DOI: 10 - Royal Society of Chemistry

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Resistance test to confirm removal of the parent PC support. ... the original α-(BEDT-TTF)2I3/PC film through surface tension; the conducting side of the.
Electronic Supplementary Material (ESI) for Materials Horizons. This journal is © The Royal Society of Chemistry 2014

Electronic Supplementary Information for Silk/Molecular Conductor Bilayer Thin-Films: Properties and Sensing Functions Eden Steven, Victor Lebedev, Elena Laukhina, Concepció Rovira, Vladimir Laukhin, James S. Brooks, and Jaume Veciana I.

Non-homogeneous formations of BEDT-TTF crystals on Bombyx mori silk.

Figure S1. Formations of BEDT-TTF crystals after immersion into BEDT-TTF/formic acid solutions: (a) for the case of a Bombyx mori silk film, and (b) for the case of a Bombyx mori silk fiber. In both cases, crystals form outside the host substrate, indicating the insolubility of BEDT-TTF in either processed or natural silk materials.



Experimental details on the face-down layer transfer.

Figure S2. Outline of the first stage of the face-down layer transfer of the strain sensing (BEDT-TTF)2I3-based layer. (a) The target silk film was cut to a desired size. (b, c) The cut silk film was dipped into a bath of silk solution for 1 second to coat both sides of the silk film and removed immediately. (d, e) Position the solution coated silk film on a glass petri-dish and remove excess solution by tapping both sides of the silk film against the glass surface. (f) Lay the wet silk film on the glass surface and position the bilayer film on top of the silk film with conducting side facing the silk film. Optional: the bilayer film can be pre-treated by argon plasma for 10 seconds to improve homogenous adhesion to the silk film. The plasma treatment does not influence the quality of the conducting layer as confirmed by resistance measurement before and after the plasma treatment. (g, h) The bilayer film is carefully laid on wet silk film and laminate using smooth PTFE. It is important to make sure that the excess silk solution is removed before lamination in order to prevent the silk solution from spilling over the top of the PC film. (i) The laminated film is then dried at 23 oC for at least 1 hour before proceeding with PC removal process.


Figure S3. Outline of the second stage of the face-down layer transfer of the strain sensing (BEDT-TTF)2I3-based layer. (a) A photograph of the silk/conducting (BEDT-TTF)2I3 layer/polycarbonate “sandwich” dried at 23 oC. (b,c) Removal of PC using drops of DCM. (d) Resistance test to confirm removal of the parent PC support. (e) Peel-off of the silk film covered with the transferred conductive (BEDT-TTF)2I3 layer (new BL film) from the bottom of the Petri-dish. (f) The new BL film stored between 2 glass slides to maintain flatness.

Figure S4. Photographs showing the gradual removal of the parent polycarbonate substrate by washing with DCM; the images were monitored using an optical microscope (Olympus BX51).



Experimental details on face-down conducting layer deposition to paper


Figure S5. Face-down deposition of conducting -(BEDT-TTF)2I3 layer on paper substrates. (a) First the target paper substrate is wet with water which promotes preliminary adherence of the original -(BEDT-TTF)2I3/PC film through surface tension; the conducting side of the original film faces down. (b) While the paper is still wet, DCM was poured over the PC film where the PC dissolves away into the underlying paper substrate, leaving the conducting (BEDT-TTF)2I3 crystallites in intimate contact with the paper substrate. To minimize the amount of PC residue in the paper, multiple layers of absorbent may be placed underneath the paper substrate. The process can be repeated for multi-layer deposition. (c) Photograph of first layer deposition, where adherence of crystallites to the fibrous textured paper is observed. (d) Photograph of second layer deposition, showing less influence of the paper texture on the


crystallite network morphology. The electrical resistance is greatly reduced after the second layer deposition.

