INCREASING TRANSPARENCY OF NANOFIBER SHEETS

1 . A method comprising:

drawing a first nanofiber sheet from a nanofiber forest, the first nanofiber sheet having a fixed end integral with the nanofiber forest and a free end opposite the fixed end, wherein a plurality of nanofibers of the first nanofiber sheet are aligned with a drawing direction of the first nanofiber sheet; attaching a strain element to the free end;

applying strain to the free end by elongating the strain element in a direction not parallel to the alignment of the nanofibers;

attaching the strained free end of the nanofiber sheet to a support, the support maintaining the applied strain in the first nanofiber sheet;

removing the first nanofiber sheet from the nanofiber forest; and

stacking a second nanofiber sheet on the first nanofiber sheet.

2 . The method of claim 1 , further comprising:

drawing the second nanofiber sheet from the nanofiber forest, the second nanofiber sheet having a second fixed end integral with the nanofiber forest and a second free end opposite the second fixed end, wherein a plurality of nanofibers of the second nanofiber sheet are aligned with the drawing direction of the second nanofiber sheet;

attaching the strain element to the second free end;

applying strain to the second free end by elongating the strain element in a second direction not parallel to the orientation of the nanofibers;

attaching the second strained, free end of the second nanofiber sheet to a second support, the second support maintaining the applied strain in the second nanofiber sheet; and

removing the second nanofiber sheet from the nanofiber forest.

3 . The method of claim 1 , further comprising forming a plurality of gaps in one or both of the first nanofiber sheet and the second nanofiber sheet in response to applying the strain.

4 . The method of claim 3 ,

wherein an average gap size of the gaps is from 8 microns on a side to 45 microns on a side, and

wherein:

applying the strain to the first nanofiber sheet and the second nanofiber sheet comprises straining each sheet by a factor of 3; and

a transparency of the stacked first nanofiber sheet and the second nanofiber sheet to radiation in the visible spectrum is 90%.

5 . (canceled)

6 . The method of claim 2 , wherein a transparency of the stack of the first nanofiber sheet and the second nanofiber sheet to radiation having a wavelength of 550 nm is from 72% to 88%.

7 . The method of claim 2 , wherein the first nanofiber sheet and the second nanofiber sheet are stacked relative to have their corresponding nanofiber alignment directions not parallel to one another.

8 . The method of claim 1 , wherein an angle between nanofiber alignment directions of the first nanofiber sheet and the second nanofiber sheet are from 45° to 135°, excluding 0°.

9 . The method of claim 1 ,

wherein the second nanofiber sheet is in an as-drawn state, and

wherein the method further comprises densifying the second nanofiber sheet by exposing the second nanofiber sheet to a solvent and removing the solvent before the stacking.

10 . (canceled)

11 . A method comprising:

drawing a nanofiber sheet from a nanofiber forest, the nanofiber sheet having a fixed end integral with the nanofiber forest and a free end opposite the fixed end, wherein a plurality of nanofibers of the nanofiber sheet are aligned in a direction parallel to a drawing direction of the nanofiber sheet;

attaching a strain element to the free end;

applying strain to the free end by elongating the strain element in a direction not parallel to the alignment of the nanofibers; and

attaching the strained, free end of the nanofiber sheet to a support, the support maintaining the applied strain in the nanofiber sheet.

12 . The method of claim 11 , further comprising removing the strain element from the strained free end.

13 . The method of claim 11 , further comprising applying the method of claim 11 to the fixed end of the nanofiber sheet.

14 . The method of claim 13 , further comprising severing the fixed end from the nanofiber forest after applying the strain to the fixed end.

15 . The method of claim 11 , wherein the strain is applied in a direction from 45° to 135° relative to the direction of alignment of the nanofibers within the nanofiber sheet.

16 . The method of claim 11 , wherein the nanofiber sheet has a first width prior to straining and a second width after straining, the second width greater than the first width.

17 . The method of claim 16 , wherein the second width is from 2.5 times to 3 times the first width.

18 . The method of claim 16 , wherein a transparency to radiation having a wavelength of 550 nm is at least 80%.

19 . A transparent nanofiber sheet produced by a method comprising:

drawing a nanofiber sheet from a nanofiber forest in a drawing direction, the nanofiber sheet having a fixed end integral with the nanofiber forest and a free end opposite of the fixed end, wherein a plurality of nanofibers of the nanofiber sheet is aligned in an alignment direction that is parallel with the drawing direction;

attaching a strain element to the free end;

elongating the strain element in a direction different from the alignment direction, such that a width of the free end is increased to be larger than a width of the fixed end;

attaching the elongated free end to an inelastic support; and

removing the nanofiber sheet from the nanofiber forest.

20 . The transparent nanofiber sheet produced by the method of claim 19 , wherein the width of the free end is 2.5 times to 3 times wider than the width of the fixed end.

21 . The transparent nanofiber sheet produced by the method of claim 19 , wherein the width of the free end is 1.5 times to 2 times wider than the width of the fixed end.

22 . The transparent nanofiber sheet produced by the method of claim 19 , wherein the width of the free end is 1.1 times to 2.5 times wider than the width of the fixed end.

23 . The transparent nanofiber sheet produced by the method of claim 19 , wherein a transparency in a visible radiation spectrum of the free end of the nanofiber sheet is 10% to 15% greater than the fixed end of the nanofiber sheet.

24 . The transparent nanofiber sheet produced by the method of claim 19 , wherein the plurality of nanofibers includes multi-walled nanofibers.

25 . The transparent nanofiber sheet produced by the method of claim 19 ,

wherein the produced transparent nanofiber sheet includes:

a first end having a first width;

a second end having a second width that is greater than the first width; and

the inelastic support attached to the second end, the inelastic support configured to maintain a strain applied to the second end, wherein the strain is applied in a strain direction different from the alignment direction of the plurality of nanofibers forming the nanofiber sheet,

wherein a transparency in a visible radiation spectrum of the second end of the nanofiber sheet is greater than the first end of the nanofiber sheet.