Benchtop nanocontact replication via unconventional polycarbonate molding: From fingerprint phantom, designed nanostructure, to superhydrophobicity

Thesis type
(Thesis) Ph.D.
Date created
In this thesis, a benchtop protocol for one-to-one replication of micro and nanostructures is described. Polycarbonate (PC) replicas are constructed via unconventional solvent-assisted molding using a polydimethylsiloxane (PDMS) negative to imprint the softened PC. The versatility of this protocol is highlighted by the broad array of applications that have been explored, from the preparation of 3D fingerprint phantoms and replication of designed nanostructures, to the creation of superhydrophobic surfaces. To achieve the best molding performance we characterized how solvent compatibility, time, and physical disruption modulate degree of crystallization and the PC morphology. By making an impression of a fingerprint into solvent-softened PC and casting it with PDMS, a 3D reproduction of the fingerprint (namely, a fingerprint phantom) can be created. Such a phantom contains all three levels of details on human fingerprints. The phantoms are detected by conventional optical and capacitive fingerprint scanners and match well with the original fingerprints. Improved fingerprint scanners and algorithms which enhance security by detecting third level details (such as sweat pores) could be developed using these phantoms as imaging standards. Replicas of structural "masters" with much smaller features than fingerprints can be constructed with this protocol; length scales down to 100 nm can be successfully replicated across large (>10 cm) areas. Confirmed with electron and atomic force microscopy, PC replicas are as effective as masters, enabling the duplication and preservation of expensive lithographically designed masters. Exact reproduction of a nanostructured master is important for lowering the cost of fabricating materials which utilize micro/nanoscale features, such as electronics, optics, sensors, and structural elements. It has been shown that the growth and development of crystalline spherulites are interrupted and limited by the molding operation. Understanding how crystallization can be regulated during solvent assisted molding is essential for developing nanofabrication techniques that utilize other polymers susceptible to crystallization. Controlled PC crystallization was further utilized to fabricate superhydrophobic PDMS. The porous network of spherulites developed is rough on the µm-scale while the spherulites consist of nanoscale tendrils. By casting PDMS from PC the extensive multi-scale roughness is transferred, producing PDMS with an optimized water contact angle of 172±1° and a sliding angle less than 1°. The performance of the superhydrophobic PDMS is superior to those constructed with more elaborate laser etching and plasma sputtering techniques.
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Supervisor or Senior Supervisor
Thesis advisor: Yu, Hua-Zhong
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