Evaluating the use of self-assembled monolayer (SAM) release coatings for replicated optics

Abstract

space Materials laboratory, The aerospace corporation, el segundo, ca, usa ABSTRACT Carbon fiber-reinforced composite replicated mirrors offer weight savings, higher stiffness, tailorable CTEs, higher thermal conductivities, and excellent damage tolerant mechanical properties in comparison to traditionally processed glass mirrors. These mirrors can also be rapidly manufactured by replicating the surface of a high-precision glass mandrel multiple times. The mold release coating used is critical and must be on the molecular scale, uniform, and exhibit low adhesion in order to produce high-fidelity replication. This study investigates the use of a self-assembled monolayer (SAM) as the mold release agent for the manufacture of replicated mirrors. We have synthesized and tested perfluoropolyether (PFPE) coatings formed on glass substrate via self-assembly. Ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy were used to characterize the morphology, thickness uniformity and the chemical profile of the coatings. The release force necessary to remove the replicated surfaces from the mandrel is critical and was directly related to the surface distortion of the replica. The release force increased with each successive replication due to pinholes and defects. Incorporating a secondary, lower molecular weight SAM reagent significantly reduced both surface agglomeration and transfer of SAM material to the replicated resin surface. A 60% reduction in the replica release force and a 50% improvement in the replica surface figure were achieved due to reductions in the defect density of the SAM coating.

Metal Atom Desorption from Organofluorine Surfaces: What Factors Govern Desorption?

“…However, when the film thickness is increased, a polymerized layer is further formed on the silane-coupled monolayer (center figure), the polymer chains on the surface become easy to move, and the metal becomes difficult to deposit (p-FTS). On the other hand, in FG93 where metal is not deposited even at the monolayer level, it is suggested that the perfluoroalkyl chain contains flexible parts such an ether moiety like perfluoropolyether (right figure), [31][32][33][34][35][36] and thus, it is easy to move. Scheme 2b is a qualitative model of the adsorption potential curve that explains the relationship between the difference in surface molecular mobility and the ease of desorption of metal atoms.…”

Effect of gamma radiation on the stability of UV replicated composite mirrors

“…The cured resin layer can be separated from the mandrel via the use of a monolayer release layer, whose synthesis and deposition details are elsewhere. 4 A uniform bond line was controlled with a shim (75-μm thick) producing a replication ∼32 mm in diameter. The replicating resin layer (RL) cure was done by UV exposure through the glass mandrel and then separated at the monolayer-coated glass and RL interface.…”

“…Achieving high fidelity replications (SFE ¼ λ∕20) is critically dependent on the type of replicating resin used, the quality of the master, the process of application, and the type of release monolayer film applied to the mandrel material. 4 However, even though replicated mirrors have been processed for over 30 years, literature data with respect to the dimensional stability of high-precision grade replicated composite mirrors are less well-defined than that of their heavier glass counterparts. Unlike Zerodur ® , beryllium, and ULE ® , composite replicated resin materials, such as epoxies, are significantly more sensitive to dimensional fluctuations caused by thermal and environmental conditions.…”

Stress mitigation of replicated composite mirrors via multi-layer replication

“…Furthermore, the glass master can be used an infinite number of times. More details describing this process as well as the critical factors necessary to achieve a high precision mirror have been described in previous publications [9,10,11,12,13].…”

“…and then parametric stability studies were performed as a function of time, humidity, and radiation environments. The driving factors of environmental stability were identified, and precision quality and stability were achieved through processing and formulation modifications [9,10,11,12,13].…”