Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

Summary

We present a procedure for highly controlled and wrinkle-free transfer of block copolymer thin films onto porous support substrates using a 3D-printed drain chamber. The drain chamber design is of general relevance to all procedures involving transfer of macromolecular films onto porous substrates, which is normally done by hand in an irreproducible fashion.

Abstract

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support substrates. Accomplishing this transfer in a highly controlled, mechanized, and reproducible manner can eliminate the creation of macroscale defect structures (e.g., tears, cracks, and wrinkles) within the thin film that compromise device performance and the usable area per sample. Here, we describe a general protocol for the highly controlled and mechanized transfer of a polymeric thin film onto an arbitrary porous support substrate for eventual use as a water filtration membrane device. Specifically, we fabricate a block copolymer (BCP) thin film on top of a sacrificial, water-soluble poly(acrylic acid) (PAA) layer and silicon wafer substrate. We then utilize a custom-designed, 3D-printed transfer tool and drain chamber system to deposit, lift-off, and transfer the BCP thin film onto the center of a porous anodized aluminum oxide (AAO) support disc. The transferred BCP thin film is shown to be consistently placed onto the center of the support surface due to the guidance of the meniscus formed between the water and the 3D-printed plastic drain chamber. We also compare our mechanized transfer-processed thin films to those that have been transferred by hand with the use of tweezers. Optical inspection and image analysis of the transferred thin films from the mechanized process confirm that little-to-no macroscale inhomogeneities or plastic deformations are produced, as compared to the multitude of tears and wrinkles produced from manual transfer by hand. Our results suggest that the proposed strategy for thin film transfer can reduce defects when compared to other methods across many systems and applications.

Introduction

Thin film and nanomembrane-based devices have recently garnered wide interest due to their potential use in a broad range of applications, ranging from flexible photovoltaics and photonics, foldable displays, and wearable electronics^1,2,3. A requirement for the fabrication of these various types of devices is the transfer of thin films to the surfaces of arbitrary substrates, which remains challenging due to the fragility of these films and the frequent production of macroscale defect structures, such as wrinkles, cracks, and tears, within the films after transfer

Protocol

1. Fabrication of the transfer tool and drain chamber system

1. Attached (Supplementary Files 1, 2) is the engineering drawing for the drain chamber assembly consisting of two parts: top and bottom. Model this device according to the specifications of the desired system (e.g., the outer diameter of the receiving substrate) and export as an STL file for 3D printing.
2. For the top part, utilize a filament printer of choice and print in the lowest resolution possible, including scaffolding wherever necessary. Adhere to the recommended parameters of the printer. It is also recommended that the top part be printed using po....

Results

The BCP membrane samples were fabricated according to the previously described procedure⁹. The samples were placed onto the lip of the loading arm of the 3D-printed transfer tool (Figure 1, left) and subsequently lowered, with a laboratory jack, onto the entrance ramp of the 3D-printed drain chamber tool (Figure 1, right). A sacrificial layer of poly(acrylic acid) (PAA) between the BCP membrane and underly.......

Discussion

While many of the steps listed in this protocol are crucial for the success of the thin film transfer, the nature of the custom-designed 3D printed drain chamber allows for broad flexibility, according to the user's specific requirements. For example, if the receiver substrate has a larger diameter than the 25-mm-diameter AAO discs utilized in this study, the drain chamber can be appropriately modified to fit the new specifications. However, there are certain aspects of the protocol that are necessary to ensure effective.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
35% sodium polyacrylic acid solution	Sigma Aldrich	9003-01-4
Amicon Stirred Cell model 8010 10mL	Millipore	5121
Anodized aluminum oxide, 0.2u thickness, 25mm diameter	Sigma Aldrich	WHA68096022
o ring neoprene 117	Grainger	1BUV7
Objet500 Connex3 3D Printer	Stratasys
Onshape 3D software	onshape
Polylactic acid filament	Ultimaker
ultimaker3 3d filament printer	Ultimaker
Vero Family printable materials	Stratasys