PEDOT/PSS-Halloysite Nanotubes (HNTs) Hybrid Films: Insulating HNTs Enhance Conductivity of the PEDOT/PSS Films

We have for the first time found that completely insulating Halloysite nanotubes (HNTs) significantly enhance electrical conductivity of PEDOT/PSS films by simply mixing. Based on this accident finding we have created highly porous and conductive PEDOT/PSS films hybridized with the HNTs. Through further optimization of the mixing condition we have obtained flexible and conductive hybrid films with high specific surface area. Based on experimental evidences we proposed a plausible mechanism of the phenomenon where the PEDOT/PSS colloidal particle with particle size of several tens nanometers well pack at the nano-channels into well-ordered structures of PEDOT/PSS particles, which show conductivity as higher as several order of magnitude than that of PEDOT/PSS particles in outside of the HNTs.


Preparation of flexible PEDOT/PSSHNTs hybrid films:
To improve the flexibility of the hybrid films certain amount (10.1, 35.1, 59.0, 81.6 mg) of polyethylene glycol (PEG), certain amount (correspondingly 44.1, 47.4, 46.7, 45.0 mg, which keeps 4% in the total mixture including the PEDOT/PSS dispersion) was added to the certain amount (correspondingly 1052.8, 1129.2, 1121.5, 1081.4 mg) of the PEDOT/PSS dispersion and the films were prepared in the same with Section 1. The films were further treated with the FA in the same with Section 3.

Measurements of electrical conductivity:
The sheet resistance of the films was measured by a standard four-probe method with a Resistivity Meter (Loresta GP Model MCP-T610). The thickness was measured with a micrometer. The electrical conductivity was calculated from the equation (1): (1) Where σ, Rs and d are conductivity, sheet resistance and thickness of the film, respectively. For every sample the sheet resistance and thickness were at four different d R S ⋅ = 1 σ positions and the values were averaged. We conducted the experiment where correlation between conductivity and HNTs-content of the hybrid films for five times.
For the EG-treated hybrid films the experiments and measurements were conducted in the same manner but only one time. The result was shown in Fig. S3C.
For the FA-treated hybrid films the experiments and measurements were conducted in the same manner. All results were shown in Fig. S1. We averaged the values of six experiments and newly presented in Fig. S3D.

SEM measurements:
SEM images of the HNTs and the hybrid films were observed by a scanning electron microscope (SEM, JEM-2100cx). The specimen was sputtered with gold before the observations.

XRD Measurements:
XRD patterns were obtained using a X-ray powder diffractometer (Bruker AXS, D8 ADVANCE). Powdered sample of HNTs was studied by placing a thin layer in conventional cavity mounts while the films were adhered on the cavity mount. The samples were scanned from 0-80° in 2θ. The Cu anode X-ray was operated to give monochromatic Cu Kα X-rays (λ=1.5418 angstrom).

TEMEDX Measurements:
TEM images and EDX spectra of the HNTs with or without PEDOT/PSS-treatment were measured by a transmission electron microscope (TEM, FEITECNAIG2). The specimen was prepared as follows: 43.5, mg of HNTs was dispersed in 1044.2 mg of the PEDOT/PSS dispersion (Clevios PH1000) and stirred for 24 h at room temperature. The HNTs were filtered and re-dispersed in the deionized water. The water dispersion of the HNTs was dropped on a copper grid and dried for the measurements. The pure HNTs were dispersed in deionized water. The dispersion containing HNTs was dropped on the copper grid and dried for the measurement.

BET Measurements:
BET measurements for surface area of pure HNTs and the hybrid films were conducted by a nitrogen adsorption technique using a NOVA 2000e Surface Area Analyser (Quantachrome), Moisture was removed from the samples prior to the surface area measurement (Fig S6)

UVVisNear IR Measurements:
UV-Vis-near IR spectra of the hybrid films were measured by reflectance mode with a UV-Vis-near IR spectroscope (Agilent AU12320005) in the wavelength range of 300-2500 nm. The PET sheet and air were used as the reference for the PEDOT/PSS film on PET sheet and the hybrid films, respectively (Fig. S7).

FTIR Measurements:
FT-IR spectra of the pure HNTs and the hybrid films were measured with a FT-IR spectrometer (Nicolet, NEXUS-470) by using pellet samples compressed with KBr. The spectra were shown in Fig. S7.

Stressstrain curve measurements:
Stress-strain curves of the film samples were measured with a mechanical tester (UTM2203) in stretching rate of 5 mm/min. Rectangular shape (8-13 mm in length; 7-10 mm in width; 0.01-0.05 mm in thickness) of the films were used for the measurements.
The results were shown in Fig. S6.