Bonding of planar poly (methyl methacrylate) (PMMA) nanofluidic channels using thermal assisted ultrasonic bonding method

Abstract

Because of extremely small dimensions of nanochannels and low rigidity of polymer, most bonding techniques which are suitable for sealing polymer microscale channels (width and depth in tens to hundreds microns) are not competent for bonding of polymer nanochannels. In this study, a new thermal assisted ultrasonic bonding method for sealing poly (methyl methacrylate) (PMMA) nanochannels was presented. Substrates were preheated to 30-40°C lower than glass transition temperature (T g ) of the material by hot plate. Then low amplitude ultrasonic vibration was employed to generate facial heat at the interface of the substrates. Influences of preheating temperature on bonding strength and dimension loss were studied. The nanochannels were successfully bonded with depth loss less than 5.3% (10.6 nm) and bonding strength of 0.21 J/cm 2 at the preheating temperature of 70°C. Thermal assisted ultrasonic bonding is proven to be competent for bonding of polymer nanochannels with high bonding strength, low dimension loss and short bonding time.

Disposable microfluidic substrates: Transitioning from the research laboratory into the clinic

“…Direct bonding includes oxygen plasma activation, [114][115][116] UV/ozone surface treatment, 117 bonding, 52,118 UV-assisted bonding, 16,33,36,119 and ultrasonic welding. [120][121][122][123][124][125] Indirect bonding includes solvent bonding, 114,115,[126][127][128] adhesive bonding, 129,130 microwave, 131 and laser bonding. 132 From a production process perspective, indirect bonding methods are convenient but the main challenge is to prevent the intermediate layer, which are sometimes dispensed as a liquid, from clogging the microchannels during the bonding step.…”

Molding and bonding of thermoplastic microfluidic devices

“…However, this method has not been widely adopted for microfluidic fabrication because of an intrinsic disadvantage that it needs special design and fabrication of energy directors in the microscale to effectively focus ultrasonic energy. The fabrication cost, therefore, is highly increased especially when the energy directors are formed on the same substrate with microchannels as shown in In the past four years, Zhang and Luo have published a series of work on a promising ultrasonic bonding process for microfluidics fabrication [166][167][168][169][170]. In this method, ultrasonic energy has been introduced in a rapid bonding process of flat thermoplastic microfluidic substrates without micro energy director, as shown in Figure 2-16(a) [167].…”

“…In contrary to ultrasonic welding, there is no polymer melting involved in this new bonding method. The use of ultrasonic energy can be integrated into other well-known bonding methods, such as solvent bonding [166] and thermal bonding [168][169][170]…”

“…In recent research [167][168][169][170], ultrasonic energy has been introduced in rapid bonding of flat thermoplastic microfluidic substrates at low temperature. In contrary to microwave bonding [242][243][244] and ultrasonic welding [159,161,165], there is no polymer melting involved in this promising bonding process [167].…”

“…It was reported that the proposed thermal assisted ultrasonic bonding can ultrasonically bond PMMA substrates at temperature 20−30 °C lower than its Tg in tens of seconds with good bond strength and minor microchannel deformation [170]. Moreover, it was applicable to bond multilayer PMMA microfluidic [169] and planar nanofluidic devices [168]. The bonding principle is believed to be thermal diffusion with the assistance of ultrasonic oscillating force acting on the substrates instead of static compression force.…”