A factorial design approach to fracture pressure tests of microfluidic BF33 and D263T glass chips with side-port capillary connections

The pressure stability of microfluidic glass chips was tested experimentally, with a special focus on the inserts for glued capillary connections. Destructive high-pressure experiments with demineralized water conducted at room temperature showed a difference in mean fracture pressure between the two tested glass types BF33 and D263T, with values of 192  ±  25 and 159  ±  25 bar, respectively. For BF33, hydrofluoric acid (HF) etching of the powder blasted (abrasive jet machined) chip insert increased the mean fracture pressure with 43  ±  9 bar, whilst for D263T a decrease of  −22  ±  8 bar resulted. Contrary to the expected surface smoothening of the HF treatment, a rougher surface was obtained, particularly for the case of D263T, which is thought to be due to the opening of median (radial) cracks caused by the powder impact during the blasting process. The roughness obscures the effect of the tapering of the insert, preventing that factor from having a statistically significant effect on the mean fracture pressure. Nevertheless, a decrease in the mean fracture pressure and a decrease in the variance of the mean fracture pressure was observed when a taper is introduced, whereas the fracture location tends to move away from the insert-microchannel intersection towards the glue meniscus. A practical solution for cases where a high-pressure stability is required is found in applying a metal clamp around the capillary insert section. This significantly increased the fracture pressure of the chip insert section with 50  ±  21 bar, by preventing bond release.