Variable charge films for controlling microfluidic flow

The device of claim 13 wherein at least 90% of the pH sensitive units are present in the region of the film between the solution-interface surface and the midpoint.

The device of claim 15 wherein the film has a solution-interface surface which contacts liquid in the microfluidic channel, a base surface contacting the interior wall and an imaginary midpoint between these surfaces wherein at least 75% of the zwitterionic repeat units are present in the region of the film between the solution-interface surface and the midpoint.

A process of derivatizing the surface of a microfluidic channel, the method comprising alternately passing solutions comprising positively charged and negatively charged polyelectrolytes through the microfluidic channel to form a polyelectrolyte film on the inner surface of the channel, the film having a thickness between about 1 and about 1000 nanometers and comprising an interpenetrating network of a predominantly positively charged polymer and a predominantly negatively charged polymer, the predominantly positively charged polymer, the predominantly negatively charged polymer or both contain (i) a pH insensitive positively or negatively charged repeat unit having a pKa greater than 9 or less than 3, and (ii) a pH sensitive repeat unit, the pH sensitive repeat unit having a pKa between 3 and 9 and complex in contact with the interior surface of a microfluidic channel whereby the pH of liquid in the microfluidic channel may be used to control the velocity or direction of electroosmotic flow of the liquid within said microfluidic channel.

A process of controlling the flow of liquid in a microfluidic channel, the process comprising changing the pH of liquid in the microfluidic channel to change the velocity or direction of flow of the liquid in the channel, wherein the microfluidic channel has an interior wall and a polyelectrolyte film on the interior wall whereby liquid carried by the channel contacts the polyelectrolyte film, and the polyelectrolyte film has a thickness between about 1 and about 1000 nanometers and comprises an interpenetrating network of a predominantly positively charged polymer and a predominantly negatively charged polymer, the predominantly positively charged polymer, the predominantly negatively charged polymer or both containing (i) a pH insensitive positively or negatively charged repeat unit having a pKa greater than 9 or less than 3, and (ii) a pH sensitive repeat unit, the pH sensitive repeat unit having a pKa of about 3 to 9.