Anisotropic wetting behavior on one-dimensional patterned surfaces for applications to microfluidic devices

A method for using a pattern to control fluid flow, the method comprising:

• depositing a photosensitive film stack over a substrate;
• forming a macroscopic pattern on the film stack, the macroscopic pattern comprising a plurality of rectangular shaped structures, wherein the plurality of rectangular shaped structures delineate a top surface of the macroscopic pattern from a surface of the substrate, each of the plurality of rectangular shaped structures comprising substantially vertical walls having a height of about 100 nm to about 10 μm and wherein the shape of the macroscopic pattern, the height of the substantially vertical walls, and a surface chemistry of the top surface controls anisotropic wetting at the top surface of the rectangular structures;
• delimiting the macroscopic pattern comprising the plurality of rectangular shaped structures, wherein a periphery of the macroscopic pattern is surrounded by a hydrophobic region to direct a fluid to the macroscopic pattern;
• and
• tuning the anisotropic wetting at the top surface of the rectangular structures to guide the fluid flow on top of the pattern, wherein the fluid flow is controlled using one or more of gravity, electric field, and magnetic field.

A method of confining liquid in limited area structures, the method comprising:

• depositing a photosensitive film stack over a substrate;
• forming a pattern on the film stack, the pattern comprising a plurality of rectangular shaped structures, wherein the plurality of rectangular shaped structures delineate a top surface of the pattern from a surface of the substrate, each of the plurality of rectangular shaped structures comprising substantially vertical walls having a height of about 100 nm to about 10 μm and wherein a shape of the macroscopic pattern, the height of the substantially vertical walls, and a surface chemistry of the top surface controls anisotropic wetting at the top surface of the rectangular structures;
• delimiting the pattern comprising the plurality of rectangular shaped structures, wherein a periphery of the pattern is surrounded by a hydrophobic region to direct a fluid to the pattern;
• and
• tuning the anisotropic wetting at the top surface of the rectangular structures to guide the fluid flow on top of the pattern;
• and
• immersing and removing the substrate in a liquid bath, wherein upon removal the liquid is confined only to the pattern.

A method of segregating particles comprising:

• providing an anisotropic hydrophobic surface comprising a pattern, a periphery of the pattern surrounded by a hydrophobic region to direct a fluid to the pattern, the pattern comprising a plurality of rectangular shaped structures, wherein the plurality of rectangular shaped structures delineate a top surface of the pattern from a surface of the substrate, each of the plurality of rectangular shaped structures comprising substantially vertical walls having a height of about 100 nm to about 10 μm and wherein the shape of the macroscopic pattern, the height of the substantially vertical walls, and a surface chemistry of the top surface controls anisotropic wetting at the top surface of the rectangular structures;
• providing a liquid comprising colloidal particles over the anisotropic hydrophobic surface, such that the liquid spreads out widely with a low vertical height and enlarged contact lines with two circular ends;
• and
• evaporating the liquid over the anisotropic hydrophobic surface, wherein the liquid evaporates with an initial decrease of the contact angle with only a small change of the contact line, such that a wide band of particles can be deposited at the two circular ends and narrow band along the contact line connecting the two circular ends.