term u201c polysiloxane u201d has the ordinary meaning understood by one of ordinary skill in the art in some embodiments the term u201c polysiloxane u201d refers to a polymer comprising siloxane repeat units the term u201c siloxane u201d has the ordinary meaning understood by one of ordinary skill in the art in some embodiments the term u201c siloxane u201d refers to a unit comprising u2014 si u2014 o u2014 where the silicon atom may bear two groups selected from hydrogen and a hydrocarbon group poly dimethylsiloxane is an example of a polysiloxane as used herein the term u201c block copolymer u201d has the ordinary meaning understood by one of ordinary skill in the art see e g r j young u201c introduction to polymers u201d chapman and hall new york 1981 pp 64 66 in some embodiments the term u201c block copolymer u201d refers to a copolymer comprising at least two distinct homopolymer blocks joined to one another e g joined end to end by covalent bonding the term u201c polymer block u201d has the ordinary meaning understood by one of ordinary skill in the art in some embodiments the term u201c polymer block u201d refers to a portion of homopolymer that constitutes a block within a block copolymer as used herein the term u201c triblock copolymer u201d has the ordinary meaning understood by one of ordinary skill in the art in some embodiments the term u201c triblock.