Figure S6. Electronic and electromechanical properties of (BEDT-TTF)2I3-covered paper produced via face-down layer transfer approach. (a) Temperature dependence of the normalized resistance of the original -(BEDT-TTF)2I3 on PC (solid line) and the deposited mixed double layered - and -(BEDT-TTF)2I3 on paper (dash line). (b) Resistance changes of the -(BEDT-TTF)2I3/paper BL film with time upon an application of 7 cycles of monoaxial elongations performed at a strain rate of 0.3 m/s. A slight drift in the resistance was observed due to a slight self-heating caused by the application of a 10 A current. The gauge factor is determined to be 5.2.



Experimental details on the face-up layer transfer.

Figure S7. Outline of the first stage of the face-up layer transfer of the strain sensing (BEDTTTF)2I3-based layer. (a) A target glass slide substrate placed on a PTFE-based plate. (b) DCM pool on the glass slide. (c) Placement of the BL film on the surface of the DCM pool (conducting side up). (d) BL film floating on the DCM pool. (e) Removal of DCM with dissolved PC using an absorbent. (f) Transferred all-organic conductive sensing (BEDTTTF)2I3 layer on the glass slide. Conductive sensing (BEDT-TTF)2I3 layer transferred on: (g) spherical glass and plastic surfaces; (h) a glass cylinder; and (i) a flat PDMS surface. It should be noted that if a thinner PC-based under-layer is desired for the transferred organic conductive sensing layer, pre-thinning can be done prior to the transfer to the receiving substrate.


Figure S8. Procedures of BL film pre-thinning for face-up layer transfer. (a) BL film on the surface of a DCM pool. (b) Removal of dissolved PC with an absorbent. (c) Peeling-off of the thinned BL film using a sharp edge. (d) Wetting of a cylindrical stainless steel rod. (e) Placement of the thinned BL film with the conductive sensing (BEDT-TTF)2I3 layer up followed by removal of DCM using an absorbent. (f) The cylindrical stainless steel rod covered with the thinned PC under-layer/transferred conductive sensing (BEDT-TTF)2I3 layer.



Humidity dependent resistance simulation.

Figure S9. Humidity dependent measurement setup. The BL film has length, width, and thickness of 2000 m, 1500 m, and 40 m, respectively. Due to the hydrophobicity of the sensing layer and the hygroscopicity of the silk layer, moisture mainly diffuses from the silk layer. Within the thin film limit, we therefore consider a 1-D moisture diffusion process.

Figure S10. Rapid humidity response of Bombyx mori silk / -(BEDT-TTF)2I3 at RH maximum sweep rate of 0.125 % / s up to 75 % RH. The RH oscillation is due to the humidity chamber stabilization. Dotted lines: RC-circuit model fitting using the time constant of 645 seconds found from the slower humidity sweep rate (~ 0.025 % / s) data in Figure 4a. As seen from the figure, although the fast time dependence follows reasonably well, the overall magnitude is less accurate, indicating a humidity response beyond the simple RC-circuit model. 8



Movie S1. Silk/-(BEDT-TTF)2I3 electric current-driven actuator. The movie view is recorded parallel to the in-plane direction of the bilayer film (12 mm × 2 mm × 40 m), where the active and silk layers are facing down and up, respectively. In the first part of the movie, a 500 A current ( 22 mW power) is used to heat the active layer (facing down) at 45 % RH and 23 oC, driving moisture out through the silk layer (facing up). The heat generated induces asymmetric shrinkage that causes the film to flex toward the silk side. As the current is turned off, the silk layer reabsorbs moisture from the environment which causes it to swell back to its original state. This relaxation process, however, is significantly slower than the flexing due to diffusion-limited moisture absorption in the Bombyx mori silk film. A more dramatic flexing is possible by increasing the operating current to 800 A (58 mW) as shown in the second part of the movie.

Movie S2. Electronic monitoring of face-down transferred -(BEDT-TTF)2I3 layer on a curved surface of a flexible pipette. In the first part of the movie, the resistance is monitored with respect to bending. In the second part, the pipette is sealed and the resistance is monitored with respect to increasing/decreasing air pressures.