Square Corner Technique

The use of the square comer technique with its conservative answers (sometimes by a factor of two or more) tends to indicate problems where there are none and may result in wasting investment and operating capital for unnecessary expansion loops. 

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It is worth remembering that microfluidic channels do not have to be straight but can be curved or serpentine in shape, especially when accommodation of longer channels/ columns is required. Even square cornered ones exist °. A new fabrication technique which enables the manufacture of raised canal-like channels on chips has been reported by Sandia National Laboratories ... 

Multiple column switching has been made possible by the construction of a cyclic CE microstructure in which four channels that are 20 mm in length are arranged to form a square, as illustrated in Figure 8.20.62 Two channels at each corner connect the loop to external reservoirs filled with separation buffer. Platinum electrodes are inserted into the reservoirs for the application of high voltages. One side of the device has a volume-defined injection scheme incorporated into it. The overall technique is called synchronized cyclic capillary electrophoresis.63... 

Real bonded joints are unavoidably formed with a fillet of adhesive spew at the overlap ends (Fig. 4.10(a)). Even if this is removed, some slight amount of adhesive still remains and truly sharp corners are not encountered. It is in these regions of maximum stress, where failure is initiated, that most analyses are remote from reality, and here Adams and co-workers at Bristol University have been amongst the main investigators, using finite-element techniques(5). Indeed the adherend corner is likely to be rounded rather than truly square, which actually has the effect of reducing stress concentrations in the adhesive layer. Joint failure begins in these spew fillets of adhesive... 

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