Polylactic acid is proving to be a viable alternative to petrochemical-based plastics for many applications It is produced from renewable resources and is biodegradable, decomposing to give H2O, CO2, and humus, the black material in soil In addition, it has unique physical properties that make it useful in diverse applications including paper coating, fibers, films, and packaging (see Figure)

Polylactic Acid Technology

Nanoparticle interaction with plasma proteins as it relates to particle biodistribution, biocompatibility and therapeutic efficacy.

Morphology evolution via self-organization and lateral and vertical diffusion in polymer:fullerene solar cell blends

Morphology evolution via self-organization and lateral and vertical diffusion in polymer:fullerene solar cell blends.

https://www.zora.uzh.ch/id/eprint/44154/1/Rabe1.pdf

Understanding protein adsorption phenomena at solid surfaces

Protein Nanoparticle Interactions: Opportunities and Challenges Morteza Mahmoudi,* Iseult Lynch, Mohammad Reza Ejtehadi, Marco P. Monopoli, Francesca Baldelli Bombelli, and Sophie Laurent National Cell Bank, Pasteur Institute of Iran, Tehran, Iran Nanotechnology Research Center, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran School of Chemistry and Chemical Biology & Conway Institute for Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland Department of Physics, Sharif University of Technology, Tehran, Iran School of Pharmacy, UEA, Norwich Research Park, Norwich,U.K. Department of General, Organic, and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, Avenue Maistriau 19, B-7000 Mons, Belgium

Protein-nanoparticle interactions: opportunities and challenges.

We report the first measurements of the glass transition temperature ${T}_{g}$ for thin freely standing polystyrene (PS) films. We have used Brillouin light scattering to measure ${T}_{g}$ for freely standing films of different thicknesses. We find that ${T}_{g}$ decreases linearly with film thickness $h$ for $h\ensuremath{\le}700\AA{}$, with a reduction of 70 K for a film with $h\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}290\AA{}$. These measurements characterize unambiguously the effects of the free surface on ${T}_{g}$ of thin polymer films. Results are compared to similar results for supported PS films [Keddie et al., Europhys. Lett. 27, 59 (1994)], and we find that their measured values are influenced strongly by the substrate.

Effect of Free Surfaces on the Glass Transition Temperature of Thin Polymer Films.

The glass transition in thin polymer films

We have used Brillouin light scattering and ellipsometry to measure the glass transition temperature ${T}_{g}$ of thin polystyrene (PS) films as a function of the film thickness $h$ for two different molecular weights ${M}_{w}.$ Three different film geometries were studied: freely standing films, films supported on a ${\mathrm{SiO}}_{x}$ surface with the other film surface free (uncapped supported), and films supported on a ${\mathrm{SiO}}_{x}$ surface and covered with a ${\mathrm{SiO}}_{x}$ layer (capped supported). For freely standing films ${T}_{g}$ is reduced dramatically from the bulk value by an amount that depends on both $h$ and ${M}_{w}.$ For $h\ensuremath{\lesssim}{R}_{\mathrm{EE}}$ (the average end-to-end distance of the unperturbed polymer molecules), ${T}_{g}$ decreases linearly with decreasing $h$ with reductions as large as 60 K for both ${M}_{w}$ values. We observe a large ${M}_{w}$ dependence of the ${T}_{g}$ reductions for freely standing films which provides the first strong evidence of the importance of chain confinement effects on the glass transition temperature of thin polymer films. For both the uncapped and capped supported films, ${T}_{g}$ is reduced only slightly $(l10\mathrm{K})$ from the bulk value, with only small differences in ${T}_{g}$ $(l4\mathrm{K})$ observed between uncapped and capped supported films of the same thickness. The results of our experiments demonstrate that the polymer-substrate interaction is the dominant effect in determining the glass transition temperature of PS films supported on ${\mathrm{SiO}}_{x}.$

Interface and chain confinement effects on the glass transition temperature of thin polymer films

The motion of polymer chain segments cooled below the glass transition temperature slows markedly; with sufficient cooling, segmental motion becomes completely arrested. There is debate as to whether the chain segments near the free surface, or in thin films, are affected in the same way as the bulk material. By partially embedding and then removing gold nanospheres, we produced a high surface coverage of well-defined nanodeformations on a polystyrene surface; to probe the surface dynamics, we measured the time-dependent relaxation of these surface deformations as a function of temperature from 277 to 369 kelvin. Surface relaxation was observed at all temperatures, providing strong direct evidence for enhanced surface mobility relative to the bulk. The deviation from bulk α relaxation became more pronounced as the temperature was decreased below the bulk glass transition temperature. The temperature dependence of the relaxation time was much weaker than that of the bulk α relaxation of polystyrene, and the process exhibited no discernible temperature dependence between 277 and 307 kelvin.

https://science.sciencemag.org/content/sci/319/5863/600.full.pdf

Measuring the Surface Dynamics of Glassy Polymers

The past 20 years have seen a substantial effort to understand dynamics and the glass transition in thin polymer films. In this Perspective, we consider developments in this field and offer a consistent interpretation of some major findings. We discuss recent experiments that directly measure mobility at or near the surface of glassy polymers. These experiments indicate that enhanced mobility near the free surface can exceed bulk mobility by several orders of magnitude and extend for several nanometers into the bulk polymer. Enhanced mobility near the free surface allows a qualitative understanding of many of the observations of a reduced glass transition temperature Tg in thin films. For thin films, knowledge of Tg by itself is less useful than for bulk materials. Because of this, new experimental methods that directly measure important material properties are being developed.

James A. Forrest

Papers

Effect of Free Surfaces on the Glass Transition Temperature of Thin Polymer Films.

The glass transition in thin polymer films

Interface and chain confinement effects on the glass transition temperature of thin polymer films

Measuring the Surface Dynamics of Glassy Polymers

Dynamics near Free Surfaces and the Glass Transition in Thin Polymer Films: A View to the Future