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PDMS reference papers

File Elastomer-supported cold welding for room temperature wafer-level bonding
This paper presents a method for room-temperature wafer level bonding that is applicable for the MEMS and NEMS packaging and fabrication processes, but does not require an applied voltage, high pressure or vacuum. By applying a layer of elastomer between the wafer and gold overlayer, we successfully bonded two silicon wafers under limited load (~3KPa) at room temperature (25'C). One of the important potential applications of this technique is to create a temporary cap wafer that would protect already released, bulk or surface-micromachined structures during the dicing process. The initial results of experiments on the detachment of the temporary cap wafers bonded using this method are presented.
File Thin PDMS Films Using Long Spin Times or Tert-Butyl Alcohol as a Solvent
Thin polydimethylsiloxane (PDMS) films are frequently used in ‘‘lab on a chip’’ devices as flexible membranes. The common solvent used to dilute the PDMS for thin films is hexane, but hexane can swell the underlying PDMS substrate. A better solvent would be one that dissolves uncured PDMS but doesn’t swell the underlying substrate. Here, we present protocols and spin curves for two alternatives to hexane dilution: longer spin times and dilution in tert-butyl alcohol. The thickness of the PDMS membranes under different spin speeds, spin times, and PDMS concentrations was measured using an optical profilometer. The use of tert-butyl alcohol to spin thin PDMS films does not swell the underlying PDMS substrate, and we have used these films to construct multilayer PDMS devices.
File Mechanical characterization of bulk Sylgard 184 for microfluidics and microengineering
Polydimethylsiloxane (PDMS) elastomers are extensively used for soft lithographic replication of microstructures in microfluidic and micro-engineering applications. Elastomeric microstructures are commonly required to fulfill an explicit mechanical role and accordingly their mechanical properties can critically affect device performance. The mechanical properties of elastomers are known to vary with both curing and operational temperatures. However, even for the elastomer most commonly employed in microfluidic applications, Sylgard 184, only a very limited range of data exists regarding the variation in mechanical properties of bulk PDMS with curing temperature. We report an investigation of the variation in the mechanical properties of bulk Sylgard 184 with curing temperature, over the range 25 ◦C to 200 ◦C. PDMS samples for tensile and compressive testing were fabricated according to ASTM standards. Data obtained indicates variation in mechanical properties due to curing temperature for Young’s modulus of 1.32–2.97 MPa, ultimate tensile strength of 3.51–7.65 MPa, compressive modulus of 117.8–186.9 MPa and ultimate compressive strength of 28.4–51.7 GPa in a range up to 40% strain and hardness of 44–54 ShA.
File Characterization study of bonded and unbonded polydimethylsiloxane aimed for bio-microelectromechanical systems-related applications
Authors have demonstrated that by controlling the mixing ratio of polydimethylsiloxane’s PDMS’s two components—base polymer part A and a curing agent part B—different mechanical properties of PDMS can be achieved. Test results show that the Young’s modulus decreases as the increasing of mixing ratios A:B. However, there is a transitional mixing ratio part A:part B=10 after which the Young’s modulus is almost independent of the mixing ratio. The PDMS’s thickness plays an important role in determining the mechanical properties. The results show that the thinner the PDMS, the stiffer it behaves. The bonding strength between two cured PDMS parts with different mixing ratios shows that it depends on the mixing ratio. A maximum bonding strength of 130 kPa occurs on a bonded couple with mixing ratios of 30A:1B and 3A:1B, respectively. The fracture on bonded specimens does not occur at the bonding interfaces. Instead it occurs at the side with a larger portion of part A. The intermediate material property formed at the interface is attributed to the diffusion layer formed. © 20
File Enhancement of the thermo-mechanical properties of PDMS molds for the hot embossing of PMMA microfluidic devices
We present a cost-efficient and rapid prototyping technique for polymethylmethacrylate (PMMA) microfluidic devices using a polydimethylsiloxane (PDMS)-based hot embossing process. Compared to conventional hot embossing methods, this technique uses PDMS molds with enhanced thermo-mechanical properties. To improve the replication performance, increases in both PDMS stiffness and hardness were achieved through several processing and curing means. First, the amount of curing agent was increased from 1/10 to 1/5 with respect to the amount of prepolymer. Second, the cured PDMS was thermally aged either over three days at 85 ◦C or for 30 min at 250 ◦C. Those combined steps led to increases in stiffness and hardness of up to 150% and 32%, respectively, as compared to standard PDMS molds. Using these enhanced molds, structures with features of the order of 100 μm in PMMA are successfully embossed using a standard laboratory press at 150 ◦C. The PDMS molds and process produce identical structures through multiple embossing cycles (10) without any mold damage or deterioration. A Y-shaped microfluidic mixer was fabricated with this technique. The successful demonstration of this enhanced PDMS-based hot embossing technique introduces a new approach for the rapid prototyping of polymer-based microfluidic devices at low-cost.
File Solvent Compatibility of Poly(dimethylsiloxane)-Based Microfluidic Devices
This paper describes the compatibility of polydimethylsiloxane (PDMS) with organic solvents; this compatibility is important in considering the potential of PDMS-based microfluidic devices in a number of applications, including that of microreactors for organic reactions. We considered three aspects of compatibility: the swelling of PDMS in a solvent, the partitioning of solutes between a solvent and PDMS, and the dissolution of PDMS oligomers in a solvent. Of these three parameters that determine the compatibility of PDMS with a solvent, the swelling of PDMS had the greatest influence. Experimental measurements of swelling were correlated with the solubility parameter, ä (cal1/2 cm-3/2), which is based on the cohesive energy densities, c (cal/cm3), of the materials. Solvents that swelled PDMS the least included water, nitromethane, dimethyl sulfoxide, ethylene glycol, perfluorotributylamine, perfluorodecalin, acetonitrile, and propylene carbonate; solvents that swelled PDMS the most were diisopropylamine, triethylamine, pentane, and xylenes. Highly swelling solvents were useful for extracting contaminants from bulk PDMS and for changing the surface properties of PDMS. The feasibility of performing organic reactions in PDMS was demonstrated by performing a Diels-Alder reaction in a microchannel.

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