# Feasibility of Storing Latent Heat with Liquid Crystals. Proof of Concept at Lab Scale
## 2 Materials and Methods
### Liquid Crystal Characterization  
The liquid crystal behavior of the biphenyl acid derivative 10-BPhCOOH was characterized by polarized light microscopy using a Leica DMRB microscope equipped with a Mettler FP82 HT hot stage and a Mettler FP90 central processor, at 10 \({}^{\circ}\)C/min heating rate. As expected, a fan-shaped texture was observed in the temperature range 170 \({}^{\circ}\)C-249 \({}^{\circ}\)C that can be assigned to a smectic C (SmC) mesophase [17] (see Figure 6a). In addition, just before the clearing point (\(\sim\)249 \({}^{\circ}\)C), a nematic (N) mesophase was identified by its characteristic schlieren texture in a very short range of temperatures (0.5 \({}^{\circ}\)C) (see Figure 6b). The occurrence of this nematic mesophase was also observed by [PERSON] _et al._[14]. Consequently, due to the very short temperature range of this mesophase, in DSC scans displayed in section 3 only a peak of the combined transition SmC-N-I is observed.  
10-BPhCOOH was further characterized by differential scanning calorimetry (DSC) with a Q100 DSC of TA Instruments (TA-Instruments Walters L.L.C., New Castle, DE, USA), performing heating/cooling ramps between 60 \({}^{\circ}\)C and 270 \({}^{\circ}\)C both at 10 \({}^{\circ}\)C/min rate. Other scan rates were not tested because this material is crystalline and hence strong variations in thermal parameters (_i.e._, temperature and enthalpy of transitions) were not expected. Also thermogravimetric (TG) analyses were carried out with a Setaran Setsys Evolution TGA Thermobalance (SERATAM Instrumentation, Caluire-et-Cuire, Lyon, France) at increasing temperature from 25 \({}^{\circ}\)C to 550 \({}^{\circ}\)C at 10 \({}^{\circ}\)C/min constant rate by using Ar as inert gas at 50 mL/min. Heat capacity measurements were obtained by Temperature-Modulated Differential Scanning Calorimetry method using a DSC Q2000 V24 of TA Instruments (TA-Instruments Walters L.L.C., New Castle, DE, USA) and sapphire as reference. The technical details of the procedure are reported elsewhere [18] and the measurement conditions were as follows. At each single determination, the sample was first stabilized at the desired temperature for 5 min and then all heat inside the probe cell was removed. Afterwards, the sample was subjected to a modulated temperature with 0.5 K amplitude and 80 s angular frequency modulation period, during 45 min.  
The dynamic viscosity of 10-BPhCOOH was measured using an Advanced Air Bearing Rheometer from Malvern Instruments Ltd., Malvern, Worcestershire UK, Model: Bohlin Gemini 2. The rheometer allows different sample geometries and integrates an oven for performing measurements up to 300 \({}^{\circ}\)C. In our case, the 10-BPhCOOH sample was placed between two stainless steel parallel plates with 40 mm diameter and 1000 \(\upmu\)m plate spacing and a shear rate ramp from 0 to 70 s\({}^{-1}\) was applied. Measurements were carried out at two different temperatures: 225 \({}^{\circ}\)C for obtaining the mesophase viscosity and 270 \({}^{\circ}\)C for the isotropic liquid viscosity.  
Figure 6: Mesophase textures observed for 10-BPhCOOH under polarized light upon cooling from isotropic liquid. (**a**) Smectic C mesophase between 170 \({}^{\circ}\)C and 249 \({}^{\circ}\)C; (**b**) Nematic mesophase at \(T=249\)\({}^{\circ}\)C.