Compositions comprising free-standing two-dimensional nanocrystals

1. A polymer composite comprising an organic polymer and a MXene composition comprising at least one layer having first and second surfaces, each layer comprising:

a substantially two-dimensional array of crystal cells,

each crystal cell having an empirical formula of M n+1 X n , such that each X is positioned within an octahedral array of M,

wherein M is at least one Group IIIB, IVB, VB, or VIB metal, or Mn

wherein each X is C, N, or a combination thereof;

n=1, 2, or 3; and

wherein at least one of said surfaces of each layer has surface terminations comprising alkoxide, carboxylate, halide, hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, thiol, or a combination thereof.

2. The polymer composite of claim 1 , wherein the MXene composition comprise amounts in the range of about 0.1 wt % to about 50 wt %, relative to the combined weight of the polymer and MXene composition.

3. The polymer composite of claim 1 , wherein the organic polymers contains an aromatic or heteroaromatic monomer moiety.

4. The polymer composite of claim 3 , wherein the monomer moiety comprises at least one phenyl, biphenyl, pyridinyl, bipyridinyl, naphthyl, or pyrimidinyl moiety, or a combination thereof.

5. The polymer composite of claim 4 , wherein the organic polymers comprise a polyester, polyamide, polyethylene, polypropylene, polyethylenenaphthalate (PEN), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyether etherketone (PEEK), polyamide, polyaryletherketone (PAEK), polyethersulfone (PES), polyethylenenimine (PEI), poly (p-phenylene sulfide) (PPS), polyvinyl chloride (PVC), or fluorinated or perfluorinated polymer.

6. The polymer composite of claim 1 , wherein the polymer is an anisotropic polymer.

7. The polymer composite of claim 1 , in a form having a configuration defined by a two-dimensional plane, wherein the organic polymer is oriented coincident with the plane of the substantially two-dimensional array of crystal cells.

8. The polymer composite of claim 1 , wherein the substantially two-dimensional array of crystal cells defines a plane, and said plane is substantially aligned with the plane of the polymer composite.

9. The polymer composite of claim 1 , wherein the flexural strength, stiffness, or both flexural strength and stiffness in the planar dimension of the polymer composite is greater than the flexural strength, stiffness, or both flexural strength and stiffness of a corresponding polymer composite without the MXene composition of claim 1 .

10. The polymer composite of claim 1 , wherein the composition comprises an electrically conductive or semiconductive surface.

11. A stacked assembly of at least two layers, each layer having first and second surfaces, each layer comprising:

a substantially two-dimensional array of crystal cells,

each crystal cell having the empirical formula of M n+1 X n , such that each X is positioned within an octahedral array of M;

wherein M is at least one Group IIIB, IVB, VB, or VIB metal;

each X is C, N, or a combination thereof; and

n=1, 2, or 3;

wherein the layers are characterized as having an average surface area and an average interlayer distance; and

wherein at least one of said surfaces of each layer has bound thereto surface terminations comprising alkoxide, carboxylate, halide, hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, thiol, or a combination thereof; and

wherein the stacked assembly comprises a conductive outer surface, such the sheet or film is capable of exhibiting a surface resistivity of less than about 50 micro-ohm-meter.

12. The stacked assembly of claim 11 having a form of a sheet or film form, wherein the sheet or film exhibits at least 50% optical tranparency to at least one wavelength of light in a range of from about 250 nm to about 850 nm.

13. The stacked assembly of claim 12 , wherein the optical tranparency is in a range of from about 70% to about 95%.

14. The stacked assembly of claim 11 , further comprising atoms, ions, or both atoms and ions of lithium, sodium, potassium, magnesium, or a combination thereof intercalated between at least two of the layers.

15. The stacked assembly of claim 14 , comprising atoms, ions, or both atoms and ions of lithium intercalated between at least two of the layers.

16. A conductor comprising the stacked assembly of claim 11 .

17. A battery comprising the stacked assembly of claim 15 .

18. The stacked assembly of claim 11 , further comprising a molecule comprising C, H, N, O, S, or a combination thereof, and having a molecular weight less than about 250 daltons intercalated between at least two of the layers.

19. The stacked assembly of claim 18 , comprising a kaolinitic intercalator intercalated between at least two of the layers.

20. The stacked assembly of claim 19 , wherein the kaolinitic intercalator is hydrazine, dimethylsulfoxide, urea, N, N-dimethylformamide, or a combination thereof.

21. An energy storage device or electrode comprising the stacked assembly of claim 15 .