Encapsulation of shock-sensitive materials and their implementation into matrices

Encapsulation;Shock-sensitive;Materials;Supersaturated;Sodium Acetate Trihydrate;Microcapsules;Composites;Matrices

Streufert, Jonathan R

关键词: Encapsulation;    Shock-sensitive;    Materials;    Supersaturated;    Sodium Acetate Trihydrate;    Microcapsules;    Composites;    Matrices;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/78511/STREUFERT-THESIS-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

This study involved the encapsulation of a dilute sodium acetate trihydrate (SAT) aqueous solution and the dispersion of synthesized microcapsules into a matrix.Two encapsulation processes were examined: mechanically mixing and microfluidic devices to form water-in-oil-in-water (W/O/W) double emulsions.It was determined by optical microscopy and scanning electron microscopy (SEM) that the microcapsules manufactured with the microfluidic device, with diameters between about 200 μm and 300 μm and a shell thickness of about 1.5 μm, were more stable out of solution and thus were selected for implementation into a matrix.These microcapsules had a shell material of UV-cured acrylate, and were shown using differential scanning calorimetry (DSC) to lose their phase change ability when put into a furnace at 70°C overnight, which is a requirement to cure the PDMS matrix.Because of this, the same UV-cured acrylate as the shell material was chosen as the matrix.The DSC confirmed the phase change retention of the microcapsules after dispersion into the matrix, and the hysteresis decreased with decreasing temperature ramp rates, with temperature differences between freezing and melting for ramp rates of 10°C/min, 5°C/min, and 1°C/min of 47.45°C, 41.10°C, and 34.39°C, respectively.Finally, dynamic mechanical analysis (DMA) was performed on samples with microcapsule volume fractions of 0%, 1%, 2%, 4%, 8%, and 16% to find their Young’s moduli.The experimental Young’s moduli did not match up well with the predicted Halpin-Tsai trends at room temperature, with the microcapsules’ contents being liquid, and at -80°C, with the contents being solid, but this was attributed to the many variables associated with the microcapsule and sample synthesis process, as well as the limitations of the analysis instruments.However, two samples that were measured at -30°C, lowered to -80°C, and raised again to -30°C to be measured again, observed Young’s modulus increases of 8.2% and 24.4%, as the first measurement was high enough for the capsules to have remained liquid but the second measurement low enough for the capsules to melt from the solid.The matrix properties remained static for both measurements, so the only difference was the capsules’ contents’ phase.If the synthesis processes and instruments’ accuracies were improved, as well as the number of samples to average over increased, it was suggested that the measurements could show the expected increase in Young’s modulus of the composites with the core solutions converting from a liquid to solid phase.