# Photo-Aligned Nematic Liquid Crystals Enable the Modulation of Thermoplasmonic Heating
## 2 Materials and Methods  
Synthesis of spherical gold nanoparticles: Spherical gold nanoparticles have been prepared according to the conventional Turkevich method [25]. This is the most commonly used approach for the synthesis of size-defined spherical gold nanoparticles through chemical reduction by sodium citrate. Briefly, in a round-bottomed flask, 600 mL of an aqueous solution of tetrachloroauric (III) acid (0.25 mM) were brought to boiling under vigorous magnetic stirring. When the boiling temperature was reached, the gold has been reduced by quickly adding 15 mL of aqueous sodium citrate solution (0.03 M). In about 15 min, the solution colour slowly turned from yellow to deep red, as a result of the full reduction of the gold salt into monodisperse gold nanoparticles with an average diameter of 20 nm. The reaction was then removed from the hot oil bath and allowed to cool down to room temperature overnight.  
Functionalization of substrates: The glass substrates were cleaned and hydroxylated with piranko solution (3:1 mixture of sulphuric acid to hydrogen peroxide 30%) for 30 min. Then, the substrates were rinsed several times, first with distilled water and then with milli-Q water before being dried under nitrogen flow. To alter the surface chemistry, the substrates were immersed in a 5% (\(v/v\)) solution of N-[3-(trimethoxysilyl)propyl] ethylenediamine in ethanol for 30 min and then rinsed with milli-Q water. Excess of water was removed using a stream of nitrogen followed by drying in a furnace at 120 \({}^{\circ}\)C for 30 min to assure good silanization.  
Gold nanoparticles arrays on planar substrates: Gold nanoparticles were deposited on glass slides by immersing the functionalized substrates in the colloidal solution for two and a half hours. The gold covered substrates were then washed with milli-Q water and dried under a stream of nitrogen.  
Deposition of the photoaligning material: PAAD-27 by BeamCo. dissolved in dimethyl-formamide (C\({}_{3}\)H\({}_{7}\)NO), which possesses a broad absorption band centered at 415 nm, has been deposited by means of a spin coater (2000 rpm for 30 s). A polarized UV lamp (\(\lambda\) = 395 nm; \(I\) = 30 mW/cm\({}^{2}\)) is used for a suitable time interval (typically 7 min) to reorient the PAAD-27 molecules perpendicularly to its polarization direction. The characteristics average polar anchoring energies of nematic LC on PAAD materials (Beamco., Orlando, FL, USA) are \(\approx\)10\({}^{-2}\) J/m\({}^{2}\), a weaker alignment than on polyimide layer [26].  
Preparation of the sample cell: The thermotropic nematic liquid crystal (NLC) E7, by Merck has been used. The sample cell was fabricated by gluing together a functionalizedglass slide and the PAAD-27 coated AuNPs monolayer, spaced by 10 \(\upmu\)m glass microspheres. The NLC has been then introduced by means of capillary flow. The surface of the glass substrate is covered with a thin organic film, such as polyimide (PI-AL1454 by JSR), using a spin coating (4000 rpm, 60 s) deposition technique. After the deposition of the coating film, a cloth (velvet) with short fibers is moved over the surface to create microgrooves that make the surface unidirectionally anisotropic. The rubbing process induces a specific orientation of the polymer molecules, which is transmitted to the LC molecules anchored on the substrates; moreover, this kind of orientational order propagates in the bulk of the LC molecules via intermolecular forces [27].  
Thermographic analysis: The thermographic analysis has been performed by means of a thermocamera (E40 by FLIR), which is characterized by a sensitivity of 0.07 \({}^{\circ}\)C and a spatial resolution of 2.72 mrad. The steady-state condition was reached after about 5 min of exposure of the sample cell to a green laser beam (\(\lambda\) = 532 nm) --Verdi G-Series by Coherent, linearly polarized--polarization direction: vertical, \(\pm 5^{\circ}\), when no further temperature variations were detected in the limit of the thermo-camera sensitivity.