Microstructuring glass surfaces using a combined masking and microslurry-jet machining process

doi:10.1016/j.precisioneng.2020.09.018

Precision Engineering

Volume 67, January 2021, Pages 172-177

https://doi.org/10.1016/j.precisioneng.2020.09.018 Get rights and content

Highlights

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Photoresist masking and microslurry-jet machining were used for microstructuring.
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Curved convex structures 30 μm in diameter and 4 μm in height were formed.
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Post-treatment, such as removal of the masking patterns, was not required.

Abstract

The combined application of a conventional photoresist masking process and microslurry-jet (MSJ) mechanical removal process was studied for microstructuring the surface of glass. Masking patterns made of a photocurable resin (SU-8) were created on the glass, and both the SU-8 patterns and exposed glass surface were simultaneously removed using the MSJ. When the sacrificial patterns of the SU-8 were removed by the MSJ, the glass surface with microstructures was created. Post-treatment, such as removal of the SU-8 patterns, was not required. Confocal microscopy results confirmed that continuously curved convex structures up to 30 μm in diameter and 4 μm in height with highly transparent glass surfaces were created. The microstructures reduced the hydrophilicity of the glass surfaces. Future studies on identifying materials compatible with glass for making masking patterns and showing good wear resistance might prove the feasibility of this method in producing structured engineering surfaces.

Introduction

A variety of manufacturing processes have been developed and evaluated for structuring engineering surfaces at the microscale. Applications range from modifying tribological properties, for which the relationship between friction and surface textures is researched [1,2], to inducing hydrophobicity by microstructuring surfaces [3], where contact angle measurements are used to assess the hydrophobicity or hydrophilicity of the surfaces. Convex microstructural features might offer additional advantages in this context [4]. The manufacturing processes for engineering surfaces can involve techniques such as spraying, where material is added to surfaces for generating random or hierarchical roughness [5]; these manufacturing processes can also involve removing material such as in polymers that are microstructured using photolithographic techniques [6]. The latter manufacturing process uses a masking pattern with a high-resolution microstructure attached to the substrate surface before chemical etching [7,8]. Etching is also applicable to glass substrates [9]; however, material removal might be more cost-effective and time-efficient with a mechanical process. Furthermore, influence of side-etching should be considered to obtain a high-resolution microstructure. Current mechanical structuring processes for engineering glass surfaces lack sufficient detail at the microscale [10] owing to the brittleness of glass.

Therefore, in this research, an abrasive slurry-jet [11], more specifically a microslurry-jet (MSJ) [12], was used for microstructuring of glass surfaces. The MSJ process is a wet blasting process, where a water jet comprising small and hard particles with micrometre dimensions (slurry) was sprayed onto the substrates. Earlier studies have shown that applying the MSJ method could structure engineering surfaces (surfaces made of alloys, plastics, glass, and ceramics) to the order of nanometers in the vertical direction without the occurrence of microscopic cracks and microstructural defects on these surfaces [13,14]. Moving the MSJ nozzle during the machining process can provide continuously curved surface textures; however, the surface structures in the horizontal direction depend on the size of the nozzle, causing limitations in the machining resolution [15]. Hence, to compensate for this limitation, the combined application of a conventional photoresist masking process and the MSJ mechanical removal process was considered [16,17].

The aim of the current study was to research and assess the feasibility of using this combined masking and MSJ process for mircostructuring glass surfaces in terms of the machining accuracy and changes in the hydrophobic/hydrophilic characteristics of the machined surfaces.

Section snippets

Micromachining of glass surface by combined masking and MSJ process

Fig. 1 illustrates the micromachining process. Flat glass composed of SiO₂ with 13% Na₂O and 10% CaO was the material used for processing; it was ultrasonically cleaned using methanol, acetone, and ultrapure water. The organic compounds and other contaminants on the glass surface were also removed using piranha solution (a 3:1 mixture of sulfuric acid and 30% hydrogen peroxide, and up to 40% hydrogen fluoride) [18,19].

In the resist coating process, SU-8 3050, a photocurable epoxy resin (KAYAKU

Results and discussion

Fig. 4 shows the glass surfaces after the masking processes, with the sacrificial patterns formed as indicated in Fig. 1(4) and Fig. 2. The photoresist was precisely patterned to obtain the Type-A, Type-B, and Type-C patterns shown in Fig. 2. Confocal laser microscopy analysis confirmed that the target heights of the sacrificial patterns, namely 15, 30, and 60 μm, were achieved.

Fig. 5 shows the processed glass surface after the MSJ process (see Fig. 1(6) for a schematic representation of this

Conclusions

The combined application of the photoresist masking and MSJ mechanical removal processes for creating microstructures can be directly applied for processing numerous engineering materials to create structured surfaces. The results of this work showed that this process can be applied successfully to glass. The resulting convex microstructural features up to 30 μm in diameter and 4 μm in height are beneficial in enhancing the hydrophobicity of glass surfaces. Post-treatment, such as removal of

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by JSPS KAKENHI Grant Number 19KK0096, the Environment Research and Technology Development Fund (1–1908) of the Environmental Restoration and Conservation Agency of Japan, and the Interdisciplinary Research Project of the Institute of Industrial Nanomaterials (IINa), Kumamoto University.

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Microstructuring glass surfaces using a combined masking and microslurry-jet machining process

Highlights

Abstract

Introduction

Section snippets

Micromachining of glass surface by combined masking and MSJ process

Results and discussion

Conclusions

Declaration of competing interest

Acknowledgements

Biotribology

Biotribology

Appl Surf Sci

Precis Eng

J Solid State Chem

Appl Surf Sci

Appl Surf Sci

J Manuf Process

J Mater ProcessTechnol

J. Mech. Behav. Biomed. Mater.

Tribol Int

Int J Adhesion Adhes

Mater Lett

Biosens Bioelectron