Monolayer film and hydrophilic material comprising the same

A method for producing stacks, comprising:

• a step of preparing a mixture including a monomer composition and a solvent, the monomer composition including a monomer (I) represented by General Formula (1) below and a polyvalent monomer (II) having two or more (meth)acryloyl groups and being free of sulfonic group, carboxyl group and phosphoric group in a monomer (I)/polyvalent monomer (II) molar ratio of 1/1000 to less than 1/30, the solvent including a compound with a solubility parameter a of not less than 9.3 (cal/cm3);
• a step of applying the mixture onto at least one surface of a substrate;
• a step of removing at least part of the solvent from the mixture applied;
• and
• a step of polymerizing the monomer (I) and the monomer (II) present in the mixture resulting from the above steps;
• the method thus producing a stack having a monolayer film on at least one surface of the substrate, the monolayer film having at least one anionic hydrophilic group selected from a sulfonic group, a carboxyl group and a phosphoric group, the anion concentration ratio (Sa/Da) of the anion concentration (Sa) at the outer surface of the monolayer film to the anion concentration (Da) at the middle point between the inner surface in contact with the substrate and the outer surface being not less than 1.1;
• [X]s[M1]1[M2]m (1)
• (in Formula (1), s indicates 1 or 2;
• 1 and m indicate integers satisfying s=l+m/2;
• M1 is at least one monovalent cation selected from hydrogen ion, ammonium ions and alkali metal ions;
• M2 is at least one divalent cation selected from alkaline earth metal ions;
• and
• X is at least one monovalent anion selected from groups represented by General Formulae (1-1) to (1-4) below:
• (in Formulae (1-1) to (1-4), J and J′ are each independently H or CH3;
• n indicates 0 or 1;
• and Rs are each independently an aliphatic hydrocarbon group of 1 to 600 carbon atoms optionally substituted at a carbon atom with at least one group selected from aromatic groups, aliphatic cyclic groups, ether groups and ester groups)).