animation 1. The filtration cell being assembled
Figure 1. (A) Filtration setup without UV diode array (B) Schematic of the complete microfluidic dead-end filtration setup.
Electric arc SWCNTs (40 mg, lot no. 02-A011, Carbon Solutions) were dispersed in deionized water (18.2 MΩcm, pH = 6.93) from an Arium pro UV (Sartorius) using 2 wt% sodium deoxycholate (BioXtra, 98+%). After tip sonication for for 45 min (0.9 WmL-1) in an ice bath, the dispersion was centrifuged at 45,560g for 1 h (Beckman Optima L-80 XP, SW 40 Ti rotor). The obtained supernatant was than enriched by filtering them through a 300 kDa membrane (NMWL Biomax polyethersulfon, Merck Milipore) in order to reduce the water and surfactant content. For a typical filtration experiment, we used 20 ml containing 1.2 μg mL-1 SWCNTs and 0.006 wt% sodium deoxycholate.
Membranes were obtained from it4ip with a diameter of 47 mm, a porosity of 6 × 108 and a thickness of 25 µm.
Prior to filtration, the setup needs to be filled up with deionized water reaching the filter sieve in the filtration holder (cf. Animation 1 A). The membrane can then be placed on to the sieve and should remain slightly wetted. After reassembling the filter holder without the lid, a slight pressure due to compressed water below the membrane should be released by opening the valves for a short time. After the system is at equilibrium, the SWCNT dispersion is carefully added by using a pipette before closing the lid. At this point, a flow program is chosen, consisting of a slow filtration regime, where the carbon nanotubes can form crystallites or attach to the membranes and a fast filtration regime, which is used to freeze the alignment into position.
For a 20 ml dispersion filtered onto an 80 nm pore sized membrane, the slow volume rate is usually set to 100 µL min-1 for 19,250 mL and then ramped up to 500 µL min-1 for the final pushing step, Figure 2. During filtration, the pressures of the regulator pin and chosen inline pressure sensor pout are recorded as well as the trans membrane pressure PTMP = Pin– Pout . Using Darcy’s law in combination with the volume rate then yields the total resistance Rtot, whose curvature with respect to permeated volume shows how the carbon nanotubes film is growing on the membrane using filtration blocking-laws. The UV-diode array can be used additionaly to gather information on the retention of the membrane in place.
Figure 2. Experimental parameters recorded during a 20 mL filtration of an 1.2 μg mL-1 EA-SWCNT dispersion in 0.006 wt % DOC on a 80 nm pore sized membrane. The volume rates were set to 100 µL min-1 and 500 µL min-1, respectively, while the pressures (Pin, Pout and PTMP= Pin– Pout) are measured and the total resistance Rtot is calculated.
In Figure 3 (A), several cross-polarized light images of the carbon nanotube film on a membrane were stitched together, showing global alignment. Additionally a scanning electron microscopy image is provided in Figure 3 (B). Therefore, the SWCNT-film has been transferred to silicon by using chloroform to dissolve the membrane and 2-propanol to clean the surface.
Figure 3. (A) Cross-Polarized image of the global aligned membrane in bright (45 %) and dark (0%) orientation . (B) Scanning electron microscopy of aligned single-walled carbon nanotubes utilizing our microfluidic dead-end filtration setup.
This application note is based on the paper Rust, C., Li, H., Gordeev, G., Spari, M., Guttmann, M., Jin, Q., … & Flavel, B. S. (2021). Global Alignment of Carbon Nanotubes via High Precision Microfluidic Dead‐End Filtration. Advanced Functional Materials, 2107411.
How can we help you?
Name*
Email*
Message
Newsletter subscription
We will answer within 24 hours
By filling in your info you accept that we use your data.
Do you want tips on how to best set up your microfluidic experiment? Do you need inspiration or a different angle to take on your specific problem? Well, we probably have an application note just for you, feel free to check them out!
Microfluidics is the science of handling small amounts of liquids, inside micrometer scale channels. Discover how to handle fluids for your microfluidic experiments.
This application note demonstrates a smart use ouf Elveflow's Pressure sensor and sensor reader for Direct-Ink-Writing flow control.
Learn how to set up your development environment for Elveflow products with this comprehensive tutorial.
This user guide will show you how to run microfluidic colocalization studies of single molecule spectroscopy.
This application note explores the basic principle of pneumatic pumps and a flow controller based on the basic principle of pneumatic pumps, known as pressure driven flow control. It also demonstrates the applications of pressure driven flow control in a range of industrial & research fields.
Flow regulation is a compulsory operation in most of the microfluidics operations. In some applications such as 2D or 3D cell culture, flow regulation is essential since accurate micro-environmental parameters control is required. Elveflow do it’s best to make this operation as easy as possible to help you to focus on what really matter in your setup.
Study the impact of molecular transport on cell cultures with a cross flow membrane chip and microfluidic instruments.
Precise liquid injection system for manipulation of small volumes of fluids using the MUX distribution and the MUX recirculation valve.
This application note explains how to set up a robust and reproducible microfluidic platform for liposomes assembly with improved encapsulation efficiency and reduced polydispersity in size.
This application note describes how to combine and synchronise liquid perfusion and imaging using an Olympus spinning disc confocal microscope together with an Elveflow pressure-driven flow controlled microfluidic system.
Mixing is a crucial step for several microfluidic applications like chemical synthesis, clinical diagnostics, sequencing and synthesis of nucleic acids
This application note describes how microfluidic can be employed as a nanoparticle generator based on the example of PLGA bead generation.
Learn how to perform PLGA nanoparticle preparation with Elveflow instruments and a microfluidic chip
The application note describes how to convert various units of shear stress and/or pressure from one to another: shear stress conversion from Pascal, atmosphere, and N/m²...!
Get a quote
Collaborations
Need customer support?
Serial Number of your product
Support Type AdviceHardware SupportSoftware Support
Subject*
I hereby agree that Elveflow uses my personal data Newsletter subscription
Message I hereby agree that Elveflow uses my personal data Newsletter subscription