Results of development and experimental verification of a bench-top system for synthesis of highly porous polymer matrices are presented. Synthesis of the matrices is based on the initial plasticization of a raw polymer material provided using a subcritical/supercritical fluidic agent with the follow-up foaming of the plasticized polymer due to gradual depressurization of a working volume of the high-pressure reactor. The design of the reactor makes it possible to provide the quasi-real-time optical control of the polymer foaming using various optical probes (e.g., the small-angle diffuse transmittance measurements at various wavelengths, the multi-speckle diffusing wave spectroscopy, the polarimetric measurements using a transmitted light, the direct imaging of a foamed volume in the trans-illumination mode, etc.). The optical control is carried out through a set of sapphire glass windows symmetrically located around the working volume of the reactor. A precise control of the pressure and temperature in the working volume is synchronized with the optical probing of the foamed volume. Bench-top tests of the developed system were carried out using two extreme foaming modes: the quasi-adiabatic foaming under the condition of fast depressurization of the working volume, and the quasiisothermal foaming provided with the extremely slow depressurization and the constant temperature in the working volume. In the experiments, a granular polylactide from the PURACORB Inc. was used as the raw polymer material and carbon dioxide was applied as the plasticizing/foaming agent. The results of pilot foaming experiments for these extreme modes of polylactide foaming are presented.
A technique of the low-coherence reflectometry was applied to characterize the structure of foamed polylactide matrices. This technique is based on the analysis of the decaying output of a low-coherence scanning interferometer with a diffusively backscattering probed sample in the object arm. Estimations of the decay rate for the interferometer output allowed us to characterize the influence of the foaming parameters on the mean transport free path of light propagation in the examined foamed matrices. It was established that foaming in the vicinity of the critical point of the plasticizing and foaming agent (carbon dioxide) leads to a smaller average size of pores in the synthesized matrices compared to the foaming parameters far from the critical point.
Features of diffusing light probes of aged liquid foams are discussed. These probes were carried out using broadband and laser radiation with the wavelength of 532 nm. Experimental data were obtained for aged samples of Gillette shaving cream as a model foamed substance. The coefficients of diffusion and collimated transmittance were applied for characterization of the structural changes in the aged wet foams. Also, the changes in the liquid fraction due to gravitational drainage were monitored using volumometric measurements in the course of the foam aging. Obtained empirical data on the diffuse and collimated transmittance were used as the reference values for correction of the spectral measurements in the visible range with a broadband source of probe light. The problem of correction of the collimated transmittance partially corrupted by the diffusing component of multiply scattered light is discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.