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Polypropylene Nanodroplets by Nanolayer Breakup Yi Jin, Anne Hiltner and Eric Baer Case Western Reserve University, DMR 0349436. heat. Center for Applied Polymer Research.

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slide1

Polypropylene Nanodroplets by Nanolayer Breakup

Yi Jin, Anne Hiltner and Eric Baer

Case Western Reserve University, DMR 0349436

heat

Center for Applied Polymer Research

A dispersion of isotactic polypropylene (PP) nanoparticles was produced by interfacially driven breakup of PP nanolayers. Layer-multiplying coextrusion was used to fabricate an assembly of several hundred PP nanolayers about 12 nm thick sandwiched between thicker polystyrene (PS) layers, Figure 1. When the layered assembly was heated into the melt, the PP nanolayers broke up to form a dispersion of PP droplets in a PS matrix. Particle size analysis revealed that 90 % of the PP was present as 30 nm nanoparticles, Figure 2.

The nanoparticles were small enough and numerous enough that most did not contain a primary nucleus. When cooled from the melt, the droplets crystallized by homogeneous nucleation at about 40 oC, Figure 3. The droplets were found to be in the smectic form by WAXD. The smectic particles transformed to the alpha form upon heating. This result provided direct evidence for an intermediate smectic phase in the process whereby homogeneous nucleation leads to alpha form crystals in confined nanoparticles. The possibility for incorporating nucleating agents into the nanoparticles offers a unique opportunity to study mechanisms of crystal nucleation in polymers.

Figure 1. PP nanolayers breakup to form nanoparticles

Figure 3. The PP nanoparticles crystallize by homogeneous

nucleation in the smectic form.

Y. Jin, et at. J. Polym. Sci.: Part B: Polym. Phys., 2006, 44, 1795.

Figure 2. 90% of the PP is in the form of nanoparticles

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Forced-Assembly of Polymer Nanolayers – Broader Impact

Anne Hiltner and Eric Baer

Case Western Reserve University, DMR 0349436

AB Feedblock

Melt Pump A

Extruder A

Extruder B

Melt Pump B

Layer

Multipliers

Skin Layer

Extruder

Transfer Tube

Skin Layer Feedblock

Exit Die

Skin

Skin

Center for Applied Polymer Research

The unique layer-multiplying coextrusion process at Case Western Reserve University combines two polymers as perfectly alternating assemblies of hundreds or thousands of continuous microlayers or nanolayers, Figure 1. Since its inception, numerous innovations in this “forced-assembly” process have resulted in thinner layers and improved layer uniformity. It is now possible to coextrude polymer nanolayers, in which the individual layers can be as thin as 5 nm. In addition, a high level of layer uniformity makes possible large-scale fabrication of 1D photonic crystals (Bragg crystals).

The unique materials that can be fabricated through these process innovations have lead to fundamental advances in polymer physics, with new insights into the nature of the polymer interphase and the nature of homogeneous nucleation. Technological innovations have been made in gradient refractive index lenses, nonlinear optical materials, and tunable 1D photonic crystals. The process is “student-friendly”, and is routinely operated by teams that include our undergraduate researchers, Figure 2.

Figure 2. A postdoc, an REU student, and a graduate student work as a team on the nanolayer coextrusion process.

Figure 1. Schematics of layer-multiplication and the coextrusion process with an image of the coextruded layers.

Interphase Materials by Forced Assembly of Glassy Polymers by R. Y. F. Liu, et al. Macromolecules 2004, 37, 6972.

Multilayer Polymer Gradient Index (GRIN) Lenses, by E. Baer, A. Hiltner, J. S. Shirk, U.S. Allowed Patent Application 10/941,986 (2004).