# Extending Cooling Rate Performance of Fast Scanning Chip Calorimetry by Liquid Droplet Cooling
## 2 Experimental
### Materials and Sensors  
Different cooling liquids, including water (bi-distilled), ethanol (Sigma-Aldrich, St. Louis, MO, USA, 99.8%), acetone (Sigma-Aldrich, 99.9%), glycerol (Sigma-Aldrich, 99.5%), silicon oil (Sigma-Aldrich, Wacker (Burghausen, Germany)) and commercial cold-spray (Liqui Moly, \(-45\)\({}^{\circ}\)C), were tested in this work. The glycerol and silicon oil require additional cleaning with acetone after each quenching, which is not preferable for some materials but can expand the list of possible cooling agents if needed. Water, even after being mixed with ethanol, was accumulating over several runs on the sensor membrane and its surroundings. It was not possible to remove it completely without using acetone or heating of the whole sensor to relatively high temperatures. The remaining water layer on the sample surface introduces significant disturbances to the FSC measurements after cooling. Chilled pure ethanol was also tested. For chilled ethanol experiments, the ethanol bottle was cooled to \(-50\)\({}^{\circ}\)C and transported in a thermally isolated box. Then, chilled ethanol was deposited on the sensor as fast as possible using the approach shown in Figure 4 to avoid heating during transportation. Later on, the injector with ethanol was chilled with the cold-spray, thus giving more reliable cooling. The additional cooling was seen through the increased viscosity of the ethanol. Chilled ethanol may cause a misleading temperature measurement because of cooling the thermopile cold junctions.  
The cold-spray was delivered in pressurized bottles. Therefore, it needs first extraction of the liquid out of the bottle nozzle and then providing the cold-spray towards the liquid cooling injector. The aim was to deposit a cooling liquid on the sensor without an upcoming gas front, because the gas movement will cause sample temperature oscillations and premature heater off triggering.  
Sensors of different lateral size were used for the experimental test of the cooling rate performance of the droplet cooling, namely, the large Mettler Toledo Flash DSC UFS1 sensor and the medium-sized XI95 sensor (comparable to the UFH1 sensor from Mettler Toledo), with heated-area sizes of 500 \(\upmu\)m diameter and 60 \(\times\) 80 \(\upmu\)m\({}^{2}\), respectively.  
The deposited droplets of the coolant were varied in size. In the case of the UFS1 sensor, the droplets were also placed on the different sides of the sensor. The moving droplet was causing a gas movement in front of it, which was detected by the sensor. Triggering sensitivity and delay were adjusted for each particular cooling agent to avoid triggering by the cold gas moving in front of the droplet. The aim was to switch off the heater simultaneously with arriving of the cooling liquid. Typical triggering deviations of the amplified thermopile voltage of 10-20 mV (ca. 5-10 K) were selected.  
For further testing of liquid droplet cooling under realistic conditions, molten HDPE, PBN and indium samples were cooled. HDPE with a melting temperature \(T_{\mathrm{m}}\) of 414 K and from previous FSC experiments [31; 32] known cooling rate dependent crystallization temperatures was used. HDPE Paxon was provided by ExxonMobil and PBN by Teijin ShojiEurope GmbH. Indium of high purity (99.9%), as typically used for temperature calibration of calorimeters, was selected as a material with minor effects due to crystallization kinetics. Mass of HDPE was estimated from heat capacity value at fixed temperature. Mass of the PBN sample was estimated from the value of the glass transition step in heat capacity. For HDPE and indium, the solidification peak was visible on cooling, and therefore, the reheating was not necessary.  
In case of PBN, in order to confirm the vitrified state of the sample after the droplet-cooling cycle, the sample was measured on heating in normal FSC mode. Prior to the measurement reheating cycle, the cooling agent was dried for 30 s.