A filler fluid for a fluidic device, comprising: a silicone oil which is or comprises polydimethylsiloxane (PDMS); and a siloxane block co-polymer solubilized in the silicone oil, wherein less than 0.1% of the volume fraction of the siloxane block co-polymer in the filler fluid is miscible with an aqueous liquid selected from water and other aqueous buffers; and further, wherein the siloxane block co-polymer is selected from the group consisting of: dimethylsiloxane-(45-50% ethylene oxide) block co-polymer, dimethylsiloxane-(30-35% ethylene oxide) block co-polymer, (35% hydroxyethylene oxypropylmethylsiloxane)-(dimethylsiloxane) co-polymer, (hydroxyethyleneoxypropylmethylsiloxane)-(3,4-dimethoxyphenylpropyl)methylsiloxane-dimethylsiloxane terpolymer, poly(dimethylsiloxane), monoglycidyl ether terminated, poly(dimethylsiloxane), bis(hydroxyalkyl) terminated, Poly(dimethylsiloxane), hydroxy terminated, monocarbinol terminated polydimethylsiloxane, asymmetric, dodecylmethylsiloxane-hydroxypolyalkyleneoxypropyl methylsiloxane co-polymer, (60-70% dodecylmethylsiloxane)-(30-40% 2-phenylpropylmethylsiloxane) co-polymer, wherein n ≥ 10, poly(dimethylsiloxane), hydroxy terminated, silanol terminated polytrifluoropropylmethylsiloxane, (15-20% tridecafluorooctylmethylsiloxane) - (80-85% dimethylsiloxane) co-polymer, poly(3,3,3-trifluoropropylmethylsiloxane). a silicone oil which is or comprises polydimethylsiloxane (PDMS); and a siloxane block co-polymer solubilized in the silicone oil, wherein less than 0.1% of the volume fraction of the siloxane block co-polymer in the filler fluid is miscible with an aqueous liquid selected from water and other aqueous buffers; and further, wherein the siloxane block co-polymer is selected from the group consisting of: dimethylsiloxane-(45-50% ethylene oxide) block co-polymer, dimethylsiloxane-(30-35% ethylene oxide) block co-polymer, (35% hydroxyethylene oxypropylmethylsiloxane)-(dimethylsiloxane) co-polymer, (hydroxyethyleneoxypropylmethylsiloxane)-(3,4-dimethoxyphenylpropyl)methylsiloxane-dimethylsiloxane terpolymer, poly(dimethylsiloxane), monoglycidyl ether terminated, poly(dimethylsiloxane), bis(hydroxyalkyl) terminated, Poly(dimethylsiloxane), hydroxy terminated, monocarbinol terminated polydimethylsiloxane, asymmetric, dodecylmethylsiloxane-hydroxypolyalkyleneoxypropyl methylsiloxane co-polymer, (60-70% dodecylmethylsiloxane)-(30-40% 2-phenylpropylmethylsiloxane) co-polymer, wherein n ≥ 10, poly(dimethylsiloxane), hydroxy terminated, silanol terminated polytrifluoropropylmethylsiloxane, (15-20% tridecafluorooctylmethylsiloxane) - (80-85% dimethylsiloxane) co-polymer, poly(3,3,3-trifluoropropylmethylsiloxane). dimethylsiloxane-(45-50% ethylene oxide) block co-polymer, dimethylsiloxane-(30-35% ethylene oxide) block co-polymer, (35% hydroxyethylene oxypropylmethylsiloxane)-(dimethylsiloxane) co-polymer, (hydroxyethyleneoxypropylmethylsiloxane)-(3,4-dimethoxyphenylpropyl)methylsiloxane-dimethylsiloxane terpolymer, poly(dimethylsiloxane), monoglycidyl ether terminated, poly(dimethylsiloxane), bis(hydroxyalkyl) terminated, Poly(dimethylsiloxane), hydroxy terminated, monocarbinol terminated polydimethylsiloxane, asymmetric, dodecylmethylsiloxane-hydroxypolyalkyleneoxypropyl methylsiloxane co-polymer, (60-70% dodecylmethylsiloxane)-(30-40% 2-phenylpropylmethylsiloxane) co-polymer, wherein n ≥ 10, poly(dimethylsiloxane), hydroxy terminated, silanol terminated polytrifluoropropylmethylsiloxane, (15-20% tridecafluorooctylmethylsiloxane) - (80-85% dimethylsiloxane) co-polymer, poly(3,3,3-trifluoropropylmethylsiloxane).