Metal oxide particles surface modified with quaternary ammonium group, and method for producing same

A metal oxide particle having a surface modified with a silyl group and having an aggregation ratio (average particle size measured by dynamic light scattering/average diameter of primary particles measured in an SEM image) of 5.0 or less,

• the silyl group being at least one group selected from the group consisting of a silyl group represented by general formula (1):
• —Si(X)n-[L-CR1(OH)—C(R2)2-A]3-n (1),
• wherein
• X is the same or different, and each represents a hydroxy group, a hydrolyzable substituent, a non-hydrolyzable substituent, a bond with Si of another silyl group via —O—, or a bond with a metal atom on the particle surface via —O—;
• n is 0, 1, or 2;
• L is a linkage group;
• R1 is a hydrogen atom, or an alkyl group that may contain an amino group, a hydroxy group, or an unsaturated bond;
• R2 is the same or different, and each represents a hydrogen atom, or an alkyl group that may contain an amino group, a hydroxy group, or an unsaturated bond;
• and
• A is a quaternary ammonium group, and
• a silyl group represented by general formula (2):
• wherein
• X′ is the same or different, and each represents a hydroxy group, a hydrolyzable substituent, a non-hydrolyzable substituent, a bond with Si of another silyl group via —O—, or a bond with a metal atom on the particle surface via —O—;
• n′ is 0, 1, or 2;
• L′ is a linkage group;
• and
• A′ is a quaternary ammonium group.