Abstract
In the present study, a hot embossing process employing a hydrophilic polydimethylsiloxane (PDMS) mold was investigated considering the effect of the surface wettability of the mold on the replication quality of microfeatures. To turn the hydrophobicity of native PDMS into hydrophilicity, Silwet L-77 was employed as a surfactant in preparing a mold for a microcavity. Hot embossing experiments imprinting the microfeature onto thermoplastic sheets were performed with both a surfactant-modified mold and a native PDMS mold. A design of the experiment approach based on an orthogonal array was employed to investigate the effects of the relevant factors, including wettability and processing parameters. The characteristic dimensions of the hot-embossed microfeature were measured to evaluate the replication quality. The increased wettability of the PDMS mold surface was found to efficiently improve the replication quality of the microfeature. The major processing parameters of the hot embossing process, such as the embossing temperature, pressure, and time, were also investigated.
Highlights
The hot embossing process is a mass replication technique for fabricating micro- or nano-features in polymers.1,2 After both a thermoplastic polymer sheet and a precisely patterned mold insert, or stamp, are placed between two flat platens, the temperature of the polymer sheet is increased
The mold insert or stamp is the most important component in the hot embossing process. It should be prepared with precise microor nano-scale cavities, which are filled with the polymer melt during the hot embossing process to form micro- or nano-features on the surface of the polymer sheet
The present study considered these three parameters to identify the effects of the surface wettability of the mold inserts
Summary
The hot embossing process is a mass replication technique for fabricating micro- or nano-features in polymers. After both a thermoplastic polymer sheet and a precisely patterned mold insert, or stamp, are placed between two flat platens, the temperature of the polymer sheet is increased. Compared to other micro- or nano-feature replication processes, such as injection molding, thermoforming, and casting, the hot embossing process shows several advantages, including relatively simple operation, easy replacement of mold inserts, cost-effectiveness, and flexible manufacturing. It should be prepared with precise microor nano-scale cavities, which are filled with the polymer melt during the hot embossing process to form micro- or nano-features on the surface of the polymer sheet It should have good mechanical and thermal properties, because both heating and high pressures are applied for good replication quality. The low elastic modulus can cause unnecessary mold deformations, which reduce the replication accuracy, under applied pressures, this can be minimized by precisely controlling the processing parameters Another benefit of PDMS is the easy modification of the surface properties. The effects of the relevant processing parameters were investigated in both cases to further understand the effects of the enhanced surface wettability of the PDMS mold
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