A fullerene derivative, used as a lubricant, includes, in a molecule: a fullerene backbone; and n pyrrolidine rings each being condensed to the fullerene backbone, each of the pyrrolidine rings including one aryl group including a group including m perfluoropolyether chains, m being an integer from 2 to 5 and n being an integer from 1 to 5.

A lubricant including an ionic liquid, which includes a conjugate acid (B.sup.+) and a conjugate base (X.sup.), and is protic, wherein the conjugate acid includes a straight-chain hydrocarbon group having 10 or more carbon atoms, and wherein the conjugate base is represented by the following general formula (1): ##STR00001##
where n is an integer of from 0 to 6 in the general formula (1).

A lubricant including an ionic liquid, which includes a conjugate acid (B.sup.+) and a conjugate base (X.sup.), and is protic, wherein the conjugate acid includes a straight-chain hydrocarbon group having 10 or more carbon atoms, and wherein the conjugate base is represented by the following general formula (1): ##STR00001##
where n is an integer of from 0 to 6 in the general formula (1).

A lubricant including an ionic liquid, which includes a conjugate acid (B.sup.+) and a conjugate base (X.sup.), and is protic, wherein the ionic liquid is represented by the following general formula (1): ##STR00001##
where R.sup.1 and R.sup.2 each represent a hydrogen atom or R.sup.1 and R.sup.2 form a benzene ring together with carbon atoms to which R.sup.1 and R.sup.2 are bonded, and R.sup.3 represents a straight-chain hydrocarbon group having 10 or more carbon atoms in the general formula (1).

A lubricant including an ionic liquid, which includes a conjugate acid (B.sup.+) and a conjugate base (X.sup.), and is protic, wherein the ionic liquid is represented by the following general formula (1): ##STR00001##
where R.sup.1 and R.sup.2 each represent a hydrogen atom or R.sup.1 and R.sup.2 form a benzene ring together with carbon atoms to which R.sup.1 and R.sup.2 are bonded, and R.sup.3 represents a straight-chain hydrocarbon group having 10 or more carbon atoms in the general formula (1).

A carbon dioxide/co-fluid mixture is provided for use in a refrigeration cycle in which the carbon dioxide is alternately absorbed and desorbed from the co-fluid. Suitable co-fluids are selected from the class of alkoxylated carboxylic amides, wherein the amides are cyclic or non-cyclic. It has been discovered that N-2,5,8,11-tetraoxadodecyl-2-pyrrolidinone and its homologs exhibit an advantageous property of a high rate of desorption at lower temperatures.

A carbon dioxide/co-fluid mixture is provided for use in a refrigeration cycle in which the carbon dioxide is alternately absorbed and desorbed from the co-fluid. Suitable co-fluids are selected from the class of alkoxylated carboxylic amides, wherein the amides are cyclic or non-cyclic. It has been discovered that N-2,5,8,11-tetraoxadodecyl-2-pyrrolidinone and its homologs exhibit an advantageous property of a high rate of desorption at lower temperatures.

A lubricant, which includes an ionic liquid including a conjugate base and a conjugate acid including 2 or more cations in a molecule of the conjugate acid, wherein the conjugate acid includes a monovalent group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and an acid that is a source of the conjugate base has a pKa in acetonitrile of 10 or less.

A lubricant, which includes an ionic liquid including a conjugate base and a conjugate acid including 2 or more cations in a molecule of the conjugate acid, wherein the conjugate acid includes a monovalent group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and an acid that is a source of the conjugate base has a pKa in acetonitrile of 10 or less.

A lubricant including an ionic liquid including a conjugate base and a conjugate acid, wherein the conjugate acid includes a straight-chain hydrocarbon group having 6 or greater carbon atoms and a straight chain hydrocarbon group s having 6 or greater but 14 or less carbon atoms, and wherein a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less.