Embodiments of the present disclosure generally relate to processes and apparatus for carbon nanotube formation, and more specifically, to processes and apparatus for carbon nanotube alignment. In an embodiment, a process for aligning carbon nanotubes is provided. The process includes introducing an aqueous solution to a pressure-controlled system that includes a silanated glass element, a porous membrane, and a container. The process further includes applying a pressure differential across the porous membrane to draw the aqueous solution from the silanated glass element, through the porous membrane, and to the container at a flow rate to form a filtrate disposed within the container and a retentate disposed above the porous membrane, the retentate comprising carbon nanotubes. The process further includes optically detecting a position of a meniscus of the aqueous solution in the silanated glass element. Apparatus for forming and aligning carbon nanotubes are also disclosed.