Thermal characterization and analysis of microliter liquid volumes using the three-omega method

Abstract

Thermal phenomena in many biological systems offer an alternative detection opportunity for quantifying relevant sample properties. While there is substantial prior work on thermal characterization methods for fluids, the push in the biology and biomedical research communities towards analysis of reduced sample volumes drives a need to extend and scale these techniques to these volumes of interest, which can be below 100 pl. This work applies the 3ω technique to measure the temperature-dependent thermal conductivity and heat capacity of de-ionized water, silicone oil, and salt buffer solution droplets from 24 to 80 °C. Heater geometries range in length from 200 to 700 μm and in width from 2 to 5 μm to accommodate the size restrictions imposed by small volume droplets. We use these devices to measure droplet volumes of 2 μl and demonstrate the potential to extend this technique down to pl droplet volumes based on an analysis of the thermally probed volume. Sensitivity and uncertainty analyses provide guidance for relevant design variables for characterizing properties of interest by investigating the tradeoffs between measurement frequency regime, device geometry, and substrate material. Experimental results show that we can extract thermal conductivity and heat capacity with these sample volumes to within less than 1% of thermal properties reported in the literature.

Thermal Conduction in Vertically Aligned Copper Nanowire Arrays and Composites

“…Due to the temperature coefficient of resistance of the metal, the resistance of the line is also perturbed at frequency 2ω, leading to an overall voltage oscillation at frequency 3ω, which is detected using a lock-in amplifier. We implement this measurement by growing the NW array directly above an electrically-isolated metal line that is 49 and is adapted to contain a buried electrode to facilitate electrodeposition onto the center of the device 50 as shown in Fig. 4.…”

Frequency-domain hot-wire sensor and 3D model for thermal conductivity measurements of reactive and corrosive materials at high temperatures

“…26is affected by κ and ρC can be examined by studying the sensitivity of the model to each material parameter. 36,42 The sensitivity of the model relates how much the measured temperature rise would change in response to a change in the sample thermal conductivity (κ) or heat capacity (ρC), via the normalized derivative with respect to thermal conductivity, (κ/T) ⋅ ∂T/∂κ, or heat capacity, (ρC/T) ⋅ ∂T/∂ρC. Figure 8 shows the in-phase and out-of-phase sensitivities of the hot-wire measurement (using a 5 mm long, 25 μm diameter Pt wire) to sample κ and ρC over a 1-1000 Hz spectrum for gas-like [ Fig.…”

“…The 3ω method has primarily been used for characterizing solid materials although earlier specific heat spectroscopy studies [37][38][39] have shown the promise of frequency-domain techniques for investigating the properties of liquids and phase changes. More recent work has been done to extend 3ω method to liquids [40][41][42] and soft materials; 43 however, they still retain the basic geometry of the planar 3ω method that includes parasitic heat flux through the supporting substrate that usually has much higher thermal conductivity than the liquid or soft material being studied. In order to ensure as much of the generated heat flux propagates through the liquid sample, wire geometries immersed or embedded in the sample are ideal, limiting the parasitic conduction pathways to the wire axis itself.…”

In-situ thermal transport measurement of flowing fluid using modulated photothermal radiometry

“…The ability of in-situ thermal conductivity measurement of flowing fluids could be useful for the operational safety and diagnosis of these systems [6,7]. Despite a multitude of techniques available for the thermal conductivity measurement of stagnant fluids, including the transient hot-wire (THW) method [8,9], steady-state method [10][11][12], laser flash analysis (LFA) [13,14], 3ω technique [6,15,16], and time or frequency domain thermoreflectance techniques (TDTR/FDTR) [17], there are still challenges of applying these techniques for in-situ diagnostics, especially under the harsh environment (such as high temperature and/or with corrosive fluids).…”