A deep understanding of the degradation of cellulose diacetate (CDA) polymer is crucial in finding the appropriate long-term stability solution. This work presents an investigation of the reaction mechanism of hydrolysis using electronic density functional theory calculations with the B3LYP/ 6-31++G** level of theory to determine the energetics of the degradation reactions. This information was coupled with the transition-state theory to establish the kinetics of degradation for both the acid-catalyzed and noncatalyzed degradation pathways. In this model, the dependence on water concentration of the polymer as a function of pH and the evaporation of acetic acid from the polymer is explicitly accounted for. For the latter, the dependence of the concentration of acetic acid inside the films with the partial pressure on the surrounding environment was measured by sorption isotherms, where Henry's law constant was measured as a function of temperature. The accuracy of this approach was validated through comparison with experimental results of CDAaccelerated aging experiments. This model provides a step forward for the estimation of CDA degradation dependence on environmental conditions. From a broader perspective, this method can be translated to establish degradation models to predict the aging of other types of polymeric materials from first-principles calculations.
Metal-Organic Frameworks (MOFs) with open metal sites (OMS) interact strongly with a range of polar gases/vapors. However, under ambient conditions, their selective adsorption is generally impaired due to a high OMS affinity to water. This led previously to the privilege selection of hydrophobic MOFs for the selective capture/detection of volatile organic compounds (VOCs). Herein, we show that this paradigm is challenged by metal(III) polycarboxylates MOFs, bearing a high concentration of OMS, as MIL-100(Fe), enabling the selective capture of polar VOCs even in the presence of water. With experimental and computational tools, including single-component gravimetric and dynamic mixture adsorption measurements, in situ infrared (IR) spectroscopy and Density Functional Theory calculations we reveal that this adsorption mechanism involves a direct coordination of the VOC on the OMS, associated with an interaction energy that exceeds that of water. Hence, MOFs with OMS are demonstrated to be of interest for air purification purposes.
A novel strategy is proposed to synthesize metal–organic
framework (MOF)–gelatin bionanocomposites by taking profit
of the thermo-reversible character of gelatin and the liquid–liquid
phase separation process, that is, coacervation. This enables the
formation of bionanocomposites based on a series of chemically stable
Zr4+ dicarboxylate MOFs (UiO-66 and MOF-801) differing
by their hydrophilic–hydrophobic balance and their chemical
functionality. Bionanocomposites with homogeneous and uniform distribution
of MOF particles in the gelatin matrix as well as a high MOF loading
(up to 90%) without compromising their porosity were prepared as
a result of an excellent physico-chemical matching between MOFs and
gelatin. Finally, this series of bionanocomposites were shaped into
films or monoliths, and they have shown high performance for the selective
adsorption of acetic acid in the presence of humidity. These composites
can be regarded as highly efficient adsorbents for cultural heritage
preservation.
A generalized lock-in detection method is proposed to extract amplitude and phase from optical interferometers when an arbitrary periodic phase or frequency modulation is used. The actual modulation function is used to create the reference signals providing an optimal extraction of the useful information, notably for sinusoidal phase modulation. This simple and efficient approach has been tested and applied to phase sensitive spectroscopy and near-field optical measurements. We analyze the case where the signal amplitude is modulated and we show how to suppress the contribution of unmodulated background field.
In this work, we report on the measurement of the thermal conductivity of thin insulating films of SiO 2 obtained by thermal oxidation, and Al 2 O 3 grown by atomic layer deposition (ALD), both on Si wafers. We used photoreflectance microscopy to determine the thermal properties of the films as a function of thickness in the 2 nm to 1000 nm range. The effective thermal conductivity of the Al 2 O 3 layer is shown to decrease with thickness down to 70% for the thinnest layers. The data were analyzed upon considering that the change in the effective thermal conductivity corresponds to an intrinsic thermal conductivity associated to an additional interfacial thermal resistance. The intrinsic conductivity and interfacial thermal resistance of SiO 2 were found to be equal to 0.95
ACCEPTED MANUSCRIPTA C C E P T E D M A N U S C R I P T W/m.K and 5.1x10 -9 m 2 K/W respectively; those of Al 2 O 3 were found to be 1.56 W/m.K and 4.3x10 -9 m 2 K/W.
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